After much analysis of new data on the sound generated by the Spruce Mountain Wind turbines, the final judgment may come down to one non-scientific observation.
“’Loud’ isn’t a defined term,” said Todd Presson, chief operating officer for Patriot Renewables LLC, the company that built the turbines. “It may be some people are more sensitive. It’s all perception.”
This past summer camp owners on Concord and Shagg ponds in Woodstock complained about noise from the 10 SMW towers about a mile away.
SMW’s state permit calls for noise limits of 55 decibels during the day and 45 at night, at either the property boundary or 500 feet from a residence (or “receptor”).
In early August Patriot Renewables invited the concerned residents, as well as town officials and DEP representatives, to an informational meeting on the tower property.
The company also contracted with Resource Systems Group, Inc. of White River Junction, Vt. to set up monitoring equipment at the home of Pat Mabey on Concord Pond, in order to try to pinpoint conditions at the times future complaints would be reported.
Those attending the meeting visited the Mabey property with Patriot and RSG representatives to see the equipment that had been put in place.
Some residents told Patriot that for them, it was difficult to go from the usual quiet or background noise of singing birds to the repetitive sound of turning blades.
Following that meeting, for a total of three weeks in August and September the monitoring equipment recorded decibel levels as well as temperature, humidity, wind direction and other factors that might affect the sound propagation in a way that was annoying to some.
The residents were asked to notify Patriot whenever the sound was at a level that concerned them, so RSG could analyze the data at those times in particular.
At Tuesday’s Woodstock selectmen’s meeting RSG presented the results to the board.
RSG engineer Ken Kaliski defined and presented data on sound frequency, pressure and power to try to describe how sound is generated by the turbines. He said in addition to evaluating data when complaints were lodged, he had sampled sound recordings every 10 minutes over the period of the monitoring.
The only times the decibel levels exceeded the permitted limits were when birds, insects, rain or people were making noise near the equipment, he said. After those sounds were filtered out, the decibel levels were between 23 and 32 decibels.
Kaliski also played recordings of the turbine and background sound, which those in the room had difficulty hearing.
There were no violations of permit conditions at Concord Pond, he said.
According to the RSG written report, “We found no clear trend, but periods of audibility and notifications from neighbors were more likely during certain periods that primarily corresponded with higher winds from the northwest during the night.
“We postulate that turbine noise may be more noticeable during these times because the north side of Concord Pond is shielded from northwest winds by Davis Mountain, thus reducing background wind-induced noise.
“However, we cannot be definitive about this relationship, since the wind turbines were operating almost exclusively with northwest winds during the monitoring periods, and notifications of high sound levels were also received when winds were from the opposite direction.”
Peter Guldberg of Tech Environmental, which did an independent review of the RSG monitoring for the Maine Department of Environmental Protection, reached a similar conclusion.
The wind turbines, he said in a letter, are most audible “late at night and in the early morning hours, when background sound levels can be well below 30 dBA. The residents who have filed complaints are evidently characterizing any audible turbine sound from SMW during those times as ‘high’ because at those times it is the most noticeable sound.”
After Tuesday’s presentation, Selectman Steve Bies was critical of communication glitches that had made it difficult during the summer for residents to reach a “hot line” set aside for complaints.
Presson said callers had mistakenly gotten a hot line intended for construction-related concerns while the wind farm was under construction in 2011. He said he did not realize that line was still operating.
But, said Bies, “It was your responsibility to inform them how to contact you. It’s not their responsibility for getting through.”
Presson apologized for the problem.
Bies was also critical of an attempt by Patriot last summer to get permission from DEP to remove required permanent monitoring equipment near the wind turbines on Spruce Mountain.
Presson said there had been technical difficulties, and after gathering enough data to show the turbines were in compliance, they applied to discontinue monitoring.
“But after there were objections [from residents] we decided to work through the problems,” he said.
Selectman Rick Young commented that he knew of two camp owners on Concord Pond who “to this day have never heard [the turbines].”