The Montana Department of Environmental Quality said any interested party that wanted to provide input on the plan had until September 30 to do so.
Signal Peak is seeking to expand the area of its Bull Mountain mine permit near Roundup by 7161 acres and grow the mine from five longwall panels to 14 longwall panels.
The producer, which initially submitted its request in October 2012, is also seeking the ability to disturb 20 surface acres as well as the continuance of its mining activities.
The DEQ determined the company’s application was complete in December 2012 and deemed it acceptable earlier this month on September 3.
The agency is accepting all comments via mail to its Helena office or by email.
The mine’s application can also be viewed in its entirety online at the Montana DEQ web site.