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Scientific Investigations Report 2009–5076

Prepared in cooperation with the Virginia Department of Environmental Quality and the U.S. Environmental Protection Agency

Mercury Loads in the South River and Simulation of Mercury Total Maximum Daily Loads (TMDLs) for the South River, South Fork Shenandoah River, and Shenandoah River: Shenandoah Valley, Virginia

By Jack Eggleston

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Due to elevated levels of methylmercury in fish, three streams in the Shenandoah Valley of Virginia have been placed on the State's 303d list of contaminated waters. These streams, the South River, the South Fork Shenandoah River, and parts of the Shenandoah River, are downstream from the city of Waynesboro, where mercury waste was discharged from 1929–1950 at an industrial site. To evaluate mercury contamination in fish, this total maximum daily load (TMDL) study was performed in a cooperative effort between the U.S. Geological Survey, the Virginia Department of Environmental Quality, and the U.S. Environmental Protection Agency. The investigation focused on the South River watershed, a headwater of the South Fork Shenandoah River, and extrapolated findings to the other affected downstream rivers. A numerical model of the watershed, based on Hydrological Simulation Program–FORTRAN (HSPF) software, was developed to simulate flows of water, sediment, and total mercury. Results from the investigation and numerical model indicate that contaminated flood-plain soils along the riverbank are the largest source of mercury to the river. Mercury associated with sediment accounts for 96 percent of the annual downstream mercury load (181 of 189 kilograms per year) at the mouth of the South River. Atmospherically deposited mercury contributes a smaller load (less than 1 percent) as do point sources, including current discharge from the historic industrial source area. In order to determine how reductions of mercury loading to the stream could reduce methylmercury concentrations in fish tissue below the U.S. Environmental Protection Agency criterion of 0.3 milligrams per kilogram, multiple scenarios were simulated. Bioaccumulation of mercury was expressed with a site-specific exponential relation between aqueous total mercury and methylmercury in smallmouth bass, the indicator fish species. Simulations indicate that if mercury loading were to decrease by 98.9 percent from 189 to 2 kilograms per year, fish tissue methylmercury concentrations would drop below 0.3 milligrams per kilogram. Based on the simulations, the estimated maximum load of total mercury that can enter the South River without causing fish tissue methylmercury concentrations to rise above 0.3 milligrams per kilogram is 2.03 kilograms per year for the South River, and 4.12 and 6.06 kilograms per year for the South Fork Shenandoah River and Shenandoah River, respectively.

First posted November 30, 2009

For additional information contact:
USGS Virginia Water Science Center
1730 East Parham Road
Richmond, VA 23228

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Suggested citation:

Eggleston, Jack, 2009, Mercury loads in the South River and simulation of mercury total maximum daily loads (TMDLs) for the South River, South Fork Shenandoah River, and Shenandoah River—Shenandoah Valley, Virginia: U.S. Geological Survey Scientific Investigations Report 2009–5076, 80 p., available online at




Data Collected by the U.S. Geological Survey for This Study

Data Compiled From Other Sources

Development of Time-Series Data

Conceptual Model of Mercury Fate and Transport in the Watershed

Watershed Model Development

Watershed Model Results

Simulation of Mercury Total Maximum Daily Load (TMDL)



References Cited

Appendix 1. Data sources used to define point-source loading in the model

Appendix 2. User's Control Input File for the Calibrated South River Watershed Model Under Existing Conditions (Available only online at

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