Water-Quality and Ground-Water-Flow Patterns Identified in the Aquifer Underlying the Vicinity of Belvidere, Illinois

Data collected during 1993-96 by the U.S. Geological Survey (USGS) and U.S. Environmental Protection Agency (USEPA) in support of a ground-water study of the glacial drift (sand and gravel) and bedrock aquifers underlying Belvidere, Ill., and vicinity are presented in a report recently released by the USGS. Patrick Mills, hydrologist and principal author of the report said, "The study was prompted by spradic detections of volatile organic compounds (VOC's) in water supplied by the city of Belvidere's wells open to the bedrock aquifers." Most detections have been at concentrations below the maximum contaminant levels (MCL's), established by the USEPA for protection of public-water supplies; however, persistent detections of VOC's above MCL's at two of the wells require that the well water be processed before distribution to eliminate the VOC's. During the past century, various industrial facilities have operated within the vicinity of this city of 18,000 residents. Three hazardous-waste sites in the area, including two landfills, are on the U.S. Environmental Protection Agency National Priority List (commonly referred to as Superfund sites).

During July 1993, water samples were collected and ground-water levels were measured in almost 200 wells in an 80 square-mile area that includes Belvidere. Supplemental data were collected during 1994-96. The samples were analyzed primarily for VOC's, such as solvents and petroleum-related compounds; samples were analyzed selectively for other organic and trace-metal constituents. "The data collected provide an understanding of the regional ground-water quality and the factors that may account for the distribution of chemicals of industrial origin identified in the aquifers," Mills added.

Two VOC's were detected at concentrations below MCL's in samples from one of the six city water-supply wells in use during the study. VOC's were detected in 43 percent of the 115 wells that were sampled. Twenty-seven specific VOC's were identified in samples; most of the detections were below MCL's. Five specific VOC's were detected at concentrations above MCL's, with the solvents trichloroethane (TCE) and tetrachloroethane (PCE) the most frequently detected.

VOC's with the highest concentrations generally were from samples collected from monitoring wells installed near hazardous-waste sites, including the three Superfund sites. VOC's were detected in samples from at least five industrial areas within the city of Belvidere. Most VOC's, especially those with concentrations above MCL's, were detected in the uppermost glacial drift aquifer. Ground-water discharge to the Kishwaukee River appears to limit the horizontal and vertical distribution of industrial chemicals in the glacial drift and Galena-Platteville aquifers. Distribution of VOC's in the Galena-Platteville aquifer seems to be through primarily fractures in the aquifer. Most of the public-water supply wells in Belvidere are open, in part, to this aquifer.

Copies of the report titled, "Potentiometric levels and water quality in the aquifers underlying Belvidere, Illinois, 1993-96" by P.C. Mills, C.A. Thomas, T.A. Brown, D.J. Yeskis, and R.T. Kay has been released as U.S. Geological Survey Water-Resources Investigations Report 98-4220. Copies are available at the U.S. Geological Survey, 221 North Broadway Avenue, Urbana, Illinois. The report can be purchased at a cost of $4.00 from the U.S. Geological Survey, Branch of Information Services, Box 25286, MS 517, Federal Center, Denver, CO, 80225.