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samples collected. To date, 3,828 wells have been, and continue to be, tested and evaluated at CWSs across the state. Based upon available data, 3,517 (92 percent) of these wells are currently viewed as using a sanitarily safe source of groundwater. Of the 311 (8 percent) CWS wells that have shown bacterial contamination, 302 wells have addressed, or are addressing, sanitary defects or corrected monitoring location concerns. The remaining 9 wells are in the process of being evaluated for necessary corrective actions.
To further focus outreach and technical assistance efforts, the Illinois EPA has initiated evaluation of potential correlations among bacteria occurrence, hydrogeology, and other factors. As a first step, occurrence data was referenced to wells using geologically confined or unconfined aquifers. Of the CWS wells that are currently viewed as having sanitarily safe source water, approximately 65 percent utilize geologically confined aquifers.
Further analysis indicates that 183 (or 59 percent) of the 311 wells, initially viewed as having bacterially contaminated water, use confined aquifer systems (Figure 4), and 179 of these wells have been addressed. Bacterial sample detections for 128 of these confined wells were determined to be related to improper collection procedures and/or devices or integrity issues.
Additionally, evaluation shows a high percentage of CWS wells with bacterial contamination to be in proximity of a river or stream. If the 150 detections (from Table 4) determined to be related to improper collection procedures and well deficiencies are
Figure 4. Community Water Supply Wells Assessed for Pathogenic Contaminants in Confined and Unconfined Aquifers
