EPA has collected soil, sediment, surface water and biota data to complete the remedial investigation (RI) at the Operable Unit (OU) No. 2 of the Carson River Mercury Superfund Site (CRMS). The goal of the study is to select a remedy that eliminates, reduces, or controls risks from site-related compounds of concern to human health and the environment. Specifically, the RI involves the investigation and study of the heavy metals contamination and the associated tributaries into the Carson River watershed resulting from site-related contaminant migration and to evaluate past and current releases and their impact to human health and the environment.

The Site includes mercury-contaminated soils at former mill sites, mercury contamination in waterways adjacent to the mill sites, and mercury contamination in sediments and banks fish and wildlife over more than a 80 mile length of the River, beginning near Carson City, Nevada and extending downstream to the Lahontan Valley and ultimately at its terminus at the USFWS Stillwater National Wildlife Refuge. Contamination at the Site is a legacy of the Comstock mining era of the late 1860s, when mercury was imported to the area for processing of gold and silver ore. Ore mined from the Comstock Lode was transported to the mill sites, where it was crushed and mixed with mercury to amalgamate the precious metals (Washoe Process). The mills were primarily 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 River drainage, primarily in the form of mercury-contaminated tailings.