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Miniature of Hydrogeology and ground-water availability in southwest McLean and southeast Tazewell counties. Part 2: aquifer modeling and final report

Hydrogeology and ground-water availability in southwest McLean and southeast Tazewell counties. Part 2: aquifer modeling and final report

Part of: Electronic Documents of Illinois

In 1993, with funding from the Long Range Water Plan Steering Committee (LRWPSC), the Illinois State Water Survey (ISWS) and the Illinois State Geological Survey (ISGS) began a study of the sand-and-gravel aquifers in southwest McLean and southeast Tazewell Counties to estimate the availability of ground water and determine the hydrogeologic feasibility of possibly developing a regional water supply. The study area includes the confluence of the buried Mahomet and Mackinaw Bedrock Valleys (confluence area) and contains part of one of the largest sand-and-gravel aquifers in Illinois, the Sankoty-Mahomet Sand aquifer. The study had two goals: (1) to determine the quantity of water a well field in the Sankoty-Mahomet Sand aquifer could yield, and (2) to determine the possible impacts to ground-water levels and existing wells that might occur in the Sankoty- Mahomet Sand aquifer and overlying aquifers from the development of a well field pumping 10-15 million gallons of water a day (mgd). Two major tasks were completed to meet the study goals. The first task was a hydrogeologic characterization of the glacially deposited (glacial-drift) aquifers within the confluence area. Results of the hydrogeologic characterization were published in 1995 (Herzog et al., 1995a and b) and a summary of their findings are in the appendices. The second task, and the subject of this report, was the development of a computer-based, mathematical model of the ground-water flow in the glacial deposits (ground-water flow model). The ground-water flow model was used to simulate the effects of a hypothetical well field for various locations within the study area and to provide an estimate of the amount of ground water a regional well field could yield from the Sankoty-Mahomet Sand aquifer within the confluence area. The characterization of the hydrogeology of the glacial-drift aquifer system was simplified to allow the development of a ground-water flow model. The generalized hydrogeology resembled a layer cake with uneven layers, some of which were discontinuous. The layers included relatively impermeable bedrock overlain by three sand-and-gravel aquifer layers that are generally separated by aquitard layers. Due to the complexity of the spatial distribution of the sand-and-gravel deposits above the Sankoty-Mahomet Sand aquifer, these shallower deposits were generalized as two aquifer layers. Although none of the aquifer deposits represented by the shallower aquifer layers are capable of sustaining a 10-15 mgd water supply, the thickness, distribution, and hydraulic properties of these deposits are important for a complete understanding of the hydrology of the model area. In some parts of the area covered by the ground-water flow model, two or more of the aquifer layers are in direct contact, providing a 'window' of hydraulic connection between the aquifer layers. In other parts of the model area, one or more of the aquifer layers are absent. Using the information from the hydrogeologic mapping and water-level data, chloride concentrations, and percent modern carbon data from observation wells, an updated conceptual understanding of the groundwater flow system for the Sankoty-Mahomet Sand aquifer was developed that described the movement of ground water into and out of the model area. Ground water in the Sankoty-Mahomet Sand aquifer generally flows through the Mahomet Bedrock Valley from the southeast, westward to the Illinois River and northward through the Mackinaw Bedrock Valley. The natural ground-water discharge areas for the Sankoty-Mahomet Sand aquifer in the study area are the Mackinaw River in the west-central part of the study area and Sugar Creek in the southwestern part of the study area. In some areas very close to the rivers, ground water is flowing upward from the Sankoty-Mahomet Sand aquifer through the upper aquifers and into the stream beds. There is a slight hydraulic gradient (slope) east of the model area that steepens where the flow enters the study area, even though the aquifer volume increases. This slope increase is caused by a greater amount of recharge entering the aquifer due to hydraulic connections with overlying aquifers. The areas of connection are more numerous in the west and north portions of the model area, as demonstrated by increases in water levels, decreases in chloride concentrations, and increases in modern carbon isotope concentrations in the Sankoty-Mahomet Sand aquifer. Down gradient of these connections, the chloride concentrations remain low, which suggests that the influx of ground water through these connections provides the majority of the recharge in these areas. Water pumped from the Normal west well field south of Danvers, which has wells penetrating into one of these upper aquifer connections, has low chloride values, indicative of water coming from the upper sands. Although the size of the original study area was about 260 square miles, the area to be modeled (model area) was expanded to 1,100 square miles. This expansion was necessary to reduce the effects of the model boundary conditions on simulated water levels in the study area. The simulated water levels are strongly influenced by the boundary conditions, which reduce the accuracy of the simulated water levels near the boundaries. The ground-water flow model was developed using Visual Modflow software. Three aquifer layers sandwiched between four aquitard layers are simulated in the model. Bedrock forms the lowest aquitard; till units form the others. The hydraulic property values of each hydrogeologic unit were assigned to the corresponding layer in the ground-water flow model where the unit was present. When a unit was absent, the layer was assigned the value of an overlying or underlying hydrogeologic layer. The model's boundary conditions control the regional flow into and out of the study area, discharge to and from the streams, infiltration from precipitation, and removal of water by production wells. The model was calibrated to match water levels measured in area wells in 1994 and to match the baseflow gains and losses in the Mackinaw River and Sugar Creek. The mean absolute error of the simulated water levels was 4.99 feet, which was only slightly greater than the errors associated with the potentiometric surface maps, indicating a good match between the model and the characterization of the ground-water flow system. The ground-water flow budget calculated using the model shows that 80 percent of the water coming into the model is from infiltration of precipitation, 11 percent is from the regional Mahomet aquifer in the east, and 8 percent is from river leakage. The budget also shows that 57 percent of the surface and ground water that leaves the model area does so through discharge to the rivers, 33 percent to the regional ground-water flow to the north and to the west, and the remaining 10 percent to existing production wells. (See online pub for remining abstract...)

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Human Services Plan: State Fiscal Year 2008

Part of: Electronic Documents of Illinois

The Illinois Unemployment Insurance Act, the federal Wagner-Peyser Act, and the federal Workforce Investment Act WIA of 1998 authorize the Unemployment Insurance, Employment Service and Labor Market Information programs. Through its administration of these programs the Illinois Department of Employment Security IDES plays a central role in improving Illinois' economic environment and the prosperity of its people.

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Illinois Multi-Year Strategy to Control Drug and Violent Crime FFY 2004

Part of: Electronic Documents of Illinois

The Illinois Criminal Justice Information Authority convened a Criminal Justice Planning Assembly in which policy makers, service providers, researchers, practitioners, and elected officials participated. The results are a Criminal Justice Plan for the State of Illinois. A primary purpose of the Plan was the development of a framework for a comprehensive statewide approach to coordinating the allocation and expenditure of all federal and state funds appropriated to the Authority and made available for juvenile and criminal justice purposes. Based on these drug and violent crime issues, the input received and its discussion, the Authority has identified seven priorities for FFY2004. These priorities are consistent with and supportive of the National Drug Control Strategy.

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Illinois Libraries Fall 2002

Part of: Electronic Documents of Illinois

Contents include: The Jewel of Lisle by Daniel K. Blewett; A Comparison of Two State Academic Library Consortia: Illinois ILCSO and Missouris MOBIUS, How They and Their Library Catalogs Work by Xiaotian Chen; Educational Materials On Three Health Related Topics: Suicide, Alcohol and Sleep by James T. Struck.

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Illinois Property Tax Rate and Levy Manual

Part of: Electronic Documents of Illinois

The Property Tax Rate and Levy Manual has been prepared by the Department of Commerce and Community Affairs to serve as a guide for all non-home rule units of government in Illinois. All tax rates are in conformance with the Illinois Compiled Statutes 1998 State Bar Association Edition. Not included are provisions for tax levies available only to the Chicago Park District, Chicago School District, and the Metropolitan Water Reclamation District of Greater Chicago. Certain levies generally available to special districts are listed on pages 29 and 30 and are not repeated in the section pertaining to the particular types of districts. Home rule municipalities and counties are not bound by the rate limitations and requirements contained in this manual. The purpose of the manual is to help local officials realize available sources of revenue which may be used to finance their respective unit of governments services. The manual is designed to serve as an information tool for local officials. Provisions of the manual should not be enacted without the advice of legal counsel.

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Illinois Libraries

Part of: Electronic Documents of Illinois

Contents include: The Response of Public Libraries to the Events of September 11, 2001 by Leigh S. Estabrook; Evaluation of Illinois LSTA Fiscal Year 1998-2002 by Debra Wilcox Johnson; Russia: Into the Unknown by Michael P. Ragen; Searching for Chinese Bibliographic Records in ILLINET Online by Junlin Pan.

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Illinois Labor Relations Board. Compliance Examination for the two years ended June 30, 2007

Part of: Electronic Documents of Illinois

Report on the Illinois Labor Relations Board's compliance with State of Illinois statutes and regulations for the two years ended June 30, 2007.

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Illinois Natural History Survey Reports

Part of: Electronic Documents of Illinois

Contents include: The art and science of communicating nature; Possible displacement mechanisms in non-native crayfishes; Nutrients in Illinois streams; How does suburbanization influence pest problems?; Are small, isolated prairie preserves sustainable?; Species spotlight -- black and yellow garden spider; The naturalist's apprentice -- capture a garden spider's web

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Illinois Natural History Survey Reports

Part of: Electronic Documents of Illinois

Mapping the Diversity of Amphibians and Reptiles in Illinois A Perplexing Pest Problem in Peppers in Illinois Database Gathers Taxonomic Information Channel Catfish Populations in the Upper Mississippi River System Species Spotlight: Halloween Spider The Naturalist's Apprentice: Spider Web Maze

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Illinois Mammals Activity Book

Part of: Electronic Documents of Illinois

When using this activity book, students will become familiar with the traits and appearance of 16 mammal species that live in the state of Illinois.

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