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Making good decisions: Risk characterisation and management of CCA post hotspots at vineyards and kiwifruit orchards

TR 2018/11

Report: TR 2018/011

Author: Michelle Begbie (Waikato Regional Council), Jackie Wright (EnRiskS) and Rachel Rait (Malborough District Council).

About this report

Copper, chrome, arsenic (CCA) treated timber posts have been used in vineyards and kiwifruit orchards for decades.  Over time, CCA leaches from the posts and accumulates in soil adjacent to each post.  Because kiwifruit and vineyards employ ~500-600 posts per hectare, there are numerous ‘micro-hotspots’ containing elevated CCA in each resulting residential section; and currently, there is no consistency within the contaminated land sector for undertaking effective risk characterisation on this issue.  Arsenic is the most toxic of the three components to human health, and so the focus of this document is the health risk posed by arsenic.

Regional and unitary authorities have a role in determining the nature and extent of contaminated land, while territorial authorities use this information to evaluate the suitability of proposed land use, subdivision and land redevelopment.  Local government agencies work closely to ensure that decisions are made effectively and consistently.

This document uses available literature, NZ case studies and new research to prepare generalised risk characterisation for residential landuse scenarios at these sites; and options for practical and cost-effective mitigation techniques.  The aim is to help those contributing organisations to make good decisions regarding contamination status, and what measures could be undertaken during earthworks and site preparation to mitigate risk to human health.

This project has received considerable in kind support from Marlborough District Council, and financial and peer review support from the following local government organisations: Marlborough District Council, Otago Regional Council, Environment Canterbury, Bay of Plenty Regional Council and Tasman District Council.

Read or download the report

Making good decisions: Risk characterisation and management of CCA post hotspots at vineyards and kiwifruit orchards [PDF, 580 KB]


1 Introduction 1
2 Scope and limitations 2
3 A regulator's role 3
4 Literature review 4
4.1 Fence post impact on soil and groundwater quality 4
4.2 Application of soil standards to protect human health 6
5 Case studies 9
6 Risk characterisation 13
6.1 General 13
6.2 Distribution of soil impacts 13
6.3 Potential risks to health 15
7 Soil mixing as a mitigation method 19
8 Effective soil mixing techniques 22
9 Outcomes applicable to good decision making 24
Bibliography 25
Appendix A. Case study details 30
Appendix B. Overview of regulatory decisions on applications of CCA treated timber
Appendix C. Exposure and risk calculation 47