GROUNDWATER CONTAMINATION IN KARST TERRAIN OF ILLINOIS CAVERNS

The sinkhole plain of southwestern Illinois and associated caves are highly vulnerable to groundwater contamination. This includes the subterranean stream within Illinois Caverns, a relatively long cave in the sinkhole plain. Contaminants associated with private septic systems and agricultural activities, such as bacteria from septic effluent and livestock, and nitrate and pesticides from row crops, are directly washed into the shallow karst aquifer without filtration.

Twenty-eight sample locations were selected from within Illinois Caverns. Ninety-two water samples were collected from ceiling seeps, streams from side passages, and the main cave stream in the summer of 1996 and winter and spring of 1997. The samples were tested in the lab for anions and cations, alkalinity, bacteria (fecal coliform, total coliform, total aerobic bacteria), and pesticides (alachlor and atrazine). The isotopes of carbon (¹³C), oxygen (¹⁸O), and hydrogen (²H) of selected samples were also tested in the lab. Temperature, specific conductivity, and pH were measured in the field.

The data were analyzed to identify the character and extent of contamination present. Elevated concentrations of nitrate and pesticides were detected in most of the groundwater samples and are directly related to row crop agriculture. We also found that the waters of Illinois Caverns contained large concentrations of fecal coliform, fecal streptococcus and a variety of other bacterial species. The presence of bacteria in water could indicate the presence of harmful pathogens capable of causing health problems. Total bacteria found in summer of 1996, winter of 1997, and spring of 1997 was 889 colonies/100ml, 4761 colonies/100ml, and 1943 colonies/100ml respectively, with the highest amounts occurring in the winter season. Fecal streptococcus was found in all samples. Those collected during the summer of 1996, the winter of 1997, and the spring of 1997 had bacterial concentrations of 1.1%, 39.5%, and 3.6% respectively, with the highest concentration occurring in the winter season. These data suggest that during the colder winter season when there is less recharge, there is less dilution of contaminants. Chloride/bromide ratio data suggest that some areas of the Illinois Caverns groundwater basin and thus some of the fecal bacteria are fed by waters contaminated with private septic systems and by livestock waste.