The California Coastal Commission has rejected plans by Pacific Gas and Electric to conduct a seismic survey later this month to gain better understanding of earthquake faults near the Diablo Canyon nuclear power plant. The CCC vote affirmed staff recommendations that the information gained did not justify the likely effects on ocean life.
The survey would have included about nine days worth of airgun activity; the airguns fire bursts of pressurized air up to four times per minute. The sound created by the burst of air is loud enough to penetrate deep into the ocean floor, with echoes revealing geological information. The project’s environmental assessment documents project that the sound could be audible for up to 60 miles alongshore, and 150 miles offshore; sound loud enough to trigger behavioral changes extends for 2-3 miles, and sound loud enough to cause injury extends to about a half mile. The survey tracks (purple and blue above) come within a mile or so of one corner of a Marine Protected Area (orange outline above).
While most local species would be minimally affected (less than one percent of regional stock hearing sounds loud enough to trigger behavioral reactions), the potential impact on harbor porpoises were a sticking point for the CCC—75% of the local stock was expected to experience some level of behavioral change. (Ed. note: Harbor porpoises are known to be more sensitive to noise than many species; some environmental assessments extend the behavioral impact zone for them out to the audibility distance; I’m not sure if that was done here, but it would seem plausible, given the much higher proportion of the regional population expected to be affected.) Though PG&E said that any negative effects were likely to be minor and temporary (and NMFS agreed, in issuing draft federal Incidental Harassment Authorization in September). The CCC disagreed, in part because PG&E has already established that the Diablo Canyon plant can survive nearby earthquakes; some CCC members spoke in favor of simply closing the plant when it’s up for license renewal, which would negate the need for further earthquake study.
“These tests are not going to do us any good in terms of protecting the public welfare,” said Commissioner Jana Zimmer. “And on the other side of it, the impacts on the marine environment are very clear and I think have been understated.”
For more detailed coverage, see articles from the Santa Cruz Sentinel/San Jose Mercury News and The (San Luis Obispo) Tribune. The most recent project description from PG&E is here; and the NMFS draft IHA includes tables detailing the projected numbers of animals to be affected.