2010-07-22_REPORT - C1980007 - Laserfiche WebLink

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after mining for identifying landslides, rockfalls, vegetation, etc. Monument Dam: E-1 longwall mining was more than one mile from Monument Dam during the report period; therefore, monthly monitoring and weekly visual Photographed landslides to north and south of dam inspections were not required. either by air or other method, annually. According to the 4''' quarter 2009 seismic monitoring report, the largest Surveyed monuments on dam and on north, south, seismic event recorded at the West Elk Mine was 0.0006 g, far below the and east edges of reservoir, premining through 0.15 g threshold that requires resurveying Monument dam and the postmining. Frequency: Dam axis either quarterly reservoir; therefore, those activities were not required. or annually (conflicting text in permit), then monthly when E-seam longwall mining is within I mile Appendix D contains the required annual photos of the landslides to the (frequency on reservoir edges is unspecified). north and south of the dam. Visually inspected monument transects (dam and Yes Appendix C of the report contains data that indicates all monitoring reservoir edges) for cracks, 1 month through 2 to 3 frequencies and data requirements were met for Monument Dam and the months after mining in E-1 or E-12. (Frequency not reservoir, including survey data of the dam and edge of the reservoir specified in permit.) collected by the robotic total station, results of visual inspections of the dam reported on the operator's inspection forms, and piezometer water Measured water levels in dam crest piezometers, level data for the dam. The data indicate no significant movement on the monthly Apr - Oct, when accessible.: dam and some additional movement of the landslide in the area of the Visually inspected dam structure for cracks, weekly south abutment of the dam. while longwall mining is within I mile. The operator has been discussing with DRMS the possible need to revise the subsidence monitoring plan to increase its clarity. Resurveyed monuments on dam and reservoir edges ASAP when seismic event has PGA >0.15 . Conducted sufficient post- mining monitoring to verify subsidence prediction 2.05.6(6I(i))(F) Yes The traverses in the Fall 2009 study included observations of new and previously identified subsidence features. The report describes changes to the previously existing features that have occurred since previous visual inspections. The Fall 2009 report describes recent surface subsidence activity, including: a) continuing rockfall and slabbing in the West Flatiron area, b) no new subsidence features in the Box Canyon area, c) rockfall has largely ceased on the east side of Sylvester Gulch since the Fall Accurately predicted 2.05.6(6)(d)(i) Yes 2008 report, d) mining induced cracks and a sink-hole and non-mining induced cracks in soft subsidence. material at methane drainage wells pads (some features have been regraded), e) complete or partial healing of some of the subsidence cracks found during previous reporting periods. These impacts are consistent with the subsidence prediction in the permit application. Prevented imminent or actual material damage or 2.05.6(6)(d)(i) Yes diminution of use of