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West Elk Mine <br />Maps 14 and 19 show the overburden thickness above the B and E Seams respectively. The <br />overburden is typically greater than 600 feet for both the B and E Seams in the South of Divide <br />permit revision area and Apache Rocks area, and for the B Seam in the Box Canyon azea. <br />Maximum overburden thickness for the E Seam is in excess of 1,200 feet and in excess of 2,300 feet <br />for the B Seam. Based on the joint spacing measured in the field, the tightness of the joints <br />expected at greater overburden depths, and the theoretical permeabilities, fracture-related <br />permeability in and neaz the B and E Seams under more than 500 feet of cover is expected to be <br />very low, on the order of 5 x 10~ cm/sec (5 feet per year), or less. <br />Fault-Related Groundwater Inflows <br />In Mazch and April 1996, MCC mined through a fault system (known as the BEM Fault) <br />containing a significant amount of water. Initial inflow rates were measured in excess of 2,000 <br />gpm. Similaz to other observed inflows to the mine, these flows decreased over time. By early <br />May the discharge from this fault system had declined to about 250 gpm and, from August <br />1996 to July 1997, generated a relatively constant inflow rate of approximately 85 gpm. In eazly <br />July 1997, this inflow ceased when the same fault system was encountered to the northeast in the <br />14SE Tailgate. Flow from this azea was initially approximately 200 gpm but quickly diminished to <br />less than 100 gpm. <br />Fault dischazges remained relatively constant until the BEM fault system was again encountered <br />in February 1998 in the 24SE Headgate. At that time, inflows were estimated to be <br />approximately 200 gpm from the floor at cross-cut 8 and flow from the 14SE Tailgate area <br />ceased. On May 28, 2003, the BEM Fault was once again encountered between cross-cut 20 and <br />21 in the 22SE Headgate. Initial inflow from this location was estimated at 3,500 gpm, but <br />rapidly declined to about 200 gpm within about 2 weeks. <br />In January 1997, a second water-bearing fault system (known as the 14HG Fault) was <br />encountered. Initial flow rates were near 8,000 gpm, tapering off to less than 250 gpm by eazly <br />Mazch 1997. An exploratory horizontal borehole penetrated this same fault system in July 2003 <br />about 200 feet south of Cross Cut 32 in the 22SE Headgate. Mine development work crossed the <br />fault system in August of 2003 resulting in an estimated initial inflow rate of 100 gpm which <br />decreased to about 35 gpm within a few days. <br />Mapping of these fault systems by Mayo and Associates (1998) indicated that the BEM Fault <br />exhibits an en echelon pattern, as it strikes northeast toward the 14SE Tailgate. The primary <br />fault zone splays into a horsetail fault as it extends northeast from the B East Mains to the <br />Box Canyon Mains, eventually transferring to the 14HG Fault zone. The transition area <br />between the two fault zones has an abundance of slips, shear zones, small faults, and short <br />duration faults with unusual orientations. Although the trend of both fault systems may be <br />projected to the cliff faces in the Minnesota Creek drainage, neither fault has been identified <br />on the surface and borehole, and monitoring well data showed no indication of the fault or <br />associated water. <br />Stephen Robertson and Kirsten (SRK, 1998) also evaluated the style, geometry and origin of <br />faulting in the vicinity of West Elk Mine. SRK mapped three inferred, extensional faults pazallel <br />?.04 -71 RevisedNavember 2004 PR/0 <br />