In 1991, the U.S. Geological Survey (USGS) began the full-scale National Water Quality Assessment (NAWQA) program. The long term goals of the NAWQA program are to describe the status of, and trends in, the quality of a large, representative part of the Nation's surface- and ground-water resources and to identify the major natural and human factors that affect the quality of these resources. In addressing these goals, the program will produce a wealth of water quality information that will be useful to policy makers and managers at the National, State, and local levels.
The NAWQA program emphasis is on regional scale water-quality problems. The program will not diminish the need for smaller scale studies. and monitoring presently designed and implemented by State, Federal, and local agencies to meet specific needs. The NAWQA program, however, will provide a framework for understanding the regional and national water-quality conditions that cannot be acquired from smallscale programs and studies.
Study-unit investigations of 60 hydrologic systems that include parts of most major river basins and aquifer systems throughout the Nation are the building blocks of the national assessment. The 60 study units range in size from 1,000 to more than 60,000 mi2; (square miles) and include 60 to 70 percent of the Nation's population served by public water supplies. Twenty study-unit investigations were started in 1991, 20 additional investigations are starting in 1994, and 20 more are planned to start in 1997. The lower Illinois River Basin was selected by the USGS as 1 of 20 study units that will be investigated starting in 1994.