2014-04-17_REPORT - M1977004 - Laserfiche WebLink

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Pitch Reclamation Project Colorado Mined Land Reclamation Board — 2013 Annual Reclamation Report confusing. This report uses the former naming scheme, which omits the "year" from the monitoring point identification. Therefore, MP- 99 -85, reverts back to MP -85, for example. During the 2012 survey, monitoring point P -04 was replaced with a new monument due to settlement of well backfill. There are currently 92 monitoring points in the North and South pits to monitor surficial slope movement. Of these 92 monitoring points, 10 had annual displacement magnitudes that were greater than survey error, as shown on the summary table presented as Appendix A. By comparison, eight points had annual displacement magnitudes greater than survey error for the 2011 -2012 monitoring period. Displacement for monitoring points where displacement was not detected, or was less than calculated survey error is indicated as "ND" or non - detectable. For the first time since survey monitoring began in 1994, there was no detectable displacement at the North Pit slopes in 2013. It has been typical for the greatest magnitudes of displacement at the North Pit slopes to occur in the northeast corner of the pit, in the area of the slides that occurred during mine operation. During the 2012 — 2013 monitoring period, no detectable displacement is evidence from the survey data. One point, MP -43, which is located above the crest of the north wall of the North Pit in the peat bog area, had 0.10ft/yr of displacement. The sense of the displacement is roughly perpendicular to the slope gradient and is likely indicative of localized settlement. There were nine survey monitoring points in the South Pit that had displacement greater than survey error. These include HS -4, H -5, MP -92, MP -S8, MP -63, S -1, MP -91, MP -11 and MP -S12. Displacement ranged from 0.03ft/yr to 0.37ft/yr at these South Pit locations. By comparison, maximum displacement in 2010 at the east wall of the South Pit was 0.72ft/year and 2.0 ft/year in 2008. The current maximum displacement at the east wall of the North Pit is 0.10 ft/yr at MP -43. During the previous monitoring period, there was 0.24 ft/yr displacement at MP -39. The current maximum displacement at the east wall of the South Pit is 0.37 ft/yr at MP -92. 4.2 Inclinometer Evaluation Three slope inclinometers were installed in 2003 to monitor areas of the North Pit. Annual survey data has been collected since July, 2003. Two slope inclinometers (198 -2 and 198 -2) are located on the south wall of the North pit and the other (198 -3) is above the crest of the east wall of the North Pit, a shown on Figure 3. Results from the inclinometer survey in 2013 indicate that the inclinometer displacement data are all below the threshold of error for the three installations. Total error, the sum of systematic and random error, associated with the slope inclinometer probe is +/- 0.3 inches per 100 feet of depth according to the manufacturer (Durham - Slope Indicator, Inc.). The error associated with inclinometer 198 -2 is 0.75 inches, 198 -2 is 1.27 inches, and 198 -3 is 1.5 inches according to the depth of each installation. The data collection system was repaired, tested and calibrated by Slope Indicator, Inc. in 2011. Baseline data for these inclinometers were initially collected on July 29, 2003. The initial baseline readings for these installations were corrupted due to data collection equipment failure and subsequently replaced in 2011 with more recent surveys. The inclinometer data collection equipment was tested on site prior to collecting data for the 2012 surveys. The revised baseline survey date for 198 -1 is August 8, 2007. The revised baseline survey date for 198 -2 and 198 -3 is August 1, 2006. The impact of using more recent baseline surveys is essentially inconsequential, because any displacement indicated by the surveys has consistently been below error tolerances. In addition to the loss of baseline surveys, all other surveys prior to 2006 are no longer available. Pitch 2013 Reclamation Report 14Apri12014.Docx 20