2008-03-31_PERMIT FILE - C1980007A (34)

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Vest Elk Mbie surface outcrops was normally greater than one foot and typically six feet or more. Based on theoretical considerations and the measurements performed at the site, fractured rock permeability at the site can be high, greater than 1 x 10-3 cm/sec (1,000 feet per year). The fracture opening necessary for relatively high permeability can only occur near the surface in the active groundwater zone. Penneability at depth is typically much lower than near the surface because of higher in-situ stresses and limited hydraulic communication with the active zone. Maps 14 and 19 show the overburden thickness above the B and E Seams respectively. The overburden is typically greater than 375 feet for both the B and E Seams in the South of Divide permit revision area and Apache Rocks area, and for the B Seam in the Box Canyon area. Maximum overburden thickness for the E Seam is in excess of 1,200 feet and in excess of 2,300 feet for the B Seam. Based on the joint spacing measured in the field, the tightness of the joints expected at greater overburden depths, and the theoretical penneabilities, fracture-related permeability in and near the B and E Seams under more than 500 feet of cover is expected to be very low, on the order of 5 x 10"6 cnn/sec (5 feet per year), or less. Fault-Related Groundwater Inflows In March and April 1996, MCC nnined through a fault system (known as the BEM Fault) containing a significant amount of water. Initial inflow rates were measured in excess of 2,000 gpm. Similar to other observed inflows to the mine, these flows decreased over time. By early May the discharge from this fault system had declined to about 250 gpm and, from August 1996 to July 1997, generated a relatively constant inflow rate of approximately 85 gpm. hi early July 1997, this inflow ceased when the same fault system was encountered to the northeast in the 14SE Tailgate. Flow from this area was initially approximately 200 gpm but quickly diminished to less than 100 gpm. Fault discharges remained relatively constant until the BEM fault system was again encountered in February 1998 in the 24SE Headgate. At that time, inflows were estimated to be approximately 200 gpm from the floor at crosscut 8 and flow from the 14SE Tailgate area ceased. On May 28, 2003, the BEM Fault was once again encountered between crosscut 20 and 21 in the 22SE Headgate. Initial inflow from this location was estimated at 3,500 gpm, but rapidly declined to about 200 gpm within about 2 weeks. In January 1997, a second water-bearing fault system (known as the 14HG Fault) was encountered. Initial flow rates were near 8,000 gpm, tapering off to less than 250 gpm by early March 1997. An exploratory horizontal borehole penetrated this same fault system in July 2003 about 200 feet south of Cross Cut 32 in the 22SE Headgate. Mine development work crossed the fault system in August of 2003 resulting in an estimated initial inflow rate of 100 gpm, which decreased to about 35 gpm within a few days. Mapping of these fault systems by Mayo and Associates (1998) indicated that the BEM Fault exhibits an en echelon pattern, as it strikes northeast toward the 14SE Tailgate. The primary fault zone splays into a horsetail fault as it extends northeast from the B East Mains to the Box Canyon Mains, eventually transferring to the 14HG Fault zone. The transition area between the two fault zones has an abundance of slips, shear zones, small faults, and short 2.04-72 Revised June 2005 PRI Q Marla 2006; Rev. Apri12006 PR10, Sep. 2007PR12