WASHINGTON, June 15 (TNSFR) -- The U.S. Department of Agriculture Forest Service has begun the environmental review process for a proposal by Stillwater Mining Co. to expand operations its County Mine in Montana, a project that could extend production of platinum group metals for another 36 to 42 years. The agency, acting jointly with the Montana Department of Environmental Quality, announced plans to prepare an environmental impact statement and opened a 30-day public comment period.