FINAL REPORT Evaluation of Seawater Desalination Projects ...

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EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA redundancy and reliability to the treatment facility. The stated operating pressures are reasonable for this application. Considering that the conceptual design effort for this project’s RO plant occurred in 2003, it is expected that the anticipated energy recovery performance is relatively conservative compared to current approaches that benefit from recent advances in energy recovery devices. Conclusion The treatment design for the Sand City project, consisting of RO operated directly on well water is an appropriate approach that has been successfully implemented at many locations. The design has been developed only to the conceptual level. However, no serious omissions or fatal flaws in the treatment process are anticipated. Waste Stream Fate Identified Brine from the desalination process would be disposed either in HDD wells or via connection to the MRWPCA’s treated wastewater outfall to the Pacific Ocean. 17 Descriptions of the fate of cleaning chemicals and other waste streams were not identified. Studies considering an HDD system for brine disposal have determined that such a system is technically feasible in the Fort Ord area. Such a disposal concept could be an issue, however, because the regional aquiclude (Seaside Clay) is absent in the area, creating a window with direct hydrologic communication with the underlying aquifer (the Paso Robles Aquifer system). Additional modeling is needed to determine the potential effects of mixing desalination brine and seawater with freshwater in the Paso Robles aquifer. Brine discharge to the MRWPCA’s treated water wastewater outfall is technically feasible although initial studies indicate that capacity may not be available for all outfall flow conditions. Additional studies are needed to determine if storage or operational modifications can be made to accommodate all outfall operating parameters. This could include the evaluation of seasonal storage to manage the occurrence of when brine discharge exceeds outfall capacity during high-flow periods. Availability of Historical Feedwater Quality Data and Sanitary Survey No source water quality information was provided in any of the reviewed documents. Additional work will be needed to develop these data. Future test wells would need to be drilled and water quality samples obtained. Long-term water quality impacts will also need to be evaluated. Quality of Supporting Documentation The quality of the work prepared in support of this project is good; however, much of the work has been to determine the project’s feasibility. A good portion of this feasibility-related Monterey Peninsula Water Management District 3-16
EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA work is focused on seawater intake and brine disposal. Since there are limited data available on similar types of installations, the amount of feasibility-level assessments is appropriate. Specific desalination treatment plant sites and specific pipeline alignments have not been determined. The reviewed material showed various alternatives for the proposed facilities. Supports Local Area and Regional Objectives The SCDP supports local area objectives by addressing the water supply deficit associated with SWRCB Order No. 95-10 and by providing 500 ac-ft per year to reduce overdraft of the Seaside Groundwater Basin. As proposed, the project would not supply water to areas outside the CAW service area. Omissions or Fatal Flaws Additional study of the use of radial wells or horizontal directionally drilled wells and other aspects of the SCDP is needed to determine their appropriateness for use in this application. A previous study of the SCDP 18 identified the following information needs to further assess project feasibility and water supply yields: Geologic/Hydrogeologic • Assess the near shore subsurface conditions along the beach (e.g., State Parks and Seaside area) to evaluate feasibility of the reconfigured shoreline parallel HDD collector well concept. • Conduct aquifer pump tests at suitable collector and disposal sites once locations of facilities are better defined to refine predicted system yields. Seawater Intake • Further evaluate suitable locations for radial collector wells to identify suitable locations for stand-alone system or to augment onshore HDD configuration. • Finalize detailed evaluation of the revised HDD configuration in order to determine project feasibility. • Further evaluate onshore HDD well collector configuration to improve operations and feasibility. • Evaluate water quality and potential pre-treatment processes resulting from infiltration of surface water from Roberts Lake. • Drill test well(s) and conduct extended pumping test(s) to measure response to pumping in coastal aquifer within the underlying Paso Robles aquifer. 18 Camp Dresser & McKee, Monterey Peninsula Water Management District, Sand City Desalination Project, Feasibility Study, April 16, 2004, pages 7-5 and 7-6 Monterey Peninsula Water Management District 3-17
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FINAL REPORT Evaluation of Seawater Desalination Projects ...

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