FINAL REPORT Evaluation of Seawater Desalination Projects ...

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