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Newmont Corporation <br /> July 23, 2020 <br /> Page 5 <br /> the surface, as evidenced by springs which appeared prior to hydraulic controls being imposed by <br /> pumping BF5. The no-action remediation option is unacceptable due to the large discharge of <br /> groundwater exiting the West Pit since a portion of this discharged groundwater would likely <br /> migrate downgradient in the alluvial aquifer and subsequently discharge to Rito Seco. <br /> 3.3 Alluvial Well Field Simulation <br /> The model simulations related to an alluvial well field are based on controlling West Pit discharges <br /> under a no-pumping scenario in the West Pit, whereby the alluvial wells create a hydraulic stall <br /> situation so the discharged water can be controlled and pumped to treatment. In this scenario there <br /> is pumping of a set of alluvial wells in the area where model simulations indicate groundwater <br /> exits the West Pit. In the alluvial well field remediation scenario, groundwater leaving the West <br /> Pit ranges from 135 gpm for the BASE model to 140 gpm for the UPFLOW model,while the total <br /> amount of pumping from the well field is estimated to be 80 gpm for the BASE model and 90 gpm <br /> for the PITWALL or UPFLOW models. <br /> The groundwater exits the West Pit in a narrow region that is illustrated with the concentration of <br /> the flow lines for the BASE or the PITWALL models (Figure 7). Alluvial wells are marked by <br /> yellow squares. While the alluvial wells capture a portion of the groundwater exiting the West Pit, <br /> as well as alluvial groundwater between the alluvial well field and Rito Seco, groundwater flow <br /> paths show some of the water leaving the West Pit is not captured by the simulated alluvial well <br /> field and discharges to the Rito Seco(Figure 7). This is also an unacceptable remediation scenario <br /> if the alluvial wellfield cannot capture all of the water being discharged from the West Pit.Varying <br /> the number of wells and well spacings in the alluvium could not provide 100 percent capture of <br /> the West Pit discharge. <br /> 3.4 Interceptor Trench Simulation <br /> An interceptor trench was simulated in the models using the MODFLOW-2005 drain package. <br /> The elevation of the bottom of the trench is 8,575 feet. Placement of the trench in the groundwater <br /> model(interceptor trench shown in yellow)expands over the length of window where groundwater <br /> is simulated as exiting the West Pet (Figure 8). All groundwater exiting the West Pit is captured <br /> in these simulations The total amount of groundwater capture is between 215 and 219 gpm. This <br /> flow is greater than the flow exiting the West Pit because the trench bottom elevation is lower than <br /> both the groundwater elevation in the West Pit and the groundwater elevation in the alluvium south <br /> of the trench location. Approximately an additional 80 gpm of water captured in the trench is from <br /> the alluvial groundwater to the south of the trench and not from the West Pit. The current <br /> cumulative flow rate pumped to treatment is approximately 205 gpm. Therefore, there is no <br /> advantage in this remediation scenario, as it is estimated that there will be more flow to treat using <br /> an interceptor trench than under the current BF5 and alluvial well pumping. <br />