• Feasibility Studies
• Site Characterization

Camp Far West Reservoir, California

• Sierra Trinity Abandoned Mine Lands Agency Group
• U.S. Forest Service
• Bureau of Land Management
• California State Water Resources Control Board
• Nevada County Resource Conservation District

To Be Determined

• Mercury
• Methylmercury

View of the bank of the Camp Far West Reservoir, California Click on image for larger version

The Challenge

The Sierra Trinity Abandoned Mine Lands Agency Group is faced with the difficult challenge of what to do about fish contaminated with mercury in the Camp Far West Reservoir and the Bear River and South Yuba River Watersheds, California. The fish are bioaccumulating mercury from contaminated sediments washed down from long-abandoned gold mines in the Sierras (see inset). The contaminated sediments have accumulated along river banks and flood plains, and on the bottom of reservoirs. Several reservoirs and rivers receiving drainage from abandoned gold-mining areas in the foothills of the Sierras do not meet water-quality standards. Resource managers are tasked with remediating the sources of contamination to comply with Total Maximum Daily Load (TMDL) allocations. The dual objectives of this task are to decrease concentrations and loads in rivers and streams and to reduce the bioaccumulation of mercury in fish consumed by humans and wildlife.

Mercury-Contaminated Sediments

Several man-made reservoirs in the foothills of the Sierras have been accumulating mercury-contaminated sediments. USGS scientists have demonstrated that mercury and other metals in the bottom sediments of reservoirs, lakes, and estuaries can be moved into the overlying water through chemical and biological activities. The rate that solutes, such as methylmercury, move in and out of sediments, known as the benthic flux, can be positive (into the water from bottom sediments) or negative (out of the water into bottom sediments). The magnitude and variability of the benthic flux determines whether or not methylmercury in the bottom of reservoirs represents a significant source of this toxic form of mercury to the environment. Understanding the magnitude of this flux is a critical part of the equation for determining remediation objectives and setting allocations for the TMDL process.

The Question

How significant are sources and sinks of dissolved total mercury and dissolved methylmercury associated with the bottom sediments of reservoirs relative to major surface-water inputs? This was the question posed to USGS scientists for the Camp Far West Reservoir, California. The Bear River has transported mercury-contaminated sediments into the reservoir and these sediments are stored in the bottom of the reservoir. The bottom sediments have been known to be a potential source of mercury, but the magnitude of the source was not known. USGS scientists applied methods developed by the USGS’s Toxic Substances Hydrology Program to estimate the magnitude of the bottom sediments in the reservoir as a source of mercury by quantifying the benthic flux of mercury.

The scientists collected sediment cores from three locations in the reservoir. The cores were taken to a laboratory where incubation experiments were conducted. During the incubations, concentrations of mercury species in water overlying the cores were monitored over time. Linear regressions of the time-series data were used to calculate the benthic flux of the solutes.

Results from the experiment showed that the benthic flux of mercury and methylmercury into the reservoir varied with location and time of year. A significant (and possibly predominant) percentage of dissolved total mercury in the reservoir’s water presently comes from the bottom sediments in the reservoir. The flux of total dissolved mercury was in the same range as the total dissolved mercury that rivers were discharging into the reservoir. Methylmercury flux was consistently lower than the load of methylmercury from the rivers. Understanding this variability will be key to developing and assessing the feasibility of any potential plans for remediation of contaminated sediments in the reservoir.

No Free Lunch: Balances in Environmental Systems

One of the options for resource mangers to reduce the mercury contamination in fish is to control or reduce the amount or load of mercury the Bear River and others discharge into the reservoir. This would be an advantageous action even if the reservoir was not a concern; however, the decrease in mercury loads from the rivers would most likely be compensated initially by increases in the benthic flux of mercury from the bottom sediments. This is because the management-induced change would result in a greater concentration difference between the water in the reservoir and the bottom sediments at the sediment-water interface. The magnitude of the benthic flux would be enhanced by larger concentration differences at the interface. The long-term outlook for this option is that concentrations of mercury in the reservoir are expected to decrease slowly after loads from rivers are controlled due to the burial of contaminated sediment with sediments containing fewer contaminants.

Remediation: What is Being Done

The USGS has been a participant in the Sierra Trinity Abandoned Mine Lands Agency Group. A major focus of the group is to determine the distribution, transport, and fate of mercury and methylmercury in the vicinity of historic hydraulic placer-deposit gold mines. The Group is coordinating its efforts to remediate or remove contamination sources in the watershed that pose the greatest risk and implement management systems that reduce the load of mercury in the watershed’s rivers and streams so water-quality objectives can be met. The results from the study of mercury in the sediments of the Camp Far West Reservoir, California, are being used to guide remediation efforts of the Group.

Technology Transfer

At Camp Far West Reservoir the USGS is applying methods that were developed by the Toxic Substances Hydrology Program for an investigation of the cycling of toxic metals in the southern part of San Francisco Bay. The methods have also been applied at investigations of contaminated sediments in Lake Coeur d'Alene, Idaho, and Lahontan Reservoir, Nevada.

• Benthic Fluxes of Metals and Nutrients Studies, Camp Far West Reservoir, California, Investigation
• Bioaccumulation of Mercury by Fish and Fish-Forage Organisms in Camp Far West Reservoir, Yuba and Placer Counties, California
• Mercury Bioaccumulation in Fish in a Region Affected by Historic Gold Mining: The South Yuba River, Deer Creek, and Bear River Watersheds, California, 1999, Open-File Report 00-367
• Bear River Mercury Cycling Project
• Mercury and Arsenic Contamination Associated with Abandoned Mine Lands, Bear River and South Yuba River Watersheds
• Environmental Mercury in California
• New Method for Assessing Bed Sediment Contamination
• Benthic Flux Method Photo Gallery

• James Kuwabara, USGS, National Research Program, Menlo Park, CA,
• Brent R. Topping, USGS, National Research Program, Menlo Park, CA,
• Mark Marvin-Dipasquale, USGS, National Research Program, Menlo Park, CA,
• Paul F. Woods, USGS, Idaho Distric, Boise, ID,
• Charles N. Alpers, USGS, California District, Sacramento, CA,
• A. Robin Stewart, USGS, National Research Program, Menlo Park, CA,

• Kuwabara, J.S., Alpers, C.N., Marvin-Dipasquale, Topping, B.R., Carter, J.L., Stewart, A.R., Fend, S.V., Parchaso, F., Moon, G.E., and Krabbenhoft, D.P., 2003, Sediment-water Interactions Affecting Dissolved-mercury Distributions in Camp Far West Reservoir, California: U.S. Geological Survey Water-Resources Investigations Report 03-4140, 61 p.
• Kuwabara, J.S., Berelson, W.M., Balistrieri, L.S., Woods, P.F., Topping, B.R., Steding, D.J., and Krabbenhoft, D.P., 2000, Benthic flux of metals and nutrients into the water column of Lake Coeur d'Alene, Idaho---Report of an August, 1999, pilot study: U.S. Geological Survey Water-Resources Investigations Report 00-4132, 74 p.
• Kuwabara, J.S., Marvin-Dipasquale, M., Praskins, W., Byron, E., Topping, B.R., Carter, J.L., Fend, S.V., Parchaso, F., and Krabbenhoft, D.P., 2002, Flux of dissolved forms of mercury across the sediment-water interface in Lahontan Reservoir, Nevada: U.S. Geological Survey Water-Resources Investigations Report 02-4138, 48 p.
• Kuwabara, J.S., Woods, P.F., Berelson, W.M., Balistrieri, L.S., Carter, J.L., Topping, B.R., Fend, S.V., 2003, Importance of sediment-water interactions in Coeur d’Alene Lake, Idaho--Management Implications: Environmental Management, v. 32, no. 3, p. 348-359.
• Topping, B.R. and Kuwabara, J.S., 2003, Dissolved nickel and benthic flux in south San Francisco Bay--A potential for natural sources to dominate: Bulletin of Environmental Toxicology and Chemistry, v. 71, p. 46-51.
• Topping, B.R., Kuwabara, J.S., Parchaso, F., Hager, S.W., Arnsberg, A.J., and Murphy, F., 2001, Benthic flux of dissolved nickel into the water column of South San Francisco Bay: U.S. Geological Survey Open-File Report 01-89, 50 p.

Other Studies Using the Same Methods to Determine the Benthic Flux of Metals

• Lake Coeur d'Alene Remediation Assessment
• Nickel Cycling in the South San Francisco Bay
• Mercury Transport in the Carson River Basin

USGS Studies Related to Mercury Remediation

• Yolo Bypass Studies, Yolo Bypass, Sacramento, California; Cache Creek, California
• Evaluation of the Effectiveness of Remediation Dredging--The Fox River Deposit N Demonstration Project, Lower Fox River, near Kimberly, Wisconsin
• Mercury Cycling in the Everglades

Mercury Information

• USGS Mobile Atmospheric Mercury Laboratory Makes an Impact
• Effect Of Mercury on Aquatic Ecosystems
• USGS Mercury Research Laboratory
• Mercury Contamination of Aquatic Ecosystems: U.S. Geological Survey Fact Sheet FS-216-95
• Other USGS Mercury Activities

San Francisco Bay Information

• Varied Human Influences on Estuaries -- San Francisco Bay, California
• Access USGS - San Francisco Bay and Delta