On this page: What makes a site contaminated , background levels, sources of contamination, what we’re doing, cleaning up contaminated sites
A wide variety of industrial and farming activities can result in chemical contamination of soil, air and water. Some sites within our region have high concentrations of hazardous substances and are considered contaminated sites. Waikato Regional Council is working with site owners, the city and district councils and health authorities to reduce the risks associated with contaminated sites.
What makes a site contaminated
A site is considered to be contaminated when hazardous substances are found at significantly higher concentrations than their normal (background) levels, and there is, or is likely to be, a risk to human health or the environment.
Some hazardous substances occur naturally in soil, air and water without contamination caused by people. For example, lead and mercury occur as a result of weathering of rocks or from geothermal areas.
While many chemicals, particularly trace elements, are needed by living organisms in order to live and grow, they are often only needed in minute amounts1. Above a certain level even these chemicals can become toxic, interfering with the complex biochemical reactions of plants and animals.
Other hazardous substances do not occur naturally and are created by people. Over time, some of these have become widespread in our environment. One example is the organochlorine DDT, which was previously used as a pesticide.
The Ministry for the Environment has surveyed typical levels of organochlorines (such as dioxins, PCBs and DDT) throughout New Zealand. They found that the Waikato region’s air, soil and water contain only low levels of these contaminants. The survey did not assess organochlorine levels at contaminated sites or in farm soils. Contaminated sites and farm soils may have higher concentrations of organochlorines from past uses.
Sources of contamination
There are a number of activities that may contaminate sites. The Ministry for the Environment has put together a Hazardous Activities and Industries List (HAIL) to help identify potentially contaminated sites. This is a list of 52 specific land uses that can potentially cause contamination.
Examples of sites in our region that may be contaminated include:
- sheep dips (contaminated with arsenic and organochlorine insecticides such as dieldrin)
- timber treatment sites
- former gasworks
- scrap yards
- service stations.
Contaminated sites can release hazardous substances into the environment through:
- stormwater runoff
- leaching into ground water
- loss to air, for example by evaporation or being transported on fine particles (wind blown dust).
What we’re doing
Contaminated sites threaten our environment and need to be managed. To assess how much of a threat they pose we need to identify the number of sites in the region. These will be places where hazardous substances are currently, or have historically, been used, stored or disposed of.
Waikato Regional Council has been working in conjunction with the Ministry for the Environment to develop a set of guidelines for identifying contaminated sites. The Classification and Information Management Protocols for Contaminated Land will form the basis by which we are managing contaminated sites in our region.
The management of contaminated sites involves four steps:
- Identification of contaminated sites.
- Assessment of risk to human health or the environment.
- Remediation of high risk historic sites.
- Minimisation of contamination caused by currently operating sites.
Find out more about how contaminated sites are being managed.
Progress so far
Waikato Regional Council has compiled an initial Selected Land Use list of about 3,400 sites from across the region that are potentially contaminated (see the HAIL). This list was compiled from phone book records and business directory listings dating back to 1930.
The graph below shows the distribution of potentially contaminated sites (as a percentage of the total) among the city and district councils.
At present 107 sites in the region are listed as Category 1 – Confirmed Contaminated. However, the actual number of contaminated sites is likely to be much higher as more sites are investigated and tested.
Currently we are working with the city and district councils in our region to both identify and manage contaminated sites.
Find out about the clean-ups at the Hamilton Gasworks and Rotowaro Carbonisation Plant.
Cleaning up contaminated sites
Waikato Regional Council shares information on contaminated sites with health authorities, and the city and district councils. We work together to investigate and assess the degree of risk of both existing and potentially contaminated sites. Where owners can be identified we work with them to manage the risks at their site, for example the remediation of the Hamilton Gasworks.
Where owners cannot be identified, or are unable to manage the risks at a contaminated site, we work with local communities and other agencies to seek central government funding for remediation or management. This approach was used to clean up the Rotowaro Carbonisation Plant.
Find out more
Place an order if you would like a published paper copy of our factsheets on:
- Pesticide contamination of ground water in the Waikato region.
- Ground water quality.
- Chemicals needed by living organisms are termed “essential”. For people, these include trace elements such as iron, copper, iodine, selenium and zinc.