AWWA SOURCES66395

This paper describes the process undertaken by Sweetwater Authority (a member agency of San Diego County Water Authority - SDCWA) and Malcolm Pirnie, Inc. to identify the appropriate amount of annual water supplies to purchase from a proposed seawater desalination plant. To identify this quantity, Sweetwater and Malcolm Pirnie assessed the following factors: risk of spill from the reservoirs; increased reliability with supply diversification; and, benefit for developing local supplies during a shortage allocation under the SDCWA Drought Management Plan. Five alternatives were analyzed to determine the appropriate annual quantity to purchase. The alternatives represent a range of demand conditions, from fairly conservative (10% of historic demands) to worst case (the third year of a multiple dry year). The alternatives analyzed were: 10% of historic 10-year total demands; 10% of projected 10-year total demands; average SDCWA demands over the past 10 years; projected SDCWA demands over a single dry year; and, projected SDCWA demands over a multiple dry year period. Includes tables.