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for Water Year 2009 of 1,630 occurring on 5/13/2009. <br />Regional Surface Water Quality The San Miguel River, into which Tuttle Draw and Coal <br />Canyon flow, originates in the volcanic San Juan Mountains of Tertiary Age. However, the <br />down stream portions of the San Miguel River Basin are chiefly underlain by the Dakota <br />Sandstone, the Morrison Formation and the Mancos Shale. Of these rocks, the Morrison <br />Formation and the Mancos Shale have the greatest potential for influencing water chemistry <br />through solution of readily available minerals. <br />According to Iorns (et al. 1965a), at times of high flow generated largely by snowmelt runoff <br />from the upland areas underlain by volcanic rocks, the water is of the calcium bicarbonate sulfate <br />type. During low flow, the water contains less bicarbonate and greater amounts of calcium and <br />sulfate. As flow progresses downstream, the water quality features higher percentages of <br />magnesium, potassium, sulfate and chloride. Generally, Total Dissolved Solids (TDS) varies <br />inversely with discharge, and also increases in the downstream direction. <br />Iorns, et. al., (1965a), states that streams flowing from the Uncompaghre Plateau and entering the <br />Dolores River between the San Miguel River and the mouth of the Dolores commonly exhibit a <br />calcium bicarbonate water type with an average TDS of less than 300 ppm. These streams flow <br />largely over the Glen Canyon Group and the Dakota Formation. Historic water quality samples <br />taken at Naturita, Colorado indicate that the San Miguel River has a weighted average TDS of <br />316 ppm and an average TDS discharge of 101 tons per square mile Specific conductance <br />ranges between 318 and 730 umhos, and the mean Sodium Adsorption Ratio (SAR) is about 0.7. <br />Based on these values, waters of the San Miguel at Naturita are classified as C2 -S1, which <br />categorizes the San Miguel River as being good for irrigation use. <br />As of 1957, approximately 15,000 acres underlain by Dakota sandstone were actively irrigated <br />between Placerville and Naturita, Colorado (Iorns, et. al., 1965a). Using historic stream flow <br />information, Iorns, et. al., (1965a) estimated a water budget for the San Miguel River in this <br />vicinity, and concluded that the TDS contribution to the San Miguel River from irrigation is <br />about 2.8 tons /year per acre of irrigated land. As of 1957, waters of the San Miguel River <br />(except at the mouth during low flows) were suitable for domestic use, while during low flow, <br />high levels of sulfate would render the water unsuitable. <br />SITE SPECIFIC SURFACE WATER INFORMATION <br />NHN Permit Area Geomorphology Map 2.04.7 -1 delineates the NHN permit area. The NHN <br />permit area is located just north of Tuttle Draw, in the eastern portion of the gently sloping <br />plateau referred to as Second Park. This area as shown of Map 2.04.5 -1 includes the mildly <br />sloping upland area between Tuttle Draw (to the south and east) and Coal Canyon (to the north <br />and west). The area surface is developed on the weathered dip slope surface of the northeastern <br />flank of the Nucla Syncline that has been subsequently dissected by both Tuttle Draw (and <br />tributaries) and tributaries of Coal Canyon. With the completion of the Colorado Cooperative <br />Company's main irrigation ditch in about 1905, most of the surface deposits (soils) have been <br />intensively modified by both cultivation and irrigation water. The 2 Park Lateral irrigation <br />ditch runs along a ridge line that is the stream divide between Tuttle Draw and Coal Canyon, (see <br />Section 2.04.7 Page 16 November 2011 <br />