Desalination plant raises questions about water conservation potential
The rain gutter in Rick Longinotti’s backyard descends underground, carrying roof water to an underground storage cistern.
“It didn’t cost anything but sweat and muscle,” says Longinotti, a local environmentalist, founder of Transition Santa Cruz and member of bicycle advocacy group People Power. He believes conservation efforts could make the Santa Cruz Water District’s desalination plant obsolete—perhaps even before it’s built.
The planned plant will pull five million gallons of seawater from the Monterey Bay each day, using reverse osmosis to produce 2.5 million gallons of drinkable water. The remaining brine will be trucked to a water plant, diluted with treated wastewater, and released into the Bay.
No date for construction has been set, but the district will solicit designs for the new plant in April. Data from a year-long trial project will be published this spring, detailing the results of a small-scale plant constructed at the Long Marine Lab in 2008. An energy minimization and greenhouse gas reduction report is also in the works, according to water district officials.
Yet Longinotti believes plans for desalination are premature. “Any new growth in Santa Cruz should be offset by conservation, not desalination,” he says.
Longinotti’s 1,500-gallon storage cistern holds just enough to care for his drought tolerant yard through July. More importantly, he says the project has changed his behavior. “It took a lot of work,” he says, “and now I pay attention to every drop I use.”
Last year Santa Cruz demonstrated that mild restrictions save almost as much water per day as a desalination plant will produce. By limiting sprinkler use between May and October, the water district conserved one to two million gallons a day, cumulating in 300 million gallons of total savings. “The majority of people complied with our requirement to limit watering to twice weekly,” says Toby Goddard, water conservation manager for the Santa Cruz Water District.
Yet district policies don’t support long-term restrictions. “It’s not necessary to put people through these restrictions in wet years. There is adequate water most of the time,” says Goddard. “It’s not the policy right now to impose restrictions when none are needed.”
The problem is that most city water comes from surface sources like the San Lorenzo River and its streams. There is little infrastructure for long-term water storage, so saving water during a wet season does not build up reserves for a drought year.
As populations grow, the strain placed on surface sources will be greater, says Goddard, increasing our vulnerability during drought years. Santa Cruz is expected to grow by 11,000 people by 2030. This number includes 4,000 additional students predicted to enroll at UC Santa Cruz (UCSC) during its expansion, and additional staff, maintenance crews and teaching faculty.
Loch Lomond
The answer may be to maintain higher levels in Loch Lomond—the city’s only source of water storage. Most of the water taken from the lake goes to people’s gardens. As Loch Lomond is only tapped when surface sources are maxed out, limiting sprinkler use can help offset growth.
“Loch Lomond has been identified as the only available water source for growth,” says Longinotti, “because surface sources are utilized at maximum capacity during normal parts of the year. “ He adds that “The water for UCSC expansion will effectively come from the Loch,” although Goddard was unable to confirm this.
According to state water rights, the city can withdraw 1.04 billion gallons of water from Loch Lomond each year, representing 37 percent of the lake’s total capacity. If Loch Lomond were managed with a higher priority for drought insurance, lake levels would remain high during wet years, providing a water surplus for dry spells. Longinotti believes the water department should aim for Oct. 1 levels no lower than can be fully recharged by the driest winter on record.
“Last summer we cut water use by 14 percent by limiting landscape watering, and Loch Lomond was at 90 percent capacity at the end of the 2009 dry season,” says Longinotti. “Even a repeat of the driest winter on record should fill the lake to capacity.”
In seven out of 10 years, heavy rains cause the Loch to spill over, and conserving during these years might not impact future levels. Yet requiring multi-year conservation efforts during dry cycles might have an impact.
To save even more water, conservation rebates could facilitate gray water and rain collection. Gray water hoses can now be run from a single washing machine without need for a permit, thanks to rule changes implemented by the California Department of Housing and Community Development last July. This might save a small family 8,000 gallons of water a year.
An inch of rain on a 100 square-foot-roof will yield 600 gallons of water. Storage cisterns that hold up to 3,000 gallons can be purchased for the patio, if digging up the back yard isn’t an option. This might not provide enough water for the lawn, but it could maintain a low flush toilet for a year. Toilets currently account for 30 percent of all city water used indoors.
Goddard agrees that saving water leaves us more resilient. Yet taking population growth into account, Santa Cruz would face shortages of six million gallons a day during a worst-case scenario drought. Each year the average Santa Cruz family uses 25,000 gallons of water outdoors, and 60,000 inside, and this has to come from somewhere.
“We do plan to offset most of our growth with improvements in water efficiency,” confirms Goddard, “but we can’t assume conservation methods like gray water will be widely implemented.” Rainwater harvesting opportunities are limited in the Central Coast’s Mediterranean climate—at least for half of the year, he says. And the public will only comply with so many conservation restrictions.
The Desalination Energy Footprint
Energy inefficiency is the biggest criticism of desalination. During trials at the Long Marine Lab, the quality and efficiency of several reverse osmosis methods were compared.
“We found all treatment trains produced good water quality, but some are better with energy use than others,” says Linette Almond, deputy water director and engineering manager for the Santa Cruz Water Department.
Energy use cannot be predicted before the final filtration process has been selected. Yet Almond says energy-efficient plants take 12.5 kilowatt hours to produce 1,000 gallons of purified seawater. In contrast, it takes three-kilowatt hours to treat 1,000 gallons of river water. Even despite solar, offsets and energy conservation, desalination is one of the least efficient sources of water.
The city adopted climate action goals requiring a 30 percent reduction in greenhouse gasses by 2020, and an 80 percent reduction by 2050, surpassing state-wide reduction requirements implemented under Assembly Bill 32—the Global Warming Solutions Act signed by Gov. Arnold Schwarzenegger in 2006.
“I don’t see how we will meet these goals if a desalination plant is running,” says Longinotti, “while scientists say there are low-impact methods for brine disposal, there isn’t any way around the energy efficiency issue.”
Almond says the plant will not service Santa Cruz year round. It will supply water during drought years, and even then only during the summer months. In wet months, the plant will help the Soquel Creek Water District—producing 2.5 million gallons of water a day for Capitola, Aptos and Soquel.
Still, the energy will have to come from somewhere—regardless of who picks up the tab. The project receives support from both water districts, and while permitting and environmental impact reviews may yet throw a wrench in the machine, the plant project is moving full speed forward.
A subsurface study is currently being conducted to evaluate seawater intake opportunities, and sand and geology conditions are being evaluated for a slant well. While screens will help protect large fish, a second study is counting the larvae and eggs that will be impacted by intake structures.
