DEQ Press Releases

Davin, Moira

Montana DEQ & Custer Gallatin Seeking Public Comment: Draft Environmental Assessment for Stillwater East Boulder Expansion

BIG TIMBER—The Montana Department of Environmental Quality and the Custer Gallatin National Forest are releasing a Draft Environmental Assessment for Sibanye Stillwater Mining Company’s East Boulder Mine to expand the Stage 6 tailings storage facility, located approximately 23 miles south of Big Timber, Mont. in Sweet Grass County.


The Draft Environmental Assessment evaluates the environmental impacts resulting from the proposed Stage 6 expansion of the existing tailing 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, where the facility could not expand to Stage 6, and the proposed action.


The proposed action would expand the permitted disturbance area from approximately 238 acres to 286.85 acres and would authorize Sibanye Stillwater Mining Company to construct Stage 6 of the tailings storage facility, which is an amendment to existing Federal and state plans and raises the height of the impoundment 14 feet in elevation above what was previously authorized. The construction would secure storage of future tailings and thereby accommodate continued mining operations at the East Boulder Mine. The Stage 6 construction also includes extension of the tailings storage facility’s operations plan from 2027 to 2033 (based on current production), along with relocation and improvements to portions of two National Forest System roads (Lewis Gulch Road and East Boulder Road), construction of a new power line and relocation of existing mine facilities (i.e., soil stockpiles, underdrains, guard house and existing power line). All activities would occur within the existing footprint of the permit boundary (396.58-acres).


The Draft Environmental Assessment, along with Sibanye Stillwater Mining Company application and supporting project documents are available online at: or


Public comment is encouraged electronically at: or by navigating to, click on Land and Resource Management (left-hand side), then projects and comment on the project. Hardcopy is also accepted by mailing: Custer Gallatin National Forest, Attn: Robert Grosvenor, 805 Scott Street, Gardiner, MT 59030.  Electronic comments must be submitted in one of the following formats including: email, plain text (.txt), rich text format (.rtf), or Word document (.doc).  In keeping with precautionary measures related to the COVID-19 pandemic, the office is not open at this time for hand-delivered submissions.  All comments should be postmarked by June 15, 2020.  All public comment received is part of the public record.                                                                

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