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HomeMy WebLinkAboutCT 05-12; Ocean Street Residences; Tentative Map (CT) (10)• ' May 9, 2005 Mr. Tim Clark Prospect Point Development 1020 Prospect Ave, Suite 314 La Jolla, CA 92037 Corporate Office 16486 Bernardo Center Drive, #278 San Diego, CA 92128 Phone/Fax: (858) 451-3505/ (858) 487-0096 www.ise.us RE: ACOUSTICAL AND GROUND VIBRATION SITE ASSESSMENT OCEAN STREET RESIDENTIAL DEVELOPMENT-CARLSBAD, CA ISE REPORT #05-052 Dear Mr. Clark: At your request, Investigative Science and Engineering {ISE} have performed an acoustical and ground vibration site assessment of the proposed Ocean Street residential development project located in the City of Carlsbad, CA. The main focus of the assessment was to identify any impact potential due to nearby operations along the San Diego Northern Railway {SDNR}. The results of that survey, as well as predicted future noise and vibration levels at the project site, are presented in this letter report. • INTRODUCTION AND DEFINITIONS Existing Site Characterization The proposed Ocean Street residential development site consists of approximately 3.05 acres within the northwest quadrant of the City of Carlsbad {refer to Figure 1 below} and is physically addressed as 2303 Ocean Street, Carlsbad, CA 92008. The subject site is currently developed with 50 apartment units in three separate buildings that were built in the mid-1960's. Access to the existing apartments is provided from Ocean Street via residential driveways located at each end of the development. An existing residential development, the Rue Des Chateaux condominiums, resides to the immediate west with mixed single-and multi-family residential uses to the south along Ocean Street. Buena Vista Lagoon forms the northern property line of the project site while a private access drive to a single-family residential structure forms the eastern boundary. The San Diego Northern Railway {SDNR} mainline right-of-way resides immediately opposite the private drive to the east {refer to Figure 2 on Page 3}. Elevations onsite range between 10-to 45-feet above mean sea level (MSL} as viewed from north to south with the site having mostly a depressed nature with respect to the surrounding properties. ACOUSTICS -VIBRATION-4/R QUALITY -FORENSIC ENGINEERING -EXPERT WITNESS-ENVIRONMENTAL ASSESSMENTS Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 2 of23 Pac/flc Ocean FIGURE 1: Project Vicinity Map-Ocean Street Residences (ISE 5/05) 2005 lnvc l•gr~livc Sc• n c and t ngmc m lr ~mi 0 y. % % 1 1Y. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 3 of23 SAN tMEGO 'NORTHERN RAfLW~Y (SON"R) .,~~ "c~ ~-~-,., t; \ l \f ~/ \ ~ • ..s~~ ._-1<- .. ._-1<- c./ N '~ ·•· • il s q. ~ ~ft 0 1 00 200 300 400 500 FIGURE 2: Project Location Map -Ocean Street Residences (ISE 5/05) 2005 lnvr I g<~llvo Scwnco and £ngm nng Inc -------------------------------, Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 4 of 23 Project Description The project is proposing to demolish the existing apartment buildings onsite and construct 35 new stacked-flat condominium units within the original project site footprint as can be seen in Figure 3 below. Amenities would include a pool and spa area as well as limited outdoor recreation space that would be classified as sensitive outdoor use space. The closest separation distance between the proposed development condominiums and the SDNR alignment is 175 feet. FIGURE 3: Proposed Site Development Plan (Jack Henthorn & Associates, 4/05) Acoustical Definitions Sound waves are linear mechanical waves. They can be propagated in solids, liquids, and gases. The material transmitting such a wave oscillates in the direction of propagation of the wave itself. Sound waves originate from some sort of vibrating surface. Whether this surface is the vibrating string of a violin or a person's vocal cords, a vibrating column of air from an organ or clarinet, or a vibrating panel from a loudspeaker, drum, or aircraft, the sound waves generated are all similar. All of these vibrating elements alternately compress the surrounding air during forward motion and expand it on the backward movement. 2005 tnvcsltgaltvc Sctonco and Engineering. Inc Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 5 of23 There is a large range of frequencies within which linear waves can be generated, sound waves being confined to the frequency range that can stimulate the auditory organs to the sensation of hearing. For humans this range is from about 20 Hertz (Hz or cycles per second) to about 20,000 Hz. The air transmits these frequency disturbances outward from the source of the wave. Sound waves, if unimpeded, will spread out in all directions from a source. Upon entering the auditory organs, these waves produce the sensation of sound. Waveforms that are approximately periodic or consist of a small number of periodic components can give rise to a pleasant sensation (assuming the intensity is not too high), for example, as in a musical composition. Noise, on the other hand, can be represented as a superposition of periodic waves with a large number of components. Noise is generally defined as unwanted or annoying sound that is typically associated with human activity and which interferes with or disrupts normal activities. Although exposure to high noise levels has been demonstrated to cause hearing loss, the principal human response to environmental noise is annoyance. The response of individuals to similar noise events is diverse and influenced by the type of noise, the perceived importance of the noise and its appropriateness in the setting, the time of day, and the sensitivity of the individual hearing the sound. Airborne sound is a rapid fluctuation of air pressure above and below atmospheric levels. The loudest sounds that the human ear can hear comfortably are approximately one trillion (or 1x1012) times the acoustic energy that the ear can barely detect. Because of this vast range, any attempt to represent the acoustic intensity of a particular sound on a linear scale becomes unwieldy. As a result, a logarithmic ratio originally conceived for radio work known as the decibel (dB) is commonly employed. A sound level of zero "0" dB is scaled such that it is defined as the threshold of human hearing and would be barely audible to a human of normal hearing under extremely quiet listening conditions. Such conditions can only be generated in anechoic or "dead rooms". Typically, the quietest environmental conditions (extreme rural areas with extensive shielding) yield sound levels of approximately 20 dB. Normal speech has a sound level of approximately 60 dB. Sound levels above 120 dB roughly correspond to the threshold of pain and would be associated with sources such as jet engine noise or pneumatic equipment. The minimum change in sound level that the human ear can detect is approximately 3 dB. A change in sound level of 10 dB is usually perceived by the average person as a doubling (or halving) of the sounds loudness. A change in sound level of 1 0 dB actually represents an approximate 90 percent change in the sound intensity, but only about a 50 percent change in the perceived loudness. This is due to the nonlinear response of the human ear to sound. As mentioned above, most of the sounds we hear in the environment do not consist of a single frequency, but rather a broad band of frequencies differing in sound level. The intensities of each frequency add to generate the sound we hear. The method Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad. CA ISE Report #05-052 May9, 2005 Page 6 of 23 commonly used to quantify environmental sounds consists of determining all of the frequencies of a sound according to a weighting system that reflects the nonlinear response characteristics of the human ear. This is called "A" weighting, and the decibel level measured is called the A-weighted sound level (or dBA). In practice, the level of a noise source is conveniently measured using a sound level meter that includes a filter corresponding to the dBA curve. Although the A-weighted sound level may adequately indicate the level of environmental noise at any instant in time, community noise levels vary continuously. Most environmental noise includes a conglomeration of sounds from distant sources that create a relatively steady background noise in which no particular source is identifiable. For this type of noise, a single descriptor called the Leq (or equivalent sound level) is u!!ed. Leq is the energy-mean A-weighted sound level during a measured time interval. It is the 'equivalent' constant sound level that would have to be produced by a given source to equal the average of the fluctuating level measured. For most acoustical studies, the study interval is generally taken as one-hour and is abbreviated Leq-h; however, other time intervals are utilized depending on the jurisdictional preference. Another similar acoustical descriptor known as the Single Event Level (or SEL) is u!!eful in describing sounds that are of a short duration (such as a single train pass by) or of a highly fluctuating nature. SEL is defined as that constant sound level that has the same amount of energy in one second as the original noise event. Thus, SEL is similar to Leq in that the total sound energy is integrated over the measurement period, but instead of then averaging it over the entire measurement period (as is done with Leq); a reference duration of one-second is used. Thus, a simple relationship between Leq and SEL can be developed that allows the calculation of the hourly Leq from a series of smaller SEL's. This representation can be seen as, where, n SEL; T Leq = lOlog~)oto -lOlog- '=' To SEL, is the Single Event Level at time interval 'i' T is the time interval of the event, T0 is a reference time duration (typically one second) n is the number of time intervals For the calculation of Leq-h the above equation reduces to, n SEL; n SEL; Leq(h) = 10Log10(~)o to) -l0Log10 (3600) = 10Log10(~)o to)-35.56 i=l i=l To describe the time-varying character of environmental noise, the statistical noise descriptors L 10, L50, and L90 are commonly used. They are the noise levels Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocearl Street Residential Development-Carlsbad, CA ISE Report #05-052 May9. 2005 Page 7 of 23 equaled or exceeded during 1 0 percent, 50 percent, and 90 percent of a stated time. Sound levels associated with the L 10 typically describe transient or short-term events, while levels associated with the L90 describe the steady state (or most prevalent) noise conditions. In addition, it is often desirable to know the acoustic range of the noise source being measured. This is accomplished through the maximum and minimum measured sound level (Lmax and Lmin) indicators. The Lmin value obtained for a particular monitoring location is often called the acoustic floor for that location. Finally, a sound measure employed by the State of California (and adopted by the City of Carlsbad) is known as the Community Noise Equivalence Level (or CNEL) is defined as the "A" weighted average sound level for a 24-hour day. It is calculated by adding a 5-decibel penalty to sound levels in the evening (7:00p.m. to 10:00 p.m.), and a 10-decibel penalty to sound levels in the night (10:00 p.m. to 7:00a.m.) to compensate for the increased sensitivity to noise during the quieter evening and nighttime hours. Ground Vibration Motion Definitions Vibration is generally defined as any oscillatory motion induced in a structure or mechanical device as a direct result of some type of input excitation. The object (either structure or machine) of interest typically has sufficient inertia (defined as the quantity 'm') so that by Newton's first law of motion, its rest state is one of zero vibration with the velocity (v) = 0. Input excitation, generally in the form of an applied external force (Fex1) or displacement, is the mechanism required to start some type of vibratory response. Thus, d -(mv)="' F=O dt £..,Ext Once an object begins to respond to an applied excitation, its natural tendency is to vibrate as a linear combination of its natural frequencies. A natural frequency is defined as the frequency at which an object will vibrate if set into motion and allowed to move freely. Any continuous system of particles (such as a building or motor assembly) will have an infinite number of natural frequencies, with each one adding to the overall response in a sea of ever-decreasing contributions. As the frequency (f) of the excitation approaches one of the objects natural frequencies the magnitude of the objects vibratory response (e.g., displacement) increases until, when the two frequencies are exact, a condition known as resonance arises. At resonance, the amplitude of the response of the object theoretically approaches infinity. The only natural mechanism available to temper the catastrophic effects of resonance is the objects own inherent level of damping. Little is currently known about the actual physical mechanisms that produce damping in an object, although, a great deal is known about what effects it produces. Damping can be thought of as a type of 'drag force or resistance' that is always present Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 8 of 23 to some degree in an object and serves to remove energy from the vibrating system as it moves. Artificial damping is used routinely in mechanical devices and takes the form of shock absorbers, viscous isolation materials, and simple friction. In structures or soils/rock, damping is generally present within the material itself and hence is called 'material damping'. The cause of this damping is due to the interactions between the molecular lattice structures comprising the material itself. Damping of surface (or Rayleigh) waves in soils typically occurs as a combination of distance attenuation (radiation damping) and material damping. The latter is commonly approximated using a linear damping model that assumes the overall material damping to increase as a function of distance between the source and receiver (i.e., the more soil between the source and receiver, the greater the material damping level). The final inherent property of a vibrating system is its stiffness (k). The stiffness of a system is what allows an object to store the energy imparted to it through an excitation and redistribute it in the form of a vibration. Without some form of stiffness, an object simply will not vibrate. Mechanical forms of stiffness take the forms of springs while in a structural and soil system the stiffness is inherent in the material. Table 1 on the following page provides a tabular representation of typical vibration sources and their effects on buildings, equipment, and humans. The peak ground velocity produced by various disturbances is given throughout a wide spectrum ranging from the infinitesimal to the severe. This figure is a compilation from various sources (textbooks, research papers, international standards, and past demonstrated engineering tolerance levels). Additionally, a graphical representation of the range of ambient ground motion typically observed is shown in Figure 4 on Page 10. As can be seen, there is no such thing as a perfect zero vibration area since even the Earth itself produces micro scale (teleseismic) vibration that can be readily measured with sensitive instrumentation. For most practical applications, induced mechanical and/or structural vibrations are a thing to be avoided since they are generally unwanted and according to their magnitude can produce physical discomfort, misalignment of equipment, loosening of mechanical fasteners, product defects, and skewed research results. In the case where the excitation frequency is close to resonance or of sufficient magnitude (such as in an earthquake), severe structural damage can occur. Finally, in a manner similar to the measurement of environmental noise, ground borne vibration varies as a function of time (t) and/or frequency. Thus it is convenient to describe this ground motion in terms of single number descriptors such as the maximum and/or peak particle velocities (LmaxvRMs or LmaxwEAK). Similar metrics for minimum vibration levels are employed where applicable, however the lowest threshold is typically limited by some outside source or even the Earth itself (again refer to Figure 4 ). For most ground motion studies, the study interval is typically short (under five minutes); however, other time intervals are utilized depending on the jurisdictional preference. • Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 9 of 23 TABLE 1: Typical Vibration Sources and Sensitivities TYPICAL VIBRATION SOURCES EFFECTS OF VIBRATION Peak Ground Velocity Transportation Construction Structural Human People & (In/Sec) Sources Sourcea Natural Sourcaa Damage Perception Equipment Tolerance 100 -San Francisco, CA Earthquake 4/18/06 ..Santa Cruz, CA Earthquake Intolerable 10 10/17189 -Coalinga, CA -Structural Human Exposure Earthquake 512183 Damage (ISO Llm~s) ~Minor Damage 1 Minute Blasting at 50 ft. Extremely 1 Hours Unpleasant ·low Probability of 1.0 Damage Very Unpleasant 8 Hours Unpleasant 24 Hours Pile--Driving ·Typical Moooquake at SOft. 0.1 -Very Safe Buildings Strongly Truck or dozer Noticeable Computers at 50ft. Subway Train (Meas. Easily Noticeable above tunnel Office 0.01 Motor Vehicle TraffiC Jackhammer Barely PerceptJbte Residences at 50 Ft. on Rough at SO ft. Road'Ytay and Elevated Highway 0.001 Motor Vehicle Traffic Optical Microscopes at 50 Ft. on Smooth Blasting@ 500ft. -MicroMeteorite lmparceptible Roadway and At~ Impacts at 50 ft. grade Highway Pile Driving Electronic Truck at 50 Ft. on at 500ft. Microscopes 0.0001 Rough Roadway Source: ISE 1997-2004 APPLICABLE SIGNIFICANCE CRITERIA City of Carlsbad The Noise Element of the City of Carlsbad identifies certain sound levels that are compatible with various land uses. According to the City of Carlsbad Noise Guidelines Manual, sound levels up to 60 dBA CNEL are compatible with sensitive outdoor use areas within residential land uses. This standard is applied to vehicular traffic, aircraft over flight, and rail generated noise. The City also requires an interior noise study (compliant with State of California CCR Title 24 standards) where exterior exposure is in excess of the above land use criteria. Proposed outdoor areas contained within the Ocean Street residential development that would be classified as usable outdoor living space, would include the pool and spa area as well as common recreation space adjacent to the lagoon as shown in Figure 3. ' 2005 lnvcsliga/Jvc Science and Engincenng, Inc. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 10 of 23 N 1 o-2 1/J ........... E -1 o-4 c 0 -+-' 0 .._ 1 o-6 Q) Q) u Earth u <( Normal 1 o-8 Modes 1 o-10 Maximum Earthquake :+-e ve> ~~-~oO,, »<S'' , ,._,<"', , ~~- Normal Modes Surface Waves Teleseismic Body Waves Local Body Waves 10-5 10-4 1 o-2 10-1 Frequency, Hz FIGURE 4: Typical Ground Vibration Levels (NASA Lunar and Planetary Institute -1995) State of California CCR Title 24 The California Code of Regulations (CCR), Title 24, Noise Insulation Standards, states that single-and multi-family dwellings, hotels, and motels located where the CNEL exceeds 60 dBA, must obtain an acoustical analysis showing that the proposed design will limit interior noise to less than 45 dBA CNEL. Worst case noise levels, either existing or future, must be used for this determination. Future noise levels must be predicted at least ten years from the time of building permit application. The City of Carlsbad has adopted the CCR Title 24 standards. U.S. Bureau of Mines Rl 8507 Vibration Criteria The United States Bureau of Mines provides a well-defined impact guide to vibration on structures. This assessment was originally developed to catalog the observable effects of blasting on structures due to ground vibration. The criteria are well accepted for all types of ground vibration excitation since the fundamental parameter in all cases is the peak particle velocity (LmaxvPEAK) of the receiving structure. This criterion is identified below in Table 2. c 2005 lnvesttgaftv(' Scwnco and EnginC'anng I• r Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 11 of23 TABLE 2: US Bureau of Mines Rl 8507 Ground Vibration Standards VIbration Frequency Component (I) (Hz.) 2.5 to 10.0 11.0to40.0 >40.0 Maximum Allowable Peak Particle Velocity (Lmaxv, .. K) (Inches per second) 0.05 0.05 X f 2.0 It is noted for clarification that the maximum allowable peak particle velocity for the range of frequencies between 11.0 and 40.0 Hz. is limited to the value of 0.05 times the dominant frequency (f). Thus, if the frequency were 30.0 Hz. the maximum allowable particle velocity at the monitoring point would be 1.5 inches per second. The above standards are based upon the Bureau of Mines report Rl 8507, "Structure Response and Damage Produced by Ground Vibrations from Surface Blasting". This criterion presented, which is similar to the earlier Bureau of Mines Bulletin 656, sets the maximum peak particle velocity as a function of frequency. It has been shown by the Bureau that these vibratory excitation levels would produce negligible effects (displacement, fatigue, and damage) in conventionally constructed structures (i.e., structures built within the past 100 years). For conventionally constructed structures, such as the surrounding residential structures, a common upper rule-of-thumb for vibration exposure is a maximum of 2.0 inches per second (with the applicable adjustments for frequency as shown in Table 2). Levels for historic or antiquated structures are typically half this value, or 1.0 inches per second (again, adjusted for frequency content). ISO Human Vibration Standards The International Organization for Standardization (ISO) has developed design goals based on human response to vibration. Typical tolerance requirements pertaining to vibration effects on machines and structures are generally a function of the object's construction, projected service life, materials used, design strategy, operational environment, and resilience to unexpected types of loading. For the types of equipment proposed, these factors (and many more) contribute to the overall service life of the structure. ISO Standard 2631 Part 2 (Evaluation of human exposure to whole body vibration - Continuous and shock induced vibration in buildings) contains guidelines pertaining to human exposure to vibration. The recommended continuous excitation levels (in LeqVRMs) are based upon the various types of activities and building occupancy. These levels fall within the 'Easily Noticeable' to 'Barely Perceptible' range within the second to the last column of Table 1. The complete ISO human vibration standards are given in the last column of Table 1. Additionally, maximum (or shock induced) vibration levels have a lower recommended level as shown in Table 3 below. The criteria is based upon the maximum RMS 1/3 octave band level (LmaxVRMs) measured and would be utilized when siting a proposed vibration sensitive project. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 12 of23 TABLE 3: ISO 2631 Recommended Maximum Single Event Vibration Levels Land Use Classification Residential (Daytime) Resider'ltial (Nighttime) School Areas (Anytime) Office Buildings Source: ISO Standard 2631 -Part 2 • ANALYSIS METHODOLOGY Ambient Noise Monitoring Procedure Recommended RMS Maximum 1/3 Octave Band VIbration Laval (In/sac) 0.007 0.005 0.007 0.015 A Quest Model 2900 ANSI Type 2 integrating sound level meter was used as the acoustical data collection device. The meter (denoted as NML 1) was mounted to a tripod approximately five feet above the ground and was placed in the center of an existing outdoor space (BBQ patio area) approximately 180 feet from the SDNR alignment. Monitoring was performed during afternoon commuter rail activity. The monitoring location is shown graphically in Figures 5a through -c on the following page. All equipment was calibrated before testing at ISE's acoustics and vibration laboratory to verify conformance with ANSI S1-4 1983 Type 2 and IEC 651 Type 2 standards. Ambient Vibration Monitoring Procedure In a similar manner, vibration-monitoring location VML 1 was instrumented using a Kinemetrics Ranger Model SS-1 moving-coil short period field seismometer. This instrument, which is a terrestrial version of the lunar seismometer developed for NASA, is a direct velocity-reading instrument capable of measuring inertial changes into the micro-inch-per-second range (the equivalent of footfalls one city block away). Location VML 1 was placed at the edge of an existing outdoor space (BBQ patio area) approximately 175 feet from the SDNR alignment. This location corresponds to the nearest condominium structure proposed under the development plan and is shown in Figures 5c through -e. The generator constant of the seismometer used was 9070 mV/in/sec with a natural period of one second. The seismometer was positioned in the vertical (z-axis) direction consistent with the ground excitation direction for rail activity. All signals were fed through shielded cable to a Stanford research Systems Model SR 760 FFT spectrum analyzer for analysis and recording. The cable length used was at least 75 feet to ensure adequate isolation of the experimenter and the monitoring location. Measurements were taken for both the ambient background condition as well as for active rail pass by events. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 13 of23 FIGURES 5a through -e: Ambient NoiseNibration Monitoring Setup (ISE, 5/05) © 2005 lnvcsttgattvo Sctonco nnd Engmoonng Inc. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad. CA ISE Report #05-052 May 9, 2005 Page 14 of 23 Traffic Segment Impact Assessment Approach The ISE RoadNoise v2.0 traffic noise prediction model which is based upon Caltrans Sound 32 Traffic Noise Prediction Model with California (CALVENO) noise emission factors (based on FHWA RD-77-108 and FHWA/CA/TL-87/03 standards) was used to calculate the worst-case vehicular traffic noise levels along major servicing roadways adjacent to the proposed development site. The model assumed a 'hard-site' propagation rule (i.e., 3.0 dBA loss per doubling of distance (DD) between source and receiver) to account for worst-case line of sight conditions. No adjustments were taken for existing structures or soft topography (which would further reduce onsite noise levels), thereby yielding a representative worst-case noise contour set. Traffic noise model input included predicted future (SANDAG Series 10 year 2030) Average Daily Traffic (ADT) levels for Carlsbad Boulevard (CR S21) assuming a 10% flow pattern and a 96/2/2 (automobiles/medium trucks/heavy trucks) mix. The modeled traffic speed was 35 MPH per posted conditions. All other identified roadways would have trip generation levels far below the 2,000 ADT level (which is the threshold where the 60 dBA CNEL noise contour leaves road right of way). For peak hour traffic percentages between approximately 8 and 12 percent, the energy-mean A-weighted sound level is equivalent to the 24-hour Community Noise Equivalent Level (CNEL). Outside this range, a maximum variance of up to two dBA occurs between Leq-h and CNEL. Rail Noise Impact Assessment Procedure The San Diego Northern Railway (SDNR) alignment produces an approximate daily 12 (daytime) and 3 (evening) rail round trips due to commuter and freight travel (Source: North County Transit District, 1999-2005). This condition is not expected to change in the future. The average rail speed adjacent to the project site is 30 to 35 MPH depending on whether the traffic is slowing upon approach/departure to the Carlsbad Village Station (for commuter traffic) or continuing into San Diego (for freight an non-stop commuter traffic). The impact methodology employed herein was to model the rail noise exposure using an energy-based approach. Acoustic performance for the existing rail activity was examined using pass by emission levels or Single-Event Noise Levels (SELs), which are an indicator of the acoustic energy generated by a single train pass by as a function of speed (Source: Mitigation Compliance and Conformity Assessment, NCTD Oceanside- Escondido Sprinter Rail Project, ISE Report #03-088 dated March 14, 2004, and the Noise and Vibration Technical Report for the Oceanside-Escondido Rail Project, Ogden Environmental and Energy Services, 10/96). As shown previously, this reduces to, n SEL1 l..eq(h) = 10Log10(L10 10 )-35.56 i=l Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 15 of23 From the calculated hourly Leq values above, an equivalent CNEL can be derived based upon the proposed hourly operational data. This level is determined via the following expression: where, 1 n ( Leq(day)1 Leq(evening+5); Leq(night+10); J CNEL = 10Log10 -L 10 10 + 10 10 + 10 10 n i=t Leq(x)1 is the equivalent sound level during period 'x' at time interval 'i' and 'n' is the number of time intervals. Or treating each time interval separately yields, CNEL = 10Log10 L 10 IO + L 10 10 + L 10 10 1 [ p [ L•q(day), J q [ L<q(.,.,.ing+5), J , ( uq(night+IO), J] p+q+r i=l i=l i=l This is the form in which CNEL is most commonly calculated. The calculated Leq and CNEL values due to rail noise exposure at the closest sensitive receptor point within the project site were examined using this formulation. Soil Damping Estimation Procedure The relative soil damping level was based upon empirical field data obtained in the past by ISE (1997-2005) by examining the relative decay of the average soil response spectrum over a fixed distance. This method, which could be considered a modification of the Half-Amplitude method of engineering dynamics, calculates the relative amount of soil damping present in a particular vibratory mode. Typical soil (material) damping levels (i.e., the Material Damping Percentage per foot or ~(%) I ft) for the sandy soil types found at the project site would range between 0.05% to 0.1 %. Given this, a median level of 0.075% will be used for the Ocean Street residential project site, as it is representative of the soil conditions onsite and within the surrounding community. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 16 of23 Rail-Related Ground Motion Modeling A ground vibration assessment was performed using ISE's WaveProp 2.0 Program. The WaveProp program calculates the maximum theoretical ground response based upon a single degree of freedom (SDOF) dynamic curve fit of the experimental data. The program essentially seeks to mathematically fit the following SDOF system, to the experimentally measured data as a function of time and distance. In the above expression, u, u and u represent the acceleration, velocity, and displacement motion of the soil, s represents the level of soil damping per foot, Wn represents the natural frequency of the system (which is a function of the soil type) and H(O.) is the applied initial input excitation (rail induced ground vibration) as a function of frequency. The model output is a graphical representation of the vibratory decay response as a function of distance from the source. Boundary Element Analysis of Rayleigh Wave Propagation Additionally, a more refined method of predicting ground motion due to construction activity was performed using ISE's R-Wave 2.6 Program . The R-Wave program calculates the maximum theoretical Rayleigh wave response using a constrained boundary element method based upon input considerations such as maximum soil particle excitation and dynamic material properties. The motion of the advancing Rayleigh waves particle response for which the model predicts as a function of frequency (for dispersion analysis) and depth below the soil/rock is shown graphically in Figure 6 below. • • • • • '-----1 ELLIPTICAL MOTION I FIGURE 6: Typical Rayleigh Wave Propagation Profile 2005/nvcstrgatJVn Sc1arrcc nnd l ng111carmg Inc Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 17 of23 Rayleigh waves are the slowest of all the seismic wave types and in some ways the most complicated. They are dispersive waves (with the soil particles moving in retrograde elliptical paths), so the particular speed at which they travel depends on the wave period and the near-surface geologic structure. These waves also decrease in amplitude with depth. Typical speeds for Rayleigh waves are on the order of 1 to 5 km/s. A complete treatment and discussion of the model and underlying theory can be found in the following document, "Determination of Blast-Induced Dynamic Soil Response Using Axisymmetric Boundary Elements-© Rick Tavares, UCI Press, 2001 ". • FINDINGS I RECOMMENDATIONS Existing Ambient Noise Conditions Testing conditions during the monitoring period were sunny with an average barometric pressure reading of 29.99 in-Hg, an average easterly wind speed of 2 to 4 miles per hour (MPH), and an approximate mean temperature of 74 degrees Fahrenheit. The results of the sound level monitoring are shown below in Table 4. The values for the equivalent sound level (Leq-h), the maximum and minimum measured sound levels (Lmax and Lmin), and the statistical indicators L 10, L50, and L90, are given for the monitoring location. The observed existing dominant noise source was from distant traffic activity along Carlsbad Boulevard, nearby infrequent helicopter activity along the 1-5 corridor, and periodic rail pass by events. TABLE 4: Measured Ambient Sound Levels-Ocean Street Residential Development II 1-Hour Noise Level Descriptors in dBA Site Start Time Laq Lmax Lmln L10 L50 L90 NML 1 (with rail activity) 3:00 PM 52 67 41 54 45 42 Measurements performed by ISE on 513/05. Noise levels on site were consistent with the observed community setting and depressed topography with respect to any nearby roadways. The value for the equivalent sound level (Leq-h) for the project site averaged 52 dBA during the afternoon period monitored. This is consistent with the topography of the monitoring location, which isolates most environmental sounds except rail noise. Background noise levels (i.e., L90 levels) were considerably lower than their energy equivalent counterparts (Leq-h) indicating the infrequency of the noise events and would be indicative of a rail-noise-only condition. The acoustic floor, as indicated by the Lmin metric, was found to be 41 dBA regardless of the presence of rail activity. Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 18 of 23 Existing Ambient Ground Motion Conditions The ambient ground vibration response is shown below in Figure 7 for three different ambient trials (A1 through A3) and four different train pass by events {T1 through T4) at location VML 1. The calculated responses exclude the previously identified system resonance of one second. As can be seen from the plot, there is very little variation in ambient ground motion throughout the structural/human range (0 to 50 Hz) of interest with baseline motion averaging 8.26 x 1 o·7 inches per second (or 0.826 micro-inches per second for LeqVRMs). This motion is quite probably the culmination of nearby roadway and pedestrian activity and coastal wave action. Given this, the subject property currently experiences negligible baseline ground motion (in the absence of rail activity). Humans would classify this motion as being non- perceptible. The addition of train pass by motion produced elevated ground response yielding average values of 1.15 x 1 o·5 inches per second (or 11 .5 micro-inches per second for LeqVRMs) with the average maximum band level of 7.33 x 10·5 inches per second (or 73.3 micro-inches per second for LmaxVRMs) being indicated. No peak particle exceedances were noted. Figure 8 provides a synopsis of the average ground motion survey results. As can be readily seen from the plot, the measured ground levels drop to the zero point at frequencies above 30 Hz, which is consistent with rail activity observed by ISE in the past. Rail activity, as measured at the proposed project site, would be non-impactive to either humans or structures. l.OOE-Q) i l.OOE·04 l ~ l.OOE-QS .5 1; ~ l.OOE-Q6 "' l .OOE·07 0 0 0 0 "' "' .., ... • "' "' g: !!!l 1l! 21! I!! 11"1 .... .,; ai 9 ,.; ... ~ !:i oi -~ .... ..... :il "' ~ ~ 11"1 11"1 11"1 11"1 ;!; ;$; ... "' .... M 11"1 ": "' ... • ..; ~ ~ .... .,; ,.; oi ... ~ ~ ~ "' "' "' M "' "' M oot fr.quency in Hz. FIGURE 7: Measured Ground Motion Profile at Closest Property Boundary (VML 1 = 175 Feet) 2005 It vosltgaltv(' Scwnw and Lngmoermg In -Al -AJ. A3 -n -T2 TJ -T4 Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May9, 2005 Page 19 of23 7.00E-OS ] 6.00E-OS ~ S.OOE-05 I 4.00E-OS .s c ~ 3.00E-OS ~ 2.00E-OS l.OOE-05 O.OOE+OO 0 0 ci 0 01 01 01 s: .... .... "' ... l'i ~ .0 cxi ci ... II) II) CD II) ... ... ... \D \D ... .... "' ": ~ ... .... Ill ... ..; "' ... 01 ... .... \D cxi ci ... ... ... ... .... N .... N .... Frequency In Hz. -AVGTRAIN -AVG BACKGROUND ~ \D "' "' "' "' .r ~ ... .... Ill ": ~ ... l'i "' ... .,; ... .... .0 cxi .... .... .... .... .... .... .... .... FIGURE 8: Average Ground Motion Profiles at Closest Property Boundary (VML 1 = 175 Feet) Predicted Vehicular Noise Levels along Adjacent Roadways The results showing the effect of traffic noise increases on the various identified servicing roadway segments associated with the proposed project site are presented in Table 5 on the following page. For each roadway segment examined, the average daily traffic volume (ADT) and observed/predicted speed are shown along with the corresponding reference noise level at 50-feet (in dBA). Additionally, the line-of-sight distance to the 60 and 65 dBA CNEL contours are provided as an indication of the worst-case traffic noise contour placement. The worst-case impact contour distance of 415 feet for Carlsbad Boulevard is still outside the placement of the proposed development (which is at least 430 feet distant). Further, the effect of proposed structural placement and soft topography within the development plan would further reduce noise exposure to any sensitive outdoor space by at least 5 to 10 dBA, which would preclude the presence of any exterior acoustical impacts from this or any other roadway. Thus, the resultant sound levels on site would be consistent with that identified during the ambient field survey. Given these findings, no sensitive outdoor use spaces would be exposed to adverse noise conditions. 2005 lnvcsltg<~ltvo Scten o and lngmccnng Inc Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 20 of23 TABLE 5: Worst-Case Noise Contours near Proposed Ocean Street Project Site p.. ....... ~"""""'""""" I .1 Contour Diet. (feet) Roadway Segment Name ADT Vehicle SPLat 65dBA 60dBA Speed 50 feet CNEL CNEL State Street to Carlsbad Village Drive. 18,000 35 69.2 132 415 n Entire Roadway Segment <1,000 25 54.1 4 13 Q(l) Notes: o Average Daily Trips, Source SANDAG Traffic Prediction Model, 5/05. o All vafues given in dBA CNEL. Contours assumed to be line-of-sight perpendicular (.i) distance. Predicted Rail Noise Emission Levels As previously indicated, the San Diego Northern Railway (SDNR) alignment produces an approximate daily 12 (daytime) and 3 (evening) rail round trips due to commuter and freight travel. This equates to roughly two pass by events per hour at any given point along the alignment (as was observed during the onsite field monitoring). The single event noise level (SEL) for any given pass by event ranged between 70.9 to 78.9 dBA at the closest residential receptor location depending on the locomotive unit used, warning systems employed (horn/bells), direction of travel (cars being pulled or pushed), and relative speed. For this analysis the worst-case level of 79 dBA SEL will utilized which more than accounts for the observed variation in noise generation. Following the aforementioned methodology, the hourly equivalent sound level due to round trip rail activity would be, 2 79 Leq(h) = 10Log10(~)0ID)-35.56 = 46.45 dBA z 46.5 dBA i~l The community equivalent sound level due to the identified daily rail operations would therefore be, CNEL=10Log10 -L 1010 + L 10_10_ =48.06dBAz48.1dBA 1 [ 12 ( 46.5) 3 ( 46.5+5 )] 15 '"' '"' Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development-Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 21 of 23 Thus, no acoustical impacts are indicated due to rail activity adjacent to the project site. No remedial mitigation would be required as part of this project. It should be noted though, that although this level is numerically below the 60- dBA CNEL threshold established under CCR Title 24, maximum sound levels due to rail operations could reach instantaneous peaks above 90 dBA due to signaling and warning devices. Operation of such devices during nighttime hours could result in nuisance impacts to sensitive receptors within the development. Thus, it is recommend that interior noise reduction methods (i.e., specialized door and window treatments) equivalent to a sound transmission classification (STC) rating of 30 be examined for potential inclusion into the project design to remediate these issues. Rail-Related Ground Motion Findings A ground vibration assessment was performed using ISE's WaveProp 2.0 Program. The WaveProp program calculates the maximum theoretical ground response based upon a single degree of freedom (SDOF) dynamic curve fit of the empirical data shown in Figure 8 above. The results for a pure 5 Hz wave motion (the worst-case lowest excitation frequency) is shown below in Figure 9 for the soil damping level identified (i.e., 1;, = 0.00075 per foot). Higher frequency content levels were found to produce results similar to that shown in Figure 8 (since the ground motion is driven to zero by the time the wave reached 50 feet from the rail edge -the limits of NCTD's right of way). 0.00001 .....---------------- ~00007 i 1 0.00008 Jr MOOO!i .. ! 0.00004 ~ :e 0.00003 l 1 M0002 a.. 0.00001 .. 100 , .. 200 300 Distance From RIIH Edge (ft) ... FIGURE 9: Predicted Ground Velocity (Source: f= 5.0 Hz., ref= 175', ~1ft= 0.00075, At= 1.0 s) ... Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 22 of23 Boundary Element Analysis of Rayleigh Wave Propagation Finally, the ground motion produced by any surface excitation (such as rail motion) is in-fact a surface wave and would be classified as a Rayleigh-type wave. Wave generation of this type is common during earthquakes (although of a much higher amplitude). These waves have a characteristic 'rolling' motion similar to that of an oceanic wave (as was shown in Figure 6 above). Using ISE's R-Wave 2.6 Program, a prediction of the 'through the ground' response of the observed rail activity is obtained. The results showing the expected vertical and horizontal source wave motion is shown below in Figures 1 Oa and -b for the measured 7.33 x 1 o·5 inches per second source level recorded at the closest sensitive receptor. ~ -!> <b ~ <?> Jr-:F:=RE:-:QU=EN-=:::C~Y ::-:IN-:-:Hz::-1! FIGURE 10a: Predicted Vertical Surface Vibration Levels (175-Feet from Source) 0 lnv ' gatwe Sc:.tell( e and f. n trw ""fl lr Mr. Tim Clark Acoustical and Ground Vibration Site Assessment Ocean Street Residential Development -Carlsbad, CA ISE Report #05-052 May 9, 2005 Page 23 of23 FIGURE 10b: Predicted Horizontal Surface Vibration Levels (175-Feet from Source) As can be seen from the results, no appreciable energy is transmitted through the ground due to the observed and measured rail activity. These findings would be classified as highly uneventful from an engineering standpoint. No significant ground motion impacts are expected. No remedial vibration mitigation would be required. Human (ISO) Vibration Impacts Based upon the findings, the predicted ground motion levels would fall into the category of being imperceivable by humans. Thus, no significant impacts are expected. Should you have any questions regarding the above conclusions, please do not hesitate to contact me at (858) 451-3505. Sincerely, Rick Tavares, Ph.D. Project Principal Investigative Science and Engineering, Inc. Cc: Jeremy Louden -ISE lfJO" lnvc<>l•fl .11vc Sc101• CJ 'llld f ngu o r ng 111