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<br />(,.oJ <br />'" <br />.... <br />~, <br /> <br />nance costs, cost of water lost in reject, and costs insensitive to mem-. <br />branes. <br /> <br />E. Plant Sizing Study <br /> <br />The purpose of this study was to recommend a design production capacity <br />for the Yuma Desalting Plant. The recommended 96 Mga1/d plant size was <br />based on operational characteristics for a spiral wound reverse osmosis <br />desalting process capac1e of producing 254 p/m product water when the <br />MODE water salinity is 3,200 p/m. The desalting plant would be capable <br />of recovering 70 percent of the plant feed water, The actual desalting <br />plant might not have these exact operational characteristics and might not <br />be entirely a single-process plant; however, any purchased desalting <br />plant must perform substantially the same as the one presented here. This <br />study was used as a base case, from which an equivalent quantity of <br />membrane desalting equipment was purchased, Specifically, contracts were <br />awarded to two spiral-wound reverse osmosis equipment manufacturers for <br />a total of 95.67 Mga1/d of installed capacity producing product water <br />(combined) of about 283 p/m. <br /> <br />In the study, the desalting plant is operated for 13 sequences of possible <br />hydrologic conditions. Four levels of annual We11ton-Mohawk Irrigation <br />and Drainage District (WMIDD) drainage flows are considered: <br /> <br />1, 173,000 acre-feet <br />2. 167,000 acre-feet <br />3. 140,000 acre-feet <br />4. 167,000 acre-feet <br />decreasing uniformly to <br />140,000 acre-feet by <br />140,000 acre-feet <br /> <br />1977 through 1996 <br />1982 through 1996 <br />1982 through 1996 <br />1981 <br /> <br />1987 <br />1988 through 1996 <br /> <br />A desalting plant size was determined for each level of WMIDD drainage <br />flow. Then, several of these plant sizes were tested to see what would <br />happen if greater than expected drainage flows occurred. <br /> <br />The primary factor affecting the size of the proposed desalting plant is <br />the quantity of drainage flow. There is a high degree of certainty <br />expressed by the Technical Field Committee that drainage requirements <br />will decrease to 167,000 acre-feet annually by 1981, <br /> <br />A 96-Mga1/d plant would be adequate 85 percent of the time to treat 167,000 <br />acre-feet of drainage. About 15 percent of the time, the desalting plant <br />would operate at its maximum capacity and some drainage would have to be <br />bypassed. The average annual bypass is estimated.to be about 2,000 acre- <br />feet. <br /> <br />A high probability exists that surplus flows will be available fordel1very <br />to Mexico during calendar years (CY) 1981 throu9h 1986. This will result <br />in reduced or no plant production about 69 percent of the time before the <br /> <br />12 <br />