Superfund Construction Project - Funding Pending Upper Tenmile Creek Mining Area Superfund Site Helena, Montana Site Description vvEPA The UpperTenmile Creek Mining Area Superfund site is located primarily within Lewis and Clark County, southwest of Helena, Montana. It consists of 53 square miles of the Upper Tenmile Creek watershed and includes the community of Rimini and the Landmark subdivision. Helena has relied upon Upper Tenmile Creek as a source of 50 to 85 percent of its drinking water. EPA added the site to the National Priorities List in 1999. The community of Rimini relies on groundwater for domestic water supply, and has been receiving bottled water for drinking water since the beginning of the Superfund response in the late 1990s. Site Status and Cleanup Actions to Date • EPA signed a record of decision in 2002. The selected remedy's major components addressing mine waste, soil and sediment include: o Excavating and disposing of contaminated materials from high-priority mine sites and from contaminated yard soils from residences and recreational cabins, o Monitoring water quality and sediment quality in Tenmile Creek after cleanup of waste rock tailings and acid-mine drainage are complete. o Excavating, transporting and disposing of contaminated roadway materials underlying Rimini Road. • The major components of the selected remedy addressing surface and groundwater include: o Cap and regrade collapsed shafts and adit portals, and construct drainage features to prevent or reduce stormwater and snowmeltfrom entering mine workings and contributing to acid-mine drainage, o Implement institutional controls to prevent use of new drinking water wells where contaminated aquifers exist, o Control waste rock, tailings and acid-mine drainage, augment stream flows during low-flow periods, and naturally attenuate contaminants in surface water, o Build a new community water system for Rimini residents using groundwater from deep wells. • Cleanup activities conducted since the record of decision was signed in 2002 include: o 2003 to present: EPA has removed tens of thousands of cubic yards of mine waste and contaminated soils from residential properties, roads and mine sites, o 2006: EPA conducted a treatability study for metals removal from the Susie mine adit discharge, o 2008: EPA amended the record of decision to provide individual septic systems and changed the source of the Rimini community water system from groundwater to treated surface water from Tenmile Creek, as no suitable deep-well source could be located. o 2010: EPA conducted an investigation of adit discharge source control of Lee Mountain and Upper Valley Forge/Susie mine sites. o 2010-2011: Remediation of Rimini and Landmark properties with access agreements completed, o 2011: Landmark subdivision potable water evaluation completed, o 2011: RV Ranch Phase I shallow soil sampling, o 2012-2013: Lee Mountain mine and Little Lily mine cleanup, o 2014-2015: National Extension mine and Bunker Hill mine cleanup. Project Pending Funding, as of the end of Fiscal Year 2019 This work includes the construction and operation of a passive treatment system for the National Extension mine's discharge, the cleanup (excavation and disposal at the Luttrell mine waste repository) of mine sites in the Minnehaha Creek drainage, and hauling remaining wastes from the Landmark community to the Luttrell mine waste repository. Funding Through Fiscal Year 2019 EPA has provided approximately $79 million for cleanup activities at the site. May 2020 ------- |