COTATI VILLAGE #2
NOISE & VIBRATION ASSESSMENT
Cotati, California
June 7, 2024
♦ ♦ ♦
Prepared for:
Heather Gurewitz, AICP
Senior Planner
M-Group
1275 4th Street #265
Santa Rosa, CA 95404
Prepared by:
Fred M. Svinth, INCE, Assoc. AIA
429 East Cotati Avenue
Cotati, CA 94931
(707) 794-0400
Job No.: 24-029
INTRODUCTION AND SUMMARY
This report presents the results of an environmental noise assessment completed for the proposed Cotati Village #2 residential development located on a + 5.6 Acre site at 7515 Alder Avenue in Cotati, California (see Figure 1). The project proposes to construct two, four-story buildings totaling 126 residential units and a separate 2,250 ft2 commercial building. The purpose for this noise assessment is to evaluate the compatibility of the development with respect to the environmental noise levels at the project site and evaluate noise impacts upon sensitive receptors in the area. The Setting Section of this report presents the fundamentals of environmental noise and vibration, describes regulatory criteria that are applicable in the project’s assessment, and summarizes the results of a survey of the existing noise environment at the project site and vicinity.
Figure 1: Project Site, Vicinity and Measurement Locations
SETTING
FUNDAMENTALS OF ENVIRONMENTAL NOISE
Noise may be defined as unwanted sound. Noise is usually objectionable because it is disturbing or annoying. The objectionable nature of sound could be caused by its pitch or its loudness.
Pitch is the height or depth of a tone or sound, depending on the relative rapidity (frequency) of the vibrations by which it is produced. Higher pitched signals sound louder to humans than sounds with a lower pitch. Loudness is the intensity of sound waves combined with the reception characteristics of the ear. Intensity may be compared with the height of an ocean wave in that it is a measure of the amplitude of the sound wave.
In addition to the concepts of pitch and loudness, there are several noise measurement scales, which are used to describe noise in a particular location. A decibel (dB) is a unit of measurement, which indicates the relative amplitude of a sound. The zero on the decibel scale is ST-1
ST-3
(LT-1 Vill #1)
ST-2
based on the lowest sound level that the healthy, unimpaired human ear can detect. Sound levels in decibels are calculated on a logarithmic basis. An increase of 10 decibels represents a ten-fold increase in acoustic energy, while 20 decibels is 100 times more intense, 30 decibels is 1,000 times more intense, etc. There is a relationship between the subjective noisiness or loudness of a sound and its intensity. Each 10-decibel increase in sound level is perceived as approximately a doubling of loudness over a fairly wide range of intensities. Technical terms are defined in Table 1.
There are several methods of characterizing sound. The most common in California is the Aweighted sound level (dBA). This scale gives greater weight to the frequencies of sound to which the human ear is most sensitive. Representative outdoor and indoor noise levels in units of dBA are shown in Table 2. Because sound levels can vary markedly over a short period of time, a method for describing either the average character of the sound or the statistical behavior of the variations must be utilized. Most commonly, environmental sounds are described 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. The most common averaging period is hourly, but Leq can describe any series of noise events of arbitrary duration.
The scientific instrument used to measure noise is the sound level meter. Sound level meters can accurately measure environmental noise levels to within about plus or minus 1 dBA. Various computer models are used to predict environmental noise levels from sources, such as roadways and airports. The accuracy of the predicted models depends upon the distance the receptor is from the noise source. Close to the noise source, the models are accurate to within about plus or minus 1 to 2 dBA.
Since the sensitivity to noise increases during the evening and at night -- because excessive noise interferes with the ability to sleep -- 24-hour descriptors have been developed that incorporate artificial noise penalties added to quiet-time noise events. The Community Noise Equivalent Level (CNEL) is a measure of the cumulative noise exposure in a community, with a 5 dB penalty added to evening (7:00 pm - 10:00 pm) and a 10 dB addition to nocturnal (10:00 pm - 7:00 am) noise levels. The Day/Night Average Sound Level (DNL or Ldn) is essentially the same as CNEL, with the exception that the evening time period is dropped and all occurrences during this three-hour period are grouped into the daytime period.
EFFECTS OF NOISE
Sleep and Speech Interference. The thresholds for speech interference indoors are about 45 dBA if the noise is steady and above 55 dBA if the noise is fluctuating. Outdoors the thresholds are about 15 dBA higher. Steady noises of sufficient intensity (above 35 dBA) and fluctuating noise levels above about 45 dBA have been shown to affect sleep. Interior residential standards for multi-family dwellings are set by the State of California at 45 dBA Ldn. Typically, the highest steady traffic noise level during the daytime is about equal to the Ldn and nighttime levels are 10 dBA lower. The standard is designed for sleep and speech protection and most jurisdictions apply the same criterion for all residential uses. Typical structural attenuation is 12-17 dBA with open windows. With closed windows in good condition, the noise attenuation factor is around 20 dBA for an older structure and 25 dBA for a newer dwelling. Sleep and speech interference is therefore possible when exterior noise levels are about 57-62 dBA Ldn with open windows and 65-70 dBA Ldn if the windows are closed. Levels of 55-60 dBA are common along collector streets and secondary arterials, while 65-70 dBA is a typical value for a primary/major arterial.
Levels of 75-80 dBA are normal noise levels at the first row of development outside a freeway right-of-way. To achieve an acceptable interior noise environment, bedrooms facing secondary
roadways need to be able to have their windows closed, those facing major roadways and freeways typically need special glass windows.
Table 1: Definitions of Acoustical Terms Used in this Report Term Definitions
Decibel, dB A unit describing the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the pressure of the sound measured to the reference pressure.
The reference pressure for air is 20.
Sound Pressure Level Sound pressure is the sound force per unit area, usually expressed in micro-Pascals (or 20 micro-Newtons per square meter), where 1 Pascal is the pressure resulting from a force of 1 Newton exerted over an area of 1 square meter. The sound pressure level is expressed in decibels as 20 times the logarithm to the base 10 of the ratio between the pressures exerted by the sound to a reference sound pressure (e.g., 20 micro-Pascals). Sound pressure level is the quantity that is directly measured by a sound level meter.
Frequency, Hz The number of complete pressure fluctuations per second above and below atmospheric pressure. Normal human hearing is between 20 Hz and 20,000 Hz.
Infrasonic sound are below 20 Hz and Ultrasonic sounds are above 20,000 Hz.
A-Weighted Sound Level,
dBA
The sound pressure level in decibels as measured on a sound level meter using the A-weighting filter network. The A-weighting filter de-emphasizes the very low and very high frequency components of the sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise.
Equivalent Noise Level,
Leq
The average A-weighted noise level during the measurement period. The hourly Leq used for this report is denoted as dBA Leq[h].
Day-Night Level, Ldn The equivalent noise level for a continuous 24-hour period with a 10-decibel penalty imposed during nighttime and morning hours (10:00 pm to 7:00 am).
Community Noise
Exposure Level, CNEL
CNEL is the equivalent noise level for a continuous 24-hour period with a 5-decibel penalty imposed in the evening (7:00 pm to 10:00 pm) and a 10-decibel penalty imposed during nighttime and morning hours (10:00 pm to 7:00am) L1, L10, L50, L90 The A-weighted noise levels that are exceeded 1%, 10%, 50%, and 90% of the time during the measurement period.
Ambient Noise Level The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location.
Intrusive That noise which intrudes over and above the existing ambient noise at a given location. The relative intrusiveness of a sound depends upon its amplitude, duration, frequency, and time of occurrence and tonal or informational content as well as the prevailing ambient noise level.
Source: Handbook of Acoustical Measurements and Noise Control, Harris, 1998.
Annoyance. Attitude surveys are used for measuring the annoyance felt in a community for noises intruding into homes or affecting outdoor activity areas. In these surveys, it was determined that the causes for annoyance include interference with speech, radio and television, house vibrations, and interference with sleep and rest. The Ldn as a measure of noise has been found to provide a valid correlation of noise level and the percentage of people annoyed. People have been asked to judge the annoyance caused by aircraft noise and ground transportation noise.
There continues to be disagreement about the relative annoyance of these different sources.
When measuring the percentage of the population highly annoyed, the threshold for ground vehicle noise is about 50 dBA Ldn. At a Ldn of about 60 dBA, approximately 12 percent of the population is highly annoyed. When the Ldn increases to 70 dBA, the percentage of the population highly annoyed increases to about 25-30 percent of the population. There is,
therefore, an increase of about 2 percent per dBA between a Ldn of 60-70 dBA. Between a Ldn of 70-80 dBA, each additional decibel increases the percentage of the population highly annoyed by about 3 percent. People appear to respond more adversely to aircraft noise. When the Ldn is 60 dBA, approximately 30-35 percent of the population is believed to be highly annoyed. Each decibel increase to 70 dBA adds about 3 percentage points to the number of people highly annoyed. Above 70 dBA, each decibel increase results in about a 4 percent increase in the percentage of the population highly annoyed.
Table 2: Typical Noise Levels in the Environment
Common Outdoor Noise Source Noise Level (dBA) Common Indoor Noise Source 110 dBA Rock band
Jet fly-over at 1,000 feet
100 dBA
Gas lawn mower at 3 feet
90 dBA
Diesel truck at 50 feet at 50 mph Food blender at 3 feet 80 dBA Garbage disposal at 3 feet
Noisy urban area, daytime
Gas lawn mower, 100 feet 70 dBA Vacuum cleaner at 10 feet Commercial area Normal speech at 3 feet
Heavy traffic at 300 feet 60 dBA
Large business office
Quiet urban daytime 50 dBA Dishwasher in next room
Quiet urban nighttime 40 dBA Theater, large conference room Quiet suburban nighttime
30 dBA Library
Quiet rural nighttime Bedroom at night, concert hall
(background)
20 dBA
Broadcast/recording studio
10 dBA
0 dBA
Source: Technical Noise Supplement (TeNS), Caltrans, November 2009.
FUNDAMENTALS OF GROUNDBORNE VIBRATION
Ground vibration consists of rapidly fluctuating motions or waves with an average motion of zero. Several different methods are typically used to quantify vibration amplitude. One is the Peak Particle Velocity (PPV), and another is the Root Mean Square (RMS) velocity. The PPV is defined as the maximum instantaneous positive or negative peak of the vibration wave. The RMS velocity is defined as the average of the squared amplitude of the signal. The PPV and RMS vibration velocity amplitudes are used to evaluate human response to vibration. In this section, a PPV descriptor with units of mm/sec or in/sec is used to evaluate construction generated vibration for building damage and human complaints. Table 3 displays the reactions of people and the effects on buildings that continuous vibration levels produce. The annoyance levels shown in Table 3 should be interpreted with care since vibration may be found to be annoying at much lower levels than those shown, depending on the level of activity or the sensitivity of the individual. To sensitive individuals, vibrations approaching the threshold of perception can be annoying.
Table 3: Reaction of People and Damage to Buildings for Continuous Vibration Levels Vibration Level,
PPV (in/sec) Human Reaction Effect on Buildings
0.006 to 0.019 Threshold of perception,
Possibility of intrusion Vibration unlikely to cause damage of any type
0.08 Vibrations readily perceptible
Recommended upper level of the vibration to
which ruins and ancient monuments should be
subjected
0.10 Level at which continuous
vibrations begin to annoy people
Virtually no risk of “architectural” damage to
normal buildings
0.20 Vibrations annoying to people in
buildings
Threshold at which there is a risk of
“architectural” damage to normal dwellings such
as plastered walls or ceilings.
0.4 to 0.6
Vibrations considered unpleasant
by people subjected to continuous
vibrations
Vibration at this level would cause
“architectural” damage and possibly minor
structural damage.
Source: Transportation Related Earthborne Vibrations (Caltrans Experiences), Technical Advisory, Vibration TAV02-01-R9601, California Department of Transportation, February 20, 2002.
Low-level vibrations frequently cause irritating secondary vibration, such as a slight rattling of windows, doors or stacked dishes. The rattling sound can give rise to exaggerated vibration complaints, even though there is very little risk of actual structural damage. In high noise environments, which are more prevalent where groundborne vibration approaches perceptible levels, this rattling phenomenon may also be produced by loud airborne environmental noise causing induced vibration in exterior doors and windows.
Construction activities can cause vibration that varies in intensity depending on several factors.
The use of pile driving and vibratory compaction equipment typically generate the highest construction related ground-borne vibration levels. Because of the impulsive nature of such activities, the use of the peak particle velocity descriptor (PPV) has been routinely used to measure and assess ground-borne vibration and almost exclusively to assess the potential of vibration to induce structural damage and the degree of annoyance for humans.
The two primary concerns with construction-induced vibration, the potential to damage a structure and the potential to interfere with the enjoyment of life are evaluated against different vibration limits. Studies have shown that the threshold of perception for average persons is in the range of 0.008 to 0.012 in/sec PPV. Human perception to vibration varies with the individual and is a function of physical setting and the type of vibration. Persons exposed to elevated
ambient vibration levels such as people in an urban environment may tolerate a higher vibration level.
Structural damage can be classified as cosmetic only, such as minor cracking of building elements, or may threaten the integrity of the building. Safe vibration limits that can be applied to assess the potential for damaging a structure vary by researcher and there is no general consensus as to what amount of vibration may pose a threat for structural damage to the building.
Construction-induced vibration that can be detrimental to the building is very rare and has only been observed in instances where the structure is at a high state of disrepair and the construction activity occurs immediately adjacent to the structure.
REGULATORY BACKGROUND
The State of California and the City of Cotati have established regulatory criteria that are applicable in this assessment. The State of California Environmental Quality Act (CEQA) Guidelines, Appendix G, are used to assess the potential significance of impacts pursuant to local General Plan policies, Zoning Code standards, or the applicable standards of other agencies. A summary of the applicable regulatory criteria is provided below.
State CEQA Guidelines. CEQA contains guidelines to evaluate the significance of effects of environmental noise attributable to a proposed project. Under CEQA, noise impacts would be considered significant if the project would result in:
(a) Generation of a substantial temporary or permanent increase in ambient noise levels in the vicinity of the project in excess of standards established in the local general plan or noise ordinance, or applicable standards of other agencies, (b) Generation of excessive groundborne vibration or groundborne noise levels, (c) For a project located within the vicinity of a private airstrip or an airport land use plan or where such a plan has not been adopted within two miles of a public airport or public use airport, if the project would expose people residing or working in the project area to excessive noise levels.
2022 California Building Code, Title 24, Part 2. The current version of the California Building Code (CBC) requires interior noise levels attributable to exterior environmental noise sources to be limited to a level not exceeding 45 dBA Ldn/CNEL in any habitable room.
City of Cotati General Plan (adopted 3.24.15) The Noise Element of the City of Cotati’s General Plan provides the following Goal, Policies, and Implementation Measures which are relevant to the proposed project:
GOAL N-1 Create a Pleasant Sound Environment by Minimizing Exposure to Harmful and Annoying Noise.
OBJECTIVE N-1A Minimize Noise Levels to Enhance the Quality of Existing and Future Land Uses
Policy N 1.1: Ensure the noise compatibility of existing and future uses when making land use planning decisions.
Policy N 1.2: Require development and infrastructure projects to be consistent with the Land Use Compatibility for Community Noise Environments standards indicated in Table N-1 to ensure acceptable noise levels at existing and future uses.
Policy N 1.3: Require development to mitigate excessive noise through best practices, including building location and orientation, building design features, placement of noise-generating equipment away from sensitive receptors, shielding of noise-generating equipment, placement of noise-tolerant features between noise sources and sensitive receptors, and use of noise-minimizing materials such as rubberized asphalt.
Policy N 1.4: Require mixed-use projects to minimize noise exposure within the indoor areas of nearby residential areas through the use of noise attenuating building materials, engineering techniques, and site design practices. Site Design practices may include locating mechanical equipment, loading bays, parking lots, driveways, and trash enclosures away from residential uses and providing noise attenuating screening features onsite.
TABLE N-1: LAND USE COMPATIBILITY FOR COMMUNITY NOISE ENVIRONMENT
LAND USE CATEGORY
EXTERIOR NOISE EXPOSURE, LDN
55 60 65 70 75 80
Single Family Residential
Multi-Family Residential, Hotels, and Motels
Outdoor Sports and Recreation, Neighborhood
Parks and Playgrounds
Schools, Libraries, Museums, Hospitals, Personal
Care, Meeting Halls, Churches
Office Buildings, Business
Commercial, and Professional
Auditoriums, Concert Halls, Amphitheaters
Industrial, Manufacturing, Utilities and Agriculture
NORMALLY ACCEPTABLE Specified land use is satisfactory, based upon the assumption that any buildings involved are of normal conventional construction, without any special insulation requirements.
CONDITIONALLY ACCEPTABLE: Specified land use may be permitted only after detailed analysis of the noise reduction requirements and needed noise insulation features included in the design.
UNACCEPTABLE: New construction or development should generally not be undertaken because mitigation is usually not feasible to comply with noise element policies.
Policy N 1.5: Control non‐transportation related noise from site specific noise sources.
Policy N 1.6: Support noise-compatible land uses along existing and future roadways, highways, and freeways.
Policy N 1.7: The following criteria shall be used to determine the significance, for projects required by the California Environmental Quality Act to analyze noise impacts, of noise impacts for development, transportation, and other projects that increase noise:
Stationary and Non‐Transportation Noise Sources
• A significant impact will occur if the project results in an exceedance of the noise level standards contained in this Noise Element, or the project will result in an increase in ambient noise levels by more than 3 dB.
Transportation Noise Sources
• Where existing traffic noise levels are less than 60 dB Ldn at the outdoor activity areas of noise‐sensitive uses, a +5 dB Ldn increase in roadway noise levels will be considered significant; and
• Where existing traffic noise levels range between 60 and 65 dB Ldn at the outdoor activity areas of noise-sensitive uses, a +3 dB Ldn increase in roadway noise levels will be considered significant; and
• Where existing traffic noise levels are greater than 65 dB Ldn at the outdoor activity areas of noise-sensitive uses, a +1.5 dB Ldn increase in roadway noise levels will be considered significant.
Policy N 1.8: Ensure that new development does not result in indoor noise levels for sleeping areas in excess of 45 dBA Ldn.
Policy N 1.11: Require acoustical studies and mitigation measures, where necessary, for new developments and transportation improvements that affect noise sensitive uses such as schools, hospitals, libraries, group care facilities, convalescent homes, and residential areas.
Policy N 1.15: Require new development to minimize vibration impacts to adjacent uses during demolition and construction. For sensitive historic structures, a vibration limit of 0.08 in/sec PPV (peak particle velocity) will be used to minimize the potential for cosmetic damage to the building. A vibration limit of 0.30 in/sec PPV will be used to minimize the potential for cosmetic damage at buildings of normal conventional construction.
Action N1a: Update the Land Use Code to ensure that the noise standards are consistent with this Noise Element, including Tables N-‐1 and N2, and to require new residential, mixed-‐use with a residential component, and other noise-‐sensitive development to be designed to minimize noise exposure to noise sensitive users through incorporation of site planning and architectural techniques such as:
• Locating dwellings as far from noise generators aspossible. • Locating noise sensitive interior spaces, such as bedrooms, away from noise generators. • Orienting buildings to shield noise sensitive outdoor spaces from noise generators. • Use of sound walls should be avoided or minimized, through alternative measures such as berms, setbacks, or other measures, to the maximum extent feasible andappropriate.
Action N1b: Review land use and development proposals, including use permits, for compliance with the noise requirements established in this element, including the standards established in Tables N-‐1 and N-‐2. Where necessary, mitigation measures to achieve the noise standards identified in Tables N-1 and N-2 and, where applicable to minimize exposure of sensitive uses to existing or potential vibration levels to the maximum feasible extent.
Action N1c: Require an acoustical study for all new discretionary projects, including development and transportation, with potential noise impacts. The study shall include mitigation measures necessary to ensure compliance with this Noise Element and relevant noise standards in the Land Use Code.
Action N1h: During the environmental review process, determine if proposed construction will constitute a significant impact on nearby residents and require mitigation measures in addition to the standard “best practice” controls. Suggested “best practices” for control of construction noise:
• Construction period shall be less than twelve months. • Noise‐generating construction activities, including truck traffic coming to and from the construction site for any purpose, shall be limited to between the hours of 7:00 am and 7:00 pm on weekdays and 9:00 am and 5:00 pm on Saturdays (if allowed through specific project conditions of approval). No construction shall occur on Sundays or holidays. • All equipment driven by internal combustion engines shall be equipped with mufflers, which are in good condition and appropriate for the equipment.
• The construction contractor shall utilize “quiet” models of air compressors and other stationary noise sources where technology exists.
• At all times during project grading and construction, stationary noise-generating equipment shall be located as far as practicable from sensitive receptors and placed so that emitted noise is directed away from residences.
• Unnecessary idling of internal combustion engines shall be prohibited. • Construction staging areas shall be established at locations that will create the greatest distance between the construction related noise sources and noise-‐sensitive receptors nearest the project site during all project construction.
• The required construction-related noise mitigation plan shall also specify that haul truck deliveries are subject to the same hours specified for construction equipment. • Neighbors located adjacent to the construction site shall be notified of the construction schedule in writing.
• The construction contractor shall designate a “noise disturbance coordinator” who will be responsible for responding to any local complaints about construction noise. The disturbance coordinator would determine the cause of the noise complaint (e.g., starting too early, bad muffler, etc.) and institute reasonable measures as warranted to correct the problem. A telephone number for the disturbance coordinator shall be conspicuously posted at the construction site.
EXISTING NOISE ENVIRONMENT
The proposed project is located at the northwest corner of the Gravenstein Highway and Alder Avenue intersection in Cotati and is bordered by an existing retail center to the south (between it and the Gravenstein Highway), the future Cotati Village #1 mixed use development to the east across Alder Lane, the Cotati large animal hospital to the west and a vehicle storage lot/vacant land to the north. The existing noise environment on the project site results primarily from vehicular traffic on Gravenstein Highway, with distant noise from Hwy 101 contributing to background sound levels. Other sources of noise in the area include commercial, agricultural, and residential noise in the project vicinity.
A short-term noise measurement survey was conducted at the project site on Friday June 23rd, 2023 to quantify the existing noise environment on the project site through an update of the prior survey conducted for the Cotati Village #1 mixed use development between September 15th and 17th, 2022. This noise survey included three short-term measurement locations, shown as ST-1, ST-2, and ST-3 in Figure 1. Two of these measurements (ST-1 and ST-2) were made in the vicinity of proposed buildings A and B at approximately 235 feet and 400 feet from the centerline of Hwy 116. The noise measurements were conducted with Larson Davis Laboratories (LDL) Type I Model LXT Sound Level Meters All meters were equipped with ½-inch prepolarized condenser microphones and windscreens and were calibrated with a Larson Davis Model CA250 precision acoustic calibrator prior to and following the measurement survey. The measurements at ST-1 and ST-2 were conducted simultaneously with measurements at a third location (ST-3), which was conducted at the position of the long-term measurement closest to the Gravenstein Highway conducted for the Cotati Village #1 development (indicated as LT-1in that report and as discussed below).
The prior (2022) long term noise measurement at LT-1 was made on the trunk of a tree at a height of 12 feet above grade and approximately 100 feet from the centerline of Gravenstein Hwy (see Figure 1). The measured noise levels at this location, including the energy equivalent noise level (Leq), maximum (Lmax), minimum (Lmin), and the noise levels exceeded 10, 50 and 90 percent of the time (indicated as L10, L50 and L90) are shown on Chart 1, following.
A review of Chart 1 indicates that the noise levels at site LT-1 followed a diurnal pattern characteristic of traffic noise, with the average daytime noise levels ranging from 62 to 68 dBA Leq and the average hourly nighttime noise levels ranging from 53 to 66 dBA Leq. The overall average Day/Night noise Level (Ldn) for the 48-hour monitoring period at position LT-1 was 68 dBA, with the full day (Friday 9/16/22) Ldn at 69 dBA.
The results of the current short measurements at ST-1, ST-2 and ST-3 (LT-1) which are shown in Table 4 below, indicate that the overall Ldn at approximately 235 feet from the Hwy 116 centerline was 61 dBA, while the overall Ldn at approximately 400 feet from the Hwy 116 centerline was 57 dBA. Considering these existing condition levels and the distances from the facades of Building A and B with views of Hwy 116 traffic, we would expect the traffic noise exposure at Building A to range from 56 to 62 dBA Ldn and the traffic noise exposure at Building B to range from 60 to 61 57 dBA Ldn under existing conditions.
Table 4: Short-term Measurement Results
Location Time/ Date. Lmax L01 L10 Leq L50 L90 Ldn
ST-1 (~235 ft. to CL of Hwy 116)
3:10 PM
6/6/2023 71 62 59 56 55 48 61
ST-3 (Long-term LT-1, ~115 ft. to Hwy 116 CL)
3:10 PM
6/6/2023 77 72 67 64 63 51 68
ST-2 (~400 ft. to CL of Hwy 116)
3:30 PM
6/6/2023 59 58 56 53 53 50 57
ST-3 (Long-term LT-1, ~115 ft. to Hwy 116 CL)
3:30 PM
6/6/2023 74 72 69 65 64 55 68
FUTURE NOISE ENVIRONMENT
The future noise environment on the project site would continue to result primarily from traffic on Gravenstein Hwy. Based on a review of the future versus existing traffic volumes for this roadway without the project from the traffic reports and memo for Cotati Villages 1 and 2 projects1, we have calculated the future noise environment on the project site and surroundings will increase by 3 dBA over existing noise conditions. Thus, under future conditions, the traffic noise exposure in areas of Building A with views of Hwy 116 traffic are expected to range from 59 to 65 dBA Ldn and the traffic noise exposure in areas of Building B with views of Hwy 116 traffic are expected to range from 63 to 64 dBA Ldn.
SIGNIFICANCE CRITERIA
Appendix G of the CEQA Guidelines states that a project would normally be considered to result in significant noise impacts if noise levels conflict with adopted environmental standards or plans or if noise generated by the project would substantially increase existing noise levels at sensitive receivers over a permanent or temporary basis. A significant impact would be identified for a proposed land use if it were exposed to noise levels exceeding established guidelines or standards for noise and land use compatibility. A substantial permanent noise increase would occur if the noise level increase resulting from the project is 1.5 dBA where existing traffic noise levels are greater than 65 dBA Ldn, 3 dBA Ldn where existing traffic noise levels are between 60 and 65 dBA Ldn, and 5 dBA Ldn where existing traffic noise levels are less than 60 dBA Ldn as established by the Cotati General Plan. A substantial temporary noise level increase would occur where noise from construction activities exceeds 60 dBA Leq and the ambient noise environment by at least 5 dBA Leq at adjacent land uses in the project vicinity for 1 W-Trans, “Draft Report, Transportation Impact Study for the Cotati Village Project”, 09/8/2022
a period of one year or more. Vibration levels generated during demolition or construction activities would be significant if they cause cosmetic or structural damage to adjacent buildings.
NOISE IMPACTS AND MITIGATION MEASURES
Impact 1a: Exterior Residential Noise and Land Use Compatibility. Residential uses developed at portions of the project site would be exposed to normally and conditionally acceptable noise levels. This is a less-than-significant impact.
Project drawings show that the common outdoor use area for the project, labeled the ‘Central Green Commons’, will be south of Building B and north of project parking and the ‘Woonerf’2 connecting it to Alder Lane. A review of the site plan shows that this central common open space will be as close as 275 feet from the centerline of Gravenstein Highway and will receive partial acoustical shielding from intervening structures. Based on the results of our measurement survey and future noise projections, but without consideration of any partial noise shielding, sound levels in the project common open space areas are expected to be up to 65 dBA Ldn under future conditions. Such exterior noise levels are considered “normally acceptable” for multifamily residential land uses by the City of Cotati General Plan Noise Element.
Mitigation Measure 1a: None Required.
Impact 1b: Interior Residential Noise and Land Use Compatibility. The interiors of residences on portions of the project site that would be exposed to “conditionally acceptable” noise levels such that the interior noise levels may exceed the City and State required 45 dBA Ldn level. This is a less-than-significant impact with the incorporation of noise control measures in the project design.
Interior noise levels within residential buildings of normal construction are typically 15 dBA lower than exterior noise levels with the windows partially open. With the windows closed, standard residential construction typically provides 20 to 25 decibels of exterior to interior noise reduction. Considering this, where exterior day-night average noise levels are 65 dBA Ldn or less, interior noise levels can typically be maintained below the City and State interior noise standard of 45 dBA Ldn with the incorporation of forced air mechanical ventilation systems to provide adequate fresh air when residents wish to keep their windows closed for noise control.
Where exterior noise levels are less than 60 dBA Ldn, the City and State interior noise standard of 45 dBA Ldn can typically be achieved indoors with windows open for fresh air.
Based on the results of the measurement survey and acoustical calculation, all residential units within 400 feet of the centerline of Hwy 116 with a view of traffic on this roadway will be exposed to an Ldn of 60 dBA or greater under future conditions and the closest residential units to Hwy 116 (southernmost façade of Building A) will be exposed to exterior noise levels of 65 dBA Ldn under future conditions. Considering this, the following noise control measures are assumed to be included in the final project design:
Exterior to Interior Noise Control Design Measures:
All apartments in Buildings A and B within 400 feet of the centerline of Hwy 116, as shown in Figure 2, will be equipped with a mechanical ventilation system to supply fresh air to the units while allowing residents to keep their windows closed for noise control. These mechanical ventilation systems may take the form of an acoustically rated straight air transfer duct such as the Fresh 80, 90 or 100-dB units by Fresh Ventilation (or equal), a standard central air conditioning and/or a central heating system with adequate fresh air supply, which is equipped 2 A Woonerf is a ‘Street for Living’ where vehicles are slowed by placing trees, planters, parking areas, and other obstacles in the street.
with a ‘summer switch’ to allow the fan to circulate air without cooling or heating operation, or other systems satisfactory to the local building official, which provide adequate mechanical ventilation to the residences with closed windows.
Mitigation Measure 1b: No additional measures required
Figure 2: Project Site Plan Showing Units Equipped with Mechanical Ventilation Impact 2: Project Operational Noise Generation Noise due to the use and occupation of the project residences on adjacent noise sensitive uses is not expected to significantly increase or alter the existing noise environment at these uses. This is a less-than-significant impact.
The proposed project would place new residential uses within 175 feet of the future Cotati Village #1 residential development to the east and within 200 feet of an existing multi-family housing development to the northeast. The occupation and use of the proposed homes is expected to result in the typical noises associated with residential development, including voices of the new residents, home maintenance activities, barking dogs and children. The Heating Ventilation and Air Conditioning (HVAC) and other mechanical equipment associated with multifamily residential development may also add noise the existing environment. Based on noise measurements made at similar projects the outdoor condensing units at the proposed residences may produce constant sound levels of 47 to 50 dBA Leq at 50 feet and could operate continuously during both daytime and nighttime hours. Considering these noise levels and distances to the adjacent residential uses, noise from the project HVAC equipment would be at or below ambient noise levels at these adjacent residences. Additionally, though noise resulting from occupation of the new residences may noticeably change the noise environment in some adjacent residential areas, these sources are not expected to increase noise levels in any surrounding areas by four or more dBA and the noise associated with the proposed residences is Residential units requiring
Mechanical Ventilation
not incompatible with the surrounding land uses. Therefore, project operation is not judged to result in a noise impact.
Mitigation 2: None Required.
Impact 3: Project-Generated Traffic Noise. The proposed project would not substantially increase noise levels on a permanent basis at noise sensitive uses in the vicinity.
This is a less-than-significant impact.
A significant impact would be identified if traffic generated by the project would substantially increase noise levels at sensitive receivers in the vicinity. A substantial increase would occur if the project traffic on area roadways where to result in a noise level increase of 5 dBA Ldn or greater at multi-family homes east of the project site, or by 1.5 dBA Ldn or greater at the singlefamily homes south of the project site. The traffic analysis for the Cotati Village #2 development3 indicates that it would generate 68 trips during the a.m. peak hour and 69 during the p.m. peak hour, and the traffic analysis for the Cotati Village #1indicates that it would generate 110 trips during the a.m. peak hour and 178 during the p.m. peak hour1 for a total trip generation between the Village #1 and Village #2 projects of 178 trips during the a.m. peak hour and 247 trips during the p.m. peak hour. The analysis from Cotati Village #1 traffic report also indicated there are currently 1348 am peak hour trips and 1251 pm peak hour trips on Gravenstein Highway adjacent to the site. Considering these volumes, traffic from both Cotati Village #1 and #2 project traffic would result in a less than 1 dBA increase in noise levels on the Gravenstein Highway. An additional review shows that under existing conditions project traffic on Alder Avenue, would result in a 3 dBA or less increase in noise levels on Alder Avenue.
Mitigation 3: None Required.
Impact 4: Exposure to Construction Generated Groundborne Vibration. Residences in the vicinity of the project site are not expected to be exposed to perceptible vibration levels from construction activities. This is a less-than-significant impact.
Construction activities would include site preparation work such as grading and the installation of utilities, foundation work, and new building framing. Construction techniques that generate the highest vibration levels, such as impact or vibratory pile driving, are not expected at this project. Construction activities would generally occur at distances of 200 feet or more from the nearest residential units to northeast. Construction activities near the southern project perimeter could occur at distances of 600 feet or more from the single-family homes to the south.
For structural damage, the California Department of Transportation uses a vibration limit of 0.5 in/sec, PPV for buildings structurally sound and designed to modern engineering standards and
0.2 in/sec, PPV for buildings that are found to be structurally sound but where structural damage is a major concern.
Project construction activities such as drilling, the use of jackhammers, rock drills and other high-power or vibratory tools, and rolling stock equipment (tracked vehicles, compactors, etc.) may generate substantial vibration in the immediate vicinity. Building framing, exterior and interior finishing, and landscaping activities are not anticipated to be sources of substantial vibration. Construction activities may extend over several construction seasons, but construction vibration would not be substantial for most of this time except during vibration generating activities (as discussed above).
Table 7 presents vibration source levels for typical construction equipment at distances of 25 and 200 feet. Jackhammers typically generate vibration levels of 0.002 in/sec PPV, drilling typically 3 W-Trans, “Memorandum of Understanding for Cotati Village 2 Project”, 04/5/2024
generates vibration levels of 0.004 in/sec PPV, and vibratory rollers generate vibration levels of
0.009 in/sec PPV at distances of 200 feet. Based on this, construction vibration levels would be well below the 0.50 in/sec PPV damage criteria at the closest residential structures.
TABLE 7 Vibration Source Levels for Construction Equipment4 Equipment PPV at 25 ft. (in/sec) PPV at 200 ft. (in/sec) Clam shovel drop 0.202 0.009
Hydromill (slurry wall) in soil 0.004 0.0004
in rock 0.008 0.001
Vibratory Roller 0.210 0.009
Hoe Ram 0.089 0.004
Large bulldozer 0.089 0.004
Caisson drilling 0.089 0.004
Loaded trucks 0.076 0.003
Jackhammer 0.035 0.002
Small bulldozer 0.003 0.0001
Mitigation 4: None Required
Impact 5: Construction Noise. Noise levels generated by project construction activities would temporarily elevate ambient noise levels at sensitive land uses in the vicinity. Major noise generating construction activities would be limited to less than one construction season or less. This is a less-than-significant impact.
The construction of the project would generate noise and would temporarily increase noise levels at adjacent residential receivers. Noise impacts resulting from construction depend on the noise generated by various pieces of construction equipment operating on site, the timing and duration of noise generating activities, and the distance between construction noise sources and noise sensitive receptors. Construction of the project would involve site improvements, such as the establishment of utilities, excavation of foundations, building erection, paving, and landscaping along with home construction. The hauling of excavated material and construction materials would generate truck trips on local roadways.
Construction activities are typically carried out in stages. During each stage of construction, there would be a different mix of equipment operating. Construction noise levels would vary by stage and vary within stages based on the amount of equipment in operation and location where the equipment is operating. Typical noise levels which during the construction of housing at 50 feet are shown in Table 6, which gives the average noise level ranges by construction phase. Site work and residential construction noise ranges from 65 to 88 dBA at 50 feet from the source.
The nearest noise sensitive uses will be 120 to 200 feet from close-in on-site work and home construction. Average noise levels produced by work at this distance would range from 74 to 88 dBA. Construction activities at these distances would range from 73 to 90 dBA, with average levels of 75 to 78 dBA. These noise levels drop off at a rate of about 6 dBA per doubling of distance between the noise source and receptor, such that noise levels produced during most site construction activities, which would occur at distances of 400 feet or more from adjacent noise sensitive uses, would produce average noise levels of 71 dBA or less. 4 Transit Noise and Vibration Impact Assessment, United States Department of Transportation, Office of Planning and Environment, Federal Transit Administration, May 2006.
TABLE 6: Typical Ranges of Leq Construction Noise Levels at 50 Feet, dBA Construction
Stage
Domestic
Housing
Office Building, Hotel, Hospital,
School, Public Works
Public Works Roads &
Highways, Sewers, and Trenches
I II I II I II
Ground Clearing 83 83 84 84 84 84
Excavation 88 75 89 79 88 78
Foundations 81 81 78 78 88 88
Erection 81 65 87 75 79 78
Finishing 88 72 89 75 84 84
I - All pertinent equipment present at site, II - Minimum required equipment present at site.
Source: U.S.E.P.A., Legal Compilation on Noise, Vol. 1, p. 2-104, 1973.
Construction of the project is expected to take less than 1 year to complete. Based on this timetable, the construction noise levels at various distances discussed above, and a consideration that once intervening structures are built, they would provide some degree of noise attenuation at the surrounding residences, we expect that the existing residences adjacent to the project site would not be exposed to construction related noise levels exceeding 60 dBA Leq for a period of greater than one year.
The following standard “best practice” controls from Action N1h as contained in Policy N 1.15 of the City General Plan are assumed to be included in the project:
• Noise‐generating construction activities, including truck traffic coming to and from the construction site for any purpose, shall be limited to between the hours of 7:00 am and 7:00 pm on weekdays and 9:00 am and 5:00 pm on Saturdays (if allowed through specific project conditions of approval). No construction shall occur on Sundays or holidays. • All equipment driven by internal combustion engines shall be equipped with mufflers, which are in good condition and appropriate for the equipment. • The construction contractor shall utilize “quiet” models of air compressors and other stationary noise sources where technology exists.
• At all times during project grading and construction, stationary noise-‐generating equipment shall be located as far as practicable from sensitive receptors and placed so that emitted noise is directed away from residences.
• Unnecessary idling of internal combustion engines shall be prohibited. • Construction staging areas shall be established at locations that will create the greatest distance between the construction related noise sources and noise-‐sensitive receptors nearest the project site during all project construction. • The required construction related noise mitigation plan shall also specify that haul truck deliveries are subject to the same hours specified for construction equipment. • Neighbors located adjacent to the construction site shall be notified of the construction schedule in writing.
• The construction contractor shall designate a “noise disturbance coordinator” who will be responsible for responding to any local complaints about construction noise. The disturbance coordinator would determine the cause of the noise complaint (e.g., starting too early, bad muffler, etc.) and institute reasonable measures as warranted to correct the problem. A telephone number for the disturbance coordinator shall be conspicuously posted at the construction site.
With the implementation of these controls, and the limited duration of the noise generating construction at the adjacent noise sensitive uses, the substantial temporary increase in ambient noise levels associated with construction activities would be less-than-significant.
Mitigation Measure 5: No additional measures required.