R97-146 ACCEPTING THE PROPOSAL AND AUTHORIZING AN AGREEMENT

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Mr. Stephen P. Swanson August 28, 1997 Page 5 the pumping well will be read with the airlines in place on the wells. Water levels in the six new monitoring wells in the Glasford Sand and confining unit will be measured by hand using an electric water level indicator at least twice per day. At least one of the Glasford Sand monitoring wells will be monitored with a data logger to provide more frequent monitoring information. Water levels in both Cisco wells will be measured at least twice daily for the DeWitt County wellfield tests. Pumping rate will be measured with a temporary meter installed in the pump discharge line for each pumping well. The data from the pumping tests will be analyzed using the appropriate analytical methods to determine the transmissivity, storage coefficient, and boundary conditions of the aquifer as well as the vertical hydraulic conductivity and leakance of the confining unit. This information will be used to deternune the response of the aquifer to sustained pumpage and the effect on the overlying Glasford Sand aquifer by constructing a digital computer model of the aquifer as described in Task 4. Task 4) Construct Digital Model of Aquifer The aquifer properties measured in Task 3 will be used to construct a digital computer model of the aquifer using the Modflow modeling package. Modflow is the industry standard for ground water flow models and is the most versatile and widely respected package available. By using Modflow, the City will have a model that will be usable for years into the future and that will be readily understandable and respected by other governmental agencies or consultants. The model will be a two layer model to simulate both the Mahomet Sand and Glasford Sand aquifers and the confining unit that separates them. The model area will include the two well fields and enough surrounding area to incorporate the wells which have reported problems. The model domain will be large enough to prevent boundary effects from interfering in the zone of interest. The aquifer boundary conditions will be set on the basis of the pumping test results. The model will be calibrated to pre-test conditions and then verified using the pumping test data to demonstrate that the model accurately reproduces the aquifer's response to pumping. After the model has been calibrated and verified, it can be used to predict the response of the aquifer to various pumping scenarios as described in the subsequent tasks. Task 5)Determine Optimal Operating Schedule For Wellfields The calibrated and verified model developed in Task 4 will be used to predict the response of the aquifer to various pumping scenarios. The model will be used to determine the