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1 ' William J. Carter March 12, 1998 Re: Response to Susan Burgmaier's comments on the 1996 Annual Hydrologic Report The Grand Junction Office of the U.S. Geological Survey supplied the following mirilmum flow information on the North Fork of the Gunnison on May 21, 1990. The minimum flows occur typically in the winter and aze measured at a point neaz Somerset. Yeaz Min Flow -CFS Yeaz Min Flow -CFS 1976 32 1983 36 ' 1977 25 1984 28 1978 21 1985 57 1979 25 1986 80 ' 1980 50 1987 75 1981 46 1988 49 1982 59 1989 54 ' According to the projection presented in Section 2.04.7(1)(b), the water inflow to the Sanbom Creek Mine may be as high as 425 gpm. The TDS concentration of a water sample taken in June ' 1992 from the Sanbom Creek mine discharge was 2,940 mg/l. Introduction of a 425 gpm flow with a TDS of 2,940 from the Sanbom Creek Mine and introduction of a 235 gpm flow with a TDS concentration of 2,731 from the Somerset Mine into a 21 cfs flow with a TDS of 151 will increase ' [he TDS concentration in the river to 328. A TDS level of 328 equates to a conductivity level of about 490 umhos/cm which is well below the threshold limit for irrigation water for salt sensitive ' species of 700 umhos/cm (ref. MLRD document dated January 1988, titled A Description of The Material Damage Assessment Process Pertaining to Alluvial Valley Floors, Surface Water, Ground Water and Subsidence at Coal Mines). ' This analysis is based on the low flow which occurred in the winter of 1978. During the irrigation season, when the TDS concentration is of most concern, the flow in the river is much higher so the ' impact from the mine flow would be much smaller. This section of the permit, the probable hydrologic consequences, will be updated if the mine ' dischazge from the Sanbom Creek Mines shows a pattern of exceeding 425 gpm averaged over a 7- day period. ' There aze no groundwater, springs, or surface water channels in the vicinity of the waste disposal azea by the old C-Seam portal and no ground water or springs exist in the West Valley Fill azea. Mine waste rock is sufficiently coarse that any water accumulation in the waste rock stockpiles will ' be insignificant. While the West Valley Fill will be constructed in an existing ephemeral drainage, all upgradient and runoff flows will be diverted azound the fill by permanent diversion. All storm ' mnoff from these areas will be contained in the sediment control structures in the Elk Creek Yazd and West Valley Fill azea(s), respectively. Any infiltration through the West Valley Fill will be intercepted by the underdrain and routed to Sedimentation Pond C." ' 25 XBOW MINING INC. 1