The complex rules of dealing with wind turbine noise limits

Report from the Legislature

Although the legislature is not in session, many legislators serve on special committees that meet between sessions. The Legislative Committee on Administrative Rules (LCAR) is one such committee, and it’s been keeping me busy this summer. LCAR consists of four Senators and four Representatives and is responsible for reviewing rules proposed by agencies of the executive branch of state government. Rules spell out the process by which an agency administers laws. Examples include the health standards of hotel accommodations, licensing of professionals, and standards for fuel oil tanks in our homes. It is LCAR’s job to review the rules to ensure that:

  1.  the rule is not arbitrary,
  2. the rule is within the authority delegated to the agency,
  3. the rule is not contrary to the intent of the legislature,
  4. the agency provided an opportunity for maximizing public input,
  5. the rule is written in a satisfactory style, and
  6. the rule is accompanied by an adequate economic impact statement.

While many rules are fairly straightforward, others generate a substantial amount of contention and involve lots of analysis, testimony, and legalistic considerations. LCAR is not a policy-making committee and can only object to a rule or a portion of a rule if it violates one of the criteria listed above. Some rules require more than one meeting to pass muster, and LCAR can point out shortcomings and ask for revisions.

One of the most complex rules we had to consider is the one dealing with limits on noise produced by wind turbines. This rule came before LCAR in May from the Public Utilities Commission (PUC) with close to a thousand pages of comments both pro and con and wasn’t adopted until this week, after several LCAR objections to certain elements on the basis of being arbitrary or contrary to legislative intent. The objections focused on a setback, the maximum sound levels for nighttime and daytime, sound propagation modeling, and post-construction noise monitoring. I apologize at this point for the following very technical explanation of our consideration of this rule.

The PUC was tasked by the legislature in 2016 with determining maximum allowable noise levels near residences to safeguard public health. This legislation was passed in response to complaints by some residents living near existing utility-scale wind facilities. The PUC examined a variety of studies and heard testimony from numerous proponents, opponents, environmentalists, and developers. One provision required a wind turbine to be located no closer than ten times its height to the nearest residence, nearly a mile in the case of a utility-scale turbine. In addition, based on a 30 decibel indoor World Health Organization criterion for undisturbed sleep and an assumption that sound levels would attenuate, i.e. diminish, by 10 – 15 decibels from the exterior of a residence to the interior, the PUC set the nighttime limit to a more conservative 39 decibels measured 100 feet from a residence. They also assumed that using a Noise Reduction Operation (NRO) mode, turbine noise could be reduced by 3 decibels, and therefore set the daytime limit to 42 decibels.

To obtain a Certificate of Public Good (CPG), a developer would be required to model the sound propagation using a standard acoustic model based on the location of every proposed turbine and existing residence using the maximum output noise level of the turbines. If the CPG were granted and the turbines built, the developer would then have to conduct measurements of the turbine sound filtering out ambient, i.e. background, sounds according to a specific protocol. Up to 200 measurements per second would be taken over several hours both during the day and at night and then analyzed and reported to the PUC periodically. You can imagine the detail that LCAR had to deal with in evaluating whether the rules as proposed satisfied the criteria above.

In objecting to the ten times height setback rule, the majority of LCAR members agreed that a distance requirement was arbitrary because there is no direct correlation between distance and sound levels. The sound levels in general decrease with distance, but the amount of decrease depends on topography, atmospheric conditions, temperature and season. In setting sound level limits, the committee agreed that decibel levels at a residence were an appropriate standard, but not distance. Setbacks are appropriate for safety and other considerations, but not for sound levels, which is what this rule deals with.

The sound level limits themselves were considered to be somewhat arbitrary in that there were various studies that specified different attenuation estimates from outside to inside. Furthermore, the most conservative values were used by the PUC, and the estimated uncertainty in both the modeling algorithm and the manufacurer’s specifications would have to be added to the model results. Environmental groups asserted that the rules would effectively preclude utility-scale wind development in Vermont. That result would be contrary to the intent of the legislature which recognizes in statute that large wind generation is an effective and competitive source of renewable energy.

Other objections were raised because the rules were not clear as to why the monitoring data had to be so granular (200 data points/second) and what constituted a violation of the sound level limits. The PUC responded to LCAR’s objections with modification to the rules to clarify modeling and monitoring protocols as well as to remove the setback requirement which they agreed was redundant with the sound limits. The use of the NRO mode to model nighttime levels was allowed, and the modeling and manufacturer uncertainties will be used as guidance rather than as a penalty for the modeling results. The monitoring measurements will be done in 1 second intervals to reduce the amount of data which will be averaged over 2 hours of data to determine actual noise levels. With these changes to the rule, LCAR voted to approve them.

Unfortunately, the conservative application of the nine decibel exterior-interior attenuation was not changed. However, since enough of the conservative assumptions were mitigated, and since the PUC asserted that the rule would not preclude utility-scale wind projects in Vermont, I felt that the rule met the criteria for approval and voted in the affirmative.

As always, feel free to contact me anytime. I can be reached by phone at (802) 233-5238 or by email. You can find this article and past articles at my website.