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<br />~ <br /> <br />r'-;3&~ <br />lJ '" .- ... ~ <br /> <br />- - ~----~------ <br /> <br />The decision to operate the plant would be made each year and <br />would depend on the quality and flow conditions of the Colorado <br />River and of local return flow. Operation of the Desalting Plant <br />is not expected to be required during surplus flow years, <br />projected to occur about 40 percent of the years. <br /> <br />Recognizing that the colorado River goes through long-term <br />periods of drought and excess, there could be several years in <br />succession when the plant would not be operating. Each fall, <br />conditions would be evaluated and a decision would be made as to <br />whether to prepare the Desalting Plant for full operation <br />beginning in January. Later on in the year, as the runoff <br />conditions became better established, the operation of the <br />Desalting Plant could be adjusted. <br /> <br />During Plant operation, Wellton-Mohawk irrigation drainage would <br />enter the Desalting Plant at about 3000 p/m and would be <br />initially treated in the pretreatment system. In pretreatment <br />the return flow would pass through trash screens, settling <br />basins, and then into the Solid Contact Reactors (SCR). While in <br />the SCR's, lime and ferric sulfate would be added. Rapid mixing <br />would then facilitate the formation of floc that would bond to <br />suspended solids, settle and clarify the water. Following <br />clarification in the SCR's the water would pass through dual <br />media gravity filters to remove remaining suspended solids and be <br />~tored in a clearwell. <br /> <br />The pretreatment system is designed for a maximum capacity of <br />104 Mgaljd, or 97,300 acre-feet per year. The pretreatment <br />process reduces the salinity of the Wellton-Mohawk drainage by <br />about 10 percent producing feed water for the Reverse Osmosis <br />system with a salinity of about 2,700 p/m. <br /> <br />From the pretreatment clearwell the water is pumped through ~he <br />Reverse osmosis process. During the Reverse Osmosis process the <br />water is forced under pressure through membranes and the salinity <br />in the water is removed and concentrated into a salt brine <br />solution. Following treatment about 30 percent of the water <br />treated (28,800 acre-feet) would be discharged as salt brine to <br />the Santa Clara Slough. <br /> <br />The remaining 70 percent (68,500 acre-feet) would be discharged <br />as desalted product water. During the initial startup years the <br />new membranes are expected to reduce salinity of the product <br />water to about 150 p/m. After about 3 years of operation the <br />salinity of the product water is expected to stabilize at about <br />500 p/m. <br /> <br />The desalted water would be blended with excess Wellton-Mohawk <br />drainage, local return flows, and Imperial Dam releases to <br />accommodate both the salinity differential provisions, and the <br />1.36Maf NIB delivery requirements for Mexico. The quantity and <br /> <br />7 <br />