FINAL REPORT Evaluation of Seawater Desalination Projects ...

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EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA this on-line time would require redundancy in all treatment processes and pumping facilities. No references are made to the redundancy levels in the treatment plant design or to the basis of the cost estimates. 4.2 Monterey Bay Regional Seawater Desalination Project (MBRSDP) The CDR provides significant general information about the Monterey Bay Regional Desalination Project (MBRSDP), 29 although in many cases there is less supporting detail than would typically be provided at the conceptual level. For example, the CDR indicates that the desalination plant will be in compliance with the applicable requirements of both the federal Safe Drinking Water Act (SDWA) and Title 22 of the California Code of Regulations, although it does not specify how the required pathogen removal and inactivation credits will be achieved. 30 While the proposed treatment process, including clarification, media or membrane filtration, cartridge filtration, and reverse osmosis (RO), should be sufficient for meeting the physical pathogen removal requirements, there is no indication of how the CDHS would allocate the removal credit among these processes. Supplemental information provided by Poseidon Resources in a letter dated July 14, 2006, provided additional detail with respect to the manner in which pathogen removal and inactivation would be achieved. Treatment Process Giardia Credit Virus Credit Sedimentation / Filtration 2-log 1-log Reverse Osmosis 2-log 2-log Disinfection (Free Chlorine) 2-log 1-log TOTAL 6-log 4-log Poseidon indicated that it anticipates the desalination plant will need to be designed to achieve 4-log Giardia and 3-log virus reduction. This is inconsistent with the state and federal regulations governing surface water treatment, however, which specify 3-log Giardia and 4-log virus reduction, as well as 3-log Cryptosporidium reduction, which is not mentioned in Poseidon’s analysis. Because seawater collected via an open intake would be 29 Pajaro/Sunny Mesa Community Services District in Cooperation with Poseidon Resources Corporation, Monterey Bay Regional Desalination Project Conceptual Design Report, April 2006. 30 In a June 28, 2006 email, a representative of Poseidon Resources stated that it has been working closely with CDHS on permitting large-scale desalination projects in California and has received conditional approval for a project in Huntington Beach. Poseidon Resources believes that it understands what is required to obtain CDHS approval for the MBRSDP. These statements were not verified. Monterey Peninsula Water Management District 4-3
EVALUATION OF SEAWATER DESALINATION PROJECTS PROPOSED FOR THE MONTEREY PENINSULA considered surface water, the desalination plant must comply with these regulations. In addition, it is unlikely that 2-log disinfection of Giardia would be achievable in a contact tank, as the combination of high chlorine dosage and/or the large tank size necessary to achieve this inactivation would be extremely unusual in a water treatment plant. Nevertheless, the other log removal / inactivation credits suggested for the various processes relative to both Giardia and viruses are within the range of those typically permitted by the CDHS, and a 0.5-log Giardia inactivation using free chlorine, as required by the CDHS under its policy of providing multiple barrier protection, is reasonable to expect in the desalination plant’s contact tank. Moreover, the removal of Cryptosporidium permitted by the CDHS is typically similar to that for Giardia. Thus, despite the inaccuracies in Poseidon’s analysis of pathogen reduction, it is likely that the proposed combination of treatment processes would be sufficient to achieve the requisite pathogen removal. The CDR indicates that chloramines will be added downstream of the product water storage tank, and that the product water transfer line would provide adequate contact time to comply with CDHS disinfection requirements. Chloramines constitute a relatively weak primary disinfectant, however, and no supporting detail is provided to justify its use, particularly in a 30 water transfer line. Supplemental information provided by Poseidon Resources in a letter dated July 14, 2006, tacitly refutes the CDR, specifying that free chlorine (vs. chloramines) will be applied in the product water storage tank (vs. the water transfer line) to achieve primary disinfection. In addition, the letter notes that if all purchasers of the water from the desalination plant utilize either chlorine or chloramines as a residual disinfectant, then the MBRSDP will likewise apply this disinfectant at the effluent of the plant. If the various purchasers do not each use the same residual (i.e., secondary) disinfectant, however, then only free chlorine will be used. In the latter case, each purchaser using chloramines would be obligated to provide facilities for applying ammonia to the delivered water at its own cost. Likewise, the CDR notes that pesticides and agricultural runoff will not be a factor for source water quality, but there is no rationale to substantiate this assertion. 31 A full water quality analysis for all regulated drinking water contaminants should be conducted during the piloting phase prior to full-scale project implementation. The CDR does cite low total organic carbon (TOC) levels (more consistent with typical ambient seawater concentrations than those reported by Duke Energy for its Moss Landing Harbor Units 6 and 7 intake and discharge), and coupled with the use of coagulation and polymer in the pretreatment process prior to any chlorine addition, the formation of chlorinated disinfection by-products should not be an issue. 31 In a June 28, 2006 email, a representative of Poseidon Resources stated that monthly water quality monitoring has been conducted since October 2005. The program has included collecting seawater samples from the Moss Landing Harbor. The samples were tested for 300 constituents including pesticides and other agricultural runoff constituents, as regulated under the California Ocean Plan and the state and federal Safe Drinking Water Acts. Poseidon Resources concluded from the testing program that pesticides and agricultural runoff will not be a factor. The data provided by Poseidon Resources do not support this conclusion. Monterey Peninsula Water Management District 4-4
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FINAL REPORT Evaluation of Seawater Desalination Projects ...

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