New Drill Holes Aid Aquifer Mapping and Extend Boundaries of Coal Seam

Closeup of Somer Township boring As part of research undertaken to study the Mahomet Aquifer, funded by the Illinois American Water Company, geologists from the Quaternary Geology Section, Hydrogeology Section, and Coal Section at the Illinois State Geological Survey assisted in the retrieval of sediment and bedrock cores during the drilling of groundwater monitoring wells in Champaign and Piatt Counties. Information collected from drilling these boreholes will improve geologic maps being developed for the area and provide a better understanding of the subsurface geology in east-central Illinois.

The drilling of three new boreholes on property owned by Orr Farms Incorporated, Somer Township, and Stanton Township provided additional information about the glacial history and formation of the Mahomet Bedrock Valley. From the cores, sediments were identified that had been deposited under and in front of glaciers from centers of accumulation over northeastern Canada, possibly associated with the oldest glacial advance into the region. These sediments are similar to glacial deposits uncovered during drilling on the University of Illinois campus in 2009 and those previously mapped in west-central Indiana.

Additional information obtained from the bedrock core indicates that the subcrop of the Herrin Coal and Pennsylvanian rocks—observed in core from recently drilled boreholes on the University of Illinois campus—extends further north. A well drilled on Somer Township property (located approximately 5 miles north of Urbana) yielded a 4.7-foot-thick coal seam that is thought to be the Herrin Coal. The Stanton Township well (about 8 miles northeast of Urbana) yielded traces of oil in lower Pennsylvanian sandstone.