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West Elk Mine <br />percent (0.002) and there is no measurable risk of long -tern surface cracks in the internal portions of panels, <br />based on MCC's mining experience to date. Furthermore, the crack connection would need to stay open and <br />clear for long enough to impose a measurable hydrologic change, and this is highly unlikely given the <br />subsurface changes that will be occurring in the aftermath of longwall mining. <br />In a hypothetical situation where a connection were established, the stream channels in question have <br />small drainage basins with average annual surface flows of approximately 200 acre-feet per square mile per <br />year. Cracks will close via "healing" and "sealing," as discussed in response to other questions. <br />These calculations are substantiated by the actual mining experience at West Elk Mine. For example, during <br />the unusually wet late spring and summer of 1995, there were no increased inflows to the longwall panels <br />beneath Gribble Gulch and Lone Pune Gulch. Also, as stated in the October 24, 1994 CDMG Decision <br />Document on the Jumbo Mountain Tract (see page 31), "A direct fracture connection to the mine was not <br />established in Lone Pine Gulch under a cover as low as 120 feet (when F Seam mining was occurring)." <br />Similarly, mining of the B East Mains beneath Sylvester Gulch did not produce a connection with the <br />surface. The groundwater emanating from the B East Mains fault had, and continues to have temperatures in <br />excess of 80°F. This combined with the lack of tritium, 14C and 180 isotopes_, (Mayo 1998) indicates this <br />water is not connected to local surface waters. <br />Additional considerations regarding 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 area <br />contributes only 22 percent of the Dry Fork of Minnesota Creek drainage basin flows as measured above <br />the Lower Dry Fork gage. Because the area is on a south -facing slope, however, the actual percentage of <br />surface runoff will be lower. MCC's 1986 Minnesota Creek Augmentation Plan, Case No. 86CW38 <br />(approved by the Colorado _Water Court), provides for total replacement of the annual streainflow <br />generated in the Dry Fork basin. For these reasons, impacts to the Dry Fork of Minnesota Creek will be <br />minimal due to B and/or E`Seam mining. <br />2. Mining in the Box Canyon permit area will not measurably impact the surface water hydrologic balance <br />of the North Fork. As previously stated, 100 percent of the mining area has a B Seam overburden <br />thickness of more than 500 feet, thus all but eliminating the possibility of surface water capture by the <br />mine workings. <br />3. Based on the B Seam mining plan, including Panel 25, and including the Box Canyon pennit revision <br />area, it is not anticipated that there will be direct mining impacts to Sylvester Gulch. Longwall Panel 25 <br />will be mined up -dip opposite of the gulch grade which will not result in ponding in Sylvester Gulch. <br />4. The potential for subsidence fractures extending upward from the panel 25 workings and <br />intersecting the channel of Sylvester Gulch at the land surface will be greatest in SWI/4 <br />SW1/4 Section 15, T.13 S., R. 90)A7., where overburden thickness is approximately 500 feet <br />and the projected combined height of the caved zone and fractured zone is 270 feet. The <br />combined height of the caved zone and fractured zone is calculated as follows, based on the <br />discussion of subsidence in 2.05.6(6)(e)(i)(d): 22.5 X 12 -foot mining height = 270 feet. The <br />thickness of the overburden exceeds the combined height of the caved zoite and liactuie zoite <br />by 230 feet, indicating stream flow capture will not result from Panel 25 mining. <br />In summary, based on the small amount of surface flow that occurs annually, the low probability <br />of surface cracking due to subsidence, and the depth of cover and the character of the overburden <br />materials within the permit area, the projected mine subsidence will not significantly impact the streams. <br />2.O5-194 Revised June 2005 PRIO, January 2006. March 2006; Rev. A -lay 2006 PRIO, A'ov. 2006 TR107:Sep. 2007 PR12;Feb 2008 PRl2 <br />