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<br />1'\"--6 <br />Ll.CCJ <br /> <br />No additional facility costs. <br /> <br />Minor additional facility <br />costs. <br /> <br />Recognizing the significant cost savings, the alum process <br />appears to be preferred when treating Colorado River water. <br /> <br />(*** DESALTING PLANT ALTERNATIVES WILL ASSUME 'ALUM PROCESS WHEN <br />TREATING COLORADO RIVER WATER, AND PARTIAL LIME SOFTENING WHEN <br />DESALTING WELLTON-MOHAWK WATER *.*) <br /> <br />CRLORIliE SYSTEM <br />Gas chlorine will be used for disinfection of both pre-filtered <br />and post-filtered water. For pre-filtered raw water, a ton <br />cylinder chlorination system will be provided. Small metal <br />buildings will protect the chlorinators, ton cylinders, water <br />supply booster pumps and other chlorination equipment. The <br />chlorination system for post filtered water already exists. <br /> <br />PRODUCT CLEARWELL <br />Following treatment the Yuma water will be stored in a clearwell <br />to be located just east of the SCR's. The clearwell was sized to <br />~ store 25 percent of the ultimate daily capacity to be provided to <br />the city. Two optional designs were considered for this level of <br />comparison. Other clearwell options should be considered before <br />advancing into specification design. The two designs compared <br />were a partially underground reinforced concrete clearwell, and a <br />field of above ground glass-lined steel tanks. <br /> <br />A partially underground concrete clearwell would allow treated <br />water to flow by gravity into the clearwell storage. The <br />partially underground clearwell would also minimize solar <br />heating. City pumps would pump the water from storage and <br />integrate the treated water into their water distribution system. <br />However foundation treatment and high ground-water conditions <br />resulted in higher construction costs. To design for stability <br />against flotation the depth of the partially underground <br />clearwell was limited for on the maximum ground-water surface, <br />and the minimum water surface in the clearwell. With the depth <br />restricted, the overall lateral area of the clearwell varied <br />directly with the designed storage capacity. <br /> <br />To store the water above ground a field of glass-lined steel <br />tanks could be constructed and the treated water would be pumped <br />up into the tanks. City pumps would pump from the above ground <br />tanks and integrate the water into the city's distribution <br />system. The energy required to lift the treated water into <br /> <br />20 <br />