GROUND-WATER STUDIES IN ILLINOIS

Why do we study ground water?

Ground water is an important source of water supply in Illinois. About 2.5 million people in Illinois are supplied from ground-water resources. Total ground-water withdrawals in the State was approximately 953 million gallons per day in 1995. Ground-water withdrawals account for about 21 percent of the total water withdrawn for public-water supplies in Illinois. Tens of thousands of persons in the State rely on ground water from residential wells as their sole source of water. The largest amount of ground-water withdrawals is in the northern one-third of the State where large supplies of potable water are available in aquifers that range in depth from about 10 feet to about 1,500 feet.

Ground-water quality is a major concern in Illinois. Water-quality degradation or contamination results from point and nonpoint sources throughout the State. In many industrialized parts of the State, including the metropolitan areas of Chicago, Rockford, and St. Louis, ground water in aquifers in the glacial deposits and bedrock has been degraded by improperly contained or disposed chemicals. In many agricultural areas, the quality of ground water in the underlying shallow aquifers has been degraded by the routine application of agricultural chemicals. Surface-water quality has been degraded in some areas because of the influx of contaminated ground water.

What do we do?

The U.S. Geological Survey (USGS), Illinois Water Science Center, performs various ground-water activities primarily within the State of Illinois. The USGS has conducted numerous hydrologic studies in Illinois since 1955 concerned with ground-water quantity and quality. Many of these studies are done in cooperation with local, State, and Federal agencies and organizations. These studies include:

• studying regional patterns and trends in ground-water quality based on a network of 117 wells in shallow and deep glacial aquifers in central Illinois, lower Illinois River Basin, as part of the National Water-Quality Assessment Program.

• studying long-term trends in ground-water quality in the upper Illinois River Basin as part of the USGS National Water-Quality Assessment Program.

• cooperative studies with the U.S. Environmental Protection Agency, Region 5, concerning ground-water quantity and quality at hazardous-waste sites located in cities and towns such as Rockford, Byron, and Belvidere, in regional areas such as southeast Chicago/northwestern Indiana and in the Galena-Platteville aquifer underlying much of northern Illinois and southern Wisconsin.

• monitoring a network of up to 13 wells to observe water-level fluctuations (an indicator of changes in ground-water storage resulting from climatic variability and pumpage) until 1998.

• studying radium in ground water from aquifers used for public supply in northern Illinois.

Various State of Illinois agencies are responsible for ground-water assessment, management, and protection programs in Illinois. Some of these agencies include the Illinois Department of Natural Resources*, which includes the State Geological* and State Water Surveys* and the Office of Water Resources*; the Illinois Environmental Protection Agency*; the Illinois Department of Public Health*; and the Illinois Pollution Control Board*.

*External Web site that is not associated with the U.S. Geological Survey.