Hard-rock mining from the 1870s through the late 1960s left arsenic, cadmium, lead, zinc, copper, mercury, silver, and other metals in soil, groundwater, surface water, and sediment across about 77 square miles near Basin, Montana. EPA added the site to the Superfund National Priorities List in October 1999 after screening investigations found high contamination, including arsenic in the Basin Elementary School yard and elevated lead and arsenic in residential yards. The site is also known as Basin Mining Site and Basin School Yard.
Cleanup is organized into six operable units covering different geographic areas and facilities. In the Town of Basin, EPA excavated roughly 5,000 cubic yards of contaminated soil and mine waste between 1998 and 2002, with residential cleanup finishing in November 2004. Removal actions at the Buckeye/Enterprise, Crystal, and Bullion mines were completed by 2002, with wastes placed in the jointly managed Luttrell Repository. The Crystal Mine and Bullion Mine each have Records of Decision from April 2015 calling for treatment systems, engineered caps, soil amendments, bioremediation, and wetland construction. Remedial designs for those two mines were completed in 2015, and remedial action is anticipated pending federal funding. A new remedial investigation and feasibility study for the Town of Basin began in September 2024, with completion estimated between December 2026 and February 2027. Two five-year reviews have confirmed the remedy remains protective of human health and the environment, with the most recent completed in September 2023.
Contaminants identified at the site include arsenic, cadmium, copper, lead, mercury, zinc, aluminum, antimony, iron, manganese, selenium, silver, and thallium. These have been found in soil, groundwater, surface water, sediment, leachate, and solid waste. Physical construction is not yet complete across the entire site. Human exposure and groundwater migration status are both listed as insufficient data, meaning assessments have not yet produced reliable information to determine whether people face unacceptable exposure risks or whether contaminated groundwater migration is stabilized. EPA is also evaluating how an October 2025 lead directive will affect cleanup decisions at the site.
The site has seen some return to productive use. As of December 2024, 11 businesses were operating on-site, employing 47 people and generating about $908,678 in annual sales. Community members can review site records at the EPA Superfund Records Center in Helena, Montana, at 10 West 15th Street, Suite 3200, open Monday through Friday from 8:00 a.m. to 4:30 p.m., reachable at 406-457-5046 or toll-free at 866-457-2690. Questions about cleanup can be directed to EPA, the Montana Department of Environmental Quality, and the United States Forest Service.
