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Recharge to bedroc': ~cui`=rs ;curs p:^imarily in the spring anh early summer when snowmelt and surface-water runoff is abundant, and when evapotranspiration is at a ~ni,nimum. Recharge to these aquifers is limited by the permeability of rock strata and the size of the recharge area exposed to surface water. Recharge of bedrock aquifers also occurs through deep percolation of water through overlying sediments. Low permeabilities of overlying clayey and silty soils, and shales and siltstones limit vertical recharge of underlying sandstone and coal aquifers. Discharges from bedrock strata are primarily through springs to the surface system. The flow characteristics of the springs are related to: 1. The lateral extent and thickness of the associated aquifer, Z. The distance between the springs and the aquifer recharge areas; and, 3. The penneabilities and ground water storage characteristics of the associated aquifer. Springs issuing from thin laterally discontinuous sandstones (lenticular and interbedded sandstones) that occur close to the aquifer outcrops exhibit variable seasonal flow. Springs supplied by regionally extensive, thick sandstones or coal aquifers located a great distance from recharge areas exhibit steady perennial flow. Surface Water The following description of surface water in the Yampa River Basin discusses the general physical characteristics of the drainage, a detailed narrative of flow regimes and an analysis of water quality parameters. Flow and water quality characteristics of natural springs and spoils springs are noted. Water use in the basin is also described. The major perennial tributaries to the Yampa River are, from upstream to downstream: Oak Creek, Elk Creek, Trout Creek, Grassy Creek, Elkhead Creek, and the Williams Fork. Trout Creek, Grassy Creek, the Williams Fork River and Dry Creek, an intermittent tributary, are affected by mining. Trout Creek has two major tributaries which have been affected by mining: Middle Creek and Fish Creek. These creeks flow in a northeasterly direction towards Trout Creek, which flows north to the Yampa River. Foidel Creek was an intermittent stream prior to mining that drained the 'cckman Park area and flowed northeasterly into Middle Creek. It has been transformed into a perennial, effluent-dominated stream by mine inflow discharges from the Foidel Creek underground mine and spoil spring discharges from the surface mines. Peak discharges of all the Yampa's tributaries are a consequence of snowmelt and incident precipitation during the period from April to June. Fish Creek has an average base flow of approximately 3 cfs and a 10-year, 7-day low flow of 1.6 cfs. The base flow originates from ground water contribution to the streams. 9oettcher (1972) estimated that roughly twenty-five percent of the total stream flow in Fish Creek comes from ground water discharge. peak discharge in Fish Creek, near the proposed permit area, occurs during the period from Piarch through June, when the combination of snnwmelt, incident precipitation and ground water contribution result in discharge rates in excess of twenty-five (25) cfs. The lack of ground water ;~