Over objections of Central Coast residents and environmental groups, Pacific Gas & Electric plans to map earthquake fault zones near its Diablo Canyon nuclear plant by blasting high-decibel air cannons under the surface of the ocean.
PG&E;'s plan calls for towing a quarter-mile-wide array of underwater "air cannons" that emit 250-decibel blasts into the ocean every 15 seconds for 12 straight days. The sonic reflections would be picked up by underwater receivers and analyzed to provide detailed 3-D images of the geometry, relationships and ground motions of several fault zones near the Diablo facility, which generates enough energy to meet the needs of more than 3 million Northern and Central Californians.
"What we're after with this survey is the geophysical equivalent of a CT scan — a combination of imagery and information that we could slice and dice and scrutinize in great detail," said Jearl Strickland, director of nuclear projects for PG&E.; "These kinds of surveys are being performed right now around the world with no problems."
Opponents say the method threatens sea creatures from Central Coast rockfish to whales, and they dispute PG&E;'s claims that there are no alternative, less harmful technologies available for the job.
"We're not saying seismic testing isn't needed," said Andrew Christie, director of the Santa Lucia Chapter of the Sierra Club. "We want them to take the time to explore potential alternatives that could do less environmental harm and provide better data."
Of particular concern are potential effects at the Point Buchon State Marine Reserve, a protected sanctuary, as well as on a population of about 2,000 harbor porpoises that reside in and around scenic Morro Bay. Harbor porpoises are acutely sensitive to manmade sounds, which makes them especially vulnerable to hearing loss and injury during the survey.
PG&E; says environmentalists' fears are unfounded. The utility acknowledges that environmental effects will be significant and likely to include temporary displacement of most of Morro Bay's harbor porpoise population. But PG&E; says it believes the survey's benefits outweigh the environmental costs. The California Public Utilities Commission ordered PG&E; to conduct the risk assessment.
The utility initially planned to survey 90 square miles of coastline for 30 days beginning Nov. 1. But facing questions from state permitting agencies about potential environmental effects, PG&E; on Thursday scaled back the scope and duration of the project's first phase to demonstrate its safety and effectiveness.
The modified proposal would survey 51 square miles, stretch over 12 days and focus on portions of the Hosgi, Los Osos and newly discovered Shoreline fault zones in the Estero Bay area. It would not reach into the Point Buchon area.
If all goes according to plan, the project will be expanded next year to include two other areas targeted for surveys near Diablo Canyon, including a portion of Point Buchon.
The California Coastal Commission plans to vote Nov. 10 on PG&E;'s request for a coastal development permit needed to begin work offshore. Later, the California Department of Fish and Game must accept or reject PG&E;'s request for permits to harass, but not injure or kill, protected fish and marine mammals in the survey area.
In a recent letter to the Coastal Commission, the Natural Resources Defense Council warned that approval of the permits would "set a harmful and legally dubious precedent of allowing adverse impacts to the biologically significant habitats and species in California's marine protected areas in the absence of compelling public need to do so."
The organization also argued that the survey is not essential to assessing earthquake risks and is not likely to result in improvement in the nuclear plant's safety. In a separate letter to the commission, the Surfrider Foundation suggested that in-depth analysis of existing seismic data and "worst-case-scenario models" would provide equally effective emergency preparedness and response strategies.
Other critics have suggested that PG&E; use a larger vessel capable of towing longer lines attached to 10, instead of four, geophone receivers to record the echoes of the blasts. That way, researchers could cover a wider area in a shorter period.
PG&E; dismissed that idea because a larger vessel would not be able to traverse relatively shallow waters, which it says is essential to the study.
The survey was scheduled for November and December to avoid the peak breeding seasons of harbor porpoises and southern sea otters, as well the highest densities of migrating blue, fin and humpback whales. Certified "protected species observers" will be onboard vessels at sea and in airplanes, on the lookout for injured animals and carcasses. High-intensity blasts will be preceded by low-frequency sound waves aimed at scaring off fish and marine mammals.
If a sea otter were observed in the vessel's path, or a whale were spotted within a mile of the operation, the air cannons would be shut down within seconds, PG&E; said. The number of southern sea otters in the proposed study area is 352, according to the U.S. Fish and Wildlife Service.
The death or injury of an endangered species would trigger an investigation that could potentially result in prosecution, according to Christine Patrick, spokeswoman for the National Oceanographic and Atmospheric Administration.
"All those precautions might help animals that can swim away," said environmental activist Julie Tacker of Los Osos. "But what about those that can't, such as abalone, clams and starfish?"
Those kinds of animals tend to congregate near shore and are not expected to be affected by the air cannons, which would be pointed straight down in water more than 75 feet deep, PG&E; officials said.
Similar high-energy seismic surveys are planned for 2013 in coastal waters off Southern California Edison's San Onofre Nuclear Generating Station in northern San Diego County.