News Release

December 11, 2007	Melanie Clark	307-778-2931	mlclark@usgs.gov
	Myron Brooks		mhbrooks@usgs.gov

Powder River Basin Study -- Water Quality Affected by Variety of Factors

U.S. Geological Survey (USGS) scientists who analyzed 15 years of water-quality data (1991-2005) in the Powder River structural basin reported that water-quality in the basin was highly variable due to multiple factors including drought, the basin’s geologic controls, and different land uses.

“This initial data analysis shows few trends, but it is important to have information on the condition of the streams in the area. These initial data, and data currently being collected, will be essential to determine if there are long-term changes to the rivers related to the area’s coal bed natural gas development.” stated USGS hydrologist Melanie Clark. Clark examined data from the Powder, Tongue, Belle Fourche, and Cheyenne River Basins.

The study, conducted in cooperation with the Wyoming Department of Environmental Quality, indicated no significant long-term trends (1991-2005) in specific conductance for selected sites in the Tongue, Powder, and Belle Fourche River drainage basins when the data were adjusted for streamflow variability. Specific conductance is an indirect measure of the amount of dissolved minerals in the water. Streamflow has been less than average in response to drought conditions in the drainage basins during 2001 to 2005.

“The one parameter that did show an upward trend was SAR, the Sodium Adsorption Ratio, analyzed in the Powder River Basin.” stated Clark. “However, this upward trend can not be directly related to the energy development, because a site upstream of the development also showed an upward trend in SAR.” High SAR values can indicate that the water is not suitable for irrigation.

The USGS continues to monitor stream conditions in the Basin, in both Wyoming and Montana, in cooperation with Federal, State, and local agencies.

Copies of the USGS report “Water-Quality Characteristics for Sites in the Tongue, Powder, Cheyenne, and Belle Fourche River Drainage Basins, Wyoming and Montana, Water Years 2001-2005, with Temporal Patterns of Selected Long-Term Water Quality Data” published as Scientific Investigations Report 2007-5146 are available free of charge by calling 1–888–ASK–USGS (1–888–275–8747). The report also may be viewed online at: http://water.usgs.gov/pubs/sir/2007/5146/ .

USGS provides science for a changing world. For more information visit www.usgs.gov

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