Two large stretches of beach in the county would be subject to levels of noise that are potentially harmful to humans if PG&E is allowed to proceed with its planned high-energy offshore seismic surveys this month.
A stretch of coastline north of Diablo Canyon nuclear power plant to the tip of the Morro Bay sand spit and another stretch from Cayucos to Harmony would receive from 154 to 160 decibels of sound, enough to cause harm to people who are submerged in the ocean for periods of 15 minutes or longer, according to PG&E.
In an effort to reduce the human exposure, PG&E would post warning signs at affected beach parking lots, trailheads and ocean access points containing information about the expected duration of the surveys and the levels of possible exposure, said Blair Jones, PG&E spokesman.
Scuba divers are considered at greatest risk due to their ability to stay submerged for long periods of time. As a result, dive boats would be prohibited from active survey areas.
Navy research shows that 154 decibels is the threshold for harm to humans but only if it occurs for 15 minutes or more, Jones said. The utility considers this a conservative estimate because natural features such as undersea rocks and kelp beds could attenuate the sound levels.
“Naturally occurring noise levels at beach surf zones reach approximately 145 decibels,” Jones said.
The proposal by PG&E to conduct the surveys faces a make-or-break hearing before the state Coastal Commission on Wednesday in Santa Monica. Staff is recommending the commission deny the application due primarily to the harm the testing could do to marine life.
The surveys would consist of emitting 250-decibel blasts of sound into the ocean every 15 seconds for nine days from late November through the end of the year. The utility proposes more testing for the same period next year if the first year of testing proves effective.
While opposition to the testing has centered on damage to marine mammals and other sea life, concern about potential impacts to swimmers, surfers and divers is also significant, county supervisors said in a letter to the Coastal Commission stating the board’s opposition to the testing as proposed.
“If it proves necessary to close areas of the ocean to these activities, then a closure protocol must be developed and mitigation for the lost recreational resource must be addressed,” the board said in the letter.
Supervisors have supported seismic surveys in the past but say the current proposal is inadequate because it fails to properly mitigate environmental and economic impacts and lacks an independent third-party review of the survey designs.
The San Luis Obispo County chapter of the Surfrider Foundation has spearheaded opposition to seismic testing due to potential human impacts. Chapter President Brad Snook said he expects a large turnout of members at Wednesday’s hearing and that the commission will be sympathetic to their concerns.
Unlike other state and federal agencies that have considered the seismic surveys, one of the commission’s main mandates is to improve coastal access. Posting warning signs on affected beaches and restricting diving will diminish that access.
“We need people to turn out and let our state officials know that needlessly putting citizens and our natural resources in harm’s way is unacceptable,” said Stefanie Sekich-Quinn, Surfrider Foundation’s California policy manager.