dunlin decommissioning es december 2012 - appendices a to f eia.pdf

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FAIRFIELD ENERGY LTD

DUNLIN ALPHA PLATFORM

DECOMMISSIONING EIA

ASSESSMENT APPENDICES A TO F

Report Reference. P1623_RN3027_Rev1.doc

Issued 04 December 2012

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DUNLIN ALPHA PLATFORM DECOMMISSIONING EIA

DOCUMENT RELEASE FORM

Title:

DUNLIN ALPHA PLATFORM DECOMMISSIONING EIA ASSESSMENT APPENDICES A TO F

Client: FAIRFIELD ENERGY LTD

Report Reference: P1623_RN3027_REV1.DOC

Date of Issue: 04 December 2012

Hard Copy Digital

Distribution: FAIRFIELD ENERGY LTD No: n/a PDF

Intertek METOC No: n/a PDF

Prepared By: Nicholas Morley, Colin McPherson, Alistair Bird

Project Manager: Authoriser:

Alistair Bird Alistair Bird pp Beth Monkman

Rev No Date Reason Author Checker Authoriser

Rev 0 07/08/2012 Issued for Client Comment NM, CMcP BM AB

Rev 0-A 21/09/2012 Client comments addressed NM, CMcP BM BM

Rev 1 04/12/2012 Client comments addressed APB BM BM

COPY NUMBER: (applies to hard copies only) Intertek METOC is the trading name of Metoc Ltd, a member of the Intertek group of companies



REPORT REFERENCE: P1623_RN3027_REV1.DOC 04/12/2012

CONTENTS

APPENDIX A BASELINE ENVIRONMENT ................................................................... A-1

A.1 INTRODUCTION AND SOURCES OF INFORMATION ........................................................... A-2

A.2 PHYSICAL AND CHEMICAL ENVIRONMENT ..................................................................... A-3

A.3 BIOLOGICAL ENVIRONMENT ......................................................................................... A-4

A.4 SOCIO-ECONOMIC ASPECTS ...................................................................................... A-11

A.5 ONSHORE LOCATIONS ............................................................................................... A-13

A.6 REFERENCES............................................................................................................ A-19

APPENDIX B BASIS FOR ASSESSMENT ................................................................... B-1

B.1 INTRODUCTION ........................................................................................................... B-2

B.2 ASSESSMENT METHOD ................................................................................................ B-2

B.3 ASSESSMENT ASSUMPTIONS ....................................................................................... B-4

B.4 REFERENCES............................................................................................................ B-12

APPENDIX C WELLS PLUGGING AND ABANDONMENT .......................................... C-1

C.1 INTRODUCTION ........................................................................................................... C-2

C.2 WELLS P&A ASPECTS ................................................................................................. C-2

C.3 SUMMARY OF WELLS P&A IMPACTS ............................................................................. C-5

APPENDIX D TOPSIDES REMOVAL ........................................................................... D-1

D.1 BASE CASE (REVERSE INSTALLATION) .......................................................................... D-2

D.2 TOPSIDES REMOVAL COMPARATIVE ASSESSMENT ........................................................ D-6

D.3 SUMMARY OF ENVIRONMENTAL IMPACTS ...................................................................... D-9

D.4 REFERENCES............................................................................................................ D-10

APPENDIX E CGB AND DRILL CUTTINGS PILE ........................................................ E-1

E.1 INTRODUCTION ........................................................................................................... E-2

E.2 IMPACTS ASSOCIATED WITH PHYSICAL PRESENCE OF CGB ........................................... E-3

E.3 CELLS CONTENTS IMPACT ASSESSMENT ...................................................................... E-4

E.4 DRILL CUTTINGS ......................................................................................................... E-9

E.5 SUMMARY OF ENVIRONMENTAL IMPACTS .................................................................... E-27

E.6 REFERENCES............................................................................................................ E-30

APPENDIX F CUMULATIVE IMPACTS ........................................................................ F-1

F.1 INTRODUCTION ........................................................................................................... F-2

F.2 CLIMATE CHANGE IMPACTS ......................................................................................... F-4




F.3 SUMMARY – CUMULATIVE IMPACTS ............................................................................... F-4

F.4 REFERENCES.............................................................................................................. F-5

TABLES

TABLE A-1: SUMMARY OF BASELINE PHYSICAL/CHEMICAL ENVIRONMENT .......................................... A-4

TABLE A-2: SUMMARY OF BASELINE BIOLOGICAL ENVIRONMENT ....................................................... A-5

TABLE A-3: SUMMARY OF KEY ENVIRONMENTALLY SENSITIVE PERIODS ............................................ A-5

TABLE A-4: SPECIES OF CONSERVATION SIGNIFICANCE .................................................................. A-7

TABLE A-5: SENSITIVE PERIODS FOR FISH SPAWNING AND NURSERY ................................................ A-7

TABLE A-6: SEABIRD VULNERABILITY ............................................................................................... A-9

TABLE A-7: ANNUAL VALUE (£) OF LANDINGS FOR THE ICES AREA SURROUNDING DUNLIN 1 ........... A-12

TABLE A-8: EXAMPLES OF PROTECTED AREAS ON THE NE COAST OF ENGLAND ............................. A-13

TABLE A-9: EXAMPLES OF PROTECTED AREAS ON THE SW COAST OF NORWAY ............................. A-16

TABLE B-1: IMPACT SEVERITY CATEGORISATION ............................................................................. B-2

TABLE B-2: SEVERITY CATEGORISATION.......................................................................................... B-3

TABLE B-3: WELLS PLUGGING AND ABANDONMENT ......................................................................... B-5

TABLE B-4: TOPSIDES AND MSF REMOVAL ...................................................................................... B-6

TABLE B-5: ONSHORE DECOMMISSIONING AND MATERIALS DISPOSAL ............................................. B-9

TABLE B-6: CGB AND DRILL CUTTINGS AFTER DECOMMISSIONING ................................................ B-10

TABLE B-7: ACCIDENTAL EVENTS .................................................................................................. B-11

TABLE C-1: WELLS P&A ATMOSPHERIC EMISSIONS ......................................................................... C-3

TABLE C-2: WELLS P & A IMPACTS .................................................................................................. C-5

TABLE D-1: WASTE WATER DISCHARGE DURING DECOMMISSIONING ................................................ D-3

TABLE D-2: BASE CASE ATMOSPHERIC EMISSIONS (OFFSHORE AND ONSHORE) .............................. D-4

TABLE D-3: COMPARISON OF TOPSIDES REMOVAL OPTIONS IMPACTS ............................................. D-7

TABLE D-4: COMPARISON OF CO2 EMISSIONS ESTIMATES FOR TOPSIDES REMOVAL OPTIONS ........ D-8

TABLE D-5: TOPSIDE REMOVAL IMPACTS ......................................................................................... D-9

TABLE E-1: ATMOSPHERIC EMISSIONS FROM NAVIGATION AID MAINTENANCE .................................. E-4

TABLE E-2: CELL CONTENTS – MAJOR COMPONENTS ...................................................................... E-6

TABLE E-3: CELL CONTENTS – OTHER COMPONENTS ....................................................................... E-6

TABLE E-4: DRILLING HISTORY ...................................................................................................... E-10

TABLE E-5: DIMENSIONS OF THE DUNLIN CUTTINGS PILE ............................................................... E-16

TABLE E-6: ORGANIC CONTAMINANTS ASSOCIATED WITH CUTTINGS.............................................. E-19

TABLE E-7: TYPICAL METAL CONCENTRATIONS ............................................................................. E-19

TABLE E-8: COMPARISON OF DUNLIN CUTTINGS PILE WITH OSPAR 2006 CRITERIA ...................... E-20




TABLE E-9: ENVIRONMENTAL IMPACTS OF OPTIONS WITH RESPECT TO THE BASE CASE ................. E-22

TABLE E-10: DRILL CUTTINGS DECOMMISSIONING SUMMARY ........................................................ E-26

TABLE E-11: SUMMARY OF CGB AND DRILL CUTTINGS IMPACTS .................................................... E-29

TABLE F-1: OVERALL CO2 EMISSIONS FROM DUNLIN A DECOMMISSIONING PROGRAMME ................ F-4

FIGURES

FIGURE A-1: MAP OF MARINE CONSERVATION AREAS ................................................................... A-10

FIGURE A-2: SEASONAL VARIATION IN FISHING ACTIVITY (2002-2007) ............................................ A-12

FIGURE E-1: CRITERIA FOR ACCEPTABILITY OF CUTTINGS PILES (OSPAR 2006A) ......................... E-12

FIGURE E-2: EXTENT OF CUTTINGS PILE IN 1996 (SHELL 1997) ..................................................... E-14

FIGURE E-3: EXTENT OF CUTTING PILE IN 2008 (GEL 2009) ......................................................... E-15

FIGURE F-1: LOCATION OF DUNLIN IN RESPECT TO OTHER CGBS .................................................... F-3




GLOSSARY

< Less than

> Greater than

A AC Acceptability Criteria

ALARP As Low As Reasonably Practicable

AUMS Aberdeen University Marine Science

B BAC Background Assessment Criteria

BAP Biodiversity Action Plan

BC Baseline Concentrations

BTEX Benzene, Toluene, Ethylbenzene, and Xylenes

C CEFAS Centre for Environment, Fisheries and Aquaculture Science

CGB Concrete Gravity Base

CH4 Methane

CO Carbon Monoxide

CO2 Carbon Dioxide

CoP Cessation of Production

D dB Decibel

DCP Drill Cuttings Pile

DECC Department of Energy and Climate Change

Defra Department for Environment, Food and Rural Affairs

DP Dynamic Positioning

DTI Department of Trade and Industry

E EC European Commission

EIA Environmental Impact Assessment

ES Environmental Statement

GBq Giga bequerels

G GIS Geographical Information Service

H HLCV Heavy Lift Construction Vessel

HR Conservation (Natural Habitats &c.) Regulations 1994 (as amended)

H2S Hydrogen Sulphide

I IBA Important Bird Areas

ICES International Council for the Exploration of the Seas

J JNCC Joint Nature Conservation Committee

JIP Joint Industry Project

K km Kilometre

km2 Square Kilometres

km2yr Square Kilometres year

L LAT Lowest Astronomical Tide

M µgl-1 Microgram per litre

µgm-3 Microgram per cubic metre

µPa Micro pascal

m Metre

m2 Square metre

m3 Cubic metre

M Million

MFA Marine Fisheries Agency




mgl-1 Milligram per litre

mgkg-1 Milligrams per kilogram

MMO Marine Management Organisation

ms-1 Metres per Second

MSF Module Support Frame

N N2O Nitrous Oxide

NM Nautical Mile

NNS Northern North Sea

NO2 Nitrogen Dioxide

NORM Naturally Occurring Radioactive Material

NOx Nitrogen Oxides

NW Northwest

O OBM Oil Based Mud

OGUK Oil and Gas UK

OSPAR Convention for the Protection of the Marine Environment of the North East Atlantic (Oslo Paris Convention)

P PAH Polycyclic Aromatic Hydrocarbons

P&A Plugged and Abandoned

PON Petroleum Operations Notice

R ROV Remotely Operated Vehicle

S SAC Special Area of Conservation

SCANS Small Cetaceans in the European Atlantic and North Sea

SEA Strategic Environmental Assessment

SMRU Sea Mammal Research Unit

SOx Sulphur Oxides

SPA Special Protection Area

SSSI Site of Special Scientific Interest

SW Southwest

T T Tonne

THC Total Hydrocarbons

U UK United Kingdom

UKCS United Kingdom Continental Shelf

UKOOA United Kingdom Offshore Operators Association (now Oil and Gas UK)

V VOC Volatile Organic Carbon

W WBM Water Based Mud



REPORT REFERENCE: P1623_RN3027_REV1.DOC A-1 04/12/2012

Appendix A Baseline Environment




A.1 Introduction and Sources of Information

This baseline description presents a summary of the Dunlin Cluster environmental data taken from other more detailed reports which are referenced at the end of this Appendix.

The baseline describes the current conditions around the Dunlin Alpha (Dunlin A) platform to allow a comparison to be made with any predicted changes, recognising that there are natural environmental variations including seasonal variation in the plant and animal populations.

The level of detail provided for different aspects of the baseline environment is commensurate with the level of likely interaction between the decommissioning activities and the environment. Surface water species (birds) and water column species are described in some detail. Benthic communities are described briefly as there will be only limited interaction with the benthic ecology as a result of the CGB remaining in place.

An understanding of the baseline environment has been achieved through a review of primary field studies and a review of secondary resources such as existing documentation and literature. The primary and secondary information sources for the Dunlin Cluster are listed below:

A.1.1 Primary data

Dunlin Development Debris Clearance, „Mud Mound‟ and Environmental Baseline Survey (Gardline Geosurvey Ltd 2009, Gardline Environmental Ltd 2009a)

Osprey Debris Clearance, Habitat Assessment and Environmental Baseline Survey (Gardline Environmental Ltd 2009b)

Remotely Operated Vehicle (ROV) video recording of Dunlin A conductors (Fairfield Betula Ltd 2008).

Strategic Environmental Assessment of the Mature Areas of the North Sea SEA 2 (DTI, 2001)

A.1.2 Secondary data

Other data on particular elements of the physical, biological and socio-economic environment were obtained from the appropriate agencies. Examples of some of the key secondary data sources are given below.

Maritime Data Online Geographic Information System (GIS) (Anatec UK Ltd 2007)

Survey data for surrounding oil installations (AUMS 1990, IOE 1988)

Block-specific seabird vulnerability tables for the UK (JNCC 1999)

Cetacean population estimates and distribution (SCANS-II 2008, Reid et al. 2003)

Marine and Fisheries Agency commercial fishery catch and landing statistics for the period 2002 to 2007 (MFA 2008)




Oil and Gas UK (2009). Data Review for an Industry-Wide Response to Cuttings Pile Management Final Report. Prepared by ERT (Scotland) Ltd. Physical / Chemical Environment

UK Offshore Energy Strategic Environmental Assessment, Environmental Report ( DECC, 2011)

A.2 Physical and Chemical Environment

To evaluate any likely impact of the options considered for the decommissioning of Dunlin A, the present day environmental conditions need to be understood. The current environmental status reflects historical operational and disposal practices of the offshore and marine industries. Over time, the results of these activities have been modified by the effects of wind, wave and tidal currents, both on the seabed and in the water column.

The Dunlin Cluster of fields is located in Blocks 211/23 and 211/24 of the UK Continental Shelf in the Northern North Sea (NNS), some 500km north-northeast of Aberdeen and 11.2km from the boundary line with Norway, and lies in water depth of approximately 150m.

The meteorological conditions of the region are characterised by rapidly changing weather conditions. Wind direction is commonly from the south and southwest throughout the year, but north and northeast winds can dominate between May and August. Predominant wind speeds throughout the year represent moderate to strong breezes (6-13m/s), with the highest frequency gales during winter months (November – March) (DTI, 2001a).

The water current patterns in the area are complex with various strong non-tidal currents interacting with relatively weak tidal flow. The general pattern of water movement in the North Sea may be strongly influenced by short-to-medium term weather conditions, resulting in considerable seasonal and interannual variability (DTI, 2001a).

Tidal currents in the area predominantly flow approximately southeast and northwest. Non-tidal (residual) currents are directionally more unpredictable in this area of the NNS. Average current velocities are 0.50ms-1-1ms-1 at the surface decreasing with depth to 0.20ms-1-1ms-1 near the seabed. The depth average current speed is 0.46ms-1-1ms-1 (AMEC plc 2008).

The significant wave height ranges from 8.7m (monthly) to 11.4m (annual) with the maximum 100-year significant wave height estimated to be 15.6m (AMEC plc 2008).

The seabed surface around Dunlin A consists of fine to gravelly sands with some shell debris. The surface is characterised by a number of natural and man-made features including minor depressions, cobbles and small boulders, extensive anchor scarring, rock dumps, and items of debris. (Gardline Environmental Ltd 2009a, b)

A drill cuttings accumulation covers part of the Dunlin A CGB structure and adjacent seabed. The cuttings were generated from the start of drilling wells in 1978 and are composed of the remnants of the sand and rock brought to the surface as the well progressed to the oil-bearing zones. In addition to this geological material the cutting pile contains residual drilling mud, used to keep the drill bit lubricated and cooled. During the early period of operations oil based muds (OBM) were used and discharged in association with the cuttings.




These discharges were effectively banned in 1996, after which only cuttings drilled using water based muds (WBM) could be discharged.

The oil content of the cuttings accumulation on the seabed has been monitored and the present-day residual levels are documented as being below OSPAR reporting thresholds. No further cuttings will be added to the accumulation as current drilling practice at Dunlin requires all drill cuttings to be shipped to shore for disposal. Further information on cuttings at Dunlin is provided in Appendix E.4. Table A-1 summarises the baseline physical and chemical environment.

Table A-1: Summary of baseline physical/chemical environment

Bathymetry 134m – 160m

Wind No single predominant wind direction, wind direction commonly ranges from the S and SW throughout the year. N and NE winds are frequent, and sometimes predominate, between May and August.

Wave Height 8.7m (monthly) to 11.4m (annual)

Current Surface 0.50 to 1.0ms-1

Seabed 0.20 to 1.0ms-1

Seabed Features Generally characterised by features including minor depressions and cobbles/small boulders, extensive anchor scarring, drill cuttings accumulation, rock dumps and items of debris.

Sediment

Seabed sediments are typical of the region and consist of fine to medium quartz sand with shell fragments and gravel overlying sandy silty clay. Hydrocarbon concentrations in the area are slightly elevated above North Sea background concentrations. All metal concentrations, with the exception of barium, are below their respective OSPAR allowable background concentrations.

A.3 Biological Environment

This section describes the components of the biological environment which will be considered when assessing the decommissioning impacts. Any potential impacts are expected to be localised and confined to organisms that live in or on the seabed and, to a lesser extent, in the water column.

As described earlier, the seabed surrounding the Dunlin platform has been modified by platform activities since the mid 1970s and must be considered in that context.

A summary of the baseline biological environment is provided in Table A-2.

Key environmentally sensitive periods of the year are summarised in Table A-3.

The purpose of the tables is to identify any periods during the year where the target species may be considered to be more sensitive to external impacts. These sensitivities are usually related to breeding cycles or migration transits. The tables are used to inform impact assessment (and development of mitigation measures) for any environmental aspects which exceed the significance criteria in Appendix B2.




Table A-2: Summary of baseline biological environment

Plankton High plankton productivity during spring, begins to decline through the summer with an occasional small increase in autumn. Communities dominated by Thalassiosira spp and calanoid copepods (DTI, 2001a)

Benthic Communities

Benthic communities are typical for this region of the NNS and are dominated by the polychaetes Minuspio cirrifera, Exogone veruera and Aricidea catherinae, Molluscs and Thyasira sp. No evidence of any species or habitats of conservation significance under the EC Habitats Directive (92/43/EEC) (DTI, 2001a).

Fish

Dunlin lies within the spawning grounds of the demersal species haddock, saithe, Norway pout and blue whiting. In addition to spawning, the waters of the Dunlin area also act as nursery grounds for haddock, Norway pout, blue whiting and mackerel. (Ellis et al, 2012; Coull et al, 1998; DTI, 2001b)

Marine Mammals

The waters of the Dunlin area are rich and diverse in cetacean populations with nine species observed in the vicinity of the development. Peak whale numbers recorded between July and August (Reid et al, 2003, SCANS-II, 2008).

Seabirds Most abundant species are fulmar, guillemot, gannet and kittiwake. Herring gulls and great black-backed gulls are widespread in winter months. Puffins are present April to July and razorbills in late summer. (JNCC, 1999)

Protected Areas

There are no existing protected sites within 40km of the Dunlin area. However, the Osprey field is located approximately 1.5km south of an area listed under Annex I of the EC Habitats Directive as stony reefs (outer shelf/upper slope iceberg plough mark zone). (JNCC, 2012)

Table A-3: Summary of key environmentally sensitive periods

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Finfish and Shellfish

Seabirds

Marine mammals

Key Very high High Moderate Low

Sources: JNCC 1999, Coull et al 1998, Ried et al (2003)

A.3.1 Plankton

The plankton community around the Dunlin area is typical of that found in the NNS owing to the continual exchange of waters and individuals from the Atlantic, Baltic and North Sea. The composition of the plankton community will vary depending upon the season and, on a longer term basis, on the interactions on an oceanic scale between the Atlantic and the NNS (DTI, 2001a).

In summary the dinoflagellate genus Ceratium (e.g. C. fusus, C. furca and C. tripos) dominates the phytoplankton community along with a constant abundance of the diatom Thalassiosira spp. The principal organisms which constitute the zooplankton comprise the Calanus sp, although there is an introduction of oceanic species via the inflow of Atlantic waters, such as Salpa




fusiformis, Calanus finmarchicus and Metridia lucen throughout the summer and late autumn (DTI 2001a).

Rates of primary plankton production vary throughout the year and are dependent on a number of factors including the availability of nutrients and light. Typically, peaks in production occur in late spring with a decline over the summer months. A smaller peak is also observed in the autumn. The lowest rate of productivity is reached during the winter months owing to the lack of light.

A.3.2 Benthic Communities

Animal communities which live on the surface or in the surface layers of the seabed are termed benthic communities. There have been several surveys undertaken that have recorded the benthic ecology of the area within and surrounding the Dunlin area, e.g. Gardline Environmental Ltd (2009a,b), IOE (1988) and AUMS (1990).

The seabed surface in the Dunlin area displays a mixture of boulder groups, extensive anchor scarring and smooth sand. These support a diverse range of animal communities. Analysis of the 2008 data indicates that the benthic community is generally similar over the whole area. There is a wide range of animal types across the site, with no clear dominant species. Bristle worms (polychaetes) contributed the majority of the recorded individuals. (Gardline Environmental Ltd 2008a, b).

The Dunlin area contains a benthic community which is typical for the NNS and is characteristic of those found in fine sediments in water depths greater than 100m in the region (Fairfield Betula Ltd 2008).

A survey of the Dunlin A platform (Fairfield Energy Ltd 2008) observed Lophelia pertusa on the well conductors and top of the CGB in those areas not covered by the drill cuttings. Lophelia pertusa is a stony coral which develops in cold, dark, nutrient-rich waters between 100 to 400m deep. It lives in colonies ranging from a few polyps to many thousands living together as a reef. As a reef building organism it is often important, in the deep-water environment, for creating new habitats or modifying the surrounding habitats, thereby increasing the abundance and diversity of other species in the area. This species is protected under the EC Habitats Directive 1992, Annex II.

A.3.3 Fish

Analysis of fisheries catch statistics (2000 - 2007) from the MFA provides an indication of the type of species currently present in the Dunlin area. It should be noted that this does not provide a definitive guide to the fish in the area and the levels of catch do not correspond directly to community structure, but it does serve as a useful indicator.

The majority of information to date has been concerned with commercial fish; however, recent data (Ellis et al. 2012) includes some consideration of species of conservation, rather than commercial, significance.

There are several fish species of conservation importance in the NNS. Table A-4 presents species classified as priority species on the UK Biodiversity Action Plan (UK BAP) list. The UK list of priority species and habitats sets out a conservation approach for 1,150 species and 65 habitats (JNCC 2012a) of




which 87 species are only found in a marine environment. Their inclusion on the list means that the UK government will take action to maintain their current range and abundance.

Table A-4: Species of Conservation Significance

Description Habitat Species Occurrence

Finfish

Pelagic

Mackerel*

Herring

Blue whiting

Low

Low

Low

Demersal

Whiting

Plaice

Ling*

Hake*

Cod*

Sandeels

Low

Low

Low

Low

High

Low

* Species which are also of commercial significance (in terms of value)

The conservation species of basking shark, tope and porbeagle are all likely to occur in small numbers throughout the North Sea, and the common skate occurs at low density throughout the NNS. However, these species are considered to be rare in the waters surrounding the Dunlin area (DTI 2001b).

Fisheries sensitivity maps (Coull et al. 1998 and Ellis et al 2012) have been used to identify the spawning grounds (location where eggs are laid) and nursery grounds (location where juveniles are common) for fish species in the vicinity of the Dunlin blocks (Table A-5). The Dunlin area lies within the spawning grounds of the demersal species haddock, cod, saithe and Norway pout. In addition to spawning, the waters of the Dunlin area also act as nursery grounds for the commercially important species mackerel, haddock, Norway pout and blue whiting (Coull et al. 1998).

Table A-5: Sensitive periods for fish spawning and nursery

Species Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Haddock N N N N N N

Mackerel N N N N N N N

Saithe S S SN SN N N

Mackerel N N N N N N N

Norway pout SN SN SN SN SN N N

Ling N N N N N N

Hake N N N N N N N N

Anglerfish N N N N N N N N

Cod SN SN SN SN N N

Whiting N N N N N N N

Blue whiting N N N N N

Spurdog N – no seasonal data

S = Spawning, N = Nursery. Source: Coull et al. (1998) and Ellis et al (2012)

Spawning in the vicinity of the Dunlin A platform occurs between January and May. Juveniles of one or more of the species in Table A-5 may be present in




the region for most of the year, with the majority present during the summer months. Additionally, Ellis et al (2012) provides an indication of the intensity of the presence of these species:

Cod spawn in high densities in the area.

Blue-whiting nurse in high densities in the area.

All other species nurse and/or spawn in low densities in the area.

The commercial fisheries catch around the Dunlin A platform (Block 211/23) is dominated by the open water (pelagic) species Atlantic mackerel and the near seabed (demersal) species Atlantic haddock and Atlantic cod.

Catches also include whiting, saithe, ling, megrim, pollack, hake, halibut, catfish and the Norway lobster.

The estimated value of the commercial fish catches is given in Table A-5 in Appendix A.4.2. Block 211/23, as a whole, is important for fisheries in the NNS.

A.3.4 Seabirds

Several bird species, likely to be present in the vicinity of the Dunlin platform, are protected and therefore any potential impact from the decommissioning options must be considered. Their presence is transient in nature and seasonal, depending on the main breeding seasons.

Species present in the Dunlin area throughout the year include kittiwakes, fulmars, guillemots and gannets. Kittiwakes are more widespread through the winter months together with herring gulls and great black-backed gulls. In addition, puffins are present in their pre-breeding and breeding seasons (April to July) and razorbills are present in late summer when they move offshore to moult and raise their chicks (Skov et al. 1995, Stone et al. 1995). Of the 59 species of birds which are named in the UK BAP list of priority species, only the herring gull is expected to be found in the Dunlin area.

Seabirds are sensitive to changes in the quality of the marine environment, especially to changes in fish stocks (food sources) and to oil pollution. The susceptibility of seabirds to surface pollutants, specifically hydrocarbons, following breeding and undergoing moulting at sea, as specified by the Joint Nature Conservancy Council (JNCC 1999), has been assessed for the immediate area around Dunlin (Table A-6). Offshore species that are most vulnerable are those that spend a great amount of time on the sea surface (such as the Atlantic puffin and common guillemot), while more aerial species such as northern fulmars, northern gannets and black-legged kittiwakes are of lower vulnerability.




Table A-6: Seabird vulnerability

Block Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

211/23

211/17

211/18

211/19

211/24

211/29

211/28

211/27

211/22

Key Very high High Moderate Low

Source: Ried et al,2003

A.3.5 Marine Mammals

The waters surrounding the Dunlin A platform contain a number of marine mammals, including whales, dolphins and seals. Several species are protected under the EC Habitats Directive, Annex II. Of the protected species, the harbour porpoise is the most common as this is the most abundant marine mammal in NW European shelf waters (Reid et al. 2003). Other cetaceans are seen less frequently in the area, with sightings occurring predominantly in the summer months. The minke whale, killer whale and pilot whale have been sighted in the vicinity of the Dunlin platform on a more regular basis than other species of cetacean. Peak whale numbers are recorded in July and August with high levels also observed in February and May (Reid et al. 2003, SCANS-II 2008). The total numbers vary on an annual and seasonal basis.

Grey seals and harbour seals have breeding colonies in the Shetland and Orkney Islands to the southwest of the Dunlin area. Both species travel considerable distances on feeding trips, up to 60km or more (although this is relatively rare) from their haul-out sites on land. As the Dunlin area is more than 130km from the nearest coastline, it is unlikely that seals will be found in the vicinity of the development.

A.3.6 Marine Conservation Areas

There are no existing protected sites within 40km of the Dunlin A platform. However, the platform is located approximately 7.4km south of an area listed under the EC Habitats Directive, Annex I, as stony reefs (outer shelf/upper slope iceberg ploughmark zone), refer to Figure A-1. This is an area of seabed that has been identified under the Natura 2000 process as having the potential to qualify as a protected habitat. It is important to note that an area that has been identified as Potential Annex I Habitat (PAIH) could become designated as a Special Area of Conservation and, therefore, must be treated as though fully protected.




Figure A-1: Map of Marine Conservation Areas




A.4 Socio-Economic Aspects

A.4.1 Existing infrastructure

Hydrocarbon exploitation in the area began in the early 1970s. There are several producing oil and gas fields within 50km of Dunlin, including the Thistle, Cormorant, Murchison, Brent, Eider and Tern developments.

A.4.2 Commercial fisheries

Commercial fisheries statistics are collected for UK waters and are provided by the Marine and Fisheries Agency (MFA). In order to map where fish catches were obtained, the sea areas around the coast of the UK have been divided into specific areas with unique reference numbers and are administered by the International Council for the Exploration of the Seas (ICES).

Catch statistics for 2004 to 2011 (MMO 2012) were obtained for ICES rectangle 51F1, within which the Dunlin area is located. The area surrounding the Dunlin A platform is significantly less than the total area of this rectangle which is some 3,000 km2. Statistical data on catches in this ICES rectangle provides details on receiving port, species landed (live weight in tonnes) and value of species. The data considers vessels using both UK and foreign ports but does not take into account foreign vessels landing at foreign ports.

The Dunlin area is predominantly used by Scottish fishing fleets and is considered a commercially important ground for both pelagic and demersal species. Approximately 145 species are reported as landed from ICES rectangle 51F1. Of these the most commercially valuable species are listed in Table A-5.

Around 5350 tonnes of fish and shellfish, worth over £4 million, are landed each year from ICES rectangle 51F1.

In terms of commercial value, the overall catch (live weight tonnes) is dominated by the pelagic species Atlantic mackerel. The demersal Atlantic cod and Atlantic haddock are also species of value in the region. The shellfish catch is of lower value (around £3500 per year), with the majority of the catch represented by Norway lobster (nephrops norvegicus) and low-value squid.

An idea of the importance of commercial fishing in the immediate vicinity of Dunlin A can be gained by comparing the annual value of landings from ICES rectangle 51F1 with those in the surrounding area (50F0, 50F1, 51F0, 52F0 and 52F1). This is displayed in Table A-5. It should be noted that the annualised data has been derived for slightly different periods between 2004 and 2011 in different offshore blocks. The table indicates that the adjacent ICES rectangle 50F0 is the most productive and commercially valuable area in the region followed by 51F1.




Table A-7: Annual value (£) of landings for the ICES area surrounding Dunlin 1

ICES Rectangle Atlantic mackerel

Atlantic cod

Atlantic haddock

Anglerfish (Monks)

Nephrops TOTAL

50F0 12,406,168 1,653,260 1,575,979 2,307,994 2,151,040 20,094,441

50F1 1,332,742 312,310 279,734, 283,822 18,265 1,947,139

51F0 3,528,595 183,862 192,085 212,911 23,243 4,140,696

51F1 3,786,411 118,630 180,969 132,604 2,090 4,220,704

52F0 308,836 15,073 40,883 230,655 26 595,473

52F1 1,208,490 8,587 17,173 12,947 13 1,247,210

Grand total (2004 – 2011) from all rectangles

22,571,242 2,291,722 2,007,089 3,180,933 2,194,677 32,245,663

Catch from rectangle 51F1 as a percentage of total species specific catch from the area

16.77% 5.17% 9.01% 4.16% 0.09%

1One ICES rectangle represents 3,000km

2

Despite this, fishing activity in the vicinity of Dunlin A is generally low during most of the year (January to September) with peaks only occurring in October, November and December (see Figure A-1).

Figure A-2: Seasonal variation in fishing activity (2002-2007)

k

10k

20k

30k

40k

50k

60k

70k

Ja

n

Fe

b

Ma

r

Ap

r

Ma

y

Ju

n

Ju

l

Au

g

Se

p

Oct

No

v

De

c

Month

Liv

e W

eig

ht

Ca

tch

(to

nn

es

)

50F0 50F1 51F0 51F1 52F0 52F1

Source: MFA (2008)

A.4.3 Shipping and other users of the sea

Shipping activity in the area is considered to be of low density (Anatec UK 2007), and is primarily due to vessels passing between Aberdeen and the various oil and gas installations in the area. Fishing vessels are also likely be present in the Dunlin area but are excluded from the 500m safety zone around the platform and other associated structures that require protection.

There is a lightly-used recreational sailing route well to the north of Dunlin A (to the north of the Thistle platform) as well as one non-dangerous unprotected




wreck 4km from Osprey. A power and communication cable connecting Dunlin A to the Brent C platform lies to the southeast of Dunlin A. There are no military practice and exercise areas, munitions or dumping sites within 100km of Dunlin A.

A.5 Onshore Locations

Any material removed during the decommissioning of the Dunlin platform will be brought ashore for processing and final disposal. Two representative locations have been chosen; the northeast coast of England and the southwest coast of Norway. The following section provides an overview of the baseline environments of these two regions in order to better understand how they may be affected by decommissioning activities onshore. Both the northeast coast of England and the southwest coast of Norway have been the sites of previous activities in the decommissioning of large oil and gas platforms, and any Dunlin-related work would take place at established decommissioning facilities and would not require the construction of new facilities.

A.5.1 Northeast Coast of England

The physical environment of the northeast coast of England is characterised by sand flats with areas of rocky foreshore, interspersed with several large river estuaries, consisting of intertidal areas made up of mud and sand. Several of these large estuaries have historically been the site of a variety of heavy industries, including ship building, steel making and industrial chemical production. This has led to a large human influence on the geography of these estuaries in the form of the dredging and widening of navigable channels, and the construction of dockyards and quaysides. The largest population centres of the region are also located on these river estuaries, Newcastle-upon-Tyne on the River Tyne in the north, with Sunderland on the River Wear immediately to the south, and Middlesbrough 65km south on the River Tees estuary (Teesmouth) (JNCC, 1995).

Protected sites

The shoreline and estuarine environments of the northeast of England incorporate numerous environmentally sensitive areas, which are protected by both national and international conservation designations. Table A-8 provides a summary of the types of protected sites found in the area

Table A-8: Examples of protected areas on the NE coast of England

Designation Examples on NE English coast

Special Areas of Conservation (SACs)

SACs in the area include: the Durham coast SAC, containing the only example of vegetated sea cliffs on magnesian limestone exposures in the UK; and the Berwickshire and North Northumberland Coast, an inshore SAC covering mudflats and sandflats, rocky reefs and sea caves, and as a habitat for grey seals.

Special Protection Areas (SPAs) The Teesmouth and Cleveland Coast is designated as an SPA because of its importance as a habitat for little tern, ringed plover, and a variety of wintering waterfowl.

Ramsar sites There are three sites recognised under the Ramsar Convention on Wetlands in the area, Lindisfarne, The




Designation Examples on NE English coast

Teesmouth and Cleveland Coast and the Northumbria Coast.

National Nature Reserves (NNR)

National Nature Reserves on the NE English coast include the Durham Coast, an area of magnesian limestone and boulder clay supporting grassland that is home to numerous wild flowers and butterflies. The area is also home to many birds and supports an important breeding population of little terns. The Teesmouth reserve is a coastal site with a range of habitats including intertidal mud flats and sandflats, sand dune systems, saltmarsh and grazing marsh.

Site of Special Scientific Interest (SSSI)

There are substantial areas of SSSI along the coastline, including the Northumberland Shore and the Durham Shore, both of which are semi-continuous groups of SSSI

Sources: JNCC 2012, DTI 2002, Natural England (2012)

Birdlife

A number of internationally important seabird colonies are found along the northeast coast of England and large numbers of breeding seabirds are associated with these in spring and early summer. Many of the estuaries in the area support important populations of migratory and wintering wildfowl and waders, as well as breeding birds. As noted in Table A-8, several areas along the coast have been designated as protected sites. Breeding waders occurring on the region‟s salt marshes and wet coastal grasslands include redshank, oystercatcher and lapwing. Several areas of the coast, for example near Teesmouth and at Holy Island, are significant breeding areas for low densities of ringed plover (DTI, 2002, Barne et al 1995)

During mid-winter the northeast coast of England is a major staging and migratory flyway for the east Atlantic, with many birds moving between their arctic breeding grounds and their wintering areas on the African, Mediterranean and European coasts. For example, Teesmouth and the Cleveland coast are important for breeding terns, for wintering water birds (e.g. cormorant, shelduck, sanderling and purple sandpiper) and for the passage of ringed plover, sanderling, knot, purple sandpiper, redshank and greenshank (DTI, 2002, Barne et al 1995)).

Marine Mammals

The Farne Islands and Teesmouth support breeding colonies of common seals and grey seals (both of which are listed in Annex II of the EC Habitats Directive).

Grey seals can be seen regularly throughout the region, and there is a major breeding colony on the Farne Islands. There are also two established colonies of common seals in the region: a very small one on Holy Island Sands and a slightly larger one in the mouth of the highly industrialised River Tees, which was recolonised in the 1990‟s after an absence of almost 100 years (Barne et al 1995).




Fish and Shellfish

Many different types of fish are found in the North Sea with diversity highest in the central and northern North Sea and in inshore waters. Fish species that have spawning grounds along the northeast coast of England include herring, lemon sole, sandeel and Nephrops. Herring, cod, whiting, plaice, lemon sole, sprat and Nephrops use these inshore waters as nursery areas (Coull et al 1998) Most of the commercially important fish species spawn between January and June, although sandeel and herring are exceptions which spawn outside this period (DTI, 2002).

In addition, Salmon and sea trout are known to occur in the largest six rivers and the coastal seas of this region. In the period October to January, Atlantic salmon and sea trout migrate from salt water to freshwater to spawn, usually in fast flowing streams and rivers. Salmon migrate close to the coast as they return to spawn in their home rivers on the northeast coast of England (DTI, 2002).

Human activities

The North Sea is one of the world‟s most important fishing grounds and supports a range of coastal and offshore fisheries. Along the northeast coast of England, there are fisheries for crab, lobster, whelk, and cockles as well as netting for a number of fish species, including salmon, cod, herring and sole (DTI 2002). Along the northeast coast, coastal fisheries (within 6NM of the coast) form an important source of income for many communities, and there are several important fishing ports along this coast including North Shields, Blyth, Amble and Hartlepool.

The northeast coast, particularly in areas near the main river estuaries, has a continuing history of industrial development, including steel production, chemical production and shipbuilding. Although these industries are not as prevalent as they once were, they still have a significant presence along the coast. Examples include the Port Clarence oil refinery, the Wilton International chemical plant in Teesside, and the Wallsend ship yard on Tyneside. Areas of the coast are now beginning to be used for renewable energy projects, such as the wind farms at Blyth (DTI, 2002)

The landscape along much of the northeast coast away from the main industrial areas is unspoiled and is popular for many recreational activities, including walking, angling, golf, watersports, visiting beaches, bird watching.

Impacts of decommissioning activities

Areas along the northeast coast of England where decommissioning operations could take place are primarily sited in locations with a history of heavy industry, having a large local population and a variety of business and other industries.

A.5.2 Southwest Coast of Norway

The southwest coast of Norway, particularly the region known as Vestlandet, is made up of a mountainous and forested mainland dissected by several large fjords, including the two largest fjords in Norway, Sognefjorden in the north and Hardangerfjord in the south, with the rugged western coastline protected by an archipelago of hundreds of islands at the mouths of the fjords. The landscape is characterised by rocky shorelines with inland areas of mountain ranges,




moorland and forest. The majority of the region‟s populated areas lie in coastal areas and in narrow strips of farmable land along the edges of the fjords. The two largest population centres in the region are the cities of Bergen and Stavanger.

Protected sites

Environmentally sensitive area in Norway may be designated for protection for features including landscape, flora and fauna and in some cases cultural significance. Table A-9 provides a summary of the types of protected sites found on the southwest coastline of Norway.

Table A-9: Examples of protected areas on the SW coast of Norway

Designation Examples on SW Norwegian coast

Landscape Protected Areas

Landscape Protected Areas in the region include deciduous forests on two island s in Hardangerfjord with important populations of yew and holly. There are also several Landscape Protected Areas along the southern shore of Sognefjorden, and extending high into the mountains above, designed to protect the distinctive flora, fauna and geological formations of these areas.

Nature Reserve

Along the coastline of the region there are many Nature Reserves designated to protect important seabird breeding colonies, in particular on the many smaller uninhabited islands along the coast. Inland, reserves have been designated for the protection of ancient coniferous and deciduous forests as well as bogs, often protected for the unique habitat they provide to plants, and freshwater lakes and wetlands, again designated as important habitats for birdlife.

Other Protected Sites

There are several other protected sites along the southwest coast of Norway, particularly in the coastal areas to the south of Stavanger. These are mainly designated for the protection of bird breeding and wintering grounds. Species found in these areas include a variety of gulls, shags, guillemots, ducks and cormorants. These areas also protect the flora and fauna associated with the seabird area.

Sources: http://www.environment.no/

Birdlife

The southern and western coasts have few and relatively small colonies of species such as herring gull, great black-backed gull, common gull, arctic tern and common tern. However, some lesser black-backed gull colonies number thousands of pairs, and some remote islands have hundreds of breeding pairs of shag. In the south, puffin, common guillemot, razorbill, black guillemot, kittiwake and fulmar also breed, but in relatively small numbers compared to further north. The common eider is a common breeder along the entire coastline.

There are two Important Bird Areas (IBAs) in the region, both near Stavanger. The Jæren wetland system is the core breeding area for corncrake in Norway, and one of the most important wintering and staging areas for inland waterbirds, with more than 10,000 visiting in winter. The Kjørholmane seabird

http://www.environment.no/




reserve, which is the southernmost seabird colony of notable size in Norway, has important populations of shags and lesser black-backed gulls (Birdlife International, 2012).

Marine Mammals

Many of the species of marine mammals sighted near the coast of the northeast of England are also found across the North Sea along the coast of Norway. These species include minke whale and harbour porpoise. Killer whales are also sighted along the entire coast of Norway, most in the north but they have been sighted as far south as Stavanger (Reid et al, 2003).

Harbour seals are a relatively stationary species that lives in breeding colonies along the entire Norwegian coast and in some fjords. There is also a small breeding colony of grey seals on the southwest coast. Outside the breeding season grey seals disperse over wider areas in order to find food. On occasion, ringed seals and harp seals also migrate southwards along the Norwegian coast in search of food (Fisheries.no, 2012a).

Fish and Shellfish

Different types of fish are found in the North Sea off the southwest coast of Norway, with diversity highest in the central and northern North Sea and in inshore waters. Fish species that have spawning grounds along the southwest coast of Norway include mackerel, saithe and Norway pout. These species, plus cod and haddock, use these waters and waters immediately offshore as nursery areas (Coull et al 1998).

Common shellfish species living in the waters of the Norwegian southwest coast include brown crab, Norway lobster and European lobster (IMR, 2012).

Human activities

Fishing is Norway‟s second largest export activity, and the waters off the southwest coast are one of its most important fishing grounds. Fishing is a particularly important industry in the rural coastal areas. The main commercial species landed include Norway pout, herring, mackerel and blue whiting. Aquaculture or fish farming in Norway has grown into a major industry along the entire coast. Salmon and trout are the main farmed species, although cod, other marine species and shellfish are also farmed (Fisheries.no (2012b)).

The southwest coast of Norway is a popular recreation destination for both Norwegians and tourists. Sailing and cruises are popular in the fjords and along the coastline, while on land; outdoor pursuits such as hiking, hunting and angling are popular.

There is some history of heavy industry along the southwest coast of Norway, with several shipyards and fabrication yards, including those on the island of Stord and in Vats associated with the construction of offshore oil platforms. Another aspect of this industry is the large oil refinery at Kollsnes near Bergen and at Kårstø, north across the Boknafjorden from Stavanger. There are also hydroelectric aluminium smelters such as the one south of Haugesund.

Bergen and Stavanger, the two most populous areas in the region, are large modern cities with a variety of industrial and business sectors. Both cities have long-standing connections to the oil and gas industry and are the locations of many associated industries and supply bases.




Impacts of decommissioning activities

Although more sparsely populated than the northeast coast of England, decommissioning operations that take place on the southwest coast of Norway have the same potential to create disturbance for local populations. While often relatively remote, decommissioning yards along this coast are sometimes sited in locations with several other industries present, and can have a local population in fairly close proximity.




A.6 References

AMEC plc. (2008) Dunlin A Safety Case Volume 1. AMEC report 0052-47-000-RPT-001. Version A3. Issued for use 14/04/08.

Anatec UK Ltd (2007). Maritime Data Online GIS system. www.maritimedata.co.uk

AUMS (1990). Shell Osprey Field Baseline Environmental Survey 1989.

Barne, J.H, Robson, C.F, Kaznowska, S.S, Doody, J.P and Devidson, N.C (1995). Coasts and seas of the United Kingdom, Region 5 North-east England: Berwick-upon-Tweed to Filey Bay. Published by JNCC.

Birdlife International (2012), Important Bird Areas Database, Available Online at http://birdlife.org/datazone/site/search [Accessed April 2012]

Coull, K.A., Johnstone, R., and Rogers, S.I. (1998) Fisheries Sensitivity Maps for British Waters. Published and distributed by UK Oil and Gas.

DTI (2001a). Strategic Environmental Assessment of the Mature Areas of the Offshore North Sea SEA2

DTI (2001b) North Sea Fish and Fisheries. Technical Report 003 to inform SEA2. Prepared by Rogers, S., Stocks, R. and Newton A. Available online at http://www.offshore-sea.org.uk/consultations/SEA_2/TR_SEA2_Fish.pdf [Accessed May 2009]

DTI (2002). Strategic Environmental Assessment of Parts of the Central & Southern North Sea SEA3

Ellis, J., Milligan, S. Readdy, L., Taylor, N and Brown, M. (2012). Spawning and Nursery Grounds of Selected Fish Species in UK Waters. Science Services Technical Report No. 147. CEFAS, Lowestoft.

Fairfield Betula Ltd (2008). Dunlin Alpha PON15D Variation 28 Update 1

Fairfield Energy Ltd (2008). ROV footage file reference 49180_49_EL76~119_2008-ROV_08-05-24_09-10-45_1.pkt.

Fisheries.no (2012a), Ecosystems and Stocks, Marine Mammals. Available online at: http://www.fisheries.no/ecosystems-and-stocks/marine_stocks/mammals/ [Accessed April 2012]

Fisheries.no (2012b), Aquaculture. Available online at http://www.fisheries.no/aquaculture/Aquaculture/ [Accessed April 2012]

Gaurdline Environmental Ltd (2009a). UKCS 211/23 Dunlin Development Debris Clearance. @Mud Mound@ and Environmental Baseline Survey. December 2008. Environmental Baseline Report Prepared for Fairfield Energy Ltd. Reference 7859.1 Draft report issued 16-Mar-09

Gardline Environmental Ltd (2009b) UKCS 211/23 Osprey Debris Clearance, Habitat Assessment and Environmental Baseline Survey. Environmental Baseline Report Prepared for Fairfield Energy Ltd. November/December 2008. Reference 7858. Draft report issued 11-Mar-2009.

http://www.maritimedata.co.uk/




IMR (2012), Norwegian Institute of Marine Research, Shellfish database. Available online at: http://www.imr.no/temasider/skalldyr/en [Accessed April 2012]

JNCC (1999). Seabird Vulnerability in UK Waters: Block Specific Vulnerability.

JNCC (2012a). UK Protected Sites. Available online at http://jncc.defra.gov.uk/default.aspx?page=4 [Accessed April 2012]

JNCC (1995) Coastal and Seas of the United Kingdom; Region 5 North –east England Berwick-upon-Tweed to Filey Bay

Marine and Fisheries Agency. (2008). Landing/catch statistics for ICES Rectangles 49F0, 49F1, 50F0, 50F1, 51F0 and 51F1 from 2002 to 2007.

MMO (2012). Landing/catch statistics for ICES rectangles 50F0, 50F1, 51F0,

52F0 and 52F1. Marine Management Organisation.

Natural England (2012). Designated Areas. Available online at http://www.naturalengland.org.uk/ourwork/conservation/designatedareas/default.aspx [Accessed April 2012]

Oil and Gas UK (2009). Data Review for an Industry-Wide Response to Cuttings Pile Management Final Report. Prepared by ERT (Scotland) Ltd. ERT 1987. Issued February 2009.

Reid, J.B., Evans, P.G.H., and Northridge, S.P. (2003). Atlas of Cetacean distribution in north-west European waters.

SCANS-II (2008). Small Cetaceans in the European Atlantic and North Sea. Final Report submitted to the European Commission under project LIFE04NAT/GB/000245. Available from SMRU, Gatty Marine Laboratory, University of St Andrews, St Andrews, Fife, KY16 8LB, UK. Not yet approved.

Skov, H., Durinck, J., Leopold, M.F., and Tasker, M.L. (1995). Important Bird Areas for seabirds in the North Sea. Birdlife International, Cambridge

Stone, C.J., Webb, A., Barton, C., Ratcliffe, N., Reed, T.C., Tasker, M.L., Camphuysen, C.J. and Pienkowski, M.W. (1995). Seabird Atlas of the North Sea: An Atlas of Seabird Distribution in north-west European waters. Joint Nature Conservation Committee, Peterborough, UK.



REPORT REFERENCE: P1623_RN3027_REV1.DOC B-1 04/12/2012

Appendix B Basis for Assessment




B.1 Introduction

The Dunlin Decommissioning Programme describes a series of activities associated with the decommissioning of the Dunlin A platform, together with a description of the end point of this process. These activities can be organised in three time frames, as follows:

Prior to the platform becoming hydrocarbon free. During this period the wells will be plugged and abandoned (P&A). Some of these activities will take place before Cessation of Production (CoP) and some post-CoP. For the purpose of this assessment no distinction is drawn.

After the platform becomes hydrocarbon free. This will be when the topsides are removed. For topsides decommissioning the platform will have been flushed and cleaned as part of the CoP activity. Removal of the topsides is addressed in two phases: (1) Removal of topsides modules and (2) Removal of the module support frame (MSF) followed by the installation of aids to navigation.

The final decommissioned state when the CGB and drill cuttings remain in situ, and aids to navigation are installed on one of the legs

This appendix identifies the key environmental aspects of the decommissioning programme and summarises the assumptions made for conducting the environmental impact assessments which follow in subsequent appendices.

B.2 Assessment method

The overall approach to the Dunlin EIA is described in Section 3.2. Criteria used for the categorisation of impact severity, likelihood and overall risk are provided again here.

Potential environmental impacts have been categorised using the severity classes set out in environmental risk assessment guidance produced by UKOOA (UKOOA 1999) as follows:

Table B-1: Impact Severity Categorisation

Severity Class Criteria

1 Negligible Change unlikely to be noticed against background variability

2 Minor Change within normal variability but could be noticed / monitored. Some users may need to modify behaviour

3 Moderate Localised change but with good recovery back to existing variability. May contribute to cumulative impact. Nuisance potential to some users.

4 Major Medium term (2 year) change in ecosystem or activity over a wide area with recovery to normal variability unlikely within 10 years

5 Severe Long term (10 year) change to ecosystem over wide area with low probability of recovery to normal range

These potential impacts have been assessed using a risk matrix, shown in Table B-2, based upon International Standard BS EN ISO 17776:2002 (Ref. 7 ).




This has been adapted for use by Fairfield Energy to provide the criteria for the Dunlin A Decommissioning Programme.

Table B-2: Severity Categorisation

The coloured zones in Table B-2 indicate broad risk acceptability and tolerability levels as follows:

Acceptable. Risks are accepted without further reduction other than the routine management process of continual improvement.

Tolerable. Risks are accepted provided that the risks are reduced to As Low As Reasonably Practicable (ALARP).

Unacceptable. Risks cannot be justified under the current criteria.




B.3 Assessment Assumptions

The Dunlin decommissioning programme has been evaluated by considering the environmental aspects of the decommissioning activities which have the potential to:

Influence key decommissioning decisions,

Lead to an environmental impact of moderate severity or greater, defined as “Localised change but with good recovery back to existing variability. May contribute to cumulative impact. Nuisance potential to some users.”, or

Contribute to climate change.

In addition the following assumptions were made:

Where decommissioning activities are within the range of activities that normally occur when the platform is in routine operation, the impacts of such activities were not assessed.

In the case of well plugging and abandonment, where activities are regulated by the Wells Notification Procedure and Production Operation Notices (PONs), the impacts of such activities were not addressed.

On this basis the following activities were excluded:

Use and discharge of chemicals consistent with routine platform-based drilling activities

Overboard discharges consistent with those encountered during normal operations or during routine shut down (for example to render the platform hydrocarbon free)

Domestic waste and logistics associated with maintaining normal complement of persons on board.

Waste and overboard discharge associated with routine supply operations

Transboundary impacts were also excluded on the basis that any impacts (e.g. resulting from atmospheric emissions and oil spills) will be within those previously encountered during normal operations.

Tables B.3 to B.7 describe the assumptions that have been made to enable potential environmental impacts of the decommissioning activities to be predicted. Environmental aspects taken forward are indicated in bold.

The Tables group the decommissioning activities as follows:

Table B.3 Wells plugging and abandonment

Table B.4 Topsides removal and CGB decommissioning preparation

Table B.5 Onshore decommissioning and materials disposal

Table B.6 CGB and drill cuttings after decommissioning

Table B.7 Accidental events




Table B-3: Wells Plugging and Abandonment

Decommissioning Activity Environmental Aspects Assumptions made as basis of impact assessment

Plug and abandon (P&A) wells

Emissions from combustion equipment :

Installation power generation

Logistics

Materials recycling / disposal

Use of chemicals

Discharge of sewage, grey water, food waste and drainage water

Waste generation

Dunlin A has 48 well slots and 45 wells are to be plugged and abandoned in the course of decommissioning the platform.

Well P&A activities will be undertaken in parallel with other activities and will not prolong occupation of the platform.

38 of the 45 wells will be abandoned prior to CoP.

All wells will involve recovery of a 140m-long well conductor containing multiple casing diameters separated by cement.

Waste generation and discharge of sewage, grey water, food waste and drainage water are not expected to exceed that experienced during normal production operations of the platform (not considered further)

Flush and clean wells, set plugs

Combustion emissions associated with drilling rig (e.g. mud pump) operations

Chemicals / cement use

Between 15 and 20 days rig time per well (20 taken as worst case).

2 x 2.5MW generators working continuously at 45% capacity (to provide backup capacity should one generator fail), resulting in a fuel use of 11.25 tonnes per day.

Emissions associated with Dunlin platform operation accounted for elsewhere.

No planned discharges – Chemical returns from the plugged and abandoned wells will be pumped into an existing injection well. The injection well will be plugged and abandoned last; chemical returns from this well will be contained and shipped to shore. Risk of accidental release of chemicals remaining onboard the platform.

All activities and offshore use of chemicals will be covered by well intervention permits (PON15Fs) (not considered further)

Isolate and recover tubing

Removal and disposal of marine fouling

Cleaning of recovered conductors prior to return to shore

NORM scale removal

Marine growth will be removed from the conductors as they are lifted into the drill floor. Total volume is estimated as less than 10 tonnes, the majority of which will fall into the sea as the conductors are withdrawn.

One 140m-long conductor containing multiple casing diameters separated by cement is to be recovered per well, totaling 6720m.

Recovery of a variety of lengths of production tubing from inside the wells, totaling 145,000m, with the potential to contain low Level Naturally Occurring Radioactive Material (NORM).

Recovered tubing and marine growth will be transported to shore using existing supply boat capacity. There will be no additional vessel operations as a result of these operations. Onshore aspects included in table B.5




Table B-4: Topsides and MSF Removal


Phase 1 – Topsides Modules Removal

Deconstruction crew - platform-based


Helicopter transport for crew change

Installation based assumptions are :

130 workers for 130 days.

3 helicopter trips to Aberdeen every 14 days

Deconstruction crew - vessel-based (flotel and HLCV)

Vessel based assumptions are :

Flotel based crew (130 workers for 80 days)

HLCV based crew (170 workers & crew for 30 days)

4 helicopters every 14 days

Platform-based power generation (Utilities, pumps, cranes etc)

Diesel bunkering, storage and use

Exhaust gas emissions

Installation fuel use estimated at 5 tonnes per day (including HVAC, lighting and platform cranes) for 280 days.

Vessel operations (Propulsion, station keeping, utilities, cranes etc)

Fuel use

Exhaust emissions

Noise

Navigational obstruction

Anchoring (drill cutting disturbance)

Vessel operations estimated as :

HLCV DP positioning over 30 days

Standby vessel 130 days

Supply vessel 20 return trips between installation and onshore supply base (assumed to be Aberdeen)

Only fuel use and exhaust emissions considered significant.

Underwater noise levels may be elevated while HLCV on site.

Navigational obstruction considered to be consistent with regular operation of platform.

The cuttings piles are local to the CGB. Any anchoring of vessels will be remote from the cuttings pile.

Equipment repair and maintenance

Waste generation Environmental impact consistent with routine platform maintenance for systems required during deconstruction, therefore considered insignificant

Empty and clean all pipes, equipment and vessels

Chemical Use

VOC emissions

Overboard discharge

Flushing and cleaning of pipes and vessels will follow procedures routinely followed for planned maintenance shutdowns. Gross risings will be pumped to Cormorant A for processing through the TAQA system. Process modules will then have only residual quantities of mobile hydrocarbons.

Decommissioning of the drains will follow that of the production modules. Any overboard





General and hazardous waste generation discharge will follow flushing operations – there will be no overboard discharges following the final shutdown of the process system, any further fluid waste will be routed to storage tanks and sent to shore for treatment and disposal.

Once the separation of modules and equipment takes place, all open ends of pipework, vessels, tanks and equipment will be sealed to avoid any spillages of residual fluids.

General and hazardous waste generation will be consistent with that of a major shutdown and therefore has minimal potential to lead to moderate severity impacts (or greater). Exhaust emissions from power generation addressed elsewhere.

Chemical use and discharge will be managed within PON 15 permits applicable to the operation.

Accordingly all environmental aspects are judged to be insignificant.

Disconnect modules & secure equipment, separate modules and lift onto transport barges

Incident risk (unplanned events)

Other aspects (e.g. exhaust emissions from cranes) already addressed

Impacts judged insignificant other than impacts from unplanned events (see incident risk table B-7)

HLCV transfer of large modules to onshore decommissioning facility

Emissions from propulsion


Near shore navigational risks

Near shore noise / nuisance (e.g. dust)

Incident risk

Assume 4 days passage (to site and from site to decommissioning facility) plus 1 day offloading. Estimated 240 tonnes fuel used during transit.

Other impacts deemed insignificant in comparison to normal vessel operations.

Incident risk – see table B-7.

Phase 2 – Topsides MSF Removal

Deconstruction crew - vessel based (Flotel and HLCV)


Helicopter transport for crew change

Vessel-based assumptions are :

Flotel-based crew (130 workers for 80 days)

HLCV-based crew (170 workers & crew for 21 days)

4 helicopters every 14 days

Vessel operations (Propulsion, station keeping, utilities, cranes etc)

Fuel use

Exhaust emissions

Noise

Navigational Obstruction

Anchoring (drill cutting disturbance)

Vessel spread assumptions :

Flotel DP positioning over 80 days

HLCV DP positioning over 21 days

Standby vessel 101 days

Supply vessel 12 return trips between installation and onshore supply base (assumed to be Aberdeen)





Only fuel use and exhaust emissions impacts considered significant.

Noise and navigational obstruction as Phase 1 above.

Remove MSF, steel columns and other steelwork

Remove marine fouling

Fuel use

Exhaust emissions

Separation of 4 columns (500 tonnes each) and transfer to barges.

Fouling removal and local disposal will lead to dispersion of marine growth to the water column and seabed. However no environmental effects are anticipated given the relatively low quantities of a naturally occurring discharge, therefore the impact for fouling removal is deemed insignificant

Aspects with the potential to cause impacts (e.g. exhaust emissions from HLCV) have been included in the fuel use estimates for the HLCV above. Therefore the impact of these operations is considered insignificant.

Removal of conductor frames Remove marine fouling

Incident risk (dropped object)

ROV operations to cut away conductor frames (3 frames at depths of circa +8m, 40m and 80m, each weighing 200 tonnes)

Aspects with the potential to cause impacts (e.g. exhaust emissions from HLCV) have been included in the fuel use estimates for the HLCV above. Therefore the impact of these operations is considered insignificant, other than impacts from unplanned events (see incident risk table B-7)

Installation of navigation structure

Offshore lift, installation and commissioning of light tower to top of one CGB leg

The installation of the navigation structure will be completed by the support vessel (2 days operations assumed). Transfer to site is assumed to be accounted for within general vessel operations.

HLCV transfer MSF to shore Emissions from propulsion

Near shore navigational risks

Near shore noise / nuisance (e.g. dust, odour)

Incidents

Assume 4 days passage (to site and from site to decommissioning facility) plus 1 day off loading. Estimated 240 tonnes fuel used during transit.

Other impacts deemed insignificant in comparison to normal vessel operations.

Incident risk – see table B-7

Debris clearance

Post decommissioning survey

Physical presence / movement of vessels

Drill cuttings disturbance

Impacts from vessel operations have been accounted for above.

There are no major dropped objects known to lie within the drill cuttings pile, therefore there will be no disturbance caused to the drill cuttings pile during recovery operations.




Table B-5: Onshore Decommissioning and Materials Disposal


Onshore Deconstruction

Temporary storage of modules during disassembly

Odour

Visual Impact

Minimal amounts of marine growth (which is the primary cause of odour during decommissioning) will be transported onshore. Minimal amounts of potentially odorous fluids transported onshore due to offshore cleaning and flushing. Decommissioning yards subject to local environmental health legislation regarding odour.

Topsides removal will involve transport to shore of several smaller sections of topsides, none of which are large enough to significantly alter the visual impact of an existing onshore facility.

Cleaning of modules prior to disassembly

Heat and power use, exhaust gas emissions

General waste generation

Hazardous waste generation

Spill risk (see table B-7)

Chemical use

Water use

Odour / VOC emissions

Waste water treatment

Noise

Modules will be received from the HLCV at the onshore receiving site and be dismantled into smaller sections for onward transportation to recycling and disposal sites.

Total quantity of received materials (topsides and MSF) is 20,103 tonnes. The estimated quantity of residual materials within the topsides, the majority of which will remain in the modules brought ashore, is 36 tonnes (Section 6.6). Of this the majority (21 tonnes) is residual hydrocarbon sludge.

The degree of separation into individual material streams will depend on the choice of location. All work will be carried out under suitably licensed conditions and subject to environmental and waste management plans.

Dismantling will be undertaken by combination of hot and cold cutting with precautions in place to ensure any potential contaminants are captured and suitably managed. Decommissioning yards are fully bunded to ensure that any spills are captured and treated.

Potential for local nuisance (odour, noise) is recognised given proximity of dismantling facilities to local communities. However facilities are generally sited in areas used for heavy industry, Activities will be within those routinely carried out at site and would be subject to site specific assessment and controls.

In summary, onshore decommissioning aspects are not expected to lead to impacts of moderate or greater severity.

The onshore decommissioning impact is therefore assessed for emissions of greenhouse gases only.

Transfer to intermediate materials recovery facility & materials

Heat and power use, exhaust gas emissions

Noise / nuisance / traffic

Waste water treatment

General waste generation

Hazardous waste generation

Spill risk (see table B-7)

Waste handling and disposal Landfill

Thermal treatment

Materials Disposal

Transfer to materials disposal Exhaust gas emissions Materials will be recovered according to the hierarchy for re-use of equipment, recycling of





end point Noise / nuisance / traffic materials, thermal recovery. Impacts will be managed within the licensed materials

recovery sites and will therefore not be at a level with potential for moderate or greater

severity.

The only aspects expected to generate significant impacts are:

Atmospheric emissions from smelting (including well tubulars)

Materials sent to landfill

Metals smelting Combustion emissions

Odour

Plastics recovery

Thermal recycling Combustion emissions

Odour

Landfill

Presence of landfill

Atmospheric emissions

Leachate management

Table B-6: CGB and Drill Cuttings after Decommissioning

Activity Aspect Assumptions made as basis of impact assessment

Physical presence while

structure intact

Continued loss of seabed habitat

Modification of seabed currents / scour

Navigational hazard (lit)

500m exclusion zone retained

CGB has a footprint of 104 m x 104 m (10,816 m2)

Seabed currents at site are not sufficient for scour.

Inspection and maintenance Regular service and inspection visits for

navigation and structural integrity

Annual inspection of navigation aids, with 2 yearly maintenance visits, by helicopter.

Structural failure of one or

more legs

Navigation hazard (unlit) including part

collapsed leg

Disturbance of drill cuttings pile

Debris on seabed

Leg supporting navigation aid fails in 250 years at approx 23m below sea surface.

Leg falls to seabed in a small number or large pieces with associated smaller debris. Leg assumed to fall onto drill cuttings pile.

Structural failure affecting

cells containment

Potential release of gas (H2S)

Discharge of liquid CGB contents

Dispersion of mobile solid contents

Contamination from exposed contents

Exposure of elements of drill cuttings pile

Debris on seabed

Structural failure of CGB cells containment following collapse of leg. Such a failure will

have been preceded by progressive loss of liquids containment over many years allowing

weak circulation of seawater through CGB.

Disturbed sections of drill cuttings accumulation will become exposed to seawater for the

first time.

Continued presence of drill

cuttings accumulation

Physical presence

Leaching of hydrocarbon to water column

Continued sediment contamination

Drill cuttings pile extends the footprint of the CGB structure by a further 4,950 m2




Table B-7: Accidental Events

Activity Aspect Assumptions made as basis of impact assessment

Dunlin A platform-based

decommissioning – minor

incidents

Minor leaks / spills from vessels and pipelines

Bunkering spillage

Fires from cutting

Loss of residual fluids from modules during

transfer to vessels

Accidental releases will be minimised through a combination of activity-based risk

assessment, and operational, preventative and local response procedures during

decommissioning, Residual risk of minor overboard discharge via platform drainage

system, however environmental effects will be small, localised and short-lived and

therefore considered not sufficient to lead to moderate impacts.

Impacts considered insignificant.

Vessel-based minor incidents

Bunkering spillage

Loss of residual fluids from modules during

transfer to vessels

As above.

Onshore deconstruction –

minor incidents

Fires from cutting

Loss of residual fluids from modules

As above.

Vessel spill (e.g. collision)

Worst case loss of containment Collision involving total loss of inventory is a remote possibility. Credible worst case is

taken to be loss of containment of largest fuel tank on largest vessel (HLCV). This would

have greatest impact if it occurred in inshore areas; such (rare) events do tend to occur in

more congested and constrained inshore areas.

Disturbance of drill cuttings by

dropped objects

Small items (e.g. pipework)

Whole modules

Structural failure of a leg

Small objects are considered to cause only minor, local and short-lived effects. Larger

objects e.g. a whole module or debris from failure of a leg, would provide more extensive

disturbance leading to :

Sections of the drill cuttings becoming exposed for the first time in many years

Potential extension of area of sediment contamination

Extent of impact will depend on the energy of the falling material, which is taken to be

greatest for the structural failure of a leg. Eventual failure of all four legs is certain to occur

and is highly likely to impact on the drill cuttings, albeit beyond 200 years into the future.

Helicopter crash Fuel spill Rare event. Helicopters carry relatively small quantities of fuel (and fuel is volatile so will

evaporate quickly). Not considered further.




B.4 References

UKOOA (1999). Offshore Environmental Statement Guidelines.



REPORT REFERENCE: P1623_RN3027_REV1.DOC C-1 04/12/2012

Appendix C Wells Plugging and

Abandonment




C.1 Introduction

Table B-3 identifies the environmental aspects associated with the plugging and abandonment (P&A) of the 45 wells drilled from the Dunlin A platform. This appendix assesses the impacts of those activities considered to have the potential for moderate impacts, as defined in Section B.2, that is: “Localised change but with good recovery back to existing variability. May contribute to cumulative impact. Nuisance potential to some users”.

All well P&A operations will be carried out using existing well intervention equipment onboard the Dunlin A platform. Accordingly, environmental impacts are expected to be similar to those associated with routine well intervention operations carried out during the lifecycle of the platform. Such activities can be managed through existing environmental management arrangements and are therefore considered not to pose a moderate or greater risk to the environment, and are excluded from further assessment.

Those aspects where the extent of the activity is considered potentially sufficient to warrant further assessment are:

Combustion emissions (which can contribute to local air quality issues and climate change) from:

Platform-based power generation

Onshore materials disposal

Chemical use during P&A operations

Marine growth removal and disposal

NORM scale removal and disposal

These aspects are reviewed in the following sections.

C.2 Wells P&A Aspects

C.2.1 Atmospheric Emissions

Table C-1 shows estimates of atmospheric emissions during the wells P&A operations, based on fuel use and timescale estimates outlined in Appendix B (Table B-3).

Also shown in Table C-1 are estimated CO2 emissions from onshore disposal and recycling of waste materials. These are derived from the weight of materials returned to shore (estimated at a worst case of 5,100 tonnes of steel well tubing, etc.) and using the emission factors provided in the Institute of Petroleum “Guidelines for the calculation of estimates of energy use and gaseous emissions in the decommissioning of offshore structures” (Referenced in Appendix D as IoP(2000)).




Table C-1: Wells P&A Atmospheric Emissions

Source Engine Type

Fuel Used (Tonnes, Total)

Emissions (Tonnes)

CO2 CO NOx N2O CH4 mmVOC SOx

Dunlin Platform

Diesel 10,125 32,400 159 601 0 0 20.3 40.5

Offshore subtotal 10,125 32,400 159 601 0 0 20.3 40.5

Onshore Activities

Dismantling1 454 1,452 26 1.8

Recycling 4,896 8 19.4

Totals (where calculated)

38,748 635 61.7

1Calculated assuming onshore dismantling powered by diesel with an engine efficiency of

30%

Offshore, combustion emissions will produce approximately 32,400 tonnes of CO2, 40 tonnes of SOx and 600 tonnes of NOx during the estimated 900 days it will take to plug and abandon all 45 wells.

Fairfield Energy and all decommissioning contractors will undertake practical steps in order to minimise atmospheric emissions, including ensuring efficient operations, keeping power generation equipment well maintained and monitoring fuel consumption. Air quality impacts resulting from emissions generated by well P&A (offshore and onshore) are considered minor and risks associated with this impact are acceptable.

C.2.2 Chemical Use

Operations to P&A wells involve a range of chemicals employed to stop the well flowing (a „kill mud‟), to make up cement plugs for the well, and to treat the well against corrosion and microbial contamination. The majority of the chemicals used in these operations will remain in the well after it is plugged. Some volume of chemicals may be returned to the Dunlin A platform from where they will be pumped into an existing injection well. The injection well will be the final well to be plugged and abandoned during these operations. Fluids from this final well will be shipped to shore for treatment and disposal.

As noted in Appendix B, chemicals use and discharge is excluded from this assessment. Operations requiring the use of chemicals will be covered by well intervention chemical permits (PON15Fs). While the above plan for P&A operations will insure that there is no discharge of chemicals to sea during these operations, there remains an inherent risk of accidental release.

C.2.3 Marine growth removal and disposal

Well conductor pipe which has been exposed to seawater for a prolonged period of time is likely to be colonised by marine growth, such as seaweeds, shellfish and cold water corals. During decommissioning these colonies are considered a waste by-product, and must be dealt with as such. During the wells P&A programme at Dunlin A, well conductor pipe will




be raised onto the drill floor of the platform once the associated well has been plugged and abandoned. During this process it is expected that most of the lightly attached marine growth (such as seaweeds) will become detached from the tubing and will be allowed to fall to the sea, where it will decompose naturally. Efforts will be made to remove further amounts of marine growth manually on the drill floor. This growth will also be disposed of directly to sea.

It is expected that some more firmly attached marine growth, such as mussels, will be transported to shore with the conductor pipe. As with all waste from the decommissioning process, the conductor pipe will be sent to a regulated waste collection centre, prior to being sent for disposal or recycling. Any remaining marine growth will be removed at this waste collection centre as it is generally incompatible with the disposal or recycling process. The marine growth removed onshore will be treated following appropriate local regulations governing the treatment, storage and transport of waste. Disposal options for marine growth vary, however, common disposal methods include sending to landfill and composting.

Minimal impact on the environment will be ensured by requiring the waste contractor to have a regulated plan for the removal and disposal of marine growth onshore and hence risks associated with this aspect of the project are considered acceptable.

C.2.4 NORM scale

Naturally Occurring Radioactive Material (NORM), also described as Low Specific Activity (LSA) material, can be found in many geological formations and may be brought to the surface during oil and gas exploration and production. NORM is governed by legislation with strict controls on its handling, storage and disposal. The accumulation and disposal of radioactive waste is regulated in the UK under the Radioactive Substances Act 1993. Operators and contractors are also required to develop appropriate working procedures and training to control, protect and minimise the exposure of workers because of the hazardous radioactive nature of the material.

Pipework such as well tubing that has been used to carry production fluids may be contaminated with scale containing NORM. During the well P&A programme, the production tubing from the well will be removed and sent to shore for disposal or recycling. As it will not be possible to remove NORM scale offshore, contaminated materials will be treated as a hazardous waste and sent to an appropriately certified waste contractor onshore for treatment and disposal. NORM scale is commonly disposed of by being encased in concrete and landfilled in a secure location approved by regulators.

Minimal impact on the environment will be ensured by having an appropriate radioactive waste management plan offshore, and by confirming that the onshore waste contractor has a regulated plan for the removal and disposal of NORM scale. Overall the risk level is considered acceptable.




C.3 Summary of Wells P&A Impacts

Impacts associated with well P&A are summarised in Table C-2 below (risk levels are defined according to the classification in Section B.2):

Table C-2: Wells P & A Impacts

Aspect Impact Risk Level Comment

Atmospheric Emissions

Impact on air quality (climate change impacts are addressed under cumulative impacts in Appendix F)

Acceptable Minor, localised impacts on air quality.

No environmental receptors identified at Dunlin A

Onshore emission subject to existing permit requirements.

Marine Growth Disposal

Impact on marine water quality/ onshore waste disposal

Acceptable Limited impact of marine growth disposal in deep sea environment.

Onshore disposal at licensed facility.

NORM scale disposal

Impact of NORM waste on receiving environment

Acceptable NORM waste disposal at licensed facility.



REPORT REFERENCE: P1623_RN3027_REV1.DOC D-1 04/12/2012

Appendix D Topsides Removal




D.1 Base Case (Reverse Installation)

The Base Case for decommissioning the Dunlin A topsides and MSF (Module Support Frame) is for their complete removal and disposal onshore. The method for doing this will be the reverse of the original installation procedure, and is described in Section 11.

Appendix B (Tables B-4 and B-5) identifies the environmental aspects associated with topsides and MSF removal. Several of the identified aspects do not warrant further assessment as they do not pose a moderate environmental impact, under the adopted criterion of “Localised change but with good recovery back to existing variability. May contribute to cumulative impact. Nuisance potential to some users”. Typically these aspects were considered to fall within the normal operational activity of the platform (including work required to render the Dunlin process system free of hydrocarbons during a maintenance shut down). Such activities can be managed through existing environmental management arrangements so that they do not pose a moderate or greater risk to the environment. The existing management arrangements are also assumed to provide adequate protection across the seasonal range of sensitivities identified in Appendix A.3.

While the baseline environmental assessment recognises periods when there are very high vulnerabilities for fish (Table A-3), these are mainly related to breeding activities. Fish are unlikely to be sensitive to activities and discharges occurring during Dunlin decommissioning as spawning and nursery areas are very large in comparison with the area likely to be influenced. It is however also acknowledged that environmental management plans and mitigation measures developed at later stages will also consider such variations.

Those aspects where the extent of the activity was considered significant enough to warrant further assessment are:

Discharge of sewage, grey water, food waste and drainage water over an extended period (130 days) by platform-based deconstruction crew

Discharge of sewage, grey water, food waste and drainage water over an extended period (211 days) by vessel-based deconstruction crew

Combustion emissions from:

Platform-based power generation

Helicopter transport

Vessel propulsion and power generation

Onshore disassembly and materials disposal

Subsea noise generation by vessels

Spill risk from diesel bunkering and storage, or from vessel collision

These aspects are reviewed in more detail in the following sections.




D.1.1 Base Case Overboard Discharges

Discharges of sewage, grey water, food waste and drainage water from the platform are expected to be in the region of 28.6 m3 per day based on personnel on board (PoB) of 130. This is considered to fall within the values expected during normal operational activity of the platform (during, for example, a maintenance shut down). Table D-1 gives an estimate of these discharges from the platform, heavy lift crane vessel and flotel during the two phases (Phase 1 topsides modules and Phase 2 MSF removal) of the decommissioning process.

Table D-1: Waste Water discharge during decommissioning

Discharge source Duration (days) Grey water (m3)1

Sewage (m3)1 Total Waste Water (m3)

Phase 1. Topsides modules

Dunlin platform 130 2,535 1,183 3,718

HLCV 30 765 357 1,122

Phase 2. MSF removal

Flotel 80 1,560 728 2,288

HLCV 21 536 250 785

Totals 5,396 2,518 7,913 1Estimates based on 150 litres of grey water per person per day and 70 litres of sewage/black water per

person per day

The platform-based deconstruction crew will be moved to the flotel once the preparation for the separation of the platform living quarters modules has begun. There will therefore be only a small increase in the number of PoB (taking into account the permanent crew of the flotel) such that the associated discharges will not increase significantly compared to that experienced during the normal operation of the platform.

Any flotel used in these operations will comply with standards set out in the International Convention for the Prevention of Pollution from Ships (MARPOL) 1973, as amended by the Protocol of 1978. Waste storage procedures will be in line with the garbage management plans and current legislation governing discharges to sea from vessels. With this mitigation in place it is unlikely that there will be any significant environmental impact and the risk associated with such an impact is considered acceptable.

D.1.2 Base Case Atmospheric Emissions

Table D-2 below provides estimated atmospheric emissions during the Base Case topsides removal operations, based on fuel use and timescale estimates outlined in Appendix B (Table B-3). Phase 1 (topsides modules) and Phase 2 (MSF) emissions have been combined where applicable to provide total emissions estimates.

Also shown are estimated CO2 emissions from onshore activities. These are derived from the weight of materials returned to shore (estimated at 20,000 tonnes of topsides material), and using the emission factors provided in the Institute of Petroleum “Guidelines for the calculation of estimates of energy use and gaseous emissions in the decommissioning of offshore structures” (Referenced in Appendix D as IoP(2000)).




Table D-2: Base Case Atmospheric Emissions (Offshore and Onshore)

Source Engine Type


Emissions (Tonnes)


Dunlin Platform Diesel 650 2,080 10.21 38.61 0 0 1.3 2.6

Helicopter Gas Turbine (Air)

131 418 0.68 1.63 0.03 0.01 0.10 0.26

Flotel Marine Diesel

130 417 1.04 7.69 0.03 0.35 0.31 0.26

HLCV Marine Diesel

1,220 3,904 9.76 71.98 0.27 3.29 2.93 2.44

Standby Vessel Marine Diesel

2,772 8,870 22.18 164 0.61 7.48 6.65 5.54

Supply Vessel Marine Diesel

1,840 5,888 14.72 109 0.40 4.97 4.42 3.68

Offshore subtotal 6,743 21,578 58.58 392 1.34 16.11 15.71 14.79

Onshore Activities

Onshore Dismantling 1,779 5,692 106 7.11

Disposal/Recycling 19,200 32 76

Totals 46,470 530 97.9 1Calculated assuming onshore dismantling powered by diesel with an engine efficiency of

30%

Offshore, combustion emissions will contain approximately 21,578 tonnes of CO2, 15 tonnes of SOx and 392 tonnes of NOx during the 210 day topsides removal campaign.

Fairfield Energy and all decommissioning contractors will undertake practical steps in order to minimise atmospheric emissions, including ensuring efficient operations, keeping power generation equipment well maintained and monitoring fuel consumption. Air quality impacts associated with emissions generated during topside removal are considered minor and risks associated with this impact are acceptable.

D.1.3 Subsea Noise

Underwater noise has the potential to affect the behaviour of marine mammals, and, at higher received levels, could cause harm.

No use of explosives is planned during the decommissioning of Dunlin A, hence the most significant noise source will be from vessels. Typical broadband source levels for small to mid-size vessels such as supply/support vessels are generally in the 165-180 dB (re: 1μPa) range, although these can be as high as 190 dB (re: 1μPa) for dynamic positioning (DP) thrusters at peak levels (OSPAR, 2009).

These levels are below the harm threshold for permanent hearing threshold shift (PHTS) of 230 dB re 1µPa at 1m (JNCC, 2009). Peak levels are potentially sufficient to cause avoidance behaviour in marine mammals over a distance of several kilometres, particularly for the larger cetaceans. However, DP thrusters will only operate at such levels for very short periods of time, under conditions where background (ocean wave) noise levels will also be high.




In this respect noise impacts could approach those of a dynamically positioned mobile drilling unit. At worst, there is potential for moderate impact with a medium likelihood (tolerable risk).

D.1.4 Accidental Risk

Accidental events are incidents or non-routine events with the potential to trigger impacts that would otherwise not be anticipated during the normal course of decommissioning. The severity of impact from accidental events can be greater than those from routine operations, but the probability of an accidental event occurring is typically much lower.

Therefore, plans are required that are specifically designed to avoid the occurrence of incidents and which respond to the event as quickly and effectively as possible. In addition to mobilising the operator‟s resources, additional resources from external parties such as government agencies are often an inherent part of the incident response.

Incidence of minor spills on the platform during decommissioning will be minimised through risk identification and planning to ensure appropriate training, controls and mitigation are in place. Such spills are excluded from further assessment.

Dropped objects could disturb the drill cuttings pile and this is addressed in Appendix E.4.7.

Of greater potential significance are major spills from fire or vessel collision. By the time of decommissioning the platform will be hydrocarbon free, such that potential impacts from fire are likely to be lower than during normal platform operations.

Loss of containment of the largest fuel tank involved in the decommissioning operation, onboard the HLCV, is taken as the worst credible spill scenario during decommissioning. If this occurred at an offshore location the main concern would be vulnerability of seabirds. Seabird vulnerability at Dunlin is generally low, although can be high during March, July, October and November (Appendix A.3.3.).

Marine diesel is a low viscosity distillate fuel. Diesel contains a high proportion of lighter hydrocarbons, such that evaporation is an important process contributing to the removal of spilt diesel from the sea surface. Evaporation will be enhanced by higher wind speeds and warmer sea and air temperatures.

The general behaviour of a diesel spill at sea can be summarised as follows:

A slick of diesel will elongate rapidly in the direction of the prevailing wind and waves.

Very rapid spreading of the low viscosity diesel will take place.

Some diesel fuels may form an unstable emulsion at the thicker, leading edges of the slick.

Speed of physical dispersion of the surface slick increases with wind speed. Up to 95% of a slick may disperse within about 4 hours of the spill event in 15 knot winds and associated wave action.




Overall the spill impacts at sea are considered to be minor with low probability of occurrence, hence the risk level is acceptable.

Loss of containment in inshore waters could result in serious risk to the environment. With onshore winds this could result in rapid spreading to coastal and intertidal areas before spill response measures could be deployed. It is emphasised that such events are very rare. However, they are more likely to occur at inshore locations where navigational constraints and traffic densities are more demanding, although no more likely to do so than incidents from other shipping activities in inshore areas. Accordingly, potential impact severity is considered major with likelihood low, hence the risk level is tolerable.

All stages of the operation will be carefully assessed for spill risk and detailed plans put in place to avoid, control and mitigate spills. For activities in inshore areas this will include careful attention to route planning, consultation with relevant harbour authorities and third party assessment of plans.

D.2 Topsides Removal Comparative Assessment

In addition to the Base Case for topsides removal, two other removal solutions have been considered:

Offshore deconstruction where each of the modules is cut into manageable pieces offshore and removed. This is sometimes referred to as „Piece Small‟.

Single Lift, whereby the entire topsides is removed in a single piece for deconstruction at an onshore facility.

Offshore deconstruction (Piece Small) is an established method for topsides decommissioning. It requires the largest amount of offshore work but has the potential to reduce the requirement for a dedicated onshore decommissioning base for all but a few large pieces of material. It also allows waste to be processed and sorted prior to being transported to shore, so that it can be sent directly to appropriate disposal or recycling sites. This method also has the benefit of reducing the number of offshore heavy lifts required, but it would involve a high number of other lifts and shipping movements. A description of the operations involved in this topsides removal method is presented in Section 11.1.2.

The Single Lift method is the most technically challenging of the topsides removal options. It is likely to be the solution requiring the least amount of offshore operations (and therefore offshore impacts). A description of the operations involved in this topsides removal method is presented in Section 11.1.3.

A comparison of the environmental impacts of the three topsides removal options is given in Table D-3 below.




Table D-3: Comparison of Topsides Removal Options Impacts

Activity

Impact Associated with Topsides Decommissioning Option

Reverse Installation (Base Case)

Piece Small Single Lift

Offshore

Platform-based preparation and topsides dismantling

130 days by crew of 130 (limited by bed space).

Standby vessel (full time)

Supply vessel (weekly)

280 days by crew of 130 (limited by bed space).


30 days by workforce of 80 on support vessel

Two specialised twin lift vessels, estimated at 2 days travel to site and 1 day conducting lifting operations. (+ days to demobilise each)

One heavy transport vessel to transport topsides structure to decommissioning yard, transit time to site estimated at 1 day, transit time to decommissioning yard estimated at 1 day.

Navigation aid installed on CGB from support vessel (5 days)

55 days standby vessel.

Vessel-based completion of topsides dismantling and transfer to shore facility

30 days HLCV.



Intensive use of supply vessels to ship materials to shore

Vessel-based preparation for and removal of MSF and other steelwork on CGB.

Installation of navigation aids on CGB

80 days flotel by crew of 160 (includes flotel crew)

21 days HLCV (follows demobilisation of flotel).



21 days HLCV (130 workers + 40 crew)


Two supply vessels (weekly)

Onshore

Onshore Dismantling/Processing

Topsides modules to be transported to onshore decommissioning site then further dismantled/cut up. Waste materials to be separated and sent onwards to appropriate recycling/disposal facility.

Only the MSF and potentially the flare boom and platform cranes will require further dismantling onshore. All other waste material will be sorted prior to transport to shore and transported directly to recycling/disposal sites. This option presents the lowest environmental impact for onshore dismantling.

Once onshore, dismantling as per Piece Small method offshore. This option presents the highest environmental impact for onshore dismantlement.

Disposal/Recycling

All three decommissioning options are expected to generate approximately the same amount of

waste material. Following transport to shore, materials will be recovered according to the waste

hierarchy for re-use of equipment, recycling of materials or thermal recovery depending on the

type of waste. Impacts will be managed within the licences of the recycling/disposal sites.




Based on Table D-3, the environmental aspects considered potentially significant for topsides removal are as follows:

Overboard discharge impacts would be acceptable in all three cases given that they would be similar or lower to those experienced during normal platform operations. The total quantities discharged would be broadly proportional to the extent of offshore activity such that Single Lift would cause the minimum impact and Piece Small the greatest.

All three options would involve use of DP vessels, although the Single Lift option would have the shortest duration and therefore minimum impact. The Base Case (reverse installation) would be likely to have the highest impact given that the flotel and HLCV would be on station for the longest period.

Incident risk is dominated by the threat of spill inshore. All three options would involve at least one trip by a large HLCV or heavy transport vessel. However, the Piece Small option would involve multiple trips.

Table D-4 below provides a comparison of the available estimated CO2 emissions for the three options.

Table D-4: Comparison of CO2 Emissions Estimates for Topsides Removal Options

Activity generating CO2 Emissions

CO2 Emissions

Base Case (Reverse Installation)

Piece Small Single Lift

Offshore

Offshore 21,578 33,653 12,237

Onshore

Dismantling 5,692 Note 1

Recycling/Disposal 19,200

Total

46,470 Note 1

Note 1: Quantitative data for onshore dismantling for both Piece Small and Single Lift are not available. However, it is clear that shore-based activities would have access to more effective equipment, therefore it can be expected that there would be:

A reduction in onshore emissions for the Piece Small alternative as much of the deconstruction would have already been carried out offshore. However, this reduction will be considerably less than the corresponding increase in offshore emissions.

An increase in onshore emissions for the Single Lift alternative as more onshore deconstruction would be required. Any increase would be considerably smaller than the corresponding decrease in offshore emissions.




D.3 Summary of environmental impacts

The potential environmental impacts of making the Dunlin A topsides hydrocarbon free are within the range of normal platform operations (for example, for maintenance shut down) and can therefore be taken to be acceptable.

Once hydrocarbon free, overboard discharges will be minimal, associated only with platform, vessel and flotel accommodation.

The impacts associated with topside removal are summarised in Table D-5 below:

Table D-5: Topside Removal Impacts


Overboard discharge (sewage, grey water, food waste and drainage)

Marine water quality

Acceptable Discharge volumes will fall within values expected during normal operation.

Flotel discharge will comply with MARPOL standards.

Atmospheric Emissions Impact on air quality (climate change impacts addressed under cumulative impacts in Appendix F)

Acceptable Minor, localised impacts on air quality.

No environmental receptors identified at Dunlin A.

Onshore emissions subject to existing permit requirements.

Subsea Noise (vessels) Impact on marine mammals

Tolerable Peak noise levels (dynamic positioning thrusters) experienced for very short periods.

Background noise levels (ocean waves) high.

Incidents or non-routine events

Offshore impacts on seabirds

Acceptable

Low probability of spill.

Rapid dispersion of diesel spill.

Generally low level of seabird vulnerability (except for March, July, October and November).

Inshore impacts (marine ecology/seabirds)

Tolerable (although within acceptable risk level for normal port operations)

Higher risk of incident due to navigational constraints and traffic density.

Variety of sensitive receptors in inshore waters.

Comparison of the topsides removal Base Case with the alternatives of Piece Small and Single Lift options suggest that, if available, the Single Lift option would have the lowest potential impacts. Atmospheric emissions will be minimised and it may also offer lower risk of inshore spills since only a single trip to shore is required (compared with two for the Base Case and many for Piece Small). Fairfield Energy intends to investigate the availability of this option nearer the time of decommissioning. Such investigation would include assessment of subsea noise.




D.4 References

BMT Cordah (2004), Environmental Statement in support of the decommissioning of the North West Hutton facilities. A report for BP Exploration, June 2004

JNCC (2009) "The Protection of marine European Protected Species from injury and disturbance"

Oil and Gas UK (2011). Oil and Gas UK Facilities Report 2011, Atmospheric Emissions for 2009. Oil and Gas UK.

OSPAR (2009) Overview of the impacts of anthropogenic underwater sound in the marine environment.

IoP(2000) Guidelines for the calculation of estimates of energy use and gaseous emissions in the decommissioning of offshore structures. Institute of Petroleum, 2000

Shell (2007), Indefatigable Field Platforms and Pipelines Decommissioning Programmes, Shell U.K. Limited, May 2007

Total (2003), Frigg Field Cessation Plan, Total E&P Norge AS, MCP01-00-A-00-0006, rev. 02a, May 2003

Total (2006), MCP-01 Decommissioning Programme, Total E&P UK Ltd, February 2006



REPORT REFERENCE: P1623_RN3027_REV1.DOC E-1 04/12/2012

Appendix E CGB and Drill Cuttings Pile




E.1 Introduction

Fairfield Energy has recommended (Section 12.1) that the Dunlin A concrete gravity base (CGB) be granted a derogation in accordance with OSPAR Decision 98/3. This is on the basis of other studies which demonstrate that:

In situ decommissioning is the only technically feasible method of dealing with the structure as it is not practical to float the structure or deconstruct it on location.

It is the preferred approach with respect to safety, involving the minimum of offshore activity in general and diver-based activity in particular.

This approach will not lead to unacceptable environmental impacts.

As a result, while the topsides and all external steelwork will be removed, the CGB will be decommissioned in situ and remain on location. The likely end condition will be as follows:

The base structure of the CGB has a seabed footprint of 104m x 104m (10,816m2) and rises to approximately 30m above seabed.

The four legs will remain in place, rising from the base structure to 8m below sea level.

One of the four legs will be fitted with an extension tower to support a navigation aid.

Dunlin drill cuttings are present on the top of the base structure and on the surrounding seabed. See Appendix E.4 for further information on drill cuttings.

The current 500m exclusion zone around the CGB will be maintained (an area of 0.79 km2).

There will be regular helicopter visits to inspect the navigation aid and a helicopter-based maintenance operation at two-year intervals.

The CGB contains residual quantities of hydrocarbons, sediments and contaminants associated with the separation and storage of hydrocarbons during the first phase of the platform‟s operational life.

Over a long period of time there will be progressive failure of the legs, currently estimated to commence around 250 years into the future. It is likely that the leg supporting the navigation aid will experience the greatest environmental loads and fail first, most likely at a point some 23m below sea level, where the leg geometry changes. Given the robustness of the CGB base and the low ocean currents close to the seabed, it is likely that failure of lower leg sections and the base itself will not occur for 1000 years or more.

Potential environmental impacts associated with the presence of the CGB after decommissioning are:

Loss of seabed habitat

Obstruction to shipping and a potential hazard

Loss of fishing grounds




Operational impacts associated with the maintenance of the navigation aid, and any monitoring of the structure

Environmental impacts associated with release of the cells contents

It is also recognised that by leaving the structure on the seabed, material (e.g. reinforcing bar) which would otherwise be available for recovery is lost. In a comparative assessment the energy cost of replacing this material would need to be accounted for. However, at Dunlin it has already been established that it is not technically feasible to remove the structure from the seabed such that this comparison is not appropriate. In effect, this material is already „lost‟ such that the energy cost of its replacement is not an impact of the decommissioning programme.

Consultation associated with development of the derogation case for the CGB identified the environmental impacts associated with shipping hazards and release of the cells contents to be the main areas of potential concern. Cells contents were the subject of a separate assessment (Metoc 2011) which is summarised in Appendix E.3.

E.2 Impacts Associated with Physical Presence of

CGB

There are a number of potential impacts associated with the long-term presence of the CGB on the seabed. The potential loss of biodiversity associated with the footprint of the CGB was considered to be minor (and unavoidable) in comparison to the broader issues associated with navigation and fisheries and hence was not considered further.

The Dunlin area is important for fishing. However, the area of the 500m exclusion zone around the platform is negligible when compared to the overall fishing grounds available in the region, even when considered in the context of the cumulative impacts of all current oil and gas exclusion zones. OGUK (2010) state that “there are over 600 offshore oil and gas installations in the North Sea, 470 of which are in UK waters”. This suggests that all North Sea installations would have a combined exclusion zone area of less than 550km2, less than 0.1% of the total area of the North Sea of some 750,000km2 (OSPAR 2012). The density of platforms in the UK sector of the North Sea is a little greater than that for the North Sea as a whole such that the combined exclusion zones of platforms on the UKCS represent less than 0.13% of the UKCS area.

This area of the northern North Sea experiences low levels of shipping, such that navigational concerns in the region will mainly relate to other oil and gas activity and fishing, rather than to the Dunlin CGB. Prior to failure of the legs, the risks of ship collisions will be very low given that the CGB and the exclusion zone will be marked on nautical charts, and the CGB will be marked with a navigation aid. Hence the risk is considered acceptable.

After the legs fail, the navigation aid would no longer be present and risk will increase. It is anticipated that the likely first failure point on the legs will be at 23m below sea level, which could then result in a navigational hazard to vessels. Two risks would arise:

A minor severity impact risk with the CGB being a nuisance to some users of the sea, albeit beyond 250 years hence; and




A possible major impact should there be an incident involving loss of a vessel

Referring to the risk matrix in Section B.2, both of the above risks would fall into the tolerable category, which requires that risks are managed to be As Low as Reasonably Practicable (ALARP).

On this issue, Fairfield Energy has already identified that removal of the legs to a level below 55m below sea level with disposal on the seabed may be a technically viable alternative, which may be preferred. At present this solution, which may be permitted under OSPAR 98/3, is understood not to be allowed under UK Government policy. Should a change to UK Government allow this option, Fairfield Energy will determine whether this alternative should be considered further.

The aid to navigation installed on the CGB leg will be inspected annually by helicopter, and will be serviced every five years, also by helicopter. The environmental impact in terms of atmospheric emissions for performing these operations at the Dunlin A CGB has been assessed in Table E-1. In practice it is expected that these operations will occur in conjunction with inspections and servicing on other navigation aids installed on similarly decommissioned installations.

Table E-1: Atmospheric Emissions from Navigation Aid Maintenance

Source Engine Type


Emissions (Tonnes)


Helicopter (Annual)

Gas Turbine (Air)

2 6.4 0.01 0.03 0 0 0 0

Helicopter (250 year total)

Gas Turbine (Air)

500 1,600 2.6 6.25 0.11 0.04 0.4 1

E.3 Cells Contents Impact Assessment

The potential of the CGB cells contents to pose an unacceptable risk to the environment has previously been assessed by Intertek METOC (2011). The work was directed at meeting the OSPAR requirements for assessing the disposal of offshore concrete structures at sea by:

Describing the characteristics of the substances within the CGB cells, indicating the form in which they are present and the extent to which they may escape

Assessing the potential impacts on the environment following such a release from the cells and the extent to which there is potential for an unacceptable impact

The assessment was carried out in two stages. Firstly the potential contents of the cells were evaluated on both an “Upper Bound” and “Best Estimate” basis. The Upper Bound was then used to test the potential for unacceptable impacts on the environment.




The main findings of the assessment are summarised in the sections below.

E.3.1 Cells Contents

The contents of the cells were evaluated from knowledge of the materials passed into and through the cells during platform operations, and the physical and chemical processes which led to a build-up of residual quantities within the cells.

During the operational life the use of the CGB storage cells was reduced over a number of years and then completely ceased, at which point the bulk oil and trapped attic oil was removed and replaced with seawater. The history of cell use is summarised below:

1978-1995: Cells used for oil-water separation and bulk oil storage. Records show that all four cell groups were in use, but with Group D being used the least frequently.

1995-2007: Cells only used occasionally for oil-water separation, mainly during start-ups and plant upsets when the oil did not meet export requirements. New equipment installed to allow produced water treatment and three phase separation on the topsides with direct oil export.

2007-Present: Cells no longer in use. Attic oil removal completed in 2007 to allow final isolation of the cells.

The overwhelming component of the cells contents is seawater. In addition to the seawater, there are four „carrier‟ materials which between them contain all of the various components which may be in the cells in significant quantities. The carrier materials are:

Wax deposits adhering to the walls of the cells as a result of cooling through the cell walls. The deposited wax will also contain trapped oil.

Inert solids, which being heavier than both oil and water have settled to the base of the cells.

Precipitates (scale) formed as a result of the mixing of produced water and seawater within the cells, and then settling to the base of the cells.

Oil and wax which will have been sequestered by heavier materials and drawn down to the base of the cells.

All of the above were derived directly from Dunlin operational records and the results of the analysis of fluid samples taken in 2010. Total quantities of each of the major components of the residual material are shown in Table E-2.

Hydrocarbons and reservoir formation water contain a number of classes of components with potential for toxic effects. These include:

PAHs and BTEX – all aromatic carbon molecules

Heavy metals

NORM (naturally occurring radioactive materials)




It is also likely that residual quantities of production chemicals will be present. Those which partition with the hydrocarbons can be assumed to be present at the concentrations at which they were used at the time, if they were used continuously. If used for only part of the time they will be further diluted. Those which partitioned with the water phase will be present at trace levels only, because the small amounts of residual produced water has been substantially diluted by seawater subsequently used to refill the cells.

Table E-2: Cell Contents – Major components

Best Estimate Upper Bound

(tonne) (tonne)

Sea water 250,000 250,000

Hydrocarbons 1,600 5,400

Scale 216 1,400

Inert solids 370 1,300

While the above figures are presented as a Best Estimate, it must be noted that the assumptions used to derive the estimates were generally conservative and the actual quantities present in the cells are likely to be substantially lower.

The Best Estimate values for residues at the base of the cells suggest a thickness of approximately 200mm, made up of hydrocarbons, scales, sand and clay (but excluding water content of the bottom residues). This is an average thickness. Variation within and among the cells, and inclusion of water, could make actual levels of base residual materials higher at some locations.

The Best Estimate of thickness of material deposited on the outer walls is 12mm at the top of the cells, tapering down to zero thickness around 20m from the top of the cells.

It is thought highly unlikely that quantities could be higher than the Upper Bound quantities.

Table E-3: Cell Contents – other components

Best Estimate Upper Bound

(tonne) (tonne)

Aromatic hydrocarbons

BTEX 22 100

PAH 1.3 4.5

Metals 2.8 18.8

NORM 90 GBq 1700 GBq




E.3.2 Environmental Impact Potential

It is certain that at some date in the future the CGB will lose containment. The most likely scenario is that in the first instance this will arise from corrosion of currently plugged pipework such that there will be a weak exchange of liquid contents with seawater over a substantial period, in advance of any major structural collapse of the CGB. Solid contents in the cells would then be subjected to long-term biodegradation before being fully exposed to the environment. Alternatively, it is possible to envisage higher energy failures (for example, collapse of one of the legs onto the cells) which would result in rapid loss of contents and distribution of a proportion of the solid contents onto the surrounding seabed, contaminating the sediments. In the unlikely event that this occurred in advance of loss of liquids containment, this would be accompanied by rapid release of the seawater in the cells.

It is also likely that lighter oils trapped in the residues at the base of the cells, or in the wax on the cells walls, will, over time, diffuse back into the liquid contents and become trapped in the attic spaces in the top of the cells. There is therefore potential for formation of a surface slick.

Each of these pathways (water column contamination, sediment contamination and surface slick) was been assessed for potential to cause an unacceptable risk to the environment, using the Upper Bound estimates for cell contents.

Water Column Contamination

The oil and gas industry routinely assesses the harm potential of discharges into the marine environment. As a result there are well established methods for such assessments. The eventual discharge of cells contents cannot be viewed as a regulated discharge. However, the regulatory framework does provide a useful benchmark against which to assess the acceptability of a potential discharge.

In the Cells Contents Impact Assessment (Intertek METOC 2011), Acceptability Criteria (AC) were established for each of the components in the cells liquid contents and applied at a 500m radius from the cells, following release from the CGB.

The water column assessment addressed both the impacts associated with loss of liquid contents from the cells (immediately following loss of containment) and longer term impacts associated with diffusion into the water column from solid contents, concluding that:

Initial release of liquid contents is likely to be gradual, due to corrosion of existing pipework connections into the cells. In the highly improbable event of a major structural failure occurring in advance of a more gradual release, the complexity of the cells structure is such that it is unlikely that this would result in the whole of the liquid inventory entering the water column over a short period (several minutes). However, if this were to occur, the concentrations of contaminants at the 500m boundary would be likely to exceed AC but their effects would be of short duration (i.e. a few hours), with the majority of components being rapidly degraded to non-toxic products. Environmental impacts would therefore be minor. Over the longer




term, metals and NORM are expected to diffuse from the solid residual material into the water column at a rate which is insignificant in terms of elevated component concentrations at the 500m boundary.

Similarly, organic (e.g. BTEX and PAH) contamination of the water column at 500m is also expected to be at levels significantly lower than the limiting AC. BTEX will degrade rapidly and therefore will pose little risk to the environment. PAHs are highly persistent; however, they are strongly retained by particulate material and are unlikely to enter the water column from sediments.

Sediment Contamination

In addition to diffusion of components from solid residues into the water column, ingestion of sediments by biota and subsequent bio-accumulation through the food chain provides another potential pathway for environmental harm.

This can take two forms: chronic impacts resulting from low dose levels over an extended period (i.e. 30 years) and acute impacts resulting from much higher doses over a short period (typically less than 24 hours).

The following conclusions were drawn from assessment of sediments:

None of the components assessed could be delivered at sufficient rate, or for long enough duration, to lead to a significant (more than 1%) proportion of the chronic dose in humans.

None of the components within the cells is capable of concentrating into the food chain in sufficient quantity to deliver an acute dose to humans.

Only sessile, non-resistant species living on the outer boundary of the contaminated zone will be able to accumulate toxic levels of contaminants. These represent a very small portion of the regional population.

Surface Contamination

It is likely that hydrocarbons will slowly accumulate in the attic spaces of the CGB cells through gradual diffusion from the residues on the outer walls and base of the cells. One cell in each of the four cell groups directly received oil through inlet/outlet piping bellmouths near the top of the cells. Bottom residues are likely to have preferentially formed in these cells. It is therefore likely that a significant proportion of the future attic oil will accumulate in these cells, with a maximum of 27 tonnes of oil trapped in the attic of any cell after 1000 years.

The most likely loss of containment event is failure due to corrosion of the pipework between the bellmouth and Leg B of the CGB (assuming the leg were still in place). This could be some tens of years after decommissioning and therefore could predate more general structural failure by hundreds of years. Assuming the integrity of the leg is maintained, oil would weather within the leg such that the likelihood of a substantive spill would be low.

However, it is possible that future attic oil could be released through a more general structural failure, such that a larger quantity is released. A spill of




500 tonnes was modelled (to reflect the Upper Bound inventory of an entire cell group). This indicated that in the unlikely event of such a release, lighter oils such as diesel would dissipate within about 40km of the CGB, while heavy oil fractions would have a less than 5% probability of being carried ashore.

E.3.3 Overall Finding

The overall findings from the Cells Contents Impact Assessment (Intertek METOC 2011) are summarised as follows:

Available records and understanding of the physical and chemical processes leading to build up of residual contents in the CGB cells provide an adequate basis for characterising the cells contents, and for opining on the likelihood of an environmentally unacceptable outcome following eventual loss of containment.

While it was recognised that there are differences between the Best Estimate and Upper Bound evaluations for cell contents, these are considered not to be sufficient to undermine the description of the characteristics of the substances within the CGB, and the extent to which they may escape.

Acceptability Criteria were established for each of the components of the cells contents. These were derived from various sources and set to reflect levels of impact which society currently deems broadly acceptable. All components were assessed against these criteria using the Upper Bound cell contents estimates combined with conservative assumptions for release impacts. („Conservative‟ in that the assumption will tend to increase the assessed impact).

With few exceptions, the assessment of worst case release scenarios for all components identified to be potentially present in significant quantities, showed that impacts are likely to be well within the Acceptability Criteria. For the few cases where criteria were approached or could be exceeded, further qualitative assessment indicated that impacts will be either insignificant or both short-lived and minor.

Cumulative and in-combination impacts were also assessed qualitatively and found not to be significant.

Given the conservative nature of assumptions and calculations undertaken, the above conclusions indicate that the residual contents of the CGB do not pose an unacceptable risk when CGB containment is eventually lost and the contents become exposed to the environment.

E.4 Drill Cuttings

E.4.1 Introduction

The drill cuttings and associated drilling muds discharged at Dunlin A have accumulated on the roof of the base structure of the CGB and on the surrounding seabed. The cuttings resulted from the drilling of 45 wells and 53 sidetracks between 1977 and 2001 (NRG 2012). The quantities of cuttings estimated to have been generated during this period are shown in Table E-4. During this period there was an increase in the ratio of oil based




mud (OBM) to water based mud (WBM) used for drilling, as the proportion of sidetrack drilling increased, rising to 10.9 in the period between 1996 and 2001.

Table E-4: Drilling History

1977-1983 1984-1989 1990-1995 1996-2001 Total

Wells 22 14 7 2 45

Sidetracks 0 9 19 25 53

WBM Cuttings (m3) 3835 2440 1220 349 7844

OBM Cuttings (m3) 7611 5966 4791 3809 (1) 22177

Ratio OBM/WBM 2.0 2.4 3.9 10.9 2.8

Note (1) the OBM cuttings in the period would not have been discharged

It should be noted that the quantities of drill cuttings generated (given in the above table) would be expected to be considerably higher that the measured volume of the cuttings accumulation on the seabed, for two reasons:

The OBM cuttings generated since 1996 will have been returned to shore for treatment and disposal.

More significantly, the smaller cuttings will have dispersed more widely following discharge near the surface, such that only the larger cuttings would have accumulated into a discernible „pile‟.

Drill cuttings accumulations are typically considered to be made up of two broad areas:

An inner part, sometimes termed the yolk. As discussed below this is likely to remain largely unchanged with time.

An outer contaminated area, termed the white. Natural processes (biodegradation, burial and dispersal) act to degrade this portion of the pile such that contamination levels and the affected area will reduce significantly over time.

The following sections describe the available information relating to the potential environmental impacts of the Dunlin drill cuttings. The base case is taken to be that the cuttings pile will remain in situ, allowing natural regeneration. This strategy is compared with two alternatives:

Cover the cuttings pile, isolating it from the environment.

Remove the cuttings pile.

E.4.2 Data Sources

Data used in the assessment of the drill cuttings comes from a variety of sources. Broadly these comprise local area surveys, investigations into cuttings piles associated with decommissioned facilities in the North Sea, and investigations into the behaviour of cuttings piles.




Dunlin area surveys.

There have been a number of surveys of the cuttings pile at Dunlin, although no direct measurements of conditions within the pile (within 200m of the installation) have been possible. Thus information from these surveys is limited to the physical extent of the pile (both yolk and white), and investigations of the biology and chemistry of the white. These investigations include:

1985 survey; total hydrocarbon content (THC), single transect, closest approach 500m (Shell 1986),

1987 survey; THC, single transect, closest approach 200m (Shell 1988)

1996 survey; Physical extent of cuttings pile, on CGB and on seabed (Shell 1997)

2006 survey; Hydrocarbons, cruciform survey, closest approach 100m (BMT 2007)

2008 survey; Physical extent of cuttings pile on seabed, hydrocarbons, metals and biology, closest approach 250m (GEL 2009)

Sector reports for North Sea OBM cuttings pile environmental effects.

There are a number of assessments which provide typical ranges of values for contaminant concentrations (normally hydrocarbons and metals) in the core material of OBM cuttings piles. These include:

A general review of the contaminant status of the North Sea (CEFAS 2001)

Review of the chemistry of drill cutting piles (Bruer et al 2004)

A report on sediments and cuttings piles in the Ekofisk area (DNV 2006)

The general conclusion of these reports is that the most significant component of the cuttings pile is the base oil employed to make up the drilling mud, and that the main environmental impact of this is a result of de-oxygenation of the cuttings piles and surrounding sediment, rather than any toxicological effect.

Sector reports for WBM cuttings pile environmental effects.

While the main environmental concerns relate to OBM cuttings piles, there have been a series of reports into WBM cuttings piles investigating the possible adverse effect of chemicals used as components of the drilling muds. These include:

A review of effects of discharge of WBM, including data from the North Sea and Gulf of Mexico (Neff 2005)

A review of WBM discharges with respect to cold (Arctic) waters (Neff 2010)

The general conclusion of these reports (and within the reports cited below) is that WBM-generated cuttings piles are not of significant environmental concern, beyond the immediate and local impact of physical smothering.




Chemical components of WBM are not present in sufficient quantity to present a toxicological hazard and are normally non-persistent with no tendency to bio-accumulate.

Sector reports for the disposal of cuttings piles.

Since 2000 there have been a series of reports intended to identify the best strategy for dealing with drill cutting piles in the North Sea, in accordance with principles set out by the OSPAR Convention. These are summarised in:

UKOOA Drill Cuttings Initiative Phase III. Final Report (UKOOA JIP, 2005)

Data review to inform industries response to the JIP (ERT, 2009)

Comparative assessment of decommissioning options for offshore oil and gas facilities (PSI 2005)

As a general conclusion to these reports it was stated that, for all cuttings piles on the UKCS, the best option was to leave the piles in situ. It is also recommended (PSI 2005) that a minimum of two surveys should be undertaken, with an interval of three years, and that the results of these surveys should be used as a basis for planning future monitoring, which is expected to last for at least 50 years.

E.4.3 Criteria for Best Environmental Strategy

OSPAR (2006) established two criteria for “The Best Environmental Strategy” for disposal of a drill cuttings pile containing OBM residues. The two criteria, which are illustrated in Figure E-1, are:

The rate of oil release to the environment

The persistence of the contamination from the cuttings pile

Figure E-1: Criteria for Acceptability of Cuttings Piles (OSPAR 2006a)




Rate of oil release

There are two thresholds for rate of oil release:

If the rate of oil release is less than 10 tonnes (and persistence less than 500 km2years), the potential environmental impact can be considered insignificant and the best environmental strategy is judged to be to leave the pile in situ without further intervention

If the rate is between 10 and 100 tonnes per year, a risk of environmental impact is recognised and further studies must be carried out to establish the Best Environmental Strategy for disposal of the cuttings pile

For rates greater than 100 tonnes per year it is likely that intervention to cover or remove the pile will be required to mitigate environmental impacts

The rate of hydrocarbon emission is calculated based on either:

i. an estimated leaching rate of 521mgm-2day-1 (ERT 2009) from the main pile (the yoke). (This would require an area of 52,100m2 to exceed the criteria)

ii. an estimated erosion rate based on removal of the outer 0.1cm of the yolk of the pile each year (ERT 2009)

Both of these methods result in an estimate of hydrocarbon emissions, which is related only to the surface area of the cuttings pile, either evaluated by surveys or estimated based on the number of wells contributing to the pile (ERT 2009). The value estimated according to the erosion rate is approximately 1.4 times the value estimated from leaching rates. As the Dunlin CGB is in a water depth of 150m (and seabed currents are low, even under storm conditions), erosion is unlikely to occur at a significant rate, hence leaching is expected to be the dominant mode of oil loss from the cuttings pile.

Persistence

The second OSPAR criterion is that the persistence of the contaminated (>50mgkg-1) area should not exceed 500km2yr (i.e. the criterion would be exceeded if an area of 500km2 remains contaminated for one year, or an area of 1km2 remains contaminated for 500 years).

Thus if the annual emissions are less than 10 tonnes and the persistence is less than 500km2yr the recommended Best Environmental Strategy is to leave the cuttings pile in situ and allow natural degradation to occur.

In practice, all known cuttings piles in the North Sea (including Dunlin) are within these criteria. The base case for all North Sea cuttings piles is therefore that they will be lift in situ and be allowed to degrade naturally.

E.4.4 Dunlin Cuttings Description

The physical extent of the core (or yolk) of the Dunlin cuttings pile has been surveyed twice (in 1996 and 2008) using side-scan sonar to define the presence of deposits. The survey in 1996 (Figure E-2) investigated the




cuttings piles on both the CGB roof and the surrounding seabed, while the 2008 survey (Figure E-3) was restricted to the cuttings on the seafloor.

Figure E-2: Extent of Cuttings Pile in 1996 (Shell 1997)




Figure E-3: Extent of Cutting Pile in 2008 (GEL 2009)

Table E-5 below summarises the main characteristics of the pile based on the reports of these surveys (Shell1997 and GEL 2009). Comparison of the two surveys indicates:




The seabed area reported for 2006 is very much lower than that for 1996, by a factor of about 4.5

The estimated volume reported for 2006 is slightly greater than the upper bound reported for 1996.

Table E-5: Dimensions of the Dunlin Cuttings Pile

Survey Date 1996 2008 Total

Location CGB Seafloor Seafloor Minimum Maximum

Max

thickness(m) 4 11 15 - -

Volume (m3) 1,514 - 4,000

6,517 - 10,356

11,320 8,031 15,320

Reported

surface area 3,331 22,246 4,951 8,282 25,577

Probable

surface area

(m2) 3,331 7,620 4,951 8,282 10,951

The 1996 survey was used as the basis for the information reported on the Dunlin drill cuttings in the industry response to the JIP (ERT 2009). It gives both a maximum and a minimum estimate for the volume of the cuttings deposits; however, it only gives a single (maximum) surface area. From the extent of the pile shown in Figure E-2, it appears that the reported area and the maximum volume were based on the area enclosed by the 150.4m depth contour.

The 2008 survey addressed only the portion of the cuttings on the seabed and at first sight appears to show a large reduction in the surface area. It is noted however that the estimated volume is similar (and slightly greater than) the 1996 survey, which suggests that the area reported for the 1996 survey relates to a very thin layer (with little volume). It is likely that the apparent discrepancy is due to a combination of differences in survey technique (and/or interpretation) and degradation of the thin layer between 1996 and 2008. As the only data for the cuttings on the roof of the CGB is from the 1996 survey, the total core pile area (the yoke) has been estimated by combining this (3331m2) with the more conservative estimate of surface area on the seafloor, also from 1996 (7620m2). This gives a total area is 10,951m2.

E.4.5 Extent of contamination

The above information relates to the physical extent of the cuttings (the yoke). The outer area (the white) of a cuttings pile is defined as the area where total hydrocarbon concentration (THC) in the sediment remains greater than 50mgkg-1, concentrations below this value being deemed too low to cause adverse environmental effects.

There have been a number of assessments:

Samples from a single transect to the SE (160º) of the CGB, obtained in 1985 while drilling was ongoing, suggest that THC concentrations




in the sediments were around 100mgkg-1 at 500m SE of the Dunlin CGB but decreased to <50mgkg-1 by 800m from the CGB (Shell 1986)

Survey data obtained in 1987, again from a single transect to the SE of the CGB, suggested that elevated (<50mgkg-1) sediment THC concentrations extended to about 1200m from the CGB (Shell 1988). THC Concentrations from samples taken closer to the CGB showed a steady increase from 53mgkg-1 at 1200m to 221mgkg-1 at 500m from the CGB. At 200m from the CGB a concentration of 14,757mgkg-1 was reported

A more extensive, cruciform, survey in 2006 (BMT 2007) shows that THC concentrations reduce from approximately 8,700mgkg-1 at 100m SE of Dunlin to below 50mgkg-1 at about 500m from the CGB in all directions, except to the SE. By 1000m from the CGB THC concentrations were <40mgkg-1 in all directions.

Samples taken during 2008 (GEL 2009) suggest that the outer boundary of the contaminated zone may have retreated. This survey suggests that THC concentrations are >50mgkg-1 only within about 500m of the centre. In addition the report concluded that there was no evidence for anthropogenic stress gradients between the sample sites, even where there was indication of contamination. This suggests that natural remediation of the outer fringes of the pile is taking place, through biodegradation or burial of contaminants.

Taking all surveys into account, a conservative worst case assessment for the maximum radius of the outer fringe would be within 800m of the centre of the SE face, giving a total outer fringe area (including the CGB) of 2km2. The estimated outer fringe area reported for Dunlin, based on the 1996 survey data (ERT 2009) was slightly smaller at 1.77km2. Both of these assume a circular footprint; however, the contaminated area is unlikely to be symmetrical about the centre point. Survey results from the most extensive survey (BMT 2007) suggests that the contaminated zone is extended towards the SE (i.e. in the direction surveyed in 1996) but is restricted to within 500m of the centre to the NW and SW. BMT concluded that the likely contaminated area covered about 1.114km2 in 2006.

Oil Release

Based on the hydrocarbon leaching rates previously cited, a cuttings pile of the maximum estimated area (25,577m2) for Dunlin would result in annual emissions of 4.86 tonnes. However, as discussed in Appendix E.4.4, this is likely to be a substantial overestimate. Based on the revised estimate of total yolk area (10,951m2) the annual emissions are likely to be around 2.08 tonnes per year. Even if the higher values are correct the greatest estimated oil emission rate is well below the lower OSPAR criterion for acceptability of 10 tonnes per year.

As a result of redox reactions at the interface between the anoxic interior of the cuttings pile and seawater, ferro-manganese crusts may eventually form (Chester 1990). If present these will decrease any exchanges between the interior of the pile and the overlying seawater, thus it is possible that the hydrocarbon migration rate will decrease in mature piles.




Persistence

The persistence of an OBM cuttings pile is derived from the area of the white, i.e. the area where hydrocarbon concentrations in the sediment remain greater than 50mgkg-1. A contaminated area of the worst case size of 2km2 for the Dunlin white would have to persist for 250 years to exceed the OSPAR persistence acceptability criteria, while an area of the size considered to have existed in 2006 would have to persist for 450 years.

Modelling results from comparable cuttings piles (UKOOA 2005, ERT 2009) suggests that the persistence value can be calculated by multiplying the area of the white (in km2) by an empirically derived factor of 70.7 years (ERT 2009). This factor relates to the rate at which the size of the white decreases (i.e. to the half life of the white). Using this factor, the best estimate for the persistence of the Dunlin contaminated area is 70.3km2yr with an upper bound of 126km2yr.

Other Contaminants

There are no direct data for conditions within 100m of the centre of the Dunlin cuttings pile. However, there is no evidence for any unusual conditions existing at Dunlin (e.g. use of non-standard drilling muds or geological anomalies). It is therefore assumed that contaminant concentrations are similar to those found in cuttings piles generated over the same time period in the North Sea, as reported in the literature (Table E-6 and Table E-7).

While cuttings piles with OBM contain a wide range of toxic components (e.g. heavy metals, aromatic compounds) at concentrations greater than the North Sea background, the main cause of adverse effects on the environment is the high total hydrocarbon content, both in the immediate cuttings pile and in the adjacent area (Bruer et al 2004). The hydrocarbons in the cuttings pile will both deplete oxygen in the sediments (through natural biodegradation processes) and prevent penetration of oxygen to the inner parts of the pile (normally the result of bioturbation or diffusion). This will lead to the establishment and maintenance of anoxic conditions, where the main oxidant is sulphate. This is reduced to sulphide by microbial activity, at a relatively shallow depth in the sediment, preventing the establishment of the normal ecosystem. Thus cuttings piles are characterised by a low biodiversity and biological activity is dominated by anaerobic bacteria. As a result the hydrocarbon content of the core of a cuttings pile is unlikely to change significantly with time.




Table E-6: Organic Contaminants Associated with Cuttings

Concentration in Cuttings

North Sea Background Assessment Criteria

CEFAS 2001 UKOOA 2004 DNV 2005

Shell 2006 OSPAR 2005

N. Sea N. Sea Ekofisk 2/4 A Dunlin

100m SE

All in mgkg-1

THC 30,000-150,000 8,100-150,000 20,000 – 88,000 14,000 17-120

Napthalenes (N) 75 0.39 0.008

Phenanthrenes (P) 3 21 0.032

Dibenzothiophenes (D) 24

NPD 20 - 70 45

Anthracene 12 0.069 0.005

Fluoranthene 0.1 0.22 0.039

Pyrene 0.5 0.56 0.024

Chrysene 0.3 0.3 0.020

Benzo (a) anthracene 0.1 0.072 0.016

Benzo (a) pyrene 0.007 0.076 0.030

PAH 6.7-22.4

PCB None detected None detected None detected 0.0015

Table E-7: Typical Metal Concentrations

Metal Concentration in Cuttings North Sea Background

CEFAS 2001 DNV Bruer et al 2004

Bruer et al 2004 OSPAR 2005

All in mgkg-1

Sand/Muddy Sand

BC BAC

Barium 1000-24,400 800-2100 2080-229,000 14/125

Cadmium 0.1-8 0.4 – 0.7 <0.1-10 - 0.2 1

Copper Max 110 51 -83 75-374 2/13 20 100

Mercury 0.1-33 0.09 – 0.47 <0.1-32.6 0.05 0.5

Nickel 1-49 - 26.3-137 2/15 30 50

Lead 16-173 54 - 209 62.3-4785 2/22 25 50

Zinc 2-435 100 - 550 550-2511 11/58 90 500

Data obtained from a series of samples taken between 2km and 10km from the Dunlin CGB (GEL 2009) suggest that contaminant concentrations are within the range considered as typical for this area of the North Sea. Evidence in the report indicates that the contaminants were of remote origin rather than locally sourced.

THC concentrations ranged between 10.4 and 20.4mgkg-1, predominantly unresolved, suggesting a high degree of weathering. The combined NPD concentration was in the range 0.002 to 0.015mgkg-1, while the total PAH range was 0.033 to 0.106mgkg-1, suggesting a dominance of pyrogenic (combustion, e.g. power generation, natural fires) over petrogenic (drilling) sources.




Maximum concentrations of metals reported in cuttings piles exceed the OSPAR background concentrations (BC) and background assessment criteria (BAC) while barium concentrations (for which no BC or BAC are available) are greater than those normally found in non-contaminated muddy sand (Table E-8). However, metals in cuttings piles are largely associated with insoluble mineral phases such as sulphides and are unlikely to be available (Bruer et al 2004).

Summary

Based on 1997 and 2008 surveys, the Dunlin cuttings pile falls well below the criteria for OSPAR acceptability for cuttings piles.

Table E-8: Comparison of Dunlin Cuttings Pile with OSPAR 2006 Criteria

Emissions Persistence

Tonnesyr-1

km2yr

Best Estimate Worst case Criterion Best Estimate Worst Case Criterion

1.6 6.81 10 79 141 500

E.4.6 Degradation with time

Drilling ceased at Dunlin by 2002 (NRG 2012), while the discharge of cuttings generated using OBM ceased in the North Sea by 1997 (OSPAR 2006b). This means that at the time of Dunlin decommissioning (2018 for example) any oil based cuttings will have been degrading naturally for 20 years or more.

Data from Ekofisk 24/A (with an OBM cuttings pile generated by 12 wells drilled between 1974 and 1994, and a THC concentration of 22,500mgkg-1 in the core) suggest that the surface area of the white reduced by about 50% over a period of three years (ConocoPhillips 2007). Similarly, data cited in ERT (2009) for a number of Norwegian offshore installations suggest that the white will reduce by 60-95% of the original area over 10 years. It may therefore be expected that the contaminated zone associated with the Dunlin cuttings pile will decrease substantially with a half-life estimated to be between three and 10 years. This suggests that the Dunlin white will decrease to the area of the yolk (10,951m2) in about 70 years.

E.4.7 Cuttings Pile Disturbance

Disturbance of the cuttings during decommissioning will be minimised, although risk from dropped objects is recognised. Given the continued presence of the CGB, risk of disturbance from fishing can be discounted.

However it is known that at some point in the future the CGB legs will fail. This is estimated to occur beyond 250 years after decommissioning and the first failure point is expected to be approximately 23m from the top of the leg. There are a range of failure scenarios, the most conservative being that which results in the maximum potential energy from the falling material resulting in disturbance of the remaining cuttings pile.




Unless disturbed, the cuttings pile core is likely to remain substantially unaltered over a period of hundreds to thousands of years (UKOOA JIP 2005). As previously discussed, the pile at the time of leg failure can therefore be summarised as both the yoke and white having an area of between around 8,000 and 10,951m2.

In order for the disturbed pile to fall outside of the OSPAR acceptability criteria:

The surface area of the yolk would have to increase to above 52,100m2 to exceed the oil leaching rate – an increase in pile extent by a factor of about five.

The area of the white would have to increase to more than 7.09km2 in order to exceed the 500km2 per year persistence criterion – an increase by a factor of about 650.

In view of the high oil content of the cuttings pile (i.e. 77% generated with OBM and containing up to 150,000mgkg-1 hydrocarbons at discharge) it is considered unlikely that dropped object impact will result in plume generation because oil is likely to remain adhered to the cuttings. Thus the large increases in surface area required to exceed the criteria are unlikely to occur.

It is recognised that over time all the legs will fail, probably with 10s to 100s of years between failures. Each failure will also be associated with significant debris which may to an extent cover the pile, reducing leaching rates. There will be some disturbance which will displace and expose sections of the cuttings pile. Resulting increases in oil release rate are likely to be short term, reducing as the newly exposed areas give up their oil and through redevelopment of a crust. Given that such releases are unlikely to be greater than already experienced and will happen well into the future (when environmental loading from operational releases of hydrocarbons through North Sea oil and gas activity will almost certainly have ceased), the potential environmental impacts are assessed as no more than existing impacts, and they are unlikely to approach the lower OSPAR thresholds.

Overall therefore, although disturbance by leg failure has the potential to increase the rate of oil release and persistence, any increases are unlikely to have significant environmental impact.

E.4.8 Comparison of Drill Cutting Options

The Dunlin cuttings pile is of a size which meets the criteria whereby the Best Environmental Strategy is to leave it in situ. However, there are two factors specific to Dunlin which should also be considered to establish whether this general result can be applied:

The continued presence of the CGB such that the seabed will not be returned to its original state.

The likelihood that at some point in the future the cuttings will be disturbed by failure of the legs.

As discussed in Appendix E.4.1, there are three fundamental options for decommissioning cuttings piles:




Leave the cuttings pile as it is, allowing natural regeneration (The base case).

Cover the cuttings pile, isolating it from the environment.

Remove the cuttings pile.

Table D-9 summarises the potential environmental impacts of each of the options, given the Dunlin specific conditions. Colour coding reflects the severity scale described in Section B.2 (white – negligible; green – minor; blue – moderate)

Table E-9: Environmental Impacts of options with respect to the Base Case

Sediments Water column Surface Ecosystems

Wider environment

Long term

Base case

Contamination footprint meets acceptability criteria

Hydrocarbon emissions meet acceptability criteria

Negligible

Yolk effectively sterile

White recovering

Emissions to atmosphere from monitoring programme

Risk of partial remobilisation when CGB structure fails

Cover

No significant change to contamination footprint

Decrease in hydrocarbon emissions

None expected

Increase in local species diversity

Impact on source area for cover material

Increased lifetime of yolk.

Non-natural habitat

Combustion emissions

during covering

Continued risk of partial remobilisation when CGB structure fails

Remove

May increase contamination footprint through settling of mobilised cuttings

Temporary increase in emissions from exposed sediment Possible short

term sheen formation

Faster re-establishment of natural benthic ecosystem

Impact on receiving site

Reduced long term impact, although the continuing presence of the CGB would greatly diminish this benefit.

Mobilisation of

yolk

contaminants

during dredging

Potential for

impacts on birds

and mammals

during

decommissioning

Emissions to

atmosphere

during

decommissioning

The above table suggests that there is no clear benefit from either of the alternatives compared to the base case (leave cuttings in situ). The base case presents two issues judged to have potentially moderate significance and two minor. The “Cover” and “Remove” options have respectively two or three potentially moderate issues, and both have four minor ones.

For Dunlin the potential benefits of reduced emissions by covering the pile may be offset by the fall in rate at which it loses hydrocarbons such that when the CGB eventually fails, contamination levels may be higher. For the Remove option the potential benefit associated with removal from the seabed of the cuttings is reduced by the continued presence of the CGB.

The downsides of the two alternatives compared with the base case result from the increased use of vessels, increases in emissions to the atmosphere and impacts on remote sites, used either to source covering




material or for disposal of cuttings residue. Additionally, the increased risk of incidents (in particular oil spill during operations) is a further significant source of risk to marine ecosystems and birds.

PSI undertook a comparative study of drill cuttings decommissioning scenarios (PSI 2005). This concluded that, notwithstanding the advantages of leaving a clean seabed (which will not be the case for Dunlin as the CGB will remain in place), any net environmental advantage of removing drill cuttings to shore is uncertain, while the financial cost may be considered excessive. The option to cover the pile does offer protection from remobilisation by falling objects, and is likely to allow recolonisation of the cuttings pile area, albeit within an artificial habitat. However, it imposes considerable negative impacts in terms of resource extraction.

The cuttings pile used as an example in PSI (2005) contained 40,000 tonnes of cuttings, which would be expected to have a volume of around 17,000m3. This is within the range of estimates for the Dunlin pile and is used here to inform qualitative further comparison of the options for the Dunlin cuttings. The financial information includes the estimated cost to the UK taxpayer (and has not been corrected for inflation).

Covering

Covering would be expected to be technically feasible, although there may be issues with working around the CGB and the platform legs. Covering would require a layer of material of sufficient depth to protect the underlying material from dropped object impact damage. If natural materials were to be used it is likely that this would involve a volume comparable to the volume of the original cuttings pile. At least the outer layer of the covered pile would need to be of rock, similar in size to protection used in pipe laying. Use of contaminated sediments from within the white area as a substrate for the rock would be possible. Artificial coverings would also be possible. For example, a total of about 600 standard (18m2) pipeline mattresses would be required to cover the yolk. A proportion of these could be recycled from Dunlin pipelines.

During the installation of the protective layer there would be a risk of remobilisation of contaminants from the pile. However, this would not be expected to be significant if imported (i.e. clean) material were used. If material from within the white were to be used this would increase the mobility of contaminants on a temporary basis.

Following burial, the yolk of the cuttings pile would be partially or completely isolated from the environment. This would therefore lead to a decrease in annual emissions of hydrocarbons, although the source would remain.

During the covering operations there would be an increased risk of disturbance or injury to marine mammals as a result of the presence and manoeuvring of vessels.

Following covering of the pile it is expected that colonisation would take place. However, the resulting ecosystem would be based on an artificial structure. It would therefore be unlikely to represent the baseline regional ecology.




In addition to the local impacts of covering, there would be potential for a significant environmental impact at the source site for any materials used.

Based on PSI (2005) the cost of this option was estimated to be approximately £15.3M, with overall emissions of 13,815 tonnes of CO2.

Removal

Three options for disposal following removal of the cuttings pile can be considered:

Disposal to the seabed

Onshore treatment

Reinjection

Disposal to the seabed is dismissed as a non-viable option as it does not improve, and is likely to increase, the environmental impact of the cuttings, while increasing the financial and energy costs from the base case. It is also unlikely to be legally acceptable as the option would constitute dumping at sea.

Removal and treatment onshore would leave the seabed clear of cuttings (although the CGB and the outer contaminated zone would remain). However the marine operational impacts of removing the pile are considered significant as well as those for onshore treatment and disposal. The PSI report estimated that 38,587 tonnes of material would go to landfill, with the remainder (1,413 tonnes of hydrocarbons) recovered. In addition (and not covered in the report) dredging would be likely to require between 10 and 20 times the cuttings volume of seawater (UKOOA JIP 2002), i.e. up to 306,000m3 of water. If treated to the current standard for hydrocarbons in produced water (30mgl-1) this would result in the discharge of up to 9.2 tonnes of hydrocarbons over the period of operations.

Removal of an isolated cuttings pile (i.e. without any associated infrastructure) would provide some potential benefit to the fishing industry, but with an associated negative impact on fish stocks. In the case of Dunlin, where the CGB will remain in place, removal of the cuttings pile would not benefit fishing.

During the period of operations there would be an increased risk of disturbance or injury to marine mammals as a result of the presence and manoeuvring of vessels.

Following removal of the pile it would be expected that the benthic species would recolonise, eventually returning to the baseline ecosystem, although this would likely be modified by the presence of the CGB.

The financial cost of this option was estimated to be £58.2M with estimated 28,989 tonnes of CO2 emissions.

In addition to removal to shore, a potential disposal route would be to reinject the cuttings, either at Dunlin or at a remote site. Neither of these options was considered within PSI 2005. Prior to reinjection the cuttings would have to be lifted to the surface, milled and slurrified. Injection would require suitable receiving wells, either existing or new. It would also involve a risk of failure of the receiving well or infrastructure, requiring an alternative disposal method. It can be assumed that the environmental




impacts of reinjection at Dunlin would be similar to those of removal of the cuttings pile to shore. Injection off site would increase the risk of harmful effects to the wider environment. Energy and financial costs are likely to be intermediate between those for the Cover and Remove to shore options. Reinjection of cuttings piles offsite is not currently allowed on the UKCS under international conventions. Reinjection of cuttings was not considered further.

Conclusions

In summary, all of the decommissioning options for the Dunlin cuttings are technically feasible, although there would be very significant differences in operational impacts and end results.

Given the likely disturbance of the cuttings pile when the CGB legs fail, and the continued presence of the CGB, neither the Cover option nor the Remove option would offer clear benefits. Both however involve significantly higher impacts and risks during decommissioning. Table D-9 below summarises the advantages and disadvantages for each of the allowed options.




Table E-10: Drill Cuttings Decommissioning Summary

Option Advantages Disadvantages

Base Case – Leave in situ for natural degradation

No safety risk

No decommissioning emissions

No disposal Issues

Minimum costs

Long term contaminant source

Physical footprint

Vulnerable to disturbance

Long term monitoring programme required

Cover and isolate Low leaching rate from pile

Protection from (minor) accidental disturbance

No disposal issues

Reduced degradation rate & pile lifetime increased

Continued vulnerability to major disturbance

Minor risk of contaminants mobilisation during covering

Operational impacts during covering

Use of resources

Long term monitoring programme may be required

Remove and treat onshore

Seabed clear of major contamination source

Not vulnerable to disturbance

Significant mobilisation of contaminants during removal operations

Combustion emissions & discharges during removal operations

Disposal issues (cuttings and liquid waste)

Monitoring may be required

E.4.9 Drill Cuttings – Cumulative Impacts

The Scientific Review Group of the Oil & Gas UK (OGUK) Drill Cuttings Initiative (UKOOA JIP 2002) concluded that, at present, effects of drill cuttings piles across the North Sea are highly localised. The total area of cuttings piles in the North Sea was estimated to be approximately 1,605km2 (0.3% of the total North Sea area). As a comparison, fishing, dredging and spoil dumping are estimated to affect between 130,000 and 369,000km2 of seabed annually, i.e. between 17% and 49% of the North Sea area.

Hydrocarbons and other contaminants are considered to be largely immobile within the cuttings pile. The only significant contamination is from the hydrocarbons which are released, through erosion, degradation and leaching, at a rate which is small compared with other sources of hydrocarbons estimated to be released in excess of 330 tonnes per year. The total hydrocarbon releases from cuttings piles represents less than 5% of this figure.

Overall this suggests that the Dunlin cuttings pile will not make a significant contribution to cumulative impacts from cuttings pile in the region, and therefore the impacts identified as potentially moderate in Table D-8 can be judged to be minor. As previously noted, the specific circumstances associated with the continued presence of the CGB mean that in comparison with other locations, the Dunlin site even more strongly favours the option to leave the cuttings in situ, and it can therefore be concluded that this is the Best Environmental Strategy for the Dunlin cuttings.




At Dunlin, it is also necessary to assess the impacts of cuttings in combination with the potential impacts associated with release of the contents of the CGB cells. Recalling that the main environmental impact of cuttings is a result of de-oxygenation of the cuttings piles and surrounding sediment, rather than any toxicological effect, potential cumulative impacts will be associated with increase in the extent and persistence of the deoxygenated area.

There are likely to be three potential stages of contents release of the Dunlin cells:

Early loss of liquids containment, resulting in weak circulation of seawater through the cells and commencement of degradation of the solids content once anoxic conditions within the cells cease.

Partial structural failure of the CGB resulting in exposure of solids content. It is possible that this could occur when one of more of the legs fail (beyond 250 years from now) but is more likely to be later (circa 1000 years).

Extensive failure of the structure with broad exposure of residual solids content.

The initial phase where liquids containment is lost can be ignored from the perspective of deoxygenation of seabed sediments.

By the time there is any likelihood of exposure of solids content, the area contaminated by cuttings will be similar to the existing area of the core cuttings pile (the yoke) plus any increase associated with disturbance by the failure of the legs. Assuming that the footprint of deoxygenation associated with the CGB is similar to its current footprint (10,816 m2), the affected area would be this plus the portion of the core pile on the seabed (4,951 m2) an area of 15,767 m2.

In order for this to represent a potential concern when judged against the OSPAR criteria, the disturbance caused by the legs and failure of the CGB would have to increase the affected area as follows:

The surface area of the yolk would have to increase to above 52,100m2 to exceed the oil leaching rate – an increase in pile extent by a factor of more than three

The area of the white would have to increase to more than 7.09km2 in order to exceed the 500km2 per year persistence criterion – an increase by a factor of approximately 500.

Given that debris from structural failure will partially cover both cuttings and cells contents, the likelihood of increases in effective area on this scale is very small.

Accordingly, environmental impacts from the cuttings pile are considered to be minor even when cumulative and in-combination impacts are considered.

E.5 Summary of Environmental Impacts

Fairfield Energy has recommended (see Section 12.1) that the Dunlin A CGB be granted a derogation in accordance with OSPAR Decision 98/3.




This is on the basis of other studies which demonstrate this to be the preferred option.

There are no significant operational decommissioning impacts associated with the CGB or cuttings accumulation, since the strategy is to leave both in situ and undisturbed. The main environmental impacts are therefore associated with their continued presence, as follows:

Continued, permanent physical presence on the seabed, largely intact for 1000 years or more and thereafter progressively degrading to seabed rubble. The current 500m exclusion zone will be maintained.

Gradual seepage/weak discharge of liquid contents once liquids containment is lost, which is likely to be relatively soon after decommissioning.

Exposure of residual solids contents in the CGB cells following more substantial degradation of the structure. This could be as early as circa 250 years after decommissioning (due to leg failure) but is more likely to be around 1000 years or longer.

Continued leaching of hydrocarbons from the drill cuttings (up to 4.9 tonnes per year)

Deoxygenation of seabed sediments, initially affecting an area of up to 2km2 (worst case basis), reducing towards the area of the core accumulation of 0.11 km2 over time.

Impacts associated with the maintenance of the navigation aid on the CGB and continued monitoring of the CGB structure, calculated to generate 6.4 tonnes of CO2 per annum or 1,600 tonnes over the next 250 years.

Navigational hazard. It is assumed that the CGB will be permanently marked on charts and hazards mitigated by the navigation aid while at least one of the legs is intact. Present non-oil and gas related shipping intensity is very low. This hazard is therefore most significant for fishing vessels given the general significance of the area for fishing. However the presence of the CGB structure and the exclusion zone means that vessels are unlikely to knowingly deploy nets in the immediate vicinity.

Once the legs have failed (beyond 250 years hence) there will be a potential hazard to shipping because the remains of the legs are likely to be within 55m of the surface. Further degradation of the legs to below this level is likely not to occur until 1000 years in the future. Residual risks associated with this hazard are assessed as tolerable indicating that they should be reduced to ALARP.

The permanent presence of the remains of the CGB is acknowledged as a direct impact of oil and gas production at Dunlin. However, given that it is not feasible to remove the installation, this is unavoidable and therefore not an impact of the decommissioning programme itself.

Similarly, the loss of containment of the CGB leading to release of liquids content and eventual exposure of residual solids is also unavoidable. In this respect such impacts can be argued as not being impacts of the




decommissioning programme. However, they have been assessed and are found to be tolerable.

The long-term continued presence of the core of the drill cuttings accumulation could be avoided by alternative decommissioning strategies. However, based on currently available information, the drill cuttings accumulation falls within OSPAR thresholds below which drill cuttings impacts can be considered insignificant.

The proposed strategy of minimum intervention for the drill cuttings, leaving them to degrade naturally, has been compared qualitatively with the alternative strategies of covering and of removal for onshore disposal. Given the continued presence of the CGB and the potential for disturbance at some point in the future it has been concluded that the Dunlin site even more strongly favours the option to leave the cuttings in situ when compared with sites which could otherwise be returned to their natural state. Accordingly, it is confirmed that leaving the drill cuttings in situ and uncovered is the Best Environmental Strategy for the Dunlin cuttings. This is therefore considered an acceptable outcome. Further work to characterise the drill cuttings pile is planned to confirm the current findings.

Navigational hazards are considered to be of minor significance while the navigation aid is present. However, there is significant residual risk once the CGB legs fail (beyond 250 years in the future). Fairfield Energy has identified complete removal of the CGB legs and disposal on the seabed as a technically viable alternative. However, at present this option is understood to be prohibited by UK Government policy. This alternative is therefore considered as currently not available and has not been assessed. Fairfield Energy will revisit this option should there be a change to UK policy in this respect.

Table E-11: Summary of CGB and Drill Cuttings Impacts


Physical presence of CGB structure

Navigation hazard Acceptable (navigational aid intact)

Risk of ships collision very low.

Tolerable (navigational aid not intact) – (alternatives, including removal of legs, to be monitored)

Increased risk of collision when navigational aid not intact.

Physical presence of CGB structure

Impact on marine water and sediments due to release of cell contents

Acceptable For the majority of components impacts are likely to be well within Acceptability Criteria even in the case of worse case release.

Drill cutting pile (release of contaminants)

Impacts on marine water quality

Acceptable Hydrocarbons released through erosion, degradation and leaching is small compared with other sources of hydrocarbons.

Hydrocarbons and other contaminants within the cuttings pile are considered largely immobile.




E.6 References

BMT (2007) Sediment hydrocarbon concentrations around Brent D, Dunlin A and Gannet A 2006 Report No A.SHL.114.

Breuer E. Stevenson A.G. Howe J.A. Carroll J. Shimmield G.B (2004) Drill cuttings accumulations in the Northern and Central North Sea: a review of environmental interactions and chemical fate. Marine Pollution Bulletin 48 12-25.

CEFAS (2001) Contaminant status of the North Sea. SEA2 Technical Report TR004.

ConocoPhillips (2007) Environmental monitoring of drill cuttings in piles included in the Ekofisk I cessation plan. Forum for offshore miljøovervåking 2007.

DNV (2006) Monitoring, characterization and profiling of selected drill cuttings piles. Report Number 2006-0653.

ERT (2009) Data review for an industry-wide response to cuttings pile management: Final report. Report No ERT 1987 for Oil and Gas UK.

GEL (2009) UKCS 211/23 Dunlin development: Debris clearance, mud mound and environmental baseline survey December 2008 Environmental baseline report.

Intertek Metoc (2012), Dunlin Alpha Decommissioning Cells Contents Impact Assessment, P1215C_RN2478_Rev0, June 2011

Neff J.M. (2010) Fate and effects of water based drilling muds and cuttings in cold-water environments. Report Prepared for Shell Exploration and Production Company Houston Texas.

Neff JM. (2005) Composition, environmental fates, and biological effect of water based drilling muds and cuttings discharged to the marine environment: A synthesis and annotated bibliography. Report prepared for the Petroleum Environmental Research Forum. Washington DC: American Petroleum Institute.

NRG (2012) Drill cuttings review. Draft report prepared for Fairfield Energy.

OGUK (2010) Knowledge Centre, Technical perspective, http://www.oilandgasuk.co.uk/knowledgecentre/technical_perspective.cfm

OSPAR (2005) Agreement on Background Concentrations for Contaminants in Seawater, Biota and Sediment (OSPAR Agreement 2005-6).

OSPAR (2006a) Recommendation 2006/5 on a management regime for offshore cuttings piles (OSPAR Commission 2009).

OSPAR (2006b) OSPAR Report on Discharges, Spills and Emissions from Offshore Oil and Gas Installations in 2004 (OSPAR Commission, 2006).

OSPAR (2012) The North East Atlantic, Region II – Greater North Sea http://www.ospar.org




PSI (2005) Decommissioning of offshore oils and gas facilities: Decommissioning scenarios: A comparative assessment using flow analysis.

Shell (1986) A survey of the seabed sediment hydrocarbon concentration around Dunlin A and Cormorant A platforms, 1985. Environmental report No 19/86.

Shell (1988) July 1987 Environmental Survey of Shell‟s Tern Eider and Dunlin Oilfields Report No IOE/87/616.

Shell (1997) Drill cuttings survey 1997 Report No P97-145/06.

UKOOA (2000) UKOOA JIP Drill cuttings initiative: Phase I Final Report.

UKOOA (2002) UKOOA JIP Drill cuttings initiative: Phase II Final Report.

UKOOA (2005) UKOOA JIP 2004 Drill Cuttings initiative: Phase III Final Report.



REPORT REFERENCE: P1623_RN3027_REV1.DOC F-1 04/12/2012

Appendix F Cumulative Impacts




F.1 Introduction

It is generally acknowledged that there are difficulties in assessing cumulative environmental impacts in the EIA for a single project. To this end, DECC‟s Strategic Environmental Assessment (SEA) process addresses, as one of its objectives, cumulative impacts on a sector basis. More can be learned about the SEA process at http://www.offshore-sea.org.uk/site/

One of the findings of the 2009 UK Offshore Energy SEA carried out by DECC was: “Cumulative effects in the sense of overlapping ‘footprints’ of detectable contamination or biological effect were considered to be either unlikely (accidental events), or very limited (for physical damage, emissions, discharges), since monitoring data indicates that the more stringent emissions, discharge and activity controls introduced over recent years have been effective and there is no evidence for significant cumulative effects from current activities” (DECC, 2009). While this general conclusion for the sector as a whole suggests cumulative impacts are unlikely, it is nonetheless important that specific potential impacts are also identified for Dunlin A decommissioning. The following mechanisms could potentially give rise to cumulative environmental impacts:

Operational impacts associated with decommissioning could combine with other activities carried out at the same time, most likely to be other oil and gas related activities.

Long term impacts associated with the drill cuttings could combine with impacts from other similar drill cuttings accumulations.

The impacts of the physical presence of the CGB after decommissioning could interact and exacerbate those of other facilities granted OSPAR derogation to remain in situ.

The Dunlin A Platform is situated close to the eastern boundary of UKCS Block 211/23. Within this Block there are two fields, both of them subsea tie-backs to Dunlin: Osprey approximately 6km north northwest, and Merlin, approximately 7km northwest of Dunlin. In addition, there has been drilling in the Dunlin South West Field, approximately 4km from Dunlin. The nearest platform to Dunlin A is Thistle, approximately 11km to the north of Dunlin. There are also three platforms 14-20km from Dunlin: Murchison to the northeast, Brent D to the south and Statfjord B in the Norwegian sector to the southeast. Figure E.1 shows the position of the Dunlin A platform in relation to the Shetland Islands and the international boundary between UK and Norwegian waters. Locations of other CGB structures that might be candidates for in situ decommissioning are also shown. The nearest CGB platforms are three located in the Statfjord field, approximately 10km to the east and southeast. There are also three CGBs in the Brent field, some 15km to the south, one in the Cormorant field, some 30km to the southwest, and one in the Ninian field, some 30km to the south.

http://www.offshore-sea.org.uk/site/

http://www.offshore-sea.org.uk/site/




Figure F-1: Location of Dunlin in respect to other CGBs

Operational decommissioning impacts were addressed in Appendix C and the only impacts identified with potential for cumulative effects were subsea noise and CO2 emissions (which are addressed in Appendix F2 below). For noise, there is a medium likelihood of disturbance effects on larger cetaceans over significant areas through a combination of subsea noise from DP vessels with those of other exploration, production or decommissioning activities.

Potential cumulative impacts associated with the continued presence of the CGB and drill cuttings accumulation include:

Shipping. As oil and gas activities cease, associated marine vessel activity will also reduce, with no foreseen additional shipping activities expected. It is considered therefore that the risk of ship collision with an individual decommissioned platform is not increased by the presence of other decommissioned platforms. Accordingly, there would not be any cumulative impact for shipping.

Fisheries. Fishing vessels typically travel at between two and four knots while trawling, hence the transit time between Dunlin A and the nearest platform, which could also remain in situ, is between 1.5 and 2.5 hours. The presence of the decommissioned Dunlin A platform, taken together with other platforms, would not have any cumulative impact on fishing activity.




Drill cuttings accumulations. It was noted in Appendix D2 that the main impact from cuttings accumulation results from de-oxygenation of the cuttings piles and surrounding sediment, rather than any toxicological effect. Furthermore, natural degradation of cuttings contamination means that the extent of the area affected reduces to that of the core accumulation in a relatively short period of time (of the order 70 years). For Dunlin this footprint is unlikely to extend much more than 150m from the platform. Given the distances between Dunlin A and other drill cuttings accumulations (several kilometres) there is no risk of overlapping footprints, and the long term residual area affected is approximately 0.15km2.

F.2 Climate Change Impacts

The preceding Appendices have identified emissions of CO2 from offshore operations, onshore activities and ongoing maintenance of the navigation aid on the CGB. By their nature, the potential effect of each of these on climate change is cumulative, alongside other emissions from the oil and gas sector and from human activity. The total CO2 emissions from all decommissioning sources (over the expected three-year decommissioning period) is estimated to be 86,818 tonnes. This compares with annual operational emissions from the Dunlin platform of 83,000 tonnes (2010 data).

Table F1 below summarises overall CO2 emissions from the Dunlin A Decommissioning Programme.

Table F-1: Overall CO2 emissions from Dunlin A Decommissioning Programme

Decommissioning Activity CO2 Emission

Wells P&A Offshore 32,400

Wells P&A Onshore 6,348

Removal of Topside (Base case) Offshore 21,578

Removal of Topside Onshore 24,892

Maintenance of navigational aid 1,600

Total 86,818

F.3 Summary – cumulative impacts

The only factors identified to have the potential for cumulative environmental impacts are the effects on marine mammals of subsea noise, and the possible long-term atmospheric effects of combustion emissions.

Subsea noise would be in the range of routine drilling activity and is considered tolerable.

CO2 emissions would be minimised. The Base Case for topsides removal gives the lowest emissions of the options currently available using proven technology. Fairfield Energy will consider the availability of Single Lift for topsides removal nearer to the time of decommissioning to see whether this would be the better option. Until such time, the current approach of the Base Case minimises the unavoidable emissions to negligible levels and is therefore considered acceptable.




F.4 References

DECC (2009). UK Offshore Energy Strategic Environmental Assessment.

dunlin decommissioning es december 2012 - appendices a to f eia.pdf

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