2010-12-21_REPORT - M1977004 - Laserfiche WebLink

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Homastaka 2010 Geotechnical Observations Pitah Raclamati? . P- act Indian Creek and Tie Camp Creek Waste Rock Dumps e) "10600 -10400" Level Site Description: Identical to that of past reports for 1996 through 2009. 2010 Observations: Piezometer IC10440 was located in this area; however, it was lost in September 1996. Piezometer IC10525 is also representative of this area of the waste rock dump. The 2010 data for that piezometer was described in the previous section. -? f) "10400 - 10370" Level Site Description: Identical to that of past reports for 1997 through 2009. During 1997, Homestake reconstructed the face of the permanent low-grade stockpile located on the Indian Creek Waste Rock Dump. The purpose of the slope reconstruction was to reduce the potential for infiltration and promote more rapid runoff from the slope. No seepage was observed in this area in 2010. 2010 Observations: The 2010 field observations are similar to those reported in past reports. Piezometer IC10360 is located in this area. Water levels in this piezometer averaged about 221.43 feet bgs in 2010, with a seasonal fluctuation of 9.98 feet. Despite a record snow pack in 2009 and a heavy snow pack in 2008, the water level rise in IC10360 over the past three years is below the levels recorded from 2002 through 2007. The total depth of this piezometer is 260 feet and the thickness of the dump is approximately 240 feet. During the winter of 2007, wildlife knocked off the casing of piezometer IC10370 and kicked debris into the 2 inch pipe. Prior to this time, the piezometer had never shown seasonal water levels fluctuations greater than one foot, with the averaged water level of 190.7 feet bgs. The bottom of this piezometer is 192 feet bgs. In 2009, the piezometer was flushed with pressurized water to within three feet of its historical depth of 192 feet bgs. Now the total depth is approximately 189 feet bgs. In 2010 the water level rise was less than a foot and consistent with its historic behavior. g) "10300 - 10100" Level Site Description: The Indian Creek Waste Rock Dump was regraded in 1994 following procedures approved in the February 1994 Technical Revision. During 1995, several minor, localized areas of slope instability were noted, corrected, and reported in the 1995 Annual Geotechnical Report. 2010 Observations: Field observations indicate that the repairs performed in 1995 were successful and no new areas of surficial instability (slips) were observed from 1996 through 2010. Piezometer IC10300 is located in this area. Field records indicate that the 10300 piezometer was originally drilled to a total depth of 210 ft. The final depth of the installation was not recorded in the field record at that time. Inspection of IC10300 in 2008 indicated that the bottom of the standpipe had become filled with silt to a depth of about 180 ft. bgs, as indicated by sounding the total depth of the standpipe. A steel surge block was lowered into the standpipe, and rather than encountering a blockage, the surge block became partially submerged in the slurry-like material, which covered the steel surge block when it was returned to the surface. It was concluded that the water levels recorded over the previous few years were from a small interval of water perched on the silt in-filling, and because of the blockage in the standpipe, not indicative of water levels in the underdrain. Homestake Pitch Reclamation Project Page 2 2010 Annual Geotechnical Report December 20, 2010 M-1977-004HR 2010AnnualGeotechnicalReportText_Final.doc