Excessive Wind Turbine Noise

Faulty Noise Testing Practices and Consequences

By Chris Kapsambelis November 30, 2020

State Law and Regulations

In the state of Massachusetts, noise is limited to 10 dBA above ambient. The Massachusetts Department of Environmental Protection (MassDEP) is responsible for how this standard is interpreted and applied. In a document titled “Noise Pollution Policy Interpretation,” MassDEP states:

• Noise is defined as “sound of sufficient intensity and/or duration as to cause a condition of air pollution.”
• Air pollution means “the presence in the ambient air space of one or more air contaminants or combinations thereof in such concentrations and of such duration as to: (a) cause a nuisance; (b) be injurious, or be on the basis of current information, potentially injurious to human health or animal life, to vegetation, or to property; or (c) unreasonably interfere[s] with the comfortable enjoyment of life and property or the conduct of business.”

Based on this document, as an air pollutant, noise is supposed to be regulated as the combination of sound from all sources.

In the MassDEP acceptance of noise pollution studies related to wind turbine noise, the first thing to notice is that wind‐turbine noise is assessed in isolation, and not in combination with all other sources as the definition of air pollution noise requires. As a result, wind‐turbine noise above ambient that exceeds the legal limit of 10 dBA, to as much as 20 dBA and more, is permitted. This false acceptance of twice the legal limit by MassDEP explains the large number of noise complaints by local residents.

Wind‐Turbine Testing Protocol

The wind‐turbine test procedures accepted by MassDEP fail to measure the combined noise level above ambient necessary to establish the maximum noise impact on the community, as required. To determine compliance, the MassDEP accepts a process whereby the combined noise is measured, followed by a period where the turbines stop rotating and measurements of the ambient sound levels are recorded. This method fails to get a true measure that can satisfy the definition of noise air pollution contained in the referenced document “Noise Pollution Policy Interpretation.”

A list of these failures follows:

1. By measuring the maximum noise level in the middle of the night when noise from existing sources is mostly missing, only the noise emitted by the wind turbines is measured. This is in conflict with the definition of Air Pollution, which is regulated as a combination from all sources.
2. Ambient sound, measured with the wind turbines off, fails to record the ambient sound level that existed before the turbines were installed. High levels of nighttime wind due to windshear, when the wind at rotor level is 5 times stronger than that at ground level, generates aerodynamic noise by striking the stationary blades. This can result in a 5 dBA increase in ambient levels over that of preconstruction.
3. While daytime measurements can satisfy air pollution requirements to include noise from all sources, MassDEP has accepted results taken when noise other than that generated by wind turbines was absent, and has permitted reductions attributed to noise from sources other than wind turbines. These procedures are in conflict with the state’s definitions of noise as an air pollutant and air pollutants as regulated in combination from all sources.
4. Daytime ambient measurements with the turbines off fail to satisfy the definition of Air Pollution as the combined noise from all sources. If air pollution is the combined noise from all sources, then ambient sound must be the left‐over sound when sound from all identifiable sources is absent. The only time that condition can be satisfied is in the quiet of night when sound from all other identifiable sources can be missing.

Conclusions

To satisfy the intent of the law on air pollution, the current practice of measuring the increase above ambient sound as the difference between wind turbine “ON” followed shortly by measurements with the wind turbines “OFF” must be abandoned.

In order to measure the maximum noise (Lmax) from the wind turbines in combination with any existing sources of noise, a time must be selected during the day when all identifiable noise sources are active.

In order to avoid the aerodynamic noise from the stationary rotor blades, the ambient sound level (L90) needs to be determined prior to installation. The best time for this is the middle of the night when all existing sources of noise are silent.

Once these steps are taken, an assessment of compliance can be made based on the difference between the highest maximum sound with the turbines “ON” in combination with any other sources of noise and the preconstruction minimum (L90) at night when all sources of noise are silent.