62 Muriwai Road, Waimauku, Auckland
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62 MURIWAI ROAD, WAIMAUKU, AUCKLAND WASTEWATER ASSESSMENT FOR PROPOSED 9 LOT SUBDIVISION FOR TRAVERSE LTD SEPTEMBER 2017 | REV 3 | SUITE E | 31 BARTLEY TERRACE | DEVONPORT, AUCKLAND 0624 | T: 09 445 8338 | W: gwe.co.nz 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. Page ii 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 Page iii 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. Page 1 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