Hydrogeology and Ground-Water Availability in Southwest McLean and Southeast Tazewell Counties, Vol. 2

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Excerpt from Hydrogeology and Ground-Water Availability in Southwest McLean and Southeast Tazewell Counties, Vol. 2: Aquifer Modeling and Final ReportThe characterization of the hydrogeology of the glacial-drift aquifer system was simplified to allow the development of a ground-water ¿ow 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 ¿ow 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-ievel data, chloride concentrations, and percent modern carbon data from observation wells, an updated conceptual understanding of the ground water ¿ow 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 ¿ows 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 ¿owing 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 in¿ux ofground 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.About the PublisherForgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.comThis book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.