Contamination from old sheep dip sites

In 1995/6, Waikato Regional Council surveyed 35 groundwater wells and found that two were contaminated with the insecticide dieldrin. The dieldrin levels were considerably higher than the maximum acceptable values for drinking water set by the Ministry of Health. In both cases the dieldrin originated from old sheep dip sites located near the wells.

From 1996 Waikato Regional Council have studied and continued to monitor the extent of pesticide contamination in the region’s groundwater.

Samples were taken from 35 wells in two areas where pesticides are regularly used:

• Pukekohe/Pukekawa
• Hamilton Basin/southern Hauraki Plains.

The insecticide dieldrin was found to exceed maximum accepted values (MAV) set for drinking water in New Zealand, at two groundwater wells causing risk to human health.

In both cases, the dieldrin originates from old sheep dip sites located near the wells, causing local contamination of nearby soil and groundwater.

Dieldrin was regularly used in sheep dips during the 1950-1960s. Government required the use of chemicals such as dieldrin for the control for parasites on sheep until 1966.

Sheep dips contaminated the soil and the groundwater below from:

• disposal of chemicals
• chemicals dripping from animals.

Although it has not been used for over 30 years, dieldrin is still contaminating groundwater decades later. This highlights the persistence and the long-lasting nature of this pollutant.

It is estimated that there are several thousand old dieldrin dip sites in the region. Unfortunately many old sheep dip sites are located beside farm water supply wells.

Waikato Regional Council is currently helping to develop national guidelines for managing contaminated sheep dip sites.

In 1997 we sponsored a study by the Waikato Pesticides Awareness Committee (WaiPAC) on soil contamination at four former sheep dip sites in the region. The study found that soil and groundwater had been contaminated from past use of chemicals such as dieldrin and arsenic. It’s likely that many other former sheep dip sites will also have similar contamination.

Many of New Zealand's international markets want to know their food is produced in an environmentally responsible way. Industry groups are looking at ways to reduce pesticide contamination, in response to market requirements.

If you’re concerned about potential contamination of groundwater in your area or on your property, contact us for advice on sampling and site management onWaikato Regional Council's Freephone 0800 800 401.

Download our brochure [PDF, 718 KB] on sheep dips, spray booths and footbaths.

Find out more about groundwater monitoring in the Waikato region.

For national drinking water standards visit the Te Whatu Ora website (online publications).