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USBR/MWD SALINITY MANAGEMENT STUDY FINAL REPORT w 0) IV ~ The primary benefit of reducing the salinity of CRA water is that it would reduce dependence upon SWP water for salinity management. The disadvantage of desalting Colorado River supplies is that a portion of the supply is lost (from 120,000 acre-feet per year to meet a 500-mg/L target to 240,000 acre-feet per year to meet a 200-mg/L target.) The lost supply is a result of rejection through the reverse osmosis membranes of about 20 percent of the water volume as the brine stream. Disposal of the brine is a relatively expensive and raises unresolved environmental issues. Technical Appendix 12 provides additional information on the CRA desalination option and costs. An added advantage of desalting irrigation drainage water (from the Coachella and Imperial valleys) is that available supply to MWD via the Colorado River Aqueduct would increase, since this is a new supply. The brine disposal issue is the same as with CRA desalting. The desalted irrigation drain water would require pumping and transportation to the CRA. In all options, the salinity level for CRA water pumped from Lake Havasu is considered to be 750 mglL, membrane treatment technology is used, and design and construction would take eight years, with full operations starting in 2006. Table 3-3 summarizes the pertinent information regarding these options. Note that the rate impacts in Table 3-3 reflect project costs and water supply change benefits or costs. T bl 3 3 P t' I D If P . t a e - oten la esa In!! rO.lec s Colorado River Water/ Colorado RIver Aqueduct (CRA) Agricultural Drainage Water I Target TDS in CRA 200 mgIL 500 mglL 500 mgIL Source Water TDS 750 mgIL 750 mglL 2,400 mglL Capital Cost (1997) $2.7 billion $2.4 billion $1.1 billion Debt Service Payment $264 million $227 million $131 million Rate Impact $186/AF $155/AF $781AF Brine Disposal 0.24 MAFN 2 0.12 MAFN 0.11 MAFN MWD Supply Changes loses 0.24 MAFN loses 0.12 MAFN gains 0.35 MAFN 1 Costs excludes Salton Sea mitigation. 2 MAFN - million acre-feet per veor. Metropolitan recently initiated planning a demonstration project with Coachella Valley Water District to assess the practicality of capturing agricultural drainage, and desalting it. BOOKMAN-EDMONSTON ENGINEERING, INC. 3-16 O:lJ.OCAlRESIANDYSISALlNITYVUNE98-217SECT3.DOC 0712019810:59AM Section 3 Evaluation of Potential Regional Salinity Management Strategies . . .