FINAL REPORT Evaluation of Seawater Desalination Projects ...

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EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA 3.3 Sand City Desalination Project (SCDP) Project Purpose The proposed 7.5 mgd/8,400 ac-ft per year desalination plant would allow CAW to meet the provisions of SWRCB Order No. 95-10 and the court decision in the Seaside Groundwater Basin adjudication, provide a supplemental supply to meet needs in excess of CAW’s current total valid rights (6,880 ac-ft per year 15 ), and to continue to provide a reliable supply of water to existing Monterey Peninsula customers. Customers Identified The project would provide water to existing CAW service area customers. Technology Appropriate/Demonstrated on this or Similar Supply The technical description for this project is included in both the Final Phase 1 Technical Memorandum 16 and the Board Review Draft Environmental Impact Report (EIR). 17 A notable aspect of this project is that the source seawater is obtained from a shoreline well field. While the proposed treatment process is based on the use of reverse osmosis to accomplish the desalination treatment objectives of the project, the extensive pretreatment required for open-intake feed sources is avoided with this well source. Post-treatment chemical addition is still provided to condition the product water to meet aesthetic, compatibility, and regulatory objectives. Factors to be considered for the project to be expanded are listed below: • Intake (many of these considerations are interrelated) o Additional beachfront property o Local aesthetic impact (on former Ford Ord property, if applicable) o Influence of expanded well field on local hydrogeology • Desalination plant o Sufficient space for footprint of expanded plant, including larger clearwell 15 3,376 ac-ft per year from Carmel River sources and 3,504 acre-feet per year from the Seaside Groundwater Basin. 16 Camp Dresser & McKee, Inc., Monterey Peninsula Water Supply Project Alternatives – Final Phase 1 Technical Memorandum, March 2003. Monterey Peninsula Water Management District 3-14
EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA o Availability of additional land (if necessary based on analysis of expanded desalination plant footprint) • Concentrate discharge • Cost o Blended water quality vs. NPDES discharge limits for TDS and other WQ parameters (as applicable) o Capacity of outfall to accommodate increased brine flow o Potential sacrifice of outfall capacity allocated for future development in the area in favor of allocating unused capacity for brine o Minimization of stormwater capacity in the outfall and how this might be mitigated (e.g., storage tanks, ASR well, if possible, etc.); storage tanks for this purpose could be more costly than those for other purposes given the need for corrosion resistant materials o Both capital and O&M; the plant will cost more; however, the unit total life cycle cost (i.e., amortized) may be reduced as a result of economies of scale • Permitting Pretreatment System o A revised EIR may be necessary o Other permits would also have to accommodate the expanded capacity, as applicable The ability of seawater wells to reliably provide RO feed water that is low in suspended solids has been demonstrated in numerous full-scale installations. The benefits of this source vs. open intakes include the avoidance of the capital and O&M expense of the pretreatment, avoidance of entrainment impacts, increased reliability, and, often, reduced RO membrane fouling. The pretreatment equipment defined for this project consists of cartridge filtration and antiscalant addition, which is sufficient for this application. While the wells do not yet exist, preventing verification of the feed water quality, it is reasonable to anticipate suspended solids levels that are acceptable for RO. Reverse Osmosis The Final Phase 1 Technical Memorandum and the Board Review Draft EIR describe a traditional approach to seawater RO design that has been successfully implemented at other sites. The design consists of four 33 percent-capacity RO trains, which provide substantial 17 Jones & Stokes Associates, Monterey Peninsula Water Management District Water Supply Project, Board Review Draft Environmental Impact Report, December 2003. Monterey Peninsula Water Management District 3-15
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FINAL REPORT Evaluation of Seawater Desalination Projects ...

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