A Regional Ground-Water Quality Characterization of the Rockford Area, Winnebago County, Illinois

摘要

This report summarizes an investigation of regional ground-water quality in the Rockford area in north-central Illinois. The investigation was launched to determine if regional ground-water contamination,principally by volatile organic compounds (VOCS), has occurred in the Rockford area. A number of investigations conducted by local and state agencies have documented the presence of VOCs in the ground water atseveral locations in or near the city of Rockford, Illinois. An estimated 300 wells, including 16 public water supply wells, have been affected by the presence of organic compounds in over 20 instances ofground-water contamination in Winnebago County documented since 1970. Analysis of ground-water samples was undertaken in a 76-square mile area around Rockford to examine the potential for regional contamination of ground water by hazardous substances. Sixty-nine private domestic and industrial wells were sampled and analyzed for 18 VOCs and 4 trace metals. Results of these determinations were compiled along with information from previous investigations, including Illinois Environmental Protection Agency sampling results from 48 local municipal water wells, to determine areas of ground-water contamination within the study area. Ground-water (depth-to-water) measurements were also obtained, and a map of the potentiometric surface of the sand andgravel aquifer was prepared to determine the direction of ground-water movement. The locations of industrial facilities that may be handling hazardous substances were also mapped. Total VOC concentrations found in the sampled wells ranged from nondetectable to over 500 ~g L-1. Of the 69 wells sampled, ten contained 5 ~g L-1 or more total VOCs. Of those ten, seven contained concentrations in excess of the U.S. Environmental Protection Agency (USEPA) Recommended Maximum Contaminant Level (RMCL) of 5 ~g L-1 for trichloroethene (TCE) in drinking water. Two of those wells also exceeded the USEPA lifetime health advisory of 70 ~g L-1 for cis-1,2-dichloroethene. None of the wells sampled exceeded the RMCL for any of the four trace metals. Despite the fact that several wells were found to contain VOCs,the preponderance of information collected during this study shows that regional contamination of ground water in the Rockford area has not occurred. Much of the ground water used by the residents and industry in the Rockford area was found to be of satisfactory quality with regard to VOCs and selected trace metals. However, this information should not minimize the problems identified in several parts ofRockford. One area in southeast Rockford is significantly contaminated with VOCs. Over 100 homes in the area obtain water from shallow wells water with total VOC concentrations in excess of 100 ~g 1-1. The USEPA RMCL for many of these contaminants is only 5 ~g 1-1. A more detailed investigation of this area conducted by the Winnebago County Health Department in 1984 produced similar results. Data collected from thesetwo investigations show that the contamination extends approximately two miles from 20th Street west to the Rock River. A nearby public water supply well, Rockford Unit Well 35, is finished much deeper in the sand and gravel and also exhibits elevated vac concentrations. Thearea is bordered by a variety of industrial facilities that may have introduced the contaminants into the ground water. More specific information on the contaminated area is needed to develop water supply alternatives for the residents of the area and to provide better management of the ground-water resource for public andindustrial use. Follow-up investigations should be conducted to determine the source, magnitude, and extent of contamination in southeast Rockford. The response of contaminant movement to various pumpingpatterns created by the numerous high-capacity wells in the area shouldbe evaluated. Such investigations will provide information important to the implementation of possible ground-water protection measures in the Rockford area.A methodology for the investigation of regional ground-water quality is also presented in the report. This methodology is presented as a guide for planning and executing similar investigations inIllinois. This methodology should help to provide some consistency in the design of such efforts undertaken by other groups or agencies in the state.