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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> meteoric water accounts for approximately 2 gpm (3.22 AF/yr), and inflow from the <br /> Santa Fe Formation along the western flank of the West Pit accounts for less than 2 gpm <br /> (<3.22 AF/yr). The remaining portion of extracted groundwater (16 to 21 gpm, or 25.81 <br /> to 33.87 AF/yr) is attributed to inflow to the Pit backfill from the Precambrian aquifer <br /> where it is adjacent to the former Pit walls and up through the base 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 will be <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 will be discharged separately to a tailing's impoundment, approximately one- <br /> mile southwest of the West Pit or to evaporation Ponds within the West Pit. <br /> 7.3 Simulated Groundwater Impacts <br /> Installation of the slurry wall will affect the shallow groundwater flow system in and <br /> around the Pit. The slurry wall will effectively divert groundwater that is currently <br /> entering into the southern portion of the Pit through an "alluvial window" (where <br /> alluvium is in direct contact with mine backfill). That redirected groundwater will revert <br /> back to flow patterns similar to pre-mining conditions, wherein the alluvial groundwater <br /> system predominately flows parallel to sub-parallel to the Rito Seco drainage (and not <br /> into the Pit). A portion of that groundwater will discharge into the Rito Seco. Following <br /> installation of the slurry wall, groundwater inside of the Pit will be predominately <br /> sourced from the Precambrian bedrock unit that exists north of, and beneath, the Pit. <br /> Following installation of the slurry wall, the extraction rate from within the Pit will be <br /> substantially reduced. Model simulations indicate that an extraction rate of between 20 <br /> and 25 gpm is sufficient to maintain the water level elevation in the Pit at or below the <br /> prescribed Discharge Permit level. The potentiometric surface resulting from the 22 gpm <br /> extraction simulation (from well BF-5) indicates that the water level within the Pit <br /> remains below the Discharge Permit limit (8582 ft amsl-NGVD29) (Figure G-7). The net <br /> change in water levels between the pre- and post-slurry wall potentiometric surfaces for <br /> the 22 gpm extraction simulation is shown on Figure G-8. Water levels show large <br /> increases outside of the Pit with the greatest changes occurring along the central and east <br /> portions of the wall. <br /> 8.0 PROPOSED MONITORING PROGRAM <br /> Based on the modeling results, wells inside of the Pit will provide the best indication of <br /> the effectiveness of the slurry wall installation. Wells outside of the Pit will show a rise in <br /> water levels, generally increasing going from west to east. <br /> There are monitoring programs currently in place (prescribed under DP CO-045675, TR- <br /> 26 and TR-31) that include monthly water level measurements and quarterly water <br /> April 2025 12 Engineering Analytics,Inc. <br />