On May 16, Shoalhaven City Council was notified by Sikorsky Aircraft Australia, who provide maintenance services to HMAS Albatross, from the nearby Aviation Technology Park, that it had had an unintentional waste water discharge containing PFAS, into the Shoalhaven sewerage system in March this year.

The sewerage system flows to the Nowra sewerage treatment plant which ultimately discharges into the Shoalhaven River near Terara, approximately 2km east of the Princess Highway.

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Mrs Krough said by the time the waste water was discharged into the Shoalhaven River it had been treated at the Nowra works.

"It would have been heavily diluted" she said.

"There was 100,000 litres in the discharge, we treat six million litres a day at the Nowra plant.

"From a dilution perspective that wasn't our main concern, it was how this had happened in the first place.

"How this could physically happen? How it could happen from a management perspective? That is the main focus of our investigation."

Shoalhaven City Council is the lead investigator of the incident with EPA providing support and advice.

"We don't know how the discharged happened," Mrs Krough said.

"That's what we are investigating.

"We advised the EPA as soon as Sikorsky advised us of the unintentional discharge into the sewerage system.

"Sikorsky had been waiting for approval to do a treated discharge into the sewer, where they treat waste water before putting it into the sewer.

"That approval was in place but we understand when they went to do the treatment, they discovered the waste water had already been released.

"From our perspective there are a number of questions Sikorsky needs to answer.

"We are looking at their whole system process to ensure this can't happen again.

"We will go through the due process and find out the facts."

She confirmed the first council knew of the incident, which reportedly happened in March, was when Sikorsky self reported.

"We were notified on May 16 and advised the EPA and Health straight away as our regulatory body and as our protocols require," she said.

"From the treatment perspective EPA has decided no additional notifications were required on the current restrictions in place on the river.

"The main issue is from a regulatory perspective, how could this have happened?"

Mrs Krough confirmed a quantity of treated waste water from the Nowra treatment works was still being discharged into the Shoalhaven River.

"That is why we are doing the major upgrade of both the Nowra and Bomaderry treatment plants, which are actually being commissioned at the moment, which will allow both schemes to be joined with Shoalhaven Water's Reclaimed Water Management Scheme (REMS)," she said.

The project, the largest ever public works project to be undertaken in the Shoalhaven, is worth $110 million.

"At the moment only one local farmer and the Shoalhaven Ex-Servicemen's Worrigee Links golf course has access to the Nowra treatment water," Mrs Krough said.

"Once work is completed the two plants will become part of the REMS program."

Sikorsky Australia confirmed "an incident had occurred".

"The matter has been reported to the appropriate authority for further investigation," the spokesperson said.

"As such, we are unable to comment at this time."