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West Elk Mine <br />• well. This continues to be the case despite the BEM Fault inflows first encountered in 1996 and <br />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 />• 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 />primazily 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 aze 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 Assessment -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 dischazge 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 />Spring flows aze typically less than 10 gpm with annual dischazge peaks in the spring which <br />generally diminish to no flow in the fall. <br />• Mining of the B and F Seams to date has shown little groundwater inflow, except for the two <br />fault system inflows as noted above. The average rate of inflow between 1982 and 1995 had <br />been about 12 gpm, with a peak inflow rate estimated at 50 gpm in the B Seam and 10 gpm <br />in the F Seam. In 1996 this average inflow rate increased as a result of mining through the <br />• BEM Fault to approximately 200 gpm. This is based on observed and measured inflows <br />from the fault system (approximately 235 gpm or 301 acre-feet over 291 days) and estimated <br />2.05-150 Revised November7004 PRIO <br />