On Thursday June 11, two speakers made presentations on Wind Turbine Noise to the Sustainable Las Vegas group. This meeting was part of SLV’s current efforts to inform the public about sustainable issues. This topic is especially timely since San Miguel County is currently revising their county wind ordinance to more adequately address the issue of the siting of large turbine wind towers.
Jim Cummings, from the Acoustic Ecology Institute in Santa Fe, spoke about the audible noise associated with Wind Turbines. I am a retired molecular biologist from Villanueva, I spoke about the health effects of inaudible, low frequency noise. Both presentations are available at http://www.newmexicocare.org/1pages/vad.html#slides .
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Mr. Cummings explained the 3 sources of audible noise coming from a wind turbine. The first source is the size of the turbine itself. In general, as turbine size increases, the noise level coming from the turbine itself increases. As each blade passes by the tower on the downswing, the accumulated energy is “pitched” off the tip of the blade. This noise impulse moves outward and can travel for long distances. The second source of noise is related to amplitude modulation of the 3 blades. It is often described as a swishing or thumping sound, the rhythm in agreement with the blade-passing frequency. If the variation in this noise is greater than 5 decibels, this continuous variation is clearly perceptible resulting in noise with an increased annoyance factor.
The third factor influencing turbine noise is atmospheric effects, especially at night. In “stable” night-time conditions, the wind is often very low at ground level, but strong enough to initiate turbine rotation at the height of the tower. At night, turbine noise is the dominant source of noise in the environment, the increased level is more easily noticed and travels farther. In the early morning as the air warms, the inversion layer above the turbine pushes the sound towards the ground.
Europe has more experience with commercial size wind farms. The European standard for siting towers from a residence is sometimes based on a distance (1 kilometer or ~0.6 miles), sometimes on a baseline noise level (called the L90, or the quietest 6 minutes during the quietest time of night), and sometimes on some combination. Approximately one tenth of the 133 wind farms in England were found to have triggered some noise complaints in a study published in 2007.
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I introduced the topic of Low Frequency Sound or LFN. LFN is measured with a C-weighted sound meter. Audible sound is measured with an A-weighted meter. The Wind Industry currently uses only A-weighted measurements and therefore severely underestimates the level of LFN present. LFN is sound that is not heard but is rather felt as a vibration. These vibrations are picked up by specialized protein molecules located on the outer surface of cells, especially cells lining the bronchial tubes, the intestines and the walls of arteries.
We have known about the possible negative health effects of LFN since astronauts were propelled into space riding on top of a rocket. The effects are considered powerful enough that our military has sponsored over 40 years of research about the feasibility of using LFN as a non-lethal weapon. The exposure to LFN from a wind farm would be at a lower level than that used in the military studies but would be constantly present.
There are hundreds of studies of the effects of LFN on people living near high traffic areas or near large airports; or exposed on the job to large ventilation equipment or to the noise of airplane and helicopter engines. These studies show that long-term exposure to LFN results in many adverse health effects. This has led a number of acoustical engineers to recommend that the siting distance be increased to at least 2 miles and that the increase above the baseline L90 is limited to 5 decibels. When people live too close to a wind turbine, and are exposed to levels of LFN greater than 50 to 60 decibels, they may notice an immediate sensitivity, through the impact on a region of the inner ear. There may be problems with balance, dizziness or vertigo, pain in the chest or abdomen, or an increase in migraine headaches.
Most people will experience sleep disturbance, experiencing an increase in their cortisol level and the normal pattern of secretion will be disturbed. Increased cortisol is the response the body makes to increasing stress. Any disease that has a stress component will be negatively impacted. There is also a fairly immediate reaction in the elderly, with an increased incidence of hypertension or a need to increase anti-hypertension medication. Chronic exposure to high levels over a period of years will impact the cardiovascular system of most people.
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The meeting closed with a short discussion on what local people could do to help make our government agencies more responsive to the health and welfare of its citizens. Discussion focused on asking the readers of the Optic to give their input into drafting of the new San Miguel County Wind Ordinance. At the May 5th County Commissioners meeting, Alex Tafoya of the County Planning and Zoning office, stated that the current draft of the County Wind Ordinance would appear on the County website. There will also be an opportunity for any citizen to comment on the proposed changes in a special meeting that the board of Commissioners will call.
I commented that the current San Miguel County standard for siting commercial wind turbines has two major problems. The first is the absence of a maximum noise level based on some volume above the L90 (quietest nighttime) level, and the second is the absence of any requirement that the noise levels be determined with a C-weighted sound meter If the ordinance could establish “real” guidelines (i.e. maximum sound levels of L90 + 5dB (decibels) and a maximum of 15dB difference between the A-weighted and C-weighted measurements, the county could ensure the safety of the citizens of our community. Such guidelines would also benefit developers, who could choose the right size turbine for any location they think could be economically and sustainably developed.
Readers are welcome to visit http://www.newmexicocare.org/index.html for more information.
Eileen Mulvihill lives in Villanueva