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Title I Worlcs and Capital Costs "'- ,I ": _'-.1 - '.. -'_._'.,...~ , ",. ".._".'.,,-~,- .'. t. Photograph 2.-Dperators load reverse osmosis desalting element into 12-inch pressure vessel. provided pressure vessels to produce the remaining 50 MGD of desalted water. These vessels, 12 inches in diameter and 20 feet long, are the largest in the industry. Each pressure vessel will contain spiral- wound, semipermeable membranes. These membranes, through the process known as reverse osmosis, will remove dissolved materials (mostly mineral salts) from the pretreated water. '- The YDP is sized to accommodate about 108,000 acre-feet of irrigation drainage per year, with a salinity of about 2,900 to 3,200 ppm. When operated at full capacity, about 98,000 acre-feet of saline irrigation drainage will be fed into the plant, pro- ducing about 68,500 acre-feet of desalted water (product water) with a salinity of about 250 to 300 ppm and about 29,500 acre-feet of reject stream with a salinity of about 9,400 ppm. The product water will be blended with about 10,000 acre-feet of untreated irrigation drainage. This blended water will be returned to the Colorado River, mixed with other river water, and then delivered to Mexico at the Northerly International Boundary, upstream from Morelos Dam. (See figure 1.) The reject, or concentrate, stream from the YDP will first flow through an energy recovery system and then to the Bypass Drain, where it will be combined with excess untreated WMIDD irrigation drainage (if any) and conveyed to Santa Clara Slough. Year-to-year operations will vary according to river conditions and the volume and quality ofWMIDD irrigation drainage to be recovered. During years of surplus water conditions on the Colorado River, the YDP will be placed in standby status. Otherwise, these variations will be reflected in minor 9