62 Muriwai Road, Waimauku, Auckland

62 MURIWAI ROAD, WAIMAUKU, AUCKLAND

WASTEWATER ASSESSMENT FOR PROPOSED 9 LOT SUBDIVISION

FOR TRAVERSE LTD

SEPTEMBER 2017 | REV 3

62 Muriwai Road, Waimauku Wastewater Assessment

62 MURIWAI ROAD, WAIMAUKU, AUCKLAND

WASTEWATER ASSESSMENT

FOR TRAVERSE LTD

Document title: 62 Muriwai Road, Waimauku, Auckland, Wastewater Assessment

Version: 3

Date: September 2017

Prepared by: Patrick O’Riordan, Senior Engineer, GWE Consulting

Reviewed by: Gareth Williams, Wastewater Specialist, GWE Consulting

Approved by: Gareth Williams, Wastewater Specialist, GWE Consulting

File name: W:\Projects\Residential\62 Muriwai Road, Waimauku\WW Assessment\62 Muriwai Road, Waimauku, Wastewater Assessment Rev 2 - Council Response.docx

GWE Consulting Ltd Suite E 31 Bartley Terrace Devonport Auckland 0624

PO Box 32-311 Devonport Auckland 0624

T: 09 445 8338 W: www.gwe.co.nz

COPYRIGHT: The concepts and information contained in this document are the property of GWE Ltd. Use or copying of this document in whole or in part without the written permission of GWE constitutes an infringement of copyright.

LIMITATION: This report has been prepared on behalf of and for the exclusive use of GWE’s client, and is subject to and issued in connection with the provisions of the agreement between GWE and its client. GWE accepts no liability or responsibility whatsoever for or in respect of any use of or reliance upon this report by any third party.

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62 Muriwai Road, Waimauku Wastewater Assessment

Table of Contents

1. Introduction...... 1 2. Property / Site Details ...... 1 3. Proposal ...... 2 4. Site Assessment ...... 2 4.1 Subsoil Investigation ...... 2 4.2 Geotechnical Report ...... 3 5. Discharge Details ...... 4 5.1 4-Bedroom Dwelling on each Lot ...... 4 5.2 Design Wastewater Volumes ...... 4 6. Wastewater Treatment ...... 5 7. Land Disposal ...... 6 7.1 Land Disposal Method ...... 6 7.2 Disposal Field Ground Conditions ...... 7 7.3 Floodplain ...... 7 7.4 Proximity to Underground Pipes ...... 8 7.4.1 Existing Stormwater Pipe in Lot 4 ...... 8 7.5 EDA Slope Angle ...... 8 8. Statutory Assessment ...... 8 9. Conclusion and Recommendations ...... 8 APPENDIX A Design Flow Calculations ...... I APPENDIX B Concept Site Plan ...... III APPENDIX C Permitted Activity Criteria Tables ...... IV

List of Figures

Figure 1 Site Location Plan – 62 Muriwai Road, Waimauku ...... 1

List of Tables

Table 1: Proposed lot sizes for subdivision at 62 Muriwai Road, Waimauku ...... 2 Table 2: Summary of Soil Profile Descriptions ...... 3 Table 3: Design flows for proposed subdivision at 62 Muriwai Road, Waimauku ...... 4 Table 4: Wastewater treatment system suppliers ...... 5 Table 5: Proposed land disposal systems for 9 lot subdivision at 62 Muriwai Road, Waimauku ...... 6 Table 6: Site specific design requirements ...... 7

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1. Introduction This assessment report was prepared by GWE Consulting Ltd (GWE) for Traverse Ltd as our client. The recommendations in this memorandum are based on the information provided within the brief received from the client. The wastewater assessment is in accordance with Auckland Regional Council Technical Publication No. 58: On-site Wastewater Systems: Design and Management Manual (TP58). This report will address the following:

• Determine the underlying soil conditions at the site and propose a suitable loading rate; • quantify the wastewater volume, site area and irrigation field areas for establishing a 4 bedroom dwelling on each residential lot; • provide site plans showing proposed building platforms, and the general location of the proposed primary/reserve irrigation field areas for each residential lot; • provide costs for suitable treatment and disposal systems; provide summary and conclusion.

2. Property / Site Details The site, situated at 62 Muriwai Road, Waimauku, is legally described as Lots 5 and 6, DP 466496, with a total area of 14,811m2. The site is located in a rural environment and is currently used for grazing cattle. The site borders residential properties. A relatively new subdivision is in the process of build out at Solan Heights and is located to the west and north west of the site. The location of the property is indicated in red below (Figure 1).

Source: http://maps.auckland.govt.nz/alggi/

Figure 1 Site Location Plan – 62 Muriwai Road, Waimauku The site is accessed via a concrete driveway that provides vehicular access to the proposed development site. To the east of the site, several new dwellings are in the process of being constructed. Land slopes up from the east, gently at first (eastern part) and then steeper towards the west of the site at 20-30°. Along the southern boundary there is a stream that collects surface waters from the middle of the site, conveying them to the east, before flowing into larger tributaries to the north east. The property is predominantly pasture (currently used for grazing) with trees located on the site, predominantly around the permitter, with a shelter belt of trees running in a north to south direction in the middle of the site.

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3. Proposal We have been supplied with a proposed subdivision site plan and cut and fill plan, prepared by Cato Bolam Consultants, which confirms the layout of the proposed subdivision (dated 07/2017). The plan indicated that it is proposed to form a 9 Lot residential subdivision. Each of the lots will vary in size from 1,502 to 1,886m2. Each lot will be serviced by an on-site wastewater treatment and disposal system and the system will be designed to meet the design requirements of TP58 (2004) and of the Auckland Unitary Plan. The proposed lot sizes are shown in Table 1 below:

Table 1: Proposed lot sizes for subdivision at 62 Muriwai Road, Waimauku Residential Lot Gross Area Lot 1 1,537m2 Lot 2 1,537m2 Lot 3 1,537m2 Lot 4 1,502m2 Lot 5 1,600m2 Lot 6 1,600m2 Lot 7 1,600m2 Lot 8 1,600m2 Lot 9 1,886m2

As part of this assessment we will provide details of flow generated from each residential lot, the required level of treatment, present typical treatment options and an indicative site plan showing the location of irrigation fields, separation distances, etc. This assessment will provide support to the subdivision consent process.

4. Site Assessment A site investigation was undertaken at the site on 21st October 2016 by a GWE Wastewater Specialist, experienced in wastewater treatment. The site inspection and recorded site evaluation information was prepared in accordance with the Site Evaluation Investigation Checklist (Appendix E, TP58).

4.1 Subsoil Investigation A detailed assessment of soils underlying the proposed land disposal areas was undertaken during the site visit. Soil profiles were assessed using auger-holes, with 3 hand auger holes (AH1 to AH3) completed to a depth of up to 1.2 mbgl (metres below ground level) within the location of the proposed irrigation field areas. Auger-hole locations are indicated in Figure WW-1 (Appendix B). A summary description of soils encountered in the boreholes, including relevant soil structure and textural features and horizontal depths are outlined in Table 2 below. No percolation testing was undertaken. NOTE – at the time of resource/building consent a full site investigation will be required on each residential lot to fully determine the level of treatment and site specific constraints with respect to wastewater.

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Table 2: Summary of Soil Profile Descriptions HORIZON DESCRIPTION – SOIL TEXTURE DRAINAGE CATEGORY AH1

Moderate to slow 0.0 – 0.2m TOPSOIL, brown, damp, friable. 4-5 draining

CLAY, with some silt, orange brown, damp, moderate plasticity. At 0.2 – 1.2m Slowly draining 6 0.9m, becomes orange, moist, high plasticity. 1.2 m No groundwater encountered AH2

Moderate to slow 0.0 – 0.2m TOPSOIL, brown, damp, friable. 4-5 draining

0.2 – 1.2m CLAY, with some silt, orange brown, damp, moderate plasticity. Slowly draining 6 1.2 m No groundwater encountered AH3

Moderate to slow 0.0 – 0.2m TOPSOIL, brown, damp, friable. 4-5 draining

Moderate to slowly 0.2 – 1.2m SILT, clayey, yellow-brown-orange, damp, stiff, moderate plasticity. 5-6 draining 1.2 m No groundwater encountered

A physical inspection of the soil profile indicates the soils at the site are predominantly comprised of CLAY/SILT. This signifies the soils are moderate to slow draining. Auckland Regional Council TP 58 (2004) guidelines indicate that the soil category is 6. The water table was not encountered at any of the exploratory positions at the maximum depth of 1.2 m. The results of the site investigation can therefore be summarised as follows: ▪ soils at the site are comprised mostly of CLAY/SILT, with a corresponding ARC Soil Category of 6; ▪ loading rates for the wastewater disposal system design should be based upon an ARC Category 6 soil; ▪ there was no visual evidence of existing surface drainage channels at the site during the site visit; ▪ the water table was not encountered at a depth of 1.2 m during the site visit. In addition, there was no evidence, based on the observed soil oxidation state (colour) which indicated the winter water table level was within 1.2 m of the ground surface.

4.2 Geotechnical Report A Geotechnical Report for the site was carried out by CMW Geosciences in February 2017 in support of the Resource and Earthworks Consent to Auckland Council. The geotechnical site investigation included drilling of 6 hand augurs to depths of 5m throughout the site. The findings of the report are consistent with the hand augurs drilled by GWE Consulting as part of the wastewater site investigation. The findings have indicated that the near-surface soil conditions are silty CLAY and CLAY with high plasticity in places. This indicates that the soil assessment of Category 6 in line with ARC TP 58 as outlined above is accurate. The CLAY dominant soils are overlain with topsoil varying in depth from 200mm to 400mm below ground level.

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The location of the Hand Augurs carried out by CMW Geosciences are outlined in the site plan attached and are also available in the CMW Geosciences report titled: “Land Development Geotechnical Works Specification For: 63 Muriwai Road, Waimauku”, Document Reference: AKL2016_0583AC Rev 0.

5. Discharge Details The type of treatment plant for each residential lot, together with the effluent quality must be determined at the detailed design stage and is based on site specific constraints. We wound anticipate that a site- specific design (that meets TP58 2004 design guidelines) will be carried out at the resource/building consent stage.

5.1 4-Bedroom Dwelling on each Lot We understand that the subdivision is to be carried out to enable a 3-4-bedroom dwelling to be legally established on each of Lots 1 - 7 as a permitted activity under the Auckland Unitary Plan and as a Restricted Discretionary Activity under a discharge consent on Lots 8 and 9. It should be noted that this allowance for a discharge consent is based on provisional design only. We have provided a preliminary wastewater design information below.

5.2 Design Wastewater Volumes It is proposed that the water supply for the 9 lot subdivision will be sourced via rainwater roof collection. Roof water will be diverted to ~23m3 tanks located on each lot. We have used a per capita flow allowance of 160litres per person per day (TP58 – Table 6.2) on the assumption that the water reduction fixtures outlined in Table 3 below, are installed.

Table 3: Design flows for proposed subdivision at 62 Muriwai Road, Waimauku Development 9 Lot Subdivision (Residential) 4 bedrooms = 6 occupants @ 160litres/hd/day = 960 Litres per lot No. of Persons 18 lots @ 960litres = 17,280Litres Water Supply Roof water supply – water diverted to ~23m3 water tanks located on each lot Full Water Reduction Fixtures include combined use of (TP58 Domestic Wastewater Flow Allowances, Table 6.2): ▪ dual flush 6/3 litre toilet cisterns ▪ shower flow restrictors ▪ low pressure aerator faucets (taps) ▪ front load/low water consumption water conserving automatic washing machines ▪ low water use dishwasher Water Reduction Fixtures ▪ no garbage grinders ▪ bath allowed

Fixed Orifice flow control (FOFC) devices in all water use outlets and flow restriction valves to achieve the following flow rates: ▪ laundry faucets 10 L/min ▪ kitchen faucets 9 L/min ▪ bathroom faucets 6 L/min ▪ shower rose 9 L/min Daily Flow Allowances 160 L/ person/ day (based on TP58) Design Flow Rate per lot 960 Litres/day Water Meter A water meter is required to be fitted at the discharge outlet point of the wastewater treatment system. Daily readings over peak occupancy should be taken and recorded, and then at regular intervals to show compliance with the specified flow

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rate. If this is exceeded the owner should contact GWE Consulting Limited to ensure design requirements are still being met. Other Notes No grey-water reuse recycling proposed

6. Wastewater Treatment The treatment plant and disposal systems must be designed to meet the requirement of TP58 (2004), namely: ▪ minimum design flow volumes of 160litres/hd/day for roof water supply (with bath and standard water saving devices); ▪ the installation all modern low water use fixtures is recommended e.g. dual flush toilets, low flow shower heads, low water use dishwashers, etc.; ▪ the minimum effluent quality must be advanced secondary; ▪ the treated effluent is to be dispersed on site using pressure compensating dripper irrigation (PCDI); ▪ a minimum reserve area of 33% is require for sub-surface PCDI installation and 50% for surface laid; ▪ the site area to wastewater volume ratio (A:V) must be >1.5; ▪ the minimum separation to groundwater is 900mm for Category 6 soils; ▪ the disposal system must be installed a minimum of 3.0m from any habitable dwelling; ▪ the disposal fields must be installed a minimum of 1.5m from the site boundaries. In Table 4, we have presented several manufacturers of on-site wastewater treatment systems that produce secondary effluent quality. All of these suppliers are based on or have approved agents in the Auckland Region.

Table 4: Wastewater treatment system suppliers WASTEWATER TREATMENT 4 Bedroom Dwelling – up to 6 occupants The following suppliers manufacture treatment systems that produce a minimum of advanced secondary quality effluent: Primary / Secondary Treatment Innoflow Technologies Ltd Reflections Treatment Systems Oasis Clearwater Ltd Site specific and will depend on a full site evaluation Tertiary treatment UV disinfection may be required to meet separation distances requirements to surface waters and roadside drains $15-25k +GST fully installed (does not include design report costs, building Estimated Cost consent application fees, etc.) Minimum requirement - visual and audible alarm located at plant Telemetry Alarm System Remote telemetry system preferable System location 3 m clear of all habitable dwelling and 1.5 m clear of boundaries

The type of treatment plant for each site, together with the effluent quality must be determined at the detailed design stage and is based on site specific constraints. The systems presented in the table above are based upon the site-specific characteristics and the suitability of the receiving environment to accept secondary quality treated effluent.

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7. Land Disposal

7.1 Land Disposal Method It is proposed that loading be undertaken via at surface or sub-surface pressure compensating dripper irrigation system, at a loading rate of 3 mm/day (in accordance with TP58 Drip Irrigation design criteria, Table 9.2). A plan of the location design and dimensions of the disposal fields is included as Figure 2 (Appendix B) Design details and sizes of the proposed disposal fields are outlined in Table 5 below:

Table 5: Proposed land disposal systems for 9 lot subdivision at 62 Muriwai Road, Waimauku LAND DISPOSAL SYSTEM Drip irrigation (Ref: Soil Assessment) Surface Laid Pressure Compensating Dripper Irrigation (PCDI) Uniraam PCDI lines at 1.0m centres (pinned to surface) and mulched/planted

Type Sub-surface Laid Pressure Compensating Dripper Irrigation (PCDI) Uniraam PCDI lines at 0.5m centres in grassed areas Lot 6, 7 and 8 Shall be Sub-surfaced laid only.

Installation of air release valves (ARV), non-return valves (NRV) and flushing taps to be installed.

Soil Category 6 (TP58 soil category description, Table 5.1)

Loading Rate 3 mm/day (TP58 Drip Irrigation design criteria, Table 9.2) Loading Method Pump High water level alarm is installed in pump chamber – audible/visual alarm Pump Pump Chamber Volume – system specific Emergency Storage volume – >960 Litres (min.24 hours at maximum flow) Primary Disposal Area 320 m2 (approximate location, design and dimensions shown in Appendix B) 160 m2 (50 % Reserve, TP58 Table 5.3) (Ref: Appendix B) Reserve Disposal Area Or 105 m2 (33 % Reserve for Sub-surface laid Disposal field) Surface watercourse – >15m (complies with ARC PA) NOTE – roadside drains and proximity to streams may require to be mitigated with UV disinfection Water supply bore – N/A (complies with ARC PA) Groundwater – greater than 1.2 m (complies with ARC PA) Separation Distances Buildings/Houses –3 m (complies with ARC PA) Property Boundary - 1.5 m (complies with ARC PA) Surface Stormwater Lies – Greater than 15m for Advanced Secondary Treatment and greater than 10m for tertiary treatment Underground Pipes – Greater than 5m from underground pipes All underground pipes shall be backfilled in clay. Stormwater Controls Surface water diversion drain must be installed upslope of all disposal area (subject Required to site specific design)

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The following table provides details of the PEAK design wastewater flow volumes, anticipated level of treatment required and the size of the irrigation fields.

Table 6: Site specific design requirements Peak Design Minimum Level of Total minimum Comments Residential Lot Flow Treatment irrigation Field Areas Lot 1 960 litres/day Secondary 480m2 Lot 2 960 litres/day Secondary 480m2 Lot 3 960 litres/day Secondary 480m2 Lot 4 960 litres/day Secondary 480m2 Lot 5 960 litres/day Secondary 480m2 Lot 6 960 litres/day Tertiary 425m2 Lot 7 960 litres/day Tertiary 425m2 >10m from stream Lot 8 960 litres/day Tertiary 425m2 >10m from stream Lot 9 960 litres/day Tertiary 480m2 >10m from stream

7.2 Disposal Field Ground Conditions The soils at the site have been classified as category 6 CLAY in line with Auckland Council TP 58 characterised as slow draining. The loading rate is set at 3mm/day for the soils in line with TP 58. Effluent disposal fields shall not be placed on areas of engineered fill. Where fill is to be placed on the disposal field it shall be non-engineered topsoil. Where possible, the entire primary disposal field for each site shall be located on undisturbed ground ie. no areas of engineered fill within the primary disposal field. Where it is not possible to avoid the requirement to place engineered fill on a site, a maximum of 33% of the reserve disposal field may be placed on fill. As indicated on Cato Bolam Proposed Cut/Fill Plan Lot 1, Lot 2, Lot 7 and Lot 8 have areas of disposal field which is indicated to be filled. As indicated on the site plan, these areas shall be brought up to the desired finished level using layers of 300mm sandy loam with 200mm of topsoil over the top. Similarly should the cut area of Lot 9 be required for onsite wastewater disposal via PCDI the area shall be remediated with 300mm of imported top soil. Insofar as possible areas of cut and or filled land should be avoided as part of the wastewater disposal field design. As noted above GWE Consulting Ltd. have recommended that the PCDI disposal field can be surface laid on Lots 1 – 5 and Lot 9 or sub-surface laid on all sites. The disposal fields shall be planted in accordance with Auckland Council TP 58 Appendix G.

7.3 Floodplain No EDA shall be located in the 1% AEP as indicated by the GWE Consulting Ltd Flood Assessment of the site. The flood assessment has indicated the 1% AEP Flood plain to be RL24.25m. For the purposes of Lot 8, which is the only lot indicated to be affected by the floodplain GWE propose building up the level of the disposal field to a minimum of RL25m. This shall be done by using a non-engineered sandy-loam type fill, rolled in 300mm layers to achieve the minimum required elevation with 200mm of topsoil overlaid. The disposal field shall for lot 8 be sub-surface laid PCDI at 0.5m centres to a maximum depth of 150mm and planted with suitable species as per TP 58 Appendix G. We propose the following should be added as a consent condition:

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X. The effluent disposal field on lot 8 shall be place on at RL25m or above. Ground in this area shall be built up using a non-engineered sandy-loam type fill, rolled in 300mm layers to achieve the minimum required elevation with 200mm of topsoil overlaid

7.4 Proximity to Underground Pipes The site plan prepared by Cato Bolam indicates that there shall be no new stormwater pipes within 3m of any disposal field.

7.4.1 Existing Stormwater Pipe in Lot 4 There is an existing 225mm stormwater line running through Lot 4. The depth to invert of this pipe shall be 1.45m, the cover above the pipe shall be approximately 1.2, however this may leave only 0.85m of cover between the disposal field and the pipe. To mitigate for this GWE recommend allocating the area near the pipe as reserve disposal field where possible. Should the reserve disposal field be required for any reason in the future, the area above the pipe shall be built up with top soil to a coverage of 1.2m above the pipe 3m either side. An anti-seepage collars should also be installed on the pipe at the downstream edge of the disposal to insure no short circuiting can occur along the length of the pipe which may leave the site. We propose the following be added to the conditions of consent: X. Where a pipe passes under an effluent disposal field or reserve field, an anti-seep collar (or similar option) is to be fitted at the site boundary to prevent wastewater tracking down the bedding of the pipe.

7.5 EDA Slope Angle The slope angle indicated as per the revised site plan from Cato Bolam Sheet No. E300 indicates the disposal fields shall be on areas mostly with a slope angle between 0 and 15 degrees.

8. Statutory Assessment In accordance with Rules E5.4 (Activity Table), E5.6.1 (General Standards for Activities) and E5.6.2.1 (Permitted Activity Standards) of the Auckland Unitary Plan Operative in part, the following proposal to discharge domestic wastewater on each residential lot at 62 Muriwai Road, via a land disposal system, will be a permitted activity – providing the design meets the requirements of TP58 (2004).

9. Conclusion and Recommendations It is proposed to undertake a subdivision of the property at 62 Muriwai Road, Waimauku. The subdivision will create 9 residential sections that will vary in size from 1,502 to 1,886m2. Each lot will be required to install a new advanced secondary onsite treatment and disposal system that is designed to meet TP58 (2004) and Auckland Unitary Plan requirements. Based on a 4-bedroom dwelling on each residential lot (and using 160 litres/hd/day), the PEAK wastewater flow generated will be 960litres/day. A site specific on-site wastewater treatment and disposal field design will be required for the resource/building consent applications for each lot. The wastewater will be treated to a minimum of advanced secondary quality; however, site specific constraints may require the addition of a UV disinfection unit. The collection, treatment and disposal system will be supplied and installed by a suitable provide of technologies available within the Auckland region – see Table 4 in this report. Based on the PEAK flow of 960 litres/day generated from a 4-bedroom dwelling, and using a 3mm/day loading rate, the primary irrigation field area will be 320m2 and a 50% reserve area will be 160m2. A total of 480m2 per lot is required. Page 8

APPENDIX A Design Flow Calculations

DESIGN FLOW LOAD CALCULATION 62 Muriwai Road, Waimauku - 9 residential lots

At maximum occupancy, number of people: 960 litres / day

9 lots, each consisting of a 4 bedroom dwelling: OR

4 bedroom house – 6 people @ 160 litres/hd/day = 960 litres 0.96 m3/day

Site Area 1,502 – 1,913 m2

Area to volume ratio >1.5 for each lot

Water Source Roof supply

Minimum secondary Treated Effluent Quality treatment

Site soil category 6

Wastewater disposal will be via surface laid PCDI in proposed irrigation field areas. 1.0m line spacing. Lines to be mulched and planted.

Wastewater disposal will be via sub-surface laid PCDI in proposed irrigation field areas. 0.5m line spacing.

Primary Field Area = 960 (litres/d)/3 (mm/d) = 320m2

Reserve Field area = 50% = 160m2

Wastewater design loading rate for PCDI 3 mm /day

Required disposal area 320 m2

Required reserve area (50% of disposal area) 160 m2

Total area required 480 m2

APPENDIX B Concept Site Plan

III

APPENDIX C Permitted Activity Criteria Tables