2025-04-11_REVISION - M1988112 (2)

Home Browse Search

Newmont Corporation July 23, 2020 Page 7 range between 29 and 39 gpm,which is approximately the inflow into the West Pit from the North Pit area and the Precambrian unit. Groundwater levels may rise above the ground surface, similar to that described for the partial cutoff wall. The option of a full cutoff wall without managing water levels on the West Pit side is unacceptable as there will be untreated discharges from the West Pit. The total volume of discharging water is considerably less with either the partial cutoff wall or the full cutoff wall in place. 3.7 Partial Cutoff Wall with Pumping of BF5 The partial cutoff wall remediation simulation was modified to include a groundwater pumping component of flow of well BF5 at a rate of 20 gpm for the BASE model, and 50 gpm for the PITWALL and UPFLOW models. Simulations for a partial cutoff wall with this hydraulic control results in maintaining a lower groundwater level on the upgradient side of the cutoff wall. The sources of groundwater flow into the West Pit are estimated to be primarily from groundwater migrating from the North Pit and from the Precambrian unit. Simulated groundwater flow into the West Pit is estimated to be 37 gpm for the BASE model. The higher simulated pumping rate at BF5 in the PITWALL and UPFLOW models increases this groundwater flow resulting in an estimated rate of 59 gpm and 60 gpm respectively. Even with BF5 pumping at nominal rates,groundwater flow exits the West Pit model from seepage through the cutoff wall at an estimated rate of 16 gpm for the BASE model, and 9 gpm for the PITWALL and UPFLOW models. However,these low estimated outflow rates are commensurate with the estimated outflows in the current operations water balance (Section 3.1). Flow lines in Figure 10 illustrate how the lower pumping rate in the BASE model allows for water to be diverted around the cutoff wall preventing alluvial water from entering the West Pit. Some of the groundwater leaving the West Pit may be captured by alluvial well M33, and to a lesser degree, M32. This remediation scenario may be a viable option as less water would require treatment. However,increased groundwater levels in the West Pit area as a result of the presence of the cutoff wall needs to be reviewed in terms of where water may discharge to the ground surface and where that water may migrate. Additional remediation simulations with different pumping rates should be considered to estimate an optimal pumping rate that would minimize the amount of water sent to treatment and maintain lower groundwater levels within the West Pit area to prevent groundwater from reaching the ground surface.