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Dewatering Evaluation Report <br /> Varra Pit 124 <br /> Weld County,Colorado <br /> Page 4 <br /> To simulate mine dewatering constant head line sinks were assigned to cells within the pit areas <br /> with head values approximately four feet above the bedrock elevation, which accounts for the <br /> predicted seepage face. To account for significant differences in bedrock elevations linear <br /> gradients were assigned to the line sinks. Varra does not intend to mine more than two pits at any <br /> one time and as a worst case scenario dewatering was simulated for the entire central and <br /> northwest pits — the largest pits within the mine boundary. Predicted groundwater contours <br /> resulting from mine dewatering are presented on Plate 6. <br /> Varra intends to line the mined out pits for water storage. To evaluate the effects of lining the <br /> three cells on the local groundwater hydrology, barrier walls were assigned near the excavation <br /> limits of the referenced cells. Plate 1 depicts boundary conditions for the lined pits. As mentioned <br /> model assigned wells were used to obtain pre-mining model predicted water levels at four <br /> locations (MW-1 — MW-4). These predicted water levels were used as a comparison to various <br /> simulations, including shadow and mounding effects. To simulate filled ponds, the interior of the <br /> reservoirs were assigned constant head values at an elevation slightly below ground surface <br /> elevations (4675 feet above mean sea level). A simulation was then run to predict the effects of <br /> the lined reservoirs on the groundwater hydrology. Plate 1 depicts the initial calibration computer <br /> simulation output. Table 1, presents the predicted water level changes as a result of lining the <br /> mined out pits. <br /> Table 1—Lined Pit Water Level Comparison Points <br /> Point Calibration Water Level Post Lining Water Level Elevation Difference(ft) <br /> MW-1 4680.39 4680.64 0.25 <br /> MW-2 4681.37 4681.82 0.45 <br /> MW-3 4674.07 4673.90 -0.17 <br /> MW-4 4675.32 4674.91 -0.41 <br /> Results <br /> A review of plate 6 shows that the groundwater hydrology north of the Big Thompson River and <br /> east and south of the South Platte River is unaffected by dewatering. The model predicts a <br /> drawdown of 4 to 5 feet 1,550 feet west of Pit 124. A review of Table 1, shows that the lining of <br /> mined pits will have a de minimis effect on groundwater hydrology. Predicted post lining head <br /> levels immediately up and downgradient of the barrier walls are within the range of normal <br /> seasonal water table elevation changes. <br /> Conclusions <br /> The results of analytical and numerical solutions indicate that the proposed mine dewatering <br /> activities will not adversely affect the regional groundwater hydrology. Based on the location of <br /> registered water wells, the saturated aquifer thickness west of the mine is sufficient to provided <br /> adequate well yields. The predicted drawdown associated with the mine dewatering represents <br />