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This SOW does not include conducting site inspections or contacting well owners to verify the presence, condition, or location of the existing legal uses including domestic supply wells or permitted wells identified from the District ' s database. TASK 1 -2 : Hydrogeologic Conceptual Model and Groundwater Model Configuration Prior to groundwater model construction, PBS&J proposes the design of a hydrogeologic conceptual model . A hydrogeologic conceptual model of an aquifer system is a simplified, qualitative description of the physical system. The conceptual model may include , but is not limited to, a description of the aquifers and confining units that make up the aquifer system, boundary conditions, flow regimes. sources and sinks of water, and general directions of groundwater flow. The site hydrogeologic conceptual model is based on information collected for Task 1 - 1 . To accomplish the second half of Task 1 -2, PBS&J proposes to evaluate the hydrogeologic system with MODFLOW 2000(Harbaugh et. al, 2000) . MODFLOW 2000 (Harbaugh et. al, 2000) is a three- dimensional, finite difference-modeling program which is cell or grid based and calculates flow in three- dimensions using finite difference techniques. Upon completion of the hydrogeologic conceptual model , a groundwater model grid will be assigned such that the aspects discussed and presented in the hydrogeologic conceptual model are adequately evaluated. This would require assigning the physical and hydraulic boundaries of the hydrogeologic conceptual model within MODFLOW 2000 (Harbaugh et. al , 2000) . Examples of physical boundaries include impermeable layers ( i.e., clay deposits), surface water bodies, or man made structures. Examples of hydraulic boundaries include groundwater divides and flow lines. TASK 1 -3 : Groundwater Model Calibration PBS&J proposes to calibrate the groundwater model in steady-state and transient conditions. The difference between the two techniques is that transient simulations are needed for time dependent analyses. Transient simulations produce a data set of hydraulic heads for every time step ( I through nTn) while steady-state simulations produce only one hydraulic head data set. For groundwater modeling, steady-state simulations are less complicated in terms of data management and, for this reason, are the first calibration step . The model will be calibrated by altering model input parameters until simulated hydraulic heads approached hydraulic heads in the unconfined and leaky confined aquifer(s) . This is accomplished through manual alterations of the parameters and/or the use of inverse modeling codes such as PEST (Watermark Numerical Computing, 2000), UCODE (Hill et . al , 1998), or MODFLOWP (Hill et. al, 2000) . The final steady-state calibrated model generates the predicted heads numerically through MODFLOW 2000 (Harbaugh et. al, 2000) and will be used as the basis for the transient model. If the transient model does not mimic observed conditions, the model will be re-evaluated and re-calibrated. TASK 1 -4: Groundwater Model Sensitivity Analysis PSB&J proposes a sensitivity analysis after model calibration. The analysis involves repeating model predictions after systematically modifying the model input parameters and calculating the sum of the squared residuals of the simulated hydraulic heads. This is then compared to the calibrated model to determine which model input parameters are the most sensitive to change ( Le . , greater uncertainty) and, in turn, an area of focus for future investigation. Page 3 of 5