A Skyhawk crash in 1996 is the most likely source of contamination in drinking water provided to the Rangitikei town of Bulls, a regional council officer says.
The pilot ejected safely and no one was hurt in the crash, but potentially contaminating firefighting foam with PFAS compounds was used at the Kakariki site.
Horizons Regional Council science manager Abby Matthews said groundwater and soil around Ohakea Air Force Base was found to be contaminated with PFAS compounds late last year.
The compounds were in a lot of manufactured products, and especially the firefighting foam used at the air base until 2002. They were very persistent in the environment.
Their effects on human health are unknown. More testing was done, and low levels were found in the Bulls water supply. The level was well below drinking water guidelines.
The presence of the compounds was unexplained, because known groundwater flow from Ohakea was in another direction.
The Manawatū and Rangitīkei district councils wanted to know the source, because the contamination could get worse.
If the Skyhawk crash wasn't the source there could be others, Matthews said, such as landfills, wastewater, industrial activity or spoil moved from Ohakea.
The Horizons Regional Council would investigate. Councillors have approved $100,000 for the task, and Wellington-based company Jacobs New Zealand has been contracted to do the work.
Once possible sources of PFAS were found around Bulls and Ohakea, samples would be taken.
The New Zealand Defence Force NZDF was also investigating, and was in its third round of sampling - this time of animals and plants as well as soil and water.
Horizons was in discussion with the Government over who will pay for the latest investigation, strategy manager Nic Peet said. It could be the Government, or the polluter.
Investigation was to start before a decision about who pays, because the council did not want to delay.
Horizons has had difficulty getting full information about the situation from the NZDF, but Peet said that was improving.
"It's definitely got better, but there are still some gaps that we are anxious to see filled."
A NZDF spokesperson said it was working to provide further information by June 6.
Meanwhile, Ohakea residents were hoping Government would put in a new water scheme for them, giving them uncontaminated water from a new and deeper bore, their committee chairman Andy Russell said.
"That would go a long way to solving many of the issues."
Some residents would also like to be tested, to ensure the compounds haven't affected their health.
It was too early to talk about remediating and mitigating the contamination, a NZDF spokesperson said. The first priority was to find the full extent of the contamination and provide safe drinking water.
Once investigations by Horizons were completed, the culprit could be prosecuted.