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Engineering Analytics, Inc. 1600 Specht Point Road Suite 209 Fort Collins,CO 80525 970.488.3111 www EngAnalytics.com <br /> Technical Memorandum <br /> To: Devon Hornvedt,Newmont U.S.A. From: Errol Lawrence, PG <br /> Limited Melissa Chalona, PE <br /> Company: BMRI Date: May 5, 2023 <br /> EANo.: 210105:10 <br /> Re: Revisions to Modeling of Potential Hydraulic <br /> Controls to Reduce Groundwater Flow to the West <br /> Pit, San Luis Project <br /> CC: Julio Madrid, Battle Mountain Resources <br /> Steven Carino, Battle Mountain Resources <br /> Karen DeAguero, Newmont U.S.A. Limited <br /> EXECUTIVE SUMMARY <br /> Engineering Analytics, Inc. (EA) has revised and updated numerical groundwater flow models <br /> utilized for assessing the relative effectiveness of potential hydraulic control measures for reducing <br /> groundwater inflow into the West Pit of the former San Luis Mine. Recent hydrologic <br /> investigations(EA,2022 and 2023)corroborate the conceptualization that most of the groundwater <br /> flowing into the West Pit is sourced from the alluvial aquifer and enters through the south end of <br /> the pit(EA, 2021). The models were revised to incorporate results of the recent hydrologic testing <br /> and to include a deeper layer to evaluate potential vertical groundwater movement between <br /> hydrologic units. The model domain and associated calibration targets were updated to reflect <br /> current survey data using North American Datum (NAD) 83, Colorado State Plane South (CSPS) <br /> projection. <br /> The revised model was calibrated to the same conditions as the original model, representing <br /> relatively static, non-pumping conditions that existed following termination of mine dewatering, <br /> and the current pumping of the pit backfill that reverses the natural hydraulic gradient between the <br /> West Pit and Rito Seco. The overall calibration of the revised model was improved compared to <br /> the original model. <br /> Four options were evaluated and included the no-action option, alluvial extraction wells, slurry <br /> wall without pumping, and slurry wall with pumping. <br /> Revisions to Modeling Hydraulic Controls, West Pit <br /> May 2023 1 Engineering Analytics,Inc. <br />