Charles M Salter Associates Inc BAY MEADOWS PHASE II SPAR 2 SAN MATEO, CALIFORNIA RESIDENTIAL INTERIOR NOISE ANALYSIS Prepared for: Kim Havens Wilson Meany Sullivan Four Embarcadero Center, Suite 3330 San Francisco, CA 94111 Fax: (415) 273-5285 E-mail: khavens@wmspartners.com Prepared by: CHARLES M. SALTER ASSOCIATES, INC. Timothy G. Brown, Principal Consultant Robert P. Alvarado, Vice President 130 Sutter Street, Suite 500 San Francisco, CA 94104 Phone: (415) 397-0442 Fax: (415) 397-0454 CSA Project No. 08-0439 130 Sutter Street San Francisco California 94104 Tel: 415 397 0442 Fax: 415 397 0454
Page 2 of 14 DESCRIPTION Previously, we prepared an Environmental Noise and Vibration Feasibility Assessment dated 16 August 2006 for the project. That report contains information regarding our on-site noise and vibration measurements, City and State acoustical criteria, future vehicular noise analysis, and preliminary mitigation assessment for noise and vibration affecting the proposed land-uses. Based on the updated site drawings, we have refined the interior noise analysis for the residential land-uses proposed at the Bay Meadows Phase II SPAR 2 project in San Mateo, California. The purpose of the study is to quantify the interior noise environments at the residential areas and determine the compatibility of the development with the applicable acoustical standards. This letter summarizes the project s acoustical standards, interior noise analysis, and a discussion of preliminary mitigation measures to allow the project to meet the criteria. The proposed residential parcels RES4, RES5, RES6, RES8, and RES9b consist of multi-family units with RES9a consisting of single-family dwellings. Since the architectural design is still being developed, this report does not provide a finalized set of mitigation measures. Instead, it provides preliminary mitigation measures as necessary to meet the applicable standards. A review of these mitigation measures with any required modifications will be prepared as the design progresses. The parcels are located along Delaware Street, Kyne Street, and Baze Road, adjacent to Derby, Landing, and 31 st Avenues. The major noise source is vehicular traffic along 31 st Avenue and Delaware Street. Noise generated by train operations along the adjacent railway also contributes to the noise environment, but not as significantly due to acoustical shielding provided by the proposed commercial buildings (i.e., STA 1 through 5). In summary, interior noise levels can be reduced to meet the project acoustical standards by incorporating sound rated assemblies at some exterior building facades. Standard exterior wall construction (e.g. stucco, single-stud framing, etc.) will be sufficient and no additional exterior wall mitigation will be required. For detail regarding our previous on-site acoustical measurements, please refer to the 16 August 2006 report. In addition, those readers not familiar with the fundamental concepts of environmental acoustics may refer to Appendix A and Figure A1.
Page 3 of 14 ACOUSTICAL CRITERIA We understand that the following mitigation measures are required for the project 1 : Interior Noise Analysis Prior to the issuance of the building permits, the project sponsor shall implement the following measures: (Mitigation Measure Noise-BM3) A. Prepare an interior noise analysis as part of the final design of the proposed residential uses. The analysis shall demonstrate how interior noise levels would achieve a 45 db DNL where the exterior noise levels would exceed 60 db DNL. Noise control measures shall be designed according to the type of building construction and specified sound rating for each building element. The noise analysis shall be submitted to the City with the final design of proposed residential uses for SPAR implementation of this condition shall be prior to issuance of any Certificate of Occupancy for each phase and monitored by the Building Division. (Building) (Mitigation Measure Noise-BM3a) B. Based upon existing and projected future noise levels, sound-rated windows and wall constructions shall be incorporated into the residential land uses to achieve an acceptable interior noise level of 45 db DNL. Construction methods may include resilient channels, staggered studs, double-stud walls, acoustic doors and acoustic widows. If the windows must remain closed to obtain the required noise reduction, then mechanical ventilation shall be installed in these units. This measure shall be incorporated into the project plans prior the issuance of each building permit. The implementation of this condition shall be monitored and verified by the Building Division. (Building) (Mitigation Measure Noise-BM3b) C. The project sponsor shall provide a letter from an acoustical engineer indicating that the project(s) comply with the interior noise analysis submitted for the individual residential developments. (Building) Noise Analysis Near Caltrain Tracks - For all proposed sensitive uses within 530 feet of the centerline of the Caltrain tracks, the project sponsor shall conduct a detailed noise analysis. The results of that analysis shall be used by the project sponsor to implement measures that would ensure interior noise levels would be no higher than 45 dba 2. The City shall not issue a building permit for any proposed sensitive uses (such as schools, hospitals, rest homes, long term care facilities, mental care facilities, residential uses, places of worship, libraries, and passive recreation uses) on the project site where the interior noise level standard of 45 dba would be exceeded. The analysis shall be submitted to the City prior to issuance of each building permit for each phase. The implementation of this condition shall be monitored and verified by the Building Division. The project sponsor shall provide a letter from an acoustical engineer indicating that the projects comply with the Caltrain tracks noise analysis submitted for the individual residential developments. (Building) (Mitigation Measure Noise-BM7) The above mitigation measures are consistent with City and State building code requirements. 1 Provided via e-mail 26 November 2007. 2 We are assuming that 45 dba refers to the Day-Night Average Noise Level (DNL) which is consistent with the requirement in section BM3a and the State Building Code.
Page 4 of 14 NOISE ENVIRONMENT To quantify the noise environment affecting the proposed residential locations, we reviewed the drawings for the parcels, dated 18 June 2007 (RES4, RES5, RES6, and RES9a) and 12 August 2008 (RES8 and RES9b). We also reviewed the 16 November 2007 project drawings for commercial locations STA 1 through 5, which would provide acoustical shielding for the residential locations from the railway. We prepared a refined traffic noise model of the 2020 ABAG plus project to reflect the setback distances from roadway lane centerlines to adjacent building facades. For facades exposed to a DNL exceeding 60 db, the resulting cumulative train and vehicular traffic noise was quantified for the residential facades as follows: Location RES8 RES9a RES9b TABLE 1: CALCULATED NOISE LEVELS AT RESIDENTIAL FACADES Exterior Noise Level (DNL) 70 db or less depending on setback from 31 st Avenue 70 db or less depending on setback from 31 st Avenue and Delaware Street 70 db or less depending on setback from 31 st Avenue and Delaware Street Our calculations indicate that facades for buildings within RES4, RES5, and RES6 would be exposed to a DNL less than 60 db. ASSESSMENT OF NOISE Interior Noise Mitigation To allow the project to meet the interior acoustical requirement of a DNL not exceeding 45 db in residential dwellings, sound rated assemblies (i.e., windows and exterior doors) will be required at some of the building facades. We have prepared Figures 1 through 4 indicating the required preliminary mitigation measures in terms of Sound Transmission Class (STC) 3 ratings to allow the project to meet the criteria. Since the specified ratings are based on assumed unit layouts (e.g. approximately 150 to 200 square-feet with 8-foot ceilings, carpeted or hard surface floors, approximately 25% to 50% window to wall area ratio, side or corner locations), a qualified acoustical engineer must review the design phase drawings and refine the mitigation measures as necessary. 3 Sound Transmission Class (STC) A single-figure rating standardized by ASTM and used to rate the sound insulation properties of building partitions. The STC rating is derived from laboratory measurements of a particular building element and as such is representative of the maximum sound insulation. Increasing STC ratings correspond to improved noise isolation.
Page 5 of 14 STC ratings for selected assemblies should be based on independent laboratory testing performed in accordance with ASTM E-90 and comprise the entire window assembly, including the frame. If non-tested assemblies are to be used, a qualified acoustical consultant should review the glazing and frame submittals, and the STC rating of the glass may need to be increased. As stated in mitigation measure BM3b, If the windows must remain closed to obtain the required noise reduction, then mechanical ventilation shall be installed in these units. Windows can be still be operable, however maintaining consistency with State Building Code acoustical standards would require an alternate means of providing outside air to habitable spaces (e.g., HVAC with fresh-air intake, etc.) for facades exposed to an exterior L dn of 60 db, or greater. This corresponds to units containing the following facades: TABLE 3: LOCATIONS REQUIRING VENTILATION FOR ACOUSTICAL MITIGATION Location Building RES8 Building RES9a Building RES9b Impacted Facades All southern, eastern, and western facades within 110-feet of the 31 st Avenue centerline All homes within 110-feet of the 31 st Avenue centerline All homes within 120-feet of the Delaware Street centerline All southern, eastern, and western facades within 110-feet of the 31 st Avenue centerline All northern, western, and southern facades within 85-feet of the Delaware Street centerline In conclusion, the mitigation provided in this report addresses the future noise environment (i.e., cumulative railway and vehicular noise levels) and will allow the project to reduce interior noise levels to meet all requirements specified in the acoustical criteria section above. * * *
Page 6 of 14 This concludes our residential interior noise analysis for the Bay Meadows Phase II SPAR 2 project in San Mateo, California. Should you have any questions, please call us. CHARLES M. SALTER ASSOCIATES, INC. Timothy G. Brown Principal Consultant Robert P. Alvarado Vice President
Page 11 of 14 A P P E N D I X A FUNDAMENTAL CONCEPTS OF ENVIRONMENTAL NOISE This section provides background information to aid in understanding the technical aspects of this report. Three dimensions of environmental noise are important in determining subjective response. These are: The intensity or level of the sound The frequency spectrum of the sound The time-varying character of the sound Airborne sound is a rapid fluctuation of air pressure above and below atmospheric pressure. Sound levels are usually measured and expressed in decibels (db), with 0 db corresponding roughly to the threshold of hearing. The "frequency" of a sound refers to the number of complete pressure fluctuations per second in the sound. The unit of measurement is the cycle per second (cps) or hertz (Hz). Most of the sounds, which we hear in the environment, do not consist of a single frequency, but of a broad band of frequencies, differing in level. The name of the frequency and level content of a sound is its sound spectrum. A sound spectrum for engineering purposes is typically described in terms of octave bands, which separate the audible frequency range (for human beings, from about 20 to 20,000 Hz) into ten segments. Many rating methods have been devised to permit comparisons of sounds having quite different spectra. Surprisingly, the simplest method correlates with human response practically as well as the more complex methods. This method consists of evaluating all of the frequencies of a sound in accordance with a weighting that progressively deemphasizes the importance of frequency components below 1000 Hz and above 5000 Hz. This frequency weighting reflects the fact that human hearing is less sensitive at low frequencies and at extreme high frequencies relative to the mid-range. The weighting system described above is called "A"-weighting, and the level so measured is called the "A-weighted sound level" or "A-weighted noise level." The unit of A-weighted sound level is sometimes abbreviated "dba." In practice, the sound level is conveniently measured using a sound level meter that includes an electrical filter corresponding to the A-weighting characteristic. All U.S. and international standard sound level meters include such a filter. Typical sound levels found in the environment and in industry are shown in Figure A-1. Although a single sound level value may adequately describe environmental noise at any instant in time, community noise levels vary continuously. Most environmental noise is a
Page 12 of 14 conglomeration of distant noise sources, which results in a relatively steady background noise having no identifiable source. These distant sources may include traffic, wind in trees, industrial activities, etc. and are relatively constant from moment to moment. As natural forces change or as human activity follows its daily cycle, the sound level may vary slowly from hour to hour. Superimposed on this slowly varying background is a succession of identifiable noisy events of brief duration. These may include nearby activities such as single vehicle pass-bys, aircraft flyovers, etc. which cause the environmental noise level to vary from instant to instant. To describe the time-varying character of environmental noise, statistical noise descriptors were developed. "L10" is the A-weighted sound level equaled or exceeded during 10 percent of a stated time period. The L10 is considered a good measure of the maximum sound levels caused by discrete noise events. "L50" is the A-weighted sound level that is equaled or exceeded 50 percent of a stated time period; it represents the median sound level. The "L90" is the A-weighted sound level equaled or exceeded during 90 percent of a stated time period and is used to describe the background noise. As it is often cumbersome to quantify the noise environment with a set of statistical descriptors, a single number called the average sound level or "L eq " is now widely used. The term "L eq " originated from the concept of a so-called equivalent sound level which contains the same acoustical energy as a varying sound level during the same time period. In simple but accurate technical language, the L eq is the average A-weighted sound level in a stated time period. The L eq is particularly useful in describing the subjective change in an environment where the source of noise remains the same but there is change in the level of activity. Widening roads and/or increasing traffic are examples of this kind of situation. In determining the daily measure of environmental noise, it is important to account for the different response of people to daytime and nighttime noise. During the nighttime, exterior background noise levels are generally lower than in the daytime; however, most household noise also decreases at night, thus exterior noise intrusions again become noticeable. Further, most people trying to sleep at night are more sensitive to noise. To account for human sensitivity to nighttime noise levels, a special descriptor was developed. The descriptor is called the DNL (Day/Night Average Sound Level), which represents the 24-hour average sound level with a penalty for noise occurring at night. The DNL computation divides the 24-hour day into two periods: daytime (7:00 am to 10:00 pm); and nighttime (10:00 pm to 7:00 am). The nighttime sound levels are assigned a 10 db penalty prior to averaging with daytime hourly sound levels. For highway noise environments, the average noise level during the peak hour traffic volume is approximately equal to the DNL.
Page 13 of 14 The effects of noise on people can be listed in three general categories: Subjective effects of annoyance, nuisance, dissatisfaction Interference with activities such as speech, sleep, and learning Physiological effects such as startle, hearing loss The sound levels associated with environmental noise usually produce effects only in the first two categories. Unfortunately, there has never been a completely predictable measure for the subjective effects of noise nor of the corresponding reactions of annoyance and dissatisfaction. This is primarily because of the wide variation in individual thresholds of annoyance and habituation to noise over time. Thus, an important factor in assessing a person's subjective reaction is to compare the new noise environment to the existing noise environment. In general, the more a new noise exceeds the existing, the less acceptable the new noise will be judged. With regard to increases in noise level, knowledge of the following relationships will be helpful in understanding the quantitative sections of this report: Except in carefully controlled laboratory experiments, a change of only 1 db in sound level cannot be perceived. Outside of the laboratory, a 3 db change is considered a justnoticeable difference. A change in level of at least 5 db is required before any noticeable change in community response would be expected. A 10 db change is subjectively heard as approximately a doubling in loudness, and would almost certainly cause an adverse community response.
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