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News Release

U.S. Department of the Interior
U.S. Geological Survey

Release: December 13, 2010
Sue C. Kahle

John Clemens

Chamokane Aquifers Mapped In Detail

[Editors: More information about the study is on-line at .]

TACOMA, Wash.--Scientists have sorted out and mapped the aquifers in the Chamokane Creek Basin in great detail, giving a more accurate picture of how streams and groundwater interact, according to a report published by the U.S. Geological Survey.

The USGS report is the first part of a two-phase study to describe the basin's water resources and to develop a computer model that can be used to assess how changes in groundwater use in the basin may affect streamflow.

Chamokane Creek Basin is a 179-square-mile area that borders and partially overlaps the Spokane Indian Reservation in southern Stevens County in northeastern Washington State. The Spokane Tribe, the State of Washington, and the Federal government are interested in learning more about the effects of additional groundwater development within the basin on Chamokane Creek. Results from the USGS study will be used to evaluate the effects of potential increases in groundwater withdrawals on groundwater and surface-water resources within the basin.

Most of the basin is closed to additional groundwater or surface-water appropriations, with the exception of permit exempt uses of groundwater. The effects of increased use of groundwater on the surface water system of the basin is unknown and is driving the study of the areas' water resources.

To study how water moves throughout the basin, water levels were measured in nearly 100 wells during three study periods: autumn 2007, spring 2008, and late summer 2008. Additionally, water-levels were measured monthly in 25 wells from March 2008 through December 2009. Stream flow was measured at 28 sites throughout the basin during the same time periods.

Two major sand and gravel aquifers were identified and are separated by a massive clay and silt layer up to 300 feet thick. The timing and magnitude of seasonal water-level fluctuations in these aquifers are very similar, indicating that these aquifers are hydraulically connected in places.

The second phase of the study will assess how changes in groundwater use may affect streamflow and is planned to be completed by August 2011.

The report, "Hydrogeologic Framework, Groundwater and Surface-Water Systems, Land Use, Pumpage, and Water Budget of the Chamokane Creek Basin, Stevens County, Washington," by Sue C. Kahle, William A. Taylor, Sonja Lin, Steven S. Sumioka, and Theresa D. Olsen, is published as U.S. Geological Survey Scientific Investigations Report 2010-5165 and is available on the Web at .

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