bp sdeis app h background sound level surverys hessler cape vincent

8/7/2019 BP SDEIS App H Background Sound Level Surverys Hessler Cape Vincent

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Environmental Resources Management Southwest, Inc.206 East 9th Street, Suite 1700

Austin, Texas 78701

(512) 459-4700

Background Sound Level Surveys - HesslerAppendix H

February 2011

Project No. 0092352


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Member National Council of Acoustical Consultants

Noise Control Services Since 1976

Hessler Associates, Inc.Consultants in Engineering Acoustics

3862 Clifton Manor PlaceSuite BHaymarket, Virginia 20169 USAPhone: 703-753-1602Fax: 703-753-1522Website: www.hesslernoise.com

REPORT NO. 1810-030608-0

REV: 0

DATE OF ISSUE: MARCH 8, 2008

ENVIRONMENTAL SOUND LEVEL SURVEYWINTERTIME CONDITIONS

CAPE VINCENT WIND FARM

TOWNS OF CAPE VINCENT AND LYMEJEFFERSON COUNTY, NY

PREPARED FOR:

BP Alternative Energy N. A., Inc.

Prepared by:

David M. Hessler, P.E., INCE

Principal Consultant

Hessler Associates, Inc.


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CONTENTS

1.0 INTRODUCTION 1

2.0 BACKROUND SOUND LEVEL SURVEY 1

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES 12.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS 22.3 INSTRUMENTATION AND SURVEY DURATION 62.4 SURVEY WEATHERCONDITIONS 72.5 SURVEY RESULTS WORST-CASE SOUND LEVELS 102.6 SURVEY RESULTS TYPICAL SOUND LEVELS 14

2.7 FREQUENCY CONTENT OF BACKGROUND SOUNDS 18

3.0 CONCLUSIONS 21

Graphic A General Site Map Showing Background Survey Positions


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Member National Council of Acoustical Consultants 1Noise Control Services Since 1976


1.0 INTRODUCTION

Hessler Associates, Inc. has been retained by BP Alternative Energy to evaluate potential noiseimpacts from the proposed Cape Vincent Wind Farm Project on residents in the vicinity of the

project area, which is located in Jefferson County, NY just east of the Town of Cape Vincent.

The study consists of three phases:

x A field survey of existing background sound levels during leaf-on, summertimeconditions

x A field survey of existing background sound levels during leaf-off, wintertime conditions

x An impact assessment based on the measured levels of background sound from both

surveys and the predicted project sound levels developed from an analytical noise model

This interim report covers the second phase, the wintertime survey, which was carried out in late

December of 2007 and early January of 2008. The leaf-on, summertime field survey wascompleted in September of 2007 (Hessler Associates, Inc., Report 1801-112607-0, Nov. 27,

2007). A noise modeling and impact assessment will eventually be prepared based on the results

of both surveys once a turbine layout has been developed.

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, whilelow 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 ofhow much, if at all, it exceeds the pre-existing background level under comparable conditions.

The evaluation of new sound sources on the basis of their audibility above the natural backgroundlevel 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 essentiallydefines 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.

2.0 BACKGROUND SOUND LEVEL SURVEY

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES

The purpose of the survey was to determine what minimum environmental sound levels are

consistently present and available at the nearest potentially sensitive receptors to mask or obscure

potential noise from the project under wintertime conditions when the trees are bare and leaf rustleand insect noise are absent. A number of statistical sound levels were measured in consecutive 10

minute intervals over the entire survey. Of these, the average (Leq) and residual (L90) levels are

the most meaningful.


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The average, or equivalent energy sound level (Leq), is literally the average sound level over each

measurement interval. This is the typical sound level most likely to be observed at any givenmoment.

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 measurementinterval 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.

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 withwind 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 three met towers within the site area forlater correlation to the sound data.

2.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS

At the time of the survey the number of turbines and their specific locations were still being

worked out. The general extent of the project area was known from the distribution of land

owners who had concluded leasing agreements with the project. The site area can be broadlydefined as the eastern half of the Town of Cape Vincent, beginning several miles back from the

bank of the St. Lawrence River and extending to the Lyme town line. Some turbines are also

being tentatively considered in the western part of Lyme generally from the town line with Cape

Vincent to the village of Three Mile Bay.

The site area is rural and can be characterized as consisting mostly of farms on relatively largetracts 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 Lymewhere 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.

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 monitorswere placed at isolated farms and while others were located near the three relatively high

population density areas mentioned above.


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Position 1 8718 County Road 8 Cape Vincent

Typical farm. Monitor placed on a fencepost behind the barn (slightly different location than used

in the summer survey).

Figure 2.2.1 Position 1 Looking North.

Position 2 30485 CR 4 Rosiere (Cape Vincent)Monitor located on a fence post at a farm near the center of Rosiere.

Figure 2.2.2 Position 2 Looking Southeast towards Barn

Position 3 Huff Road and Route 12E Cape VincentMonitor located on a utility pole about 40 ft. from edge of Route 12E, the principal road in the

area. The objective of this position was to measure sound levels representative of those

experienced at the homes along Route 12E, such as the farm house in the background of Figure

2.2.3.


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Figure 2.2.3 Position 3 Looking West towards Huff Road(photo from summer survey)

Position 4 27323 Fox Creek Road Cape Vincent

Typical farm. Monitor located on a utility pole near the house.

Figure 2.2.4 Position 4 Looking Northeast towards House

Position 5 8559 Church St. Three Mile Bay, Lyme

Monitor located on a post in an open field about 200 ft. behind the house and barn. This position

conservatively represents sound levels in the village of Three Mile Bay, since the meter wasplaced on the outskirts of the village and away from much of the normal man-made noise present

around the homes.


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Figure 2.2.5 Position 5 Looking South towards the Village(just beyond the barn)

Position 6 Opposite 27140 CR 57 Lyme

Monitor located on a gate post in an open field across the road from the homes along CR 57 facingChaumont Bay.

Figure 2.2.6 Position 6 Looking East(CR 57 to right just past first few trees)


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Position 7 29766 CR 6 Cape Vincent

Monitor located on fence post in rear yard of house.

Figure 2.2.7 Position 7 Looking North(Photo from Summer Survey)

2.3 INSTRUMENTATION AND SURVEY DURATION

Rion NL-32 and NL-22 sound level meters (ANSI Type 1 and 2, respectively) were used at 6 of

the 7 positions. A Norsonic 118, ANSI Type 1, 1/3 octave band analyzer was used at Position 7 torecord the frequency spectrum of the sound as well as the overall A-weighted levels measured by

the other instruments.

The meters were all enclosed in watertight cases with the microphones supported 12 to the side or

above each case to minimize any local reflections.

The microphones were protected from wind-induced self-noise by extra-large 7 diameter weather

resistant foam windscreens (ACO Type WS7-80T). The Norsonic meter had a special

environmental microphone housing for the summer survey but a 7 windscreen consistent with theother instruments for the winter survey. 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.

Figure 2.3.1 illustrates a typical wind speed profile based on IEC 61400-111.

1International Electromechanical Commission (IEC) 61400-11:2002(E) Wind Turbine Generator Systems Part 11:

Acoustic Noise Measurement Techniques, Second Edition 2002-12.


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Standardized Wind Speed Profile

per IEC 61400-11 for a Typical Critical Wind Speed

of 6 m/s at 10 m

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90

0 1 2 3 4 5 6 7 8 9 10

Wind Speed, m/s

HeightAboveGroundLevel,m

Standard IEC

Height = 10 m

Typ. Hub Height = 80 m

Mean Anemometer Height = 43 m

Monitor Height = 1 m

Figure 2.3.1

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). In any event, self-generated wind noise affects only the extreme lower frequencies and,

except in extremely high wind conditions, has little or no influence on the measured A-weightedlevel (the principal quantity sought in the survey) since the lower frequencies are heavilysuppressed before the spectrum is summed to give an overall A-weighted level. Consequently, the

measured values are considered valid and free of any meaningful or significant self-generated

contamination. This subject is discussed further in Section 2.7.

All equipment was field calibrated with a Brel and Kjr Type 4230 calibrator at the beginning of

the survey and again at the end of the survey. The observed calibration drift of all the instruments

was equal to or less than +/- 0.4 dB for all instruments.

The survey was carried out over a 20 day period from December 14, 2007 to January 3, 2008.Due to variances in battery life not all of the instruments operated for the entire period but most

recorded until the last few days of December, or roughly for two weeks.

2.4 SURVEY WEATHERCONDITIONS

The weather conditions during the survey period were generally overcast and cold. On 17 of the

20 days it snowed with accumulations ranging from a trace to a half an inch.

Winds during the survey were fairly light about half of the time and moderate to high the

remainder of the time, with 4 or 5 periods of very strong winds as can be seen Figure 2.4.1, which


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shows the general conditions of temperature, barometric pressure and wind for the survey period

as observed at Watertown, NY, some 20 miles southeast of the site.

Figure 2.4.1 General Weather Data for the Survey Period as Observed in Watertown, NY

The wind speed at the site itself was measured at three met towers distributed over the projectarea. The figure below, Figure 2.4.2, shows the average wind speed measured by all three towers

by the anemometers at elevations in the 40 to 44 m range. Since these three results are generally

similar the typical site-wide wind speed can reasonably be considered the average of all three

(Figure 2.4.3). This average wind speed at a nominal height of about 43 m was 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. The 10 m wind speed is importantbecause turbine sound levels are expressed as a function of the wind speed at this standardized

elevation.


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Wind Speed Measured by Three On-site Met Towers at an Elevation of 40 to 44 m

Wintertime Conditions

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Date and Time

WindSpeed,m/s

Tower 7080, 40 m Anemometer



Figure 2.4.2 Measured Wind Speeds at the Site during Sound Survey Period(40 to 44 m Anemometers)

Average Wind Speed Measured by Three On-site Met Towers at a Mean Elevation of 43 m

and Wind Speed Normalized to a Standard Elevation of 10 m

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Average Wind Speed at about 43 m

Normalized Wind Speed at 10 m

Figure 2.4.3 Average and Normalized Site-Wide Wind Speeds during Sound Survey Period


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2.5 SURVEY RESULTS WORST-CASE SOUND LEVELS

As discussed above in Section 2.1 the L90, or residual, sound level is a conservative measure of

background sound levels in the sense that it filters out short-duration, sporadic noise events that

cannot be relied upon to provide consistent and continual masking noise to obscure potentialturbine noise. This level represents the quiet, momentary lulls between all relatively short

duration events, such as cars passing by or tractor activity in a neighboring field. As such, it is the

near worst-case background level with regard to evaluating potential impacts from a new source.

The L90 sound levels over consecutive 10 minute periods for all 7 positions are plotted below for

the survey period.

As-Measured Residual (L90) Sound Levels vs Time at All Positions


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Date and Tim e

SoundPressureLevel,dBA

Position 1

Position 2

Position 3

Position 4Position 5

Position 6

Position 7

Figure 2.5.1 10 minute L90 Sound Levels at All Monitoring Positions

This plot shows that most of the positions follow the same general trend but that certain positionshave significantly higher sound levels some or most of the time. Specifically,

x While showing consistent levels during high noise (windy) periods, sound levels atPosition 4 (turquoise) remain fairly elevated in the 30s (dBA) during quiet periods when

most other positions go down into the 20s or lower. This behavior is all the more odd

because this position (only) showed below average sound levels during the summer

survey.


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x Sound levels at Position 3 (yellow) are tightly grouped with most other positions all of

the time except for a period of inexplicably high levels from about 11:00 a.m. on 12/17 to

the afternoon of 12/19.

x Levels at Position 5 (purple) are also consistent with the mean trends until just after the

Christmas Eve storm when the sound levels remain well above most other locationsthrough the end of the survey.

Because the higher sound levels occurring at these three positions dont have an obvious

explanation, there is no way of determining if these levels are likely to occur on a repeatable basis.

Therefore we do not believe that the identified periods of unusually high sound levels should be

considered in the determination of a design basis background level. The figure below shows the

same plot as Figure 2.5.1 with Position 4 completely deleted and with the partial periods of highnoise at Positions 3 and 5 eliminated.

Residual (L90) Sound Levels vs Time at All Positions Except 4

and Deleting Anomalous Data at Positions 3 and 5


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Date and Tim e


Position 1

Position 2

Position 3

Position 5

Position 6

Position 7

Figure 2.5.2

This plot shows much more clearly that a general site-wide sound level trend is present and thatthe higher levels observed at some positions for some of the time were essentially aberrations. It

can be seen from Figure 2.5.2 that the average sound level of all the remaining positions after

elimination of the unusually high measurements would represent a conservative and realistic site-wide design level (plotted in Figure 2.5.3).


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Site-wide Residual (L90) Sound Level vs Time - Wintertime Conditions

Design L90 Background Level (Average of All Positions Deleting Anomalously Higher Levels)

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2.5.3 Design L90 Background Level

This design L90 sound level is plotted along with the average wind speed at 10 m in Figure 2.5.4below.


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Average L90 Background Sound Level vs. Normalized Wind Speed


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WindSpeed,m/s

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Wind Speed at 10 m

Design L90 Level

Figure 2.5.4 Design L90 Sound Level and Concurrent Wind Speed

In stark contrast to the results of the summertime survey where there was only a vague correlationbetween the background sound level and wind speed (largely due to insect noise), the wintertime

measurements show that background sound levels are very closely related to wind. This result is

common in rural areas where man-made and natural sounds unrelated to wind (such as insects) areminimal. Figure 2.5.4 shows that sound levels generally approach or exceed 50 dBA during very

windy conditions and drop to the low 20s when winds are light. This extremely large dynamic

range (about 30 dBA) shows that wind speed cannot be neglected when determining what the

background sound level is likely to be during windy conditions when the turbines are operating.

Figure 2.5.5 is a regression analysis, which quantitatively determines the mean L90 sound level as

a function of wind speed. Sound levels over the wind speed range of interest from cut-in at

about 3 m/s to 10 m/s when all turbines are generally operating at full power - are tabulated below.

Table 2.5.1 Measured L90 Sound Levels at Integer Wind Speeds (from Fig. 2.5.5)Wind speed at

10 m, m/s3 4 5 6 7 8 9 10

Worst-CaseL90 Sound

Level, dBA -

Wintertime

24 27 30 34 37 40 44 47


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Regression Analysis of Site-wide L90 Sound Level vs. Normalized Wind Speed

Worst-Case Sound Levels - Wintertime Conditions

y = 3.372x + 13.362

R2 = 0.7174

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0 1 2 3 4 5 6 7 8 9 10 11 1

Wind Speed at 10 m above Ground Level, m/s


2

Figure 2.5.5 Regression Analysis of L90 Sound Levels vs. Wind Speed

2.6 SURVEY RESULTS TYPICAL SOUND LEVELS

As opposed to the momentary, near-minimum sound levels captured by the L90 statistical

measure, the Leq, or average, sound level quantifies the typical sound level that might be heardat any given time. The Leq sound levels for all positions except 4 (where unsually high sound

levels were observed) are plotted below in Figure 2.6.1 for the survey period.


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Average (Leq) Sound Levels vs Time at All Positions Except 4


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Date and Time

SoundPressureLevel,dB

Position 1

Position 2

Position 3

Position 5

Position 6Position 7

Figure 2.6.1 10 minute Leq Sound Levels

This plot shows that all of the positions follow the same general trend except for Position 3, which

is somewhat higher almost all of the time. Neglecting the high levels at this monitoring station theremaining positions, plotted in Figure 2.6.2, more clearly display a consistent pattern. The

average of these five remaining (quietest) positions is considered a reasonable design value for thesite-wide, typical sound level (Figure 2.6.3).


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Average (Leq) Sound Leve ls vs T ime at All Positions Except 3 and 4


0

10

20

30

40

50

60

70

80

12/14/0712:00

12/15/070:00

12/15/0712:00

12/16/070:00

12/16/0712:00

12/17/070:00

12/17/0712:00

12/18/070:00

12/18/0712:00

12/19/070:00

12/19/0712:00

12/20/070:00

12/20/0712:00

12/21/070:00

12/21/0712:00

12/22/070:00

12/22/0712:00

12/23/070:00

12/23/0712:00

12/24/070:00

12/24/0712:00

12/25/070:00

12/25/0712:00

12/26/070:00

12/26/0712:00

12/27/070:00

12/27/0712:00

12/28/070:00

12/28/0712:00

12/29/070:00

12/29/0712:00

12/30/070:00

12/30/0712:00

12/31/070:00

12/31/0712:00

1/1/080:00

1/1/0812:00

1/2/080:00

1/2/0812:00

1/3/080:00

Date and Time


Position 1

Position 2

Position 5

Position 6

Position 7

Figure 2.6.2 10 minute Leq Sound Levels at All Monitoring Positions Except 3 and 4

Site-wide Average (Leq) Sound Leve l vs T ime - Wintertime Conditions

Design Leq Background Level (Average of All Positions Except 3 and 4)

0

10

20

30

40

50

60

70

80

12/14/0712:00

12/15/070:00

12/15/0712:00

12/16/070:00

12/16/0712:00

12/17/070:00

12/17/0712:00

12/18/070:00

12/18/0712:00

12/19/070:00

12/19/0712:00

12/20/070:00

12/20/0712:00

12/21/070:00

12/21/0712:00

12/22/070:00

12/22/0712:00

12/23/070:00

12/23/0712:00

12/24/070:00

12/24/0712:00

12/25/070:00

12/25/0712:00

12/26/070:00

12/26/0712:00

12/27/070:00

12/27/0712:00

12/28/070:00

12/28/0712:00

12/29/070:00

12/29/0712:00

12/30/070:00

12/30/0712:00

12/31/070:00

12/31/0712:00

1/1/080:00

1/1/0812:00

1/2/080:00

1/2/0812:00

1/3/080:00

Date and Time


2.6.3 Design Leq Background Level


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This design Leq sound level is plotted along with the average wind speed at 10 m in Figure 2.6.4

below.

Site-wide Design Leq Background Sound Level vs. Normalized Wind Speed


0

2

4

6

8

10

12

14

16

18

20

12/14/0712:00

12/15/070:00

12/15/0712:00

12/16/070:00

12/16/0712:00

12/17/070:00

12/17/0712:00

12/18/070:00

12/18/0712:00

12/19/070:00

12/19/0712:00

12/20/070:00

12/20/0712:00

12/21/070:00

12/21/0712:00

12/22/070:00

12/22/0712:00

12/23/070:00

12/23/0712:00

12/24/070:00

12/24/0712:00

12/25/070:00

12/25/0712:00

12/26/070:00

12/26/0712:00

12/27/070:00

12/27/0712:00

12/28/070:00

12/28/0712:00

12/29/070:00

12/29/0712:00

12/30/070:00

12/30/0712:00

12/31/070:00

12/31/0712:00

1/1/080:00

1/1/0812:00

1/2/080:00

1/2/0812:00

1/3/080:00

Date and Time

WindSpeed,m/s

0

10

20

30

40

50

60

70Normalized Wind Speed at 10 m

Design Leq Level

Figure 2.6.4 Design Leq Sound Level and Concurrent Wind Speed

As with the L90 levels in Figure 2.5.4, there is a clear correlation between wind speed and thetypical Leq sound level. The only real difference is that the magnitude of the Leq sound level atany given time is significantly higher because the average sound level does not exclude

momentarily louder sounds, such as from trees rustling in a wind gust. Such events, in effect, are

figured in yield a truly average sound level as opposed to the L90, which represents the

quietest lulls that occur only a small fraction of the time.

Figure 2.6.5 is a regression analysis, which quantitatively determines the mean Leq sound level as

a function of wind speed. Sound levels over the wind speed range of interest from cut-in at

about 3 m/s to 10 m/s when all turbines are generally operating at full power - are tabulated below.

Table 2.6.1 Measured Leq Sound Levels at Integer Wind Speeds (from Fig. 2.6.5)

Wind speed at

10 m, m/s3 4 5 6 7 8 9 10

Typical Leq

Sound Level,dBA -

Wintertime

34 37 40 42 45 48 51 53


22/48



Regression Analysis of Site-wide Leq Sound Level vs. Normalized Wind Speed

"Typical" Sound Level - Wintertime Conditions

y = 2.7337x + 25.892

R2 = 0.5424

0

5

10

15

20

25

30

35

40

45

50

55

60

65

70

0 1 2 3 4 5 6 7 8 9 10 11 12

Wind Speed at 10 m above Ground Level, m/s


Figure 2.6.5 Regression Analysis of Leq Sound Levels vs. Wind Speed

2.7 FREQUENCY CONTENT OF BACKGROUND LEVELS

The frequency content of the background levels was recorded by a 1/3 octave band analyzer at

Position 7 for the first week of the survey (a power interruption apparently occurred at the heightof a storm on 12/23 precluding further measurements). Figure 2.7.1 below is a plot of the A-

weighted L90(10 min) sound levels measured vs. time and wind speed at this position from 12/14

to 12/23. Four points, A through D, are identified that mark typical maxima (during windy

periods) and minima (during relatively calm periods). The linear frequency spectra (without anyweighting) for each of these points are shown in Figure 2.7.2.


23/48



L90 Background Sound Level at Position 7 vs. Normalized Wind Speed


0

2

4

6

8

10

12

14

16

18

20

12/14/0712:00

12/15/070:00

12/15/0712:00

12/16/070:00

12/16/0712:00

12/17/070:00

12/17/0712:00

12/18/070:00

12/18/0712:00

12/19/070:00

12/19/0712:00

12/20/070:00

12/20/0712:00

12/21/070:00

12/21/0712:00

12/22/070:00

12/22/0712:00

12/23/070:00

12/23/0712:00

Date and Time

WindSpeed,m/s

0

10

20

30

40

50

60

70



Position 7 - L90

A B C D

Figure 2.7.1 A-weighted L90 Sound Level vs. Time at Position 7

Unweighted 1/3 Octave Band Spectra of Typical Maxima and Minima

L90(10 min) at Position 7

0

10

20

30

40

50

60

70

80

6.3Hz

8.0Hz

10Hz

12.5

16Hz

20Hz

25Hz

31.5

40Hz

50Hz

63Hz

80Hz

100Hz

125Hz

160Hz

200Hz

250Hz

315Hz

400Hz

500Hz

630Hz

800Hz

1.0k

1.25k

1.6k

2.0k

2.5k

3.15k

4.0k

5.0k

6.3k

8.0k

10.0k

12.5k

16.0k

20.0k

dBA

1/3 Octave Band Center Frequency, Hz

SoundPressureLevel,dB(Lin)

Spectrum A Dec. 15 - 5:20

Spectrum B Dec. 16 - 20:20

Spectrum C Dec. 18 - 1:10

Spectrum D Dec. 23 - 18:20

Wind-induced Microphone Self-Noise

Figure 2.7.2 Un-weighted Frequency Spectra at Selected Minima and Maxima


24/48



The un-weighted, or linear, frequency spectra in Figure 2.7.2 show the actual sound levels for

each of these time snapshots. They are typical of environmental sound levels in the sense that thelower frequencies on the left-hand side of the chart have fairly high magnitudes and the higher

frequencies on the right-hand side have low values. A moderate amount of low frequency sound

exists in all environments even in remote areas during calm wind conditions. Because the

human ear is very insensitive to low frequency sound it is not perceptible in most environmentsand can only be detected with instruments.

This mismatch between the sound energy that is actually present and what is subjectively

perceived by the ear is the reason that A-weighting was developed. Simply put, A-weightingapplies adjustment factors to the actual (linear) sound level spectrum that bring it into much better

agreement with the way sounds are perceived giving A-weighted levels a much more tangible

meaning. Specifically, large constants of up to 70 dB are subtracted from the lowest frequencybands gradually diminishing to 0 dB at 1000 Hz, small positive values are added to the frequencies

around 2000 Hz and small subtractions are made in higher frequencies. These artificial

adjustments make the frequency spectrum look essentially like it subjectively sounds; i.e. the

highest magnitude frequency bands are the frequencies most clearly audible and the frequency

bands with relatively low levels (generally more than 10 dB below the maximum values) add

nothing the total level and are largely or completely imperceptible.

Figure 2.7.3 below shows the same sound level spectra shown in Figure 2.7.2 with A-weighting

applied.

A- weighted 1/3 Octave Band Spectra of Typical Maxima and Minima

L90(10 min) at Position 7

0

10

20

30

40

50

60

6.3Hz

8.0Hz

10Hz

12.5

16Hz

20Hz

25Hz

31.5

40Hz

50Hz

63Hz

80Hz

100Hz

125Hz

160Hz

200Hz

250Hz

315Hz

400Hz

500Hz

630Hz

800Hz

1.0k

1.25k

1.6k

2.0k

2.5k

3.15k

4.0k

5.0k

6.3k

8.0k

10.0k

12.5k

16.0k

20.0k

dBA



Spectrum A Dec. 15 - 5:20

Spectrum B Dec. 16 - 20:20

Spectrum C Dec. 18 - 1:10

Spectrum D Dec. 23 - 18:20Wind-induced Microphone Self-Noise

Irrelevant to A-wtd Level

Frequencies Dominating A-wtd Level

2.7.3 A-weighted Frequency Spectra at Selected Minima and Maxima

In Figure 2.7.2 the un-weighted spectra during windy conditions, B and D, exhibit very elevated

sound levels in the frequency bands below about 40 Hz. This noise is not actually present in the

environment but is a false signal generated by wind infiltrating the windscreen (despite being

oversize) and blowing over the microphone. This effect is, for all practical purposes,


25/48



unpreventable but is confined to the very lowest frequencies where, importantly, it does not have

any appreciable influence on the measured A-weighted sound level. As illustrated in Figure 2.7.3,the artificially elevated frequencies below 40 Hz are at least 20 dB below the maximum values and

therefore totally inconsequential when A-weighting is applied to the spectra. An overall A-

weighted sound level expressed, for example, as a level of 53 dBA - is the logarithmic sum of

the A-weighted frequency spectrum. Logarithmic, as opposed to arithmetic, addition means thatthe maximum values strongly govern the result and that lesser values have little or no influence onthe overall sum. In general, values that are 10 dB or more below the highest values do not

contribute in any meaningful way to the total. For example, a level of 50 dB plus 40 dB equals a

total of 50 dB the 40 dB component effectively contributes nothing.

The fact that false signal noise in the lowest frequencies (illustrated in Figure 2.7.2) is nearly

unavoidable during windy conditions, particularly with standard, non-specialized windscreens, isthe fundamental reason that wind turbines are widely but mistakenly believed to produce high

levels of low frequency and infrasonic noise. Any casual measurement of an operational wind

turbine, measured by definition during windy conditions, will (falsely) indicate high levels of low

frequency noise. Numerous field studies, including our own, show that if the turbine were

shutdown and the measurement repeated under the same wind conditions the same apparent levels

of low frequency noise would still be present.

In general, the frequency content of the background levels measured at Position 7 have a

broadband and featureless character as illustrated in Figure 2.7.3. The peak (perceptible) soundoccurs in the 200 to 2000 Hz range exactly where wind turbine sound is also most prominent.

Because of this similarity, wind-driven natural sounds can be expected to provide a meaningful

amount of masking against project sound levels.

3.0 CONCLUSIONS

A field survey of existing sound levels during leaf-off, wintertime conditions was carried out at

the Cape Vincent Wind Farm site in late December of 2007 and early January of 2008. The

objective of the survey was to determine how much background masking sound there is at the site

to potentially obscure project noise during the cold weather months when the trees are bare andinsect noise is absent.

The survey results indicate that, if anomalously high levels at certain times at certain positions areneglected, sound levels over the entire site area are reasonably similar in magnitude at any given

time, follow the same temporal trends and depend heavily on wind speed. Regression analyses of

wind speed vs. sound levels show that the following sound levels are likely to exist over the wind

speed range of interest (3 to 10 m/s) during the winter.

Table 3.0.1 Measured L90 and Leq Sound Levels at Integer Wind Speeds

Wind speed at

10 m, m/s3 4 5 6 7 8 9 10

Typical Leq

Sound Level,dBA -

Wintertime

34 37 40 42 45 48 51 53

Worst-Case

L90 Sound

Level, dBA -

Wintertime

24 27 30 34 37 40 44 47


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A review of the frequency content recorded at one position indicates that project area sound levels

during the winter are broadband and fairly featureless in character with the maximum perceptiblesound energy centered in the 200 to 2000 Hz range the same range where wind turbine sound is

most prominent.

END OF REPORT TEXT


27/48




3862 Clifton Manor PlaceSuite BHaymarket, Virginia 20169 USAPhone: 703-753-1602Fax: 703-753-1522Website: www.hesslernoise.com

REPORT NO. 1810-112607-0

REV: 0

DATE OF ISSUE: NOVEMBER27, 2007

ENVIRONMENTAL SOUND LEVEL SURVEYSUMMERTIME CONDITIONS

CAPE VINCENT WIND FARM

TOWNS OF CAPE VINCENT AND LYMEJEFFERSON COUNTY, NY

PREPARED FOR:

BP Alternative Energy N. A., Inc.

Prepared by:

David M. Hessler, P.E., INCE

Principal Consultant

Hessler Associates, Inc.


28/48




CONTENTS

1.0 INTRODUCTION 1

2.0 BACKROUND SOUND LEVEL SURVEY 1

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES 12.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS 22.3 INSTRUMENTATION 102.4 SURVEY WEATHERCONDITIONS 112.5 OVERALL SURVEY RESULTS 132.6 FREQUENCY CONTENT OF BACKGROUND SOUNDS 17

3.0 CONCLUSIONS 19

Graphic A General Site Map Showing Background Survey Positions


29/48



1.0 INTRODUCTION

Hessler Associates, Inc. has been retained by BP Alternative Energy to evaluate potential noiseimpacts from the proposed Cape Vincent Wind Farm Project on residents in the vicinity of the

project area, which is located in Jefferson County, NY just east of the Town of Cape Vincent.

The study consists of three phases:

x A field survey of existing background sound levels during leaf-on, summertimeconditions

x A field survey of existing background sound levels during leaf-off, wintertime conditions

x An impact assessment based on the measured levels of background sound from both

surveys and the predicted project sound levels developed from an analytical noise model

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 outwhen seasonal conditions permit. An impact assessment will then be prepared based on the results

of both surveys.

The measurement of existing sound levels at the site is necessary to determine how much naturalmasking 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 readilyperceptible. 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.

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 Impactspublished 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 nosignificant impact and a potentially adverse impact. Hence the need to determine what the

background sound level is.

2.0 BACKGROUND SOUND LEVEL SURVEY

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES

The purpose of the survey was to determine what minimum environmental sound levels are

consistently present and available at the nearest potentially sensitive receptors to mask or obscure

potential noise from the project under summertime conditions when the trees are leafed out. A

number of statistical sound levels were measured in consecutive 10 minute intervals over theentire survey. Of these, the average (Leq) and residual (L90) levels are the most meaningful.


30/48



The average, or equivalent energy sound level (Leq), is literally the average sound level over each

measurement interval. This is the typical sound level most likely to be observed at any givenmoment.

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 measurementinterval 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.

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 withwind 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 forlater correlation to the sound data.

2.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS

At the time of the initial field survey the number of turbines and their specific locations were still

being worked out. The general extent of the project area was known from the distribution of land

owners who had concluded leasing agreements with the project. The site area can be broadlydefined as the eastern half of the Town of Cape Vincent, beginning several miles back from the

bank of the St. Lawrence River and extending to the Lyme town line. Some turbines are also

being tentatively considered in the western part of Lyme generally from town line with Cape

Vincent to the village of Three Mile Bay.

The site area is rural and can be characterized as consisting mostly of farms on relatively largetracts 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 Lymewhere 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.

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 monitorswere placed at isolated farms and while others were located near the three relatively high

population density areas mentioned above.


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Position 1 8718 County Road 8 Cape Vincent

Typical farm. Monitor placed on a fencepost near the barn.

Figure 2.2.1 Position 1 Looking North.

Figure 2.2.2 Position 1 Looking Northeast.


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Position 2 30485 CR 4 Rosiere (Cape Vincent)

Monitor located on a fence post at a farm near the center of Rosiere.

Figure 2.2.3 Position 2 Looking West towards

Church of St. Vincent de Paul

Figure 2.2.4 Position 2 Looking Southeast towards Barn


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Position 3 Huff Road and Route 12E Cape Vincent

Monitor located on a utility pole about 40 ft. from edge of Route 12E, the principal road in the

area. The objective of this position was to measure sound levels representative of thoseexperienced at the homes along Route 12E, such as the farm house in the background of Figure

2.2.5.

Figure 2.2.5 Position 3 Looking West towards Huff Road

Figure 2.2.6 Position 3 Looking North towards Route 12E


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Position 4 27323 Fox Creek Road Cape Vincent

Typical farm. Monitor located on a utility pole near the house.

Figure 2.2.7 Position 4 Looking Northeast towards House

Figure 2.2.8 Position 4 Looking West towards Barns


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Position 5 8559 Church St. Three Mile Bay, Lyme

Monitor located on a post in an open field about 200 ft. behind the house and barn. This position

conservatively represents sound levels in the village of Three Mile Bay, since the meter was

placed on the outskirts of the village and away from much of the normal man-made noise presentaround the homes.

Figure 2.2.9 Position 5 Looking South towards the Village(just beyond the barn)

Figure 2.2.10 Position 5 Looking North away from the Village


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Position 6 Opposite 27140 CR 57 Lyme

Monitor located on gate post in an open field across the road from the homes along CR 57 facing

Chaumont Bay.

Figure 2.2.11 Position 6 Looking East

(CR 57 to right just past first few trees)

Figure 2.2.12 Position 6 Looking Southwest(CR 57 to left beyond the trees)


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Position 7 29766 CR 6 Cape Vincent

Monitor located on fence post in rear yard of house.

Figure 2.2.13 Position 7 Looking North

Figure 2.2.14 Position 7 Looking West


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2.3 INSTRUMENTATION AND SURVEY DURATION

Rion NL-32 and NL-22 sound level meters (ANSI Type 1 and 2, respectively) were used at 6 ofthe 7 positions. A Norsonic 118, ANSI Type 1, 1/3 octave band analyzer was used at Position 7 to

record the frequency spectrum of the sound as well as the overall A-weighted levels measured bythe other instruments.

The meters were all enclosed in watertight cases with the microphones supported 12 to the side or

above each case to minimize any local reflections.

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 while

remaining Rion instruments had weather-treated 3diameter foam windscreens. The Norsonic

meter had a special environmental microphone housing where the microphone tip is protectedfrom 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. Figure 2.3.1 illustrates a typical wind speed profile based

on IEC 61400-111.

Typical Wind Speed Profile

at a Wind Speed of 6 m/s

per IEC 61400-11

0

10

20

30

40

50

60

70

80

90

0 1 2 3 4 5 6 7 8 9 10

Wind Speed , m/s

HeightAboveGroundLevel,m

Standard IEC

Height = 10 m

Anemometer Height = 60 m

Typ. Hub Height = 80 m

Background Sound

Measurement Microphone

Height = 1 m

Figure 2.3.1

1International Electromechanical Commission (IEC) 61400-11:2002(E) Wind Turbine Generator Systems Part 11:

Acoustic Noise Measurement Techniques, Second Edition 2002-12.


39/48



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 inconsequentialwind speeds of about 3 or 4 m/s during the wind conditions of greatest interest (6 to 8 m/s at 10

m). In any event, self-generated wind noise affects only the extreme lower frequencies 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 thespectrum is summed to give an overall A-weighted level. Consequently, the measured values areconsidered reasonably valid and free of any meaningful or significant self-generated

contamination.

All equipment was field calibrated at the beginning of the survey and again at the end of the

survey. The observed calibration drift of all the instruments was between 0 to - 0.4 dB with most

in the 0 to -0.2 dB range.

The survey was carried out over an 18 day period from August 23 to September 9, 2007. Because

of an apparent AC power interruption the frequency recording monitor at Position 7 ran only for

the first several days while all other meters operated perfectly.

2.4 SURVEY WEATHERCONDITIONS

Although the amount of cloud cover varied from clear to overcast at various times, the weather

conditions during the survey period were generally fair with no significant precipitation after the

first day when a very strong thunderstorm passed over the area.

Winds during the survey were fairly light, although two periods of moderate winds (Aug. 24 26

and Sep. 7 8) were captured.

The general conditions of temperature, barometric pressure and wind for the survey period are

shown in the chart below (Figure 2.4.1) as observed at Watertown, NY, some 20 miles southeast

of the site.

It is important to note that the survey was carried out during summertime conditions with theleaves 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 thetime of the survey resulting in elevated sound levels on most evenings and at other times of day.


40/48



Figure 2.4.1 General Weather Data for the Survey Period as Observed in Watertown, NY

The wind speed at the site itself was measured at two met towers distributed over the project area:one near Monitor Position 1 in the northern part of the site and the other near Position 4 in the

southern end. The 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 isassociated with farmland with some vegetation. The 10 m wind speed is important because

turbine sound levels are expressed as a function of the wind speed at this standardized elevation.


41/48



Measured Wind Speed at 60 m (Towers 4207 and 4208) and

Wind Speed Normalized to Standard 10 m Elevation

0

2

4

6

8

10

12

14

8/23/0712:00

8/24/070:00

8/24/0712:00

8/25/070:00

8/25/0712:00

8/26/070:00

8/26/0712:00

8/27/070:00

8/27/0712:00

8/28/070:00

8/28/0712:00

8/29/070:00

8/29/0712:00

8/30/070:00

8/30/0712:00

8/31/070:00

8/31/0712:00

9/1/070:00

9/1/0712:00

9/2/070:00

9/2/0712:00

9/3/070:00

9/3/0712:00

9/4/070:00

9/4/0712:00

9/5/070:00

9/5/0712:00

9/6/070:00

9/6/0712:00

9/7/070:00

9/7/0712:00

9/8/070:00

9/8/0712:00

9/9/070:00

Date and Time

WindSpeed,m/s

Average Wind Speed at 60 m


Figure 2.4.2 Measured Wind Speeds at Site during Sound Survey Period

2.5 OVERALL SURVEY RESULTS

As discussed above in Section 2.1 the L90, or residual, sound level is a conservative measure of

background sound levels in the sense that it filters out short-duration, sporadic noise events thatcannot be relied upon to provide consistent and continual masking noise to obscure potential

turbine noise. This level represents the quiet, momentary lulls between all relatively short

duration events, such as cars passing by or tractor activity in a neighboring field. As such, it is thenear worst-case background level with regard to evaluating potential impacts from a new source.

The L90 sound levels over consecutive 10 minute periods for all 7 positions are plotted below for

the survey period.


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Residual (L90) Sound Levels vs Time at All Positions

0

10

20

30

40

50

60

70

8/23/0712:00

8/24/070:00

8/24/0712:00

8/25/070:00

8/25/0712:00

8/26/070:00

8/26/0712:00

8/27/070:00

8/27/0712:00

8/28/070:00

8/28/0712:00

8/29/070:00

8/29/0712:00

8/30/070:00

8/30/0712:00

8/31/070:00

8/31/0712:00

9/1/070:00

9/1/0712:00

9/2/070:00

9/2/0712:00

9/3/070:00

9/3/0712:00

9/4/070:00

9/4/0712:00

9/5/070:00

9/5/0712:00

9/6/070:00

9/6/0712:00

9/7/070:00

9/7/0712:00

9/8/070:00

9/8/0712:00

9/9/070:00

Date and Time


Pos it ion 1 Pos it ion 2 Pos it ion 3 Pos it ion 4

Posit ion 5 Posit ion 6 Posit ion 7

Figure 2.5.1 10 minute L90 Sound Levels at All Monitoring Positions

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 consistentlylower 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 ofinsect noise, or the fact that the monitor was not particularly close to any trees and was exposed to

less wind-induced noise.

In any event, the general trend in site-wide sound levels can be seen much more clearly if the

Position 4 data are removed, as in Figure 2.5.2. Although there is some inevitable local variation,

all of these levels at these widely distributed locations in a diversity of settings follow a muchmore consistent pattern. No one position is consistently higher or lower than the mean value,

which is plotted in Figure 2.5.3.

A daily trend is clearly evident in the average site-wide sound level where it briefly reaches aminimum in the early morning hours (on some days more than others) and then rapidly increases.

These minima are generally associated with a temporary reduction in insect noise followed by a

sudden resumption of insect noise possibly augmented by an increase in man-made and naturalsounds in the morning.

The average L90 value plotted in Figure 2.5.3 is considered a design value that reasonably

represents the likely sound level anywhere in the site area. Except for occasional nighttime lulls, it

can be seen that sound levels typically range between about 40 and 55 dBA.


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Residual (L90) Sound Levels vs Time at All Positions Except 4

0

10

20

30

40

50

60

70

8/23/0712:00

8/24/070:00

8/24/0712:00

8/25/070:00

8/25/0712:00

8/26/070:00

8/26/0712:00

8/27/070:00

8/27/0712:00

8/28/070:00

8/28/0712:00

8/29/070:00

8/29/0712:00

8/30/070:00

8/30/0712:00

8/31/070:00

8/31/0712:00

9/1/070:00

9/1/0712:00

9/2/070:00

9/2/0712:00

9/3/070:00

9/3/0712:00

9/4/070:00

9/4/0712:00

9/5/070:00

9/5/0712:00

9/6/070:00

9/6/0712:00

9/7/070:00

9/7/0712:00

9/8/070:00

9/8/0712:00

9/9/070:00

Date and Time


Position 1 Position 2 Position 3

Position 5 Position 6 Position 7

Figure 2.5.2 10 minute L90 Sound Levels at All Monitoring Positions Except 4

Average Residual (L90) Sound Level vs Time at All Positions Except 4

0

10

20

30

40

50

60

70

8/23/0712:00

8/24/070:00

8/24/0712:00

8/25/070:00

8/25/0712:00

8/26/070:00

8/26/0712:00

8/27/070:00

8/27/0712:00

8/28/070:00

8/28/0712:00

8/29/070:00

8/29/0712:00

8/30/070:00

8/30/0712:00

8/31/070:00

8/31/0712:00

9/1/070:00

9/1/0712:00

9/2/070:00

9/2/0712:00

9/3/070:00

9/3/0712:00

9/4/070:00

9/4/0712:00

9/5/070:00

9/5/0712:00

9/6/070:00

9/6/0712:00

9/7/070:00

9/7/0712:00

9/8/070:00

9/8/0712:00

9/9/070:00

Date and Time


2.5.3 Average L90 Background Level at All Positions Except 4


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The average L90 design sound level is plotted along with the average wind speed at 10 m in

Figure 2.5.4 below.

Average Residual (L90) Sound Level Compared to Concurrent Wind Speed

0

2

4

6

8

10

12

8/23/0712:00

8/24/070:00

8/24/0712:00

8/25/070:00

8/25/0712:00

8/26/070:00

8/26/0712:00

8/27/070:00

8/27/0712:00

8/28/070:00

8/28/0712:00

8/29/070:00

8/29/0712:00

8/30/070:00

8/30/0712:00

8/31/070:00

8/31/0712:00

9/1/070:00

9/1/0712:00

9/2/070:00

9/2/0712:00

9/3/070:00

9/3/0712:00

9/4/070:00

9/4/0712:00

9/5/070:00

9/5/0712:00

9/6/070:00

9/6/0712:00

9/7/070:00

9/7/0712:00

9/8/070:00

9/8/0712:00

9/9/070:00

Date and Time

Win

dSpeedat10m,m/s

0

10

20

30

40

50

60


Wind Speed at 10 m

Average L90

Figure 2.5.4 Background L90 Sound Levels and Wind Speed

This plot shows that, for summertime conditions at least, background sound levels over the site

area are not directly driven by wind-induced natural sounds. The two traces would generally

parallel each other if this were the case, rising and falling at the same times. This lack of

correlation indicates that sounds from such sources as crickets, distant farm equipment and localroads dominate the sound level observed at any given location and that wind-induced sounds are

very secondary.

This is shown quantitatively in Figure 2.5.5, which is a regression analysis of sound levels as a

function of wind speed. As shown by the trend line there is only a very slight tendency towards

louder sound levels during windier conditions. In essence, the likely background sound level from

the point where the turbines would begin to operate (at a wind speed of around 3 to 4 m/s) to the

point where they reach maximum sound output (roughly 8 to 9 m/s) ranges from 45 to 50 dBA. In

many cases, the critical wind speed where turbine noise is generally the greatest relative to theamount of available masking noise is about 6 m/s. The survey data indicate that a sound level of

about 47 dBA is likely to exist at this wind speed under summertime conditions.


45/48


46/48



Residual (L90) Sound Level vs Time at Position 7

Compared to S ite-wide Average

20

25

30

35

40

45

50

55

60

65

70

8/23/0712:00

8/23/0713:00

8/23/0714:00

8/23/0715:00

8/23/0716:00

8/23/0717:00

8/23/0718:00

8/23/0719:00

8/23/0720:00

8/23/0721:00

8/23/0722:00

8/23/0723:00

8/24/070:00

8/24/071:00

8/24/072:00

8/24/073:00

8/24/074:00

8/24/075:00

8/24/076:00

8/24/077:00

8/24/078:00

8/24/079:00

8/24/0710:00

8/24/0711:00

8/24/0712:00

8/24/0713:00

8/24/0714:00

8/24/0715:00

8/24/0716:00

8/24/0717:00

8/24/0718:00

8/24/0719:00

8/24/0720:00

8/24/0721:00

8/24/0722:00

8/24/0723:00

8/25/070:00

8/25/071:00

8/25/072:00

8/25/073:00

8/25/074:00

8/25/075:00

8/25/076:00

8/25/077:00

8/25/078:00

8/25/079:00

8/25/0710:00

8/25/0711:00

8/25/0712:00

8/25/0713:00

8/25/0714:00

8/25/0715:00

8/25/0716:00

8/25/0717:00

Date and Time


Position 7

Site-wide Average

(Except 4)

A B C D E

Figure 2.6.1 Overall A-weighted Sound Level vs. Time at Position 7

Selected Maximum and Minimum Frequency Spectra at Position 7

0

10

20

30

40

50

60

70

6.3Hz

8.0Hz

10Hz

12.5Hz

16Hz

20Hz

25Hz

31.5Hz

40Hz

50Hz

63Hz

80Hz

100Hz

125Hz

160Hz

200Hz

250Hz

315Hz

400Hz

500Hz

630Hz

800Hz

1.0k

1.25k

1.6k

2.0k

2.5k

3.15k

4.0k

5.0k

6.3k

8.0k

10.0k

12.5k

16.0k

20.0k

dBA


SoundPressureLevel,dB

Spectrum A 8/23 20:00

Spectrum B 8/24 5:00

Spectrum C 8/24 20:00

Spectrum D 8/25 1:20

Spectrum E 8/25 5:00

Figure 2.6.2 Frequency Spectra at Selected Minima and Maxima


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Figure 2.6.2 clearly shows that insect noise peaking at 5000 Hz strongly affected the overall sound

levels when they were at a maximum and, significantly, also when they were at a minimum.

The overall A-weighted value of a sound is the logarithmic summation of the frequency spectrum

and is much more sensitive to the high end of the spectrum than the low end (just as the human ear

is). That is why the strong low frequency tone at 12.5 Hz in Spectrum C has relatively littleimpact on the total A-weighted level. The origin of this tone is unknown but may have been a

truck idling or helicopter fly-over.

In general, the continual dominance of insect noise, which is clearly unrelated to wind oratmospheric conditions, explains why the site sound levels during the summer at least - do not

exhibit any real dependence on wind speed.

3.0 CONCLUSIONS

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. The objective of

the survey was to determine how much background masking sound there is at the site topotentially obscure project noise during the summer when people are likely to be outside andwhen windows are likely to be open.

The survey results indicate that, except for one anomalous location, sound levels over the site areaare reasonably consistent and follow the same temporal trends.

A comparison of the average site-wide L90 sound level to concurrent wind speed as measured by

two on-site met towers indicates that environmental sound levels have very little dependence on

wind speed and range from about 45 to 50 dBA over the wind speed range of importance to windturbine impact analyses generally from about 3 to 9 m/s as measured at 10 m.

A review of the frequency content recorded at one position indicates that project area sound levels

during the summer are strongly dominated by insect noise at 5000 Hz and vary up and down overthe course of each day largely in accordance with insect activity. At no time, including daily

minima, was this high frequency insect noise absent. The dominance of this noise source explains

why sound levels have no real correlation to wind speed and wind-induced sounds.

An additional field survey is planned for this winter to measure project area sound levels without

any leaves on the trees and without any of this insect activity. A subsequent noise impact

assessment will be prepared based on the results of both the summer and winter background

surveys.

END OF REPORT TEXT


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