ASA Lay Language Papers
161st Acoustical Society of America Meeting

Wind Turbine Noise Regulations at State and Local Levels

Isaac H. C.  Old – IOld@rsginc.com
Resource Systems Group
White River Junction, VT 05001

Emily J. Eros – EEros@rsginc.com             
Resource Systems Group
White River Junction, VT 05001

Edward C. D. Duncan – Eduncan@rsginc.com
Resource Systems Group
White River Junction, VT 05001

Popular version of paper 3aNSa5
Presented Wednesday morning, May 23, 2011
161st ASA Meeting, Seattle, Wash.

Wind power is one America’s fastest-growing renewable energy sources.  In 1998, the total generation capacity of utility-scale wind turbines was 2,000 megawatts (MW).1 In just over a decade, that level soared to 30,000 MW, placing the United States second, after Germany, for its gross generation capacity. Wind power is a viable part of clean energy infrastructure. However, like any power source, wind energy has downsides. Much opposition toward wind turbines centers upon their visual impacts and concerns about potential dangers to avian populations. A third, often less publicized issue is the noise produced by the rotating turbine blades.  Though wind turbines do not produce as high of sound emissions as many other industrial noise sources, they do produce a “whooshing” sound that has the potential to annoy and disturb those nearby – particularly at night. Part of the problem is that wind farms are often located in rural areas that typically have low existing sound levels.  Consequently, the moderate noise produced by the turbines becomes more prominent. Such impacts on nearby residents can be minimized through proper planning and siting. Thus, noise standards should be part of any set of wind turbine siting regulations.

Unlike countries such as the UK and Denmark, the United States does not have a quantitative national noise standards or guidelines for wind turbines. Some state regulations are in place, but these vary significantly. This paper examines wind turbine noise regulations (or lack thereof) in Iowa, Washington, Pennsylvania, and Michigan to provide examples of noise ordinances and their implications at the state and local levels.

State standards

As of 2010, Iowa had the second-highest installed wind capacity in the United States and was the only state that generates over 15% of its energy from wind.  No statewide regulations exist for utility-scale wind power, however.  Projects with capacities greater than 25 MW require approval from the Iowa Utilities Board (IUB), but the IUB does not have specific regulations governing wind power generation. Noise regulation is instead left to the discretion of county and local governments.

Statewide noise legislation was set in 1975 through Washington Administration Code (WAC) 173-60. The code categorizes noise sources and receivers as residential, commercial, or industrial and sets different sound limits depending on the source and receiver involved. As industrial noise sources, wind turbines may not generate sound levels in excess of 55 decibels (dBA) during the day and 45 dBA at night at the property lines of lands not leased by the wind developer. This legislation does not declare its intent, explain its rationale, or provide background references. Nonetheless, its standard levels do protect against sleep deprivation and other health effects. Furthermore, the code encourages additional, local ordinances as “The department conceives the function of noise abatement and control to be primarily the role of local government.” Despite this statement, few counties in Washington have developed their own noise guidelines specific to wind turbines.

Michigan and Pennsylvania have each developed a sample set of guidelines, which local governments may choose to adopt or modify as desired. Michigan’s 2007 guidelines state that the sound level generated by a utility-scale wind energy system shall not exceed 55 decibels (dBA) at the property lines of non-leased lands. If existing background sound levels exceed 55 dBA, the standard is the ambient sound level plus three decibels. Pennsylvania similarly sets a 55 dBA limit, but applies it to the exterior of homes on non-leased property.

Detailed commentary follows Michigan’s standard. Its authors reference a 1974 EPA study and the WHO Community Noise Guidelines. Based on these documents, Michigan’s 55 dBA guideline is described as “too low to produce hearing loss or long-term health effects” or interfere with speech between two persons located within four meters of one another. It should be noted, though, that this standard may not protect against sleep disturbance. The 1999 WHO guidelines, referenced in the Michigan document, state that sleep disturbance may occur when noise levels exceed 45 dBA, averaged over the night. Michigan, however, states that most sleep disturbance occurs for reasons other than outdoor noise, and that habituation to nighttime noise events occurs. It further points to a 17 dB reduction in indoor sound levels, reducing the 55 dBA limit to a 38 dBA level indoors. This statewide guideline protects against hearing loss and long-term health effects but may not protect against sleep disturbance or annoyance in some cases.

Local standards

At times, wind turbine noise ordinances appear poorly informed about acoustics and their limits seem arbitrarily high. Washington Township in Pennsylvania, for example, sets a noise limit of 60 decibels in its code of ordinances. It does not state whether the limit applies to residences or property lines, or whether the sound is A-weighted.  If applied outside a residence, this sound level is similar to that of a television outside a bedroom window, although sound from a television and wind turbine are qualitatively different. Other limits seem extremely low. Whatcom County in Washington provides one such example. In 2008, the county drafted an amendment to its noise ordinance, which would limit the maximum outside sound level to 30 dBA or 5 dBA above ambient, whichever is lower. The county’s rationale is explained in the ordinance. The previous standard of 55 dBA, it states, “does not adequately protect rural residents from adverse health effects associated with large wind turbine noise”. The 30 dBA limit would represent the lowest absolute limit that the authors encountered in their research. This level restricts wind turbines to a whisper-quiet level at property lines, essentially barring them from the county entirely. While the document contains many references to literature on wind turbine acoustics, a limit of 30 dBA is extremely low, particularly if ambient noise levels are higher than the limit itself.

Well-researched and documented standards are rare, but do exist. Centerville Township, Michigan, provides one such example. Originally spearheaded by an interested layperson, the town formed a subcommittee that spent four years meeting with experts, studying academic literature, traveling the Great Lakes region to interview residents about wind turbines in other regions, and holding local meetings. Their recommendations were adopted as a 19-page ordinance with the most comprehensive, well-referenced, and complete noise standard that these researchers have encountered. The Centerville standard dictates that daytime (6 am to 10 pm) sound levels generated by wind turbines may not exceed the greater of 35 dBA or the background sound level plus 5 dBA, and nighttime sound levels may not exceed the background level plus 5 dBA. This standard is applied at the closest property line and locations within one mile of the turbines. In addition, low-frequency noise may not exceed certain 1/3 octave band levels within the project area and a one-mile radius thereof.

Five decibels was selected as a difference below which wind turbine noise would not be noticeable. Therefore, this standard dictates that daytime levels must be whisper-quiet at the property line and barely- or imperceptible at night. This standard is very conservative and protects against not only hearing loss, health effects, and speech interference, but also annoyance and perceptibility. As a result, the ordinance is restrictive to wind developers considering the township’s generating potential.

Summary

This research indicates that different priorities of state, county, and municipal governments are apparent in various noise ordinances. The decision to permit a wind farm in any given location involves a trade-off between economic benefits, energy independence, environmental impacts, human health, and individual convenience. In any given area, local values may differ; residents and their government representatives may determine different standards regarding what is an acceptable noise level in their particular region. Nevertheless, poorly informed standards can be nearly as detrimental to a community as a lack of standards. It is the authors’ opinion that states, counties, and localities should develop well-informed limits that show

• A clear understanding of what the legislation is intended to protect
• An understanding of the fundamentals of noise and the literature on noise impacts and wind turbine-specific issues
• An intention to protect against hearing loss, long-term health impacts, and sleep deprivation through quantitative limits, whether absolute or relative