A historic legal settlement last week offers the prospect of justice to scores of residents of Williamtown and two similar sites in Queensland and the Northern Territory affected by toxic fire retardant chemicals widely used by the Australian military.

But questions remain about why it took the federal government so long to agree to this deal and what still needs to be done to clean up the mess.

In the Federal Court last week, the Department of Defence finally agreed to pay compensation for polluting sites with chemicals known as per- and poly-fluoroalkyl (PFAS) that were used in firefighting drills.

The risks from PFAS have been known for decades and 3M, the US manufacturer, started to phase them out almost 20 years ago.

But the federal government was slow to react and it was only lawsuits in the US that alerted residents here to the risks. About five years ago it emerged, thanks to an investigation by the Sydney Morning Herald and the Newcastle Herald, that on a single road in Williamtown there were 50 suspicious cases of cancer.