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-38- The Middle Creek mine has a high potential of impacting water levels in, and ground water discharges from, the Twentymile sandstone aquifer, the Wadge coal-overburden aquifer, and the alluvial aquifers of Middle, Fish and Trout Creeks. This mine may also impact the water quality of these aquifers. At this time, the magnitude of the ground water quality and quantity impacts of this mine have not been fully predicted, but the permit application is still under review by the Division. The Cumulative Hydrologic Impact Study may be revised upon receipt of amore detailed discussion of the probable hydrologic consequences for this mine. Seneca II Mine The Seneca II strip mine is located on the plunging tow of the Tow Creek Anticline. A portion of the mine is in the Grassy Creek drainage and a portion is in the Fish Creek drainage. The Grassy Creek portion has ground water which is tributary to the Hayden Syncline and Sand Wash Basin and is, thus, not hydrogeologically adjacent to the study area. The Fish Creek portion, however, is hydrologically adjacent to the Twentymile Park Synclinal Basin. The Wadge and Wolf Creek seams are mined at the Seneca II Mine. Mining occurs on the steeply dipping northwestern flank of the Twentymile Park Basin. The Seneca II Mine will impact ground water levels in the Middle Coal Group aquifers during mining. After mining, water from the spoils aquifer may impact the quality of ground water in the Middle Coal Group aquifers and the Twentymile sandstone aquifer. The Seneca II Mine will affect alluvial ground water quality indirectly through surface water discharges from the mine. Cumulative Ground Water Impacts of Coal Mining in the Twentymile Park Basin The eight mines in the Twentymile Park Synclinal Basin are all located in recharge areas of the aquifers of the Mesaverde Group. The ninth mine, the Middle Creek Mine, is located in a discharge area (Figure 3). All of the mines, except for the Seneca II Mine, are also adjacent to alluvial aquifers within the Trout Creek drainage basin. The adjacency of these mines to the tightly folded structural basin and to the alluvial aquifer system indicates that the coal mines in the Twentymile Park Synclinal Basin will produce cumulative hydrologic impacts on ground water. The strata between the Trout Creek sandstone of the Iles Formation and the Lewis Shale have two points of ground water discharge from the Twentymile Park Basin, one through the narrow Hayden Synclinal fold to the northwest, and the other throuyh outcrops and subcrops of these strata to the stream/alluvial systems of Trout Creek and its tributaries in the northeastern part of the structural basin. Strata between the i4ancos shale and the Trout Creek sandstone will primarily discharge ground water from the basin through the Hayden Syncline. (These statements represent interpretations of Plate 19 of Bulletin 1027-D, Geo]ogic Map of Part of Routt and Moffat Counties, Colorado, by M.W. Bass, M.R. Campbell, and J.B. Eby, 1955.)