carson river mercury site

DEER RUN RD TO DAYTON IN RIV

The Carson River Mercury Site includes mercury-arsenic-lead-contaminated soils at former mill sites, mercury contamination in waterways adjacent to the mill sites, and mercury contamination in sediments, fish and wildlife over more than a 80 mile length of the Carson River, beginning near Carson City, Nevada and extending downstream to the Lahontan Valley. Contamination at the site is a legacy of the Comstock mining era of the late 1800s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals. The mills were located in Virginia City, Silver City, Gold Hill, Dayton, Six Mile Canyon, Gold Canyon, and adjacent to the Carson River between New Empire and Dayton. During the mining era, an estimated 7,500 tons of mercury were discharged into the Carson River drainage, primarily in the form of mercury-contaminated tailings. Today, the mercury is in the sediments and adjacent flood plain of the Carson River and in the sediments of Lahontan Reservoir, Carson Lake, Stillwater Wildlife Refuge, and Indian Lakes. Nevada State Health Division advisories recommend limited or no consumption of fish and ducks at the Site due to high levels of mercury. In addition, tailings with elevated mercury levels are still present at and around the historic mill sites, particularly in Six Mile Canyon. EPA, the U.S. Geological Survey, the U.S. Fish and Wildlife Service, the Nevada Division of Environmental Protection (NDEP), University of Nevada researchers, and others have carried out studies to determine the extent of contamination, evaluate the human health and ecological risks, and better understand the processes that govern the movement and toxicity of the mercury. To better manage the site investigation and cleanup, EPA has established two Operable Units (OU) for the site. OU 1 consists of the old mill sites and related tailings above the high water mark. OU2 consists of the Carson River from the area of New Empire Mill to its terminus in the Carson Sink.