County Questions Diablo Seismic Analysis Methods

By Published On: July 20, 2012

Seismic studies for Pacific Gas & Electric’s Diablo Canyon nuclear plant are being customized to underwater terrain and conducted in concert with government, academics, and industry, according to a July 13 letter to San Luis Obispo County. San Luis Obispo County supervisor Bruce Gibson, a geophysicist, questioned the equipment PG&E plans to use because it may be inconsistent with “state-of-the-art seismic reflection imaging practices.” The public deserves application of the “best possible seismic survey technology,” he added in a June 20 missive to the utility. Concerns about the testing impacts to aquatic flora and fauna remain. PG&E noted in a detailed response how it plans to carry out initial two- and three-dimensional studies of the geological marine terrain surrounding the facility. The county board of supervisors made no follow up in its July 17 meeting. Gibson noted he’s still evaluating PG&E’s response. Gibson suggested methods to decrease the environmental impacts of testing. The utility countered that the terrain discourages alternatives. PG&E was granted $16.7 million by the California Public Utilities Commission in 2010 to conduct seismic testing. After the initial spending authorization, the utility went back to the commission for an additional $47 million for the studies. The latter request remains pending. Environmental effects from the technologies used for the studies are expected to be significant, according to a draft Environmental Impact Report from the State Lands Commission in March. Whales, porpoises, and sea otters are presumed to be deafened by sonic blasts. Marine biological resources, air quality, greenhouse gas emissions, and recreation are also expected to be impacted. For instance, the environmental report establishes that the decibel level from hardware used in the studies would be far beyond literal earsplitting levels. That is, an ear drum ruptures at 160 decibels. The seismic studies are set to use equipment that producer twice that degree in underwater tests. Despite that, environmentalists of the anti-nuclear variety support the studies. In essence, they believe the more the public knows about earthquake hazards to the nuclear facility--and the resulting risk of radioactive releases--the more interest there will be in shutting down the facility. PG&E is seeking a 20-year license extension for Diablo Canyon through the Nuclear Regulatory Commission. Uncharacteristically, federal regulators put the brakes on approving the nuclear plant’s relicensing in June 2011. The commission determined that while the relicensing process continues at the staff level, a final response is to wait on seismic data received from the state studies. Feeding into this is the 2008 revelation of the Shoreline fault within a kilometer of the facility. That discovery started the Central Coastal California Seismic Imaging Project, with academic, industry, and governmental involvement. According to PG&E, a study of the Shoreline fault in 2011 found some challenges for further studies as the area is “underlain by the highly chaotic Mesozoic Franciscan Formation.” That discovery begs the question of how to conduct further 3D studies, or if they would be accurate, noted Jearl Strickland, PG&E director, nuclear projects. More well-known is the Hosgri fault. That fault lies 5 kilometers from the plant. That fault was discovered in the 1970s when PG&E was building the Diablo facility. The nuclear plant is designed to withstand a 7.5 magnitude earthquake.

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