Gas company Inpex has been fined after it was found to have released PFAS from its new $37 billion LNG processing plant site on Darwin Harbour.

Key points: The Federal Government found Inpex evaporated PFAS water at its plant instead of trucking it away

The Federal Government found Inpex evaporated PFAS water at its plant instead of trucking it away Inpex was fined $12,600 for infringing its environmental management plan

Inpex was fined $12,600 for infringing its environmental management plan Inpex says it paid the fine even though it believed it had complied with the plan

A Federal Environment and Energy Department investigation found the release of the PFAS in September last year put wildlife, including dolphins, and dugongs at risk.

Under its approved environmental management plan, Inpex was required to store water containing PFAS (per-fluoroalkyl and poly-fluoroalkyl substances) from firefighting exercises held on the site, and then transport the water interstate for treatment at a licensed facility.

Instead, the Department found that "in September 2018 Inpex boiled wastewater from firefighting tests that contained PFAS".

The Federal Environment Department found the release could put turtles, dolphins and dugongs at risk. ( ABC News: Jane Bardon )

The activity, the Department said, "is likely to have released PFAS into the air and therefore may have placed the immediate environment, including Darwin Harbour, at risk of heightened PFAS levels."

The Department concluded that posed a threat to the harbour's wildlife.

"Darwin Harbour is habitat for EPBC Act listed threatened and migratory species including dugongs, multiple cetacean species, two sawfish species, saltwater crocodiles and multiple sea turtle species," it said.

It fined Inpex $12,600 in April.

Inpex claims no leak

Inpex said that when it tested its firefighting systems a large amount of wastewater, containing a small amount of PFAS, was generated.

Inpex said that a process called "enhanced evaporation", designed to minimise the load of wastewater it would be required to truck interstate, was then used.

"Enhanced evaporation was used to reduce the amount of wastewater needing to be transported," it said.

The company said that it paid the fine even though it believed it had complied with its environment management plan.

"At no stage in this process did wastewater leak into the external environment," it said.

"Inpex considers this process was done in accordance with all approvals but nevertheless made the requested payment when a notice was subsequently received."

'What action is going to be taken?'

The findings of the Federal Environment Department's investigation were revealed through a Freedom of Information by the Australian Conservation Foundation.

"It's good that the Federal Environment Department is cracking down on toxic pollution spills, which are a threat to precious wildlife, but a $12,600 fine clearly does not send an adequate signal to business," the foundation's nature program manager Jess Abrahams said.

The Department said the fine issued to Inpex was "proportional enforcement relative to the offence and (Inpex's) compliance history".

It noted that news of the PFAS release would be controversial in a city where there is already PFAS contamination from the use of fighting foam on defence bases, saying "communities affected by PFAS contamination … are highly sensitised to the issue".

Larrakia woman Donna Jackson said Indigenous people regularly eat shellfish on the estuaries of Darwin Harbour. ( ABC News: Jane Bardon )

Former Larrakia Indigenous ranger Donna Jackson co-authored the PFAS assessment report on which the Northern Territory Government based its advice to limit shellfish intake from Darwin Harbour creeks to three times a week.

"I don't understand why Inpex would think that in 2018, when there is so much knowledge about PFAS, that they would make this decision, and what action is going to be taken over this?" Ms Jackson said.

The Northern Territory Environment Protection Authority has told the ABC it hasn't finished its investigation into the PFAS release by Inpex.