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-23- The main streams and tributaries to Fourmile Creek, North Thompson Greek, Middle Thompson Creek, and Coal Creek cut across the Iles Formation and the coal-bearing strata of the Williams Fork Formation at right angles to strike. This suggests that the resistant Upper, Middle and Rollins sandstone members have been breached by the streams along fracture or fault zones. The existence of fracture controlled stream valleys is supported by mine inflow data. The occurrence of inflows into the three mines are greatest adjacent to and under stream valleys. The inflow rates also mimic the flow characteristics of the adjacent stream. Monitoring is being conducted to identify inflow rates and sources. Perennial inflows are associated with perennial streams, and ephemeral inflows are associated with ephemeral drainages. The increased inflows associated with the stream system are a function of the higher vertical permeability of the strata resulting from secondary fracture porosity in the stream valleys. The quantities of mine inflows and of the associated stream depletion are functions of 1) the area of mine workings adjacent to the streams, 2) the thickness of strata overlying the mine, 3) the litholoyy of the overlying and underlying strata, 4) the stream flow characteristics, and 5) the mining methods in the area of the streams. Surface Water The major river of this study area is the Roaring Fork River. The Roaring Fork joins with the Colorado River at the town of Glenwood Springs. For the purpose of this CHIS, the mouth of the roaring Fork will serve as the cumulative surface water impact reference point. All mines considered in this CHIS are tributary to the Roaring fork. Please refer to Figure No. 2 for locations of all affected drainages, and Tables 2 and 3 for surface water quantity and quality characteristics. The Coal Basin hlines affects the Coal Creek Drainage. This stream joins the Crystal River at the town of Redstone. The Snowmass operation is located within Thompson Creek's drainage basin just north of Coal Basin. Thompson Creek joins the Crystal kiver ]1 miles downstream from Redstone. The Crystal River flows toward the town of Carbondale, where it joins with the Roaring Fork River. One-half mile downstream of this confluence is the Snowmass Coal Company loadout facility. Five miles downstream of the confluence of the Roaring Fork and the Crystal Rivers, is the confluence with Founnile Creek. The Sunlight Mine is located on Fourmile Creek, 7.2 miles above this confluence. The Roaring Fork gaging station (the point defining the study watershed) is located 4.2 miles downstream of the Fourmile Creek confluence with the Roaring Fork River at Glenwood Springs, Colorado. Streams in the region cross the outcrops of the Lower INesaverde Group (Iles and Lower Williams Fork Formation) at right angles to the strike of rock strata. This seems to indicate that these stream valleys have formed in zones of weakness such as fault and fracture systems, since these strata are relatively resistant to erosion. Other tributaries flow through strike valleys formed in less resistant shale units.