Lake Winds Energy Park sound study findings to be shared 

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

SOUND STUDY

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.”