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SUBSIDENCE IMPACTS 1987 <br />Colorado Westmoreland Inc. completed only submain type development in 1987, <br />Mining occurred only in the Orchard Valley West Mine. Pillar extraction in the <br />Orchard Valley West Mine is not anticipated until at least 1989. Little, if <br />any, subsidence resulted in 1987 with similar expectations in 1988. <br />SURVEY MONITORING <br />The Colorado Westmoreland Inc. Monitoring Program within the permit area con- <br />sists of a wide spaced and three high resolution grids. Emphasis was directed <br />toward these high resolution grids. Stations 19, 27, 28-69, 74, 90, 92, 93, <br />201-224, Temp 1-3, 250, and 306 were surveyed twice (June and November) during <br />1987. In addition, stations 6-8, 88, 89 and Temp 4 were added to the list for <br />the November survey. The survey of high resolution stations 28-69 were plotted <br />on an original profile map that also includes the 1986 subsidence (see Appendix <br />G). Field surveying was conducted with double angle/distance methods for in- <br />creased accuracy. <br />Minor and consistent settlement has accumulated within the high resolution grid <br />stations 28-57 located over the 11 North Panel, These stations settled in near- <br />ly equal amounts (0.175 ft .). Minor settlement in this area is expected, but to <br />have a block of equal settlement seems unlikely. The reason for this may be <br />that one or more of the permanent survey instrument stations had physically <br />moved, thus providing a common difference for this group. Similar reference can <br />be made to the 1986 survey results. <br />Some stations over the 12 North Panel showed minor settlement and minor heave, <br />and some showed no movement at all. These were stations 58-69. <br />• Stations over the 5 North and 9 East Panels showed minor sporadic settlement <br />which was considered normal. These were stations 201-224 and 42-51. <br />All stations discussed thus far are part of the high resolution grids overlying <br />the Orchard Valley Mine, Subsidence in this area proceeded at a very small mag- <br />nitude. as anticipated. Wide spaced stations indicate similar results. <br />As expected, little if any subsidence occurred over the Orchard Valley West Mine <br />area during 1987. Survey results of stations 90, 92, and 93 verified this con- <br />clusion. Stations 88 and 89 were established for future reference a[ the Or- <br />chard Valley West Mine. <br />Because little or no additional subsidence movement has occurred over the 11 <br />North and 12 North Panels, CWI anticipates that final subsidence has occurred, <br />Based on the data from the two panels, an angle of draw was calculated in the <br />1986 Annual Hydrology and Subsidence Report. The calculated angle of draw <br />(16~), is smaller than what CWI had originally projected and used for affected <br />area determinations. Refer to the calculations in Appendix G of the 1986 re- <br />poct, <br />VISUAL MONITORING <br />Visual subsidence monitoring was accomplished by occasional inspections. These <br />visual inspections were done simultaneous with survey monitoring as well as at <br />other times. Concentrated efforts were made in areas where retreat mining had <br />occurred, <br />• The results of these visual inspections indicated no additional surficial subsi- <br />dence in 1987. An increase of subsidence was not apparent over 9 East, 11 <br />North, 12 North, nor 5 North, all of which were retreat mined in 1985 and/or <br />1986. <br /> <br />