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Fracture permeability generally decreases with depth as the fractures are made <br />progressively tighter by increasing overburden pressure. Evidence for this can be <br />observed in both the American Tunnel and the Terry Tunnel. At locations deep within <br />the mine, water enters each tunnel only where major fractures are encountered, and <br />most of the back and rib of the tunnel is dry. However, as the portals are approached <br />decreasing overburden pressure allows relatively minor joints to transmit water and <br />dripping water becomes common. <br />In the deeper parts of the flow system, significant quantities of water are transmitted <br />only by major fractures. This is demonstrated by the fact that the deeper part of the <br />present American Tunnel (beyond the Daylight Corner at approximately 2700 feet <br />from the outside end of track') has intercepted 1350 gpm of ground water. Of this <br />1350 gpm, 90 percent can be accounted for from the intersection of five major <br />fracture zones ithe Washington vein, the Sunnyside vein, the Brenneman vein, a <br />fracture zone at the 0700 runaround, and a fracture zone located 3020 to 3220 feet <br />from the end of track (see section 4.2.11. Figure 6 is a schematic diagram showing <br />the manner in which fracture permeability changes with depth. <br />' All footages along the American Tunnel are referenced to track repair footages as marked <br />on the tunnel wall. The track repair footages have a zero point just outside of the portal. <br />sunnylwpltreci12251 ~Mar1993.Rpt 1 6 <br />Hal SIITI011 HYDRO-SERRCH <br />