Geologic, Geophysical, and Hydrologic Investigations for a Supplemental Municipal Groundwater Supply, Danville, Illinois

Danville obtains its water from Lake Vermilion, a reservoir located on the North Fork Vermilion River. There have been problems with both water quantity and quality. Runoff in the North Fork watershed decreases during times of low precipitation, resulting in lower water levels at Lake Vermilion and possible water shortages for Danville. Nitrate concentrations (as nitrogen) in the lake water occasionally exceed the maximum contaminant level (MCL) of 10 mg/L for drinking water. The Danville-Lake Vermilion area is located over the Danville Bedrock Valley. Within this bedrock valley are sand and gravel outwash deposits that are sources of groundwater for wells in the area. An investigation of the potential for using groundwater from these deposits to supplement Danville's water supply indicated that • the availability of groundwater is limited because the sand and gravel aquifers in the Danville Bedrock Valley are not extensive, • groundwater pumpage from any additional high capacity wells will most likely cause a decline in the water levels of existing wells, • the quantity of groundwater needed for a supplemental supply may exceed the rate of groundwater recharge, • induced infiltration of water from Lake Vermilion may not significantly increase the availability of groundwater, • the concentration of nitrate in the groundwater may increase significantly as a result of any induced infiltration from Lake Vermilion. Available data indicate a high potential for the occurrence of thick, extensive deposits of sand and gravel within the confluence area of the Danville and Mahomet Bedrock Valleys in northern Vermilion County. An exploration program in the area from Lake Vermilion northward would better characterize the hydrogeology of these aquifers and define groundwater availability for all current and potential users. Test holes drilled into bedrock would ensure the evaluation of the entire sequence of the glacial deposits, particularly the thickness of sand and gravel aquifers