The Anaconda Copper Mine covers more than 3,400 acres in Mason Valley near Yerington, Nevada. Copper mining ran from 1918 to 1978, leaving behind roughly 900 acres of contaminated tailings, 400 acres of waste rock, and 300 acres of disposal ponds. The site was proposed for the National Priorities List in 2016 and has been undergoing cleanup work since 2002, with remedial action formally beginning in February 2020.
Groundwater beneath the site contains arsenic, cadmium, cobalt, copper, lead, manganese, mercury, molybdenum, selenium, and zinc in an acidic plume that has moved northward past the property boundary. Uranium was detected in off-site domestic wells north and west of the mine starting in 2004. Residents whose wells exceeded the uranium drinking water standard received bottled water until city water service reached them. The City of Yerington Water System and Yerington Paiute Water System are tested regularly and meet federal drinking water standards. Fugitive dust from tailings piles poses an inhalation risk during high wind events, and several on-site surface water areas contain heavy metals and low pH levels that threaten wildlife.
The site is divided into eight operable units, covering sitewide groundwater, a pit lake, process areas, evaporation ponds and sulfide tailings, waste rock areas, oxide tailings, the Wabuska Drain, and the Arimetco area. The Arimetco unit is the furthest along. A Record of Decision was issued in July 2017, and a follow-up amendment was issued in January 2021. Construction of new evaporation ponds was completed in May 2020, and remedial action in the Arimetco area is estimated to finish between October and December 2026. The other seven operable units are still in investigation or feasibility study stages, with combined studies estimated to wrap up between February and April 2027.
The Nevada Division of Environmental Protection (NDEP) took over site management in 2018 and works directly with Atlantic Richfield Company, the primary responsible party. Because the site can affect Tribal lands, EPA remains involved and works directly with the Yerington Paiute Tribe on those matters. An Environmental Covenant Agreement signed in September 2019 restricts activities like installing drinking water wells, excavating, or disturbing cleanup elements without NDEP approval.
Community members can contact the EPA Community Involvement Coordinator with questions. Site records are available at the Lyon County Library in Yerington and through the Nevada Division of Environmental Protection website.
