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DRAFT MEMORANDUM
To: Lee Lisceki, Jones & Stokes
From: Darren Nielson, ATS Consulting, LLC
Date: March 7, 2005
Subject: Construction Noise Analysis – La Loma Bridge
725 South Figueroa Street, Suite 1580 Los Angeles, CA 90017 t 213 488 7770 f 213 488 0270 www.ATSConsulting.com
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page i
Table of Contents
Introduction & Summary .............................................................................................................................. 1
Project Description........................................................................................................................................ 1
Alternatives ............................................................................................................................................4
Fundamentals of Sound................................................................................................................................. 5
Criteria .......................................................................................................................................................... 6
City of Pasadena.....................................................................................................................................6
Caltrans...................................................................................................................................................7
Existing Noise Environment ......................................................................................................................... 8
Construction Noise Levels ............................................................................................................................ 9
Mitigation.................................................................................................................................................... 14
List of Figures
Figure 1. Map of Project Region.................................................................................................................. 2
Figure 2. Project Vicinity Map .................................................................................................................... 3
Figure 3. Typical Noise Levels .................................................................................................................... 7
Figure 4. Graph of the Hourly Leqs at Site M3 ........................................................................................... 9
Figure 5. Aerial Photograph of the Noise Measurement Sites................................................................... 10
List of Tables
Table 1. Summary of Noise Measurements ................................................................................................. 8
Table 2. Summary of Equipment Noise Levels ......................................................................................... 11
Table 3. Summary of Construction Phases ................................................................................................ 12
Table 4. Predictions of Construction Noise Levels.................................................................................... 13
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 1
INTRODUCTION & SUMMARY
This memorandum summarizes the construction noise analysis for the proposed La Loma Bridge
Rehabilitation Replacement Project. The analysis predicts construction noise levels for the three
alternatives being considered by the City of Pasadena and the California Department of Transportation.
The findings of the analysis are:
Construction will result in a temporary increase in local noise levels in the neighborhoods near the
bridge.
Noise generated by most construction equipment/activities will be below the City’s standard of 85
dBA at 100 feet.
Noise from the hoe rams and sandblasting are likely to exceed the City’s standard of 85 dBA.
The daily Leqs for most phases of construction are estimated to be between 70 and 74 dBA at the
nearest residences.
The daily Leqs for phase 3 and phase 9 are estimated to be 83 and 78 dBA, respectively. These
phases are predicted to be substantially louder than the other phases due to the use of hoe rams (phase
3) and sandblasting equipment (phase 9).
The construction Contractor will be required to comply with Caltran’s Standard Specifications and
Standard Provisions, including limiting construction to between the hours of 7:00 a.m. and 9:00 p.m.
Monday through Saturday.
Additional measures will be necessary to reduce noise from the hoe rams and sandblasting.
PROJECT DESCRIPTION
The Public Works Department of the City of Pasadena, in cooperation with the California Department of
Transportation (Caltrans) and Federal Highway Administration (FHWA), is proposing to improve the
existing La Loma Road Bridge to meet current seismic codes and standards. The 378-foot long
reinforced concrete bridge was built in 1914 over the Arroyo Seco, a major tributary to the Los Angeles
River. The existing bridge was listed on the National Register of Historic Places (National Register) on
July 14, 2004. Figure 1 is a map of the project region and Figure 2 is a map of the project vicinity.
Deteriorated bridge conditions include rusted roadway expansion joints due to improper drainage;
exposed reinforcing bars due to inadequate concrete cover; cracks and spalls throughout the bridge;
substandard seismic design; and non-standard roadway geometrics. The City of Pasadena, in cooperation
with Caltrans and FHWA, is seeking to rectify these conditions through the use of local funds,
Transportation Equity Act for the 21st Century (TEA 21) federal funding, and funding to be obtained
from the Federal Highway Bridge Repair and Rehabilitation (HBRR) Program.
Three build alternatives are under consideration: (1) retrofit and rehabilitation, (2) replacement with a
new box-girder design and (3) replacement with a new open-concrete arch design. The no-build
alternative will also be addressed in the environmental document. Retrofit and rehabilitation would make
the bridge structurally sufficient such as to withstand a design seismic event as well as improve the
bridge’s overall function. Rehabilitation would address improvements to preserve and continue to use the
existing La Loma Road Bridge, although major components might be reconstructed. The second and
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 2
Figure 1. Map of Project Region
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 3
Figure 2. Map of Project Vicinity
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 4
third build alternatives would replace the existing bridge with an entirely new cast-in-place concrete
girder bridge or an open concrete arch bridge.
The length of the proposed bridge would vary depending on the structure type, but would be similar to the
existing bridge. The width of the bridge under each of the alternatives would be 44 feet, including two 5-
foot standard sidewalks, which is 4 feet wider than the existing bridge. The rehabilitated or new bridge
would continue to provide two traffic lanes, one in each direction.
The existing spandrel arch bridge has two main spans and three approach spans supported on three piers
and six rows of columns in the Arroyo Seco. All of the new bridge alternatives are proposed to have two
piers in the Arroyo Seco. There are no vertical clearance limits to be maintained over the Arroyo Seco
Flood Control Channel. The bent conditions for the proposed new bridge have been chosen to keep an
open channel running under the bridge.
There are two pedestrian/equestrian trails that currently run underneath the La Loma Bridge, which run
parallel to the channel on each bank. During most of construction period, at least one trail would remain
open to through traffic, and pedestrians and equestrians would be protected by a temporary overhead
structure. Short-term closures may be necessary at certain times during the construction process.
A temporary platform would also be constructed, from bank to bank, over the Arroyo Seco channel to
allow construction workers (but not construction equipment) to access the piers of the Bridge and to catch
any construction debris before it enters the channel and, consequently, affects waters of the U.S.
The bridge would be closed during construction, which is expected to last approximately 18 months.
The project would be subject to both California Environmental Quality Act (CEQA) and federal National
Environmental Policy Act (NEPA) regulations. The City of Pasadena would be the lead agency under
CEQA and FHWA would be the lead agency under NEPA. Caltrans would be a responsible agency.
Alternatives
No Build
The no-build alternative would result in no structural or physical changes to the bridge, or the surrounding
environment. Under this alternative, the bridge would continue to deteriorate.
Existing Bridge Retrofit and Rehabilitation Alternative
The existing structure has inadequate strength and displacement capacities at the piers, arch ribs, arch
struts, spandrel columns, footings, transverse floor beams, and expansion joints. Retrofit describes the
strengthening, reinforcement, and other activities necessary to enable the bridge to withstand earthquake
forces generally in accordance with current seismic design standards. Rehabilitation includes aesthetic
elements and repairs that would contribute to the bridge’s overall appearance and function but are not
required to ensure its seismic performance. Both retrofit and rehabilitation address improvements that
would be implemented to preserve and continue to use substantial portions of the existing La Loma Road
Bridge. In addition to the proposed retrofit strategies for the various structural components of the existing
bridge, all loose surface concrete would be located and removed to sound concrete, exposed surfaces and
reinforcing bar would be thoroughly cleaned and patched with concrete of like color, and architectural
features and surface textures would be replicated to the greatest extent possible using form liners. These
activities should effectively rehabilitate the existing bridge.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 5
The existing steel bridge railing would be removed, during the removal of the existing bridge deck, and
replaced with “urn” balusters and concrete caps design similar to the original railing and would be
constructed to meet current standards of the Caltrans Type 26 barrier. The existing light poles would also
be removed and replaced with architectural concrete posts with single globe fixtures, which would
reproduce the lighting’s original appearance.
Box Girder Design Bridge Replacement Alternative
Replacement refers to options that would replace the existing bridge with an entirely new bridge structure.
A cast-in-place post-tensioned concrete box girder alternative represents what is considered to be the most
cost-effective replacement. Structures of this type are commonly built throughout California.
A box girder superstructure offers a clean and simple appearance with virtually no maintenance.
Architectural features can be included as rustication on the pier column faces and the exterior of the
barrier railings, and in the shape of the exterior box girder web. A more ornamental railing treatment
could be developed for enhanced aesthetics.
Open-Concrete Arch Design Bridge Replacement Alternative
Given the architectural heritage of bridges in the City of Pasadena, an arch bridge is both a structurally
viable and aesthetically pleasing alternative for the La Loma bridge replacement. The alternative
presented here is in harmony with the tradition of arch bridges, but recognizes the economic advantages
of modern construction materials and design techniques.
The proposed arch alternative would consist of three spans (of 110 feet, 155 feet, and 110 feet) without
pier or spandrel columns. In contrast to the original structure, this alternative would feature a wide, single
arch rib, supporting the superstructure at its vertex. This alternative would be continuous from abutment
to abutment. By using a transversely and longitudinally post-tensioned concrete box girder, the
superstructure would be light in weight and oblique in appearance. During construction, the arch would
be erected on falsework. After the arch ribs are in place, the superstructure could be supported by the
falsework placed on top of the arch rib. The “open” arch configuration and single arch rib gives the
structure a graceful, airy, appearance while helping to control construction costs.
FUNDAMENTALS OF SOUND
Sound is mechanical energy transmitted by pressure waves in a compressible medium such as air. Noise
is generally defined as unwanted or excessive sound. Sound can vary in intensity by over one million
times within the range of human hearing. Therefore, a logarithmic scale, known as the decibel scale (dB),
is used to quantify sound intensity.
Sound is characterized by both its amplitude and frequency (or pitch). The human ear does not hear all
frequencies equally. In particular, the ear deemphasizes low and very high frequencies. To better
approximate the sensitivity of human hearing, the A-weighted decibel scale (dBA) has been developed.
On this scale, the human range of hearing extends from approximately 3 dBA to around 140 dBA.
Figure 3 includes examples of A-weighted noise levels from common indoor and outdoor activities.
Using the decibel scale, sound levels from two or more sources cannot be directly added together to
determine the overall sound level. Rather, the combination of two sounds at the same level yields an
increase of 3 dBA. The smallest recognizable change in sound levels is approximately 1 dBA. A 3-dBA
increase is generally considered perceptible, whereas a 5-dBA increase is readily perceptible. A 10-dBA
increase is judged by most people as an approximate doubling of the sound loudness.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 6
Two of the primary factors that reduce levels of environmental sounds are increasing the distance
between the sound source to the receiver and having intervening obstacles such as walls, buildings or
terrain features between the sound source and the receiver. Factors that act to increase the loudness of
environmental sounds include moving the sound source closer to the receiver, sound enhancements
caused by reflections, and focusing caused by various meteorological conditions.
There a number of metrics used to characterize community noise exposure, which fluctuates constantly
over time. One such metric, the equivalent sound level (Leq), represents a constant sound that, over the
specified period, has the same sound energy as the time-varying sound. Noise exposure over a longer
period of time is often evaluated based on the Day-Night Sound Level (Ldn). This is a measure of 24-
hour noise levels that incorporates a 10 dBA penalty for sounds occurring between 10 pm and 7 am. The
penalty is intended to reflect the increased human sensitivity to noises occurring during nighttime hours,
particularly at times when people are sleeping and there are lower ambient noise conditions. Typical Ldn
noise levels for light and medium density residential areas range from 55 to 65 dBA.
CRITERIA
City of Pasadena
Section 9.36 of the City of Pasadena Municipal Code contains noise level regulations regarding
construction activities and equipment. These regulations are summarized below:
9.36.110(A): No person shall operate any pile driver, power shovel, pneumatic hammer, derrick power
hoist, fork lift, cement mixer or any other similar construction equipment within a
residential district or within 500 feet there from between the hours of 9:00 p.m. of one
day and 7:00 a.m. of the next day or between the hours of 9:00 p.m. of Saturday and 7:00
a.m. of Monday.
9.36.110(B): No person shall perform any construction or repair work on buildings, structures or
projects within a residential district or within a radius of 500 feet there from between the
hours of 9:00 p.m. of one day and 7:00 a.m. of the next day, in such a manner that a
reasonable person of normal sensitiveness residing in the area is caused discomfort or
annoyance, or between the hours of 9:00 p.m. of Saturday and 7:00 a.m. of Monday.
9.36.120 It is unlawful for any person to operate any powered construction equipment if the
operation of such equipment emits noise at a level in excess of 85 dBA when measured
within a radius of 100 feet from such equipment. (Ord. 5118 § 3.10, 1973)
In addition, the City of Pasadena Revised Noise Element of the General Plan (2002) includes two policies
related to construction noise
Policy 7c The City will encourage construction and landscaping activities that employ techniques
to minimize noise.
Policy 7d The City will enforce noise level restrictions contained in the City of Pasadena Noise
Regulations (Chapter 9.36 of the Municipal Code), except during federal, State, or local
emergencies (such as power generators required for energy emergencies).
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 7
Noise Level
Outdoor Activities (dBA) Indoor Activities
110 Rock Concert
Jet Fly-over, 1,000 ft
100
Gas Lawn Mower, 3 ft
90
Diesel Truck, 50 ft & 50 mph Food Blender, 3 ft
80 Garbage Disposal, 3 ft
Gas Lawn Mower, 100 ft 70
Normal Speech, 3 ft
Heavy Traffic, 300 ft 60
Large Business Office
Quiet Urban Daytime 50 Dishwasher in Next Room
Quiet Urban Nighttime 40 Theater
Quiet Suburban Nighttime
30 Library
Quiet Rural Nighttime Bedroom at Night
20
Broadcast/Recording Studio
10
Lowest Threshold of Hearing 0 Lowest Threshold of Hearing
Source: Caltrans, Technical Noise Supplement, 1998
Figure 3. Typical Noise Levels
Caltrans
Caltrans does not have any specific limits or criteria for construction noise levels. However, there is
some guidance provided in the Traffic Noise Analysis Protocol (1998). Section 1.4.5 of the protocol
states that construction noise is only substantial in exceptional cases, such as pile driving and crack-and-
seat pavement rehabilitation operations. The Standard Specifications and Standard Provisions used in
construction contracts provide limits on construction noise levels and are used as appropriate. Normally,
construction noise levels should not exceed 86 dBA (Lmax) at a distance of 15 meters (50 feet) from the
construction activity.
If construction noise on any highway project is anticipated to be a substantial problem, the following
items should be examined during the project process:
a) Land-uses or activities that may be affected by noise from construction of a project.
b) Measures necessary to minimize or eliminate adverse construction noise impacts on the community
that could be incorporated into the plans or specifications.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 8
EXISTING NOISE ENVIRONMENT
The La Loma Bridge is located in a residential area. Single-family houses are located on both sides of the
bridge along La Loma Road, Arroyo Boulevard, and Rockwood Avenue. The nearest residences are
within approximately 300 to 400 feet of the center of the bridge. The Arroyo Seco, which is located
below the bridge, is used for recreational purposes and is not considered noise sensitive for the purpose of
this analysis.
Measurements of environmental noise levels were taken at three sites in the residential areas adjacent to
the La Loma Bridge. These sites are summarized below and are shown in Figure 5:
M1: A short-term noise measurement was taken on Rockwood Avenue south of the La Loma Bridge.
The microphone was placed in front of a single-family residence on the west side of the road facing
the Arroyo Seco.
M2: This site is located on the east side of the La Loma Bridge on Arroyo Boulevard. A short-term
measurement was taken on the sidewalk in front of the residence on the east side of the road,
approximately 150 feet south of La Loma Road.
M3: A 24-hour measurement was taken in the yard of a single-family residence on the north side of
La Loma Road, west of the bridge. The microphone was in the corner of the yard closest to the road.
Local traffic was the dominant noise source at all three of the noise measurement sites. Secondary noise
sources include aircraft over-flights, landscaping equipment, and typical residential activities. Distant
traffic noise from local freeways (I-120 and SR 134) is noticeable during the day and is likely more
pronounced at night. Table 1 is a summary of the measurements results and Figure 4 is a plot of the
hourly Leqs over the 24-hour period at site M3. As can be seen in both the figure and table, the daytime
sound levels are generally between 55 and 57 dBA Leq.
Table 1. Summary of Noise Measurements
Site
Parameter
M1 M2 M3
Date 4/14/04 4/14/04 2/16/05
Start Time 9:15 AM 9:40 AM 12:00 PM
Duration 15 minutes 15 minutes 24 hours
Leq 50 dBA 58 dBA 56 dBA
Ldn -- -- 58 dBA
Notes:
Leq is over a 15-minute period for sites M1 and M2 and over a 15-hour
period (7 AM to 10 PM) for site M3.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 9
Figure 4. Graph of the Hourly Leqs at Site M3
CONSTRUCTION NOISE LEVELS
Construction of the proposed project will require the use of heavy equipment that could generate high
noise levels in the immediate project area. Construction noise is a function of the type and number of
pieces of equipment, their usage rates, and their location on the work site.
Noise from construction activities is estimated to decrease by 6 dBA per doubling of distance. For
example, a noise level at 80 dBA at 50 feet would decrease to 74 dBA at 100 feet. As much of the
construction will occur either at the bottom of the Arroyo Seco or along its slopes, the adjacent residences
will be partially shielded by the existing topography. In order to generate conservative (high) estimates of
construction noise, shielding has not been factored into the analysis. Also, because construction activities
would occur at many different locations on and around the bridge, we have used the center of the bridge
as a reference point.
Noise from equipment operating in the Arroyo Seco could be reflected off the canyon walls. Reflected
noise has the potential to make activities occurring in one location sound like they are coming from
somewhere else. Reflections can also decrease the acoustic benefits of shielding where the direct path
between the construction activities and the receiver is blocked by the terrain. As previously mentioned,
this analysis does not account for any shielding. Due to the size of the canyon and the lack of large
reflective surfaces (i.e., the canyon walls are covered by soil and foliage), reflections are not anticipated
to be a significant issue. Construction activities in the Arroyo will not result in any “amplification” of the
noise levels.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 10
Figure 5. Aerial Photograph of the Noise Measurement Sites
This analysis looks at (1) the noise level from each individual piece of equipment/activity according to the
City of Pasadena Municipal Code, (2) the average daily noise level from each phase of construction, and
(3) the average daily noise level over the entire construction period. The first step in the analysis is to
determine the reference sound level for each piece of equipment. This was done using standard industry
guidelines and professional experience. Table 2 lists the equipment that is expected to be used during
construction and the reference sound level at 50 feet. The sound levels at 100 feet (City Standard) and
325 feet (the approximate distance to the nearest residence) were then predicted using the equation:
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 11
⎛ 50 feet ⎞
Sound Level = Reference Sound Level + 20 * log ⎜
⎜ Distance ⎟
⎟
⎝ new ⎠
As can be seen in Table 2, the highest noise levels are associated with the hoe rams, stitch drilling, and
water-jet cutting. The reference sound levels at 50 feet are between 90 and 95 dBA for these types of
equipment. The reference sound level for most other equipment is between 80 and 85 dBA at 50 feet. It
is important to note that the specific equipment and processes used during construction will be determined
by the contractor. This analysis is based on reasonable estimates of the usage rates, intensity of use, etc.
For example, noise from sandblasting can vary by 20 to 30 dBA depending on the air pressure of the
equipment (the blast stream used to propel the abrasive) and the abrasive mix (how much mixture is fed
through the nozzle). Our estimate is based on normal use of typical equipment for this type and size of
job.
Table 2. Summary of Equipment Noise Levels
Sound Level, dBA
Equipment/Activity Nearest
50 ft 100 ft
Residence
Concrete-pumping Station 82 76 60
Crane 83 77 61
Diamond-blade Cutting 76 70 54
Drill Rig 85 79 63
Excavator 85 79 63
Hoe Rams 95 89 73
Mechanical Crushes 85 79 63
Post-tensional Equipment 70 64 48
Sand-blasting Equipment 90 84 68
Spring-action Hammers 85 79 63
Stitch Drilling 90 84 68
Trucks 88 82 66
Water-jet Cutting 90 84 68
Welding equipment 73 67 51
Notes: Nearest residence is approximately 325 feet from the center of the bridge.
Sources: U.S. Environmental Protection Agency, “Noise from Construction Equipment
and Operations, Building Equipment and Home Appliances,” NTID300.1, December 31,
1971; ATS Consulting, LLC, 2005.
The next steps of the analysis look at construction noise in terms of the average noise for each
construction period and then average over the entire duration of construction activities. Construction has
been divided into ten phases. Many of these phases are common to each of the alternatives. Table 3 is a
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 12
summary of each construction phase, including a brief description, a list of the types of equipment to be
used, and the duration.
Table 3. Summary of Construction Phases
Phase Duration (days)
Description Equipment
No. Alt 1 Alt 2 Alt 3
1 Utilities Relocation Excavator, crane, trucks 20 20 20
Temporary Support of
2 Crane, trucks, welding equipment -- 18 18
Excavation
Excavator, crane, trucks, spring-action hammers,
Remove Existing
3 welding equipment, hoe rams, mechanical crushers, 24 18 18
Bridge Deck
water jet and diamond blade cutting, stitch drilling
Temporary Support of
4 Existing Columns and Crane, trucks, welding equipment 4 -- --
Ribs
Construct New
Crane, trucks, welding equipment, concrete pumping
5 Abutments/Retrofit 12 18 18
station
Existing Abutments
Construct New Piers #2 Crane, trucks, welding equipment, concrete pumping
6 -- 40 40
and #3 station, drill rig
Construct New Crane, trucks, welding equipment, concrete pumping
7 52 -- --
Concrete Deck station
Construct New CIP/PS
Crane, trucks, welding equipment, concrete pumping
8 Concrete Box Girder 0 80 100
station, post-tensional equipment
Superstructure
Construct Decorative Crane, trucks, welding equipment, spring-action
9 64 -- --
Railing and Lighting hammers, sand-blasting equipment
Seismic Retrofit of Crane, trucks, welding equipment, concrete pumping
10 86 -- --
Existing Structure station
Total Duration 262 194 214
Notes: Alt 1 = Rehab/Retrofit; Alt 2 = Replace/Box Girder; Alt 3 = Replace/Arches
Source: Jones & Stokes, 2005.
Construction is scheduled to occur during the daytime hours. Therefore, the average sound levels for
each construction phase and the entire duration are in terms of daily Leq. The sound levels were
estimated by:
1. Calculating the Average Sound Level (Leq) for Each Piece of Equipment over the Construction Day:
Using the reference sound level (Lref), the number of days each piece of equipment would be used
per phase, the total duration of each phase, and the percent of time used per work day, the daily Leq
for each piece of equipment was calculated by:
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 13
⎛ ⎜ Lref ⎟
⎛ ⎞
⎛ Days Used ⎞ ⎞
Leq = 10 * log ⎜ 10 ⎝ 10 ⎠ No. of Pieces ⎜
⎜ ⎟ ⎟
⎟ % time used per day ⎟
⎜ ⎝ Total Days ⎠
⎝ ⎠
2. Calculating the Daily Leq for Entire Phase: The average sound level over the entire phase was
calculated by taking the energy sum of the daily Leqs for each piece of equipment.
3. Calculating the Daily Leq for the Entire Construction Period. The average daily Leq for the entire
construction period was estimated for each alternative by calculating the weighted energy average of
the daily Leq for each phase. The weighting is the duration of each phase divided by the entire
construction period.
Table 4 is a summary of these three steps. The daily Leqs are shown at a distance of 325 feet, which is
the approximate setback of the nearest residence from the center of the bridge.
Table 4. Predictions of Construction Noise Levels
Phase Daily Leq at 325 feet, dBA
Description
No. Alt 1 Alt 2 Alt 3
1 Utilities Relocation 70 70 70
2 Temporary Support of Excavation -- 69 69
3 Remove Existing Bridge Deck 83 83 83
4 Temporary Support of Existing Columns and Ribs 72 -- --
Construct New Abutments/Retrofit Existing
5 72 72 72
Abutments
6 Construct New Piers #2 and #3 -- 72 72
7 Construct New Concrete Deck 71 -- --
Construct New CIP/PS Concrete Box Girder
8 -- 74 74
Superstructure
9 Construct Decorative Railing and Lighting 78 -- --
10 Seismic Retrofit of Existing Structure 71 -- --
Average for Entire Alternative 77 76 76
Notes: Alt 1 = Rehab/Retrofit; Alt 2 = Replace/Box Girder; Alt 3 = Replace/Arches
For all three alternatives, construction activities will be limited to the hours of 7 a.m. to 9 p.m. Monday
through Saturday following Section 9.36.110(A) of the City of Pasadena Municipal Code. Section
9.36.120 of the Code also limits the sound level of each piece of equipment to 85 dBA at 100 feet. As
shown in Table 2, only the hoe rams are expected to exceed this level. The hoe ram would be required for
all three alternatives as part of the demolition of the existing bridge deck (phase 3). Depending on the
type of equipment used, noise from sandblasting may also exceed 85 dBA at 100 feet. Sandblasting
would only be required for phase 9 of Retrofit/Rehab alternative.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 14
Most of the phases are predicted to generate a daily Leq between 70 and 74 dBA at the nearest residences.
This is approximately 14 to 18 dBA higher than the existing daytime Leq. The two loudest phases will be
the removal of the existing bridge deck (phase 3) and construction of decorative railings and lighting
(phase 9). Phase 3 is common to all three alternatives and will require the use of three of the four loudest
pieces of equipment/activities, hoe rams, water-jet cutting, and stitch drilling. At the nearest residence,
the average daily Leq will be approximately 83 dBA. This phase will last for approximately 18 to 24
working days, depending on the alternative. Sandblasting will be required for phase 9 under the
Retrofit/Rehab Alternative (Alt 1). This is predicted to result in an average Leq of 78 dBA at 325 feet for
a period of 64 days.
MITIGATION
As part of the construction contract, the Contractor will be required to follow the noise specifications in
Section 7 of Caltran’s Standard Specifications for Construction of Local Streets and Road (July, 2002).
The mitigation measures related to noise to be included in the construction contract are:
N1: The Contractor shall comply with all local sound control and noise level rules, regulations and
ordinances which apply to any work performed pursuant to the contract.
N2: Each internal combustion engine, used for any purpose on the job or related to the job, shall be
equipped with a muffler of a type recommended by the manufacturer. No internal combustion
engine shall be operated on the project without a muffler.
As a result, the contractor will be prohibited from working after 9 p.m. and before 7 a.m. on weekdays
and Saturdays and anytime on Sunday or national holidays. Furthermore, pursuant to Section 9.36.120 of
the City of Pasadena Municipal Code, the Contractor will be required to ensure that no equipment
exceeds 85 dBA measured at 100 feet. In order to demonstrate that this level will not be exceeded, the
following measure should also be included in the construction contract:
N3: The contractor shall be required to provide the City with documentation prior to the start of
construction demonstrating that each piece of heavy equipment that will be used on the
construction site for more than 16 hours conforms to Section 9.36.120 of the City of Pasadena
Municipal Code.
As the hoe ram and sandblasting are likely to generate noise levels in excess of the 85 dBA standard at
100 feet, additional mitigation is recommended.
N4: Wherever feasible, the construction contractor shall do the following in order to reduce noise
from hoe rams and sandblasting:
Hoe Ram
1. Use alternate methods for demolition and breaking concrete such as saw cutting.
2. Shorten the duration of phase 3 by adding extra equipment and workers or by working
extended days (but still within hours allowed by the Municipal Code).
3. Provide notice to local homeowners in advance of phase 3 construction activities (this will
not decrease sound levels but is more of a courtesy).
Sandblasting
4. Enclose sandblasting activities with acoustical curtains or temporary, portable sound barriers.
Draft Memo: Construction Noise Analysis – La Loma Bridge
March 7, 2005
Page 15
5. Adjust the pressure and abrasive mix levels to the lowest possible levels.
Since construction activities would be temporary and would generally be below the City standards, with
the implementation of measures N1-N3 and, wherever feasible, N4, noise impacts are anticipated to be
less than significant.
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