Santos' coal seam gas wastewater facility in the Pilliga forest was judged legal by the court.

People for the Plains argued the company’s Leewood wastewater facility, which was assessed as a petroleum exploration project, should be treated by as an independent development that would have to go on public exhibition.

However, on Monday, the Land and Environment Court decided the approval was valid, which means the facility can now begin operating and is expected to treat up to 1.5 million litres of CSG wastewater every day.

Wilderness Society spokesperson Naomi Hodgson said the packed court room was left “disappointed and deflated” by the judgement.

“If an industrial facility of this scale and nature does not require public scrutiny and an environmental impact statement, then it’s quite clear the laws need to be looked at further and strengthened,” Ms Hodgson said.

“Despite the outcome, we are still determined to protect the region from CSG.”

Environmental Defenders Office principal solicitor Sue Higginson, who represented People for the Plains in the court case, said the group would look at the judgement closely to explore their options for an appeal.

“The public exhibition of major developments is a key foundation of a well-functioning planning system,” Ms Higginson said.

“It’s a right that has been embedded in Australia’s environmental law since the ‘70s, for good reason: public participation brings about better planning decisions and ensures transparency and accountability. Without this fundamental right, we’d be a much poorer nation.”

A Santos spokesperson said the company welcomed the decision.

“This reverse osmosis plant is similar to those used across the world and will be used to treat salty ground water produced by Santos’ exploration and appraisal operations to a very high standard, so it can be used for irrigation activities,” the spokesperson said.