st. lawrence wind noise impact assessment 2008 _ october

7/29/2019 St. Lawrence Wind Noise Impact Assessment 2008 _ October

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Hessler Associates, Inc.Consultants in Engineering Acoustics

3862 Clifton Manor PlaceSuite BHaymarket, Virginia 20169 USAPhone: 703-753-1602

Fax: 703-753-1522Website: www.hesslernoise.com

REPORT NO. 1829-082108-A

REV: ADATE OF ISSUE: OCTOBER 22,2008

NOISE IMPACT ASSESSMENT

ST.LAWRENCE WIND FARM PROJECT

TOWN OF CAPE VINCENT

JEFFERSON COUNTY,NY


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CONTENTS

1.0 INTRODUCTION 1

2.0 SUMMARY OF PREVIOUS FIELD SURVEY RESULTS 1

2.1 OBJECTIVE AND MEASUREMENT QUANTITIES 2

2.2 BACKGROUND SOUND LEVELS 3

3.0 PROJ ECT NOISE MODELING AND IMPACT ASSESSMENT 6

3.1 ASSESSMENT CRITERION 63.2 TURBINE SOUND LEVELS 83.3 CRITICAL DESIGN LEVELS 103.4 NOISE MODELINGMETHODOLOGY 12

3.5 MODEL RESULTS AND IMPACT ASSESSMENT 123.6 LOWFREQUENCY SOUND LEVELS 133.7 CUMULATIVE SOUND LEVELS FROM ADJACENT BPPROJECT 153.8 CONSTRUCTIONSOUND LEVELS 15

4.0 CONCLUSIONS 17

REFERENCES 20

Plot 1A Predicted Project Sound Contours to NY SDEC 6 dBA Criterion West EndPlot 1B Predicted Project Sound Contours to NYSDEC 6 dBA Criterion Main Project AreaPlot 2 Predicted Project Sound Contours - Cumulative Sound Level Assessment


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1.0 INTRODUCTION

Hessler Associates, Inc. has been retained by St. Lawrence Windpower, LLC to evaluate potentialsound impacts from the proposed St. Lawrence Wind Farm (the Project) located in the Town ofCape Vincent (Jefferson Co.), New York.

Current plans call for the installation of 53 Acciona AW 82/1500 (1.5 MW) wind turbines inlargely open farm country to the east of the town. Each unit has a three-bladed rotor, 82 m indiameter, and is mounted on an 80 m tubular tower.

Field surveys of background sound levels during both summer and winter conditions were carriedout in August and December of 2007 (Hessler Associates, Inc., Report 1804-011908-0, 1/21/08[Ref. 1]) to determine how much natural masking sound there might be - as a function of windspeed - at the nearest residences to the Project. The relevance of this is that high levels ofbackground noise due to wind-induced natural sounds, such as tree rustle, would tend to reducethe audibility of the turbines while low levels of natural sound would permit operational soundemissions from the turbines to be more readily perceptible. For a broadband, atonal sound sourcethe audibility of, and potential impact from, the new sound is a function of how much, if at all, itexceeds the pre-existing background level.

Using the existing background sound levels reported in the January 2008 study as a baseline, ananalytical noise model of the Project was developed to predict the sound level contours associatedwith the Project over the site area and thereby determine if Project sound levels are likely toexceed the background level at any off-site, or non-participating residences and, if so, what thelikelihood of an adverse impact might be.

The primary basis for evaluating potential Project noise is the Program Policy Assessing andMitigating Noise Impacts issued by the New York State Department of EnvironmentalConservation (NYSDEC), Feb. 2001. This assessment procedure is incremental in the sense that asimplified first level noise impact evaluation is initially carried out to determine if anyresidential receptors may experience a noticeable increase in sound level followed by a more indepth second level noise impact evaluation if any sensitive receptors are identified as beingpossibly affected. The procedure essentially defines a cumulative increase in overall sound levelof 6 dBA as the threshold between no significant impact and a potentially adverse impact.


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consecutive 10 minute intervals over each survey period. 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. While useful and informative, this measure needs to be viewed with somecaution when the survey objective is to quantify the mean minimum background level - since itcan be, and often is, influenced by noise events that are relatively loud in magnitude but short induration, such as a car passing close by the monitoring position. For example, one such event cansignificantly elevate the average level over a short to moderate integration period and yield a resultthat may well be unrepresentative of the quieter times during the sample.

In order to avoid this pitfall, the residual, or L90, statistical sound level is commonly used toconservatively quantify background sound levels. The L90 is the sound level exceeded during90% of the measurement interval and has the quality of filtering out sporadic, short-duration noiseevents thereby capturing the quiet lulls between such events. It is this consistently presentbackground level that forms a conservative basis for evaluating the audibility of a new source.

These levels are graphically illustrated in the following example.

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90

M M M M

SoundPressureLevel,dBA

PASSING TRAFFIC, TYPICAL

PARTICULARLY LOUD

VEHICLE

L90, RESIDUAL L EVEL

Leq ,TRUE AVERAGE

1-MINUTE LULL IN TRAFFIC

1/2-MINUTE

LULL IN

TRAFFIC

L10


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high amplitude insect noise generally concentrated in the 5 kHz region of the frequency spectrum.

This noise varies inconsistently on a diurnal basis, often reaching a maximum in the evening hoursand a minimum during the early morning hours. However, even during quietest periods theoverall A-weighted sound levels are dominated by noise at 5 kHz (insect noise).

In the winter, on the other hand, and in the total absence of insect activity, sound levels are highlydependent on wind speed, or, more specifically, 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 percentage

of the time, and for the typical, or average (Leq) sound level for both seasons.

The plot below quantifies the relationship between wind speed (normalized to the reference heightof 10 m) and the measured 10 minute L90 sound levels for wintertime conditions.

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

Wintertime Conditions

y =2.6355x +20.776

R2 =0.6451

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SoundPressureLevel,dBA


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Regression Analysis of Site-wide Leq Sound Lev el v s. Normalized Wind SpeedWintertime Conditions

y =2.1529x +29.758

R2 =0.5057

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

SoundPressureLevel,dB

Figure 2.2.2 Wind Speed vs. Leq Sound Level Regression Wintertime Conditions

As mentioned above, summertime sound levels were found to show little dependence on windspeed. The relationship between the L90 background level and wind speed for summertimeconditions is given below in Figure 2.2.3. There is considerable scatter to the data and only a mild

increase with wind speed is apparent. In general, these data indicate that sound levels during thesummer are heavily influenced by natural sounds, primarily insects and crickets, that have nothingto do with wind speed, meaning that sound levels are relatively high and consistent even duringlow wind conditions. For example, the mean sound level in a light 3 m/s wind was found to beabout 29 dBA, which is extremely quiet, during the winter and roughly 42 dBA in the summer.


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

y =0.7185x +40.085

R2 =0.0647

0

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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

SoundPressureLevel,dB

2

Figure 2.2.3 Wind Speed vs. L90 Residual Sound Level Regression Summertime Conditions

In summary, the summer and winter background sound level over the range of relevant wind

speeds are tabulated below.

Table 2.2.1 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


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Conservation (2001). This guideline is fundamentally based on the perceptibility of the new

source above the existing background sound level at the nearest residences, or other potentiallysensitive receptor locations, such as schools or churches.

It is a well-established fact for a new broadband, atonal sound source that a cumulative increase inthe total sound level of about 5 or 6 dBA at a given point of interest is required before the newsound begins to be clearly perceptible or noticeable to most people. Cumulative increases ofbetween 3 and 5 dBA are generally regarded as negligible or hardly audible. Lower sound levelsfrom the new source are completely buried in the existing background sound level and aretotally inaudible. The specific language relating to these perceptibility thresholds in the NY SDEC

program policy (Section V B(7)c) is a follows:

Increases ranging from 0-3 dB should have no appreciable effect on receptors.Increases from 3-6 dB may have potential for adverse noise impact only in caseswhere the most sensitive receptors are present. Sound pressure increases of morethan 6 dB may require closer analysis of impact potential depending on existingSPLs [sound pressure levels] and the character of surrounding land use andreceptors.

What this essentially says is that an increase in the total ambient sound level of 6 dBA or less is

unlikely to constitute an adverse community impact. While this could be interpreted that a projectsound level that is 6 dBA higher than the background is nominally acceptable, it is moreconservative to treat the 6 dBA increase as a cumulative total; i.e. when the background andproject sound levels are added together the new total level is 6 dBA higher than the backgroundlevel alone.

From a technical standpoint, because decibels add logarithmically1, a 6 dBA cumulative thresholdis taken to mean that the sound level from the Project could exceed the existing background levelby up to 5 dBA before there is a need for closer analysis. For example, a background sound level

of 37 dBA plus a Project-only level of 42 dBA would yield a new total level of 43 dBA, or 6 dBAabove the original level.

The program policy outlines an incremental approach towards evaluating sound level increasesand potential impacts. Once the background sound level is established by means of a field surveya First Level Noise Impact Evaluation is carried out where sound from the future Project is


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distance losses). In this case, any receptors outside the 6 dBA cumulative increase contour are

considered to have a low probability of disturbance while any receptors inside the contour mightbe adversely impacted and some form of mitigation should be investigated.

Preliminary noise modeling carried out on this Project indicates that a First Level evaluationwould reveal that a potential for adverse impact exists at some residences in the site area.Consequently, the modeling analysis discussed below begins with a Second Level Impact analysis.

3.2 TURBINE SOUND LEVELS

The sound emissions of the Acciona AW 82/1500 wind turbine as a function of wind speed areknown from field tests carried out for Acciona by independent acoustical engineers, WINDTESTKaiser-Wilhelm-Koog GmbH, in accordance with IEC 61400-11 [Ref. 2]. The values are reportedin a document entitled WT 5489/06 Summary of results of noise emission measurement [Ref.4]. The following sound power levels are published as a function of wind speed at thestandardized measurement height of 10 m.

Table 3.2.1 Acciona WT 82/1500 Sound Power Levels vs. Wind Speed

Wind Speed at 10 m Height, m/s Sound Power Level, dBA re 1 pW

6 101.7

7 102.5

8 102.2

9 101.8

10 101.5

The octave band frequency spectrum for the maximum noise wind speed of 7 m/s is given below.

Table 3.2.2 Acciona AW 82/1500 Sound Power Level Spectrumduring a 7 m/s Wind

Octave BandCenterFrequency, Hz

63 125 250 500 1k 2k 4k 8k dBA


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In general, the ostensible magnitude of a sound power level is always considerably higher than the

sound pressure level near a source because of the area term. For example, the sound pressure levelat 100 m from a typical wind turbine might be about 53 dBA and the area term might be on theorder of 51 dBA with a resulting total power level of 104 dBA re 1 pW (the units of power levelsare always denoted as decibels with reference to 1 picoWatt, 10-12 W).

The fundamental advantage of a power level is that the sound pressure level of the source can becalculated at any distance; hence its importance to noise modeling.

The limited frequency resolution of the octave band power level spectrum shown in Table 3.2.2

does not provide any significant information as to whether the noise is tonal or not. A finer 1/3octave band, or better, spectrum is needed to see if any prominent discrete tones exist. Figure3.2.1 below is a plot of the 1/3 octave frequency spectrum for this model turbine during a 7 m/swind. This chart shows that the noise is distinctly broadband in nature; i.e. evenly and smoothlydistributed over the audible frequency spectrum. Any significant tones would appear as singlebands protruding significantly above the adjacent bands.

Sound Power Level Frequency Spectrum in 1/3 Octave Bands

Maximum Noise Operating Po int (7 m/s Wind)

Acc ion a AW 82/1500 Wind Turb ine

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120

SoundPowerLevel,dBre1pW


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3.3 CRITICAL DESIGN LEVELS

From the field surveys it was determined that the background sound level varies with wind speed,at least during wintertime conditions when insect sounds are not present. From Table 3.2.1 in thepreceding section it can be seen that the turbine sound level also varies with wind speed. In orderto carry out the ambient-based NYSDEC assessment procedure some specific background levelmust be established against which to compare Project sound and calculate cumulative increases.

In terms of potential noise impact and perceptibility the worst-case combination of backgroundand turbine sound levels would occur at the wind speed where the background level was lowest

relative to the turbine sound level or, in other words, where the differential between thebackground level and turbine sound power level is greatest. The following charts show that thisworst-case situation does not occur at the highest wind speeds (>=7 m/s) when this model turbineproduces the maximum sound levels but rather at a slightly lower wind speed of 6 m/s.

Table 3.3.1 Comparison of ConservativeWintertimeL90 Background and Turbine Sound Levelsto Determine Critical Design Level (at MaximumDifferential)

Integer Wind Speed atStandardized Hgt. of

10 m, m/s

6 7 8 9 10

WintertimeBackground SoundLevel, L90, dBA

37 39 42 44 47

Turbine Sound PowerLevel, dBA re 1 pW

101.7 102.5 102.2 101.8 101.5

Differential, dB 65 63 60 58 54

The maximum differential of 65 dB during a 6 m/s wind means that sound from the project wouldhave the greatest probability of being audible under these conditions in the wintertime. At higherwind speeds turbine sound level increase, but only negligibly, while the masking backgroundsound level increases significantly.


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Consequently, for design purposes a wintertime background level of37 dBA and a turbine sound

power level of 101.7 dBA re 1 pW will be used as the critical design values in the soundmodeling assessment.

This approach is conservative in that turbine noise will be less audible at all other wind speeds.

Because the frequency content of the turbine sound power level at 6 m/s is not given in the testreport, the octave bands have been estimated by subtracting 0.8 dB from the 7 m/s data. Theresulting spectrum below will be used in the modeling study. Note that a power level value hasalso been estimated for the 31.5 Hz octave band (not reported in the test report).

Table 3.3.3 Acciona AW 82/1500 Sound Power Level Spectrumduring a 7 m/s Wind andEstimatedDesign Level Spectrumat 6 m/s

Octave BandCenterFrequency, Hz

31.5 63 125 250 500 1k 2k 4k 8k dBA

Sound PowerLevel at7 m/s,dB re 1 pW

- 105.1 104.6 103.6 101.2 97.6 91.0 83.6 73.5 102.5

AdjustmentFactor, dB

- -0.8 -0.8 -0.8 -0.8 -0.8 -0.8 -0.8 -0.8 (-0.8)

Estimated Lwat6 m/s, dB re1 pW DesignLevel

107 104.3 103.8 102.8 100.4 96.8 90.2 82.8 72.7 101.7

In terms of the NYSDEC 6 dBA increase criterion, a design background sound level of 37 dBAmeans that Project noise impacts may occur wherever a Project-only sound level of42 dBA ormore exists. Recall that a background level of 37 dBA plus a Project sound level of 42 dBAwould result in a 6 dBA cumulative increase: 37 +42 =43 dBA.

This critical design assumption using a background sound level of 37 dBA as a baseline value isalsoconservative in the followingways:


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3.4 NOISE MODELINGMETHODOLOGY

Using the design sound power level spectrum in Table 3.3.3 above, a worst-case sound levelcontour plot for the site was calculated using the Cadna/A, ver. 3.6.115 noise modeling programdeveloped by DataKustik, GmbH (Munich). This software is essentially an automated version ofISO 9613-2 Acoustics Attenuation of sound during propagation outdoors [Ref. 11] (the mostcommon and accepted methodology for calculating sound propagation worldwide) and enables theProject and its surroundings, including terrain features, to be realistically modeled in three-dimensions. Each turbine is represented as a point sound source at a height of 80 m above thelocal ground surface (design hub height).

The site plan used in the analysis was current as of October 1, 2008.

Field tests of operational wind projects indicate that the mean sound level at any location due to acomplex arrangement of wind turbines can be very accurately predicted using ISO 9613 with thefollowing two assumptions:

An omni-directional wind

A moderate ground absorption coefficient of 0.5

The sound level from each turbine is assumed to be the nominally maximum downwind soundlevel in all directions simultaneously. In other words, although physically impossible, an omni-directional 6 m/s wind is assumed.

The ISO ground absorption coefficient ranges from 0 for water or hard concrete surfaces to 1 forabsorptive surfaces such as farm fields, dirt or sand. It has been found that a middle value of 0.5 isappropriate for rural farming country in the sense that predicted sound levels agree very well withmeasurements of turbine-only sound levels over a variety of wind speeds.

3.5 MODEL RESULTSRELATIVE TO NYSDECCRITERION AND IMPACT ASSESSMENT

Preliminary modeling indicated that a potential for community noise impacts exists with thisProject. This early modeling work essentially performed the function of the First Level NoiseImpact Assessment in the NYSDEC assessment procedure and made it clear that a Second Level


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indicates that the overwhelming majority of non-participating residences will be subject to sound

level increases of less than 6 dBA, and in most cases, much less than 6 dBA. There are only fourhouses just inside of the nominal 42 dBA threshold:

One house at the intersection of Rt. 12E and Deerlick Road (Plot 3A)

Three non-participating houses on CR 8 (between Rt. 12E and McKeever Road) (Plot3B)

All other Off-Site residences are beyond the 42 dBA threshold. A handful of participating

residences are also located within the area where the Project sound level is likely to be between 42and 44 dBA.

A predicted project-only sound level of 42 dBA or higher means that under normal day-to-daycircumstances of wind and weather operational sounds from the nearest turbines are likely to beclearly audible much of the time - at least when it is windy; the Project is silent during calm or lowwind conditions. Experience indicates that sound levels of this nominal or mean magnitude maybe regarded as objectionable by some people some of the time largely because wind turbine noiseis highly variable with time. The wind doesnt always blow in a perfectly steady or continuousmanner but rather occurs in the form of gusts and relative lulls and is subject to sudden shifts in

direction that can lead to short-term changes in sound emissions making the sound morenoticeable than it would be if it were perfectly constant. In general, the Project sound level much like the background sound level - under normal circumstances is likely to have a variance of+/- 5 dBA from the mean predicted level. Additionally, on rare occasions (1 to 2% of the time)when a passing storm, frontal system or otherwise disturbed airflow passes through the Projectsound level may substantially increase above the mean for brief periods (on the order of 5 to 20minutes). Atmospheric phenomena, such as temperature inversions, can also temporarily elevateor enhance the Project sound level at a given location.

In short, wind and weather conditions will develop from time to time causing Project sound levelsto increase, sometimes substantially, over the nominally predicted level but, based on fieldmeasurements of similar projects, these unavoidable and inevitable excursions are infrequent,short-lived and the vast majority of the time sound levels will be close to the mean predictedvalue.


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windy conditions. Taken at face value any casual measurement of a wind turbine is likely to

falsely indicate high levels of low frequency noise. The fact of the matter is that if themeasurement were repeated without the turbine in operation essentially identical levels of lowfrequency noise would be measured.

A study has been recently completed by Sondergaard [Ref. 12] with the specific objective ofdetermining whether large wind turbines produce significant low frequency noise. Extremelycareful measurements were made based on the IEC 61400 measurement procedure using multipleelaborate wind screens over a microphone placed on a reflective ground plate (where the windvelocity is theoretically zero) to minimize self-noise contamination. The results of this testingshow that for a typical 1.5 MW turbine its sound levels taper down steadily in magnitude towardsthe low end of the frequency spectrum and that the sound energy below about 40 Hz is actuallycomparable to the sound energy in the natural rural environment where the measurements weremade (as shown in Figure 3.6.1).


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proximity to wind projects despite the lack of any clear cause. Research [Ref. 14] showing that

these symptoms and complaints cease once the subjects leave the project area seems credible, sothere should be an awareness that adverse physical impacts may occur that are thought to beassociated with noise but, in fact, are of unknown origin.

3.7 CUMULATIVE SOUND LEVELS FROM THE ADJACENT WIND PROJECT

A number of the turbines in the proposed BP Cape Vincent Wind Project to the southeast of theProject are close enough that the sound levels at some residences between the two projects arelikely to experience slightly higher sound levels than they would if the St. Lawrence Wind Farm

existed in isolation.

Plot 2 shows the mean sound level contours that can be expected with both projects operatingtogether (based on a preliminary/proposed site arrangement obtained from BP). While the BPturbines would clearly reshape the 42 dBA impact threshold in many places, a comparison withPlots 1A and 1B shows that only a few non-participating residences that were formerly close tobut outside of the 42 dBA contour would be inside of the threshold if the BP project were added.

These residences or groups of residences (marked A through D in Plot 2) are properties that areprimarily affected by the St. Lawrence Project and where the sound from the adjacent projectwould be secondary. Other homes to the southeast of the St. Lawrence site area would be

predominately impacted by the BP project.

The actual change in sound exposure at Locations A through D would be fairly small due to thiscumulative affect. The following table summarizes the predicted sound levels with the St.Lawrence Wind Farm alone and with both projects.

Table 3.7.1 Potential Cumulative Sound Impacts

Location Expected Sound Levelwith Only the St.

Lawrence Project, dBA

Potential Sound Levelwith Both Projects in

Operation, dBA

CumulativeIncrease,

dBA

A 40.6 42.5 1.9

B 41.2 42.2 1.0

C 41.4 42.2 0.8


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the sounds from Project construction are likely to be faintly perceived as the far off sound of

diesel-powered earthmoving equipment characterized by such things as irregular engine revs, backup alarms, gravel dumping and the clanking of metal tracks.

Construction of the Project is anticipated to consist of several principal activities:

Access road construction and electrical tie-in line trenching

Site preparation and foundation installation at each turbine site

Material and subassembly delivery

Erection

The individual pieces of equipment likely to be used for each of these phases and their typicalsound levels as reported in the Power Plant Construction Noise Guide (Empire State ElectricEnergy Research Corp., [Ref. 7]) are shown below in Table 3.8.1. It should be noted that thereference used for equipment sound levels is quite old, dating back to 1977, and that the levels init are roughly 5 dBA higher than the values that can be found in more recent references, such asfrom the FHWA [Ref. 13] for modern construction equipment. These older, higher values havebeen deliberately used purely to be conservative.

Also shown in the table below are the maximum total sound levels that might temporarily occur at

the closest non-participating residences (at least 1000 ft. away) and the distance from a specificconstruction site at which its sound would drop to 40 dBA. A bland, steady sound of level of 40dBA is generally considered so quiet (about the sound level in a library) that it is not usuallyviewed as objectionable even when the background, or masking, sound level is low. Unlike forthe operational Project, wind speed is irrelevant to the background level during the constructionphase because there will be times when construction is occurring during calm and quiet periods.

Table 3.8.1 Construction Equipment Sound Levels by Phase

Equipment Description Typ. Sound

Level at 50ft., dBA[Ref. 7]

Est.

MaximumTotal Levelat 50 ft. perPhase, dBA*

Max. Sound

Level at aSetback

Distance of1000 ft., dBA

Distance

until SoundLevel

Decreases to40 dBA, ft.

Road ConstructionandElectrical LineTrenching


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What the values in this table generally indicate is that, depending on the particular activity, soundsfrom construction equipment are likely to be significant at distances of up to 5500 feet whichmeans that construction will occur close enough to many homes within the Project that it will beclearly audible.

At the very worst, however, sound levels ranging from 56 to 63 dBA might temporarily occur overseveral weeks at homes 1000 ft. from turbine construction sites. Such levels would not generallybe considered acceptable on a permanent basis or outside of normal daytime working hours (whenall Project construction is planned), but as a temporary, daytime occurrence construction noise ofthis magnitude may go unnoticed by many in the Project Area. For others, Project constructionnoise may be an unavoidable but temporary impact.

The estimated sound levels at 50 ft. in Table 3.8.1 also demonstrate that a maximum allowablesound level of 80 dBA recommended in the NYSDOT construction noise guidelines is only likelyto occur at, or within 200 ft. of any specific construction site (a 12 dB reduction from themaximum level of 92 dBA at 50 ft. down to 80 dBA would occur at a distance of about 200 feet).Consequently, construction activities at the site of each turbine will result in sound levels that aresubstantially below 80 dBA at any homes due to the setback distance of at least 1000 feet. Theremay be some cases; however, where road construction or trenching operations occur closer to

homes. A short-term sound level of 80 dBA or more is theoretically possible where this distanceis less than about 200 feet, but such instances are considered unlikely because there aren't manyinstances where construction activities are required that close to homes and also becauseconservative values from a somewhat antiquated 1977 reference [Ref. 7] have been deliberatelyused for the equipment.

Noise from the very small amount of daily vehicular traffic to and from the current site ofconstruction should be negligible in magnitude relative to normal traffic levels and temporary induration at any given location.

4.0 CONCLUSIONS

Two fairly extensive field surveys were completed to measure the background sound levels thati i h j d b h i d di i d f i d


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wintertime background sound level that is likely to exist under these conditions is 37 dBA. The

L90 level during the summer under these same wind conditions is about 44 dBA. Forconservative design purposes a sound level of37 dBA has been taken to represent the background,year-round level during a critical 6 m/s wind.

In the New York State Department of Environmental Conservations Program Policy Assessingand Mitigating Noise Impacts an increase in total sound level up to 6 dBA is characterized ashaving potential for adverse noise impact only in cases where the most sensitive of receptors arepresent and is suggested as a threshold for determining what areas might be adversely impactedby a new noise source and what areas should see no appreciable effect. For this site a 6 dBAcumulative increase is associated with a Project-only sound level of42 dBA (37 +42 =43 dBA,or 6 dBA above the background level).

A Second Level modeling study carried out per the NYSDEC guideline showed that the 6 dBAincrease limit, which conservatively equates to a Project-only sound level of 42 dBA, is expectedto occur well short of nearly all non-participating residences. Only three residences on CR 8 andone at the intersection of Rt. 12E and Deerlick Rd. were found to have a nominal Project soundlevel that was slightly above the potential impact threshold. All remaining homes in the Projectarea, and particularly the numerous houses along the St. Lawrence River shoreline, are welloutside of the region where Project noise may be significant.

A predicted Project-only sound level of 42 dBA or higher means that under normal day-to-daycircumstances of wind and weather operational noise from the nearest turbines is likely to beclearly audible much of the time, except during calm or near calm conditions. Turbulent airflowsometimes leads to short-term increases in sound emissions that make the sound more noticeablethan it would be if it were perfectly constant. In general, Project sound emissions under normalcircumstances is likely to have a variance of +/- 5 dBA from the mean predicted level. On rareoccasions when a passing storm, frontal system or otherwise disturbed airflow moves over the sitesound levels can substantially increase above the mean for brief periods (on the order of 5 to 20

minutes). In addition, atmospheric phenomena, such as temperature inversions, can temporarilyelevate or enhance the Project sound level at a given location.

In short, wind and weather conditions will develop from time to time causing Project sound levelsto increase over the nominally predicted level but field experience indicates that these unavoidableandinevitableexcursionsareinfrequent short livedandthevastmajorityof thetimesoundlevels


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Although concerns are often raised with respect to low frequency noise emissions from windturbines, no adverse impact of any kind related to low frequency noise is expected from thisProject. The results of a carefully controlled field study are discussed demonstrating that a typical1.5 MW wind turbine produces no significant noise below about 40 Hz. In addition, the maximum(conservatively) predicted C-weighted sound level at any receptor is at least 17 dBC below the 75dBC minimum threshold of perception per ANSI B133.8.

Unavoidable but mild noise impacts may occur during the construction phase of the Project.Construction noise, sounding similar to that of distant farming equipment is anticipated to besporadically audible at many homes within the immediate Project vicinity on a temporary basis.

The maximum magnitude of construction sound levels at the nearest homes to individual turbinelocations is not expected to exceed 56 to 63 dBA depending on the particular activity. Higherlevels are possible where homes are relatively close to trenching and road building activities.

END OF REPORT TEXT


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REFERENCES

1. Hessler Associates, Inc., Report No. 1804-011908-0, Environmental Sound Level SurveyResults Summer and Wintertime Conditions, St. Lawrence Wind Farm, Jan. 21, 2008.

2. International Electromechanical Commission (IEC) 61400-11:2002(E) Wind TurbineGenerator Systems Part 11: Acoustic Noise Measurement Techniques, Second Edition2002-12.

3. American National Standards Institute (ANSI) S12.36-1990, Survey Methods for the

Determination of Sound Power Levels of Noise Sources, 1990.

4. WINDTEST Kaiser-Wilhelm-Koog GmbH, WT 5489/06Summary of results of the noiseemission measurement, in accordance with IEC 61400-11 and MEASNET, of a WTGStype Acciona AW 82/1500 IEC IIIb T80A LM40.3P, October 31, 2006

5. American National Standards Institute (ANSI) S1.13-1995, Measurement of SoundPressure Levels in Air, 1995.

6. American National Standards Institute (ANSI) B133.8-1977Gas Turbine InstallationSound Emissions, Appendix B, 1989.

7. Empire State Electric Energy Research Corporation, Power Plant Construction NoiseGuide, Bolt Beranek and Newman Report 3321, May 1977.

8. Pedersen, E. and Persson Waye, K., Human Response to Wind Turbine Noise Annoyance and Moderating Factors, Proceedings from Wind Turbine Noise:Perspectives for Control, Berlin, October 2005.

9. van den Berg, G.P., Mitigation Measures for Nighttime Wind Turbine Noise,Proceedings from Wind Turbine Noise: Perspectives for Control, Berlin, October 2005.

10. Berglund, B., Linvall, T., Schwela, D., Guidelines for Community Noise, World HealthOrganization, 1999.


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