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.
Land use in the study area is primarily agricultural. Corn and soybeans are the major crops in the basin. Major cities in the basin are Peoria (population 114,000), Springfield (105,000), and Decatur (84,000). The 1990 population in the basin was 1.33 million.
The climate of the lower Illinois River Basin is continental. Summers generally are hot and humid, and winters are cold. Mean daily temperatures in July, typically the hottest month, range from 23 to 26°C (degrees Celsius). Mean daily temperatures in January, typically the coldest month, range from 6 to 3°C. Mean annual precipitation in the basin is 36 inches.
The major aquifers in the basin are composed of glacial deposits of Quaternary age and bedrock of Pennsylvanian to Mississippian age. Many of the major Quaternary aquifers are in buried bedrock valleys.
The Illinois River is a primary channel for the transport and disposal of much of the State's human, animal, industrial, and agricultural wastes. Sediments from the Chicago metropolitan area in the upper Illinois River Basin have distinct chemical characteristics; these characteristics have been identified in sediments in the lower Illinois River Basin.
High concentrations of nitrate and agricultural chemicals are expected in parts of the basin. Results of recent statewide studies in and near the basin indicate that concentrations of nitrate and agricultural chemicals exceeded U.S. Environmental Protection Agency maximum contaminant levels (MCL's) for drinking water in surface and ground water. In 1990, about 9 million pounds of atrazine were applied in Illinois, nearly one-sixth of the national total and more than any other State. Several recent studies of the quality of ground water from public supply wells throughout Illinois have shown the presence of concentrations of nitrate, pesticides, and volatile organic compounds above drinking water MCL's.
Dissolved oxygen is needed to support aquatic life. During the 1988 summer low-flow period, dissolved oxygen concentrations in the lower Illinois River decreased to 2 ppm (parts per million), which is below the U.S. Environmental Protection Agency aquatic life criterion of 5 ppm. Domestic and industrial wastes that are discharged to the Illinois River can produce ammonia and consume oxygen, resulting in seasonal shortages of dissolved oxygen, but the study of the upper Illinois River showed that changes in wastewater-treatment practices reduced the ammonia concentrations in effluent discharged to streams from some wastewater facilities.
European zebra mussels-an exotic species that has recently been found in the basin-compete with native species, create operational problems for hydraulic structures and water intakes, and affect the supply of dissolved oxygen. Studies by the Illinois Department of Natural History during the flood of 1993 showed zebra mussel densities of less than 1 per square meter north of Peoria, but up to 61,000 per square meter near the confluence of the Illinois and Mississippi Rivers at Grafton, Ill.
-Kelly L. Warner and Arthur R. Schmidt
Information on technical reports and water-quality data related to the NAWQA program can be obtained from:
Lower Illinois River Basin NAWQA
U.S. Geological Survey
221 North Broadway
Urbana, Illinois 61801
|September, 1994||FS 94-018|
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