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w cn "... --.l USBR/MWD SALINITY MANAGEMENT STUDY FINAL REPORT e RESOURCE IMPACT Figure 3-8 illustrates the relative amounts of CRA deliveries to be curtailed over 6-, 9- anl 12- month blending periods. The significant increase in CRA layoff for year-round blending compared to 6-month blending occurs because Metropolitan would otherwise deliver nearly 100 percent CRA water to the blended area in the winter months when demands are low. Conversely, some SWP water is always needed in the blended area to meet the higher summer demands during the 6-month April through September blending period. Inspection of Figure 3-8 raises two significant resource questions: 1. Is there sufficient SWP water to quantitatively make up for the CRA layoff'? 2. Is the CRA layoff compatible with efforts to establish a 4.4 million acre-foot per year California plan for the Colorado River? In developing its Colorado River strategy, Metropolitan is considering diverting some of it CRA water to groundwater storage facilities. Metropolitan is also considering expanded exchanges with the Coachella Valley Water District and the Desert Water Agency. Such storage or exchange operations could recover beneficial use of the CRA water Metropolitan would otherwise not pump from the Colorado River in order to meet its salinity targets. .. However, the amount of CRA water that may be placed into storage or exchanged will have A limits, depending upon how these potential opportunities materialize. _ The ability of the SWP to supply water needed for blending is uncertain during the first few months of the year. This ability also varies from year to year in response to hydrologic conditions. Analyses show that on average, a Metropolitan salinity target can be met in about 7 out of every 10 years; in the other years SWP supply will be insufficient. It can also be concluded from Figure 3-8 that Metropolitans need for SWP water to meet a salinity target (such as 500 to 550 mgIL) diminishes when SWP water is of good (low TDS) quality. Success in the CALFED process in reducing the salinity of SWP water on a sustained basis is critical to the long-term blending practice. Figure 3-9 illustrates the regional economic benefits of 6- or 9-month, or year-round blending. Progress in potential CALFED and CRA storage and exchange arrangements could greatly reduce the resource constraints to a year-round blend policy to achieve 500 mgIL compared to the baseline salinity conditions. e BOOKMAN-EDMONSTON ENGINEERING, INC. 3-12 O:ILOCAlRESIANOYSISALlNfTYIIUNE9B-2\7SECT3.DOC 07/20/9810:59 AM Section 3 Evaluation of Potential Regional Salinity Management Strategies