The USGS National Water-Quality Assessment (NAWQA) Program will describe its findings from two decades of monitoring at over 6,600 wells that tap extensive aquifers supplying most of the groundwater pumped for drinking water, irrigation, and other uses in the U.S. Among the findings was that one in five (22 percent) samples contained at least one contaminant at a concentration of potential concern for human health. NAWQA used contaminant data, along with detailed information on geology, hydrology, geochemistry, chemical use, and water use, to explain how and why vulnerability to contamination varies across the Nation and to predict future water quality changes. USGS will describe the occurrence of contaminants in groundwater, how natural features and human activities can affect groundwater quality, and how models are used to predict contaminant concentrations in unmonitored areas and inform decisions necessary to protect groundwater resources, given a growing population and current development stresses.

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