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4.0 MODEL SIMULATIONS 4.1 Exisfing Conditions Steady-state modeling of the irrigation season was used to calibrate system equilibrium to the measured water levels mentioned in Section 3.11. Monthly water level readings and other reported data can be seen in Appendix D. The aquifer was modeled as consisting of alluvium from the existing ground surface to the top of bedrock. Civil Resources evaluated the claystone bedrock as an aquitard, thereby forming the bottom of the model (see Figure 2a). The observed water levels used to calibrate the steady-state model are shown on Figure 6. Calibration is the process of refining input parameters and boundary conditions within reason so the model reflects observed water levels. Parameters including: 1) hydraulic conductivity; 2) bedrock elevations outside of the Site boundaries; 3) recharge rates; and 4) river slopes were adjusted during calibration. Water levels west of the Site were extrapolated from known measurements to the river elevation (hydraulic head) and water levels to the north and south were extrapolated based on the known Site gradients, generally maintaining a depth often to twenty feet below the ground surface. The groundwater levels to the east of the Site were estimated from the reported depths on the list of permitted wells in the area. The river slope was estimated from the USGS Quadrangle and the river elevation was extrapolated upstream and downstream from the surveyed level north of the Site. Hydraulic conductivities were adjusted within the range stated in Section 3.6 on Table 2. The recharge rates discussed in Section 3.8 (Table 3) were used in the calibration runs. Depth to bedrock at the Site was mapped from the 35 plus geotechnical borings and generally ranges from 36 feet in the central eastern margin to over 50 feet on the western margin. The bedrock near the eastern margin of the Site slopes moderately toward the west and flattens somewhat near the northwest Site margins and towards the South Platte River. Depth to bedrock east of the Site was contoured to match the geologic mapping and observed bedrock outcroppings approximately one mile east of the Site. Figure 7 shows the modeled groundwater contours. Table 7 below reports the steady-state modeled water levels and the measured water levels at the Site. Figure 6a shows a graph of the location versus site groundwater level. Overall, the model matched the existing water levels to a good degree of accuracy. Table 7 Measured and Modeled Site Groundwater Levels Well Observed[ Modeled Difference ft CRMW01 4911.87 4911.76 0.11 CRMW02 4911.01 4910.96 0.05 CRMW03 4915.69 4915.57 0.12 CRMW04 4922.67 4923.01 -0.34 CRMW05 4924.82 4925.02 -0.20 CRMW06 4922.66 4922.80 -0.14 CRMW07 4925.05 4925.01 0.04 Notes: 1.Observed values are average measured water levels from the 2004 imgadon season, June 23, 2004 to Odoher 15, 2004. Groundwater Model Report - SW TKO Water Storage Project - 7 - February 2005