The ABC reported on Monday night that the 335-page experts' report has put more than 300sq.km of prime agricultural land in south-eastern Queensland at risk from “a cocktail of toxic chemicals and explosive gases” with soils around the former UCG project already showing permanent acidification.

The state government is pursuing a $6.5 million criminal prosecution of Linc for "gross interference" to the health and wellbeing of former workers at the plant as well as "serious environmental harm".

The report found concentrations of hydrogen in the soil at “explosive levels” and abnormal amounts of methane it believes are being generated from the coals that Linc ignited during its trials.

The ABC asked the magistrate in the case to release other documents that show four departmental investigators were hospitalised with suspected carbon monoxide poisoning during soil testing at the site in March

The carcinogen benzene was also detected in the soil.

Earlier this year the government became so concerned it declared an excavation exclusion zone on 314sq.km around the Linc facility where landholders are banned from digging any hole deeper than two metres.

It told landholders there were otherwise no immediate concerns with air and water quality in the region.

The wide-ranging investigation, conducted by consultants Gilbert & Sutherland and investigators from the University of Queensland, concluded that Linc injected air into the coal seams it wanted to ignite at pressures that were not suitable for the geological conditions, causing the surrounding rocks and overburden to fracture, breaking the seal and allowing the gas to escape from the ignited coal seam into the surrounding soils.

"We have found gases in quantities above the explosive limit. In our reconnaissance boreholes, explosive levels have been found that indicate very much higher concentrations in the soil atmosphere," Gilbert & Sutherland reported.

"The degree of contamination is widespread, of high impact and, in part, irreversible,” the report says.

It found the contaminants and biogenic methane are at risk of release during normal land use including agricultural operations.

"Placing contaminants within the overburden where they will be re-entrained over time as the groundwater level re-establishes potentially exposing these landholders to these contaminants over time and potentially impacting soil and ecological health and land use," the report noted.

Linc, which is now based in Singapore, has denied any wrong-doing and says the government lacks sufficient scientific evidence.

It says there are naturally occurring sub-soil processes at fault, and it has refused to pay a further $22 million in financial guarantees to help cover the cost of any clean-up.

The company says it would need to restructure its global operations to meet any such demand, given it has convertible notes due for payment in 2018 of almost $US140 million

Gilbert & Sutherland’s report flatly contradicts Linc’s claims it is not at fault and concluded that there is no other possible source of contamination given the contaminants are all known products of UCG activities and have the same gas fingerprint as those established under laboratory conditions.

It further concluded that Linc should have known it was unsafe to ignite the coal seam because it had fractured the rocks, with contamination of syngas and wastes inevitable.

Last month Linc was also slugged a $US20,000 ($A27,000) fine for violating permit requirements in its exploration work around the UCG potential of the Cook Inlet.

Its US production is around 1400bopd from the Gulf Coast and Wyoming.