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News Release

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

Release: August 19, 1997
Luis A. Fusté, Information Officer

Model Used to Predict Where Ground Water is Most Vulnerable to Nitrate

Water wells in the Puget Sound Basin that are most at risk to elevated levels of nitrate have been identified with the help of a new statistical model, according to a fact sheet published by the Department of the Interior, U.S. Geological Survey (USGS).

The model links regularly collected water-quality data with information about la nd use and geologic deposits at the land surface to produce a map of at-risk areas. The map shows at a glance where wells of a given depth are most vulnerable t o nitrate.

While nitrate occurs naturally in ground water, elevated levels are typically caused by septic systems and by applying animal manure and agricultural fertilizer to the land. Its presence in ground water above natural levels means that it is possible that other contaminants from the land surface may be reaching the wate r table.

Jim Tesoriero, USGS hydrologist who designed the model and co-authored the fact sheet, commented on what the model showed about the Puget Sound Basin: "Agricultural areas with permeable deposits at the surface, such as the Lower Nooksack Valley, are among the most vulnerable areas to high nitrate levels." He added it was somewhat surprising that urban areas with these permeable deposits, such as parts of Tacoma and Olympia, are also at relatively high risk.

Tesoriero is currently leading a USGS study in Whatcom County that will evaluate how quickly natural processes decrease nitrate concentrations in ground water.

The maps produced using this model can help in targeting ground-water monitoring programs and in planning future land use, such as where to allow development us ing septic systems. They are also useful tools for educating the public about th e potential of ground-water contamination from land use.

The four-page color fact sheet is a product of the USGS National Water-Quality A ssessment (NAWQA) Program, which is designed to assess current water-quality con ditions, describe how water quality is changing, and improve understanding of th e natural and human factors that affect water quality. For more information, vis it the Puget Sound Basin NAWQA home page at

Copies of Fact Sheet 061-97 "Predicting Ground-Water Vulnerability to Nitrate in the Puget Sound Basin" by M. L. Erwin and A. J. Tesoriero are available free fr om the U.S. Geological Survey, 1201 Pacific Avenue, Suite 600, Tacoma, WA, 98402 , telephone (253) 593-6510, or by Email at Copies are a lso available at some area libraries.

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