Laserfiche WebLink
West Elk Mine <br />1 As indicated in Section 2.05.6 (6) (e) (i) (C&D), Depth of Surface Cracks, subsidence-induced <br />surface cracks, to the degree they develop, will generally extend no deeper than 25 to 35 feet. <br />Combining the maximum eapected surface crack depth (50 feet) with the maximum predicted <br />caved and fracture zone height (280 feet), reveals that a minimum overburden depth of 330 <br />feet should be sufficient to ensure that surface water does not reach the mine workings. Map <br />19 shows the E Seam overburden thicknesses for the West Elk Mine coal lease azea. To establish a <br />connection between the neaz surface zone and the caved zone, the overburden in the proposed <br />pemut revision azea needs to be less than 330 feet thick under the worst conditions. The <br />overburden in the SOD mining azea is 375 feet or more. Consequently, there will always be a zone, <br />which deforms but does not experience cracking from either the mine workings up or from the <br />surface down. <br />For a connection to be established, a surface crack will actually need to occur. As previously <br />discussed, in 2.05, the probability of a surface crack at any given location over a pillaz is only 0.2 <br />percent (0.002) and there is no measurable risk of long-term surface cracks in the internal portions <br />of panels, based on MCC's mining experience to date. Furthermore, the crack connection would <br />need to stay open and clear for long enough to impose a measurable hydrologic change, and this is <br />highly unlikely given the subsurface changes that will be occurring in the aftermath of longwall <br />mining. <br />In a hypothetical situation where a connection were established, the stream channels in question <br />have small drainage basins with average annual surface flows of approximately 200 acre-feet per <br />squaze mile per yeaz. Cracks will close via "healing" and "sealing," as discussed in response to <br />other questions. <br />These calculations are substantiated by the actual mining experience at West Elk Mine. For <br />example, during the unusually wet late spring and summer of 1995, there were no increased inflows <br />to the longwall panels beneath Gribble Gulch and Lone Pine Gulch. Also, as stated in the October <br />24, 1994 CDMG Decision Document on the Jumbo Mountain Tract (see page 31), "A direct <br />fracture connection to the mine was not established in Lone Pine Gulch under a cover as low as 120 <br />feet (when F Seam mining was occurring)." Similazly, mining of the B East Mains beneath <br />Sylvester Gulch did not produce a connection with the surface. The groundwater emanating from <br />the B East Mains fault had, and continues to have temperatures in excess of 80°F. This combined <br />with the lack of tritium, 14C and 180 isotopes, (Mayo 1998) indicates this water is not connected to <br />local surface waters. <br />Additional considerations regazding surface water effects include the following: <br />1. Mining in the Apache Rocks permit revision area will not measurably impact the surface water <br />hydrologic balance of the Dry Fork of Minnesota Creek. Based strictly on surface acreage, this <br />azea contributes only 22 percent of the Dry Fork of Minnesota Creek drainage basin flows as <br />measured above the Lower Dry Fork gage. Because the area is on asouth-facing slope, <br />however, the actual percentage of surface runoff will be lower. MCC's 1986 Minnesota Creek <br />Augmentation Plan, Case No. 86CW38 (approved by the Colorado Water Court), provides for <br />1.05-163 Revised June 2005 PRIO <br />