2011-04-19_REPORT - M1977004 - Laserfiche WebLink

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The slump above the bench at the east wall of the South Pit was the first slope displacement feature noticed in this area. By the fall of 2010, it was evident that the slope displacement in this area is related to movement of structures associated with the Chester Fault system. Slope displacement currently involves the full height of the east wall of the south pit in the affected area, which is at the south portion of the South Pit. Observation and maintenance will continue in this area. 4.2 Inclinometer Evaluation Three inclinometers were installed in October 1998 (198-1, 198-2, and 198-3) to monitor any subsurface movement within the south and east walls of the North Pit. The inclinometer locations are provided on the Slope Displacement Vectors drawing presented in Appendix A. Inclinometer 198-1 is located on the lowest bench on the south wall of the North Pit; 198-2 is located on the 10,600 ft. bench of the south wall and; 198-3 is located above the crest of the east wall and above the headscarp. Inclinometer readings were taken on September 14, 2010. Data collected in 1999 through 2010 from all three inclinometers indicates a relatively constant rate of subsurface displacement of about 0.04 feet per year which is within the survey instrument error margin of +/- 0.3 inches per 100 ft. of depth (SRK Consultants Inc. 2011). The more recent inclinometer surveys (August 2007, November 2008, August 2009, and September 2010) reflect that little slope displacement has occurred when compared to the revised baseline inclinometer survey for the respective installations (July 2003). The new baseline reading was established after the original baseline ' reading data file of June 1999 was corrupted. The consequences of changing the baseline reading are minimal, because of the consistently low magnitude of slope displacement that has been observed at the site. Homestake will continue to closely monitor these inclinometers given the isolated slope displacement noted in the previous section on the northeast corner of the North Pit and the resaturation of the Pinnacle underground mine workings in the area of the south wall of the North Pit as discussed in Section 4.3. It should be noted that two temporary inclinometers were installed in piezometers P-8 and P-10 during the winter of 1997-1998 to provide data in the spring of 1998. These inclinometers were made redundant by the installation of inclinometers 198-1, 198-2, and 198-3. The inclinometers in P-8 and P-10 remain installed, but are not surveyed on a regular basis. Should surface monuments detect increasing slope movement, data could likely be collected from these combination >r piezometers/inclinometers. Pitch Reclamation Project Colorado Mined Land Reclamation Board 2010 Annual Reclamation Report 18