The Federal Environment Department ruled against the advice of the Government's own water experts when deciding Adani's North Galilee Water Scheme, in Central Queensland, did not require a full environmental assessment.

Key points: Department of Agriculture and Water Resources told Environment Department Adani project could have "significant impact on water resources"

Department of Agriculture and Water Resources told Environment Department Adani project could have "significant impact on water resources" That description should trigger part of legislation relating to water management and require full environmental assessment

That description should trigger part of legislation relating to water management and require full environmental assessment Environment Department maintains water project does not need that level of assessment

Documents obtained under Freedom of Information (FOI) and provided to the ABC by activist group Lock the Gate Alliance showed the Department of Agriculture and Water Resources wrote to the Environment Department suggesting the project could activate what is known as the "water trigger".

The "water trigger" was established in 2013, specifically to ensure gas and coal mining projects likely to have a significant impact on the country's water resources, underwent a full environmental assessment.

But in September, the Department of Environment ruled Adani's water project, which has plans to extract up to 12.5 billion litres of water a year from a river in Queensland to support the Carmichael coal mine, did not activate the trigger because it considered the water project separate to the mine.

The new documents show that conclusion was counter to the view of experts in the Department of Agriculture and Water Resources, which was expressed to the Department of Environment before it made its decision.

The Department of Environment initially refused access to the documents, only revealing them once Lock the Gate Alliance appealed against that decision.

The submission from the Department of Agriculture and Water Resources read:

"The department considers the proposed action could have significant impact(s) on a water resource, in relation to coal seam gas development and large coal mining development, protected under the EPBC Act."

According to the act, that description fits the requirement needed to activate the "water trigger".

Warwick Giblin is managing director of consultancy OzEnvironmental and has worked in environmental management for decades.

Mr Giblin told the ABC the FOI document was important.

"It's significant on a number of counts," he said.

"It said the project could have significant impacts on the water, not just any impacts but significant ones."

The North Galilee Water Project is still being assessed by the Federal Government, which involves a less rigorous review, via "preliminary documentation".

According to the Department of the Environment's assessment manual, that approach is used when the degree of public concern associated with a proposal is "low", when the degree of confidence of the impacts is "high", and when those impacts are "short-term or recoverable".

Mr Giblin said the FOI documents showed that form of assessment was probably inadequate.

"The Department of Agriculture and Water Resources says that to make a judgement you need robust baseline data on surface and groundwater," he said.

Mr Giblin said collecting that data could take three years and was not something that could be done without a full environmental assessment.

"You're kidding yourself really if you make a decision in the absence of that information," he said.

Action will 'clearly have an impact on water resources'

The principal solicitor at the Queensland Environmental Defenders Office, Sean Ryan, said the Environment Department should explain how it came to its decision to not require a full environmental assessment.

"It is concerning when these significant environmental laws are not applied to an action that clearly will have a significant impact on water resources," he said.

Carmel Flint from the Lock the Gate Alliance said she was astounded by the situation.

"We were really shocked to see that these documents had given some pretty clear advice to the department that there was a serious risk to water resources and that they ignored that and pushed thorough the Adani project without requiring an environmental impact assessment," she said.

"So it just raises real questions about what's going on inside government.

"We've got a department who has this key role of looking after water and agriculture basically raising this concern, saying they consider there would be a significant impact on water resources, and they've effectively been overruled.

"That's just not good enough."

Adani 'has been subject to more than 150 ... conditions'

In a written statement from both the Department of Environment and the Environment Minister, assurances were made that the advice of the Government's other departments was considered.

"The Adani project has been subject to more than 150 state and federal government conditions, so we are confident any potential impacts are being adequately assessed," the statement read.

Ms Flint is calling on Environment Minister Melissa Price to act.

"We're really calling for the Minister now to urgently step in and reverse the decision and require a proper environmental impact assessment and fully apply the water trigger," she said.

"We'd also really like to know how it was that this advice came to be ignored by the Department for Environment."

Adani successfully argued its water project was a standalone one, and not part of a coal-seam-gas or large-coal-mining development.

It is an argument the company stands by.

"The definition of 'large coal mining development' relates to impacts on water-resources activities that form part of the process to extract coal," an Adani spokesperson said in a statement.

"This assessment already occurred in 2015 through the Environmental Impact Statement process [for the Carmichael mine].

"The pipeline is considered associated infrastructure, which is not part of the coal-extraction process and therefore does not require assessment under the water trigger."

Mr Giblin said that argument made no sense.

"Unequivocally, there is no mine unless it has access to water and I think it's rather cute [to] suggest that somehow this project — which is only triggered because of this mine proposal — is a separate project," he said.

In a statement, the miner said the amount of water it would be looking to take equated "to 12.5GL of water or less than 1 per cent of the annual water flow available in the Belyando Suttor River catchment".

"This water can only be taken when the river system is in flood, after other users, like farmers, have taken their share, and only when the river is flowing at a rate of 2,592 megalitres per day," it said.

The full statement from the Federal Department of Environment and Environment Minister is below: