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Hydro Investigation Results <br /> Santa Fe Formation-West Pit Battle Mountain Resources Inc. <br /> retained by BMRI to provide an assessment of potential hydraulic control options for the <br /> optimization/reduction/elimination of waste water treatment associated with ongoing remediation <br /> of impacted groundwater derived from the West Pit. EA has developed numerical groundwater <br /> flow models to aid in the assessment. <br /> Initial results of the West Pit groundwater models indicate that, under the current pumping <br /> conditions(approximately 200 gpm from backfill recovery well BF5),the majority of groundwater <br /> influx into the West Pit enters through a portion of an"alluvial window" along the south-southeast <br /> side of the pit. The volume of groundwater water entering into the West Pit through this alluvial <br /> window relative to that entering from the surrounding and underlying bedrock units is a critical <br /> factor in evaluating the long-term effectiveness of potential remedial alternatives such as a slurry <br /> wall, interceptor trench, or extraction wells. Hydrologic testing conducted in 2021, reported in <br /> Engineering Analytics(2022),confirmed that most of the groundwater enters the West Pit through <br /> the alluvial aquifer. However, one well was only screened within the underlying Santa Fe Fm and <br /> it showed a significant hydraulic response during the hydrologic testing. <br /> EA conducted additional investigation designed to further characterize hydrologic properties of <br /> the Santa Fe Fm along the southeast edge of the West Pit. The hydrologic properties of interest <br /> include transmissivity, saturated thickness,and hydraulic conductivity. The investigation included <br /> the drilling, installation, and development of one well identified as WP-6. Then continued by <br /> conducting a pumping test on WP-6 while monitoring hydraulic responses in surrounding wells. <br /> The hydrologic data collected and analyzed from this investigation will be incorporated into the <br /> West Pit groundwater models for further evaluation of the feasibility of remedial alternatives to <br /> reduce the volume of West Pit groundwater that must be treated prior to discharge. <br /> This technical memorandum summarizes the results and analyses of the testing that was conducted <br /> in November 2022 to characterize the hydrologic properties of the Santa Fe Fm and its hydraulic <br /> relationship to the overlying alluvial aquifer. <br /> 2.0 HYDROLOGIC INVESTIGATION <br /> EA coordinated and supervised the drilling, completion, and development of one well, identified <br /> as WP-6, located along the southeast boundary of the West Pit(Figure 1). Hydrologic testing was <br /> conducted utilizing the new well. Attachment A includes a borehole log and well construction <br /> diagram for the new well. <br /> Several existing wells in the immediate vicinity(WP-1,WP-2,WP-3,WP-4 and PW-4)were used <br /> as observation wells during the testing. The locations of the pumping well and observation wells <br /> are shown on Figure 1. Wells WP-1, WP-3, and WP-4 are completed in the alluvial aquifer. The <br /> alluvial aquifer encountered in the observation wells generally consists of gravelly sand to sandy <br /> gravel, with some clay. Well WP-2 is completed within the lower portion of the alluvium and the <br /> upper portion of the Santa Fe Fm. The alluvial aquifer in WP-2 contains more clay than was seen <br /> in the other wells. The contact between the alluvial aquifer and the underlying Santa Fe Fm is <br /> typically associated with a weathered clay unit that transitions with depth into interbedded <br /> claystone and sandstone units. Well PW-4 is completed within a silty to fine-grained sandstone <br /> February 2023 2 Engineering Analytics,Inc. <br />