Toxic firefighting foam that has been illegal in New Zealand for 12 years has been discovered in two firetrucks and storage sheds at Nelson Airport, the Environmental Protection Authority (EPA) says.
The authority said it has been conducting a nationwide investigation into the foam.
The foam contains the longlasting, potentially cancer-causing chemical PFOS, which was banned in 2006.
The authority has issued a compliance order telling the airport not to use the foam for firefighting training, and only to use it in emergencies if it has to while it comes up with a plan to get rid of it.
The airport has until 16 March to come up with a plan to get rid of it.
The airport is beside the sea, to the south of Tahunanui beach next to the suburb of Annesbrook.
Nelson city's water supply comes from the Maitai and Roding Rivers, which have catchments inland.
The Nelson City Council said there were no known ground or surface water intakes in the vicinity of Nelson Airport.
'Not knowing is no defence' - EPA
Nelson Airport said it did not know it had bought and had been using the toxic foam.
Chief executive of the council-owned airport, Rob Evans, told RNZ it had hundreds of litres of the foam - but that it was only ever used in firefighter training once every two years.
There were no household water supplies the foam could have gotten into but he would be ordering water testing around the airport anyway, he said.
"We're putting in place to dispose ... of what we have and to also test water tables around the airport just to ensure there's no further contamination."
The airport's four firefighters had been given health information and would be offered free blood tests.
EPA chief executive Allan Freeth said he was "surprised" to find banned foam being used.
"Not knowing is no defence," he said. "The onus is on anyone using this foam."
Foam has contaminated water in Marlborough and Manawatu
The foam has contaminated drinking water supplies in Marlborough and Manawatu, and triggered water testing around Defence bases in Auckland and Canterbury.
The Defence Force, which stopped using the foam in 2002, knew in mid-2015 that groundwater around the Woodbourne and Ōhakea bases was contaminated.
People living near the airbases were told in December 2017 that seven households were found to have been contaminated beyond drinking water safety guidelines, which were set in April 2017.
Free blood tests have been offered to five households near Ōhakea and two near Woodbourne, and they have been offered an alternative water supply.
PFOS is listed as a persistent organic pollutant under the Stockholm Convention, and the Hazardous Substances and New Organisms Act.
What is the foam?
A fire retardant used by the Fire Service, Defence Force, Marsden Point oil refinery and airports. The foam contains the chemicals PFOS and PFOA - man made chemical compounds which don't break down.
These are the most commonly used of the perfluoroalkyls chemical family, or PFAS, and diffuse extremely readily in air, dust, surface and groundwater, soil and sediment.
Human bodies get rid of PFOA and PFOS from their systems much more slowly than other animal species.
PFOA and PFOS are found in other things too, including some carpets, waterproof jackets, non-stick frying pans, and sneakers. Since 2010, some companies have been signing up to stop using these chemicals.
It has been banned in firefighting standards in New Zealand since 2006 and hasn't been used by the Defence Force since 2002.