Western Australia's Chief Justice has ruled that some of the environmental approvals for the controversial $40 billion Kimberley gas hub were unlawful.

Chief Justice Wayne Martin ruled that three of the Environmental Protection Authority's (EPA) decisions to grant approval to the project were unlawful and invalid.

The EPA's chairman Paul Vogel made the final decision on the project on his own.

He decided to allow the project to go ahead at James Price Point, north of Broome, after four out of five EPA board members declared conflicts of interest.

Dr Vogel had allowed three of the board members to be a part of the early decision-making process.

The Chief Justice said the decisions taken at those meetings were invalid.

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The Wilderness Society and traditional owner Richard Hunter last year launched legal action against the EPA and the Environment Minister over the approvals for the gas hub, which would accommodate Woodside.

Woodside subsequently scrapped its onshore processing plans due to escalating costs, however, the court proceedings continued.

The Wilderness Society's Peter Robertson has called for Dr Vogel and former environment minister Bill Marmion to stand down.

"As soon as we discovered the extent of the conflicts of interest on the EPA board, before they made their decision, we wrote to the EPA and we wrote to the Minister and said they cannot proceed with this decision," he said.

"[Marmion] was told at that time that he should not proceed with that decision because it was likely to be unlawful and he ignored that.

"They ignored us and I believe [Vogel] has made a fatal error in judgement and his position as chairman of the EPA now very much needs to be brought into question."

The WA Premier Colin Barnett says the EPA members and the EPA chairman have done nothing wrong.

"In no way did they behave improperly or seek to gain in any way so their integrity is not in doubt at all," he said.

Mr Robertson has previously said that once the EPA members declared their conflict, a separate group of people should have been appointed to assess the project.

"Instead of having a minimum of three EPA board members, they reduced it to just one member of the five member EPA board making the final decision," he said.

"That is just a gross misuse of decision making processes of the EPA."

'Sad state of affairs'

WA's Opposition Leader Mark McGowan says the process around the gas hub project was mishandled from the beginning and the Government needs to be held accountable.

"The minister of the day bears responsibility but also the Premier bears responsibility," he said.

"This was his project, he was the one who mucked it up, he was the one who put the Kimberley through all this turmoil.

"He's the one who has cost the state so many millions of dollars."

The Wilderness Society says the legal challenge was expensive but it felt it had to go ahead with it.

"[It's about] restoring some confidence and faith in the way that the EPA operates and the way it conducts its environmental assessments," Mr Robertson said.

"If groups like us don't do things like this then they, the Government, will end up getting away with very shonky decision making processes and that can't be allowed to happen."

"When you see an independent statutory body being reduced to nothing more than basically a political facilitation agency for the government, then that's a very, very sad state of affairs for Western Australia, and for our environment and future generations."

Government to seek advice on ruling

Environment Minister Albert Jacob says he will seek advice from the State Solicitors' Office on the ruling.

"From my experience, those rulings are generally fairly lengthy and require some good reading and good consideration," he said.

He says he will comment on the ruling later.

The head of the EPA is on a site visit in the Goldfields but a spokeswoman says necessary steps will be taken once the authority has fully considered the ruling.

The state has been ordered to pay two-thirds of the Wilderness Society's legal costs.

The ruling could also have ramifications for other projects.

Lawyer Patrick Pearlman says other decisions made by the EPA could be called into question.

"My understanding is that there are a number of other EPA proceedings in which questions about section 12 interests arose and I've got a number, something like 40 running around in my head, where that question applies," he said.

"Whether or not it has any fallout from that, I suppose, is probably something for Parliament."

The Wilderness Society hopes the court ruling will be the end of any development at James Price Point, and says it will fight any further development applications.

The Greens have also called on the Government to abandon any future attempts to industrialise the site but Mr Barnett says the government will most likely re-submit its plans to the EPA.

The Premier is confident the original approval will stand.

"Most fair-minded people would acknowledge that the environmental decision itself is correct, what was invalid is the actual process," he said.

The State Government has been pushing ahead with plans to compulsorily acquire the land.

It plans to secure almost 3,500 hectares of land on the coast north of Broome in case other companies would like to pursue the development.

Woodside, with its partner Shell, is believed to be pursuing floating LNG technology for its Browse Basin gas, an offshore processing option.