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West E[k Mine <br />• 2. If a spring source is located within the fracture zone, the spring may either be lost or, <br />particulazly for springs in the upper part of the fracture zone, it may relocate to a lower <br />position. This is supported by Leavitt and Gibbens (1992) who state, "The results for <br />springs are somewhat surprising, as previously held notions suggest that springs are highly <br />susceptible to longwall mining effects. However, these data indicate that springs aze more <br />resilient than dug wells and that more than half of the springs used for domestic water <br />supplies continue to flow, or resumed flow after mining. In a number of locations after a <br />spring ceased to flow, a new spring was reported downslope from the original site. This <br />phenomenon suggests a redistribution of groundwater flow in the neaz surface <br />environment." <br />3. Many colluvial and alluvial springs originate within the uppermost subsidence zone, where <br />surface fractures can occur. In the very unlikely event that a spring source, or the spring <br />itself, happens to be impacted by a surface crack, flow reductions (particularly on a <br />temporary basis) and/or spring relocation could occur. <br />With these concepts as background, it is feasible to define the probable hydrologic consequences for <br />colluvial/alluvial springs and bedrock springs. <br />ColluviaUAl[uvial Spring Impacts <br />• Roughly two-thirds of the springs in the SOD permit area are colluvial in nature. There is <br />considerable spring monitoring data for West Elk Mine and the majority of the relevant data aze for <br />colluvial springs. As noted above, the relevant data appear to demonstrate that F and B Seam <br />mining has not affected the monitored springs. This is not surprising in light of the thick <br />overburden at the mine and the fact that surface cracks are so infrequently observed. <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 upward 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 upwazd 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 />defmition) "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 />• <br />2.05-198 Revised June 2005 PRIG, January 2006, March 2006; Rev, May 1006 PRIO <br />