2009-04-20_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board 2008 Annual Reclamation Report maximum displacement was 1.95 ft/yr at monitoring point S-4 which moved at a rate of 0.93 ft/year during the previous monitoring period. While displacement for the last two years is greater than previously observed in these areas, the magnitude is still relatively low. The small slump at the east wall of the South Pit does not present any risk to personnel or monitoring activity. The northeast comer of the North Pit is the area where the two 1983 slope failures took place. Site inclinometers (discussed in the following section) do not show comparable slope displacement values for the same period as they are not located in either area where monument displacement occurred. In 2009, the northeast corner of the North Pit and the slump above the east wall of the South Pit will be inspected as soon as the areas are free of snow and again after the summer rains. The bench on the east wall of the South Pit where the small slump is located was graded in 2008 to minimize drifting of snow and allow a more stable configuration to facilitate optimum drainage and minimal infiltration of surface water. After snowmelt in 2009, the area will continue to be monitored closely, shaped, and revegetated to support stability and optimum drainage 4.2 Inclinometer Evaluation Three (3) 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; 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 November 24, 2008. Data collected in 1999 through 2008 from all three inclinometers indicates a relatively constant rate of subsurface displacement of 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., April 2008). Homestake will monitor these inclinometers closely 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. 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 7