HomeMy WebLinkAboutAppendix O-Sound Level AssessmentAPPENDIX O
Sound Level Assessment for Avila Ranch Development Project
Avila Ranch Development Project
Final EIR
This Page Intentionally Left Blank.
Sound Level Assessment for
Avila Ranch Project
Vachell Lane and Buckley Road
San Luis Obispo, CA
requested by
Avila Ranch, LLC
735 Tank Farm Road, Suite 240
San Luis Obispo, CA. 93401
June 25, 2015
45dB.com
David Lord, PH.D.
Acoustics Consulting
P.O. Box 1406
San Luis Obispo
California 93406
tel. 805.704.8046
email: dl@45db.com
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Table of Contents
1.0 Description and Criteria ..................................................................................4
2.0 Regulatory Setting ..........................................................................................4
2.1 State Regulation ...................................................................................4
2.2 Local Regulation ..................................................................................6
2.3 Airport Land Use Plan ........................................................................6
3.0 Existing Sound Levels ...................................................................................10
4.0 Future Sound Levels .......................................................................................11
5.0 Discussion and Conclusions ..........................................................................11
5.1 Exterior Glazing ................................................................................12
5.2 Exterior Doors Facing Noise Source ................................................14
5.3 Exterior Walls ....................................................................................15
5.4 Supplemental Ventilation ...................................................................15
6.0 REFERENCES ..............................................................................................37
7.0 APPENDIX A: Glossary of Acoustical Terms ..............................................38
8.0 Measurements, Calculations and Modeling .................................................41
8.1 Wind Measurement ............................................................................41
8.2 Precision of Sound Level Meters. ................................................41
8.3 Sound Level Measurement Method ................................................41
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List of Figures
Figure 1. Site Plan .................................................................................................5
Figure 2. Acceptable Noise Exposure ..................................................................7
Figure 3. Airport Land Use Plan .........................................................................8
Figure 4. Airport Land Use Plan, revised ..........................................................9
Figure 5. CALGreen Code ................................................................................13
Figure 6. Existing Sound Level Contours .......................................................16
Figure 7. Future Sound Level Contours, Year 2035 .......................................17
Figure 8. Station One Sound Level .................................................................18
Figure 9. Station One hourly Leq ....................................................................19
Figure 10. Station Two Sound Level ................................................................20
Figure 11. Station Two hourly Leq .................................................................21
Figure 12. Station Three Sound Level ...........................................................22
Figure 13. Station Three hourly Leq .............................................................23
Figure 14. Station Three hourly Leq .............................................................24
Figure 15. Station Four Sound Level ...........................................................25
Figure 16. Station Four hourly Leq .............................................................26
Figure 17. Station Five Sound Level ...........................................................27
Figure 18. Station Five hourly Leq .............................................................28
Figure 19. Station Six Sound Level ...........................................................29
Figure 20. Airport Departures .......................................................................30
Figure 21. Station Six hourly Leq ..............................................................31
Figure 22. Outdoor Activity Area Noise Mitigation .................................32
Figure 23. Weather Data, January 23, 2015 ...............................................33
Figure 24. Weather Data, January 24, 2015 .............................................34
Figure 25. Weather Data, January 26, 2015 .............................................35
Figure 26. Weather Data, January 27, 2015 ............................................36
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Sound Level Assessment for
Avila Ranch Project
Vachell Lane and Buckley Road
San Luis Obispo, CA
1.0 Description and Criteria
This sound level assessment is for the proposed development of Avila Ranch with regard
to surrounding noise levels from all sources that have potential impact on noise sensitive uses.
The possible noise sources examined in this study are vehicular traffi c, as well as air traffi c
from San Luis Obispo County Regional Airport. In addition there are potential stationary noise
sources from neighboring commercial activities along the north boundary. The Avila Ranch
site is bordered by Vachell Lane to the west and by Buckley Road to the south. Commercial
activities, including loading and aggregate mixing operations occur to the northwest of the site.
The northeast of the site is closest to the San Luis Obispo County Regional Airport. The general
layout and confi guration of the site, along with sound level measurement locations are shown in
“Figure 1. Site Plan” on page 5.
The purpose of this sound level study is to assess the exterior noise environment of the
subject property and to provide recommendations on the control of exterior-to-interior noise with
respect to regulations, policies and/or local ordinances. This report provides a description of the
environmental noise survey methodology, a discussion of applicable noise standards, results of
the noise survey, future noise level projections, and exterior-to-interior noise mitigation recom-
mendations for the proposed residential development.
Existing sound levels were measured continuously on the proposed site at 10-second
intervals over a 24-hour period on Friday and Saturday, January 23 - 24, 2015, and on Monday
and Tuesday, January 26 - 27, 2015. An acoustic model with sound level contours was generated
for the site based on topography, noise sources and measured sound level values.
2.0 Regulatory Setting
Noise is regulated at the federal, state and local levels through regulations, policies and/or
local ordinances. Local policies are generally adaptations of federal and state guidelines, adjusted
to prevailing local condition. Refer to “7.0 APPENDIX A: Glossary of Acoustical Terms” on
page 38 for further defi nition of metrics and terminology.
2.1 State Regulation
The State of California’s Guidelines for the Preparation and Content of Noise Element
of the General Plan (1987). These guidelines reference land use compatibility standards for
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Figure 1. Site Plan
The plan below shows adjacent roads, Vachell Lane to the west and Buckley Road to the south,
each of which is a potential noise source. Two stations 1 and 5, measure noise from those roads.
Two stations 2 and 3, are located in the relatively quiet interior of the site. Potential stationary
and operating noise from AirVol Block is measrued at station 4 in the northwest corner of the
site. Station 6 is located in the northeast corner of the site, which is nearest the airport, and is
otherwise sheltered from stationary and transportation noise. The location of the six Sound
Level 24-hour measurement stations distributed around the site is shown. The geographic
coordinate of each site is listed below:
Station 1: 35.236807, -120.674414
Station 2: 35.237686, -120.671067
Station 3: 35.238978, -120.668318
Station 4: 35.241.258, -120.672064
Station 5: 35.236972, -120.669616
Station 6: 35.240476, -120.662504
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community noise environments as developed by the California Department of Health Services,
Offi ce of Noise Control. Sound levels up to 65 Ldn or CNEL are determined to be normally
acceptable for multi-family residential land uses. Sound levels up to 70 CNEL are normally
acceptable for buildings containing professional offi ces or defi ned as business commercial.
However, a detailed analysis of noise reduction requirements is recommended when new offi ce
or commercial development is proposed in areas where existing sound levels approach 70 CNEL.
All new Multi-Family housing must comply with California Code of Regulations (CCR)
Title 24 – included in the California Building Code (CBC), Section 1207, “Sound Transmission”
– which specifi es the maximum level of interior noise due to exterior sources allowable for new
residential developments. Division II of the CBC, Appendix 12 presents acoustical requirements
in general terms, with more specifi c language provided in Division IIA of Appendix 12. CCR
Title 24 also defers to local requirements if applicable. The Noise Element of the City of San
Luis Obispo General Plan specifi es a maximum allowable interior noise level of 45 dBA Ldn
for multi-family projects which is consistent with the above policies for interior noise and also
extends this requirement to new single family dwellings. The San Luis Obispo Noise Element
also states that 60 dBA Ldn or less is the exterior noise goal for outdoor common areas, defi ned
as areas intended for the use and enjoyment of residents.
2.2 Local Regulation
Transportation Noise: Guidelines for transportation noise exposure are contained in City
of San Luis Obispo, General Plan Noise Element and Noise Guidebook (1996). The maximum
noise exposure standards for noise-sensitive land uses are shown in “Figure 2. Acceptable Noise
Exposure” on page 7.
2.3 Airport Land Use Plan
The location of the Avila Ranch site is shown in “Figure 3. Airport Land Use Plan” on
page 8, in relation to the Airport Land Use Plan Airport Noise Contours. The site is partially
within the Projected 50 dB airport noise contour and partially within the Projected 55 dB airport
noise contour. The actual 55 dB airport noise contour is off-site.
The Airport Land Use Plan (ALUP), adopted December 1973 and amended May,
2005, establishes Maximum Allowable Interior Noise Exposure from Aviation Related Noise
Sources in Table 4, page 18: The maximum is judged from the “single-event interior aviation
noise level,” and prescribes the noise attenuation required in relation to the “single-event noise
contour.” The reference event for determination of required single event noise mitigation is
assumed to be the straight-in arrival of a regional airline jet landing on Runway 29 and the
straight-out departure of a regional airline jet from Runway 29. Measurements are to be of the
maximum noise level, are to be A-weighted, and are to be obtained using a Fast response time.
(It should be noted that aircraft arrivals are substantially less noisy than aircraft departures.)
For Residential Dwellings, the ALUP prescribes a maximum allowable interior noise
level of 50 dBA and allows normal construction materials and methods when the residence
is located at or below the 65 dB Noise Contour. At 65 dB sound level or below, “normal
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Figure 2. Acceptable Noise Exposure
City of San Luis Obispo: Acceptability of new noise-sensitive uses exposed to transportation
noise sources. Noise Element of the General Plan.
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Figure 3. Airport Land Use Plan
Location of Avila Ranch site in relation to the Airport Land Use Plan Airport Noise Contours.
The site is partially within the Projected 50 dB airport noise contour and the Projected 55 dB
airport noise contour. The actual 55 dB contour is off-site.
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Figure 4. Airport Land Use Plan, revised
Location of Avila Ranch site in relation to the Airport Land Use Plan Airport Noise Contours,
revised form, supplied by the Airport Land Use Commission.
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construction techniques are assumed to provide adequate noise attenuation.” The ALUP
guidance for exterior to interior noise attenuation for this setting is construction with 15 dB
attenuation, which is construction that uses ordinary materials and methods. However, since
the ALUP was written, ordinary construction has improved sound attenuation. (see “Figure 5.
CALGreen Code” on page 13.) In general, the ALUP requires that peak hour interior sound
levels be reduced below Leq = 45 dBA.
3.0 Existing Sound Levels
Existing sound levels on the site were measured at six stations, located across the
proposed Avila Ranch site. Sound level at each measurement station was recorded at 10-second
intervals for a 24-hour period. Recorded sound level data consist of:
Average sound level, dBA,
Peak sound level, dBA, and
SEL (Sound Exposure Level) normalized to one second.
Audio recording of each event over 60 dBA.
From the measured data, existing hourly LEQ values were calculated and an overall
Community Noise Equivalent Level (CNEL) was calculated for each measurement station For
an explanation of technical defi nitions, see “7.0 APPENDIX A: Glossary of Acoustical Terms”
on page 38. The six sound level measurement stations were placed in the following locations:
(a) Station 1. Located at the southwestern corner of the site and approximately 300 feet
toward the interior from the intersection of Buckley Road and Vachell Lane. These two
roads form a large, linear transportation noise source with potential impact on the site.
See “Figure 1. Site Plan” on page 5.
(b) Station 2. Located in the quiet interior of the site. This location is subject to
occasional low levels of wildlife sounds and occasional overfl ight noise. Other than
aircraft overfl ight, this is a relatively quiet location on the site, not near surface transpor-
tation or major stationary noise sources. Although there are currently some agricultural
operations and activities in the vicinity, those noise sources were accounted for on audio
recordings made at the site, and were minimal during the noise measurement period. See
“Figure 10. Station Two Sound Level” on page 20.
(c) Station 3. Located in the quiet interior of the site. This location is subject to
occasional low sound levels made by wildlife and occasional overfl ight noise. Other than
aircraft overfl ight, this is a relatively quiet location on the site, not near surface transpor-
tation or major stationary noise sources. Although there are currently some agricultural
operations and activities in the vicinity, those noise sources were accounted for on audio
recordings made at the site, and were minimal during the noise measurement period. See
“Figure 12. Station Three Sound Level” on page 22.
(d) Station 4. Located next to the northwest boundary of the property, adjacent to
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the current AirVol Block manufacturing facility with loading and staging areas, and a
potential 24-hour daily operation. Only a portion of the sampled noise was “stationary
noise” such as compressors, stationary mixers, etc., separated from the overall operating
noise from the AirVol operation. In total, the stationary component of the noise at the
property line was lower than 50 dBA. See “Figure 15. Station Four Sound Level” on
page 25.
(e) Station 5. Located in the middle of the southern boundary of the site, approximately
300 feet from Buckley Road. This location has an unobstructed ‘view’ of the road and is
far enough away from Vachell Lane to measure only Buckley Road transportation noise.
This is the measurement site with the highest sound level values. See “Figure 17. Station
Five Sound Level” on page 27.
(f) Station 6. Located in the northeast corner of the site, this station is closest to the
San Luis Obispo County Regional Airport, and is otherwise in a quiet location with
little background noise. The primary source of noise measured at this site was aircraft
overfl ight, which can be seen in the individually plotted results. See “Figure 19. Station
Six Sound Level” on page 29.
The hourly LEQ for each of the measurement sites was derived from measured sound
level data. In addition, for each measurement location the 24-hour Ldn and CNEL values were
calculated (see “7.0 APPENDIX A: Glossary of Acoustical Terms” on page 38 for defi nitions)
4.0 Future Sound Levels
Existing measured sound levels provide a baseline from which future sound levels can be
predicted. Future sound levels are related to growth of Average Daily Traffi c (ADT) growth rates
on the surrounding roads, and increased activity at nearby commercial operations and increases
in number of fl ights at the San Luis Obispo County Regional Airport. The general relationship of
traffi c growth and sound level is that with a doubling of traffi c ADT, there will be a concomitant
increase of 3 dB sound level.
Therefore, if existing sound levels are 53 dBA at a certain location on the proposed site,
and if transportation growth results in a doubling of ADT volume, then the sound level will
increase to 56 dBA at that same location in the future:
5.0 Discussion and Conclusions
The 24-hour existing sound levels on the undeveloped site are clearly shown at each of
the measurement stations and in “Figure 6. Existing Sound Level Contours” on page 16. In
the area of the site along Buckley Road, sound levels may exceed CNEL = 60 dBA threshold
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in CCR Title 24. Residential units planned in the this area will require noise mitigation of any
potential outdoor activity areas that are confi rmed to be above 60 dBA, as illustrated in “Figure
22. Outdoor Activity Area Noise Mitigation” on page 32. If exterior sound level is below
CNEL = 60 dBA, no additional sound attenuating construction is necessary. If windows are
required to be shut to meet the interior 45 dBA requirement, then a mechanical ventilation alter-
native is required.
The measured sound level of air traffi c for fl ights to and from San Luis Obispo County
Regional Airport is shown for a 24-hour period in “Figure 19. Station Six Sound Level” on page
29 and in “Figure 21. Station Six hourly Leq” on page 31.
The Ldn / CNEL value of 51 dBA for Station Six represents the 24-hour average sound
level at the location nearest the airport, with a minimum of surface transportation noise. The
existing sound level value is lower than the projected sound level of CNEL 55, shown in “Figure
3. Airport Land Use Plan” on page 8.
Summary of disposition of regulatory requirements:
(a) City Noise Element outdoor activity area less than CNEL = 60 dBA; Mitigation may
be required and is described below for area facing Buckley Road.
(b) City Stationary Noise Ordinance less than Leq = 50 dBA: This limit is not exceeded
in the northwest corner of the development, near AirVol operation.
(c) Airport Land Use Plan recommendation that interior sound levels not exceed Leq 1
hr = 45 dBA in peak one hour period. (see calculation in “Figure 5. CALGreen Code”
on page 13)
(d) California Energy Commission CALGREEN code requirement less than Leq = 45
dBA during peak one hour period. (see “Figure 5. CALGreen Code” on page 13)
(e) State Building Code requirement that interior noise level not exceed annual CNEL
= 45 dBA: This standard is met or exceeded in above instances and with mitigations
described below.
5.1 Exterior Glazing
Windows are inherently the weak link of a residential project’s exterior acous-
tical envelope. Therefore, proper selection and installation of exterior glazing elements are
paramount to achieving CCR Title 24 interior noise limits. Frames of windows and doors must
be sealed with dual beads of resilient, acoustical sealant to provide an airtight seal. Also, dual
beads of resilient, acoustical sealant must be applied to window casings before installation.
Manufacturer’s instructions for installation of acoustically rated window assemblies must be
followed carefully, so that installed windows retain their rated acoustical performance.
Recommendations are presented in terms of the Outdoor-Indoor Transmission Class
(OITC) and Sound Transmission Class (STC) acoustical performance ratings, both of which
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Figure 5. CALGreen Code
The California Green Building Standards Code (CCR Title 24, Part 11) provides standards
for acoustical transmission values in noisy environments, as shown in the table below. The
proposed development meets the requirements of 5.507.4.2 Performance method, illustrated and
described in the following way:
Standard construction materials and techniques used for new developments in Southern
California result in a minimum exterior-to-interior noise attenuation of 12 dBA with windows
open (for natural ventilation) and minimum 20 dBA with windows closed.
Therefore, the worst case resulting interior noise level (LEQ = 1 hr.) due to airport activity (refer
to “Figure 21. Station Six hourly Leq” on page 31) will occur during the Station Six one-hour
LEQ = 53 dBA at 16:00 to 17:00. The interior sound level during that hour would be 53 dB
minus 20 dB = 33 dBA with windows closed.
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should be met by the window manufacturer by providing test data for the specifi c window
assembly types submitted for this project.
Traditionally, manufacturers of exterior doors and windows have used the single-number
Sound Transmission Class (STC) metric to rate the acoustical performance of their products.
However, STC is a metric optimized for the spectral shape (or tonal quality) of human speech,
as it was originally developed as a means to rate the degree of sound isolation between dwelling
units in the late 1950s.
The Outdoor-Indoor Transmission Class (OITC), as defi ned in the ASTM Standard
E1332, is the preferred metric for rating the sound performance of building shell materials. OITC
ratings are tied to a typical noise spectrum shape from transportation sources, which are rich in
low frequency, bass-type sounds, as opposed to the frequencies of human speech or television
audio. Both OITC and STC rating values are calculated from 1/3-octave band transmission loss
data for specifi c building shell components.
Exterior window glazing recommended for residential units exposed to potential noise
above Ldn = 60 dBA is a minimum OITC 24 / STC 30. If practical, glazing systems with
dissimilar thickness panes are preferred to avoid the “harmonic resonance” that occurs with
panes of equal thickness. However, all of this project’s recommended acoustical design ratings
should be achievable with commercially available window assemblies.
5.2 Exterior Doors Facing Noise Source
According to Section 1207.7 of the California Building Code, the following applies to
residential unit entry doors from interior spaces:
Entrance doors together with their perimeter seals shall have STC ratings not less than
26. Such tested doors shall operate normally with commercially available seals. Solid-core
wood-slab doors 1 3/8 inches (35 mm) thick minimum or 18 gage insulated steel-slab doors with
compression seals all around, including the threshold, may be considered adequate without other
substantiating information.
Based upon the results of the exterior noise study for this project, standard entrance doors
as described above, will provide adequate acoustical insulation at exterior project entries. These
should have a combined STC 28 rating for any door and frame assemblies. Any balcony and
ground fl oor entry doors located at bedrooms should have an STC rating similar to the minimum
STC window ratings. While design criteria are the same for all habitable spaces, bedrooms are
the most sensitive habitable spaces in a residential unit.
In general, an STC 28 door rating can be achieved with a standard door that is supplied
with improved acoustical gaskets at the jambs and threshold, although any supplier must provide
an acoustical rating submittal. It is typical for an STC 30 rated exterior entry to include side and
head jamb gaskets of the non-porous kind, such as Pemko™ Siliconseal (S88) or approved equal,
to avoid fl anking transmission of sound into the project units. The door bottom should be fi tted
with a fully gasketed, lap-joint type threshold or with another form of door bottom/threshold with
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gasket that provides a proper acoustical seal. Thresholds and frames of all exterior doors should
be carefully caulked before setting.
5.3 Exterior Walls
The exterior wall assemblies for this project have not been specifi ed at this time. Where
outdoor sound levels exceed Ldn = 60 dBA, typical constructions would likely consist of a
stucco or engineered building skin system over sheathing, with 4” to 6” deep metal or wood
studs, fi berglass batt insulation in the stud cavity, and one or two layers of 5/8” gypsum board
on the interior face of the wall. As the project design is developed and site planning is modifi ed,
sections and details for the exterior facades may require further review.
The ultimate degree of sound isolation provided by the building shell is highly dependent
on the quality of workmanship and attention to detail that is followed during construction. The
following recommendations are aimed at delivering the full sound isolating potential of the
building shell:
(a) If possible, avoid electrical outlets in exterior walls exposed to noise. If this is not
possible, apply outlet box pads such as those manufactured by Hilti to all electrical boxes.
Carefully seal around all edges of electrical outlet boxes and other penetrations with
non-hardening acoustical sealant.
5.4 Supplemental Ventilation
Noise levels above Ldn = 60 dBA are predicted for some of the project’s exterior
facades before mitigation. A typical bedroom/living room window will allow for a reduction of
approximately 12 decibels when open, as used for natural ventilation. In this instance interior
sound levels are expected to be (60 - 12 = 48 dBA). Therefore, it is not expected that interior
noise requirement of Ldn = 45 dBA or less can be met with open windows. The State Building
Code requires that supplemental ventilation adhering to OITC/STC recommendations must be
provided for the project’s residential units with habitable spaces facing noise levels exceeding
Ldn = 60 dBA, so that the opening of windows is not necessary to meet ventilation requirements.
Supplemental ventilation can also be provided by passive or by fan-powered, ducted air
inlets that extend from the building’s rooftop into the units. Ducted air inlets must be acoustically
lined through the top-most 6 ft in length and incorporate one or more 90-degree bends between
openings, so as not to compromise the noise insulating performance of the residential unit’s
exterior envelope.
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Figure 6. Existing Sound Level Contours
Site Plan, existing site, showing sound level contours expressed as CNEL = dBA
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Figure 7. Future Sound Level Contours, Year 2035
Site Plan, future predicted sound level contours expressed as CNEL = dBA, based on increased
traffi c count (ADT) for 2035. Buildings are shown in plan only and not modeled in three dimen-
sions, therefore ground transportation sound levels in the interior of the site may be lower than
depicted here.
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Figure 8. Station One Sound Level
Station One Sound Level, measured every 10 seconds over a 24-hour period. The sound level
meter is located 75 feet west of nearest traffi c lane. Peak sound levels are generally identifi ed as
motorcycles or trucks. Sound levels are dBA, slow meter setting
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Figure 9. Station One hourly Leq
Station One Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated LDN/
CNEL for the 24-hour period is 59 dBA, including calculated penalties for evening and nighttime
noise.
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Figure 10. Station Two Sound Level
Station Two Sound Level, measured every 10 seconds over a 24-hour period. The sound level
meter is located in the interior of the site, in a quiet location. The occasional peak sound levels
are generally identifi ed as aircraft overfl ights. Sound levels are dBA, slow meter setting
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Figure 11. Station Two hourly Leq
Station Two Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated LDN/
CNEL for the 24-hour period is 52 dBA, including calculated penalties for evening and nighttime
noise.
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Figure 12. Station Three Sound Level
Station Three Sound Level, measured every 10 seconds over a 24-hour period. The sound level
meter is located in the interior of the site, in a quiet location. The occasional peak sound levels
are generally identifi ed as aircraft overfl ights. Sound levels are dBA, slow meter setting
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Figure 13. Station Three hourly Leq
Station Three Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated
LDN/CNEL for the 24-hour period is 51 dBA, including calculated penalties for evening and
nighttime noise.
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Figure 14. Station Three hourly Leq
Station Three Sound Levels: Example of data collected over a typical one-hour period for every
measurement station, including Leq for each 10 sec. period, Lmax and SEL.
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Figure 15. Station Four Sound Level
Station four Sound Levels, measured every 10 seconds over a 24-hour period. The sound level
meter is located at the AirVol Block shared boundary. Peak sound levels are generally identifi ed
as industrial operations, as well as arriving and departing forklifts and delivery vehicles. Sound
levels are dBA, slow meter setting.
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Figure 16. Station Four hourly Leq
Station Four Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated LDN/
CNEL for the 24-hour period is 56 dBA, including calculated penalties for evening and nighttime
noise.
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Figure 17. Station Five Sound Level
Station fi ve Sound Levels, measured every 10 seconds over a 24-hour period. Peak sound levels
are generally motorcycles and trucks. Sound levels are dBA, slow meter setting.
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Figure 18. Station Five hourly Leq
Station Five Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated
LDN/CNEL for the 24-hour period is 59/60 dBA, including calculated penalties for evening and
nighttime noise.
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Figure 19. Station Six Sound Level
Station six Sound Levels, measured every 10 seconds over a 24-hour period. Peak sound levels
are generally airplane and helicopter fl yovers. Sound levels are dBA, slow meter setting.
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January 23, 2015 PM departures
San Luis Obispo County Airport
January 24, 2015 AM departures
San Luis Obispo County Airport
Figure 20. Airport Departures
Information taken from http://www.fl ightstats.com which are in agreement with the fl ight
departure sound levels in “Figure 19. Station Six Sound Level” on page 29.
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Figure 21. Station Six hourly Leq
Station Six Sound Levels, expressed as hourly Leq over a 24-hour period. The calculated LDN/
CNEL for the 24-hour period is 51 dBA, including calculated penalties for evening and nighttime
noise.
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Figure 22. Outdoor Activity Area Noise Mitigation
Where exterior sound levels exceed CNEL = 60 dBA, especially facing transportation noise from
Buckley Road, noise mitigation shall be required. The feasibility of berming for noise mitigation
is illustrated below: “no berm” on left and, “with berm” on right. Substitution of lower berm
height and partial noise wall may be made for equivalent performance.
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Figure 23. Weather Data, January 23, 2015
Atmospheric conditions that may affect sound level measurements are shown. Wind speed
above 10 mph on the afternoon of January 23, 2015 from 2 pm to 7 pm may have caused a small
increase in sound levels below 45 dBA, measured during that time. There would be no effect on
accuracy of sound levels measured above 50 dBA.
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Figure 24. Weather Data, January 24, 2015
Atmospheric conditions that may affect sound level measurements are shown. Wind speed above
10 mph on the afternoon of January 24, 2015 from 1 pm to 3 pm and around 7 pm may have
caused a small increase in sound levels below 45 dBA, measured during that time. There would
be no effect on sound levels measured above 50 dBA.
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Figure 25. Weather Data, January 26, 2015
Atmospheric conditions that may affect sound level measurements are shown. Wind speed at
10 mph on the morning of Monday, January 26, 2015 at 7 am may have caused a small increase
in sound levels below 45 dBA, measured during that time. There would be no effect on sound
levels measured above 50 dBA.
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Figure 26. Weather Data, January 27, 2015
Atmospheric conditions that may affect sound level measurements are shown. Wind speed did
not exceed 10 mph on Tuesday, January 27, 2015. There would be no wind effect on sound
levels measured on that day.
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6.0 REFERENCES
1. American National Standards Institute, Inc. 2004. ANSI 1994 American National Standard
Acoustical Terminology. ANSI S.1.-1994, (R2004) , New York, NY.
2. American Society for Testing and Materials. 2004. ASTM E 1014 - 84 (Reapproved 2000)
Standard Guide for Measurement of Outdoor A-Weighted Sound Levels.
3. Berglund, Birgitta, World Health Organization. 1999. Guidelines for Community Noise
chapter 4, Guideline Values.
4. Bolt, Beranek and Newman. 1973. Fundamentals and Abatement of Highway Traffi c Noise,
Report No. PB-222-703. Prepared for Federal Highway Administration.
5. California Department of Transportation (Caltrans). 1982. Caltrans Transportation
Laboratory Manual.
6. ______. 1998. Caltrans Traffi c Noise Analysis Protocol For New Highway Construction and
Highway Reconstruction Projects.
7. ______. 2006. California Transportation Plan 2025, chapter 6.
8. California Resources Agency. 2007. Title 14. California Code of Regulations Chapter 3.
Guidelines for Implementation of the California Environmental Quality Act Article 5.
Preliminary Review of Projects and Conduct of Initial Study Sections, 15060 to 15065.
9. City of San Luis Obispo. City of San Luis Obispo General Plan, Noise Element.
10. Federal Highway Administration. 2006. FHWA Roadway Construction Noise Model User’s
Guide Final Report. FHWA-HEP-05-054 DOT-VNTSC-FHWA-05-01.
11. Harris, Cyril.M., editor. 1979 Handbook of Noise Control.
Avila Ranch page 38 6/25/15
7.0 APPENDIX A: Glossary of Acoustical Terms
A-Weighted Sound Level (dBA)
The sound pressure level in decibels as measured on a sound level meter using the inter-
nationally standardized A-weighting fi lter or as computed from sound spectral data to
which A-weighting adjustments have been made. A-weighting de-emphasizes the low
and very high frequency components of the sound in a manner similar to the response of
the average human ear. A-weighted sound levels correlate well with subjective reactions
of people to noise and are universally used for community noise evaluations.
Airborne Sound
Sound that travels through the air, differentiated from structure-borne sound.
Ambient Sound Level
The prevailing general sound level existing at a location or in a space, which usually
consists of a composite of sounds from many sources near and far. The ambient level is
typically defi ned by the Leq level.
Background Sound Level
The underlying, ever-present lower level noise that remains in the absence of intrusive or
intermittent sounds. Distant sources, such as traffi c, typically make up the background.
The background level is generally defi ned by the L90 percentile noise level.
Community Noise Equivalent Level (CNEL):
The Leq of the A-weighted noise level over a 24-hour period with a 5 dB penalty applied
to noise levels between 7 p.m. and 10 p.m. and a 10 dB penalty applied to noise levels
between 10 p.m. and 7 a.m.
Day-Night Sound Level (Ldn):
The Leq of the A-weighted noise level over a 24-hour period with a 10 dB penalty
applied to noise levels between 10 p.m. and 7 a.m.
Decibel (dB):
The decibel is a measure on a logarithmic scale of the magnitude of a particular quantity
(such as sound pressure, sound power, sound intensity) with respect to a reference
quantity.
DBA or dB(A)
A-weighted sound level. The ear does not respond equally to all frequencies, but is less
sensitive at low and high frequencies than it is at medium or speech range frequencies.
Thus, to obtain a single number representing the sound level of a noise containing a wide
range of frequencies in a manner representative of the ear’s response, it is necessary
to reduce the effects of the low and high frequencies with respect to the medium
frequencies. The resultant sound level is said to be A-weighted, and the units are dBA.
The A-weighted sound level is also called the noise level.
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Energy Equivalent Level (LEQ):
Because sound levels can vary markedly in intensity over a short period of time, some
method for describing either the average character of the sound or the statistical behavior
of the variations must be utilized. Most commonly, one describes ambient sounds in
terms of an average level that has the same acoustical energy as the summation of all the
time-varying events. This energy-equivalent sound/noise descriptor is called LEQ. In this
report, an hourly period is used.
Field Sound Transmission Class (FSTC):
A single number rating similar to STC, except that the transmission loss values used to
derive the FSTC are measured in the fi eld. All sound transmitted from the source room to
the receiving room is assumed to be through the separating wall or fl oor-ceiling assembly.
Outdoor-Indoor Transmission Class (OITC):
A single number classifi cation, specifi ed by the American Society for Testing and
Materials (ASTM E 1332 issued 1994), that establishes the A-weighted sound level
reduction provided by building facade components (walls, doors, windows, and combina-
tions thereof), based upon a reference sound spectra that is an average of typical air, road,
and rail transportation sources. The OITC is the preferred rating when exterior facade
components are exposed to a noise environment dominated by transportation sources.
Percentile Sound Level, Ln:
The noise level exceeded during n percent of the measurement period, where n is a
number between 0 and 100 (e.g., L10 or L90)
Sound Transmission Class (STC):
STC is a single number rating, specifi ed by the American Society for Testing and
Materials, which can be used to measure the sound insulation properties for comparing
the sound transmission capability, in decibels, of interior building partitions for noise
sources such as speech, radio, and television. It is used extensively for rating sound
insulation characteristics of building materials and products.
Structure-Borne Sound:
Sound propagating through building structure. Rapidly fl uctuating elastic waves in
gypsum board, joists, studs, etc.
Sound Exposure Level (SEL)
SEL is the sound exposure level, defi ned as a single number rating indicating the total
energy of a discrete noise-generating event (e.g., an aircraft fl yover) compressed into a 1-
second time duration. This level is handy as a consistent rating method that may be
combined with other SEL and Leq readings to provide a complete noise scenario for
measurements and predictions. However, care must be taken in the use of these values
since they may be misleading because their numeric value is higher than any sound level
which existed during the measurement period.
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Subjective Loudness Level
In addition to precision measurement of sound level changes, there is a subjective charac-
teristic which describes how most people respond to sound:
•A change in sound level of 3 dBA is barely perceptible by most listeners.
•A change in level of 6 dBA is clearly perceptible.
•A change of 10 dBA is perceived by most people as being twice (or half) as loud.
Avila Ranch page 41 6/25/15
8.0 Measurements, Calculations and Modeling
8.1 Wind Measurement
Sound level measurements become less reliable when average wind speed is greater than 11
m.p.h. at the measurement site. Therefore, wind speed and direction are measured periodically
at the measurement site and the results are correlated with wind data from a nearby established
weather station. A Larson Davis WS 001 windscreen is used as wind protection for all micro-
phones and is left in place at all times.
Wind speed and direction were noted throughout the measurement period and compared
with data from the nearby National Weather Service weather station at San Luis Obispo
County Regional Airport. A Davis Turbo Wind meter was used to measure wind speed at the
measurement site to cross-check wind speeds at the airport. The Turbo Wind meter is a high
performance wind speed indicator with exceptional accuracy.
8.2 Precision of Sound Level Meters.
The American National Standards Institute (ANSI) specifi es several types of sound levelmeters
according to their precision. Types 1,2, and 3 are referred to as “precision,” “generalpurpose,”
and “survey” meters, respectively. Most measurements carefully taken with a type 1 sound level
meter will have an error not exceeding 1 dB. The corresponding error for a type 2 sound level
meter is about 2 dB.
The sound level meters used for measurements shown in this report are Larson-Davis
Laboratories Model 820. These sound level meters meet all requirements of ANSI s1.4, IEC
651 for Type 1 accuracy and include the following features: 110 dB dynamic range for error
free measurements. Measures FAST, SLOW, Unweighted PEAK, Weighted PEAK, Impulse,
Leq, LDOD, LOSHA, Dose, Time Weighted Average, SEL, Lmax, Lmin, LDN. Time history
sampling periods from 32 samples per second up to one sample every 255 seconds.
Field calibration of each sound level meter with an external calibrator is accomplished before
and after all fi eld measurements. Laboratory calibration of the all instruments is performed
at least biannually and accuracy can be traced to the U.S. National Institute of Science and
Technology standard.
8.3 Sound Level Measurement Method
The protocol for conducting sound level measurements is prescribed in detail by the
American Society for Testing and Materials (ASTM) in their E 1014 publication and the
CalTrans Traffi c Noise Analysis Protocol. The procedures and standards in those documents are
met or exceeded for sound level measurements shown in this report. The standards of ASTM E
1014 are exceeded by using Type 1 sound level meters for all measurements in this report instead
of the less accurate Type 2 meters. Therefore, the precision of the measurements in this report is
likely to be better than +/- 2 dB as stated in ASTM E1014. Particular and specifi c sound sources
are identifi ed by listening to synchronous audio recordings of peak sound level events.
Avila Ranch page 42 6/25/15
Caltrans Noise Measurement Guidelines: Caltrans makes available general guide-
lines for taking into account environmental elements in noise measurements. The following
is an excerpt from their guidelines. The Traffi c Noise Analysis Protocol contains Caltrans
noise policies, which fulfi ll the highway noise analysis and abatement/mitigation requirements
stemming from the following State and Federal environmental statutes:
• California Environmental Quality Act (CEQA)
• National Environmental Policy Act (NEPA)
• Title 23 United States Code of Federal Regulations, Part 772 “Procedures for Abatement
of Highway Traffi c Noise and Construction Noise” (23 CFR 772)
• Section 216 et seq. of the California Streets and Highways Code
Noise Contour Modeling
Noise contours incorporating the measured sound level values were generated using CADNA/A,
an acoustical modeling program that incorporates the TNM 2.5 algorithms, and which was
developed to predict hourly Leq values for free-fl owing traffi c conditions. This computer
modeling tool, made by Datakustik GmbH, is an internationally accepted acoustical modeling
software program, used by many acoustics and noise control professional offi ces in the U.S. and
abroad. The software has been validated by comparison with actual values in many different
settings. The program has a high level of reliability and follows methods specifi ed by the
International Standards Organization in their ISO 9613-2 standard, “Acoustics – Attenuation
of sound during propagation outdoors, Part 2: General Method of Calculation.” The standard
states that, “this part of ISO 9613 specifi es an engineering method for calculating the attenuation
of sound during propagation outdoors in order to predict the levels of environmental noise at a
distance from a variety of sources. The method predicts the equivalent continuous A-weighted
sound pressure level under meteorological conditions favorable to propagation from sources
of known sound emissions. These conditions are for downwind propagation under a well-
developed moderate ground-based temperature inversion, such as commonly occurs at night.”
The computer modeling software takes into account source sound power levels, surface refl ection
and absorption, atmospheric absorption, geometric divergence, meteorological conditions, walls,
barriers, berms, and terrain variations. The CADNA/A software uses a grid of receivers covering
the project site.