2010-04-19_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board 2009 Annual Reclamation Report about 0.04 inches per year which is within the survey instrument error margin of +/- 0.3 inches per 100 ft. of depth (SRK Consultants Inc. 2009). The more recent inclinometer surveys (August 2007, November 2008, August 2009) 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 be collected from these combination piezometers/inclinometers. The inclinometer probe was last calibrated in 2003. The probe manufacturer recommends yearly calibration. However, due to the infrequent use of the probe (one event per year), and careful transportation and storage of the probe, annual calibration is not warranted. The probe results are verified during data collection, which is inherent to the process. Therefore, the results to date are reliable. However, SRK recommends calibration every four years from this point forward. The probe will be calibrated prior to the next (2010) monitoring event. 4.3 Pinnacle Mine Workings Monitoring A concrete plug was constructed in the Pinnacle Adit in September 1995. Authorization for the placement of the Pinnacle Adit plug was requested by Homestake in April 1995, through Technical Revision #4 (TR4) - Pinnacle Adit Closure, Pitch Project, Technical Revision for Permit #77-4HR (Golder Associates, Inc.). Conditional approval of the Technical Revision request was granted by the Colorado Division of Minerals and Geology, in a letter dated May 26, 1995. • 9