Water Quality | Stillwater Mining Company | Stillwater East Boulder Mine | Sweet Grass County | Comment Period Closes November 7, 2025
APPLICANT NAME:
Stillwater Mining Company
FACILITY NAME:
Stillwater East Boulder Mine
FACILITY LOCATION:
Sweet Grass County, Montana
RECEIVING WATER:
East Boulder River and associated ground water
PERMIT NUMBER:
MT0026808
The Stillwater East Boulder Mine is an underground platinum and palladium mine with an associated mill and lined tailings impoundment. The mine is located approximately 32 miles southeast of Big Timber, Montana. This permitting action is a major modification of the 2023 MPDES permit.
The applicant has requested a modification implementing the water quality standards change from Base Numeric Nutrient Criteria applied in the 2023 renewal to the narrative nutrient criterion at ARM 17.30.637(1)(e) with respect to the Facility’s water quality-based effluent limit for total nitrogen. Further, a permit condition may be modified under the “reopener” conditions in a permit when the condition is established under ARM 17.30.1361(2)(g). This modification implements the narrative nutrient criterion as it applies to the East Boulder Mine. This modification establishes a revised final effluent limitation for total nitrogen, adds a Nutrient Bioassessment Special Condition, and removes the nutrient compliance schedule put in place in the 2023-issued permit. All other permit conditions remain in full effect.
Associated Materials:
Comment Period Ends: November 7, 2025
Send Comments To:
DEQ Water Quality Division
Water Protection Bureau
PO Box 200901
Helena, Montana 529620
Or electronically to: DEQWPBPublicComments@mt.gov
Tags: MEPA, Public Comment and Water