Clayton panel rethinking law on wind

By NANCY MADSEN
TIMES STAFF WRITER
SUNDAY, FEBRUARY 15, 2009
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CLAYTON — The town's wind committee got a tutorial on noise and advice on rewriting the noise standard in the local wind development ordinance at its meeting Thursday night.

After the session, some members said it may be time to consider changing the law.

The committee had a teleconference with Gregory C. Tocci, principal at Cavanaugh Tocci Associates, Sudbury, Mass. Mr. Tocci's firm evaluated the noise studies done in Clayton by consultant CH2MHill for Iberdrola and in Cape Vincent by consultant Hessler Associates for BP Alternative Energy.

Clayton's current law allows for 50 decibels of noise measured at off-site residences, schools, hospitals, churches or public libraries. But Mr. Tocci recommended the committee use a set number of decibels above ambient noise levels as a standard.

"If you use an arbitrary number, you run the risk that it is too low or too high," he said.

Audible sound is measured in decibels as A-weighted sound.

"When a new facility is introduced, a person's judgment isn't necessarily based on the A-weighted sound itself, but how the A-weighted sound compares to the sound in the environment before it was introduced," he said.

According to the state Department of Environmental Conservation, the increase should be less than six decibels.

"It is very likely to say that 50 decibels allowed in the law would be more liberal than the DEC would allow," he said.

Mr. Tocci said it is entirely possible that in the country, background noise could be in the 20 decibel range.

"It may rise to more than 40 in the day or 70 in cities," he said.

He explained a few common terms of noise measurement. Background sound is termed "L90," or the noise level that is exceeded 90 percent of the time. "L10" is noise that is exceeded 10 percent of the time. The average of noise energy measured over time is "Leq."

He recommended basing a noise standard on the L90, or background noise. Transient sounds, such as a dog bark or a car passing by, would not influence the L90, but could influence the Leq.

"There's an advantage in using the background sound level because transients are not included," he said. "The sound of a truck comes and goes, but a wind turbine stays."

Sound should be measured either in the winter or in both winter and summer.

He said the state gives no guidelines on how sound should be measured. The wind industry generally uses 10-minute intervals, but Mr. Tocci recommended hour-long intervals measured over the course of a week.

"The low points are not as low, and the high points are not as high," he said.

He also said sound monitors should be placed every one-quarter of a mile, and sometimes even farther apart based on the topography and number of nearby houses.

In the Horse Creek draft environmental impact statement, CH2MHill tried to correlate wind speed and noise level. Mr. Tocci said this was a reasonable assumption, but the measurements were inappropriate to show greater wind speed meant more noise.

"Wind speed needs to be measured reasonably close to the sound monitor to have a relationship to the sound level," he said. "Wind has nothing to do with background noise in the way they measured it."

The consultants used only five sound monitoring stations and fewer wind speed devices. They also used wind measurements from 10 meters — or almost 33 feet — above the surface.

"Because it's a phenomenon at ground level, the best correlation would be measuring wind at ground level," Mr. Tocci said.

He explained that industry standards have allowed researchers to use data from 10 meters above the ground and then calculate what the wind speed would be at the surface and at a wind turbine's hub height. That may no longer be appropriate, based on a recently published paper.

After talking to Mr. Tocci, many on the committee agreed the wind zoning ordinance needed to be revised, at least as far as the noise requirement is concerned.

"Do we need to proceed with changing the law?" member Leslie E. Drake asked. "I've digested enough to say it needs to be changed."