Western Darling Downs residents say they are being kept in the dark about possible widespread contamination from Linc Energy's experimental coal gasification plant at Chinchilla, west of Brisbane.

The ABC obtained a secret State Government report that found hundreds of square kilometres of prime land in the southeast Queensland food bowl are at risk from a cocktail of toxic chemicals and explosive gases.

The study, commissioned by the Environment Department, alleges Linc's trial plant had caused irreversible damage to strategic cropping soil, contaminated aquifers, and made workers sick from exposure to poisonous gases.

After the biggest probe in its history, involving 100 investigators, the department launched a $6.5 million criminal prosecution of the company, alleging it was responsible for "gross interference" to the health and wellbeing of former staff as well as "serious environmental harm".

The Palaszczuk Government refused to comment on the 335-page experts' report, which has been disclosed to Linc but not to landholders such as Shay Dougall from nearby Hopeland.

Ms Dougall wants to know why the investigation results are being kept from the people potentially at most risk.

"Not one comment about what is being done to manage the health and safety of the landholders who've been exposed to this 24/7, and who've been complaining about it for the past three years," she said.

"We've experienced nausea, sore eyes, headaches when we've been exposed to the odour.

"I don't understand it, it's an unacceptable approach for the Government to be using.

"But this is the Government's approach: it's allowed this activity to happen, it's allowed this to happen with no base site testing, not enough oversight and management, and no parachute.

"And here we are suffering the results of this poorly managed experiment at our detriment and we're still guessing what's to be done."

Ms Dougall said she wanted a "very overt, very detailed" plan to be devised and shown to landholders.

"Like this is the plan for managing the contamination, this is the plan for going forward and ensuring it's contained and for the best part made good," she said.

All we want is absolute truth, Mayor says

The Environment Department put a caution zone of 320 square kilometres around the controversial site, where successive Queensland Governments allowed Linc to ignite seams of coal underground in the hope of producing cheap diesel fuel.

Western Downs Mayor Ray Brown admitted he was worried, even though the department assured him there was no immediate risk to human health.

"All we're after from both the Government and the company involved is the actual truth; that's all we want for our people is the truth, what we need to be dealing with," Cr Brown said.

"Because we understand the underground coal gasification was a demonstration plant, we are all aware of that.

"It was under control and monitored by the government, over many governments, by the way, it's not just one.

"All we want for our people is the absolute truth, be forthcoming with it so we can make determinations on it.

"It's in prime agricultural land in the Hopeland district, and our number one concern at the moment is the environment, and that includes people."

In a statement to the ABC, Linc Energy denied all charges against it.

It said the Environment Department had begun legal proceedings "without sufficient scientific evidence".

Linc said naturally occurring sub-soil processes were the most likely cause of the gases detected, and the investigation represented a "monumental mishandling of Queensland's strained financial resources".