HomeMy WebLinkAbout8.2 Attch 8 Environmental Noise AssessmentROSEN
GOLDBERG
DER &
LEWITZ, INC.
ENVIRONMENTAL NOISE ASSESSMENT FOR:
Kidango Child Care Center
Dublin, CA
RGDL Project #: 10-003
PREPARED FOR:
City of Dublin
100 Civic Plaza
Dublin, CA 94568
PREPARED BY:
Harold S. Goldberg, P.E.
Principal Consultant
DATE:
19 March 2010
1100 Larkspur Landing Circle #375 • Larkspur CA 94939 . Tel 415 464 0150 a Fax 415 464 0155 • RGDLacoustics.com
ATTACHMENT 8
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
1. Introduction
Page 1
19 March 2010
The Kidango child care center (the project) is located at 7500 Amarillo Road, on a
portion of the old Nielsen Elementary School site. Nielsen Elementary school was
closed in 2008. Subsequently the Kidango facility began operations and it has an
outdoor play area along the north property line. Currently a chain link fence and a
wooden fence separate the Kidango site from the backyards of residential
properties.
This study presents the results of noise measurements at the site and estimates of
the noise levels with maximum enrollment. Comparisons are made with the
ambient noise levels without the child care center, both before and after the closure
of Nielsen. The project generated noise levels are assessed with respect to the
noise and land use compatibility standards of the City of Dublin's General Plan.
2. Environmental Noise Fundamentals
Noise can be defined as unwanted sound. It is commonly measured with an
instrument called a sound level meter. The sound level meter captures the sound
with a microphone and converts it into a number called a sound level. Sound levels
are expressed in units of decibels. To correlate the microphone signal to a level
that corresponds to the way humans perceive noise, the A-weighting filter is used.
A-weighting de-emphasizes low-frequency and very high-frequency sound in a
manner similar to human hearing. The use of A-weighting is required by most local
General Plans as well as federal and state noise regulations (e.g. Caltrans, EPA,
OSHA and HUD). The abbreviation dBA is sometimes used when the A-weighted
sound level is reported.
Because of the time-varying nature of environmental sound, there are many
descriptors that are used to quantify the sound level. Although one individual
descriptor alone does not fully describe a particular noise environment, taken
together, they can more accurately represent the noise environment. The
maximum instantaneous noise level (Lmax) is often used to identify the loudness of a
single event such as a car passby or airplane flyover. To express the average
noise level the LeQ (equivalent noise level) is used. The Leq can be measured over
any length of time but is typically reported for periods of 15 minutes to 1 hour. The
background noise level (or residual noise level) is the sound level during the
quietest moments. It is usually generated by steady sources such as distant
freeway traffic. It can be quantified with a descriptor called the L90 which is the
sound level exceeded 90 percent of the time.
To quantify the noise level over a 24-hour period, the Day/Night Average Sound
Level (DNL or Ld„) or Community Noise Equivalent Level (CNEL) is used. These
descriptors are averages like the LeQ except they include a 10 dB penalty during
nighttime hours (and a 5 dB penalty during evening hours in the CNEL) to account
for peoples increased sensitivity during these hours.
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
Page 2
19 March 2010
In environmental noise, a change in noise level of 3 dB is considered a just
noticeable difference. A 5 dB change is clearly noticeable, but not dramatic. A
10 dB change is perceived as a halving or doubling in loudness.
3. Acoustical Criteria
3.1. City of Dublin General Plan
The Noise Element of the City's General Plan has policies regarding noise and
land use compatibility. Table 1 provides guidelines for the compatibility of land
uses with various noise exposures. The City uses the Community Noise
Equivalent Level (CNEL) descriptor. A CNEL of 60 dBA or less is considered
normally acceptable for residential land use.
Table 1: Land Use Compatibility for Community Noise
Environments
COMMUNITY NOISE EXPOSURE (0)
Land Use Category Normally Conditionally Normally Clearly
Acceptable Acceptable Unacceptable Unacceptable
(Noise Insulation)
Features Reguired
Residential 60 or less 60.70 70.75 Over 75
Motels, hotels 60 or less 60.70 70.80 Over 80
Schools, churches, nursing 60 or less 60.70 70.80 Over 80
homes
Neighborhood parks 60 or less 60.65 65 - 70 Over 70
Offices: retail commercial 70 or less 70.75 75 - 80 Over 80
Industrial 70 or less 70.75 Over 75
Conditionally acceptable exposure requires noise insulation features in building design. Conventional construction,
but with closed windows and fresh air supply systems or air conditioning will normally suffice.
3.2. City of Dublin Noise Ordinance
Chapter 5.28 of the City of Dublin's Municipal Code prohibits "...loud, or
disturbing, or unnecessary, or unusual or habitual noise or any noise which
annoys or disturbs or injures or endangers the health, repose, peace or safety
of any reasonable person of normal sensitivity present in the area". The Noise
Ordinance states that it is appropriate to consider the level and character of the
noise as well as the level and character of the background noise. Since the
City's Noise Ordinance does not contain quantifiable noise level limits, it is not
possible to apply the Noise Ordinance as a threshold for assessing project
generated noise in the context of this noise study.
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
4. Existing Noise Environment
Page 3
19 March 2010
To quantify the existing ambient noise at the site a series of noise measurements
were made at a location along the property line between the outdoor play area and
the adjacent homes which front along Ladera Drive (see Figure 1). The sound level
meter microphone was located 8 feet above the ground and about 1 foot above the
top of the existing wood fence. This position allowed the play area noise to be
quantified without the acoustical effects of the fence (either reflection or shielding).
Most of the homes in the area have two stories and the noise level at second floor
windows would not be substantially affected by the property line fence.
Table 2 shows the results of the noise measurements from four periods on
Wednesday February 10`h, 2010. During two of these periods there were children
present in the play area and the dominant noise source was the voices of the
children. Other sounds such as balls bouncing, balls hitting the chain link fence as
well as tricycles and scooters were audible but did not significantly affect the overall
sound levels. During the other two periods the children were in the classrooms and
the major noise source was distant traffic on 1-580. The CNEL from distant traffic
noise is generally 3 to 5 dBA greater than the Leq during the daytime; therefore, the
CNEL at the property line is approximately 52 dBA from distant traffic.
Table 2: Noise Measurement Results, 10 February 2010
Number of
Children in Play A-Weighted Noise Level, dBA
Date/Time Area Leq Lmax L2 L8 Lee Leo Lso
10:31 - 11: 07 AM 12 65 82 73 70 66 62 56
11:08 - 11:36 AM None 47 59 52 49 48 46 44
11:37 - 12:00 PM 20 67 80 74 71 67 64 59
12:00 - 12:15 PM None 49 63 56 51 48 46 44
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
Page 4
19 March 2010
Figure 1: Site Plan and Ambient Noise Measurement Location
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5. Analysis
-
CHAIN LINK FENCE
5.1. Play Yard Noise Levels
The measured noise levels of children playing at the site (Table 2) were used
as a basis for determining the noise levels that would be generated by the
project with maximum enrollment. The measured average noise level (Leq) at
the property line was 65 dBA with 12 children playing and 67 dBA with 20
children playing. According to the project description, the maximum number of
children using the outdoor play area will be 48. Since noise levels will increase
at a rate of 3 dBA per doubling of children, the future noise level with 48
children would be 4 to 6 dBA greater than the measured noise levels with 12 to
20 children. It is not expected that the addition of a play structure will
significantly affect the noise level from the play area since the dominant noise
source is the children's voice and not the play equipment.
The predicted noise levels with the maximum number of children (48) in the
play are shown in Table 3. The Leq (average noise level), the L50 (median
noise level) and Lmax (maximum noise level) are representative of the hours
that the children are in the play area. The CNEL is a 24-hour average and
therefore averages in the times when the children are not in the play yard. The
project description indicates that the children will use the play area for one hour
before lunch and one-hour after lunch.
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
Table 3: Project Generated Noise Levels
Page 5
19 March 2010
L
L CNEL (dBA)
Location
(dBA) eo
(dBA) max
(dBA)
Children
only
Children and
distant traffic noise
At Residential Property Line 71 68 80 60 61
In backyard 68 65 77 57 58
At Upstairs Windows 65 62 74 54 56
The noise levels shown in Table 3 are based on the noise measurements that
were conducted at the top of the property line fence. Although this is the most
conservative assessment location it is not representative of what a person
would hear when they are inside the house or standing in the backyard.
For a person in the backyard of an adjacent home, the play yard noise would be
reduced by the existing 5-1/2 to 6 foot high wood fence separating the play area
and the backyards. A reduction would occur because the fence breaks the line-
of-sight between the person standing in the backyard and the children in the
play area. A solid barrier that breaks the line of the sight between a noise
source and receiver provides a noise reduction of at least 5 dBA. Since some
of the fence is constructed with butted boards, there are gaps that would tend to
limit the noise reduction provided by the fence. Therefore, the fence is
estimated to provide at least 3 dBA of noise reduction for the backyards.
Although the proposed play structure will effectively increase the height of some
of the children, calculations indicate that the line of sight would remain blocked
between the children on all but the highest platform and a person in the
backyard 10 feet from the fence. Therefore, the estimated 3 dBA noise
reduction provided by the wooden fence is reasonable with the addition of the
proposed play structure.
Second floor rooms in residences would overlook the property line fence and
receive no noise reduction from the fence. Since these rooms are farther from
the play area than the property line, play area noise levels would be about
6 dBA less due to the attenuation of noise with distance.
5.2. Increase in Noise with Respect to Condition After the Closure of Neilsen
Elementary School
The CNEL is estimated to be 52 dBA at the property line in the absence of
Kidango and the Neilsen Elementary School. In the residential backyards, the
traffic noise would be about 3 dBA less due to acoustical shielding provided by
the property line fence.
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
Page 6
19 March 2010
The addition of play area noise from the project would increase the CNEL at
second floor windows from 52 to 56 dBA. The CNEL in backyards would
increase by 9 dBA from 49 dBA to 58 dBA.
Table 4: Increase in CNEL (dBA) with Respect to Condition After the
Closure of Neilsen Elementary School
Location Existing Future Increase
In backyard 49 58 9
Second floor 52 56 4
windows
5.3. Increase in Noise with Respect to Condition Before the Closure of Neilsen
Elementary School
The existing condition before the closure of Nielsen would have included noise
from Nielsen students playing in the yards combined with distant traffic noise.
Since noise measurements were not conducted before the closure of Nielsen in
2008, estimates are made based on noise measurement data from other
schools'.
In this future condition, the noise from Kidango children replaces the noise from
Nielsen children. In the backyards, this will result in a net increase in CNEL of
3 dBA (increase = future - existing; 58 - 55 = 3). Although there were many
more children attending Nielsen than the maximum enrollment of Kidango, the
Kidango children are concentrated in one area, very close to the property line,
while the Nielsen children were spread out over a larger area.
Table 5: Increase in CNEL (dBA) with Respect to Condition Before the
Closure of Neilson Elementary School
Location Existing Future Increase
In backyard 55 58 3
At upstairs windows 56 56 0
Lafayette Elementary School, San Francisco, CA, 2009, enrollment 460 with maximum of 260 children
on playground at any time; Browns Valley Elementary, Vacaville, CA, 2005 with 131 children in the play
yard ; Dublin Elementary, Dublin, CA, March 2008.
Kidango Preschool, Dublin, CA
Environmental Noise Assessment
Page 7
19 March 2010
6. Conclusion
The composite of project-generated play yard noise and distant traffic noise will
result in a CNEL of 58 dBA in the backyards and a CNEL of 56 dBA at the setback
of the second floor of the homes. These noise levels are less than CNEL 60 dBA
which is the upper limit of the range considered "normally acceptable" for
residential development as established by the City's General Plan. Therefore, the
project would not cause the noise levels at the adjacent residences to exceed
normally acceptable noise levels with respect to the City of Dublin's General Plan
noise standards.
File: 10-003_Kindango Noise Report 18mar90.doc