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Although the FAA contends that the NorCal changes will translate to $6.5 million in annual fuel savings, critics have said that this amount is relatively insignificant given the size of the metroplex. Landesmann further argued that this financial benefit for the private airline industry does not justify the severe disturbances now plaguing numerous communities in the region.
One problem with the FAA's analysis is that it averages sound levels over a 24-hour period. As a result, the measurement tends to mask the hardships residents can face at specific times of day.
"They have a responsibility to do realistic sound measurements that adequately measure the impact that they are putting on a community," said John Leopold, a supervisor in Santa Cruz County, which has also been hit with a substantial increase in noise complaints since the implementation of the NorCal Metroplex project. A relatively low-flying plane could cause a major disruption for a single minute, but if it happens several times in the middle of the night, that can clearly be significant for residents, Leopold said. "They could say that, on average, it doesn't cause a problem, but if it's 1 a.m., it doesn't take that many flights to wake you ... and ruin the quality of life in your neighborhood." (The FAA's 24-hour averages do take into account that nighttime flights cause greater disturbances, but critics said the metrics are inadequate).
Santa Cruz County residents have filed more than 8,000 noise complaints in recent months with San Francisco International Airport (SFO), when last year there was only one complaint from the area. And Leopold said he's received roughly seven hundred emails with complaints about jet noise since March when the FAA switched to the new NextGen procedures, thereby increasing loud traffic over parts of Santa Cruz. That constitutes the most intense feedback he has ever received on a single issue in his seven years as a supervisor, he said.
For residents and local elected officials throughout the region, the widespread backlash clearly contradicts the FAA's findings last year that the new flight routes would have "no significant impact," even in areas underneath the new aerial highways. In addition to Santa Cruz and Palo Alto, parts of San Mateo County have also seen a surge in jet noise disturbances and complaints, prompting residents from Portola Valley and Woodside — roughly 25 miles south of SFO — to file a petition in federal court against the FAA, challenging its environmental assessment.
In general, the FAA's threshold for aircraft noise that causes adverse impacts is unreasonably high, critics said. That inadequacy is exacerbated by the fact that the measurements fail to meaningfully consider existing levels of quiet in certain areas.
Increased decibel levels, even relatively minor ones, can also create hazards in some of the most sensitive habitats in California — where there are no human residents to speak up, and where noise pollution can have significant consequences.
The noise from commercial jets can be confusing — and hazardous — at times because it mimics a number of natural sounds in wilderness areas. Kurt Fristrup, a National Park Service senior scientist and leading expert in natural sounds, has experienced this firsthand. Fristrup, who is based in the NPS's offices in Fort Collins, Colorado, regularly hikes the state's "fourteeners" — mountains with an elevation higher than 14,000 feet — and has on occasion been confused by the noises around him.
"The sounds of high-altitude jets are remarkably like some other sounds in nature," including that of thunder, avalanches, and flash floods, said Fristrup, in a recent phone interview. Despite his extensive hiking experience and years of research on natural sounds, he said he has sometimes doubted that hazardous weather conditions were occurring in the wilderness — because he thought maybe he was just hearing another jet flying above.
"We get used to common sounds," he continued, explaining that because aircraft flights are so frequent over some parks, "the presence of jet noise sort of reduces people's expectations or conditions them not to notice it as much." In other words, people are increasingly accepting jet noise as a normal part of the wilderness.
In the same way that the NPS has a responsibility to protect the physical resources of national parks — often working to restore a park's conditions to its natural state before human intervention — the federal agency is also obligated to preserve natural sounds. Both the Organic Act of 1916 (which established the NPS as a government body) and the Wilderness Act of 1964 (which created landmark conservation principles) identify natural sounds as a resource that requires protection. And in 2006, the NPS updated its own soundscape management policies to state that the park service will take actions to prevent or minimize all human-caused noise that adversely affects park resources.
"If we have a natural condition, we will work to not let it get worse, and if we have an impact, we will work to get it back to natural," explained Rocchio, the San Francisco-based NPS official.
NPS experts have published extensive research illustrating why the natural soundscape is a vital component of wilderness ecosystems. Just as habitat fragmentation from roads can make it harder for animals and species to survive, loud noises can negatively impact natural processes. For example, noise pollution can interfere with intra-species communication, courtship and mating, nurturing and protecting young, predator and prey dynamics, and the establishment of territories.