SOUTHERN CALIFORNIA’S ENVIRONMENT At the Crossroads : The Ocean: <i> OUR SEA, ITS CREATURES AND MAN</i> : San Onofre--Cooling System Is the Threat

Driving past the San Onofre nuclear power plant on the northern San Diego County coast, it’s hard not to think about the radiation inside the domed reactor buildings.

But San Onofre’s impact on the environment is caused not by radioactive contamination, which is negligible, but by the plant’s cooling system.

Each day, San Onofre draws enough ocean water to cover a one-square-mile area 14 feet deep. The sea water pumped into the plant from near the shoreline is often naturally murky. But when it is returned to the ocean, it is pushed offshore, where it mixes with clearer waters. Eventually, the muddy water passes over the biologically rich San Onofre kelp bed, a key habitat sheltering hundreds of species of plants, fish and invertebrates.

A 15-year California Coastal Commission study recently concluded that water from the power plant has reduced natural light in the kelp forest by an average of 16%. Moreover, the plume may be increasing silt deposits on the ocean floor. Scientists believe the low light and higher sediment levels may be responsible for a 60% decrease in the growth rate of kelp in the San Onofre area.

Fish living near the bottom of the kelp forest have been reduced by 70%. Aside from the impact on the kelp habitat, the commission’s review panel calculated that 56 tons of fish are killed each year when they are sucked into the plant’s cooling water intake system.

Fish Lost

Several hundred tons of fish, mainly “fodder” eaten by other sport and commercial species, are believed lost because their larvae are killed when they are flushed through the cooling system. The experts estimate that 13% of the queenfish stock in the Southern California Bight (between Point Conception and Cabo Colnett in northern Baja California) has been lost, 6% of white croakers and 5% of California grunion. A 5% loss of white croakers translates to about 3 million fish or 300 tons.

But the news isn’t all bad. The numbers of small invertebrates such as worms and clams and shrimp-like crustaceans near the plant have increased, most likely because organic matter in the muddy plume falls to the ocean floor and becomes a major source of food for them.

To lessen the San Onofre plant’s impact on marine life, the review panel has called for--and the Coastal Commission is evaluating--a combination of measures such as building an artificial reef and scheduling routine plant shutdowns to coincide with periods when fish larvae are most plentiful.