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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> Figure G-6 shows the potentiometric surface for the fourth quarter of 2024 (using the <br /> vertical projection of CSPS NGVD29). The arrows indicated on the map show the <br /> inferred groundwater flow direction based on the potentiometric data. Groundwater flow <br /> is generally perpendicular to the potentiometric contours. The area where groundwater <br /> flows into the West Pit is coincident with the "alluvial window" a section where the <br /> alluvium is in direct contact with the pit's backfilled materials. Based on hydrologic data <br /> and numerical groundwater modeling, it is estimated that over 80 percent of the <br /> groundwater captured at extraction well BF-5R is sourced from the alluvial aquifer. The <br /> potentiometric surface indicates there is a groundwater divide that has developed near <br /> monitoring well M-20. Alluvial groundwater west of M-20 generally flows along the Rito <br /> Seco drainage, whereas groundwater east of M-20 flows toward the West Pit. West of M- <br /> 20, the edge of the West Pit is in direct contact with the much lower permeability Santa <br /> Fe Formation, which restricts groundwater flow into or out of the Pit. <br /> Groundwater that is recovered from the extraction wells within the backfill of the West <br /> Pit and from extraction wells in the alluvial aquifer downgradient of the West Pit are <br /> treated to appropriate surface water standards at an onsite facility and then discharged <br /> into the Rito Seco under DP CO-0045675. Brine and sludge generated from the onsite <br /> treatment are discharged separately to a tailings impoundment, approximately one mile <br /> southwest of the West Pit. <br /> 6.0 ASSESSMENT OF HYDRAULIC CONTROL OPTIONS FOR WEST PIT <br /> GROUNDWATER MANAGEMENT <br /> Engineering Analytics, Inc. (EA), on behalf of BMRI, conducted an assessment of <br /> potential hydraulic control options for the optimization/reduction/elimination of <br /> wastewater treatment of impacted groundwater from the West Pit. The assessment <br /> included review of historic documents and site environmental data, site hydrologic <br /> investigations and the development of numerical groundwater models. <br /> The site hydrogeologic investigations included:(1) drilling of borings along the south and <br /> west edges of the West Pit to better define subsurface geology (Engineering Analytics, <br /> Inc. 2019a), (2) installation and testing of a series of wells completed in the shallow <br /> alluvial aquifer along the southeast edge of the West Pit (Engineering Analytics, Inc. <br /> 2022), and (3) installation and testing of a well completed in the underlying Santa Fe <br /> Formation that acts as an aquitard between the alluvial and Precambrian aquifers <br /> (Engineering Analytics, Inc. 2023a). These field investigations were conducted to better <br /> characterize geologic and aquifer properties in the vicinity of the West Pit and to <br /> validate/confirm the site hydrogeology and the results of the numerical modeling. <br /> Numerical groundwater flow models were developed to estimate the hydraulic response <br /> of the West Pit groundwater flow system to various potential hydraulic control measures <br /> (EA, 2019, 2023b). MODFLOW-SURFACT (HydroGeoLogic Inc., Version 3.0, 1996) <br /> was the initial code used to simulate groundwater flow in the project area. MODFLOW- <br /> SURFACT is a proprietary version of the widely used MODFLOW code for simulating <br /> groundwater flow. MODPATH (Pollock, 1994) was used to delineate groundwater <br /> April 2025 9 Engineering Analytics,Inc. <br />