2009-04-20_REPORT - M1977004 - Laserfiche WebLink

Home Browse Search

Pitch Reclamation Project Colorado Mined Land Reclamation Board 2008 Annual Reclamation Report 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 since 1994 to monitor any periodic surficial slope movement. 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 new monuments have been installed, including 12 in the South Pit. 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 any displacement to be reported as a velocity in terms of ft/year. Surveys of all accessible monuments were conducted on October 24, 2008 with the previous survey performed on September 24, 2007. The surveys are actually conducted over several consecutive days with the median date used to represent the data set. Of the 83 points surveyed for the 2007-2008 period, 47 had annual magnitudes greater than survey error, as shown in Table 1. By comparison, 49 points had annual magnitudes greater than survey error for the 2006-2007 monitoring period. Of the 12 additional monuments that were added in 2004 to monitor the slide at the east wall of the South Pit, eight 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., April 08, 2009). Prior annual reports have noted that the possibility exists for an increase in slope displacement with increased precipitation. It appears that the higher than average snow pack in 2007-08, and heavier rainfall in 2008, resulted in increased slope displacement primarily in two places: the northeast corner of the North Pit, and the small slump feature above the east wall of the South Pit. At the northeast corner of the North Pit the maximum displacement for the 2007-08 monitoring period was 0.65 ft/year at monitoring point MP-65, which had a displacement of 0.64 ft/yr during the previous monitoring period. At the slump above the east wall of the South Pit, the • 6