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West Elk Mine <br />Fork (on the north side of the drainage divide) and to the Dry Fork (on the south side of the divide), <br />so the water will not be lost to the system. <br />This analysis conservatively assumes that surface cracks, which develop will remain open and that <br />they will not close with time. However, crack closure is, indeed, very likely. An important <br />mitigating factor regarding surface water loss into subsidence cracks is "healing" due to expansion <br />of the materials in the crack. To investigate this subject relative to West Elk Mine, Mr. Rold met <br />with Mr. Pat Rogers and Mr. Jeff Hynes of the Colorado Geological Survey in January, 1995. Both <br />men are experts in the subject of swelling soils and Mr. Hynes is the Colorado Geological Survey's <br />principal expert on subsidence research and evaluation (see references for examples of Mr. Hynes' <br />publications). <br />Both Mr. Rogers and Mr. Hynes stated that, if the expansive shales and claystones of the Mesaverde <br />Formation in the subsurface were not at their highest attainable water saturation, the addition of <br />water in a subsidence crack would produce additional swell. More importantly, the introduction of <br />waters will increase the plasticity index of the shales or claystones. The higher the plasticity index <br />of a shale or claystone, the more easily it deforms under the overburden pressure assisting in crack <br />closure. To put it simply, "the wetter a mud ball gets, the easier it is to mold." WWE agrees with <br />this analysis because overburden materials within the Mesaverde Formation contain numerous shale <br />layers and lenses, which tend to undergo plastic deformation under compression. This seals <br />fractures, which may develop in response to subsidence. In addition, siltation will assist in the <br />filling of surface cracks, which may develop, further reducing the potential to transmit water <br />• downward. <br />Another important factor in minimizing the potential loss of surface water to the mine workings is <br />the depth of cover. D. Y. Dixon states in The Impacts of Three Longivall Coal Mines on Streamfloly <br />in the Northern Appalachian Coal Fields (1989) that streamflow showed fewer effects of <br />undermining with increased overburden thickness. Additionally, K.L. Joluison (1992) found in a <br />study of two longwall mining sites in the northern Appalachian coal field where the depth of mining <br />is 500-600 feet, that longwall mining beneath the two stream valleys did not lessen the quantity or <br />quality of shallow groundwater in the valleys, nor did it affect streamflow. <br />Subsidence impacts on streams above two longwall mines studied recently in Utah help provide a <br />basis for further estimating impacts in the permit area. The basic conclusion from the studies <br />conducted at the Utah mines is that there has been no impact to date on stream base flow where the <br />overburden thickness is more than 500 to 600 feet. Some details are described below for two Utah <br />study areas: <br />1. The area is located within USFS lands on the North Fork of Miller Creelc at Cyprus Plateau's <br />Star Point Mine. Longwall mining panels were driven beneath this perennial stream in <br />overburden that ranges in thickness from 50 to 1,100 feet. Subsidence cracks and diversion of <br />streamflmN, were obsei \'ed above the rani-dng panels tiie o :%Crburden thickness was less <br />than 300 feet to about 500 feet. However, no cracks or reduction of stream base flow were <br />observed where the overburden exceeded 500 feet (USGS 1995). <br />2.05-192 Revised June 200.1 PRIG. Januai7, 2006, March 2006; Rev. Mail 2006 PRIG, Nov. 2006 TR707; Sep. 2007 PR12; Feb 2008 PR72 <br />