Pesticides in ground water in the Western Lake Michigan Drainages, Wisconsin and Michigan, 1983-1995

In 1991, the U.S. Geological Survey (USGS) began implementation of the National Water-Quality Assessment (NAWQA) Program. The long-term goals of the NAWQA Program are to describe the status and trends in the quality of a large, representative part of the Nation's surface- and ground- water resources, and to identify, describe, and explain, if possible, the major factors that affect the observed water quality (Hirsch and others, 1988). The program consists of study-unit investigations that include parts of most major river basins and aquifer systems in the country. The Western Lake Michigan Drainages study unit encompasses a 20,000-square-mile area in eastern Wisconsin and the Upper Peninsula of Michigan that drains to Lake Michigan and Green Bay (figure 1).