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Once-Through Once-Over

A controversial proposal to more than double the size of the Potrero power plant in San Francisco faces an important March 21 vote of the S.F. Bay Conservation and Development Commission (BCDC). The commission will decide whether or not to back the Mirant Corporation's plan to construct a "once-through" cooling system for its natural gas turbines, which supply local electricity.

The plant currently generates about 360 megawatts. The new construction would add another gas-fired turbine, and produce 570 more megawatts. Neighborhood activists and environmentalists have long opposed the new plant, citing air quality, noise, and environmental justice concerns.

Aquatic activists have other concerns. Once-through cooling constantly sucks Bay water to cool the turbines and recirculates it, heated, back into the ecosystem. The older turbines use this technology, taking approximately 226 million gallons of water per day. The new generator would add another 228 million gpd to that total.

BayKeeper's Jonathon Kaplan says that alternative technologies can be used to cool the turbines without causing so much damage, among them air cooling with fans or a "hybrid" air/water system using less water.

Mirant admits that millions of fish and other critters are killed by the coolers, but insists that once-through is the best available technology. Mirant's Ron Kino says there isn't room on the 20-acre power plant site for the alternative system's cooling towers. Another possibility, using San Francisco's "gray water," may not be feasible either, he says, because the city may not be able to provide a water supply on a 24-hour, 365-day-a-year basis.

"Their assessment is inadequate," counters Kaplan, pointing out that the company didn't even consider the purchase of nearby properties to accommodate new towers.

A staff report from the California Energy Commission (CEC) largely supports Kaplan's position. "The proposed use of once-through cooling creates potentially significant impacts on aquatic biological resources that may not be mitigable," it states. The staff also concluded that either hybrid or dry cooling would work, and it favored using reclaimed city water, which, it noted, would reduce the amount of treated water discharged into the Bay.

BCDC is scheduled to take up the issue at its next month's meeting. Its vote is technically a recommendation to the CEC, which has the final decision on which cooling system the plant will use. O'B

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