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-23- Some fractures and faults transect the Mesaverde Formation and extend vertically to the surface. These faults and fractures produce narrow bands of secondary porosity within the rack strata. Uue to the low per~oeability of the rock strata within the Mesaverde Forrnation, these faults and fractures provide the primary path throuyh which water flows both vertically between rock strata and horizontally within ruck strata. When faults and fractures are encountered within the mines in the north Fork region, they yenerally produce mine inflows. The flow characteristics of each mine inflow associated with faults and fractures depend upon the lateral extent and the proximity of the fault or fracture to a stream valley. N11 inflows from these sources are characterized by an initial surge of water which then either decreases, or ceases completely with time. Since must stream channels in the North Fork drainage basin are developed in zones of weak fractured rock associated with fracturing and faulting (Uunrutl, 1970), mine inflows from fractures and faults below these streams mimic the temporal flow characteristics of the overlying streans. In Hawk's tJest Mine, an inflow was encountered under the epne~neral drainaye of Hawk's Nest Creek. The rates of inflow beneath this drainaye fluctuated seasonally with a slight lay time in response to the flows in the overlying strewn. In the Somerset Mine, inflows beneath Huobard Creek are continuous and do nut show rnucn seasonal variation. Inflows from faults and fractures located outside stream valleys (such as in the Orchard Valley Kline) yenerally dry up with time ur flow intermittently at discrete points along the fault or fracture. Those wlricn continue to flow have flow rates which diminish to a trickle. Juch inflows inay represent the dewatering of lenticular sandstone units with limited recharge areas, or .nay represent flows throuyh fracture zones extending to the surface which have narrow recharge zones on steep slopes. Description of the Surface Water Reyi~ne The North Fork of the Gunnison River is the major drainaye for the general area. Smaller streams in or adjacent to the life-of-mine areas are alt tributary to the worth Fork (Figure 1). Figure 4 contains the drainage map of the study area with the locations of streams and reservoirs which are described in the followi~ry discussion. The North Fork has an annual streamflow at Somerset of approximately 313,7UU acre-feet per year (1962-19131). The flow is regulated by the Paonia Reservoir 5 miles upstream of the town of Somerset, which became operational in 19ti2. Water yields during that period have ranged fruin a high of 451,3UU acre-feet per year in water year 1962 to a low of 232,270 acre-feet in water year 1977. Flow records for the North Fork of the Gunnison are given in Table 2. Water quality parameters for the North Fork are given in Table 3. NS indicated, waters in the North Fork are a calcium bicarbonate type. There are moderate levels of sulfate. Salinity averages lass than IOU my/l.