Leviathan Mine covers about 250 acres in Alpine County in California's eastern Sierra Nevada, near Markleeville. It operated as an underground and open-pit mine from the 1860s until the early 1960s. The site was placed on the National Priorities List, which identifies the country's most contaminated sites, in May 2000. A permanent cleanup remedy has not yet been chosen, and major milestones such as construction completion and removal from the list remain ahead.
The core problem is acid mine drainage. Sulfide minerals in mine waste react with water and oxygen to form sulfuric acid. That acid pulls metals out of surrounding rock and carries them into groundwater, surface water, soil, and stream sediment. Five separate drainage sources on the site release mining-influenced water. Contaminants of concern include aluminum, arsenic, cadmium, chromium, copper, iron, lead, nickel, selenium, and zinc. Human exposure control and groundwater migration control both have insufficient data, so assessments cannot yet confirm whether human exposures are controlled or whether contaminated groundwater is stabilized.
Three treatment systems are running as early cleanup actions while long-term planning continues. A lime treatment system collects two discharges into lined ponds and treats water seasonally. A biological treatment system runs year-round on a third discharge, handling more than three million gallons of impacted water annually. A high-density sludge plant treats two more discharges seasonally from May to October using diesel generators. Since treatment began, water quality in downstream Leviathan and Bryant creeks has improved noticeably. Earlier work included a sitewide removal action carried out by the EPA from October 1997 through September 1998, as well as additional removal actions conducted between 2000 and 2006.
The potentially responsible parties are Atlantic Richfield Company and the California Regional Water Quality Control Board. They are completing a remedial investigation and feasibility study, which started in July 2000 and is still ongoing. That study will identify long-term cleanup options and include human health and ecological risk assessments. A proposed plan for a permanent, year-round remedy is estimated to be released between July and December 2027. After public comment, EPA will issue a record of decision and move into final remedy design.
Community members who want to stay informed or ask questions can contact the EPA directly. Georgia Thompson is the Community Involvement Coordinator, David Yogi is also available as a point of contact, and Freyja Knapp serves as the Remedial Project Manager. EPA also coordinates with state and federal agencies and the Washoe Tribe as cleanup planning moves forward.
