2012-04-19_REPORT - M1977004 (2)

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2011 Annual Reclamation Report 0.20ft/yr displacement at MP96 -69. The current maximum displacement at the East Wall of the South Pit is 1.84 ft/year at MP05 -92, which had a displacement of 0.53 ft/year during the previous monitoring period. During 2008, repairs were made to improve drainage at the slump above the East Wall of the South Pit. In the fall of 2010, additional survey monitoring points were added, and some were replaced because they were compromised by slope movement, resulting in a net gain of two monitoring points. Also in 2010 at the East Wall of the South Pit, the tension cracks were graded closed on the bench and on parts of the slope adjacent to the bench that were accessible to the backhoe. The bench was also crowned longitudinally across the slump to promote drainage. These maintenance measures will be continued as needed to optimize drainage from the area of slope displacement. 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 southern portion of the East Wall 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 data are comprised of readings taken at the same 2 -ft intervals, on an annual basis. A difference in the position of the casing may be indicative of slope displacement, if the magnitude indicated meets or exceeds instrument error margins. Inclinometer data collected in 1999 through 2010 from all three inclinometers is well below the survey instrument error margin of +/- 0.3 inches per 100 ft. of depth (SRK April 2011). The more recent inclinometer surveys reflect that little or no 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. Noting problems that occurred in 2010, at the end of the year the inclinometer equipment was sent to the manufacturer, Slope Indicator, Inc. (SINCO) in Redmond Washington, for repair and calibration. Equipment function and calibration remained an issue during the 2011 monitoring season and resulted in collection of faulty data. However, there is no indication of slope displacement at the inclinometer locations, as evidenced by surface survey, monitoring and visual observation. The data recorder, inclinometer probe, and probe cable were sent to the equipment manufacturer in December 2011 and all equipment has been repaired and calibrated. A thorough field test of the equipment is planned for May 2012. Data will be recorded and analyzed prior to the annual monitoring event scheduled for July 2012. 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, these inclinometers will continued to be monitored. Pitch 2011 Reclamation Finalreport 19Apr12.Doc 12