Volatile Organic Compounds (VOCs)
Sixty wells in the lower Illinois River Basin were analyzed for 73 volatile organic compounds (VOC's). On the basis of a reporting level of 0.20 micrograms per liter (mg/L), VOC's were detected in only six of more than 4,300 analyses. Four different VOC's were detected in samples taken from five wells. At least three of these detections may be the result of well disinfection practices, resulting in the formation of chloroform. Carbon tetrachloride, detected near the reporting level, also may have been present because of the use of bleach as a well disinfectant. Another compound detected near the reporting level, 1,2,3,4-tetramethyl benzene (TeMB), has no current known uses. Methyl tert-butyl ether (MTBE), a common fuel oxygenate, also was detected at a concentration of less than 1 mg/L. Five of the six detections were in samples from wells completed in the shallow glacial drift aquifer in the Galesburg/Springfield Plain. Only one detection was for a sample from the deep glacial drift aquifer, indicating shallow aquifers may be more susceptible to VOC contamination than deep aquifers in the LIRB. Based on these results, VOC contamination does not appear to be a major concern at present (1996) with respect to ground-water quality in rural areas of the LIRB.

VOC Detections

Chloroform	4.7 mg/L
Chloroform	0.37 mg/L
Chloroform	0.31 mg/L
Carbon tetrachloride	0.24 mg/L
MTBE	0.59 mg/L
TeMB	0.22 mg/L