Agenda - Planning Commission - 08/07/2008

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Due to variation in noise performance of different turbine models, standards to address noise that specify turbine size may produce varied results, and local governments should adopt a standard for noise measured at the property line. windy conditions, noise levels may be slightly higher, but so will ambient wind-related noise, such as that made by wind in trees. Noise levels are reduced by a factor of four for each doubling of distance (as measured from the turbine to the listener). Thus, off-property . noise intrusion from a residential WEe is typi- cally very limited. Due to variation in noise performance of different turbine models, standards to address noise that specify turbine size may produce varied results. so local govern-' ments should adopt a standard for noise measured at the property line. In general, it is appropriate to use the same standard for "nuisance noise" that the community applies to all other activities in the zoning . district. Adding the caveat "or 10 decibels above ambient noise levels" gives some leeway to turbine owners during very windy conditions when ambient noise lev- els rise and neighbors are less likely to be outdoors. This caVeat also helps if the neighborhood is already impacted by another noise source, such as a freeway. By measuring noise at the property line, the tur- bine owner can limit it byusing a quieter model, increasing setbacks, adding a fence' or hedge along the property line, or other techniques. SAfETY IMPACTS AND STANDARDS Safety is, of course.Cjn important concern. Local governments should address three main issues when writing zoning and permitting standards for WECs: structural failure, electri- cal failure, and climbing potential. This sec- tion concludes with a brief discussion of safety-related issues associated with wind- farms. Although risks for small wind are mini- mal, opponents often raise safety concerns, and planners should be aware of these con- cerns and be prepared to respond. Structural Failure One concern with wind turbines near property boundaries is that the supporting pole or tower could fall down. However. structural fail- ure in a WEC is extremely unlikely. A turbine is a significant investment. as are the engi- neered towers and poles on which they are installed. WECs are not sold as do-it-yourself appliances. Rooftop models must be installed on structures that are engineered to accom- modate the additional weight and stress. The likelihood of structural failure in a properly installed WEC is not more likely than for a flag pole, and is much less likely than for trees. Even so, a setback requirement of 1.1 to 1.5 times the total height of the WEG O.e:, tower or pole height plus rotor radius) is a reasonable requirement. Such setbacks address a range of potential impacts including safety, noise, and aesthetics, and can give neighbors peace of mind. In most cases the local building in;pec- tor can verify that installation conforms to approved plans. It is not necessary to require an engineer to certify installation. except in cases where a red uced setback is to be approved with recorded consent of the adja- cent property owner, Because WECs are installed by profes- sionals, additional certifications add unnec- essary expense for a small WEC owner. Soil testing is generally unnecessary and is often cost prohibitive; it should only be required if soils are so weak as to merit testing for ZONINGPRACTlCE 7.08 AMERICAN PLANNING ASSOCIATION I pagE; 5