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• <br />West Elk Mine <br />These zones are discussed at length in Section 2.05.6 (6)(e)(i)(C&D) Subsidence Zone Description. <br />The following conservative interpretation can be applied to the subsidence zones: <br />If a spring source is located within the caved zone, the spring may be lost and the source <br />water may be discharged into the mine workings. (Peng 1992). <br />2. If a spring source is located within the fracture zone, the spring may either be lost or, <br />particularly 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 are 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 near 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 />ColluviaUAlluvial Spring Impacts <br />Roughly two-thirds of the springs in the SOD and Dry Fork pen -nit areas are colluvial in nature. <br />There is considerable spring monitoring data for West Elk Mine and the majority of the relevant <br />data are for colluvial springs. As noted above, the relevant data appear to demonstrate that F and B <br />Seam 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 and. Dry Fork mining areas, the overburden thickness for the E Seam <br />ranges from 375 to 1,200 feet. <br />Springs (and their sources) can be affected by subsidence in nvo 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/f-actured <br />zone extending upward from the nine 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) Strewns for estimate of surface crack probability) and the typical maximum <br />depth of such cracks in the South of Divide min mg area is conservatively estimated at 25 to 35 <br />feet. <br />2.O5-198 Revised June 2005 PR10, January 2006, March 2006; Rev. May 2006 PRIG. Nov. 2006 TR107; Sep. 2007 PR12;Feb 2008 PR12 <br />