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aquifers in this area, consists primarily of clay, sand, and lenticular, discontinuous gravel layers. Stream flows aze the primary source of recharge to the alluvial aquifers. Alluvial deposits in the Twentymile Park area display characteristics depositional patterns. Major deposition occurs m areas where reduced stream gradients or a meandering stream pattern results in reduced flow velocities. Alluvial deposition is limited in areas where stream gradients are relatively steep and in areas where the stream channel has eroded to or intersects resistant bedrock. Consequently, the alluvial deposits do not tend to be continuous. The locations of significant alluvial deposits in the Foidel Creel drainage in the vicinity of the permit area are shown on Map 15, Alluvial Valley Floors and Water Rights. Mapped alluvial deposits in Foidel Creek tend to be limited in extent. Several shallow wells completed in these deposits indicate that they are usually less than 20 feet thick and the depth to ground water is less than 10 feet. The limited extent of the Foidel Creek alluvial deposits, and the lack of base flow in the creek indicates that these deposits are relatively insignificant to the area ground water hydrologic system. Near the confluence with Middle Creek, stream gradients are relatively low and more extensive floodplain has developed. The floodplains of Foidel and Middle Creeks merge in this area. Drilling and shallow well completion in this area indicates that the alluvial deposits may reach 30 feet in thickness. The alluvial deposits in this area have been studied in some detail and documented in the Energy Mine No. 3 permit application submitted by Colorado Yampa Coal Company (historic permit number 76-16, and current permit number C-84-062). Unconsolidated streamlaid deposits occur in Middle Creek from its confluence with Foidel Creek, downstream to the confluence with Trout Creek. Along this section of Middle Creek, which is approximately 2.1 miles long, alluvial deposits are fairly extensive with thicknesses up to 30 feet. Alluvial deposits are also found within the floodplain of Fish Creek. The location of these deposits is shown on Map 15, Alluvial Valley Floors and Water Rights. The configuration and depositional characteristics of the alluvial deposits along Fish Creek are similar to those in other area streams. However, unlike Foidel and Middle Creeks, discharge from confined aquifers, particularly the Twentymile Sandstone, constitute a significant proportion of the total recharge to the Fish Creek alluvial aquifer. Boettcher (1972) estimates that 25% of the total flow in Fish Creek above the old USGS Station 0944100 upstream from any of TCC or CYCC's operations may be attributed to ground water discharge. The contribution of ground water aquifers to Fish Creek within the Twentymile Park Basin is considered in a later section. Water quality data indicate that prior to 1981 there were not significant influences from discharges from disturbed areas to Foidel Creek upstream from these alluvial monitoring wells, particularly the S-]0 well. The S-]0 well data shows very little change in water quality over the period of.1979 to 1985. This data indicates that alluvial water quality in this locality has probably not been influenced by mining activities. Water quality is characterized by sodium bicarbonate dominance and total dissolved solids concentrations of about 750 mg/I. The water quality data forth the S-5 and S-6 wells indicate that water quality in the Foidel Creek alluvium in this locality is typically of mixed type with a tendency for dominance of sodium and sulfate. Total dissolved solids concentrations are in the range of 800 to ]300 mg/I. The data from these wells suggest some influence from mining related activities, particulazly at solute concentrations show a slightly increasing trend over the period of record. The water quality data from the alluvial wells might be expected to show seasonal Fluctuations reflecting recharge of the alluvium during spring runoff ,but this is not readily observable. Plots of selected chemical parameters versus time (Figures 4-b through 4-f, Ground Water Quality Data) show significant variation but do not show any consistent trends. This suggests that ground water flow in the alluvium is relatively stagnant, with limited Flushing during the spring runoff' period. This is consistent with the relatively clayey nature of the Foidel Creek alluvium, which tends to limit the rate of recharge and ground water movement. Permit Renewal No. 3 2.04-23 12/10/98