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<br />e <br /> <br />I <br /> <br />'. <br /> <br />. <br /> <br />,,,. . -. S;,\,f <br />,..,~-;;..~;. __ 1 + <br /> <br />increase of.5 to 1.0 degrees fahrenheit caused by reduced late <br />summer flows is also predicted. <br /> <br />Ridqes Basin Reservoir <br /> <br />Releases made from Ridges Basin Reservoir to Basin Creek after <br />traveling 5 miles to the Animas would not adversely affect the <br />river's water quality. The water in Ridges Basin Reservoir would <br />be of adequate quality for the proposed irrigation, recreation and, <br />once treated, municipal and industrial uses. The fate of the heavy <br />metals pumped into Ridges Basin Reservoir is dependent on many <br />factors, most of which indicate that the reservoir sediments would <br />retain most of the metals, substantially reducing the potential for <br />water quality problems. The vegetation in the reservoir basin is <br />sparse, limiting initial reduced oxygen conditions in the reservoir <br />bottom. The basin bedrock is mainly a marine shale formation that <br />produces alkaline ground water. All these findings, plus the fact <br />that a large portion of the inflowing metals are in suspended form <br />rather than in solution, indicate the metals should accumulate and <br />precipitate in the reservoir sediments. Because water is being <br />pumped into the reservoir, the inflow of high concentrations of <br />metals such as those found during mining activity pollution spills <br />can be easily controlled. <br /> <br />If unpredictable reducing conditions occurred in the reservoir <br />bottom during operation of the reservoir, some of the metals could <br />come into solution. Iron and manganese would be the first, with <br />some others following in trace amounts. These reduced metals would <br />remain in solution until coming into contact with oxygen-enriched <br />water near or below the inlet level in the reservoir and then would <br />precipitate and be redeposited in the bottom sediments (Hutchinson, <br />1957). If metal problems do occur sometime during the reservoir's <br />life, aeration techniques for controlling their distribution are <br />available. <br /> <br />The mean summer epilimnetic concentration of chlorophyll A in the <br />Ridges Basin Reservoir is expected to be between 5 and 13 <br />micrograms per liter, rendering the reservoirs classification as <br />mesotrophic (Baker and Adams 1982). <br /> <br />La Plata River <br /> <br />Construction would take place during low or no-flow periods, <br />resulting in only slight increases in turbidity and sediment <br />concentrations. with the project, changes in water quality are <br />probable, such as increased salinity, nutrients, coliform <br />organisms, and trace elements. The total dissolved solids <br />concentration just downstream of the La Plata Diversion Dam would <br />increase from the present flow-weighted average of 90 mg/l to <br />approximately 230 mg/l on the La Plata River because of water being <br />introduced from the Animas River through Ridges Basin Reservoir. <br />The level of total dissolved solids upstream of the proposed <br />Southern ute Diversion Dam would increase with the project from the <br />current flow weighted average of 535 mg/l to approximately 610 <br />mg/l. This change reflects irrigation return flow from project <br /> <br />13 <br />