EPA director of regulatory operations Stephen Budgen said the authority's investigation found evidence that every coal mine in the Namoi region had buried their tyres without the necessary licence conditions.

The investigation followed allegations that a Whitehaven Coal mine had buried waste tyres in June 2020.

"We found instances of tyres being buried without necessary licence conditions at various times between 2014 to 2020," he said.

"While no environmental harm was found to have occurred, the EPA issued official cautions to all six of the open cut coal mines we investigated."

The Northern Daily Leader contacted Whitehaven, which owns all but one of the coal mines, for comment - but it declined.

Maules Creek resident Libby Laird said the mining companies had gotten away with just a slap on the wrist over the burial of burying "potentially hundreds of giant machinery tyres over a six-year period without an environmental licence".

"These tyres are buried deep underground and could have a disastrous impact on our groundwater and local environment," she said.

"The EPA's own guidelines say cautions can be issued to companies if the offence is 'minor'. I would argue that the burial of hundreds of giant machinery tyres without permission is not a minor offence."

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She said the huge tyres will make land rehabilitation difficult or even impossible.

Lock the Gate Alliance NSW spokesperson Georgina Woods said coal mine operator Whitehaven should be stripped of its right to operate in NSW.

"Only last week Whitehaven was fined in the Land and Environment Court for offences committed at its Narrabri Underground Mine, and this week is in court again to be sentenced for stealing a billion litres of water at Maules Creek - a crime to which the company has already pleaded guilty," she said.

"These offences come on top of at least 35 other offences the company has been fined or cautioned over since 2012. Whitehaven is a repeat offender and the penalties it has received so far have clearly not prompted a change in its attitude."

The EPA did not find evidence that these tyres were brought onto the mine sites from other areas.

In April Whitehaven applied for approval to bury as many as 150 tyres at its Werris Creek Coal Mine.