HomeMy WebLinkAbout8.1 Attch 6 Noise Study
ROSEN
GOLDBERG
DER &
LEWITZ, INC.
Acoustical and A.idiovisual Consultants
ENVIRONMENTAL NOISE ASSESSMENT FOR:
Kidango Child Care Center (Revised Plan)
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:
18 November 2010
1100 Larkspur Landing Circle #375 • Larkspur CA 94939 • Tel 415 464 01 50 • Fax 41 5 464 0155 • RGDLacoustics.com
Attachment 6
Kidango Preschool (Revised Plan), Dublin, CA Page 1
Environmental Noise Assessment 18 November 2010
1. Introduction
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. Kidango proposes to relocate the outdoor play area farther to the south,
away from the nearest property line.
This study presents the results of noise measurements at the site and estimates of
the noise levels with maximum enrollment and the relocated outdoor play area.
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 Ldn) or Community Noise Equivalent Level (CNEL) is used. These
descriptors are averages like the Leq except they include a 10 dB penalty during
Kidango Preschool (Revised Plan), Dublin, CA Page 2
Environmental Noise Assessment 18 November 2010
nighttime hours (and a 5 dB penalty during evening hours in the CNEL) to account
for peoples increased sensitivity during these hours.
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 CIBA 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 Cateaorv Normally Conditionally Normally Clearly
Acc ble Acceptable Unacceptable Unacceptable
(Noise Insulation)
Features Required
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 (Revised Plan), Dublin, CA Page 3
Environmental Noise Assessment 18 November 2010
4. Existing Noise Environment
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 10th, 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 Leo 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 A-Weighted Noise Level, dBA
Date/Time Children in Play
Area
Leq Lmax L2 L8 L25 L50 L90
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 (Revised Plan), Dublin, CA Page 4
Environmental Noise Assessment 18 November 2010
Figure 1: Site Plan and Ambient Noise Measurement Location
i
w^ Y F
Y.
u.
weo.roR
c PREBClIOt51. ~
f
t now
r CURRWNT
IMANGO
PCAYMM
®
;if}
III I
5. Analysis
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 at the proposed play area location. The measured noise
levels were adjusted to account for the increased enrollment, the duration of
outdoor play time and the distance from the proposed play area to the residences.
According to the project description, there will be a maximum of 24 children using
the outdoor play area at one time and there will be five play times throughout the
day. Three play times will be in the morning between 9 A.M. and 12 noon; the
fourth play time will be from 2:45 to 3:15 P.M.; and, the fifth play time will be from
5:00 to 5:45 P.M.
The measured noise level (Leq) at the property line adjacent to the current play area
was 65 dBA with 12 children playing and 67 dBA with 20 children playing. Noise
levels will increase at a rate of 3 dBA per doubling of children. The proposed
location of the play area will be is significantly farther from the residences than its
current location. Noise levels will decrease with distance at a rate of 6 dB per
doubling of distance. 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.
Kidango Preschool (Revised Plan), Dublin, CA Page 5
Environmental Noise Assessment 18 November 2010
The predicted noise levels with the maximum number of children (24) 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 time 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.
Table 3: Project Generated Noise Levels
CNEL (dBA)
Location Leq 1-5o L,
(dBA) (dBA) (dBA) Children and
Children only distant traffic
noise
At Residential Property Line of 55 52 67 47 53
homes along Ladera Drive
At Residential Property Line of 53 50 65 46 53
homes along San Sabana Road
The noise levels shown in Table 3 are based on the noise measurements that were
conducted at the top of the property line fence. This is the most conservative
assessment location since it does not take into account the sound attenuation
provided by existing wood fences. Table 3 also shows the CNEL from the
combination of the children and the ambient noise from distant traffic. This total
CNEL is dominated by the noise from distant traffic, which alone causes a CNEL of
52 dBA.
Tables 4 and 5 shows the increase in CNEL from the project. In Table 4 the
existing condition is after Neilson Elementary School closed but before the Kidango
Preschool began operations. Under this scenario the increase in CNEL is 1 dBA.
In Table 5 the existing condition is before Neilson Elementary School closed and
includes noise from Nielsen Elementary School 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'. Under this scenario the CNEL decreases
by 5 dBA.
' 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 (Revised Plan), Dublin, CA Page 6
Environmental Noise Assessment 18 November 2010
Table 4: Increase in CNEL (dBA) with Respect to Condition After the
Closure of Neilsen Elementary School
Location Existing Future Increase
At Residential Property Line of 52 53 1
homes along Ladera Drive
At Residential Property Line of 52 53 1
homes along San Sabana Road
Table 5: Increase in CNEL (dBA) with Respect to Condition Before the
Closure of Neilson Elementary School
Location Existing Future Increase
At Residential Property Line of 58 53 -5
homes along Ladera Drive
At Residential Property Line of 58 53 -5
homes along San Sabana Road
6. Conclusion
The composite of project-generated play yard noise and distant traffic noise will
result in a CNEL of 53 dBA at the residential property lines. 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 Revised Noise Report _1717ovIO.doc