EPA Superfund Site

FLAT CREEK IMM

MT | EPA ID MT0012694970

About this site’s exposure pathways: As of September 2025, the Flat Creek IMM Superfund site is considered Current Human Exposure Not Under Control (HENC). Residents and recreational users of the Flat Creek watershed (Operable Unit 2 OU2) can be exposed to elevated concentrations of arsenic, lead and antimony and other metals in floodplain and streambank deposits, tailings and waste rock, streambed sediment, surface water, and groundwater.
Groundwater in the area is relatively shallow and influenced by the Clark Fork River. Public well water is treated, and the Town of Superior tests these wells for water quality in accordance with federal standards. Some residents obtain water from private wells. However, EPA is not aware if these wells are currently used as a source of drinking water. Site groundwater and surface water contamination will be addressed as part of OU2. Currently, OU2 is in the remedial investigation⁄feasibility study (RI⁄FS) phase of the Superfund process. These exposure pathways are considered unacceptable based on EPA risk-based criteria because elevated concentrations generally relate to concentrations greater than three times background and⁄or above associated screening levels, or human health and aquatic water quality standards, as applicable. To date, the US Forest Service is working on the ongoing removal of Flat Creek streamside tailings. Once that work is completed, EPA will investigate any remaining contamination in the Flat Creek watershed and develop a Record of Decision (planned date is September 2029) to address risks to human health and the environment posed by that remaining contamination. EPA currently anticipates that human exposure will be under control by March 2034 because Remedial Action is anticipated to be completed in the watershed by that date.
If you are potentially impacted by risks inherent at this site, EPA has an ongoing community outreach program including providing residents and recreationalists with information to reduce exposures to potentially contaminated sources. EPA prioritized its resources to address contamination in the town of Superior, Operable Unit 1 (OU1). EPA removed contaminated soil from 33 properties, the school track, and the fairgrounds in 2002, 2010 and 2011. EPA issued a Record of Decision for OU1 in 2012 to address the remaining contaminated yards. Cleanup began in September 2013 and finished in November 2013. Since then, 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 residential soil 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 began planning activities evaluate the potential presence and extent of soils that may present current and future-potential exposure risk to sensitive populations. 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.