FINAL REPORT Evaluation of Seawater Desalination Projects ...

EVALUATION OF SEAWATER DESALINATION PROJECTS
PROPOSED FOR THE MONTEREY PENINSULA
o Availability of additional land (if necessary based on analysis of expanded
desalination plant footprint)
• Concentrate discharge
• Cost
o Blended water quality vs. NPDES discharge limits for TDS and other WQ
parameters (as applicable)
o Capacity of outfall to accommodate increased brine flow
o Potential sacrifice of outfall capacity allocated for future development in the
area in favor of allocating unused capacity for brine
o Minimization of stormwater capacity in the outfall and how this might be
mitigated (e.g., storage tanks, ASR well, if possible, etc.); storage tanks for this
purpose could be more costly than those for other purposes given the need for
corrosion resistant materials
o Both capital and O&M; the plant will cost more; however, the unit total life
cycle cost (i.e., amortized) may be reduced as a result of economies of scale
• Permitting
Pretreatment System
o A revised EIR may be necessary
o Other permits would also have to accommodate the expanded capacity, as
applicable
The ability of seawater wells to reliably provide RO feed water that is low in suspended
solids has been demonstrated in numerous full-scale installations. The benefits of this source
vs. open intakes include the avoidance of the capital and O&M expense of the pretreatment,
avoidance of entrainment impacts, increased reliability, and, often, reduced RO membrane
fouling. The pretreatment equipment defined for this project consists of cartridge filtration
and antiscalant addition, which is sufficient for this application. While the wells do not yet
exist, preventing verification of the feed water quality, it is reasonable to anticipate
suspended solids levels that are acceptable for RO.
Reverse Osmosis
The Final Phase 1 Technical Memorandum and the Board Review Draft EIR describe a
traditional approach to seawater RO design that has been successfully implemented at other
sites. The design consists of four 33 percent-capacity RO trains, which provide substantial
17 Jones & Stokes Associates, Monterey Peninsula Water Management District Water Supply Project, Board
Review Draft Environmental Impact Report, December 2003.
Monterey Peninsula Water Management District 3-15