A 10-year study by the U.S. Geological Survey's (USGS's) National Water-Quality Assessment (NAWQA) Program provides a national-scale view of pesticide occurrence in streams and groundwa-ter. The 1992-2001 study builds upon a preliminary analysis from NAWQA's first phase of studies during 1992-1996 (1,2). Pesticide data available from various studies prior to 1992 did not allow national assessment because of limited and variable geographic coverage (usually focusing on individual states or regions), sparse and inconsistent inclusion of pesticides in use, and variable sampling designs (3-5).
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