1988-04-11_PERMIT FILE - C1981008A

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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-S1, 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 (lorns, et al . 1965a). Using historic streamflow information, lorns 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 Drainage Basin Geomorphology. Exhibit 7-1 delineates the areas named First and Second Park. The Nucla Mine is located on the gently sloped upland just north of Tuttle Draw, in the southern portion of the Second Park. The Nucla East mining area includes the mildly sloping upland area immediately north of Calamity Draw, located approximately in the middle of the First Park. Both the First and Second Parks are relatively flat (gently sloping) areas formed by regional uplift of sedimentary rocks that have been subsequently dissected by both Tuttle and Calamity Draws. Both Parks consist primarily of recent deposits of undifferentiated eolian silts and sands that overlay the Dakota and Burro Canyon Formations. With the completion of the Colorado Cooperative Company's Main Irrigation Ditch in about 1910, these deposits have been intensively reworked by cultivation using irrigation water to form a broad rolling valley across the First and Second Parks. The Nucla Mine is situated entirely within the Tuttle Draw watershed. The drainage area of Tuttle Draw to its confluence with the San Miguel River is approximately 14.5 square miles. The watershed in the upland area is largely covered with pinyon-juniper and mountain brush vegetation. In the lower portions (Second Park) the watershed is mostly irrigated pasture and rangeland. The overall drainage pattern in Tuttle Draw is mostly 7-106 Revised 04/11/88