On day five of the exhausting record-longest IPC public hearing, Mr Jackson told Commissioners farmers don't back the proposed $3.6 billion scheme.

"Our members have considered this project carefully and believe it poses an unacceptable risk to the water resources, soil and air quality, local food and fibre production and rural communities in western New South Wales," he said.

Mr Jackson told the IPC the government's own independent water expert panel identified the scheme could affect groundwater.

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The public hearings, which attracted a record 404 registrations to speak against the project, are the climax of a two-decade struggle over the plan to construct 850 coal-seam-gas wells in and around the Pilliga forest. They could be the final stage before the IPC refuses approval or signs off on the scheme.

Some 68 people were slated to speak on the project on Friday, with the seven-day hearings set to continue on Saturday before going on hiatus for a week.

Commissioners spent the week listening to residents tell them the project will make or break the town of Narrabri, with the local business chamber calling the mining plan a "wonderful opportunity", while dozens of farmers and experts took turns denouncing it as a threat to groundwater, the region's ecology and the planet's climate.

Gunnedah Indigenous elder Dolly Talbott told the IPC the project threatens to destroy "vast tracts of intact sacred places and burials" and said Santos failed to properly consult with the region's traditional owners.

"I'm not an alarmist or exaggerating risk," she said.

"Santos already has a legacy of toxic contamination of aquifers and I fear for my family and community and all communities reliant on the Great Artesian water supply."

She said the IPC should conduct consultation on country, saying elders were unable to reveal secret sacred information in a public hearing.

Ms Talbott was defeated earlier this week after challenging approval of the Shenhua Watermark open-cut coal mine on the Liverpool Plains in Federal court.

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Tessa Rainbird, of Tamworth Parents and Friends for Climate Action, showed the IPC the faces of children she said they would be failing if they approved the project.

By the time her one-year-old daughter is 12, she said, human decisions will have already determined whether she has a future.

"It is with this knowledge that I appeal to you with unapologetic emotion on her behalf," she said.

"To secure our continued existence on the planet we need to halve our projected greenhouse gas emissions by 2030, a goal which we are far from being on track to achieve and one which the Narrabri Gas Project would work actively against."

She finished by asking the Commissioners to "please think of our children".

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Lee O'Connor of the Coonamble and District Chamber of Commerce told the IPC of their 80-odd members just one business backed the project.

Their members cite the region's water supply, climate, economic impact on agribusiness for their opposition, she said.

The Narrabri gas project would create more economic problems than it would solve, she said, and compared its impact on employment to a "small feedlot".

Wilderness Society representative Eleanor Lawless told Commissioners the proposed project would threaten the potentially endangered Pilliga mouse.

"It may be a small brown mouse but it is our small brown mouse and we can't fail it," she said.

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