A group in Maine has petitioned the state Board of Environmental Protection to amend the noise rules in the state Site Location Law to set lower limits for wind farm noise than for other sources of community noise.  The group, the Citizen’s Task Force on Wind Power, is formally asking the state to consider a question that has become central to siting controversies nationwide: is the nature of wind turbine noise different enough from road or factory noise to warrant lower noise limits?  The BEP will hold public hearings to consider the question.

A growing number of acousticians and medical professionals have raised concerns that standard community noise standards are not likely to provide the same level as protection from wind farm noise as they do from other noise sources.  There are several reasons put forward for this, including:

• The prevalence of amplitude modulation.  The pulsing quality to the sound, rising and falling slightly in loudness at about once a second, adds to its noticeability and annoyance (this is often related to the presence of a wind shear, or higher wind speeds at the top of the turbine blade rotation than at the bottom).
• The low-frequency character of turbine noise.  Separate from the controversial question of direct health effects from exposure to moderate levels of infrasound, wind turbine noise is weighted toward lower frequency audible sound as well, which travels farther than higher frequencies, penetrates homes better, and is not fully represented in A-weighted dB measurements.
• The unpredictable 24-hour nature of the sound.  Other common community noise sources quiet down at night, often becoming totally inactive, rather than continuing at the allowed 45dB.
• Large difference of turbine noise and natural ambient at night is disruptive. Night time wind farm noise at current 45dB standard can easily be 15-25dB louder than quiet rural ambient noise level.

Currently, state regulators are relying on the state’s generalized community noise standards in approving wind farms.  According to Cynthia Bertocci, an analyst for the BEP, a public hearing will be held to address the petition to change the regs for wind farms, though a date has not yet been set.  The Citizen’s Task Force proposes nighttime noise limits of 35dB at homes; while turbines would still be audible outside in many cases (night time ambient in rural areas is often 20-25dB, and sometimes even lower), noise inside should be minimal.  This would like require setbacks of close to a mile.