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The NAWQA Program

Potential Contaminant Sources. The study of public-supply well vulnerability is one of five national priority topics being addressed by the National Water-Quality Assessment (NAWQA) Program in its second decade, which began in 2001. Other topics include effects of urbanization on stream ecosystems (USGS Fact Sheet 042-02); ecological effects of nutrient enrichment (USGS Fact Sheet 118-03); mercury in stream ecosystems (USGS Fact Sheet 016-03); and sources, transport, and fate of agricultural chemicals (USGS Fact Sheet 2004-3098). In addition, assessments of anthropogenic organic contaminants in source waters for many of the Nation’s largest surface- and ground-water community water systems are being conducted.

During the Program’s first decade (1991-2001), NAWQA scientists assessed surface- and ground-water chemistry, stream hydrology, habitat, and biological communities in 51 major river basins (“Study Units”). The assessments characterize the ambient water resource—the source of about 60 percent of the Nation’s drinking water and water for industrial, irrigation, and recreational uses. During its first decade, NAWQA made baseline assessments of pesticides, nutrients, volatile organic compounds, trace elements, dissolved solids, and radon, as well as the condition of aquatic habitats and fish, insect, and algal communities. These findings are described in hundreds of reports, available at the NAWQA Web site above.

In the second decade of studies, 42 of the 51 study units are planned to be reassessed to determine trends at many of the streams and ground-water monitoring sites; to fill critical gaps in the characterization of water-quality conditions; and to build upon earlier NAWQA findings that show how natural features and human activities affect water quality and aquatic ecosystems.

TANC drilling.

How Does the TANC Study Fit In?

The TANC Study builds on studies from the first decade of the NAWQA program that found low levels of mixtures of contaminants in ground water near the water table in urban areas across the Nation (in about 90 percent of monitoring wells) and, less frequently, in deeper ground water typically developed for public supply.

TANC team scientists are investigating how the linkage between contaminant sources and public-supply wells is affected by processes that occur below land surface. Because subsurface processes and management practices differ among aquifers and public-water systems, public-supply wells in different parts of the Nation are not equally vulnerable to contamination, even where similar contaminant sources exist. The study is identifying these important differences, as well as similarities, in a complementary set of aquifer systems, urban settings, and public-water systems.