R2002-79 AUTHORIZING AGREEMENT - Laserfiche WebLink

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r • ' Summary This proposal is being developed in response to the findings of a recent report, CR2001-11, by the Illinois State Water Survey, that indicates a hydraulic connection exists between the Mahomet Aquifer, the overlying aquifer materials, and the Sangamon River. This connection has significant implications in that it influences the rate of recharge and discharge to the aquifer and influences the flow volume in the Sangamon � River. The connection was unknown until this last year and previous interpretations have assumed the Mahomet Aquifer was hydraulically isolated from the overlying materials by a low permeability till. We propose to install a series of observation wells near Decatur #2 (Cisco Well Field) in the Wedron, Glasford, and Mahomet Aquifers, set up monitoring stations along the Sangamon River, then perform a step test and an aquifer test on Decatur #2lasting 30 days. The water level information gathered during the test will be evaluated to determine the aquifer properties near Decatur #t2 and to delineate the areas of connection between the various aquifers and the Sangamon River. We propose a 1 year study, starting April 15, 2002, that will include drilling in the Spring and Summer of 2002, testing Decatur #2 in September or October 2002, and completing a report of the fmdings by April 1, 2003. Project Goals � The project goals are to delineate the areas of connection between the unconsolidated aquifers and determine the aquifer properties of the Mahomet Aquifer in the vicinity of Decatur #2, so that we can develop a new conceptual model of the flow system in this part of the Mahomet Aquifer. This new understanding of the system will allow researchers and water users in the area to better evaluate the impacts of changes in withdrawals as they relate to well interference and efficient use of the available water resources. For the Mahomet Valley Water Authority, this information will provide data relevant to the potential for well interference problems in the shallow aquifers in the area. For the City of Decatur, these data will provide more accurate interpretation of the possible impacts from increased or sustained use of the DeWitt and Cisco well fields. Cooperative Requirements Cooperation will be key to the success of this project. ISWS staff will work with the City of Decatur to utilize Decatur #2 for the pumping test. Modifications to the discharge pipe will be necessary to accommodate the measurement of flow rate during the test. The City of Decatur will be responsible for making the piping modifications at the wellhead, as well as for turning the pump on and off during the step test and the aquifer test. The MVWA will assist the ISWS in securing permission to install monitoring wells on right-of-ways and private properry, where necessary. , The Illinois State Geological Survey has proposed to work in the area during the Spring and Summer of 2002 to provide a detailed cross-section across the Mahomet Valley using high-resolution geophysics. The ISWS and the ISGS have agreed to tailor their efforts near the proposed study site so that the data the ISGS collects, including drilling several borings to confirm their geophysical interpretations, will be useful in completing this project. The advantage for the sponsors is the availability of additional geologic data as well as the installation of several additional observation wells in the confirmation boreholes that would not have been utilized for this effort otherwise.