Cheaper, Better Desalination Gets a Fresh Look
No single resource has had more of an influence on California's development patterns than water. The essential liquid has been pivotal to a range of historical and political conflicts, from the pillaging of the Owens Valley by Los Angeles to the damming of the Hetch Hetchy Valley by San Francisco.
The U.S. Supreme Court has had to mediate disputes involving California and its neighboring states over Colorado River water. As recently as the 1980s, droughts were scary enough that even normally anti-growth Santa Barbarans voted for two major new supplies: state water and desalinated seawater.
Other thirsty coastal communities closely watched Santa Barbara's experience with building a desal plant. Unfortunately, Santa Barbara's experiment — built at a cost of $34 million and employed for only three months during 1992 — is considered by advocates as the black eye in the desal water supply trend, though city officials still call the plant a "drought supply."
But Santa Barbara's expensive desal story overshadows what has really been happening during the last 10 years. The cost of desal has dropped by 50%, the technology for developing efficient filter membranes has improved greatly, and the demand for new water sources has remained as urgent as ever. And for many communities in the state, desal has emerged as a leaner and viable alternative to new dams, reservoirs and pipelines.
Counter to popular belief, most desal plants operating in California are not by the sea, and they do not use seawater. Instead, most plants treat "brackish" water —- groundwater that has high levels of dissolved solids due to seawater intrusion or other contamination, or even sewer effluent. Three such plants have come online in since 1998 in Riverside, San Bernardino, and San Diego counties. The product is typically blended with other sources — usually imported water. These reverse-osmosis systems require far less expensive filter membranes than do plants that treat seawater. Furthermore, they can avoid complicated coastal resource-related permits.
Casey Jaworksi is a water engineer for the city of Oceanside, a city whose experience with desal operations is typical in California today. During the 1960s, Oceanside stopped using local groundwater because it had become contaminated by seawater intrusion, he said. Usually induced by over-pumping by agricultural users, seawater migration into underground aquifers has emerged as a problem up and down the California coast.
In 1994, Oceanside opened a desal plant three miles inland from its sandy beaches, Jaworski explained. Using a reactivated well site, the plant immediately began supplying 2 million gallons per day, 7% of the city's demand. A current expansion of the plant will yield 6 million gallons a day, thereby handling 15% of the projected local demand.
The project was spurred by financial incentives offered by the nation's largest water supply agency, the Metropolitan Water District of Southern California. The Met offers $250 per acre foot subsidy for its member agencies that produce from local supplies.
Immediately south of Oceanside, the City of Carlsbad is involved in the better understood, albeit rarer, type of desal plant, the kind that actually uses seawater. In conjunction with officials from the San Diego Water Authority, Carlsbad is considering entering a deal with Connecticut-based Poseidon Resources to develop seawater desal operations at the Cabrillo power plant in Carlsbad. A second plant would be developed at a power plant in Chula Vista.
Proponents say that Carlsbad's Cabrillo facility alone would produce 9.3% of San Diego County's domestic supply. The proposed plant would use the same technology as a facility scheduled to go on line in 2003 in Tampa, Florida, another fast-growing region with water demand pressures and supply constraints.
In this new generation of seawater desal technology, the plant is coupled with an existing power plant, which already has seawater intakes for cooling. The desal plant diverts some of this supply and processes it through the latest filtering membranes. It then discharges the concentrated remains with the power plant supply effluent. The Tampa plant, which will produce 25 million gallons per day, will be the largest such plant in North America used for domestic supplies.
Even though the cost of seawater desal is becoming competitive with developing other surface water sources, obstacles remain. Environmental concerns about discharging hyper-salted waste byproduct into the ocean is one hurdle. The reliance on electric power to drive the filtration is another. Such impacts, however, need to be weighed against the formidable environmental challenges of developing new reservoirs and pipeline systems. The trend is clearly working against the latter.
Globally, desal is viable where other more traditional sources are either depleted or otherwise unavailable, according to water engineer Ben Movahed, of Watek Engineering in Maryland. Island and desert regions are where most seawater systems operate.
"If you have other sources, you want to use those. Desal is a system of last resort," Movahed said.
So does the emergence of desal in California's urban coastal communities suggest that the region has reached a holding capacity? With popular support and political stomach for 1950s-era public works plumbing projects absent, the ocean may represent that last resort.
Water Costs to Consumer, per 1,000 Gallons
Existing traditional supply: $0.90-$2.50
New desalted water
Traditional + brackish $1.20-$2.75
Traditional + seawater $1.10-$3.05
(source: American Membrane Technology Association)
Stephen Svete, AICP, is president of Rincon Consultants, Inc., a Ventura-based consulting firm.