EPA Superfund site
UPPER TENMILE CREEK MINING AREA
Human exposure is NOT currently under control
Data limitations: Proximity to a Superfund site boundary does not mean your property is contaminated. EPA site boundaries show the area designated for cleanup, not the full extent of contamination. Groundwater plumes can extend beyond site boundaries. This tool shows publicly available EPA federal data. It is not affiliated with or endorsed by EPA, and is not a substitute for a professional environmental assessment.
About this site's exposure pathways
As of August 2026, the Upper Tenmile Creek Mining Area Superfund site is considered Current Human Exposure Not Under Control (HENC). Concerns for the human exposure pathways include three residential soil remedial actions yet to be taken, potential community access to nearby waste piles from former mining operations (approximately 35 of the original 70 piles have not yet been addressed), and untreated adit water released at the Site.
The 2008 Record of Decision Amendment indicates drinking water for the Rimini community will be sourced from Tenmile Creek to address the human ingestion pathway concerns. However, there are eight major contributing adit discharges and associated outfall sediment loads that require remediation before the creek may be used as a drinking water source. Currently, most residences in Rimini, and those nearest the Tenmile Creek in the Landmark Subdivision, are provided drinking water via the EPA Bottled Water Program administered through a cooperative agreement with Lewis & Clark County. Use of private drinking water wells is considered unacceptable because levels of arsenic and other mining-associated metals levels exceed the drinking water standards (MCLs) by orders of magnitude.
EPA is taking steps to address uncompleted portions of the selected remedy. All other planned remedial action projects are waiting for design and remedial action funding. If you are potentially impacted by risks inherent at this site, please contact the Lewis & Clark County Health Department at (406) 457-8900 or (406) 447-8351 for information and assistance related to the EPA Bottled Water Program. EPA currently anticipates that human exposure will be under control by December 2040 pending receiving funding to conduct the work.