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Surface waters draining from the sedimentary rock basins associated with the coal deposits may yield higher TDS concentration due to the greater amounts of soluble salts in these rock types. Also, surface water quality in streams draining the area varies on a seasonal basis. The primary drainages in the Upper Yampa River Subbasin related to coal mining activities include both small tributaries and major tributaries. The major tributaries of interest are Trout Creek, Fish Creek, and Oak Creek. These streams general exhibit perennial flow. The small tributaries are Foidel Creek, Middle Creek, and Grassy Creek. These streams flow intermittently in response to snow melt and rainfall events and exhibit no natural base flow (ground water component of flow). Foidel Creek and Middle Creek below Foidel Creek both now flow perennially as a result of underground mine dewatering, and spoil spring discharges leaving the Eckman Park/Foidel Creek Mine complex. A11 disturbed area drainage from the Energy Mine No. 3 enters Middle Creek, which flows north-northeast to Trout Creek and ultimately into the Yampa River (Figure 21. Water discharge and quality data (1975-19831 from U.S.G.S Gaging Station 09243700, located on Middle Creek just above the mine site (see Map 4a of the permit application) were submitted with the permit application. The following discussion simrtnarizes that data and information. Peak discharge in Middle Creek generally occurs from mid-April through mid-June and is the result of snow melt, incident precipitation and alluvial ground water discharge. Maximum recorded discharge is 172 cfs. High monthly discharge occurs in May and averages 21.3 cfs. During the summer months, June through August, the average discharge is 2.03 cfs. There is no flow for numerous days during the year on Middle Creek above Mine No. 3. This no flow condition generally occurs in the fall; therefore, Middle Creek is considered to have no base flow. Surface waters are calcium-bicarbonate in character with a pH range between 7,2 and 8.5. TDS concentrations range from 230 mg/1 to 608 mg/1. TDS concentration sometimes shows an inverse relation to streamflow. Total suspended solids (TSS1 range from 5 mg/1 to 599 mg/1. TSS concentration is highest during the high flow periods of snow melt runoff and after intense precipitation events. Detailed water quality analyses for Middle Creek are compiled in Tables 27, 28, and 29 of the permit application. -23-