The U.S. Environmental Protection Agency has ordered the Atlantic Richfield Company to complete a comprehensive investigation of the Leviathan Mine Superfund site to determine long-term cleanup actions at the former mine located near California-Nevada border in Alpine County.
Since the site was added to the EPA's national priority list in 2000, the agency has continued to focus on controlling and cleaning up the acid mine drainage from the site, which is upstream from lands of the Washoe Tribe of Nevada & California.
The EPA has been successful in requiring the capture and treatment of the acid mine drainage during the summer months when access to the site is not affected by snow. The EPA will evaluate how to expand the collection and treatment system to a year-round system.
"Completing the investigation and cleanup evaluation for this site is the next step toward a long-term solution for this mine site," said Keith Takata, the Superfund Division director of the EPA's Pacific southwest region. "The EPA will work with the affected states, tribes, and communities to determine a final cleanup action."
The EPA's evaluation will include assessing potential risks from surface waters, groundwater, sediments, soils, and flora and fauna impacted by mine run-off.
The assessment will include specific Washoe Tribal cultural uses of that area's resources affected by the mine. The open-pit mining of sulfur from the site left wastes and underground conduits that result in acid mine drainage into the Leviathan Creek/Bryant Creek watershed, which drains into the East Fork of the Carson River, a major source of water supply and a habitat for fish.
Unless treated, the releases contain elevated concentrations of metals and metalloids, most notably arsenic, as well as iron, aluminum, chromium, cobalt, copper, nickel and zinc. The low pH and high metals content of the acid mine drainage historically limited most aquatic life in Leviathan Creek and portions of Bryant Creek downstream of the mine until response activities were initiated.
The site was initially developed as an underground mine for gold, copper and copper sulfate, starting in 1863. From 1954 through 1962, Anaconda Copper Mining Company conducted open pit mining, later acquired by Atlantic Richfield.
In 1984, the state of California acquired approximately 495 acres of the mine to clean up and abate water quality problems associated with historic mining.
The Lahontan Regional Water Quality Control Board, which was delegated authority over the mine property, constructed evaporation ponds in an attempt to reduce the impact from some of the mine releases.