BIG TIMBER—The Custer Gallatin National Forest (CGNF) and the Montana Department of Environmental Quality (DEQ) have issued a joint Final Environmental Assessment (Final EA) for Stillwater Mining Company’s (SMC) East Boulder Mine Stage 6 Tailings Storage Facility Expansion Project, located approximately 23 miles south of Big Timber, in Sweetgrass County, Mont.  

The Final EA evaluates the potential environmental impacts resulting from the proposed Stage 6 expansion of the existing tailings storage facility pursuant to the requirements of the Montana Environmental Policy Act and National Environmental Policy Act. Two alternatives were analyzed: the no action alternative, in which SMC would not be allowed to construct the expansion, and the proposed action.  

The proposed action would expand the permitted disturbance area from 243.88 acres to 286.85 acres and would authorize SMC to construct Stage 6 of the tailings storage facility, raising the height of the impoundment 14 feet in elevation above what was previously authorized. The proposed action would also extend the tailings storage facility operations from the year 2027 to 2033 (based on current production), along with relocation and improvements to portions of two National Forest System roads, and relocation of existing mine facilities. The relocation of existing mine facilities includes, but is not limited to: two pump houses, a guard shack, stock piles and a pipeline within the mine permit boundary. Project activities would disturb 56.74 acres.  

DEQ and CGNF prepared a joint environmental assessment that discloses the impacts of the no action and proposed action alternatives. The agencies’ decision-making processes are separate from one another and will be documented on their websites. DEQ’s decision is to approve or deny SMC’s proposed Amendment 003 to Hard Rock Mining Operating Permit No. 00149. CGNF’s decision is to approve or deny a revised East Boulder Mine Plan of Operations.  

CGNF has chosen the proposed action as its selected alternative and has prepared a Draft Decision Notice (DN)/Draft Finding of No Significant Impact (FONSI) available for viewing at: https://www.fs.usda.gov/project/?project=55061 [fs.usda.gov]

The proposed project is subject to the Forest Service objection process pursuant to 36 Code of Federal Regulations (CFR) 218 subparts A and B.  Information about how to submit objections pursuant to 36 CFR 218 subparts A and B is available on the CGNF website at the link listed above.  

DEQ has also selected the proposed action and will document this selection in a Decision Letter, which will be sent to SMC and posted on the DEQ website along with the Final EA at: http://deq.mt.gov/Public/ea/hardrock

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