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Schwartzwalder Mine -Hydrologic Evaluation of Mine Closure and Reclamation 32 <br />5.2.2 Sources of Inflow <br />During mining, water inflow to the Schwartzwalder mine occurred from several sources including <br />infiltration of groundwater through porous bedrock; infiltration of groundwater along faults, fractures, <br />pegmatites and other permeable structures; and; recharge by precipitation and surface water through <br />bedrock in the upper levels of the mine. <br />The slow infiltration of groundwater through unfractured bedrock was a minor component of the total mine <br />inflow. Packer permeability tests indicate that the primary hydraulic conductivity of bedrock is on the <br />order of 10-' cm/sec or lower (Section 4.1.2). If it is assumed that inflow to the mine is analogous to a large <br />well with a diameter of 500 feet and a depth of 2,200 feet, the steady state inflow from unfractured bedrock <br />with a hydraulic conductivity of 1 x 10-' cm/sec can be calculated using the large well methods described <br />by Singh and Atkins (1985). Flow to the mine at its maximum extent can be approximated using the Theim <br />equation for steady-state radial flow to a well: <br />_ 2~LKH <br />Q ln(R~rn) <br />where: Q = Volumetric inflow to the mine [L3T'] <br />L = Length of the well screen [L] <br />K = Hydraulic conductivity [LT"'] <br />H = Drawdown [L] <br />R = Radius of influence [L] <br />rh = Radius of the well bore or mine workings [L] <br />The inflow to the mine from unfractured bedrock at full depth is calculated to be 64 gpm, or one third the <br />total flow to the underground workings, based on the equation and assumptions stated above. <br />Recharge to groundwater by infiltration of precipitation at the site is estimated to be about three inches per <br />year. This estimate is derived from baseflow calculations for Ralston Creek (Section 3.1), and water level <br />fluctuations in Monitoring well MW11 (Section 4.1.1). Using the average annual infiltration rate of 8.8 <br />gpm developed from mine pumping records, the direct recharge capture area for the entire mine in the fully <br />dewatered condition is calculated to be about 56.8 acres. <br />The recharge area captured by the upper workings (Steve Level and above) is narrowly defined by <br />topography and is estimated to be about nine acres (Figure 20). Based on this area and the 3-inch per year <br />infiltration rate, the average annual inflow to the upper workings is estimated to be about 1.4 gpm or about <br />733,000 gallons per year. <br />4109B.071116 Whetstone Associates <br />