whitehead & associates

Blue Mountains Sewage Management Options Study

Whitehead & Associates Environmental Consultants Pty Ltd

Whitehead & Associates Environmental Consultants

197 Main Road Cardiff NSW 2285 Australia Telephone +61 2 4954 4996 Facsimile +61 2 4954 4996 Email [email protected]

Blue Mountains

Sewage Management Options Study

May 2014

Prepared for: Blue Mountains City Council

Prepared by: Jasmin Kable & Joe Whitehead


197 Main Road

CARDIFF HEIGHTS

NSW 2285

Telephone: (02) 4954 4996

Facsimile: (02) 4954 4996

Email: [email protected]



Document Control Sheet

Document and Project Details

Document Title: Blue Mountains Sewage Management Options Study

Author(s): Jasmin Kable and Joe Whitehead

Project Manager:

Joe Whitehead

Date of Issue: 08 May 2014

Job Reference: 1214

Synopsis: Sydney Water has provided a subsidised pump-out service to lots within the Blue Mountains City Council local government area that were a part of the Priority Sewerage Program whilst they awaited connection to the sewer network. It has been advised that this scheme is now complete and that the subsidy will be discontinued; affecting 72 lots that remain reliant on pump-out. The Blue Mountains Sewage Options Study investigates the potential of on-site wastewater management options and alternative off-lot options for these 72 privately owned lots that are currently on pump-out.

Client Details

Client: Blue Mountains City Council

Contact: Strategic Planning Specialist (Environment) Michelle Maher

Document Distribution

Version Number

Date Status DISTRIBUTION – NUMBER OF COPIES (p – print copy; e – electronic copy)

Client Council Other

1214-1 08/05/14 Draft 1e 0 1e, 1p

1214-2 22/05/14 Final 1e

1214-3 29/05/14 Final Revision 1e

Document Verification

Checked by:

Issued by:

Joe Whitehead Jasmin Kable

Document Certification This study has been prepared following the standards and guidelines set out in the following documents, where applicable:

Standards Australia / Standards New Zealand, (2012) AS/NZS 1547:2012 On-site Domestic Wastewater Management;

Environment & Health Protection Guidelines: On-site Sewage Management for Single Households (Department of Local Government, 1998); and

Sydney Catchment Authority Current Recommended Practice Designing and Installing Onsite Wastewater Systems (SCA, 2012).

To our knowledge, it does not contain any false, misleading or incomplete information. Recommendations are based on an honest appraisal of the sites opportunities and constraints, subject to the limited scope and resources available for this project.



Contents

Acronyms ..................................................................................................................................... 1

1. Introduction ........................................................................................................................ 1

2. Scope of Study .................................................................................................................. 2

3. Site and Soil Assessment – Council Lots .......................................................................... 3

4. Determination of Available Effluent Management Areas ................................................... 9

4.1. Planning Considerations ................................................................................................ 9

4.2. Overview ........................................................................................................................ 9

4.3. Methodology ................................................................................................................ 10

4.3.1 Setback Buffer Distances ..................................................................................... 10

4.3.2 Development Area ................................................................................................ 11

4.3.3 Lot Slope ............................................................................................................... 11

4.4. Council Lot Assessment .............................................................................................. 13

4.5. Private 72 Lot Assessment .......................................................................................... 13

5. OSSM Options Assessment ............................................................................................ 16

5.1. Overview ...................................................................................................................... 16

5.2. OSSM Options ............................................................................................................. 16

5.2.1 Secondary Treatment ........................................................................................... 16

5.2.2 OSSM Land Application Options .......................................................................... 20

5.2.3 Additional Options ................................................................................................. 23

5.3. Land Application Area Sizing ....................................................................................... 24

5.3.1 Design Wastewater Loads and Occupancy .......................................................... 24

5.3.2 Design Loading Rate ............................................................................................ 25

5.3.3 Subsurface Irrigation Area Sizing ......................................................................... 26

5.3.4 Mound Sizing ........................................................................................................ 27

5.4. OSSM Feasibility and Excess Volumes ....................................................................... 28

6. Off-lot Options Assessment ............................................................................................. 36

6.1. Overview ...................................................................................................................... 36

6.2. Partial On-lot Management .......................................................................................... 36

6.3. Sewer Options ............................................................................................................. 36

6.3.1 Grinder Pump Low-Pressure Sewer: .................................................................... 36

6.3.2 STEP/STEG Effluent Sewer ................................................................................. 37

6.3.3 Extend Conventional Sewer Main ......................................................................... 37

7. Feasibility ......................................................................................................................... 39

8. Conclusion ....................................................................................................................... 42

9. References ...................................................................................................................... 43

10. Appendices ...................................................................................................................... 44


Acronyms

AWTS Aerated Wastewater Treatment System

BMCC Blue Mountains City Council

BOD5 Biochemical Oxygen Demand

DCP Development Control Plan

DEM Digital Elevation Model

DIR Design Irrigation Rate

DLR Design Loading Rate

EMA Effluent Management Area

ETA Evapotranspiration-absorption System

GIS Geographic Information System

LAA Land Application Area

LGA Local Government Area

OSSM On-site Sewage Management

NorBE Neutral or Beneficial Effect

PSP Priority Sewerage Scheme

SCA Sydney Catchment Authority

STEG Septic Tank Effluent Gravity

STEP Septic Tank Effluent Pump

TSS Total Suspended Solids

WELS Water Efficiency Labelling Standards


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1. Introduction

Blue Mountains City Council (BMCC) adopted the Blue Mountains Sewage Strategy (2008) which outlines the strategic approach to resolving the long-term sewage issues within the BMCC Local Government Area (LGA). A Sydney Water subsidised pump-out service has been provided to lots that were in the Priority Sewerage Program (PSP) whilst they awaited connection to the sewer network. Sydney Water advised that in June 2012 that they had completed the PSP in the BMCC LGA and no further properties would be connected to the sewer network. Furthermore, Sydney Water has since written to their pump-out customers advising them that this pump-out subsidy would be removed on 1 July 2013. This has since been extended to 1 July 2014 after negotiations between BMCC and Sydney Water.

There are a total of 72 privately owned lots, located throughout the BMCC LGA, that fall outside the PSP area and remain on the Sydney Water subsidised pump-out service. The majority of these lots fall beneath the minimum area of 4,000m2 for sustainable On-site Sewage Management (OSSM) under current, and proposed, BMCC planning documents (BMCC Better Living Development Control Plan, 2010).

The aim of this BMCC Sewage Management Options Study is to investigate a range of alternative wastewater management options for residential lots within BMCC that are currently not serviced by reticulated sewer; with a particular emphasis on the 72 privately owned lots that currently receive the pump-out subsidy.

The BMCC LGA falls within the Sydney Catchment Authority (SCA) area and consequently additional consideration for OSSM options is needed for the protection of the Sydney drinking water catchment. Under the State Environmental Planning Policy (Sydney drinking water catchment) 2011 (the SEPP), any development in the catchment that requires consent form Council, including any OSSM system, must show a neutral or beneficial effect on water quality (NorBE). The SCA Current Recommended Practice Designing and Installing Onsite Wastewater Systems (SCA, 2012) was developed to provide technical information to help design, install, inspect and assess on-site hydraulic effluent management systems in the Sydney drinking water catchment and helps to meet the requirements of the SEPP as they apply to OSSM systems. This SCA guideline (SCA, 2012) was adopted by Council and should be used in conjunction with other current recommended best practice guidelines; AS/NZS 1547:2012 and Environment & Health Protection Guidelines: On-site Sewage Management for Single Households (DLG, 1998)

The results of this study will inform the preparation of the revised Blue Mountains Sewage Strategy and be used to review various controls within Local Environmental Plans and Development Control Plans (DCP) that apply in the Blue Mountains, including the minimum area required for OSSM.


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2. Scope of Study

The scope of this study is to:

- Request and receive electronic copies of all available, relevant and necessary background documentation, previous studies undertaken by Council and mentioned in the brief and GIS layers;

- Review the documentation and data outlined above and prepare base mapping for the subsequent site assessments;

- Visit the eight (8) prescribed sample lots (once), owned by Council, and undertake site investigations relevant to OSSM and record in tabular form data on these lots sufficient to characterise them for OSSM. These lots will be used to determine a range of site characteristics for the Blue Mountains;

- Assess a broad range of commercially available and approved on-site water reduction devices, wastewater treatment options and land application system alternatives that would be appropriate for the Council lots and make recommendations on their suitability for the 72 privately owned lots under consideration;

- Assess a range of effluent management options including partial on-site reuse, extension of existing Sydney Water reticulated sewerage services, common effluent collection and management systems, pump-to-sewer systems and pump-out systems and identify their suitability for individual or cluster servicing of the 72 lots under consideration. This assessment will include an assessment of their environmental impacts and management implications;

- Undertake a brief assessment of the feasibility and appropriateness of all the above options (and combinations thereof) for the 72 lots, including a GIS based assessment of likely minimum lot sizes required for various options based on available information about the sites (some of which is to be provided by Council); and

- Liaise with SCA as well as Council in developing sewage management options.

This study has been confined to an assessment of the potential suitability of each property for OSSM based on site and soil constraints of the land. No assessment has been made of any planning or other environmental constraints that may impact on the suitability of a property for OSSM.


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3. Site and Soil Assessment – Council Lots

Site and soil assessments relevant to OSSM were conducted on eight (8) prescribed, Council owned lots to determine a range of representative site characteristics for the Blue Mountains and to determine if they could potentially be used to assist in the management of wastewater from the 72 privately owned lots. The site and soil assessments were conducted on 9th and 10th April 2014 by Whitehead & Associates. A total of one test pit to depth of refusal was undertaken on each of the lots and representative soil samples were taken. Table 1 summarises the site and soil constraints for the application of wastewater on each of the Council lots.

In general, the lots were heavily vegetated with mixed native tree and shrub species and the groundcover consisted of organic matter debris. The majority of the lots were located either along ridgelines or on the side slopes. The gradient of the lots was generally quite 15-40% when located on side slopes. The soils on the Council lots were classified within three broad soil landscapes; Medlow Bath, Wollangambe, and Warragamba Soil Landscapes (King, 1994). Typically the soil profiles were shallow with bedrock located at approximately 500mm depth. The soils were generally derived from sandstone parent rock and can be classified as a category 1 (as per AS/NZS 1547:2012) soil; clayey sand. The soil texture and evidence from the test pits indicated that indicative drainage within the soil would be rapid; however, gleying observed in the subsoil suggests that some degree of horizontal subsurface flow occurs at the bedrock interface.


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Table 1: Site and Soil Characteristics of the 8 Council Lots

Site & Soil Characteristics

Lot 1 Lot 2 Lot 3 Lot 4 Lot 5 Lot 6 Lot 7 Lot 8 Lot 9

Address

57 Georges Pde

54-56 Shipley Rd

45 Kent St 22-26 Clarendon St

9-15 Walker St

49-55 Kent St

104-108 Kent St

147-151 Grand Canyon Rd

369-408 Great Western Hwy

Township Mount Victoria

Blackheath Bullaburra Wentworth Falls

Wentworth Falls

Bullaburra Bullaburra Medlow Bath Katoomba

Planning Number (Lot/DP)

13 / 221988 187 / 751647 4 / 29496 97 / 31895 92 / 31895 6 / 29496 35 / 29859 26 / 28056 6 / 10148

Lot Area (m2) 1,287 4,946 835 2,023 2,417 3,340 2,304 2,758 48,900

Zoning

Environmental Living (E4)

Environmental Management (E3)







Environmental Conservation (E2) and far east of lot is Special Purpose Classified Road (SP2rd)

Elevation (m AHD)

1050-1036 1058 822 812-808 829 822 750 1029 1047

Topography

Narrow ridgeline along road

Slight slope. Crest in the middle of the lot

Ridgeline along the road. The lot is located on the side slope grading away from the road

- On ridgeline. Lot slopes gradually up to the centre of the lot from the road

Ridgeline along the road. The lot is located on the side slope grading away from the road

- Lot drops off significantly from the road

Slope decreases upslope


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Slope

Entirely >20%

Northern portion is <20% and southern portion is ~30%

<20% <20% <20% <20% All <20% except western boundary ~25%

Northern portion is <20% and southern portion is an escarpment between 40% and 60%

Majority of lot is <20%, except for the eastern and western boundaries are between 20% and 35%

Lot aspect

NE-E Crest in middle of lot – test pit location had W aspect

SE E SE SEE NNW SE Variable – N (crest located at southern boundary) but S at location of test pit

Environmental Buffers

Groundwater bores located adjacent to NNW and SW corners

Vegetation

Moderately vegetated with mixed native grasses and trees

Very heavily vegetated with mixed native grasses and eucalypt trees.

Heavily vegetated with mixed native grasses and trees.

- Heavily vegetated with mixed native grasses and trees. Shrub vegetation around the edges of the lot

Heavily vegetated with mixed native grasses and trees

Vegetated with mixed native grasses and trees

Extremely vegetated with mixed native grasses and trees

Heavily vegetated with mixed native grasses and trees

Exposure Poor Poor Poor - Slightly Poor Poor Poor Poor


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moderate – poor

Surface Condition

Poor. Covered with organic matter debris, surface rocks of various sizes and rock outcrops

Covered with organic matter debris


- Covered with organic matter debris. Some isolated rock outcrops and sandstone fragments scattered on the surface.


Covered with organic debris

Good. Covered with organic matter debris


Erosion

Water erosion observed

Erosion along access tracks

- - - - - - Pedestrian tracks. Gully erosion in places

Other

- Rock shelf located in SE corner of lot adjacent to road that extends as a rock outcrop to the NNW

- - - - - - National Park located to the east of the lot

Test Pit Coordinates1 (244460,6281839)

(247545, 6274583)

(260144, 6265897)

- (258580, 6268516)

(260144, 6265897)

(260270, 6266227)

(250342, 6271406)

(248830, 6267774)

Soil Landscape Wollangambe (wo) erosional

Warragamba (wb) colluvial

Medlow Bath (mb) residual






Wollangambe (wo) erosional

1 Coordinate Reference System: Map Grid of Australia 1994 Zone 56 (eastings, northings)


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(west and north adjacent to lot is Warragamba)

with southeast portion (~1/5th of lot) Warragamba

Soil Bore Log

1/1 0-300mm Fine Sandy Loam Reddish brown 5YR 4/3 EAT 3/5

2/1 0-300 Clayey Sand Brown 10YR 4/3 EAT 3/6 5-10% coarse fragments

3&6/1 0-350mm Sand Dark yellowish brown 10YR 4/4 EAT 5

- 5/1 0-300/400mm Clayey Sand Apedal Strong brown 7.5YR 5/8 EAT 3/5

3&6/1 0-350mm Sand Dark yellowish brown 10YR 4/4 EAT 5

7/1 0-200mm Sand Apedal Dark yellowish brown 10YR 4/6 EAT 5/6 More organic than 7/2

8/1 0-700mm Clayey Sand – Sand Mod. Structure Yellowish red 5YR 5/8 & 4/6 EAT 3/5 Red mottles

9/1 0-600mm Clayey Sand Apedal-weak structure Strong brown 7.5YR 4/6 EAT 3/5 ~30% coarse fragments

1/2 300-400mm Fine Sandy Clay – Light Clay Brownish yellow 10YR 6/6 EAT 3 20-30% coarse fragments Weathered sandstone bedrock

Bedrock at 300mm

3&6/2 350-500mm Clayey Sand Strong brown 7.5YR 4/6 & 5/6 EAT 3/5

- Bedrock at 300/400mm (weathered sandstone)

3&6/2 350-500mm Clayey Sand Strong brown 7.5YR 4/6 & 5/6 EAT 3/5

7/2 200-1000mm Sand Apedal Yellowish brown 10YR 5/8 EAT 5/6

8/2 >700mm Medium Clay Crumbly structure (talc-like) Light grey 2.5Y 7/2 EAT 2 (swelling)

Bedrock at 600mm

Bedrock at - Ironstone at - - Ironstone at Weathered - -


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400-450mm 500mm 500mm bedrock at 1000mm

Indicative Drainage

Good, but most likely any water runs off as sheet flow. Water seepage in test pit at 1m in bedrock.

Good - - OK. Moist subsoil with gleying evident along subsoil/ bedrock boundary

- - Very poor. Mottling of subsoil at 550-700mm followed by gleying at 700mm. Very saturated subsoil; although no water pooling in test pit.

-


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4. Determination of Available Effluent Management Areas

4.1. Planning Considerations

This study and its findings have been confined to an assessment of the potential suitability of each property for OSSM based on soil and site assessments. In addition to the findings of this study, there are other planning requirements (i.e. town planning or environmental constraints) that need to be considered that may further limit the ability for OSSM on the site. A merit assessment of all planning issues will be needed before Council can approve an OSSM system for any given lot. Any application to install an OSSM system and the accompanying Water Cycle Management Study must address these issues.

4.2. Overview

The potential options for OSSM on each of the lots refer to the amount of adequate area available for OSSM. This available Effluent Management Area (EMA) broadly refers to available areas (i.e. not built out or used for a conflicting purpose) where OSSM will not be unduly constrained by site and soil characteristics. Available EMA on a developed lot is determined by the following factors:

Maintenance of appropriate setback buffers from property boundaries, buildings, driveways and paths, groundwater bores, dams, and intermittent and permanent watercourses; and

Total development area (including the dwelling, sheds, pools, driveways and paths, gardens unsuitable for effluent reuse, and any other hardstand areas, etc).

Available areas may be unsuitable or constrained for OSSM due to other factors, including (but not limited to):

Excessive slope;

Excessively shallow soils;

Heavy (clay) soils with low permeability;

Excessively poor drainage and/or stormwater run-on; and

Excessive shading by vegetation.

The ‘thresholds’ for the above factors are influenced by current national and state guidelines but are largely qualitative. Furthermore, the degree of constraint depends on the type of effluent disposal system and generated effluent quality. Physical constraints can often be overcome or substantially mitigated by a range of measures (such as terracing, importing suitable quality topsoil fill, installing stormwater diversions, draining soils, removing vegetation or planting effluent-assimilating vegetation etc.), thereby increasing the ‘suitability’ of the available area.

Due to the topography of the locality, the degree of slope was also considered in the amount of available EMA on any given lot considered by this study.

Hence, the nominal available EMA for any given lot was determined by subtracting the following factors from the total lot area:


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Area within setback buffers;

Percentage of lot that is developed; and

Area that has a slope greater than 20% (considered unsuitable for OSSM).

If should be noted that an individual site specific design is needed to confirm the results from this study and to determine the most appropriate location for the Land Application Area (LAA) within the available EMA.

4.3. Methodology

The area of available EMA for each lot in the study was analysed in QGIS™ using the Geographic Information System (GIS) data provided by BMCC. An overview of the methodology is described below.

4.3.1 Setback Buffer Distances

Buffer distances from available EMAs are required to minimise risk to public health, maintain public amenity and protect sensitive environments. The SCA Current Recommended Practice Designing and Installing Onsite Wastewater Systems (2012) in Table 2.4, prescribes minimum setback distances for both primary and secondary treated OSSM systems. The prescribed setback distances for secondary treatment of effluent are listed as follows:

6m from buildings;

4m if area is up-gradient and 2m if area is down-gradient or flat from property boundaries, driveways, swimming pools, retaining walls, paths and walkways and recreation areas;

100m from permanent and intermittent watercourses (150m to a SCA named river);

40m from a dam or drainage depression; and

100m from a groundwater bore or well used for domestic consumption.

The prescribed setback distances are conservative, to take into consideration a diverse range of site and soil conditions throughout the locality. The potential of soils to assimilate nutrients and attenuate pathogens is highly variable due to a broad range of interdependent physical and chemical properties. The Sydney Catchment Authority Current Recommended Practice Designing and Installing Onsite Wastewater Systems (2012) may allow for a reduction in setback distances if it can be demonstrated that the site and soil conditions support the reduction. This is particularly true for higher level treatment systems, which produce effluent that is virtually pathogen-free and relatively low in nutrients. In the case where a reduction in the prescribed setback distances is needed, a justification matrix based approach as per Table R1 and R2 in AS/NZS 1547:2012 should be undertaken.

The aforementioned setback distances were applied, using QGIS™, to the 72 privately owned and 8 Council owned lots to determine the available EMA for each given lot. Due to the expanse of the study, for the setback distances relevant to property boundaries etc, an average 3m setback buffer was applied to all boundaries.


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4.3.2 Development Area

The proportion of development on any given lot needs to be taken into account and excluded from the available EMA. Development refers to structures such as the dwelling, driveways, garages, sheds, swimming pools and any other hardstand areas that have been constructed and cannot be utilised for OSSM. The percentage of development on any given lot varies slightly with total lot size. An estimate of the development percentage for three broad lot size classes was determined for a representative sample of the indicated 72 private lots, using aerial photography analysis in QGIS™. A representative sample, minimum 20%, of the total lots for each lot size class, was assessed using random selection. The approximate development percentages were as follows:

<1,000m2: 31%;

1,000m2 – 4,000m2: 27%; and

>4,000m2: 18%.

This shows that with an increase in total lot size there is a proportional decrease in total development area. In order to maintain conservatism, a representative development area of 31% was used in the assessment of the available EMA on each of the lots. It should be noted that this potential development area could be located within the same buffer area as the other factors used to determine the available EMA; setback distances and lot slope. However, due to the broad nature of this study, no correction factor was applied.

4.3.3 Lot Slope

AS/NZS 1547:2012 (Table K1) details a range of factors likely to limit the selection and applicability of land application systems, with slope gradient identified as one critical factor. The slope of the land is strongly linked to the technology, design and cost of a land application system installation. Steep slopes, particularly when combined with shallow or poorly drained soils, can lead to surface breakout of effluent downslope of the LAA. Conventional soil absorption systems will most likely be unsuitable and these lots will require a detailed site assessment and specific system design to produce a sustainable outcome. These steeply sloping sites are generally unsuitable for trenches and beds and can also be problematic for surface irrigation techniques. Conversely, flat and gently sloping sites are less likely to experience such problems and are considered less constrained. Each land application system has a suggested maximum slope for installation as indicated in AS/NZS 1547:2012; for example conventional soil absorption systems are not recommended to be installed on slopes greater than 15%.

It is important that there is an even application of effluent throughout a LAA. It is important to ensure that all pipework within the LAA is laid level and that the LAA is designed to follow the natural contour of the land.

For this study, based on the different land application systems, slopes greater than 20% (11.3°) were considered too steep for OSSM. Therefore, regions within a lot with a slope >20% were excluded from the available EMA. The methodology for determining the slope of a given lot is as follows.

Surface elevation was gridded (maximum cell size of 20m), with no vertical exaggeration, from 10m contours, to create a Digital Elevation Model (DEM) using


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QGIS™. Gridded slope data was then derived from the DEM to calculate the average slope for each lot and the change of slope throughout the lot as percent grade.


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4.4. Council Lot Assessment

Table 2 outlines the available EMA for each of the 8 Council owned lots. The available EMA refers to the residual areas not otherwise occupied by buffers, development or slope greater than 20%. This was calculated using the aforementioned methodology in QGIS™. It would found that Council lots 3 and 5 had minimal and Council lots 1 and 4 had no available EMA for wastewater management.

Table 2: Available EMA Determined for the 8 Council Lots

Lot Number

Address Total Lot Area

(m2) Available EMA

(m2)

1 57 Georges Pde, Mount Victoria 1,287 -

2 54-56 Shipley Rd, Blackheath 4,946 2,881

3 45 Kent St, Bullaburra 835 451

4 22-26 Clarendon St, Wentworth Falls 2,023 -

5 9-15 Walker St, Wentworth Falls 2,417 391

6 49-55 Kent St, Bullaburra 3,340 2,682

7 104-108 Kent St, Bullaburra 2,304 1,744

8 147-151 Grand Canyon Rd, Medlow Bath 2,758 804

9 369-408 Great Western Hwy, Katoomba 48,900 27,592

4.5. Private 72 Lot Assessment

Table 3 outlines the available EMA for each of the 72 private lots. The available EMA refers to the residual areas not otherwise occupied by buffers, development or slope greater than 20%. This was calculated using the aforementioned methodology in QGIS™.

The average available EMA per lot size category is as follows:

<1,000m2 (4): 266m2;

1,000m2 – 4,000m2 (48): 806m2; and

>4,000m2 (20): 3,288m2.

It was found that there were 5 private lots that had no available EMA as per the applied criteria; lots 11, 15, 34, 43 and 44.


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Table 3: Available EMA Determined for the 72 Private Lots

Lot Number Total Lot Area (m2) Available EMA (m2)

1 1,278 590

2 1,310 554

3 1,728 580

4 1,539 405

5 22,466 2,371

6 1,237 312

7 1,192 39

8 704 287

9 753 307

10 745 306

11 2,013 0

12 1,956 158

13 2,027 899

14 2,015 1,034

15 9,264 0

16 2,921 1,590

17 4,736 81

18 5,054 185

19 3,877 320

20 2,414 1,278

21 2,417 1,280

22 2,334 1,232

23 1,029 374

24 9,312 2,314

25 3,117 463

26 2,698 1,311

27 2,623 1,408

28 6,588 3,685

29 1,010 428

30 1,010 430

31 5,481 983

32 5,646 584

33 4,242 429

34 4,032 0

35 4,032 50

36 2,759 1,494

37 2,759 1,493

38 2,758 1,095

39 1,962 521

40 1,839 586


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Lot Number Total Lot Area (m2) Available EMA (m2)

41 13,588 8,223

42 2,055 1,039

43 11,791 0

44 1,021 0

45 1,748 719

46 3,512 132

47 2,070 437

48 5,681 1,041

49 6,667 3,238

50 2,420 1,279

51 3,424 1,558

52 2,577 589

53 2,168 490

54 2,436 1,297

55 2,428 1,177

56 2,622 1,366

57 2,426 1,201

58 2,898 1,576

59 2,851 1,516

60 3,231 382

61 32,224 13,874

62 21,380 9,144

63 2,177 1,135

64 1,729 875

65 2,020 1,044

66 1,011 431

67 2,037 557

68 469 165

69 2,162 31

70 4,828 714

71 21,865 8,106

72 24,162 10,738


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5. OSSM Options Assessment

5.1. Overview

This section outlines the various OSSM options that would be suitable for the 72 privately owned lots that can accommodate either all or part of their wastewater load on-site. Current systems on existing lots may need to be upgraded in order to meet the requirements for each system as specified by Sydney Catchment Authority Current Recommended Practice Designing and Installing Onsite Wastewater Systems (2012).

Using the various design flow allowances and soil types, the minimum required LAA can be determined by means of a monthly water balance approach. The required LAA (total load) can then be compared to the available EMA (potential load) for any given lot to determine whether wastewater can be sustainably managed on-site or if there is an excess, whereby alternate designs or off-lot options need to be investigated.

5.2. OSSM Options

5.2.1 Secondary Treatment

Given the inherent site and soil constraints exhibited in the Blue Mountains locality, as outlined in Section 3 of this report, primary treatment systems are not considered appropriate as they significantly limit effluent disposal and reuse options and pose a higher risk to public and environmental health compared to secondary or tertiary treatment systems. A minimum effluent quality standard of ‘secondary treatment’ is recommended for the 72 private lots. NSW Health provides accreditation for domestic secondary treatment systems in NSW. The system selected for use at any given lot must be accredited by NSW Health or, if non-accredited; site-specific process/design information should be submitted to BMCC and SCA for approval prior to installation.

Options for secondary treatment include (but are not limited to):

Aerated Wastewater Treatment Systems (AWTS);

Aerobic Sand or Textile Filter Systems;

Biological Filter Systems;

Composting systems;

Sand (Wisconsin) Mounds (combined treatment and disposal); and

Membrane Filters.

A detailed list of NSW Health accredited systems can be found at:

http://www.health.nsw.gov.au/environment/domesticwastewater/Pages/default.aspx

We have assumed a nominal average cost of $25,000 – $30,000 for supply and installation of a secondary treatment system.

Disinfection units are typically installed as a standard component of proprietary secondary treatment systems, or can be installed as an add-on by the system supplier. We recommend that a disinfection system is installed with all AWTS. Domestic systems typically use one or a combination of the following disinfection methods:

Ultra Violet (UV) irradiation


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Chlorination

Where existing septic tanks are performing adequately (or have this capability), they can be retained and used as part of the secondary treatment system. The suitability of the existing tank for this purpose needs to be thoroughly assessed by a suitably qualified wastewater professional.

Effluent treatment quality

Based on the typical accreditation requirements (NSW Health, 2005), we would expect treated effluent to be of a (minimum) secondary standard as follows:

5-day Biochemical Oxygen Demand (BOD5): <20mg/L;

Total Suspended Solids (TSS): < 30mg/L;

Total coliforms (with disinfection): < 10cfu/100mL; and

Free Available Chlorine: between 0.5 and 2.0mg/L.

The above standards are maximum values.

Nutrient reduction performance in proprietary and custom-built treatment systems is variable, depending on system design and operating conditions (including influent wastewater strength); however, general nutrient targets would be 30mg/L and 10mg/L for total nitrogen and phosphorus, respectively.

A brief description of these secondary treatment systems is provided below.

AWTS

Domestic AWTS are pre-fabricated, mechanically aerated wastewater treatment systems designed to treat domestic (<2,000L/day) wastewater flows. They are tank-based systems, comprising of either one or two separate tanks that typically employ the following processes:

settling of solids and flotation of scum in an anaerobic primary chamber. This stage is omitted in some models and existing septic tanks could be used for this purpose as discussed previously;

oxidation and consumption of organic matter through aerobic biological processes using mechanical aeration;

clarification – secondary settling of solids;

disinfection – usually by chlorination but occasionally using ultraviolet irradiation; and

regular removal of sludge to maintain the process.

AWTS are commonly supplied as stand-alone, proprietary systems, but they can be configured to use existing septic tanks as the primary treatment chamber or as a pre-treatment stage.

Good maintenance of AWTS is essential to ensure a consistently high level of performance. By law, AWTS systems are required to be serviced quarterly by an approved maintenance contractor.

It is important to note that AWTS are not always the most suitable secondary treatment option for residential or non-residential facilities for the following reasons:


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they are usually more susceptible to poor performance due to variations in hydraulic and pollutant loads than other options (e.g. shock or intermittent loads typical of holiday home use);

they are also typically more susceptible to the impacts of cleaning agents, detergents, antibiotics and other chemicals;

they have a number of moving parts that are critical to the production of secondary effluent and are reliant on high levels of servicing and maintenance;

they have comparatively high operation costs (mainly from electricity use); and

both field assessment and monitoring data from Australia and other countries suggest that their performance is highly variable due to the above factors.

The expected occupancy of the dwelling needs to be assessed for any given lot, as it is not recommended that AWTS be approved where it is apparent or likely that the dwelling will be intermittently occupied. It is suggested that alternative and preferably more passive secondary systems be required.

Despite this, AWTS can be operated to adequately manage and treat wastewater and should be considered. They are often the preferred choice of householders as they are well established in the marketplace, there is a broad variety of brands and installers, and they are typically cheaper than alternative secondary treatment systems.

Sand Filters

Sand filters provide secondary treatment for effluent that has already undergone primary treatment in a septic tank or similar device. They typically contain approximately 600mm depth of filter media (usually medium to coarse sand, but other media can be incorporated) within a lined excavation containing an underdrain system.

Selection of the filter media is critical and a carefully designed distribution network is necessary to ensure even distribution across the media surface. A dosing well and pump (or other dosing device) is normally used to allow periodic dosing. Depending on the desired level of treatment, sand filters can be single-pass or may incorporate partial recirculation.

Sand filters are proven to be an effective and reliable secondary treatment device, consistently capable of achieving BOD <10mg/L and TSS <10mg/L and often better. Sand filter design and sizing is done on a site-by-site basis.

Media Filters

These systems operate under the same principles as sand filters but utilise a proprietary textile media in replacement of the sand. This allows higher loading rates and therefore a smaller footprint with a unit approximately 1.2m x 1m x 0.8m required for a typical home. These systems are typically more capable of overcoming a lot of the constraints of AWTS listed above, and have significantly lower operating costs and better performance.

Biological Filter Systems

A fairly recent innovation in on-site wastewater treatment is the vermiculture/biological trickling filter. Some such systems can be retrofitted into suitable septic tanks.

These systems use alternating layers of filter media and organic matter (such as peat) contained within a plastic tank. Raw wastewater is discharged directly to the top of the


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filter and a rich humus layer develops that separates the solids from liquid prior to composting the solids with the aid of soil micro- and macro- fauna, including earthworms. The system is a passive, biologically-driven treatment process that mimics processes occurring in nature. Test results indicate these systems can achieve secondary treatment quality or better. The system is better at handling shock loads and intermittent use (for example holiday homes) than septic tanks and AWTS, as the treatment organisms produce dormant eggs, spores and so on, which hatch and reproduce when food supply (raw wastewater) resumes. Disinfection units using either UV or chlorination are an optional add-on during installation of the system. Maintenance is only required annually and energy use is substantially lower than AWTS.

Composting Systems:

Composting toilets rely on the action of microorganisms in an aerobic environment. Composting systems are usually dry (waterless) or wet systems that contain vermiculture (worms). Compost humus and any liquid effluent generated require appropriate subsurface disposal. The liquid effluent would also still require secondary treatment prior to subsurface disposal. When dry composting toilets are used, design considerations must also be made for other factions of wastewater generated on-lot; so they are generally used in conjunction with a greywater treatment system. Wet composting toilets are more adaptable to various types of dwellings as the entire wastewater load is generally collected in one tank, unlike the dry composting toilet.

Sand (Wisconsin) Mounds

Sand mounds can be used for both primary treated and secondary treated effluent; and also provide a means of land application. Sand mounds are raised soil absorption systems comprising of layered fill, into which effluent is dosed. Effluent receives further treatment as it percolates down through the mound and is then absorbed by the natural soils below the mound. Before construction the existing ground surface is prepared by scarification, ploughing or deep ripping. This is vital to improve moisture infiltration to the subsoils and reduce the risk of lateral moisture flows, particularly where the natural soils are heavy-textured. Approximately 400mm of sand, with specific grading and size characteristics, provides the basal layer. Above this sits a 225mm gravel distribution bed containing a pressurised effluent distribution system. The gravel bed is covered by a geofabric filter cloth and then a further layer of sand is laid, ensuring that at least 200mm of material covers the gravel bed at the edges. The mound is finished with good quality topsoil (approx. 100mm thick) and is then turfed; alternatively it can be carefully landscaped with suitable small herb and shrub species.

The use of sand mounds is becoming increasingly popular in Australia. They are particularly useful for overcoming specific site and soil constraints such as limited available land application area, shallow depth to the watertable or impermeable soil horizons. Their design is based on the Wisconsin Mound, a system developed in the USA in the 1970s for receiving septic tank effluent on constrained sites. AS/NZS 1547:2012 includes information on selection, design and construction of sand mounds.

Membrane Filters

Membrane technology is becoming well established in onsite and community wastewater management (as well as in the broader water industry). Membrane filters work by pushing or pulling wastewater through a porous membrane resulting in the


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removal of any particles that are larger than the design pore size. There are five levels of membrane filtration:

Microfiltration (0.1 – 10 micron (µm), most common in wastewater treatment);

Ultrafiltration (0.001 – 0.1µm, sometimes used for polishing of highly treated effluent);

Nanofiltration;

Reverse Osmosis (0.0001µm); and

Dialysis and electrodialysis.

Domestic OSSM systems with membrane technology typically use microfiltration, delivering a high quality of effluent that generally meets tertiary treatment criteria. Additional UV or chlorination is sometimes used, especially in areas with sensitive downstream receivers. Membrane systems are significantly more expensive than other secondary treatment systems and have substantially higher power requirements. However, this higher level of tertiary treatment offers potential internal reuse, thereby reducing demands on the required land application area.

5.2.2 OSSM Land Application Options

There are various methods available for effluent application, including; evapotranspiration-absorption systems (ETA), conventional absorption systems, surface irrigation, subsurface irrigation, raised beds/mounds (Wisconsin mounds), Ecomax mounds and Evapocycle systems. The main site and soil characteristics exhibited in the BMCC LGA that limit the use of certain systems refer to shallow soil depth, significant slopes, small available lot area, highly vegetated with poor exposure and high hydraulic conductivity category 1 soils. Certain site and soil characteristics can be overcome or reduced through mitigation and careful design; however, with this generally comes additional costs.

Evapotranspiration-absorption systems:

Evapotranspiration absorption (ETA) systems involve the subsurface absorption of effluent into the soil and evapotranspiration by vegetation. ETA beds are unlined and have wide and shallow dimensions. They are filled with either media or a durable self-supporting arch resting on gravel or sand. The depth and overall basal area of the bed is governed by soil type, proposed wastewater volume, climate and site features. Secondary treated effluent would be pressure-dosed to the bed(s) to ensure even distribution of the effluent. Effluent is generally distributed the length of the bed via a system of slotted or drilled 100mm distribution pipes and filters through the gravel and sand to the underlying soil. A clogging layer or biomat develops along the bottom and sides of the bed and acts as a further filter. Capillary action draws effluent up through the sand in the upper part of the ETA bed from the storage in the void spaces in the gravel bed beneath to supply the root zone of the vegetation (usually grass) on the top of the bed to optimise evapotranspiration. Nutrients within the effluent are taken up by the vegetation planted on the bed, or, in the case of phosphorus, may be adsorbed onto the soil.

ETA beds are often used where site limitations prevent the use of conventional absorption trenches. As evapotranspiration forms a major component of the water balance for these systems, deep-drainage or seepage is minimised, preventing impacts


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to shallow watertables. ETA beds are not considered the best practicable option for the study lots as the category 1 soils (sand) present would mean the primary removal mechanism would be through absorption via the bottom area and sidewall biomat zones, rather than through evapotranspiration. As a result, this may lead to wastewater not being properly treated before reaching the groundwater table. Rainfall exceeds evaporation for typically 7-8 months of the year in the Blue Mountains area. As evapotranspiration forms a major component of these systems, the generally poor exposure associated with highly vegetated lots, limits the system’s capacity. ETA beds also require a minimum of 600mm separation distance from the base of the land application system, which will not be achieved on the majority of the lots due to shallow bedrock. The recommended maximum slope for a bed is 10%. Slope is an obvious inhibiting factor as the study lots generally have a significant slope due to their location along ridgelines or side slopes. Refer to Section 11 SCA guidelines (2012) and Appendix L AS/NZS 1547:2012 for more detail.

Conventional absorption trenches and beds:

Conventional absorption trenches utilise the subsurface absorption of effluent into the soil rather than evapotranspiration. Conventional absorption beds follow the same principle but allow for some evapotranspiration as they are generally wider and shallower in design. Trenches and beds are not considered appropriate for the lots identified in this study given the presence of category 1 soils with high hydraulic conductivity and also the very large trench lengths that would be required using contemporary sizing methodologies which are impractical to service. The use of these conventional systems on soils with high hydraulic conductivity increases the risk of groundwater pollution by untreated effluent. The soils throughout the study lots are generally quite shallow, experiencing bedrock at approximately 500mm depth. The SCA guidelines (2012) state that trenches cannot be installed when soil depth is less than 750mm. The minimum separation requirement from the base of the land application system to the limiting layer is 600mm as per AS/NZS 1547:2012. Absorption systems require a maximum of 600mm depth from the surface for utilisation and also need to adhere to the minimum 600mm separation to the limiting layer requirements. Therefore, the minimum depth required for the sustainable installation and operation of an absorption system (trench) is 1200mm, which is deemed to be unachievable throughout most localities within BMCC. The shallow bedrock also presents construction issues necessitating bedrock to be excavated. Due to the increase in soil disturbance and erosion caused by construction on steep slopes, the recommended maximum slope for a trench is 15%. Slope is an obvious inhibiting factor as the study lots generally have a significant slope due to their location along ridgelines or side slopes. Conventional septic tanks with below-ground soil absorption trenches/beds offer limited opportunity for effective reuse of effluent and do not represent current best practice and are not recommended for these study lots. Refer to Section 10 SCA guidelines (2012) and Appendix L AS/NZS 1547:2012 for more detail.

Surface irrigation systems:

Surface spray irrigation has historically been the favoured method of managing secondary treated effluent; however, due to concerns over the potential for human contact with effluent and also the poor management practices that have been associated with “moveable” type spray lines, it is being used less commonly in new installations and is no longer considered best practice.


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Surface irrigation systems provide distribution of secondary treated effluent to the ground surface via coarse spray heads. Given general locality conditions such as significant slope, bedrock outcrops and the proximity to neighbouring developments, there exists an increased risk of effluent runoff, ponding and spray drift. Based on these constraints and the potential risk to human health, this option is considered unsuitable and has not been investigated further in this study. Refer to Section 12 SCA guidelines (2012) and Appendix M AS/NZS 1547:2012 for more detail.

Subsurface irrigation systems:

Subsurface irrigation systems are an increasingly common management option for OSSM. Properly designed irrigation systems apply effluent at much lower volumetric rates and over larger areas than absorption trenches and beds. Effluent is applied at a rate that more closely matches plant evapotranspiration requirements leading to more effective effluent reuse. The reliance on soil absorption is relatively low and hence the risk of contaminants accumulating in the soil or leaching to groundwater is also low.

Subsurface (pressure-compensating) drip irrigation is suitable within lawn and landscaped areas and applies effluent within the root-zone of plants for optimum irrigation efficiency. It is an ideal option for ensuring even, widespread coverage of the proposed LAA. Subsurface drip irrigation installation does not require any bulk materials or heavy machinery and irrigation lines can be simply installed with a small trench digger or “ditch-witch”. Pressure-compensating drip irrigation pipe designed for use with wastewater should be used to ensure distribution of effluent at uniform, controlled application rates. Lateral lines should be spaced to provide good and even coverage of the area they service. Generally they should be no more than 600mm apart, roughly parallel and along the contour as close as possible. Installation depth will be between 100mm and 150mm, to maximise beneficial uptake of the treated effluent by grass cover. Specialist advice must be obtained for designing and installing an irrigation system.

Subsurface irrigation systems can generally be installed on slopes up to 30% without specific design which suits the locality constraints. The 600mm required depth below the base of the land application system is still required, but due to the installation depth at approximately 150mm depth, the total required soil depth is 750mm comparable to 1200mm for conventional absorption systems. Where soils are less than 750mm deep, mounds should be utilised or soil should be imported to increase the soil depth. Individual site and soil assessments of the 72 private lots are required to confirm the soil depth and design accordingly. Refer to Section 13 SCA guidelines (2012) and Appendix M AS/NZS 1547:2012 for more detail.

Typically pressure-compensating subsurface drip irrigation costs in the order of $6 – $10 per square metre to install.

Raised beds/mounds (Wisconsin mound):

Wisconsin mounds are raised beds of selected filter media (graded sand), which are constructed above the existing ground surface. Refer above in Section 5.2.1 for more detail. Wisconsin mounds allow treated wastewater to be sustainably applied at relatively higher rates than by irrigation as they provide enhanced evaporation and bed storage and allow for further treatment and nutrient assimilation. They have the benefit of reducing the total land area required for effluent application, but require a permanent dedicated space with a buffer area (which can be landscaped). Mounds are suited to


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areas of high groundwater or where native soils are thin and suits soils of varying drainage characteristics. The mound will increase the vertical separation distance to the limiting horizon, whether that be bedrock or the groundwater table. Care should be taken with construction on significant slopes to prevent the risk of toe seepage. Fill may need to be imported to level the site.

It is acknowledged that Wisconsin mounds do not specifically include nutrients as a controlling factor in sizing and design. In consideration of this, wastewater should be treated to a minimum secondary standard before disposal via the mound. Refer to Section 9 SCA guidelines (2012) and Appendix N AS/NZS 1547:2012 for more detail.

Ecomax mounds:

Nutrient removal mounds are variants on traditional sand mounds or Wisconsin mounds where specific media are used to sorb nutrients (phosphorus and nitrogen). Experience in the Blue Mountains and elsewhere in NSW indicates that only where such mounds incorporate all of the critical design features of traditional sand mounds or Wisconsin mounds, in particular the mound form which assists significantly with evapotranspiration, in addition to the incorporation of nutrient sorbing media, have these systems proven satisfactory in operation. Some Ecomax mounds have been constructed in this manner and they afford a possible option where phosphorus management is required. Care should be taken to avoid constructing Ecomax systems where they are cut into hillslopes and where they do not have a pronounced mound form as such systems commonly exhibit hydraulic problems.

Evapocycle systems:

The Evapocycle system is a proprietary raised bed with some capacity for effluent management by evapotranspiration. Any effluent not managed by evapotranspiration is disposed of by seepage through lateral absorption beds. Little performance data is available on these systems and they have not as yet obtained NSW Health accreditation. The performance of such systems should be established and rigorous testing data obtained to determine their suitability for use in the Blue Mountains.

5.2.3 Additional Options

There are additional options that can be utilised to reduce the design wastewater load and consequently the required LAA; including, water reduction devices and a split-stream system with internal reuse via a third pipe reticulation system.

Water saving devices need to be approved under the Water Efficiency Labelling Standards (WELS) scheme, which is governed by AS/NZS 6400:2005, and will be given a water efficiency rating. WELS approved devices and Smart Watermark approved devices refer to indoor and outdoor devices, respectively.

The costs associated with retrofitting existing dwellings with such systems would be substantial when compared to the other potential options discussed above. Also, whilst these devices can potentially reduce wastewater generation, their installation and use cannot be assured or enforced and they therefore are not considered a sustainable basis on which typical design hydraulic loads can be reduced.

Combinations of partial on-lot land application combined with partial off-lot land application, or total off-lot land application by use of common effluent disposal systems also offer potential solutions.


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5.3. Land Application Area Sizing

Two OSSM land application system options, subsurface irrigation and mounds, were investigated further to determine the LAA that they would require based on various occupancy scenarios. These required LAAs were then compared to the available EMA on each of the identified 8 Council and 72 private lots to determine the sustainability of OSSM or if an excess was generated and off-lot options needed to be investigated.

5.3.1 Design Wastewater Loads and Occupancy

It is important to size the OSSM system and LAA based on the appropriate wastewater load for the dwelling to ensure effective treatment and system operation is maximised. Typical domestic wastewater design flow allowances for residential premises are provided in Table 2.1 of the Sydney Catchment Authority Current Recommended Practice Designing and Installing Onsite Wastewater Systems (2012) and must be determined using the ‘Neutral or Beneficial Effect on Water Quality Assessment Guideline’ (SCA, 2011).

The design wastewater loading is based on the:

Number of potential bedrooms;

Nature of the water supply i.e. tank or reticulated; and

Wastewater loading per bedroom based on the nature of the water supply.

The recommended design flow allowances for residential premises connected to a reticulated water supply or tank water supply are 150L/p/day and 100L/p/day, respectively. The typical occupancy rate for residential dwellings is 2 persons per bedroom up to 4 bedrooms and 1 person per bedroom thereafter.

Table 4 outlines the design wastewater flow allowances for a domestic dwelling. For other developments involving wastewater, refer to the ‘Septic Tank and Collection Well Accreditation Guideline’ (NSW Health, 2011) or other reference source approved by SCA. The design wastewater flow allowances should be used to conservatively inform system design and sizing of a minimum LAA. Where water supply information was not supplied, it was implied that the lot is connected to the reticulated water supply to ensure conservatism.

Table 4: Domestic Design Wastewater Flow Allowances

Number of bedrooms

Flow Allowances

Reticulated/Bore Water Supply (150L/p/day)

Tank Water Supply (100L/p/day)

1-2 potential bedrooms 600L/day 400L/day

3 potential bedrooms 900L/day 600L/day

4 potential bedrooms 1,200L/day 800L/day

>4 potential bedrooms 1,200L/day, plus 150L for each additional bedroom

800L/day plus 100L/day for each additional bedroom


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Annual septic pump-out volumes (as of 10th April 2013) of the 72 private lots were provided by Council. These pump-out volumes were used to calculate an indicative occupancy of the dwellings on each of the lots based on the design wastewater loadings outlined above in Table 4. If an estimate of the occupancy of the dwelling was not available, then it was inferred that it was a 4 bedroom dwelling with a design wastewater load of 1,200L/day. From this analysis, an indicative occupancy status was derived as follows:

51 permanently occupied dwellings;

18 intermittently occupied dwellings; and

3 dwellings with unknown occupancy status.

5.3.2 Design Loading Rate

Soil category Design Loading and Irrigation Rates (DLR/DIR) are used to determine the size of the required LAA. The DLR/DIR are determined from the soil category based on the soil texture and structure for the most restrictive soil layer within the clearance depth set by the SCA guidelines (2012) and not the shallower soils within which the land application system is installed. These are conservative rates at which effluent can be applied to the native soil to provide sufficient treatment and prevent surface surcharge/runoff. The system designer should identify those factors that may cause over estimation of the appropriate DLR/DIR, such as steep slopes and shallow soil depth, and alter the DLR/DIR accordingly as per Tables L1-N1 AS/NZS 1547:2012.

The main soil types across BMCC are coarse grained sandy soils from the Hawkesbury and Narrabeen Group of sandstones and fine-grained clay based soils from the Wianamatta shales. There are eight (8) different soil landscapes throughout the 72 private and 8 Council lots as identified in this study by the Soil Landscapes of Katoomba 1:100,000 sheet (King D, 1994); Medlow Bath, Warragamba, Wollangambe, Faulconbridge, Hawkesbury, Gymea, Mount Sinai and Mount Sinai Variant A. The soil landscape for each lot has been identified, but a detailed soil assessment is required to confirm characteristics and adequately size the required LAA for any given lot.

Table 5 below outlines the limiting soil category and associated DIR for each of the soil landscapes. The DIRs range between 3.5 and 5mm/day for the soil landscapes.


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Table 5: DIR values relative to limiting soil category for the soil landscapes located within the lots in this study

Soil Landscape2 Landscape Type Limiting Soil

Category3 DIR (mm/day)

Medlow Bath (mb) Residual Clayey Sand 5

Warragamba (wb) Colluvial Clayey Sand 5

Wollangambe (wo) Erosional Clayey Sand 5

Faulconbridge (fb) Residual Sandy Clay Loam 3.5

Hawkesbury (ha) Colluvial Sandy Clay Loam 3.5

Gymea (gy) Erosional Clayey Sand 5

Mount Sinai4 (ms) Vestigial Clayey Sand 5

Mount Sinai Variant A (msa) Vestigial Clayey Sand 5

5.3.3 Subsurface Irrigation Area Sizing

Water balance modelling was undertaken to determine sustainable application rates and to estimate the necessary size of the LAA for subsurface irrigation required to manage the proposed hydraulic load on each of the 8 identified Council lots and 72 private lots. The procedures for this generally follow the DLG (1998) guidelines and AS/NZS 1547:2012.

The water balance used is a monthly model adapted from the “Nominated Area Method” described in DLG (1998). These calculations determine minimum LAA sizes for given effluent loads for each month of the year. The water balance can be expressed by the following equation:

Precipitation + Effluent Applied = Evapotranspiration + Percolation + Storage

Irrigation areas are calculated to achieve no net excess of water and hence zero storage for all months. The water balance conservatively assumes a retained rainfall coefficient of 0.9; that is, an estimated 90% of rainfall will percolate into the soil within the LAA and 10% will run off. The rainfall hydraulic load is incorporated into the water balance to ensure that runoff from the LAA will not occur under typical (design) climate conditions. Due to the various limiting soil categories throughout the identified lots, various DIR between 5 and 3.5mm/day were applied to determine the appropriate LAA for each lot.

Table 6 below provides details of the inputs for the monthly water balance for subsurface irrigation for the identified lots. Table 7 summarises the results for the various scenarios and can be used to determine the required LAA/maximum potential loads for each lot. Representative printouts of the water balance spreadsheets for a 4 bedroom dwelling connected to a reticulated water supply are provided in Appendix A.

2 King D, 1994 3 This is an assumption of the most limiting soil category for the average soil horizon within the soil landscape. This is highly dependent on the landform element location. 4 Predominately bedrock at or near surface (poor soil development)


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Table 6: Model Inputs for the Monthly Hydraulic Balance

Model Inputs for Monthly Water Balance

Parameter Units Value Comments

Daily Hydraulic load

L/day variable Based on 150L/p/day for reticulated water supply, for variable occupancy rates as per SCA guideline (2012).

Precipitation mm/month mean monthly Silo Data Katoomba (-33.70, 150.30) (1940-2014).

Pan evaporation mm/month mean monthly Silo Data Katoomba (-33.70, 150.30) (1940-2014).

Retained rainfall unitless 0.9 Assumption that 90% of rainfall remains on site and infiltrates the soil.

Crop factor unitless 0.8-0.7

Conservative annual value for turf grasses (adjusted for season). Crop factors vary depending on the type of plant being grown, local soil conditions, time of year, and exposure of the Site (NSW DECC, 2005).

Design irrigation rate

mm/day variable 5, 4, and 3.5mm/day as per Table M1 AS/NZS 1547:2012.

Table 7: Subsurface Irrigation Monthly Water Balance Results

Results - Minimum LAA Requirements

Design Loading

Rates 5mm/day 4mm/day 3.5mm/day

Dwelling Size

Reticulated Water Supply

Tank Water Supply


Tank Water Supply


Tank Water Supply

2 bdr 300m2 200m2 600m2 400m2 1,200m2 800m2

3 bdr 450m2 300m2 900m2 600m2 1,800m2 1,200m2

4 bdr 600m2 400m2 1,200m2 800m2 2,400m2 1,600m2

5 bdr 675m2 450m2 1,350m2 900m2 2,700m2 1,800m2

It was found that subsurface irrigation would not be sustainable if wastewater was loaded at any lower rate than 3.5mm/day on the soils within BMCC. If the loading rate was decreased, the required LAA size would counteractively increase. This scenario would result in surcharge as wet weather storage is not allowed within BMCC.

5.3.4 Mound Sizing

Water balance modelling was also undertaken to determine sustainable application rates and to estimate the necessary size of the LAA for effluent treatment and disposal via a sand (Wisconsin) mound to manage the proposed hydraulic load on each of the 72 identified private lots. The procedures for this generally follow the DLG (1998) guidelines and AS/NZS 1547:2012, as well as the proprietary design model used by


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Whitehead & Associates which conforms to the design recommendations in AS/NZS 1547:2012 with minor modifications based on experience with this type of land application system.

The sand (Wisconsin) mound calculation to determine the required minimum LAA is as follows. The design wastewater load is divided by the recommended loading rate for the mound at the gravel manifold/sand interface. The AS/NZS 1547:2012 outlines in Section N2.2 that the loading rate should not exceed 40mm/day. This results in the area of the manifold within the mound. Generally, the manifold is approximately 1m wide. General assumptions were made with regards to the final mound footprint based on 1 to 3 side slope and end slope batters. Therefore, 6m was added to the manifold area for side slope length and this was multiplied by 7m for the end slopes to give the total mound area. The equation is as follows.

Design Load L/day / Loading Rate 40mm/day = (m2 manifold + 6) x 7m width = Total Mound m2

Table 8 below applies this equation to calculate the required LAA for mound systems for various dwelling sizes.

Table 8: Wisconsin Mound LAA Sizing

Results- Minimum LAA Requirements

Dwelling Size Mound Footprint (m2)

Reticulated Water Supply Tank Water Supply

2 bdr 147m2 112m2

3 bdr 200m2 147m2

4 bdr 252m2 182m2

5 bdr 278m2 200m2

5.4. OSSM Feasibility and Excess Volumes

The required LAAs to manage the potential load generated for any given lot are detailed in Tables 7 and 8 for subsurface irrigation and mound OSSM systems, respectively. Both systems are considered to be appropriate OSSM options for the given locality constraints; however, individual site assessment and site specific design is required to determine the suitability and feasibility of each option prior to selection and construction. The difference between the LAA requirements between the two options is notable; however, consideration of the greater costs associated with mound construction should be made.

Table 9 lists the total lot area, available EMA or maximum load that the lot can accommodate, the potential load generated and the required LAA for each of the identified 72 private lots. Figure 1 shows an example of a private lot. Management of the potential load onsite needs to be achieved within the available EMA on each lot. Any part of the load that can’t be sustained onsite is considered to be an excess and partial or entire off-lot options need to be considered. It is important to note that lots can be augmented to create more favourable conditions for OSSM and reduce or remove constraints; for example, importation of fill to level a portion of a site with a considerable slope to allow it to become useable area for OSSM.

For example, if:


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Available EMA is 200m2;

DIR of site soils is 5mm/day; and

Design wastewater load is 1200L/day for a 4 bedroom house connected to a reticulated was supply; then

The maximum load that the site can accommodate is 1000L/day (DIR x Available EMA). As the design wastewater load is 1200L/day, an excess of 200L/day will be generated by that site that cannot be accommodated on-site. Sustainable LAA sizing for subsurface irrigation and mounds for this design scenario are 600m2 and 252m2, respectively. Therefore, total OSSM appears not to be an option for this site without specific assessment and design, and partial or entire off-lot options should be investigated.

Whilst the available EMA and DIR for the site can determine the nominal maximum load that can be potentially accommodated by a site, the results still need to be confirmed by a detailed water balance as sometimes a greater area is required to sustainably manage wastewater on-site. This is because the nominal calculation does not account for the meteorological contributions, i.e. the addition of rainfall to the LAA. Therefore, although a lot may not show that it has an excess load in Table 9 below, this does not mean that it can manage wastewater entirely on-site where the water balance results indicate otherwise. In the case of all the lots, design needs to be confirmed by a site and soil assessment and site specific design.


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Table 9: Determination of OSSM feasibility for the 72 private lots

Lot Total Lot Area m2

Available EMA m2

DIR mm/day Maximum

Load L/day Potential

Load L/day5 Excess Load

L/day

Irrigation LAA Sizing

m2

Mound LAA Sizing m2

1 1,278 590 3.5 2066 1,200 0 2,400 252

2 1,310 554 3.5 1937 1,200 0 2,400 252

3 1,728 580 3.5 2030 1,200 0 2,400 252

4 1,539 405 3.5 1419 900 0 1,800 200

5 22,466 2,371 3.5 8297 1,200 0 2,400 252

6 1,237 312 3.5 1092 900 0 1,800 200

7 1,192 39 3.5 138 900 762 1,800 200

8 704 287 3.5 1004 900 0 1,800 200

9 753 307 3.5 1074 900 0 1,800 200

10 745 306 3.5 1070 900 0 1,800 200

11 2,013 0 5 0 900 900 450 200

12 1,956 158 5 789 900 111 450 200

13 2,027 899 5 4496 1,200 0 600 252

5 The potential load based on a reticulated water supply for each lot was determined by an approximation of the number of bedrooms in the dwelling as per the pump-out volumes interpretation and from broad site assessment conducted by BMCC staff.


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Available EMA m2

DIR mm/day Maximum



L/day


m2

Mound LAA Sizing m2

14 2,015 1,034 5 5171 1,200 0 600 252

15 9,264 0 5 0 600 600 300 147

16 2,921 1,590 5 7951 1,200 0 600 252

17 4,736 81 5 405 900 495 450 200

18 5,054 185 5 926 900 0 450 200

19 3,877 320 5 1598 600 0 300 147

20 2,414 1,278 5 6391 1,200

0 600 252

21 2,417 1,280 5 6399 1,200 0 600 252

22 2,334 1,232 5 6158 1,200 0 600 252

23 1,029 374 5 1870 900 0 450 200

24 9,312 2,314 4 9258 900 0 900 200

25 3,117 463 5 2313 900 0 450 200

26 2,698 1,311 5 6556 900 0 450 200

27 2,623 1,408 5 7042 900 0 450 200

28 6,588 3,685 5 18423 1,350 0 675 278

29 1,010 428 5 2140 900 0 450 200


32


Available EMA m2

DIR mm/day Maximum



L/day


m2

Mound LAA Sizing m2

30 1,010 430 5 2,149 900 0 450 200

31 5,481 983 5 4,916 900 0 450 200

32 5,646 584 5 2,922 1,350 0 675 278

33 4,242 429 5 2,143 900 0 450 200

34 4,032 0 5 0 900 900 450 200

35 4,032 50 5 249 900 651 450 200

36 2,759 1,494 5 7,468 1,200 0 600 252

37 2,759 1,493 5 7,465 900 0 450 200

38 2,758 1,095 5 5,477 900 0 450 200

39 1,962 521 5 2,606 900 0 450 200

40 1,839 586 5 2,929 1200 0 600 252

41 13,588 8,223 5 41,113 900 0 450 200

42 2,055 1,039 5 5,197 900 0 450 200

43 11,791 0 5 0 900 900 450 200

44 1,021 0 5 0 900 900 450 200


33


Available EMA m2

DIR mm/day Maximum



L/day


m2

Mound LAA Sizing m2

456 1,748 719 5 3,595 0

46 3,512 132 5 662 900 238 450 200

47 2,070 437 5 2,183 1,200 0 600 252

48 5,681 1,041 5 5,204 900 0 450 200

49 6,667 3,238 5 16,189 900 0 450 200

50 2,420 1,279 5 6,394 1200 0 600 252

51 3,424 1,558 5 7,789 600 0 300 147

52 2,577 589 5 2,946 600 0 300 147

53 2,168 490 3.5 1,715 1,200 0 2,400 252

54 2,436 1,297 5 6,483 1,200 0 600 252

55 2,428 1,177 5 5,883 1,200 0 600 252

56 2,622 1,366 5 6,831 900 0 450 200

57 2,426 1,201 5 6,003 900 0 450 200

58 2,898 1,576 5 7,879 900 0 450 200

6 Lot 45 is a preschool/day care centre and does not conform to domestic wastewater scenario’s.


34


Available EMA m2

DIR mm/day Maximum



L/day


m2

Mound LAA Sizing m2

59 2,851 1,516 5 7,582 900 0 450 200

60 3,231 382 5 1,911 900 0 450 200

61 32,224 1,3874 3.5 48,559 900 0 1,800 200

62 21,380 9,144 4 36,576 1,200 0 1,200 252

63 2,177 1,135 5 5,674 900 0 450 200

64 1,729 875 5 4,375 1,200 0 600 252

65 2,020 1,044 5 5,220 1,200 0 600 252

66 1,011 431 5 2,156 900 0 450 200

67 2,037 557 5 2,784 900 0 450 200

68 469 165 5 826 900 74 450 200

69 2,162 31 3.5 107 900 793 1,800 200

70 4,828 714 5 3,571 900 0 450 200

71 21,865 8,106 3.5 28,370 1,200 0 2,400 252

72 24,162 10,738 3.5 37,582 1,200 0 2,400 252


35


36

6. Off-lot Options Assessment

6.1. Overview

For those lots that cannot sustainably manage wastewater on-site, as shown in Table 9, alternative off-lot options need to be investigated as they cannot sustainably manage all or part of their wastewater on-site. Off-lot options include, but are not limited to, partial on-lot OSSM and partial off-lot disposal and sewer options such as grinder pump low-pressure sewer, STEP/STEG effluent sewer and an extension of the existing sewer main. It may be the case that some lots have no capacity to manage wastewater more economically or in a more environmentally sustainable manner than by the pump-out system currently in-place.

6.2. Partial On-lot Management

Although a lot may not have sufficient available EMA to manage their wastewater entirely on-lot, there is a potential for partial on-lot and partial off-lot wastewater management. The off-lot management option could be pump-out, but with partial on-lot management the volume remaining for off-lot disposal would be reduced, consequently reducing the associated costs. If this option was to be adopted, an individual site and soil assessment and design would still be required. It is recommended that the partial on-lot portion follow the same principles as the OSSM options but provide for only that part of the wastewater load which can be sustainably managed on-lot. For this study, the potential for partial on-lot was based on the available EMA for any given lot being greater than 100m2. This value takes into account the construction restrictions of a mound for design purposes and allows for a sufficient portion of the wastewater load to be managed on-lot.

6.3. Sewer Options

A number of options are available to link the presently un-serviced private lots to the existing sewer.

6.3.1 Grinder Pump Low-Pressure Sewer:

Low pressure grinder pump sewers overcome some of the limitations of traditional gravity sewers by providing pressure from each connected lot to convey wastewater through a reticulation system, allowing shallower, smaller diameter pipes. Each connected property is serviced by a small pump-well (‘pot’) with a grinder pump and level sensors/controls that collects household sewage by gravity drainage from the house. The grinder pump macerates the gross solids and converts wastewater to a slurry consistency, which possesses different physical, chemical and hydraulic properties to raw wastewater. In particular, BOD5 is much higher in macerated wastewater.

The macerated wastewater is pumped to a flexible, low-pressure sewer main installed at grade, typically along the front of properties in the road easement. The macerated effluent is conveyed along the sewer main by the combined pressure from on-lot grinder pumps. The main would connect to the existing Sydney Water sewer system.


37

Grinder pump pressure sewers are increasingly being installed by water authorities and private enterprise throughout Australia. There are a variety of proprietary grinder pump systems available in Australia, including E One™, widely used by Sydney Water.

6.3.2 STEP/STEG Effluent Sewer

This option is broadly similar to the grinder pump pressure sewer described above; except that household wastewater is conveyed by gravity to an on-lot interceptor tank (effectively a large septic tank) which provides primary treatment. The treated effluent is then pumped (Septic Tank Effluent Pump - STEP) or conveyed by gravity (Septic Tank Effluent Gravity - STEG) to an effluent sewer main by small diameter flexible pipeline. The effluent sewer main is similar to that used in the grinder pump sewer, with smaller diameter pipes permissible due to the removal of solids from the effluent. The effluent is conveyed by a combination of gravity and pressure from STEP tank pumps.

There is scope to use existing septic tanks as interceptor tanks if they are adequately sized (at least 4,000L), located and functioning well (e.g. not corroded, leaking or missing components).

STEP tanks are used for lots below the hydraulic line of the sewer and incorporate a pump vault, controlled by liquid level sensors. These are not energy intensive and are typically 0.4kW. These effluent sewer systems are well established overseas, particularly in the US and New Zealand, and are available from several providers in Australia.

These systems could connect to the existing Sydney Water sewer system.

6.3.3 Extend Conventional Sewer Main

The option to extend the existing sewer main is another potential off-lot option. By assessing the distance between the 72 private lots and the existing sewer main network, it has been identified that there are 15 lots that are within the prescribed 75m buffer to the sewer network. These lots have the potential to be sewered by Sydney Water. Figure 2 shows an example of the vicinity of the sewer to some of the private lots.


38


39

7. Feasibility

The feasibility of both the OSSM and off-lot options for each of the 72 private lots was assessed and the results are highlighted in Table 12 below. It should be noted that this is a broad scale study and that individual site assessments are needed to confirm the results or offer alternative design. It was found that there were 39 out of the 72 (54%) properties that could potentially utilise subsurface irrigation as a sustainable OSSM option. It was found that there were 58 out of the 72 (80%) private lots that could potentially utilise mounds as a sustainable OSSM option. Therefore, 58 out of the 72 private lots could potentially utilise entire OSSM rather than an off-lot or pump-out option. It was found that 62 out of the 72 private lots (86%) could utilise partial on-lot and partial off-lot wastewater management. It was found that potentially 15 out of the 72 (21%) private lots could potentially connect to the existing sewer network, managed by Sydney Water, as they are located less than 75m away from the existing network.

Table 12: Feasibility of Wastewater Management Options for the 72 Private Lots

Lot OSSM -

SSI OSSM - Mounds

Potential OSSM

Options

Partial On-lot/ Partial

Off-lot

Potential Off-lot

Options

1 0m

2 0m

3 0m

4 0m

5

6 53m

7 55m

8 55m

9 45m

10 38m

11

12

13

14

15

16

17 0m

18 0m

19

20

21

22

23


40

Lot OSSM -

SSI OSSM - Mounds

Potential OSSM

Options


Off-lot

Potential Off-lot

Options

24 45m

25 42m

26

27

28

29

30

31

32

33

34

35

36

37

38

39

40

41

42

43

44

45 n/a n/a n/a n/a

46

47

48

49

50

51

52

53 0m

54

55

56

57

58

59

60


41

Lot OSSM -

SSI OSSM - Mounds

Potential OSSM

Options


Off-lot

Potential Off-lot

Options

61

62

63

64

65

66

67

68 70m

69

70

71

72


42

8. Conclusion

This study assessed the 72 privately owned lots that are currently on pump-out as part of the Sydney Water pump-out subsidy scheme to determine their potential for both OSSM and off-lot wastewater management. It was found that OSSM, partial on-lot and partial off-lot wastewater management or connection to the sewer could be potentially utilised by 65 out of the 72 lots. Lots 11, 15, 34, 35, 43, 44, and 69 were found in this study to have no wastewater management option alternative other than pump-out, which is currently being utilised.

The results of this study show that although 52 out of the 72 private lots were currently less than the 4,000m2 minimum lot size for sustainable OSSM, as stipulated in the BMCC DCP (2010), the constraints to OSSM primarily depend on the available EMA, potential load generated and the specific OSSM treatment and land application system to be used. This is indicated by 58 out of the 72 private lots found to be potentially suitable for OSSM. Therefore, although Council currently require a minimum of 4,000m2 as a guide, a number of lots investigated in this study offer the potential for OSSM solutions, each of which Council will consider on their own merits.

Due to the broad scale of this study, the results should be used as an informative tool only. Individual site and soil assessment, together with site specific design should be conducted for each of the 72 privately owned lots.

Results of this study will be used to inform the preparation of a revised BM Sewage Strategy.


43

9. References

Blue Mountains City Council, (2008) Blue Mountains Sewage Strategy.

Blue Mountains City Council, (2010) Blue Mountains Better Living Development Control Plan.

Department of Local Government (DLG), (1998) Environment & Health Protection Guidelines: On-site Sewage Management for Single Households.

King D., (1994) Soil Landscapes of Katoomba 1:100,000 Sheet.

NSW Department of Environment and Climate Change (NSW DECC), (2005) Guidelines for the Use of Effluent by Irrigation.

NSW Health, (2001) Septic Tank and Collection Well Accreditation Guideline.

Standards Australia/Standards New Zealand, (2005) AS/NZS 6400:2005 Water Efficient Products – Rating and Labelling.

Standards Australia/Standards New Zealand, (2012) AS/NZS 1547:2012 On-site Domestic Wastewater Management.

Sydney Catchment Authority (SCA), (2011) Neutral of Beneficial Effect on Water Quality Assessment Guideline.

Sydney Catchment Authority (SCA), (2012) Current Recommended Practice Designing and Installing Onsite Wastewater Systems.


44

10. Appendices


45

APPENDIX A

Monthly Water Balances – Subsurface Irrigation LAA Sizing


46

Sit

e A

dd

ress

:B

MC

C 5

mm

/day

DIR

INP

UT

DA

TA

De

sign

Wa

ste

wa

ter

Flo

wQ

1,2

00

L/d

ayF

low

Allo

wa

nce

150

L/p

/dD

esi

gn Ir

riga

tion

Ra

teD

IPR

35

mm

/we

ek

No.

of b

ed

room

s4

Da

ily D

IR5

.0m

m/d

ay

Litr

es

per s

q.m

. pe

r day

- b

ase

d o

n T

ab

le M

1 A

S/N

ZS

15

47:2

01

2 fo

r se

cond

ary

effl

uent

Occ

up R

ate

2N

om

ina

ted

Lan

d A

pplic

atio

n A

rea

L6

00m

sq

Cro

p F

act

orC

0.7

-0.8

unitl

ess

Est

ima

tes

eva

potr

ansp

iratio

n a

s a

frac

tion

of p

an e

vapo

ratio

n; v

ari

es w

ith s

easo

n a

nd c

rop

typ

eR

uno

ff C

oe

ffici

ent

0.9

until

ess

Pro

po

rtio

n of

rai

nfa

ll th

at r

em

ain

s on

site

and

infil

tra

tes;

func

tion

of s

lop

e/co

ver,

allo

win

g fo

r a

ny ru

noff

Ra

infa

ll D

ata

Mea

n M

ont

hly

Dat

a (1

940

- 2

014

)E

vap

ora

tion

Dat

aM

ean

Mo

nthl

y D

ata

(19

40 -

20

14)

Pa

ram

ete

rS

ymb

ol

Fo

rmu

laU

nit

sJa

nF

eb

Ma

rA

pr

Ma

yJu

nJu

lA

ug

Se

pO

ctN

ov

De

cT

ota

l

Day

s in

mon

thD

\da

ys31

2831

3031

3031

3130

3130

3136

5

Rai

nfal

lR

\m

m/m

onth

163

181

155

109

101

121

6277

6699

115

114

1,36

2.0

Eva

pora

tion

E\

mm

/mon

th16

612

710

970

4327

3254

8111

413

016

51,

118.

0

Cro

p F

acto

rC

0.75

0.70

0.70

0.70

0.70

0.70

0.70

0.70

0.80

0.80

0.80

0.80

OU

TP

UT

S Eva

potr

ansp

iratio

nE

TE

xCm

m/m

onth

125

8976

4930

1922

3865

9110

413

283

9.9

Per

cola

tion

B(D

PR

/7)x

Dm

m/m

onth

155.

014

015

5.0

150.

015

5.0

150.

015

5.0

155.

015

0.0

155.

015

0.0

155.

01,

825.

0O

utpu

tsE

T+B

mm

/mon

th27

9.5

228.

923

1.3

199.

018

5.1

168.

917

7.4

192.

821

4.8

246.

225

4.0

287.

02,

664.

9

INP

UT

SR

etai

ned

Rai

nfal

lR

RR

*run

off c

oef

mm

/mon

th14

6.7

162.

913

9.5

98.1

90.9

108.

955

.869

.359

.489

.110

3.5

102.

61,

226.

7

Effl

uent

Irrig

atio

nW

(QxD

)/L

mm

/mon

th62

.056

.062

.060

.062

.060

.062

.062

.060

.062

.060

.062

.073

0.0

Inpu

tsR

R+

Wm

m/m

onth

208.

721

8.9

201.

515

8.1

152.

916

8.9

117.

813

1.3

119.

415

1.1

163.

516

4.6

1,95

6.7

ST

OR

AG

E C

AL

CU

LA

TIO

NS

tora

ge r

emai

ning

from

pre

viou

s m

onth

mm

/mon

th0.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

0S

tora

ge fo

r th

e m

onth

S(R

R+

W)-

(ET+

B)

mm

/mon

th-7

0.8

-10.

0-2

9.8

-40.

9-3

2.2

0.0

-59.

6-6

1.5

-95.

4-9

5.1

-90.

5-1

22.4

-234

.0C

umul

ativ

e S

tora

geM

mm

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Max

imum

Sto

rage

for

Nom

inat

ed A

rea

Nm

m0

.00

VN

xLL

0L

AN

D A

RE

A R

EQ

UIR

ED

FO

R Z

ER

O S

TO

RA

GE

m2

280

509

405

357

395

600

306

301

232

237

239

202

60

0m

2

No

min

ate

d A

rea

Wa

ter

Ba

lan

ce

& S

tora

ge

Ca

lcu

lati

on

s

Silo

Da

ta -

Kat

oo

mb

a (-

33.7

0,

Silo

Da

ta -

Kat

oo

mb

a (-

33.7

0,

MIN

IMU

M A

RE

A R

EQ

UIR

ED

FO

R Z

ER

O S

TO

RA

GE

:


47

Sit

e A

dd

ress

:B

MC

C 4

mm

/day

DIR

INP

UT

DA

TA

De

sig

n W

aste

wa

ter F

low

Q1,

20

0L

/day

Flo

w A

llow

anc

e15

0L

/p/d

De

sig

n Irr

iga

tion

Ra

teD

IPR

28

mm

/we

ek

No

. of b

ed

roo

ms

4D

aily

DIR

4.0

mm

/da

yL

itre

s p

er s

q.m

. pe

r da

y -

base

d o

n T

able

M1

AS

/NZS

15

47:2

012

for

seco

nda

ry e

fflue

ntO

ccup

Ra

te2

Nom

ina

ted

Lan

d A

ppl

icat

ion

Are

aL

1,2

00

m s

qC

rop

Fa

cto

rC

0.7

-0.8

unitl

ess

Est

ima

tes

eva

potr

ansp

irat

ion

as

a fr

act

ion

of p

an

eva

po

ratio

n; v

arie

s w

ith s

eas

on

and

cro

p ty

pe

Run

off C

oef

ficie

nt0

.9un

tile

ssP

ropo

rtio

n o

f rai

nfa

ll th

at r

ema

ins

ons

ite a

nd in

filtr

ate

s; fu

nctio

n o

f slo

pe/c

ove

r, a

llow

ing

for

any

run

off

Rai

nfa

ll D

ata

Mea

n M

onth

ly D

ata

(19

40

- 2

014

)E

vapo

ratio

n D

ata

Mea

n M

onth

ly D

ata

(19

40

- 2

014

)

Pa

ram

ete

rS

ymb

ol

Fo

rmu

laU

nit

sJa

nF

eb

Ma

rA

pr

Ma

yJu

nJu

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ug

Se

pO

ctN

ov

De

cT

ota

l

Day

s in

mon

thD

\da

ys31

2831

3031

3031

3130

3130

3136

5

Rai

nfal

lR

\m

m/m

onth

163

181

155

109

101

121

6277

6699

115

114

1,36

2.0

Eva

pora

tion

E\

mm

/mon

th16

612

710

970

4327

3254

8111

413

016

51,

118.

0

Cro

p F

acto

rC

0.75

0.70

0.70

0.70

0.70

0.70

0.70

0.70

0.80

0.80

0.80

0.80

OU

TP

UT

S Eva

potr

ansp

iratio

nE

TE

xCm

m/m

onth

125

8976

4930

1922

3865

9110

413

283

9.9

Per

cola

tion

B(D

PR

/7)x

Dm

m/m

onth

124.

011

212

4.0

120.

012

4.0

120.

012

4.0

124.

012

0.0

124.

012

0.0

124.

01,

460.

0O

utpu

tsE

T+B

mm

/mon

th24

8.5

200.

920

0.3

169.

015

4.1

138.

914

6.4

161.

818

4.8

215.

222

4.0

256.

02,

299.

9

INP

UT

SR

etai

ned

Rai

nfal

lR

RR

*run

off c

oef

mm

/mon

th14

6.7

162.

913

9.5

98.1

90.9

108.

955

.869

.359

.489

.110

3.5

102.

61,

226.

7

Effl

uent

Irrig

atio

nW

(QxD

)/L

mm

/mon

th31

.028

.031

.030

.031

.030

.031

.031

.030

.031

.030

.031

.036

5.0

Inpu

tsR

R+

Wm

m/m

onth

177.

719

0.9

170.

512

8.1

121.

913

8.9

86.8

100.

389

.412

0.1

133.

513

3.6

1,59

1.7

ST

OR

AG

E C

AL

CU

LA

TIO

NS

tora

ge r

emai

ning

from

pre

viou

s m

onth

mm

/mon

th0.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

00.

0S

tora

ge fo

r th

e m

onth

S(R

R+

W)-

(ET+

B)

mm

/mon

th-7

0.8

-10.

0-2

9.8

-40.

9-3

2.2

0.0

-59.

6-6

1.5

-95.

4-9

5.1

-90.

5-1

22.4

-234

.0C

umul

ativ

e S

tora

geM

mm

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

Max

imum

Sto

rage

for

Nom

inat

ed A

rea

Nm

m0

.00

VN

xLL

0L

AN

D A

RE

A R

EQ

UIR

ED

FO

R Z

ER

O S

TO

RA

GE

m2

365

884

612

508

589

1200

411

402

287

295

299

243

1,2

00

m2

No

min

ate

d A

rea

Wa

ter

Ba

lan

ce

& S

tora

ge

Ca

lcu

lati

on

s

Silo

Dat

a -

Ka

too

mba

(-3

3.7

0,

Silo

Dat

a -

Ka

too

mba

(-3

3.7

0,

MIN

IMU

M A

RE

A R

EQ

UIR

ED

FO

R Z

ER

O S

TO

RA

GE

:


48

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