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Revisions to Modeling Hydraulic Controls, West Pit Devon Hornvedt <br /> San Luis Project Newmont USA Limited <br /> The calibrated model was then used to simulate a no-action option and various hydraulic controls <br /> measures. The no-action simulation indicates that alluvial groundwater entering into the West Pit <br /> through the southeast end of the alluvial window will exit the pit through the west end of the <br /> window and eventually discharge to the Rito Seco. <br /> Results of the alluvial extraction well simulation indicate complete capture of groundwater that <br /> would otherwise exit the West Pit through the alluvial window using a total extraction rate of 95 <br /> gallons per minute(gpm) from the combined five wells. <br /> The simulation of the slurry wall without pumping indicates that alluvial groundwater is generally <br /> deflected around the wall and does not enter the West Pit. However, the potentiometric surface <br /> within the West Pit rises above the ground surface after approximately seven years in response to <br /> inflow along the pit walls through the Precambrian and Santa Fe Formation units.This rise in water <br /> level elevation within the West Pit would result in surface discharge and the eventual topping of <br /> the slurry wall. <br /> The slurry wall simulations that include extraction from well BF-5 at 20 gpm indicate that no <br /> groundwater is discharged from the West Pit. The potentiometric surface within the West Pit <br /> stabilizes at an elevation of approximately 8,584 feet above mean sea level (ft amsl). The volume <br /> of water that would require treatment is reduced from 200 gpm under current conditions to <br /> approximately 20 gpm. <br /> Based on simulations using the revised and updated West Pit model, the most effective means of <br /> hydraulically controlling groundwater movement from the West Pit to the Rito Seco and reducing <br /> the volume of water that will require treatment, is the installation of a slurry wall along the south <br /> and west boundary of the Pit. <br /> 1.0 INTRODUCTION <br /> Engineering Analytics, Inc. (EA) was retained by Battle Mountain Resources, Inc (BMRI) to <br /> provide an assessment of potential hydraulic control options for the reduction or elimination of <br /> wastewater treatment associated with ongoing remediation of impacted groundwater derived from <br /> the West Pit of the former San Luis Mine in southern Colorado. The initial assessment included <br /> the development of numerical groundwater flow models for comparison of the relative <br /> effectiveness of potential hydraulic control measures in reducing groundwater inflow into the pit <br /> (EA, 2019). Simulated options included no-action (as a baseline), pumping from alluvial wells, <br /> placement of an interceptor trench, and installation of a slurry wall with pumping and without <br /> pumping. Results of the initial modeling indicated that the most effective hydraulic control <br /> measure to reduce groundwater inflow into the West Pit is the installation of a slurry wall coupled <br /> with limited pumping from within the pit. <br /> The conceptual site hydrologic model is that groundwater flow into the West Pit occurs <br /> predominately through the alluvial window along the south boundary of the pit. Groundwater flow <br /> from the pit walls through the Precambrian basement and Santa Fe Formation,and/or upward flow <br /> May 2023 2 Engineering Analytics,Inc. <br />