2014-04-17_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2013 Annual Reclamation Report 4. MONITORING AND ANNUAL REPORTING 4.1 Slope Movement Vector Analysis Survey monuments have been installed at the Pitch Reclamation Project to monitor surficial slope displacement in the North and South pits. The area east of the North Pit and south of Northing 113,500 is referred to as the South Wall of the North Pit; and the area east of the pit lake and north of Northing 113,500 is referred to as the East Wall of the North Pit. Monitoring points are also present on the east wall of the South Pit. The first monitoring points were installed at the east and south walls of the North Pit in 1994. Some of the monuments have been destroyed due to re- grading, and critical ones were replaced with new monuments having different identification numbers. In 1996, six monitoring points were installed to replace points at the East Wall of the North Pit. In 1997, 14 monitoring points were installed to monitor shallow slope movement that was observed on the south wall of the North Pit. In 1998 and 1999, five monitoring points were installed at existing locations including inclinometer collars. In 2000, 11 monitoring points were installed in the North and South pits. A monitoring point was placed at the collar of piezometer P -09 at the east wall of the South Pit in 2001. In 2005, 13 monitoring points were installed to monitoring shallow slope displacement observed on the east wall of the South Pit. In 2010, six of the monitoring points on the east wall of the South Pit that were installed in 2005 were abandoned because they had been compromised by slope displacement and tension crack formation. At that time, eight new monitoring points were installed to replace the abandoned installations and positioned to provide a profile of the slope. The slump above the bench at the east wall of the South Pit was the first slope displacement feature noticed in this area. 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. As noted previously in section 3.3, in 2010 the tension cracks were graded closed on the bench and on parts of the slope adjacent to the bench that were accessible by 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. No grading was required in 2013 due to minimal displacement. There was no evidence of displacement on the cracks at the surface of the upper bench that traverses the slope displacement.. Displacement on these cracks has been up to 6- inches per year during years of high precipitation, but has slowed in the past few years in response to the relatively low precipitation. All monument locations are provided on the Slope Displacement Vectors drawing presented in the figure in Appendix A. Surveys are usually conducted as close to one year intervals as possible, allowing the magnitude of total displacement to be reported as a velocity in terms of ft/year. Surveys of all accessible monuments were conducted between July 16, 2013 and July 23, 2013.. Because the surveys are conducted over several consecutive days, the median date was used to represent the data set. In 2010- 2011, names of monitoring points were modified to show the year the monument was set. This change was made to differentiate when a new baseline was established for a particular monitoring point. For example, MP99 -85 is monitoring point MP -85, which was established in 1999. However, this nomenclature was abandoned for the 2012 report because it was found to be cumbersome and Pitch 2013 Reclamation Report 14April2014.Docx 19