EPA Superfund Site

CARPENTER SNOW CREEK MINING DISTRICT

MT | EPA ID MT0001096353

About this site’s exposure pathways: As of September 2025, the Carpenter Snow Creek Mining District Superfund site is considered Current Human Exposure Not Under Control (HENC). The planned activities to address the solid source pathway at the Town of Neihart Community Soils Operable Unit (OU) 1 are to implement the selected remedial action outlined in the 2009 Record of Decision (ROD) to remove residential soils contaminated with lead and arsenic, and to work with Cascade County Health Department to implement institutional controls. The cleanup standards in the ROD are 400 mg⁄kg for lead and 100 mg⁄kg for arsenic and are currently being re-evaluated.
EPA has also completed site-wide remedial investigations and is working on a feasibility studies at OU2 and OU3 that addresses solid and aqueous source mine waste and fluvial deposits in the Carpenter and Snow Creek watersheds. EPA will follow this with Records of Decision to address the solid source media in Operable Unit 3 (Carpenter Creek) and OU2 (Snow Creek), which are planned for 2027. EPA also anticipates procuring a Design and Engineering Contractor to help prepare the OU4 (Neihart Slope) and OU5 (Belt Creek Tailings) feasibility study, proposed plan and ROD in late 2026.
In addition, EPA and the US Forest Service have conducted multiple removal actions to reduce human exposure and address multiple safety hazards. These include on site demolition of degraded chemicals and dynamite, removal of electrical transformers containing Polychlorinated biphenyl (PCB) fluids, surface water diversions, and excavation and on-site placement of over 50,000 cubic yards of mine waste. EPA will continue to use removal authority to address the mine waste piles that have the greatest potential to erode in nearby surface water bodies until a final OU5 ROD can be issued in 2031. EPA is also working with two Potentially Responsible Parties (PRPs) to pilot test source control measures to address mine-influenced waters coming from two discharging mine adits in the Carpenter Creek (OU3) drainage.
EPA continues to provide residents and recreationalists with information to reduce exposures to potentially contaminated sources such as soils, sediments, surface water and groundwater. Remedial action completion of a final aqueous (water) source remedy media is anticipated to be completed in 2041. This exposure pathway is considered unacceptable based on EPA risk-based criteria because on site workers, residents and recreationalists can be exposed through direct contact to mine waste and sediment containing thallium, manganese, lead and arsenic in contaminated source materials, fluvial deposits and residential soils as well as mine influenced water discharging from multiple adits containing concentrations of lead, iron, zinc, cadmium, copper and thallium above federal maximum contaminant levels.