Bay Water on Tap?

What Desalination Could Bring

There is growing interest among Bay Area water agencies in augmenting traditional water supplies with water from San Francisco Bay or the Pacific Ocean. In 2002, the Marin Municipal Water District (MMWD) revived a 1990 proposal to use water desalination to produce up to 15 million gallons per day (mgd) to supplement water in MMWD reservoirs and imported from the Russian River. In October 2003, the first phase of a joint study was completed by a partnership including East Bay Municipal Utility District (EBMUD), the San Francisco Public Utilities Commission (SFPUC), the Contra Costa Water District (CCWD) and the Santa Clara Valley Water District (SCVWD). The joint study looked at a Bay Area Regional Desalination Project, which could consist of one or more desalination facilities, with a potential capacity of up to 120 million gallons per day.

That capacity is attractive to agencies which are concerned about adequate water supply to address emergency needs, potential droughts, and the demands of a growing population. In addition, desalination provides a reliable quantity of water, unlike rivers and reservoirs dependent on rainfall. Despite conservation, and long-range maintenance and seismic retrofit plans, water agency planners expect future water shortages somewhere in the region.

Although desalination plants have been built around the world, including a few in California, a number of factors formerly made desalination sufficiently difficult or expensive so that most water agencies put it far down on their list of water supply alternatives. The first of these is energy. In the Bay Area, desalination would probably be done using a process called reverse osmosis, which forces salt water through thin membranes that block the salt and allow fresh water to pass through. The extremely fine filtering membranes have such small openings that only clean water can get through, but it takes a great deal of energy to create enough pressure to force the water from one side of the membrane to the other. Distillation, an alternative desalination process used in many other parts of the world, also needs large amounts of energy for heat to boil the water.

Another problem is siting. New facilities of any kind are often unwelcome along a waterfront, yet the facility needs to be in a location which allows it to take in large quantities of water without excessive impacts on marine life. Turbid or contaminated water is undesirable, since this will make pretreatment more difficult. Every two gallons of marine water will yield approximately one gallon of fresh water and one gallon of concentrated brine that must be treated or diluted before disposal. Desalination plants are typically located near wastewater treatment outfalls or electric power plants where existing water discharges offer the means to dilute the brine so it can be safely discharged without affecting marine organisms or otherwise degrading water quality or the health of the environment. These factors create technological challenges and add expense to desalination projects.

These concerns all apply in the Bay Area and are being addressed in the desalination studies which are moving forward. The regional partnership looked for sites near power plants and existing dischargers to the bay to maximize the potential for power cost savings and minimize environmental impacts.

According to Hasan Abdullah, EBMUD's desalination project coordinator, "the Mirant Power Plant in Pittsburg was of great interest to the group, because it is close to EBMUD and CCWD facilities and because it would provide an onsite power source and an existing inlet for drawing in the water, as well as an outfall which could be used to dilute the brine waste." The other two sites chosen for additional exploration are a site in Oakland near the Bay Bridge, and an oceanside site in San Francisco. MMWD's preferred site would be on the San Quentin Peninsula in San Rafael, where a nearby wastewater treatment plant outfall would provide fresh water to dilute the brine to the salt levels of the Bay.

The Bay Conservation and Development Commission, which has jurisdiction over siting facilities at the edge of the Bay, is preparing a report on the potential impacts of desalination plants which is scheduled for completion in September.

The Environmental Impact Report for the Marin project will be available later this year and will probably be certified in early 2005. Bob Castle, Water Quality Manager for MMWD, says the district may also repeat pilot tests done in 1990 to evaluate improved microfilter technology. "We'd probably use these as an opportunity for the public to see the equipment and taste the result," says Castle, noting that in 1990, 95% of the people who took part in taste-tests preferred the desalinated water.

Phase 2 of the Regional Desalination Project will begin in June; it is a six-month Pre-Feasibility Study, which will analyze the three sites and further define the potential facilities. The study will consider how each participating agency might use the desalted water, solutions to geotechnical and pretreatment waste issues, conceptual engineering of the treatment facilities, and how the agencies would work together. The next step, once funding has been obtained, is a $4 million detailed feasibility and environmental study which would develop specifics about locations, technologies, what facilities would look like, potential benefits, and environmental impacts. This phase would include public outreach. The information from this phase would contribute to a final project description which would be submitted to the boards of the participating agencies for decisions on how to proceed.

Construction costs of a new jointly-used facility are estimated at $450-700 million, depending on the location and the capacity. Operating costs would depend on the project, and all agencies would need to invest in pipelines and other distribution facilities. For Marin, construction costs would be $100 million for a 10 mgd plant, which includes $35 million in distribution improvements.

All five agencies will need to weigh the costs, the benefits, and the environmental impacts against those incurred in obtaining additional water from other sources. Those costs, both economic and environmental, have risen for many districts. Keeping water in rivers for environmental benefits has constrained supplies, and using untapped groundwater or reservoirs can mean building expensive new facilities. Alternatively, a recent study by the Pacific Institute concludes that urban water conservation, reclamation and recycling could supply the state's needs for decades to come. However, Castle notes that MMWD, like EBMUD, has already aggressively pursued both water conservation and water recycling. At this point, expanding water recycling is almost twice as expensive for MMWD as implementing desalination. Some districts may find reclaimed and recycled water is cheaper than desalinated water, but so far these alternatives have been unacceptable to drinking water customers.

Depending on precipitation to fill reservoirs and pipelines may soon create too much uncertainty for good water planning as the population grows. Even if no Bay Area desalination facilities are approved in the next few years, they it is likely they will eventually play a role in the region's water supply.

Bay Area Regional Desalination Project: Hasan Abdullah, EBMUD, 510-287-0550; habdullah@ebmud.com

Marin Municipal Water District: Bob Castle, 415-945-1556; bcastle@marinwater.org

California Dept. of Water Resources: http://www.owue.water.ca.gov/recycle/index.cfm

California Coastal Commission, http://www.coastal.ca.gov

Pacific Institute, http://www.pacinst.org/

Water Education Foundation, http://www.watereducation.org; Western Water Magazine, "Tapping the World's Largest Reservoir: Desalination", January/February 2003