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The Division was concerned about reactivation of these features by subsidence of the <br />land surface resulting from coal extraction. An extensive study by Rocky Mountain <br />Geotechnical was completed in 1986 that addressed the relationship between <br />subsidence and the potential reactivation of slide bodies above the Beaz No. 3 Mine. <br />The study concluded that the general mass movement mechanism was small, shallow <br />slope failures rather than large, deep failures. The report concluded that the landslide <br />features above the Bear No. 3 Mine were unstable and that failures would occur <br />regardless of subsidence effects. No subsidence effects were expected to occur in the <br />critical toe area of any of the slide bodies. Subsidence in these areas was to be <br />controlled by split pillar removal. <br />In 1986 a debris flow at the site displaced the Beaz Mine fan. In 1993 the area of the <br />access road immediately below the fan slid, dropping the upper road approximately six <br />feet. It is not known if the debris flows were reactivated by mining activity. Beaz Coal <br />Company has performed subsidence monitoring quarterly with reports submitted semi- <br />annually. Asprovided for in the permit application, monitoring stopped two yeazs after <br />the reclamation of the road. <br />The study by Rocky Mountain Geotechnical indicates that mining of the C-Seam <br />would result in propagation of fractures upwazd through the geologic section for <br />approximately 360 feet. Strata between the C-Seam and the massive sandstone at the <br />top of the lower coal bearing member would be rnbbilized to some degree. No <br />rubbilization of the overlying E- and F-Seams was expected to occur. Subsidence of <br />the land surface was expected to a maximum of six to eight feet in the northwestern <br />part of the mine. <br />The permit application required that the operator conduct subsidence monitoring of <br />each mined panel, beginning just prior to retreat mining of that panel. Subsidence <br />monitoring of that panel would continue for a period of two years after retreat mining <br />had occurred. The concern was that the subsidence effects might cause landslides or <br />reinitiate historic landslides. With the cessation ofmining in 1996, there was no more <br />subsidence monitoring above mined panels at the Bear No. 3 Mine. <br />The subsidence monitoring results confirmed the conclusions of the subsidence <br />predictions. The maximum and minimum predicted subsidence values corresponded <br />satisfactorily with the maximum and minimum observed subsidence values. Observed <br />subsidence values ranged from negligible to about 6 feet. Shortly after retreat mining <br />underneath the subsidence monuments began, subsidence commenced. The elevations <br />of most of the subsidence monuments decreased steadily although, for a few stations, <br />the rate of change in elevation varied. Subsidence ofthe monuments generally stopped <br />within about a year or so after retreat mining stopped under that monument. <br />It was predicted that subsidence would have, at most, a small effect on landslides in the <br />azea but that there would not be any long term impacts. The subsidence monitoring <br />observations demonstrated that landslides were not initiated by the effects of <br />subsidence and that there were no long term impacts. <br />29 <br />