EPA Superfund Site

BASIN MINING AREA

MT | EPA ID MTD982572562

About this site’s exposure pathways: As of September 2025, the Basin Mining Area Superfund Site (Site) is considered Insufficient Data to make a Human Exposure evaluation (HEID). EPA uses this HEID Human Exposure status when there is insufficient data⁄evidence to determine whether actual or reasonably anticipated human exposures are occurring, and⁄or whether those exposures are above acceptable risk-based levels.

Soil cleanups for residential lead and arsenic were completed in the early 2000s for OU1, the Town of Basin, at the Site. Residential properties exceeding 800 mg⁄kg lead levels were addressed; recently, the EPA has provided an Updated Soil Lead Guidance for CERCLA sites and RCRA Corrective Action Facilities (Updated Lead Guidance) on January 17, 2024. This has lowered the recommended regional screening level for lead-contaminated soil to 200 mg⁄kg for residential soil-lead sites and the EPA is evaluating how this change may impact the cleanups that were completed and determine if additional investigation and⁄or cleanup is needed. Based on the Updated Lead Guidance, the EPA will begin planning and potentially undertaking activities to collect sufficient residential soil and other site data, including prior remedy-backfill materials, to make an evaluation to determine the presence and potential extent of soils that may present current and future-potential exposure risk to sensitive populations.

The EPA currently anticipates that there will be sufficient data to make a Human Exposure determination by 12/1/2031 because up to 3 years may be needed to complete planning, obtain funding, coordinate with the state, collect additional data, and complete site-specific human health risk assessment updates. While implementation of the Updated Lead Guidance may take several years, the EPA will share information on planned activities and results as they become available.

In the meantime, and out of an abundance of caution, if you live near the Basin Mining Area Superfund Site (especially properties without previous soil-replacements and within the community of Basin), residents can have children, especially those under 7, tested for lead exposure annually. The EPA site team will communicate with residents affected by this guidance about the specific next steps the Agency will take in their community. Residents may also contact the sites Community Involvement Coordinator regarding any questions or concerns you have.