FINAL REPORT Evaluation of Seawater Desalination Projects ...

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
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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