The Department of Defence says a chemical associated with various cancers and other health problems is continuing to spread more than half a decade after it was found to be leaching into the Katherine township's drinking water.
Department representative Dan Fankhauser told a town meeting in Katherine on Tuesday night PFAS had spread more than 25 kilometres to the suburb of Cossack.
He said it had contaminated water relied upon for drinking through bores.
"PFAS above health base guidance values were not previously found in this location during the investigation phase," Mr Fankhauser said.
"Through these results we were able to notify affected property owners and provide them with water supply support and prevent them consuming PFAS impacted water above health base guidance values."
PFAS leached into the Katherine River and spread kilometres through the highly connected aquifer during firefighting training at the Tindal RAAF Base between 1988 and 2004.
The government advised against eating fish caught from the river, the local swimming pool was closed, bore-reliant properties surrounding the base were delivered bottled water by Defence and residents lined up for blood tests.
A major study on the health effects of PFAS in Katherine last year found there was no conclusive evidence of increased risk of cancer or disease.
But those views differed from researchers who were concerned about reproductive issues and other international health agencies, such as the European Environment Agency, which has "high certainty" of links to liver damage, kidney and testicular cancer.
Contaminated soil to be removed
About 40kg of PFAS migrates down the Katherine River from RAAF Base Tindal, where contaminated soil has been left sitting, every year.
Mr Fankhauser said more than 5,300 tonnes of "highly PFAS contaminated soils" would be excavated and destroyed off base in Victoria this year.
He said more than 28,800 tonnes of "lower concentration PFAS impacted soil" would be cleaned up and distributed at the base.
Mr Fankhauser said a lack of licensed providers able to destroy PFAS – typically through incineration – had been a setback in removing the contaminated soil.
"Our focus has been to firstly ensure those areas that we know have previously had firefighting foams containing PFAS to be separated while we develop a remediation strategy," he said.
"Not all soil will be shipped interstate, those that contain much lower levels of PFAS will be able to be treated on site and then redistributed elsewhere on the base."
He said there were ways to contain PFAS when it was in very low concentrations in the soil.
"Where that's possible we will ensure that we follow those protocols," he said.
Health and water concerns linger
A number of community updates have been held in Katherine since PFAS was discovered.
Attendance has dwindled as the years have passed.
About a dozen residents showed up to Tuesday's meeting.
Mr Fankhauser said the department was with Katherine residents "for the long haul".
But long-term resident Merlyn Smith said the lengths taken to address the contamination in affected communities was insufficient and left her feeling unassured.
"I've been buying bottled water since 2017," she said.
"There has been no point of use test at my property, this has been unregulated and unmanaged prior to 2017 … it coats all plumbing and infrastructure."
She said she was concerned she had passed on PFAS to her children through breastfeeding.
She said they played on sport fields watered by contaminated bores.
Another resident questioned the department's clean up strategy.
In addition to committing to removing soil this year, it has continued to clean up contamination sites at Katherine, Oakey and Williamtown by filtering water and pumping it back into aquifers.
Katherine resident Brian Wrigglesworth said he didn't understand why water would be pumped into the ground instead of being used at the PFAS treatment facility.
"In the dry season, the town can't [maintain] the supply of water … and it just seems a waste to me to pump it back into the ground," he said.
Mr Fankhauser said the department had addressed PFAS using a balance of proven and emerging technologies.
He said the department would "employ all reasonable measures to address PFAS on site [and] to address it more broadly in the community".
