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Mr. Stephen P. Swanson <br /> August 28, 1997 <br /> Page 6 <br /> amount of mutual interference between wells for scenarios with different number of wells <br /> pumping. We will seek your input to compile a list of likely scenarios. At this time, we <br /> foresee potential pumping scenarios of two, four, six and eight wells pumping in the <br /> DeWitt County wellfield with one or both of the Cisco wells pumping. Different <br /> combinations of pumping wells will be simulated to deterniine the scenario that produces <br /> the least interference between wells for periods of 60, 90, and 200 days, as well as for a <br /> steady state(continuous pumping) scenario. The water quality data collected in Task 2 <br /> will be incorporated into the evaluation to determine which pumping schedules are likely <br /> to meet the discharge permits for the DeWitt wellfield. <br /> Task 6)Determine Egpected Impact on Surrounding Wells <br /> After the most favorable pumping strategies have been identified, the drawdown in the <br /> Mahomet Sand and Glasford Sand aquifers for the area sunounding the well field will be <br /> determined from the model output. This information will be used to produce maps <br /> showing the predicted drawdown in each of the two aquifers for the various pumping <br /> scenarios of different numbers of wells pumping and duration of pumping as determined in <br /> Task 4. This analysis is expected to be sufficient to estimate future drawdown at any <br /> point in either aquifer within the modeled domain. <br /> Task 7) Conduct Eatended Wellfield Capacity Test (Optional) <br /> After the future drawdown for various pumping scenarios has been predicted by the <br /> model, the City may elect to conduct an extended pumping test of both well fields at the <br /> highest projected pumping rate for a period of 30 days. As an optional service,we will <br /> provide the manpower and equipment required to operate both wellfields on a continuous <br /> basis for 30 days. We will measure water levels in the observation wells and pumping <br /> wells for the duration of the test. This test will confirm the reliable capacity of both <br /> wellfields. Prior to the test, we will conduct an additional model run to predict the � <br /> response of both aquifers to the extended test. The model results will be compared to the � <br /> test results to serve as an additional verification of the model predictions. �� <br /> Task 8)Training City Staff on Modeling Package(Optional) ', <br /> The Modflow modeling package that will be used for this project is a flexible and powerful I <br /> modeling package, but it is difficult to use without a user interface program. We will use <br /> one of several commercially available Modflow interface program to build the data files <br /> and process the output files for the model. The packages we may use include ModelCad, <br /> Visual Modflow, Groundwater Vistas, or others. Our intention is to select a program that <br /> meets the needs of the project and that is user friendly to the degee that the City's <br /> personnel can learn to manipulate the model input files for future needs. We will work <br />