The government-owned firefighting service at Darwin Airport "disregarded" directives designed to prevent the release of potentially toxic PFAS chemicals into nearby waterways, an investigation has found.

Key points: The investigation was sparked by whistleblower allegations made by a former Darwin Airport firefighter

The investigation was sparked by whistleblower allegations made by a former Darwin Airport firefighter It found Airservices' Darwin unit "failed to comply" with measures designed to manage PFAS chemicals on-site

It found Airservices' Darwin unit "failed to comply" with measures designed to manage PFAS chemicals on-site A spokesman for Airservices said the company "takes its environmental management responsibilities very seriously"

The corporation responsible for the service, Airservices Australia, also failed to act after being alerted to problems with wastewater disposal at the site and after "repeated indications of non-compliance".

The review was sparked by allegations made by a whistleblower firefighter who said that firefighting foam containing PFAS chemicals was being "covertly dumped" from the site.

Investigators from the Federal Department of Infrastructure interviewed Airservices staff and examined documents about the site's environmental management dating back to 2010.

"The investigation found that … [the Darwin airport service] failed to comply with a number of national directives from Airservices and its own local instructions," he said.

"This resulted in non-conformances that may have had potential adverse impacts on the environment."

But the report has not found any breaches of the Federal Airports (Environment Protection) Regulations, nor recommended any sanctions against Airservices Australia.

It recommended the entity expand its current environmental monitoring program to include routine testing of surface and groundwater.

It also recommended a risk assessment of PFAS leaching from the fire training ground at the site and an external audit of its environmental management system.

Non-compliance 'should have triggered intervention'

PFAS chemicals were historically used in firefighting foams at airports and on defence bases around the country, but were phased out in most locations from around 2010.

Darwin's airport is only now transitioning to a PFAS-free foam, but that work is not due to be finished until mid-2019.

Darwin's Rapid Creek flows alongside the northern boundary of the airport. ( ABC News: Xavier La Canna )

The whistleblower's claims were condensed into eight core allegations — the report found three were substantiated in part or in full, with insufficient evidence to prove one of the remaining five.

It found there was a "recurring issue" with the analysis of the quality of wastewater being discharged.

"Airservices did not monitor stormwater quality or act on the recommendations [from regular audits] with regards to assessing the risk of releasing wastewater to stormwater [drains]," the report found.

"Additionally, Airservices did not respond to issues identified in the audit and assurance reports that indicated Darwin personnel were not operating in accordance with national directives and local instructions.

"Such repeated indications of non-compliance should have triggered intervention."

In one instance, the report found the Darwin station "disregarded" a directive to only use one particular training ground in the dry season in order to avoid discharge of wastewater into stormwater.

It also confirmed wastewater had been used for irrigation purposes on the defence side of the airport.

The report noted that Airservices had revised its environmental management systems during the course of the investigation.

But it said "insufficient time [had] elapsed" to determine if practices had changed.

Last year an independent panel advised the Australian Government there was limited or no evidence to link exposure to PFAS chemicals with human disease, but health effects could not be ruled out.

Airservices 'takes environmental responsibility seriously'

In a statement to the ABC, a spokesman for Airservices said the company "takes its environmental management responsibilities very seriously".

"Airservices has already implemented improvements that address the majority of issues identified and is acting on the report's other recommendations," the spokesperson said.

"Of the eight allegations investigated, six were disproven or unsubstantiated, and there were no regulatory breaches identified."

The company noted that the whistleblower had been "terminated for reasons not related to this investigation".