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Battle Mountain Resourc~ • <br />January 25, 2000 <br />Page 3 <br />the curtain wells have generally declined since July 1999, although the extent of water level decline <br />varies among the locations. The extent of water level decline is governed by: (1) the hydraulic <br />chazacteristics of the aquifer material in the vicinity of the pumping well, (2) the proximity of the <br />pumping well to the backfill, and (3) overall well efficiency. Differences in w~:ll response [o <br />pumping, as shown in Figure 3, demonstrate the potential heterogeneity of the <<Iluvial aquifer <br />hydraulic properties. In addition, the proximity of the pumping well to the backfill influences the <br />water level because the backfill acts as a constant head boundary, and the shape of the cone of <br />depression (and steady-state water depth in the pumping well) will be fixed by the groundwater <br />level in the backfill. Groundwater levels in M-21 and M-22 have also declined, but with less than <br />one year of measurements the decline cannot be ascribed with certainty to pumping of the curtain <br />wells. <br />WATER QUALITY <br />The combined effects of water management controls implemented to date are al:.o reflected in <br />changes in the water quality observed at different locations in the vicinity of the West Pit. <br />Original Seep <br />Prior to initiation of the water management plan described in TR-26 the concentrations of sulfate, <br />total dissolved solids (TDS), and dissolved manganese at the original seep were relatively constant. <br />Since July 1999 the concentrations of sulfate, TDS, and manganese have steadily declined, which is <br />consistent with a decreasing influence of groundwater seepage from the West Pit into the Rito Seco <br />alluvium (Figure 4). <br />Rito Seco Stream Stations <br />The effectiveness of the TR-26 water management as implemented to date can best be shown by <br />evaluating the water quality of the Rito Seco as measured at the surface water samF ling locations <br />RS-2 and RS-5. A standazd precept of hydrogeology is that late season flows in pen:nnial streams <br />is due primarily to the discharge of groundwater (e.g., Fetter, 1988). Thus, water quality <br />3801 Automation Way, Suite 100, Fort Collins, Colorado 80525 <br />Telephone (970) 223-9600 /FAX (970J 223-7171 <br />