What is an aquifer An aquifer is a

What is an aquifer? An aquifer is a geologic unit that can store and transmit water at rates fast enough to supply reasonable amounts of water to a well. The Mahomet aquifer consists of saturated glacial sand gravel below fourteen counties, from the Illinois-Indiana state line west to the Illinois River. The aquifer lies on top of the bedrock, and in the eastern three quarters of the area, it is deeply buried below younger fine-grained sediment. Figure courtesy of the Illinois State Geological Survey

Why is the Mahomet aquifer important? The Mahomet aquifer supplies water to more than 800, 000 people in east-central Illinois. It supplies most of the drinking water in this area. Water is pumped from wells to provide drinking water, to irrigate farmland, and to use for commercial and industrial purposes. The aquifer provides about 220 million gallons of water per day. The aquifer is recharged by rain that infiltrates the soil. This water may be used by plants or flow along the one of the flow paths shown in the figure.

How did the Mahomet aquifer form? Before the first glacial episode in Illinois, river valleys were carved into the bedrock. The deepest and widest valley carved into the bedrock was the Mahomet Bedrock Valley. The Mahomet Bedrock Valley was part of a much larger river system known as the Teays-Mahomet River System that once drained the Appalachian Mountains westward to the Ancient Mississippi River. The Mahomet Bedrock Valley was subsequently filled in and buried by glacial sediment deposited during the earliest glacial episodes.

As glaciers crossed east-central Illinois, meltwater flowing in front of and under the ice carried a large amount of sediment. Much of the Mahomet Bedrock Valley is filled with sand gravel deposited by glacial meltwaters. The valley was completely filled in by the end of the Illinois Episode glaciation. Collectively, these deposits of sand gravel form the Mahomet aquifer. In some places, the aquifer is 250 feet thick.

Monitoring groundwater levels As part of a U. S. Geological Survey program to monitor groundwater levels in the nation, scientists from the Prairie Research Institute and U. S. Geological Survey are measuring the water level in observation wells installed in the Mahomet aquifer, including several in the Sangamon River Forest Preserve. The data collected from the wells will inform water management in the future.

How do scientists monitor groundwater? This diagram shows the inside of a observation well. The water-level data collected from observation wells in the Mahomet aquifer and adjacent aquifers are being used to help determine the effects of increased pumping and climate change on these aquifers. The change in water level over time is used to determine such effects. Water levels are recorded manually in the field or remotely using sensors. View of well protectors at the Lake of the Woods Forest Preserve

On March 11, 2015, the U. S. Environmental Protection Agency designated a portion of the Mahomet Aquifer System as a sole source aquifer. This action adds a level of review for projects using federal funds, which may adversely impact it. Under the federal Safe Drinking Water Act, an aquifer supplying at least 50% of the drinking water consumed in the overlying area is designated a sole source, meaning no alternative water sources could meet the demand of the area. URL: http: //www. epa. gov/r 5 water/gwdw/mahomet/. Accessed March 11, 2015

How can we protect the aquifer? Properly seal abandoned wells to prevent contamination (hire a licensed professional). Unused or abandoned water wells pose one of the greatest threats to our water supply. They provide a direct route for pollutants to reach an aquifer. Protecting our groundwater from contamination is important for managing water resources. Once water is contaminated, it takes decades or longer to clean. Often the damage is permanent. For more information visit http: //www. epa. illinois. gov/topics /drinking-water/private-well-users/abandoned-wells/index

Many thanks to the geoscientists who prepared and edited this content, including Andrew Stumpf Edward Mehnert Lisa Anderson George Groeschen

For Further Reading Kempton, J. P. , W. H. Johnson, P. C. Heigold, and K. Cartwright, 1991, Mahomet Bedrock Valley in east-central Illinois: Topography, glacial drift stratigraphy, and hydrogeology, in W. H. Melhorn and J. P. Kempton, eds. , Geology and hydrogeology of the Teays-Mahomet Bedrock Valley system: Boulder, Colorado, Geological Society of America, Special Paper 258, p. 91– 124. URL: http: //dx. doi. org/10. 1130/SPE 258 Panno, S. V. , and H. Korab, 2000, The Mahomet aquifer: The Illinois Steward, v. 9, no. 1, p. 19– 21. URL: http: //www. mahometaquiferconsortium. org/sams. ILS. html Regional Water Supply Planning Committee, 2009, A plan to improve the planning and management of water supplies in east-central Illinois: Mahomet Aquifer Consortium, 92 p. URL: http: //www. rwspc. org/documents/ECIWater. Plan_062909. pdf Roadcap, G. S. , H. V. Knapp, H. A. Wehrmann, and D. R. Larson, 2011, Meeting east-central Illinois water needs to 2050: Potential impacts on the Mahomet aquifer and surface reservoirs: Illinois State Water Survey, Contract Report 2001 -08, 188 p. URL: http: //www. sws. uiuc. edu/pubs/pubdetail. asp? Call. Number=ISWS+CR+2011 -08 Soller, D. R. , S. D. Price, J. P. Kempton, and R. C. Berg, 1999, Three-dimensional geologic maps of Quaternary sediments in east-central Illinois: United States Geological Survey, Geologic Investigations Series Map I-2669. URL: http: //pubs. usgs. gov/imap/i-2669