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and underburden is limited to fractured zones owing to the presence of impermeable layers. i Horizontal movement is controlled by intergrenular permeability (particle sixes and degree . ii of cementing) ea well as fractures. Ground water movement (vertical or horizontal) in the coal aquifers is principally Governed by the presence of fractures. The recharge areas to the bedrock aquifers ere of limited extent es the units dip more steeply than [he ground surface and rapidly become confined. The main sources of recharge to the alluvial aquifers at and proximate to the Yoest Mine are discharge from hydraulicelLy Connected bedrock equiferc, infiltration of precipitation, and discharge of streemflow through the channel beds. On the side tributaries that predominantly exhibit ephemeral flow, recharge to the underlying alluvium is limited to the snowmelt period. Studies of the nearby Piceence Basin (which is climeticelly similar to the Tampa River Basin) predicted en average recharge of 0.66 inches per year (Peeks et el., 1974). Based on this similarity, warner and Dele (1982) used 0.5 inches es en annueL recharge rate for their ground water simulation model of the Yampa River Basin. Hvdrogeoloaic Boundaries. Hydrogeologic boundaries within and adjacent to the Yoest • permit arse ere primarily defined by geologic structure. Erosion along the northerly-plunging axis of the Fish Creek anticline has resulted in localized recharge boundaries for the wedge coal and overburden (see Exhibit b-2, Tab 6, Geology). The wolf Creek coal outcrop in the southern portion of the permit area also parallels the Fish Creek anticline, providing a recharge boundary to this unit. No significant faults or unconformities ere present within the permit area, although fracturing may augment recharge in some areas. Downgredient, stream and saturated alluvium exert only minimal influence on bedrock units as discharge boundaries since most units dip far below significant downgredient streams and associated alluvium. The wedge overburden may provide some recharge component to the upstream reach of Sege Creek (see Exhibit 7-2). Aquifer testing did not reveal the presence of hydrologic boundaries, although the tests conducted (variable discharge, slug injection) and yields produced stressed a relatively small portion of the aquifer. The variable nature of the strata suggests that minor lithologic boundaries may be present due to pinch-outs, degree of fracturing, cementation, etc. Permeability of the Unsaturated Zone. The unsaturated zone, also known es the vadose • zone, is that area above the water table where fluid pressure is less than atmospheric. 24