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2 . 05 . 6 Page 24 <br /> A second consideration, illustrated by the area above <br /> Section 3 East , is the thickness of overburden. Generally, the <br /> thicker the overburden, the less likely ground subsidence will <br /> reach the surface . Overburden at the King Coal Mine is shallow <br /> (maximum 300 feet) compared to some Colorado Western Slope <br /> operations with overburden of 1000 to 2000 feet . The shallow <br /> overburden would increase the probability of surface subsidence. <br /> However, the shallow overburden has resulted in a much reduced <br /> stress field around the mine workings which enables much higher <br /> recovery of coal . <br /> A third consideration is completeness of coal recovery. <br /> Where 90% or more of the coal (excluding main entry and barrier <br /> pillars ) can be successfully recovered from a given mining <br /> section, ground disturbance is more likely to cause uniform <br /> settling of surface strata rather than the creation of cracks and <br /> joints . Coal recovery within sections at the King Coal Mine has <br /> generally been above 90% after pillar extraction. This should <br /> cause a gradual trough shaped settling with little cracking or <br /> jointing - surface is and will be monitored for the formation of <br /> these trough shaped features . <br />