HomeMy WebLinkAbout8.2 Attch 4 Env Noise Analysis ROSEN
GOLDBERG
DER &
LEWITZ, INC.
A(oustical and Audiovisual Consultants
ENVIRONMENTAL NOISE ANALYSIS FOR:
Dublin Day Care Ordinance
Dublin, CA
RGDL Project#: 12-090
PREPARED FOR:
City of Dublin
100 Civic Plaza
Dublin, CA 94568
PREPARED BY:
Harold S. Goldberg, P.E.
Principal Consultant
DATE:
1 April 2013
1100 Larkspur Landing Circle#375•Larkspur CA 94939 •Tel 415 464 0150•Fax 415 464 0155#RGDLacoustics.com
ATTACHMENT 4
Dublin Day Care Ordinance, Dublin, CA Page 1
Environmental Noise Analysis 1 April 2013
1. Introduction
The City of Dublin, California is proposing a Zoning Ordinance Amendment to
allow for the establishment of Day Care Centers as a permitted use. The purpose
of the Amendment is to adopt a set of development standards that would allow the
City to streamline the approval process for Day Care Centers without a Conditional
Use Permit review.
Currently, Day Care Centers that are proposed adjacent to residential areas are
typically required to prepare a site specific noise report addressing the potential
impact of outdoor play area noise on the surrounding residential uses. It is
envisioned that with the Zoning Ordinance Amendment, the noise study would not
be required if the proposed Day Care Center meets adopted Development
Standards.
This report summarizes the current City noise standards and policies and
recommends new development standards. The new standards are derived from
the noise level generated by children in an outdoor play area with consideration of
the existing ambient noise level at the nearby noise sensitive land use. In addition,
the recommended development standards consider the physical attributes of the
proposed Day Care Center including location, site layout and operating conditions.
In essence, these new standards can be applied by the City Planning Staff without
the need for acoustical measurements or noise modeling.
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
ROSEN
GOLDBERG
DFR&
LEWITZ,INC. 1100 Larkspur Landing Circle#375*Larkspur CA 94939 *Tel 415 464 0150*Fax 415 464 0155♦RGDLacoustics.com
Dublin Day Care Ordinance, Dublin, CA Page 2
Environmental Noise Analysis 1 April 2013
freeway traffic. It can be quantified with a descriptor called the Lgo 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 Ldp) 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.
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. It should be noted that the City's
compatibility standards are normally intended to be used for traffic and transit
noise.
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 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.
ROSEN
GOLDBERG
DER&
LEWITZ,INC. 1100 Larkspur Landing Circle#375 a Larkspur CA 94939 •Tel 415 464 0150+ Fax 415 464 0155♦RGDLacoustics.com
Dublin Day Care Ordinance, Dublin, CA Page 3
Environmental Noise Analysis 1 April 2013
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.
3.3. Increase in Noise
The California Environmental Quality Act Guidelines require the determination
of whether a project will generate a substantial increase in noise levels in the
project vicinity above levels existing without the project. CEQA does not
specify a method for determining when a project would cause a significant
increase in noise. Likewise, the City of Dublin does not have criteria for
determining when a noise increase is significant. A recent FAA Draft Policy
discusses screening and impact thresholds for increases in aircraft noise. For
the purposes of this analysis, these thresholds are used to assess the
significance of noise increases due to the Day Care Centers as follows — an
increase in CNEL is significant if it is;
• 5 dBA or greater and the future CNEL is less than 60 dBA or
• 3 dBA or greater and the future CNEL is 60 dBA or greater and less
than 65 dBA or
• 1.5 dBA or greater and the future CNEL is 65 dBA or greater.
4. Development Standards
The intent of the development standards is to identify whether a proposed Day
Care Center would result in a "less than significant" noise impact. This
determination requires that the noise from the outdoor play area not exceed a
CNEL of 60 dBA at the property line of the nearby residential land use and that the
increase in noise is less than the thresholds presented in Section 3.3. When this
analysis is conducted by an acoustical specialist for a site specific noise study, it
normally entails the calculation of play area noise levels based on previous
acoustical measurements of other play areas, as well as on-site ambient acoustical
measurements.
To derive a set of development standards to screen for potentially significant noise
impacts, typical parameters that are used in a noise impact analysis were reduced
to their related physical attributes as follows:
ROSEN
GOLDBERG
DER&
LEWITZ,INC. 1100 Larkspur Landing Circle#375*Larkspur CA 94939 s Tel 415 464 0150+Fax 415 464 0155•RGDLacoustics.com
Dublin Day Care Ordinance, Dublin, CA Page 4
Environmental Noise Analysis 1 April 2013
0 Factors related to Project Generated Noise:
• Distance between outdoor play area and residences.
• Number of children using the play area.
• Duration of play area usage.
• Presence of intervening buildings or terrain (between play area and
residences).
0 Factors related to Ambient Noise Levels:
• Distance between residences and major roadways.
• Presence of intervening buildings or terrain (between residences and
roadways)
To derive the various development standards, a series of hypothetical Day Care
Center scenarios were assessed using previously measured data. The Day Care
Center play area was assumed to generate an average noise level (Leq) of 67.5
dBA at a distance of 50 feet from the center of the play area when there are 50
children using the play area. This relationship was developed over the course of
several previous site specific Day Care Center noise studies and is based on
acoustical measurements of similar facilities. Distance effects are based on the
standard attenuation rate of 6 dBA per doubling of distance between the source
and receiver.
To account for the number of children, a rate of 3 dBA per doubling of children was
used. The duration of play was accounted for through the use of the CNEL, which
is the average noise level over an entire day. For example, there will be a 3 dBA
increase in CNEL for each doubling in duration of play area use and a 3 dBA
decrease for each halving in the duration of play area.
The ambient noise levels are accounted for by considering the location of the
existing residences near the day care play area relative to major roadways. Since
there can be a relatively large variation in ambient noise levels for seemingly
similar locations, generalizations are made based on RGDL's experience with
ambient noise level measurements with an effort to maintain a conservative
analysis. This means that ambient noise levels are assumed to be on the lower
end of the anticipated range since noise impacts are more likely to occur when
ambient noise levels are lower.
The recommended development standards are presented in Table 1. This table
presents the number of children and duration of play area usage depending on the
distance to the nearest residential property line and the location relative to ambient
noise sources (roadways). Tables 2 and 3 provide guidance for the numeric input
needed to use the Table 1.
The recommended development standards do not include a factor for the sound
attenuation provided by a solid fence or wall that might exist at the residential
property line. Though a solid fence or wall might provide noise reduction for
ROSEN
GOLDBERG
DER&
LEWITZ,INC. 1100 Larkspur Landing Circle#375 o Larkspur CA 94939 .Tel 415 464 0150+Fax 415 464 0155•RGDLacoustics.com
Dublin Day Care Ordinance, Dublin, CA Page 5
Environmental Noise Analysis 1 April 2013
neighboring residents at the first floor elevation, it might not have an effect
because second floor rooms could overlook the wall. Also, the wall could block
both the play area noise and the ambient noise. If the ambient noise is reduced by
the same amount as the play area noise, then the increase in noise is the same
whether or not there is a wall. To help minimize the potential for complaints, the
City should consider requiring a solid fence or wall separating the play area from
the residential lot in addition to the recommended standards in Table 1.
Table 1: Maximum Number of"Children x Hours per Day"' for the Outdoor
Play Area of a Day Care Center
Ambient
Noise Level
Quieter Moderate Noisier
Distance
from Play Area
to Residence
15— 19 feet 4 12 18
20-24 feet 7 20 33
25—29 feet 10 35 50
30—39 feet 16 50 75
40— 49 feet 28 90 130
50— 59 feet 45 140 200
60— 74 feet 60 200 300
75— 99 feet 100 300 450
100 feet or greater 180 500 800
Notes:
1. "Children-Hours per Day" is calculated by multiplying the number of children in the play
area by the duration of the play periodand is summed over the course of the day. For
example if 30 children use the play area for four 45-minute periods per day then the total
"children-hours per day" is equal to 90 (the calculation is 30 x 4 x%). See example in
Table 2.
2. Ambient noise level is divided into three categories and refers to the ambient noise level
at the existing residential property line nearest to the proposed outdoor play area. Most
locations are"Moderate." A location is"Quieter" if it is at least 500 feet from the edge of
a freeway, at least 200 feet from the edge of an arterial or Class I collector, and the line
of sight to all roadways (except residential and residential collector streets) is blocked by
buildings or terrain (vegetation is not included). A location is"Noisier' if it is within 150
feet of the edge of a freeway(with or without a soundwall), or within 75 feet of an arterial
ROSEN
GOLDBERG
DER&
LEWITZ,INC. 1100 Larkspur Landing Circle#375+Larkspur CA 94939•Tel 415 464 0150+Fax 415 464 0155•RGDLacoustics.com
Dublin Day Care Ordinance, Dublin, CA Page 6
Environmental Noise Analysis 1 April 2013
or major collector street and the property line location has at least partial line-of-sight to
the roadway. All other locations are considered "Moderate".
3. The distance(rounded to the nearest foot)from the play area to the residence is the
shortest, straight-line distance between the nearest residential property line and the
center of the play area. If a portion of the play is blocked from the property line by the
building then disregard the blocked portion in the distance measurement and pro-rate
the"Children-Hours per Day" by the percentage area that is not blocked. If all of the
play area is blocked from the property line by the building then multiply the actual
distance by a factor of 2 to obtain distance from play area to residence.
Table 2: Example Calculation for Children x Hours per Day
Play Period First Second Third
Duration (Hours) 1 0,7 0.5 TOTAL
Number of Children 70 40),/X'
0 X 30
Children x Hours co 30 15:::) 115
Example: +
There are three play periods per day.
0 The first is 60 minutes long and there are 70 children outdoors
0 The second is 45 minutes long and there are 40 children outdoors
0 The third is 30 minutes long and there are 30 children outdoors.
The table is used by entering the duration and number of children for each play
period column. The duration is converted from minutes to hours before entering. The
bottom row is calculated for each play period column by multiplying the duration by
the number of children. Then the Total is calculated by adding all the Children x
Hours in the bottom row together.
Table 3: Blank Table for Calculation of Children x Hours per Day
Play Period First Second Third Fourth Fifth
Duration>(Hours) TOTAL
Number of Children
Children Hours
ROSEN
GOLDBERG
DER&
LEWITZ,INC. 1100 Larkspur Landing Circle#375®Larkspur CA 94939 +Tel 415 464 0150+Fax 415 464 0155+RGDLacoustics.com