PARCHED by four years of drought - and with forecasts of more to come - California is turning to seawater to help quench its growing thirst. The state's average influx of 600,000 new residents a year over the 1980s has accelerated the depletion of many communities' already-tenuous freshwater supplies. Over the same period, various technologies have been developed and improved - helping make seawater a viable alternative to conventional sources. Thus, many communities are not just seeking to alleviate the current drought by turning saline water into fresh. They are investigating desalination as at least a minor contributor, and perhaps a major one, to solving long-term water problems.
First plant opened
San Nicolas Island (off the coast between Los Angeles and San Diego) opened the state's first major desalination plant on Oct. 11, generating 12,000 gallons of drinking water a day from the ocean. A second plant will open this year, enabling the 27-square-mile island to seal its groundwater wells and get all its water from the ocean.
The Marin [County] Municipal Water District currently operates a pilot desalination plant near the north end of San Francisco Bay. Although the bay is less salty than the ocean, it is more clouded with silt from rivers, industrial waste, and microscopic marine life. The plant is experimenting with various types of pre-treatment filtration systems to clean bay water before it goes into the desalination plant. The district hopes to raise $55 million to $65 million to build its own desalting plant and is developing a proposal for voters by November 1991.
Santa Barbara is months away from building a $25 million plant to supply one-third of the city's needs by 1992. Pending city approval, Ionics Inc., a company headquartered in Watertown, Mass., will build, own, and operate the plant to supply water to the city for five to 10 years. Perhaps hardest hit by the drought, Santa Barbara's main water source - the Cachuma Reservoir - is at 15 percent capacity. Its secondary source, Gibraltar Reservoir, is empty.
``Even if we get normal rainfall for two years, we'll need some kind of supplemental supply,'' says Pete Ramsdell, city spokesman for drought affairs.
The Metropolitan Water District (MWD), which supplies water to southern California, is considering building several very large distillation operations, utilizing waste heat from electricity-generating plants for greater energy efficiency.
``We see desalting water as a long-term solution,'' says MWD's Tim Skrove, who is studying the feasibility of demonstration projects. ``But it will be years before anything large-scale will be in place.''
Other California communities considering desalination include San Luis Obispo, Monterey, San Diego, Morro Bay, Ventura, and Oxnard. A plant due to open on Santa Catalina Island this year will supply water for more than 600 condominiums.
``If there were viable alternatives for importing water we wouldn't be doing this,'' says Robert S. Castle, senior engineer of the Marin Water District. ``But all of the easy water in California has been spoken for for quite some time.''
Ted Kuepper, an environmental engineer for the Naval Civil Engineering Laboratory in Port Hueneme, Calif., says: ``If the drought continues, we'll be seeing these plants all along the coast.''
So far, no other states have seawater desalination, although reverse osmosis is commonly used in Florida to purify brackish water for drinking. Desalination is energy-intensive, experts note, and perhaps best suited to the oil-rich kingdoms of the Middle East. Half the desalting plants in use worldwide are in that region.
The cost of desalted water, high everywhere, differs from project to project. In general, the cost of a year's supply for two average families of four - about 292,000 gallons or one acre-foot (the amount of water it takes to cover an acre of land with a foot of water) - would be as much as $2,000. The same amount of normal ground water would cost about $150, according to Mark Silbernagel, project engineer on the San Nicolas operation.
Although the Marin plant would be comparable in size to Santa Barbara's - producing 5,000 acre-feet annually - it would cost nearly twice as much. The water it would produce would be cleaner than Santa Barbara's and more expensive at up to $2,400 per acre-foot. (Costs of Santa Barbara's desalinated water is projected to be $1,866 per acre-foot.) The Marin facility would be built as a permanent fixture, while the other facility will be housed in trailers.
There are several ways of removing the salt that makes up 3.5 percent of salt water: distillation, freezing, electrodialysis, and reverse osmosis, the process used on San Nicolas and in most commercial plants, including the Marin and Santa Barbara projects. Reverse-osmosis systems squeeze seawater against a thin plastic membrane that allows pure water - but not dissolved salts - to pass through.
Less energy required
Although reverse-osmosis pumps consume high quantities of electricity, the systems usually require far less energy than desalination plants that must boil seawater so fresh water can be extracted from steam.
``With oil prices going where they are going, that becomes significant,'' says Arthur Whipple, president of Campbell-based Aqua Design Inc., which has built 100 reverse-osmosis desalination plants, mostly in the Caribbean.
Marin Water District spokesmen contend that desalination plants may be less expensive than the two most likely alternatives: shipping spring runoff water from the Russian River in Sonoma County to Marin's system, or buying water from the Yuba River, nearly 100 miles away. Mr. Castle puts the price of a Russian River water project at $120 million and estimates it would cost $180 million for water from the Yuba River.
Building pipelines to distant areas is becoming politically more difficult because of the permitting process and other requirements, and because anyone with excess water is reluctant to let go of it, says Bill Katz, a spokesman for Ionics Inc. Environmental impact assessments are required for desalination projects. Both Marin's Castle and Santa Barbara's Mr. Ramsdell claim current public reports show that environmental impact is negligible.