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creeks would be augmented by surface runoff of differing chemistry. However, many surface <br /> drainages pass over sulfide-bearing rocks and some have a pH as low as 4.4. <br /> The permeability characteristics of the majority of the ground-water flow system have not been <br /> affected by the excavation of the underground workings of the Sunnyside Mine. Dewatering of <br /> the mine has reduced the hydraulic head by about 850 feet and locally induced a ground-water <br /> gradient toward the underground workings. Most ground water entering the underground <br /> workings flows out of the American Tunnel; in effect taking a faster flow path to the Cement <br /> Creek watershed than it would have had under natural gradients. <br /> Flow from the American Tunnel portal (at the lowest level of the mine) was measured at 3.1 <br /> million gallons per day (mgd) in October of 1991. In the deeper parts of the American Tunnel <br /> (farther than approximately 2500 feet from the portal) the majority of water transmitted to the <br /> tunnel originates from a few major fracture zones. Minor joints transmit a significant amount <br /> of water only in the first 2500 feet of the tunnel. More than half of the discharge of the <br /> American Tunnel enters the tunnel downstream of the SJCMV property line. <br /> A large percentage of the surface water from the head of Eureka Gulch drains into the <br /> underground workings of the Sunnyside Mine via the Lake Emma Hole and other locations <br /> where workings intersect the land surface. The majority of the surface water entering the mine <br /> drains to Eureka Gulch via the Terry Tunnel (approximately 900 feet above the level of the <br /> sanjuan\sunny\110361\oet91.Rpt 2 <br />