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West Elk Mine <br />West E/k Mine Eaverience <br />WWE's evaluation ofthe 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 azea as well While the E Seam overburden thickness is some of the shallowest <br />encountered at West Ells 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 aze 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 />• 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 BEM 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 similaz <br />displacement have been encountered elsewhere in the mine, but have had little or no <br />groundwater yield. Amore 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 />aze not aquifers. The Cumulative Hydrologic Impact ~Issessment -North Fork of the <br />Gunnison River (CHIA, CDMG 2001) describes the coal seams of the Mesaverde <br />Formation as "poor aquifers with very low transmissivities" and the laterally <br />discontinuous lenticular sandstones within the Upper 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 />205-I75 Revised June 1005 PRIG, January 2006, ~Llarch 2006; Rev. May 2006 PR10 <br />