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Chapter IV <br /> volume would be between 76 and 92 feet high. To compact and fill this volume to 90 <br /> percent of the original mass would result in a subsidence choke at heights between 760 <br /> and 920 feet. This height is much less than the average depth of cover, hence surface <br /> • subsidence will not occur. (See Appendix IV-F-3 for further discussion on the <br /> subsidence bulking factor). <br /> There are no indications of surface subsidence in Coal Basin even though there were <br /> extensive mining operations for several years around the turn of the century and <br /> continuously on a much larger scale since 1956. An on-site inspection of the most <br /> likely area where subsidence could occur, above Nos. 1 and 2 mines, was conducted <br /> on September 12, 1980 by two representatives of Willard Owens Associates, Inc., Mr. <br /> John G. Roscoe, Mining Engineer; Ms. Nancy B. Lamm, Project Geologist; and <br /> Mr.Douglas Bowman, Environmental Coordinator for Mid-Continent Resources, Inc. <br /> They could find no evidence that the land area above these two mines had been <br /> affected by subsidence (See Willard Owens Subsidence Inspection Report at Appendix <br /> IV-F-1). <br /> Based on four years of monitoring data, Dr. Collins' study reads as follows: <br /> — Subsidence of the land surface over mined-out areas of <br /> theCoal Basin mines has been detected by the <br /> subsidence monitoring program initiated by MCR in <br /> 1981. Maximum subsidence detected to date is 2.10 <br /> feet, at a point now apparently stable (MC-4). This <br /> amount of subsidence resulted from the extraction of at <br /> least 8 feet of coal, and possibly as much as 16 feet <br /> is (see discussion in paragraph 3 above). There are no <br /> visible surface effects of subsidence, such as cracks, <br /> hummocked profiles or subsidence induced slumps or <br /> landslides in the large portion of the area inspected for <br /> such features. There has been no subsidence damage <br /> to the few structures, primarily mine ventilation fans, or <br /> to power lines or light-use roads located over mined-out <br /> areas. There are no known aquifers above the coal <br /> beds being mined in the area, and renewable resource <br /> lands are restricted to small livestock and wildlife <br /> summer grazing areas. Neither MCR, White River <br /> National Forest (letter of 10/14/80) nor Gunnison <br /> National Forest (letter of 9/1/80) plan any change of use <br /> of the renewable resource lands, or any structures. <br /> Therefore it is determined that subsidence that has <br /> occurred has not resulted in material damage to or <br /> diminution of reasonably foreseeable use of structures <br /> or renewable resource lands. <br /> The very nature of the renewable resources identified <br /> with the land above and within the areas of possible <br /> 33 <br />