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1 <br />' Once the model was calibrated to match the groundwater levels reported from the well data, the <br />existing slurry wall was simulated in the model to establish the groundwater levels that currently <br />exist. Tltis simulation with the existing slurry wall was used as the baseline and can be seen in <br />' Figure No. 3. The results of this simu]ation were compared to the water levels recorded in the <br />monitoring data around the existing slung wall and match fairly reasonably. <br />The next step included, in addition to the existing slurry wall, the proposed dewatering operation <br />at the North Taft Hill Expansion site in the GMS model. This simulation computed new <br />' groundwater levels with the dewatering operation in the model. Figure No. 4 shows the <br />groundwater levels with the dewatering operation. <br />' The difference between the baseline and the dewatering condition shows the potential impacts of <br />the proposed operation, as presented in Figure No. 5. <br />' EXISTING AND PREDICTED GROUNDWATER CONDITIONS <br />Modeling results indicate that along the western side of the property the drawdown caused by [he <br />' operation is approximately 5 to 6 feet. A drawdown of 1 foot occurs at a maximum distance of <br />1800 Feet to the west from the pit boundary. Along the eastern side of the property, the estimated <br />drawdown ranges from 2 to 4 feet, with a 1-foot drawdown occurring at a distance of 2400 feet <br />' from the pit boundary. Figure No. 5 shows the range and magnitude of the projected aquifer <br />drawdowns. Due to the fact that groundwater flow is generally northwest to southeast, the zone <br />of influence on the east extends to a further distance than on the west, which is as expected. The <br />' figure also shows that the anticipated drawdowns on the west side are slightly greater than the <br />drawdowns on the east side. This is a direct result of the "mounding" and "shadowing" effects <br />caused by the existing slurry wall, as reported in the previous study. The mounding is causing <br />' the water table to the west to increase slightly, and the shadowing is causing the water table to <br />the east to decrease. Because of this fact, the drawdowns to the proposed dewatering trench will <br />be slightly larger on the west than on the east. This is also reflected in Figure No. 5. <br />' WMN has developed a monitoring program to obtain water level information in surrounding <br />wells. Details of this well monitoring will be made available upon request through the applicant. <br />1 <br />1 ' <br />1 <br />1 <br /> <br /> <br /> <br />