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Engineering Analytics,Inc. 1600 Specht Point Rd. - Suite 209 Fort Collins,CO80525 Ph 970.488.3111 Fax 970.488.3112 <br /> 2 <br /> Technical Memorandum <br /> To: Devon Horntvedt, Newmont Mining From: Errol Lawrence, PG <br /> Company Melissa Chalona, PE <br /> Eric Roads, EIT <br /> Company: BMRI Date: February 21, 2023 <br /> EANo.: 210105:10 <br /> Re: Hydrologic Investigation Results, <br /> Santa Fe Formation, Southeast Portion of the West <br /> Pit, Battle Mountain Mine <br /> Cc. Julio Madrid, Battle Mountain Resources <br /> Steven Carino, Battle Mountain Resources <br /> EXECUTIVE SUMMARY <br /> EA conducted an investigation to further characterize hydrologic properties of the Santa Fe <br /> Formation (Fm) aquifer along the southeast edge of the West Pit where groundwater flows into <br /> the pit through an alluvial window. The volume of groundwater water entering the West Pit <br /> through this alluvial window relative to that entering from the surrounding bedrock is a critical <br /> factor in evaluating the long-term effectiveness of potential remedial actions. <br /> The investigation included the drilling, installation, and development of one well (identified as <br /> WP-6), conducting a pumping test of WP-6, and analysis of those test results. <br /> Results of the test analyses indicate that the consolidated sediments of the Santa Fe Fm aquifer <br /> have very low transmissivity (less than 0.12 ft2/d) and hydraulic conductivity of approximately <br /> 0.003 ft/d. These values are consistent with estimates from previous investigations and are more <br /> than three orders of magnitude lower than estimates for the alluvial aquifer. <br /> The Santa Fe aquifer discharge into the West Pit along the eastern perimeter is calculated as <br /> approximately 0.022 gpm — much less than the 173 gpm previously estimated for the alluvial <br /> aquifer. The results of the WP-6 pumping test in the Santa Fe Fm aquifer are consistent with the <br /> conceptualization;the alluvial aquifer discharge into the West Pit accounts for the bulk of the water <br /> that is currently being extracted from well BF-5. <br /> 1.0 BACKGROUND <br /> Battle Mountain Resources, Inc. (BMRI) operates a groundwater management plan that is <br /> designed to prevent discharge of mine-impacted groundwater from the backfilled West Pit of the <br /> former San Luis Mine into the adjacent Rito Seco drainage. Engineering Analytics, Inc. (EA)was <br /> February 2023 1 Engineering Analytics,Inc. <br />