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West Elk Minae <br />West Elk Mine Eznerience <br />WWE's evaluation of the probable hydrologic consequences draws heavily on information <br />obtained from current and previous mining of the F and B Seams, respectively, at West Elk <br />Mine. As described previously in the Subsidence Survey section, WWE (working closely with <br />Messrs. Rold and Dunrud) has determined that previous experience regarding subsidence and <br />hydrologic consequences for the current permit area correlates to the South of Divide permit <br />revision area as well. While the E Seam overburden thickness is some of the shallowest <br />encountered at West Elk Mine, the mine -induced subsidence is well understood and its impact can <br />be reasonably predicted. This continues to be the case despite the BEM Fault inflows first <br />encountered in 1996 and the January 1997 inflows from the 14HG Fault. <br />A large database of hydrologic information, for both water quality and quantity, has been <br />collected for springs, groundwater, and surface water at West Elk Mine. These data have been <br />collected since 1977 and are contained within this permit document, associated permit revision <br />or renewal application "Adequacy Responses," Quarterly Hydrology Reports (1977 to 1987), and <br />Annual Hydrology Reports (1982 to present). <br />In general, the mining experience at West Elk Mine to date indicates the following features of <br />the hydrologic system and changes resulting from mining: <br />o The primary permeability of the bedrock units is very low (approximately 1x10-6 cm/sec) and <br />groundwater encountered in the Mesaverde Formation is generally finite in volume and <br />primarily held in joints and open fractures in the bedrock. Age -dating of these small inflows <br />has not occurred so it is difficult to assess the origin of this water. However, it is suspected <br />that groundwater found deeper -than approximately 500 feet has been held in the formation <br />for an extensive length of time and is therefore part of the inactive water system. Noted <br />exceptions are the inflows of groundwater from the BEld1 and 14HG fault systems. These <br />unprecedented inflows represent the first significant (>100 gpm) groundwater inflows to the <br />mine from a fault system or other source. Faults or fracture systems with similar <br />displacement have been encountered elsewhere in the mine, but have had little or no <br />groundwater yield. A more thorough discussion of these fault systems is provided later <br />in this section. <br />The bedrock units within the Upper and Lower Coal Members of the Mesaverde Formation <br />are not aquifers. The Cumulative Hydrologic Impact Assessment - North Fork of the <br />Gunnison River (CHIA, CDMG 2001) describes the col seams of the Mesaverde <br />Formations as "poor aquifers with very law and the laterally <br />discontinuous lenticular sandstones within the Uppe. Mesaverde Formation as able to <br />"support only localized ground water flows, and are considered to be insignificant in <br />terms of the overall hydrologic balance". <br />® Most groundwater discharge from the system is from springs exiting the steep outcrop faces <br />formed by incised drainages such as Dry Fork, Lick Creek, Box Canyon, North Fork, and <br />Sylvester Gulch or from colluvium, generally in association with landslides. Springs <br />typically occur on the south or west sides of drainages on the down -dip outcrop exposures. <br />2.05-175 Revised June 2005 PRIG, January 2006, Alarch 2006; Rev. Ala -v2006 PRIG. \'ov. 2006 TRIO 7; Sep. 2007 PR72;Feb 2008 PRI2 <br />