The Toxic Substances Hydrology (Toxics) Program is investigating factors and processes that control the transport and fate of contaminants in unsaturated zones (the zone in the subsurface between the land surface and underlying aquifers). Toxics Program scientists are developing methods for measuring and modeling the transport and fate of many different types of contaminants in the unsaturated zone. Such measurement tools, interpretive approaches, and modeling packages are needed for the design and management of waste-disposal facilities, to understand how nonpoint-source contaminants are transported to ground water, the cleanup of contaminated sites, and the monitoring of remediation systems. The unsaturated zone is particularly important at sites in the arid western United States that are being relied upon to isolate a significant portion of the Nation's radioactive and other hazardous wastes for periods up to thousands of years. The information presented on this page cuts across lines drawn by individual investigations and projects so that information on contaminant transport in surface-water can be presented in one place.

Investigations and Research Activities

• Waste Disposal and Contaminant Migration in the Arid Southwest, Amargosa Desert Research Site, Nevada
• Crude Oil Contamination in the Shallow Subsurface, Bemidji, Minnesota
• Processes Affecting the Natural Attenuation of Gasoline in Ground Water, Galloway Township, New Jersey
• Unsaturated Zone Field Studies
• Unsaturated Zone Flow Project
• Environmental Tracers of Surface-Water/Ground-Water Interactions
• Field Applications of Unsaturated Zone Flow Theory
• Transport of Emerging Contaminants Through the Unsaturated Zone

Fact Sheets

• Simulating transport of volatile organic compounds in the unsaturated zone using the computer model R-UNSAT: USGS Fact Sheet FS-019-98
• Ground water contamination by crude oil near Bemidji, Minnesota: USGS Fact Sheet FS-084-98

Thermocouple psychrometer installation for evaluating an evapotranspiration landfill cover at Fort Carson, Colorado
(Click on Image for a Larger Version)

Headlines

• New Model Allows for More Accurate Simulation of Tritium Movement in the Unsaturated Zone
• Widespread Accumulations of Natural Perchlorate in Southwestern Soils
• Pharmaceuticals Found in Soil Irrigated with Reclaimed Water
• Ground-Water Recharge Affects Fate of Petroleum Contaminant Plumes
• Desert Plants Reveal Contaminant Transport Pathways
• New Model Improves Understanding of the Transport of Carbon Isotopes in the Unsaturated-Zone
• Using Plants To Detect Tritium Contamination
• High Nitrate in the Desert? What’s Going On?
• New Book on Soil Analysis Methods Destined to Become a Classic
• Are Deserts Still Drying Out Since the Ice Age?
• The Atmosphere - A Potential Source of MTBE to Ground Water

Bibliography

• Publications on the Unsaturated Zone (455 Publications)

New Publications

Upcoming Publications

• Transport of tritium contamination from the shallow unsaturated zone to the atmosphere in an arid environment: Garcia, C.A., Andraski, B.J., Stonestrom, D.A., Cooper, C.A., Johnson, M.J., Michel, R.L., and Wheatcraft, S.W., Vadose Zone Journal (IN PRESS).
• The effect of grain-coating mineralogy on the storage and transport of nitrate and sulfate in the unsaturated zone: Reilly, T.J., Fishman, N.S., and Baehr, A.L., Vadose Zone Journal (IN PRESS).

Newly Published

• Differences in evaporation between a floating pan and class A pan on land: Masoner, J.R., Stannard, D.I., and Christenson, S.C., 2008, Journal of the American Water Works Association, v. 44, no. 3, p. 552-561, doi:10.1111/j.1752-1688.2008.00181.x.
• Method for estimating spatially variable seepage loss and hydraulic conductivity in intermittent and ephemeral streams: Niswonger, R.G., Prudic, D.E., Fogg, G.E., Stonestrom, D.A., and Buckland, E.M., 2008, Water Resources Research, v. 44, W05418, doi:10.1029/2007WR006626.

Soil moisture probes and tensiometers installed in the side of a pit for monitoring a tracer test in the unsaturated zone at the Bemidji Crude Oil Spill Research Site, Minnesota. Note black oil-contaminated sand on pit walls.
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