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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> An additional investigation was conducted in monitoring wells installed in the <br /> southeastern portion of the alluvial window to provide estimates on the volume of <br /> alluvial groundwater that is flowing into the West Pit (Engineering Analytics, Inc. 2020, <br /> included as Appendix B). The investigation included the drilling, installation, and <br /> development of five wells (WP-1 through WP-5 shown in Figure G-3), conducting <br /> several short-term pumping tests, and conducting a 24-hour pumping test and analysis of <br /> those test results. Results of the test analyses indicate that the unconsolidated sediments <br /> of the alluvial aquifer have generally high transmissivity(generally greater than 500 ft2/d)' <br /> and hydraulic conductivity (on the order of tens of feet per day). These values are <br /> consistent with estimates from previous investigations and are in the range of those <br /> expected for an unconsolidated silty to clean, sand and gravel unit (Freeze and Cherry <br /> 1979). <br /> Attempts to fully characterize the backfill material were hindered because of limitations <br /> of pump capacity relative to the potential well yield of that unit. Negligible drawdown <br /> was observed even at pumping rates of 90 gpm during aquifer testing of the backfill <br /> wells. A minimum value of hydraulic conductivity was estimated at 280 ft/d (BMRI, <br /> 1999b). Even this minimum value is substantially greater than the hydraulic conductivity <br /> of the surrounding Precambrian, Santa Fe, and alluvial aquifers. The high hydraulic <br /> conductivity value of the backfill results in a relatively flat potentiometric surface within <br /> the West Pit, even after continuous pumping of well BF-5 at approximately 200 gpm for <br /> almost twenty years. The maximum saturated thickness encountered in backfill wells was <br /> approximately 128 feet and the minimum was 32 feet. The backfill hydrologic unit is <br /> unconfined. Porosity is estimated at upwards of 30 to 40 percent. The specific yield <br /> (drainable porosity) will be some portion of the total porosity. <br /> The hydraulic gradient between the West Pit backfill and the alluvial aquifer is strongly <br /> influenced by pumping or lack of pumping from within the West Pit. This is most clearly <br /> shown in potentiometric surface maps from 1999, after mine dewatering ceased (Figure <br /> G-4), and 2017, and with backfill well BF-5 operating at approximately 200 gpm (Figure <br /> G-5). Both of those figures use the vertical projection of CSPS NGVD29 for water level <br /> elevations. <br /> 4.3 Aquifer Recharge and Discharge <br /> Key components in addressing the hydrologic system of the West Pit study area are <br /> aquifer recharge and discharge. Recharge refers to the addition of water to a hydrologic <br /> unit. Recharge commonly occurs as the result of infiltration of surface water or <br /> precipitation on or near areas of outcrop. Recharge can also occur through the movement <br /> of groundwater between hydrologic units, both horizontally and vertically. Discharge <br /> occurs when groundwater exits the hydrologic unit. Discharge from a hydrologic unit can <br /> occur via pumping wells, evapotranspiration, seeps, springs, and vertical or horizontal <br /> movement to another hydrologic unit. <br /> Precipitation in the vicinity of the West Pit was initially reported in the Exhibit K of the <br /> 1989 Mine Permit application as 15.3 inches per year (in/yr) (BMRI, 1988). In Technical <br /> Revision 26 to the Permit, a value of 12 in/yr is cited(BMRI, 1999a). The average annual <br /> April 2025 6 Engineering Analytics,Inc. <br />