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Newmont Corporation <br /> July 23, 2020 <br /> Page 2 <br /> This memo provides a summary of updates to the models (items 1 through 6) and results of model <br /> simulations of remediation scenarios from the updated BASE, PITWALL, and UPFLOW models <br /> (items 7, 8 and 9). <br /> 2.0 SUMMARY OF MODEL UPDATES <br /> Several iterations of restructuring the bottom elevation of the model were required to achieve the <br /> observed groundwater flow gradients in area of the West Pit and observed saturated thickness of <br /> the alluvium. Discussions with HYS, which addressed model simulated alluvial aquifer saturated <br /> thickness,resulted in a final modification to the bottom elevation structure after the online meeting <br /> with LWS, HYS, AE, and BMRI (June 15, 2020). Model simulations using the most current <br /> bottom modification are comparable to those presented at the online meeting on June 15, 2020 and <br /> conclusions discussed at that meeting have not changed. <br /> 2.1 Boundary Elevation Adjustment <br /> Restructuring the bottom elevation required additional modification to the general-head boundary <br /> elevations for the boundary located in row 1 (north boundary) and column 1 (west boundary) in <br /> the West Pit groundwater models. These boundary elevations, which control the general direction <br /> and gradient of groundwater flow in the model,were modified by lowering the boundary elevation <br /> from the original elevations to produce groundwater levels in the area of the West Pit that are <br /> generally close to the observed water levels in that area. <br /> 2.2 Well BF5 Discharge Estimates <br /> Pumping data in the West Pit was re-evaluated to provide a more accurate estimate of the pumping <br /> rate in the West Pit. Recorded discharge from past years were reviewed. The average pumping rate <br /> of backfill well BF5 was estimated at 189.8 gallons per minute(gpm)with a standard deviation of <br /> 38 gpm. This is less than the 200 gpm used in the original models by HYS. However, 200 gpm is <br /> within a standard deviation of the average pumping rate calculated by LWS. <br /> 2.3 Sensitivity Analysis <br /> Sensitivity analysis was performed to assess which model parameters could be estimated for model <br /> calibrations. Composite scaled sensitivity (CSS) is a measure of the totals amount of information <br /> that is available from the simulated observations for a parameter. Parameters with less than one <br /> percent CSS relative to the parameter with the largest CSS lack sufficient sensitivity for parameter <br /> estimation. These insensitive parameters were assigned values estimated by HYS. <br />