St.Lawrence wind farm SDEIS Noise Study 2008

7/29/2019 St.Lawrence wind farm SDEIS Noise Study 2008

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Member National Council of Acoustical ConsultantsNoise 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. 1804-011908-0

REV: 0DATE OF ISSUE:JANUARY 21,2008

ENVIRONMENTAL SOUND LEVEL SURVEY RESULTSSUMMER AND WINTERTIME CONDITIONS

ST.LAWRENCE WIND FARM

TOWN OF CAPE VINCENTJEFFERSON COUNTY,NY

PREPARED FOR:

Acciona Wind Energy USA, LLC

Prepared by:

David M. Hessler, P.E., INCEPrincipal ConsultantHessler Associates, Inc.


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Member National Council of Acoustical ConsultantsNoise Control Services Since 1976


CONTENTS

1.0 INTRODUCTION 1

2.0 SURVEY METHODOLOGY 1

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES 12.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS 22.3 INSTRUMENTATION 9

3.0 SURVEY RESULTS - SUMMERTIME 10

3.1 SURVEY WEATHER CONDITIONS 103.2 OVERALL SURVEY RESULTS 123.3 FREQUENCY CONTENT OF BACKGROUND SOUNDS 19

4.0 SURVEY RESULTS - WINTERTIME 21

4.1 SURVEY WEATHER CONDITIONS 214.2 OVERALL SURVEY RESULTS 23

5.0 CONCLUSIONS 30

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 Acciona Wind Energy USA to evaluate potentialnoise impacts from the proposed St. Lawrence Wind Farm Project on residents in the vicinity ofthe project area, which is located in the Town of Cape Vincent, New York.

This report covers only the first phase of the project, which is to quantify current backgroundsound levels in the site area during both summertime and wintertime conditions.

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 theproject. The relevance of this is that high levels of background noise due to wind-induced naturalsounds, 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 readilyperceptible. Because it would be incorrect, for example, to compare the maximum turbine soundlevel, which occurs only during windy conditions, with the background level during calm andquiet conditions, the background sound level must be determined as a function of wind speed. Fora 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 backgroundlevel 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 absoluteterms by comparing expected future sound levels (developed from modeling) to the pre-existinglevel of background sound (determined from field measurements). The procedure essentiallydefines 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 measure the existingbackground sound levels and establish a datum against which to compare predicted project soundlevels.

2.0 SURVEY METHDOLOGY

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES

The purpose of the surveys was to determine what minimum environmental sound levels areconsistently present and available at the nearest potentially sensitive receptors to mask or obscurepotential noise from the project under both warm weather and cold weather seasonal conditions.A number of statistical sound levels were measured in consecutive 10 minute intervals over eachsurvey. Of these, the average (Leq) and residual (L90) levels are the most meaningful.

The average, or equivalent energy sound level (Leq), is literally the average sound level over eachmeasurement interval. This is the typical sound level most likely to be observed at any given

moment.

The L90 statistical sound level, on the other hand, is commonly used to conservatively quantifybackground 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 capturingthe quiet lulls between such events. It is this consistently present background level that forms aconservative, or worst-case, basis for evaluating the audibility of a new source. By definitionsuch a sound level exists only 10% of time while 90% of the time a higher sound level is present.


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An additional factor that is important in establishing the minimum background sound levelavailable 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 ofroughly 3 or 4 m/s (measured at a reference elevation of 10 m). Turbine sound levels increasewith wind speed up to about 8 or 9 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 ismost significant the level of natural masking noise is normally also relatively high due to tree orgrass rustle thus reducing the perceptibility of the turbines. In order to quantify this effect, windspeed was measured over each survey period in 10 minute increments by a 80 m met tower locatedwithin the site area for later correlation to the sound data.

2.2 SITE DESCRIPTION AND MEASUREMENT POSITIONS

At the time of the field surveys the number of turbines and their specific locations were still beingdeveloped; however, the general extent of the project area was known from the distribution of landowners who had concluded leasing agreements with the project. The site area can be broadlydefined as the western half of the Town of Cape Vincent between the St. Lawrence River and aline running parallel to the river roughly 4 miles inland.

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. The actualvillage of Cape Vincent lies some distance away from any proposed turbine locations.

The site topography is flat. In terms of vegetation, the area is a largely even mixture of open fieldsand wooded areas. Most of the homes and farm houses have at least a few trees immediatelyaround the house.

Six measurement locations were chosen to evenly cover and represent the entire area as shown inGraphic A. The specific positions are listed below along with photographs of each location. Avariety of settings were chosen - such as near wooded areas, in open fields, near homes and remotefrom homes, etc. in an effort to determine a typical sound level representative of the entire site

area.


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Position 1 Wood Farm, County Road 9The monitor placed at the edge of a wooded area bordering a large open tract of farm land. The

measurement position was selected so that it was far enough away from the dairy barns and mainfarm area so that noise from normal farm activities and milking machines was negligible.

Figure 2.2.1 Position 1 Looking Northeast towards Farm.

Figure 2.2.2 Position 1 Looking Northwest


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Position 2 7242 Millens Bay Road (County Road 8)

Monitor located on a fence post in an open area somewhat removed from the house and barn area.

Figure 2.2.3 Position 2 Looking North toward House

Figure 2.2.4 Position 2 Looking Southwest


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Position 3 33835 Route 12EMonitor located on a post immediately adjacent to the bank of the St. Lawrence River. Thislocation was intended to measure the sound levels typically experienced at the numerousresidences along the river in this area.

Figure 2.2.5 Position 3 Looking Northeast up River

Figure 2.2.6 Position 3 Looking West across the St. Lawrence River


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Position 4 4224 Branche RoadTypical area farm. Monitor located on a utility pole near the farmhouse and barns.

Figure 2.2.7 Position 4 Looking West towards Barns

Figure 2.2.8 Position 4 Looking South towards Neighboring House


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Position 5 2481 Route 12 EMonitor located on an idle grain conveyor immediately behind the farmhouse. This house islocated directly on Route 12E, which is the principal road in the area. The measurement positionwas set back from the road roughly the same distance as the house.

Figure 2.2.9 Position 5 Looking Southeast,House just Visible on Right-hand Edge of Photo

Figure 2.2.10 Position 5 Looking West


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Position 6 Triple A Farm, Hell St.Monitor located on a silo support behind several barns. Area not subject to a significant amountof local noise due to farm operations.

Figure 2.2.11 Position 6 Looking West

Figure 2.2.12 Position 6 Looking Northeast


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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 5 of

the 6 positions. A Norsonic 118, ANSI Type 1, 1/3 octave band analyzer was used at Position 6 torecord 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 boxes with the microphones supported away from thecases to minimize any local reflections.

The 5 Rion microphones were protected from wind-induced self-noise by extra-large 180 mm (7)diameter foam windscreens (ACO Model WS7-80T). The Norsonic meter had a specialenvironmental microphone housing (Norsonic Type 1212) where the microphone tip is protectedfrom wind by mesh covered slots and an external foam windscreen. In each case, themicrophones were situated at a fairly low elevation of approximately 1 m so that they wereexposed to relatively low wind speeds. Figure 2.3.1 illustrates a typical wind speed profile basedon IEC 61400-111.

Typical Wind Speed Profil e

at a Wind Speed of 6 m/s

per IEC 61400-11

0

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90

0 1 2 3 4 5 6 7 8 9 10

Wind Speed, m/s

HeightAboveGround

Level,m

Standard IEC

Height = 10 m

Anemometer Height = 60 m

Typ. Hub Height = 80 m

Background SoundMeasurement Microph one

Height = 1 m

Figure 2.3.1

Wind speed normally diminishes rapidly close to the ground, theoretically going to zero at thesurface; 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

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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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. As a result the measured values areconsidered valid and reasonably 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 thesurvey. The observed calibration drift of all the instruments was between +0.2 / -0.5 dB with mostin the +/-0.2 dB range.

The summertime survey was carried out over an 17 day period from August 22 to September 8,2007. Because of an AC power interruption the frequency recording monitor at Position 6 ranonly for the first several days while all other meters operated for the full period.

The wintertime survey ran from December 14, 2007 to January 4, 2008. The monitor at Position 1operated for the entire 20 day period but the others typically ran for about 15 days before losingbattery power in the extremely cold conditions. The Norsonic meter only ran a few hours on

internal batteries before cutting out due to a problem with the AC power adapter. In general, theNorsonic 118 meter is not intended for long-term outdoor service as an environmental monitor,particularly in harshly inclement weather. As a final note on winter survey, the windscreen onMonitor 2 blew off during a period of very high winds on the afternoon of December 23 - so thedata beyond that point has been neglected.

3.0 SURVEY RESULTS - SUMMERTIME

3.1 SURVEY WEATHER CONDITIONS

Although the amount of cloud cover varied from clear to overcast at various times, the weatherconditions during the survey period were generally fair with no significant precipitation after the

second 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 26and Sep. 7 8) were captured.

The general conditions of temperature, barometric pressure and wind for the survey period areshown in the chart below (Figure 3.1.1) as observed at Watertown, NY, some 20 miles southeastof 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 significantlyhigher sound levels than might be observed at the same location when the trees are bare. Inaddition, 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.


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Figure 3.1.1 General Weather Data for the Summer Survey Period as Observed in Watertown, NY

The wind speed at the site itself was measured by an 80 m met tower. The figure below, Figure3.1.2, shows the average 10 minute wind speed measured by the anemometer at an elevation of 40m and the wind speed normalized to a standard 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 somevegetation. The 10 m wind speed is important because turbine sound levels are expressed as afunction of the wind speed at this standardized elevation.


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Wind Speed Measured by On-site Met Towe r at 40 m

and Normalized to 10 m - Summertime Conditions

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Date and Time

WindSpeed,m/s

40 m Anemometer

Normalized Wind Speed at 10 m

Figure 3.1.2 Measured Wind Speed at Site during the Summer Sound Survey Period

3.2 OVERALL SURVEY RESULTS

As discussed above in Section 2.1 the L90, or residual, sound level is a conservative measure ofbackground 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 potentialturbine noise. This level represents the quiet, momentary lulls between all relatively shortduration 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 6 positions are plotted below forthe summer survey period.


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Residual (L90) Sound Levels vs Time at All Positions

Summertime Conditio ns

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Date and Time

SoundPressureLevel,dB

Position 1

Position 2

Position 3

Position 4

Position 5Position 6

Figure 3.2.1 10 minute L90 Sound Levels at All Monitoring Positions

This plot shows that, despite the varied settings, sound levels over the site area roughly follow thesame temporal trends except at Position 4 (turquoise trace), where the levels are consistentlyhigher than at all other locations. The reason for this anomalous behavior is not clear but may be

associated with the slightly elevated nature of the position on the crest of a rise (locally increasingwind-induced sounds) or with local noise from farming operations.

Although there is some inevitable local variation, the sound levels at the remaining positionsgenerally intertwine and have similar, though certainly not identical values, most of the time.Consequently, the average of these 5 positions (omitting Position 4) is considered a reasonablygood representation of the L90 sound level anywhere within the site area (Figure 3.2.2).

A daily trend is evident in Figure 3.2.2 where the average site-wide sound level 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 asudden resumption of insect noise in the morning - possibly augmented by an increase in man-made and other natural sounds.

Except for occasional nighttime lulls, it can be seen that sound levels typically range betweenabout 40 and 50 dBA.


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Site-wide Residual (L90) Sound Level v s Time - Summertime Condit ions

Design L90 Background Lev el (Average of All Positions Except 4)

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Date and Time


3.2.2 Average L90 Background Level at All Positions Except 4

The average L90 design sound level is plotted along with the average wind speed at 10 m inFigure 3.2.3 below.


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Average L90 Background Sound Leve l vs. Normalized Wind Speed

Wintert ime Conditions

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Date and Time

WindSpeed,m/s

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SoundPressureLevel,dBA


Site-wide L90 - Design Level

Figure 3.2.3 Background L90 Sound Levels and Wind Speed

This plot shows that, for summertime conditions at least, background sound levels over the sitearea are not predominantly driven by wind-induced natural sounds. The two traces wouldgenerally parallel each other if this were the case, rising and falling at the same times. This lack ofcorrelation 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 arevery secondary.

This is shown quantitatively in Figure 3.2.4, which is a regression analysis of sound levels as afunction of wind speed. As shown by the trend line there is only a very slight tendency towardslouder sound levels during windier conditions. In essence, the likely background sound level fromthe point where the turbines would begin to operate (at a wind speed of around 3 to 4 m/s) to thepoint where they reach maximum sound output (roughly 8 to 9 m/s) varies only slightly from

about 43 to 46 dBA. In many cases, the critical wind speed where turbine noise is generally thegreatest relative to the amount of available masking noise is about 6 m/s. The survey data indicatethat a sound level of about 44 dBA is likely to exist at this wind speed under summertimeconditions.


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

Summertime Conditions

y =0.7185x +40.085

R2 =0.0647

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


2

Figure 3.2.4 Regression Analysis of L90 Sound Levels vs. Wind Speed

All of the sound levels discussed so far have been the L90 statistical levels that represent the near-minimum sound level that occurs only a small percentage of the time. The measured average, orLeq, sound levels, representing typical conditions are reported below.

Figure 3.2.5 shows the Leq sound level measured at all positions over the survey period.


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Ave rage (Leq ) Sound Leve ls vs Tim e at A ll Pos it ions

Summertime Conditions

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Date and Tim e


Position 1

Position 2Position 3

Position 4

Position 5

Position 6

Figure 3.2.5 Leq(10 min) Sound Levels at All Positions

As with the L90 levels, most of the positions have generally similar values at any given time withthe exception of Position 4, which is typically higher. The average of the remaining 5 positions(except 4) is considered a reasonable representation of the site-wide average, or typical, soundlevel. This design value is plotted in Figure 3.2.6.


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Site-w ide Average (Leq) Sound Level vs Time - Sum m ertim e Conditions

Design Leq Backgr ound Le vel (Average of All Positions Except 4)

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Date and Tim e


Figure 3.2.6 Design Leq Site-wide Sound Level

A regression analysis of this Leq design level vs. wind speed is shown in Figure 3.2.7. Again, aswith the L90 data, there is no clear correlation; however, it can be seen that the typical soundlevel during the wind speed range of interest (3 to 9 m/s) is in the45 to 50 dBA range.


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Regre ss ion Analysis of Site-wide Le q Sound Level vs. Norm alized Wind Speed

Summ ertime Condit ions

y =0.7175x +43.333

R2 =0.0908

0

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

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


Figure 3.2.7 Regression Analysis of Leq Summer Sound Levels vs. Wind Speed

3.3 FREQUENCY CONTENT OF BACKGROUNDLEVELS

The frequency content of the background levels was recorded by a 1/3 octave band analyzer atPosition 6 for the first few days (only) of the summer survey. Figure 3.3.1 below is a plot of theA-weighted sound levels measured vs. time at this position for the first several days of the survey.

The site-wide average sound level is also shown indicating that the levels at this position, whileslightly higher, are similar to and reasonably representative of those measured at the otherlocations. Five spectra, designated as A through E, are marked at various minimum and maximumpoints. These spectra are plotted in Figure 3.3.2.


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Residu al (L90) Sound L evel vs Tim e at Position 6

Compared to Site-wide Average

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16:00

8/24/07

18:00

8/24/07

20:00

8/24/07

22:00

8/25/07

0:00

8/25/07

2:00

8/25/07

4:00

8/25/07

6:00

8/25/07

8:00

8/25/07

10:00

D a t e a n d T i m e

Position 6

Average Site-wide

Design Level

BA C D E

Figure 3.3.1 Overall A-weighted Sound Level vs. Time at Position 6


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Selected Maximum and Minimum Frequency Spectra at Position 6

0

10

20

30

40

50

60

70

6.3

Hz

8.0

Hz

10Hz

12.5

16Hz

20Hz

25Hz

31.5

40Hz

50Hz

63Hz

80Hz

100Hz

125Hz

160Hz

200Hz

250Hz

315Hz

400Hz

500Hz

630Hz

800Hz

1.0

k

1.2

5k

1.6

k

2.0

k

2.5

k

3.1

5k

4.0

k

5.0

k

6.3

k

8.0

k

10.0

k

12.5

k

16.0

k

20.0

k

dBA

1/3 Octave Band Center Frequency, Hz


Spectrum A

Spectrum B

Spectrum C

Spectrum D

Spectrum E

Insect Noise

Unidentified Noise Event

Figure 3.3.2 Frequency Spectra at Selected Minima and Maxima

Figure 3.3.2 clearly shows that insect noise peaking at 5000 Hz strongly affected the overall soundlevels when they were at a maximum and, significantly, also when they were at a minimum. Thisgenerally implies that site-wide sound levels are driven by high frequency and relatively high

amplitude insect sounds essentially all the time during this season. This continual dominance byinsect noise, which is clearly unrelated to wind or atmospheric conditions, explains why the sitesound levels during the summer at least - do not exhibit any real dependence on wind speed.

The temporary spike in sound levels designated as Spectrum C is evidently associated with somelocal noise event.

4.0 SURVEY RESULTS - WINTERTIME

4.1 SURVEY WEATHER CONDITIONS

The weather conditions during most of the winter survey, which was carried out betweenDecember 14, 2007 and January 4, 2008, were overcast with almost continuous periods of lightsnow or rain. Temperatures were generally at or near the freezing point much of the time dippingdown to as cold as -13 deg. F on one occasion. Several periods of high wind were captured.

The general conditions of temperature, barometric pressure and wind for the survey period areshown in the chart below (Figure 4.1.1) as observed at Watertown, NY.


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Figure 4.1.1 General Weather Data for the WinterSurvey Period as Observed in Watertown, NY

The wind speed at the site itself was measured by an 80 m met tower. The figure below, Figure4.1.2, shows the average 10 minute wind speed measured by the anemometer at an elevation of 40m and the wind speed normalized to a standard elevation of 10 m.


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Wind Speed Measured by On-site Met Tower at 40 m

and Normalized to 10 m - Wintertime Conditions

0

2

4

6

8

10

12

14

16

18

12/14/07

12:00

12/15/07

0:00

12/15/07

12:00

12/16/07

0:00

12/16/07

12:00

12/17/07

0:00

12/17/07

12:00

12/18/07

0:00

12/18/07

12:00

12/19/07

0:00

12/19/07

12:00

12/20/07

0:00

12/20/07

12:00

12/21/07

0:00

12/21/07

12:00

12/22/07

0:00

12/22/07

12:00

12/23/07

0:00

12/23/07

12:00

12/24/07

0:00

12/24/07

12:00

12/25/07

0:00

12/25/07

12:00

12/26/07

0:00

12/26/07

12:00

12/27/07

0:00

12/27/07

12:00

12/28/07

0:00

12/28/07

12:00

12/29/07

0:00

12/29/07

12:00

12/30/07

0:00

12/30/07

12:00

12/31/07

0:00

12/31/07

12:00

1/1/08

0:00

1/1/08

12:00

1/2/08

0:00

1/2/08

12:00

1/3/08

0:00

1/3/08

12:00

1/4/08

0:00

1/4/08

12:00

Date and Tim e

WindSpeed,m/s

40 mAnemometer


Figure 4.1.2 Measured Wind Speed at Site during the Winter Sound Survey Period

4.2 OVERALL SURVEY RESULTS

The L90 sound levels over consecutive 10 minute periods at all positions are plotted below inFigure 4.2.1 for the survey period.


27/34



Residual (L90) Sound Levels vs Time at All Positions

Wintertime Conditions

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

1/3/0812:00

1/4/080:00

1/4/0812:00

Date and Tim e


Position 1

Position 2

Position 3

Position 4

Position 5

Figure 4.2.1 10 minute L90 Sound Levels at All Monitoring Positions

As with the summer measurements, it can be seen that the sound levels at Position 4 are generally

higher than the mean level at all other locations. Consequently, the site-wide L90 design level,plotted in Figure 4.2.2, has been taken as the average of all positions except 4. In contrast to thesummer results where the levels were range-bound largely between about 40 and 50 dBA, thesound levels measured in the winter vary significantly with time from lows around 20 dBA topeak levels above 50 dBA.


28/34



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

Design L90 Background Level (Average of All Positions Except 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

1/3/0812:00

1/4/080:00

1/4/0812:00

Date and Tim e


4.2.2 Average L90 Background Level at All Positions Except 4

The average L90 design sound level is plotted along with the average wind speed at 10 m inFigure 4.2.3 below.


29/34



Average L90 Background Sound Leve l vs. Normalized Wind Speed

Wintertime Conditio ns

0

2

4

6

8

10

12

14

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18

20

12/14/071

2:00

12/15/070

:00

12/15/071

2:00

12/16/070

:00

12/16/071

2:00

12/17/070

:00

12/17/071

2:00

12/18/070

:00

12/18/071

2:00

12/19/070

:00

12/19/071

2:00

12/20/070

:00

12/20/071

2:00

12/21/070

:00

12/21/071

2:00

12/22/070

:00

12/22/071

2:00

12/23/070

:00

12/23/071

2:00

12/24/070

:00

12/24/071

2:00

12/25/070

:00

12/25/071

2:00

12/26/070

:00

12/26/071

2:00

12/27/070

:00

12/27/071

2:00

12/28/070

:00

12/28/071

2:00

12/29/070

:00

12/29/071

2:00

12/30/070

:00

12/30/071

2:00

12/31/070

:00

12/31/071

2:00

1/1/080

:00

1/1/081

2:00

1/2/080

:00

1/2/081

2:00

1/3/080

:00

1/3/081

2:00

1/4/080

:00

1/4/081

2:00

Date and Time

WindSpeed,m/s

0

10

20

30

40

50

60


Wind Speed at 10 m

Design L90 Sound Level

Figure 4.2.3 Background L90 Winter Sound Levels and Wind Speed

This plot shows that the temporal variance observed in the sound levels is almost whollyattributable to the wind; i.e. sound levels rise and fall in direct proportion with the wind speed andwind-induced sounds in the environment. This close correlation strongly suggests that all otherpossible sources of environmental sound - such as from road traffic, farm machinery, planes flyingover, etc. are very secondary if not completely inconsequential.

A regression analysis of the L90 background sound level vs. wind speed is shown below in Figure4.2.4. Although there is still some inevitable scatter, the R2 correlation between the dataset andthe linear trend line is many orders of magnitude higher (0.64) than the summer correlation (0.06).

This analysis shows that a sound level of about37 dBA is likely to exist at the normally criticalwind speed of 6 m/s, when the turbine sound power level is often maximum relative to the amountof background masking noise available.


30/34



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

Wintert ime Conditions

y =2.6355x +20.776

R2 =0.6451

0

5

10

15

20

25

30

35

40

45

50

55

60

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



2

Figure 4.2.4 Regression Analysis of L90 Winter Sound Levels vs. Wind Speed

All of the sound levels discussed so far have been the L90 statistical levels that represent the near-minimum sound level that occurs only a small percentage of the time. The measured average, orLeq, sound levels, representing typical conditions are reported below.

Figure 4.2.5 shows the Leq sound level measured at all positions over the winter survey period.


31/34



Average (Leq) Soun d Level s vs Time a t Al l Positi ons


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

1/3/0812:00

1/4/080:00

1/4/0812:00

Date and Tim e


Position 1

Position 2

Position 3

Position 4

Position 5

Figure 4.2.5 Leq(10 min) Sound Levels at All Positions - Winter

As with the L90 levels, most of the positions have generally similar values at any given time withthe exception of Position 4, which is typically a bit higher. The average of the remaining positions(except 4) is considered a reasonable representation of the site-wide average, or typical, soundlevel. This design value is plotted in Figure 4.2.6.


32/34



Site-wide Average (Leq) Sound Level vs Time - Wintertime Conditions

Design Le q Background L evel (Average of All Positions Except 4)

0

10

20

30

40

50

60

70

80

12/14/07

12:00

12/15/07

0:00

12/15/07

12:00

12/16/07

0:00

12/16/07

12:00

12/17/07

0:00

12/17/07

12:00

12/18/07

0:00

12/18/07

12:00

12/19/07

0:00

12/19/07

12:00

12/20/07

0:00

12/20/07

12:00

12/21/07

0:00

12/21/07

12:00

12/22/07

0:00

12/22/07

12:00

12/23/07

0:00

12/23/07

12:00

12/24/07

0:00

12/24/07

12:00

12/25/07

0:00

12/25/07

12:00

12/26/07

0:00

12/26/07

12:00

12/27/07

0:00

12/27/07

12:00

12/28/07

0:00

12/28/07

12:00

12/29/07

0:00

12/29/07

12:00

12/30/07

0:00

12/30/07

12:00

12/31/07

0:00

12/31/07

12:00

1/1/08

0:00

1/1/08

12:00

1/2/08

0:00

1/2/08

12:00

1/3/08

0:00

1/3/08

12:00

1/4/08

0:00

1/4/08

12:00

Date and Tim e


Figure 4.2.6 Design Leq Site-wide Sound Level - Winter

A regression analysis of this Leq design level vs. wind speed is shown in Figure 4.2.7. It can beseen that the typical sound level at the likely critical wind speed of 6 m/s is about43 dBA.


33/34



Regressio n Analysis of Site-wide Leq Sound Lev el v s. Normalized Wind Speed


y =2.1529x +29.758

R2 =0.5057

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 1



2

A

Figure 4.2 7 Regression Analysis of Leq Sound Levels vs. Wind Speed - Winter

5.0 CONCLUSIONS

A field survey of existing sound levels during leaf-on, summertime conditions was carried out atthe St. Lawrence Wind Farm site in late August and early September of 2007 followed by asimilar survey during leaf-off, wintertime conditions from mid-December 2007 to early January2008.

The objective of the surveys was to determine how much natural background masking sound thereis at the site to potentially obscure project noise during the warm weather months when people arelikely to be outside and when windows are likely to be open and also during cold weather monthswhen people are much less apt to be outside.

The survey results indicate that, except for Position 4 in both surveys, sound levels over the site

area are reasonably consistent and follow the same temporal trends. Design values for site-widesound levels have been taken as the average of all positions except 4, where somewhat highersound levels were consistently observed.

In the summertime survey it was found that environmental sound levels have virtually nodependence on wind speed and are driven essentially at all times by high amplitude insect noisegenerally concentrated in the 5 kHz region of the frequency spectrum. This noise variesinconsistently on a diurnal basis, often reaching a maximum in the evening hours and a minimumduring the early morning hours. However, even the during quietest periods overall A-weightedsound levels are dominated by noise at 5 kHz (insect noise).


34/34


In the winter, on the other hand, and in the total absence of insect activity, sound levels arecompletely dependent on wind speed and on wind-induced sounds.

Regression analyses relating sound level to wind speed have been carried out for both the worst-

case L90 sound level, which is the near-minimum sound level that occurs only a small percentageof the time, and for the typical average (Leq) sound level for both seasons. The results of theseregressions are summarized in the following table showing the nominal sound level associatedwith integer wind speeds in the range of interest.

Table 5.0.1 Measured Mean Background Sound Levels as a Function of Wind Speed

Integer Wind Speed at 10 m above grade, m/sType of SoundLevel 3 4 5 6 7 8 9 10

Worst-case, L90Summertime, dBA

42.2 43.0 43.7 44.4 45.1 45.8 46.6 47.3

Typical, LeqSummertime, dBA

45.5 46.2 46.9 47.6 48.4 49.1 49.8 50.5

Worst-case, L90Wintertime, dBA

28.7 31.3 34.0 36.6 39.2 41.9 44.5 47.1

Typical, LeqWintertime, dBA

36.2 38.4 40.5 42.7 44.8 47.0 49.1 51.3

END OF REPORT TEXT

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St.Lawrence wind farm SDEIS Noise Study 2008

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