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Dewatering Evaluation Report <br />Varra Pit 122 <br />Weld County, Colorado <br />Page 4 <br />levels (obtained from current monitoring well data) were compared to the model predicted <br />elevations. The model was adjusted using trial and error methods of reassigning river boundary <br />conductance and general head elevations until the model predicted water table elevations closely <br />matched measured water levels. The calculated head values for the model assigned wells were <br />then used as observed levels so that subsequent model simulations would predict changes to <br />groundwater hydrology compared to the calibrated simulation. The calibration simulation <br />included seepage from the river boundaries (ditches) and the pumping of cell A of Pit 116 — which <br />is reflective of current field conditions. The calibration simulation is depicted on Plate 4. The <br />observed head values referenced above are depicted on Plates 5 and 5A. As the mining at Pits 116 <br />and 122 will likely be concurrent, multiple lining and dewatering scenarios were evaluated. Plates <br />6-11 depict the effects of concurrent mining and reclamation activities for pits 116 and 122. <br />Varra intends to line cells A and B of Pits 116 and 122 for water storage (Plate 1). To evaluate the <br />effects of lining the four cells on the local groundwater hydrology, barrier walls were assigned near <br />the excavation limits of the referenced cells. Plate 12 depicts boundary conditions for the lined <br />pits. Plate 13 depicts the calibration model output that was used to compare pre -mining to post <br />mining water levels. Head elevations, obtained from the calibration runs, were recorded at six <br />locations immediately up and downgradient of the pits as depicted on Plate 14. To simulate filled <br />ponds, the interior of the reservoirs were assigned a constant head value of 4796 feet, which is <br />slightly below ground surface. A simulation was then ran to predict the effects of the lined <br />reservoirs on the groundwater hydrology. Plate 14 depicts the computer simulation output. Table <br />1, presents the predicted water level changes as a result of lining the mined out pits.