Whitehaven Coal, which owns mines near Boggabri, Werris Creek, Gunnedah, Narrabri and Maules Creek, is among the companies being investigated.

In May it received permission to bury around 600 tyres at Tarrawonga Mine and a further 68 at Werris Creek Mine, but there are concerns some may have been buried prior to gaining approval, or at other sites such as Maules Creek where it was not permitted to do so.

Lock the Gate Alliance (LTGA) has accused the company of getting approval through the back door.

The EPA said all mines in the region were being watched closely in order to ensure each site was abiding by its own set of rules and environmental law.

"The NSW EPA is investigating allegations that tyres have been buried at coal mines in the Namoi region," a spokesperson confirmed.

"The EPA will continue to monitor all environmental impacts of the mines, including end-of-life tyre waste, and ensure compliance with licence conditions."

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No decisions or penalties are yet to come from the investigation, but if wrongful behaviour is found to have been committed then LTGA is calling for strong action, stating it was time the state government "threw the book" at Whitehaven.

The alliance has written to the NSW Department of Planning, Industry and Environment Department, as well as the EPA, calling for the company to be heavily prosecuted for any breaches of conditions.

Its decision not to recycle tyres has also come under the blowtorch from environmental groups, but the company said it is looking at opportunities to do so, while also working with the EPA on its inquiry.

"On-site disposal of tyres is permissible in NSW under certain circumstances and is a practice observed by industry participants both here and in other jurisdictions around Australia," a spokesperson said.

"We always work cooperatively with the EPA, we have been discussing this matter with the EPA for some time and understand the agency is reviewing tyre disposal across the whole North West NSW region with a view to ensuring practical and consistent approaches.

"We acknowledge the interest in, and importance of, good tyre stewardship; it is an area industry is looking at more closely and Whitehaven is committed to reviewing its approach regularly to assess the feasibility and cost-effectiveness of alternative approaches."

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