FINAL REPORT Evaluation of Seawater Desalination Projects ...

EVALUATION OF SEAWATER DESALINATION PROJECTS
PROPOSED FOR THE MONTEREY PENINSULA
redundancy and reliability to the treatment facility. The stated operating pressures are
reasonable for this application. Considering that the conceptual design effort for this
project’s RO plant occurred in 2003, it is expected that the anticipated energy recovery
performance is relatively conservative compared to current approaches that benefit from
recent advances in energy recovery devices.
Conclusion
The treatment design for the Sand City project, consisting of RO operated directly on well
water is an appropriate approach that has been successfully implemented at many locations.
The design has been developed only to the conceptual level. However, no serious omissions
or fatal flaws in the treatment process are anticipated.
Waste Stream Fate Identified
Brine from the desalination process would be disposed either in HDD wells or via connection
to the MRWPCA’s treated wastewater outfall to the Pacific Ocean. 17 Descriptions of the fate
of cleaning chemicals and other waste streams were not identified.
Studies considering an HDD system for brine disposal have determined that such a system is
technically feasible in the Fort Ord area. Such a disposal concept could be an issue,
however, because the regional aquiclude (Seaside Clay) is absent in the area, creating a
window with direct hydrologic communication with the underlying aquifer (the Paso Robles
Aquifer system). Additional modeling is needed to determine the potential effects of mixing
desalination brine and seawater with freshwater in the Paso Robles aquifer.
Brine discharge to the MRWPCA’s treated water wastewater outfall is technically feasible
although initial studies indicate that capacity may not be available for all outfall flow
conditions. Additional studies are needed to determine if storage or operational
modifications can be made to accommodate all outfall operating parameters. This could
include the evaluation of seasonal storage to manage the occurrence of when brine discharge
exceeds outfall capacity during high-flow periods.
Availability of Historical Feedwater Quality Data and Sanitary Survey
No source water quality information was provided in any of the reviewed documents.
Additional work will be needed to develop these data. Future test wells would need to be
drilled and water quality samples obtained. Long-term water quality impacts will also need
to be evaluated.
Quality of Supporting Documentation
The quality of the work prepared in support of this project is good; however, much of the
work has been to determine the project’s feasibility. A good portion of this feasibility-related
Monterey Peninsula Water Management District 3-16