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- 14 - C. SURFACE WATER THE SURFACE WATER MONITORING PROGRAM WILL CONSIST OF QUARTERLY MONITORING OF FIELD PARAMETERS OF THE COLORADO RIVER DOWNSTREAM OF THE PRESENT SAMPLING SITE CR-2. VIII. PROBABLE HYDROLOGIC CONSEQUENCES OF MINING AT THE COAL RIDGE #1 MINE The Coal Ridge #1 Mine is located along the flank of the Grand Hogback Monocline, adjacent to the Colorado River in Garfield County, Colorado. Glenwood Springs, the county seat, which owns a portion of the coal to be mined, is seven miles east of the project, and the town of New Castle is located approximately 1.5 miles north and west. The topography of the mine area ranges from 5600 feet in elevation at the Colorado River up to 7585 feet at the crest of the Grand Hogback. The general geology and topography of the mine site is shown in Figure 1. Bedrock outcrops at the mine site include the Upper Cretaceous-aged Mancos Shale and the Mesa Verde Formation. The stratigraphy specific to the mine site is shown in Figure 2. The Mancos Shale is a highly erodable formation consisting of two thick marine shale members separated by a limestone member, and is at least 4000 feet. thick in the mine area. The Mancos Shale conformably underlies and intertongues with the lowermost formation of the Mesa Verde Group. The Mesa Verde Group is composed of the lowermost Iles Formation, Williams Fork Formation, and an overlying 2000 feet of undifferentiated deltaic-type deposits. The Iles and Williams Fork Formations are typified by interbedded shales, siltstones, sandstones and coal. The Rollins Sandstone is generally considered as the uppermost unit within the Iles formation, forming the contact with the Williams Fork Formation. The Rollins is typified by fine to medium-grained sandstone that weathers to light buff. Bedding is commonly massive. The Wheeler Coal of the Williams Fork Formation will be mined at Coal Ridge No. 1. This coal overlies the Rollins Sandstone. In portions of the area, the Wheeler seam is split into a lower and main member. The lower Wheeler is described as generally being 15 feet thick and underlies the main Wheeler by 30 feet. The Wheeler seam is more persistent and in the mine area is described as being 15.5 to 22.5 feet thick. These coals are overlain by approximately 400 feet of coal-bearing shale. Two mappable sandstone units occur within the Williams Fork Formation, approximately 400 and 600 feet, respectively, above the Wheeler Coals. These sandstone units are the Middle Sandstone and the Upper Sandstone, both of which are similar to the Rollins Sandstone. These units are in turn overlain by 2000 feet of undifferentiated Mesa Verde Group. This member is typical of upper deltaic formations consisting of channel sandstones, siltstone, shale and lenticular thin coal beds.