2014-12-08_REVISION - C1981044 (2)

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Mine removed coal from the F seam in the lower Williams Fork. The No. 6 Mine portal was used to access and mine coal from the E seam in the lower Williams Fork. (The adjacent surface pits of the Trapper Mine take coal from the upper Williams Fork. The I seam of Trapper probably correlates to the P seam of the Williams Fork Mines, No. 5. mine) Geologic Structural Setting. The Williams Fork Mines are situated on the northeast flank of the northwest plunging Moffat Anticline. The Moffat Anticline is part of the larger -scale Axial uplift that extends northwestward across northwest Colorado to the Uinta Mountains in northeast Utah. The northeast limb of the Moffat Anticline dips northward into the Big Bottom syncline. Although only small - displacement gravity faults have been found in the permit area, the large displacement Moffat thrust fault probably lies several thousand feet beneath the ground surface of the permit area. The surface trace of the Moffat thrust is two miles southwest of the permit area. Local Coal Mining History. Previous mining within the Williams Fork Mines permit area included: the Fields Mine which operated in the E seam during the 1930s; the Wise Mine and the Wise Hill No. 2 which operated in the C seam (below the E seam) in the 1940s and 1950s; the Leo White and Baker Mines which operated in the Hart seam (between the F seam and Twentymile sandstone); and the Wise Hill Nos. 3 and 4, which operated in the Hart seam during the 1970s. Surface Water Features. Drainages within and adjacent to the permit area (on the north- facing slope) are ephemeral and generally extend south to north down the slope in a dendritic pattern. These drainages flow primarily in response to snowmelt or heavy rains. Flows in these drainages that do not infiltrate into the ground or evaporate eventually enter the Williams Fork River, and then flow the short distance to the confluence with the Yampa River in the northwest corner of the permit area. Yampa River Flows. Flow in the Yampa River depends primarily on snowmelt from the winter snowpack on the high mountain slopes surrounding the drainage basin. The lower intermittent and ephemeral drainages produce only a small part of the total water yield of the basin (Colorado Water Conservation Board, 1969). About 64 percent of the flow occurs in May and June with up to 84 percent occurring from April to July at selected gaging stations within the drainage basin (Steele, et al., 1979). Minimum flows generally occur from August through February. Irons, et al. (1965) reported that summertime flows in streams of the basin from July through October generally include a large component of ground water discharge. Extremes recorded at the Maybell Gaging Station are a maximum flow of 17,900 cfs on May 19, 1917, and a minimum of 2.0 cfs on July 17 -19, 1934. Annual variation in yield may also be great. Historical annual yield has varied from 345,000 acre -feet in 1977 to 2,135,000 acre -feet for the Yampa River in 1917. Average annual yield amounts to 1,116,000 acre -feet. Williams Fork River Flows. The Williams Fork River is a major tributary of the Yampa River. The Williams Fork drains approximately 350 square miles, or ten percent of the Yampa River Valley. The Williams Fork fluctuates seasonally like the Yampa, but is more dependent on snowmelt, and there is less ground water discharge to sustain the flows of the river during low flow periods. Flows in the Williams Fork in the permit area typically range between 2500 cfs during spring runoff and less than 100 cfs during low flow. Williams Fork Mines 6 Permit Renewal 06 C- 1981 -044 December 8, 2014