Preliminary Feasibility Assessments of Land Passage Options (LEI, 2017:A5D1)
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[LEI, 2017:A5D1] Preliminary Feasibility Assessments Of Land Passage Options (LEI, 2017:A5D1) Prepared for Wairoa District Council Prepared by October 2017 Preliminary Feasibility Assessments of Land Passage Options (LEI, 2017:A5D1) Wairoa District Council This report has been prepared for the Wairoa District Council by Lowe Environmental Impact (LEI). No liability is accepted by this company or any employee or sub-consultant of this company with respect to its use by any other parties. Quality Assurance Statement Task Responsibility Signature Project Manager: Hamish Lowe Prepared by: Phil Lake, Pat Knerlich, Angela Lane Reviewed by: Hamish Lowe Approved for Issue by: Hamish Lowe Status: Final Prepared by: Lowe Environmental Impact Ref: RE-10292-WDC-A5D1-HRLP_RI_Prelim_Assmts- P O Box 4467 171012-Final.docx Palmerston North 4442 Job No.: 10292 | T | [+64] 6 359 3099 | E | [email protected] Date: October 2017 | W| www.lei.co.nz Revision Status Version Date Author What Changed and Why 2 10/10/17 HL Incorporate comments from client 1 29/9/17 AL Draft to client TABLE OF CONTENTS 1 EXECUTIVE SUMMARY ............................................................................ 1 1.1 Background ............................................................................................................. 1 1.2 Option 1a - Status Quo System With UV Treatment .................................................... 1 1.3 Option 1b - High Rate Land Passage (HRLP) and River Discharge ................................ 1 1.4 Option 2 - Rapid Infiltration (RI) and Coastal Discharge .............................................. 2 1.5 Option Evaluation .................................................................................................... 2 1.6 Recommendations ................................................................................................... 3 2 INTRODUCTION ...................................................................................... 4 2.1 Background ............................................................................................................. 4 2.2 Purpose .................................................................................................................. 4 2.3 Scope ..................................................................................................................... 4 3 DISCHARGE OPTION SELECTION PROCESS ........................................... 5 3.1 General ................................................................................................................... 5 3.2 Stakeholder Group ................................................................................................... 5 3.3 Land Passage Options .............................................................................................. 6 4 DESIGN PARAMETER CONSTRAINTS ...................................................... 7 4.1 Existing Treatment System ....................................................................................... 7 4.2 Treated Wastewater Flows and Quality ...................................................................... 7 4.3 Discharge Controls ................................................................................................... 7 5 TANGATA WHENUA CONSIDERATIONS .................................................. 9 5.1 Wastewater and Maori Worldviews in Wairoa ............................................................. 9 5.2 Cultural Values and Tikanga ...................................................................................... 9 5.3 Cultural Acceptability of Discharge Options ............................................................... 10 6 SITE DESCRIPTIONS ............................................................................. 11 6.1 Site Identification ................................................................................................... 11 6.2 Wairoa River Estuary Discharge Site ........................................................................ 12 6.3 HRLP Site .............................................................................................................. 13 6.4 RI Site .................................................................................................................. 15 7 POTENTIAL DESIGN OPTIONS .............................................................. 21 7.1 Preamble .............................................................................................................. 21 7.2 Option 1a: Status Quo System With UV ................................................................... 21 7.3 Option 1b: HRLP System and River Discharge .......................................................... 22 7.4 Option 2: RI System and Coastal Discharge.............................................................. 28 7.5 Associated Costs .................................................................................................... 32 8 OPTION EVALUATION CRITERIA .......................................................... 33 8.1 Overview ............................................................................................................... 33 8.2 Technical Feasibility ............................................................................................... 33 8.3 Social and Recreational Values ................................................................................ 33 8.4 Environmental Values ............................................................................................. 34 8.5 Cultural Values ...................................................................................................... 34 8.6 Legal and Planning Requirements ............................................................................ 35 8.7 Financial Values ..................................................................................................... 35 9 OPTION EVALUATION RESULTS ............................................................ 36 9.1 General ................................................................................................................. 36 10 CONCLUSIONS ...................................................................................... 39 11 RECOMMENDATIONS ............................................................................ 41 12 REFERENCES ......................................................................................... 42 13 APPENDICES.......................................................................................... 43 Appendix A: Discharge Option Selection Process Appendix B: Soil Drainage Test Methodology & Results 1 EXECUTIVE SUMMARY 1.1 Background The Wairoa wastewater treatment system (WWTS) requires a replacement discharge consent to be lodged with the Hawke’s Bay Regional Council at the end of 2018. Based on hapu and community engagement, and direction provided by a range of regulatory policies, some form of land discharge is preferred. The use of a land discharge system that provides for contact with Papatūānuku is a preference for tangata whenua; whereby the wastewater’s discharge does not have a negative impact on the mauri of the surrounding waterways. A range of land passage options are possible, but affordability is a critical element when considering their feasibility. The Wairoa Stakeholder Group has reviewed a wide variety of possible options and has sought further information on the use of a high rate land passage system (HRLP) prior to reaching the current river discharge location, and the use of a rapid infiltration (RI) system near the coast and to the west of Whakamahi Lagoon. These two options are considered along with a third, being a status quo option with some further treatment to reduce pathogen levels. These options are: 1a – Status Quo System With UV 1b – HRLP System and River Discharge 2- RI System and Coastal Discharge This report provides a preliminary assessment of the feasibility and constraints of each system at two sites. 1.2 Option 1a - Status Quo System With UV Treatment The current discharge structure will require further modifications if this is to be an option for future discharge. Adding a UV system would decrease pathogen loading of treated wastewater entering the Wairoa River, and this would achieve an improvement in water quality in the river and estuary, improve recreational acceptability, protect public health for recreation and seafood consumption, and slightly improve ecosystem health protection. However, its lack of land passage means that it does not address cultural values. This current method of discharge will still be required if an HRLP system is installed (Option 1b), although the current location of this outfall pipe could be altered if hydraulic modelling of the discharge pipeline highlights this to be the best option. The current discharge pipeline and diffuser are within the coastal marine area as defined by the Regional Council Environment Plan (RCEP) and also (obviously) within the flood hazard risk zone. Its proximity to the ocean means that it is at risk of coastal hazards such as erosion, tsunami and climate change effects. 1.3 Option 1b - High Rate Land Passage (HRLP) and River Discharge The process of the flow through a HRLP system aims to revitalise the mauri of the wai. This concept and the proposed structure is based on the inclusion of specific aspects of tikanga as identified in a report specifically prepared to identify Wairoa specific tangata whenua values. It | Wairoa District Council – A5D1 – Preliminary