Possible Impacts of Low Frequency Wind. Rita B. Messing, Ph.D. Carl Herbrandson, Ph.D. Risk Assessment Course, Feb. 2011

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1 Possible Impacts of Low Frequency Wind Turbine Noise on Public Health Rita B. Messing, Ph.D. Carl Herbrandson, Ph.D. Risk Assessment Course, Feb. 2011

2 Environmental Review of LWECS in Minnesota Large Wind Energy Conversion Systems (5-25 MW) can be permitted by the PUC or by delegated counties. LWECS >25 MW must be permitted by the PUC. All LWECS must undergo environmental review: determining the need for the project, the size, the time in service, and analysis of health and environmental effects, and alternatives. The review process allows several opportunities for public comment.

3 Permitting LWECS in Minnesota Site layouts have to optimize wind resources. Developers must control areas at least 5 rotor diameters in the prevailing wind direction (1,300-1,700 feet) and 3 rotor diameters in the cross-wind direction (800 to 1,000 feet). These are essentially minimum setback distances where easements have not been obtained. Otherwise, Minnesota noise rules specify maximum nighttime noise in residential areas of 50 db(a), amounting to modeled setbacks of about 700 feet (may be underestimated).

4 Purpose of the MDH White Paper A request for a Contested Case Hearing on the Bent Tree project (Freeborn County) had been made. The Clay County project also generated early public comment. Public health was a major concern. More large projects were known to be in development. Therefore, a white paper was needed having more general application to guide decisionmaking. Public Health Impacts of Wind Turbines was released by the PUC in May 2009 and a public comment period ended September 15.

5 Noise Impacts on People (published reports) Annoyance and sleep interruption increase as night- time noise at homes increases above 35 db(a) (generally less than ½ mile). 25% to 50% of respondents report annoyance when noise measurements are above 40 db(a) but prevalence is unknown because of varying or unreported response rates. When residents report economic benefits, annoyance decreases. The noise has been described as thumping, pulsating, beating.

6 Noise Impacts on People (un-reviewed reports; not random samples; not measured db) The most common complaints are decreased quality of life, poor sleep, headaches. h Less frequent complaints include palpitations, migraines, tinnitus, vertigo, nausea, panic/anxiety. Wind turbine syndrome has been postulated to be mediated by discordant stimulation of the vestibular system. However, study participants i t report that even unusual symptoms are associated with audible noise and vibration.

7 Pulsing Noise from Wind Turbines furthest t (quietest) 20 mph Shear: source of aerodynamic 10 mph modulation noise Distance-to- Blade noise closest (loudest) If wind speeds are different at the top and bottom of blade rotation, blade noise will vary between top and bottom: shear. Shear may also be caused by terrain or structures on the ground. (Towers range up to meters, and blades are up to 50 meters long.)

8 Wind turbine noise is broad spectrum. But, as distance increases, low frequency noise becomes more pronounced. Low frequency noise is also less attenuated by buildings. Figure from U.K. Dept. of Transport and Industry, 2006

9 Measurement in db(a) may underestimate low frequency noise 120 re Level 20 μpa) Sou und Pressu (db relative to db(c) isopleth 20 db(a) isopleth Frequency (Hz) Equivalence curves for different frequencies, when sound meter readings in db are taken with A or C-weighting filters.

10 Annoyance from wind turbine noise is not solely related to db(a) (figure from Pedersen and Waye, JASA (2004)116: 3460) WHO (1999) recommends that if db(c) is greater than 10 db more than db(a) the low frequency components of noise may be important and should be evaluated separately.

11 Recommendations Noise modeling for proposed projects should be done at appropriate heights above ground, include db(a) isopleths and isopleths for db(c) db(a) greater than 10 db. Setback distances for wind turbines less than ½ mile should reflect priorities iti and attitudes of the community compensation of nearby residents should be considered.

12 Public Health Impacts of Wind Turbines p