Laserfiche WebLink
West Elk Mine <br />zone, which does not have direct hydrologic communication with the neaz-surface groundwater <br />system within the Dry Fork drainage. <br />Permeability and Factors InRuencinp Permeability <br />Table 5 and Table 6 summarize the available permeability data for the mine property obtained from <br />pumping and slug tests. Most of the permeability information has been presented previously in F <br />Seam pernut applications. However, two slug tests of B Seam wells were performed by GeoWest <br />personnel in October 1988 (Exhibit 17) and laboratory permeability analyses were performed <br />on core plugs obtained from the lower Mesaverde Formation and the Rollins Sandstone per <br />Mayo and Associates (1998). <br />In general, it can be stated that the alluvium and colluvium are more permeable than the bedrock <br />units and that the uppermost bedrock units aze more permeable than those at depth. The <br />permeability of the alluvium is approximately 1 x 10-6 cm/sec. The slug and pumping tests provide <br />a measure of horizontal permeability. Vertical permeability is typically at least a factor of three to <br />five times lower than horizontal permeability. <br />A major factor that influences permeability of the bedrock at the site is jointing (and other fracture <br />discontinuities) and faulting. To clarify, fractures differ from faults in that fractures have no <br />relative offset across fracture planes. The location of fractures and faults within the bedrock is <br />sometimes difficult to assess particularly if bedrock units are poorly exposed or if there is <br />minimal offset at the surface. As a result, significant linear features can be mapped as an <br />initial means to assess potential faulting and fracturing of the bedrock formations. Site- <br />• specific evaluation of exposed bedrock outcrops are used to assess joint spacing and openings <br />(apertures). <br />Major lineaments (longer than 2,000 feet in length) are shown on Map 24. Several drainages within <br />the property appeaz to be fracture controlled. Although not evident from aerial photos, the North <br />Fork most likely represents a major fracture zone. Jointing can be observed in the steep cliff <br />outcrops along the North Fork and springs are occasionally seen discharging from the joints. The <br />hydrologic investigations conducted by MCC have shown that most springs on the property <br />dischazge neaz or above the F Seam. This indicates the fracture zones aze tighter or have not <br />propagated through shale seams below the F Seam to the same extent as above the F Seam. As <br />discussed previously in Section 2.04.7, there are a few springs discharging between the F and E <br />Seams and little indication of groundwater dischazge below that level. <br />There is little data available for joint spacing or aperture at the site. MCC collected a limited <br />amount of joint mapping information in 1973-1974. The three major joint orientations at the site are <br />E-W with a 90E dip or slight eastwazd dip, N-S with 90E or slight eastwazd dip and N SOE with a <br />90E dip. The shallowest dip measured as part of this study was 71E. Joint spacing measured in <br />surface outcrops was normally greater than one foot and typically six feet or more. Based on <br />theoretical considerations and the measurements performed at the site, fractured rock permeability <br />at the site can be high, greater than 1 x 10-3 cm/sec (1,000 feet per year). <br />The fracture opening necessary for relatively high permeability can only occur neaz the surface in <br />the active groundwater zone. Permeability at depth is typically much lower than neaz the surface <br />because of higher in-situ stresses and limited hydraulic communication with the active zone. <br />2.04 -7/ Revised Nwembei 2004 PR70 <br />