Laserfiche WebLink
Mining and Reclamation Permit Amend.-M-1988-112 <br /> Groundwater Management Plan Battle Mountain Resources,Inc. <br /> precipitation for the area most likely lies within the range of those values. The actual <br /> value of precipitation is of less importance than the fraction that will infiltrate to and <br /> recharge the groundwater system. <br /> A "rule of thumb estimate" often used to estimate the proportion of annual precipitation <br /> that recharges groundwater is around 5 to 10%. The percentage is controlled by many <br /> variables including, but not limited to, soil and vegetation cover, temperature, slope, <br /> permeability and porosity of the overlying material, depth to groundwater, etc. The actual <br /> percentage is difficult to quantify in the field. <br /> The Rito Seco provides recharge to the alluvial aquifer system. Upstream from the West <br /> Pit where the Rito Seco turns northward, the drainage is incised into Precambrian rock <br /> and there is little alluvial material along the river banks. The alluvium is present along the <br /> banks of Rito Seco from slightly east of the West Pit and out across the remainder of the <br /> study area (and out to the San Luis Valley). No substantial seeps are discharging from the <br /> Precambrian material along the valley wall. Therefore, most of the saturation of the <br /> alluvium upgradient of the West Pit is likely the result of discharge from the Rito Seco. <br /> Discharge of groundwater in the vicinity of the West Pit occurs primarily through <br /> pumping wells, evapotranspiration, seeps and springs, and lateral flow into surrounding <br /> hydrologic units and the Rito Seco. Pumping losses occur from extraction wells <br /> completed within the West Pit backfill and two alluvial wells located south of the West <br /> Pit. Recent rates of extraction from the West Pit backfill are up to 200 gpm (from well <br /> BF-5). The recent combined rate of extraction from alluvial wells M-32 and M-33 is <br /> approximately 15 gpm. <br /> Substantial evapotranspiration occurs along the banks of the Rito Seco, as can be <br /> observed by the abundant vegetative growth. Some water is lost through evaporation <br /> from the holding ponds that are included in the West Pit groundwater management, but <br /> with respect to a water budget, that water is accounted for through extraction via the <br /> wells. <br /> Seeps were observed along the north banks of the Rito Seco following re-establishment <br /> of the hydraulic gradient from the West Pit to the stream. The seeps appear to have dried <br /> up in response to pumping from the West Pit. <br /> Alluvial groundwater moves into and out of the West Pit backfill along the "window" <br /> where the two units are in direct contact. The relative movement of groundwater is in <br /> direct response to the difference in hydraulic heads between the two units. Lowering of <br /> the hydraulic head in the West Pit via pumping, as is currently the case, results in <br /> groundwater flowing from the alluvial aquifer into the West Pit. Without pumping, <br /> alluvial groundwater enters West Pit along the east end of the "window" but then flows <br /> out of the west end of the "window" back into the alluvium and toward the Rito Seco. <br /> April 2025 7 Engineering Analytics,Inc. <br />