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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 minter periods. Figure-5 shows the <br />net effect of the raining operation as the difference between the baseline water table <br />elevations and the water table elevations as simulated during the mining operation. <br />The resulu of the modeling show that the maximtrrrr extent of the drawdown in the water <br />table will occur adjacent to the site. The modeling shon~s a maximtrrrr drawdown resulting <br />from the dewatering operation of seven feet approximately one half mile south of the site. <br />The resulu 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 results of the modeling, in order to completely dewater both piu 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 surrotmding <br />groundwater elevations by effectively recharging the sturotmding aquifer. This would help <br />protect the two wells located to the north and northeast of the site. <br />Records from 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 ptrrnp in the well is not currently <br />known. Based on the resulu 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 cturent depth of the ptunp 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 mill have a large impact on <br />groundwater levels in the area, they may effect to some degree the movement of <br />grotmdwater in the area. For this reason, the effects of the two tmlined lakes were simulated <br />and compared against pre-mining mater levels. <br />Like the other unlined lakes in the area, the taro lakes on the site were modeled as areas of <br />relatively high hydraulic conductivity. The hydraulic conductivity was assturred to be two <br />orders of magnitude greater than that of the surrounding alluvium. 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 resulu of the simulation of reclamation conditions show only localized <br />minor variations in the groundwater elevations surrounding the site. <br />Sensitivity Analysis <br />As pan of the modeling efforts, a sensitivity analysis was completed to determine the effect <br />of cenain parameters variation on the model resulu. 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 anal}sis. For the anal}5is, the parameter was varied <br />Lafarge West, Inc. -6- Applegate Group, Inc. <br />Duckworth Pit Groundwater Study March, 2004 <br />