Levin Wastewater Land Application Re-consenting: The Pot Site Characterisation (LEI, 2015:B7a) Prepared for Horowhenua District Council Prepared by February 2017 Levin Wastewater Land Application Re-consenting – The Pot Site Characterisation Horowhenua District Council This report has been prepared for the Horowhenua 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: Sian Cass Reviewed by: Hamish Lowe, Rob Potts, Katie Beecroft Approved for Issue by: Hamish Lowe Status: Final Prepared by: Lowe Environmental Impact Ref: RE-10093-HDC-Site Characterisation-Pot-170202 P O Box 4467 Palmerston North 4442 Job No.: 10093 | T | [+64] 6 359 3099 | E | [email protected] Date: 02 February 2017 | W| www.lei.co.nz Revision Status Version Date Reviewer What Changed & Why 1 17/07/2015 HL Initial draft and review 2 28/11/2016 HL Updated data from more current reports. 3 01/02/2017 KB Soil characteristics report incorporated because of repetitious and small size of report. TABLE OF CONTENTS 1 EXECUTIVE SUMMARY ............................................................................ 1 2 INTRODUCTION ...................................................................................... 3 2.1 Purpose .................................................................................................................. 3 2.2 Background ............................................................................................................. 3 2.3 Scope ..................................................................................................................... 3 3 SITE LOCATION ....................................................................................... 5 3.1 Site Location ........................................................................................................... 5 3.2 Site Ownership ........................................................................................................ 5 4 SITE CHARACTERISTICS ......................................................................... 6 4.1 Landform ................................................................................................................ 6 4.2 Vegetation .............................................................................................................. 7 4.3 Climate ................................................................................................................... 8 4.4 Surface Water & Artificial Water Courses .................................................................. 10 4.5 Buffers .................................................................................................................. 10 5 SOIL CHARACTERISTICS ....................................................................... 13 5.1 General ................................................................................................................. 13 5.2 Test Location Selection ........................................................................................... 13 5.3 Soil Hydraulic Conductivity ...................................................................................... 14 5.4 Soil Chemistry ....................................................................................................... 19 6 IRRIGATION ASSESSMENT ................................................................... 22 6.1 Current Irrigation ................................................................................................... 22 6.2 Pine Management .................................................................................................. 22 6.3 Harvest Strategy .................................................................................................... 22 6.4 Potential Irrigation Sites at The Pot ......................................................................... 23 7 CONCLUSIONS AND RECOMMENDATIONS ........................................... 24 8 REFERENCES ......................................................................................... 27 9 APPENDICES.......................................................................................... 28 Appendix A Figures Appendix B Soil Hydraulic Conductivity Graphs Appendix C Soil Chemical Analysis 1 EXECUTIVE SUMMARY Horowhenua District Council (HDC) is considering modifications to a number of their wastewater treatment plants (WWTP) and associated discharges. This includes the operation of the Levin WWTP and discharges at what is referred to as The Pot. The Pot receives treated wastewater from Levin’s WWTP to a storage pond on-site: Pot Pond). The surrounding area is irrigated from the pond to a mix of pine trees and grass. The pine trees are mature and require harvesting. This report describes the general site characteristics at The Pot including the soils and vegetation. The attributes relevant for an upgraded irrigation design for the currently irrigated land and any additional irrigation area available at The Pot are listed below. Site Location • The Pot is 110.5 hectares, and located 7 km west of the Levin township. The Tasman sea is 600 m from the most western boundary and the Waiwiri Stream is the property’s southern boundary; • The north and east boundary may permit less buffer distance due to the eastern boundary being owned by HDC and the northern property owners interest in receiving some of the wastewater. Site Ownership • Two land titles at The Pot are owned by HDC and two are owned by Muaūpoko Lands Trust. The land administered by Muaūpoko Lands Trust has renewed the lease to HDC and maintains The Pot site availability for irrigation. Landform • Landform is steep dunes with flat areas in between; • Up to 7% of the site has steep slopes that will require irrigation rates that avoid mobilising the sandy soil and encourages permanent vegetative cover; and • Additional factors are listed in the results and conclusions of the soil report (Landcare 2016:B9). Vegetation (Boffa Miskell, 2016:B10) • Vegetation is mixed grass and pine plantation with isolated patches of natives, swamp species and undeveloped vegetation; • Irrigation will need to avoid ‘kanuka forest’ (north side of the Pot Pond) and ‘carex sedge wetland’ (NW portion of The Pot) because of their recognition as regionally threatened habitat types identified in Horizons One Plan Schedule F; and • Pre-works fish rescue and transfer was recommended (Boffa Miskell 2016:B10) if any drains are diverted or filled in. Climate • Climate data sets from Levin Aws weather station provide a suitable reference for irrigation design; • Wind conditions are unlikely to limit irrigation design; • Irrigation will be beneficial for the site as predicted climate change conditions develop; and • Maintaining tree production on the westerly boundary is a valuable attribute to protect the irrigation infrastructure and spray drift. Surface Water & Artificial Water Courses • The Waiwiri Stream south and the Tasman sea west will require suitable protection from nutrient loads from wastewater irrigation; • Drains around The Pot site direct shallow groundwater to the Waiwiri Stream; • Irrigation should be avoided on wet areas at The Pot; and • Flood risks are low. | Horowhenua District Council - The Pot Site Characterisation | P a g e | 1 | Buffers • Buffer distances set by the Horizons One Plan for other effluent products applied to land are appropriate for the irrigation area at The Pot; • The gas main crosses The Pot north south and located within a 12 m wide buffer; and • All buffers identified above would occupy 43 ha and leave 67 irrigable hectares of the 110 ha property. Soils (McLeod, 2016:B9) • All soils have been correlated to the Part Foxton-Omanuka Association. These are predominantly well drained sandy soils located on dunes. Interdunal areas are wet and peaty and not considered suitable for irrigation. Soil Hydraulic Conductivity • There are no restrictive layers through the soil profiles that would affect irrigation, except some peaty interdunal areas; • One irrigation application rate for the whole property is appropriate; • The K-40mm should be used instead of the Ksat to determine the irrigation application rate because it better represents the soils ability to hold water and limit drainage into groundwater. Holding the water in the soil maximises the opportunity for plant uptake and soil attenuation of nutrients from the wastewater; • The result from the K-40mm tests suggest that a design irrigation rate of 72 mm/day would be an appropriate application rate for irrigation; • A lower application rate may be considered for the following reasons: • Nutrient loading effects; • The sites attenuation ability, which may result in a further reduction of the actual rate; • Avoidance of excessive drainage from the sandy soils to groundwater that may also be contributing to the wetness in low lying areas; and • Physical soil characteristics are itemised in Table 1.1. Table 1.1: Soil Physical Properties *Bulk *Porosity *Macroporosity Ksat K-40mm density (%) (%) (mm/hr) (mm/hr) (g/cm3) 1.19 ± 0.10 54 ± 4 17 ± 6 964 ± 869 9.0 ± 4.4 *Landcare field tests (2014) Soil Chemistry • pH is low on irrigated pine production sites and supplemental fertiliser to adjust the pH may be necessary depending on production requirements; • The land is not constrained by fertility issues for