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Environmental Impact Assessment: Proposed Reverse Osmosis Plant, Iron –ore Handling
Facility, Port of Saldanha
Specialist Marine Impact Assessment
Prepared for:
PD Naidoo and Associates Pty (Ltd) & SRK Consulting Engineers and Scientists Joint Venture (PDNA/SRK JV)
Jointly prepared by:
CSIR, Natural Resources and the Environment, PISCES Environmental Services (Pty) Ltd and
Nina Steffani, Marine Environmental Consultant
May 2008
Env ir onment al Ser v ices (Pt y ) Lt dPISC ES
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CSIR/NRE/ECO/ER/2007/0149/C (Draft)
Prepared for:
PD Naidoo and Associates Pty (Ltd) and SRK Consulting Engineers and Scientists Joint Venture (PDNA/SRK JV)
On behalf of:
Transnet Capital Projects This report was compiled by:
Roy van Ballegooyen CSIR, Natural Resources and the Environment PO Box 320, Stellenbosch 7599, South Africa Tel: + 27 21 888 2572 Fax: + 27 21 888 2693 Email: [email protected]
Dr Andrea Pulfrich PISCES Environmental Services (Pty) Ltd
PO Box 31228, Tokai 7966, South Africa Tel: + 27 21 782 9553 Fax: + 27 21 782 9552 Email: [email protected]
Nina Steffani Marine Environmental Consultant
21 Skippers End, Zeekoevlei 7941, South Africa Tel: + 27 21 705 9915 Fax: + 27 21 705 9915 Email: [email protected]
Published by:
CSIR P O Box 395 0001 PRETORIA Republic of South Africa
Issued and printed by, also obtainable from:
CSIR P O Box 320 STELLENBOSCH 7599 South Africa
Tel: + 27 21 888-2400 Fax: +27 21 888-2693 Email: [email protected]
The report to be cited as:
Van Ballegooyen, N. Steffani and A. Pulfrich 2007. Environmental Impact Assessment:
Proposed Reverse Osmosis Plant, Iron –ore Handling Facility, Port of Saldanha - Marine
Impact Assessment Specialist Study, Joint CSIR/Pisces Report,
CSIR/NRE/ECO/ER/2007/0149/C, 190pp + 198pp App.
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Marine Impact Assessment Specialist Study
EIA for the proposed Reverse Osmosis Desalination Plant in Saldanha Bay i
SCOPE OF WORK
The Iron Ore Handling Facility at the Port of Saldanha (including the proposed upgrades to the
facility), will require increased water supplies for dust suppression measures. It is proposed that a
Reverse Osmosis (RO) seawater desalination plant be constructed to meet this water demand. In
terms of existing legislation, this proposed activity (i.e. the construction and operation of an RO Plant)
requires that a Basic Assessment of potential environmental impacts be undertaken.
PD Naidoo & Associates (Pty) Ltd and SRK Consulting Scientists and Engineers Joint Venture
(PDNA/SRK Joint Venture) have been appointed by Transnet to undertake a Basic Assessment for a
proposed RO plant at the Port of Saldanha. The PDNA/SRK JV, in turn, have contracted the CSIR to
undertake the Specialist Marine Impact Assessment for the Basic Assessment. CSIR has sub-
contracted PISCES Environmental Services (Pty) Ltd and Nina Steffani (Independent Consultant) to
provide the ecological assessment component of this specialist study, while the Coastal Systems
Research Group of the CSIR Natural Resources and the Environment Unit, has undertaken the water
quality modelling to characterise the predicted changes in water quality associated with the proposed
discharges from the RO Plant.
Under this agreement the CSIR and its sub-consultants are to:
• Advise on the design of the RO Plant early in the process;
• Undertake an assessment of potential environmental impacts in the marine environment
associated with the construction and operation of an RO Plant;
• Identify the environmentally preferred site and intake and discharge positions from the
alternatives identified through the Basic Assessment process.
The detailed terms of reference for this study are contained in Section 1 of this report.
Roy van Ballegooyen
Coastal Systems Research Group Stellenbosch, South Africa
Natural Resources and the Environment CSIR May 2008
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Marine Impact Assessment Specialist Study
EIA for the proposed Reverse Osmosis Desalination Plant in Saldanha Bay iii
EXECUTIVE SUMMARY
Introduction The Iron Ore Handling Facility at the Port of Saldanha (including the proposed upgrades to the
facility), will require increased water supplies for dust suppression measures. It is anticipated that
ultimately a total of 3600 kℓ of water per day will be required for this purpose. The municipality
currently supplies water to the Iron Ore Handling Facility, but Transnet propose to supplement this
supply with additional sources of freshwater or to offset present water requirements. Of all potential
sources of such water, seemingly the most feasible is that of a Reverse Osmosis (RO) plant, for the
desalination of seawater.
In terms of existing legislation this proposed activity (i.e. the construction and operation of an RO
Plant) will require that a Basic Assessment of potential environmental impacts be undertaken.
Consequently, the PDNA/SRK Joint Venture approached the CSIR and Pisces Environmental
Services (Pty) Ltd to undertake a Marine Specialist Study to assess the impacts of the construction
and operation of the RO Plant on the marine environment. In summary, the CSIR was asked to:
• Advise on the design of the RO Plant early in the process and identify any fatal flaws
associated with any of the alternative sites, or the proposed project;
• Assess the significance of the potential impact of the proposed development on the marine
environment for each of the alternative sites (taking into consideration the differences in project
design in the case of each alternative site);
• Recommend mitigation measures to minimise impacts associated with the proposed RO Plant
and enhance benefits; and
• Identify an environmentally preferred site.
Project Description Three alternative locations within the Port of Saldanha are being considered for the location of the
RO plant (see figure below). At the three proposed sites, there are various opportunities and
constraints in terms of the specific intake and discharge alternatives that may be considered (see
Table 3.1 in the main body of this report). These are described in generic terms, followed by a
detailed description of the various alternatives assumed and assessed for the three proposed
locations for the RO Plant.
The development alternatives at these three sites include a number of combinations of intake and
discharge infrastructure relevant to each of these sites as summarised in the Table below. Intake
structures considered are beach wells, pipeline intakes or borehole intakes. Discharge structures
considered are various pipeline discharge configurations comprising primarily single point or multi-
point diffuser structures.
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Proposed locations for the RO Plant.
Development alternatives used in this assessment.
Site Alternative # Alternative Intake/Discharge Infrastructure Locatio ns
Site 1 1 a) Beach well intake and pipeline discharge (Big Bay)
b) Pipeline intake and pipeline discharge (Big Bay)
Site 2 a) Beach well intake and pipeline discharge (Small Bay)
b) Pipeline intake and pipeline discharge (Small Bay)
Site 3
a) Pipeline intake (Small Bay) and pipeline discharge (Small Bay)
b) Pipeline intake (Small Bay) and pipeline discharge (Big Bay)
c) Borehole intake on quay (adjacent to existing iron-ore stockpiles) and pipeline discharge (Caisson 3, Big Bay)
d) Borehole intake on quay (adjacent to Multi-purpose Terminal) and pipeline discharge (Caisson 3, Big Bay)
Greater detail of these combinations of intake and discharge infrastructure are contained in Figures
3.3 to 3.5 in the main body of the report. 1 A beach well intake and beach well discharge option was also considered for Site 1, however the
groundwater specialist study indicated the beach sediment conditions were such that that a beach well discharge is considered not feasible
Small Bay
Big Bay
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Key Issues and sources of Impact The key issues identified in the course of the public participation phase of the Basic Assessment
(also referred to as EIA in this document) and the environmental screening process for the proposed
RO Plant relate to the construction phase, operational phase and decommissioning phase.
Key issues in the construction phase include the disturbance of the beach in the case of intake
beach wells and the seabed (and possibly associated sediment dynamics) in the case of pipeline
intakes and discharges.
Most of the key issues and major potential impacts are associated with the operational phase . The
key issues related to the presence of pipeline infrastructure and brine discharges into the marine
environment are:
• altered flows at the intake and discharge resulting in ecological impacts (e.g. entrainment of
biota at the intake, low distortion/changes at the discharge, and affects on natural sediment
dynamics);
• the effect of elevated salinities in the brine water discharged to the bay;
• biocidal action of residual chlorine and/or other non-oxidising biocides such as
dibromonitrilopropionamide (DBNPA) in the effluent;
• the effects of co-discharged waste water constituents; including possible tainting effects
affecting both mariculture activities and fish factory processing in the bay;
• the effect of the discharged effluent having a higher temperature than the receiving
environment; and
• changes in dissolved oxygen that include:
• direct changes in dissolved oxygen content due to the difference between the ambient
dissolved oxygen concentrations and those in the discharged effluent, and;
• indirect changes in dissolved oxygen content of the water column and sediments due to:
i) changes in phytoplankton production as a result of changes in nutrient dynamics
(both in terms of changes in nutrient inflows and vertical mixing of nutrients), and;
ii) changes in remineralisation rates (with related changes in nutrient concentrations in
near bottom waters) due to near bottom changes in seawater temperature
associated with the brine discharge plume.
Additional engineering design considerations, not strictly constituting issues to be considered within
the Basic Assessment of potential environmental impacts, include the following:
• structural integrity of the intake and discharge pipelines (e.g. related to shoreline movement);
• potential re-circulation of brine effluents if intakes and discharges are situated in close
proximity to one another. The model results however indicate that this will not be a concern for
all of the intake and discharge options considered in this study;
• the permeability and particle size distributions of the sands (should beach intake and/or
discharge wells be considered as a viable option); and
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• water quality of feed-waters that may require specific mitigation measures or planned flexibility
in the operations of the RO Plant.
The potential impacts during the de-commissioning phase are expected to be minimal in
comparison to those occurring during the operational phase, and no key issues related to the marine
environment are identified at this stage. The minimum anticipated life of the RO plant is 25 years.
The individual RO modules will be replaced as and when required during this period. No
decommissioning procedures or restoration plans have been compiled at this stage, as it is
envisaged that the plant will be refurbished rather than decommissioned after the anticipated 25
years, as the beach wells and boreholes (if used) are expected to have a considerably longer lifespan
than the RO modules. A full decommissioning will require a separate EIA at the time of
decommissioning.
Changes in Environment due to Plant Discharges Model simulations were undertaken of the various options. The results for changes in salinity,
seawater temperature and the footprint of biocide and potential co-discharges for all of the site
alternatives are summarised in the figures below.
Available mariculture
concessions
Available/existing mariculture concessions
Existing mariculture concession
s
Available mariculture
concessions
Available/existing mariculture concessions
Existing mariculture concession
s
Available mariculture
concessions
Available/existing mariculture concessions
Existing mariculture concession
s
Available mariculture
concessions
Available/existing mariculture concessions
Existing mariculture concession
s
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Assessment of Environmental Impact The potential impacts associated with construction activities, the operation of the plant (brine and co-
discharges) and the long-term impacts associated with the intake and discharge structures are
assessed below.
Impacts During Construction
In the absence of detailed engineering specifications describing the construction of the intake and
discharge structures (both pipeline or beach wells), the assessment is based on generic assumptions
for such constructions. Should the final construction specifications be sufficiently different to those
assumed in this report, the impacts associated with the construction phase will need to be re-
evaluated. For the intake structure along the quayside for Site 3 and the proposed discharge
structure at Caisson 3, the impacts will be minimal as these construction activities will be utilising
existing infrastructure as their basis and construction activities will not be extensive.
Summary of construction impacts for the various Sit es and associated intake and discharge combinations.
Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Construction Impacts
Construction of Beach Well intakes
no mitigation Medium Medium n/a n/a n/a
with mitigation No significant mitigation possible other than avoiding beach well construction
n/a n/a n/a
Construction of borehole intakes
no mitigation n/a n/a n/a n/a Very low
with mitigation n/a n/a n/a n/a No mitigation
required
Construction of Intake pipelines
no mitigation Medium Medium Very low Very low n/a
with mitigation
Limited mitigation is possible using “best practice” mitigation measures during
construction. It is not possible to propose specific mitigation measures
based on existing known detail of construction activities
None deemed necessary other than normal environmental ‘best practice’
n/a
Construction of discharge infrastructure:
Comprises a pipeline with diffuser for Site 2 and f or discharges into Small Bay and Big Bay from Site 3 (i.e. development options 2a, 2b, 3a and 3b), and a pipeline with a more complicated discharge infrastructure than simply a diffuser at Site 1 and for a discharge at Caisson 3 from Site 3 (i.e. development options 1a, 1b, 3c and 3d)
no mitigation Very low Medium Medium Medium Very low
with mitigation
None deemed necessary other
than the use of “best practice” mitigation measures during
construction.
Limited mitigation is possible using “best practice” mitigation measures during construction. It is not possible to propose specific mitigation measures based on existing known detail
of construction activities
None deemed necessary other
than the use of “best practice” mitigation measures during
construction.
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Impacts during Operation of the RO Plant
The impacts on the marine environment associated with the operation of the RO Plant include those
associated with entrainment of biota, flow distortion and changes in sediment dynamics and of
greatest concern potential impacts on water quality in the marine environment associated with
discharges from the RO Plant. These are tabulated below.
Assessment Criteria
Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Operational Impacts (other than Water Quality) of I ntake and discharge operation
Entrainment of Biota (Pipeline Intakes)
no mitigation Medium Medium Medium Medium n/a
with mitigation Low Low Low Low n/a
Entrainment of Biota (Beach Well Intakes)
no mitigation insignificant insignificant n/a n/a n/a
with mitigation No mitigation deemed necessary n/a n/a n/a
Entrainment of Biota (Borehole intakes along Causew ay)
no mitigation n/a n/a Insignificant Insignificant Insignificant
with mitigation n/a n/a No mitigation deemed necessary
Flow Distortion
no mitigation Low Low Low Low Low
with mitigation Insufficient detail in project description to define specific mitigation measures, however appropriate engineering design should negate any potential impacts
Impacts on Sediment Dynamics
no mitigation insignificant Low Low Low insignificant
with mitigation No mitigation required
No detailed mitigation can be recommended as insufficient detail in project description, however appropriate
engineering design should negate any potential impacts
No mitigation required
Specific Impacts associated with the discharged bri ne (and associated co-discharged)
Salinity
no mitigation Low Low Low Low Low
with mitigation No mitigation specified/considered, other than optimal discharge diffuser design
Temperature
no mitigation Low Low/Medium * Low Low Low
with mitigation No mitigation specified/considered, other than optimal discharge diffuser design
Oxygen (no O2 scavengers)
no mitigation Low Low Low Low Low
with mitigation Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water. This will only occur should chlorine be used as a biocide that results in a potential discharge of
residual chlorine into the marine environment.. Presently the project description specifies that chorine will not be used in this role
Oxygen (with O2 scavengers)
no mitigation Medium Medium Medium Medium Medium
with mitigation Very Low Very Low Very Low Very Low Very Low
Oxidising Biocides (NaOCl): Beach well or borehole intakes
no mitigation Low Low n/a n/a Low
with mitigation If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
n/a n/a
No mitigation likely to be
required, other than optimal discharge
diffuser design
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Assessment Criteria
Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Oxidising Biocides (NaOCl): Pipeline intakes
no mitigation Medium Medium Low Low n/a
with mitigation** Very Low Very Low Very Low Very Low n/a
Non-oxidising Biocides (DBNPA): Beach well or bore hole intakes
no mitigation Low Low n/a n/a Low
with mitigation*** If biocide dosage is as specified, no
mitigation is likely to be required, other
than optimal discharge diffuser design
n/a n/a
No mitigation likely to be
required, other than optimal discharge
diffuser design
Non-oxidising Biocides (DBNPA): Pipeline intakes
no mitigation Medium Medium Low Low Low
with mitigation*** Low Low Very Low Very Low Very Low
Co-discharges (beach well or borehole intakes)
no mitigation Low Low n/a n/a Low
with mitigation****
Very Low Very Low n/a n/a Very Low
Co-discharges (pipeline intakes)
no mitigation Low Low//Medium Low Low n/a
with mitigation****
Very Low Very Low Very Low Very Low n/a
* Note that the intensity of the thermal impacts at Site 2 may be reduced and assumed to be low, i) given appropriate engineering design mitigation (i.e. assuming that it would be possible to locate the pipeline intake in a manner that would ensure sufficiently lower seawater temperatures at the intake) or ii) if it is assumed that beach well intake water temperatures are lower than the near surface water temperatures assumed in the modelling.
** A proposed mitigation for oxidising biocides such an sodium hypochlorite (if required and to be applied to the extent necessary) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however as this does potentially exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment, the mitigation preferred is that of carefully monitored and managed dosing to ensure minimal residual chlorine concentrations in the discharge.
*** The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
**** Mitigation in unlikely to be required except for perhaps Site 2, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern. The assessment with mitigation assumes mitigation measures whereby particulates are removed from the flocculant/backwash sludge to the extent required and disposed elsewhere than the marine environment.
“No-development” Alternative
The “no-development” alternative implies that the RO Plant and associated infra-structure will not be
commissioned. From a marine perspective this is undeniably the preferred alternative, as all
identified non-negligible impacts associated with beach disturbance and effluent discharge will not
occur and therefore will no longer be of concern and/or require mitigation. This must, however, be
seen in context with the existing need for additional water to implement the required dust mitigation
measures, the proposed extensions to the Port, as well as the use of possible alternative water
sources for dust control. Furthermore, it needs to be weighed up against the potential positive socio-
economic impacts undoubtedly associated both with the RO Plant project itself, as well as the Port
extension.
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Project Impacts and Environment Interaction Poin ts
The figures providing the maximum footprint in terms of salinity, seawater temperature, biocide and
potential co-discharge impacts show that the plume footprints do not extend as far as any existing or
proposed mariculture activities, seawater intakes for fish processing factories, recreational and
commercial gill-netting areas, or National Parks and Marine Protected Areas. At Site 2, however,
the plumes extend close to the eastern boundary of the area demarcated for seaweed
harvesting.
Conclusions
Each Site and its associated intake and discharge combinations has its own unique set of potential
impacts. However if these sites were to be ranked qualitatively in terms of their potential impacts,
their ranking would be as tabulated below. A ranking of 1 indicates the most preferable option in
terms of minimising overall impacts on the marine environment.
Qualitative Ranking of Options
Overall Ranking
Site 1
Site 2
Site 3 (Small Bay discharge)
Site 3 (Big Bay
discharge)
Site 3 (Caisson 3 discharge)
4 5 3 2 1
All Sites (except perhaps for Site 2) remain viable options. Site 2, whilst not environmentally fatally
flawed in terms of the existing proposed project, is not recommended as it does have a significantly
larger impact area than the other sites. It also constitutes a discharge into a relatively quiescent and
poorly flushed region of the bay where there are existing water quality concerns and neither the
waves nor currents are sufficient to efficiently disperse the effluent plume and potential backwash
sediments. Accordingly the public perceptions around potential impacts a RO plant discharge in such
a location would be the most negative. Furthermore, Site 2 is expected to have significant limitations
mainly in terms of the limited assimilative capacity of Small Bay when dealing with possible future
increases in discharges to the marine environment e.g. possible discharges from other
industrial/processing activities or the expansion of RO plant operations (although, it should be noted
that no more than the 3 RO plant modules are being proposed by Transnet).
Recommendations
The recommendations from this study include mitigation measures (optional and required) and
monitoring requirements to be able to better assess and manage potential impacts.
Mitigation Measures
The recommended mitigation measures are listed below for both the construction and operational
phases of the RO Plant. These are listed in the following table with a clear indication of whether they
are required or merely recommended.
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Recommended and Essential Mitigation Measures
Mitigation Necessity
Construction Impacts: - Limiting and restricting vehicular traffic on the beach - Good house-keeping - Active rehabilitation above high water mark
Required Required Required
Use of sub-surface intakes (beach wells/boreholes) Optional (highly recommended)
Pipeline intakes: - Adjustment of intake velocities and/or velocity caps - Use of intake screens - Operational cleaning (pigging) of intake pipes
Required Required Optional
Discharges: - Evaporation ponds / crystallisation - Beach well disposal - Carefully controlled dosing of biocides based on feedback from
monitoring systems - Dechlorination of brine discharge - Reduction of residual DBNPA concentration in effluent to be
discharged by designing the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge, or to revert to the use of an oxidising biocide (chlorine) in this role.
- Aeration of brine discharge - Removal of sludge particles from backwashing of RO modules - Optimal diffuser design based on acceptable water quality
target values
Not feasible Not feasible
Required
Required only if chlorine is used in systems discharging to the marine
environment (presently not indicated) and then only in the case of pipeline intakes as chlorine dosing for beach
well and borehole intakes is assumed to be low
Required only in the case of pipeline intakes as DBNPA dosing for beach
well and borehole intakes is assumed to be low
Optional but highly recommended if chlorine is used in systems discharging to the marine environment (presently
not indicated) and sodium metabisulfite is used to neutralise chlorine residuals in the effluent stream discharged to the
marine environment
Optional, to be undertaken to the extent required (i.e. as informed by the monitoring results for the discharge.)
Required
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Monitoring Recommendations
The monitoring recommendations are as follows:
Monitoring Activity Nature and Duration
Establishment of a baseline of intertidal and shallow subtidal invertebrate macrofaunal communities before any construction commences (Site 1 only)
Once-off survey Required
(Site 1 only)
Development of a monitoring programme to study the impact of the brine on potentially affected communities, particularly the subtidal benthic communities.
Surveys at recommended 6-monthly intervals (DWAF, 2007) or annually (whichever deemed more appropriate) over a period of approximately 4 years.*
Required
Monitoring of dissolved oxygen in the near bottom waters in the immediate vicinity of the discharge and at a nearby reference site to confirm that backwash material does not affect the dissolved oxygen concentrations to the extent that specific further mitigation measures need to be invoked (see mitigation measures for backwash material in table on previous page).
Once-off time series monitoring of dissolved oxygen concentration in the near bottom waters in the immediate vicinity of the discharge and at a nearby reference site for a minimum 6 month period (Nov-Apr) but preferably for 12 months.
Required
Monitoring of the RO plant effluent after commissioning for heavy metals.
Depending on plant design and associated perceived risks, monitoring over a range of operational conditions until a profile of the discharge in terms of heavy metal concentrations is determined.
Required
Toxicity testing of the RO Plant effluent at discharge point for a full range of operational scenarios (i.e. shock-dosing, etc).
Monitoring to continue until a representative profile of the discharge in terms of particularly biocide concentrations is determined.
Required
Monitoring (or audit of process chemical once RO Plant is commissioned) to ensure that tainting substances are absent from the RO Plant effluent.
Depending on plant design and associated perceived risks, monitoring over a range of operational conditions until it is confirmed that no tainting substances are present. However, it may be sufficient to simply audit the process chemicals used to confirm the absence of tainting substances.
Required
Monitoring to confirm performance of the discharge system and the numerical model predictions
Monitoring of salinity, temperature and total suspended solids in the near-field.
Required
Monitoring to confirm the numerical model predictions
As detailed above for confirmation of discharge system performance, but over a slightly more expansive area.
Optional
* Recommended intervals could be reduced to annual surveys if deemed appropriate and/or indicated by preliminary survey results from initial surveys.
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TABLE OF CONTENTS
SCOPE OF WORK ............................................................................................................................................... I
EXECUTIVE SUMMARY ................................................................................................................................ III
TABLE OF CONTENTS .................................................................................................................................XIII
LIST OF FIGURES........................................................................................................................................... XV
LIST OF TABLES............................................................................................................................................XIX
ABBREVIATIONS, UNITS AND GLOSSARY............................................................................................XXI
1 INTRODUCTION.......................................................................................................................................... 1
1.1 BACKGROUND ........................................................................................................................................ 1 1.2 SCOPE OF WORK..................................................................................................................................... 2 1.3 STRUCTURE OF THE REPORT................................................................................................................... 2 1.4 LEGISLATIVE AND PERMITTING REQUIREMENTS.................................................................................... 4
2 PROJECT DESCRIPTION ........................................................................................................................ 11
2.1 DESCRIPTION OF THE RO PLANT FACILITIES ........................................................................................ 11 2.2 LIFE SPAN OF PROJECT......................................................................................................................... 12 2.3 PROPOSED PLANT CAPACITY ................................................................................................................ 12 2.4 CONSTRUCTION AND COMMISSIONING OF INFRASTRUCTURE................................................................ 13
3 IDENTIFICATION AND SELECTION OF ALTERNATIVES............................................................. 17
3.1 GEOGRAPHICAL SETTING...................................................................................................................... 17 3.2 SITING ALTERNATIVES ......................................................................................................................... 18 3.3 CONCEPTUAL DESIGNS OF POSSIBLE INTAKE AND DISCHARGE STRUCTURES....................................... 20
3.3.1 Intake Alternatives ........................................................................................................................... 20 3.3.2 Discharge Alternatives .................................................................................................................... 28
3.4 “NO-DEVELOPMENT” ALTERNATIVE .................................................................................................... 31 3.5 SUMMARY OF DEVELOPMENT ALTERNATIVES...................................................................................... 31
4 APPROACH TO THE STUDY .................................................................................................................. 33
4.1 METHODOLOGY.................................................................................................................................... 34 4.1.1 Environmental Baseline................................................................................................................... 34 4.1.2 Modelling......................................................................................................................................... 34 4.1.3 Environmental Impact Assessment .................................................................................................. 36
4.2 LIMITATIONS AND ASSUMPTIONS......................................................................................................... 39
5 DESCRIPTION OF THE AFFECTED ENVIRONMENT...................................................................... 43
5.1 PHYSICAL ENVIRONMENT..................................................................................................................... 43 5.1.1 General ............................................................................................................................................ 43 5.1.2 Climate and Winds........................................................................................................................... 43 5.1.3 Tides ................................................................................................................................................ 45 5.1.4 Waves............................................................................................................................................... 46 5.1.5 Currents ........................................................................................................................................... 51 5.1.6 Water Column Stratification............................................................................................................ 51 5.1.7 Seawater Temperature..................................................................................................................... 54 5.1.8 Salinity ............................................................................................................................................. 56 5.1.9 Water Quality .................................................................................................................................. 56
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5.2 BIOLOGICAL ENVIRONMENT ................................................................................................................. 58 5.2.1 Sandy Substrate Habitats and Biota ................................................................................................ 58 5.2.2 Rocky Habitats and Biota ................................................................................................................ 63 5.2.3 Pelagic Communities ....................................................................................................................... 64 5.2.4 Birds ................................................................................................................................................ 66 5.2.5 Beneficial Uses ................................................................................................................................ 67 5.2.6 Existing Environmental Impacts...................................................................................................... 72 5.2.7 Potentially Threatened Habitats and Beneficial Uses ..................................................................... 76
6 IDENTIFICATION OF KEY ISSUES AND SOURCES OF POTENTIAL ENVIRONMENTAL IMPACT ....................................................................................................................................................... 77
6.1 CONSTRUCTION PHASE......................................................................................................................... 77 6.2 OPERATIONAL PHASE ........................................................................................................................... 78 6.3 DECOMMISSIONING PHASE ................................................................................................................... 79
7 MODELLED CHANGES IN THE MARINE ENVIRONMENT DUE TO THE RO PLANT EFFLUENT DISCHARGES TO THE MARINE ENVIRONMENT...................................................... 81
7.1 INTRODUCTION..................................................................................................................................... 81 7.2 ASSUMED INTAKE AND DISCHARGE LOCATIONS.................................................................................... 81 7.3 INTAKE CHARACTERISTICS................................................................................................................... 89 7.4 DISCHARGE CHARACTERISTICS............................................................................................................ 90 7.5 SCENARIOS SIMULATED........................................................................................................................ 95 7.6 MODEL RESULTS.................................................................................................................................. 97
7.6.1 Analysis of results ............................................................................................................................ 97 7.6.2 Summary of results in terms of exceedance of selected water quality guidelines .......................... 100
8 ASSESSMENT OF ENVIRONMENTAL IMPACTS ............................................................................ 111
8.1 IDENTIFICATION OF POTENTIAL ENVIRONMENTAL IMPACTS .............................................................. 111 8.1.1 Construction of Intake and Discharge Structures.......................................................................... 111 8.1.2 Permanent Intake and Discharge Structures................................................................................. 113 8.1.3 RO Plant Effluents ......................................................................................................................... 116
8.2 ASSESSMENT OF POTENTIAL ENVIRONMENTAL IMPACTS ................................................................... 148 8.2.1 Assessment of Impacts During Construction ................................................................................. 148 8.2.2 Assessment of Impacts Associated with Brine Discharge .............................................................. 150 8.2.3 Assessment of Impacts Associated with Intake and Discharge Structures..................................... 159
8.3 “NO-DEVELOPMENT” ALTERNATIVE .................................................................................................. 160 8.4 PROJECT IMPACTS AND ENVIRONMENT INTERACTION POINTS............................................................ 161
9 CONCLUSIONS AND RECOMMENDATIONS ................................................................................... 163
9.1 ENVIRONMENTAL ACCEPTABILITY AND COMPARISON OF ALTERNATIVES ......................................... 163 9.2 PREFERRED ALTERNATIVE ................................................................................................................. 165 9.3 RECOMMENDATIONS........................................................................................................................... 171
9.3.1 Mitigation Measures...................................................................................................................... 171 9.3.2 Monitoring Recommendations....................................................................................................... 175
10 REFERENCES........................................................................................................................................... 177
Appendix A: Possible implications of policy, legislation and approval and licensing procedures for
the proposed RO Plant water discharge
Appendix B: Hydrodynamic and Water Quality Model Set-up and Calibration Appendix C: Model Results
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LIST OF FIGURES
Figure 2.2a: Proposed layouts for the Phase 2A development of Iron-ore export facilities in Saldanha Bay. 15
Figure 2.2b: Proposed layouts for the Phase 2B development of Iron-ore export facilities in Saldanha Bay. 15
Figure 3.1: The Saldanha Bay/Langebaan Lagoon system showing major port infrastructure. 17
Figure 3.2: Proposed locations for the RO Plant. 19
Figure 3.3a: Location and extent of intake beach wells and location of discharge structures at Site 1 (PDNA/SRK Joint Venture, 2008). 21
Figure 3.3b: Location and extent of intake beach wells and location of discharge structures at Site 2 (PDNA/SRK Joint Venture, 2008). 22
Figure 3.4a: Location of pipeline intake and discharge structures at Site 1 (PDNA/SRK Joint Venture, 2008). 23
Figure 3.4b: Location of pipeline intake discharge structures at Site 2 (PDNA/SRK Joint Venture, 2008). 24
Figure 3.4c: Location of pipeline intake discharge structures at Site 3 for the with an intake and discharge configuration (option 3a) comprising a pipeline intake in Small Bay and pipeline discharge into Small Bay (PDNA/SRK Joint Venture, 2008). 25
Figure 3.4d: Location of pipeline intake discharge structures at Site 3 for the with an intake and discharge configuration (option 3b) comprising a pipeline intake in Small Bay and pipeline discharge into Big Bay (PDNA/SRK Joint Venture, 2008). 26
Figure 3.5a: Location and number of intake boreholes alongside the existing iron-ore stockpiles (PDNA/SRK Joint Venture, 2008). 29
Figure 3.5b: Location and number of intake boreholes alongside the existing MPT (PDNA/SRK Joint Venture, 2008). 30
Figure 5.1: Wind roses of the winds measured at Port Control in Saldanha Bay (see inset). 44
Figure 5.2: Wave height measured at the Slangkop Directional Waverider, located off Kommetjie on the Cape South-west coast (34°12'14.40"S, 18°17' 12.01"E, 70 m depth) for the period 2001 to 2007. 47
Figure 5.3a: Simulated wave conditions in Saldanha Bay for large offshore swell conditions and low winds (Offshore Hmo = 3.6 m , Tp=13 s, Direction = SW’ly, Local wind = 3 m/s S’ly). 48
Figure 5.3b: Simulated wave conditions in Saldanha Bay for moderate offshore swell conditions and very strong winds (Offshore Hmo = 1.3 m , Tp=11 s, Direction = SW’ly, Local wind = 20 m/s S’ly). 48
Figure 5.4a: Flood tide surface and bottom currents in Saldanha Bay during spring tide and under relatively calm conditions. 49
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Figure 5.4b: Ebb tide surface and bottom currents in Saldanha Bay during spring tide and under relatively calm conditions. 49
Figure 5.5a: Schematic of the wind driven and tidal currents in Saldanha Bay under S wind conditions. 50
Figure 5.5b: Schematic of the wind driven and tidal currents in Saldanha Bay under NW wind conditions. 50
Figure 5.6a: Surface and bottom water temperature and flow in Saldanha Bay under strong SE wind conditions (i.e. during the “active” upwelling phase). 52
Figure 5.6b: Surface and bottom water temperature and flow in Saldanha Bay after a strong SE wind event (i.e. relaxation phase of upwelling). 52
Figure 5.7: Vertical temperature structure of the water column along the “profile line” or cross-section indicated in Figure 5.6b. The upper panel shows the “active” upwelling phase while the lower panel shows the water column structure during the relaxation phase of the upwelling cycle. 53
Figure 5.8: Simulated surface and bottom water temperatures at North Buoy in Small Bay (see inset), showing the various temporal scales and magnitudes of seawater temperature variability in Saldanha Bay. 54
Figure 5.9: Conservation areas in Saldanha Bay (adapted from Taljaard and Monteiro, 2002). 68
Figure 5.10: Current mariculture lease holders in Saldanha Bay. 70
Figure 5.11: Designated beneficial use areas in Saldanha Bay (adapted from Taljaard and Monteiro, 2002). 72
Figure 7.1a: Proposed location of intake and discharge structures for Site 1. 82
Figure 7.1b: Proposed location of intake and discharge structures for Site 2. The yellow dotted line encloses the potential area within which beach wells may be located. 82
Figure 7.1c: Proposed location of intake and discharge structures for pipeline discharges into Small and Big Bay for Site 3. 83
Figure 7.1d: Proposed location of borehole intakes (adjacent to stockyard and MPT) discharge location for a pipeline discharge from Site 3 at Caisson 3. The intake boreholes will be located within the linear distance marked by the white lines in the figure opposite the existing iron-ore stockyard and the MPT (see Figures 3.5a and 3.5b in Section 3 for more detail). 83
Figure 7.2: Schematic of the near-field behaviour of a dense effluent. 95
Figure 7.3: Comparative maximum dimensions of the elevated salinity “footprint” (∆S < 1 psu or S < 36 psu) for all discharge sites. 102
Figure 7.4: Comparative maximum dimensions of the elevated temperature “footprint” (∆T < 1 ºC) for all discharge sites. 104
Figure 7.5: Comparative maximum dimensions of the biocide “footprint” (oxidising biocide concentration <3 µg.ℓ-1 or DBNPA residual concentrations less than the target values assumed to be appropriate) for all discharge sites. 106
Figure 7.6: Comparative maximum dimensions of the plume “footprint” (achievable dilution < 50) for all discharge sites. 109
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Figure B.1: Position of the instrumentation providing the data used to calibrate the model. 2
Figure B.2a: The computational grid used in the hydrodynamic simulations for which a detailed calibration has been undertaken (i.e. Phase 2 studies for the iron-ore expansion project – Smith et al., 2007). 4
Figure B.2b: A zoomed in view of the computational grid used in the hydrodynamic simulations for which a detailed calibration has been undertaken (i.e. Phase 2 studies for the iron-ore expansion project – Smith et al., 2007). 5
Figure B.3: The computational grid used for the initial RO Plant discharge simulations. 6
Figure B.4: The computational grid modified to increase the spatial resolution in the vicinity of the Caisson 3 discharge location. 7
Figure B.5: The computational grid used in the wave simulations. 8
Figure B.6: The higher resolution bathymetry used in additional to the South African Navy chart bathymetry data. 9
Figure B.7: Location of the Slangkop waverider buoy relative to the waverider buoy within Saldanha Bay. 11
Figure B.8: The Slangkop wave data from 19 October 2006 to 15 December 2006. 12
Figure B.9a: OCEANOR wave data from 30 June 1999 to 1 January 2000. 13
Figure B.9b: OCEANOR wave data from 1 January 2000 to 1 July 2000. 14
Figure B.10: Comparison between Delft3D-WAVE simulations and measurements at location A (Seapac 71079). The estimated accuracy of the SEAPAC measurements indicated in the plots are based on the work of Schüttrumpf et. al. (2006). 15
Figure B.11: Comparison between Delft3D-WAVE simulations and measurements at location B (Seapac 71079 and S4). The estimated accuracy of the SEAPAC measurements are based on the work of Schüttrumpf et. al. (2006). 16
Table B.1 Wave model parameters 17
Figure B.12: Theoretical clear sky radiation for the period simulated. 20
Figure B.13: Measured cloudiness converted to percentage cloud cover from cloudiness estimates in octals made daily at the Cape Columbine lighthouse at 08:00, 14:00 and 20:00 B). 20
Figure B.14: Air temperatures measured at Saldanha Port Control for the period simulated. 21
Figure B.15: Relative humidity (%) measured daily at 08:00B, 14:00B and 20:00 B) at the Cape Columbine lighthouse. 21
Figure B.16a: Water levels and wind time series input for the modelling from 30 June 1999 to 1 January 2000. 23
Figure B.16b: Water levels and wind time series input for the modelling from 1 January 2000 to 1 July 2000. 24
Figure B.17: Water levels and wind time series input for the modelling from 19 October 2006 to 15 December 2008. 25
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Figure B.18: Measured and modelled bottom currents at position A (see Figure B.1) from 22 October 2006 to 5 November 2006 29
Figure B.19: Measured and modelled bottom currents at position A (see Figure B.1) from 5 November 2006 to 22 November 2006. 29
Figure B.20: Scatterplots of the measured and modelled bottom currents at position A (see Figure B.1). 30
Figure B.21: Measured and modelled bottom currents at position B (see Figure B.1). 30
Figure B.22: Measured and modelled bottom currents at position B (see Figure B.1) from 3 December 2006 to 15 December 2006. 31
Figure B.23: Scatterplots of the measured and modelled bottom currents at position B (see Figure B.1). 31
Figure 6.24: Comparison between measured and modelled temperatures at position C (see Figure B.1) from 23 November 2006 to 3 December 2006. 32
Figure B.25: Comparison between measured and modelled temperatures at position C (see Figure B.1) from 3 December 2006 to 15 December 2006. 33
Figure B.26: Regression plots of the measured and modelled surface and bottom temperatures at position C (see Figure B.1). 33
Figure B.27: Measured and modelled temperatures at North Buoy (see Figure 6.2) from 1 July1999 to 1 October 1999 34
Figure B.28: Measured and modelled temperatures at North Buoy (see Figure 6.2) from 1 October 1999 to 1 January 2000. 34
Figure B.29: Measured and modelled temperatures at North Buoy (see Figure B.1) from 1 January 2000 to 1 April 2000. 35
Figure Captions for Figures in Appendic C are listed in Appendix C.
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LIST OF TABLES
Table 2.1: Proposed RO plant capacity for the various development phases of the Saldanha Bay Iron-ore Export Expansion project. 12
Table 3.1: Development alternatives used in this assessment (confirmed by Transnet on 22 November 2007). 32
Table 5.1: Tidal characteristics for Saldanha Bay. 45
Table 5.2: Wave height exceedances measured at a wave buoy near the entrance to Small Bay.46
Table 5.3: Dominant species/taxa in Saldanha Bay as reported from benthic macrofauna studies conducted in 1975, 1999 and 2004 (adapted from Atkinson et al., 2006). 60
Table 5.4: Current Mariculture lease holders in Saldanha Bay. 69
Table 7.1: Location of the intake and discharges for the various proposed sites. 85
Table 7.2: Main characteristics and conceptual design of intake structures for the RO plant. 86
Table 7.3: Main characteristics and conceptual design of discharge structures for the RO plant. 91
Table 7.4: Discharge rates and salinity of the brine discharge for the various development phases and plant capacities. 93
Table 7.5: The five intake and discharge combinations simulated in the hydrodynamic and water quality modelling. 96
Table 7.6: Summary of effluent plume dimensions around the discharge point (based on exceedances of the salinity water quality guidelines for cumulative periods of 6 hours and approximately 5 days), and the magnitude of the salinity elevation at the intake. 101
Table 7.7: Summary of effluent plume dimensions around the discharge point (based on exceedances of the temperature water quality guidelines for cumulative periods of 6 hours and approximately 5 days), and the magnitude of the temperature elevation at the intake. 103
Table 7.8: Summary of effluent plume dimensions around the discharge point (based on exceedances of the biocide water quality guidelines) for cumulative periods of 6 hours and approximately 5 days, respectively. 105
Table 7.9: Summary of effluent plume dimensions around the discharge point (based on non-exceedances of a required dilution of 50 times) for cumulative periods of less than 6 hours and less than approximately 5 days, respectively. 107
Table 7.10: Summary of effluent plume dimensions around the discharge point (based on non-exceedances of a required dilution of 100 times) for cumulative periods of less than 6 hours and less than approximately 5 days, respectively. 108
Table 8.2: Likely profile of residual concentrations of DBNPA in discharges to the marine environment from the RO Plant. (after Klaine et al., 1996) 133
Table 8.3: Potential chemicals used for the Reverse Osmosis process - information as supplied by Transnet on 5 December 2007. Quantities based on intakes flows of 8000 m3.day-
1. 140
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Table 9.1: Summary of potential impacts for the various Sites and associated intake and discharge combinations. 167
Table 9.2: Optional and required mitigation measures 174
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ABBREVIATIONS, UNITS AND GLOSSARY
Abbreviations
ANZECC Australian and New Zealand Environment and Conservation Council
CD Chart Datum
CIP Clean in Place
CSIR Council for Scientific and Industrial Research
CTD Conductivity-Temperature-Depth probe
DBNPA dibromonitrilopropionamide, a non-oxidising biocide
DMF Dual Media Filters
DSP Diarrehetic Shellfish Poisoning
DWAF Department of Water Affairs and Forestry
E East
EC50 median effective concentration
EDTA Ethylenediaminetetraacetic acid
EIA Environmental Impact Assessment
ESE East-southeast
HAB Harmful Algal Blooms
LC50 median lethal concentration
MCM Marine and Coastal Management
MPA Marine Protected Area
MPT Multi-purpose terminal
NaOCl Sodium Hypochlorite
NOEC no observed effect concentration
NNW North-northwest
TNPA Transnet National Ports Authority
NWA National Water Act (1998)
NSF National Sanitation Foundation
NW Northwest
PDNA PD Naidoo & Associates (Pty) Ltd
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PNEC predicted no effect concentrations
PSP Paralytic Shellfish Poisoning
RO Reverse Osmosis
RSA Republic of South Africa
RSA DWAF Republic of South Africa, Department of Water Affairs and Forestry
SBWQFT Saldanha Bay Water Quality Forum Trust
SE Southeast
SLS Sodium lauryl sulphate
SSE South-southeast
SSW South-southwest
STPP Sodium tripolyphosphate
SWRO Seawater Reverse Osmosis
TOC Total Organic Carbon
TRC Total Residual Chlorine
TSP Trisodium phosphate
WSW West-southwest
Units used in the report
cm centimetres
g.kg-1 grams per kilogram
g C.m-2 .day-1 grams Carbon per square metre per day
gfd gallons per square foot per day
h hours
ha hectares
kg kilogram
km kilometres
km2 square kilometres
µg.ℓ-1 micrograms per litre
Mℓ Megalitres
m metres
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mm millimetres
m2 square metres
m3.day-1 cubic metres per day
m3.hr-1 cubic metres per hour
m3.s-1 cubic metres per second
m3 yr-1 cubic metres per year
m.s-1 metres per second
mg.ℓ-1 milligrams per litre
ng.ℓ-1 nanograms per litre
mg Chl a.m-3 milligrams Chlorophyll a per cubic metre
ppt parts per thousand
psu practical salinity units which in the normal oceanic salinity ranges are the
same as parts per thousand (ppt)
% percentage
~ approximately
< less than
≤ less than or equal to
> greater than
≥ greater than or equal to
°C degrees centigrade
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Glossary
Acute toxicity Rapid adverse effect (e.g. death) caused by a substance in a
living organism. Can be used to define either the exposure or
the response to an exposure (effect).
Aerobic the condition where oxygen is present, e.g. a biochemical
process or condition occurring in the presence of oxygen.
Anaerobic the condition where oxygen is absent, e.g. a biochemical
process or condition occurring in the absence of oxygen.
Anoxia: The absence or near absence of oxygen, i.e. < 0.1 ml O2/ℓ.
Baroclinic A condition in the ocean in which isobaric (pressure) and
constant-density surfaces are not parallel, typically resulting in
vertically sheared flows driven by these density differences in
the water column.
Benthic Referring to organisms living in or on the sediments of aquatic
habitats (lakes, rivers, ponds, etc.).
Benthos The sum total of organisms living in, or on, the sediments of
aquatic habitats.
Benthic organisms Organisms living in or on sediments of aquatic habitats
Biodiversity The variety of life forms, including the plants, animals and
micro-organisms, the genes they contain and the ecosystems
and ecological processes of which they are a part.
Biocide A substance, such as a chlorine, that is capable of destroying
living organisms if applied in sufficient doses.
Biomass The living weight of a plant or animal population, usually
expressed on a unit area basis.
Biota The sum total of the living organisms of any designated area.
Bioturbation The displacement and mixing of sediment particles by benthic
fauna (animals) or flora (plants).
Bivalve A mollusk with a hinged double shell.
Community structure All the types of taxa present in a community and their relative
abundance.
Community An assemblage of organisms characterized by a distinctive
combination of species occupying a common environment and
interacting with one another.
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Contaminant Biological (e.g. bacterial and viral pathogens) and chemical
introductions capable of producing an adverse response
(effect) in a biological system, seriously injuring structure or
function or producing death.
Decarboxylation A chemical reaction in which a carboxyl group (-COOH) is split
off from a compound as carbon dioxide (CO2).
Detritus Unconsolidated sediments composed of both inorganic and
dead and decaying organic material.
Dilution The reduction in concentration of a substance due to mixing
with water
Dissolved oxygen (DO) Oxygen dissolved in a liquid, the solubility depending upon
temperature, partial pressure and salinity, expressed in
milligrams/litre or millilitres/litre
Diurnal Having a 24 hour cycle or recurring on a 24 hour basis.
Drfit-line A line of debris left by waves at the high-tide line.
Ecosystem A community of plants, animals and organisms interacting with
each other and with the non-living (physical and chemical)
components of their environment
Effluent A complex waste material (e.g. liquid industrial discharge or
sewage) that may be discharged into the environment.
Environmental impact A positive or negative environmental change (biophysical,
social and/or economic) caused by human action
Environmental quality A statement of the quality requirement for a body of water to
objective be suitable for a particular use (also referred to as
Resource Quality Objective)
Epifauna Organisms, which live at or on the sediment surface being
either attached (sessile) or capable of movement.
Eutrophication Strictly speaking, means an increase in chemical nutrients
(typically compounds containing nitrogen or phosphorus) in an
ecosystem. However this term is often used to mean the
resultant increase in the ecosystem's primary productivity (i.e.
excessive plant growth and decay) and even further impacts,
including lack of oxygen and severe reductions in water quality.
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Far-field The region beyond the near-field where secondary dilution
effects such as dispersion by environmental flows, etc
predominate rather than initial dilution effects due to buoyancy
forcing and entrainment.
Guideline trigger values These are the concentrations (or loads) of the key performance
indicators measured for the ecosystem, below which there
exists a low risk that adverse biological (ecological) effects will
occur. They indicate a risk of impact if exceeded and should
‘trigger’ some action, either further ecosystem specific
investigations or implementation of management/remedial
actions.
Habitat The place where a population (e.g. animal, plant, micro-
organism) lives and its surroundings, both living and non-living.
Half-life The time required for a pollutant to lose one-half of its original
coconcentration.
Headloss The head or pressure lost by water flowing in a pipe or
channel, caused by the roughness of the pipe or channel walls.
Hydrolysis The decomposition of organic compounds by interaction with
water
Infauna Animals of any size living within the sediment. They move
freely through interstitial spaces between sedimentary particles
or they build burrows or tubes.
Initial dilution Dilution that occurs in the near-field whilst the effluent plume is
still under the influence of strong buoyancy forcing and
entrainment effects.
LC50 (Median Lethal Concentration) A statistically derived concentration of a substance that can be
expected to cause death in 50% of test animals.
Level of Concern (LOC) A level (concentration) of a pollutant or toxicant at above which
the toxicant will pose a threat to an ecosystem or component
thereof.
Lowest Observed Effect The lowest tested concentration which produces a statistically
Concentration (LOEC) significant effect on the test organism in relation to the control
within a certain exposure time
Macrofauna Animals >1 mm.
Macrophyte A member of the macroscopic plant life of an area, especially
of a body of water; large aquatic plant.
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Mariculture Cultivation of marine plants and animals in natural and artificial
environments
Marine discharge Discharging wastewater to the marine environment either to an
estuary or the surf zone or through a marine outfall (i.e. to the
offshore marine environment)
Marine environment Marine environment includes estuaries, coastal marine and
near-shore zones, and open-ocean-deep-sea regions.
Meiofauna Animals <1 mm.
Metabolism The conversion or breakdown of a substance from one form to
another by a living organism
Near-field A region in close proximity to the discharge where buoyancy
forcing and entrainment effects primarily determine plume
dynamics
Nucleophilic A chemical compound or group that is attracted to nuclei and
tends to donate or share electrons
Oligotrophic Refers to a body of water with very low nutrient levels. Usually
these waters are poor in dissolved nutrients, have low
photosynthetic productivity, and are rich in dissolved oxygen.
Osmotic pressure The hydrostatic pressure produced by a solution in a space
divided by a semi-permeable membrane due to a differential in
the concentrations of solute.
Pollution The introduction of unwanted components into waters, air or
soil, usually as a result of human activity; e.g. hot water in
rivers, sewage in the sea, oil on land.
Population Population is defined as the total number of individuals of the
species or taxon.
Pycnocline A transition layer of water in the ocean, with a steeper vertical
density gradient than that found in the layers of ocean above
and below, i.e. a narrow range of depths at which density
changes abruptly between warm surface waters and deeper,
colder waters.
Recruitment The replenishment or addition of individuals of an animal or
plant population through reproduction, dispersion and
migration.
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Reverse Osmosis A filtration process that removes dissolved salts and metallic
ions from water by forcing it through a semi-permeable
membrane that removes molecules larger than the pores of the
membrane.
Sediment Unconsolidated mineral and organic particulate material that
settles to the bottom of aquatic environment.
Sludge Residual sludge, whether treated or untreated, from urban
wastewater treatment plants
Species A group of organisms that resemble each other to a greater
degree than members of other groups and that form a
reproductively isolated group that will not produce viable
offspring if bred with members of another group.
Subtidal The zone below the low-tide level, i.e. it is never exposed at
low tide
Supralittoral zone Also known as the spray zone, is the area above the spring
high tide line that is regularly splashed, but not submerged by
ocean water.
Surf zone Also referred to as the ‘breaker zone’ where water depths are
less than half the wavelength of the incoming waves with the
result that the orbital pattern of the waves collapses and
breakers are formed.
Suspended material Total mass of material suspended in a given volume of water,
measured in mg.ℓ-1l.
Suspended matter Suspended material in the water column.
Suspended sediment Unconsolidated mineral and organic particulate material that is
suspended in a given volume of water, measured in mg.ℓ-1.
Swash zone part of the foreshore washed by waves
Tainting This refers to the change in taste of seafood products as a
result of the presence of objectionable chemical constituents
which may greatly influence the quality and market price of
cultured products.
Taxon (Taxa) Any group of organisms considered to be sufficiently distinct
from other such groups to be treated as a separate unit (e.g.
species, genera, families).
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Thermocline A transition layer of water in the ocean, with a steeper vertical
temperature gradient than that found in the layers of ocean
above and below, i.e. a narrow range of depths at which
temperature changes abruptly between warm surface waters
and deeper, colder waters.
Toxicity The inherent potential or capacity of a material to cause
adverse effects in a living organism.
Turbidity Measure of the light-scattering properties of a volume of water,
usually measured in nephelometric turbidity units.
Turgor pressure The pressure of the cell contents against the cell wall, in plant
cells, determined by the water content of the vacuole, resulting
from osmotic pressure. i.e. the hydrostatic pressure produced
by a solution in a space divided by a semipermeable
membrane due to a differential in the concentration of solute.
Uncatalyzed Not subject to the process of catalysis that is the process
whereby the rate of a chemical reaction (or biological process)
is increased by means of the addition of a species known as a
catalyst to the reaction.
Vulnerable A taxon is vulnerable when it is not Critically Endangered or
Endangered but is facing a high risk of extinction in the wild in
the medium-term future.
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1 INTRODUCTION
The Iron Ore Handling Facility at the Port of Saldanha (including the proposed upgrades to the
facility), will require increased water supplies for dust suppression measures. It is anticipated that
ultimately a total of 3600 kℓ of water per day will be required for this purpose. The municipality
currently supplies water to the Iron Ore Handling Facility, but Transnet propose to supplement this
supply with additional sources of freshwater. Of all potential sources of such water, seemingly the
most feasible is that of a Reverse Osmosis (RO) seawater desalination plant.
In terms of existing legislation this proposed activity (i.e. the construction and operation of an RO
Plant) will require that a Basic Assessment of potential environmental impacts be undertaken.
1.1 Background
SRK Consulting and PD Naidoo & Associates (Pty) Ltd have been jointly appointed by Transnet to
undertake a Basic Assessment for a proposed RO plant at the Port of Saldanha. The principal
objectives of the Basic Assessment are to:
• Assess the potential impacts associated with the construction and operation of the proposed
RO plant;
• Provide an assessment of all the alternatives, including the three location alternatives
(including various combinations of intake and discharge infrastructure at the various sites) and
the no development alternative;
• Indicate whether the sites are environmentally acceptable or unacceptable for an RO plant in
terms of the respective impacts assessed by the relevant specialists;
• Recommend appropriate and practical mitigation measures to minimise the negative impacts
and maximise potential benefits associated with the three sites; and;
• Indicate the environmentally preferred site.
During the screening phase of the project a number of specialist studies were identified as being
necessary. These included a specialist study on the potential environmental impacts in the marine
environment, with a focus on predicting i) the behaviour and footprint of the brine discharge plume for
a number of proposed discharge locations and under a representative range of environmental
conditions, and ii) the associated potential impacts on the marine ecology.
Consequently, the PDNA/SRK Joint Venture approached the CSIR and Pisces Environmental
Services (Pty) Ltd to undertake a Marine Specialist Study to assess the impacts of the construction
and operation of the RO Plant on the marine environment.
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1.2 Scope of Work
The detailed Terms of Reference specific for this Specialist Marine Impact Assessment are to:
• Advise on the design of the RO Plant early in the process;
• Identify any fatal flaws associated with any of the alternative sites, or the proposed project;
• Recommend and implement additional terms of reference, based on professional expertise and
experience;
• Based on previous specialist studies (e.g. for the Phase 1B and Phase 2 iron-ore Terminal
Upgrade EIAs), existing knowledge of the area, and additional studies where required, provide
a brief baseline description of the marine environment (including aspects relating to water
quality, currents, marine ecology, etc.) that may be affected by the proposed RO Plant;
• Assess the significance of the potential impact of the proposed development on the marine
environment for each of the alternative sites (taking into consideration the differences in project
design in the case of each alternative site), according to the standard impact assessment
methodology supplied by PDNA/SRK Joint Venture and outlined in Section 4.1.3 of this report;
• Briefly describe any relevant legislative and permitting requirements that apply to the location
of the RO Plant (e.g. authorisation required for the construction of structures below or near the
high water mark, disposal of brine to the marine environment, etc);
• Recommend mitigation measures to minimise impacts associated with the proposed RO Plant
and enhance benefits;
• Identify an environmentally preferred site;
• Prepare a report comprising both baseline information and an impact assessment;
• Attend an integration workshop with the project team to discuss all the specialist studies;
• Address marine issues raised by registered Interested and Affected Parties; and
• If required, to attend a public meeting to discuss the issues highlighted during the public
participation phase.
1.3 Structure of the Report
This report describes the effects on the marine environment (i.e. the coastal zone below the high
water mark) of the construction and operation of the proposed RO Desalination Plant and
significance within the context of the receiving environment in Saldanha Bay. The report outlines the
approach to the study, assesses impacts identified by marine specialist consultants, and makes
recommendations for mitigation, monitoring and management of these impacts. The report is
structured as follows:
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• Chapter 1: Introduction - provides an introduction and background to the proposed project,
outlines the Terms of Reference and report structure and includes a brief overview of the
legislation relevant to the proposed activity;
• Chapter 2: Project Description - provides an overview of the proposed RO Plant, giving
some technical detail on the project designs being considered and the volume, nature and
water quality of the proposed discharges from the RO Plant;
• Chapter 3: Identification and Selection of Alternat ives - describes the study area, and
identifies and summarises various alternative project scenarios that will be considered as part
of the proposed development;
• Chapter 4: Approach to the Study - provides an overview of the modelling approach applied
in the assessment and the scenarios simulated in the modelling study. Information sources,
assumptions and limitations to the study are provided, and the assessment methodology is
outlined;
• Chapter 5: Description of the Affected Environment - briefly describes the receiving
biophysical environment that could be impacted by the RO Plant. Existing impacts on the
environment are discussed and sensitive and/or potentially threatened habitats or species are
identified;
• Chapter 6: Identification of Key Issues and Source s of Potential Environmental Impact –
here key issues identified during the public consultation and environmental screening process
for the proposed RO Plant are identified and summarised in terms of the construction phase,
operational phase and decommissioning phase;
• Chapter 7: Anticipated Changes in the Marine Envir onment due to the Effluent - provides
a detailed description of the discharge plume modelling studies undertaken and a summary of
the modelling results;
• Chapter 8: Assessment of Environmental Impact - identifies and assesses the significance
of potential direct, indirect and cumulative environmental impacts on the marine environment
associated with the construction and operation of the RO Plant, based on information provided
by the client and the results of the modelling studies. The impacts identified for each of the
three alternative sites are assessed and summarised separately;
• Chapter 9: Conclusions and Recommendations - here the environmental acceptability of
the development alternatives are discussed, and the environmentally preferred alternative is
identified. A comparison between the “no development” alternative and the proposed
development alternatives is also included. Mitigation measures and monitoring
recommendations are presented;
• Chapter 10: References - provides a full listing of all information sources and literature cited
in this document.
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1.4 Legislative and Permitting Requirements
The primary policy and legislation that needs to be considered is that related to the brine (and co-
discharges) from the proposed RO Plant. Under South African legislation the effluent water
discharge (and potential associated co-discharges) from the proposed RO plant in Saldanha Bay is
classified as “industrial wastewater” and thus requires a license, under Section 21 of the National
Water Act 1998 (NWA) for disposal to the marine environment. In terms of policy, legislation and
practice the following documents are of relevance:
• South Africa’s “Operational policy for the disposal of land-derived wastewater to the
marine environment ” (DWAF, 2004a-c) that captures the legislative framework of relevance to
this study;
• National Water Quality Management Framework (DWAF, 2002); and;
• Documentation of relevance to licensing a wastewater discharge to the marine environment
(e.g. DWAF, 2000, 2003a, 2003b).
The key management institutions and role-players in the decision on the acceptability of the proposed
water discharges into Saldanha Bay are the Saldanha Bay Water Quality Forum Trust (SBWQFT) in
an advisory role, the DWAF2 and the DEAT, all of whom will ensure transparent and adequate
stakeholder and public participation.
Specifically, environmental quality objectives need to be set for the marine environment, based on
the requirements of the site-specific marine ecosystems, as well as other designated beneficial uses
(both existing and future) of the receiving environment. The identification and mapping of marine
ecosystems and the beneficial uses of the receiving marine environment provide a sound basis from
which to derive site-specific environmental quality objectives (Taljaard et al. 2006). To ensure that
environmental quality objectives are practical and effective management tools, they need to be set in
terms of measurable target values, or ranges for specific water column and sediment parameters, or
in terms of the abundance and diversity of biotic components.
The South African Water Quality Guidelines for Coastal Marine Waters (DWAF 1995) provide
recommended target values (as opposed to standards) for a range of substances, but these are not
exhaustive. Therefore, in setting site-specific environmental quality objectives, the information
contained in the DWAF guideline document is supplemented by additional information obtained from
2 The DWAF previously has indicated that the Water Quality Management Plan developed by the SBWQFT
and associated studies (e.g. Taljaard and Monteiro, 2002, Monteiro and Kemp, 2004), together with representations from the DEAT, will play a significant role in its decision-making, i.e. the present Saldanha Bay water quality management plan and associated scientific studies, together with the relevant policy legislation and licensing procedures, will form the basis upon which a decision is made on the viability of the proposed RO Plant discharge into Saldanha Bay and the subsequent granting of a licence for such a discharge. The reader is referred to Section 8.1.3 of this report for more detailed discussion of the requirements of the SBQWQFT Water Quality Management Plan and associated requirements.
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published literature, best available international guidelines (e.g. ANZECC 2000; World Bank 1998),
as well as site-specific data and information (e.g. obtained through numerical modelling outputs).
The relevant and expanded set of target values for the Benguela Current Large Marine Ecosystem
countries (Angola, Namibia and South Africa) are summarised in Taljaard (2006).
Saldanha Bay supports an important mussel farming industry. In South Africa, standards controlling
the quality of fish and shellfish flesh for human consumption (i.e. concentration limits of constituents
as required by law) are set out in the following legislation:
• Foodstuffs, Cosmetics and Disinfectants Act (Act 54 of 1972), Regulation - Marine food, 2
November 1973.
• Foodstuffs, Cosmetics and Disinfectants Act (Act 54 of 1972), Regulations related to metals
and foodstuffs, 9 September 1994.
In principle, these food quality standards should be met if the quality of the water from which these
organisms are harvested or cultured complies with the recommended target values for mariculture,
as specified in the South Africa Water Quality Guidelines for Coastal Marine Waters (DWAF, 1995).
The specific water quality guidelines adopted for this study are summarized in Chapter 8.
The possible implications of the policy, legislation and approval and licensing procedures referred to
above, for the proposed RO Plant water discharge into Saldanha Bay, are summarized in Appendix
A.
In addition to the above, there will need to be due consideration of the requirements of the following
policy and legislation related primarily to the siting and construction of the RO Plant and its
associated intake and discharge infrastructure. A more detailed description of these policy and
legislation requirements is given in DWAF (2007). It should be noted however that in this specialist
report, only marine impacts (i.e. impacts below the high water mark) are considered, with a specific
focus on the intake of seawater and discharge of brines from the proposed RO Plant and associated
infrastructure (including the impacts of possible intake and discharge through beach wells where
deemed feasible). Construction impacts and any ongoing impacts (e.g. disruption of sediment
transports in the marine environment) therefore are limited to those occurring below the high water
mark. Thus only specific aspects (text in bold) of the policy and legislation described below is of
relevance to this study.
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In addition to the requirements of the NWA policy and legislation, the following also are of relevance
to the siting, construction and operation of an RO Plant:
• National Environmental Management Act (Act No 107 o f 1998): The NEMA serves as the
framework legislation, promoting sound environmental management, co-operative governance
and sustainable development. The NEMA also contains the principle that environmental
management must place people and their needs at the forefront of its concern, and serve their
physical, psychological, developmental, cultural and social interests equitably. Specifically, one
of these principals, according to Section 2(4)(r), is that: “sensitive, vulnerable, highly
dynamic or stressed ecosystems, such as coastal sho res, estuaries, wetlands or similar
systems require specific attention in management an d planning procedures, especially
where they are subjected to significant human resou rce usage and development
pressure” . As summarised in DWAF (2007), of specific interest to the marine impacts of
desalination are the following activities, which are listed in Regulation 386 (Appendix C) and
which therefore need to follow a “basic assessment” procedure:
2: Construction or earth moving activities in the s ea or within 100 metres inland of
the high-water mark of the sea, in respect of –
2(d) embankments
2(e) stabilising walls;
2(f) infrastructure, or
2(g) buildings
3: The prevention of the free movement of sand, including erosion and accretion, by
means of planting vegetation, placing synthetic material on dunes and exposed sand
surfaces within a distance of 100 metres inland of the high-water mark of the sea.
5: The removal or damaging of indigenous vegetation of more than 10 square metres
within a distance of 100 metres inland of the high-water mark of the sea.
6: The excavation, moving, removal, depositing or comp acting of soil, sand, rock
or rubble covering an area exceeding 10 square metr es in the sea or within a
distance of 100 metres inland of the high-water mar k of the sea .
12: The transformation or removal of indigenous vegetation of 3 hectares or more or of
any size where the transformation or removal would occur within a critically endangered
or an endangered ecosystem listed in terms of section 52 of the National Environmental
Management: Biodiversity Act, 2004 (Act No. 10 of 2004).
13: The abstraction of groundwater at a volume where any general authorisation issued
in terms of the National Water Act, 1998 (Act No. 36 of 1998) will be exceeded.
25: The expansion of or changes to existing facilit ies for any process or activity,
which requires an amendment of an existing permit o r license or a new permit or
license in terms of legislation governing the relea se of emissions, pollution,
effluent.
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NEMA also governs issues such as the Control of Vehicles in the coastal zone . The
Minister has proclaimed regulations under section 44 of the NEMA to control the use of
vehicles in the coastal zone in order to protect and conserve the sensitive ecosystem of the
coastal zone. The regulatory authorities have indicated that Transnet will not need to obtain a
permit for vehicle access to the beach for the pre-feasibility studies and construction activities
proposed.
• Integrated Coastal Management Bill (Draft): The main purpose of this Bill is to establish a
system of integrated coastal and estuarine management in South Africa, including norms,
standards and policies, in order to promote the conservation of the coastal environment, and
the ecologically sustainable development of the coastal zone. Chapter 7 of the Bill deals with
the protection of coastal resources.
Section 57 defines the principal that adverse effects need to be avoided, and also provides a
clear link with NEMA, which will be discussed. Section 57(b) specifically draws the attention to
the operator of a pipeline that ends in the coastal zone (sub-section (iv)) and any person who
produce a substance which causes an adverse effect (sub-section (v)). Section 58 stipulates
that authorisation needs to be applied for at the r elevant authority if an activity which
might have a possible adverse effect on the marine environment is planned.
Section 63 of the Bill deals with specific activities which are prohibited in the “coastal buffer
zone” (see DWAF, 2007 for more detail). Activities listed in Part A of Schedule 3 are prohibited
in the coastal buffer zone, while activities listed in Part B of Schedule 3 require a permit. All
activities within coastal public property and exclusive economic zones listed in Part C of
Schedule 3 also require a permit.
Activities of importance to desalination in Part A include:
• The disposal of solid waste, rubble, unprocessed sewage or any other effluent likely to
cause an adverse effect on the coastal environment.
Activities of importance to desalination in Part B include:
• The erection, construction, placing, or any significant alteration or extension of a building
or structure;
• The construction or any significant alteration or extension of a road;
• The clearing of indigenous vegetation other than cultivated indigenous vegetation;
• The stabilization or destabilization of dunes.
Activities of importance to desalination in Part C include:
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• The erection, construction, placing, alteration or extension of a building or structure on or
in any coastal public property, including an artificial reef, or any structure designed to
prevent coastal erosion or to promote accretion of the seashore;
• �The disturbance of any coastal public property in a manner that has or is likely to
have an adverse effect on the coastal environment, including any excavations,
dredging, draining, drilling or tunnelling;
• The destruction, damage or disturbance of any coast al public property in a manner
that has or is likely to have an adverse effect on biodiversity or habitat;
• �The abstraction of water from coastal waters for ag ricultural, commercial or
industrial purposes, including for aquaculture and desalination, or in a manner that
is likely to have an adverse effect;
• The stabilization or destabilization of dunes.
Section 74 of the Bill makes provision for permits to be issued, in co-operation with the NWA,
to discharge effluent into coastal waters.3 No reference, however, is made to the need to apply
for the abstraction of seawater (DEAT, 2007). The requirement for such a permit may however
be implicit in that all activities listed under Part C of Schedule 3 require a permit and one of
these activities is ”the abstraction of water from coastal waters for ag ricultural,
commercial or industrial purposes, including for aq uaculture and desalination, or in a
manner that is likely to have an adverse effect.”
• Sea Shore Act (Act No 21 of 1935): The Sea Shore Act provides the legal decision-making
legislation for all sea-related construction work. This administrative function and authority is
delegated to the Provincial Department responsible for environmental management. It should
be noted that the Act also does not address other issues such as the management of the
Admiralty Reserve, found along the high water mark in certain sections of the coast
(Department of Environmental Affairs and Tourism, 2000).
• National Ports Act 12 of 2005: The National Ports Act 12 of 2005 and its delegated
authorities may be of relevance in terms of some of the developments proposed. Specifically,
where a land-based activity, which requires a licence under section 21 of the NWA, falls within
a commercial harbour area, the Transnet National Ports Authority, as the landowner, is
responsible to ensure that such an activity meets the requirements of the relevant laws (DEAT,
2007).
• National Heritage Resource Act (Act No 25 of 1999): The National Heritage Resource Act
(NHRA) states in section 38 that it is required that any person who intends to under take a
development, such as the construction of a pipeline in excess of 300 m in length, or any
3 This bill presently is in draft form and consequently as yet there are no such permit requirements.
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development or activity which will change the chara cter of the site, must, at the very
early stages, notify the responsible authority and supply details regarding the intended
development. If the NEMA requires the assessment of a heritage resource, then the
comments and recommendations of the heritage resource authority must be obtained, and
unless this authority stipulates that section 38 of the NHRA does not apply, the Act clearly
stipulates what such an assessment must include. Should there be construction activities
in the marine environment, it is likely that the op inion of a marine archaeologist may be
required prior to environmental approval of the pro ject. Note that this specialist study
explicitly excludes issues to be assessed in terms of the NHRA).
Also of relevance here are:
• Marine Living Resources Act 18 of 1998
• National Environmental Management: Biodiversity Act [No. 10 of 2004]
• National Environmental Management Protected Areas A CT 57 of 2003 as amended by the
National Environmental Management: Protected Areas Amendment Act 31 of 2004
If due consideration is given to NEMA, the NWA, the principles in the Integrated Coastal
Management Bill and associated environmental legislation, compliance with the above legislation is
likely to be ensured.
It is however recommended that there is adequate and timeous consultation with both the DWAF and
DEAT regarding the intake and discharges, as well of the infrastructure, associated with the proposed
RO Plant. Transnet Projects has indicated that such consultation has occurred and is ongoing.
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2 PROJECT DESCRIPTION
2.1 Description of the RO Plant Facilities
The proposed RO Plant comprises the following:
• An RO plant containment building (approximately 2400 m² surface footprint) with room for three
RO modules, an electric sub station, a motor control room, a pump house, a store room, office
and ablution facilities and space for parking;
• Sea water supply and brine discharge via pipelines, beach wells or boreholes;
• Submersible pumps and piping for the extraction and discharge of sea water;
• A sea water intake storage tank alongside the RO building;
• A potable water storage tank alongside the RO building;
• Storage reservoir(s) totalling 5 Mℓ, 48 hour potable water storage capacity next to the existing
potable water reservoir or at the alternative site adjacent to the borrow pit area;
• A small service road connecting the RO building to the nearest road infrastructure; and
• All requisite electrical and communication facilities between the RO installations and the Iron
Ore Handling Facility.
The basic process for the treatment of water in the proposed RO plant is as follows (PDNA/SRK Joint
Venture, 2007). Sea water is supplied through a seawater intake and appropriately treated or
supplied and pre-filtered through beach wells or boreholes and then pumped to a seawater buffer
storage tank (Figure 2.1). The salt water is then pumped at high pressure through to the RO
membranes. The desalinated water is piped to the potable water tank and the concentrated sea
water (brine) is released back in to the ocean through discharge pipes with appropriate diffuser
structures or beach wells. The concentrated sea-water may or may not require treatment before
being disposed, but this will be addressed as part of this specialist study.
Figure 2.1: Indicative components of an RO Plant (P DNA/SRK Joint Venture, 2007).
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2.2 Life Span of Project
The anticipated life span of the RO plant is 25 years. After this period it is likely that the RO units will
be refurbished or replaced and that the RO Plant will continue to operate. It is, however, not clear
whether or when “re-construction” or major maintenance will be required should beach
wells/boreholes be used at the point of intake and/or discharge as considered for all 3 of the
proposed sites.
2.3 Proposed Plant Capacity
There is an immediate requirement for potable water/freshwater for dust suppression measures
associated with the Phase 1A and 1B expansion of the Saldanha Bay iron-ore export facilities. It is
intended that the initial phase of the RO Plant (Phase 1A/1B) comprising output from a single RO unit
(1200 kℓ/day capacity) be commissioned in approximately March 2009, depending on authorisation of
the project by DEAT. The freshwater requirement will increase with the proposed further Phase 2A
development of the iron-ore export facilities when the requirement will be such that a further 2 RO
units will need to be commissioned. It is anticipated that the additional 2 RO units will need to be
operational some 6 months to one year after the initial commissioning of the first RO unit.
The development phases and the associated RO plant capacities required are indicated in Table 2.1
below. These are based on the potable water requirements for the various phases as tabulated in
Figure 11 of the Saldanha Iron Ore Terminal Water Supply and Demand Report (Transnet Report by
Alistaire Dick, 28 May 2007) and as amended in feedback at a meeting with Transnet (SRK offices on
13 August 2007) where a potable water recovery rate of 45% was specified.
Table 2.1: Proposed RO plant capacity for the vari ous development phases of the Saldanha Bay Iron-ore Export Expansion project.
Development
Phase
Number of 1200 k llll
RO Units Required
Potable Water
Produced
(m3/day)*
Brine Discharge
Volumes
(m3/day)
Intake
Volumes
(m3/day)
Phase 1A/1B 1 1200 1467 2 667
Phase 2A/2B 3 3600 4 400 8 000 * 1000 m3/day = 1000 kℓ/day = 1 Mℓ/day
It should be noted that, although the intention would be to initially install only one of the three RO
units, the full capacity of the proposed plant with three units has been assessed for the purposes of
the Basic Assessment and this marine specialist study.
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2.4 Construction and commissioning of infrastructur e
It is planned that the RO support infrastructure (pipelines, beach wells, boreholes, buildings, etc)
however will be sized for the full three modules (3600 kℓ/day) and installed during the initial phase of
the project (approximately Sept 2008 to March 2009). This may include potential beach wells for
both intake of seawater and/or discharge of the brine from the RO Plant. Should beach wells be
constructed and/or intake discharge pipelines be installed, the full infrastructure will be installed
during the initial construction phase. Consequently no further disruption of the beach is expected
once the RO support infrastructure is installed during the initial construction phase. Thus it will only
be the additional RO modules that will be installed in a phased approach (i.e. initial installation of one
RO unit followed by installation of additional 2 RO units some 6 to 12 months later). It is not
anticipated that the installation of the additional 2 RO units will have any environmental impacts as
the installation activities will be confined to buildings within the existing infrastructure.
Construction activities of relevance to assessing marine impacts include:
• The construction of seawater intakes that may include the impacts of beach well construction
for intake waters, beach sumps and other appropriate intake infrastructure;
• The construction of discharge structures (including possible beach well discharges).
Beach wells for intake are being proposed only for Site 1 and Site 2 (see Figure 3.2 in Section 3).
The option of discharge beach wells, initially considered for only Site 1, is no longer deemed to be
feasible (SRK, 2007) and is consequently excluded from this marine impact assessment. Discharge
beach wells thus are not being considered for any o f the proposed sites .
The construction activities associated with intake and discharge structures are as follows. The
installation of pipeline intakes and/or discharges will require the standard techniques for the
construction of such infrastructure that include the provisions of an on-land construction site (albeit
limited) for pipeline laying activities and possible other activities such as trenching through the surf-
zone and/or associated activities below the high-water mark. Presently the siting and detailed design
of such intake pipelines (and associated intake structures) as well as the exact nature of the
discharge pipelines and discharges structures (diffusers, etc) remains non-specific. It is intended that
this study of potential environmental impacts, together with other engineering design considerations,
will inform the exact nature of such infrastructure. Consequently, presently only a generic description
of construction activities is possible. Should there be a requirement for the drilling of beach wells,
access will be required for a drilling rig and support vehicles to possibly provide drilling media, fuel,
etc. The exact nature of the construction activities will depend on the beach well design which will
come from the successful RO Plant tenderer. The drilling activities involved are similar to those that
will be employed to sink the test wells as described for the groundwater assessment studies (Visser
et al., 2007).
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The physical layout of the port is likely to change over time. In particular the proposed Phase 2A and
2B developments4 will result in significant infrastructural changes in the marine environment,
however, only Site 1 and some of the discharge options from Site 3 (see Section 3 for details of the
proposed RO Plant locations) is likely to be affected by these changes.
Under the assumption that the RO discharge plume and its associated impacts will be of limited
spatial extent (and therefore not substantively affected by the proposed changes to the marine
environment i.e. dredging and reclamation), the initial assessment considers only the proposed RO
discharges under the Phase 1A and 1B development scenario, i.e. under a development scenario
where there are no changes in the marine environment compared to the presently existing situation.
Had these initial results indicated that the RO discharge plume extents would be significant, it would
have been necessary to assess further development scenarios (i.e. Phase 2A and 2B) in the
assessment. The proposed layouts associated with the Phase 2A and 2B developments are given in
Figures 2.2a and 2.2b.
In all cases the plume dynamics may be affected to some degree, however these differences in
plume behaviour are not deemed sufficient to warrant detailed modelling studies of these discharge
options under the various Phase 2 development scenarios.
As noted above, changes in the discharge plume behaviour under the Phase 2 development
scenarios are only likely to be substantive for Site 1 and possibly two of the discharge options for
Site 3, namely brine discharges alongside the causeway into Big Bay and at caisson 3. Should the
large reclamation area be constructed during Phase 2 (see Figures 2.2a and 2.2b) there is likely to
be some changes in the plume dynamics for a discharge at Site 1 (development options 1a & 1b).
These changes are likely to result in stronger flows at or near the discharge location, particularly
under southerly wind conditions. This is likely to result in greater dispersion of the plume. However a
relatively quiescent area is likely to develop in the lee of the reclamation area (between the
reclamation area and the causeway), particularly under southerly wind conditions. There is potential
for the accumulation of discharged brine should it reach this area before being significantly dispersed.
The modelling results indicate that the plume dimensions are likely to be sufficiently limited that this
will not occur. The changes in the plume dynamics for a discharge at Caisson 3 from Site 3 are
expected to be limited, the most likely change being enhanced dispersion of the RO Plant discharge
plume due to increased tidal (and upwelling) flows past Caisson 3 associated with extensions in the
shipping channel proposed for Phase 2.
4 Phase 2A will expand the iron-ore handling capacity of the Port of Saldanha to approximately 67 MTPA
and will require the construction of an additional single berth. It is anticipated that the dredging activities associated with the Phase 2A development will commencce in early 2010, however there remains a degree of uncertainty around this date due to a number of factors (e.g. dredge equipment availability, environmental approvals, etc). Phase 2B (following immediately after Phase 2A or delayed for a period of approximately 5 to 10 years later) will expand the iron-ore handling capacity of the Port of Saldanha to approximately 93 MTPA and will require extension of the dredge channel and the construction of a further additional berth (i.e. a total of two additional berths compared to presently existing berthing facilities).
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Figure 2.2a: Proposed layouts for the Phase 2A deve lopment of Iron-ore export facilities in Saldanha Bay.
Figure 2.2b: Proposed layouts for the Phase 2B deve lopment of Iron-ore export facilities in Saldanha Bay.
Proposed Reclaim Area dimensions
Proposed Phase 2A shipping channel
Proposed Reclaim Area dimensions
Proposed Phase 2B shipping channel
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A discharge into Big Bay from Site 3 (development option 3b) may result in the accumulation of warm
salty waters in the dredge channel when developed to its maximum proposed extent Phase 2 of the
proposed iron-ore export expansion project, should the discharge plume not be sufficiently dissipated
before reaching the deeper waters of the proposed shipping channel. The modelling results indicate
that under worst case conditions there is a possibility of such an occurrence approximately for up to a
total duration of 24 hours within a season, however propeller wash is likely to dissipate any such
plume reaching the shipping channel. Such occurrences, if and to the extent that they occur, will not
change the conclusions of this study.
Similar behaviour could occur for a discharge from Site at Caisson 3, however the potential
consequences at this site are considered to be significantly less than indicated above for a discharge
from Site 3 into Big Bay. The reason for this is that the plume dimensions for a discharge at Caisson
3 are significantly smaller than for a discharge into Big Bay from Site 3. Furthermore, the tidal
flushing at Caisson 3 and consequently dispersion of the brine plume is likely to increase under the
Phase 2 development scenarios (although the brine may spread somewhat more extensively into the
proposed extended dredge channel into Big Bay).
The observations indicate that a detailed modelling study of the potential RO Plant discharges under
the Phase 2 port layouts is not indicated
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3 IDENTIFICATION AND SELECTION OF ALTERNATIVES
3.1 Geographical Setting
Saldanha Bay is situated on the west coast of South Africa, approximately 120 km north of Cape
Town and is directly linked to the shallow, tidal Langebaan Lagoon (Figure 3.1). The bay contains
five offshore islands, namely Malgas, Jutten, Marcus, Meeuw and Schaapen Island.
Figure 3.1: The Saldanha Bay/Langebaan Lagoon syste m showing major port infrastructure.
Saldanha Bay is the only natural harbour of significant size on the west coast of South Africa, and
hosts a substantial fishing industry and fish processing factories. In 1971 the harbour was upgraded
into an international port, which was followed by two major developments:
• a causeway that linked Marcus Island to the mainland, providing shelter for ore-carriers, and
• the construction of the iron ore causeway, which was later extended to provide for the import
of oil.
Reclaim dam
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A multipurpose terminal was later added to the iron-ore causeway and a small-craft harbour was built
to cater for the increase in recreational and tourism activities in the bay. The construction of the iron
ore causeway essentially divided Saldanha Bay into two sections: a smaller area bounded by the
causeway, the northern shore and the ore causeway (called Small Bay); and an adjacent larger,
more exposed area called Big Bay, which leads into Langebaan Lagoon. Langebaan Lagoon forms
part of the West Coast National Park and is internationally recognised as a Ramsar site in terms of
the Convention on Wetlands of International Importance, especially as waterfowl habitat. Small Bay,
Big Bay and Langebaan Lagoon can be considered to comprise one large ecosystem with strong
interdependencies between the various regions in this semi-enclosed coastal embayment.
Reference to a semi-enclosed coastal embayment does not imply that there is not significant
exchanges and flushing of the various sub-components (i.e. Small Bay, Big Bay and Langebaan
Lagoon) by water from the adjacent continental shelf. Estimated exchanges between the various
regions of the bay are as tabulated in the footnote below5.
3.2 Siting Alternatives
Three alternative locations within the Port of Saldanha are being considered for the location of the
RO plant (Figure 3.2). At the three proposed sites, there are various opportunities and constraints in
terms of the specific intake and discharge alternatives that may be considered (see Table 3.1).
These are described in generic terms, followed by a detailed description of the various alternatives
assumed and assessed for the three proposed locations for the RO Plant.
A detailed description of the three proposed sites follows.
• Alternative 1: Located to the east of the Iron Ore Handling Facility. The RO plant would be
situated in the vicinity of the coastal dunes, with both intake and discharge occurring in Big
Bay. It is proposed that the intake waters are provided via seawater supply beach wells or a
pipeline intake from the surf-zone. The discharge infrastructure comprises a 20 to 30 m
“diffuser” pipeline laid along the existing revetment. Brine discharge would be into the larger
5 Estimated exchanges between the various regions of the bay are as tabulated below.
Exchange fluxes* Location of cross-section Neap tides
(m3.s-1) Spring tides
(m3.s-1)
Flux across the mouth of Small Bay 210 1 680
Flux across the mouth of Big Bay (i.e between Saldanha Bay and the adjacent continental shelf)
1 100 7 950
Flux across the mouth of Langebaan Lagoon (both channels)
500 3 260
* It should be noted that the salt input into Saldanha Bay from the RO Plant discharge are only 0.012%, 0.06% and 0.026% of the salt fluxes through the mouth of Big Bay, the mouth of Small Bay and through the two channels at the mouth of Langebaan Lagoon under Neap tides, respectively . Under Spring tides the percentages are almost an order of magnitude less than those for Neap tides.
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Saldanha Bay (Big Bay). The two intake and discharge combinations considered under
alternative 1 are summarised in Table 3.1.
• Alternative 2: Located north and northwest of the Iron Ore Handling Facility. The RO plant
would be established in an area currently containing stockpiles of gravel and construction
rubble. Intake options include beach well intakes or surf-zone (sump) intakes. The discharge
option considered is a pipeline discharge into the North-eastern corner of Small Bay. The two
intake and discharge combinations considered under alternative 2 are summarised in Table
3.1.
• Alternative 3: Located on the southern section of the Quay of the Iron Ore Handling Facility.
The RO plant would be positioned on a gravel area adjacent to the Multi-purpose Terminal
(MPT). There is no beach of sufficient size in this area for intake beach wells. Consequently,
seawater supply and brine discharge would need to be via a pipeline intake or borehole intakes
along the causeway. A number of alternative discharge locations are possible, namely a
discharge into Small Bay, a discharge at depth into Big Bay or a discharge at Caisson 3 at the
end of the causeway. The four intake and discharge combinations considered under
alternative 3 are summarised in Table 3.1.
Figure 3.2: Proposed locations for the RO Plant.
Small Bay
Big Bay
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3.3 Conceptual Designs of Possible Intake and Disch arge Structures
The conceptual designs of possible intake and discharge structures follows.
3.3.1 Intake Alternatives
The three intake alternatives for the supply of seawater to the RO Plant, namely beach wells,
boreholes and feed-water pipelines, are described in more detail below:
Beach Wells
Beach intake wells with submersible pumps have been proposed as a means of supplying seawater
to the RO Plant. The proposed intake wells will consist of perforated PVC and stainless steel
cylinders of 300 - 500 mm diameter equipped with continuous-slot stainless steel screens. The wells
will be sunk above the high water mark vertically to a maximum of 20 m into the beach sediments.
The tops of the wells will protrude out of the surface of the beach by approximately one metre. As an
alternative, horizontal collector wells with horizontal collector pipes could be used. Seawater filtered
through the sand will percolate into the wells from where it will be pumped by underground pipeline
(not exceeding 360 mm internal diameter) to the seawater buffer tank. However, the amount of water
that can be taken in by subsurface intakes is a function of the type of substrate, its permeability and
other geotechnical characteristics (California Coastal Commission, 2004). Beach wells will not work
well in areas where the substrate contains high proportions of silt or clay, or where the sandy
substrate is unstable or insufficiently deep to ensure that the intakes are not exposed during seasonal
sand movement or storms.
For the Saldanha Bay RO Project, this has been determined for Site 1 by a specific geohydrological
groundwater study (Visser et al., 2007) and shoreline stability studies associated with proposed
future port developments in Saldanha Bay (Smith et al., 2007). Numerical modelling conducted as
part of the groundwater study indicated that ~10 vertical intake wells drilled 50 m apart parallel to the
shoreline above the high water mark at Site 1 would be required to abstract the anticipated raw water
demand of 8000 m3/day for the RO plant (Figure 3.3a). Alternatively, if horizontal collector wells are
decided on, at least two with ~100 m of horizontal collector pipes each will be required (Visser et al.,
2007). Although no similar detailed studies have taken place to date for the proposed beach well
intakes at Site 2, a worst case scenario of up to 10 intake wells, spaced ~50 m apart have been
proposed for this site (Figure 3.3b).
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Figure 3.3a: Location and extent of intake beach we lls and location of discharge structures at Site 1 (PDNA/SRK Joint Venture, 2008).
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Figure 3.3b: Location and extent of intake beach we lls and location of discharge structures at Site 2 (PDNA/SRK Joint Venture, 2008).
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Figure 3.4a: Location of pipeline intake and discha rge structures at Site 1 (PDNA/SRK Joint Venture, 2 008).
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Figure 3.4b: Location of pipeline intake discharge structures at Site 2 (PDNA/SRK Joint Venture, 2008) .
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Figure 3.4c: Location of pipeline intake discharge structures at Site 3 for the with an intake and discharge configuration (option 3a) comprising a pipeline intake in Small Bay and pipeline discharge into Small Bay (PDNA/SRK Joint Venture, 2008).
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Figure 3.4d: Location of pipeline intake discharge structures at Site 3 for the with an intake and discharge configuration (option 3b) comprising a pipeline intake in Small Bay and pipeline discharge into Big Bay (PDNA/SRK J oint Venture, 2008).
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Designed with appropriate intake velocities and installed at the proper depth within the substrate,
beach wells can operate with negligible effects on local marine life. A further operational advantage
is that the natural filtering effects of the beach sediments ensure that the feed-water is comparatively
clean, thereby reducing the necessity for the use of pre-treatment substances, and thus reducing
operating costs as well as likely discharges of concern.
Single-point Intakes
As an alternative, feed-water may be supplied by a single-point intake. The intake will be located
either in the surf-zone or just beyond (Site 1 – see Figure 3.4a), in the quay wall (Site 3 – see Figures
3.4c and d), or up to 75 m offshore (Site 2 – see Figure 3.4b).
Surf-zone intakes typically consist of one or more excavated sumps sunk into the sediments a
distance of ~15-20 m below the high water mark in the surf-zone. The sumps will be covered in sand
transported through the area by waves and currents. The feed-water is thus drawn in through the
overlying sediments, which act as a natural filter thereby removing fine particulate material and
improving water quality delivered to the seawater buffer tank. The intakes and associated pipelines
usually deliver seawater to a pump house located above the high water mark, from where the
seawater is pumped to the buffer tank at the RO Plant. In essence therefore, a surf-zone intake is
similar to a beach well intake.
However, depending on specific circumstances an alternative deeper water structure may be
considered that lies beyond the active surf-zone. Pipeline intakes for desalination plants are
commonly 1-m in diameter and composed of HDPE (High Density Polyethylene), however for the
small volumes being considered here the pipelines diameters are likely to be only 0.2 to 0.4 m
diameter HDPE pipelines for intakes and 0.25 to 0.5 m diameter HDPE pipelines for discharges. The
pipeline diameter must be sufficiently large so that the total headloss is limited, but not too large as
this may result in settlement of solids within the pipeline. HDPE is a flexible material and can
relatively easily accommodate seabed level fluctuations without leading to unacceptable stresses in
the material. The seaward end of the pipeline is usually stabilised within a concrete intake structure
placed on the seabed.
To obtain the warmest water possible to ensure maximum efficiency of the RO process, the intake
needs to be near the sea surface, but at the same time at sufficient depth to avoid the ingress of
floating debris and possible oils (i.e. approximately -1 m Chart Datum or deeper). If located too near
the seabed, intakes have a greater chance of entraining sediments re-suspended during rough sea
conditions, or near-bottom low oxygen waters and/or associated poor quality waters (if present). The
intakes will be fitted with appropriate screens to further minimise entrainment of foreign matter.
To avoid scour around the structure through wave and current action, some form of rock protection is
usually placed around the intake structure to ensure its stability. As fine sediments and organic
matter in the feed-water not captured by the screens will block the filters and/or membranes of a RO
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Plant, a receiving sump large enough to accommodate the anticipated sediment loads is usually
installed between the intake and seawater buffer tank. The entrained sediment settles in the sump,
which needs to be regularly removed and disposed of in an environmentally acceptable manner.
Onshore, and within the nearshore area off Sites 1 and 2, the feed-water pipeline will most likely
need to be trenched. In the offshore area it will be lying on, or partially within, the seabed sediments,
and will most likely be kept in place by weight collars. For Site 3 the single point intake will be
attached to the quayside.
Borehole Intakes
A further intake alternative that has been proposed for Site 3, is the intake of feed-water via a series
of boreholes drilled into the causeway. Two approximate locations have been proposed for these
intake boreholes. The first is a series of boreholes with a 50 m spacing drilled along the rail
embankment toe alongside the existing iron-ore stockpiles (Figure 3.5a). The second option
considered for intake boreholes is a linear series of boreholes with a 50 m spacing located adjacent
to the MPT (Figure 3.5b).
The actual number of boreholes to be drilled at each of these locations will depend on the seawater
yields from each borehole. Currently up to 10 boreholes are proposed for the rail embankment toe
alongside the existing iron-ore stockpiles (Figure 3.5a), or alternatively, up to 10 boreholes adjacent
to the MPT (Figure 3.5b). These borehole intakes are expected to have the same advantages as
beach wells in terms of reducing the necessity for the use of pre-treatment substances and thus
reducing operating costs as well as likely discharges of concern.
3.3.2 Discharge Alternatives
Brine-discharge Beach Wells
Brine discharge through beach wells was initially considered for Site 1. However, geotechnical
studies have indicated that the transmissivities of the sediments are too low to accommodate
discharge beach wells (Visser et al., 2007).
Surf-zone Discharge
A surf-zone discharge is likely to comprise a concrete discharge channel with or without a screen. It
is likely that the discharge will occur just above the high water mark with the brine flowing into the
active surf-zone. At Site 2, that is sheltered from swell entering the bay, such a surf-zone would be
limited or, on occasion, non-existent.
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Figure 3.5a: Location and number of intake borehole s alongside the existing iron-ore stockpiles (PDNA/SRK Joint Venture, 2008).
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Figure 3.5b: Location and number of intake borehole s alongside the existing MPT (PDNA/SRK Joint Venture, 2008).
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Single-port Discharge at Depth
Where discharge occurs through a pipeline at depth, it is anticipated that the end of the pipeline (if
comprising a single port diffuser) will be directed upwards at approximately 40 to 60 degrees from the
horizontal, to ensure adequate mixing of the dense brine through the water column. The
performance of such a single port diffuser will need to be such that it is consistent with the near-field
behaviour of the brine effluent as assumed in this study. A predicted6 near-field or initial dilution
exceeding 507 is recommended. It may be necessary to design and construct a simple multi-port
diffuser to meet appropriate near-field dilution requirements8. In this study, we have assumed a
relatively conservative or “worst case” near-field behaviour (i.e. effluent remains in the bottom one
third to half of the water column depending on water depth), providing some leeway in engineering
design possibilities should they be required to improve the near-field dilution of effluents.
3.4 “No-development” Alternative
The “no-development” alternative for the RO Plant implies the establishment of alternative water
sources for dust control as part of the port expansion. Possible alternatives investigated included
additional potable water from municipal supplies, reclaimed sewage (treated effluent), groundwater,
and seawater. However, due to the potential lack of available yields, environmental costs, and to
ensure suitable water quality, these alternative water sources were not considered as feasible
options during the planning stages of the port development, and will therefore not be dealt with
further here.
3.5 Summary of Development Alternatives
The development alternatives include a range of sites at which it is proposed to locate the RO plant
as well as a number of combinations of intake and discharge infrastructure relevant to each of these
sites. Table 3.1 below summarises all of the development alternatives considered in this study.
More precise detail of the proposed location and combination of the various intake structures together
with associated discharge infrastructure are described in Chapter 7.
6 The predicted near field dilution are typically obtained using near-field models such as CORMIX (Jirka et al.,
1996) or UOUTPLM (Baumgartner et al., 1971; US-EPA, 1985). These models are typically used for engineering design despite their limitations (i.e. their inability to accurately predict near- and/or far-field impacts accurately should there be an accumulation or build-up of effluent in the immediate vicinity of the discharge). These models assume that the effluent, at all times, is being diluted with “clean” ambient waters, which is not always necessarily the case. These models if used in isolation and not in conjunction with far-field models, depending on the flow rates that are considered, do not always provide a conservative assessment. In this study we have assumed conservative near-field behaviours (i.e. have not undertaken near-field modelling) and based the assessment on a far-field model (Delft3D-FLOW that takes into account that the ambient water entrained are not necessarily “clean” but may already be somewhat contaminated.
7 A dilution of 50 implies that each unit volume of effluent is mixed (diluted) with 50 unit volumes of the ambient waters into which the effluent is being discharged.
8 It should be noted that for Site 1, the discharge structure proposed comprises a pipeline running for a length of approximately 30 m along the revetment (see Table 7.3), although a multi-port diffuser of similar length just offshore of the revetment could be considered at the “pipeline” discharge location indicated in Figures 3.3a and 3.3b.
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Table 3.1: Development alternatives used in this as sessment (confirmed by Transnet on 22 November 2007).
Site Alternative # Alternative Intake/Discharge Infrastructure Locatio ns
Site 1 9 a) Beach well intake and pipeline discharge (Big Bay)
b) Pipeline intake and pipeline discharge (Big Bay)
Site 2 a) Beach well intake and pipeline discharge (Small Bay)
b) Pipeline intake and pipeline discharge (Small Bay)
Site 3
a) Pipeline intake (Small Bay) and pipeline discharge (Small Bay)
b) Pipeline intake (Small Bay) and pipeline discharge (Big Bay)
c) Borehole intake on quay (adjacent to existing iron-ore stockpiles) and pipeline discharge (Caisson 3, Big Bay)
d) Borehole intake on quay (adjacent to Multi-purpose Terminal) and pipeline discharge (Caisson 3, Big Bay)
Note: For Site 3 the RO Plant building will be located on the southern extremity of the MPT. Other
elements of the infrastructure (water storage reservoirs, etc) may be located closer to the
iron-ore stockpiles.
9 A beach well intake and beach well discharge option was also considered for Site 1, however the
groundwater specialist study (Visser et al., 2007) indicated the beach sediment conditions were such that a beach well discharge is not feasible.
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4 APPROACH TO THE STUDY
This marine specialist study comprises two components, namely:
• the physico-chemical characterisation and (where appropriate) assessment of potential
impacts, primarily the brine discharges, on the marine environment due to the construction and
operation of the proposed RO Plant, and;
• an assessment of the associated potential ecological impacts in the marine environment.
The physico-chemical characterisation of potential impacts, mainly comprises a three dimensional
numerical modelling of transport and fate of discharges from the RO desalination plant.
Based on the above physico-chemical characterisation of impacts, an assessment of the potential
ecological impacts in the marine environment has been undertaken. As determined by the terms of
reference for the marine ecological component of this specialist study, this ecological assessment
has adopted primarily a ‘desktop’ approach utilising existing information, for the purpose of the EIA.
Based on the review of available information from international peer-reviewed scientific literature, and
internal reports and EIAs available on the internet, the ecological assessment component of the
report identifies the nature and magnitude of impacts on marine communities likely to result from the
RO Plant, in the context of natural and other anthropogenic impacts in the Saldanha Bay area.
In summary, the impact assessment is structured as follows:
• A description of the marine and coastal ecosystems and biological communities of the region,
including:
− Climate and weather of the region;
− Physical oceanography of the region;
− Water quality within the bay;
− Beach and nearshore ecology;
− Rocky intertidal ecology;
− Pelagic communities and shore birds; and
− Beneficial uses and existing impacts.
• A description of the project background and design, including the identification of all
development options and alternative scenarios to the proposed project, including the ‘no-
development’ option. These have been described as a number of scenarios to be assessed for
potential impacts in the marine environment. As the ‘no-development’ option is unlikely to
influence the potential impacts identified as being associated with the proposed project and
being assessed here, this alternative is not discussed further in this specialist report;
• Identification and assessment of potential environmental impacts (both physical and ecological
impacts, as well as those on beneficial uses in the region);
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• Recommendation of mitigation measures and management actions for marine and coastal
issues of concern; and
• Identification of monitoring requirements.
4.1 Methodology
The methods and the motivation for using these methods are described below.
4.1.1 Environmental Baseline
The baseline description of the receiving environment in the vicinity of the proposed RO Plant is
limited to a ‘desktop’ approach utilizing existing information and data only. This was sourced and
reviewed from existing studies conducted in the area, as well as information available on the internet.
These included the ‘State of the Bay’ report (Atkinson et al., 2006), scientific literature, previous
environmental impact assessments for various developments in Saldanha Bay, e.g. Phase 1 and 2 of
the expansion of iron ore loading facilities, and from personal knowledge of one of the authors (N.
Steffani), especially of the rocky shore environment.
While a literature research and review are usually adequate for a study of this nature, a lack of
baseline information on sandy beach macrofauna was identified. Consequently, in the event of
beach wells and/or surf-zone discharges being considered in the potential engineering design,
existing information on this habitat is inadequate to confidently base an assessment of the impacts.
More appropriate in this case would be to design and implement a quantitative baseline survey of
beach macrofauna in the area on which to base the assessment. In the absence of such data we
have invoked the pre-cautionary principle in determining the significance of potential impacts, i.e. we
have assumed a significance rating that ensures that the potential impacts are not underestimated.
4.1.2 Modelling
The purpose of the modelling undertaken as part of this assessment is to predict the transport and
fate of the brine discharge (including potential co-discharges) from the RO plant for the various RO
plant locations and combinations of intake and discharge structures.
The modelling studies have been undertaken for the maximum planned plant capacity (i.e. 3 RO
Plant modules generating 3.6 Mℓ of potable water per day with an intake volume of 8 Mℓ per day and
a discharge volume of approximately 4.4 Mℓ per day). Based on the project description available at
the commencement of the model simulations, the brine discharge specified in the model is assumed
to comprise an effluent with a salinity of approximately 63 practical salinity units (psu), a zero
temperature elevation above the ambient water temperature at the intake10 and containing a residual
of oxidising biocide (potentially NaOCl at a discharge concentration of 0.1 mg.ℓ-1) or non-oxidising 10 A comprehensive sensitivity study (van Ballegooyen et al., 2008) has been undertaken that indicates that
the results of this study assuming a zero temperature elevation above the ambient water temperature at the intake remain valid for temperature elevations of up to 5 ºC above the ambient water temperature at the intake.
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biocide (assumed to be DBNPA at a discharge concentrations ranging between 1.15 mg.ℓ-1 and
2.475 mg.ℓ-1). Potential co-discharges and their likely concentrations have been specified, however,
the exact residual concentrations at the discharge point will need to be confirmed. The modelling
study has been designed to accommodate this uncertainty by including the discharge of a
conservative tracer that is a proxy for all co-discharges providing that the behaviour of the co-
discharge is conservative after discharge into the marine environment (i.e. does not decay or
transform into other substances). Should the co-discharge constituent decay or be transformed, the
approach taken will provide a conservative result, i.e. the potential impacts will be assessed as being
greater than would be the case in reality. In the (unlikely) event of the transformation resulting in
more toxic constituents, the modelling approach taken then would not be considered conservative.
Based on the co-discharges specified, no clear potential synergistic effects could be identified.
The discharges are significantly less than those that would be assessed for discharge from, for
example, a power plant (typically 5 to 10 times the magnitude of the discharge being considered
here), of a similar magnitude to those recently assessed for a proposed RO plant discharging to an
open coastline along the East Coast of South Africa, but significantly less (5 and 13.5 times smaller)
than those discharged from an existing RO plant into the Bushman’s River estuary (Bornman and
Klages, 2004).
Potential assessment approaches include:
• Simple near-field studies based on conceptual designs and near-field models. However the
build-up of effluent cannot be simulated by these near-field models as in these models it is
assumed that the effluent is continually diluted by ‘clean’ water. Consequently such near-field
models provide results that are not necessarily conservative, particularly when simulations are
undertaken in relatively poorly flushed embayments such as Small Bay, Saldanha Bay.
• More comprehensive three dimensional (3D) hydrodynamic and water quality modelling where
the potential build-up of effluent is explicitly taken into consideration but where near-field
behaviours need to be schematised (in this case as a bottom discharge or an optimally
designed diffuser where the effluent is mixed throughout the water column or at least a
significant proportion thereof). This type of study does not depend on a specific discharge
design but can consider a broad range of possible near-field behaviours.
• More sophisticated water quality modelling where bay productivity, oxygen concentrations and
nutrient dynamics are explicitly simulated. This is the nature of previous studies undertaken for
potentially larger (5 to 10 times) brine discharges.
Whilst the “footprint” of the brine (and any associated pollutants) is relatively modest and could
possibly be assessed using a near-field model only, here it has been deemed prudent to undertake a
fully three-dimensional hydrodynamic and water quality study to ensure a quantitative assessment
should there be accumulation of effluent around the discharge location. However, given that the
“footprint” or impacted area is relatively modest, it is deemed that a detailed study, where bay
productivity, oxygen concentrations and nutrient dynamics are explicitly simulated, is not warranted
here.
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The scenarios simulated will be for the conceptual designs (shoreline discharge, discharge at depth
through single or multi-port diffusers) that are appropriate for the particular discharge location.
A total of 5 discharge locations have been assessed (see Chapter 7), namely:
• a discharge into Big Bay alongside the existing reclamation dam for Site 1;
• a discharge into the NE corner of Small Bay from Site 2;
• a discharge alongside the causeway into Small Bay from Site 3;
• an alternative discharge from Site 3 alongside the causeway into Big Bay; and
• a discharge located at Caisson 3 in the vicinity of the southern extremity of the causeway
separating Small Bay and Big Bay.
Each of the above discharge scenarios will be simulated for a range of environmental conditions
comprising:
• a two month late summer period when the bay is most stratified resulting in relatively quiescent
bottom waters and limited vertical mixing;
• a two month winter period when the water column is well-mixed resulting in more active vertical
mixing and typically stronger bottom flows; and
• a “worst case” one month simulation comprising a both calm and stratified period (typically April
to June in Saldanha Bay) that is representative of the calmest period in 15 years or more in
Saldanha Bay.
4.1.3 Environmental Impact Assessment
The Environmental Impact Assessment is based on the results of the three-dimensional
hydrodynamic and water quality numerical modelling study (Chapter 7).
The information for the assessment of impacts related to the brine discharge (and other co-
discharges) was drawn from various scientific publications as well as information sourced from the
Internet and provided by Transnet Projects. The sources consulted are listed in the reference list
(Chapter 10). The method used to assess the potential environmental impacts is described below.
The significance of all potential impacts that would result from the proposed project is determined in
order to assist decision-makers. The significance rating of impacts is considered by decision-makers,
as shown below.
• INSIGNIFICANT: the potential impact is negligible and will not have an influence on the
decision regarding the proposed activity.
• VERY LOW: the potential impact is very small and should not have any meaningful influence
on the decision regarding the proposed activity.
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• LOW: the potential impact may not have any meaningful influence on the decision regarding
the proposed activity.
• MEDIUM: the potential impact should influence the decision regarding the proposed activity.
• HIGH: the potential impact will affect a decision regarding the proposed activity.
• VERY HIGH: The proposed activity should only be approved under special circumstances.
The significance of an impact is defined here as a combination of the consequence of the impact
occurring and the probability that the impact will occur. The significance of each identified impact
was thus rated according to the method described below.
1. The Consequence Rating for the impact is determined by adding the score for each of the
three criteria (A-C) listed below:
Rating Definition of Rating Score
A. Extent – the area over which the impact will be experienced 0
Local Confined to the project or study area or part thereof (i.e. site specific) 1
Regional Confined to the region, which may be defined in various ways, e.g. cadastral, catchment, topographic
2
(Inter) national Nationally or beyond 3
B. Intensity – the magnitude of the impact in relation to the sensitivity of the receiving environment None 0 Low Natural and/or social functions and processes are negligibly altered 1 Medium Natural and/or social functions and processes continue albeit in a
modified way 2
High Natural and/or social functions or processes are severely altered 3 C. Duration – the time frame for which the impact will be experienced None 0 Short-term Up to 2 years 1 Medium-term 2 to 15 years 2 Long-term More than 15 years 3
A Consequence Rating is subsequently determined by combining the scores of these three criteria
as follows:
Combined Score (A+B+C) 0 – 2 3 – 4 5 6 7 8 – 9 Consequence Rating Not significant Very low Low Medium High Very high
The probability of the impact occurring was assessed according to the following definitions:
Probability – the likelihood of the impact occurring
Improbable < 40% chance of occurring Possible 40% - 70% chance of occurring Probable > 70% - 90% chance of occurring Definite > 90% chance of occurring
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2. The overall significance of the impact is determined as a combination of the consequence
and probability ratings as indicated in the table below:
Significance Rating Consequence Probability
Insignificant Very Low & Improbable Very Low & Possible
Very Low Very Low & Probable Very Low & Definite Low & Improbable Low & Possible
Low Low & Probable Low & Definite Medium & Improbable Medium & Possible
Medium Medium & Probable Medium & Definite High & Improbable High & Possible
High High & Probable High & Definite Very High & Improbable Very High & Possible
Very High Very High & Probable Very High & Definite
3. The status of the impact (i.e. whether the effect of the impact will be negative or positive) is
noted.
4. The level of confidence in the assessment of the impact is stated as either high, medium or
low.
Practical mitigation measures that can be implemented effectively to reduce the significance of the
impact are identified and described. The impact is then re-assessed following mitigation, by
repeating Steps 1-5 to demonstrate how the extent, intensity, duration and/or probability changed
after implementation of the proposed mitigation measures.
Mitigation measures are described as either:
• Essential : must be implemented and are non negotiable; or
• Optional : must be shown to have been considered and sound reasons provided if not
implemented.
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4.2 Limitations and Assumptions
The following are the assumptions and limitations of the study:
• The study is based on the project description made available to the specialis ts at the time
of the commencement of the studies (plant capacities, discharge locations, constituents,
volumes, etc.) and as updated on 22 November 2007, 5 December 2007 and mid-January
2008. The assessment is restricted to only those constituents specified by Transnet as being
contained within the effluents from the RO plant. Based on feedback from Transnet at the time
of the commencement of the model simulations, the modelling study has explicitly assumed
that there is no change of the seawater temperature between the intake and the discharge
structures. Thus the only thermal impacts being assessed in the modelling study are the
ambient temperature differences that exist between the intake location and discharge location.
Subsequently Transnet has indicated that the assumption of no change of the seawater
temperature between the intake and the discharge structures is not necessarily correct and that
the temperature elevation between the intake and discharge point will ultimately depend on the
detail of the system design (i.e. retention time in the brine basin, hydraulic design, energy
recovery device specifics, etc.). Consequently a further comprehensive sensitivity an alysis
has been undertaken (van Ballegooyen et al ., 2008) that confirms that the results of this
study that assumes a zero temperature elevation abo ve the ambient water temperature
at the intake remain valid for temperature elevatio ns of up to 5 ºC above the ambient
water temperature at the intake .
Based on information available at the time of undertaking the modelling studies, if utilised, the
residual oxdising biocide (NaOCl) concentration in the effluent stream is assumed to be
0.1 mg.ℓ-1 . Furthermore a continuous discharge has been assumed, however subsequent
communications has indicated that if a non-oxidising biocide is utilised it will be applied in
shock doses. As the modelling study did not explicitly simulate discrete shock treatment
processes, to ensure the validity of the modelling study as well as a conservative approach to
assessment, it is assumed that the residual oxidising biocide concentrations will be managed
such that a residual biocide concentration of 0.1 mg.ℓ-1 is not exceeded at the point of
discharge at any stage of the treatment process (i.e. at any stage during the shock treatment
process). Furthermore, it has been stated that non-oxidising biocides will be utilised in a
“shock treatment” rather than continuous dosing mode. Similarly, to ensure the validity of the
modelling study as well as a conservative approach to assessment, it is assumed that the
residual concentrations of the preferred biocide11, i.e. the non-oxidising biocide (DBNPA), will
be managed such that residual non-oxidising biocide concentrations will not exceed a range of
between 1.15 mg.ℓ-1 and 2.475 mg.ℓ-1 (see Section 8.1.3.4) at the point of discharge at any
stage of the treatment process (i.e. at any stage during the shock treatment process.
11 The RO membranes proposed for use comprise the most recent and efficient membrane technology,
however this implies the use of membrane material that is affected by the sodium hypochlorite (the oxidising biocide) and this results in deterioration of the membranes. It is for this reason that the use of DBNPA is proposed as this does not affect the membranes in the same way.
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• The assessment is limited to the project description as supplied to the specialists by Transnet
at the time that this assessment was undertaken and the issues that could be identified using
the detail provided in the project description. Specifically, a number of aspects of the
engineering design had not yet been finalised at the time of the study (e.g. exact number and
design of beach wells, detailed description of construction activities, etc), making confident and
comprehensive assessments of potential marine impacts related to these activities difficult.
Where such detail is missing from the project description a generic, but conservative, approach
to the assessment (i.e. precautionary approach) has been undertaken.
• The three dimensional modelling study comprises a far-field model and does not resolve
detailed near-field features of the discharge plume s. For this reason we have assumed
that the resolution in the modelling is inadequate to provide detail within an approximate 50 m
radius of the discharge point. Consequently we have assumed that the water quality guidelines
may regularly be exceeded within a 50 m radius of the discharge point, despite the fact that this
will not necessarily be the case. This constitutes a conservative approach.
• Unlike near-field models such as CORMIX, the far-field modelling undertaken here
incorporates the effects of the accumulation / re-circulation of effluent in the vicinity of the
discharge and the consequent reduction in the dilution/dispersion of the effluents in the
discharge plume. The far-field modelling undertaken here also provides a much more realistic
simulation of environmental conditions in the marine environment than is typically possible for
near-field models. The implementation of near-field models requires a detailed rather than a
conceptual description of the discharge structures (i.e. alternatives such as an open channel of
single/multi-port diffuser outfall) that is not yet available for this study. As it is intended that this
study inform which of the above discharge locations and structures is environmentally
acceptable or preferable, the modelling study has been based on broad concept ual
discharge designs that parameterise the near-field behaviour of the plume . This
combination of conceptual designs and assumed associated near-field effluent behaviour is
deemed adequate for the purposes of this study that is intended to assess primarily the
potential far-field impacts in the receiving environment. The performance of the discharge
infrastructure when designed and constructed will need to be such that it is consistent with (or
better than) the near-field behaviour of the brine effluent assumed in this study. In this study
we have assumed a relatively conservative near-field behaviour (i.e. effluent remains in the
bottom one third to half of the water column), providing some leeway in engineering design
possibilities should they be required to improve the near-field dilution of effluents.
• The three dimensional modelling study is based on e xisting measurements (i.e. design
and associated environmental measurement for Saldanha Bay) and no new measurement
were obtained specifically for this study. The existing observations are deemed to be adequate
for the purpose of using the model to predict discharge plume behaviours.
• Other than the detailed modelling component of the study, the ecological assessment is
limited to a “desktop” approach and thus relies on existing information only. No new data or
measurements (physical or biological) have been obtained as part of this study.
• While a literature research and review are usually adequate for a study of this nature, a lack of
baseline information on sandy beach macrofauna was identified. Consequently, in the
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event of beach wells and/or surf-zone discharges being considered in the potential engineering
design, existing information on this habitat is inadequate to confidently base an assessment of
the impacts. More appropriate in this case would be to design and implement a quantitative
baseline survey of beach macrofauna in the area on which to base the assessment.
• The assessment is based on the current Port configu ration , and therefore does not
consider future port expansions not clearly covered under the current specifications of the
Saldanha Bay Iron-ore Expansion Project (i.e. Phase 2). If deemed necessary, the scenarios
comprising discharges into Big Bay could be simulated with the “maximum” proposed changes
in port layout. However, the “footprint” of the effluent discharged from the RO Plant under the
various discharge scenarios is sufficiently limited in extent to not be influenced sufficiently by
the changes in port layout to invalidate the conclusions of this study (see Section 2.4 for more
detail).
• Some important conclusions and associated assessments and recommendations made in the
EIA section of this study are based on results from the detailed three dimensional modelling
study. The predictions of these models, whilst considered to be robust in terms of the
major discharge constituent (salinity) 12, need to be validated by field observations and
subsequent monitoring . If field observations and monitoring, however, fail to mirror predicted
results, the forecasted impacts will need to be re-assessed.
• Potential changes in the marine environment such as sea level rise and/or increases in the
severity and frequency of storms related to climate change are not explicitly considered
here . Such scenarios are difficult to assess due to the uncertainties surrounding climate
change. Should evidence or more certain predictions of such changes become available,
Transnet should re-assess their development and management plans to include the impacts of
these anticipated macroscale changes. However, it is not expected that these climate changes
will affect the effluent plume behaviour to the extent that the conclusions of this study will be
altered. (These changes may however significantly affect the existing beneficial or designated
uses in the bay.) The most significant change that may occur due to long-term climate change
is a change in the beach configuration at Site 1 (and most probably to an insignificant extent at
Site 2) that may need to be considered when designing intake beach wells. It is expected that
the beach in the vicinity of Site 1 will continue to accrete as it has done since the construction
of the causeway. Should Phase 2 of the Saldanha Bay Iron-ore Expansion Project proceed, it
is predicted that the present rate of accretion of the beach at Site 1 will be slower than would
be the case if not further development take place (Smith et al. 2007).
12 Should the field observations and monitoring fail to mirror the model predictions for the various
constituents of the effluent stream, the concentration of constituents of concern in the effluent stream can be reduced by the various mitigation measures proposed. The only exception is the salinity of the brine discharge that is inherent to the RO Plant operation and that can only be manipulated by changing RO Plant efficiencies and then not to any significantly degree. It is for this reason that it is important that the reported model predictions of salinity “footprints” in the marine environment, are considered to be robust.
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5 DESCRIPTION OF THE AFFECTED ENVIRONMENT
Here a detailed description is given of the physical, chemical and biological environment of Saldanha
Bay.
5.1 Physical Environment
5.1.1 General
The Saldanha Bay-Langebaan system can be divided into Outer Bay, Saldanha Bay (comprising Big
Bay and Small Bay) and Langebaan Lagoon (Figure 5.2a and b). The boundary between Big Bay
and Small Bay is the iron-ore causeway built in 1974/75 which impacts significantly on the water
circulation in Saldanha Bay. Most of the commercial activities in Saldanha Bay are concentrated in
Small Bay or just outside of Small Bay while Langebaan Lagoon remains largely pristine.
There are no significant river inputs into either Saldanha Bay or Langebaan Lagoon, consequently
the Saldanha Bay-Langebaan Lagoon system is marine with its waters originating in the shelf waters
of the adjacent Benguela upwelling system (Shannon and Stander, 1977). In winter, however, there
is a small seepage of fresh water due to rain (Day, 1981).
The overall surface area of the Saldanha Bay-Langebaan system is estimated to be 9.61×107 m
2. Of
this surface area, Small Bay comprises 1.41×107 m
2, Big Bay 4.31×10
7 m
2 and Langebaan Lagoon
3.89×107 m
2. The mid-tide volume of the whole system is 7,34×10
8 m
3. Of this total volume, Small
Bay contributes 1.28 ×108 m
3, Big Bay 5.17×10
8 m
3 and Langebaan Lagoon 8.91×10
7 m
3 (Weeks et
al., 1990).
5.1.2 Climate and Winds
Saldanha Bay and Langebaan Lagoon are situated on the Cape West Coast, approximately 100 km
north of Cape Town. The climate of this area is mild to cool and is strongly influenced by the cold
Benguela Current that moves up the west coast of Southern Africa. Temperatures are mostly less
than 20°C and rarely exceed 30°C (CSIR, 1996). The area has a semi-arid Mediterranean climate
with an average annual rainfall of about 300 mm. Most of the rainfall occurs in winter with summers
generally being dry. Coastal fogs caused by the interaction between cold marine air (the result of the
Benguela Current) and the warmer land mass are common, particularly in autumn. There is a strong
seasonality in the winds over Saldanha Bay, reflecting the changes in the synoptic weather patterns
prevailing at different times during the year. Southerly winds pre-dominate in this region for most of
the year, modulated by short periods of calm conditions or north-westerly winds which are associated
with the propagation of coastal lows southwards along the west coast of southern Africa. Only in the
mid-winter months do north to north-westerly winds predominate.
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Figure 5.1: Wind roses of the winds measured at Por t Control in Saldanha Bay (see inset).
Port Control
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Wind data from Port Control in Saldanha Bay (Figure 5.1) indicate that in summer the winds are
predominantly southerly with significant southwesterly and to a lesser extent southeasterly wind
components. In autumn the winds are predominantly southerly with the development of a
northwesterly wind component as the season progresses. The regular passage of cold fronts in
winter results in predominantly northwesterly winds with the occurrence of significant southwesterly
and southeasterly wind components. The spring wind regime is similar to the summer wind regime
but with increased southeasterly wind components.
The winds along the West Coast have a significant diurnal component (Jury and Guastella, 1987)
that is clearly observable in the wind records for Saldanha Bay. The wind speed typically reaches a
maximum in the late afternoon when the sea breeze cycle is at its maximum. These diurnal changes
in the winds are expected to impact significantly on the heat fluxes at the sea surface over a 24 hour
period.
The interannual variability in the winds along the West Coast has been well documented
(Taunton-Clarke, 1990; Taunton-Clarke and Shannon, 1988; Shannon et al., 1992).
5.1.3 Tides
The tides along the west coast of southern Africa, including Saldanha Bay, are semi-diurnal (two high
and two low tides per tidal day). The tidal characteristics for Saldanha Bay (Table 5.1) are typical of
a micro tidal regime and indicate an approximate 2 m tidal range during spring tides.
Table 5.1: Tidal characteristics for Saldanha Bay.
Tidal Characteristic Tidal level relative to Chart Datum (m)
Highest Astronomical Tide 2.03
Mean High Water Springs 1.75
Mean High Water Neaps 1.27
Mean Level 0.99
Mean Low Water Neaps 0.70
Mean Low Water Springs 0.24
Lowest Astronomical Tide 0
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5.1.4 Waves
The wave conditions inside the bay are sheltered compared to those outside the bay, since all energy
reaching the bay has to pass through the relatively narrow channel between Marcus Island and
Elandspunt. The median significant wave height measured in the entrance to the bay is 1.1 m, while
the greatest occurrence of peak periods lies in the 10 to 12 s range. The seasonal wave height
exceedances measured at a buoy near the entrance to Small Bay are summarised for the various
seasons in Table 5.2 below.
The wave height outside the bay can be deduced from the wave data recorded at Slangkop, west of
the Cape Peninsula, where the median significant wave height is 2.3 m. Figure 5.2 shows the wave
rose measured at Slangkop. The most frequent direction of wave approach is from the south-west.
In addition to waves originating from offshore and refracted into the bay, small wind-waves (up to
some 1 m in height) are generated by strong winds within Saldanha Bay.
Simulated wave conditions for large offshore swell conditions and strong wind conditions are plotted
in Figures 5.3a and 5.3b, respectively.
Table 5.2: Wave height exceedances measured at a wa ve buoy near the entrance to Small Bay.
Significant Wave Height (H mo) Exceeded (m)
1% 5% 10% 25% 50%
Summer 2.38 1.85 1.64 1.35 1.07
Autumn 2.77 2.15 1.84 1.41 1.09
Winter 3.57 2.63 2.27 1.79 1.35
Spring 2.82 2.18 1.89 1.50 1.14
All Seasons 2.96 2.25 1.94 1.51 1.15
Measurements of long wave energy in Saldanha Bay indicate significant energy in the period range
of 30 s to 200 s.
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Figure 5.2: Wave height measured at the Slangkop Di rectional Waverider, located off Kommetjie on the Cape South-west coast (34°12'14.40 "S, 18°17'12.01"E, 70 m depth) for the period 2001 to 2007.
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Figure 5.3a: Simulated wave conditions in Saldanha Bay for large offshore swell conditions and low winds (Offshore H mo = 3.6 m , Tp=13 s, Direction = SW’ly, Local wind = 3 m/s S’ly).
Figure 5.3b: Simulated wave conditions in Saldanha Bay for moderate offshore swell conditions and very strong winds (Offshore H mo = 1.3 m , Tp=11 s, Direction = SW’ly, Local wind = 20 m/s S’ly).
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Figure 5.4a: Flood tide surface and bottom currents in Saldanha Bay during spring tide and under relatively calm conditions.
Figure 5.4b: Ebb tide surface and bottom currents i n Saldanha Bay during spring tide and under relatively calm conditions.
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Figure 5.5a: Schematic of the wind driven and tidal currents in Saldanha Bay under S wind conditions.
Figure 5.5b: Schematic of the wind driven and tidal currents in Saldanha Bay under NW wind conditions.
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5.1.5 Currents
The currents in the bay are predominantly forced by the wind and the tide, the relative importance of
the two processes changing with depth and location in the bay. In general, wind is the dominant
physical forcing mechanism determining the surface layer current speed and direction in both Small
and Big Bay (van Ballegooyen et al., 2002). Tidal forcing (Figure 5.4a and b) is stronger at depth, in
the vicinity of the mouth of Saldanha Bay (Shannon and Stander, 1977) and with increasing proximity
to Langebaan Lagoon (Weeks et al., 1991a). In the surf-zone, wave-driven currents are expected to
dominate.
Although residual flows associated with the tides occur in the bay, the greatest exchange between
Saldanha Bay and the shelf is a consequence of synoptic weather events occurring on time scales of
3 to 10 days. South-southeasterly wind events are reported to result in a general surface outflow and
a subsurface inflow of cold bottom water (Spolander, 1996; Monteiro and Largier, 1999), while
indications are that northwesterly wind events lead to the inflow of surface waters in the northern
region of the mouth of Saldanha Bay (Figure 5.5a and b). Thus the surface, mid-water and bottom
currents often are observed to be flowing in different, and at times, opposite directions. While this is
expected in a highly stratified water column, observations of three-dimensional flow structure are not
restricted to strongly stratified conditions. Weeks et al. (1991b) recorded an event in late winter
(August 1990) where the flow was strongly three-dimensional under well-mixed conditions.
During periods of slack winds, tidal currents dominate and are the sole mechanism for flushing the
bay. The tidal currents are generally weak, however strong tidal flows are observed at the entrance
to the lagoon, particularly during spring tides. During tidal exchange, it is estimated that
approximately half of the lagoon water passes through the Lagoon entrance channels into Saldanha
Bay (Shannon and Stander, 1977) and velocities of up to 1.0 m.s-1 are observed in the two channels
connecting Big Bay and Langebaan Lagoon (Krug, 1999).
5.1.6 Water Column Stratification
The water column structure in Saldanha Bay is seasonal, varying from a strongly thermally stratified
water column for most of the year (August to May) to well-mixed conditions during the mid-winter
months (June to July). For most of the year, strong stratification is maintained by atmospheric heat
fluxes into the surface waters and the inflow of cold bottom waters from upwelling on the adjacent
open shelf, with the local winds acting to vertically mix the water column and break down the
thermocline (Monteiro and Largier, 1999). During the mid-winter months the water column within the
bay is largely well-mixed both due to reduced heat fluxes into surface waters and the reduced
occurrence of south to south-easterly winds that drive the upwelling over the adjacent shelf which in
turn drives cold bottom waters into the bay.
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Figure 5.6a: Surface and bottom water temperature a nd flow in Saldanha Bay under strong SE wind conditions ( i.e. during the “active” upwelling phase).
Figure 5.6b: Surface and bottom water temperature a nd flow in Saldanha Bay after a strong SE wind event (i.e. relaxation phase of upwelling).
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The above processes control the thermocline dynamics and vertical mixing of the water column
which, together with wind- and tidally-driven currents, ultimately determine the behaviour of
biogeochemical parameters and pollutants within the bay.
Figure 5.7: Vertical temperature structure of the w ater column along the “profile line” or cross-section indicated in Figure 5.6b. The upper panel shows the “active” upwelling phase while the lower panel shows the wat er column structure during the relaxation phase of the upwelling cycle.
The variability in the water column stratification is predominantly synoptic and responds strongly to
wind-forcing which has a periodicity of 6 to 10 days in this region (Nelson and Hutchings, 1983). A
typical sequence of events in the bay is as follows.
The dominant south to southeasterly winds over the bay and adjacent shelf result in upwelling over
the adjacent shelf which sets up a baroclinic pressure gradient which drives cold bottom water into
the bay on a time scale of one or two days (Figure 5.6a and 5.7 – upper panel). This constitutes a
strong buoyancy input which acts to strengthen the thermocline within the bay. However, the same
strong south to southeasterly winds results in vigorous vertical mixing of the water column within the
bay as well as a heat loss from the surface waters. These processes act to reduce the water column
stratification. Initially the mixing processes dominate and the water column becomes well-mixed,
particularly in the shallower regions. However, after a period of approximately 24 hours or more the
effects of the input of cold bottom waters predominate and the thermocline starts to strengthen. With
the passing of the coastal low, the winds typically moderate resulting in either calm conditions or
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weaker northwesterly winds. The resulting reduction in the vertical mixing of the waters in the bay
results in the rapid appearance of a strongly stratified water column within the bay. This is followed
by the retreat of the cold bottom waters from the bay under NW or calm wind conditions (Figure 5.5b
and 5.7 – lower panel). This sequence of events is important as not only does it explain the high
degree of natural temperature variability observed in the bay, but it also describes the physical
processes that serve to reduce the thermal impacts associated with a thermal discharge into the bay.
Typically any additional anthropogenic heat input into the bay would be removed by mixing of these
heated waters with the cold bottom waters or by heat loss to the atmosphere.
5.1.7 Seawater Temperature
The natural seawater temperature fluctuations in Saldanha Bay are substantial and typically occur on
four time scales, namely diurnal, synoptic, seasonal and interannual (Figure 5.8).
Figure 5.8: Simulated surface and bottom water temp eratures at North Buoy in Small Bay (see inset), showing the various temporal scales an d magnitudes of seawater temperature variability in Saldanha Bay.
Thermistor chain data in Small Bay (Monteiro and Largier, 1999; CSIR, 1995) indicate that the
diurnal temperature changes are greatest in summer when the surface waters experience diurnal
surface bottom
surface bottom
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temperature changes of typically 0,5°C to 1°C but u p to 2°C on occasion. Much larger diurnal
temperature fluctuations may occur at a specific depth in the deeper waters due to increased or
decreased vertical mixing mainly associated with diurnal changes in local wind velocity. In winter,
when heat fluxes into the surface waters are smaller and the water column is largely unstratified, the
diurnal temperature fluctuations are substantially reduced at all depths in the water column.
Changes in the synoptic weather events lead to substantial variability in water column temperature
both within the bay and over the adjacent shelf region (CSIR, 1976; CSIR, 1995; Monteiro and
Largier, 1999; Shannon, 1985). These temperature changes occur as a result of advection of warm
surface or cold bottom waters into Saldanha Bay from the adjacent shelf region as well as vertical
mixing of the water column by local winds in the bay. Investigations by Spolander (1996) and
Monteiro and Largier (1999) indicate that changes in atmospheric heat fluxes at the surface are
expected only to play a secondary role in the synoptic seawater temperature variability.
The thermistor chain data in Small Bay (CSIR, 1995; Monteiro and Largier, 1999) show that the
temperature at any particular depth may change during a synoptic cycle by as much as 6°C to 8°C in
summer and 1°C to 2°C in winter. This is mostly du e to changes in the vertical mixing of the water
column due to local winds, however, advection of cold bottom waters into Small Bay also play a
significant role in these temperature fluctuations during the upwelling season (Monteiro and Largier,
1999). There is an indication in both thermistor chain data (Sea Fisheries Research Institute) and
CTD profiles (CSIR, 1976) that there is flow of warmer surface waters into the Saldanha Bay under
northwesterly wind conditions.
Long-term (daily) sea surface temperature observations within Small Bay (Greenwood and
Taunton-Clark, 1992) indicate that the mean seasonal change in sea surface temperature is about
6°C. The magnitude of seasonal changes in sea surf ace temperature is expected to be highest in
Langebaan Lagoon and much smaller near the more exposed mouth of Saldanha Bay, however, we
are not aware of any temperature time-series of sufficient length to substantiate the above statement.
The seasonal changes in water temperature of the deeper waters in the bay (approximately 2.5 °C)
are substantially less than those observed in the surface waters of the bay.
Daily sea surface temperature observations in Small Bay indicate that the interannual sea surface
temperature variability typically has a magnitude of between 1°C and 2°C ( Greenwood and
Taunton-Clark, 1994). These longer period changes in temperature are most likely due to persistent
changes in the local synoptic weather conditions. Monteiro and Brundrit (1990) have documented
four major episodic inflows of higher temperature and higher salinity oceanic waters into Big Bay that
occurred between 1974 and 1979, however, the temperature signal associated with these episodic
events is largely masked in the surface waters by seasonal temperature variations due to changes in
atmospheric heat input and vertical mixing of the water column.
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In summary, the temperature of the surface waters in Saldanha Bay are determined by atmospheric
heat fluxes at the sea surface, entrainment of cooler subsurface waters into the surface layers and
horizontal exchange of the surface waters with the adjacent lagoon and shelf waters. The
temperature of the bottom water is predominantly determined by upwelling inflows and vertical mixing
of the warmer surface waters into the deeper waters of the bay under strong local wind conditions.
5.1.8 Salinity
The salinity of the water in Saldanha Bay has been monitored at frequent intervals in conjunction with
temperature and shows little variation over time. Salinities of the inshore waters along the west coast
typically vary between 34.6-34.9 psu and the salinity values recorded for Saldanha Bay usually fall
within this range. Atkinson et al. (2006) report salinities from various sources that range between
34.7 and 35.2 psu and average approximately 34.9 psu. During summer months wind-driven coastal
upwelling bring cooler less saline water into Saldanha Bay. Consequently the salinity within the bay
usually is slightly lower in summer than in winter when the upwelling front breaks down and warmer,
more saline surface waters enter the bay.
5.1.9 Water Quality
Oxygen
The primary sources of oxygen in the marine environment are atmospheric oxygen, which enters the
system via gaseous exchange across the air-sea surface interface and in situ production via
photosynthesis of algae and other aquatic plants. Dissolved Oxygen (DO) is measured as a
concentration (mg. ℓ-1) or as a percent saturation (%). Of critical importance to marine organisms are
the fate and behaviour of dissolved oxygen and the factors affecting fluctuations in DO levels. The
principal anthropogenic activity resulting in changes in DO concentrations in the marine environment
is the addition of organic matter. In the Saldanha Bay system, Small Bay experiences a fairly regular
oxygen deficit during the late summer and winter months, whilst Big Bay experiences less frequent
and lower magnitude oxygen deficits (Atkinson et al., 2006). Monteiro et al. (1990) attributed the
oxygen deficit in Small Bay largely to anthropogenic causes, namely reduced flushing rates (due to
the causeway and ore jetty construction) and discharges of organic rich effluents from fish processing
factories. There is evidence of anoxia in localized areas of Small Bay (e.g. under the mussel rafts,
within the yacht basin) that is caused by excessive organic inputs (Stenton-Dozey et al. 2001).
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Turbidity
The water of Saldanha Bay is fairly turbid, the turbidity comprising both organic and inorganic
particulates. During active upwelling it is expected that the turbidity of particular the bottom waters
will decrease, however, under strong wind conditions both wind and wave action result in significant
water column turbidity, the light coloured sediments resulting in significant discolouration of the
waters within particularly Big Bay. The waters of Langebaan Lagoon, in contrast, are typically very
clear and of low turbidity.
Dissolved trace metals
The Mussel Watch Programme regularly records concentrations of Cadmium, Copper, Lead, Zinc,
Iron and Manganese present in the flesh of mussels. The data collected in Small Bay as part this
programme indicate that there do not appear to be significant increases in concentrations of heavy
metals in the flesh of mussels in Saldanha Bay. Consequently, the quality of the water can be
considered suitable for mariculture purposes and heavy metal accumulation is currently not a
concern (Atkinson et al., 2006).
Microbial Contamination
Pathogenic microorganisms, which are primarily introduced into coastal waters by faecal pollution,
pose a risk to both water users and mariculture ventures. Regular monitoring of microbiological
indicators within Saldanha Bay, initiated by the Saldanha Bay Water Quality Forum Trust, began in
1999 (Monteiro et al., 2000), and the data set covering the six year period from 1999 to 2005 was
summarized by Atkinson et al. (2006). In most areas of Small Bay the target limits for mariculture
and/or recreational uses set by the South African Water Quality Guidelines (DWAF, 1995) were
exceeded. Within Big Bay the faecal coliform counts were much lower, falling within the
recommended limits for recreation at all sites. At sites close to Langebaan town, however, bacterial
counts were in excess of target values for mariculture purposes (Atkinson et al., 2006).
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5.2 Biological Environment
Saldanha Bay and Langebaan Lagoon fall within the Namaqua biogeographic province that extends
from Cape Point to Lüderitz within the southern Benguela upwelling region (Emanuel et al., 1992).
The bay and the lagoon together form one of the few sheltered habitats along the South African West
Coast, with graded changes in wave action and substratum between Saldanha Bay and Langebaan
Lagoon. The lagoon, which is shallow (2-6 m deep), 16 km long and 2-3 km wide, is fully marine with
a strong tidal exchange (Shannon and Stander, 1977). It has extensive intertidal sandflats and salt
marshes (Day, 1959). Marine ecosystems within the bay comprise a range of habitats each
supporting a characteristic biological community. Habitats in the Saldanha Bay system include:
• Sandy intertidal and subtidal substrates,
• Macrophyte beds,
• Intertidal rocky shores and subtidal reefs,
• Salt marshes,
• Unvegetated sand flats,
• Sea grass beds, and
• The water body
The biological communities in each of these habitats are described briefly below, with the main focus
on potentially sensitive communities, which may be affected by the proposed project.
5.2.1 Sandy Substrate Habitats and Biota
The benthic biota of soft bottom substrates constitutes invertebrates that live on, or burrow within, the
sediments, and are generally divided into macrofauna (animals >1 mm) and meiofauna (<1 mm).
Intertidal Sandy Beaches
Sandy beaches are one of the most dynamic coastal environments. The composition of their faunal
communities is largely dependent on the interaction of wave energy, beach slope and sand particle
size, which is called beach morphodynamics. Three morphodynamic beach types are described:
dissipative, reflective and intermediate beaches (McLachlan et al., 1993). Generally, dissipative
beaches are relatively wide and flat with fine sands and high wave energy. Waves start to break far
from the shore in a series of spilling breakers that ‘dissipate’ their energy along a broad surf zone.
This generates slow swashes with long periods, resulting in less turbulent conditions on the gently
sloping beach face. These beaches usually harbour the richest intertidal faunal communities.
Reflective beaches have low wave energy, and are coarse grained (>500 µm sand) with narrow and
steep intertidal beach faces. The relative absence of a surf-zone causes the waves to break directly
on the shore causing a high turnover of sand. The result is depauperate faunal communities.
Intermediate beach conditions exist between these extremes and have a very variable species
composition (McLachlan et al., 1993; Jaramillo et al., 1995; Soares, 2003). This variability is mainly
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attributable to the amount and quality of food available. Beaches with a high input of e.g. kelp wrack
have a rich and diverse drift-line fauna, which is sparse or absent on beaches lacking a drift-line
(Branch and Griffiths, 1988; Field and Griffiths, 1991).
There is a noticeable scarcity of published information on the intertidal beach biota of Saldanha Bay
as work on the West Coast of South Africa has primarily focussed on ‘open coast’ beaches (e.g.
Soares 2003). Day (1959) gives an account of four sandy shores from the Saldanha Bay system,
comparing the more wave-exposed beaches of Saldanha Bay with the sheltered beaches in
Langebaan Lagoon. He describes an increase in species richness and a significant change in
species composition with increasing shelter. His work, however, was carried out prior to the
construction of the causeway and ore jetty, and thus prior to the changes in wave and current pattern
in the bay. Over the past few years, Zoology students from the University of Cape Town have
sampled beaches in the bay as part of their course work. These data are, however, unpublished and
the quality of the data is questionable, but a short summary of the results is none the less provided
here (unpublished UCT student data from 1995 and 1996, provided by Prof. C. Griffith). Most of the
beaches sampled are in Langebaan Lagoon or at the head of the lagoon; the only beach sampled in
Saldanha Bay is at Lynch Point. An ‘open coast’ beach at 16 Mile Beach was also surveyed. The
results confirm the dramatic change in species richness and composition between the exposed
Saldanha Bay beach and the sheltered lagoon beaches. At Lynch Point, the fauna is sparse, and
includes the semi-terrestrial isopod Tylos granulatus and the talitrid amphipod Talorchestia spp. in
the supralittoral zone (above the high water spring mark (HWS)), and the amphipods Pontogeloides
latipes, Eurydice longicornis, the polychaetes Glycera tridactyla and Scololepis squamata in the
midlittoral zone. The mysid Gastrosaccus psammodytes was found at, and below, the low tide level.
A similar faunal composition was recorded from 16 Mile Beach (unpublished UCT student data from
1995 and 1996). The macrofaunal species encountered are generally ubiquitous to the West Coast
(Day 1959; Soares 2003). In contrast, the extremely sheltered intertidal flats in Langebaan Lagoon
harboured >30 species (Day (1959) recorded 55 species), many of which are either South Coast
species known to occur on the West Coast only in Langebaan Lagoon, typical estuarine species, or
species normally found in pools and crevices on exposed rocky shores (Day 1959). Noteworthy is
that many of the typical West Coast beach species (e.g. Tylos, Talorchestia, Eurydice) are not found
in the lagoon.
No data were found on sandy beach biota north of Lynch Point or from Small Bay. Due to the
general lack of knowledge of sandy shore fauna in Saldanha Bay it is strongly recommended that a
baseline survey of sandy intertidal habitats in the vicinity of the proposed RO Plant be undertaken
before any construction work commences, i.e. at Site 1 and at Site 2 should it be anticipated that
construction activities with disrupt the sandy shore fauna. The purpose of such surveys are both to
provide a baseline to assess construction impacts as well as the data and necessary understanding
to inform future impact assessments.
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Subtidal Sandy Habitats
The structure and composition of benthic soft bottom communities is primarily a function of water
depth and sediment grain size, but other factors such as current velocity, organic content, and food
abundance also play a role (Snelgrove and Butman, 1994; Flach and Thomsen, 1998; Ellingsen,
2002). Benthic infauna is the preferred group for environmental monitoring studies, and first
accounts of benthic assemblages in Saldanha Bay date back to the 1940s. Major developments
have occurred in the bay since then and changes in benthic community structure as a result of
anthropogenic impacts have been reported by numerous authors (Christie and Moldan, 1977;
Moldan, 1978; Jackson and McGibbon, 1991, amongst others). For example, in Small Bay there has
been a shift from communities dominated by suspension-feeders to communities characterized by
deposit-feeders. More specifically, the sea pen Virgularia schultzei, a suspension feeder, was
historically widespread in the bay, but was not been recorded at all after 1989. Although it re-
appeared in Big Bay in 2004, it is still absent in Small Bay. On the other hand, the deposit-feeding
polychaete Polydora sp. has undergone a dramatic increase over the last decades, especially in
Small Bay (Jackson and McGibbon, 1991). This shift in community composition has been attributed
to changes in water circulation patterns in the Bay, as well as organic pollution from fish factories and
mussel farming in Small Bay.
Table 5.3: Dominant species/taxa in Saldanha Bay as reported from benthic macrofauna studies conducted in 1975, 1999 and 2004 (adapted f rom Atkinson et al., 2006).
Taxa Common name Scientific name
Echiuroidea Tongue worm Ochaetostoma capense
Pennatulacea Sea pen Virgularia schultzei
Echinodermata Sea cucumber Holothuroidea
Brittle star Ophiuroidea
Pelecypoda Tellinid mussel Tellina gilchristi
Tellinid mussel Macoma crawfordii
Black mussel Choromytilus meridionalis
Gastropoda Plough snail Bullia digitalis
Crustacea Mud prawn Upogebia capensis
Sand prawn Callianassa kraussi
Three-legged crab Thaumastoplax spiralis
Crown crab Hymenosoma orbiculare
Amphipods Various species
Isopods Various species
Polychaeta Segmented worms Various species
The most recent study on benthic macrofauna was commissioned by the Saldanha Bay Water
Quality Forum in 2004 (Anchor Environmental Consultants, 2004), and is summarized by Atkinson et
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al. (2006) and compared to previous studies. Table 5.3 lists the dominant benthic macrofauna
species in Saldanha Bay.
The mud prawn Upogebia capensis is one of the most dominant species in the bay, particularly so in
Small Bay (Anchor Environmental Consultants, 2004). Other important species in Small Bay include
the polychaete Polydora sp., the amphipod Ampelisca spinimana, the tongue worm Ochaetostoma
capense and the crab Thaumastoplax spiralis, which lives commensally in the tube of the tongue
worm (Day, 1974). Aside from the mud prawn and the tongue worm, Big Bay was dominated by two
amphipod species (Ampelisca spinimana and Urothoe grimaldi), and the polychaete Orbinia
angrapequensis. In 2004, the sea pen Virgularia schultzei made a first reappearance in the Bay after
being absent for >10 years, but its occurrence was restricted to Big Bay while it was still absent from
Small Bay. Upogebia capensis, Ochaetostoma capense and Callianassa kraussi contributed the most
to the overall biomass in Small Bay and Big Bay, respectively. In the turbulent surf zone, particularly
between 2 – 5 m depth, the faunal diversity is usually lower and primarily includes amphipods and
polychaetes (Christie, 1976).
Dominant species in unvegetated sandflats in Langebaan Lagoon are the sand prawn Callianassa
kraussi, U. capensis, Ampelisca palmata (amphipod), Notomastus latericeus (polychaete) and
Cirolana hirtipes (isopod). In the mid-1990s, the alien invasive Mediterranean mussel Mytilus
galloprovincialis began establishing dense intertidal beds on the centre sandbanks of Langebaan
Lagoon (Hanekom and Nel, 2002). This invader had previously been restricted to rocky shores along
the South African coastline (Griffiths et al., 1992). The alien mussel beds significantly altered natural
community structure by the creation of a new habitat, which promoted the establishment of rocky-
shore hard-substrate species. Furthermore, the mussel beds excluded many sediment-dwellers
through smothering, and by denying burrowing species access to surface waters (Robinson et al.,
2002). Interestingly, after supporting an estimated biomass of nearly 8 t in 1998, the population had
died-off completely by mid-2001, with only empty shells and anoxic sand remaining (Robinson et al.,
2007a). The reason for the die-off is, however, unknown. In an effort to prevent the re-settlement of
M. galloprovincialis in this area, South African National Parks began removing all dead mussel shells
from the centre banks in late 2001, as these shells offer a suitable settlement substrate for mussel
larvae. The removal aided in the recovery of the previously invaded areas. However, 5 months after
clearance more than 50% of the species recorded in non-invaded areas were still absent from
cleared areas, including the important bioturbator Callianassa kraussi (Robinson et al., 2007a).
Subtidal macrophyte beds are dominated by the agarophyte alga species Gracilaria gracilis, which
occurs in Small Bay and adjacent to Schaapen Island in the southern portion of Big Bay. The alga is
also characteristic of the subtidal sandy sediments in the Langebaan Lagoon (Schils et al., 2001).
The alga occurs on sandy substrates at 2-10 m depths, and may either be anchored or drifting
(Anderson et al., 1993). Gracilaria forms the basis of a small industry that collects cast material from
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the beaches for export to agar processing plants. Another important macroalga in Langebaan
Lagoon is Sargassum incisifolium (Schils et al., 2001).
The southern end of Langebaan Lagoon is dominated by beds of the eelgrass Zostera capensis.
Faunal species that are associated with these sea-grass beds are the snails Assiminea globulus and
Hydrobia sp., the limpet Siphonaria compressa, the polychaetes Ceratonereis erythraeensis and
Perinereis nuntia vallata, an amphipod Paramoera capensis, a crab Cleistostoma edwardsii and the
mudprawn Upogebia africana (Siebert and Branch, 2007). The invertebrate fauna of the mudflats are
an important food source for waders; for example, A. globulus is the major prey item of the curlew
sandpiper (Puttick 1980) and U. africana is important to the kelp gull, grey plover, and common tern
(http://www.environment.gov.za/soer/nsoer/resource/wetland/ langebaan_ris.htm). The inter-tidal salt
marsh vegetation in the lagoon is classified as ‘dwarf succulent shrubland’ and includes the grass
Spartina maritime and the succulent plants, Chenolea diffusa, Sarcocornia perennis, S. pillansii, and
Salicornia meyerana. The algal species growing in the salt marshes (belonging to the Bostrychietum
association) have a large geographical distribution and occur commonly in tropical mangroves and
warm temperate salt marshes. On the West Coast, however, they are restricted almost entirely to
Langebaan Lagoon (Schils et al., 2001). The salt marshes of Langebaan Lagoon are the largest
along South Africa’s shoreline, and being in a relatively pristine condition, they are thus a biologically
valuable area (Schils et al., 2001).
In general, there has been a decline in species diversity but an overall increase in biomass in the bay
from 1999 to 2004, and a corresponding decrease in biomass in Langebaan Lagoon (Atkinson et al.,
2006). It has been suggested that this is related to the increase in particulate organic carbon in the
bay, which serves as an important food source for particulate feeders such as the crustaceans (the
group that accounted for most of the observed increase in biomass).
Similarly, the epifaunal (animals living on the sediment surface) community composition appears to
have undergone dramatic changes after the harbour development (Kruger et al., 2005).
Comparisons of data from the 1960s (prior to the jetty and causeway construction) with those from a
dredge survey in 2001, demonstrated a decline in species number and a shift in species composition.
Polychaetes, in particular, showed a substantial decline in species number. The species that
contributed most to the dissimilarity between the epibenthic communities of the 1960s and the 2001
were the whelk Nassarius speciosus and the crab Hymenosoma orbiculare. Both species had
increased significantly in abundance in 2001. It was suggested that altered wave energy, a shift
towards finer sediment and increased organic matter within Saldanha Bay as a result of harbour
construction, and fish factory and mussel-farm outputs, were responsible for these changes (Kruger
et al., 2005).
Saldanha Bay is a sheltered bay and the benthic faunal and floral species occurring in the bay (e.g.
Upogebia capensis, Callianassa kraussi, Ochaetostoma capense, Nassarius speciosus, Gracilaria
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gracilis) are typical inhabitants of shallow sheltered mud or sand banks and are common to the
southern African West Coast (Day, 1974; Branch et al., 1994). Langebaan Lagoon, however, from a
biological perspective is unique in that numerous species more typical of warmer waters occur here
and certain species normally restricted to estuarine conditions are also present, despite the system
being fully marine (Day 1959; Schils et al., 2001).
5.2.2 Rocky Habitats and Biota
Intertidal Rocky Shores
Despite the known changes that have taken place within the Saldanha Bay system over the last fifty
years, almost no historical data exists on the state of rocky shores in the area. A survey covering a
range of different rocky habitats has only recently been undertaken (Atkinson et al., 2006). This
study showed that, similar to other South African rocky shores (e.g. McQuaid and Branch, 1984),
wave exposure and the type of rock substratum were important determinants of community structure.
The rocky intertidal can be divided into different zones according to height on the shore. Each zone
is distinguishable by its different biological communities, which is largely a result of the different
exposure times to air. The level of wave action is particularly important on the low shore. Generally,
biomass is greater on exposed shores, which are dominated by filter-feeders. Sheltered shores
support lower biomass, and algae form a large portion of this biomass (McQuaid and Branch, 1984;
McQuaid et al., 1985).
The rock topography is also important, and for example boulder beaches in Small Bay were found to
be impoverished in terms of species abundance and biomass compared to more wave exposed sites.
Construction of the iron ore causeway and the Marcus Island causeway altered the wave exposure
zones in the Bay. The causeway increased the extent of sheltered and semi-sheltered zones in
Small Bay, with semi-exposed shores being absent in this area (Luger et al., 1999). Although wave
exposure in Big Bay was altered less dramatically, the extent of sheltered and semi-sheltered wave
exposure areas increased after harbour development (Luger et al., 1999). Although no historical data
prior to the construction of the causeway exist, it has been suggested that the sheltering effect of the
causeway has negatively affected the intertidal communities along the Small Bay shoreline and
changed their compositions (Atkinson et al., 2006).
In terms of zonation, important species in the high shore are the grazers Littorina africana
knysnaensis, Oxystele variegata, the filter feeding barnacle Chthalamus dentatus, and the alga
Porphyra capensis. Mid-shore levels are dominated by C. dentatus, the limpets Siphonaria capensis
and Scutellastra granularis, the carnivorous whelk Burnupena sp., the algae Ulva spp. and
Caulacanthus ustulatus, and the alien mussel Mytilus galloprovincialis. At sheltered sites, the low
shore is characterized by algae such as Ulva spp., Gigartina radula, and crustose algae, and the
faunal component includes Burnupena sp., M. galloprovincialis and the indigenous mussel
Choromytilus meridionalis. At more exposed sites, the low shore is covered primarily by M.
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galloprovincialis. All of these species are widespread on western and southern Cape shores
(Emanuel et al., 1992). However, M. galloprovincialis is an alien invasive species that is displacing
the indigenous species Choromytilus meridionalis and Aulacomya ater (Robinson et al., 2007b).
Further, because of greater structural complexity within beds of M. galloprovincialis compared to
those of indigenous mussels, there have been changes to overall community composition in areas
colonised by this species (Robinson et al., 2007b).
A study of the intertidal macroalgal assemblages in Saldanha Bay and Langebaan Lagoon identified
two distinct floral entities on rocky shores: (i) Saldanha Bay (including Small Bay and Big Bay) and (ii)
Langebaan Lagoon (Schils et al., 2001). The transition between the floral entities is located at the
mouth of the Lagoon. The species richness of the bay area is greater than in the lagoon. The
change in algal composition was explained by environmental variables of which wave exposure is the
most significant. In terms of biogeographical affinities of the different algal entities it was shown that
the bay area supports a typical West Coast flora. The algal flora of the lagoon is also dominated by
West Coast species, but is typified by species characteristic of sheltered habitats, and with a number
of species which otherwise only occur on the geographically distant South Coast (east of Cape
Agulhas) (Schils et al., 2001).
Rocky Subtidal Habitats
Rocky subtidal reefs are not extensive in Saldanha Bay, but artificial habitats such as harbour
structures and their reinforcements serve as additional settlement substrates. The dominant
organisms on these structures are mussels (M. galloprovincialis and to a lesser extent C. meridionalis
and A. ater), Pyura, and whelks and barnacles with associated macroalgae. Typical kelp species
along the West Coast of South Africa are the kelps Ecklonia maxima and Laminaria pallida
(Stegenga et al., 1997). In Saldanha Bay, however, E. maxima appears to be replaced by L. pallida.
Simons (1977) considers this to be a response to reduced wave exposure within the bay. Individuals
of E. maxima occur as far as the entrance of Langebaan Lagoon but do not penetrate further into the
lagoon, whereas isolated specimens of L. pallida can be found further into the lagoon (Schils et al.,
2001).
5.2.3 Pelagic Communities
The pelagic communities are typically divided into plankton (phytoplankton and zooplankton including
ichthyoplankton) and fish, and their main predators, marine mammals (seals, dolphins and whales).
Plankton
Saldanha Bay is protected from the high-energy coastline, but remains a highly productive system
owing to its link on its western side to the Benguela upwelling system (Pitcher and Calder, 1998).
Due to the nutrient supply from this upwelling system, phytoplankton concentrations in Saldanha Bay
can attain concentrations of 18 mg Chl a .m-3 with a mean value of 8.62 mg Chl a .m-3 (Pitcher and
Calder, 1998). Highest values typically occur during the upwelling season. Phytoplankton exhibits
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short term variability in distribution as it responds to variations in light levels, induced by natural
turbidity, nutrient supply to the surface layers resulting from wind mixing of the water column, and the
presence and location of thermoclines dividing oligotrophic surface layers from cooler, nutrient rich
subsurface water. Through the above processes, high phytoplankton biomasses can occur in
surface waters, be limited to subsurface maxima associated with thermoclines, or be reduced to low
levels as characteristically occurs in winter (Pitcher and Calder, 1998). Phytoplankton production is
estimated at 3.40 g C. m-2 .day-1 (Pitcher and Calder, 1998). This is comparable to estimates for the
adjacent southern Benguela upwelling system (Shannon and Pillar, 1986). The phytoplankton
species assemblage within Saldanha Bay appears to be largely similar to that of the adjacent
continental shelf.
Harmful algal blooms (HABs) are a regular late summer feature in the southern Benguela region
(Pitcher and Calder 2000). The occurrence of on Harmful algal blooms and their dynamics has been
recently summarised by Carter (2008).
Paralytic shellfish poisoning (PSP) due to Alexandrium catenella, and diarrehetic shellfish poising
(DSP) caused primarily by Dinophysis acuminate and D. fortii pose a threat to shellfish mariculture
operations, and mussel harvesting in Saldanha Bay was compromised for the first time in 1994 by
PSP (Pitcher et al., 1994). In subsequent years, both PSP and DSP have become regular problems
for the mariculture operations in the bay (Probyn et al., 2001). The geographical scales of Saldanha
Bay are considered unsuitable for in situ development of HABs (Pitcher et al., 1994). Blooms,
however, can be advected into Saldanha Bay from the adjacent continental shelf waters, but their
development and duration in the bay is restricted by the system of exchange that operates between
the bay and the coastal upwelling system, in that there is a net export of surface waters from the bay
(Probyn et al., 2001). In contrast, blooms of the brown tide organism, Aureococcus anophagefferens,
have been recorded in Saldanha Bay but not on the adjacent continental shelf (Pitcher and Calder,
2000; Probyn et al., 2001). The blooms were mainly limited to the reclamation (oyster) dam in 1997,
but spread throughout the entire system, including Langebaan Lagoon, in 1998 (Probyn et al., 2001),
and led to retarded growth rates in mussels and oysters.
Zooplankton species in Saldanha Bay are composed predominately of species similar to those of the
adjacent continental shelf (Grindley, 1977). The zooplankton species of Langebaan Lagoon,
however, were found to be distinctly different from that of Saldanha Bay, although elements of the
Saldanha Bay communities did penetrate the lagoon to various extents. Surprisingly, the
zooplankton communities at the head of the lagoon were found to be estuarine in character, even
though the system is not an estuary. This was attributed to the wide salinity tolerance range of these
estuarine species, which enables them to withstand the hyper-saline conditions often present at the
head of the lagoon (Grindley, 1977).
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Fish
Atkinson et al. (2006) report on surveys of fish distributions in Saldanha Bay and Langebaan Lagoon,
which were conducted using a variety of sampling gear. The waters of the Saldanha Bay system
support an abundant and diverse fish fauna with a total of 48 species being recorded. Overall
species richness and abundance was highest in Langebaan Lagoon. There was a trend of
increasing fish diversity and abundance with decreasing wave exposure. This was also reported
previously by Clark (1997). For example, wave exposed beaches yielded <1 fish. per square metre
less, exposed beaches around 2 fish. m-2, and >4 fish. m-2 at the top of the lagoon where waves are
all but absent.
Dominant species in Saldanha Bay and Langebaan Lagoon are harders (Liza richardsonii),
silversides (Antherina breviceps) and gobies (Caffrogobius sp.). Other important fish species in the
bay are the white stumpnose Rhadosargus globiceps, West Coast steenbras Lithognathus aureti,
steentjie Spondyliosoma emarginatum, gurnard Cheilidonichtyes capensis, Cape sole Heteromyctus
capensis, super klipvis Clinus superciliosus, and sand shark Rhinobatos annulatus
(Atkinson et al. 2006; http://www.environment.gov.za/soer/nsoer/resource/wetland/langebaan_ris.htm).
The Saldanha Bay/Langebaan Lagoon complex is an important nursery area for a number of
ecologically important fish species as its sheltered, nutrient rich and sun-warmed waters provide a
refuge from the cold and highly energetic adjacent continental shelf (Atkinson et al., 2006).
Marine Mammals
The Cape fur seal Arctocephalus pusillus pusillus no longer breeds on islands in Saldanha Bay, but is
a regular visitor in both the inner and outer bays during all months of the year (Cooper, 1995). Five
whale species have been recorded within Saldanha Bay: Killer whale (Orcinus orca), Humpback
whale (Megaptera novaeangliae) and southern Right whales (Balaena glacialis), along with Minke
(Balaenoptera acutorostrata) and Bryde's (B. edeni) whales in the outer bay between Malgas, Jutten
and Marcus Islands (Cooper, 1995). Dusky dolphins (Lagenorhynchus obscurus) and Heaviside's
dolphin (Cephalorhynchus heavisidii) have been observed along the seaward side of the Marcus
Island causeway (Cooper, 1995).
5.2.4 Birds
Saldanha Bay and the associated islands provide important shelter, feeding and breeding habitat for
at least 53 species of seabirds, 11 of which are known to breed on the islands (Atkinson et al., 2006).
The islands of Malgas, Marcus, Jutten, Schaapen and Vondeling support breeding populations of
African Penguin, Cape Gannet, four species of marine cormorants, Kelp and Hartlaub’s Gulls, and
Swift Terns. The islands also support important populations of the rare and endemic African Black
Oystercatcher. Langebaan Lagoon provides an important habitat for 67 species of waterbirds, of
which half are waders. The lagoon has been identified as the most important wetland for waders on
the west coast of southern Africa, with 17 of the wader species being regular migrants from the
Palearctic region of Eurasia. Waterbird abundance is thus highest in summer, and decreases in
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winter. Since 1980, there has been a decline in the numbers of waders, which has been attributed to
the siltation of the lagoon reducing the amount of suitable feeding grounds, and increasing levels of
human disturbance (Atkinson et al., 2006).
5.2.5 Beneficial Uses
Besides the natural environment, beneficial uses of the coastal marine waters of South Africa are
subdivided into three categories (DWAF, 1995):
• Recreational use;
• Mariculture use (including collection of seafood for human consumption); and
• Industrial uses (e.g. intake of cooling water and water for fish processing and/or mariculture).
The identification and mapping of designated uses of the marine environment in Saldanha Bay is
drawn from the study by Taljaard and Monteiro (2002), and summarized below.
Conservation Areas
Langebaan Lagoon was designated as a Ramsar site in April 1988 under the Convention on
Wetlands of International Importance especially as Waterfowl Habitat. The Ramsar site includes the
islands Schaapen (29 ha), Marcus (17 ha), Malgas (18 ha) and Jutten (43 ha), the Langebaan
Lagoon (15 km long and 12.5 km wide), and a section of Atlantic coastline. The Langebaan Lagoon is
also included within the boundaries of the West Coast National Park, which was established in 1985.
The lagoon is divided into three different utilization zones namely: wilderness, limited recreational and
multi-purpose recreational areas (Figure 5.9). The wilderness zone has restricted access and
includes the southern end of the lagoon and the inshore islands, which are the key refuge sites of the
waders and breeding seabird populations respectively. The limited recreation zone includes the
middle reaches of the lagoon, where activities such as sailing and canoeing are permitted. The
mouth region is a multi-purpose recreation zone for power boats, yachts, water-skiers and fishermen.
However, no collecting or removal of perlemoen and crayfish is allowed in the lagoon.
There are also a number of marine protected areas (MPAs) declared under the Marine Living
Resources Act 18 of 1998 (Figure 5.9):
• Langebaan Lagoon MPA
• Sixteen Mile Beach MPA
• Malgas Island MPA
• Jutten Island MPA
• Marcus Island MPA
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Figure 5.9: Conservation areas in Saldanha Bay (ada pted from Taljaard and Monteiro, 2002).
Conservation areas of the Cape Nature Conservation Board include:
• An area within the military base, SAS Saldanha
• Vondeling Island
Mariculture Areas
The Transnet National Ports Authority (TNPA) has set aside a total of 395 ha of sea area within
Saldanha Bay for mariculture activities, of which 200 ha are situated in Big Bay, 130 ha are located in
Small Bay and a further 65 ha lie adjacent to the breakwater and Small Craft Harbour. Marine
aquaculture operations currently undertaken within these areas are:
• Mussel farming;
• Oyster farming; and
• Commercial harvesting of seaweed in Saldanha Bay.
Sixteen Mile Beach MPA
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Table 5.4 and Figure 5.10 provide a summary of the lease holders and the areas and location of their
leases.
Table 5.4: Current Mariculture lease holders in Sal danha Bay.
Lease Holder Lease Area (ha) Location
Blue Bay Aquafarm (Pty) Ltd 50.9 Small Bay
Saldanha Bay Sea Farms (Pty) Ltd 10.6 Small Bay
Blue Sapphire Pearls cc 5 Small Bay
Christopher Heineken 5 Small Bay
JDL Fisheries (Pty) Ltd 10 Small Bay
Masiza Mussel Farm (Pty) Ltd 30 Small Bay
Ocean Deli Fishing 5 Small Bay
OWK (Pty) Ltd 5 Small Bay
TELVEX 16 cc 5 Small Bay
West Coast Seaweed(Pty) Ltd 5 Small Bay
Keep the Dream 81 (Saldanha Mariculture Association) 15 Small Bay
Striker Fishing 10 Small Bay
25 Big Bay
West Coast Oyster Growers 10 Big Bay
i) Mussel Farming
The alien Mediterranean mussel Mytilus galloprovincialis and the indigenous black mussels
Choromytilus meridionalis are cultured on ropes, clustered 60 cm apart and suspended from rafts to
a depth of 6 m. Settlement of larvae onto the ropes occurs naturally from the water column. During
years of poor recruitment mussel spat may, however, be harvested off the caissons of the iron-ore
jetty to a depth of ~5 m, and subsequently transferred to the culture rafts. Mussels are harvested,
washed and graded on board a boat and juvenile mussels are hung back onto the ropes and held in
place by mesh ‘socks’ until attachment.
After the discovery of populations of the alien mussel Mytilus galloprovincialis in Langebaan Lagoon
and at the head of the lagoon near Schaapen Island, the South African National Park initiated a
project, in collaboration with the local community, to remove the alien mussel from Langebaan
Lagoon, selling these to local markets. However, after some time it was discovered that the alien
mussel populations had reduced drastically, and that > 80% of the mussels collected were in fact the
indigenous species Choromytilus meridionalis. It was thus decided to discontinue with this harvesting
initiative, and there are no further plans for harvesting of wild mussel populations (P. Nel, West Coast
National Park, pers. comm.).
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Figure 5.10: Current mariculture lease holders in S aldanha Bay.
ii) Oyster Farming
Until recently, Saldanha Bay Oyster Company farmed the Pacific oyster Crassostrea gigas in a
completely enclosed tidal dam (reclamation dam) situated in the Port of Saldanha (Figure 5.10). This
activity has now stopped. Partial reclamation of this dam is proposed as part of the Phase 1B for the
expansion of the Sishen-Saldanha Iron Ore Export Corridor development. It is proposed that the
remainder of the dam be reclaimed as part of the proposed Phase 2 expansion of the Sishen-
Saldanha Iron Ore Export Corridor development. There are, however, currently a number of new
oyster farming ventures proposed for TNPA lease areas in both Small Bay and Big Bay (see Table
5.3 and Figure 5.10).
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iii) Seaweed Harvesting
The agarophyte Gracilaria gracilis is being harvested commercially in Saldanha Bay by Taurus
Saldanha Seaweed (Pty) Ltd. The beach-cast seaweed is collected and dried, before being exported
primarily for agar processing. Annual yields, however, vary enormously and the resource has
collapsed and recovered twice over the past few decades (Anderson et al., 1996).
The first collapse occurred in 1974, after the construction of the iron ore jetty and breakwater. After
initial recovery, the resources declined again in 1989. This was attributed to over-grazing by fish in
shallow water and by keyhole limpets and urchins in deep water (Anderson et al., 1993).
A further disruption to the industry occurred in 1993, when a bloom of Ulva lactuca appeared for the
first time in Saldanha Bay and persisted throughout the summer. Ulva wash-ups contaminated the
beach and part of the commercial Gracilaria beach-cast had to be discarded (Anderson et al., 1996).
In summer, the water in Small Bay becomes highly stratified with cold nutrient-rich bottom water and
warm oligotrophic surface water. The discharge of nitrogen-rich effluents from fish factories into the
surface layer in a sector of the bay provided localised conditions for Ulva to out-compete Gracilaria at
depths of 2-5 m, demonstrating the powerful disruptive effect of eutrophication in this strongly
stratified system (Anderson et al., 1996).
Commercial and Recreational Fisheries
The commercial fishery in Saldanha Bay consists mainly of line fishing from small boats and gill
netting (Figure 5.11). Gill-netting is conducted from small ski boats close to or within the surf-zone,
primarily at night (S. Lamberth, MCM, pers. comm.). Currently, there are 15 gill-net permit holders, of
which ten operate in Langebaan Lagoon and five in Saldanha Bay (MCM, 2007). Those from
Saldanha Bay operate both in Small Bay and Big Bay, but the permit conditions allow some of the
Langebaan Lagoon permit holders to also operate up to the Iron Ore Jetty in Big Bay (MCM, 2006).
Gill-net permit holders target harders and in 1998-1999 landed an estimated 590 tons annually,
valued at approximately R 1.8 million (Hutchings and Lamberth, 2002). There is one beach-seine
netting right available for Saldanha Bay but at present this right has not been taken up (MCM, 2007).
Species such as white stumpnose, white steenbras, kob, elf, steentjie, yellowtail and smoothhound
shark support the commercial line fisheries, and also a large shore angling and recreational boat
fishery, which contributes significantly to the tourism appeal and regional economy of Saldanha Bay
and Langebaan (Atkinson et al., 2006).
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Figure 5.11: Designated beneficial use areas in Sal danha Bay (adapted from Taljaard and Monteiro, 2002).
5.2.6 Existing Environmental Impacts
Existing activities that potentially have a negative impact on the quality of the marine environment in
the Saldanha Bay system have been described in detail by Taljaard and Monteiro (2002). An
overview of these activities and sources are provided below (see Figures 5.11 and 5.12).
Discharges from seafood processing industries
There are four seafood processing industries situated in Saldanha Bay, namely:
• Sea Harvest Corporation Ltd;
• Southern Seas Fishing;
• SA Lobster Exporters (Marine Products); and
• Live Fish Tanks (West Coast) (Lusithania).
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Each of these seafood industries discharges of their effluents into the sea at Small Bay. The main
pollutants in these effluents are:
• Inorganic nitrogen;
• Organic nitrogen and carbon;
• Suspended solids; and
• Microbiological contaminants.
This nitrogen-rich discharge, particularly that from the larger fish processing factories, has been
found to have measurable effects on benthic macrofauna (Christie and Moldan, 1977), and has
caused an outbreak of the opportunistic green alga Ulva lactuca, which reduced the benthic
Gracilaria stocks in 1993/94 (Anderson et al,. 1996; Monteiro et al., 1997). The fish waste has also
been found to provide a significant source of nitrogen for seaweed cultivated throughout the northern
area of Small Bay, particularly when the water is highly stratified in summer (Anderson et al., 1999).
Sewage
In the Saldanha Bay and Langebaan area, sewage can enter the marine environment via the
following routes:
• Sewage effluent from a sewage treatment works (effluent from the Saldanha Bay sewage
treatment works is into the Bok River from where it drains into Saldanha Bay opposite the
Blouwaterbaai Resort);
• Overflow from sewage pump stations (usually the result of pump malfunction or power failures);
and
• Seepage or overflow from septic or conservancy tanks, respectively.
Storm water runoff
Although it is very difficult to characterize storm water runoff due to the widely varying contaminant
concentrations, it is one of the major non-point sources of pollution. In the case of the Saldanha Bay
and Langebaan, storm water runoff that could potentially have a marked effect on marine water
quality primarily originates from industrial areas (industrial zone where seafood processing industries
are situated and the Port of Saldanha and surrounding industrial sites), and the residential areas of
Saldanha Bay and Langebaan, including the area up to Club Mykonos.
Port activities and associated ship traffic
Activities, associated with shipping traffic and the Port of Saldanha that can potentially impact on
marine water and sediment quality in the area include:
• Ore dust fallout during ship loading operations;
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• Oil spillages;
• Dredging operations; and
• Ballast water discharge.
Activities associated with smaller harbours
There are numerous smaller harbour areas in and around Saldanha Bay and Langebaan Lagoon:
• Small craft harbours (also under the jurisdiction of the TNPA);
• Fishing harbours;
• Military harbour (SAS Saldanha);
• Yacht clubs of Saldanha Bay and Langebaan, and at Club Mykonos.
Activities and operations in harbours that could contribute to the deterioration of marine water quality
include:
• Cleaning of vessels in harbour areas, as well as emptying of water closets and toilets into
harbour areas;
• Dumping of blood water from fishing vessels into sheltered harbour areas;
• Off-cuts and offal from fish cleaning operations being washed down into storm water drains and
eventually ending up in the harbour;
• Poor waste disposal practices in the scraping and cleaning of vessels (maintenance). Anti-
fouling paints are of particular concern as these often contain significant levels of tributyl-tin, a
toxin that can result in the shell deformation in shellfish.
Mussel farming
Mussel farming in Saldanha Bay uses the Spanish raft system, where mussel are cultured on ropes
that are suspended in the water column from rafts. This mussel farming technique can affect marine
sediment and water quality through reducing the turbulence in the benthic boundary layer, and
through high sedimentation rates from faeces, pseudofaeces, fallen mussels and foulers under the
rafts. Research has shown that mussel debris under rafts can accumulate to a depth of 20 cm,
creating organic enrichment and anoxia in sediments. Benthic macrofaunal communities under the
rafts were found to be disturbed, displaying a reduction in biomass and an alteration of trophic groups
and taxa (Stenton-Dozey et al., 1999, 2001).
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Harmful algal blooms
Harmful (toxic) blooms have become a regular seasonal occurrence in the bay since 1994 (see
section 5.2.3). These blooms pose a risk to both the sensitive ecosystems in the area as well as to
beneficial uses, such as mariculture operations, and recreation and tourism.
Groundwater abstraction
Langebaan Lagoon supports extensive marsh plant communities. Some of the marsh vegetation,
e.g. bulrush, Typha capensis relies on freshwater input from groundwater. Over-exploitation of
groundwater feeding into the lagoon may therefore affect the diversity of marsh vegetation.
Littering
Littering, particularly plastics, has become a major problem associated with urban development, not
only in terms of unpleasant aesthetics, but also in terms of the physical harm caused to marine life.
Towards improving the quality of South African beaches the Department of Environmental Affairs and
Tourism initiated their Coastcare programme, involving local communities. The Saldanha Municipality
acts as implementing agent for the Coastcare programme in their region.
Figure 5.12: Existing activities potentially impact ing negatively on the marine environment in
Saldanha Bay (adapted from Taljaard and Monteiro 20 02).
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5.2.7 Potentially Threatened Habitats and Beneficia l Uses
Taking into account the wastewater characteristics of the proposed discharge from the RO plant,
potential impacts are most likely to target important marine ecosystems and beneficial uses that rely
on the health of marine organisms and plants, such as the marine aquaculture activities and the
fisheries. Certain areas of special interest likely to be impacted by discharges from the RO Plant into
the marine environment were identified. These specific areas include:
• The natural intertidal and shallow subtidal environments adjacent to the harbour;
• Commercial and recreational fisheries;
• Seaweed harvesting;
• National Parks;
• Marine Protected Areas;
• Nearby existing and proposed mariculture activities; and
• Seawater intakes to the fish factories
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6 IDENTIFICATION OF KEY ISSUES AND SOURCES OF
POTENTIAL ENVIRONMENTAL IMPACT
In the course of the public participation/consultation phase of the Basic Assessment and
environmental screening process for the proposed RO Plant, key issues were identified relating to
potential environmental impacts. These, and additional issues identified by the specialists, are
summarised briefly below in terms of the construction phase, operational phase and
decommissioning phase. They are dealt with in more detail in Section 8 of this report.
6.1 Construction Phase
The potential impacts associated with the construction of feed-water intake and brine discharge
structures into the marine environment are likely to be far less significant than impacts associated
with current and proposed port expansion activities. Nonetheless, they need to be addressed as part
of the proposed RO Plant development, and are related to:
• Onshore construction (human activity, air, noise and vibration pollution, dust, blasting and piling
driving, disturbance of coastal flora and fauna). Assessment of these impacts is not
considered to be the scope of work for this specialist study;
• Construction and installation of a surf-zone or deeper water discharge and intake via pipeline
(construction site, pipe lay-down areas, trenching of pipeline(s) in the marine environment,
vehicular traffic on the beach and consequent disturbance of intertidal and subtidal biota); and
• Construction and installation of intake wells on the beach above the high water mark, and
associated pipelines leading to and from the plant (vehicular traffic in the dunes and on the
beach, well excavations and consequent disturbance of dune and beach biota).
At all three of the alternative sites the RO Plant will be constructed a distance from the existing
shoreline. Consequently, issues associated with the location of the plant, drilling of the beach wells,
boreholes, and the associated pipelines leading from the beach wells to the plant are not deemed to
be of relevance to the marine environment, and have been dealt with by other specialist studies. The
project-specific geotechnical groundwater study (Visser et al., 2007) estimated that installation of the
10 beach wells required at Site 1 would disturb an area of 10 x 10 m each, a total of 1000 m2. In
contrast, construction of horizontal collector wells will disturb a much larger estimated area of at least
20 x 250 m (5000 m2) along the beach. In the case of surf-zone intakes, infrastructure extending into
the sea will require temporary removal of seabed material (blasting if required, piling driving and
potential increased turbidity) and seabed preparation, and potential impacts to beach biota.
It is assumed here that the design and construction of the necessary infrastructure on the beach or
extending into the sea, will take into consideration:
• the natural dynamics of the shoreline in the region;
• potential changes in shoreline stability associated with expansion of the ore terminal facilities;
and
• possible climate change issues such as sea level rise and increased storminess.
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6.2 Operational Phase
The key issues and major potential impacts are mostly associated with the operational phase. The
key issues related to the presence of pipeline infrastructure and brine discharges into the marine
environment are:
• altered flows at the intake and discharge resulting in ecological impacts (e.g. entrainment of
biota at the intake, low distortion/changes at the discharge, and affects on natural sediment
dynamics);
• the effect of elevated salinities in the brine water discharged to the bay;
• biocidal action of residual chlorine (or other non-oxidisng biocides) in the effluent;
• the effects of co-discharged waste water constituents, including possible tainting effects
affecting both mariculture activities and fish factory processing in the bay;
• the effect of the discharged effluent having a higher temperature than the receiving
environment; and
• direct changes in dissolved oxygen content due to the difference between the ambient
dissolved oxygen concentrations and those in the discharged effluent, and indirect changes in
dissolved oxygen content of the water column and sediments due to changes in phytoplankton
production as a result of changes in nutrient dynamics (both in terms of changes in nutrient
inflows and vertical mixing of nutrients) and changes in remineralisation rates (with related
changes in nutrient concentrations in near bottom waters) associated with near bottom
changes in seawater temperature associated with the brine discharge plume.
Additional engineering design considerations, not strictly constituting issues to be considered within
the EIA, include the following:
• structural integrity of the intake and outfall pipelines (e.g. related to shoreline movement);
• potential re-circulation of brine effluents if intakes and discharges are situated in close
proximity to one another. The model results however indicate that this will not be a concern for
all of the intake and dsicharge options considered in this study. Only at site 2 do the salinity
and seawater temperatures from the discharge plumes result in salinity of seawater
temperature elevations of approximately 0.5 psu and 0.5 to 1.0 ºC above ambient conditions at
the intake and then only for short durations (see model results in Appendix C).
• the permeability and particle size distributions of the sands (should beach intake and/or
discharge wells be considered), as a high proportion of fines in the beach sand could
jeopardise the durability of the intake wells and effectiveness off discharge wells; and
• water quality of feed-waters that should include consideration of possible deteriorating water
quality (particularly sediments that may be stirred up during normal port operations, capital
and/or maintenance dredging within the port, or large-scale hypoxia of bottom waters), that
may require specific mitigation measures or planned flexibility in the operations of the RO
Plant.
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6.3 Decommissioning Phase
The minimum anticipated life of the RO plant is 25 years. The individual RO modules will be replaced
as and when required during this period. No decommissioning procedures or restoration plans have
been compiled at this stage, as it is envisaged that the plant will be refurbished rather than
decommissioned after the anticipated 25 years, as the beach wells/boreholes (if used) are expected
to have a considerably longer lifespan than the RO modules. The potential impacts during the
decommissioning phase are expected to be minimal in comparison to those occurring during the
operational phase, and no key issues related to the marine environment are identified at this stage.
As full decommissioning will require a separate EIA, potential issues related to this phase will not be
dealt with further in this report.
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7 MODELLED CHANGES IN THE MARINE ENVIRONMENT DUE TO
THE RO PLANT EFFLUENT DISCHARGES TO THE MARINE
ENVIRONMENT
7.1 Introduction
The brine and co-discharges have been modelled using the Delft3D modelling suite that has been set
up to simulate both the three dimensional hydrodynamics and water quality in Saldanha Bay. The
model set-up and calibration is described in detail in Appendix B. The model simulations have been
undertaken for five intake and discharge combinations associated with 3 RO plant locations
proposed.
7.2 Assumed intake and discharge locations
A detailed description of the three proposed RO Plant sites are given in Section 3.2 of this report (see
Figure 3.2).
Due to the specific constraints at the various sites, the conceptual intake and discharge designs for
the various sites differ substantially. The assumed location of the various intake and discharge
locations are given in Table 7.1 below and are indicated in Figures 7.1a to d.
A detailed description of the various intake and discharge combinations is given in Section 3.5 of this
report where all of the options considered are summarised in Table 3.1.
The detail of the conceptual designs considered in the modelling study are provided below. The
intake and discharge combinations assessed in the modelling study are summarised in Section 7.5
and Table 7.5.
In the modelling study it is not possible to explicitly simulate either beach well intakes or discharges.
Thus only pipeline intakes have been simulated. In terms of the assessment of the proposed RO
Plant discharges into the marine environment, the only difference to the modelling outcomes due to
the assumption of pipeline intakes rather than beach well or borehole intakes is that there will be a
reduction in CIP chemicals and backwash sediments for the beach wells and borehole intake options
compared to the pipeline intakes. Provided that the intake waters for beach well and boreholes do
not have a significantly different temperature and salinity characteristics to those from pipeline
intakes, the modelling of plume dynamics and the subsequent assessment potential impacts of a RO
Plant discharge undertaken will remain valid and conservative (i.e. “worst case”) in that the CIP
chemicals and backwash sediments for the beach wells and borehole intake options are likely to be
significantly reduced compared to the pipeline intakes.
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Figure 7.1a: Proposed location of intake and discha rge structures for Site 1.
Figure 7.1b: Proposed location of intake and discha rge structures for Site 2. The yellow dotted line encloses the potential area within whic h beach wells may be located.
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Figure 7.1c: Proposed location of intake and discha rge structures for pipeline discharges into Small and Big Bay for Site 3.
Figure 7.1d: Proposed location of borehole intakes (adjacent to stockyard and MPT) discharge location for a pipeline discharge from Si te 3 at Caisson 3. The intake boreholes will be located within the linear distanc e marked by the white lines in the figure opposite the existing iron-ore stockyard and the MPT (see Figures 3.5a and 3.5b in Section 3 for more detail).
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Table 7.1: Location of the intake and discharges fo r the various proposed sites.
Development Option
1a 1b 2a 2b 3a 3b 3c & 3d
Intake Location
Site 1 Beach well
intake (1a)
Site 1 *2
Surf-zone (sump) intake* 1
Site 2
Beach well intake
Site 2 *3
Surf-zone (sump) intake* 1
Site 3 *3
Pipeline intake
Site 3 *45 Borehole
intake (Stockyard)
Site 3 *5 Borehole
intake (MPT)
Latitude 33º 00’ 29.58’’ S 33º 00’ 35.31’’ S 32º 59’ 56.63’’ S
(nominal) 32º 59’ 56.62’’ S 33º 01’ 07.89’’ S
33º 00’ 07.41’’ S to
33º 00’ 26.90’’ S
33º 00’ 56.22’’ S to
33º 001 11.77’’ S
Longitude 18º 00’ 33.17’’ E 18º00’ 36.54’’ E 17º 59’ 46.54’’ E
(nominal) 17º 59’ 38.84’’ E 17º 59’ 14.58’’ E
17º 59’ 46.69’’ E to
17º 59’ 41.11’’ E
17º 59’ 28.42’’ E to
17º 59’ 21.41’’ E
Discharge Location
Site 1 Pipeline outfall
Site 2 *3
Pipeline outfall
Site 3 *4 Pipeline outfall
(Small Bay)
Site 3 Pipeline outfall
(Big Bay)
Site 3 Pipeline outfall
(Caisson 3)
Latitude 33º 00’ 34.11’’ S to 33º 00’ 33.377’’ S
33º 00’ 02.42’’ S
33º 01’ 19.26’’ S (33º 01’ 06.43’’ S)*4 33º 01’ 39.70’’ S
Longitude 18º 22’ 22.61’’ E to 18º009’ 23.33’’ E
17º 59’ 45.59’’ E
17º 59’ 13.82’’ E (17º 59’ 29.09’’ E) 17º 59’ 08.62’’ E
*1 The option of a surf-zone intake via a sump and delivery of intake waters via pipeline to the RO Plant is identified as a pipeline intake in Table 3.1. *2 For Site 1 the intake structures considered are either beach wells or a possible pipeline intake with a possible sump located in the surf zone in an approximate –1
m CD water depth (see Table 7.2). Given that strong wind-driven currents flow from SE to NW in summer, the surf-zone intake structure is located to the SE of the proposed discharge structure comprising a pipeline discharge at the surface over an approximate 30 m distance along the revetment structure of the existing reclamation dam (Figure 7.1a). Given that it is a surf-zone intake, sediment loading may be an issue and sump structures will need to be considered. This has been the approach for the Marine Growers abalone farm just NE of the Port of Coega.
*3 Given that the current flow is predominantly clockwise around the eastern side of Small Bay, it is envisaged that the sea water intake would be situated in or near the surf-zone in an approximate -1 m CD water depth at a location west of the discharge. The discharge is likely to be a surf-zone discharge or a single port discharge in a very shallow water depth, also assumed here to be – 1 m CD. The discharge position is located in shallower water just inshore of the edge of deeper dredged area in this section of the port.
*4 Given that the current moves clockwise around the eastern side of Small Bay it is envisaged that the sea water intake would be situated north of the proposed discharge location in Small Bay in an approximate -1 m CD water depth. The discharge is likely to be a surf-zone discharge of single port discharge in a very an approximate 8 m water depth for a discharge into Small Bay or a shallower (approximately 4 m) water depth if discharged into Big Bay.
*5 The boreholes along the quayside are located at two possible locations along the causeway, namely opposite the existing iron-ore stockyard and opposite the MPT.
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Table 7.2: Main characteristics and conceptual des ign of intake structures for the RO plant.
Site 1 Site 2 Site 3 (a&b) Site 3 (c&d)
Intake Design * 1
Beach wells (10 worst case) or surf-zone sump intake via
pipeline.
A surf-zone (sump) intake via pipeline has been assumed for the purposes of the modelling
study *2.
10 Beach wells or a surf-zone (sump) intake via pipeline.
A surf-zone (sump) intake via pipeline has been assumed for the purposes of the modelling study *2
Pipeline intake in quayside
Up to 10 borehole intakes located on the causeway alongside the iron-ore stockpiles or the MPT
A pipeline intake alongside the quayside has been assumed in the
modelling study *2
Co-ordinates of intake structures
33º 00’ 29.58’’ S
18º00’ 36.54’’ E
32º 59’ 56.57’’ S
17º 59’ 38.64’’ E
33º 01’ 07.96’’ S
17º 59’ 14.62’’ E
Stockpile
33º 00’ 07.41’’ S to 33º 00’ 26.90’’ S
17º 59’ 46.69’’ E to 17º 59’ 41.11’’ E
MPT
33º 00’ 56.22’’ S to 33º 001 11.77’’ S
17º 59’ 28.42’’ E to 17º 59’ 21.41’’ E
Distance from shoreline
Approximately 65 m from the shoreline (exact distance depends on bathymetry)
Approximately 75 m from shoreline (exact distance depends on
bathymetry) Intake alongside quay wall Borehole intakes located along
causeway
Distance from discharge point
350 m 250 m
350 m (for discharge to Small Bay)
Other side of the causeway (for discharge into Big Bay)
Approximately 900 m to the closest borehole (for boreholes located
alongside the MPT) Approximately 2400 m to the
closest borehole (for boreholes located alongside the iron-ore
stockyard)
The distance between the Site 3 intake alongside the quay wall as
assumed in the modelling study and the discharge at Caisson 3 is
approximately 1000 m
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Site 1 Site 2 Site 3 (a&b) Site 3 (c&d)
Intake Depth Note 3
-1 m CD (approximately 1.865 m below MSL)
This allows for a minimum water depth of approximately 1 m at all
times
-1 m CD (approximately 1.865 m below MSL)
This allows for a minimum water depth of approximately 1 m at all
times
-1 m CD (approximately 1.865 m below MSL)
This allows for a minimum water depth of approximately 1 m at all
times
Not relevant for borehole intakes -1 m CD (approximately 1.865 m
below MSL) for intake alongside the quay wall as assumed in the
modelling study.
This allows for a minimum water depth of approximately 1 m at all
times
Intake flow rates 8000 m3/day or
92.6 ℓ. s-1 for 3 RO unit plant (assumed to be continuous)
8000 m3/day or 92.6 ℓ. s-1 for 3 RO unit plant (assumed to be continuous)
8000 m3/day or 92.6 ℓ. s-1 for 3 RO unit plant (assumed to be continuous)
8000 m3/day or 92.6 ℓ. s-1 for 3 RO unit plant (assumed to be continuous)
Intake velocity
Velocity is estimated to be approximately 0.15 m.s-1 at the intake screens and 1.0 m.s-1 in
the intake pipeline
Velocity is estimated to be approximately 0.15 m.s-1 at the
intake screens and 1.0 m.s-1 in the intake pipeline
Velocity is estimated to be approximately 0.15 m.s-1 at the
intake screens and 1.0 m.s-1 in the intake pipeline
Not of relevance for a borehole intake
*1 The assumed specifications for the intake beach well design are that supplied to date by Transnet (see Section 3.3.1).
*2 Beach wells are not explicitly considered in the modelling study. In the modelling study only surf-zone sump intakes have been considered for Sites 1 and 2 and only an intake in the quayside for Site 3 discharges. This implies that an explicit assumption has been made that the temperature of the intake waters from the beach wells will not differ significantly from that for a surf-zone sump intake at Sites 1 and 2. Similarly it is assumed that the temperature of the intake waters from boreholes situated along the causeway will not differ significantly from that of a near-surface intake at the quay wall when considering a discharge at Site 3 discharge at Caisson 3. For surf-zone sump intakes, this is a reasonable assumption. For borehole intakes along the causeway it is not clear how different the temperature of the borehole water would be compared to a near-surface intake at the quay wall. It is likely that the water temperature from the boreholes would be close to that of the seasonal mean near-surface seawater temperatures. Preliminary data from boreholes (D. Visser, pers comm.) seem to indicate that this is not an unreasonable assumption however, this cannot be confirmed without data on the borehole water temperatures. The brine and biocide concentrations in the discharge will not differ according to the nature of the intake other than that the likely biocide concentrations for beach wells/boreholes could be significantly less than those for pipeline intakes. In the modelling we have assumed oxidising biocide concentrations of 0.1 mg. ℓ-1 NaOCl or a non-oxidising concentrations ranging between 1.15 mg.ℓ-1 and 2.475 mg.ℓ-1 DBNPA.
*3 It is assumed that the intake would need to be in a water depth such that the intake remains below water under all tidal, wind and wave conditions. The intake depth is located near the surface to obtain warmest water possible but sufficiently away from the surface to avoid entrainment of debris and possible oils. Intakes at greater depth will have a greater chance of entraining sediments, low oxygen waters or H2S (if present). There is a possibility of a significant temperature difference between the intake waters and the ambient temperatures at the discharge depth and this needs to be considered when assessing the discharge. Transnet has indicated that there may be a rise in temperature of the seawater/brine discharge between the intake and discharge points. Consequently a further comprehensive sensitivity analysis has been undertaken (van Ballegooyen et al., 2008) that confirms that the results of this study (that assumes a discharge with a zero temperature elevation above the ambient water temperature at the intake), remain valid for discharges with temperature elevations of up to 5 ºC above the ambient water temperature at the intake (see Section 4.2.)
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7.3 Intake Characteristics
Important specifications for the seawater intakes include:
• the location of the discharge : - is specified in terms of actual co-ordinates and the distance
from both the shoreline and the discharge location. The exact location determines other
characteristics such as the water quality, temperature and salinity at the intake as well as the
design of the intake;
• the nature and design of the intake : - it is assumed that the intake infrastructure is likely to
comprise a surf-zone intake or beach wells at Site 1 and Site 2 and intake pipelines or
boreholes at Site 3, where there is more limited potential for installing beach wells. It is
assumed that all intakes will be designed to minimise entrainment of biota and will have self-
cleaning screens where appropriate/possible. Obviously this will not be a requirement for the
beach well/ borehole intake structures or sumps located in the surf-zone;
• the intake depth: - that influences the intake temperature. It is assumed that the intake waters
should be as warm as possible as this increases RO plant efficiency. This implies that the
intake should be located near the surface (approximately -1 m CD) where the waters are
warmer than at depth and also where there is less likelihood of the entrainment of sediments,
low oxygen water and possibly H2S if present (although considered unlikely). However the
intake should be located sufficiently deep to avoid entrainment of surface debris and possible
oil spills;
• the nature of the flows (Intermittent or continuous). Transnet has specified all flow to be
continuous as at the steady rates given in Table 7.2.. However shock dosing by biocides has
been proposed. The implications of this are discussed in Section 4.2)
The main characteristics of the intake structures at each site is summarised in Table 7.2.
There are water quality requirements for the intake waters and it is assumed that pre-treatment
processes may be needed for one or more of the following:
− biofouling prevention;
− control of biological activity (disinfection as well as dechlorination if chlorine is used);
− prevention of scaling and inorganic precipitation, including metals removal, and
− removal of other elements such as sulphur (H2S) and silica.
The use of beach wells and/or boreholes will minimise or, in some cases, remove the requirements
for pre-treatment.
The assumed specifications for the RO intake waters are (Appendix III, Wetland Consulting Services,
2007):
− 34.9 psu (actual anticipated salinity in Saldanha Bay – changed from the 35.5 psu
assumed by Wetland Consulting Services (2007);
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− Suspended solids = 8-25 mg.ℓ-1 after primary screening;
− Sea water temperatures ranging from 12-22 ºC;
− Oil: Negligible
− Algae bloom: Negligible.
The seawater temperatures, depending on the intake depth can be as cold as 9°C, however, surface
waters are expected to remain within the range specified above. It should be noted that the operating
costs of plants will increase with colder intake waters (Swartz et al., 2004) so it is anticipated that the
intakes will be located as near to the sea surface as possible where the water is warmer. The
temperature of waters from the beach wells or boreholes will be determined by the exact location of
the intakes and flow rates possible for each beach well/borehole.
Phytoplankton blooms (see Section 5.2.3) do occasionally occur in Saldanha Bay and could thus be
a factor in intake water quality. Similarly, under turbulent conditions in the bay (high wind and wave
conditions) significant turbidity due to the stirring up of bottom sediments is often visible suggesting
reasonably high turbidity conditions in the water column. However, previous dredge monitoring
studies indicated that the discolouration of the water in the bay is often associated with relatively low
suspended sediment concentrations in the water column (perhaps a consequence of the fact that the
sediments are white and highly visible). These impacts on intake waters would be significantly
reduced for beach wells and minimal for boreholes.
Typically oil in the water column should be negligible, however, Saldanha Bay is an oil terminal and
consequently oil spills are a possibility. It thus is prudent to locate the intake one or two metres
below the sea surface. These impacts on intake waters would be somewhat reduced for beach wells
and boreholes, however should an oil spill occur that results in significant quantities of dissolved
components in the water column or oiling beaches, these impacts would be significant.
Given the low oxygen conditions in Small Bay, H2S may be an issue if the intake draws on the bottom
waters within the bay, but should not be an issue if water is abstracted on the eastern side of Small
Bay or away from the seabed elsewhere in Small Bay. The bottom waters in Big Bay are considered
to be fairly well oxygenated (within the context of the large scale low oxygen water fluctuations
occurring along the West Coast), precluding risk of poor water quality at the intake as described
above. The oxygen concentrations in beach well and borehole intake waters is uncertain.
7.4 Discharge Characteristics
The specific environmental and engineering constraints at the various sites result in substantially
different conceptual designs at the various discharge locations. The main discharge characteristics
and conceptual designs are described in Table 7.3 below.
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Table 7.3: Main characteristics and conceptual des ign of discharge structures for the RO plant.
Development Phase
Site 1
Site 2
Site 3 (a) (discharge into Small
Bay)
Site 3 (b) (alternate discharge
into Big Bay)
Site 3 (c&d)
(discharge at Caisson 3)
Discharge Design
Discharge at the sea surface along an approximate 30 m
length of the revetment of the reclaim dam at a location
approximately 80 m from low water mark of adjacent shoreline with an adjacent water depth of
approximately 1.5 m through multi-port diffuser
Surf-zone discharge*1 or
pipeline discharge through single port diffuser in an approximate -
0.5 to -1m CD water depth
Single port diffuser in an approximate -8 m CD water
depth
Single port diffuser in an approximate -4 m CD water
depth
Single port diffuser in an approximate -16 to -18 m CD
water depth
Behaviour
Brine discharge sinks to bottom one third of the depth of the water column upon being
discharged (approx 0.5 m layer thickness)
Brine discharge sinks to bottom half of the depth of the water
column upon being discharged (approx 0.7 m layer thickness)
Brine discharge sinks to bottom one third of the depth of the water column upon being
discharged (approx 3.0 m layer thickness)
Brine discharge sinks to bottom approximately one third
of the depth of the water column upon being discharged (approx 2.1 m layer thickness)
Brine discharge sinks to bottom approximately one third
of the depth of the water column upon being discharged (approx 2.7 m layer thickness)
Co-ordinates of intake
structures
33º 00’ 34.11’’ S to 33º 00’ 33.377’’ S
18º 22’ 22.61’’ E to 18º009’ 23.33’’ E
33º 00’ 02.42’’ S 17º 59’ 45.59’’ E
33º 01’ 19.33’’ S 17º 59’ 13.84’’ E
33º 01’ 06.50’’ S 17º 59’ 28.94’’ E
33º 01’ 06.50’’ S 17º 59’ 28.94’’ E
Distance from shoreline
80m from shoreline but along the edge of the revetment
20 to 25 m 90 m 40 m 65 m (from end of causeway)
Distance from intake
350 m 250 m 350 m Other side of causeway 1 000 m
Discharge Depth
adjacent water depth of approximately 1.5 m
approximate -0.5 to -1m CD water depth
approximate -8.4 m CD water depth
approximate -5.0 m CD water depth
approximate -17.0 m CD water depth
Discharge flow rates
4400 m3/day or 50.9 ℓ. s-1 for 3 RO unit plant
(assumed to be continuous 24/7 discharge)
4400 m3/day or 50.9 ℓ. s-1 for 3 RO unit plant
(assumed to be continuous24/7 discharge)
4400 m3/day or 50.9 ℓ. s-1 for 3 RO unit plant
(assumed to be continuous24/7 discharge)
4400 m3/day or 50.9 ℓ. s-1 for 3 RO unit plant
(assumed to be continuous24/7 discharge)
4400 m3/day or 50.9 ℓ. s-1 for 3 RO unit plant
(assumed to be continuous24/7 discharge)
Discharge
velocity Unknown at present but will be
as specified required for an optimal discharge diffuser design
Unknown at present but will be as specified required for an
optimal discharge diffuser design
Unknown at present but will be as specified required for an
optimal discharge diffuser design
Unknown at present but will be as specified required for an
optimal discharge diffuser design
Unknown at present but will be as specified required for an optimal discharge diffuser
design
*1 A surf-zone discharge is unlikely to be used here as the wave action to assist dispersion is limited. A single-port discharge may be used where the water is slightly deeper. This area has not been surveyed. However, based on Google Earth imagery we have assumed a depth of at least -0.5 m CD. A single port discharge in shallow water was used in the model simulations
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Anticipated discharges from the RO plant comprise mainly a brine. The volumes of brine, the salinity
of the brine and associated co-discharges are tabulated below (Table 7.4) for an assumed 45%
recovery of rates of the RO modules (i.e. a brine to sea water ratio of 1:1.55).
Table 7.4: Discharge rates and salinity of the brin e discharge for the various development phases and plant capacities.
Salinity Temp
Change Biocide Other
Development Phase
Number of 1200
kℓ RO Units Required
Potable Water
Produced (m3/day)
Brine Discharge Volumes (m3/day) (psu)* 1 (ºC)*2 mg.ℓ-1*3 mg.ℓ-1*4
Phase 1A/1B 1 1200 1467 63.5 +0 0.1 see
Table 8.3
Phase 2A/2B 3 3600 4 400 63.5 +0 0.1 See Table 8.3
*1 A recovery rate of 45% of freshwater from the RO modules has been assumed here.
*2 It has been specified that there is no temperature elevation in the intake waters before discharge due to the water passing through the RO plant reticulation system. There may be a slight warming of the water as it is piped to the RO plant, stored in a buffer tank or as it is piped back from the plant to the discharge point. These effects are ignored in the modelling study where the only significant change assumed is the temperature difference between the intake waters and the ambient temperature of the waters into which the brine will be discharged. A comprehensive sensitivity analysis has been undertaken (van Ballegooyen et al., 2008) that confirms that the results of this study (that assumes a discharge with a zero temperature elevation above the ambient water temperature at the intake) remain valid for temperature elevations of up to 5 ºC above the ambient water temperature at the intake (see Section 4.2). The cleaning chemical may be heated with a 15kW heater for better chemical activation. The chemicals are recycled to the cleaning tank and finally flushed with permeate – thus the effects of the heating of the cleaning chemicals being flushed out of the system will have negligible effect on the brine discharge.
*3 Biocides comprising NaOCl with a free chlorine residual of 0.1 mg/ ℓ-1 or DBNPA with a residual concentration ranging between 1.15 mg.ℓ-1 and 2.475 mg.ℓ-1 in the discharge has been assumed for the purposes of assessment. The preferred and most likely biocide to be used is DBNPA.
*4 The discharge rates of all co-discharges is assumed to be continuous, i.e. all co-discharges are “bled” into the brine discharge 24 hours a day and 7 days per week. However Transnet (through their contractor) has indicated that shock dosing by biocides is being considered rather than continuous dosing. The implication of this in terms of the model results and associated impact assessments is discussed in greater detail in Section 4.2 that contains the assumptions and limitations of this impact assessment . Note that the water licence application places the legal onus on Transnet to fully specify all potential constituents in the proposed discharge.
The model simulations undertaken here do not explicitly describe the near-field behaviour of the
effluent. For the purpose of assessing the far-field impacts using the DELFT3D-FLOW three-
dimensional numerical model, we have assumed near-field behaviours of the discharged effluent.
As the intake is generally assumed to be near the surface, the effluent when discharged at any
location other than at or near the surface, is likely to be significantly warmer than the ambient
temperatures at depth at the discharge locations. The buoyancy of the warmer effluent discharged at
depth will help with the dispersion of the effluent plume throughout the water column, however, the
high salinity content of the brine means that the effluent remains a dense discharge that will tend to
sink to the seabed unless vigorously mixed throughout the water column. (A typical conservative
design requirement for such a dense brine are that the discharge diffuser is designed to achieve
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near-field dilutions exceeding 50 as predicted by near field models such as CORMIX (Jirka et al.,
1996) and UOUTPLM (Baumgartner et al., 1971).
For each location, either the most conservative discharge design (conservative approach) or the most
likely discharge design (based on information from Transnet) has been considered, resulting in a total
of five simulated discharge scenarios. We suggest that the most conservative discharge structure
designs (typically a single port bottom discharge) be considered to provide a worst case scenario and
that thereafter, if required, further simulations be undertaken with more optimal conceptual
engineering designs.
In the simulations undertaken we have assumed the most conservative discharge designs (typically a
single-port discharge angled upwards into the water column). An associated conservative behaviour
is assumed whereby the dense brine effluent (no matter what its temperature and despite being
jetted into the water column in the near-field) will be confined to between one third and one half of the
water depth from the seabed. This provides scope for improvement in the effluent dispersion through
the water column by more optimal diffuser designs than those conceptual designs assumed here.
The specific near-field behaviours that may be assumed are as follows:
• Single-port surface/bottom discharge : Here we assume dense brine will sink if discharged
at the surface through a single port. Consequently for both surface and bottom discharges, in
the modelling the full discharge will occur into the layers of the far-field model representing the
bottom half to one third of the vertical extent of the local water column;
• Surf-zone discharge : Despite being located in the surf zone, it is assumed that the full
discharge will occur into the layer of the far-field model representing the bottom half to one third
of the vertical extent of the local water column. This is a conservative assumption that allows
for low turbulence conditions and limited mixing of the dense effluent into the water column
expected in the surf-zone during calm, low wave periods.
• Optimal (multi-port) diffuser design at depth : While it is possible to design a diffuser that
will mix the effluent throughout the water column, this may come at elevated operational costs
(e.g. increased pumping costs). (In the model simulations only single port discharges have
been assumed where the full discharge is assumed to occur into those layers of the far-field
model representing the bottom half to one third of the vertical extent local water column, i.e. a
conservative scenario.) It is assumed that the diffuser ultimately will be designed that under all
environmental conditions that the effluent is mostly mixed throughout the water column. There
will be occasions when the effluent will not mix throughout the water column, however, this is
likely only to occur under extreme stratification and/or strong horizontal flows.
A typical near field behaviour of a dense brine discharge (simulated using CORMIX) is given in
Figure 7.2 below. In this model output the initial jetting of the dense brine upwards into the water
column can be observed. However, depending on the extent of this initial mixing, the volumes of
brine being discharged and the local environmental conditions (i.e. extent of water column
stratification, the magnitude and vertical shear in these flows), a range of near-field behaviours are
possible (NV1 to NV5 in Figure 7.2). However, it is anticipated that the brine, after being jetted up
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into the water column, will again sink towards the seabed and be advected away from the discharge
point in the near-bottom layers of the water column (as indicated in the main schematic in Figure 7.2).
Figure 7.2: Schematic of the near-field behaviour o f a dense effluent.
7.5 Scenarios simulated
A single combination of intake and discharge has been simulated for each of the proposed sites,
except for Site 3 where three possible intake and discharge combinations have been considered.
The discharge scenarios simulated in the model are as detailed in Table 7.5 below.
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Table 7.5: The five intake and discharge combinat ions simulated in the hydrodynamic and water quality modelling.
Model
Scenario#
Site
alternative Alternative Intake/Outfall Infrastructure Locations
1 Site 1 1b): Pipeline intake and pipeline outfall (Big Bay) *1
2 Site 2 2b): Pipeline intake and pipeline outfall (Small Bay) *2
3 Site 3 3a): Pipeline intake (Small Bay) and pipeline outfall (Small Bay)
4 Site 3 3b): Pipeline intake (Small Bay) and pipeline outfall (Big Bay)
5 Site 3 3c & 3d): Pipeline intake (Small Bay) and pipeline discharge at Caisson 3 (Big Bay) *3
*1 If the characteristics of the intake waters from beach well intakes at Site 1 are considered to be the
same as those originating from a pipeline intake in the surf-zone at Site 1, then this model scenario can be considered to be representative of a beach well intake and pipeline outfall into Big Bay from Site 1 (Site1 option (a) in Table 2.1). There are no model simulations representing beach well discharges at Site 1 as these are considered not to be a feasible option (Visser et al, 2007).
*2 If the characteristics of the intake waters from beach well intakes at Site 2 are considered to be the
same as those originating from a pipeline intake in the surf-zone at Site 2, then this model scenario can be considered to be representative of a beach well intake and pipeline outfall into Small Bay from Site 2 (Site2 option (a) in Table 2.1).
*3 If the characteristics of the intake waters from borehole intakes i) on the quay adjacent to existing iron-
ore stockpiles or ii) on the quay (adjacent to MPT) are considered to be the same as those originating from a pipeline intake alongside the quay at the southern extremity of the MPT quay at Site 3, then this model scenario can be considered to be representative of borehole intakes on the quay (either adjacent to the existing stockpiles or adjacent to the MPT) and a discharge from Site 3 via pipeline outfall located at Caisson 3 (Site3 options (c & d) in Table 2.1).
Each of these discharge scenarios has been assessed under a range of environmental conditions
comprising:
• a late summer period when the bay is most stratified resulting in strong surface flows and
generally significantly weaker bottom water flows;
• a winter scenario when the water column is well-mixed and surface and bottom water flows are
similar and;
• an unusually calm period the water column is likely to be highly stratified and calm conditions
and weak flows prevail resulting in potentially significantly reduced dispersion of effluents.
The summer and winter simulations are of a two-month duration, while the unusually calm period
(autumn) simulation is of a one-month duration. All model outputs have been analysed per season
and the model outputs scaled accordingly.
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The unusually calm period simulated corresponds statistically with the calmest period measured
along the west coast in more than 20 years. The calmest periods in Saldanha Bay are typically the
months of April to June. The calmest period identified in existing records measured at Cape
Columbine was that of May 1986 when the wind speeds were typically only 75% of the mean wind
speeds observed in May during other years. The calmest period in Saldanha Bay was June 2003,
while the calmest May on record was May 1997. The least interannual variability in wind speeds
observed for the months of April to June is for the month of May. In the modelling study, a “calm”
period was synthesised by scaling down the magnitude of the winds of May 1999 (that constituted an
“average” year in terms of winds speed over Saldanha Bay during May) to 75% of the wind speed
measured in Saldanha Bay in May 1999. Whilst the average or median winds speeds in Saldanha
Bay are often the lowest in June in any particular year, the month of May has been chosen for
synthesising a “calm” period as the stratification in the water column remains significant through April
to late May. It is these more stratified conditions and associated limited vertical mixing that lead to
weak near-bottom flow velocities and the accumulation of effluent discharged at depth.
The impact assessment reported in Section 8 is based on analyses of the outputs from these model
simulations, a description of the natural environment and beneficial uses that may be impacted upon.
7.6 Model Results
7.6.1 Analysis of results
The out puts from the various model simulations have been analysed for each discharge scenario as
follows:
For each of the scenarios, the changes in seawater temperature, salinity and the biocide
concentrations have been analysed per season (90 day period) as indicated, (i.e. for summer, winter
and an “autumn” period) for both surface and bottom waters. Consequently all reported days of
exceedance of a water quality guidelines are for an approximate 90 day period. For example, 45
days of exceedance represents the fact that the water quality guidelines is exceeded for roughly half
of the time in a season. These plotted results for the analyses described below are contained in
Appendix C.
The water quality guidelines and the motivation for their use are given in Section 8 of this report.
Salinity
The changes in salinity have been plotted as:
• 80%, 90%, 95% and 99% exceedance contours which indicate the ∆S values exceeded for a
total of approximately 18 days, 9 days, 5 days and less than 1 day in a season, respectively. In
keeping with a conservative approach we have reported the 99% exceedance contours only.
These 99% exceedance contours more or less represent the maximum values observed
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(maximum salinity footprint of the salinity plumes), i.e. values that, at worst, are only exceeded for
a total of 22 hours within any particular season;
• Days of exceedance of the South African Water Quality guideline of ∆S < 1 psu (or S < 36 psu).
This represents a cumulative duration of exceedance as described above;
Time series plots of “before” and after” salinity are available for analysis at a number of locations in a
radius of between 50m and 100m from each discharge and at identified sensitive locations. As for
the results indicating elevations in seawater temperature, time series plots of the predicted changes
in salinity are deemed superfluous as the spatial analyses described above are adequate in
characterising the footprint of the plume. Furthermore, due to the limited “footprint” of the discharge
plumes, in has not been necessary to plot time series at identified sensitive site in the bay. Similarly
time series plots of “before” and after” salinity a t the proposed intakes are not reported as the
influence of the discharge plumes at the proposed i ntake locations is shown by the spatial
analyses ( i.e. 99% exceedance plot of temperature and salinity) to be negligible.
Temperature
The changes in seawater temperature have been plotted as:
• 80%, 90%, 95% and 99% exceedance contours which indicate the ∆T values exceeded for a
total of approximately 18 days, 9 days, 5 days and less than 1 day, respectively. In keeping with
a conservative approach we have reported only the 99% exceedance contours that more or less
represent the maximum values observed (maximum thermal footprint of the thermal plumes), i.e.
values that, at worst, are only exceeded for a cumulative total of approximately 22 hours within
any particular season. This period represents a cumulative total that in principle could represent
a single 22 hour exceedance or, at the other extreme, 2 hourly13 exceedances on up to 11
different occasions during the season.
• Days of exceedance of the South African Water Quality guideline of ∆T < 1 ºC. This represents a
cumulative duration of exceedance as described above;
• Exceedance of the ANZECC (2000) temperature guideline that requires that the median
temperature in the environment with an operational discharge should not lie outside the 20 and
80 percentile temperature values for a reference location or ambient temperatures observed prior
to the construction and operation of the proposed discharge
• Time series plots of “before” and after” seawater temperature are available for analysis at a
number of locations in a radius of between 50 m and 100 m from each discharge and at identified
sensitive locations. These are deemed superfluous as the spatial analyses described above are
adequate in characterising the “footprint” of the plume. Furthermore, due to the limited “footprint”
of the discharge plumes, it has not been necessary to plot time series at identified sensitive site
in the bay. Similarly time series plots of “before” and after” seawater temperature at the
proposed intakes are not reported as the influence of the discharge plumes at the
13 The temporal resolution of the model output is at 2 hourly intervals except where a specific site has been targeted for
more detailed time series analysis.
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proposed intake locations is shown by the spatial a nalyses ( i.e. 99% exceedance plot of
temperature and salinity) to be negligible.
Biocides
The biocide (free chlorine or residual DBNPA) concentrations have been plotted as:
• 80%, 90%, 95% and 99% exceedance contours which indicate the µg.ℓ-1 oxidising biocide
concentrations exceeded for a total of approximately 18 days, 9 days, 5 days and less than
1 day, respectively. In keeping with a conservative approach we have reported the 99%
exceedance contours only that more or less represent the maximum values observed (maximum
footprint of biocides in the plumes), i.e. values that, at worst, are only exceeded for a total of 22
hours within any particular season;
• Days of exceedance of the selected Water Quality guideline that the biocide concentrations
should remain below 3 µg.ℓ-1or, in the case of DBNPA, below the tarrget values proposed.
Time series plots of biocide concentration are available for analysis at a number of locations in a
radius of between 50 m and 100 m from each discharge and at identified sensitive locations. As for
the results indicating elevation in seawater temper ature and salinity, time series plots of the
predicted changes in biocides are deemed superfluou s as the spatial analyses described
above are adequate in characterising the footprint of the plume.
Achievable Dilutions of a generic contaminant
To assist with the assessment of potential co-discharges (see Section 8.1.3.3), achievable dilutions
of a generic contaminant have been plotted as:
• 80%, 90%, 95% and 99% exceedance contours which indicate the achievable dilutions exceeded
for a total of approximately 18 days, 9 days, 5 days and less than 1 day, respectively. In keeping
with a conservative approach we have reported the 99% exceedance contours only that more or
less represent the maximum values observed (maximum salinity footprint of the salinity plumes),
i.e. values that, at worst, are only exceeded for a total of 22 hours within any particular season;
• Days of exceedance of the selected Water Quality guideline that state that the oxidising biocide
(NaOCl) and non-oxidising biocides (DBNPA) concentrations should remain below 3 µg.ℓ-1; and
below 0.035 mg. ℓ-1 (or 0.070 mg. ℓ-1 if a less conservative approach is taken), respectively.
The modelling results have been set-up to simulate the transport and fate of a generic dissolved
contaminant in the water column. From the information on the dispersion of this hypothetical tracer, it
is possible to calculate the achievable dilution of a generic contaminant, provided the contaminant
behaves as a conservative tracer.
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The achievable dilution (AD) in the model simulations is calculated as:
To assess compliance of individual co-discharges against the relevant water quality guidelines, the
required dilutions (RD) of any specific pollutant to ensure compliance with its associated water
quality guideline may be determined using appropriate water quality guidelines. The required
dilutions for compliance with the relevant water quality guidelines are calculated as follows:
Note that the
required dilutions to ensure compliance are dependant on the assumed background concentrations
of the relevant co-discharge constituent as these determine how “effective” the dilution process is in
lowering co-discharge constituents in the water column. The relevant water quality guideline is
assumed to have been met if the calculated achievable dilutions in the model exceed the required
dilutions determined from the constituent concentrations at the point of discharge and the relevant
water quality guideline that needs to be met.
7.6.2 Summary of results in terms of exceedance of selected water quality guidelines
The plots referred to in Section 7.6.1 above are contained in Appendix C. Due to the vast number of
plots associated with the five discharge scenarios and the respective parameters of concern (i.e.
salinity, temperature, biocides and potential co-discharges), the plume dimensions at the sea surface
and near the seabed as determined for the various parameters of concern are summarized in Tables
7.6 to 7.9 below. The plume dimension reported is the maximum distance of any plume edge from the
discharge location. The plume edge is delineated by the contour indicating where the relevant guideline has
been exceeded for no more than 6 hours within a season.
Salinity
The model results for elevated salinity are summarised in Table 7.6 below. The dimensions of the
plume indicated are the maximum dimension in any direction of the plume “footprint”, where the
dimensions of the “footprint” are determined by the exceedance of selected water quality guidelines
(1 psu and 4 psu) for periods ranging from 6 hours in a season to approximately 5 days. In the table
the figures roughly represent the dimensions of the maximum “footprint” of the effluent plume (the
“footprint” where the relevant water quality guideline or target value is exceeded for no more than 6
hour per season), while the figure in brackets indicates the spatial dimensions of the effluent
“footprint” that is exceeded for less than approximately 5 days in a season. The column indicating
the maximum elevation in salinity (∆S) of the ambient waters at the intake due to the influence of the
discharge plume does not inform the assessment of environmental impacts but rather indicates
whether or not “re-circulation” effects are likely to be a concern at the intake, whereby intake waters
are contaminated by the discharge plume waters.
ionconcentratBackgroundionconcentratguidelinequalityWater
ionconcentratBackgroundionconcentratcolumnwaterSimulatedRD
−−=
ionconcentratBackgroundionconcentratcolumnwaterSimulated
ionconcentratBackgroundionConcentrateDischAssumedAD
−−= arg
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Table 7.6: Summary of effluent plume dimensions aro und the discharge point (based on exceedances of the salinity water quality guideline s for cumulative periods of 6 hours and approximately 5 days), and the magnitude of the salinity elevation at the intake.
Maximum Discharge Plume Dimensions
(m)
Max ∆S at intake
(psu) Site WQ*1 guideline
Location in water column
Summer Winter Autumn Summer Winter Autumn
surface -*2 -*2 -*2 < 0.10 < 0.20 < 0.20 SAWQ
(∆S < 1psu) bottom 290 (160)
200 (150)
400 (180)
< 0.10 < 0.20 < 0.20
surface -*2 -*2 -*2
1 (discharge
into Big bay) (∆S < 4psu)
bottom 160 (100)
105
-*2
150 (100)
surface -*2 50 -*2 < 0.50 0.20 < 0.50 SAWQ
(∆S < 1psu) bottom 400 (200)
310 (200)
520 (400)
< 0.50 < 0.2 < 0.50
surface -*2 -*2 -*2
2 (discharge into Small
Bay) (∆S < 4psu) bottom 120
(60)
100
-*2
160 (90)
surface -*2 -*2 -*2 < 0.05 < 0.05 < 0.05 SAWQ (∆S < 1psu) bottom 50 50 50 < 0.10 < 0.10 < 0.20
surface -*2 -*2 -*2
3 (discharge
into Small Bay) (∆S < 4psu)
bottom -*2 -*2 -*2
surface -*2 -*2 -*2 < 0.05*3 < 0.05*3 < 0.05*3 SAWQ
(∆S < 1psu) bottom 120 (70)
50
(-*2) 90
(50) < 0.05*3 < 0.05*3 < 0.05*3
surface -*2 -*2 -*2
3 (discharge
into Big Bay) (∆S < 4psu)
bottom -*2 -*2 -*2
surface -*2 -*2 -*2 < 0.05*3 < 0.05*3 < 0.05*3 SAWQ
(∆S < 1psu) bottom 40
(-*2) -*2 -*2 < 0.05*3 < 0.05*3 < 0.05*3
surface -*2 -*2 -*2
3 (discharge
at Caisson 3) (∆S < 4psu)
bottom -*2 -*2 -*2
*1 SAWQ refers to the South African Water Quality guideline of 33 psu < S < 36 psu while the ∆S < 4 psu (i.e. salinity <
39 to 40 psu) guidelines is consistent with salinity thresholds where impacts are likely to be significant (see Section 8.1.3.1 for level of significance).
*2 The modelling undertaken cannot resolve detail within an approximate 50 m radius of the discharge. While the model
results indicate no plume in the relevant water depth, a conservative approach would be to assume the possibility that any of the guidelines could be exceeded within a “sacrificial zone” of 50 m around the discharge point. This does not imply that the relevant guideline will be exceeded within this radius, but rather that it remains a possibility that this will be the case due to the limited resolution of the model used to simulate the plume behaviour.
*3 The minimum value resolved in the plots of the model results is 0.05 psu which is a negligible quantity in terms of
efficiencies of the RO plant. For the alternate discharge into Bay Bay for Site 3, the separation if the intake and discharge is such that the potential elevation in salinity at the in take due to the brine discharge is negligible and certainly much less than 0.05 psu reported in the Table above.
In terms of the relative dimensions of the plume where relevant salinity guidelines are exceeded (see
Table 7.6 above and Figure 7.3 below), the various combinations of intake and discharge locations
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may be ranked as follows (1 indicates the smallest plume dimensions and most likely environmentally
preferable option while 5 indicates the largest plume dimension and likely least desirable option in
terms of environmental impacts):
Site 1 2 3
discharge into Small Bay
3 discharge into
Big Bay
3 discharge at
Caisson 3 Ranking 4 5 1 3 1
Figure 7.3: Comparative maximum dimensions of the e levated salinity “footprint” ( ∆S < 1 psu or S < 36 psu) for all discharge sites.
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Temperature
The model results for elevated seawater temperature are summarised in Table 7.7 below. The
dimensions of the plume indicated are the maximum dimension in any direction of the plume
“footprint”, where the dimensions of the footprint are determined by the exceedance of selected water
quality guidelines (1 ºC and ANZECC water quality guideline) for periods ranging from 6 hours in a
season to approximately 5 days. In the table the figures roughly represent the dimensions of the
maximum “footprint” of the effluent plume (the “footprint” where the relevant water quality guideline or
target value is exceeded for no more than 6 hour per season), while the figure in brackets indicates
the spatial dimensions of the effluent “footprint” that is exceeded for less than approximately 5 days in
a season. The column indicating the maximum temperature elevation (∆T) of the ambient waters at
the intake due to the influence of the discharge plume does not inform the assessment of
environmental impacts but rather indicates whether or not “re-circulation” effects are likely to be a
concern at the intake, whereby intake waters are contaminated by the discharge plume waters.
Table 7.7: Summary of effluent plume dimensions aro und the discharge point (based on exceedances of the temperature water quality guidel ines for cumulative periods of 6 hours and approximately 5 days), and the magni tude of the temperature elevation at the intake.
Max Discharge Plume Dimensions* 2
(m)
Max ∆T at intake
(°°°°C) Site WQ*1 guideline
Location in water column
Summer Winter Autumn Summer Winter Autumn
surface -*2 -*2 -*2 < 0.25 < 0.25 < 0.25 SAWQ
(∆T < 1 ºC) bottom 220 (50)
100*4
-*2 300
(170) < 0.25 < 0.25 < 0.25
surface -*2 -*2 -*2
1 (discharge
into Big Bay) ANZECC
bottom -*2 -*2 120
surface -*2 50 -*2 < 0.50 < 0.50 < 0.75 SAWQ (∆T < 1 ºC) bottom 650
(300) 300 -*2
650 (570) < 0.75 < 0.50 < 0.75
surface -*2 -*2 -*2
2 (discharge into Small
Bay) ANZECC bottom -*2 -*2 250
surface -*2 -*2 -*2 < 0.05 < 0.05 < 0.05 SAWQ
(∆T < 1 ºC) bottom 500 (280)
180 (-*2)
440 (250)
< 0.50 < 0.25 < 0.75
surface -*2 -*2 -*2
3 (discharge into Small
Bay) ANZECC bottom -*2 -*2 -*2
surface -*2 -*2 -*2 < 0.25*3 < 0.25*3 < 0.25*3 SAWQ (∆T < 1 ºC) bottom 440
(240) 170
(110) 430
(240) < 0.25*3 < 0.25*3 < 0.25*3
surface -*2 -*2 -*2
3 (discharge
into Big Bay) ANZECC
bottom -*2 -*2 -*2
surface -*2 -*2 -*2 < 0.25*3 < 0.25*3 < 0.25*3 SAWQ (∆T < 1 ºC) bottom 440
(170) 180 (-*2)
240 (170) < 0.25*3 < 0.25*3 < 0.25*3
surface -*2 -*2 -*2
3 (discharge
at Caisson 3) ANZECC
bottom -*2 -*2 -*2
*1 SAWQ refers to the South African Water Quality guideline of ∆T < 1 ºC while ANZECC refers to the
ANZECC (2000) guideline that the median temperature in the environment with an operational discharge should not lie outside the 20 an 80 percentile temperature values for a reference location or ambient temperatures observed prior to the construction and operation of the proposed discharge.
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*2 The modelling undertaken cannot resolve detail within an approximate 50 m radius of the discharge.
While the model results indicate no plume in the relevant water depth, a conservative approach would be to assume the possibility that any of the guidelines could be exceeded within a “sacrificial zone” of 50 m around the discharge point. This does not imply that the relevant guideline will be exceeded within this radius, but rather that it remains a possibility that this will be the case due to the limited resolution of the model used to simulate the plume behaviour.
*3 The minimum value resolved in the plots of the model results is 0.25 ºC which is a negligible quantity in terms of efficiencies of the RO plant. For the alternate discharge into Bay for Site 3, the separation if the intake and discharge is such that the potential elevation in temperature at the in take due to the brine discharge is negligible and certainly much less than 0.25 ºC reported in the Table above.
*4 The plume dimension is only 40 m in diameter but is located some 100 m distant of the discharge location.
Figure 7.4: Comparative maximum dimensions of the e levated temperature “footprint” ( ∆T < 1 ºC) for all discharge sites.
In terms of the relative dimensions of the plume where relevant temperature guidelines are exceeded
(see Table 7.7 and Figure 7.4 above), the various combinations of discharge locations and locations
of the discharge may be ranked as follows (1 indicates the smallest plume dimensions and most
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likely environmentally preferable option while 5 indicates the largest plume dimension and likely least
desirable option in terms of environmental impacts):
Site 1 2 3
discharge into Small Bay
3 discharge into
Big Bay
3 discharge at
Caisson 3 Ranking 1 5 3 3 2
Biocides
The model results for biocide concentrations are summarised in Table 7.8 below. The dimensions of
the plume indicated are the maximum dimension in any direction of the plume “footprint”, where the
dimensions of the footprint are determined by the exceedance of selected water quality guidelines
(free residual chlorine concentration < 3 µg.ℓ-1) for periods ranging from 6 hours in a season to
approximately 5 days. In the table the figures roughly represent the dimensions of the maximum
“footprint” of the effluent plume (the “footprint” where the relevant water quality guideline or target
value is exceeded for no more than 6 hour per season), while the figure in brackets indicates the
spatial dimensions of the effluent “footprint” that is exceeded for less than approximately 5 days in a
season.
Table 7.8: Summary of effluent plume dimensions aro und the discharge point (based on exceedances of the biocide water quality guidelines ) for cumulative periods of 6 hours and approximately 5 days, respectively.
Max Discharge Plume Dimensions* 2
(m) Site WQ*1
guideline
Location in water column
Summer Winter Autumn
surface -*2 -*2 -*2 1 (discharge into
Big Bay)
ANZECC (< 3 µg.ℓ-1) bottom 300
(200) 210
(150) 400
(230) surface -*2 50 -*2 2
(discharge into Small Bay)
ANZECC (< 3 µg.ℓ-1) bottom 400
(250) 360
(270) 570
(470) surface -*2 -*2 -*2 3
(discharge into Small Bay)
ANZECC (< 3 µg.ℓ-1) bottom 90
(-*2) -*2 -*2
surface -*2 -*2 -*2 3 (discharge into
Big Bay)
ANZECC (< 3 µg.ℓ-1) bottom 120
(-*2) 80
(-*2) 90
(-*2) surface -*2 -*2 -*2 3
(discharge at Caisson 3)
ANZECC (< 3 µg.ℓ-1) bottom 100
(-*2) -*2 -*2
*1 ANZECC refers to the ANZECC (2000) guideline that the biocide concentration (FRC) should not exceed
3 µg.ℓ-1 or the water quality guideline adopted for DBNPA, i.e. residual DBNPA concentrations in the effluent should not exceed 0.035 µg.ℓ-1 or 0.070 µg.ℓ-1, depending which target value is assumed to be the most appropriate given the possible residual concentrations of DBNPA in the discharge.
*2 The modelling undertaken cannot resolve detail within an approximate 50 m radius of the discharge.
While the model results indicate no plume in the relevant water depth, a conservative approach would be to assume the possibility that any of the guidelines could be exceeded within a “sacrificial zone” of 50 m
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around the discharge point. This does not imply that the relevant guideline will be exceeded within this radius, but rather that it remains a possibility that this will be the case due to the limited resolution of the model used to simulate the plume behaviour.
Figure 7.5: Comparative maximum dimensions of the b iocide “footprint” (oxidising biocide concentration <3 µg. ℓ-1 or DBNPA residual concentrations less than the targ et values assumed to be appropriate) for all discharge sites.
In terms of the relative dimensions of the plume where relevant biocide guidelines are exceeded (see
Table 7.8 above and Figure 7.5 above), the various combinations of discharge locations and
locations of the discharge may be ranked as follows (1 indicates the smallest plume dimensions and
most likely environmentally preferable option while 4 indicates the largest plume dimension and likely
least desirable option in terms of environmental impacts):
Site 1 2 3
discharge into Small Bay
3 discharge into
Big Bay
3 discharge at
Caisson 3 Ranking 4 5 1 3 1
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Achievable Dilutions (Co-discharges)
The model results for a “generic” pollutant reported in terms of achievable dilutions are summarised
in Tables 7.9 and 7.10 below. The dimensions of the plume indicated are the maximum dimension in
any direction of the plume “footprint”, where the dimensions of the footprint are determined by the
non-exceedance of selected achievable dilutions (50 times and 100 times dilution factor) for periods
ranging from 6 hours in a season to approximately 5 days.
In the tables the figures roughly represent the dimensions of the maximum “footprint” of the effluent
plume, i.e. the “footprint” where the required dilution of 50 times (Table 7.9) and 100 times (Table
7.10) are not achieved for a cumulative total duration of no more than 6 hours per season), while the
figure in brackets indicates the spatial dimensions of the effluent “footprint” where the required
dilution of 50 times (Table 7.9) and 100 times (Table 7.10) is not achieved for a cumulative total
duration of no more than approximately 5 days in a season.
Table 7.9: Summary of effluent plume dimensions aro und the discharge point (based on non-exceedances of a required dilution of 50 times) for cumulative periods of less than 6 hours and less than approximately 5 day s, respectively.
Discharge Plume Dimensions* 2
(m) Site WQ*1 guideline
Location in water column
Summer Winter Autumn
surface 80 (-*2)
-*2 -*2 1 (discharge into
Big Bay)
Dilution factor < 50 bottom 350
(200) 260
(180) 430
(360)
surface 240 (-*2)
150 (-*2)
150 (-*2)
2 (discharge into
Small Bay)
Dilution factor < 50 bottom 560
(330) 500
(390) 670
(500) surface -*2 -*2 -*2 3
(discharge into Small Bay)
Dilution factor < 50 bottom 240
(100) 50
(-*2) 150 (90)
surface -*2 -*2 -*2 3 (discharge into
Big Bay)
Dilution factor < 50 bottom 290
(140) 130 (80)
230 (160)
surface -*2 -*2 -*2 3 (discharge at
Caisson 3)
Dilution factor < 50 bottom 170
(130) 140 (90)
170 (140)
*1 The assumed generic water quality guideline assumed in the table above is that the achievable dilution of
any co-discharge needs to exceed 50 times.
*2 The modelling undertaken cannot resolve detail within an approximate 50 m radius of the discharge.
While the model results indicate no plume in the relevant water depth, a conservative approach would be to assume the possibility that any of the guidelines could be exceeded within a “sacrificial zone” of 50 m around the discharge point. This does not imply that the relevant guideline will be exceeded within this radius, but rather that it remains a possibility that this will be the case due to the limited resolution of the model used to simulate the plume behaviour.
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The required dilution target values of 50 and 100 times dilution are merely nominal conservative
required dilution that provides indicative results for potential co-discharges. The assumption here is
that the respective water quality guidelines will be sufficiently stringent for required dilutions of 50 to
100 to be necessary. The model outputs however can be re-processed assuming any specified
thresholds deemed to be representative of the pollutant of concern. In that sense the modelling
approach utilised here is entirely generic and scalable. The footprints in Figure 7.6 are based on 50
times dilution contours.
Table 7.10: Summary of effluent plume dimensions ar ound the discharge point (based on non-exceedances of a required dilution of 100 times ) for cumulative periods of less than 6 hours and less than approximately 5 day s, respectively.
Discharge Plume Dimensions* 1
(m) Site WQ*1
guideline
Location in water column
Summer Winter Autumn
surface -*1 280 (-*2)
210 (60) 1
Dilution factor < 100 bottom 500
(260) 400
(220) 580
(470)
surface 550 (380)
520 (190)
460 (260) 2
Dilution factor < 100 bottom 750
(450) 800
(550) 830
(700) surface -*1 -*1 -*1 3
(discharge into
Small Bay)
Dilution factor < 100 bottom 500
(280) 190
(140) 400
(260)
surface -*1 -*1 -*1 3 (discharge
into Big Bay)
Dilution factor < 100 bottom 500
(340) 280
(240) 460
(310)
surface -*1 -*1 -*1 3 (discharge
at Caisson 3)
Dilution factor < 100 bottom 300
(180) 280
(220) 320
(260)
*1 The modelling undertaken cannot resolve detail within an approximate 50 m radius of the discharge.
While the model results indicate no plume in the relevant water depth, a conservative approach would be to assume the possibility that any of the guidelines could be exceeded within a “sacrificial zone” of 50 m around the discharge point. This does not imply that the relevant guideline will be exceeded within this radius, but rather that it remains a possibility that this will be the case due to the limited resolution of the model used to simulate the plume behaviour.
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In terms of the relative dimensions of the plume where there is a non-exceedance of a required
dilution of 50 or 100 (see plume dimensions in Tables 7.9 and 7.10 and Figure 7.6 below), the
various combinations of discharge locations and locations of the discharge may be ranked as follows
(1 indicates the smallest plume dimensions and most likely environmentally preferable option while 5
indicates the largest plume dimension and likely least desirable option in terms of environmental
impacts):
Site 1 2 3
discharge into Small Bay
3 discharge into
Big Bay
3 discharge at
Caisson 3 Ranking 4 5 2 2 1
Figure 7.6: Comparative maximum dimensions of the p lume “footprint” (achievable dilution < 50) for all discharge sites.
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8 ASSESSMENT OF ENVIRONMENTAL IMPACTS
8.1 Identification of Potential Environmental Impac ts
The anticipated environmental impacts of potential concern to the marine environment from the
proposed Reverse Osmosis Desalination plant in Saldanha Bay identified and summarised in Section
6 primarily include those associated with construction activities in the coastal zone and ongoing
discharge of brine to the marine environment. These are described in more detail below.
8.1.1 Construction of Intake and Discharge Structur es
Pipelines
The use of intake and discharge pipelines in the engineering designs for the RO Plant will most likely
involve considerable disturbance of the high shore, intertidal and shallow subtidal beach habitats
during the construction and installation process. In the absence of engineering specifications
provided by the client, the following assessment will assume that HDPE pipelines (or similar) not
exceeding a diameter of 0.36 m will be used for both intakes and discharges.
Individual pipeline sections of 10 - 24 m are usually fabricated by the supplier and transported to the
site where they are subsequently butt-welded together into long strings. This will require a sufficiently
large and relatively flat onshore area where the pipes can be stockpiled and prepared. However
potential impacts associated with this construction area will not be further assessed here as it will
most likely either be located within the existing port area or in the dunes and well above the high
water mark (Site 1).
Depending on the oceanographic conditions on site, concrete weight collars may then be placed
around the strings to provide stability on the seabed. The pipe sections are dragged down the shore
by dozer and capped at either end before being floated out to sea by means of a tug. The air is
released from the pipe, and as it fills with water it sinks to the bottom. Depending on the required
overall length of the pipeline, the different strings making up the total pipeline are placed one behind
the other and connected by means of spool pieces. This is usually undertaken by commercial divers.
Special attention has to be paid to nearshore beach crossings where currents and breaking waves
may prevail. To avoid exposure on the beach and nearshore area, and to avoid damage by wave
forces in the surf-zone, the pipeline needs to be buried below the seabed. This usually requires the
construction of a temporary jetty to provide a stable work platform from which a trench (protected
between rows of sheetpiles) can be excavated. Excavation to a suitable depth to accommodate the
pipeline may potentially require blasting. However, at this stage the use of blasting is not part of the
project description and impacts associated with blasting are thus not assessed in this study. If
blasting becomes an option for trench-excavation a separate assessment is necessary. The pipe is
then placed in the trench and subsequently buried by earth-moving machinery. Further offshore, the
pipe is left lying on the seabed, and with time will settle into the sandy substrate.
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Pipeline launching and entrenchment will involve extensive traffic on the beach (site 1 and 2) by
heavy vehicles and machinery, as well as the potential for hydrocarbon spills. Although the activities
on the intertidal beach will be localised and confined to within a hundred metres of the construction
site, the beach sediments will be completely turned over in the process and the associated
macrofauna will almost certainly be entirely eliminated. Any shorebirds feeding and/or roosting in the
area will also be disturbed and displaced for the duration of construction activities. The invertebrate
macrofaunal species inhabiting these beaches are all important components of the detritus / beach-
cast seaweed-based food chains, being mostly scavengers, particulate organic matter and filter-
feeders (Brown and McLachlan, 1994). As such, they assimilate food sources available from the
detritus accumulations typical of this coast and, in turn, become prey for surf-zone fishes and
migratory shorebirds that feed on the beach slope and in the swash zone. By providing energy input
to higher trophic levels, they are all important in nearshore nutrient cycling, and the reduction or loss
of these macrophyte assemblages may therefore have cascade effects through the coastal
ecosystem (Dugan et al., 2003).
Jetty construction (if necessary) will most likely require the use of pile drivers, and trench excavation
will necessitate the removal of significant volumes of beach sand (i.e. a trench width of approximately
1 m width and the length of the pipeline from the beach crossing to the intake or discharge point. This
trench material is typically placed on a floating pontoon ready for backfill. This excavation process
will result in increased suspended sediments in the water column, potentially affecting light
penetration and thus phytoplankton productivity and algal growth. The impact of the sediment plume,
however, is expected to be relatively localised and of short duration (only for the duration of the
trench excavation). Settlement of the suspended material on adjacent areas of seabed may result in
smothering of the resident biota. However, some mobile benthic animals are capable of migrating
vertically through more than 30 cm of deposited sediment (Maurer et al., 1981a,b; 1982). The biota
that inhabited the excavated sediments will most likely perish. Once the pipeline has been laid and
sufficient sediments have accumulated around the pipe, the affected seabed areas with time will be
recolonised by benthic macrofauna.
Provided the construction activities are all conducted concurrently, the duration of the disturbance
should be limited to a few months. Studies on the disturbance of beach macrofauna communities on
the West Coast by beach mining activities have ascertained that, provided physical changes to beach
morphology are kept to a minimum, and sediment characteristics on the beach are not severely
altered, biological "recovery" of disturbed areas will occur within 2-5 years (Nel et al., 2003, 2004).
Disturbed subtidal communities within the wave base (<40 m water depth) might recover even faster
(Newell et al., 1998). Recovery of beach macrofaunal assemblages occurs primarily through
immigration from adjacent areas. Mitigation measures should therefore include rehabilitation of the
disturbed area immediately following construction, by removing all artificial constructions or beach
modifications created during construction from above and within the intertidal zone after completion
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of construction activities. No accumulations of excavated beach sediments should be left above the
high water mark, and any substantial sediment accumulations below the high water mark should be
levelled.
Furthermore, an adjacent portion of undisturbed beach should be allocated where populations of
macrofaunal species can survive and supplement recolonisation in impacted areas.
Beach Wells
The installation of intake beach wells will involve substantial disturbance of the high and mid-shore
beach habitats during the construction phase. The sinking of wells requires the use of a drilling rig,
which excavates the sediments to the required depth, and sleeves the cylindrical pit with PVC or
stainless steel to prevent the walls from collapsing. The stainless steel well is subsequently sunk into
the prepared excavation. Drainage pumps are most likely required to keep the pit free of water
during construction. The water is likely to be pumped across the beach into the surf-zone resulting in
localised inputs of fresh/brackish water and possibly increased suspended sediments in the water
column. This may potentially affect light penetration and thus phytoplankton productivity and algal
growth. The associated impacts are, however, expected to be relatively localised and of short
duration (only for the duration of the well construction).
Well construction will involve extensive traffic by heavy vehicles and machinery on the upper and
mid-sections of beach, as well as the potential for hydrocarbon spills. These activities will be
relatively localised and confined to within a few hundred metres of the construction site, although
their extent will ultimately depend on the number of wells to be installed. Dune vegetation and
associated fauna at the excavation sites will almost certainly be entirely eliminated, and high and
mid-shore beach macrofauna severely disturbed.
Boreholes on the Causeway
The intakes boreholes proposed to be located along the causeway will be drilled on existing
reclaimed areas and therefore are expected to have negligible impacts on the marine environment.
8.1.2 Permanent Intake and Discharge Structures
Intake of water directly from the ocean usually results in loss of marine species as a result of
impingement and entrainment. Impingement refers to injury or mortality of larger organisms (e.g. fish)
that collide with and are trapped by intake screens, and entrainment refers to smaller organisms that
slip through the screens and are taken into the plant with the feed water. Entrained material includes
holoplanktonic organisms (permanent members of the plankton, such as copepods, diatoms and
bacteria) and meroplanktonic organisms (temporary members of the plankton, such as juvenile
shrimps and the planktonic eggs and larvae of invertebrates and fish). Most studies and findings
related to entrainment have been done in association with the effects of power plant once-through
cooling systems. In these systems, entrained organisms are killed or injured due to the high pressure
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or temperatures, and in the case of RO desalination plants, when water is forced against the filters or
membranes. While some studies consider a 100% mortality rate of entrained organisms in power
plant cooling systems (California Coastal Commission, 2004), other study results suggest that the
majority of the individuals would survive passage through such a system with mortalities ranging from
10 - 20% (Bamber and Seaby, 2004). These authors noted, however, that the rate of survival is
species-specific and that generalizations from the responses of one species to those of another are
not valid. It is likely that when compared to once-through cooling systems, mortality rates in RO
plants are greater (potentially 100%) since the seawater is forced at high pressures through filters or
membranes to remove particles, including the small organisms that are taken in with the feed-water.
While the significance of both impingement and entrainment is related to the location of an intake, the
first is primarily a function of intake velocity, and the latter is more related to the overall volume of
water drawn into the RO plant. Impingement can be mitigated through structural or operational
designs to open water intakes (see Section 9.1.1). The project description specifies that the intakes
will be designed to minimise impingement of biota and will have self-cleaning screens.
Transnet Projects has indicated an estimated 0.15 m.s-1 velocity at the intake screens and 1.0 m.s-1
in the intake pipelines. The intake volumes (i.e. 8000 m3.day-1 or 92.6 ℓ.s-1) are relatively low and the
effect of entrainment is thus assessed as minor, especially if care is taken to ensure that the intake
design minimises potential entrainment impacts.
The potential of scouring of sediment around the discharge outlet is a serious design issue for an
effluent discharging-system discharging into a shallow receiving water body (Carter and van
Ballegooyen, 1998). However, the discharge volumes being considered here (i.e. 4400 m3.day-1 or
50.9 ℓ.s-1) are low and the configuration being assessed (i.e. single or multi-port diffusers jetting water
upwards into the water column) is such that the potential impacts on bottom sediments are limited.
Should such impacts occur they will be confined to the immediate vicinity of the discharge point.
The location of a discharge or intake pipeline on the shoreline, or even the shore-crossing of the
pipeline may distort sediment transport pathways in the nearshore environment (and may even
extend to the distortion of aeolian sand transport pathways if the infrastructure associated with the
discharge is located in, or extends through, the mid- and upper shore) and consequently will alter the
natural environment to some degree. This will be limited should the pipeline be trenched through the
shore-crossing. The proposed expansion of the iron-ore export facilities may further pose a problem
for the location of intake/discharge structures on the shoreline (Site 1) as accretion or erosion of the
beach may occur (Smith et al., 2007), resulting in damage or dysfunction of the intake/discharge
structures unless these considerations are included in the engineering designs.
The use of intake beach wells/boreholes provides a natural pre-filter system, resulting in fewer
chemicals required for the pre-treatment process. Beach wells also reduce issues relating to
impingement and entrainment, as well as diminishing potentially harmful algal bloom effects on the
water quality of the intake waters. This intake option as a pre-treatment strategy is thus attractive
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because of the reduction in chemical use and the potentially lower operation and maintenance costs
compared to other pre-treatment options, including media or cartridge filtration (California
Desalination Task Force, 2003a, Campbell and Jones, 2005). The use of traditional vertical beach
wells, however, is limited to smaller systems due to the large number of wells that would need to be
drilled to fulfil the pre-treatment requirements (i.e. to meet the intake volumes required).
Beach wells should only be used in areas where the impact on aquifers has been studied and
saltwater intrusion of freshwater aquifers will not occur (Younos, 2005). Although such a
situation is unlikely if the plant is situated near the seashore, special care needs to be taken to
ensure that such a risk is minimised. For example, intake beach wells for a desalination plant on the
KwaZulu-Natal north-coast situated on the beach drew fresh water from the dune area instead of
from the sea, causing serious destabilisation problems for the sensitive dune vegetation (DWAF,
2007). These potential impacts (saltwater intrusion and effects on groundwater) are not considered
to be part of the scope of this assessment.
To determine the efficacy of beach wells/boreholes for a particular site, exploratory drilling to
determine the aquifer characteristics (depth, strata) and pump tests on boreholes should be
conducted. A preliminary idea of required depth, potential discharge and number of required beach
wells/boreholes in the site area can be obtained to match the demands of the proposed plant.
Spacing between wells/boreholes at the proposed withdrawal rates is another important factor in
design planning. Surface seawater RO systems operate at a conservative flux of 7 to 9 gfd (gallons
per square foot per day). Beach well systems can be operated at 9 -10 gfd. The difference in flux
rate results from reductions in the membrane-fouling rate due to the better water quality obtained
from beach wells (California Desalination Task Force, 2003a). The results from the geotechnical
groundwater study have shown that by installing large diameter (300 – 500 mm) boreholes equipped
with continuous slot-screens the borehole yields can reach at least 10 L/s (Visser et al., 2007).
Numerical modelling indicated that ~10 vertical intake wells drilled 50 m apart parallel to the shoreline
above the high water mark at Site 1 would be required to abstract the anticipated raw water demand
of 8000 m3/day for the RO plant. Alternatively, if horizontal collector wells are decided on, at least
two with ~100 m of horizontal collector pipes each would be required. Although no similar detailed
studies have taken place to date for the proposed beach well intakes at Site 2, up to 10 intake wells,
spaced ~50 m apart have been proposed for this site. Based on yield information to date between 5
and 10 boreholes will need to be located along the causeway (D. Visser, SRK, pers. comm.) to
provide the requisite intake waters (Site 3).
As noted above, the proposed expansion of the iron-ore export facilities may further pose a problem
for the location of beach well discharge structures on the shoreline (Site 1). Studies indicate that the
accretion in the vicinity of Site 1 will be slightly less than occurs at present (Smith et al., 2007).
These changes in shoreline may result in damage or dysfunction of the discharge structures unless
these considerations are included in the engineering designs.
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8.1.3 RO Plant Effluents
The effluent water discharged from the desalination plant will constitute a high-salinity brine
(expected salinity 63.5 psu) that has been treated with a biocide, and which contains other chemical
residuals from RO membrane cleaning processes. Under current design specifications, the feed-
waters will be drawn from ~ - 1 m CD or approximately 1.9 m below mean sea level (except for the
beach well intake scenario at Site 1 and boreholes at site 3), and consequently from above the
thermocline present in the bay. The level of nitrate in these waters is assumed to be low if not
negligible, and will thus not be discussed further. Although storage of the feed-water in the buffer
tank prior to it entering the RO plant may potentially result in a slight elevation in temperature, this
increase is assumed to be negligible. (It should, however, be noted that a similar plant on the
Bushman’s River in the Eastern Cape discharged a brine more than 2ºC warmer than the seawater
temperature in the receiving environment.) For the purpose of this assessment it is thus assumed
that the discharged water will not be significantly warmer in relation to the temperature of the intake
waters (see Section 4.2 for a more detailed discussion of this assumption) However, it is possible
that the receiving water masses may potentially have lower temperatures than that of the brine
effluent, as it is expected that the high density brine will remain at the same temperature as the near
surface intake waters but will sink to the bottom in the vicinity of the discharge location (see Section
7.4). In Saldanha Bay these bottom waters may be significantly colder than the near surface waters
being drawn into the intake.
The approach taken in this study is consistent with the approach taken by the decision-making
authorities. Based on identified sensitive ecosystems and beneficial use areas and the likely
environmental impacts of the discharge, water and sediment quality target values have been
specified comprising general recommended targets as set out in water quality guideline documents,
such as those of South Africa, Australia/New Zealand and the World Bank (RSA DWAF, 1995;
ANZECC, 2000; World Bank, 1998). In the SBQWQFT Water Quality Management Plan, Monteiro
and Kemp (2004) have proposed the three ecosystem state variables (over and above the specified
water quality criteria in Table 8.1) for assessing general thresholds of ecosystem response in
Saldanha Bay. These are phytoplankton biomass, as mg C/m3, dissolved oxygen as ml O2 /ℓ and
particulate organic carbon (POC) in deposition areas as mg C/m2. These reflect the overall
productivity of the Saldanha Bay system and its biogeochemical status14.
14 Threshold levels for these variables are set at changes of 10% (or more) over the ambient condition that extend for a
period of 7 days or longer; the purpose being to be able to reliably show whether there is any net change in the system due to the proposed discharge. The 10% change is predicated on typical measurement ‘uncertainty’ for field investigations of the distributions of the variables considered (Monteiro and Kemp, 2004). The 7 day period derives from measurements showing that exposures of organisms to e.g. increased or decreased nutrient concentrations in the case of Saldanha Bay macroalgae, need to persist for at least this period prior to there being any measurable effect in biomass or physiological function. An additional reason is that Saldanha Bay is exposed to effects of upwelling on the adjacent continental shelf which, in spring/summer, typically has a 6-10 day periodicity. Thus effects that persist for periods shorter than the upwelling cycle are considered to be transient in nature; effects persisting for longer than 7 days may run across two or more upwelling cycles and may become cumulative. (For example, there was a drop in primary production in December 1999 for three weeks that resulted in mussels stopping growing for this period.) Under this system, if the analyses of the proposed discharge indicate that the identified system indicator levels are be exceeded the potential ecological consequences would need to be assessed in more detail, i.e. the exceedance of a 10% change for more that 7 days acts as a “red flag”.
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However given the scale of the discharge and associated “footprint” or impacted area is relatively
modest, it is deemed that a detailed study, where bay productivity, oxygen concentrations and
nutrient dynamics are explicitly simulated, is not warranted here. The present assessment is based
on three-dimensional modelling of plume extent followed by an ecological risk assessment as
described in Section 4.1.2 and 4.1.3).
For the purpose of this assessment the dimensions of the discharge plume in the receiving
environment are defined here by the spatial extent of exceedance of established water quality
guidelines or target values for constituents of concern. Table 8.1 provides recommended target
values derived from the national and international guidelines and pertaining to the proposed
hypersaline discharge.
As guideline or target values for the non-oxidising biocide dibromonitrilopropionamide (DBNPA)
proposed for use in the RO Plant could not be located in either the South African Water Quality
guidelines (DWAF, 1995) nor the ANZECC guidelines (ANZECC, 2000), a literature search was
undertaken to locate a suitable water quality guideline. The most sensitive marine species for which
toxicological data exists is the Eastern Oyster (Crassostrea virginica). A 48 hour exposure LC50
(median lethal concentration) of 0.72 mg.ℓ-1 of DBNPA has been reported (Kaine et al., 1996; Dow
Chemical Fact Sheet No. 253-01464-06/18/02, 34pp.) where the LC50 refers to the percentage of
abnormally developed Eastern Oyster larvae and not mortality as is normally the case. Klaine et al.
(1996) also report an 96-hour flow through study performed with Eastern Oyster that resulted in
significant reduction of shell deposition at < 0.07 mg.ℓ-1 that was considered to represent a Lowest
Observed Effect Concentration (LOEC) for Eastern Oyster. US EPA (1994) report Levels of Concern
(LOC)15 for Eastern oysters of 0.035 mg. ℓ-1 (typical species) and 0.004 mg/l (endangered species).
In this study appropriate water quality guidelines are assumed to range between 0.035 mg. ℓ-1 and
0.070 mg. ℓ-1 for DBNPA in the brine discharge.
15 Typical species LOC values are defined as ½ LC50, while LOC values for endangered species are defined as ½0 LC50.
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Table 8.1: Water quality guidelines for the dischar ge of a high-salinity brine into the marine
environment.
VARIABLE SOUTH AFRICA (DWAF 1995)
AUSTRALIA/NEW ZEALAND
(ANZECC 2000)
WORLD BANK a (World Bank 1998)
Zone of impact /
mixing zone
To be kept to a minimum, the acceptable dimensions of this zone informed by the
EIA and requirements of licensing authorities, based
on scientific evidence.
- 100 m radius from point
of discharge for temperature
Temperature
b
The maximum acceptable variation in ambient temperature is ± 1°C
Where an appropriate reference system(s) is
available, and there are sufficient resources to collect the necessary information for
the reference system, the median (or mean) temperature
should lie within the range defined by the 20%ile and
80%ile of the seasonal distribution of the ambient
temperature for the reference system,.
< 3°C above ambient at the edge of the zone
where initial mixing and dilution take place.
Where the zone is not defined, use 100
meters from the point of discharge when there
are no sensitive aquatic ecosystems within this
distance.
Salinity b 33 – 36 psu
Low-risk trigger concentrations for salinity are that the median
(or mean) salinity should lie within the 20%ile and 80%ile
of the ambient salinity distribution in the reference system(s). The old salinity
guideline (ANZECC 1992) was that the salinity change should
be < 5% of the ambient salinity.
-
Total residual
Chlorine d
no guideline, however deleterious effects recorded for concentrations as low as
2 – 20 µg. ℓ-1. A very conservative trigger value
thus is < 2 µg CL . ℓ-1.
3 µg Cl. ℓ-1 measured as total residual chlorine (low reliability trigger value at 95% protection
level, to be used only as an indicative interim working level) (ANZECC 2000) c
0.2 mg. ℓ-1 at the point of discharge prior to
dilution
Total residual DBNPA
No guideline exists, suggest values ranging between
0.035 mg. ℓ-1 and 0.070 mg. ℓ-1 No guideline found No guideline found
Dissolved oxygen
For the west coast, the dissolved oxygen should not
fall below 10 % of the established natural variation.
For the south and east coasts the dissolved oxygen should not fall below 5 mg/ℓ (99 % of the time) and below
6 mg/ℓ (95 % of the time)
Where an appropriate reference system(s) is
available, and there are sufficient resources to collect the necessary information for
the reference system, the median lowest diurnal DO
concentration for the period for DO should be > the 20%ile of the ambient dissolved oxygen concentration in the reference system(s) distribution. Where
possible the trigger value should be obtained during low
flow and high temperature periods when DO
concentrations are likely to be at their lowest.
-
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VARIABLE SOUTH AFRICA (DWAF 1995)
AUSTRALIA/NEW ZEALAND
(ANZECC 2000)
WORLD BANK a (World Bank 1998)
Nutrients
Waters should not contain concentrations of dissolved nutrients that are capable of
causing excessive or nuisance growth of algae or
other aquatic plants or reducing dissolved oxygen concentrations below the target range indicated for
dissolved oxygen (see above)
Default trigger values of PO4-P: 100 µg. ℓ-1 NOx-N: 50 µg. ℓ-1 NH4
+-N: 50 µg. ℓ-1 for the low rainfall southern Australian region (Table 3.3.8 in ANZECC 2000)
-
Chromium 8 µg. ℓ-1 (as total Cr)
Marine moderate reliability trigger value for chromium (III)
of 10 µg. ℓ-1 with 95% protection
Marine high reliability trigger
value for chromium (VI) of 4.4 µg. ℓ-1 at 95% protection.
0.5 mg. ℓ-1 (total Cr) for effluents from thermal
power plants
Iron -
Insufficient data to derive a reliable trigger value. The current Canadian guideline
level is 300 µg. ℓ-1
1.0 mg. ℓ-1 for effluents from thermal power
plants
Molybdenum -
Insufficient data to derive a marine trigger value for
molybdenum. A low reliability trigger value of 23 µg. ℓ-1 was
adopted to be used as indicative interim working
levels.
-
Nickel 25 µg. ℓ-1 (as total Ni)
7 µg. ℓ-1 at a 99% protection level is recommended for
slightly-moderately disturbed marine systems.
a The World Bank guidelines are based on maximum permissible concentrations at the point of discharge and do not explicitly take into account the receiving environment, i.e. no cognisance is taken of the fact of the differences in transport and fate of pollutants between, for example, a surf-zone, estuary or coastal embayment with poor flushing characteristics and an open and exposed coastline. It is for this reason that we include in this study other generally accepted Water Quality guidelines that take the nature of the receiving environment into account.
b Both in the case of temperature and salinity using the maximum ∆T and ∆S measured at any location at any time during the model simulations constitutes an extremely conservative approach. We nevertheless have used the dimension of the 99% exceedance of the ∆T = +1ºC contour and the ∆S = 36 psu contour as representing the “footprint” of the potential impact. This constitutes a total of approximately 6 hours per season (or one day per annum) of exposure to conditions exceeding the stated ∆T or ∆S values.
c The ANZECC (2000) Water Quality guideline for salinity is less stringent than, but roughly approximates, the South African Water Quality guideline that requires that salinity should remain within the range of 33 psu to 36 psu. Similarly the ANZECC (2000) Water Quality guideline for water temperature is less stringent than the South African Water Quality guideline that requires that water temperature does not vary by more than 1 ºC from the ambient water temperature. The ANZECC (2000) Water Quality guideline for water temperature is likely to be particularly relevant in the bottom waters of Saldanha Bay where there is significant natural temperature variability due to upwelling cycles as the ANZECC guideline explicitly takes into account this variability and the fact that the marine ecology of the region is likely to be adapted to such variability. At these depths the South African Water Quality guideline of temperature variability of < 1 ºC is likely to be very conservative (possibly overly conservative) in these circumstances.
d Chlorine “shocking” may be preferable in certain circumstances. This involves using high chlorine levels for a few seconds rather than a continuous low-level release. In this case the target value is a maximum value of 2 mg. ℓ-1 for up to 2 hours, not to be repeated more frequently than once in 24 hours, with a 24-hour average of 0.2 mg. ℓ-1 (The same limits would apply to bromine and fluorine.).
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The individual constituents of the effluent and their potential impacts on the marine environment are
discussed in more detail under separate headings below.
8.1.3.1 Salinity
All marine organisms have a range of tolerance to salinity, which is related to their ability to regulate
the osmotic balance of their individual cells and organs to maintain positive turgor pressure. Aquatic
organisms are commonly classified in relation to their range of tolerance as stenohaline (able to
adapt to only a narrow range of salinities) or euryhaline (able to adapt to a wide salinity range), with
most organisms being stenohaline.
Salinity changes may affect aquatic organisms in two ways:
• direct toxicity through physiological changes (particularly osmoregulation), and
• indirectly by modifying the species distribution.
Salinity changes can also cause changes to water column structure (e.g. stratification) and water
chemistry (e.g. dissolved oxygen saturation and turbidity). For example, fluctuation in the salinity
regime has the potential to influence dissolved oxygen concentrations, and changes in the
stratification could result in changes in the distribution of organisms in the water column and
sediments. Significant effects on stratification and oxygen concentrations (if at all) are only expected
in the very near-field. Behavioural responses to changes in salinity regime can include avoidance by
mobile animals, such as fish and macrocrustaceans, by moving away from adverse salinity and
avoidance by sessile animals by reducing contact with the water by closing shells or by retreating
deeper into sediments.
However, in marine ecosystems adverse effects or changes in species distribution are anticipated
more from a reduction rather than an increase in salinity (ANZECC, 2000). Very little information
exists on the effect of an increase in salinity on organisms in coastal marine systems, most studies
being done either on effects of a decline in salinity due to an influx of freshwater, or on salinity
fluctuations in estuarine environments, where most of the fauna can be expected to be of the
euryhaline type.
Sub-lethal effects of changed salinity regimes (or salinity stress) can include modification of metabolic
rate, change in activity patterns or alteration of growth rates (McLusky, 1981). The limited data
available include a reported tolerance of adults of the mussel Mytilus edulis of up to 60 psu (Barnabe,
1989), and successful fertilization (Clark, 1992) and development (Bayne, 1965) of its larvae at a
salinity of up to 40 psu. The alga Gracilaria verrucosa can tolerate salinity ranges from 9-45 psu
(Engledow and Bolton, 1992). The shrimp Penaeus indicus was capable of tolerating a salinity range
of 1 to 75 psu if allowed an acclimation time of around 48 hours (McClurg, 1974), the oyster
Crassostrea gigas tolerated salinities as high as 44 psu (King, 1977), and the shrimp Penaeus
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monodon survived in 40 psu saline water (Kungvankij, et al. 1986a, b, cited in DWAF 1995). Chen et
al. (1992) reported a higher moulting frequency in juveniles of the prawn Penaeus chinensis at a
salinity of 40 psu. Lethal effects were reported for seagrass species: for example, salinities of 50 psu
caused 100% mortality of the Mediterranean seagrass Posidonia oceanica, 50% mortality at 45 psu,
and 27% at 40 psu. Salinity concentrations above 40 psu also stunted plant growth and no-growth
occurred at levels exceeding 48 psu (Latorre, 2005). The high saline concentration can also lead to
an increase of water turbidity, which is likely to reduce light penetration, an effect that might disrupt
photosynthetic processes (Miri and Chouikhi, 2005). The increased salt concentration can reduce
the production of plankton, particularly of invertebrate and fish larvae (Miri and Chouikhi., 2005). One
of the main factors of a change in salinity is its influence on osmoregulation, which in turn affects
uptake rates of chemical or toxins. In a review on the effects of multiple stressors on aquatic
organisms Heugens et al. (2001) summarize that in general metal toxicity increases with decreasing
salinity, while the toxicity of organophosphate insecticides increases with increasing salinity. For
other chemicals no clear relationship between toxicity and salinity was observed. Some evidence,
however, also exists for an increase in uptake of certain trace metals with an increase in salinity
(Roast et al., 2002, Rainbow and Black, 2002).
Very few ecological studies have been undertaken to examine the effects of high salinity discharges
from desalination plants on the receiving communities. One example is a study on the macrobenthic
community inhabiting the sandy substratum off the coast of Blanes in Spain (Raventos et al., 2006).
The brine discharge from the desalination plant was approximately 12 Hm3/year (or 33 707 m3. day-
1). Visual census of the macrobenthic communities were carried out at two control locations (away
from the discharge outlet) and one impacted (at the discharge outlet) location several times before
and after the plant began operating. No significant variations attributable to the brine discharges from
the desalination plant were found. This was partly attributed to the high natural variability that is a
characteristic feature of seabeds of this type, and also to the rapid dilution of the hypersaline brine
upon leaving the discharge pipe. Other studies, however, indicated that brine discharges have led to
reductions in fish populations, and to die-offs of plankton and coral in the Red Sea (Mabrook, 1994),
and to mortalities in mangrove and marine angiosperms in the Ras Hanjurah lagoon in the United
Arab Emirates (Vries et al., 1997).
The South African Water Quality guidelines (DWAF, 1995) set an upper target value for salinity of 36
psu. The paucity of information on the effects of increased salinity on marine organisms makes an
assessment of the high salinity plume difficult. However, this guideline seems sufficiently
conservative to suggest that no adverse effects should occur for salinity < 36 psu. At levels
exceeding 40 psu, however, significant effects are expected, including possible disruptions to
molluscan bivalves (e.g. mussels/oysters/clams) and crustacean (and possibly fish) recruitment as
salinities >40 psu may affect larval survival (e.g. Bayne, 1965; Clarke, 1992). This applies
particularly to the larval stages of fishes and benthic organisms in the area, which are likely to be
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damaged or suffer mortality due to osmotic effects, particularly if the encounter with the discharge
effluent is sudden.
The model results have shown that the brine sinks to the bottom due to its greater density and is
primarily affecting the bottom third of the water column. The surface waters are not affected by the
brine.
An assessment of the effect of the brine discharge in terms of the modelling results, and for each
Alternative Site, is provided below. As a conservative measure, the assessment is based on the
‘worst-case-scenario’, which for all three sites almost exclusively appears to be during the extremely
calm weather scenario in autumn when the impacts in the bottom waters are the greatest due to
limited vertical mixing of surface and bottom waters due to primarily wind but also waves in shallow
waters.
Site 1:
At Site 1 the discharge is planned to occur via a pipeline along a 30 m length of the revetment of the
reclaim dam at a location approximately 80 m from the low water mark of the adjacent shoreline
where the water depth adjacent to the revetment is ~ 1.5 m.
The model results for the pipeline discharge indicate that the maximum extent of exceedance of the
36 psu target value is 200 m by 400 m from the brine outlet (Figure C1.2f, Appendix C), but this is
expected to occur only for a total of 0.25% (i.e. a cumulative 6 hours in a 90 day autumn-period) of
the calm weather period. Within a 90 x 50 m area around the outlet, the target value will be
exceeded >50% of the time (i.e. a cumulative total of 45 days in a 90 day autumn-period). The
maximum extent of the footprint 4 psu target value is approximately 160 m x 60 m (Figure C1.3b).
During periods of little or no stratification (e.g. winter) the plume footprint is significantly smaller due
to greater mixing of the plume throughout the vertical extent of the water column. Due to the
relatively small footprint of the plume, even under the ‘worst-case-scenario’, this impact is assessed
to be of low significance.
Site 2:
The discharge alternatives at Site 2 constitute either a surf-zone discharge or a single port diffuser at
between -0.5 m to -1 m below chart datum and 20-25 m from the shoreline. From the modelling
study it can be expected that the plume will have a maximum extent of 250 x 520 m around the
discharge outlet for a total of 0.25% (or a total duration of approximately 6 hours) of the calm weather
period (Figure C2.1f). Within 100 m of the outlet, the target value of 36 psu will be exceeded for
>50% of the time in autumn. The maximum extent of the 4 psu target value is approximately 150 m x
160 m (Figure C2.3f).
Again, during winter the plume footprint is notably smaller due to greater mixing of the plume
throughout the vertical extent of the water column. The impact is regarded as having a low
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significance due to the relatively small plume dimensions. However it should be recognised that the
discharge for Site 2 is occurring into the relatively poorly-flushed Small Bay system and would
inherently pose greater risks than the other sites considered. It could also place significant
constraints on any future increases in plant capacity should they ever be required.
Site 3:
The discharge alternatives at Site 3 constitute a single port diffuser at either 1) approximately -8 m
CD into Small Bay, 2) at -4 m CD into Big Bay, or 3) at approximately -16 to -18 m CD at Caisson 3.
These will be located alongside the iron-ore causeway at distances ranging from approximately 50 to
70 m from the causeway. In the modelling study the discharge alternatives are defined as Site 3(a)
(discharge into Small Bay), Site 3(b) (discharge into Big Bay) and Site 3(c&d) (discharge at Caisson
3).
1) In the case of a discharge into Small Bay (Site 3a), the model results indicate that even for
the worst-case-scenario the 36 psu guideline value will only be exceeded for <50 m (i.e. the
assumed resolution of the modelling study) around the outlet structure for 0.25% of the time
(i.e. a cumulative total of 6 hours within a season). Given the limitations in the resolution of
the modelling study, a conservative assumption would be to assume that the 36 psu
guideline value could be exceeded regularly within this radius although this is not necessarily
the case.
2) The modelling results indicate that the discharge into Big Bay (Site 3b) will result in a
maximum plume dimension of approximately 120 m in diameter at 0.25% of the time. The
impact is regarded as having a low significance due to the relatively small plume dimensions
3) For discharge at Caisson 3 (Site 3c&d) the model results are similar but slightly less than
those indicated for a discharge into Small Bay (Site 3a). The model results indicate that even
for the worst-case-scenario the 36 psu guideline value will only be exceeded for <50 m (i.e.
the assumed resolution of the modelling study) around the outlet structure for 0.25% of the
time (i.e. a cumulative total of 6 hours within a season). Given the limitations in the
resolution of the modelling study, a conservative assumption would be to assume that the 36
psu guideline value could be exceeded regularly within this radius although this is not
necessarily the case. The potential mitigating effects of propeller wash at Caisson 3 have
not been taken into account in the model simulations. It is expected that this will further mix
the plume with the surrounding waters and limit the dimension of the plume exceeding 36
psu.
All of the discharge options have small saline foot prints, and their impacts are therefore
considered to be of low significance. The detailed assessment of the elevated salinity in the
discharge brine is summarised in Section 8.2.2.
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8.1.3.2 Temperature
The increase in temperature of the feed-water during its progress through the RO plant is expected
to be limited (i.e. typically less than one degree Celsius) and consequently the thermal characteristics
of the discharged effluent will be largely similar to the ambient seawater temperature at the intake16.
During the summer months (or during very calm weather periods), significant stratification of the
water column occurs in Saldanha Bay, where the temperature of the shallow surface layer (<5 m) in
Small Bay can be as high as 20°C, and can be underl ain by a strong thermocline (>1 °C m -1) and a
bottom layer with temperatures of about 11°C (Monte iro et al., 1999). At Site 3, the discharge will be
at -8 m CD into Small Bay, -4 m CD into Big Bay or at approximately -16 to -18 m CD at Caisson 3..
The temperature of the discharged brine can thus be significantly warmer than that of the ambient
water at these depths. A similar scenario is assumed for Sites 1 and 2, as the high density brine is
expected to sink to the bottom.
Bamber (1995) defined four categories for direct effects of thermal discharges on marine organisms:
• Increases in mean temperature
• Increases in absolute temperature
• High short term fluctuations in temperature
• Thermal barriers
Increased mean temperature
Changes in water temperature can have a substantial impact on aquatic organisms and ecosystems,
with the effects being separated into two groups:
• influences on the physiology of the biota (e.g. growth and metabolism, reproduction timing and
success, mobility and migration patterns, and production); and
• influences on ecosystem functioning (e.g. through altered oxygen solubility).
The impacts of increased temperature has been reviewed in a number of studies along the West
Coast of South Africa, some in Saldanha Bay (e.g. Luger et al., 1997; van Ballegooyen and Luger,
1999; van Ballegooyen et al., 2004, 2005). A synthesis of these findings is given below.
Most reports on adverse effects of changes in seawater temperature on southern African West Coast
species are for intertidal (e.g. the white mussel Donax serra) or rocky bottom species (e.g. abalone
Haliotis midae, kelp Laminaria pallida, mytilid mussels, Cape rock lobster Jasus lalandii). Cook
(1978) specifically studied the effect of thermal pollution on the commercially important rock lobster
Jasus lalandii, and found that adult rock lobster appeared reasonably tolerant of increased
temperature of +6°C and even showed an increase in growth rate. The effect on the reproductive
16 A comprehensive sensitivity analysis has been undertaken (van Ballegooyen et al., 2008) that indicates that
the results of this study (that assumes a discharge with a zero temperature elevation above the ambient water temperature at the intake) remain valid for temperature elevations of up to 5 ºC above the ambient water temperature at the intake (see Section 4.2).
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cycle of the adult lobster female was, however, more serious as the egg incubation period shortened
and considerably fewer larvae survived through the various developmental stages at +6°C above
ambient temperature. Zoutendyk (1989) also reported a reduction in respiration rate of adult J.
lalandii at elevated temperatures.
Other reported effects include an increase in biomass of shallow water hake Merluccious capensis
and West Coast sole Austroglossus microlepis at 18°C (MacPherson and Gordoa, 1992) but no
influence of temperatures of <17.5°C on chub-macker el Scomber japonicus (Villacastin-Herroro et
al., 1992). In contrast, 18°C is the lower lethal limi t reported for larvae and eggs of galjoen Distichius
capensis (Van der Lingen, 1994).
Internationally, a large number of studies have investigated the effects of heated effluent from coastal
power stations on the open coast. These concluded that at elevated temperatures of <5°C above
ambient seawater temperature, little or no effects on species abundances and distribution patterns
were discernable (van Ballegooyen et al. 2005). On a physiological level, however, some adverse
effects were observed, mainly in the development of eggs and larvae (e.g. Cook, 1978, Sandstrom et
al., 1997; Luksiene et al., 2000). Other effects observed include alterations in the photosynthesis
behaviour of algal assemblages (Martinez-Arroyo et al. 2000), decreases in the duration of larval
development (e.g. barnacle larvae, Thiyagarajan et al. 2003), and suppressed growth in the post
larvae of the spiny lobster Panulirus argus due to prolonged intermoulting periods and reduced size
increments with each moult (Lellis and Russel, 1990). For a temperature increase of approximately
5°C an increased photosynthetic rate and biological community metabolism (Q10 ~ 2.5) is reported
(Parsons et al., 1977).
In Saldanha Bay, increased mean temperatures may lead to Mytilus galloprovincialis outcompeting
Choromytilus meridionalis where these species already occur (e.g. iron ore jetty and causeway) as
the juveniles of the former species grow faster in temperatures between 17 and 22°C (van Erkom
Schurink and Griffiths, 1993). Mussel farming originally harvested Choromytilus meridionalis until
Mytilus galloprovincialis started to dominate.
The brine is assumed to have low levels of nitrate as the feed-water was drawn from the surface
waters. There is thus a potential of displacement of naturally high nitrate waters by nitrate deficient
waters at depth. However, the increased mineralization of nutrients in the sediments due to
increased water temperatures will offset or partially offset this reduction in nutrients.
The South African Water Quality Guidelines recommend that the maximum acceptable variation in
ambient temperature should not exceed 1°C, which is an extremely conservative value in view of the
negligible effects of thermal plumes on benthic assemblages reported elsewhere for a ∆T of +5°C or
less. The greatest extent of the thermal plume is expected to be during the autumn calm weather
period, and the following thus focuses on these results.
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Site 1:
At Site 1 the discharge is planned to occur via a pipeline along a 30 m length of the revetment of the
reclaim dam at a location approximately 80 m from the low water mark of the adjacent shoreline
where the water depth adjacent to the revetment is ~ 1.5 m.
The model results for the pipeline discharge indicate that the maximum extent of exceedance of the
1°C above ambient temperature will occur for 300 m around the outlet for (Figure C1.5f) a total of
0.25% of the time (i.e. 6 hours in a season). Closer to the outfall, the 1°C threshold will be exceeded
for 20% of the time in a 80 m x 100m area offshore of the discharge and for 5% of the time in an 150
m x 170 m area offshore of the discharge.
Site 2:
The discharge alternatives at Site 2 constitute either a surf-zone discharge or a single port diffuser at
between -0.5 m to -1 m below chart datum and 20 to 25 m from the shoreline. The thermal footprint
(i.e. the maximum extent of exceedance of the 1°C above ambient temperature) is expected to
extend over a maximum area of 650 x 450 m (Figures C2.5b and f) for a total of 0.25% of both the
summer and the autumn calm weather period (i.e. 6 hours in a season), and cover an area of 480 x
350 m for approximately 20% of the time and 570 m x 350 m for approximately 5% of the time during
the calm autumn period (Figure C2.5f). These results indicate that the discharge at this location will
be vulnerable to potential thermal impacts during calm periods.
In addition to the exceedance of the SAWQ guideline of a maximum allowable deviation of water
temperature of less than 1°C, the near bottom water temperature at this site also exceeds the less
conservative ANZECC guideline that the change in water temperature should not lie outside the 20
and 80 percentiles of the natural undisturbed temperature variability at the site. With the proposed
discharge the median bottom water temperature exceeds the 80 percentile of the natural temperature
variability at this site during calm (autumn) conditions over an approximate area of 150 m x 250 m.
This exceedance of the ANZECC water quality guideli ne occurs under summer or winter
conditions at this site but does not occur during any season (or “worst case” c alm
conditions) at any of the other discharge sites.
Site 3:
The discharge alternatives at Site 3 constitute a single port diffuser at either 1) approximately -8 m
below CD into Small Bay, 2) at -4 m below CD into Big Bay, or 3) at approximately -16 to -18 m below
CD at Caisson 3. These will be located alongside the iron-ore causeway at distances ranging
between approximately 50 to 70 m from the causeway. In the modelling study these are defined as
Site 3(a) (discharge into Small Bay), Site 3(b) (discharge into Big Bay) and Site 3(c&d) (discharge at
Caisson 3).
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1) In the case of a discharge into Small Bay, the 1°C threshold will be exceeded in an area of
maximal 500 x 230 m for 0.25% (i.e. a total duration of 6 hours during summer) 280 m x
120m for approximately 5% of the time, and for approximately 180 x 100 m around the outlet
for <20% of the time (Figure C3.5b). The thermal footprint could be reduced if the seawater
intake was located deeper in the water column where the temperature difference between
the intake location and the discharge depth could be significantly reduced.
2) The discharge into Big Bay will result in a maximum thermal plume dimension of 440 x 250 m
at 0.25% of the time during summer (Figure C4.5b), 240 x 150 m for approximately 5% of the
time during the calm autumn period (Figure 4.5f) and 180 m for approximately 20% of the
time during the calm autumn period.
3) For discharge at Caisson 3 (Site 3c&d) the model results indicate that the discharge into Big
Bay will result in a maximum thermal plume dimension of 440 x 240 m at 0.25% of the time
during summer (Figure C5.5b), 160 x 140 m for approximately 5% of the time during the calm
autumn period (Figure 4.5f) and 70 m for approximately 20% of the time during the calm
autumn period.
All benthic species have preferred temperature ranges and it is reasonable to expect that those
closest to their upper limits (i.e. boreal as opposed to temperate) would be negatively affected by an
increase in mean temperature. However, in the case of Saldanha Bay two facts have to be noticed.
Firstly, an increase in mean temperature compared to natural ambient bottom temperatures will only
occur seasonally during periods of high stratification (i.e. strong upwelling and/or calm wind
conditions). Secondly, the sessile biota in Saldanha Bay are naturally exposed to wide temperature
ranges due to surface heating and rapid vertical mixing of the water column and intrusions of cold
bottom shelf water into the system. This can lead to rapid variations in temperature of as much as
10°C over less than 12 hours, the absolute range be ing approximately 10 to 22°C (Monteiro et al.
1999), on occasion in shallower regions reaching temperatures above this. It can thus be assumed
that the biota in these waters are relatively robust and well-adapted to substantial natural variations in
temperature. In fact, while the addition of the warmer brine effluent may at times significantly
increase bottom temperatures in the vicinity of the discharge, the effluent is likely to decrease
temperature variability in the lower water column in the region of impact (albeit with a bias towards
higher temperatures), rather than increasing temperature variability.
The application of the ANZECC water quality guideline (which requires that the median temperature
in the environment with an operational discharge should not lie outside the 20 and 80 percentile
temperature values for a reference location or ambient temperatures observed prior to the
construction and operation of the proposed discharge), is more appropriate to the high temperature
variability conditions in the bottom waters of Saldanha Bay. There is compliance with this guideline
at all discharges sites except for the discharge into the NE corner of Small Bay from Site 2 during
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autumn when an area of approximately 100 m around the discharge is predicted to exceed the
ANZECC seawater temperature guideline.
The impact of the elevated temperature of the brine in relation to the receiving waters, is thus
considered to be of low significance for all sites. The discharge from Site 2, while it exceeds the
ANZECC water quality guideline, does so only over a limited area and thus also is deemed to have
an impact of low significance.
Increased absolute temperature
The maximum observed sea surface temperature in the region typically is < 22°C. Strong wind
events are likely to mix the water column to such an extent that the bottom waters, at times, have
similar water temperatures to the surface waters. Only at the proposed discharge site in Small Bay
and at Caisson 3 for Site 3, is it less likely that this occurs. The discharged brine will not be heated
above this naturally occurring maximum temperature and therefore an increase in absolute
temperature is not expected and is not further assessed here.
Short term fluctuations in temperature and thermal barriers
Temperature fluctuations are typically caused by variability in flow or circulation driven by frequently
reversing winds or tidal streams. For example, Bamber (1995) described faunal impoverishment in a
tidal canal receiving hot water effluent where the temperature variability was ~12°C over each tidal
cycle. As noted above, the bottom waters in the bay may vary rapidly in temperature, i.e. by as much
as 10°C over less than 12 hours. Thus the ecologic al effects of brine-induced rapid changes in
temperature are not further assessed.
For thermal barriers to be effective in limiting or altering marine organism migration paths they need
to be persistent over time and cover a large cross-sectional area of the water body. The predictions
for the brine plume distributions indicate that neither condition will be met in Saldanha Bay. Over and
above this there are no known migration pathways in the system. This effect can therefore be
considered insignificant.
8.1.3.3 Dissolved Oxygen
Dissolved oxygen (DO) is an essential requirement for most heterotrophic marine life. Its natural
levels in seawater are largely governed by local temperature and salinity regimes, as well as organic
content. Coastal upwelling regions are frequently exposed to hypoxic conditions owing to extremely
high primary production and subsequent oxidative degeneration of organic matter. Along the
southern African coast, low-oxygen waters are a feature of the Benguela system, and thus of
Saldanha Bay. Small Bay does experience a fairly regular oxygen deficit during late summer and
winter months, whilst Big Bay experiences less frequent and lower magnitude oxygen deficits
(Atkinson et al., 2006). In addition, existing discharges into Saldanha Bay exacerbate these naturally
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occurring low oxygen conditions in certain areas, e.g. in the vicinity of the fish factory discharges in
Small Bay.
Hypoxic water (<2 ml O2. ℓ-1) has the potential to cause mass mortalities of benthos and fish (Diaz
and Rosenberg, 1995). Marine organisms respond to hypoxia by first attempting to maintain oxygen
delivery (e.g. increases in respiration rate, number of red blood cells, or oxygen binding capacity of
haemoglobin), then by conserving energy (e.g. metabolic depression, down regulation of protein
synthesis and down regulation/modification of certain regulatory enzymes), and upon exposure to
prolonged hypoxia, organisms eventually resort to anaerobic respiration (Wu, 2002). Hypoxia
reduces growth and feeding, which may eventually affect individual fitness. The effects of hypoxia on
reproduction and development of marine animals remains almost unknown. Many fish and marine
organisms can detect, and actively avoid hypoxia (e.g. rock lobster “walk-outs”). Some
macrobenthos may leave their burrows and move to the sediment surface during hypoxic conditions,
rendering them more vulnerable to predation. Hypoxia may eliminate sensitive species, thereby
causing changes in species composition of benthic, fish and phytoplankton communities. Decreases
in species diversity and species richness are well documented, and changes in trophodynamics and
functional groups have also been reported. Under hypoxic conditions, there is a general tendency for
suspension feeders to be replaced by deposit feeders, demersal fish by pelagic fish and
macrobenthos by meiobenthos (see Wu, 2002 for references). Further anaerobic degradation of
organic matter by sulphate-reducing bacteria may additionally result in the production of hydrogen
sulphide, which is detrimental to marine organisms (Brüchert et al. 2003).
Because oxygen is a gas, its solubility in seawater is dependent on salinity and temperature, whereby
temperature is the more significant factor. Increases in temperature and/or salinity result in a decline
of dissolved oxygen levels. The temperature in the effluent is not significantly elevated in relation to
the intake water temperature, and a reduction in dissolved oxygen is thus only expected as a result of
the elevated salinity (63.5 psu) of the brine. For example, saturation levels of dissolved oxygen in
seawater decrease with rising salinity from 5.84 ml. ℓ-1 at 15˚C and 35 psu, to 4.90 ml. ℓ-1 at 63.5 psu
(DWAF, 1995), not taking into account any biological use of oxygen due to respiration, oxidation and
degradation. In summer months the surface water can reach temperatures of 20 °C (Atkinson et al.
2006), and the DO in the brine at this temperature would decline from 5.30 ml. ℓ-1 at 35 psu to 4.49
ml. ℓ-1 at 63.5 psu. These approximate calculations translate into a 15-16% reduction of DO in the
brine. The South African Water Quality Guidelines for Coastal Marine Waters (DWAF 1995) state
that for the west coast, the dissolved oxygen should not fall below 10 % of the established natural
variation. A potential difference in DO concentration of 15 % is well within the natural variability
range of the waters in Saldanha Bay (Atkinson et al., 2006), and the potential for a reduction in
dissolved oxygen levels will also drastically reduce within a few meters of the outlet as the effluent
mixes with the receiving waters.
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As the receiving waters can be colder than the brine effluent they can potentially have a higher
solubility potential and thus potentially a higher DO concentration. However, near-bottom waters on
the West Coast are often characterised by hypoxic conditions as a result of decomposition of organic
matter and low-oxygen water generation processes. In particular, the bottom waters of Small Bay
often experience oxygen deficits (Atkinson et al., 2006), particularly during thermal stratification. It is
thus unlikely that the receiving bottom water will have notably higher oxygen concentrations than the
surface waters. Descending brine plumes may therefore act as localised suppliers of oxygenated
water to the seabed, rather than contributing to oxygen depletion. A decrease in DO levels in the
discharged brine is thus not of critical concern, and is assessed as being of low significance.
A critical factor that needs to be observed is that oxygen depletion in the brine might also occur
through the addition of sodium metabisulfite, an oxygen scavenger, which is commonly used as a
neutralizing agent for chlorine (http://www.paua.de/Impacts.htm). Should oxidising biocides be used
in pumping systems (e.g. intake pipe and RO membranes) to ensure that they are remain free of
biofouling organisms, the use of sodium metabisulfite as a neutralizing agent for chlorine may be
required, however, presently the project description is such that only non-oxidising biocides are
specified for use in pumping systems (e.g. intake pipe and RO membranes) to ensure that they are
remain free of biofouling organisms. Chlorine will only be used to treat the product (fresh water) and
thus is not expected to be discharged to the marine environment. Should sodium metabisulfite be
used as a neutralizing agent for chlorine, aeration of the effluent is recommended prior to discharge
(http://www.paua.de/Impacts.htm) However, it should be noted that there will be only a limited
requirement for the use of chlorine as a biocide in the case of beach well intakes and consequently
the use of sodium metabisulfite in a system based on beach well intakes is unlikely. It should be
emphasized here that the use of an Oxidising biocid e and thus also sodium metabisulfite as a
neutralizing agent presently is not proposed for th e Saldanha Bay RO plant, however the
impacts of an oxygen scavenger have been assessed i n this study for completeness and to
allow for the use of chlorine as a biocide of choic e should it be considered a viable alternative
to non-oxidising biocides. .
As discussed above, the expected changes in dissolved oxygen are associated with both direct
changes in dissolved oxygen content due to the difference between the ambient dissolved oxygen
concentrations and those in the effluent being discharged. However, indirect changes in dissolved
oxygen content of the water column and sediments due to changes in hydrodynamic and ecosystem
functioning in the bay are also possible.
For example, oxygen concentrations may change (particularly in the bottom waters and in the
sediments) due to:
i) changes in phytoplankton production as a result of changes in nutrient dynamics (both in
terms of changes in nutrient inflows and vertical mixing of nutrients) and subsequent
deposition of organic matter, and
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ii) changes in remineralisation rates (with related changes in nutrient concentrations in near
bottom waters) associated with near bottom changes in seawater temperature
associated with the brine discharge plume.
Several of the waste water constituents have the potential to act as nutrients for plants (e.g. Sodium
tripolyphosphate and trisodium phosphate). In principle the phosphate can act as a plant nutrient and
thus increase algal growth, however, phosphate generally is not limiting in marine environments such
as Saldanha Bay, unless there are significant inputs of nitrogen (nitrates, ammonia), which is the
limiting nutrient in such systems.
On the other hand, the discharge of the high saline brine may result in increased turbidity, potentially
reducing the light penetration for algal growth (Miri et al., 2005). Such indirect changes are difficult to
quantify, but as a pro-active measure it is recommended that pollutants in the brine that may result in
increased phytoplankton production, be reduced as much as possible.
8.1.3.4 Biocides
The use of a biocide in the intake water is undertaken to ensure that the pumping systems (e.g.
intake pipe and RO membranes) are maintained free of biofouling organisms. For example, larvae of
sessile organisms (e.g. mussels, barnacles) can grow in the intake pipe, and impede the intake flow
of the feed-water. Biofouling by algae, fungi and bacteria can rapidly lead to the formation and
accumulation of slimes and biofilms, which can increase pumping costs, plant operation costs and
can lead to the proliferation of sulphate reducing bacteria. This can ultimately result in the production
of hydrogen sulphide causing metallic corrosion problems.
There are two main groups of biocides: the oxidising biocides and the non-oxidising biocides. The
classification is based on the mode of biocidal action against biological material. Oxidising biocides
include chlorine and bromine-based compounds and are non selective with respect to the organisms
they kill. Non-oxidising biocides are more selective, in that they may be more effective against one
type of micro-organisms than another. A large variety of active ingredients are used as non-oxidising
biocides, including quaternary ammonium compounds, isothiazolones, halogenated bisphenols,
thiocarbamates as well as others. The non-oxidising biocide proposed for use in the RO Plant is 2.2
Dibromo-3-nitrilopropionamide (DBNPA) commercially identified as Hydrex 4202. DBNPA has
extremely fast antimicrobial action and rapid degradation to relatively non-toxic end products. The
ultimate degradation products formed from both chemical and biodegradation processes of DBNPA
include ammonia, carbon dioxide, and bromide ions.
DBNPA also degrades with sunlight (with the formation of inorganic bromide ion) with a reported
half-life of approximately 7 days (Dow Chemicals, Fact Sheet No. 253-01464-06/18/02). Water
quality guidelines identified as being appropriate to Saldanha Bay are indicated in Table 8.1. Based
on literature seemingly degradation end products (e.g. ammonia) will not be problematic in the
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marine environment, however it is the specific biocidal action of residual DBNPA in the effluent
streams to the marine environment that is the major concern.
The dominant degradation pathway of DBNPA involves reaction with nucleophilic substances or
organic material invariably found in water. Additional degradation reactions include hydrolysis,
reaction with soil, and breakdown through light (US EPA, 1994). The uncatalyzed hydrolysis of
DBNPA proceeds via decarboxylation to the generation of an array of degradation products. These
degradates include dibromoacetonitrile, dibromoacetamide, dibromoacetic acid,
monobromoacetamide, monobromonitrilo-propionamide, monobromoacetic acid, cyanoacetic acid,
cyanoacetamide, oxoacetic acid, oxalic acid, and malonic acid. The rate of hydrolysis is a function of
pH and temperature, and increasing either or both pH and temperature will increase the
decomposition rate. For instance, at pH 5 the half-life of DBNPA is 67 days as opposed to 63 hours
at pH 7 and 73 minutes at pH 9. In natural waters (seawater has a pH of 8), DBNPA hydrolyses
rapidly (half life < five hours) into the above mentioned degradates which continue to degrade rapidly
by aerobic and anaerobic aquatic metabolism (US EPA, 1994). Although the hydrolysis and aquatic
photolysis rate is rapid under aquatic conditions, the primary degradation pathway is through aerobic
and anaerobic metabolism. In aerobic and anaerobic aquatic metabolism studies, DBNPA degraded
with a half-life of <four hours, with a further rapid decrease of the degradate concentrations (US EPA,
1994). Exposure to sunlight is a futher factor increasing the rate of decomposition which results in
the formation of inorganic bromide ion. For example, the half-life of DBNPA was reported to be
approximately 7 days when exposed to sunlight even at a pH of 4 (Dow Chemicals, Fact Sheet No.
253-01464-06/18/02). Based on literature seemingly degradation end products (e.g. ammonia) will
not be problematic in the marine environment, however, it is the specific biocidal action of residual
DBNPA in the effluent streams to the marine environment that is the major concern. Aquatic
toxicological studies have shown that DBNPA appears to be moderately toxic to estuarine fish and
shrimp, highly toxic to estuarine mysids and very highly toxic to estuarine shellfish and larvae. It
must be noted though that, due to the fast degradation of DBNPA, toxic effects are generally acute
occurring within 24 hours of exposure, and chronic effects will not occur. Due to the rapid
degradation of DBNPA in natural waters, some risk assessment studies have concluded that the use
of DBNPA in cooling systems (once through and recirculating sytems) does not pose an
unacceptable risk to the environment (Klaine et al., 1996). Water quality guidelines identified as
being appropriate to Saldanha Bay are indicated in Table 8.1.
Transnet Projects (through their contractor) have indicated that only non-oxidising biocides (DBNPA)
will be used in any system that will result in an effluent stream entering the marine environment.
Oxidising biocides, while a viable alternative, will only be used in the treatment of the product (i.e. the
freshwater produced by the RO Plant) and will consequently not result in a discharge of residual
biocide to the marine environment. The reason for this choice is the sensitivity of the RO Plant
membranes to chorine residuals in the intake waters. In this report we have assessed both
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alternatives (i.e. oxidising and non-oxidising biocides) in systems that will result in residual
concentrations of biocides being discharged into the marine environment.
It is proposed that DBNPA will be used as filtration shock dosing injected before the dual medium
filters (i.e. added to the feed tank) in a nominal shock dosing regime of 10 ppm (i.e. 10 mg.ℓ-1) for a
10 minute duration every 4 hours. This non-oxidising biocide may also on occasion (e.g. once per
month) be added at the intake to prevent fouling of the intake systems. An alternative to this would
be the manual cleaning of such intake systems (e.g. “pigging”). The issue of concern here is the
residual biocide concentration entering the marine environment at the point of discharge into the
marine environment. In the absence of the contractor being able to indicate the residual
concentrations entering the marine environment, data was obtained from a risk assessment for
cooling towers (Klaine et al., 1996) that indicated a profile of residual concentration of DBNPA at
discharge as indicated below.
Table 8.2: Likely profile of residual concentratio ns of DBNPA in discharges to the marine environment from the RO Plant. (after Klaine et al ., 1996)
Percentile Residual concentration
(mg. ℓ-1) 0 0.00
10th 0.01 20th 0.11 30th 0.27 40th 0.46 50th 0.65 60th 0.85 70th 1.05 80th 1.26 90th 1.53
100th 2.24
Although these concentrations are for cooling waters suggesting that these residuals may be
underestimated (DBNPA biodegrades more rapidly with higher temperatures), these concentrations
are likely to be representative of the RO Plant discharges to be assessed here as the initial dosing
assumed by Klaine et al. (1996) in developing these residual concentrations was 24 ppm compared
to the more modest 10 ppm proposed for the RO Plant.
The range of expected discharge concentrations indicated above, together with the guidelines
proposed in Table 8.1, suggest that the required dilution of the effluent containing non-oxidising
biocides in the marine environment would be in the same range as that required for oxidising biocides
(NaOCl), namely approximately 33 dilutions. For example, the highest residual concentration (2.34
mg.ℓ-1) and the upper water quality target value (0.07 mg.ℓ-1) suggest a required dilution of 32.
Similarly, the 80th percentile discharge concentration (1.26 mg.ℓ-1) and the more conservative of
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water quality target value (0.035 mg.ℓ-1) suggest a required dilution of 36 to meet the water quality
target values.
In the assessment that follows, the assessment thus is based on an achievable dilution of
approximately 33. This means that all of the information and analyses for oxidising biocides (based
on an initial residual chlorine discharge concentration of 0.1 mg. ℓ-1 that is diluted by a factor of 33 to
meet the proposed water quality guideline of 3 µg. ℓ-1) are also of direct relevance to the assessment
of the proposed non-oxidising biocide (DBNPA). In all of the text that follows, where reference is
made to the water quality guideline for residual chlorine of 3 µg.ℓ-1 being achieved, it can be assumed
that it also implies that the proposed water quality guidelines for DBNPA have also been achieved.
For this reason any reference to chlorine as a biocide and the achievement of the 3 µg. ℓ-1 water
quality target value for residual chlorine can be assumed to refer to, and be relevant to, the
assessment of both oxidising biocides (chlorine and the non-oxidising biocide (DBNPA) proposed for
use in the RO Plant.
Note that the validity of the assessment for DBNPA necessarily implies that the dosing of DBNPA will
be controlled and adjusted to ensure that the residual DBNPA concentrations meet those suggested
in the Table 8.2 above, i.e. for assumed water quality guidelines or target values of of 0.035 mg. ℓ-1
and 0.07 mg. ℓ-1 (and assuming that the biocide plume dimension delineated by the 33 x dilution
contour are acceptable), the residual concentration of DBNPA in the effluent should not exceed
figures of between 1.15 mg.ℓ-1 and 2.475 mg.ℓ-1). However due to the uncertainties in the exact
residual concentration of DBNPA at the point of discharge it is assumed that there is an undertaking
that the dosing levels and dosing regimes will be adjusted to ensure that any potential environmental
impacts of significance will be avoided. The monitoring and toxicity testing proposed (Section 9) is
designed to provide the requisite information to ensure this. If required, it is possible to reduce the
residual DBNPA concentrations by designing the brine basin so as to ensure greater and sufficient
dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an
oxidising biocide (chlorine) in this role. DBNPA can also be neutralised by the addition of Sodium
Metabisulfate, however this option is not presently under consideration.
As stated above, although not presently considered an option for the RO Plant, we have also
considered and assessed the use of chlorine as a biocide. For this purpose we have assumed that
sodium hypochlorite (NaOCl) as an oxidising biocide will be added at a constant concentration of
approximately 1.0 ppm in the inlet water and that it is proposed to discharge the brine directly into the
sea.
There is thus the potential for residual quantities of chlorine and its degradation/transformation
products to be present in the effluents. The concentration of freely available chlorine (FAC) or
residual chlorine at the outlet is specified to be approximately 0.1 mg.ℓ-1 or 0.1 ppm. However, in
extreme cases, outlet concentrations may attain 2.0 mg.ℓ-1 if shock doses are used to clean the plant
(e.g. Stenton-Dozey and Brown, 1994). (It should be noted that modern plants often operate on
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polyamide membranes, which are sensitive to Oxidising chemicals such as chlorine. Neutralization is
then typically required before the feedwater enters the RO unit. Under these circumstances it can be
assumed that the brine does not contain free residual chlorine).
The chemistry associated with seawater chlorination is complex and only a few of the reactions are
given below, summarized from White (1986), DWAF (1995) and ANZECC (2000). Chlorine does not
persist for extended periods in water but is very reactive. Its by-products, however, can persist for
longer.
The addition of sodium hypochlorite to seawater results in the formation of hypochlorous acid:
NaOCl + H2O → HOCl + Na+ + OH-
Hypochlorous acid is a weak acid, and will undergo partial dissociation as follows:
HOCl → H+ + OCl-
In waters of pH between 6 and 9, both hypochlorous acid and hypochlorite ions will be present; the
proportion of each species depending on the pH and temperature of the water. Hypochlorous acid is
significantly more effective as a biocide than the hypochlorite ion. Seawater chlorination differs
greatly from that of fresh water primarily due to the high bromide concentration of seawater (average
bromide concentration in seawater is 67 mg.ℓ-1). In the presence of bromide, chlorine instantaneously
oxidises bromide to form hypobromous acid:
HOCl + Br- → HOBr + Cl--
Hypobromous acid is also an effective biocide. It is worth noting that, for a given pH value, the
proportion of hypobromous acid relative to hypobromite is significantly greater than the corresponding
values for the hypochlorous acid - hypochlorite system. Thus, for example, at pH 8 (the pH of
seawater), hypobromous acid represents 83% of the bromine species present, compared with
hypochlorous acid at 28%. Hypobromous acid can also disproportionate into bromide and bromate
which is accelerated by sunlight.
Naturally occurring organic substances (e.g. ammonia) contribute to a major part of oxidant
consumption, i.e. chlorine reacts readily with nitrogenous substances (e.g. ammonia) to form N-
chlorinated compounds, which constitute the combined chlorine. These compounds are more
persistent than the free chlorine. The reaction of hypochlorous acid with ammonia results in the
formation of chloramines. The formation of chloramine species is dependent on pH, temperature,
contact time and the relative concentrations of chlorine and ammonia. Essentially, any free chlorine
will be converted to monochloramine at pH 7 to 8 when the ratio of chlorine to ammonia is equimolar
(5:1 by weight) or less. At higher chlorine to ammonia ratios, or lower pH values, dichloramine and
trichloramine will be formed. When ammonia is present, the competing reactions of chlorine with
bromide and ammonia are likely to result in the rapid formation of both monochloramine and
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hypobromous acid. In coastal seawater, ammonia concentrations are usually lower (typically less
than 28 µg N.ℓ-1) and therefore hypobromous acid is the main species. However, when ammonia
increases, bromamines (tri-and di-bromamines) may be formed. These bromamines are highly
oxidising species and disappear rapidly to form organic bromamines. Chlorine can also react with
nitrogen-containing organic compounds, such as amino acids to form organic chloramines. Little is
known about the biocidal properties of these compounds.
In natural waters, chlorine can undergo a range of reactions in addition to those discussed above. It
will react with inorganic constituents of water such as iron (II), manganese (II), nitrite and sulphide.
The reaction of chlorine with organic constituents in aqueous solution can be grouped into several
types:
(a) Oxidation,
where chlorine is reduced to chloride ion, e.g. RCHO + HOCl → RCOOH + H+ + Cl-
(b) Addition,
to unsaturated double bonds, e.g. RC = CR' + HOCl → RCOHCClR'
(c) Substitution,
to form N-chlorinated compounds, e.g. RNH2 + HOCl → RNHCl + H2O
or C-chlorinated compounds, e.g. RCOCH3 + 3HOCl → RCOOH + CHCl3 + 2H2O
Chlorine substitution reactions can lead to the formation of halogenated compounds, such as
chloroform (e.g. reaction c), and, where HOBr is present, mixed halogenated and brominated organic
compounds. Although such reactions are significant in terms of the resultant halogenated by-
products, it has been estimated that only a few percent of the applied chlorine ends up as
halogenated organic products. Chlorine is a powerful oxidant, and a significant proportion of the
applied chlorine is likely to be consumed in reactions such as (a), leading to the formation of non-
halogenated organic products, with chlorine being reduced to chloride.
A number of other source water characteristics are likely to have an impact on the concentrations of
organic by-products present in brine water discharges: natural organic matter in water is the major
precursor of halogenated organic by-products, and hence the organic content of the source water
(often measured as total organic carbon, TOC) may affect the concentration of by-products formed.
In general, the higher the organic content of the source water, the higher the potential for by-product
formation. The ammonia concentration is likely to affect the extent of by-product formation, through
reaction with chlorine to form chloramines. Although seawater generally contains lower
concentrations of ammonia than freshwater, under certain conditions (dependent on chlorine
dose:ammonia nitrogen concentration) it can compete with bromide for the available chlorine to form
monochloramine. In addition, hypobromous acid can react with ammonia to form bromamines.
Although the sequence of reactions is complex, it is likely that the reaction of either hypochlorous or
hypobromous acid with ammonia to form halamines will reduce organic by-product formation during
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the chlorination of seawater. The pH of the incoming feed-water could also affect the nature of the
by-products formed. In general, while variations in pH are likely to affect the concentrations of
individual by-products, the overall quantity formed is likely to remain relatively constant.
The presence of certain pollutants in source waters could lead to an increase in the levels of certain
halogenated organics. The presence of phenol, for example, can lead to the formation of
chlorophenols, some of which can taint fish flesh at concentrations as low as 0.001 mg.ℓ-1 (DWAF
1995). Currently, there is no evidence of contamination of the source waters with phenol (Atkinson et
al., 2006).
Paradoxically, chlorine chemistry thus establishes that no free chlorine is found in chlorinated
seawater where bromide oxidation is instantaneous and quantitative. However, the chlorinated
compounds, which constitute the combined chlorine, are far more persistent than the free chlorine.
After seawater chlorination, the sum of free chlorine and combined chlorine is referred to as total
residual chlorine (TRC).
Marine organisms are extremely sensitive to residual chlorine, making it a prime choice as a biocide
to prevent the fouling of marine water intakes. Many of the chlorinated and halogenated by-products
that are formed during seawater chlorination (see above) are also carcinogenic or otherwise harmful
to aquatic life (Latteman and Höpner, 2002; Einav et al., 2002). Values listed in the South African
Marine Water Quality Guideline (DWAF 1995) show that 1500 µg.ℓ-1 is lethal to some phytoplankton
species, 820 µg.ℓ-1 induced 50% mortality for a copepod and 50% mortality rates are observed for
some fish and crustacean species at values exceeding 100 µg.ℓ-1 (see also ANZECC, 2000). The
lowest values at which lethal effects are reported are 10 – 180 µg.ℓ-1 for the larvae of a rotifer,
followed by 23 µg.ℓ-1 for oyster larvae (Crassostrea virginica). Sublethal effects include valve closure
of mussels at values <300 µg.ℓ-1 and inhibition of fertilisation of some urchins, echiuroids, and
annelids at 50 µg.ℓ-1. Eppley et al. (1976) showed irreversible reductions in phytoplankton
production, but no change in either plankton biomass or species structure at chlorine concentrations
greater than 10 µg.ℓ-1. Bolsch and Hallegraeff (1993) showed that chlorine at 50 µg.ℓ-1 decreased
germination rates in the dinoflaggelate Gymnodinium catenatum by 50% whereas there was no
discernable effect at 10 µg.ℓ-1. This indicated that particularly the larval stages of some species may
be vulnerable to chlorine pollution. The minimum impact concentrations reported in the South African
water quality guidelines are in the range 2 to 20 µg.ℓ-1 at which fertilisation success in echinoderm
(e.g. sea urchin) eggs is reduced by approximately 50% after 5 minute exposures. ö
For the assessment that follows a conservative water quality guideline or target value of < 3 µg.ℓ-1
(ANZECC, 2000) is used for oxidising biocides (NaOCl) and the guidelines indicated in Table 8.1
used for the non-oxidising biocide DBNPA). In all text that follows, reference to biocides implies
either chlorine or DBNPA and the reference to target values or water quality guidelines constitutes a
reference to the respective guidelines for either chlorine or DBNPA. Similarly while reference in the
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Figures contained in Appendix C refers specifically to the target value of 3 µg.ℓ-1 for chlorine, it should
be taken also to refer to the relevant target values for DBNPA.
Site 1:
At Site 1 there the discharge is planned to occur via a pipeline along a 30 m length of the revetment
of the reclaim dam at a location approximately 80 m from the low water mark of the adjacent
shoreline where the water depth adjacent to the revetment is ~ 1.5 m.
The model results for the pipeline discharge indicate that the maximum extent of exceedance of the
target value for biocide is restricted to an area of ~160 m to 180 m radius around the discharge outlet
(Figure C1.7b and f), but this is expected to occur only for a total of 0.25% of the summer and/or calm
weather period (i.e, a cumulative total of 6 hours within a season comprising 90 days). The target
value could however be exceeded within a 120 m radius of the discharge point for up to 5 days within
all seasons (Figures C1.7b,d and f).
During periods of little or no stratification (e.g. winter) the biocide plume footprint is significantly
smaller due to greater mixing of the plume throughout the vertical extent of the water column. Due to
the restricted size of the plume footprint, this impact is assessed to be of low significance, even under
the ‘worst-case-scenario’.
Site 2:
The discharge alternatives at Site 2 constitute either a surf-zone discharge or a single port diffuser at
between -0.5 m to -1 m below chart datum and 20-25 m from the shoreline. Modelling results
indicate that the biocide plume will be restricted to an area of ~400 to 550 m radius around the
discharge outlet (Figure C2.7b and f), but this is expected to occur only for a total of 0.25 % (i.e. a
cumulative duration of approximately 6 hours of the season) of the calm weather period. The target
value could however be exceeded within a 220 to 450 m radius of the discharge point for up to 5
days within the summer season and or calm autumn period (Figure C2.7b and f). Given the
limitations in the resolution of the modelling study, a conservative assumption would be to assume
that the target value for residual concentrations of biocide could be exceeded regularly within a
minimum radius of 50 m of the discharge point, although this is not necessarily the case.
The size of the plume footprint thus is relatively constrained. Consequently, the impact can be
regarded as being of low significance. However it should be recognised that the discharge for Site 2
is occurring into the relatively poorly-flushed Small Bay system that supports a number of mariculture
activities and would inherently pose greater risks than the other sites considered. This is particularly
true given the many potential biocide-related compounds that could be formed and the high nutrient
wastes (nitrogeous compounds) from these mariculture and fish processing activities in Small Bay.
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Site 3:
The discharge alternatives at Site 3 constitute a single port diffuser at either 1) approximately -8 m
below CD into Small Bay, 2) at -4 m below CD into Big Bay, or 3) at approximately -16 to -18 m below
CD at Caisson 3. These will be located alongside the iron-ore causeway at distances ranging
between approximately 50 to 70 m from the causeway. In the modelling study these are defined as
Site 3(a) (discharge into Small Bay), Site 3(b) (discharge into Big Bay) and Site 3(c&d) (discharge at
Caisson 3). In all cases, the model results indicate that the plume is restricted to within 120 m of the
outlet near the seabed in summer (when the water column is highly stratified and vertical mixing
limited) and a nominal 50 m radius in the other seasons. Only in the case of the Big Bay discharge
does the plume footprint marginally exceed a nominal 50 m radius of the discharge in seasons other
than summer.
All of the discharge options have negligible biocide footprints when compared to those at the
Alternative Sites 1 and 2, and are therefore considered to be of low significance.
8.1.3.5 Co-discharged Waste Water Constituents
Table 8.3 provides a list of chemicals used in the pre-treatment, or cleaning (CIP = Clean in Place)
process of the RO membranes. Some of the pre-treatment chemicals will be co-discharged with the
brine. This list is compiled from the information provided in the Tender applications for the
construction of the RO plant. The potential impact of biocides is discussed in the previous section;
this section deals with the other potentially co-discharged constituents of the effluent.
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Table 8.3: Potential chemicals used for the Reverse Osmosis process - information as supplied by Transnet on 5 December 2007. Quantitie s based on intakes flows of 8000 m3.day -1.
Substance Quantity Method of Storage Additional Notes
Sodium hypochlorite (NaOCl)
If utilized dosing will be
333 kg.day-1 (12% solution) that is equivalent to
40 kg.day-1 (100% solution)
58 kg.day-1 (12% solution) that is equivalent to
7 kg.day-1 (100% solution)
3333 ℓ storage tank
100 ℓ storage tank
Direct intake cleaning only & discharged with
brine (presently not under consideration as it is proposed to used
a non-oxidising biocide for this purpose)
Treating the Permeate (Fresh Water) after RO
membranes
Non-oxidising biocide DBNPA – 2.2 Dibromo-3-nitrilopropionamide (Hydrex 4202)
Design: 4 kg.day-1
Max: 7 kg.day-1
98% solution storage capacity of
100 litres
Filtration shock dosing Injected before DMF& discharged with brine
Flocculant Ferric Chloride (FeCl3)
Design: 65 kg.day-1 (40% solution) that is equivalent to 26 kg.day-1 (100% solution)
Max: 108 kg.day-1 (40%
solution) that is equivalent to 43 kg.day-1 (100% solution)
40 % solution storage capacity of
100 litres
Filtration dosing Injected before DMF & discharged with brine
Anti-scalant (SWRO) Hydrax 4104
Design: 22 kg.day-1
Max: 32 kg.day-1
100 ℓ storage tank Dosed before the RO membranes DMF &
discharged with brine
Calcium Hydroxide or Sodium Hydroxide (Caustic soda)
Design: 0.16 kg.day-1
Maximum of 0.5 kg.day-1
1000 ℓ polypropylene tank
Product water stabilization, pH Control, dissolve
organic substances and silica
Limestone (Calcium Carbonate)
Design: 39 kg.day-1 (92% solution) that is equivalent to 36 kg.day-1 (100% solution)
Max: 47 kg.day-1 (92% solution that is equivalent to 43 kg.day-1
(100% solution)
100 ℓ storage tank
Water remineralisation i.e. treating the
Permeate (Fresh Water) after RO
membranes
Citric acid H3C6H5O7.H2O
Design: 2.5 kg.day-1 (100%) Max: 9.9 kg.day-1 (100%)
100 ℓ storage tank
CIP Chemicals (low pH)
Direct intake cleaning Discharged to sewage
or waste system
Hydrochloric acid (HCL) Design: 0.3 kg.day-1 (32%)
or 0.05 kg.day-1 (100%) 100 ℓ storage tank
CIP Chemicals (high pH)
Direct intake cleaning Discharged to sewage
or waste system
Ethylenediaminetetraacetic Acid (EDTA)
Design: 1.6 kg.day-1 (100%) Max: 6.6 kg.day-1 (100%)
100 ℓ storage tank
CIP Chemicals (high pH)
Direct intake cleaning Discharged to sewage
or waste system
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Substance Quantity Method of Storage Additional Notes
Ammonium hydroxide (NaOH)
Design: 0.16 kg.day-1 (25% solution) equivalent to
0.05 kg.day-1 100 ℓ storage tank
CIP Chemicals (high pH)
Direct intake cleaning Discharged to sewage
or waste system
Sodium lauryl sulphate (SLS)
Design: 0.2 kg.day-1 (100%) Max: 0.7 kg.day-1 (100%)
100 ℓ storage tank
CIP Chemicals (high pH)
Direct intake cleaning Discharged to sewage
or waste system
Sodium Metabisulfate (SMBS)
Design: 1.6 kg.day-1 (100%) 100 ℓ storage tank
Presevration of RO membranes
Discharged to sewage or waste systems
Coagulants like ferric chloride (FeCl3) are used as part of the pre-treatment process to cause
particles in feed-water to form larger masses that can be more easily removed with filters before the
water passes through to the RO membranes. Coagulant aids (organic substances with high
molecular masses that bridge particles further together) and pH control (Calcium Hydroxide or
Sodium Hydroxide) are supplementary methods to enhance coagulation. These chemicals generate
a by-product of coagulated/flocculated materials that become entrapped within the filter-medium and
can be removed only by water-backwashing. The pre-treatment filters are backwashed with filtered
seawater every few days, producing a sludge that contains mainly sediments and organic matter, and
filter coagulant chemicals. According to the project description, a continuous dosage of approximately
8.13 mg.ℓ-1 is anticipated for the intake flow rates of 8000 m3.day-1. The discharge volume of the sludge
discharge is 336 m3.day-1 (total for 3 RO modules), however the concentration of the material in the
backwash presently is unknown. However, it is reasonable to assume that the full 65 kg.day-1 of
flocculant added will be discharged together with the brine discharge at a nominal flocculant
concentration of approximately 14.8 mg.ℓ-1. Acute toxic effects of the sludge are generally not
expected, but some evidence suggests that chronic effects could occur (Sotero-Santos et al., 2007,
e.g. reduction of fecundity in Daphnia). However, ferric chloride may cause a discoloration of the
receiving water, and the sludge discharge may lead to increases in turbidity and suspended matter.
Impacts such as reduced primary production or burial of sessile organisms by increased turbidity in
the discharge may thus occur (Sotero-Santos et al., 2007, http://www.paua.de/Impacts.htm). A
process for removal of the particles is thus recommended before discharge of the sludge. The
proposed RO plant design specifications indicate that the DMF backwash (sludge) will be blended
with the brine, a viable but less desirable alternative.
Scaling on inside tubes or on RO membranes impairs plant performance. Anti-scalants are
commonly added to the feed-water in RO plants to prevent scale formation. The main
representatives of anti-scalants are organic, carboxylic-rich polymers such as polyacrylic acid and
polymaleic acid. Acids and polyphosphates are still in use at a limited scale but on an increasingly
limited scale as they can cause eutrophication through formation of algal blooms and macro algae
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(DWAF, 2007). According to the initial list of chemicals provided, potential anti-scalant products are
Avista Vitec 3000, and Flocon 135, which is a phophinocarboxylic acid. Both products are certified
by the National Sanitation Foundation (NSF) under ANSI/NSF Standard 60 for use in producing
potable water. Polymer antiscalants have similar properties to natural humic matter or Gelbstoffe,
which are common seawater constituents (Latteman and Höpner, 2002). They have high molecular
weight, multiple carboxylic groups, metal-ion binding capacity and a high stability. LC50 values are
relatively high (generally exceeding 1,000 ppm, see Latteman and Höpner, 2002), which indicates a
low toxicity and is far above the typical dosage in desalination plants. An acute environmental risk
associated with their release into the marine environment is thus expected to be relatively low. Due
to a poor degradability, however, dispersal and relatively long residence times must be expected,
during which it cannot be excluded that antiscalants will limit the availability of biologically essential
trace metal ions (Latteman and Höpner, 2002). It is unlikely (particularly in the quantities used in the
RO Plant) that anti-scalants will promote the accumulation of metals in the sediments.
The cleaning intervals (CIP) of the RO membranes are typically three to six months depending on the
quality of the plant's feed-water (Einav et al., 2002). The chemicals used in cleaning are mainly
weak acids and detergents. In RO plants, alkaline cleaning solutions (pH 11-12) are used for
removal of silt deposits and biofilms, whereas acidified solutions (pH 2-3) remove metal oxides and
scales. Further chemicals are often added to improve the cleaning process of RO membranes, such
as detergents, oxidants, complexing agents or biocides for membrane disinfection. Neutralization of
the extremely alkaline or acidic solutions and treatment of additional cleaning agents typically is
recommended before discharge to the ocean to remove any potential toxicity
(http://www.paua.de/Impacts.htm). The chemicals Sulphuric acid, Ethylenediaminetetraacetic acid
(EDTA), Sodium tripolyphosphate (STPP), Trisodium phosphate (TSP), and Sodium lauryl sulphate
(SLS) were specified as being used in the RO membrane cleaning (Table 8.3). Although it is
specified that these chemicals will not be discharg ed to the marine environment but rather
will enter the sewage system or be transported off- site, for completeness, a short summary of
the environmental fates and effects of these chemic als is given below.
Sulphuric acid (H2SO4) is used for pH adjustment in the desalination process to reduce the pH for the
acid wash cycle. It is a strong mineral acid that dissociates readily in water to sulphate ions and
hydrated protons, and is totally miscible with water. At environmentally relevant concentrations,
sulphuric acid is practically totally dissociated, sulphate is at natural concentrations and any possible
effects are due to acidification. This total ionisation will imply also that sulphuric acid, itself, will not
adsorb on particulate matters or surfaces and will not accumulate in living tissues
(http://www.chem.unep.ch/irptc/sids/oecdsids/7664939.pdf). Sulphuric acid can be acutely toxic to
aquatic life via reduction of water pH. Most aquatic species do not tolerate pH lower than 5.5 for any
extended period. No guideline values are available for this substance but No Observed Effect
Concentration (NOEC) values were developed from chronic toxicity tests on freshwater organisms
and range from 0.058 mg.ℓ-1 for fish populations to 0.13 mgℓ-1 for phytoplankton and zooplankton
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populations, respectively (http://www.chem.unep.ch/irptc/sids/oecdsids/7664939.pdf). As seawater is
highly buffered, the limited sulphuric acid discharges proposed (0.3 kg.day-1) are not expected to
have significant impacts in the marine environment.
EDTA is an aminopolycarboxylic salt that is used as a chelating agent to bind or capture trace
amounts of iron, copper, manganese, calcium and other metals. In water treatment systems, EDTA
is used to control water hardness and scale-forming calcium and magnesium ions to prevent scale
formation (http://www.dow.com/productsafety/finder/edta.htm). Because of the ubiquitous presence
of metal ions, it has to be assumed that EDTA is always emitted as a metal complex, although it
cannot be predicted which metal will be bound. EDTA will biodegrade very slowly under ambient
environmental conditions but does photodegrade. EDTA is not expected to bioaccumulate in aquatic
organisms, adsorb to suspended solids or sediments or volatilize from water surfaces (European
Union Risk Assessment Report 2004). Toxicity tests on aquatic organisms have shown that adverse
effects occur only at higher concentrations (the lowest concentrations at which an adverse effect was
recorded is 22 mg.ℓ-1) (European Union Risk Assessment Report, 2004). On the other hand, if trace
elements like Fe, Cu, Mn, and Zn are low in the natural environment, an increased availability of
essential nutrients caused by the complexing agent EDTA is able to stimulate algal growth. Heavy
metal ions in the water are complexed by free EDTA, and a comparison of the toxicity of those
compared to the respective uncomplexed metals and free EDTA have shown a reduction in toxicity
by a factor of 17 to 17000 (Sorvari and Sillanpää, 1996). Experiments (albeit with significantly higher
trace metal concentrations than are typically observed in the environment) indicate that EDTA
decreases the accumulation of metals such as Cd, Pb and Cu, however the absorption of Hg by
mussels is seemingly promoted through complexation with EDTA (Gutiérrez-Galindo, 1981, as cited
in the European Union Risk Assessment Report, 2004). Potential promotion of the accumulation of
metals in sediments is unlikely to be a concern as in high concentrations EDTA prevents the
adsorption of heavy metals onto sediments and even can remobilise metals from highly loaded
sediments (European Union Risk Assessment Report, 2004). Within the framework of marine risk
assessment, the European Union has published a risk assessment report in which a Predicted No
Effect Concentration (PNEC) of 0.64 mg.ℓ-1 was calculated (European Union Risk Assessment
Report, 2004).
The original formulation proposed for the high pH CIP cleaning solution to be used in the RO Plant
included sodium tripolyphosphate (STPP, Na5P3O10) and trisodium phosphate (TSP, Na3PO4).
However, due to concerns around high concentrations of phosphates entering the sewage or
wastewater systems, the high pH CIP cleaning solution to be used in the RO Plant has been re-
formulated to exclude STPP and TSP. Nevertheless a description STPP and TSP and their potential
impacts of have been retained in the report. This both provides information on the alternatives that
have been considered for the high pH CIP cleaning solution to be used in the RO Plant and the
reason for the concern around the concentrations of phosphates entering the sewage or wastewater
systems should STPP and/or TSP be used.
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Sodium tripolyphosphate (STPP, Na5P3O10) is the sodium salt of triphosphoric acid, and is a typical
ingredient of household cleaning products, and is thus present in domestic waste waters. STPP is an
inorganic substance that when in contact with water (waste water or natural aquatic environment) is
progressively hydrolysed by biochemical activity, finally to orthophosphate. Acute aquatic ecotoxicity
studies have shown that STPP has a very low toxicity to aquatic organisms (all EC/LC50 are above
100 mgℓ-1) and is thus not considered as environmental risk (HERA, 2003). The final hydrolysis
product of STPP, orthophosphate, however, can lead to eutrophication of surface waters due to
nutrient enrichment, phosphate as a nutrient is not limiting in marine environments such as Saldanha
Bay unless there are significant inputs of nitrogen (nitrates, ammonia) that is the limiting nutrient in
such systems. In addition to the hydrolysis into orthophosphate, STPP can, depending on the
presence of cationic ions, precipitate in the form of insoluble calcium, magnesium or other metal
complex species (HERA, 2003).
Trisodium phosphate (TSP, Na3PO4) is a highly water-soluble cleaning agent. When dissolved in
water it has an alkaline pH. The phosphate can act as a plant nutrient, and can thus increase algal
growth, however, as noted above, phosphate as a nutrient is not limiting in marine environments such
as Saldanha Bay unless there are significant inputs of nitrogen (nitrates, ammonia) which is the
limiting nutrient in such systems. Phosphate is classified as not acutely toxic to aquatic organisms
(http://www.pesticideinfo.org/Detail_Chemical.jsp?Rec_Id=PC34419).
Sodium lauryl sulphate (SLS) (C12H25NaO4S) is an anionic surfactant, which is a class of chemicals
used for their detergent properties. SLS is biodegradable in surface waters, and biodegradation
ranges from 45 to 95% within 24 hours. Products of SLS biodegradation are carbon dioxide or
saturated fatty acids. SLS is classified as a substance of low environmental toxicity with low
bioaccumulation (OECD, 1997).
Typically the rinse water is kept in a titration container and after being treated (titration, neutralization
of the cleaning materials), it is disposed off by transporting it in closed containers to an authorized
salt disposal site. Alternatively, it is injected by continuous flow of small quantities into the brine and
discharged into the sea in the effluent (Einav et al., 2002). Transnet has undertaken to not co-
discharge these waters with the brine discharge.
In summary, the toxicity of the various chemicals u sed in the pre-treatment and CIP process
(aside from biocides) is relatively low, and none o f the products are listed as tainting
substances (DWAF, 1995). Of concern is more the po tential increase in turbidity (backwash-
sludge). To reduce the impact on the marine enviro nment, it is recommended that
particulates are removed from the backwash sludge. Whether this is necessary and/or the
extent to which this is necessary at the various pr oposed discharge locations, will be
informed by the results of the monitoring programme proposed for the brine discharge.
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The waste brine often contains low amounts of heavy metals that pass into solution when the plant's
interior surfaces corrode. In RO plants, non-metal equipment and stainless steels are typically used.
The RO brine may therefore contain traces of iron, nickel, chromium and molybdenum, but
contamination levels are generally low (Hashim and Hajjaj, 2005; http://www.paua.de/Impacts.htm).
Heavy metals tend to enrich in suspended material and finally in sediments, so that areas of
restricted water exchange (e.g. the NE corner of Small Bay) and soft bottom habitats impacted by the
discharge could be affected by heavy metal accumulation. Many benthic invertebrates feed on this
suspended or deposited material, with the risk that metals are enriched in their bodies and passed on
to higher trophic levels. At this stage, no assessment of the potential concentration of heavy metals
can be provided, as it is an incidental by-product of RO plant processes and is likely to be low. It is
therefore recommended that limits are established for heavy metal concentrations in the brine
discharges (see Table 8.1), and the brine regularly monitored to avoid exceedance of these limits.
As the effluent is likely to consist of a combination of co-discharge constituents, namely Ferric
chloride and anti-scalants (and biocides that in this assessment have been considered separately
from other co-discharges), the approach taken in assessing their potential impacts has been to model
dilution rates. The specific concentrations of all of the co-discharges at the point of discharge are,
however, not known, so dilution factors of 50 and 100 were chosen as a conservative target value for
modelling exceedances. For example, the total residual chlorine added as a biocide at a
concentration of 100 µg.ℓ-1 (0.1 mg.ℓ-1) will need to be diluted by a factor of 33 to achieve a target
value of 3 µg.ℓ-1. The dilution threshold of 50 and 100 assumed for the co-discharge assessment
would be the equivalent of requiring that the biocides in the effluent discharge be reduced to 2 µg.ℓ-1
or less and 1 µg.ℓ-1 or less, respectively. The achievable dilution thresholds of 50 and 100 therefore
is considered a suitably conservative dilution ratio for assessing potential footprints of co-discharges
(even potential tainting constituents or by-products) in the effluent. It may, however, be that for
specific co-discharge constituents significantly greater or lesser dilutions are required. The exact
required dilution will depend on the discharge concentration and the relevant water quality target
value considered appropriate for the receiving environment. Presently, none of the co-discharges
that have been specified require such high dilutions.
All proposed intake points at the three alternative sites are located in the vicinity of the iron ore
causeway and its associated ship traffic, and there is therefore a risk of oil contaminating the feed-
water. Hydrocarbon contamination of the sediment in Saldanha Bay were measured in 1999 and
found to be very low, and were not considered to pose an ecological risk (Atkinson et al., 2006).
Similar, but more extensive sampling and analyses in Big Bay (CSIR, 2007) confirm that there are
limited hydrocarbons present in the sediments. However, the potential for an oil spill accident or
contamination has to be taken into account. Oil contamination can not only affect the quality of the
potable water but can also foul the seawater intake filter, hence limiting the amount of water intake.
Internal membranes may also be fouled and disrupt the reverse osmosis process (Al Malek and
Mohamed, 2005). The direct intake structure (pipeline) will be ~ -1 m CD (i.e. on average
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approximately 1.9 m below MSL) and since spilled oil is mostly confined to surface waters, the risk of
an intake of oil is reduced. However, depending on the oil type and weather conditions, significant
quantities of oil may be dispersed into the water column. For beach wells to be affected, significant
contamination of beach sediments would have to occur, thus intake waters from beach wells are
unlikely to be subject to levels of hydrocarbon contamination that would be of concern.
Site 1:
At Site 1 the discharge is planned to occur via a pipeline along a 30 m length of the revetment of the
reclaim dam at a location approximately 80 m from the low water mark of the adjacent shoreline
where the water depth adjacent to the revetment is ~ 1.5 m.
At Site 1 the model results for this discharge configuration indicate that during the periods when there
is the least dispersion of effluent in the bottom layers, i.e. during summer (Figure 1.10b) or a calm
weather period (Figure 1.10f), a dilution of 50 will be exceeded beyond an area of 360 x 230 m
around the outfall for 99% of the time (all but 6 hours during a season) and beyond an area of 190 m
x 120 m for 95% of the time (i.e. all but approximately 5 days during a season). For an achievable
dilution less than 100 this will be restricted to a footprint of 120 x 50 m or less for 50% of the time.
Similarly during the same periods (Figure C1.9b and 1.9f), a dilution of 100 will be exceeded beyond
an area of 500 x 350 m around the outfall for 99% of the time (all but 6 hours during a season) and
beyond an area of 430 m x 250 m for 95% of the time (i.e. all but approximately 5 days during a
season). An achievable dilution less than 100 this will be restricted to a footprint of 130 x 60 m or
less for 50% of the time.
During periods of little or no stratification (e.g. winter) the co-discharge plume footprint is significantly
smaller due to greater mixing of the plume throughout the vertical extent of the water column. Unlike
for other water quality parameters such as salinity, the spatial extent of the “footprint” of the
discharge plume (i.e. non-exceedance of an achievable dilution of 50) in the surface waters is largely
similar to that at depth however the dilutions in the surface water significantly exceed those at depth.
Due to the restricted size of the plume footprint, this impact is assessed to be of low significance,
even under the ‘worst-case-scenario’. The assessment of low significance is particularly
applicable as the CIP cleaning chemicals will not b e discharged with the brine.
Site 2:
The discharge alternatives at Site 2 constitute either a surf-zone discharge or a single port diffuser at
between -0.5 m to -1 m below chart datum and 20 to 25 m from the shoreline. Modelling results
indicate that the co-discharge plume will be diluted by a factor of 50 or more beyond an area
extending 640 m offshore and 320 m during calm periods (Figure C2.10f) and beyond an area of
550 m alongshore and 500 m offshore during summer (Figure C2.10b). A dilution of 50 will be
exceeded for 95% of the time beyond an area of 300 x 300 m around the outfall during summer and
beyond an area of 550 m x 280 m during the calm autumn period. Achievable dilutions exceeding 50
will be achieved 50% of the time beyond a radius of ~300 m of the outlet Furthermore, modelling
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results indicate that the co-discharge plume will be diluted by a factor of 100 or more beyond an area
extending 800 m offshore and 700 m during calm periods (Figure C2.9f) and beyond an area of
600 m alongshore and 700 m offshore during summer (Figure C2.9b). A dilution of 100 will be
exceeded for 95% of the time beyond an area of 450 x 600 m around the outfall during summer and
beyond an area of 700 m x 500 m during the calm autumn period. Achievable dilutions exceeding
100 will be achieved 50% of the time beyond a radius of ~350 m of the outlet. Unlike for other water
quality parameters such as salinity, the spatial extent of the “footprint” of the discharge plume (i.e.
non-exceedance of an achievable dilution of 50 or 100 in the surface waters is largely similar in
shape to that at depth, however the dilutions in the surface water significantly exceed those at depth
The potential impacts of co-discharges can be regarded as being of low significance, provided that an
achievable dilution of 50 to 100 is sufficiently conservative for all co-discharge constituents and
potential by-products. This is the case for all co-discharges presently specified (See Table 8.3). The
assessment of low significance is particularly appl icable as the CIP cleaning chemicals will
not be discharged with the brine.
Site 3:
The discharge alternatives at Site 3 constitute a single port diffuser at either 1) approximately -8 m
below CD into Small Bay, 2) at -4 m below CD into Big Bay, or 3) at approximately -16 to -18 m below
CD at Caisson 3. These will be located alongside the iron-ore causeway at distances ranging
between approximately 50 to 70 m from the causeway. In the modelling study these are defined as
Site 3(a) (discharge into Small Bay), Site 3(b) (discharge into Big Bay) and Site 3(c&d) (discharge at
Caisson 3).
1) For a discharge into Small Bay, the model results indicate that a dilution of 50 will be
exceeded beyond an area of 240 x 100 m around the outfall for 99% of the time and beyond
an area of 100 m x 100 m for 95% of the time during the summer period (Figure C3.10b).
The plume dimension are similar (but slightly smaller) for the calm autumn period when the
water column is more stratified (Figure C3.10f). A dilution of 100 will be exceeded beyond an
area of 450 x 200 m around the outfall for 99% of the time and beyond an area of 260 m x
120 m for 95% of the time during the calm autumn period (Figure C3.9f). The results are
similar for the summer period when the water column is more stratified (Figure C3.9b).
2) For a discharge into Big Bay, the model results indicate that during summer (the worst case
result) a dilution of 50 will be achieved beyond an area 280 m x 150 m around the outfall for
99% of the time and beyond an area of 130 m x 100 m around the outfall for 95% of the time
(Figure C4.10b). During calm periods (the worst case result), a dilution of 100 will be
achieved beyond an area 420 m x 250 m around the outfall for 99% of the time and beyond
an area of 300 m x 210 m around the outfall for 95% of the time (Figure C4.9f).
3) For discharge at Caisson 3 (Site 3c&d) the model results indicate that the worst case results
occur for the calm autumn period. A dilution of 50 exceeded beyond an area 180 m x 170 m
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around the outfall for 99% of the time and beyond an area of 120 m x 120 m around the
outfall for 95% of the time (Figure C4.10bf). Dilutions exceeding 50 will be achieved beyond
a radius of 50 m of the discharge for 50% of the time. A dilution of 100 will be achieved
beyond an area 330 m x 320 m around the outfall for 99% of the time and beyond an area of
230 m x 230 m around the outfall for 95% of the time (Figure C4.9f). Dilutions exceeding 100
will be achieved beyond a radius of 140 m of the discharge for 50% of the time.
All of the discharge options have negligible co-discharge footprints when compared to those at the
Alternative Sites 1 and 2, and are therefore considered to be of low significance. The assessment
of low significance is particularly applicable as t he CIP cleaning chemicals will not be
discharged with the brine.
8.1.3.6 Tainting Effects
Certain chemical constituents are known to taint seafood which may greatly influence the quality
and/or market price of cultured products. Possible tainting effects may affect mariculture activities,
gillnet fisheries and fish factory processing in the bay. Especially the mariculture industry is
extremely sensitive to tainting or even the perception of tainting, and there has thus to be absolute
certainty that such effects are unlikely to occur. Presently the project description as supplied by the
TNPA does not indicate the presence of any such tainting substances. The spatial extent of the
“footprint” of the discharge plumes is relatively localised, however, and in no case do they extend as
far as proposed mariculture activities in either Big Bay or Small Bay (Figure 5.10), or to seawater
intakes for fish factory processing, which are located in the west of Small Bay (Figure 5.12). For the
discharge at depth at Caisson 3, the high density brine is expected to sink to the bottom.
Consequently, mussel spat harvested in surface waters off the caissons during years of poor
recruitment are unlikely to be affected by the discharge. Although gillnet permit holders often fish in
the shallow surf-zone waters immediately adjacent to the iron-ore causeway (S. Lamberth, MCM,
pers. comm.), the limited extent of the discharge footprints at Sites 1 and 2 are unlikely to significantly
affect these activities.
8.2 Assessment of Potential Environmental Impacts
The potential impacts associated with construction activities, the operation of the plant (brine and co-
discharges) and the long-term impacts associated with the intake and discharge structures as
assessed below.
8.2.1 Assessment of Impacts During Construction
In the absence of engineering specifications detailing the construction of the intake and discharge
structures (both pipeline or beach wells, boreholes), the following assessment is based on generic
assumptions for such constructions. While beach macrofaunal communities may recover within 2
years, the precautionary principle has been adopted, and the duration of the impact has been rated
as medium. As a result, the outcome of the consequence and significance ratings become “Medium”.
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Should the final construction specifications be sufficiently different to those described above, the
impacts associated with the construction phase will need to be re-evaluated. For the intake structure
along the quayside for Site 3 and the proposed discharge structure at Caisson 3, the impacts will be
minimal as these construction activities will be utilising existing infrastructure as their basis and
construction activities will not be extensive. The construction of the borehole intakes along the
causeway are assumed to have no impact on the marine environment
8.2.1.1 Construction of Intake and Discharge Infrastructure
Construction of Intake Beach Wells (Site 1 and Site 2, i.e. development options 1a & 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation Local High Short -
Medium Medium Definite Medium -ve high provided assumptions
correct With mitigation
No significant mitigation possible other than avoiding beach well construction
Construction of Intake boreholes (Site 3, i.e. dev elopment options 3c & 3d))
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation Local Low Medium Low Definite Very low -ve
high provided assumptions
correct With
mitigation No mitigation required
Construction of Intake pipeline (Site 1 & Site 2, i.e. development options 1b & 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation
Local High Short - Medium
Medium Definite Medium -ve high provided assumptions
correct With
mitigation Limited mitigation is possible using “best practise” mitigation measures during construction. It is not possible to
propose specific mitigation measures based on existing known detail on construction activities
Construction of Intake pipeline (Site 3, i.e. deve lopment options 3a & 3b)
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation Local Low Short Very low probable Very low -ve
high provided assumptions
correct With
mitigation Limited mitigation is possible using “best practise” mitigation measures during construction. It is not possible to
propose specific mitigation measures based on existing known detail on construction activities
Construction of Discharge Pipeline (Site 2 and Site 3 for discharges into Small Bay and Big Bay only, i.e. development options 2a, 2b, 3a and 3b)
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation Local Low Short -
Medium Medium Definite Medium -ve high provided assumptions
correct
With mitigation
Limited mitigation is possible using “best practice” mitigation measures during construction. It is not possible to propose specific mitigation measures based on existing known detail of construction activities
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Construction of Discharge infrastructure (Site 1 an d Site 3 for discharge at Caisson 3. i.e. development options 1a, 1b, 3c and 3d)
Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation
Local Low Short Very low probable Very low -ve high provided assumptions
correct
With mitigation
No mitigation deemed necessary other than the use of “best practice” mitigation measures during construction. It is not possible to propose specific mitigation measures based on existing known detail of construction activities.
8.2.2 Assessment of Impacts Associated with Brine D ischarge
8.2.2.1 Alternative Site 1
At Site 1 several intake and discharge scenarios are under scrutiny. These include intake via
pipelines and beach wells but discharge via a pipeline. These different scenarios are assessed
separately below:
Salinity
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 1a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve High
With mitigation
No mitigation considered, other than optimal discharge diffuser design
B. Pipeline discharge with intake through intake pipeline (development option 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long-term Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
Temperature
A. Pipeline discharge with intake of feedwater from intake beach wells (development option 1a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term* Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
* The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum.
B. Pipeline discharge with intake through intake pipeline (development option 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term* Low Definite Low -ve High
With mitigation
No mitigation considered, other than optimal discharge diffuser design
* The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum.
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Dissolved Oxygen
The use of sodium metabisulfite as a neutralizing agent for chlorine presently is not proposed for the
Saldanha Bay RO plant as the use of chlorine as a biocide will be limited to the product (i.e.
freshwater produced). Nevertheless the consequences of its potential use, should chlorine ultimately
be considered as the biocide of choice, is assessed As its application is independent of the intake
and discharge scenarios being considered, the assessments below evaluate the potential impacts
both with the addition of an oxygen-scavenging compound as well as without the addition of the
substance.
A. No addition of oxygen-scavenging compounds (development options 1a & 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term* Low Definite Low -ve High
With mitigation
Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water
B: With addition of oxygen-scavenging compounds
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long-term Medium Definite Medium -ve High
With mitigation* Local None Long-term Very Low Definite Very Low -ve High
* Mitigation in this case would constitute aeration of the effluent prior to discharge
Oxidising Biocide (NaOCl)
A. Pipeline discharge with intake of feed-water from intake beach wells (development options 1a &
1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve High
With mitigation
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
B. Pipeline discharge with intake through intake pipeline (development options 1a & 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long-term Medium Definite Medium -ve High
With mitigation*
Local None Long-term Very Low Definite Very Low -ve High
* The mitigation proposed (if necessary and to be applied to the extent required) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however this does potential exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment
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Non-oxidising Biocide (DBNPA)
A. Pipeline discharge with intake of feed-water from intake beach wells (development options 1a &
1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve High
With mitigation
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
B. Pipeline discharge with intake through intake pipeline (development options 1a & 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long-term Medium Definite Medium -ve High
With mitigation*
Local None Long-term Low Definite Low -ve Medium
* The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
Co-discharged Constituents
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 1a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low* Long-term Low Definite Low -ve High**
With mitigation***
Local None Long-term Very Low Definite Very Low -ve High**
* Intensity is low in the marine environment provided that the undertaking that the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site. Particulates in backwash should be greatly reduced by the use of beach wells.
** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
*** Mitigation in unlikely to be required except for perhaps Site 2, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern. The assessment with mitigation assumes mitigation measures whereby particulates are removed from the flocculant/backwash sludge to the extent required and disposed elsewhere than the marine environment
B. Pipeline discharge with intake through intake pipeline (development option 1b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low* Long-term Low Definite Low -ve High**
With *** mitigation Local None Long-term Very Low Definite Very Low -ve High**
* Intensity and the ultimate impact significance is low in the marine environment provided that there is adherence to the undertaking that CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site is adhered to.
** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description.
*** The mitigation is to remove at least large particles from the flocculant sludge/backwash to the extent that may be required, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern.
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8.2.2.2 Alternative Site 2
At Site 2 several intake and discharge scenarios are considered. These include intake via beach
wells or pipelines with discharge via a pipeline. These different scenarios are assessed separately
below:
Salinity
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
B. Pipeline discharge with intake through intake pipeline (development option 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve High
With mitigation
No mitigation considered, other than optimal discharge diffuser design
Temperature
A. Pipeline discharge with intake of feedwater from intake beach wells (development option 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low/Medium* Long-term** Low/Medium Definite Low/Medium -ve High
With mitigation No mitigation specified/considered, other than optimal discharge diffuser design
* Intensity could be considered to be medium in that it does exceed the ANZECC guidelines over a small area around the discharge. Based on the South African Water quiality guideline of ∆< 1ºC the plume impinges marginally on eastern boundary of the area demarcated for seaweed harvesting and then only for a total duration of approximately 24 hours per season. Note that the intensity of the thermal impacts at Site 2 may be reduced and assumed to be low i) given appropriate engineering design mitigation (i.e. assuming that it would be possible to locate the pipeline intake in a manner that would ensure sufficiently lower seawater temperatures at the intake) or ii) if it is assumed that beach well intake water temperatures are lower that the near surface water temperatures assumed in the modelling.
** The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum.
B. Pipeline discharge with intake through intake pipeline (development option 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low/Medium* Long-term** Low/Medium Definite Low/Medium -ve High
With mitigation
No mitigation specified/considered, other than optimal discharge diffuser design, however the thermal footprint for this site is significantly larger than the other sites**
* Intensity could be considered to be medium in that it does exceed the ANZECC guidelines over a small area around the discharge. Based on the South African Water quiality guideline of ∆< 1ºC the plume also impinges marginally on eastern boundary of the area demarcated for seaweed harvesting and then only for a total duration of approximately 24 hours per season. * With engineering design mitigation (i.e. assuming that it would be posible to locate the pipeline intake in a manner that would ensure suffieciently lower seawater temperatures at the intake) or assuming that beach well intake water temperatures will be lower that the near surface wtaer temperatures assumed in the modelling, the intensity of the thremal impacts may be reduced and assumed to be low.
** The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum. The
significance of this impact is low, however should mitigation be deemed to be necessary at Site 2, the mitigation would be to locate the intake to ensure lower seawater temperatures at the intake. This would, however, most likely lead to lower plant efficiencies.
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Dissolved Oxygen
The use of sodium metabisulfite as a neutralizing agent for chlorine presently is not proposed for the
Saldanha Bay RO plant as the use of chlorine as a biocide will be limited to the product (i.e.
freshwater produced). Nevertheless the consequences of its potential use, should chlorine ultimately
be considered as the biocide of choice, is assessed As its application is independent of the intake
and discharge scenarios being considered, the assessments below evaluate the potential impacts
both with the addition of an oxygen-scavenging compound as well as without the addition of the
substance.
A. No addition of oxygen-scavenging compounds (development options 2a & 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long-term* Low Definite Low -ve High
With mitigation Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water
B: With addition of oxygen-scavenging compounds
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long-term Medium Definite Medium -ve High
With mitigation* Local None Long-term Very Low Definite Very Low -ve High
* Mitigation in this case would constitute aeration of the effluent prior to discharge
Oxidising Biocide (NaOCl)
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser
design
B. Pipeline discharge with intake through intake pipeline (development option 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local* Medium Long-term Medium Definite Medium -ve High
With mitigation** Local None Long-term Very Low Definite Very Low -ve High
* Although local the achievable dilutions are significantly lower than the other sites. This poses greater risks in terms of potential impacts by cumulative, synergistic effects of pollutants as well as potential by-products of biocides.
** The mitigation proposed (if deemed necesarry) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however this does potentially exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment
Non-oxidising Biocide (DBNPA)
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
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B. Pipeline discharge with intake through intake pipeline (development option 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local* Medium Long-term Medium Definite Medium -ve High
With mitigation**
Local None Long-term Low Definite Low -ve Medium
* Although local the achievable dilutions are significantly lower than the other sites. This poses greater risks in terms of potential impacts by cumulative, synergistic effects of pollutants as well as potential by-products of biocides.
** The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
Co-discharged Constituents
A. Pipeline discharge with intake of feed-water from intake beach wells (development option 2a)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local* Low** Long Low Definite Low -ve High***
With mitigation**** Local None Long Very Low Definite Very Low -ve HIgh***
* Although local the achievable dilutions are significantly lower than at the other sites. This poses greater risks in terms of potential impacts by cumulative, synergistic effects of pollutants as well as potential by-products of biocides or co-discharges
** Intensity is low in the marine environment provided that the undertaking that the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site. Particulkates in backwash should be greatly reduced by the use of beach wells.
*** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
**** The mitigation is to remove at least large particles from the flocculant sludge, however this is unlikely to be necessary unless the discharge of the backwash materials proves prolematic.
B. Pipeline discharge with intake through intake pipeline (development option 2b)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local* Low/Medium** Long Low/Medium Definite Low/Medium -ve High***
With **** mitigation Local None Long Very Low Definite Very Low -ve High***
* Although the impact remains local, the achievable dilutions are significantly lower than at the other sites. This poses greater risks in terms of potential impacts by cumulative, synergistic effects of pollutants as well as potential by-products of biocides or co-discharges
** Intensity is low in the marine environment provided that the undertaking that the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site. However, in the relatively quiescent environment of Site 2 however, backwash and flocculant material will not be dispersed to the same extent at other sites and thus pose greater water and sediment quality risks than at other proposed sites, suggesting a medium intensity rating.
*** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
***** The mitigation is to remove at least large particles from the flocculant sludge/backwash to the extent that may be required, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern.
8.2.2.3 Alternative Site 3
At Site 3 several intake and discharge scenarios are under scrutiny. These include intake and
discharge via pipelines, with two discharge options being considered, namely a bottom discharge
though a single or multi-port diffuser at ~8 m depth into Small Bay and a discharge though a single or
multi-port diffuser at ~4 m depth into Big Bay. An additional scenario considers intake of the feed-
water through two alternative boreholes situated on the quay, with a subsequent pipeline discharge at
-17 m into Big Bay at Caisson 3. These different scenarios are assessed separately below:
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Salinity
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation
No mitigation considered, other than optimal discharge diffuser design
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation
No mitigation considered, other than optimal discharge diffuser design
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
Temperature
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long-term* Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
* The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum.
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term* Low Definite Low -ve High
With mitigation No mitigation considered, other than optimal discharge diffuser design
* The impact occurs during periods of moderate to strong water column stratification, i.e. ~ 9 months per annum.
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve Medium*
With mitigation No mitigation considered, other than optimal discharge diffuser design
* The groundwater report seems to confirm the assumption that the water temperature from the boreholes would be close to that of the seasonal mean sea surface temperatures.
Dissolved Oxygen
No addition of oxygen scavenging compounds
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water
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B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation
Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long Low Definite Low -ve High
With mitigation Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water
Dissolved Oxygen
With addition of oxygen scavenging compounds
The use of sodium metabisulfite as a neutralizing agent for chlorine presently is not proposed for the
Saldanha Bay RO plant as the use of chlorine as a biocide will be limited to the product (i.e.
freshwater produced). Nevertheless the consequences of its potential use, should chlorine ultimately
be considered as the biocide of choice, is assessed As its application is independent of the intake
and discharge scenarios being considered, the assessments below evaluate the potential impacts
both with the addition of an oxygen-scavenging compound as well as without the addition of the
substance.
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long Medium Definite Medium -ve High
With mitigation* Local None Long Very Low Definite Very Low -ve High
* Mitigation in this case would constitute aeration of the effluent prior to discharge
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long Medium Definite Medium -ve High
With mitigation* Local None Long Very Low Definite Very Low -ve High
* Mitigation in this case would constitute aeration of the effluent prior to discharge
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Medium Long Medium Definite Medium -ve High
With mitigation*
Local None Long Very Low Definite Very Low -ve High
* Mitigation in this case would constitute aeration of the effluent prior to discharge
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Oxidising Biocide (NaOCl)
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation*
Local None Long Very Low Definite Very Low -ve High
* The mitigation proposed (if necesarry) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however this does potential exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation* Local None Long Very Low Definite Very Low -ve High
* The mitigation proposed (if necesarry) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however this does potential exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation*
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
* It is not expected that mitigation will be required due to a reduced requirement for a biocide in intake waters from boreholes
Oxidising Biocide (NaOCl)
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation*
Local None Long Very Low Definite Low -ve Medium
* The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation* Local None Long Low Definite Low -ve Medium
* The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation
Local Low Long Low Definite Low -ve High
With mitigation*
If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design
* It is not expected that mitigation will be required due to a reduced requirement for a biocide in intake waters from boreholes
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Co-discharged Constituents
A. Pipeline intake and discharge into Small Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low* Long Low Definite Low -ve High**
With mitigation Local None Long Very Low Definite Very Low -ve HIgh**
* *Intensity and the ultimate impact significance is low in the marine environment provided that there is adherence to the undertaking that CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site is adhered to.
** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
*** The mitigation is to remove at least large particles from the flocculant sludge/backwash to the extent that may be required, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern.
B. Pipeline intake and discharge into Big Bay
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low* Long Low Definite Low -ve High**
With *** mitigation
Local None Long Very Low Definite Very Low -ve High**
* *Intensity and the ultimate impact significance is low in the marine environment provided that there is adherence to the undertaking that CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site is adhered to.
** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
*** The mitigation is to remove at least large particles from the flocculant sludge/backwash to the extent that may be required, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern.
C. Borehole intake and discharge at Caisson 3
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low* Long Low Definite Low -ve High**
With mitigation*** Local None Long Very Low Definite Very Low -ve High**
* *Intensity and the ultimate impact significance is low in the marine environment provided that there is adherence to the undertaking that CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site is adhered to.
** High as long as the list of chemicals is adhered to and the the CIP chemicals are disposed off to the sewage (waste treatment) system or to a waste disposal site as stated in the project description
*** The mitigation is to remove at least large particles from the flocculant sludge/backwash to the extent that may be required, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern. For boreholes it is highly unlikely to be a requirement.
8.2.3 Assessment of Impacts Associated with Intake and Discharge
Structures
Entrainment of Biota (Beach well intakes, i.e. deve lopment options 1a & 2a) Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation
Local None None Not significant Improbable Insignificant Neutral High
With mitigation
No mitigation deemed necessary
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Entrainment of Biota (Pipeline Intake, i.e. develop ment options 1b, 2b, 3a & 3b) Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation
Local Medium Long-term Medium Definite Medium -ve High
With mitigation Local Low Long-term Low Definite Low -ve High
* Mitigation here constitutes appropriate engineering design to avoid entrainment at the intake.
Entrainment of Biota (Boreholes intakes, i.e. devel opment options 3c & 3d)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local None None Not significant Improbable Insignificant Neutral High
With mitigation No mitigation deemed necessary
Flow Distortion (Pipeline Discharge)
Extent Intensity Duration Consequence Probability Significance Status Confidence Without mitigation Local Low Long-term Low Definite Low -ve Low*
With mitigation
Insufficient detail in project description to define specific mitigation measures, however appropriate engineering design should negate any potential impacts
* Low as insufficient detail in project description, however, it should be possible to largely mitigate any potential impacts by appropriate engineering design resulting in a very low to non-existent significance.
Sediment Dynamics (Pipeline Discharge)
Site2 and Site 3 with discharges into Small and Big Bay Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation Local Low Long-term Low Definite Low -ve Low*
With mitigation
No mitigation can be recommended as insufficient detail in project description
* Low as insufficient detail in project description, however it should be possible to largely mitigate any potential impacts by appropriate engineering design resulting in a very low to non existent significance.
Site1 and Site 3 with discharges at Caisson 3 Extent Intensity Duration Consequence Probability Significance Status Confidence
Without mitigation None* None* None Not significant Improbable insignificant -ve Low**
With mitigation No mitigation required
* Assumes that the discharge at Caisson 3 will be located in a position such that it will not affect bottom sediments
8.3 “No-development” Alternative
The “no-development” alternative implies that the RO Plant and associated infrastructure will not be
commissioned. From a marine perspective this is undeniably the preferred alternative, as all impacts
associated with beach disturbance and effluent discharge will no longer be an issue. This must,
however, be seen in context with existing proposed developments for extensions to the Port, as well
as the use of possible alternative water sources for dust control. Furthermore, it needs to be weighed
up against the potential positive socio-economic impacts undoubtedly associated both with the RO
Plant project itself, as well as the Port extension.
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8.4 Project Impacts and Environment Interaction Poi nts
Figures 7.3 – 7.6 illustrate the maximum extents of the brine, thermal and biocide plumes, and
achievable dilutions exceeding 50 times of potential co-discharges, respectively, at the three
alternative sites (and the three alternative discharge scenarios at Site 3) under the ‘worst-case-
scenario’ conditions of predominantly extended calm periods during autumn but in many cases also
during the more highly stratified conditions prevailing during the summer months. These are shown
in relation to areas of potentially threatened or sensitive habitats and other beneficial users of the
marine environment in Saldanha Bay, which were pointed out in Section 5.2.7.
From these figures it can be seen that the plume footprints do not extend as far as any existing or
proposed mariculture activities, seawater intakes for fish processing factories, recreational and
commercial gill-netting / trek-netting areas, or Marine Protected Areas and National Parks (i.e.
including the Langebaan Lagoon). At Site 2, however, the plumes do extend over the e astern
boundary of the area demarcated for seaweed harvest ing .
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9 CONCLUSIONS AND RECOMMENDATIONS
9.1 Environmental Acceptability and Comparison of A lternatives
The environmental acceptability of the development alternatives are outlined below.
Site 1
From a coastal and marine environmental perspective, Site 1 is the most “pristine” of the three
alternative sites. Although some litter is present on the beach and in the dunes, regular pedestrian
and vehicular traffic appears minimal, as access to the site is restricted. As a consequence, the
sheltered cove is used by coastal birds as a resting and feeding place, despite the nearby harbour
activities. From a visual assessment undertaken during the site visit, the beach appears dissipative
to intermediate with low to moderate wave action. Macrofaunal communities inhabiting the beach are
therefore expected to be relatively diverse, and the surf-zone may serve as a nursery area for fish.
Construction activities (beach well and/or pipeline construction) as part of the proposed development
will severely impact the beach and nearshore habitats and their associated communities. However,
provided construction activities are not phased over an extended period, the beach is not repeatedly
disturbed through persistent activities and suitable post-construction rehabilitation measures are
adopted, the macrofaunal communities are likely to recover in the short-to medium-term. The highly
localised, yet significant impacts over the short-term thus need to be weighed up against the long-
term benefits of using subsurface intakes at this site. The beach intake wells or surf-zone infiltration
galleries proposed for this site will result in pre-filtration of feed-water, thereby significantly reducing
(but not eliminating) the need for the extensive use of biocides and co-pollutants (associated with
ensuring appropriate intake water quality and for cleaning of processes resulting from lower quality
intake waters), and eliminating the impact of impingement and entrainment of biota. Furthermore, a
discharge along an extended length (30 m or more) on the revetment, together with the close
proximity to the outer edge of the surf-zone, will ensure effective dispersion of the effluent. It is
important, however, that the discharge does not occur into the surf-zone as surf-zone trapping is
likely to significantly reduce the overall dispersion of the effluent despite the greater likelihood of the
effluent being dispersed throughout the vertical extent of the water column in the surf-zone. Should
the discharge occur into the surf-zone or along the shoreline, the non-thermal impacts are likely to be
more extensive, extending in an alongshore direction away from the reclaim dam. This may
negatively affect gillnet/treknet-fishing activities in the immediate vicinity of the discharge.
Site 2
The shoreline and beach at Site 2 are already severely disturbed and altered by existing port
development and marine litter. While pipeline construction activities will nonetheless impact beach
communities, the effects are likely to be less severe than at Site 1 due to the already severely
disturbed nature of the site.
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Perhaps of greatest concern at this site is the issue of water quality. This applies both to the feed-
water, which will be drawn from Small Bay, as well as the effects of the effluent to be discharged
back into Small Bay. Due to reduced flushing rates and discharges of organic-rich effluents from fish
processing factories, eutrophication and anoxia have been reported, and target limits for pathogenic
microorganisms are often exceeded. The clock-wise circulation in Small Bay under both SE and NW
wind conditions (Figures 5.5a & 5.5b) may result in the anoxic waters extending into the eastern
corner of Small Bay, thereby potentially affecting the quality of the feed-water for the RO plant. This
may require the additional implementation of filters and/or use of chemical purifiers in the RO plant. A
continuous discharge of brine into Small Bay is also likely to further aggravate the water quality
situation within the bay, especially when considering the comparatively large extent of discharge
plumes at Site 2 relative to those predicted at the other alternative sites. Reduced circulation within
the eastern corner of Small Bay, particularly the deeper dredged areas in close proximity of the
discharge may also result in accumulation of the high density brine due to insufficient flushing.
Although impacts due to the effluents discharge are deemed not to be significant, the risks of
potentially impacting important activities such as mariculture activities in Small Bay (through potential
eutrophication, biocide and associated break-down products, co-discharges, etc) and surf-zone
gillnet/treknet fisheries adjacent to the causeway would be minimised by avoiding a discharge into
one of the “quieter” corners of the relatively poorly flushed Small Bay (i.e. relatively poorly flushed
compared to Big Bay). The quality of feed-water at the intakes to fish processing factories in the west
of Small Bay is, however, unlikely to be affected.
Site 3
As Site 3 is located on the existing iron-ore causeway, intake and discharge pipelines will be
constructed in an already artificial and altered environment. Intertidal and shallow subtidal biota will
be minimally impacted, and no beaches will be directly disturbed or macrofaunal assemblages
eliminated. Disturbance of shorebirds will also be minimal, and the impacts of construction will be
certainly the least of the three alternative options.
The proximity of shipping traffic and an intake from Small Bay, however, again raises questions as to
the quality of the feed-water.
Discharge into Small Bay at depth (-8 m) is, however, unlikely to contribute to deteriorating water
quality within the bay, as the proposed discharge will be positioned in an area where current speeds
are comparatively high, that is closer to the entrance to Small Bay, and where mixing of the water
column through propeller-wash from shipping activity can be expected. Discharge water from the RO
Plant water discharged into Big Bay (-4 m) or at depth at Caisson 3 is also likely to be rapidly mixed
as a result of exposed nature of the discharge locations in relatively high wave conditions and
increased currents. These alternative discharges into Big Bay and at Caisson 3 from Site 3 are likely
to be the options with the least potential water quality impacts due to them being discharged into the
more dispersive Big Bay environment that also is subject to little water quality concerns compared to
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Small Bay. The discharge at Caisson 3 is the preferred dischar ge location due to being in
deep water (allowing more options in terms of disch arge design and depth), at a site with
strong tidal flows and in a location where any accu mulation of brine would be mitigated by
propeller wash. Site 3 provides the greatest option s in terms of flexibility of determining the
depth of discharge with very short pipeline lengths and limited or no disruption of shoreline
environments during construction.
Of the three alternative sites, Site 3 is the most environmentally acceptable in terms of construction
activities. This holds also for a comparison of the sites when intake and discharge are done through
pipelines as in most cases the discharge plumes are smallest for Site 3 (particularly the alternate
discharge into Big Bay). This, however, needs to be seen in context with future port developments
and long-term discharges of co-pollutants and biocides in the brine, compared to the option of using
beach well or surf-zone intakes at Sites 1 and 2. The borehole options considered for Site 3 are
likely to have the same advantage in terms of minimising the requirement for the use of biocides to
prevent biofouling and also entrainment of biota.
“No-development” Alternative
In the case of the “no-development” alternative, disturbance and elimination of beach and shallow
subtidal macrofauna, through pipeline and beach well installation will not occur. Anthropogenic
activities on the beach will be limited, shorebirds feeding and nesting in the area will remain
undisturbed and dune vegetation preserved. Likewise, with the “no-development” alternative, no
brine effluent (and associated co-discharges) will be released into the marine environment, and the
risks associated with such a discharge will thus be absent.
Should development proceed, however, the marine biota at the site ultimately selected will be
affected by the hypersaline effluent (albeit spatially constrained) regardless of the final choice of site,
however only to the degree indicated for each of the proposed sites.
9.2 Preferred Alternative
Preliminary results indicate that Site 3 with a discharge at Caisson 3 (and with a borehole intakes to
minimise biocides and entrainment of biota) is the option with the least potential impacts (see Table
9.1), followed by Site 3 (with a discharge into Small Bay or Big Bay), and then Site 1. The least
preferable option is Site 2. Provided that beach wells intakes are installed at Site 1 and that these
beach wells result in significantly lowered use of biocides and reduced co-discharge of cleaning
chemicals, Site 1 is preferred over Site 3 with a discharge into Small Bay (and an assumed pipeline
intake. However given the possibility that intake boreholes are possible for all Site 3 discharge
options, the rankings are as given under the heading “Overall Ranking” at the bottom of Table 9.1. It
should be noted that, despite that fact that Site 3 with a discharge into Small Bay is assessed to not
have significant impacts, the discharge will be into Small Bay, which is perceived to be relatively
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poorly flushed and also is perceived to be susceptible to poor water quality due to existing discharges
into Small Bay.
Although Site 2 with its discharge into the NE corner of Small Bay results in the largest effluent plume
“footprints” of all of the proposed sites and associated intake and discharge combinations, it could be
deemed to be acceptable for the present project description. It is, however, not recommended due to
the higher risks associated with a discharge into a relatively quiescent region of the relatively poorly
flushed Small Bay.
The rankings are based on a ranking of one to five. Where the ranking of two options is the same,
i.e. both second best, then a ranking of third best is not allocated. This means that the lowest ranked
option will always have a ranking of 5 unless there is an equally undesirable option (i.e. both will then
be ranked a 4 and there will be no ranking of 5). The ranking themselves do not imply a weighting
indicating the relative magnitude of impacts. The assessment is thus qualitative as is the overall
ranking.
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Table 9.1: Summary of potential impacts for the var ious Sites and associated intake and discharge comb inations.
Assessment Criteria Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Dispersive nature of the site
Ranking: 4 Discharge occurs beyond surf-zone into an exposed (but nevertheless relatively quiescent) NW corner of Big Bay.
Ranking: 5 Discharge occurs into shallow waters in a quiescent corner of the relatively poorly flushed Small Bay. Limited wave and current action to disperse any particulates in the discharge
Ranking: 2
Discharge occurs in deeper waters in the relatively poorly flushed Small Bay, but closer to the mouth of the bay and at a location where flows are quite strong
Ranking: 2 Discharge occurs in deeper waters in the relatively more exposed and well-flushed Big Bay but in shallower waters
Ranking: 1 Discharge occurs in relatively deep water in a location with strong tidal flows and potential mitigation factors such as propeller wash to disperse effluents
Design Options
Ranking: 4 Site 1 allows for beach well intakes that have specific advantages in terms of minimizing biocide discharges and co-discharges and eliminating impingement and entrainment Design options are limited (i.e. being a surface discharge no sub-surface multi-port diffuser structure can be considered. This location in unlikely to interfere with future port development options
Ranking: 5 Site 2 allows for beach well intakes that have specific advantages in terms of minimizing biocide discharges and co-discharges and eliminating impingement and entrainment. Design options are limited (discharge in principle could occur in deeper waters than assessed.) The potential limitations imposed by proposed port development need to be considered
Ranking: 1 Pipeline intakes only considered. Could consider borehole intake option that has the same advantages as beach wells in terms of minimizing biocide discharges and co-discharges and eliminating impingement and entrainment Design options for discharge structure could include single- or multi-port diffusers The potential limitations imposed by proposed port development need to be considered
Ranking: 1 Pipeline intakes only considered. Could consider borehole intake option that has the same advantages as beach wells in terms of minimizing biocide discharges and co-discharges and eliminating impingement and entrainment Design options for discharge structure could include single- or multi-port diffusers The potential limitations imposed by proposed port development need to be considered
Ranking: 1 Borehole intakes option considered have the same advantages as beach wells in terms of minimizing biocide discharges and co-discharges and eliminating impingement and entrainment Design options for discharge structure could include single- or multi-port diffusers The potential limitations imposed by proposed port development need to be considered
Sensitivity of discharge location
Ranking: 3
Discharge occurs into Big Bay. Sensitive surf-zone could be excluded. No
proximity to existing mariculture operations
Ranking: 5
Discharge occurs in a quiescent corner of Small Bay that already contains
a number of other discharges and also sensitive mariculture
operations
Ranking: 3
Discharge occurs into Small Bay that already contains a number of
other discharges and also sensitive mariculture
operations
Ranking: 2
Discharge occurs into Big Bay. Sensitive surf-zone could be excluded. No
proximity to existing mariculture operations
Ranking: 1
Discharge occurs in deep water at a highly
dispersive location away from sensitive sites
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Assessment Criteria Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Construction Impacts
Construction of Beach Well intakes
no mitigation Medium Medium n/a n/a n/a
with mitigation No significant mitigation possible other than avoiding beach well construction
n/a n/a n/a
Construction of borehole intakes
no mitigation n/a n/a n/a n/a Very low
with mitigation n/a n/a n/a n/a No mitigation required
Construction of Pipeline intakes
no mitigation Medium Medium Very low Very low n/a
with mitigation Limited mitigation is possible using “best practice” mitigation measures during construction. It is not possible to propose
specific mitigation measures based on existing known detail of construction activities
None deemed necessary other than normal environmental ‘best practice’
n/a
Construction of discharges (Pipelines for Site 2 an d Site 3 for discharges into Small Bay and Big Bay an d other discharge infrastructure at Site 1 and Site 3 for discharge at Caisson 3)
no mitigation Very low Medium Medium Medium Very low
with mitigation
None deemed necessary other than the use of “best
practice” mitigation measures during construction.
Limited mitigation is possible using “best practice” mitigation measures during construction. It is not possible to propose specific mitigation measures based on existing known detail of
construction activities
None deemed necessary other than the use of “best
practice” mitigation measures during construction.
Operational Impacts (other than Water Quality) of I ntake and discharge operation
Entrainment of Biota (Pipeline Intakes)
no mitigation Medium Medium Medium Medium n/a
with mitigation Low Low Low Low n/a
Entrainment of Biota (Beach Well Intakes)
no mitigation insignificant insignificant n/a n/a n/a
with mitigation No mitigation deemed necessary n/a n/a n/a
Entrainment of Biota (Borehole intakes along Causewa y)
no mitigation n/a n/a insignificant insignificant insignificant
with mitigation n/a n/a No mitigation deemed necessary
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Assessment Criteria Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Flow Distortion
no mitigation Low Low Low Low Low
with mitigation Insufficient detail in project description to define mitigation measures, how appropriate engineering design should negate any potential impacts
Impacts on Sediment Dynamics
no mitigation insignificant Low Low Low insignificant
with mitigation No mitigation required No detailed mitigation can be recommended as insufficient detail in project description,
however appropriate engineering design should negate any potential impacts No mitigation required
Specific Impacts associated with the discharged bri ne (and associated co-discharged)
Salinity
no mitigation Low Low Low Low Low
with mitigation No mitigation specified/considered, other than optimal discharge diffuser design
Temperature
no mitigation Low Low/Medium * Low Low Low
with mitigation No mitigation specified/considered, other than optimal discharge diffuser design
Oxygen (no O2 scavengers)
no mitigation Low Low Low Low Low
with mitigation Mitigation not deemed necessary unless oxygen scavenging compounds are added to the feed-water. This will only occur should chlorine be used as a biocide that results in a potential discharge of residual chlorine into the marine environment. Presently the project description specifies that chlorine will not be used in
this role
Oxygen (with O2 scavenger)
no mitigation Medium Medium Medium Medium Medium
with mitigation Very Low Very Low Very Low Very Low Very Low
Oxidising Biocides (NaOCl): Beach well or borehole inta kes
no mitigation Low Low n/a n/a Low
with mitigation If biocide dosage is as specified, no mitigation is likely to be required, other than optimal discharge diffuser design n/a n/a
No mitigation likely to be required, other than optimal discharge diffuser design
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Assessment Criteria Site 1
Site 2
Site 3 (Small Bay)
Site 3 (Big Bay)
Site 3 (Caisson 3)
Oxidising Biocides (NaOCl): Pipeline intakes
no mitigation Medium Medium Low Low n/a
with mitigation Very Low Very Low Very Low Very Low n/a
Non-oxidising Biocides (DBNPA): Beach well or borehole intakes
no mitigation Low Low n/a n/a Low
with mitigation*** If biocide dosage is as specified, no mitigation is likely to be
required, other than optimal discharge diffuser design n/a n/a
No mitigation likely to be required, other than optimal discharge diffuser design
Non-oxidising Biocides (DBNPA): Pipeline intakes
no mitigation Medium Medium Low Low Low
with mitigation*** Low Low Very Low Very Low Very Low
Co-discharges (beach well or borehole intakes)
no mitigation Low Low n/a n/a Low
with mitigation** Very Low Very Low n/a n/a Very Low
Co-discharges (pipeline intakes)
no mitigation Low Low//Medium Low Low n/a
with mitigation**** Very Low Very Low Very Low Very Low n/a
Overall Ranking
All criteria 4 5 3 2 1
* Note that the intensity of the thermal impacts at Site 2 may be reduced and assumed to be low, i) given appropriate engineering design mitigation (i.e. assuming that it would be possible to locate the pipeline intake in a manner that would ensure sufficiently lower seawater temperatures at the intake) or ii) if it is assumed that beach well intake water temperatures are lower that the near surface water temperatures assumed in the modelling.
** A proposed mitigation (if necessary and to be applied to the extent required) is de-chlorination by the use of an oxygen scavenger such as Sodium metabisulphate, however as this does potential exacerbate impacts associated with low concentrations of dissolved oxygen in the marine environment, the mitigation preferred is that of carefully monitored and managed dosing to ensure minimal chlorine concentrations in the discharge.
*** The proposed mitigation to reduce DBNPA impacts in the marine environment is to design the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge or to revert to the use of an oxidising biocide (chlorine) in this role.
**** Mitigation in unlikely to be required except for perhaps Site 2, should monitoring studies indicate the accumulation of sediments to the extent that it becomes a concern. The assessment with mitigation assumes that particulates are removed from the flocculant/backwash sludge to the extent required.
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9.3 Recommendations
The recommendations from this study include mitigation measures (optional and required) and
monitoring requirements to be able to better assess and manage potential impacts.
9.3.1 Mitigation Measures
The recommended mitigation measures are listed below for both the construction and operational
phases of the RO Plant.
9.3.1.1 Construction Impacts
Heavy vehicle traffic associated with pipeline and well construction on the beach must be kept to a
minimum, and be restricted to clearly demarcated access routes and construction areas only. All
construction activities in the coastal zone must be managed according to a strictly enforced
Environmental Management Plan. Good house-keeping must form an integral part of any
construction operations on the beach from start-up, including, but not limited to:
• drip trays under all vehicles parked on the beach;
• no vehicle maintenance or refuelling on beach;
• accidental diesel and hydrocarbon spills to be cleaned up accordingly; and
• no concrete mixing on beach.
9.3.1.2 Operational Impacts
Intake
In the case of intake pipelines, manual cleaning of the intake structure and sump will be necessary as
marine growth, scaling and sediment settlement will occur. Most marine pipelines employ a pigging
system for regular maintenance cleaning, in which a ‘pig’ (bullet-shaped device with bristles) is
introduced into the pipeline to mechanically clean out the structure. For intake systems, the pigging
device is introduced at the intake structure and allowed to travel to the sump, from where it is
retrieved. For the discharge pipeline, it is introduced in the RO plant, and is removed again by divers
on the seaward side. Pigging is optional, but should be considered as it can reduce the costs for
biocides.
The use of subsurface intakes such as beach wells or infiltration galleries or boreholes as an
alternative to pipelines is recommended where feasible and, in the case of the first two, where these
will not cause significant negative impacts to beach topography or freshwater aquifers. While these
may have higher initial construction costs, they are likely to result in long-term operational savings
due to reduced pre-treatment and chemical requirements. They also operate with minimal effects on
local marine life in the form of entrainment and impingement. They may also be able to operate at
times when pipeline intakes need to be shut-down due to unsuitable seawater conditions, or during
port-development activities such as dredging.
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In the case of pipeline intakes, there are several alternative design or mitigation measures that can
completely avoid or reduce the impact of impingement. Intake velocities should be kept below ~0.15
m.s-1 to ensure that fish and other organisms can escape the intake current. This can be achieved
through a combination of pumping rates and intake design. Alternatively, the use of velocity caps
(concrete structures placed over the intake leaving a gap between the cap and intake) change the
predominant intake flow from vertical to horizontal, thereby significantly reducing impingement of fish,
which are better able to detect a horizontal change in water velocity. These require little ongoing
maintenance once installed. Further mitigation options involve screens, which are specifically sized
to prevent fish from entering the system while still allowing adequate water flow. Travelling screens
enable fish to be moved out of an intake system, often unharmed (California Coastal Commission
2004). These are generally installed at the landward end of a pipeline intake and built in conjunction
with a fish return system, which routes fish and a portion of the feed-water back to the ocean. Such
systems, however, involve ongoing maintenance and personnel to operate them.
Discharges
Possible mitigation measures for brine effluents include alternative discharge options such as
evaporation ponds, dilution with sewage effluents, deep well injection, crystallisation, live-stock
watering and beach well disposal (DWAF 2007). Beach well disposal was considered at Site 1,
however the results of the geotechnical study ascertained that sediment characteristics were
unsuitable and that this discharge option was thus not feasible (Visser et al., 2007). The other
alternative discharge options (e.g. evaporation ponds, crystallisation, etc) are discussed in the Basic
Assessment Report for the proposed RO Plant (PDNA/SRK JV, 2008)
Mitigation measures should also include specific selection of technologies and processes that
minimise or eliminate the need for hazardous chemicals. This will not only reduce the disposal
requirements for such substances, but also lessen the impacts of potential spills or releases from the
RO plant, thereby reducing discharges of hazardous components into the bay. Every effort should
thus be made to select the least environmentally damaging option for feed-water treatment and
cleaning of plant components.
Although the footprint of the biocide plume in general is not substantial, marine organisms are
extremely sensitive to residual chlorine. Considering the relatively close proximity of mariculture
activities and commercial and recreational fisheries, it is important, therefore, to ensure that the
residual chlorine (or other non-oxidising biocide) concentration in the discharged brine is specifically
reduced to a level below that which may have lethal or sublethal effects on the biota, particularly the
larval stages. Should the exceedance of the recommended guideline be a more persistent or
recurrent event, there could be serious implications for nearby mariculture operation. Taking the
dilution factor of the brine into account, the effects of biocide must be actively minimised by ensuring
that biocide concentrations do not exceed the No Observed Effect Concentration (NOEC) and/or the
relevant water quality target values. This can be achieved with appropriate design and
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implementation of mitigation measures, to ensure that the biocide concentrations comply with the
relevant water quality guidelines. The impacts due to chlorine can be mitigated by de-chlorination of
the brine discharge with, for example sodium metabisulfite, before discharge into the marine
environment. This may though not always succeed in eliminating chlorine toxicity as there is the
possibility that the presence of organic substances in the environment results in the production of
chlorinated residuals that are resistant to sodium metabisulfite de-chlorination (Yonkos et al., 2001).
The use of sodium metabisulfite as a neutralizing agent for chlorine is further associated with oxygen
depletion in the effluent, as the substance is an oxygen scavenger. Given that chlorine presently is
not the biocide of choice for the RO Plant and that it is intended to use only a non-oxidising biocide
(DBNPA – 2.2 Dibromo-3-nitrilopropionamide), it is unlikely that sodium metabisulfite will be utilised as a
neutralising agent17. However should chlorine become the biocide of choice and sodium metabisulfite
be required as a neutralising agent, aeration of the effluent prior to discharge is recommended,
particularly if the discharge is into Small Bay which already experiences a fairly regular oxygen deficit
in bottom waters during the late summer and winter months. A better option would be carefully
monitored dosing to ensure minimal chlorine concentrations in the discharge.
Mitigation measures to ensure low residuals of DBNPA in any discharge to the marine include
appropriate design of the brine basin so as to ensure greater and sufficient dilution of the DBNPA
residuals in the effluent stream before discharge18 or to revert to the use of an oxidising biocide
(chlorine) in this role. However, once again a better option would be carefully monitored dosing to
ensure minimal DBNPA concentrations in the discharge.
No acute toxic effects of the backwash sludge containing sediment particles and the flocculant Ferric
Chloride are generally expected. However, ferric chloride may cause a discoloration of the receiving
water, and the sludge discharge may lead to increases in turbidity and suspended matter. Impacts
such as reduced primary production or burial of sessile organisms by increased turbidity in the
discharge may thus occur. A process for removal of the particles is thus recommended before
discharge of the sludge. If this is not possible, dilution of the backwash waters by blending with the
brine flows is a potentially viable, but less desirable, alternative. However, should monitoring studies
indicate the accumulation of sediments from the flocculant/backwash sludge to the extent that it
becomes a concern (most likely only to be a concern for the sheltered Site 2), a process for
particulate removal will need to be applied to the extent necessary. The use of subsurface intake
structures such as boreholes will serve as natural filtering system thus reducing the amount of
organic matter and sediment particles in the feed water, which in turn is expected to drastically
reduce the risks associated with the discharge of the sludge with the brine.
17 Although sodium metabisulphite can be used to neutralise DBNPA residual before discharge it is not
proposed for use should DBNPA be the biocide chosen for use in the RO Plant. 18 Transnet, to ensure compliance with the more conservative water quality guideline for residual
concentrations of DBNPA (< 0.035 mg. ℓ-1 beyond the impact zone indicated in the model simulations), has committed to limiting the residual concentration of DBNPA at the point of discharge into the marine environment to an upper limit of 1.15 mg. ℓ-1.
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The model results are based on assumed conceptual designs that assume active mixing of the dense
brine into the water column during discharge. While conceptually surf-zone discharge or a single port
diffuser has been assumed, the discharge of brine particularly at the deeper discharge locations
needs to be through a diffuser or single port discharge design that results in near-field behaviour
consistent with that assumed in the modelling. A conservative discharge design nominally would be
one where initial dilutions of 50 are predicted by near-field models such as CORMIX (Jirka et al.,
1996) and UOUTPLM (Baumgartner et al., 1971). It is particularly important that the development of
a coherent density flow of brine along the seabed is avoided by ensuring as complete mixing
throughout the full extent of the water column as is possible at the point of discharge.
The optional and required mitigation measures are summarised in Table 9.2 below:
Table 9.2: Optional and required mitigation measure s
Mitigation Necessity
Construction Impacts:
- Limiting and restricting vehicular traffic on the
beach
- Good house-keeping
- Active rehabilitation above high water mark
Required
Required
Required
Use of sub-surface intakes (beach
wells/boreholes)
Required
(highly recommended)
Pipeline intakes: - adjustment of intake velocities and/or velocity
caps - intake screens - operational cleaning (pigging) of intake pipes
Required
Required Optional
Discharges: - evaporation ponds / crystallisation - beach well disposal - Carefully controlled dosing of biocides based on
feedback from monitoring systems - dechlorination of brine discharge
- Reduction of residual DBNPA concentration in effluent to be discharged by designing the brine basin so as to ensure greater and sufficient dilution of the DBNPA residuals in the effluent stream before discharge, or to revert to the use of an oxidising biocide (chlorine) in this role.
Not feasible Not feasible
Required
Required only if chlorine is used in systems discharging to the marine environment (presently not indicated) and then only in the case of pipeline intakes as chlorine dosing for beach well and borehole intakes is assumed to be low Required only in the case of pipeline intakes as DBNPA dosing for beach well and borehole intakes is assumed to be low
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Mitigation Necessity
- aeration of brine discharge - Removal of sludge particles from backwashing
of RO modules - Optimal diffuser design based on acceptable
water quality target values
Optional but highly recommended if chlorine is used in systems discharging to the marine environment (presently not indicated) and sodium metabisulfite is used to neutralise chlorine residuals in the effluent stream discharged to the marine environment
Optional, to be undertaken to the extent required (i.e. as informed by the monitoring results for the discharge.) Required
9.3.2 Monitoring Recommendations
Very little information is available on the intertidal sandy substrate communities in Small Bay and Big
Bay. Should Site 1 be chosen as the preferred site for intake and discharge structures, it is strongly
recommended that a well-designed monitoring plan be developed as part of the RO Plant
environmental requirements. This would involve establishing a baseline of intertidal and shallow
subtidal invertebrate macrofaunal communities before any construction commences, followed by
regular monitoring thereafter to assess recovery of the impacted communities following construction,
as well as responses of the communities to a continuous hypersaline discharge. Similar surveys are
recommended for Site 2 should it be anticipated that construction activities and RO plant discharges
are likely to impact upon the sandy beach fauna.
Independent of which site and design is ultimately chosen, monitoring programmes should be
developed to study the impact of the brine on potentially affected communities, particularly the
subtidal benthic communities. This recommendation is reinforced by the Guidelines for
Environmental Evaluation for Seawater Desalination which has recently been published by the
Department of Water Affairs and Forestry (DWAF 2007), in which it is stated that it is essential that
the effects of the discharge of brine into any water body, on the fish and benthos life in that water
body, be monitored according to a monitoring programme performed at 6-monthly intervals over a
period of approximately 4 years. Depending on initial results, reduced monitoring (i.e. annually) may
be acceptable. This monitoring will include measurement of the main water quality parameters such
as temperature, salinity and dissolved oxygen as a minimum. It is further recommended that every
effort be made to publish the results in a peer-reviewed journal.
Although it is predicted that the impact of discharge of backwash waters will not siginificantly affect
the oxygen concentrations in the vicinity of the discharge (particularly if beach wells or boreholes are
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used that will minimise backwash material), monitoring of dissolved oxygen in the near bottom waters
and at a nearby reference site is recommended to determine whether the removal of sludge particles
from backwashing of RO modules is required. Such monitoring should occur as a minimum for an
approximate 6 month period (November to April) after approximately 6 months of plant operation,
however monitoring for a full year is desirable. This once-off measurement campaign should be
sufficient to confirm that no specific mitigation measures are required in terms of the management of
backwash material.
The waste brine often contains low amounts of heavy metals, which tend to enrich in suspended
material and finally in sediments. It is recommended that after commissioning of the RO plant that
the effluent be monitored regularly for heavy metals until a profile of the discharge in terms of heavy
metal concentrations is determined. These heavy metal concentrations in the brine effluent would
then need to be assessed based on existing guidelines (DWAF 1995, ANZECC 2000). A summary of
these guidelines is provided in Table 8.1.
Similarly, to ensure complete confidence in the controls of the dosing regime and that the consequent
residual biocides in the discharge are being managed to concentrations that together with possible
synergistic effects other co-discharges will not have significant environmental impacts, it will be
necessary to undertake toxicity testing of the discharge for a full range of operational scenarios (i.e.
shock-dosing, etc). Such sampling and toxicity testing need only be undertaken for the duration and
extent necessary to determine an effluent profile under all operational scenarios.
The mariculture industry is extremely sensitive to tainting or even the perception of tainting. On the
basis of present information the discharges will contain negligible or no tainting substances.
Finally this assessment is based on numerical modelling results. Typical brine and thermal footprints
need to be confirmed by sampling with a conductivity-temperature-depth (CTD) probe after an initial
period of operation of the discharge both to confirm the performance of the discharge system and the
numerical model predictions. This should be done for a suitably representative range of
“conservative” environmental conditions, i.e. conditions for which dispersion of the effluent is likely to
be the most limited. It is envisaged that two to three field surveys of one to two days duration would
be adequate to confirm the performance of the discharge system and the accuracy of model
predictions. It is likely, in any case, that most of these measurements would be needed to be
included in the monitoring programmes developed to study the impact of the brine on potentially
affected communities, particularly the subtidal benthic communities.
All of the above recommendation, except for the monitoring to confirm the model predictions, are
deemed to be essential. However the performance of the outfall according to design will need to be
assessed and the same data as collected for confirming the performance of the discharge system
could be used to assess the modelling results.
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Appendix A:
Possible implications of policy, legislation and approval and licensing
procedures for the proposed RO Plant water discharge
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The implications of the policy, legislation and approval and licensing procedures described in the
above policy, legislation and associated documents for the proposed RO Plant water discharge into
Saldanha Bay, can be summarised as follows:
• In addition to the requirements of the National Water Act of 1998 and the policies and approval
and licensing procedures of DWAF, the Water Quality Management Plan (and associated
scientific studies) developed for the Saldanha Bay Water Quality Trust, together with
representations from the DEAT, will play a significant role in it a decision on whether or not the
proposed brine effluent discharge will be acceptable.
• The DWAF water quality management policy comprises a hierarchy of decision making which
contains elements of the Receiving Water Quality Objectives approach, as well as the
precautionary principle of environmental protection. This require first that there is the prevention
of waste production and pollution wherever possible (Pollution prevention principle), secondly
that there is the minimisation of pollution and waste at source (Pollution minimisation principle).
Only when these first two principles have been satisfied to the greatest extent possible, is
responsible disposal considered and then by applying the precautionary approach.
• An integrated assessment approach will need to be followed that is based on the principles of
Integrated Environmental Management, taking cognisance of concepts such as Strategic
Environmental Assessment, and Environmental Impact Assessment (EIA) and assessment of
the project from “cradle to grave” based on principles of strategic adaptive management, best
practice, consistent performance, flexibility in approach and continuous improvement.
• Alternative options of managing wastewater must be investigated as disposal to the marine
environment is not considered the ‘default’ option in coastal areas. (This is also a requirement
of the Basic Assessment and/or EIA process where the no-go option has to be explicitly
considered).
• Transparent and adequate consultation with all potential stakeholders and interested and
affected parties both prior to and after gaining approval for the disposal of effluents in Saldanha
Bay (i.e. from application through to report back on monitoring results). There will need to be
agreement upon the assumed environmental objectives for the Saldanha Bay and its surrounds
by all relevant stakeholders. In addition, after implementation of the RO Plant discharge, there
will need to be adequate and relevant ongoing monitoring to the extent appropriate. The results
of any such monitoring program will need to be communication to all stakeholders on an
ongoing basis.
• The approval and licensing procedure and the Basic Assessment/EIA process are separate
processes, each with their own specific requirements. Note that an Basic Assessment/EIA
authorisation cannot replace a water use licence application, since the former does not
necessarily address all the requirements of the National Water Act
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• It is a legal obligation for the project proponent to provide a full description of the proposed
method of effluent disposal proposed and a full characterisation of the effluent(s) in terms of:
− Flow rates (average, maximum, minimum and diurnal/seasonal variations) for
present and future scenarios
− All relevant constituents (average, maximum, minimum and diurnal/seasonal
variations) for present and future scenarios.
The specification should include all future, planned expansions in order to avoid going through
the whole process of applying for a new licence and/or the requirements for a new EIA at the
time of the future expansion.
• Discharge of land-derived wastewater to any area declared a Marine Protected Area under the
Marine Living Resources Act 18 of 1998 is prohibited. The discharge will have to be located
appropriately such that there is no discharge into such an area and similarly that there are no
adverse environmental impacts in such areas.
• Site-specific environmental quality objectives for the marine environment must take into account
the South African Water Quality Guidelines for coastal marine waters (RSA DWAF, 1995a) or
any future updates thereof.
• Exemption from compliance to wastewater standards and/or/guidelines will only be considered
in exceptional circumstances provided that the receiving water body remains fit for use in
accordance with the Receiving Water Quality Objective approach.
• A licence application will require that the potential impacts on the receiving environment are
adequately investigated in both the near and far field, taking into account other anthropogenic
activities and waste inputs so as to address possible synergistic and/or cumulative effects. A
precautionary approach must be followed in the assessment and design of any marine disposal
system in which the temporal and spatial coverage and accuracy of physical and chemical
oceanographic data do not adequately describe site-specific conditions or where the potential
impacts associated with the discharge are uncertain. Where it cannot adequately be
demonstrated that the potential environmental impacts associated with the discharge of limited
or no significance, the precautionary approach requires that one does not proceed with the
implementation of the proposed discharge system until such time that sufficient information
exists that indicates that all potential environmental impacts are found to be acceptable.
• The details on Management Systems and Pollution Prevention Methods will be critically
assessed, whereby the applicant’s ability to effectively manage the proposed wastewater
disposal facility, will be critically assessed in the licence application procedure.
• The Polluter Pays principle requires that the project proponent and its partners pay for all
environmental costs incurred for rehabilitation of environmental damage, and the costs of
preventive measures to reduce or prevent such damage, necessary studies and on-going
monitoring programs associated with the proposed discharge, should they be required. In
addition there is a possibility that in future there is likely to be a waste discharge charge
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associated with all significant discharges to the marine environment. This proposed waste
discharge charge system was planned to be implemented from 2006 onwards (RSA DWAF,
2003b), however there exists no clarity on the progress to date in implementing the proposed
waste discharge charge system. This needs to be factored in when assessing the economic
viability of a project.
• Any authority or industry responsible for the operation and management of a marine disposal
system will be subject to the implementation of an appropriate monitoring programme.
• Any authority or industry responsible for the operation and management of a marine disposal
system will be required to provide the DWAF with a regular evaluation of the performance of the
marine disposal system. Where performance evaluations indicate non-compliance with the
predetermined specifications (including the environmental quality objectives), the responsible
authority or industry will be required to propose mitigating actions to ensure compliance (e.g.
rehabilitation or alternative treatment options). The responsible authority and the industry
operating the wastewater disposal system will be required to implement such actions at their
own cost upon approval of the DWAF.
• Discharge licences are subject to review every 5 years. For a discharge such as the one
proposed there is little that is possible in terms of continual improvement of the discharge,
consequently a high degree of certainty is required around the magnitude of the potential
impacts associated with the discharge to avoid the licensing problems after the review process.
In addition, Saldanha Bay being a highly sensitive, multi-user region (e.g. mariculture activities,
close proximity to marine protected areas, etc) in terms of marine quality, will require that there
is a high degree of certainty around the magnitude of potential environmental impacts of the
proposed discharge before approval is given to proceed with the proposed discharge.
• Where a land-based activity, which requires a licence under section 21 of the NWA, falls within
a commercial harbour area, the National Ports Authority, as the landowner, is responsible to
ensure that such an activity meets the requirements of the relevant laws (DEAT, 2007).
While the above principles/requirements are focussed on larger discharge systems, many are likely to
be relevant to the proposed RO Plant discharge.
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Appendix B:
Hydrodynamic and Water Quality Model Set-up and Calibration
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B.1 Introduction
The currents in Saldanha Bay are forced by wind, waves, large-scale currents, tides, Coriolis effects
(due to the rotation of the earth), inertial effects and by baroclinic effects induced by changes in water
temperature. To be able to simulate the transport and fate of a dense RO Plant brine discharge within
Saldanha Bay requires that the three-dimensional processes typical of the hydrodynamics of
Saldanha Bay as well as the three-dimensional behaviour of the discharge plume be accurately
simulated. To meet this requirement the Delft3D computer modelling suite has been set up for
Saldanha Bay and applied to simulate the waves, and three-dimensional currents with derived
turbulence quantities.
For the hydrodynamic simulations two modules are used, namely Delft3D-WAVE and Delft3D-FLOW.
These modules are used in the so-called “online” mode which implies that the two modules operate
interactively. The Delft3D-WAVE module uses a time series of waves and calculates a wave field
every 2 hours and it uses the exact water levels from the Delft3D-FLOW module during these
calculations. Every two hours Delft3D-WAVE passes the relevant wave information to Delft3D-FLOW.
This information, together with wind and atmospheric data are used in DELFT3D-FLOW to simulate
the hydrodynamics of the bay that include processes such as upwelling, wave- and wind-driven flows
and turbulent mixing within the water column.
Prior to this RO Plant modelling study, the model was set-up and calibrated to investigate potential
environmental impacts associated with the proposed Phase 2 expansion of the iron-ore export
facilities. The locations of the instrumentation providing the calibration data are given in Figure B.1.
Two modelling simulation periods were considered:
• The first modelling period extends from 20 October 2006 to 15 December 2006. This period
coincides with a measurement campaign to ensure accurate calibration of the model, the focus
of these calibrations being on the wave and wind-driven flows in Big Bay.
• The second modelling period extends from 1 July 1999 to 1 July 2000. For this period, the
objective of the modelling was to simulate the currents that may occur for the situation with and
without the harbour alterations. During this period measurements were made of the water
column stratification in Small Bay that also have been used to calibrate the model. These
calibrations focussed on ensuring accurate simulation of the upwelling dynamics over the
adjacent shelf and their influence on flows and water column mixing processes within the bay,
the main focus being on Small Bay. These dynamics are important for the accurate simulation
of dense discharges i.e. the RO Plant discharges.
In the section that follows, the set-up of the model and its calibration for the Phase 2 expansion of the
iron-ore export facilities study, are described in detail. However, it has been necessary to modify the
computational grid for DELFT3D-FLOW used in the Phase 2 studies (Figure B.2a and b) for use in
this study in order to resolve the plume dynamics in the immediate vicinity of the proposed RO Plant
discharge locations.
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Waverider
Figure B.1: Position of the instrumentation providi ng the data used to calibrate the model.
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Two modifications of the computational grid have been made. In the first modified grid (Figure B.3),
the spatial resolution of the grid was dramatically increased in the vicinity of the initial proposed
discharge sites (Site 1, Site 2 and discharges into Small and Big Bay from Site 3). When a further
discharge site was identified, that was expected to have the least impact on the marine environment
of all options considered, it was necessary again to modify the computational grid (Figure B.4) to
ensure adequate resolution of the plume dynamics at the new site (i.e. discharge at Caisson 3 from
Site 3).
Such increases in the spatial resolution of the computational grid are expected to result in more
accurate simulation of the hydrodynamics at these locations where the spatial resolution has been
increased. Given that these changes occurred only in the computational grid of the DELFT3D-
FLOW hydrodynamics model and furthermore are localised, the original calibration exercise
undertaken for the Phase 2 expansion of the iron-ore export facilities study is deemed also to be
adequate for this study (i.e. the modelling of discharges from the RO Plant). Consequently this
calibration exercise is reported in some detail here.
B.2 Model Set-ups
B.2.1 Computational grids
Computational grids were set-up for both the wave modelling and the three dimensional
hydrodynamic modelling. The computational grid used in the wave modelling (Figure B.5) was more
extensive than that used in the hydrodynamic model (Figures B.3 and B.4) and extended offshore
into water depths exceeding 200 m, both to ensure that i) wave conditions were available over the full
extent of the hydrodynamic model and ii) that the wave conditions at the offshore boundary are
applied in water depths where refraction has not yet occurred. The lateral boundaries are also
located far from the region of interest to prevent inaccuracies in boundary conditions affecting the
calculations in the area of interest. Where the grid used by Delft3D-WAVE overlaps that of Delft3D-
FLOW, the computational grids from the two modules are exactly the same, i.e. there is no loss of
information due to interpolation between the different modules because the Delft3D-FLOW grid
coincides with the Delft3D-WAVE grid.
The hydrodynamic grids have 112 x 124 cells in the horizontal and are designed so that the grid size
is as large as 3.5 km x 4.0 km in the offshore region, but is refined to a size of approximately
20 m x 25 m in the immediate vicinity of the proposed discharges into Saldanha Bay. In the vertical,
10 sigma layers were used with the thickness of the layers from surface to seabed being 10 %, 15 %,
15 %, 15 %, 10 %, 10 %, 10 %, 8 %, 5% and 2 % of the local water depth. The thinnest layers are
located near the seabed to resolve the dense brine plume behaviour near the seabed as it will either
be discharged at these depths or rapidly sink to these depths in the immediate vicinity of the
discharge. The XY-coordinate system used in the simulations is based on the Universal Transverse
Mercator coordinate system (UTM 33 South) and the WGS84 spheroid.
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Figure B.2a: The computational grid used in the hyd rodynamic simulations for which a detailed calibration has been undertaken ( i.e. Phase 2 studies for the iron-ore expansion project – Smith et al ., 2007).
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Figure B.2b: A zoomed in view of the computational grid used in the hydrodynamic simulations for which a detailed calibration has be en undertaken ( i.e. Phase 2 studies for the iron-ore expansion project – Smith et al. , 2007).
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Figure B.3: The computational grid used for the ini tial RO Plant discharge simulations.
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Figure B.4: The computational grid modified to incr ease the spatial resolution in the vicinity of the Caisson 3 discharge location.
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Figure B.5: The computational grid used in the wave simulations.
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B.2.2 Bathymetry
The model bathymetry was obtained from the following data sources:
• S A Navy hydrographic chart of Langebaan Lagoon (SAN 2052);
• S A Navy hydrographic chart of the Entrance to Saldanha Bay (SAN 1011);
• S A Navy hydrographic chart of the Saldanha Bay Harbour (SAN 1012).
Higher resolution surveys were added in the following regions (see Figure B.6):
• From Lynch Point to the Reclamation Dam and offshore area to the bay entrance – Nov/Dec
2006 CSIR survey;
• Lynch Point to Langebaan Point – Surveys conducted in 2003 and 2005 by CSIR for PRDW;
• Region south-west of the Iron Ore Jetty, extending from Reclamation Dam to the seaward end
of the jetty – surveyed in late 2005 survey by Marine GeoSolutions.
The detailed bathymetry in the region of interest is given in Figure B.1.
Figure B.6: The higher resolution bathymetry used i n additional to the South African Navy chart bathymetry data.
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B.2.3 Wave Simulations
The wave refraction predictions were obtained by using the numerical model SWAN (Simulating
Waves Nearshore). The wave refraction model SWAN was executed within the Delft3D-WAVE
environment which provides a convenient interface for pre- and post-processing of the results. The
Delft3D-WAVE (SWAN) model is based on the discrete spectral action balance equation and is fully
spectral in all directions and frequency, implying that short-crested random wave fields propagating
simultaneously from widely different sources can be accommodated, e.g. a swell with superimposed
wind sea.
The Delft3D-WAVE model can account for refractive propagation due to currents and depth. The
model also represents explicitly the processes of wave generation by wind, dissipation by white-
capping, bottom friction and depth-limited wave breaking and non-linear wave-wave interactions
(quadruplets and triads) explicitly with state-of-the-art formulations. Wave blocking by currents is also
explicitly represented in the model. Diffraction is not modelled in SWAN, but diffraction effects can be
simulated by applying directional spreading of the waves. Wave reflection can be modelled by
specifying the location and reflection coefficient of a linear obstacle, e.g. a breakwater. In the present
application, the processes simulated were wave refraction, shoaling, bottom friction and breaking.
Local wind-wave generation within Saldanha Bay was not modelled since wind-waves were assumed
largely to be included in the boundary specifications.
In the application of SWAN, the first step is to synthesize an offshore wave climate. Once the
offshore wave climate is determined, this climate can be simulated in the model and the resulting
wave shear stresses and wave energy dissipation are used by the Delft3D-FLOW module.
Offshore wave climate
To execute Delft3D-WAVE, the model requires an offshore wave climate. For the modelling period of
20 October 2006 to 15 December 2006 used to calibrate the model wave parameters, the offshore
wave conditions for the SWAN refraction model were obtained from measurements at the Slangkop
waverider buoy (Figure B.7). The three-hourly measurements from 01 October 2006 to 31 December
2006 comprise a total of 736 data points. For the period from 01 July 1999 to 30 June 2000, hindcast
data obtained from OCEANOR were used. For this period, the hindcast wave time series consists of
1464 wave conditions at six-hourly intervals.
For the modelling, Delft3D-WAVE and Delft3D-FLOW were executed in “online” mode with a wave
calculation taking place every two hours: This implies that every two hours the water levels calculated
by Delft3D-FLOW are passed to Delft3D-WAVE which calculates the appropriate wave field and then
passes the wave shear stresses and rate of wave energy dissipation, as well as other parameters to
Delft3D-FLOW. Because the wave calculations take place at two hourly intervals, should a wave
calculation be performed at a time that does not coincide with a time in the wave time series, the
wave conditions for the modelling are obtained from the measured or hindcast data via linear
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interpolation of the significant wave height, peak wave period and mean wave direction. The
measured wave time series from Slangkop are presented in Figures B.8a and B.8b for the 20
October 2006 to 15 December 2006 period while the OCEANOR hindcast wave data is presented in
Figures B.9a to B.9b for the period 01 July 1999 to 30 June 2000. The latter data was used to
generate the one year hydrodynamic database used in both the RO Plant and the Phase 2 expansion
of iron-ore export facilities specialist studies.
Figure B.7: Location of the Slangkop waverider buoy relative to the waverider buoy within Saldanha Bay.
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Figure B.8: The Slangkop wave data from 19 October 2006 to 15 December 2006.
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Figure B.9a: OCEANOR wave data from 30 June 1999 to 1 January 2000.
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Figure B.9b: OCEANOR wave data from 1 January 2000 to 1 July 2000.
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SWAN vs 71079 (off the Iron Ore Jetty)
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
14-Nov 19-Nov 24-Nov 29-Nov 4-Dec 9-Dec
Date
Hm
o
SWAN - Madsen=0.05 Seapac 71079
SWAN vs 71079 (off the Iron Ore Jetty)
0.0
2.0
4.0
6.0
8.0
10.0
12.0
14.0
16.0
18.0
20.0
14-Nov 19-Nov 24-Nov 29-Nov 4-Dec 9-Dec
Date
Tp
SWAN - Madsen=0.05 Seapac 71079
Estimated accuracy
Seapac
Hmo: 5 % Direction: ± 5°
Wave Model Calibration
Besides the bathymetry, calculation domain and offshore wave conditions, the Delft3D-WAVE model
also has certain parameters that may be set by the user. During the 2006 measurement campaign
wave data was collected at location A with a SeaPac and at location B (the same SeaPac instrument
as used at location A but deployed at later date and also an S4 deployemnt) as shown in Figure B.1.
The wave measurements at locations A and B, together with other shallow water measurements in
Big Bay were used to calibrate the Delft3D-WAVE model (Smith et al., 2007). The comparisons
between the model simulations and these measured wave data are presented in Figures B.10 and
B.11.
Figure B.10: Comparison between Delft3D-WAVE simula tions and measurements at location A (Seapac 71079). The estimated accuracy of the S EAPAC measurements indicated in the plots are based on the work of Sch üttrumpf et. al . (2006).
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Figure B.11: Comparison between Delft3D-WAVE simula tions and measurements at location B (Seapac 71079 and S4). The estimated accuracy of the SEAPAC measurements are based on the work of Schüttrumpf et. al . (2006).
Examination of the Figures B.10 and B.11 indicates that the Delft3D-WAVE wave height and period
parameters generally compare well with the measurements. Some minor discrepancies occur that
may be the result of local wind energy not being included in these calibration simulations. In Figure
B.10, the small differences in the Delft3D-WAVE and SeaPac directions (taking into account the
SWAN vs S4
0.0
2.0
4.0
6.0
8.0
10.0
12.0
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SWAN - Madsen=0.05 S4 Seapac
Big Bay Location
0.0
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SWAN - Madsen=0.05 S4 Seapac 71079
Big Bay Location
220.0
225.0
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14-Nov 19-Nov 24-Nov 29-Nov 4-Dec 9-Dec 14-Dec
Date
Mea
n D
ir (d
eg)
SWAN - Madsen=0.05 Seapac 71079
S4
Seapac
Hmo: 5 % Direction: ± 5°
Estimated accuracy
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measurement accuracy of the SeaPac) confirms that the model represents the wave direction within
measurement accuracy at this location (i.e. in the middle of Big Bay).
The SEAPAC measurements and simulations at the jetty location A, both indicate that the waves
were small, with significant wave heights (Hmo) less than 0.5 m for most of the time (Figure B.10).
Considering that the SeaPac was placed in a water depth of 12 m, it is expected that the reliability of
the measured wave direction will be poor, due to the limited sensitivity of the SEAPAC in measuring
small waves from this depth. This is due to the fact that the wave directional information is being
derived from the small horizontal orbital current velocity components measured by the SEAPAC by
applying a transfer function, based on the Linear Wave Theory (Van Tonder, 1994). Therefore, the
direction data are not considered for as being adequate for calibration purposes and consequently
are not presented in Figure B.10. (It should be noted that the primary function of this instrument
placed at the Jetty was to measure long-waves as part of a separate study.)
Although the computational grid in the present study is different from the ones used in the study upon
which these calibrations are based ( Smith et al., 2007) , the model calibration is considered to
remain valid as the same parameter settings have been used in both studies. These are summarised
in Table B.1. Further, for the simulation undertaken for the 1999-2000 period, it was ensured that the
wave module completed the same number of iterations for both RO Plant simulations (this study) and
the Phase 2 simulations both with and without the changes to the harbour (Smith et al., 2007). The
wave module has been “on-line” with the flow module (i.e. in a coupled mode) to ensure that the
wave simulations use the correct water levels at all times.
Table B.1 Wave model parameters
Parameter Value Directional sector 0° - 360°
No. directions in directional space 36 Lowest frequency 0.03 Hz Highest frequency 0.5 Hz No. frequency bins 24
Spectrum Jonswap Spectral peak enhancement factor 2.0
Width energy distribution 18.2 - 1.66xTp for Tp < 9.3 s 1.09xTp - 7.6 for Tp > 9.3 s
Depth induced breaking Battjes and Janssen Alfa 1
Gamma 0.73 Bottom friction Madsen
Friction coefficient 0.05 Non-linear triad interactions Activated
Wind growth No Whitecapping Activated Quadruplets No
Frequency shift Activated Reflection No
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B2.4 Hydrodynamic simulations and Water Quality Sim ulations
Delft3D-FLOW (Lesser et al., 2004) is a three-dimensional hydrodynamic model that includes
formulations and equations that take into account the following processes:
• tidal forcing;
• wind forcing;
• wave forcing;
• baroclinic currents and vertical mixing induced by changes in water temperature resulting from
both advection of warmer/cooler water into the bay as well as local air-sea interactions;
• the effect of the earth’s rotation (Coriolis force).
The system of equations in Delft3D-FLOW comprise the horizontal momentum equations, the
continuity equation, the equation of state and the advection-diffusion equation for heat, salt and other
conservative tracers which are solved using the Alternating Direct Implicit scheme. Vertical
turbulence is modelled using the k-ε turbulence closure model. The computation grid is an irregularly-
spaced, orthogonal, curvilinear grid in the horizontal and a sigma-coordinate grid in the vertical. The
equations and their numerical implementation are described in detail in WL|Delft Hydraulics (2005)
and a very clear exposition is also presented by Lesser et al. (2004).
Processes included in the model
The processes modelled in the Saldanha Bay-Langebaan Lagoon system include the following:
• Tides: The Saldanha Bay-Langebaan Lagoon system has a strong marine character with its
waters originating in the adjacent Benguela Upwelling System. Tidal forcing is strong at depth,
in the vicinity of the mouth of Saldanha Bay and with increasing proximity to Langebaan
Lagoon. Tides play an important role in the forcing of currents in this system and tides have
thus been included in the modelling via water level variations applied to the model boundary.
• Wind-driven flows and mixing : In general, wind-forcing is the dominant physical forcing
mechanism determining the surface layer current speed and direction in both Small and Big
Bay as well as mixing processes in the water column. Wind times series are specified for the
whole model domain. Wind setup and Coriolis tilt effects on the water levels at the model
boundaries also have been taken into account in the simulations.
• Wave-driven flows, wave stirring and generation of turbulence : Saldanha Bay is exposed
to swell waves from the Atlantic Ocean as well as locally-generated wind-waves. It is expected
that wave-driven currents inside Saldanha Bay will be confined to the narrow surf-zone in Big
Bay and are unlikely to play a significant role in the large-scale circulation of Saldanha Bay.
However these flows are expected to play a significant role in the dispersion of effluents at
Site 1. Waves also play a significant role in the fate of fine particles via the enhancement of
bed shear stresses (i.e. stirring up of sediments) at the seabed. Explicit simulations of the
transport and fate of sediments (i.e. backwash sediments) have not been undertaken here.
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• Water column structure, Temperature and Salinity : Both the temperature and salinity of the
water column has been modelled. The pycnocline dynamics and baroclinic currents play an
important role in the hydrodynamic and water quality functioning of Saldanha Bay. Measured
salinities in Saldanha Bay lie in a limited range from 34.8 to 35.0 psu in Big Bay (Lufer et al.,
1997) and thus do not play a major role in the baroclinic dynamics and water column density
structure in the bay. Temperature effects thus almost exclusively determine the density
dynamics of the water column both within the bay and over the adjacent shelf. However, given
that the proposed brine discharge plume behaviour is highly dependant on salinity, it has been
necessary to simulate both temperature and salinity in this study.
The water column structure in Saldanha Bay is seasonal, varying from a strongly thermally
stratified water column for the most of the year (August to May) to well-mixed conditions during
the mid-winter months (June to July). The water column structure is determined by the
opposing forces of buoyancy inputs (due to atmospheric heat fluxes into the surface waters
and the input of cold bottom waters into the Bay due to upwelling forcing from the adjacent
shelf) that enhance water column stratification and mixing of the water column by primarily
winds but also waves (i.e. wind- wave- and tidally driven currents and turbulence resulting in
mixing of the water column). These processes thus control the pycnocline dynamics and
vertical mixing of the water column which, together with advective fluxes by wind- wave- and
tidally-driven currents, ultimately determine the behaviour of biogeochemical parameters and
discharges into the Bay. Thus it has been necessary to explicitly include all of these processes
in the model (e.g simulation of air-sea fluxes , wave generated turbulence, etc)..
Model input times series
The input times series to the model include sea level (predicted tides and wind-driven sea level
changes) and water column structure at the open boundaries of the model, wind and a range of
atmospheric variables. The wave information is obtained from the coupled wave model.
Air-sea fluxes
A heat flux model is incorporated to account for air-sea interactions. The incoming solar and
atmospheric radiation, air temperature and relative humidity is prescribed, while the terms related to
heat loss (evaporation, back radiation and convective heat flux) are computed by the model.
The times series of incoming solar radiation (Figure B.12) is estimated from theoretical clear sky
radiation (Seckel and Beaudry, 1973), reduced by a factor of 0.685 (assumed transmissivity of the
atmosphere in this region) and further modified (reduced) by measured cloudiness (Figure B.13)
based on the observed mean cloudiness at the nearby Cape Columbine lighthouse. The relative
humidity values (Figure B.14) used are those measured at Cape Columbine daily at 08:00B, 14:00B
and 20:00B while the air temperature time series (Figure B.15) used are those measured at Saldanha
Bay Port Control.
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Figure B.12: Theoretical clear sky radiation for th e period simulated.
Figure B.13: Measured cloudiness converted to perce ntage cloud cover from cloudiness estimates in octals made daily at the Cape Columbin e lighthouse at 08:00, 14:00 and 20:00 B).
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Figure B.14: Air temperatures measured at Saldanha Port Control for the period simulated.
Figure B.15: Relative humidity (%) measured daily a t 08:00B, 14:00B and 20:00 B) at the Cape Columbine lighthouse.
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WInd
The wind used in the simulations was based on hourly wind data measured at Sladanha Bay Port
Control in Small Bay. Since the sensor is located on a hill 50 m above mean sea level (MSL), the
measured wind speeds were reduced to represent the wind speed 10 m above MSL which is required
by the numerical model. Therefore, a correction factor of 0.9 was applied to the measured wind
speeds. Time series of wind speed and direction for the 1999-2000 model simulation period are given
in Figures B.16a and b. The wind speed and direction for the 2006 calibration period are plotted in
Figure B.17.
Sea Level at the Open Boundaries
The sea level specified at the open boundaries of the model comprises predicted tides as well as
wind-driven water level changes over the shelf.
The open boundaries are located along the three offshore edges of the model, that is the Southern,
Western and Northern boundaries. At these open boundaries, a water level time-series is specified
which is based on the predicted tide with a modification to compensate for time-varying wind setup
and Coriolis tilt effects. The 8 largest amplitude tidal constituents along the West Coast (Rosenthal
and Grant, 1989) used to predict the tide are listed in Table B.2. There is only a small tidal lag along
the west coast of southern Africa, so differences in the tidal phases between the northern, western
and southern open boundaries were ignored. The water levels at eth open boundary are specified at
2 minute intervals.
Table B.2: Tidal constituents for Saldanha Bay (Ros enthal and Grant, 1989)
Tidal
constituent
Amplitude
(m)
Phase
(degrees)
M2 0.489 90.6
S2 0.213 112.0
N2 0.132 78.8
K2 0.070 112.2
K1 0.056 134.8
MU2 0.021 64.4
O1 0.015 260.1
P1 0.014 131.0
The tide sea levels specified in the model for the full one year simulation period (1999 to 2000) is
shown in upper panels of Figures B.16a and b. The predicted sea levels for the 2006 calibration
period are plotted in Figure B.17.
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Figure B.16a: Water levels and wind time series inp ut for the modelling from 30 June 1999 to 1 January 2000.
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Figure B.16b: Water levels and wind time series inp ut for the modelling from 1 January 2000 to 1 July 2000.
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Figure B.17: Water levels and wind time series inpu t for the modelling from 19 October 2006 to 15 December 2008.
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Water column Stratification at the Open Boundaries
The model includes baroclinic effects (currents and vertical mixing) induced by changes in water
temperature resulting from both advection of warmer/cooler water into the bay as well as local
insolation effects. The inputs for the heat flux model have already been discussed (see start of this
section).
The advection of warmer/cooler water into the bay is controlled by the temperature profile specified
on the open boundaries. Based on available measurements temperature profiles for the 1999 to 2000
period (Table B.3) were developed for input into the model.
Table B.3: Seasonal temperature profiles for 1999-2 000
The temperature profiles used at the model boundaries in the monthly simulations undertaken for the
RO Plant and Phase 2 expansion of iron-ore export facilities specialist studies were obtained from
these measurements via linear interpolation and are listed in Table B.4.
Table B.4 Temperature profiles applied on model bou ndaries for 1999-2000
Temperature ( oC) Depth (m) May
1999 June199
9 July 1999
Aug 1999
Sept 1999
Oct 1999
Nov 1999
0 16 16 16 16 16 16 16 15 13 13.5 14 14 14 14 14 30 12 12 12 13 12.7 12.3 12 50 11 10.5 10 12 11 10 9 120 9 9 9 10 9.7 9.3 9 200 9 9 9 9 9 9 9 280 8 8 8 8 8 8 8
Temperature ( oC) Depth (m) Dec
1999 Jan 2000
Feb 2000
Mar 2000
Apr 2000
May 2000
Jun 2000
0 16 16 16 16 16 16 16 15 13.7 13.3 13 13 13 13 13.5 30 11.7 11.3 11 11.3 11.7 12 12 50 9 9 9 9.6 10.3 11 10.5 120 9 9 9 9 9 9 9 200 9 9 9 9 9 9 9 280 8 8 8 8 8 8 8
Temperature ( oC) Depth (m) May 1999 Aug 1999 Nov 1999 Feb 2000 May 2000 0 16 16 16 16 16 15 13 14 14 13 13 30 12 13 12 11 12 50 11 12 9 9 11
120 9 10 9 9 9 200 9 9 9 9 9 280 8 8 8 8 8
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Based on the temperature measurements taken from 23 November 2006 until 15 December 2000
and the summer profiles listed in Table B.3 and B.4, a stationary temperature profile as listed in Table
B.5 was adopted for use in the 2006 simulations used to calibrate the wave and hydrodynamic
models.
Table B.5: Temperature profile applied on model bou ndaries for 2006
Depth (m)
Temperature (°C)
0 16 15 14 30 12 50 9
120 9 200 9 280 8
In addition to this information, the model also requires certain parameter specifications. The
additional input parameters for the hydrodynamic model which were determined from the 2006
simulation period are listed in Table B.6. Thess have been used in the RO Plant modelling study.
Table B.6: Hydrodynamic model parameters
Parameter Value
Wind drag coefficient (Cd) 1.1 x 10-3 + 6.5x10-3 x Vwind
Horizontal eddy viscosity Variable (Grid dependant)
Background vertical eddy viscosity 0.0005 m2.s-1
Horizontal eddy diffusivity Variable (Grid dependant)
Background vertical eddy diffusivity 0.000001 m2.s-1
Bed friction (White-Colebrook coefficient) 0.05 m
Correction for sigma coordinates On
Horizontal Forester filter On
Vertical Forester filter Off
Time step 1 minute
The wave forcing is obtained from the rate of wave energy dissipation computed by the Delft3D-
WAVE model. The enhanced bed stresses due to the wave effects are incorporated in the model
using the friction formulation of Fredsøe (Soulsby et al. 1993).
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Calibration of the Hydrodynamic Model
The hydrodynamic model was calibrated by comparing the model results to currents and water
temperatures measured by the CSIR at the 3 locations (marked A to C in Figure B.1) for the period
20 October 2006 and 15 December 2006. The measurements were obtained during two
deployments. At location A currents were measured at 1.5 metres from the seabed for the period
20 October 2006 to 22 November 2006. Similarly, at location B currents were measured at 1.5
metres from the seabed for the period from 23 November 2006 until 15 December 2006. During this
latter period temperature was measured at a range of depths through the water column at position C.
A comparison of the modelled and predicted currents in the vicinity of the jetty (position A) is
presented in Figures B.18 and B.19. In these figures the U-component indicates the Easterly-
component of the crrent while the V-component is the Northerly-component of the current.
Scatterplots of the northerly components against the easterly components reveal the distribution of
current magnitudes and directions as shown in Figure B.20. The scatterplots show that Delft3D-
FLOW tends to predict smaller variations in velocity than those measured. The model, nevertheless
still represents the measurements very well at this particular location.
The level of calibration of the model can further be analysed by considering the performance
statistics advocated by Sutherland et al. (2004). According to Sutherland et al. (2004), the
performance of a model compared to measurements can be assessed by the adjusted relative mean
absolute error (ARMAE) where the adjustment indicates incorporation of the influence of
observational errors (OE). They also provide a classification system based on the adjusted relative
mean absolute error to assess the performance of a model compared to measurements. For current
measurements, Sutherland et al. (2004) recommend a value for the observational errors of 0.05 m.s-1
which is much larger than the average error (2% of average speed) in the SeaPac instrument which
is approximately 0.001 m.s-1. Using the value of 0.05 m.s-1 as observational error gives an excellent
calibration according to the ARMAE values listed by Sutherland et al. (2004) while an observational
error of 0.001 m.s-1 yields a reasonable calibration. This indicates that the calibration of the
hydrodynamics is sufficient in the vicinity of the jetty in Big Bay (i.e. at locations proposed for RO
Plant discharges into Big Bay).
The comparison between the bottom currents near the centre of the bay (position B in Figure B.1) is
presented in Figures B.21 and B.22. Here the model also represents the measurements fairly well
despite the fact that in this part of the bay there exist large circulation eddies driven by the interaction
between the tidal flow and wind driven currents. The scatterplots in Figure B.23 of the northerly
current components against the easterly current components also show that the measured current
distributions are complex and that there is greater variability in the measured currents than produced
by the model. However, the measured outliers in Figure B.23 along Ueast of approximately -0.16 m.s-1
are attributed to a single strong wind event on 10 December 2006. The performance statistics
outlined in the previous paragraph indicates a reasonable to good calibration for this position.
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Figure B.18: Measured and modelled bottom currents at position A (see Figure B.1) from 22 October 2006 to 5 November 2006
Figure B.19: Measured and modelled bottom currents at position A (see Figure B.1) from 5 November 2006 to 22 November 2006.
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-0.2 -0.1 0 0.1 0.2Ueast (m/s)
-0.2
-0.1
0
0.1
0.2
Uno
rth (
m/s
)
-0.2 -0.1 0 0.1 0.2Ueast (m/s)
-0.2
-0.1
0
0.1
0.2
Uno
rth (
m/s
)
Measurements Model
Figure B.20: Scatterplots of the measured and model led bottom currents at position A (see Figure B.1).
Figure B.21: Measured and modelled bottom currents at position B (see Figure B.1).
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Figure B.22: Measured and modelled bottom currents at position B (see Figure B.1) from 3 December 2006 to 15 December 2006.
Figure B.23: Scatterplots of the measured and model led bottom currents at position B (see Figure B.1).
-0.2 -0.1 0 0.1 0.2Ueast (m/s)
-0.2
-0.1
0
0.1
0.2
Uno
rth (
m/s
)
-0.2 -0.1 0 0.1 0.2Ueast (m/s)
-0.2
-0.1
0
0.1
0.2
Uno
rth (
m/s
)
Measurements Model
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Comparisons between the measured near the centre of the bay (position C in Figure B.1) and
modelled surface and bottom temperatures at the same location are presented in Figures B.24 and
B.25. The model predictions show the correct trends although the exact measured temperatures are
at times not reproduced. Additional information on the calibration is presented in the regression plots
presented in Figure B.26. These indicate that the surface temperatures are well correlated while the
model tends to indicate warmer bottom temperatures than do the measurements. The reason for this
is that on occasion the water column stratification is not sufficiently maintained in the model. The
performance statistics of Sutherland et al. (2004) may also be applied to temperatures. Using a
minimum observation error of 0.1 ºC (Seamon temperature gage), the calibration of temperatures at
this location in the model may be classified as good.
In general, it may be concluded that the model can reliably simulate the overall tidal, wind-driven,
wave-driven circulation and water column mixing processes. Differences between the modelled and
measured data, in general, may be ascribed to penetration into the bay of large–scale circulation
features over the adjacent shelf and further offshore (i.e. features generated outside the model
domain), as well as localised effects such as spatial variation of winds over the bay and rip currents
not accounted for in the model forcing. Limited spatial resolution in the computational grids also may
result in differences between the model results and measurements. This is expected to be less of an
issue for the RO Plant simulations as the resolution of computational grids used in this study
significantly exceeds that of the computational grids used in the Phase 2 modelling study and to
calibrate the model.
Figure 6.24: Comparison between measured and modell ed temperatures at position C (see Figure B.1) from 23 November 2006 to 3 December 200 6.
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Figure B.25: Comparison between measured and modell ed temperatures at position C (see Figure B.1) from 3 December 2006 to 15 December 200 6.
Figure B.26: Regression plots of the measured and m odelled surface and bottom temperatures at position C (see Figure B.1).
5 10 15 20Tmodel (oC)
5
10
15
20
Tm
eas (
oC
)
5 10 15 20Tmodel (oC)
5
10
15
20
Tm
eas (
oC
)
Surface Bottom
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Figure B.27: Measured and modelled temperatures at North Buoy (see Figure 6.2) from 1 July1999 to 1 October 1999
Figure B.28: Measured and modelled temperatures at North Buoy (see Figure 6.2) from 1 October 1999 to 1 January 2000.
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Figure B.29: Measured and modelled temperatures at North Buoy (see Figure B.1) from 1 January 2000 to 1 April 2000.
There exists additional data in the form of temperatures measurements that were taken during 1999-
2000 at North Buoy in Small Bay (indicated on Figure B.1) that can be used to further calibrate or
verify the model. The measured temperatures near the surface and near the bottom are compared
to the modelled temperatures in Figures B.27, B.28 and B.29. As indicated in these figures, the
modelled results compare very well to the measurements. Considering the position of the
measurement location (North Buoy), these results indicate that the intrusion and retreat of cold water
associated with summer upwelling and downwelling as well as the tidal fluxes into the bay are
predicted correctly.
In summary, the overall accuracy of the model. is considered sa tisfactory for the purpose of
simulating the transport and fate of the brine disc harge plumes .
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