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Identifying, Investigating and Managing Risks Associated with Former Sheep-dip Sites

Acknowledgements

Executive Summary

1 Introduction

2 Characteristics of Sheep-dip Contamination

3 Planners' Guide

4 Identifying Former Sheep-dip Sites

5 Site Investigation

6 Risk Management

7 Best Practice Tips for Common Sheep-dip Scenarios

Appendix 1: Checklist for Landowners to Assess Sheep-dip Sites and Management Options

Appendix 2: Draft District Plan Provisions for Disused Sheep Dips

Appendix 3: Current Legislation and the Role of Local Authorities

Appendix 4: The Historical and Legal Context for Sheep Dipping

Appendix 5: Applied Chemicals and their Toxicity

Appendix 6: Soil Guideline Values

Appendix 7: Case Studies

Appendix 8: Comparing Different Sheep-dip Sampling Strategies

Appendix 9: International Practices

Appendix 10: Photographs of Sheep-dip Structures

Glossary

References

Bibliography

Appendix 6: Soil Guideline Values

Derivation of dip-site-specific soil guideline values to protect human health

The general methodology provided in the Timber Treatment Guidelines (Ministry for the Environment and Ministry of Health 1997) and the Gasworks Guidelines (Ministry for the Environment 1997) was used to derive the indicative soil guideline values provided in section 5, which are consistent with existing New Zealand guidelines.

In contrast to previous guidelines, this guideline explicitly includes lifestyle-block land use as a typical New Zealand land use, which assumes that 50 percent of the produce consumed by residents is grown on-site (consumption of meat, milk and eggs of animals raised on-site is excluded). Previously this land use has been a subset of residential land use. The standard residential land-use category considered here assumes that 10 percent of the produce consumed by residents is grown on-site, while the remaining categories do not consider consumption of produce grown on-site.

The following five land-use categories were adopted.

• Lifestyle block − residential property where 50 percent of vegetables consumed are assumed to be grown on-site. The consumption of products (eggs, milk, meat) from animals raised on-site is excluded and should be considered on a site-specific basis.
• Standard residential − low-density residential property with home-grown vegetables contributing 10 percent of the total intake.
• High-density urban residential − residential with minimum opportunity for exposure to soil; no produce consumption; includes daycare centres, kindergartens, preschools and primary schools, where no gardens are present.
• Parks/recreation − parks, recreational open space, playing fields; includes secondary schools.
• Commercial/industrial (unpaved) − unpaved commercial and industrial properties. Where paving is present, its integrity and likely effectiveness in reducing exposure must be considered on a site-specific basis. No consideration of the protection of plant life has been included.

The exposure scenarios considered are largely based on those provided in the Gasworks Guidelines, while the parameter values used are based on those contained in both guidelines. They are consistent with those used internationally and are also generally considered to be representative of New Zealand for the purpose of deriving generic values. However, different parameters have been used for the dermal exposure and produce consumption pathways.

Table A.3 provides a summary of the exposure parameters used for each scenario. The equations used to derive soil guideline values are provided in Cavanagh and Proffitt (2005).

Table A.3: Summary of the exposure parameters for each land-use scenario

Contaminant-specific parameters used to derive soil guideline values in the current report are summarised in Table A.4, and a brief discussion is provided below.

Table A.4: Contaminant-specific parameters used to derive soil guideline values

The toxicological intake values provided by the World Health Organisation were generally used in the current report to provide consistency with toxicological intake values adopted by other government agencies such as the Ministry of Health, Environmental Risk Management Authority and New Zealand Food Safety Authority. With the exception of DDT, the intake values are consistent with those values used in the Drinking-water Standards for New Zealand 2005 (Ministry of Health 2005). Table A.5 provides a summary of the soil guideline values derived for individual pathways, and the final combined value.

Table A.5: Summary of soil guideline values (mg/kg) for individual pathways

The Ministry for the Environment holds more detailed information on the derivation of the soil guideline values for individual contaminants. This information can be provided on request.

Soil guideline values to protect on-site ecological receptors

A summary of the existing national and international soil guideline values for the protection of ecological receptors for the sheep-dip contaminants of concern are shown below.

Table A.6: Soil guideline values protective of on-site ecological receptors (mg/kg)

EIL - ecological investigation level; SQG_e - soil quality guideline environmental; Eco-SSL - ecological soil screening level; P - pending; NA − not available, insufficient data for derivation of an Eco-SSL; SRC_eco − serious risk concentration ecotox; IV - intervention value; MPC - maximum permissible concentration; TV - target value.

a Allowable limits in soil to which biosolids have been applied.

b Based on protection of off-site receptors.

c Revised value (Lijzen et al 2001).

d Sum of DDT, DDD and DDE.

e Sum of aldrin, dieldrin and endrin.