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The pits were modeled as constant head boundary conditions fixed at an elevation of 4855 <br />feet. The simulation was run for both the summer and winter periods. Figure-5 shows the <br />net effect of the training operation as the difference between the baseline water table <br />elevations and the water table elevations as simulated during the mining operation. <br />The results of the modeling show that the maximum extent of the drawdown in the water <br />table will occur adjacent to the site. The modeling shows a max;mum drawdown resuhing <br />from the dewatering operation of seven feet approximately one hall mile south of the site. <br />The results of the modeling also show that a practical mitigation alternative would be to <br />discharge the water from the dewatering operation into the adjacent lake to the north. Based <br />on the resulu of the modeling, in order to completely dewater both pits the estimated <br />discharge rate is approximately 1,127 gpm and 1,141 gpm for the winter and summer <br />periods, respectively. Discharging this water into the adjacent lake would help maintain <br />constant water level in the lake and would also serve to stabilize the surrounding <br />groundwater elevations by effectively recharging the stmrounding aquifer. This would help <br />protect the two wells located to the north and northeast of the site. <br />Records fmm the State Engineer's Office indicate that the domestic well located to the <br />south of the site has a depth of 24 feet. The depth of the pttmp in the well is not currently <br />known. Based on the results of the modeling, the water level in the well will remain above <br />the maximum depth of the well during the mining operation. If at any time the water levels <br />in the well fall below the current depth of the pump as a result of the mining operation the <br />pump should be lowered. <br />Simulation of Reclamation of the Site <br />Following completion of mining at the Duckworth Pit, reclamation of the site will leave two <br />unlined lakes. While it is not anticipated that the lakes will have a large impact on <br />groundwater levels in the area, they may effect to some degree the movement of <br />groundwater in the area. For this reason, the effects of the two unlined lakes were simulated <br />and compared against pre-mining water levels. <br />Like the other unlined lakes in the area, the two lakes on the site were modeled as areas of <br />relatively high hydraulic conductivity. The hydraulic conductivity was assumed to be two <br />orders of magnitude greater than that of the surrotmding alluvitun. Figure-6 shows the net <br />effect of the reclamation of the site as the difference between the baseline water table <br />elevations and the water table elevations as simulated following reclamation for summer and <br />winter periods. The results of the simulation of reclamation conditions show only localized <br />minor variations in the groundwater elevations surrounding the site. <br />Sensitivity Analysis <br />As part of the modeling efforts, a sensitivity analysis was completed to determine the effect <br />of certain parameters variation on the model results. Due to the lack of site specific <br />information on seepage rates from Idaho Creek and the Smith & Emmons Ditch, this <br />parameter was chosen for the sensitivity analysis. For the analysis, the parameter was varied <br />Lafarge West, Inc. -6- Applegate GrOUp, InC. <br />Duckworth Pit Groundwater Study March, 2004 <br />