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<br />I- <br />--.l <br />c.o <br />-1 <br /> <br />140,000-acre-foot-per-year delivery at the southerly International Boundary is <br />scheduled to be completed by 1990. <br /> <br />3. Yuma Desalting Plant (Reclamation) <br /> <br />The Yuma Desalting plant is being built on a 60-acre tract of land 6 <br />miles west of Yuma, Arizona. This site allows easy access to the Main OUtlet <br />Drain Extension which will carrv the saline drainaqe water to the olant. and <br />it is also near the Colorado River where the desalted water will be delivered. <br /> <br />The purpose of the plant is to upgrade the quality of drainage water <br />from the Welton-Mohawk Irrigation and Drainage District. This plant is a <br />portion of the permanent and definitive solution to the international problem <br />of high salinity in the Colorado River. <br /> <br />Presently, the plant is being constructed to produce about 73 <br />million gallons of desalinated or product water per day. This would result in <br />a delivery of about 67,000 acre-feet of product water per year. The product <br />water will be blended with untreated drainage water to make up an estimated <br />return flow of about 73,000 acre-feet each year. The plant is expected to <br />save about 70 percent of the total drainage flow from the Welton-Mohawk <br />Irrigation and Drainage District. <br /> <br />The operational design parameters set up for the plant determined <br />that a membrane desalting process was technically feasible and is economically <br />suitable for the Yuma Desalting plant operation. The size of the desalting <br />plant was computed using a salt balance formula. The factors included in this <br />formula are the volume of the water delivered to Mexico; the salinity <br />differential required by Minute No. 242 of the International Boundary and <br />Water Commission, United states, and Mexico; the salinity of the Colorado <br />River at Imperial Dam; the volume of drain water treated; the salinity of the <br />drain; a number of other factors related to the diffuse return flows below <br />Imperial Dam; and plant operational factors. The original capacity of the <br />desalting plant was 96 million gallons per day, which could treat 167,000 <br />acre-feet of drain flow. Whenever the salinity of the Colorado River at <br />Imperial Dam is above 949 mgjL, some drainage water would have to be bypassed. <br /> <br />A study done in 1978 by the Advisory Committee on Irrigation <br />Efficiency, Welton-Mohawk Irrigation and Drainage District, recommended <br />expansion of on-farm measures which will result in an irrigation drain flow of <br />108,000 acre-feet per year. In addition, the Colorado River Salinity Control <br />Forum has established a salinity standard at Imperial Dam of 879 mgjL. Using <br />the salt balance formula and assuming an irrigation drain flow of 108,000 <br />acre-feet and salinity of the Colorado River water at Imperial Dam of 838 <br />mgjL, a plant size of 73 million gallons per day would be required to treat <br />the irrigation return flow portion of the total drainage flow. <br /> <br />In March 1985, Reclamation awarded the last of three major contracts <br />for the construction of the Yuma Desalting Plant. The $35 million was awarded <br />to complete the desalting plant pretreatment facilities and to construct <br />equipment and office buildings, The contractor has 3.5 years to complete the <br />work. Pretreatment start-up is planned for mid-1987, and the desalting plant <br />is scheduled for completion in late 1989 or 1990. <br /> <br />VII-5 <br />