FINAL REPORT Evaluation of Seawater Desalination Projects ...

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EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA Appropriate redundancy is indicated for the collector wells, treatment process, and pumping station. 4.4 Seawater Desalination Vessel (SDV) Although a treatment process schematic is provided in the Water Standard Company (WSC) promotional presentation titled The Benefits of a Seawater Conversion Vessel, 38 there is very little information available describing the treatment processes in any detail in the literature provided by the WSC. Thus, there is no indication of how the shipboard treatment process will comply with the requirements of either the federal SDWA or Title 22 of the California Code of Regulations, particularly with respect to the manner in which the required pathogen removal and inactivation credits will be achieved. Given the proposed combination of micro filtration (MF) and RO treatment processes, it is reasonable to assume (although not certain) that the CDHS will award the requisite 2.5-log Giardia, 3-log Cryptosporidium, and 2-log virus removal credit; however, the presentation indicates that clearwell storage will be minimal, suggesting that it may be insufficient to achieve the 0.5-log Giardia and 2-log virus inactivation credit that is mandated for primary disinfection. Although WSC literature does indicate that chemicals such as chlorine used by the purchasing water system can be added on the SDV, there is no mention of any shipboard tankage with sufficient contact time to achieve primary disinfection. 39 In fact, a letter written to the California Public Utilities Commission (CPUC) asserts that a clearwell is not required, suggesting that primary disinfection will not be conducted on the SDV. 40 Note that no justification is provided for this claim in the letter 41 . Therefore, even if the CDHS allows the purchaser of the desalinated water to provide the primary disinfection at the point of receipt (i.e., rather than aboard the SDV), the purchaser would need a contact tank sized to allow all of the delivered water to be disinfected. If new facilities needed to be built for this purpose, the net cost of the water would increase. Similarly, chemical feed facilities may be necessary (at further additional cost to the purchaser) to provide residual disinfection in the distribution system. The promotional presentation, The Benefits of a Seawater Conversion Vessel, indicates that the SDV will always be positioned in areas of the best source water quality, although there is no indication of how this will be determined on an ongoing basis, either in terms of what water quality parameters will be monitored or how frequently. 38 Revised plans to use a seabed pipeline in place of shuttle vessels for product water transport makes lateral movements less likely. Proponent’s comments on the draft of this GEI/B-E report state that once the vessel is in place it will not move except as it may move against a mooring system 38 Water Standard Company, The Benefits of a Seawater Conversion Vessel (presentation), September 27, 2006. 39 Water Standard Company Facts at a Glance, 2006. 40 Water Standard Company, letter to the California Public Utilities Commission, October 25, 2006. 41 Proponent’s comments on the draft GBE/B-E report state: “…post disinfection will be accomplished using the seabed pipeline and shore line reservoir for the requisite detention time and [chlorine contact time] credits. The primary disinfectant will be added on the ship, but the contact times are met in the seabed pipeline and proposed reservoir near the shore.” Monterey Peninsula Water Management District 4-7
EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA holding it in place It is also important to note that Title 22 requires source water quality monitoring as well as periodic watershed sanitary surveys and source water assessments, and none of the literature provided by the WSC address how compliance with these requirements would be achieved for a vessel that will change location and intake depth, thereby changing the source water as well as the water quality influences (both natural and anthropogenic, as applicable). There is also no indication of whether the CDHS would approve the receipt of treated water into a municipal distribution system from a drinking water source that is not fixed, or what regulatory conditions it might mandate if it did. Because the SDV allows for various chemical additions aboard the ship, the treated water could be conditioned to match that of the local water with which it would be blended in the purchaser’s distribution system, thereby addressing both corrosion and blending concerns. If the water from a single SDV were to be delivered to two different purchasers with waters of dissimilar quality, however, it may be less feasible to condition the finished water aboard the SDV to match multiple local water supplies. In such cases, one or both of the purchasers would need to add chemical feed facilities to condition the water at added expense. Conditioning for multiple distribution systems may also be an issue in the case in which water is wheeled through the Marina Coast Water District (MCWD) system, as posited in the CPUC letter. 40 Monterey Peninsula Water Management District 4-8
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