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<br />from Ouray to Ridgway, the numbers are not indicative of a healthy <br />stream. On the contrary, Dallas Creek was very good from the bio- <br />logical standpoint. Improvement of water quality in the Uncompahgre <br />River below Ouray would be necessary to obtain the maximum benefit <br />from fishing at present arid after construction of Ridgway Reservoir. <br /> <br />Data on heavy metals indicate that under normal flow conditions <br />the metals concentrations at the Ridgway dam site are reduced to <br />levels which are below the limits shown in the Public Health Service <br />Drinking Water Standards. (13) However, manganese concentrations would <br />be above these limits at the beginning of the backwater of the proposed <br />reservoir. Further upstream the iron and manganese concentrations <br />were particularly high; values of 2.8 milligrams per liter (mg/l) and <br />0.7 mg/l, respectively, were obtained. <br /> <br />Maximum values for sulfates and total dissolved solids exceed <br />the limits cited in the PHS Drinking Water Standards(l3) at the <br />sampling stations for Dallas Creek and the Uncompahgre River near <br />Ridgway (Table V). The water quality of the Uncompahgre River at <br />Colona is very similar to that in the river near Ridgway, however, <br />between Colona and Delta the river becomes seriously polluted. The <br />primary cause of this pollution is the entrance of saline irrigation <br />return flows from the Uncompahgre Project between Montrose and Delta, <br />Colorado. <br /> <br />With a few exceptions, soils on the east side of the Uncompahgre <br />River tY4the area of the Uncompahgre Project are derived from Mancos <br />shale. Mancos shale soils are noted for their extremely high <br />contribution of salts when they are leached with water. <br /> <br />Effect of Project Operations <br /> <br />Chemical Quality <br /> <br />The combined flow of the Uncompahgre River above Ridgway, and <br />Dallas Creek and diversions from Cow Creek will make up most of the <br />storage in Ridgway Reservoir. The concentrations when weighted for <br />flow, assuming uniform mixing of the waters, provides an estimate <br />of the resultant concentrations to be released from Ridgway Reservoir. <br />Calculations indicate that expected sulfate, total dissolved solids, <br />and hardness would be about 150 mgll, 300 mg/l, and 200 mg/l, res- <br />pectively. The sulfate and total dissolved solids values are within <br />the limits of the Public Health Service Drinking Water Standards. <br />Water with a hardness of 200 mg/l is usually considered a hard water. <br />Softening to 100-125 mg/l would be desirable for domestic use. <br /> <br />24 <br />