Contamination report released

01:23, Nov 29 2012

A long-awaited report into a contaminated Thames subdivision has been released, but authorities are split on how to proceed.

The report presents the Moanataiari governance group with the bioavailability study - which means how available a toxin is for a human body to consume - a health risk assessment (HRA) and the assessment of response options (ARO) along with cost estimates.

The issue emerged after it was discovered the subdivision was built on old mine tailings and was potentially contaminated. Testing confirmed those fears and nearly 200 homes were affected.

A site specific investigation in the area west of State Highway 25 confirmed that elevated levels of arsenic, cadmium, lead and thallium were present throughout the subdivision. Yet concentrations varied and were generally higher in the east than the west.

The HRA states that with the exception of lead on two properties, the main contaminant of concern is arsenic.

It concludes that the potential human health risk ‘‘meets Government policy on risk from contaminated land’’ at properties in the western part of Moanataiari. 


‘‘Consuming home grown vegetables in the western part of Moanataiari also poses negligible risk,’’ the report says.

‘‘There are however exceptions with reference to a small number of properties that are not too dissimilar to some properties in the east of Moanataiari. These properties will need further attention during the response phase as with most properties in the east of Moanataiari.’’

The disagreement emerged through the suggested resolutions to deal with the problem.

Thames-Coromandel District Council staff recommend the Moanataiari Governance Group implements Scenario B, the non-physical works response but the Environment Ministry and Waikato Regional Council staff disagree.

Scenario B is based on an awareness programme promoting behavioural changes, providing safe soil to grow vegetables in and providing some assistance to property owners in affected areas.

But the Environment Ministry and WRC want the remedial option decision deferred until: the Ministry of Health’s comments have been considered; a peer review of the HRA, facilitated by MoH, has been considered; and a robust cost benefit analysis that incorporates both health and non-health factors is undertaken.

The report says there is no recorded medical evidence to suggest a trend over the last 60 years of the subdivision's life towards specific illnesses related to soil contamination.

‘‘Given the level of risk and Moanataiari's population, this is understandable,’’ it says.

‘‘Everyone faces potential risk of getting cancer from a variety of exposures, including contaminated soils; Moanataiari soils present a very small increased risk, additional to that risk which already exists from all other exposures; undertaking dig-and-dump type remediation could exacerbate potential risk and have an avoidable [negative] effect as contaminants are disturbed and released into the environment.’’

If it is determined that the appropriate response excludes physical remediation works then people living in Moanataiari will be exposed to a significantly lower dose of arsenic from soil than the arsenic dose that is currently received by more than 120,000 people who drink from the Hamilton city water supply.

Waikato Times