Service Description: This point feature class contains the general locations from which fish were caught to conduct tissue sampling for mercury contamination concentrations from the Lahontan Reservoir, Carson River Mercury National Priorities List Site, Nevada, USA. Samples were collected from 2011-2013 by the Nevada Department of Wildlife and analyzed by EPA's Region 9 Laboratory to assess the human health and ecological risk posed by mercury uptake. The results from the survey can be found in a related table entitled "LahontanReservoir2013mercuryfishsummaryResults_2011_13_EPA_NDOW".
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Description: This is a summary of mercury (Hg) data from fish collected in the Lahontan Reservoir area of the Carson River Basin. NDOW collected the fish and the EPA Region 9 Laboratory analyzed the tissue for mercury (Hg) for EPA's Impaired Waters Program, water resources managers and researchers working in the Carson River Basin. These data and the data tables provide results of the Lahontan Reservoir area, used by recreationalists and fishermen, in order to measure concentrations of Hg to evaluate potential human health exposure pathways. The original sources of Hg contamination in the Carson River Basin are from historic gold and silver mining and associated milling of the Comstock Lode near Virginia City, Nevada. Runoff and erosion from an estimated 236 'stamp mills', driven by flumes, resulted in a cummulative release of an estimated 7,500 Tons of elemental mercury into the Carson River Basin.
The elemental mercury, imported from mines in California and used to almalgamate the ore at the stamp mills, contaminated sediments throughout the Basin from the source area situated approximately between Carson City and Dayton, to the terminal wetlands in the Carson Sink. This area is the primary source of Hg pollution in the Basin, considering the naturally occurring mercury concentrations are close to the crustal average. During runoff and flood events, the River laterally cuts through the contaminated sediments in the overbanks and transports Hg with suspended sediments, and with concentrations rising with higher flow. When Lahontan Reservoir was built in 1915, it became a settling basin for suspended Hg from the Carson River, and while it retains up to 90 percent of influent sediments, the reservoir continues to pass significant concentrations of suspended and dissolved inorganic Hg and methylmercury (Me-Hg) downstream to the Carson Sink.
The EPA is publishing this data in support of the Carson River Mercury NPL Site in Nevada. Data was compiled and evaluated for the OU2 Remedial Investigation Report (EPA, 2017), which describes the nature and extent of contamination from the Site. The report contains the Human Health Risk Assessment and Ecological Risk Assessment. Literature and other source Hg data are summarized in the RI for surface waters, sediments, and biological tissues.
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Copyright Text: U.S. EPA, NDOW
Spatial Reference: 102100 (3857)
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