CLINTON, Ill. -- The Mahomet Aquifer, an important source of drinking water for central Illinois, is a formation of sand and gravel that runs roughly from the Indiana state line west to the Illinois River in Cass County.
It underlies parts of 14 counties, appearing on a map like a 150-mile long zigzag that juts southwest from the Indiana line near Danville to just north of Decatur before turning northwest toward Peoria and finally turning southwest again along the Illinois River.
The counties that overlie the aquifer are: Cass, Champaign, DeWitt, Ford, Iroquois, Logan, Macon, Mason, McLean, Menard, Piatt, Tazewell, Vermilion and Woodford.
The sand and gravel is well over 100 feet below ground in the eastern end of the formation and closer to the surface to the west.
Water utilities in a large swath of central Illinois tap the aquifer. Some cities, such as Normal, use it as their only water source.
In all, about 750,000 people rely on the aquifer for drinking water, as well as farms and businesses across the region.