FINAL REPORT Evaluation of Seawater Desalination Projects ...

EVALUATION OF SEAWATER DESALINATION PROJECTS
PROPOSED FOR THE MONTEREY PENINSULA
applied chlorine would diminish the disinfection potential for inactivating pathogens. Both
the efficacy of primary disinfection and the potential for DBP formation, as well as the
possible removal of these DBPs via the reverse osmosis (RO) processes need to be explicitly
evaluated during the pilot phase, as noted in the CDR. Note that while the feed for the
seawater desalination plant is planned to be withdrawn from the discharge for Units 1 and 2
prior to the point at which the cooling water flow is combined with that from Units 6 and 7
prior to discharge, Units 1 and 2 and Units 6 and 7 utilize intakes in Moss Landing Harbor
and may have similar water quality.
The CDR also does not specify how the physical pathogen removal credits for Giardia,
Cryptosporidium, and viruses would be allocated to the various treatment processes by the
CDHS; however, it is likely that the combination of membrane filtration, cartridge filtration,
and RO would achieve the required pathogen removal objectives.
Another potential water quality issue is the possible presence of synthetic organic chemicals
(SOCs) in the watershed. A report developed by The Watershed Institute at California State
University Monterey Bay 27 indicated the detection of the pesticides chloropyrifos (up to
0.145 μg/L) and diazinon (up to 0.682 μg/L) in Moss Landing Harbor. While there are no
maximum contaminant levels (MCLs) for these two compounds, the levels detected are in the
same range as the MCLs for some other regulated SOCs, which also could be present in the
watershed that drains into Moss Landing Harbor. Because the ability of the RO process to
remove various SOCs can vary depending on the compound and may not be well
documented in the literature, the pilot phase should include a full screen for SOCs (as well as
for all regulated drinking water parameters) in both the feed and RO permeate water. Note
that the 1999 NPDES permit renewal sampling did not detect the presence of any regulated
SOCs in the intake water for power plant Units 6 and 7.
The CDR specifies that the hardness, alkalinity, and pH of the RO permeate would be
adjusted via chemical applications both for aesthetic considerations and to protect the
distribution system piping. The CDR also indicates that a corrosion inhibitor may be needed.
In addition, the PEA 28 indicates that RO post-treatment would be applied with consideration
for blending with other water supplies. No total dissolved solids (TDS) target is specified,
however, nor is the potential impact of these chemical additions on the ability of the
treatment process to meet that target.
The CDR states an assumption of five percent downtime for maintenance, but indicates an
annual average daily capacity that is 97 percent of the design daily capacity. Nonetheless,
27 California State University, Monterey Bay, Watershed Institute, Monitoring Chloropyrifos and Diazinon in
Impaired Surface Waters of the Lower Salinas Region, March 31, 2004.
28 RBF Consulting, California American Water, Coastal Water Project – Proponent’s Environmental
Assessment for the Coastal Water Project, CPUC Proceeding A.04-09-019, July 14, 2005.
Monterey Peninsula Water Management District 4-2