Hallador Energy subsidiary Sunrise Coal has proposed an extension of the Oaktown 1 underground thermal coal mine in Indiana, US.
Platts quoted an Indiana state official saying that the extension plans may possibly include below the Wabash River and into reserves in Illinois that are owned by the company.
As part of its extension proposal, Sunrise Coal submitted an application and requested the Indiana Division of Reclamation for the addition of 9,690 acres of underground area to the mine.
Indiana Division of Reclamation technical services section assistant director Pete Sartoris said in an interview: "It's an extension of their current mining, which is getting pretty close to that area so they want to add it on."
Once the company obtains approval for its request, it will be able to tunnel right to the middle of the river, Sartoris added.
In order to finalise the tunnelling into Illinois, Sunrise Coal needs to obtain approval from the Illinois Department of Natural Resources.
In July 2014, Sunrise Coal acquired the Oaktown 1 and Oaktown 2 underground coal mines from Vectren Fuels in a deal worth $296m.
According to Sartoris, a final decision on the company's extension request may not take place until early 2016.
Oaktown 1 can be extended westward over a Texas Gas Transmission's natural gas storage field once the new permit is approved.