2010-12-21_REPORT - M1977004 - Laserfiche WebLink

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Homestake 2010 Geotechnical Observations Pit=, Reclamation P-je t Indian Creek and Tie Camp Creek Waste Rock Dumps In 2010, water levels in this piezometer were once again sporadic and required additional high pressure flushing to push through the silt built up in the casing. The water level readings in June, August and November are shown on Table 1, but not included in the yearly summaries at the bottom of the table. Excluding these false reading, the average depth to water was 188.8 feet bgs, down from 184.78 feet bgs in 2009. The maximum differential in 2010 was 0.3 feet, down from 8.2 feet in 2009 and 15.5 feet in 2008. However, this piezometer may have reached a point where it no longer can provide accurate information of the phreatic surface in this portion of the rock dump. In 2011, we will once again attempt to clear the silt by flushing the casing with high pressure water as soon as field conditions warrant. In the event that flushing does not restore the functionality of the piezometer, we will evaluate the purpose and need of this piezometer and decide if replacement is critical to long-term monitoring of the Indian Creek Waste Rock Dump. 2. Tie Camp Waste Rock Dump __J a) "10400 -10100" Level Site Description: The Tie Camp Waste Rock Dump was regraded in 1994 following procedures approved in the February 1994 Technical Revision. During 1995, minor, localized areas of slope instability were noted, corrected, and reported in the 1995 Annual Geotechnical Report. 2010 Observations: Piezometer TC10375 monitors the Tie Camp Creek Waste Rock Dump. In 2010, water levels averaged 168.35 feet logs, with a maximum observed seasonal fluctuation of 1.83 feet between May and June. The maximum fluctuation was down from the 2008 maximum fluctuation of 12.3 feet and 6.1 feet in 2009. This is deemed as an acceptable seasonal variation. Field observations indicate that the repairs performed in 1995 were successful and no new areas of surficial instability were observed from 1996 through 2010. In 2011, we will continue to monitor the surface conditions of the Tie Camp dump after the spring snow melt. 3. Piezometers - 2010 General Comments The 2010 water level measurements showed a maximum differential following snow melt in line with historical readings. Following the dry conditions of 2001 through 2003, the seasonal variations have increased in recent years as heavier snow packs have occurred. However, there continues to be problems related to silt and corrosion in some of the piezometers. Homestake will continue to evaluate the conditions of the piezometers and remedy the buildup of silt in the casings, as possible. We will continue to monitor and evaluate the cause and effect of seasonal spikes in the piezometric water levels, and also observe any changes in surface features of the rock dumps. There continues to be no indication of concern related to instability in either the Indian Creek or Tie Camp Creek waste rock dumps. Homestake Pitch Reclamation Project Page 3 2010 Annual Geotechnical Report December 20, 2010 M-1977-004HR 2010AnnualGeotechnicalReportText_Final.doc