The explosive revelation, contained within a defence to a class action lawsuit in Queensland, has again skewed the timeline on when the department became aware of the environmental dangers posed by the foam. 

It was previously thought to be at least four years later, on the basis of a document obtained by Four Corners showing Defence was warned of the risks in 1987. 

Residents of Williamtown, who were informed about the contamination of their properties in 2015, reacted with frustration to the shifting version of events. 

“We have no confidence in the polluter dictating the terms of any future solution when they continue to airbrush the past,” the president of the Williamtown and Surrounds Residents Action Group, Cain Gorfine, said.  

“The Prime Minister, Senator James McGrath and Defence Minister Marise Payne: we call on you now to please fix this mess and let us move on with our lives.”  

The latest admission has been made in response to a lawsuit filed by Shine Lawyers, on behalf of more than 450 people who live near the Oakey army base and have been grappling with the fallout from a plume of toxic poly- and per-flouroalkyl (PFAS) chemicals. 

A similar class action is underway over contamination from the Williamtown RAAF Base, with the case returning to court on Tuesday.  

In court papers filed by Defence’s solicitors, it was claimed the department did not become aware the chemicals could potentially cause adverse health effects in humans until May 30, 2000. 

That was roughly the time that US manufacturing giant 3M announced it would phase the chemicals out of production. 

Defence denied that all members of the Oakey class action had suffered an “interference with the use and enjoyment” of their land. It argued that inhaling dust from soil, growing plants or consuming meat from sheep and cattle reared on the land all presented a low and acceptable risk of exposure to the chemicals in humans. 

“Typical use of the land will, for most group members, present a low and acceptable risk of ongoing exposure,” the defence said.

Whether a group member had suffered such an interference would depend on the location and nature of their property, the degree to which its soil and groundwater had been affected, and how significant the consequences were, it said. 

It was also argued Shine had failed to identify the “nature of the alleged toxicity or toxic effect” of PFAS. 

The defence was filed by the Brisbane arm of King and Wood Mallesons. It describes itself as a “leading international law firm” headquartered in Asia.