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Hilltown Archives The Altamont Enterprise, July 2, 2009
Dan Driscoll sounds off on turbine noise
By Zach Simeone
As towns form committees to draft legislation on wind turbines, a major concern is sound generated by the whirling blades. Daniel Driscoll, a certified sound engineer working on such an ordinance in the town of Knox, has suggestions as to how this sound should be measured and regulated.
In June, Driscoll took part in an environmental discussion at the Empire State Plaza, hosted by the New York State Energy Research and Development Authority (NYSERDA). Driscoll was on one of three panels of experts that answered questions that day.
Driscoll was asked to join the panel, he said, because of his lengthy career as a board-certified noise-control engineer, which included work at the Department of Environmental Conservation’s Noise Bureau, the Noise Control Engineering Society, and over 20 years at the New York State Public Service Commission, where he eventually led a team that assessed the environmental impacts of noise produced by power plants.
In the weeks following that discussion, Driscoll wrote a report that summarized his answers to questions pertaining to sound generated by wind-power structures that were asked at the June discussion. In his report, he prefaces his answers to these questions with a series of broad guidelines for the creation of zoning regulations for towns like Knox.
Some towns, Knox included, prohibit “excessive” noise, Driscoll said in his report.
“While suitable for neighbor-to-neighbor disputes, the prohibition is vague and may not be enforceable in court,” said Driscoll. One solution to this is specifying a numerical noise limit. “This allows for changes in wind-turbine technology, but towns must hire qualified noise-control engineers to help with creation and enforcement of the limit,” he said.
Also important is controlling how the noise source is operated, for example, with specified hours of operation, or with setbacks from residences or property lines.
Driscoll cited examples from research he had done on setbacks in ordinances of other nearby municipalities:
“The town of Cohocton (Steuben County, N.Y.) wind-turbine ordinance has a 1,500-foot setback for wind turbines from residences, adopted pre-2007;
“In January 2007, the town of Bethany (Genesee County, N.Y.) committee recommended 1,500 feet, based in part on Cohocton's ordinance;
“A Richmondville (Schoharie County, N.Y.) committee recommended a 2,500-foot setback in a May 2009 report;
“The town of Meredith (Delaware County, N.Y.) adopted a wind-turbine ordinance in 2007 with a 3,000-foot setback. In 2008, they rescinded the 2007 law and adopted a new law prohibiting industrial-scale wind turbines, but they kept the 3,000-foot setback in case the prohibition was overruled by the courts;
“Schoharie County has a recommended law for their towns that appears to copy Meredith's 2007 law with its 3,000-foot setback; and
“A Clayton (Jefferson County, N.Y.) committee recommended a setback of 4,500 feet from hamlet and village boundaries.”
Equally crucial is limiting the permitted increase in sound levels above the background-noise level, Driscoll added.
Explaining “background noise,” he said, “If you went to a rural community, and were to observe a sound-level meter, you would see that the sound was fluctuating around, say, 28 dBA [decibels], within a very small range. That is, until a dog barked, or a bird chirped, or a plane flew over, and then the sound would increase from that baseline of 28 dBA.”
That baseline is the background sound level. Similar is the L90 the sound level that is exceeded 90 percent of the time, in the absence of intrusive sounds, like birds, dogs, and airplanes also called the residual sound level.
“People generally tend to judge how loud or intrusive a new sound is with respect to that baseline,” Driscoll went on. “If we were in more of an urban situation, where there was lot of traffic noise in nearby streets, and the background sound level were more like 50dBA, and a bird down the street chirped, you might not even hear it, or, if it were closer, people would just barely hear it, because they judge these other sounds in relation to this steady background noise.”
To limit the permitted increase above the background sound level, Driscoll said in his report, “is the most accurate way to control community noise, and is the method recommended in [the New York State Department of Environmental Conservation’s] noise policy. But,” he went on, “in addition to the complexities related to setting and enforcing a noise limit, the background-sound level must be measured in a way that adequately protects the community.”
From there, Driscoll went on to answer the first question: “What research has justified the choice of 50 dBA as an appropriate noise criterion, particularly for rural areas of the state?”
In his answer to this question, Driscoll cites a publication by the Environmental Protection Agency’s called “Information on Levels of Environmental Noise Requisite to Protect Public Health and Welfare with an Adequate Margin of Safety” or the “levels document” for short.
This document, which Driscoll said is “such a respected document in the noise control community,” uses what is called the day-night sound level, or Ldn, as a measure of noise.
“The Ldn is the sound level energy averaged over 24 hours, with a 10-dBA penalty added to nighttime sound levels (10 p.m. to 7 a.m.),” Driscoll said, the basis for the addition of 10 dBA during those hours being that the nighttime is generally quieter than the daytime, resulting in a lower background-noise level.
In the levels document, the EPA explains that, after studying community reaction to different noise levels, a day-night sound level of 55 dBA was chosen to protect people from “outdoor activity interference and annoyance,” and that this limit applies to “residential areas and farms, and other outdoor areas where people spend widely varying amounts of time, and other places in which quiet is a basis for use.”
The second question asked: “Have studies been done in New York that identify the low frequency sounds (infrasound) from wind turbines, and their effects on humans and animals?”
While Driscoll is unaware of any studies done in New York State on the subject of infrasound, or sound below the threshold of human hearing, he has heard several first-person accounts from people living near wind turbines.
“The reason for the question, I think, was they were hoping I would refer to some of the people in New York State who have been publishing comments by people who live near wind turbines, and I didn’t consider that research,” Driscoll said.
He did, however, refer to the accounts he has heard of people’s reactions to this noise, which include reports of headaches, sleeplessness, nausea “a variety of strange effects,” said Driscoll.
“What happens with infrasound is, the sound vibrates the internal organs of the body,” he went on. “There was an anecdotal report by a little girl who lives near a turbine, and occasionally, she would say to her mother, ‘I feel the hamster running around in my chest again.’ That’s infrasound.”