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• potassium, sulfate and chloride. Generally, Total Dissolved Solids (TDS) varies inversely with <br />discharge, and also increases in the downstream direction. <br />lorns et a1. (1965a) mentions that streams flowing from the Uncompaghre Plateau and entering <br />the Dolores River between the San Miguel River and the mouth of the Dolores commonly exhibit <br />a 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 316 <br />ppm and an average TDS discharge of 101 tons per square mile. Specific conductance ranges <br />between 318 and 730 umhos, and the mean Sodium Adsorption Ratio (SAR) is about 0.7. Based <br />on these values, waters of the San Miguel at Naturita are classified as C2-S1, which categorizes <br />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 (lorns, et a1. 1965a). Using historic streamflow <br />• information, lorns et a1. (1965a) estimated a water budget for the San Miguel River in this vicinity, <br />and concluded that the TDS contribution to the San Miguel River from irrigation is about 2.8 <br />tons/year per acre of irrigated land. As of 1957, waters of the San Miguel River (except at the <br />mouth during low flows) were suitable for domestic use, while during low flow, high levels of sulfate <br />would render the water unsuitable. <br />SITE SPECIFIC SURFACE WATER INFORMATION <br />Drainage Basin Geomorahology <br />Map 2.04.7-1A delineates the areas named First and Second Park. The New Horizon 1 is located <br />on the gently sloped upland just north of Tuttle Draw, in the southern portion of the Second Park. <br />The revised New Horizon 2 mining area includes the mildly sloping uplarid area between Tuttle <br />Draw (to the north) and Calamity draw (to the south). The area is located approximately in the <br />middle of the First Park. Both the First and Second Parks are relatively flat (gently sloping) areas <br />formed by regional uplift of sedimentary rocks that have been subsequently dissected by both <br />Tuttle and Calamity Draws. Both Parks consist primarily of recent deposits of undifferentiated <br />• eolian silts and sands that overlay the Dakota and Burro Canyon Formations. With the completion <br />REVISED JULY 2006 2.()4.7-27 <br />