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The amount of subsidence arising from the mining of double seam mining panels, <br />will be, typically less than 10.0 feet. Maximum strains at surface resulting from mining will <br />generally be, 7,000 u -in /in or less. The development of surface cracks due to subsidence <br />is not anticipated. Damage, if any, should therefore considered negligible to appreciable. <br />3.2 ZONES OF INTERMEDIATE SUBSIDENCE IMPACT <br />Zones with between 500 and 1,000 feet of overburden cover above the B -seam in <br />double seam mining are designated as zones of intermediate subsidence impact on Map <br />27. Subsidence magnitudes, 16.0 feet, and strains, 35,000 to 10,000 u- in /in, are predicted <br />for these zones. Appreciable to severe damage may result to surface structures, if <br />present, due to subsidence. There is a risk that subsidence fractures may occur at the <br />ground surface where the overburden within these zones is thinner and the geological and <br />mining conditions are unfavorable. <br />3.3 ZONES OF GREATEST SUBSIDENCE IMPACT <br />Zones of greatest subsidence impact are shown on Map 27 as those zones having <br />less than 500 feet of overburden cover. Large strains, 60,000 to 30,000 u- in /in, are <br />predicted within these zones. This subsidence could result in severe damage to any <br />surface structures located within these zones. There is a moderate risk of subsidence <br />cracks occurring anywhere within the zones. Experience at the Bowie #1 Mine show that <br />these high risk zones include areas where the overburden is less than 500 feet thick, and <br />where the geologic conditions are unfavorable. Subsidence cracks could result in <br />disruption of run -off water flows and perched water bearing zones. <br />These zones extend from where mining is terminated at the extent of the panel <br />development near the outcrop southward to the point where the angle of draw is projected <br />to the surface. Because of the steeply rising terrain which is present over much of the <br />North Fork Valley, the zone is generally fairly limited in extent. It is most extensive where <br />the overburden cover is reduced by the presence of valleys and gulches. <br />PR -14 -31 - 03/14 <br />