The BLM announced on Friday that it had approved the Sunset Trail Area Coal Exploration Plan, submitted by Ark Land Co on behalf of Mountain Coal Co. Both are subsidiaries of Arch Coal.

“Current reserves at the West Elk Mine are estimated to last nine to 11 years,” BLM said in the announcement.

“Exploration will provide additional data regarding the amount and quality of coal. The data is used to determine whether any additional mineable reserves are in the lease modification areas within the federal coal lease boundaries.”

The exploration plan will be conducted in 2013-14 and involve drilling 10 wells to collect core samples within the lease area.

Road upgrades needed to get a drilling rig into the area will take about two weeks to build, following which construction, drilling and reclamation activities will begin and are expected to take an average of 16 days per well. The BLM said it has limited disturbance to about half an acre.

Colorado had nine producing coal mines covering 75,000 acres, the agency said, adding that coal production on federally owned lands in Colorado overseen by the BLM generated $918.1 million to the economy in 2012.

Environmental groups have opposed and challenged the plan, claiming the expansion would damage land inhabited by lynx, black bear, elk and goshawk.

Environmental law firm Earthjustice, on behalf of the conservation groups High Country Citizens’ Alliance, WildEarth Guardians, Rocky Mountain Wild, and the Sierra Club, filed an appeal in January in an attempt to prevent the expansion.

“Protecting our forests is good for wildlife, for recreation, for clean water and our economy,” Earthjustice attorney Ted Zukoski said in January.

“BLM should ensure Colorado’s forests are conserved, not chainsawed and bulldozed.”

The West Elk longwall mine sold 5.7 million tons of thermal coal in 2011, according to the company’s website.