Mercury in the Carson River
Data on concentrations of total mercury, total methyl mercury, and suspended sediment were collected at two USGS gaging stations, Carson River near Fort Churchill, NV (10312000), and Carson River below Lahontan Reservoir, NV (10312150). These data subsequently can be used to determine seasonal loads of total mercury and methylmercury in and from Lahontan Reservoir.
Data collection occurred weekly during the rising stage of the spring snowmelt hydrograph, then every other week during the falling stage of the snowmelt hydrograph, and monthly thereafter, during low-flow conditions.
- Streamflow, water temperature, specific conductance, dissolved oxygen (DO) and pH were recorded each time water samples are collected.
- Streamflow measurements were made.
- Water samples were collected along the cross section of the river using depth-integrating techniques. At a minimum, five vertical profiles of the water column along the cross section of the river were sampled and composited.
During the gold and silver rush near Virginia City, Nevada, in the mid to late 1800's, 75 ore-processing mills were located along the Carson River and three of its tributaries (Six Mile Canyon, Seven Mile Canyon, and Gold Canyon). At most of the mills, gold was recovered from ore using mercury amalgamation. This process of gold recovery resulted in the loss of 6 to 7 tons of elemental mercury to the environment, mostly incorporated in mill tailings (Smith, 1943). Over 100 years of weathering and erosion have redistributed these mill tailings throughout the channel and flood plains of the lower Carson River Basin. Since 1915, Lahontan Reservoir has received and retained most of the mercury contaminated sediments transported in the Carson River.
Elevated concentrations of mercury in the Carson River Basin, Nevada were first reported by the USGS in 1973 (Van Denburgh, 1973). The USGS study showed high concentrations of mercury in water and bottom sediment downstream from sites where mercury was used in the late 19th century in the milling of gold and silver ore. Subsequent investigations have further documented the extent and severity of the contamination. The elevated levels of mercury have prompted the issuance of public-health warnings prohibiting the consumption of gamefish and carp from the Carson River downstream of Dayton, in Lahontan Reservoir, and in Lahontan Valley.
In August 1990, the USEPA listed the Carson River in west-central Nevada, as a site for possible remediation of mercury contamination under the auspices of the Comprehensive Environmental Response, Contamination, and Liability Act of 1980, also known as CERCLA, or Superfund. Subsequently, USEPA coined the term CRMS to identify the 100-mile reach of river designated for site investigation. This reach begins in Carson City and ends at the Stillwater National Wildlife Refuge in the Carson Desert. As part of the initial CRMS investigation, USEPA is required to do a RI/FS in order to characterize the scope of contamination of mercury which poses a potential risk to human health and to the environment of the affected area. The results of the RI/FS will assist resource managers to develop sound plans for remediating the potential risks. Recognizing the importance of fluvial transport of mercury-contaminated sediments to Lahontan Reservoir, USEPA-Region 9 requested in March 1997 that the USGS Nevada Water Science Center collect mercury and mercury-related data on the Carson River.
Hoffman, R.J., and Thomas, K.A., 2000, Methylmercury in water and bottom sediment along the Carson River system, Nevada and California, September 1998: U.S. Geological Survey Water-Resources Investigations Report 00-4013, 17 p.
Thomas, K.A., 2000, Methylmercury in water and bottom sediment along the Carson River System, Nevada and California, September 1998 [abs.]: Assessing and Managing Mercury from Historic and Current Mining Activities, U.S. Environmental protection Agency, San Francisco, Calif., November 2000, p. 93.
Hoffman, R.J., and Taylor, R.L., 1998, Mercury and suspended sediment, Carson River Basin, Nevada--Loads to and from Lahontan Reservoir in flood year 1997 and deposition in reservoir prior to 1983: U.S. Geological Survey Fact Sheet FS-001-98, 6 p.
Location: Carson River Basin, western Nevada
Start Date: 1997
End Date: 2013
Cooperator: U.S. Environmental Protection Agency
USGS Nevada Water Science Center
2730 N. Deer Run Rd.
Carson City, NV 89701
phone: (775) 887-7672
USEPA: U.S. Environmental protection Agency
CRMS: Carson River Mercury Site
RI/FS: Remedial Investigation and Feasibility Study