A second round of tests for firefighting foam contamination in Marlborough has found only one sample that exceeds the guidelines for drinking water.
That sample is from a bore that is not used for drinking water.
Two samples that tested above the guideline in the first round of tests, this time tested below it.
All the other 167 groundwater samples in the second round did not exceed the guideline.
However, 78 or almost half of them contained traces of the PFAS chemical compounds found in firefighting foam, which are longlasting and can be harmful.
Up to 45 of these bores with trace PFAS are used for drinking water.
The tests found traces of the contaminant in Blenheim's town water supply, at one of its nine drinking water bores.
The traces are at 50 times lower than the safe maximum set in New Zealand's national health guidelines.
The national guidelines are the same as Australia's and the US Environmental Protection Agency's, but much higher than the US states most badly hit by PFAS contamination, such as Minnesota.
Blenheim's water remained safe to drink, Marlborough District Council's operations and maintenance engineer Stephen Rooney said, adding that with water demand low at this time of year, they had now turned off the affected bore in Auckland Street.
"We anticipate monthly sampling for the next 12 months to monitor this emerging issue."
The bores were checked as part of a second round of tests around the Woodbourne Air Force base, after the Defence Force last December admitted contaminating groundwater there.
Out of 25 surface water samples, 13 had PFAS in them.
Two PFAS compounds in foam, PFOS and PFOA, are banned; there are hundreds of others which very little is known about although all of them are very resistant to being broken down.
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