Saying it needs to evaluate all options for new sources of drinking water, Silicon Valley’s largest water district is studying a plan to build the first seawater desalination plant along the shores of San Francisco Bay.

The Santa Clara Valley Water District, a government agency based in San Jose, has approved spending $1.7 million for Black & Veatch, a Walnut Creek firm, to conduct an engineering feasibility study over the next 12 months for a project near the bay’s shoreline in Palo Alto, Mountain View or San Jose.

Under the proposal, which is still in the early stages, the plant would take between 20 million to 80 million gallons of water a day from the bay, run it through filters to strip the salt out and serve from 10 million to 40 million gallons a day of freshwater to South Bay homes and businesses. That would provide about 11,000 to 44,000 acre-feet of water per year, enough for between 100,000 and 500,000 households.

The salty brine left over would be blended with treated wastewater from one of the South Bay’s sewage treatment plants to reduce its salinity and be released back into the bay.

“People ask us about desalination all the time,” said Tony Estremera, a member of the Santa Clara Valley Water District’s board of directors. “Can we really do it? We don’t know. It’s worth looking at. We really do need to do a serious look at it, and this is a substantial look.”

In theory, desalination can provide an endless supply of water. In 2015, crews built a $1 billion desalination plant in Carlsbad, in San Diego County. It provides 54 million gallons per day — nearly 10% of the drinking water for San Diego. It is the largest plant in North America.

But desalination is also the most expensive type of water to produce. The San Diego County Water Authority pays $3,400 an acre-foot for the Carlsbad water — more than double the cost of water it imports from other sources, and up significantly from the $2,200 it paid when the plant opened a decade ago.

By comparison, the Santa Clara Valley Water District pays about $400 an acre-foot to the federal and state government for water it draws from the Delta. However, that water is not as reliable during droughts.

Why is it so expensive? Desalination plants run 24 hours a day, blasting water through membranes at pressures higher than a fire hose, and use huge amounts of energy.

Desalinated water is far more costly than recycling wastewater, repairing leaky underground pipes, expanding groundwater storage, or giving people rebates to voluntarily remove their lawns or buy water-efficient appliances, experts say.

“This would be the first seawater desalination plant built in the Bay Area,” said Heather Cooley, director of research for the Pacific Institute, a nonprofit water research organization in Oakland. “We haven’t seen others because we have cheaper alternatives with fewer environmental impacts.”

The district proposal is likely to face significant environmental opposition because it would be near, or inside, the Don Edwards San Francisco Bay National Wildlife Refuge.

David Lewis, executive director of Save the Bay, an environmental group in Oakland, said that building pipes into a national wildlife refuge to draw millions of gallons of water a day from sensitive wetland areas that are home to endangered species would almost certainly cause a major controversy.

“The public has a deep love for the bay and has made a big investment in protecting these parts of the shoreline,” he said. “The public would not likely welcome new development of this type in that area.”

Several alternatives have been tried in the past.

In 2009, many of the largest water agencies in the Bay Area paid to construct a pilot desalination plant in Bay Point, just west of Pittsburg. It ran for more than a year.

But the group, which included the Santa Clara Valley Water District, the San Francisco Public Utilities Commission, the Contra Costa Water District and the East Bay Municipal Utility District, dropped the idea in 2012.

“The cost of the water was higher than other sources for us,” said Andrea Pook, a spokeswoman for EBMUD. “And the environmental permitting would have been challenging.”

Similarly, the Marin Municipal Water District proposed building a desalination plant on the bay near San Rafael in 2009 but shelved the plan after Marin voters approved a ballot measure in 2010 saying desalination facilities couldn’t be built without voter approval.

Building such a plant in the South Bay, which is shallow and subject to limited tidal action, would require 14 permits from federal agencies and 8 from state agencies, according to a brief environmental feasibility study that the Santa Clara Valley Water District commissioned last year.

GEI Consultants, an Oakland firm that did the study, evaluated 13 alternatives along the San Jose, Mountain View and Palo Alto shorelines. The most feasible options, it found, were to draw in water from underground pipes in the bay off Palo Alto or Mountain View. The most likely site for a desalination plant, however, is in Alviso, the study concluded, where there is more land than other possible sites near Moffett Field and the Palo Alto Baylands. The brine could be disposed of in deeper waters in the middle of the bay, or in a marsh after being blended with treated wastewater, the study found.

The cost would be in the hundreds of millions of dollars if not more than $1 billion. Specific estimates will be part of the engineering study, Estremera said.

There are 12 ocean desalination plants in California now. Most are small and serve military bases, power plants and other facilities, like the Monterey Bay Aquarium. Apart from the Carlsbad plant, there are plants in Santa Barbara and Catalina Island. Two years ago, the Coastal Commission rejected a large plant at Huntington Beach, citing environmental concerns.

In November 2022, however, the commission approved a permit for a $330 million seawater desalination facility in Marina, in Monterey County. That plant, at the site of a former sand mining factory, will produce 5 million gallons of water a day at a cost of $6,000 an acre-foot for the water-starved Monterey Peninsula.

The commission also approved a plant in Dana Point which will produce 5 million gallons a day. It would be built by the South Coast Water District in Laguna Beach and is expected to open in 2028.

“This study is really a response to the community, and our public officials,” Estremera said. “We want to take a good serious look at this and answer once and for all whether it’s possible here.”

Originally Published: July 23, 2024 at 6:00 a.m.