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West Elk Mrne <br />Kadnuck (U.S. Bureau of Mines) in her paper, Response of Surface Springs to Longwall Coal <br />Mining Wasatch Plateau, Utah, where she states, "The limited spring response observed at this site <br />may be attributed to several factors; (1) The thickness and composition of overburden present which <br />contained a massive competent sandstone, which causes bridging in the overburden, limiting <br />subsidence, (2) Presence of formations containing swelling clays, and (3) The elevation of the <br />spring above the elevation of estimated heights of fracturing and caving in the overburden." This <br />basic concept is elaborated as follows. <br />Within the South of Divide mining area, the overburden thickness for the E Seam ranges <br />from 375 to 1,200 feet. <br />Springs (and their sources) can be affected by subsidence in two different ways. First, fractures <br />can extend upwazd from the mine seam and intersect the spring or spring source. As explained in <br />Sections 2.05.6 (6)(e)(i)(C&D), Subsidence Zone Description, the height of the caved/fractured <br />zone extending upward from the mine seam is conservatively estimated at 280 feet. Secondly, <br />there is a small probability of surface cracks developing in association with the mining (see Section <br />2.05.6 (3)(b)(iii & Viii) Streams for estimate of surface crack probability) and the typical maximum <br />depth of such cracks in the South of Divide mining area is conservatively estimated at 25 to 35 <br />feet. <br />These two distances indicate that, for a spring to avoid any potential impacts, the source of the <br />spring must be at least 280 feet above the uppermost seam that is being mined and more than <br />25 to 35 feet below the ground surface. From a practical standpoint, because every spring (by <br />definition) "daylights" at the ground surface, there is an extremely small risk that any given spring <br />will encounter a surface crack. However, it is essential to recognize the following: <br />Site specific evidence demonstrates that surface cracks aze most likely to occur over chain <br />pillazs, barriers and mine boundaries. Consequently, if a spring and its source aze not located in <br />these azeas, they will be unaffected by surface cracks. This is true for most of the springs in the <br />South of Divide mining area. <br />The spring source could easily be unaffected by a surface crack, even if the spring itself is <br />affected (at the point where it surfaces). In this case, the spring would re-emerge at another <br />location. <br />1.05-166 Revisedhme 2005 PRIG <br />