PG&E’s chosen way to map offshore faults is questioned

San Luis Obispo County Supervisor Bruce Gibson is questioning whether PG&E plans to use the best technology available when it conducts high-energy seismic surveys off Diablo Canyon nuclear power plant late this year.

On June 20, Gibson sent a detailed letter to PG&E outlining the concerns he has about the equipment and techniques the utility plans to use when it maps the earthquake faults offshore. Gibson holds a doctorate in geophysics and sits on an independent peer-review panel that oversees PG&E’s seismic studies.

“Given longstanding concerns regarding the seismic threat posed by the geologic setting near Diablo Canyon — concerns heightened by the Fukushima disaster — the public deserves to know that the best possible seismic survey technology is applied to the studies PG&E is undertaking,” Gibson said in his letter, referring to the Japanese nuclear plant where damage from last year’s massive earthquake and tsunami led to a meltdown.

The county Board of Supervisors briefly discussed Gibson’s letter during its meeting Tuesday. Supervisor Adam Hill said he would like PG&E to make a presentation to the board to address Gibson’s concerns.

The offshore seismic surveys will emit very loud sounds into the ocean environment and are expected to drive away fish and possibly injure marine mammals. Hill said he wants to make sure the best possible results are obtained from the survey in order to justify the environmental impacts.

Jearl Strickland, director of nuclear projects at Diablo Canyon, said PG&E’s seismic team is available to give a presentation to supervisors. He plans to send a letter responding to Gibson’s concerns by Friday.

Specifically, Gibson said PG&E plans to use a vessel and equipment used in academic research instead of technology of a higher quality used by private industry, such as oil companies, that could yield a better look at the earthquake danger facing Diablo Canyon.

For example, private industry uses research vessels that tow larger arrays of hydrophones to pick up seismic sound blasts than the one PG&E plans to use. Strickland said that the large array suggested by Gibson would be unsuitable for the Diablo Canyon research, which will be conducted close to shore and in very shallow water.“You can’t make turns in shallow water with big arrays,” Strickland said. “The arrays tend to drop during turns and could hang up on the rocks.”

PG&E’s seismic surveys are regulated by the State Land Commission, which is expected to issue a final environmental impact study on the project within the next 10 days. The commission will hold a final hearing on the project Aug. 14 in Sacramento, Gibson said.

The commission is expected to make its final decision on the project by mid-September or early October, Strickland said. This should give PG&E enough time to conduct the planned 33 days of at-sea surveys by Dec. 15.