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Mr. Alex Schatz <br />March 30, 2007 <br />Page 5 of 7 <br />the flowrate into the system was equal to the outflow of the dewatering system. The recharge <br />was distributed across all cells in the recharge system. <br />The area northwest of Cell 7 was not modeled was a cell to be mined. Dewatering in that <br />area could temporarily dewater Fountain Creek and would likely affect the nearby wells. A <br />recharge system could be used to minimize the impacts to nearby wells and Fountain Creek. <br />Resu/ts <br />As stated above, each model run was set up as a transient model, but was run to <br />approximate equilibrium. All results were taken from the last time step when the model had <br />reached the approximate steady-state conditions. This simulates worst-case conditions whereby <br />the entire pit azeas are dewatered, and the surrounding drawdowns have reached their maximum <br />extent and magnitude. <br />Drawdown <br />Maps of predicted drawdown were created for each of the models runs (one for each pit). <br />The drawdown figures show drawdown contours relative to the pre-mining water table. <br />Predicted drawdown in area wells due to mining activities including dewatering, rechazge, and <br />slurry wall installation are presented on Tables 1 and 2. Table 1 presents drawdown information <br />for existing wells located on the Sundance property, and Table 2 presents drawdown information <br />for existing wells located outside, but within 600 feet, of the Sundance property. The effects on <br />nearby offsite wells ranges from 2 feet of water table increase (in the upgradient area as a result <br />of mounding) to 5 feet of water table decrease (in areas south and east of the site). The model <br />results indicate that the two domestic wells (Wells 6 and 8 on Figure 1 and Table 2) east of the <br />site will not be impacted by dewatering activities. <br />The drawdown due to dewatering of Cells 1 through 4 is minimal and mostly affects the <br />area west of Sundance Mine site (Figures 3 through 6). The slurry walls that will be constructed <br />around Cell 5 and Cell 6 create ground water shadows (drawdown) and mounds (increase in <br />water table) as presented on Figure 7. <br />The drawdown due to dewatering in Cells 7 and 8 is minimized by recharging the water <br />obtained from the dewatering system. Figure 8 presents the configuration of the dewatering <br />trench during mining at Cell 7 and the results of the model run. Figure 9 presents the <br />configuration of the dewatering trench during mining at Celi 8 and results of the model run. In <br />order to minimize the impact to the nearby offsite Well 21 (Figure 1) during mining at Cel] 8, the <br />recharge system along the property boundary should be operated differently during dewatering at <br />Cell 8. The recharge amount in the area four hundred feet west and 400 feet north of Well 21 <br />should be increased during dewatering at Cell 8. The model distributed the rechazge evenly <br />across the trench and then was operated by doubling the flowrate into the cells 400 west and 400 <br />north of the property corner near Well 21. <br />S:\536 -Banks and Gesso, LLCt536.4 -Sundance Pi[Uteport\Final Letter Report.doc <br />Martin and Wood Water Consultants, Inc. <br /> <br />