Federal and state regulators have launched a joint environmental review of a proposed expansion at Stillwater Mine in Montana, with a 30-day public comment period now open for residents and stakeholders to weigh in. The Custer Gallatin National Forest and the Montana Department of Environmental Quality are conducting the review together under both federal and state environmental law.

What the Expansion Involves

The proposal includes expansion of the East Side Waste Rock Storage Facility along with construction of two new tailings storage facilities — Hertzler Stage 4 and Stage 5. The project would also require relocating a portion of Nye Creek to accommodate the additional infrastructure.

If approved, the expansion would extend Stillwater Mine’s operational life by an estimated 36 to 42 years, a significant long-term commitment that makes the current review one of the more consequential permitting processes for Montana’s mining sector in recent memory.

In total, the proposed expansion would increase the mine’s disturbance boundary by approximately 145 acres. About 30 of those acres fall within National Forest System lands managed by the Custer Gallatin National Forest, which is why the federal agency is part of the joint review process.

Regulatory Framework

The environmental review is being conducted under the National Environmental Policy Act and the Montana Environmental Policy Act — the twin federal and state frameworks that govern major land-use and development decisions with potential environmental impacts. Together, these laws require agencies to evaluate alternatives, assess potential effects, and solicit public comment before making a final determination.

Custer Gallatin National Forest Supervisor Matthew Jedra stressed the importance of community participation in shaping the analysis. “Public input is vital to ensuring we conduct a comprehensive and transparent analysis of this project,” Jedra said.

The 30-day comment window gives residents, conservation groups, tribal nations, and other stakeholders a structured opportunity to raise concerns or provide support before regulators move further in the process.

Stillwater Mine’s Role in Montana

Stillwater Mine is the only palladium and platinum producing mine in the United States, making it a strategically significant operation both for Montana’s economy and for domestic supply chains of critical minerals used in automotive catalytic converters and other industrial applications. The mine is located in Stillwater County in south-central Montana, in the Beartooth Mountains near the community of Nye.

An extension of 36 to 42 years would carry the mine’s operations well into the second half of the century, providing long-term employment and tax revenue for the region. Montana has ranked among the fastest-growing state economies in recent years, and mining remains a foundational sector of that growth. Governor Greg Gianforte highlighted Montana’s fifth-place ranking for economic growth since 2021, with extractive industries playing a role in that performance.

At the same time, the project’s footprint on National Forest land and the proposed relocation of Nye Creek are the kinds of site-specific impacts likely to attract scrutiny during the comment period. Federal land-use decisions involving National Forest System acreage often draw attention from both industry and conservation interests, given the multiple-use mandate those lands carry.

What Comes Next

After the 30-day public comment period closes, the Custer Gallatin National Forest and Montana DEQ will review the submissions and incorporate relevant concerns into the environmental analysis. That analysis will inform the agencies’ eventual decision on whether to approve, modify, or deny the expansion proposal.

No timeline for a final decision has been publicly announced. Given the scale of the proposal — a multi-decade extension of a major mining operation affecting both federal and state-managed lands — the review process is expected to be thorough and could take considerable time before regulators reach a conclusion.

Stakeholders interested in submitting comments should act within the 30-day window. Details on how to submit public comment are available through the Custer Gallatin National Forest and Montana DEQ.