The results of the post-construction sound study of Lake Winds Energy Park will be presented to the Mason County Planning Commission Wednesday, Aug. 14 at 7 p.m. at the Summit Township Hall, 4879 W. Deren Road.
It’s likely that when the sound consultants hired to study the noise level of Lake Winds Energy Park present their findings Wednesday night at Summit Township Hall, those in favor will be happy and those who opposed to the 56-tower project that began operation Thanksgiving Day 2012 will find results that bolster their concerns over noise.
The report concludes “the sound levels from the wind turbines were in general compliance with sound level criteria.”
But the results also show some values exceeding the limits set in the special land use permit – numbers opponents likely will highlight.
The engineers caution that other sounds – wind and background noise – may be a factor and need to be taken into account when considering the results that exceed the limits. While the turbines operate at near the maximum allowable noise level and can be heard, according to the conclusion of the report, the incidents of exceeding the limit “do not represent a statistically significant portion of time and do not indicate systemic exceedance.”
“The planning commission will use the results to determine compliance with the sound portions of the special land use permit/zoning ordinance,” Mary Reilly, Mason County zoning and building administrator told the Daily News Monday.
She encouraged those interested in the study to attend the 7 p.m. meeting Wednesday at Summit Township Hall on Derren Road, west of South Pere Marquette Highway.
Brian Howe of HGC Engineering (Howe Gastmeier Chapnik Limited) will attend the Wednesday meeting to present the 59-page report on the sound study. He will conduct a question and answer period with those in attendance.
FROM THE REPORT
From April 24 through May 10, the Missassauga, Ontario, firm HGC Engineering conducted the study required by the special land use permit granted Consumers Energy to build the hotly contested 100 megawatt wind farm in Riverton and Summit Townships.
See SOUND STUDY, A8
from page A1
The report details the methodology used, and includes sound level data gathered by automated monitors at eight measurement locations as well as data collected by attended monitors at eight sites. Weather conditions including wind speed and direction, were monitored and recorded at four locations during the testing period. Electric power production records and hub height wind data provided by Consumers Energy is included.
Levels were measured at both pooled and unpooled parcels. Pooled parcels are those receiving payments based on the power generated by a turbine on their parcel. Unpooled parcels do not receive such payments. The special land use permit tops the sound at 55 decibels at the dwelling on pooled parcels and 45 decibels at the propety line on unpooled parcels. Consumers Energy agreed to those limits, noting they are lower limits than industry standards for wind parks.
The study also measured ambient sound – wind, rain and other natural and manmade sounds.
The results are presented as a number for a 10-minute energy equivalent average sound level – LEQ. Because the LEQ includes ambiant sound, the engineers state, “a sound level measurement cannot necessarily be compared directly to the sound level limits. Where significant background sound level exists, some form of evaluation must be made to determine the sound level contribution of the source under assessment in the absence of background sounds.”
A second sound measurement is included – L90. Acccording to HGC, an L90 sound level represents the level exceeded 90 percent of the time during a measurement. In other words, it measures more steady sounds, such as wind turbines operating, and ignores peak sounds that come and go.
INTERPRETING THE NUMBERS
On page 6 of the report, the engineers state “by simply considering LEQ and L90 sound levels, a case can be made that the turbines are above the limits for some 10-minute periods, as there were periods when the turbines were operating at full capacity and both the LEQ and L90 were above the applicable criteria. However, there are also periods when the turbines were operating at full capacity and both the LEQ and L90 were below the criteria, in addition to periods when the turbines were not operating yet and the LEQ and L90 were above the criteria (indicating high levels of background sound). As these examples illustrate, a comprehensive consideration of the turbine output, ground level wind speed, dominant noise source(s), and background sound is necessary to clearly determine if the limits are being exceeded.”
It is important, the report states, to consider ground level wind speed. As ground level wind speed increases, so does ambient noise: tree and vegetation noise, for instance.
The attended acoustic measurement portion of the study at eight monitoring locations add qualitative observations to the collection of the sound data from the instruments. They were conducted during 80-minute periods with the wind turbines on for 40 minutes and shut down for the other 40 minutes of the study period at each location. An attempt was made to schedule these when the turbines would be operating at full capacity, but the engineers said because of the variability of wind, this wasn’t always possible.
Only one of 63 L90 attended sound measurements at the eight locations exceeded sound level criteria. Eighteen of 63 LEQ measurements exceeded permit criteria, according to the report. However, the engineers state, in those 18 cases the observations made indicate the wind turbines were not the only dominant source of sound at the time.
According to Reilly, “the zoning ordinance is based on LAeq for a 10 minute interval. Data in the report is taken in “10 minute energy equivalent average sound levels designated LAeq.”
LOW LEVEL SOUND
Infrasonic sound – low frequency sound generally below the threshold of human perception – was measured at one resident’s garage to minimize the affect of wind gusts and cars driving by. According to the engineers, infrasound levels increased by 10 to 15 decibels when the turbines were on, “but remain well below the thresholds of perception.”
ON THE WEB
The first 11 pages of the sound survey report are on the website above—under the Zoning Dept and Lake Winds Energy Park sub heading.
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