Superfund Information Systems: Site Profile

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About the Superfund Redevelopment Initiative

This nationally coordinated effort provides EPA and its partners with a process to return Superfund sites to productive use. Learn more at Superfund Redevelopment Initiative.

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Redevelopment at the Site

The Carson River Mercury Superfund site spans 236 former mill sites and 130 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 in the late 1990s. 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 Division of Environmental Protection (NDEP) 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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Economic Activity at the Site

As of December 2018, EPA had data on 59 on-site businesses. These businesses employed 377 people and generated an estimated $19,810,621 in annual sales revenue. View additional information about redevelopment economics at Superfund sites.

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Activity and Use Limitations

At this site, activity and use limitations that EPA calls institutional controls are in place. Institutional controls play an important role in site remedies because they reduce exposure to contamination by limiting land or resource use. They also guide human behavior. For instance, zoning restrictions prevent land uses – such as residential uses – that are not consistent with the level of cleanup. For more background, see Institutional Controls.

It is not safe to eat mercury-contaminated fish caught in the area.  The contamination presents a serious health risk to those who consume mercury-contaminated fish.  Mercury can cause permanent damage to the nervous system and serious disabilities for developing fetuses and children.

The Nevada Division of Health (NDOH) has issued health advisories for nearby water bodies.  NDOH recommends no consumption of some fish species from Big and Little Washoe Lakes.  NDOH recommends no consumption of some any fish from the Lahontan Reservoir and the Carson River from Dayton downstream to the reservoir.  It is not safe to eat any fish caught in these areas.  For more information, visit:

Catch and release, swimming, and recreation are safe activities.

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