2025-04-11_REVISION - M1988112 (2)

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Newmont Corporation July 23, 2020 Page 3 2.4 Model Calibration The three conceptual models simulating current conditions were calibrated using non-linear regression. Current conditions include BF5 pumping 189.8 gpm in the West Pit along with two down-gradient alluvial wells M32 and M33 pumping a total of 15 gpm. Calibration was validated by simulating groundwater conditions without pumping well BF5 in each calibrated conceptual model. The simulated pre-pumping water levels were a reasonable match to observed pre-pumping water levels which support the calibration results of each conceptual model. 2.5 Multi-Model Analysis A multi-model analysis was conducted to compare the three conceptual models. The Kashyap Information Criteria (KIC) was used to rank models and assign a probability that a model represents the true, but unknown, groundwater flow system. Models that include pre- and current pumping conditions were evaluated. KIC model probabilities for the three models are 45%for the PITWALL model, 28% for the UPFLOW model, and 27% for the BASE model. Given this probability distribution between the models, each model can be considered reliable for modeling simulations results, thus providing a range of possible outcomes. 3.0 SIMULATION RESULTS Current groundwater flow conditions and remediation scenarios developed by HYS were simulated in the updated BASE, PITWALL, and UPFLOW models, as described below. The U.S. Geological software program ZONEBUDGET was then used to calculate a mass balance of flow into and out of the West Pit from different zones in the model. Zones defined correspond to hydraulic conductivity zones, with one additional zone added for the North Pit area so that the North Pit area contribution of groundwater flow into the West Pit can be calculated (Figure 1). West Pit area mass balance groundwater budgets for each conceptual model, including current conditions and remedial simulations, are listed in Table 1. These remediation scenarios include: • an alluvial well field; • an interceptor trench; • a partial cutoff wall; • a full cutoff wall; • a partial cutoff wall with pumping wells M32, M33 and BF5; and • a full cutoff wall with pumping wells M32, M33 and BF5.