The Larrakia Nation Aboriginal Corporation, representing the Traditional Owners of Darwin, has condemned the "nearly 20-year" methane leak at Santos's Darwin LNG export facility as an "outrageous environmental and cultural affront".

Larrakia Nation Chairperson, Travis Borsi, said on Tuesday that the situation is unacceptable.

"As the Traditional Owners of Darwin, we will not stand silently as our country is degraded in this way," he said.

"This ongoing methane leak is unacceptable. Our land, our health, and our climate deserve better.

"To be ignored by Santos's Managing Director and CEO when we requested a meeting only adds insult to injury. It demonstrates an arrogance that they believe they can do whatever they like on Larrakia Country. We demand action now."

Larrakia Nation Aboriginal Corporation said the leak, estimated at up to 184 kg per hour, has continued "unchecked since 2006, despite awareness from multiple regulators".

"This persistent emission has contributed significantly to the global climate crisis, particularly given methane's extreme potency over short timescales," the organisation said.

The Corporation also claimed widespread and significant regulatory failure, alleging that multiple federal and territory agencies, including NT EPA (Environmental Protection Authority), NT WorkSafe, Clean Energy Regulator, NOPSEMA, and CSIRO, were "aware but took no remedial action".

"This represents not only a regulatory failure but a failure to uphold environmental responsibilities," Larrakia Nation said in a statement.

"Allowing this leak to continue not only damages the environment, it disrespects the Larrakia people's role as custodians of Country. The integrity of our land, air, and sea has been compromised by unchecked industrial activity."

Larrakia Nation called for: "Immediate and transparent action by Santos to fully repair and contain the methane leak; a full, public independent inquiry into the regulatory oversight failures that enabled this ongoing environmental harm; and enforcement of accountability by federal and territory governments to ensure no repeat of such negligence."

NT Minister for Lands, Planning and Environment Joshua Burgoyne told National Indigenous Times the leak in the LNG tank was reported to the then Labor government, and the Territory's EPA, in 2020.

"The EPA continue their important work monitoring air quality and are best placed to work with the proponent to make sure these issues are dealt with and mitigated," he said.

NT EPA chairperson Dr Paul Vogel said the agency is aware of fugitive methane leaks from the Santos LNG tank.

"Fugitive emissions occur at all LNG facilities however, the cause of the emissions from the DLNG tank is unique to this facility," he said.

"The estimated emissions from the LNG tank leak are approximately equivalent to one per cent of Santos's facility's total annual greenhouse gas emissions and approximately 0.1 per cent of the NT's emissions.

"It is important to note that methane is not classified as a toxicant. While methane is a flammable gas and can cause asphyxiation at very high concentrations, sampling by Santos has confirmed that fugitive emissions from the tank are significantly below hazardous levels."

Dr Vogels said the NT EPA did not report the leak to the public because "at these levels they do not pose any risk of explosion and negligible risk to human health or the environment".

"According to Santos, the leak at the DLNG tank originated during its initial commissioning in 2006 due to a design fault. This was reported to the NT EPA and NT WorkSafe at the time, and an independent investigation subsequently cleared the tank for continued use," he said.

"While the NT EPA will continue to monitor the situation, the facility's fugitive methane emissions are adequately regulated through the Safeguard Mechanism and any duplicative regulation by the NT EPA of the same emissions makes no sense whatsoever."

On Tuesday, Federal Minister for Climate Change Chris Bowen was questioned on the methane leak by the Member for Kooyong Dr Monique Ryan during question time in parliament.

Dr Ryan noted that the Darwin LNG facility "has been leaking massive amounts of methane for almost 20 years".

"Three federal bodies, NOPSEMA, CSIRO and the Clean Energy Regulator have known and done nothing. Underreporting like this makes a mockery of the safeguard mechanism and of your claims about decreased emissions," she said, and asked the Minister if he would deny Santos any further approvals until it acts to rectify the problem.

"(In) relation to the particular incident, I am concerned to read about that," Mr Bowen said of the leak.

"I have asked my department to ensure that the expert review of methane emission management which I commissioned, the Government Commission, led by the former chief scientist, Dr Cathy Foley, examines the matters raised, and ensures that it's considered in their deliberations.

"And I will update the Honourable Member and the House when I've received the report from the former Chief scientist."

National Indigenous Times has contacted Santos for comment.