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Dakota coal seam at New Horizon Mine 2 ranges in thickness from 4.2 feet to 6.9 feet and is 99 <br />feet above the top of the Burro Canyon Formation. The coal dips 4.5° SW along a strike of N <br />45° W. <br />C. Surface Water <br />The San Miguel River has its source in the San Juan Mountains. These mountains are primarily <br />composed of Tertiary volcanic rocks. Iorns et. al. (1965a) has shown these waters to be of a <br />calcium bicarbonate - sulfate type during high flow periods. These waters contain less <br />bicarbonate during low flows while the calcium and sulfate concentrations increase due to less <br />dilution from snowmelt runoff. The San Miguel River traverses the interior portions of a basin <br />that is chiefly underlain by Dakota Sandstone, the Morrison Formation and Mancos Shale. The <br />Morrison Formation and Mancos Shale have the greatest potential for influencing the river water <br />chemistry. The San Miguel River drains an area of 1,080 square miles. In addition, <br />approximately 15,500 acres of irrigated land lies between Placerville and Naturita, Colorado. It <br />is estimated that 2.8 tons of Total Dissolved Solids (TDS) per acre are contributed to the waters <br />annually from this area. This results in increased levels of magnesium, potassium, sulfate and <br />chloride. Water quality samples taken from the San Miguel River at Naturita, Colorado, have a <br />weighted average of 316 milligrams per liter (mg /1) TDS. Specific conductance varies between <br />318 and 730 millimhos (mmhos). The mean sodium adsorption ratio (SAR) is about 0.7 at <br />Naturita. Water curves indicate that 90 percent of the time, flow in this river exceeds 60 cubic <br />feet per second (cfs), while flows exceed 1000 cfs about 10 percent of the time. The mean <br />discharge of the river is 351 cfs. San Miguel River waters are suitable for domestic usage except <br />at low flow periods when sulfate levels are high. <br />The Colorado Cooperative Ditch Company diverts as much as 145 cfs of water from the San <br />Miguel River approximately ten miles east of the town of Nucla. The main diversion ditch then <br />flows westerly passing just north of the town of Nucla and then flows northwestward passing <br />north of the New Horizon Mine 1. Diversion ditches distribute water to mainly agricultural users <br />in the area. Since the completion of the irrigation system for this area in about 1910, these areas <br />have been intensively reworked for irrigated agriculture. Additional uses include domestic, <br />municipal and stock pond consumption. <br />The New Horizon Mine 2 permit block is located just northwest of the town of Nucla in the <br />mildly sloping upland area between Tuttle Draw and Calamity Draw, in the northwest corner of <br />First Park. In the Mine 2 mining area, the surface water system is characterized by a "disjointed" <br />tributary drainage system almost completely controlled by return flow ditches of the local <br />irrigation network. <br />The West Lateral irrigation ditch is part of the Colorado Cooperative Company's main ditch <br />system that originates on the San Miguel River just upstream of Cottonwood Canyon (about 12 <br />miles upstream of Naturita). Construction of the main ditch commenced in 1896, and water <br />began flowing to the First Park area via the ditch in the spring of 1904 (Mercer, 1967). The main <br />ditch, as well as the main laterals, is basically an unlined open channel excavated in shallow soils <br />and sandstone. Where the ditch crosses drainages, pipes and aqueducts have been constructed to <br />carry the flow. The main ditch has an average gravity run of four feet per mile from the San <br />11 <br />