MONTPELIER >> Legislators approved a set of temporary sound limits on wind turbines Thursday morning that opponents maintained did not follow the intent of the Legislature.

Approval by members of the Legislative Committee on Administrative Rules puts the rules, until now only provisional, into full effect.

Analysts for the Public Service Board said the rules uphold what legislators wanted. The chairman of the legislative committee that approved the enabling legislation agreed.

The most controversial element requires sound levels from wind turbines to not exceed 30 decibels inside nearby homes.

The question of whether interior sound levels ought to be measured with a homeowner's windows open or closed became the point upon which the rules' opponents took their stand.

Opponents to the new rules said the standards should establish at the minimum a volume limit of 30 decibels inside a home, but measured with open windows regardless of the time of year.

The new rules stipulate that that level be measured with affected homes' windows open in the summer, and with the windows closed in the winter.

A lobbyist employed by a prominent anti-wind turbine group said the provision calling for the measurements to be done with closed windows violates the intent of legislators. The new law passed this year — Act 174 — calls for the Public Service Board to write sound rules no less restrictive than the most restrictive standards applying to any existing wind turbine of comparable size.


The most restrictive permit for an existing wind turbine, argued John Brabant of Vermonters for a Clean Environment, requires that interior sound levels remain below 30 decibels year round, regardless of whether an affected home's windows are open.

In other words, by basing winter-time sound measurements on a house with closed windows instead of open, the board's new rules actually diminish the regulatory burden wind developers bear, Brabant argued. This would pose a problem, since the board was directed through Act 174 to devise rules no less stringent than the most stringent existing permit for a turbine of comparable size.

Representatives from the Public Service Board argued that the most restrictive existing permit for a wind turbine — for the Kingdom Community Wind project in Lowell — actually doesn't require what Brabant claimed.

Instead, said PSB analyst Kevin Fink, the project's permit describes an "attenuation value" derived from sound levels measured with both open and closed windows. That attenuation value is what a developer would use to model ongoing interior sound levels without placing monitoring equipment in a homeowner's bedroom for months at a time, Fink told legislators.

A developer might use such an attenuation value as part of sound monitoring plan, which is a plan developers put in place if neighbors aren't satisfied that a turbine owner is upholding sound limits in the project's permit.

Without such a plan, the Public Service Board assumes an attenuation value of 15 decibels, so that a turbine is typically thought to comply with an interior sound limit of 30 decibels when exterior sound levels don't exceed 45 decibels.

But the sound monitoring plan is never even written unless neighbors both complain about the noise and request an alternative sound measuring process, Fink said.

Even after a plan is written, however, the 30-decibel interior sound limit Brabant describes doesn't strictly exist, Fink said.

Rather, again to avoid requiring developers to install sound monitoring equipment inside nearby residents' homes, the interior sound level in a house is derived by subtracting the home's "attenuation value" from the outside sound level. Developers propose that value to the Public Service Board, and support it with evidence gathered by testing the home's true attenuation value.

The board may refuse a developer's proposed sound monitoring plan if it doesn't appear to ensure turbines don't exceed their permits' sound limits.

The clause in the Lowell permit that Brabant referred to, of sound measurements taken from inside a home with open windows, comes from the section of that turbine's permit that spells out how developers should come up with attenuation values in the event that they're needed for a sound monitoring plan.

It does not stipulate whether the 30-decibel interior sound limit is actually measured, on an ongoing basis, with windows open or closed, Fink said.

Therefore, since the most-restrictive existing wind-turbine permit doesn't say that sound limits must not exceed 30 decibels within a home whose windows are open, the proposed rules don't establish a less-restrictive standard, Fink said. In other words, the rules don't violate the legislation's purpose, nor do they relax sound restrictions, but rather the rules add specificity that the Lowell project's permit doesn't contain.

The chairman of the House Natural Resources and Energy Committee, Rep. Tony Klein, D-East Montpelier, also chaired the conference committee made up of senators and representatives that ultimately hammered out Act 174's details.

That act is the one that required the PSB to write the new noise rules, and Klein said the new rules comply entirely with legislators' intent when they wrote the act.

Klein said he reviewed the rules and told the Public Service Board he approved of them before the board submitted the rules to the Legislative Committee on Administrative Rules. It's standard procedure for chairs of committees to review rules arising from legislation over which they presided, Klein said.

"I signed off on them," Klein said of the rules. "I said they did meet legislative intent."

"I don't really understand what the kerfuffle is," Klein said. "I think the standards for the temporary rules are pretty much what they are today."

The temporary sound standards will apply until July 1 at the latest, before which time the Public Service Board must embark upon a more lengthy and considered rulemaking process to adopt permanent wind-turbine sound standards.

Mike Polhamus writes about energy and the environment for VTDigger.