Analysis of Cape Vincent Interm Noise Report by Rick Bolton

"This interim report covers only the first phase, the summertime survey, which was carried out in late August and early September of 2007. The leaf-off, wintertime field survey will be carried out when seasonal conditions permit. An impact assessment will then be prepared based on the results of both surveys." Introduction, p.3

"The measurement of existing sound levels at the site is necessary to determine how much natural masking noise there might be - as a function of wind speed - at the nearest residences to the project. The relevance of this is that high levels of background noise due to wind-induced natural sounds, such as tree rustle, would act to reduce or preclude the audibility of the wind farm, while low levels of natural noise would permit operational noise from the turbines to be more readily perceptible. Because it would be incorrect, for example, to compare the maximum turbine sound level, which occurs only during windy conditions, with the background level during calm and quiet conditions, the background sound level must be determined as a function of wind speed. For a broadband noise source the audibility of and potential impact from the new noise is a function of how much, if at all, it exceeds the pre-existing background level under comparable conditions." Introduction, P3 - ignores that the turbine may be operating while ground level winds near residences may be calm.

The evaluation of new sound sources on the basis of their audibility above the natural background level is the approach set forth in the Program Policy Assessing and Mitigating Noise Impacts published by the New York State Department of Environmental Conservation (NYSDEC), Feb. 2001. This assessment procedure looks at potential noise impacts in relative rather than absolute terms by comparing expected future sound levels (developed from modeling) to the pre-existing level of background sound (determined from field measurements). The procedure essentially defines a cumulative increase in overall sound level of 6 dBA as the threshold between no significant impact and a potentially adverse impact. Hence the need to determine what the background sound level is. Introduction p. 3 RICK: this is true but 6 dBA is not a limit, it can be lower for sensitive persons. It is not mandatory but Hessler chose to follow it.

The L90 statistical sound level, on the other hand, is commonly used to conservatively quantify background sound levels. The L90 is the sound level exceeded during 90% of the measurement interval and has the quality of filtering out sporadic, short-duration noise events thereby capturing the quiet lulls between such events. It is this consistently present "background" level that forms a conservative, or "worst-case", basis for evaluating the audibility of a new source. RICK: I agree

An additional factor that is important in establishing the minimum background sound level available to mask potential wind turbine noise is the natural sound generated by the wind itself. Wind turbines only operate and produce noise when the wind exceeds a minimum cut-in speed of about 3 or 4 m/s (measured at a reference elevation of 10 m). Turbine sound levels increase with wind speed up to about 8 m/s when the sound produced reaches a maximum and no longer increases with wind speed. Consequently, at moderate to high speeds when turbine noise is most significant the level of natural masking noise is normally also relatively high due to tree or grass rustle thus reducing the perceptibility of the turbines. In order to quantify this effect, wind speed was measured over the entire sound level survey period at two met towers within the site area for later correlation to the sound data. RICK: GOOD

The site area is rural and can be characterized as consisting mostly of farms on relatively large tracts of land irregularly interspersed with scattered residences on smaller parcels. On the whole, the distribution of residential dwellings over the area is fairly thin but there are several areas of higher density, such as the villages of Rosiere and Three Mile Bay and along CR 57 in Lyme where there are a number of homes along the shore of Chaumont Bay. The site topography is essentially flat. In terms of vegetation, the area is a largely even mixture of open fields and wooded areas. Most of the homes and farm houses have at least a few trees immediately around the house.

RICK: villages may be more affected

Seven measurement locations were chosen to evenly cover and represent the entire area as shown in Graphic A. The specific positions are listed below along with photographs of each location. As will be noted from the pictures, a variety of settings were deliberately chosen to see if background sound levels were uniform or variable over the site area. For example, some monitors were placed at isolated farms and while others were located near the three relatively high population density areas mentioned above. RICK GOOD

Photos : microphones w/ std wind screen therefore VOID for high winds due to self induced noise

Position 3: near trees.

Position 6, fig 2.2.11 : too close to ground, near vegetation

Position 7, too close to trees

The microphones were protected from wind-induced self-noise by several different types of wind screens. Positions 1 and 4 were fitted with extra-large 7" diameter foam windscreens (RICK Known not to help much) while remaining Rion instruments had weather-treated 3"diameter foam windscreens. The Norsonic meter had a special environmental microphone housing where the microphone tip is protected from wind by mesh covered slots and an external foam windscreen. In each case, the microphones were situated at a fairly low elevation of approximately 1 m so that they were exposed to relatively low wind speeds. RICK: But inappropriately close to vegetation

Fig 2.3.1 shows std hub height 10m for noise and associated extrapolation graph. Known to be too low, winds will be 2x or more higher (van den Berg)

Wind speed normally diminishes rapidly close to the ground, theoretically going to zero at the surface; consequently, at a 1 m height the microphones were typically exposed to inconsequential wind speeds of about 3 or 4 m/s during the wind conditions of greatest interest (6 to 8 m/s at 10 m). RICK: ????? In any event, self-generated wind noise affects only the extreme lower frequencies (RICK NOT SO) and, except in very high wind conditions, has little or no influence on the measured A-weighted level (the quantity sought in the survey) since the lower frequencies are heavily suppressed before the spectrum is summed to give an overall A-weighted level. Consequently, the measured values are considered reasonably valid and free of any meaningful or significant self-generated contamination. (DOESN'T EXPLAIN MUCH)

It is important to note that the survey was carried out during summertime conditions with the leaves on the trees. Leaf rustle, even in relatively light winds, normally generates significantly higher sound levels than might be observed at the same location when the trees are bare. In addition, normal summertime noise from insects, such as cicadas and crickets, was present at the time of the survey resulting in elevated sound levels on most evenings and at other times of day. RICK: THIS VOIDS THE STUDY cicadia are known to be loud sources but the season is limited, later August only, not the entire leafing season.

e figure below, Figure 2.4.2, shows the average wind speed measured by both towers by the mast top (60 m) anemometers and the wind speed normalized to an elevation of 10 m per IEC Standard 61400-11, Equation 7. A roughness length of 0.05 was used, which is associated with "farmland with some vegetation". WHAT ARE THEY DOING WITH 0.05?) The 10 m wind speed is important because turbine sound levels are expressed as a function of the wind speed at this standardized elevation. (KNOWN BAD)

This somewhat chaotic appearing plot shows that sound levels over the site area roughly follow the same temporal trends except at Position 4 (green trace), where sound levels are consistently lower than at all other locations. The reason for this anomalous behavior is not clear but may be associated with a relative lack of vehicle noise on seldom used Fox Creek Road, a relative lack of insect noise, or the fact that the monitor was not particularly close to any trees and was exposed to less wind-induced noise. Position 4 is the EXPECTED, the others are flawed.

Position 4: only one without trees nearby or too close to the ground

In general, the continual dominance of insect noise, which is clearly unrelated to wind or atmospheric conditions, explains why the site sound levels - during the summer at least - do not exhibit any real dependence on wind speed.

A field survey of existing sound levels during leaf-on, summertime conditions was carried out at the Cape Vincent Wind Farm site in late August and early September of 2007.