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impoundment area. Storm water from the north catchment and which falls directly on the <br />surface of the tailing disposal area is stored in the impoundment area behind the dam and either <br />evaporates, or infiltrates the tailing and is captured on the liner and recirculated v a the collection <br />facilities. <br />1.3 TAILING FACILITY OPERATION <br />Although no longer used for tailing disposal, the tailing facility continues to be used for storage <br />and evaporation of pumped groundwater from wells in the backfilled west pit area and brine <br />from the water treatment plant at the mine site. These waters are transferred from the mine site <br />via a pipeline to a ponded area within the topographically lowest portion of the tailing <br />impoundment area, as shown on Figure 2. The nearest portion of the ponded sul face at the time <br />of the dam safety inspection (May 2013) was located approximately 600 feet upstream from the <br />crest of the dam. Based on recent surveys conducted in May 2013, the estimated volume of <br />water in the ponded area is approximately 25 to 30 acre -feet, and the top surface rea of the pond <br />is approximately 16 to 17 acres. The average depth of water in the pond is less han 2 feet, and <br />the maximum depth is between 2 and 3 feet. <br />1.4 EXISTING INSTRUMENTATION AND MONITORING PROGRAM <br />The subdrain and leak detection systems are monitored on a monthly basis using a water level <br />indicator. <br />Ten standpipe piezometers are installed on the embankment. Five instruments (F 6 through P 10) <br />were installed at the 8590 ft crest of the Phase I embankment in Septembei 1992. These <br />piezometers are believed to be completed in the embankment, just above the under- drainage <br />layer. Another five instruments (P11 through P16) were installed on the 8605 ft crest of the <br />Phase 11, Raise 1 embankment in March 1994. These piezometers appear to have been <br />completed at a depth of about 41 to 42 feet below the 8605 embankment crest. This would have <br />positioned those instruments at the interface between the Phase 11, Raise I dam and the <br />underlying tailing. The purpose of these piezometers appears to have been t monitor pore <br />pressures at the base of the Phase II, Raise I embankment associated with to ling placement <br />during Phase 11 of the active mine operation. All ten piezometers continue to be monitored, and <br />are typically dry. <br />San Luis Project Miller Geotechnical Consultants <br />Tailing Dam Data Report 4 February 2014 <br />