Bacteria Contamination of Groundwater in a Mixed Land-Use Karst Region

Enteric bacteria, many of which are opportunistic pathogens, were detected in groundwater from springs, wells, and a cave stream in the karst region of southwestern Illinois, and concentrations generally were very high in the springs and cave stream. The two main sources of bacterial contamination were determined to be domestic wastewater treatment discharge and livestock manure. The water chemistry in the springs and caves indicated substantial dilution of any wastewater discharge, but the dilution was not sufficient to lower bacteria concentrations to regulatory levels. High counts of enteric bacteria were found throughout the year, suggesting a continuous source of contamination, most likely domestic wastewater discharge. Although wells generally were less contaminated than springs, wells located in livestock areas usually were contaminated with enteric bacteria, and their water chemistry was indicative of contamination by animal waste.