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EPA seeks comments on Carson River Mercury Superfund Site

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Carson River Mercury Superfund Site units

The Carson River Mercury Superfund Site includes two separate areas where historic Comstock-era mining activities were most significant, marked on a map that is part of the Environmental Protection Agency's explanation its preferred plan for site cleanup. 

DAYTON — The U.S. Environmental Protection Agency is seeking public comments on its proposed plan related to mercury and the Carson River Mercury Superfund site Oct. 15-Nov. 15.

The plan aims to reduce human exposure to mercury from a section of the Carson River site that was affected by historic mining practices that used mercury to process metals.

In 1859, miners discovered large natural deposits of gold and silver, also known as the Comstock Lode, in Carson City, Virginia City, and Dayton, Nevada. From about 1860-1890, miners used mercury to process gold and silver ore at approximately 236 mills. This mining process released an estimated 14 million pounds of mercury into the environment.

In 1990, the Carson River Mercury Superfund Site was added to the EPA’s National Priorities List, which consists of some of the most toxic Superfund sites in the country. The site covers about 330 square miles and in five counties and affects more than 130 river miles in Northwestern Nevada. Historic mill sites in Carson City, Virginia City, Dayton, Washoe Valley and Pleasant Valley have mercury contamination, and waterways located next to mill sites spread mercury into the floodplain of the Carson River, according to the EPA. EPA’s site investigation has found significant amounts of mercury in soil, sediments, fish and wildlife.

The EPA has divided the site into two operable units to better manage cleanup actions. Operable Unit 1 consists of the old mill sites and tailings. Operable Unit 2 includes the Carson River and adjacent floodplain from the New Empire area to the Carson Sink.

The agency’s preferred plan for Operable Unit 2 is an interim remedy that aims to protect the community from mercury exposure, which can cause health issues. Potential health risks come namely from eating contaminated fish, wild plants and waterfowl, the EPA found. No harmful effects were found for catch-and-release fishers, agricultural workers, Fallon and Churchill County residents using water for irrigation of plans such as fruits and vegetables, and people who eat beef or dairy that have grazed on plants, according to the EPA. The proposed plan would allow the agency to employ land use controls while conducting more research on contamination at the site. The estimated cost of the plan is $23.6 million over 30 years.

The proposed plan, a recorded presentation discussing the plan, a summary brochure, and the site files are available at

Comments may be sent via email to Comments may also be provided by calling and leaving a voicemail at 1-800-231-3075. EPA will review and consider all public comments regarding cleanup at the site.


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