Is a recent Wisconsin study the smoking gun that proves wind turbine noise causes health problems?
It depends on whom you ask, and more importantly, whether that person is qualified to answer the question.
One month ago, five sound experts set up recording equipment at three homes near a Wisconsin wind farm that had been abandoned by their occupants, who blame the turbines for a variety of health issues.
Over the course of a few days, microphones picked up inaudible, low-frequency turbine noise in the home nearest to the turbines. The subsequent report prompted state Rep. Andre Jacque, R-De Pere, to call for an emergency moratorium on wind permits in the state, saying the analysis proves wind farms produce "dangerous" infrasound levels.
“These results compel them to act immediately to keep this nightmare from spreading," Jacque told the Green Bay Press-Gazette.
However, whether turbine noise is to blame for nausea, headaches and other symptoms was well beyond the limited scope of the three-day field study, which acknowledges the issue as "serious" and "possibly affecting the future of the industry," but calls for further research into the matter.
The study was intended to help inform Wisconsin's ongoing debate over wind turbine siting. The Wisconsin Public Service Commission hired Clean Wisconsin, a nonprofit environmental advocacy group, to review the proposed Highlands wind farm in St. Croix County, in western Wisconsin (Clean Wisconsin is a member of RE-AMP, which also publishes Midwest Energy News).
During hearings for that project, opponents introduced witnesses who testified about suffering adverse health effects from living near the Shirley wind farm, southeast of Green Bay, forcing them to eventually abandon their homes near the project.
A sound expert hired by Clean Wisconsin proposed a sound-measurement survey in the abandoned homes to get a better understanding of the noise levels, particularly infrasound and low-frequency noise.
The utilities commission authorized funding for the study, and the homeowners agreed to let Clean Wisconsin's acoustician into their homes to collect the measurements.
At the last moment, however, the three homeowners rescinded their invitation because an expert representing their view wasn't invited to attend the survey.
Clean Wisconsin retooled and rescheduled the study, inviting four separate acoustics consulting firms to participate, including one, Rand Acoustics, that is often hired by wind farm opponents.
What they heard
The group spent three days going from house to house listening for sound as well as using highly sensitive microphones and other equipment to detect sound inaudible to the human ear.
All five consultants (one of the firms had two acousticians present) could hear turbine noise when standing outside the homes located 1,300 feet and 3,330 feet from the nearest turbines. Only one, Robert Rand of Rand Acoustics, said he could hear noise outside the third residence, 7,100 feet from the nearest turbine.
Rand was also the only one who said he could hear turbine noise inside the homes. He said sound was audible in all three homes, while only one of the other consultants, David Hessler, said he could faintly detect noise inside the nearest home.
Infrasound and low-frequency noise, which occur naturally and are always present in some level, were detected in all three of the homes, but could only be matched to turbine noise in the home closest to the wind farm.
In the other two homes, the noise inside the house didn't match the profile of an outdoor microphone well enough to rule out other sources as the cause of the noise.
Each of the acoustics firms was given an opportunity to interpret the results, but all four agreed on the conclusions and recommendations in an eight-page consensus report.
The effort was a "good start in quantifying low frequency and infrasound from wind turbines," the sound experts' consensus conclusion begins. But it was also a very limited study with some significant shortcomings.
The group strongly recommended more testing at the Shirley wind farm. Research could produce better results with more time and equipment, as well as cooperation from the wind farm's owner, Duke Energy.
Duke Energy declined the researchers' request to periodically turn their turbines off and on so they could measure noise levels with and without the turbine blades spinning, leaving it an experiment without a control.
"An important finding on this survey was that the cooperation of the wind farm operator is absolutely essential," the report said.
The issue of how infrasound and low-frequency noise affects physical health does come up in the report, though the consensus report underscores the scientific uncertainty about the link.
"The issue is complex and relatively new. Such reported adverse response is sparse or non-existent in the peer-reviewed literature," it says.
The report adds to the body of anecdotal evidence in an appendix by Rand, who says he "is prone to seasickness" and personally experienced nausea, headaches, dizziness and other symptoms during the sound recording. He also interviewed the homeowners about their symptoms.
Rand, in a section not endorsed by the other consultants, says the illness experienced by himself and others near wind turbines may be a form of motion sickness caused by the low frequencies.
Another of the researchers, Paul Schomer, also suggests that low-frequency vibrations from the turbines could cause nausea and other symptoms by putting pressure on the ear canal, but cautions "that the wind turbines make people sick is difficult to prove or disprove."
Bruce Walker of Channel Island Acoustics reminds readers in his notes that the study was conducted by acousticians, not doctors.
"The author is not qualified to make judgments regarding human response to normally subliminal sources of acoustic excitation," Walker wrote.
The other two consulting firms note that they have measured infrasound levels at other wind farms "that substantially exceed those measured here and to the best of their knowledge there are no reported adverse effects for noise or adverse health issues."
The few anecdotes included in Rand's appendix neither prove or disprove that infrasound or low-frequency noise can make people sick. They also don't change the current scientific consensus on the topic, says Tyson Cook, staff scientist for Clean Wisconsin.
"When it comes to wind turbines in particular, there is no evidence of that happening."