2017-04-14_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2016 Annual Reclamation Report 4. MONITORING AND ANNUAL REPORTING 4.1 Slope Movement Vector Analysis Survey monuments (monitoring points) have been installed at the Pitch Reclamation Project to monitor surficial slope displacement in the North Pit and South Mine area. 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 Mine area. There are currently 90 monitoring points in the North Pit and South Mine area to monitor surficial slope movement. Surveys are 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 per year (ft/yr). The monitoring points are presented on the Slope Displacement Vectors drawing presented as Appendix A. The monitoring program and slope movement observed in the North Pit and South Mine area since program initiation includes: • 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 Pit and South Mine area. • A monitoring point was placed at the collar of piezometer P-9 at the east wall of the South Mine area in 2001. • In 2005, 13 monitoring points were installed to monitor shallow slope displacement observed on the east wall of the South Mine area. • In 2008, repairs were made to improve drainage at the slump above the east wall of the South Mine area. • In 2010, six of the monitoring points 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. 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 in Section 3.5, in 2010,tension cracks were graded closed on the bench at the east wall of the South Mine area 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. • In 2012, monitoring point P-04 was replaced with a new monument due to settlement. • In 2013, slope displacement on the east wall of the South Mine area was measured between 0.3 ft and 0.4ft. • In 2014, two new monitoring points were added. Slope displacement in the South Mine area roughly doubled in 2014 (0.6 ft to 0.8 ft)compared to 2013 due to heavier snow pack and melt off. There was no evidence of displacement on the cracks at the surface of the upper bench that traverses the slope displacement. • During the 2015 site visit, additional slope displacement in the South Mine area was noted. Specifically, slope displacement at the east wall of the South Mine area was between 1.2 ft and 3.3 ft. Tension cracks exhibited both vertical and horizontal offsets. Heavy precipitation in late spring 2015 is suspected to have contributed to these accelerations in slope displacement and related tension crack development. Regrading of the bench at the east wall of the South Pit was 17