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inspection done for Mid-Continent by [Dillard Owens Associates , <br /> r� <br /> Inc . on subsidence in Coal Basin, and upon the inspections , <br /> observations and opinions of experienced Mid-Continent <br /> mining engineers and environmental specialists . (Appendix IV-F-1) <br /> The maximum physical displacement that could <br /> occur from subsidence is the vertical disturbance related to <br /> the thickness of coal removed , and the horizontal distance <br /> measured from a point where coal has been mined by the angle <br /> of draw appropriate for the existing geologic structure of <br /> the cover material . <br /> Vertical disturbance is a function of coal <br /> thickness mined and the depth of cover . The influence of <br /> rock types and lithology is usually ignored in theoretical <br /> discussions of subsidence , but there is undoubtedly a <br /> relationship between rock units and the surface effects of <br /> subsidence as well as the effect of bulking factor upon <br /> total subsidence . <br /> Published subsidence ratios between measured <br /> subsidence and seam thickness taken from numerous mines <br /> range from 0 . 25 to 0 . 70 . Mesaverde coal mines have not been <br /> extensivelv monitored for subsidence ratios , but limited <br /> data available indicates that the average ratio is about <br /> 0 . 40 with a high value of 0 . 70 . These data are from mines <br /> shallower than those of Mid-Continent . We believe 0 . 55 is a <br /> reasonable "worst rase" ratio . (See additional discussion on <br /> this hypothesis in Appendix IV-F-3) . <br /> ' 26 <br />