ORACLE EDUCATIONAL FACILITY PROJECT ENVIRONMENTAL NOISE ASSESSMENT

Transcription

1 ORACLE EDUCATIONAL FACILITY PROJECT ENVIRONMENTAL NOISE ASSESSMENT Redwood City, California December 2, 2015 Prepared for: Shannon George David J. Powers & Associates, Inc The Alameda, Suite 200 San José, CA Prepared by: Carrie J. Janello 1 Willowbrook Court, Suite 120 Petaluma, CA (707) Project:

2 INTRODUCTION Oracle Education Foundation plans to construct a new facility for Design Tech High School on a currently undeveloped parcel of land located on the Oracle Headquarter campus in Redwood City, California. The proposed two-story building will be approximately 64,000 square feet with associated site improvements and landscaping. Additionally, parking spaces will be constructed for staff and visitors. The project site is 4.34 acres in Redwood Shores, just north of Oracle Parkway. An existing parking lot is located on the site. The site is bordered to the north and west by Belmont Slough and to the south by Oracle Parkway. This report evaluates the project s potential to result in significant impacts with respect to applicable CEQA guidelines. The report is divided into two sections: 1) the Setting Section provides a brief description of the fundamentals of environmental noise and summarizes applicable regulatory criteria; and 2) the Impacts and Mitigation Measures Section describes the significance criteria used to evaluate project impacts, provides a discussion of each project impact, and presents mitigation measures, where necessary, to provide a compatible project in relation to adjacent noise sources and land uses. 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 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 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 A- weighted 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 1

3 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 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 p.m. - 10:00 p.m.) and a 10 db addition to nocturnal (10:00 p.m. - 7:00 a.m.) noise levels. The Day/Night Average Sound Level (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. Fundamentals of Ground-borne 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 method is the Peak Particle Velocity (PPV). The PPV is defined as the maximum instantaneous positive or negative peak of the vibration wave. In this report, 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. 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. Construction activities can cause vibration that varies in intensity depending on several factors. The use of pile driving and vibratory compaction equipment typically generates the highest construction related ground-borne vibration levels. Because of the impulsive nature of such activities, the use of the PPV descriptor has been routinely used to measure and assess ground- 2

4 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 to 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. 3

5 TABLE 1 Definition of Acoustical Terms Used in this Report Term Decibel, db Definition 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 micro Pascals. Sound Pressure Level Frequency, Hz A-Weighted Sound Level, dba Equivalent Noise Level, Leq Lmax, Lmin L01, L10, L50, L90 Day/Night Noise Level, Ldn or DNL Community Noise Equivalent Level, CNEL Ambient Noise 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. 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. 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. The average A-weighted noise level during the measurement period. The maximum and minimum A-weighted noise level during the measurement period. The A-weighted noise levels that are exceeded 1%, 10%, 50%, and 90% of the time during the measurement period. The average A-weighted noise level during a 24-hour day, obtained after addition of 10 decibels to levels measured in the night between 10:00 p.m. and 7:00 a.m. The average A-weighted noise level during a 24-hour day, obtained after addition of 5 decibels in the evening from 7:00 p.m.to 10:00 p.m. and after addition of 10 decibels to sound levels measured in the night between 10:00 p.m. and 7:00 a.m. 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,

6 TABLE 2 Typical Noise Levels in the Environment Common Outdoor Activities Noise Level (dba) Common Indoor Activities 110 dba Rock band Jet fly-over at 1,000 feet Gas lawn mower at 3 feet 100 dba 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 20 dba 10 dba Bedroom at night, concert hall (background) Broadcast/recording studio Source: Technical Noise Supplement (TeNS), California Department of Transportation, September dba 5

7 TABLE 3 Reactions of People and Damage to Buildings from Continuous or Frequent Intermittent Vibration Levels Velocity Level, Human Reaction Effect on Buildings PPV (in/sec) 0.01 Barely perceptible No effect 0.04 Distinctly perceptible 0.08 Distinctly perceptible to strongly perceptible 0.1 Strongly perceptible Strongly perceptible to severe Severe - Vibrations considered unpleasant Vibration unlikely to cause damage of any type to any structure Recommended upper level of the vibration to which ruins and ancient monuments should be subjected Virtually no risk of damage to normal buildings Threshold at which there is a risk of damage to older residential dwellings such as plastered walls or ceilings Threshold at which there is a risk of damage to newer residential structures Source: Transportation and Construction Vibration Guidance Manual, California Department of Transportation, September Regulatory Background - Noise The State of California and the City of Redwood City 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, Municipal Code standards, or the applicable standards of other agencies. A summary of the applicable regulatory criteria is provided below. State CEQA Guidelines. The 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) Exposure of persons to or generation of noise levels in excess of standards established in the local General Plan or Noise Ordinance, or applicable standards of other agencies; (b) Exposure of persons to or generation of excessive ground-borne vibration or ground-borne noise levels; (c) A substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project; (d) A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project; 6

8 (e) For a project located within 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; or (f) For a project within the vicinity of a private airstrip, if the project would expose people residing or working in the project area to excessive noise levels. CEQA does not define what noise level increase would be considered substantial. Typically, project-generated noise level increases of 3 dba L dn/cnel or greater would be considered significant where exterior noise levels would exceed the normally acceptable noise level standard (60 dba L dn/cnel for residential land uses). Where noise levels would remain at or below the normally acceptable noise level standard with the project, noise level increases of 5 dba L dn/cnel or greater would be considered significant. City of Redwood City 2010 General Plan. The City of Redwood City s General Plan identifies noise and land use compatibility standards for various land uses and establishes policies to control noise within the community. Table PS-10 from the General Plan shows acceptable levels for various land uses. Schools are considered normally acceptable in noise environments of 55 dba CNEL or less. A noise environment between 55 and 65 dba CNEL would be considered conditionally acceptable. The guidelines state that where the exterior noise levels are greater than 65 dba CNEL and less than 70 dba CNEL, new development should be generally discouraged or a detailed analysis of noise reduction requirements must be made. Noise levels exceeding 70 dba CNEL are considered unacceptable and development should not be undertaken. For low density residential land uses, normally acceptable noise levels would be at or below 55 dba CNEL. Noise levels ranging from 55 to 60 dba CNEL would be considered conditionally acceptable for low density residential land uses, while levels between 60 and 75 dba CNEL would be considered normally unacceptable. Noise levels exceeding 75 dba CNEL would be considered clearly unacceptable. 7

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10 Applicable goals, policies, and programs presented in the General Plan are as follows: Goal PS-13 Policy PS-13.3 Policy PS-13.4 Policy PS-13.5 Policy PS 13-6 Policy PS-13.8 Policy PS-13.9 Program PS-63 Minimize the impact of point source noise and ambient noise levels throughout the community. Consider noise impacts as part of the development review process, particularly the location of parking, ingress/egress/loading, and the refuse collection areas relative to surrounding residential development and other noise-sensitive land uses. In accordance with the Municipal Code and noise standards contained in the General Plan, strive to provide a noise environment that is at an acceptable noise level near schools, hospitals, and other noise-sensitive areas. Limit the hours of operation at all noise generation sources that are adjacent to noise-sensitive areas, wherever practical. Require all exterior noise sources (construction operations, air compressors, pumps, fans, and leaf blowers) to use available noise suppression devices and techniques to bring exterior noise down to acceptable levels that are compatible with adjacent land uses. Implement appropriate standard construction noise controls for all construction projects. Require noise created by new non-transportation noise sources to be mitigated so as not to exceed acceptable interior and exterior noise level standards. Enforcing Construction and Maintenance Noise Regulations. Minimize noise from property maintenance equipment, construction activities, and other non-transportation noise sources by enforcing construction and maintenance hours, including vehicle start-up and preparation. Enforce standard construction noise controls such as: Limit construction to the hours of 8:00 a.m. to 5:00 p.m. on weekdays, and 9:00 a.m. to 5:00 p.m. on Saturdays, with no noise-generating construction on Sundays or holidays. Control noise from construction workers radios to the point where they are not audible at existing residences that border the project site. Equip all internal combustion engine-driven equipment with mufflers that are in good condition and appropriate for the equipment. Utilize quiet models of air compressors and other stationary noise sources where technology exists. 9

11 Locate stationary noise-generating equipment as far as possible from sensitive receptors when sensitive receptors adjoin or are near a construction project area. Prohibit unnecessary idling of internal combustion engines. Notify residents adjacent to the project site of the construction schedule in writing. City of Redwood City Municipal Code Noise Regulation. The City s Municipal Code establishes noise level performance standards for fixed sources of noise. The following sections from the Municipal Code apply to this project: Section Prohibited Noise Levels. It shall be unlawful for any person to suffer or allow noise levels to be generated by: A. Construction activities, including demolition, alteration, repair or remodeling of or to existing structures and construction of new structures on property within the City, at more than 110 db measured at any point within a residential district of the City and outside of the plane of said property; or B. An individual item of machinery, equipment or device used during construction activities, including demolition, alteration, repair or remodeling of or to existing structures and construction of new structures on property within the City, at more than 110 db measured within a residential district of the City at a distance of twenty-five feet (25 ) from said machinery, equipment or device. If said machinery, equipment or device is housed within a structure on the property, then the measurement shall be made at a distance as near to twentyfive feet (25 ) from said machinery, equipment or device as possible. Section Time Limitations. Notwithstanding the provisions in this Division to the contrary, it shall be unlawful for any person to engage in construction activities, including demolition, alteration, repair or remodeling of or to existing structures and the construction of new structures on property in a residential district or within five hundred feet (500 ) of a residential district in the City, between the hours of eight o clock (8:00) p.m. and seven o clock (7:00) a.m. the following day, Monday through Friday of any week or at any time on Saturdays, Sundays, or holidays if the noise level generated by any such activity exceeds the local ambient measured at any point within the residential district and outside of the plane of said property. Existing Noise Environment The project site is located south of Belmont Slough and north of Oracle Parkway in Redwood City. Office buildings are located south of the project site, opposite Oracle Parkway. To the north and west of the project site, opposite the Belmont Slough, are single- and multi-family residences. The noise environment at the project site results primarily from vehicular traffic along Oracle Parkway and U.S The occasional overhead aircraft associated with the San Carlos Airport may also affect the noise environment sporadically. 10

12 Existing noise contours contained in the Redwood City General Plan, as shown on Figure 1, indicate that the ambient noise environment at the project site and in surrounding areas are 55 dba CNEL or less. Figure Existing Noise Contours in Project Vicinity Project Site Source: Redwood City General Plan, October

13 NOISE IMPACTS AND MITIGATION MEASURES Significance Criteria Paraphrasing from Appendix G of the CEQA Guidelines, a project would normally result in significant noise impacts if noise levels generated by the project conflict with adopted environmental standards or plans, if the project would generate excessive ground-borne vibration levels, or if ambient noise levels at sensitive receivers would be substantially increased over a permanent, temporary, or periodic basis. The following criteria were used to evaluate the significance of environmental noise resulting from the project: A significant noise impact would be identified if the project would expose persons to or generate noise levels that would exceed applicable noise standards presented in the General Plan, Specific Plan, or Code of Ordinances. A significant impact would be identified if the construction of the project would expose persons to excessive vibration levels. Ground-borne vibration levels exceeding 0.3 in/sec PPV would have the potential to result in cosmetic damage to normal buildings. 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: a) the noise level increase is 5 dba CNEL or greater, with a future noise level of less than 60 dba CNEL, or b) the noise level increase is 3 dba CNEL or greater, with a future noise level of 60 dba CNEL or greater. A significant noise impact would be identified if construction-related noise would temporarily increase ambient noise levels at sensitive receptors. Hourly average noise levels exceeding 60 dba Leq, and the ambient by at least 5 dba Leq, for a period of more than one year would constitute a significant temporary noise increase at adjacent residential land uses. Impact 1: Noise and Land Use Compatibility. Noise levels are not expected to exceed the standards established by the City s General Plan at the outdoor use areas of the proposed project. This is a less-than-significant impact. The future noise environment will continue to be dominated by traffic noise from Oracle Parkway and U.S The proposed project would increase traffic volumes due to dropping off and picking up students, students with internships that drive to school, staff, and teachers. However, about 60% of existing students take Caltrain and BART to school, and under future project conditions, this trend is expected to continue. According to the traffic study conducted by Hexagon Transportation Consultants, Inc. in August 2015, 1 the proposed project is expected to generate a total of 289 new 1 Hexagon Transportation Consultants, Inc., Oracle Educational Facility Draft Traffic Impact Analysis, August 5,

14 trips during the peak hour in the morning and a total of 111 new trips during the peak hours in the evening. This traffic volume increase would increase noise levels at the project site by up to 2 db during the peak traffic periods. The 2030 noise contour in the City s 2010 General Plan shows the project site located in a region with future noise levels less than 55 dba CNEL. The proposed project would increase the traffic in the immediate area, but the noise level increase would be such that the expected 2030 levels would remain at or below 55 dba CNEL. Outdoor use areas for the proposed project would include the amphitheaters, public seating areas, and the park and playground areas located to the north of the building along the Belmont Slough. The amphitheaters and the public seating areas would be shielded from the traffic along Oracle Parkway by the building; therefore, noise levels at these locations would be less than 55 dba CNEL. The park and playground amenities would have a direct line-of-sight to the roadway and would be approximately 100 feet north of the centerline. With the 2 db traffic increase due to the project, the future exterior 2030 noise levels are expected to be at or below 55 dba CNEL, which meets the noise threshold for outdoor use areas at schools. This is a less-than-significant impact. Mitigation Measure 1: None required. Impact 2: Exposure to Excessive Ground-borne Vibration. Construction-related vibration would not be excessive at nearby residential land uses. This is a less-thansignificant impact. The construction of the project may generate perceptible vibration when heavy equipment or impact tools (e.g. jackhammers, hoe rams) are used. Construction activities would include preparation work, foundation work, and new building framing and finishing. For structural damage, the California Department of Transportation recommends a vibration limit of 0.5 in/sec PPV for buildings structurally sound and designed to modern engineering standards, 0.3 in/sec PPV for buildings that are found to be structurally sound but where structural damage is a major concern, and a conservative limit of 0.08 in/sec PPV for ancient buildings or buildings that are documented to be structurally weakened. No ancient buildings or buildings that are documented to be structurally weakened surround the project sites. Therefore, ground-borne vibration levels exceeding 0.3 in/sec PPV would have the potential to result in a significant vibration impact. Table 4 presents typical vibration levels that could be expected from construction equipment at a distance of 25 feet. Pile driving may be required for this project and would generate perceptible vibration at nearby land uses. Impact pile drivers typically generate vibration levels of 0.64 in/sec PPV at a distance of 25 feet. Vibration levels from pile driving would vary, depending on soil conditions, construction methods, and equipment used. Other 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 13

15 immediate vicinity. Jackhammers typically generate vibration levels of in/sec PPV, and drilling typically generates vibration levels of 0.09 in/sec PPV at a distance of 25 feet. Single- and multi-family residences are located to the north and west of the project site, opposite the Belmont Slough. The nearest sensitive receptors would be approximately 500 to 710 feet from the property line of the project site. At these distances, vibration levels due to impact pile driving would be at or below 0.04 in/sec PPV, while all other construction equipment would have expected vibration levels at or below 0.01 in/sec PPV, which would be below the 0.3 in/sec PPV significance threshold. Vibration generated by construction activities may at times be perceptible at the nearest sensitive receptors but would not be expected to result in architectural damage to these buildings. TABLE 4 Vibration Source Levels for Construction Equipment Equipment PPV at 25 ft. (in/sec) Approximate Lv at 25 ft. (VdB) Pile Driver (Impact) upper range typical Pile Driver (Sonic) upper range typical Clam shovel drop Hydromill (slurry wall) in soil in rock Vibratory Roller Hoe Ram Large bulldozer Caisson drilling Loaded trucks Jackhammer Small bulldozer Source: Transit Noise and Vibration Impact Assessment, United States Department of Transportation, Office of Planning and Environment, Federal Transit Administration, May Mitigation Measure 2: None required. Impact 3: Project-Generated Traffic Noise. The proposed project would not result in a substantial permanent noise level increase at the existing residential land uses in the project site vicinity. This is a less-than-significant impact. Typically, a significant permanent noise increase would occur if the project would increase noise levels at noise-sensitive receptors by 3 dba CNEL or greater where ambient noise levels exceed the normally acceptable noise level standard. Where ambient noise levels are at or below the normally acceptable noise level standard, noise level increases of 5 dba CNEL or greater would be considered significant. While ambient noise levels at the nearest residences located to the north and west of the project site, opposite the Belmont Slough, were not measured as part of this project, the noise environment at these locations would be predominantly the result of neighborhood traffic 14

16 and activities, which would typically result in levels at or below 55 dba CNEL. The existing noise environment would, therefore, be considered normally acceptable by the City s General Plan standards. Therefore, a significant impact would occur if the noise levels increased by 5 dba CNEL or greater. The traffic report developed by Hexagon Transportation Consultants, Inc. included peak hour traffic counts at the intersections in the immediate vicinity of the project site and did not include the streets surrounding the residences on the opposite side of the Belmont Slough. This is due to the fact that project-generated traffic would have no effect on the noise-sensitive receptors in the vicinity of the project site. Therefore, there would not be a project-generated noise level increase at these receptors. This is a less-than-significant impact. Mitigation Measure 3: None required. Impact 4: Mechanical Equipment Noise. Due to the placement and enclosures of the mechanical equipment for the building, the proposed project would not permanently increase noise levels at noise-sensitive uses in the vicinity. This is a less-than-significant impact. The proposed project would include mechanical equipment, such as heating, ventilation, and air conditioning systems. Information regarding the number, type, and size of the mechanical equipment units to be used in the proposed project was not available at the time of this study, but noise levels between 60 dba and 70 dba could be expected at a distance of 15 feet during operation. The mechanical equipment for the proposed building will be located on the roof and will be surrounded by enclosures or equipment screens. Noise levels resulting from the operation of rooftop equipment at the nearest receptors 500 to 710 feet from the project site would be 40 dba or less. Noise from mechanical equipment located on the roof within enclosures would not be expected to cause a permanent noise increase at the noise-sensitive receptors in the vicinity of the project site, and the impact is a less-than-significant impact. Mitigation Measure 4: None required. Impact 5: Outdoor Patio Noise. Outdoor patio noise on the proposed project site would not permanently increase noise levels at noise-sensitive uses in the vicinity. This is a less-than-significant impact. Outdoor patios for teaching/work and lunch are included as part of the proposed project. The patios would be located along the northern boundary of the project site between the proposed building and the student parking lot/drop-off area. Noise from socializing is dependent on the total number of people at the patio. Average noise levels from outdoor activities typically range from 72 to 74 dba Leq at a distance of 25 feet, assuming 20 to 30 people. Maximum noise levels can reach 81 dba Lmax at a distance of 25 feet. The distance from the proposed patios to the nearest residential land use would be approximately 595 feet. At this distance, average outdoor patio noise would range from 44 to 46 dba Leq, and maximum noise levels would be up to 53 dba Lmax. These noise 15

17 levels would fall within the range of typical daytime noise levels at the nearby residential land uses and would not be expected to cause a permanent noise increase. This impact is less-thansignificant. Mitigation Measure 5: None required. Impact 6: Temporary Construction Noise. Existing noise-sensitive land uses would be exposed to construction noise levels in excess of the significance thresholds. This is a significant impact. Noise impacts resulting from construction depend upon the noise generated by various pieces of construction equipment, the timing and duration of noise-generating activities, and the distance between construction noise sources and noise-sensitive areas. Construction noise impacts primarily result when construction activities occur during noise-sensitive times of the day (e.g., early morning, evening, or nighttime hours), the construction occurs in areas immediately adjoining noise-sensitive land uses, or when construction lasts over extended periods of time. Where noise from construction activities exceeds 60 dba Leq and exceeds the ambient noise environment by at least 5 dba Leq at noise-sensitive uses in the project vicinity for a period exceeding one year, the impact would be considered significant. Construction activities generate considerable amounts of noise, especially during the construction of project infrastructure when heavy equipment is used. Table 5 presents the typical range of hourly average noise levels generated by different phases of construction measured at a distance of 50 feet. Typical hourly average construction-generated noise levels for the proposed project would be about 79 to 89 dba Leq measured at a distance of 50 feet from the center of the site during busy construction periods (e.g., earth moving equipment, impact tools, etc.). Maximum noise levels generated during project construction would typically range from 90 to 95 dba Lmax, assuming the operation of jackhammers and hoe rams, at a distance of 50 feet from the center of the site. Maximum noise levels generated during foundation construction by pile driving events would typically range from 95 to 105 dba Lmax at a distance of 50 feet. Construction-generated noise levels drop off at a rate of about 6 dba per doubling of the distance between the source and receptor. Shielding by buildings or terrain can provide an additional 5 to 10 dba noise reduction at distant receptors. The nearest noise-sensitive receptors in the project site vicinity would be located north and west of the Belmont Slough and range from 500 to 710 feet from the site. At these residences, the hourly average noise levels would range from 52 to 69 dba Leq for typical construction that would not include pile driving. Maximum instantaneous noise levels experienced at the nearest residences due to pile driving activities from the proposed project would be below the 110 dba Lmax threshold specified in the City s Municipal Code. Noise generated by project construction would be expected to exceed 60 dba Leq. Although construction-generated noise levels would exceed ambient noise levels at receptors surrounding the project sites by more than 5 dba Leq, construction activities would occur in short-term durations during daytime hours only. This would be a significant impact. 16

18 TABLE 5 Hourly Average Noise Levels for Construction Equipment at 50 feet Industrial Parking Garage, Public Works Office Building, Religious Roads & Domestic Hotel, Hospital, Amusement & Highways, Housing School, Public Recreations, Sewers, and Works Store, Service Trenches Station I II I II I II I II Ground Clearing Excavation Foundations Erection Finishing I All pertinent equipment present at site. II Minimum required equipment present at site. Source: United States Environmental Protection Agency, 1973, Legal Compilation on Noise, Vol. 1, p Mitigation Measure 6: Construction for the proposed project would include site preparation, grading/excavation, trenching, exterior structural assembly, interior work, and paving. While noise generated by construction activities would temporarily elevate noise levels at noise-sensitive receptors in the project site vicinity, the implementation of construction best management practices would reduce noise. Redwood City General Plan Policy PS-13.6 requires all construction operations to use available noise suppression devices and techniques to bring exterior noise down to acceptable levels that are compatible with adjacent land uses. Policy PS-13.8 implements appropriate standard construction noise controls for all construction projects. Program PS-63 enforces construction and maintenance noise regulations by requiring the following measures: Limit construction activities to the hours of 8:00 a.m. to 5:00 p.m. on weekdays, and 9:00 a.m. to 5:00 p.m. on Saturdays, with no noise-generating construction on Sundays or holidays. Control noise from construction workers radios to the point where they are not audible at existing residences that border the project site. Equip all internal combustion engine-driven equipment with mufflers that are in good condition and appropriate for the equipment. Utilize quiet models of air compressors and other stationary noise sources where technology exists. 17

19 Locate stationary noise-generating equipment as far as possible from sensitive receptors when sensitive receptors adjoin or are near a construction project area. If impact equipment (e.g., jack hammers, pavement breakers, or rock drills) is needed during project construction, hydraulic or electric-powered equipment shall be used wherever feasible to avoid the noise associated with compressed-air exhaust from pneumatic-powered tools. However, where use of pneumatic-powered tools is unavoidable, an exhaust muffler on the compressed-air exhaust shall be used. External jackets on the tools themselves shall also be used if available and feasible. Prohibit unnecessary idling of internal combustion engines. Notify residents adjacent to the project site of the construction schedule in writing. Implementation of the above measures would reduce construction noise levels emanating from the site, limit construction hours, and minimize disruption and annoyance. With the implementation of these measures, and recognizing that noise generated by construction activities would occur over a temporary period, the temporary increase in ambient noise levels would be less-thansignificant. Impact 7: Noise and Land Use Compatibility (Aircraft). The proposed project would be located in a compatible noise environment with respect to noise generated by San Carlos Airport. This is a less-than-significant impact. San Carlos Airport is a county-owned, reliever airport for San Francisco International Airport. It is located approximately 1.2 miles southeast of the project site. The project site lies within the airport influence area outlined on the San Carlos Airport Noise Contours, which are shown in the City s General Plan. However, the site is outside the 55 dba CNEL noise contour. According to the Aircraft Noise/Land Use Compatibility Standards, the project is conditionally compatible with the level of aircraft noise. Although aircraft-related noise could occasionally be audible at the project site, noise from aircraft would not substantially increase ambient noise levels. This is a less-than-significant impact. Mitigation Measure 7: None Required. 18