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Newmont Corporation <br /> July 23, 2020 <br /> Page 9 <br /> From the model simulations, it appears that the two keys to reducing the water handling and <br /> treatment are to establish how much of the inflow is attributed to the Rito Seco alluvial or colluvial <br /> sediments east of the West Pit and design a cutoff wall that will minimize infiltration of these flows <br /> into the West Pit. <br /> 5.0 SUMMARY <br /> The three conceptual models of the West Pit have been converted to MODFLOW-2005 format. <br /> Several modifications have been made to the model as well as additional work to test the <br /> representativeness of the models, including: <br /> • bottom elevation and the elevation of boundary conditions defined in the MODFLOW <br /> general-head boundary input file; <br /> • sensitivity analysis was conducted on three conceptual models identified as the BASE, <br /> PITWALL and UPFLOW models to identify parameters that could be estimated; <br /> • non-linear regression was used to calibrate each conceptual model; and <br /> • multi-model comparison was conducted to statistically evaluate the probability of each <br /> mode. <br /> From these analyses, it appears that the PITWALL model is the most probable that it represents <br /> the groundwater flow system. However, there are other indicators that suggest there is greater <br /> uncertainty in some parameter estimates in the PITWALL model. Therefore, LWS recommends <br /> that results of each model be considered when evaluating conclusions that can be drawn from the <br /> various remediation scenarios. The three models provide a range of possible outcomes of each <br /> remediation scenario. <br /> A mass-balance groundwater budget of current conditions in the West Pit generally indicates <br /> groundwater entering the West Pit from the North Pit, Precambrian unit, and the upgradient <br /> alluvium. The current condition at the site shows the majority of the contribution of groundwater <br /> flow into the West Pit is from the Rito Seco upgradient alluvium and ranges from 68% (UPFLOW <br /> model) to 76% (BASE model). This is a critically-important conclusion from the model <br /> simulations as, if the inflow from the Rito Seco alluvium can be controlled, the water treatment <br /> handling could be significantly reduced, as the pumping of BF5 can be reduced with either the <br /> partial or full cutoff wall option. It is for that reason that we are proposing the field studies <br /> described in Section 4.0. <br /> Each remediation scenario presented herein requires treatment of some captured alluvial and <br /> backfill groundwater. The cutoff wall simulations are successful in routing most of the Rito Seco <br /> alluvial groundwater around the West Pit instead of flowing into the pit. However, some pumping <br />