2008-04-18_REPORT - M1977004 - Laserfiche WebLink

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t 1 I~ i 4.0 MONITORING AND ANNUAL REPORTING 4.1 Slope Movement Vector Analysis Survey monuments have been installed on the east and south walls of the North Pit to monitor surficial slope movement periodically since 1994. The area east of the North Pit Lake and south of Northing 113,500 is referred to as the south wall of the North Pit; and the area east of the North Pit Lake and north of Northing 113,500 is referred to as the east wall of the North Pit. This differentiation is for ease in discussing slope movement and does not imply that there is a kinematic distinguishing feature at this location. The original group of monitoring points was installed in 1994. Additional monitoring points were installed in 1996, 1997, 1998, 1999, and 2004. Since 2004, 36 knew monuments have been installed. Monument locations are provided on the Slope Displacement Vectors drawing presented in Appendix A. Surveys are usually~~conducted as close to one year apart as possible, allowing the magnitude of displacement to be reported as a velocity in terms of ft/year. Surveys of all accessible monuments were conducted on September 24, 2007 with the previous survey performed on October 3, 2006. The surveys are actually conducted over several consecutive days with the median date used to represent the data set. Of the 83 points surveyed in 2007, 49 had annual magnitudes that were greater than survey error during ';the 2006-2007 monitoring period, as shown on Table 1. By comparison, 32 points had annual magnitudes greater than survey error for the 2005- 2006 monitoring period. Of the12 additional monuments that were added in 2004 to monitor the slide at the east wall of the south pit, 11 showed displacement greater than survey ~~error. Velocity vectors were calculated for the 49 points and are depicted with green'~~circular symbols and velocity vectors on the Slope Velocity Vectors Map (Appendix A). Points with a displacement less than the survey error are shown in gray on the map(sRK consultants Inc., March 31, Zoos). In prior annual reports, it was noted that the possibility exists for an increase in slope displacement with increased preicipitation. It appears that the increased slope displacement observed during this', monitoring period may be related to higher than average rainfall that occurred during the summer of 2007. This increased displacement has been observed primarily in the northeast comer of the North Pit and the small slump feature above the east wall of the South Pit. The maximum displacement at the northeast comer of the North Pit is 0.64 ft/year. At the slump above the south wall, the maximum displacement is 0.93ft/year. While these values are 2 to 3 Pitch Reclamation Project Colorado Mined Land Reclamation Board 2007 Annual Reclamation Report 10