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2 . 05 . 6 Page 21 <br /> METHODS OF CONTROL <br /> From experience it has been found that where mining does not <br /> parallel cleat systems and pillars are extracted completely <br /> according to a pre-determined sequence, the surface will <br /> generally subside uniformly without tension cracks appearing on <br /> surface. This is the subsidence control method adopted by <br /> National King Coal , Inc. <br /> Leaving pillars results in loss of a natural resource which <br /> can never be recovered. Coal left in unmined pillars , which may <br /> be as much as 50% of a deposit, greatly reduces mine life. Due <br /> to a limited coal reserve base, National King Coal , Inc. chooses <br /> to extract coal , as completely as mining conditions permit, from <br /> pillars of developed panels or sections . Permission to leave <br /> pillars in Federal Coal leases must be obtained from the U. S . <br /> Geological Survey. National King Coal , Inc. has not sought such <br /> permission. <br /> SUBSIDENCE AT THE KING COAL MINE <br /> Field inspections of the surface of the mine plan area above <br /> active and abandoned mine workings during 1989 revealed tension <br /> cracks in surface soils above and along the north edge of Section <br /> 3 East where pillars had been removed. Cross-cuts had paralleled <br />