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Mr. Alex Schatz March 27, 2006 Page 4 of 6 Modeling of Pits Information from Western Slope Aggregates suggested that the gravel pits would only be mined to a depth of 22 to 24 feet. Consequently, the pits were modeled as continuous drains at a depth an elevation of 5,376 feet, approximately 24 feet below the ground surface elevation, rather than as drains at the bottom of the modeled alluvial layer. The drain hydraulic conductance was set to 5,000 feet squared per day. The pits were modeled one at a time in accordance with our current understanding of Western Slope's plan to mine the pits individually. Pit 1 was modeled first as a drain, and was then converted to a lake while Pit 2 was modeled as a drain. Pits 1 and 2 were then modeled as lakes while Pit 3 was dewatered and the first three pits were modeled as lake while dewatering of the fourth pit was modeled. Reclaimed pits were modeled with a hydraulic conductivity of 100,000 feet per day and Specific Yield of 100 percent to simulate open bodies of water. Results As stated above, each model run was set up as a transient model, but was run to equilibrium. All results were taken from the last time step when the model had reached steady state conditions. This simulates worst case conditions whereby the entire pit areas are dewatered, and the surrounding drawdowns have reached their maximum extent and magnitude. Drawdown Maps of hydraulic head and drawdown are given for each of the four models runs (one for each pit). The hydraulic head contours give an approximate water level elevation during mining, while the drawdown figures show drawdown contours relative to the neazby wells. Table 2 lists the approximate predicted drawdown and approximate predicted water levels in each of the wells stated to be within 600 feet of the mined areas. This table also shows the reported depth of the well (from State Engineer well permit files) and the initial static water level (if known). The drawdown due to dewatering appears only to have minimal effects beyond approximately 1 mile of the pits. Drawdown in the nearby wells ranged from 1.0 feet of drawdown to approximately 16.5 feet of drawdown for wells closer to the pits. Effects on the Colorado River The net effect of the pumping on the river varied relative to proximity of the particular pit being dewatered to the river. Table 3 lists the river leakage water balance as reported by MODFLOW at the end of each simulation (time step 100). The net effect on the river was Martin and Wood Water Consultants, Inc.