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1 <br />Homestake Mining Company -Bulldog Mine-Lower Tailing Pond <br />The only way to measure the effectiveness of the test grouting was to observe the <br />changes in ground water levels in the embankment piezometers and the pump-back rates <br />over time. This was difficult because the water levels in the piezometers also responded <br />' to the variation in the water level in the pond. It was observed in the 1983 As-Built <br />Report that an additional benefit of the grouting related to the stability of the dam cut-off <br />with respect to piping. As noted previously, dam stability was raised as an MSHA <br />' concern in June 1982. <br /> Water Seepage Correction Protect <br />' ' <br /> Between June and November 1983, D <br />Appolonia was contracted to implement the <br /> recommendations contained in their February 1983 Stability Report The remedial <br />' measures consisted of the construction of a 1350-feet slurry trench extended below the <br /> bottom of the embankment core into competent bedrock and the placement of a bentonite <br /> slurry in the trench to reduce seepage and, thereby, to reduce piping below the <br />' embankment. <br />' On October 26, 1983 HMC provided MLRD with a status report on the remedial work <br />The report stated: <br />leted from October 1982 to October 1983 <br />com <br /> . <br />p <br />' "observations and sampling of piezometers below the cutoff wall show that seepage has <br />been contained and the ground water quality is steadily improving and approaching the <br /> natural occurring quality. Since installing the cut-off wall no seepage has been observed <br />' down-stream of the cut-off wall. " <br /> In February 1984, D'Appolonia provided a draft As-Built Report for Water Seepage <br />' Correction work. The report concluded: <br /> Seepage through the dam has nearly been eliminated by the slurry trench. Seepage <br /> pressures after slurry wall construction is about 1 to 3 feet lower on the west side and <br /> center of the dam, and about the same or slightly higher on the east side of the dam. <br /> Seepage flow continued through bedrock beneath the trench because of structure <br />' discontinuities in the bedrock at a a~ % lower level or approximately /~0 gpm. Factor of <br /> safety has increased from 1.4 to 1.6 for a tailing pool at an elevation of 8936. It is <br /> recommended that the tailings discharge location be moved to the east side ojthe pond <br />' anticipating that the slimes would be deposited in the area of the pond to help retard <br /> seepage further. <br />' 3.2 Water Monitoring Program <br />a) Monitoring Wells <br />' As noted in Section 2.0, in 1978-1980, at the direction of Envirologic Systems Inc., <br />Denver, Colorado a series of piezometers was installed to monitor the seepage that was <br />1 <br />1 <br />