Superfund Sites in Reuse in Nevada

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Carson River Mercury Site

The Carson River Mercury Superfund site spans 236 former mill sites and 80 miles of the Carson River in Lyon, Storey, Carson, Washoe and Churchill counties in western Nevada. Contamination at the site resulted from historic gold and silver mining that took place during the late-1800s. Workers used mercury to extract precious metals until the end of the century, when they converted to cyanide processing. About 7,500 tons of mercury eventually contaminated the Carson River and the surrounding flood plain. A study conducted by the U.S. Geological Survey in the early 1970s identified high levels of mercury in the Carson River system. Later studies found contaminants in river sediments, which impacted fish and wildlife. EPA added the site to the Superfund program’s National Priorities List (NPL) in 1990. The Nevada State Health Division enforces an advisory against fish consumption from affected water sources. EPA removed mercury-contaminated tailings from high exposure risk areas, such as parks. Cleanup activities included the removal of contaminated soils from five residential areas in Dayton and Silver City. EPA also restored infrastructure and landscaping disturbed by cleanup activities. The Virginia City Historic District, in which many of the historic mill sites are located, depends heavily on the tourism economy. The areas surrounding the Carson River are mostly agricultural for ranching and farming. EPA and the Nevada Department of Environmental Protection continue to work with residential developers and single family homeowners in the affected towns to prevent unacceptable risk of exposure to contamination. The Comstock Mining Company, operating in Silver City, also conducts exploration, mining and processing of gold and silver in Storey and Lyon counties. The mine provides extensive environmental monitoring data to the regulators to ensure that the soils within the site footprint are adequately handling CERCLA wastes and not further releasing contaminants. EPA’s selected cleanup plan, which relies on institutional controls coordinated closely with the county building and planning departments, allows the continued industrial, commercial and residential use of the site throughout cleanup activities.
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