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Turbine noise stirs up new siting rules  

Credit:  By Jack Rodolico, Climatide, wgbh.org 12 September 2011 ~~

As of now wind turbines proposed in Massachusetts are permitted on a local level. But with an eye toward protecting human health, a network of municipal, county, and state rules will soon change how wind turbines are sited on Cape Cod.

From the Bottom to the Top

According to Steven Clarke, the Assistant Energy Secretary with the Executive Office of Energy and Environmental Affairs, “There are no statewide standards for citing any energy generation source that is smaller than 100 MW of installed capacity.” For perspective, all turbine facilities in Massachusetts come in well under this threshold.

But town councils on Cape Cod, the Barnstable County Assembly of Delegates, and the Massachusetts legislature are all advancing new rules for siting turbines that aim to keep neighborhoods quiet. The town of Bourne passed rules this month, while Barnstable County and the state could pass legislation within the next year.

Each set of rules starts at a similar baseline but diverges on specifics. While all call for limits on turbine noise, each might wind up setting different limits. Everyone agrees that a sound study is the best way to determine appropriate noise levels for a given neighborhood. In other words, an unbiased engineer studies your neighborhood and says, “People living here are used to a certain sound level.” But things get sticky when answering this question: How loud above ambient noise levels is appropriate? Here is what Bourne, Barnstable County, and the state have to say so far.

Bourne’s new rules apply to all wind turbines. Noise levels cannot exceed 6 dB(A) above ambient sound at the closest property line. An overall cap is placed at 65 dB(A) during the day and 40 dB(A) at night.

Barnstable County is proposing rules regulating turbines larger than 660 kW. Proposals would be subject to an independent sound study and (potentially) be limited to a setback distance of 10 times the rotor diameter. The county would put limits on both ambient sound (dBA) and low-frequency infrasound, which has become a controversial focal point in the debate over alleged health impacts of wind turbines. Proposals would also need contingency plans in case turbines are too loud, including reduced operating procedures and a decommissioning plan. There is still no stated cap on noise levels.

Massachusetts’ current rules cap turbine noise at 10 dB(A) above ambient noise levels. The governor’s office is still hoping for passage of the Wind Energy Siting Reform Act (WESRA). WESRA is more focused on streamlining the permitting process than regulating noise, but a sound study will be a part of any future proposal. The parameters for a sound study are still loosely defined.

Who Overrides Who?

So what happens if an industrial turbine is proposed in Bourne, which resides in Barnstable County, which in turn resides in Massachusetts?

WESRA (not yet law) is designed to allow the state to override municipal governments. In other words, if a permit is refused locally, a permit seeker could go to the state’s Energy Facility Siting Board for review. WESRA would also allow a permit seeker to skip the municipality initially, going directly to the state for a 9 to 18 month review.

However, the Cape Cod Commission (the legislative branch of Barnstable County) has jurisdiction over the state. So proposals in towns on the Cape will most likely wind up in front of the CCC, rather than the state’s Energy Facility Siting Board.

And then there is Bourne. If Bourne’s rules wind up being more restrictive than those passed by the county, turbine proposals would have to make it through the CCC and then through the Bourne Town Council. So the county gets first dibs on a proposal, but Bourne could get the last word.

But are any of these rules going to keep people’s homes quiet? Maybe, but it is hard to say right now for two reasons: People experience sound subjectively, and none of these rules have been implemented yet.

Quick guide to decibels

When it comes to sound, there’s a distinction between what’s generated and what’s perceived. The decibel scale is an indicator of loudness (perception) that is calculated from the actual power of the vibration, or sound, generated.
There are different decibel scales. The dB(A) scale is intended to reflect human hearing capacity and is most commonly used. The dB(C) scale is sometimes used in industrial settings because it gives more weight to low-frequency sounds that are harder (or impossible) for humans to hear.
The decibel scale is logarithmic. That means that adding 3dB is a doubling of sound, and adding 10dB is a ten-fold increase.
50dB(A) is roughly equivalent to the background noise in a busy office, 60dB(A) to normal conversation.

Source:  By Jack Rodolico, Climatide, wgbh.org 12 September 2011

This article is the work of the source indicated. Any opinions expressed in it are not necessarily those of National Wind Watch.

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