FLAT CREEK IMM

As of August 2026, 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, 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 whether 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 and Montana Department of Environmental Quality completed projects for removal of Flat Creek streamside tailings. EPA will investigate any remaining contamination in the Flat Creek watershed and develop a Record of Decision (planned date is September 2030) 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 2035 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 Residential Lead Directive for CERCLA Sites and RCRA Hazardous Waste Cleanup Program Facilities on October 16, 2025. This has lowered the recommended regional screening level for lead-contaminated soil to 200 mg ⁄ kg and a removal management level of 600 parts per million for residential soil-lead sites. 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 Directive, the EPA began planning activities to 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 Directive may take several years, the EPA will share information on planned activities and results as they become available.