Geochemical characterization of water, sediment, and biota affected by mercury contamination and acidic drainage from historical gold mining, Greenhorn Creek, Nevada County, California, 1999–2001

By Charles N. Alpers, Michael P. Hunerlach, Jason T. May, Roger L. Hothem, Howard E. Taylor,
Ronald C. Antweiler, John F. De Wild, and David A. Lawler



Scientific Investigations Report 2004-5251—ONLINE ONLY

Sacramento, California 2005

Prepared in cooperation with the Bureau of Land Management, the California State Water Resources Control Board, the Nevada County Resource Conservation District, and the U.S. Department of Agriculture–Forest Service

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In 1999, the U.S. Geological Survey (USGS) initiated studies of mercury and methylmercury occurrence, transformation, and transport in the Bear River and Yuba River watersheds of the northwestern Sierra Nevada. Because these watersheds were affected by large-scale, historical gold extraction using mercury amalgamation beginning in the 1850s, they were selected for a pilot study of mercury transport by the USGS and other cooperating agencies. This report presents data on methylmercury (MeHg) and total mercury (THg) concentrations in water, bed sediment, invertebrates, and frogs collected at 40 stations during 1999-2001 in the Greenhorn Creek drainage, a major tributary to Bear River. Results document several mercury contamination “hot spots” that represent potential targets for ongoing and future remediation efforts at abandoned mine sites in the study area.

 Water-quality samples were collected one or more times at each of 29 stations. The concentrations of total mercury in 45 unfiltered water samples ranged from 0.80 to 153,000 nanograms per liter (ng/L); the median was 9.6 ng/L. Total mercury concentrations in filtered water (41 samples) ranged from less than 0.3 to 8,000 ng/L; the median was 2.7 ng/L. Concentrations of methylmercury in the unfiltered water (40 samples) ranged from less than 0.04 to 9.1 ng/L; the median was 0.07 ng/L. Methylmercury in filtered water (13 samples) ranged from less than 0.04 to 0.27 ng/L; the median was 0.04 ng/L. Acidic drainage with pH values as low as 3.4 was encountered in some of the mined areas. Elevated concentrations of aluminum, cadmium, copper, iron, manganese, nickel, and zinc were found at several stations, especially in the more acidic water samples.

 Total mercury concentrations in sediment were determined by laboratory and field methods. Total mercury concentrations (determined by laboratory methods) in ten samples from eight stations ranged from about 0.0044 to 12 µg/g (microgram per gram, equivalent to parts per million). Methylmercury concentrations in these samples ranged from less than 0.00011 to 0.0095 µg/g. A field panning method was used to determine the concentration of liquid elemental mercury in 22 samples from 14 stations. Measured quantities of elemental mercury recovered by panning ranged from a trace amount estimated at 100 milligrams per kilogram (equivalent to parts per million) to 45,000 milligrams per kilogram (equivalent to 4.5 per cent, by weight).

 In total, 194 invertebrate samples were collected at 31 stations; 78 of the samples were analyzed for concentrations of THg and MeHg and used to calculate MeHg to THg ratios. A total of 69 frog samples were collected at 19 stations, and all were analyzed only for THg. Ranges of MeHg concentrations (µg/g, wet weight) in invertebrate samples and number of samples (n) were 0.0012-0.048 for banana slugs (Arionidae, n = 27), 0.027-0.39 for dobsonflies (Corydalidae, n = 14), 0.029-0.50 for predaceous diving beetles (Dytiscidae, n = 31), 0.026-0.52 for predaceous stoneflies (Perlidae, n = 18), 0.011-1.6 for dragonflies (Odonata, n = 46), and 0.061-0.55 for water striders (Gerridae, n = 56). The ratio of MeHg to THg in invertebrates was greater than 50 percent for 74 of 78 samples.

  The data from this reconnaissance sampling effort have been used by land-management agencies in selecting abandoned mine sites for remediation. The Forest Service has remediated the Sailor Flat site, and the Bureau of Land Management has initiated plans to remediate the Boston Mine drainage tunnel.


Description of Study Area
Mining History
Previous Work on Mercury Contamination
Purpose and Scope
Study Design
Sample Locations
Constituents Analyzed
Field Methods
Laboratory Methods of Chemical Analysis
Invertebrates and Frogs
Quality Assurance and Quality Control
Water and Sediments
Invertebrates and Frogs
Overall Trends
Water Quality
Summary of Results by Geographic Area
Greenhorn Creek—Headwaters
Sailor Flat Area
Buckeye Area
Boston Mine Area
South Fork Greenhorn Creek
Poore Mine Area
Starr Mine Area
Missouri Canyon Area
Greenhorn Creek—Main Stem
Greenhorn Creek at You Bet Road—Integrator Site
Summary and Conclusions
Appendix A. Map of Tunnel Locations and Photographs of Field Sites, Greenhorn Creek Drainage, Nevada County, California
Appendix B. Quality Assurance and Quality Control Plots for Chemical Analyses of Water Samples from the Greenhorn Creek Drainage, Nevada County, California
Appendix C. Locations and Characteristics of Sampling Stations and Tunnels, Greenhorn Creek Drainage, Nevada County, California
Appendix D. Quality Assurance and Quality Control Information for Chemical Analyses of Samples from the Greenhorn Creek Drainage, Nevada County, California

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