slwf sdeis narrative 2009

8/8/2019 Slwf Sdeis Narrative 2009

1/12

3.10 Noise

3.10.1 Affected Environment

The proposed St. Lawrence Windpower Project, consisting of 53 1.5 MW Acciona AW-82/1500

WTGs, will be located in the Town of Cape Vincent in Jefferson County, New York. The Project

Area consists primarily of open farmland with existing noise sources such as road traffic,

farming equipment, and natural sounds (i.e., leaf rustle, insect noise), etc. Potentially sensitivereceptors in the general vicinity of the Project include structures such as residences, schools, and

churches. Locations of non-residence receptors within 1-mile of the Project are shown in Exhibit

3.10.1. These receptors were considered as a part of the noise impact analysis and the existing

ambient acoustic conditions were assessed by completing a baseline sound level survey.

To most accurately represent ambient sound levels in the Project Area in terms of seasonal anddiurnal variation, long-term baseline sound surveys were completed during summertime and

wintertime at six different monitoring locations. The six locations were chosen to provide even

coverage throughout the Project Area. Sound levels at all six monitoring stations werereasonably consistent with each other. Similar baseline sound surveys conducted in

homogeneous rural areas have very similar results (personal comm., David Hessler).

Baseline measurements were conducted in consecutive 10-minute intervals, recording theequivalent sound level (Leq) and residual sound level (L90). The Leq value is the average sound

level over each measurement interval, which for this study was 10 minutes. Approximately halfthe time the sound level is louder than the Leq, and about half the time it is quieter than the Leq.


2/12

From a statistical perspective the Leq is the mean sound level that is most likely to be observed at

any given moment and is defined as the steady, continuous sound level, over a specified time,

which has the same acoustic energy as the actual varying sound levels over the same time.

The L90 level is essentially the lowest sound level that is consistently present when no events are

happening, for example, when it is quiet and the wind has momentarily slacked off. Itrepresents the quiet lulls between noise events, such as cars going by or planes flying overhead.

The L90 measure is considered a conservative sound level for assessing increases arising from a

proposed project because it is the near-minimum background level that only occurs, bydefinition, 10 percent of the time. The remaining 90 percent of the time a higher background

sound level exists and project noise is less perceptible. Consequently, this background level

represents the "worst-case" situation in terms of potential impact.

Both the Leq and L90 are used to provide a more complete analysis of sound. The Leq represents

an essentially normal situation, while the L90 captures the maximum potential impact that might

occur intermittently and briefly. The L90 is not the permanent or typical background sound level,

so the relative impact basing the impact on the Leq is shown to provide some context. Using theL90 is appropriate to evaluate impacts at sensitive receptors, such as residences. Both of these

statistics are illustrated in Exhibit 3.10.2.

A regression analysis was performed using the measured baseline statistical sound levels and

wind speed. The wind speed was measured in 10-minute intervals by an anemometer 40 m (131

ft.) above the ground, located within the site area. Sound levels were then plotted against themeasured wind speed, which was normalized to a height of 10 m (33 ft.). The distances from the

anemometer location to sound monitor locations ranged from approximately 0.8 mile to 7.3

miles. Results of this analysis show that winter baseline sound levels are highly dependent onwind speed.

There are no local ordinances or regulations that govern the methodology for assessment ofpotential noise associated with the Project; therefore, the primary basis for evaluating noise


3/12

impacts is the Program Policy Assessing and Mitigating Noise Impacts published by the New

York State Department of Environmental Conservation (NYSDEC, 2001). The NYSDEC

guideline document states that an incremental increase of 6 dBA over the ambient sound level,which is defined as an Leq, when considered cumulatively, is the minimum threshold at which

adverse noise impacts may potentially begin to occur.


4/12

3.10.2 Potential Impact

3.10.2 Potential Impact3.10.2.1 Construction

The proposed Project would generate noise during and after construction. The detailed ProjectNoise Impact Assessment (NIA) is included in Appendix L. Construction noise would include

noise generated during access road construction, electrical tie-in line trenching, site preparation,

foundation installation, material and subassembly delivery, and erection. Project constructionwill temporarily constitute a moderate, unavoidable impact at some homes in the Project Area.

Quantifying these impacts is difficult because construction activities will be constantly moving

from place to place, making noise impacts highly variable at any given point in time. The

individual pieces of equipment likely to be used for each phase of construction are shown below,in Table 3-29. This table also shows the maximum total sound levels that might occur at the

closest non-participating residences and the distance from a specific construction site at which itssound would drop to 40 dBA, which is a level that is generally considered acceptable even whenbackground or masking, sound level is low.

Analysis results show that sound levels ranging from 56-63 dBA might temporarily occur overseveral weeks at homes 1,000 feet from turbine construction sites. Such levels would not

generally be considered acceptable on a permanent basis or outside normal daytime workinghours,

but the noise will be temporary, occur during the daytime, and be limited in duration. For

others, Project construction noise may be an unavoidable but temporary impact. The estimatedsound levels at 50 feet in Table 3-29 also demonstrates that a maximum allowable sound level of

80 dBA recommended in the New York State Department of Transportation (NYSDOT)

construction noise guidelines is only likely to occur at, or within 200 feet of any specificconstruction site. Consequently, construction activities at the site of each turbine will result in

sound levels that are substantially below 80 dBA at any homes due to the setback distance of at

least 1,000 feet. There may be some instances during road construction or trenching operationswhere the separation distance from homes is less than 200 feet; however, the occurrences of such

instances is unlikely.


5/12

Not all vehicles are likely to be in simultaneous operation. Maximum level represents the highestlevel realistically likely at any given time.

3.10.2.2 OperationThe Applicant, SLW, has selected the Acciona AW-82/1500 WTG for the Project. Sound power

data was obtained by the WTG manufacturer and the critical operational design level was

determined for use in the acoustic noise modeling analysis. The sound power level (spl) that wasused in the noise assessment was taken directly from the certified WINDTEST measurements lab

report for Accionas 82m rotor turbine. The measurements were done in accordance with IEC

61400-11 and MEASNET of a WTGS type. The critical operational design level is the worstcase in terms of potential noise impact and perceptibility as it occurs when the differential

between the background level and turbine sound power level is greatest. At higher wind speeds

turbine sound power levels increase, while the masking background sound level also increases

significantly. The worst case acoustic condition for the proposed Project occurs at a wind speedof 6m/s, with the highest differential occurring between the wintertime L90 background level of

37 dBA and turbine sound power level (LW) of 101.7 re 1 pW at this wind speed. Table 3-30

shows the estimated frequency content of the turbine sound power level at 6 m/s, below.

The Acciona AW-82/1500 WTG sound power level spectrum at 6 m/s speed was inputted into

CadnaA (ver. 3.6.115), DataKustiks acoustic modeling program. CadnaA conforms to ISO

9613-2 Acoustics Attenuation of sound during propagation outdoors and enables the Projectand its surroundings, including terrain features, to be realistically modeled in three-dimensions.

Modeling of the current Project layout as of October 1, 2008 assumed the nominally maximum

downwind sound level from each turbine in all directions simultaneously. In other words,

although physically impossible, an omnidirectional 6 m/s wind is assumed. In addition, a


6/12

moderate ground absorption coefficient (0.5) was selected to represent the rural farming land in

the Project Area (see Exhibit 3.10.5).

A predicted Project-only sound level of 42 dBA or higher means that under normal day-to-day

circumstances of wind and weather operational noise from the nearest turbines is likely to be

clearly 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 noticeable

than it would be if it were perfectly constant. In general, Project sound emission under normal

circumstances is likely to have a variance of +/- 5 dBA from the mean predicted level. On rare

occasions when a passing storm, frontal system or otherwise disturbed airflow moves over thesite sound 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

temporarily elevate 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

levels to increase over the nominally predicted level but field experience indicates that theseunavoidable and inevitable excursions are infrequent, short-lived and the vast majority of the

time sound levels will be close to the mean predicted value. It should also be noted that Project

audibility does not cease at the 6 dBA threshold but extends further out for some distance.

Modeling results were compared to the NYSDEC cumulative incremental increase guideline of 6

dBA, which equates to a Project-only sound level of 42 dBA, as a basis for impact analysis.

Modeling results evaluating compliance with the State guideline are shown in Exhibits 3.10.6

and 3.10.7 (and in the NIA in Appendix L) in the form of sound contour maps. The area insidethe 42 dBA sound contour line (in blue) represents the region where, under the NYSDEC

criterion, sound from the Project may result in an adverse impact. These figures indicate that the6 dBA incremental increase criterion will be met at the vast majority of non-participating

residences. Only three residences on CR 8 (between Route 12E and McKeever Road) and one at

the intersection of Route 12E and Deerlick Road were found to have a Project sound level thatwas slightly above the 6 dBA potential impact threshold. All remaining homes in the Project

Area, and particularly the numerous houses along the St. Lawrence River shoreline, are well


7/12

outside of the area in which adverse Project noise impacts have been modeled based upon the

L90 analysis.

While most homes are outside of the 42 dBA sound contour line, many of these homes will


8/12

notice an increase in sound levels due to operation of the Project. Exhibits 3.10.8 and 3.10.9

show the area where sound from the Project may result sound levels of 38 dBA, a sound level

that is 1 dBA above the wintertime L90 background level of 37 dBA. While Project-relatedsound may be audible in locations where there is a 1 dBA increase over the background level, it

does not necessarily mean that it will be annoying. However, the higher the incremental increase

over existing baseline levels, the greater the possibility for future Project related noisecomplaints. Response to any increase in background sound levels is largely subjective and will

vary from person to person depending on several factors including predetermined perceptions of

the project and economic incentives. Project participants are less likely to be affected by noisethan non-participants.


9/12

For comparison, the NYSDEC recommendations for determining the potential for adverse noise

impact are presented in Table 3-31. To place the associated noise levels in context, typical sound

levels are provided in Table 3-32.


10/12


11/12

3.10.3 Mitigation Measures

As discussed above, construction noise will cause temporary unavoidable noise impacts. In an

attempt to minimize construction noise impacts, the following mitigation measures will beapplied to Project construction, as necessary and practicable:

Adhering to regular construction work hours Mondays through Saturdays, and typically

not working on Sundays or after dark;

All construction equipment will be maintained in good working condition in order to

reduce general noise emissions; When practical, heavy equipment will be shut down when not active, to minimize idling

noise;

All internal combustion engines will be fitted with appropriate muffler systems; and Adjacent landowners will be advised in advance of any significant noise-causing

activities and these will be scheduled to create the least disruption to residents. In addition, turbine locations will continue to be evaluated based upon potential noiseimpacts from the St. Lawrence project, as well as potential cumulative impacts from the

St. Lawrence and BP projects.

The Project has been purposely designed to minimize environmental noise during Project

operations by siting wind turbines as far away from existing residential receptor locations as

practicable, while keeping the Project an economically viable source of clean renewable energy.


12/12

In addition, the Project has selected the 1.5 MW Acciona AW-82/1500 WTG, which is among

the quietest wind turbines commercially available for its class, size, and power rating. It is not

expected that mitigative measures will be required during Project operations; however, thefollowing options will be considered by SLW, if needed:

Implementing a complaint resolution program whereby neighboring residents can contact

SLW with their concerns. Complaints will be logged and promptly investigated in orderto resolve any verifiable issue or exceedance condition, and mitigation may be taken on a

case-by-case basis. Elements of the complaint resolution program include: providing a

dedicated Community Relations employee, preconstruction communication, safety andenvironmental compliance briefings, providing channels for registering a complaint, and

formalized process to resolve a complaint. The details of the complaint resolution

program are provided in Appendix M.

slwf sdeis narrative 2009

Documents