Limestone is found in areas of St. Clair, Monroe and Randolph Illinois counties. The bedrock in karst areas will dissolve when rainwater and soil water, which are slightly acidic contact it. Through time, rain and soil water draining down through cracks and crevices in the bedrock have, and will continue to, dissolve enough rock to make an underground network of channels often called conduits. Typical features of karst include sinkholes , springs, caves and losing or disappearing streams - streams that lose water directly into the groundwater system. Groundwater in Karst Landscape Groundwater contamination is another area of concern in karst areas.
Sinkholes serve as direct entrance for surface water to the groundwater system.
There is little, if any, filtering of surface water runoff before it enters the groundwater through sinkholes. Even in areas where there are no sinkhole features, the soils do not filter the surface water very well before that water becomes groundwater. Effluent from private sewage disposal systems, trash thrown into sinkholes or sinkhole watersheds, and agricultural run-off all pose threats to groundwater quality.