2018-07-02_PERMIT FILE - C2010089A (19)

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Regional Surface Water Quality The San Miguel River, into which Tuttle Draw and Coal Canyon flow, originates in the volcanic San Juan Mountains of Tertiary Age. However, the downstream portions of the San Miguel River Basin are chiefly underlain by the Dakota Sandstone, the Morrison Formation and the Mancos Shale. Of these rocks, the Morrison Formation and the Mancos Shale have the greatest potential for influencing water chemistry through solution of readily available minerals. According to Iorns (et al. 1965a), at times of high flow generated largely by snowmelt runoff from the upland areas underlain by volcanic rocks, the water is of the calcium bicarbonate sulfate type. During low flow, the water contains less bicarbonate and greater amounts of calcium and sulfate. As flow progresses downstream, the water quality features higher percentages of magnesium, potassium, sulfate and chloride. Generally, Total Dissolved Solids (TDS) varies inversely with discharge, and also increases in the downstream direction. Iorns, et. al., (1965a), states that streams flowing from the Uncompaghre Plateau and entering the Dolores River between the San Miguel River and the mouth of the Dolores commonly exhibit a calcium bicarbonate water type with an average TDS of less than 300 ppm. These streams flow largely over the Glen Canyon Group and the Dakota Formation. Historic water quality samples taken at Naturita, Colorado indicate that the San Miguel River has a weighted average TDS of 316 ppm and an average TDS discharge of 101 tons per square mile. Specific conductance ranges between 318 and 730 umhos, and the mean Sodium Adsorption Ratio (SAR) is about 0.7. Based on these values, waters of the San Miguel at Naturita are classified as C2 -S 1, which categorizes the San Miguel River as being good for irrigation use. As of 1957, approximately 15,000 acres underlain by Dakota sandstone were actively irrigated between Placerville and Naturita, Colorado (Iorns, et. al., 1965a). Using historic stream flow information, Iorns, et. al., (1965a) estimated a water budget for the San Miguel River in this vicinity, and concluded that the TDS contribution to the San Miguel River from irrigation is about 2.8 tons/year per acre of irrigated land. As of 1957, waters of the San Miguel River (except at the mouth during low flows) were suitable for domestic use, while during low flow, high levels of sulfate would render the water unsuitable. SITE SPECIFIC SURFACE WATER INFORMATION NHN Permit Area Geomorphology. The NHN permit area is located just north of Tuttle Draw, in the eastern portion of the gently sloping plateau referred to as Second Park. This area as shown of Map 2.04.5-1 includes the mildly sloping upland area between Tuttle Draw (to the south and east) and Coal Canyon (to the north and west). The area surface is developed on the weathered dip slope surface of the northeastern flank of the Nucla Syncline that has been subsequently dissected by both Tuttle Draw (and tributaries) and tributaries of Coal Canyon. Section 2.04.7 Page 19 April 2016 (PR -01)