BILLINGS, Mont. (AP) — State environmental regulators have given the OK to expanding a coal mine in southeastern Montana and set a $13.7 million cleanup bond.

The Department of Environmental Quality is taking public comment through Tuesday on Westmoreland Coal Co.'s proposed 10-square mile (27-square kilometer) expansion of the Rosebud Mine.

Anne Hedges with the Montana Environmental Information Center tells The Billings Gazette she doesn't believe the bond is high enough while the Northern Plains Resource Council says the expansion sits on top of an aquifer that supplies area ranches.

Northern Plains chairwoman Becky Mitchell says because Westmoreland has filed for bankruptcy it likely will sell the mine and the eventual buyer should be scrutinized on their own merits.

Kristi Ponozzo with the DEQ says the agency cannot be prejudiced against Westmoreland because of its October bankruptcy filing.