The Carson River basin, from New Empire to Stillwater and the Carson Sink, was designated as National Priority Listed (NPL) due to historic mining activity site under the Comprehensive Environmental Response Compensation and Liability Act (CERCLA or Superfund) in August, 1990. This is Nevada's only NPL site and is being jointly managed by NDEP and the U.S. Environmental Protection Agency 9 (EPA), Region IX, in San Francisco. Millions of pounds of mercury were imported and used in approximately 250 Comstock mills to recover gold and silver. An estimated 14,000,000 pounds of mercury was lost to the environment during that process. Arsenic and lead, which were common constituents of the mined ore, were concentrated by the milling process and were also released to the environment. Therefore, the Contaminants of Concern (CoC's) at the site are Mercury, Arsenic and Lead.