EPA Superfund Site

UPPER TENMILE CREEK MINING AREA

MT | EPA ID MTSFN7578012

About this site’s exposure pathways: As of September 2025, the Upper Tenmile Creek Mining Area Superfund site is considered Current Human Exposure Not Under Control (HENC). Concerns for the human exposure pathways include one partial residential soil remedial action 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 the stockpile of contaminated residential soils that were relocated to the RV Ranch property as funding was not available to transport the material to the Luttrell Regional Repository. The soils in this stockpile contain up to 10,000 ppm lead. The remedial action levels defined in the 2002 Record of Decision are 100 parts per million for arsenic and 400 parts per million for lead.
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.
In 2024 and 2025, EPA and the Montana Department of Environmental Quality (MDEQ) have been taking measures under the Cooperative Agreement to address the mine waste sites in the Minnehaha Creek drainage and transport the temporary residential stockpile located on the RV Ranch. 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 and MDEQ currently anticipate that human exposure will be under control by December 2040 pending receiving funding to conduct the work.