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Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> discontinuous between the West Pit and East Pit, possibly disrupted by north-south <br /> striking dikes and low-angle faults (Water Management Consultants, Inc., 1994). <br /> The Santa Fe Fm is a laterally extensive stratigraphic unit extending regionally to the <br /> south and west. Groundwater flow within this unit may be fracture-dominated and may <br /> be compartmentalized by faults and igneous dikes. In general, the permeability of the <br /> Santa Fe Fm at the mine site is relatively low. The Santa Fe Fm may be hydraulically <br /> connected to the underlying Precambrian aquifer, based on drawdown observed during <br /> dewatering operations (Water Management Consultants, Inc., 1994). This suggests that <br /> the green clay may not be a competent confining unit, or that hydraulic pathways exist <br /> via faults or dikes, or localized absence of the green clay. East of the West Pit, the Santa <br /> Fe Fm is completely eroded away. <br /> The Rito Seco alluvium includes an unconfined aquifer system that is limited to the <br /> vicinity of the Rito Seco drainage. West and south of the West Pit, the alluvium generally <br /> overlies the Santa Fe Fm. Along the south wall of the West Pit, the alluvium is in direct <br /> contact with the backfill material. Slightly upstream of the West Pit,the alluvial aquifer is <br /> absent where the Rito Seco is incised into Precambrian bedrock. <br /> The backfill material is a combination of mine spoils from the Precambrian bedrock and <br /> Santa Fe Fm, laid down in alternating lifts. The backfill material is in direct contact with <br /> the Precambrian bedrock around the perimeter and base of the West Pit, with the Santa Fe <br /> Fm over portions of the west side of the pit, and with the alluvium along the shallower <br /> portions of the south side of the pit. Long-term pumping from the West Pit indicates that <br /> the permeability of the backfill material is very high. <br /> 4.2 Aquifer Properties <br /> Hydrologic properties for the Precambrian bedrock, Santa Fe Fm, alluvium, and pit <br /> backfill have been estimated from a number of hydrologic tests and water level <br /> measurements. Table G-1 provides information on the monitoring well network in the <br /> vicinity of the West Pit. Hydraulic conductivity and aquifer thickness were reported for <br /> each of the hydrologic units (BMRI 1999a). Storativity was only reported for the alluvial <br /> aquifer as that was the only hydrologic unit that involved observation wells in the testing <br /> (BMRI 1999a). Table G-2 summarizes the results of hydrologic tests conducted in the <br /> area. Figure G-3 shows the monitoring well network and hydrologic test sites. Additional <br /> description of each of the hydrologic units is provided below. <br /> As previously described, mine dewatering of the Precambrian bedrock aquifer was <br /> achieved using well DW-1 as the extraction well. Dewatering rates of 150 to 250 gpm <br /> resulted in up to two hundred feet of drawdown over an extensive area (including most of <br /> the West Pit). A single well pumping test was conducted on DW-1 in 1999 as part of a <br /> West Pit groundwater investigation (BMRI, 1999a). Results of the test indicated a <br /> hydraulic conductivity of 9 ft/d. The aquifer thickness was reported as 51 ft (which was <br /> the screen length). The total thickness of this unit is unknown. Aquifer testing was also <br /> conducted at PC-2, a Precambrian monitoring well that is located in the saddle between <br /> the West Pit and the Pink Gneiss Pit. The overlying backfill is relatively thin and is not <br /> April 2025 4 Engineering Analytics,Inc. <br />