Appendix F Environmental Noise Assessment
TIERRA VILLAS RESIDENTIAL PROJECT ENVIRONMENTAL NOISE ASSESSMENT ANTIOCH, CALIFORNIA September 8, 2009 Prepared for: John Cook CirclePoint 135 Main Street, Suite 1600 San Francisco, CA 94105 Prepared by: Jared M. McDaniel Michael S. Thill ILLINGWORTH & RODKIN, INC. Acoustics Air Quality 505 Petaluma Boulevard South Petaluma, CA 94952 (707) 766-7700 Job No.: 09-043
INTRODUCTION This assessment evaluates the significance of noise impacts resulting from the Tierra Villas residential project proposed in Antioch, California. The project proposes to construct 115 singlefamily residential units west of Heidorn Ranch Road. Included in this report is a brief description of the fundamentals of environmental noise, a summary of applicable regulatory criteria, and the results of the noise monitoring survey made at the project site. Future conditions at the site and surrounding areas are calculated and summarized. The report then evaluates impacts resulting from the project in terms of noise and land use compatibility, permanent noise level increases resulting from project generated traffic, and temporary noise level increases resulting from project construction activities. Mitigation is presented to reduce the significant noise impacts resulting from the project to less than significant levels. FUNDAMENTALS OF ENVIRONMENTAL NOISE Noise is defined as unwanted 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. Decibels and other technical terms are defined in Table 1. Most of the sounds which we hear in the environment do not consist of a single frequency, but rather a broad band of frequencies, with each frequency differing in sound level. The intensities of each frequency add together to generate a sound. The method commonly used to quantify environmental sounds consists of evaluating all of the frequencies of a sound in accordance with a weighting that reflects the facts that human hearing is less sensitive at low frequencies and extreme high frequencies than in the frequency mid-range. This is called "A" weighting, and the decibel level so measured is called the A-weighted sound level (dba). In practice, the level of a sound source is conveniently measured using a sound level meter that includes an electrical filter corresponding to the A-weighting curve. Typical A-weighted levels measured in the environment and in industry are shown in Table 2 for different types of noise. Although the A-weighted noise 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 noise from distant sources which create a relatively steady background noise in which no particular source is identifiable. To describe the time-varying character of environmental noise, the statistical noise descriptors, L 01, L 10, L 50, and L 90, are commonly used. They are the A-weighted noise levels equaled or exceeded during 1%, 10%, 50%, and 90% of a stated time period. A single number descriptor called the L eq is also widely used. The L eq is the average A-weighted noise level during a stated period of time. In determining the daily level of environmental noise, it is important to account for the difference in response of people to daytime and nighttime noises. During the nighttime, exterior background noises are generally lower than the daytime levels. However, most household noise also decreases at night and exterior noise becomes very noticeable. Further, most people sleep at night and are very sensitive to noise intrusion. To account for human sensitivity to nighttime noise levels, a descriptor, L dn (day/night average sound level), was developed. The L dn divides 1
the 24-hour day into the daytime of 7:00 AM to 10:00 PM and the nighttime of 10:00 PM to 7:00 AM. The nighttime noise level is weighted 10 db higher than the daytime noise level. The Community Noise Equivalent Level (CNEL) is another 24-hour average which includes both an evening and nighttime weighting. 2
Table 1 Definitions of Acoustical Terms Used in this Report Term Decibel, db Definitions A unit describing, the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the pressure of the sound measured to the reference pressure. The reference pressure for air is 20. Sound Pressure Level Frequency, Hz A-Weighted Sound Level, dba 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. Equivalent Noise Level, Leq L max, L min L 01, L 10, L 50, L 90 Day/Night Noise Level, L dn or DNL 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 pm and 7:00 am. Community Noise Equivalent Level, CNEL The average A-weighted noise level during a 24-hour day, obtained after addition of 5 decibels in the evening from 7:00 pm to 10:00 pm and after addition of 10 decibels to sound levels measured in the night between 10:00 pm and 7:00 am. Ambient Noise Level The composite of noise from all sources near and far. The normal or existing level of environmental noise at a given location. Intrusive That noise which intrudes over and above the existing ambient noise at a given location. The relative intrusiveness of a sound depends upon its amplitude, duration, frequency, and time of occurrence and tonal or informational content as well as the prevailing ambient noise level. 3
Table 2 Typical Noise Levels in the Environment Common Outdoor Noise Source Jet fly-over at 1,000 feet Noise Level (dba) 120 dba 110 dba Common Indoor Noise Source Rock concert Pile driver at 65 feet Large truck pass by at 50 feet 100 dba 90 dba Night club with live music 80 dba Noisy restaurant Garbage disposal at 3 feet Gas lawn mower at 100 feet 70 dba Vacuum cleaner at 10 feet Commercial/Urban area daytime Suburban expressway at 300 feet Suburban daytime 60 dba Normal speech at 3 feet Active office environment 50 dba Urban area nighttime Quiet office environment 40 dba Suburban nighttime Quiet rural areas 30 dba Library Quiet bedroom at night Wilderness area 20 dba Most quiet remote areas 10 dba Quiet recording studio Threshold of human hearing 0 dba Threshold of human hearing 4
REGULATORY BACKGROUND - NOISE The State of California, City of Antioch, and City of Brentwood establish guidelines, regulations, and policies designed to limit noise exposure at noise sensitive land uses. Appendix G of the State CEQA Guidelines, the Environmental Hazards Element of the City of Antioch General Plan, and the City of Antioch Zoning Ordinance, and the Noise Element of the City of Brentwood General Plan present the following: State CEQA Guidelines. The California Environmental Quality Act (CEQA) contains guidelines to evaluate the significance of effects of environmental noise attributable to a proposed project. CEQA asks the following applicable questions. Would the project result in: 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? Exposure of persons to or generation of excessive groundborne vibration or groundborne noise levels? A substantial permanent increase in ambient noise levels in the project vicinity above levels existing without the project? A substantial temporary or periodic increase in ambient noise levels in the project vicinity above levels existing without the project? 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, exposure of people residing or working in the project area to excessive noise levels. For a project within the vicinity of a private airstrip, exposure of people residing or working in the project area to excessive noise levels. Environmental Hazards Chapter of the General Plan. The Environmental Hazards Chapter of the City of Antioch General Plan sets forth noise and land use compatibility standards to guide development, and noise goals and policies to protect citizens from the harmful and annoying effects of excessive noise. Objectives and policies established in the Noise Element of the General Plan that are applicable to the proposed project include: 11.6.1 Noise Objective Achieve and maintain exterior noise levels appropriate to planned land uses throughout Antioch as described below: Residential Single-Family: 60 dba CNEL within rear yards Multi-Family: 60 dba CNEL within exterior open space 5
11.6.2 Noise Noise Compatible Land Use and Circulation Patterns b. Maintain a pattern of land uses that separates noise-sensitive land uses from major noise sources to the extent possible, and guide noise-tolerant land uses into the noisier portions of the Planning Area. Noise Analysis and Mitigation e. When new development incorporating a potentially significant noise generator is proposed, require noise analyses to be prepared by a qualified acoustical engineer. Require the implementation of appropriate noise mitigation when the proposed project will cause new exceedences of General Plan noise objectives, or an audible (3.0 dba) increase in noise in areas where General Plan noise objectives are already exceeded as the result of existing development. f. In reviewing noise impacts, utilize site design and architectural design features to the extent feasible to mitigate impacts on residential neighborhoods and other uses that are sensitive to noise. g. Where feasible, require the use of noise barriers (walls, berms, or a combination thereof) to reduce significant noise impacts. The barrier must have sufficient mass to reduce noise transmission and high enough to shield the receptor from the noise source To be effective, the barrier needs to be constructed without cracks or openings. The barrier must interrupt the line-of-sight between the noise source and the receptor. h. Continue enforcement of California Noise Insulation Standards (Title 25, Section 1092, California Administration Code). Temporary Construction i. Ensure that construction activities are regulated as to hours of operation in order to avoid or mitigate noise impacts on adjacent noise-sensitive land uses. j. Require proposed development adjacent to occupied noise sensitive land uses to implement a construction-related noise mitigation plan. This plan would depict the location of construction equipment storage and maintenance areas, and document methods to be employed to minimize noise impacts on adjacent noise sensitive land uses. 6
k. Require that all construction equipment utilize noise reduction features (e.g., mufflers and engine shrouds) that are no less effective than those originally installed by the manufacturer. m. Prior to the issuance of any grading plans, the City shall condition approval of subdivisions and non-residential development adjacent to any developed/occupied noisesensitive land uses by requiring applicants to submit a construction-related noise mitigation plan to the City for review and approval. The plan should depict the location of construction equipment and how the noise from this equipment will be mitigated during construction of the project through the use of such methods as: The construction contractor shall use temporary noise-attenuation fences, where feasible, to reduce construction noise impacts on adjacent noise sensitive land uses During all project site excavation and grading on-site, the construction contractors shall equip all construction equipment, fixed or mobile, with properly operating and maintained mufflers, consistent with manufacturers standards. The construction contractor shall place all stationary construction equipment so that emitted noise is directed away from sensitive receptors nearest the project site. The construction contractor shall limit all construction-related activities that would result in high noise levels to between the hours of 7:00 a.m. and 7:00 p.m. Monday through Saturday. No construction shall be allowed on Sundays and public holidays. n. The construction-related noise mitigation plan required shall also specify that haul truck deliveries be subject to the same hours specified for construction equipment. Additionally, the plan shall denote any construction traffic haul routes where heavy trucks would exceed 100 daily trips (counting those both to and from the construction site). To the extent feasible, the plan shall denote haul routes that do not pass sensitive land uses or residential dwellings. Lastly, the construction-related noise mitigation plan shall incorporate any other restrictions imposed by the city. City of Antioch Zoning Ordinance. The City of Antioch Zoning Ordinance (2005) provides noise attenuation requirements for proposed development. Specifically, Section 5-17.04 prohibits construction during sensitive evening, nighttime, and weekend hours. 5-17.04 Construction Noise Attenuation (B) It shall be unlawful for an person to be involved in construction activity during the hours specified below: On weekdays prior to 7:00 a.m. and after 6:00 p.m. On weekdays within 300 feet of occupied dwellings, prior to 8:00 a.m. and after 5:00 p.m. 7
On weekends and holidays, prior to 9:00 a.m. and after 5:00 p.m., irrespective of the distance from the occupied dwellings. City of Brentwood s General Plan. The City of Brentwood s General Plan contains policies designed to support the City s goals of protecting noise-sensitive land uses form excessive exposure to noise and preserving the rural noise environment. Action 1.1.2 states that noise created by new transportation noise sources, including roadway improvement projects, shall be mitigated at existing outdoor activity areas of sensitive land uses to 60 db L dn /CNEL or less. Where it is not possible to reduce noise in outdoor activity areas to 60 db L dn /CNEL or less using a practical application of the best available noise reduction measures, an exterior noise level of up to 65 db L dn /CNEL may be allowed provided that available exterior noise level reduction measures have been implemented and interior noise levels are in compliance with this table. Noise levels in interior spaces within residences are to be maintained at 45 dba L dn /CNEL or less. EXISTING NOISE ENVIRONMENT The Tierra Villas residential project site is located in southeast Antioch, west of Heidorn Ranch Road and southeast of the existing terminus of Prewett Ranch Drive. Residential land uses, including large-lot rural residences and single-family subdivisions, surround the site in all directions. The Heritage Baptist Church and School borders the project site to the northeast. A noise monitoring survey was conducted from March 31, 2009 to April 3, 2009 to quantify the existing noise environment at the site and in the project vicinity. The noise monitoring survey included one long-term noise measurement (LT-1), and two short-term measurements (ST-1, ST- 2), as shown in Figure 1. The noise environment at the site results primarily from intermittent traffic along Heidorn Ranch Road. Noise measurement location LT-1 was made approximately 40 feet from the center of Heidorn Ranch Road. This location was selected to represent the noise environment at the portion of residential front yards located nearest the roadway. Hourly average noise levels measured at this site typically ranged from 51 to 56 dba L eq during the day, and from 41 to 50 dba L eq at night. The calculated CNEL noise level at this location was 57 dba. These data are summarized in Appendix 1. Short-term noise measurement (ST-1) was made approximately 155 feet from the nearest residential land uses to the north and adjacent to the northwest corner of the Church property. The ten-minute average noise level during this time period was 47 dba L eq. Short-term noise measurement (ST-2) was conducted at the end of Prewett Ranch Drive, just west of the site. The ten-minute average noise level during this time period was 46 dba L eq. Table 3 summarizes the results of these measurements. 8
Table 3 Summary of Short-Term Noise Measurement Data Noise Measurement Location L max L (1) L (10) L (50) L (90) L eq CNEL ST-1: ~155 feet from the nearest residential land uses. 58 55 49 45 42 47 49 (3/31/2009, 13:50-14:00) ST-2: End of Prewett Ranch Drive. (4/3/2009, 13:20-13:30) 59 55 50 42 37 46 47 Note: CNEL approximated by correlating data collected during the short-term monitoring interval to data collected during a corresponding period at the long-term site. Figure 1: Site Vicinity and Noise Measurement Locations ST-1 Project Site Church LT-1 ST-2 9
NOISE IMPACTS AND MITIGATION MEASURES Significance Criteria The following are criteria used in this report to evaluate the significance of noise impacts; A significant impact would be identified if noise-sensitive receivers proposed by the project would be exposed to noise levels exceeding the City s guidelines for noise and land use compatibility (up to 60 dba CNEL). Satisfactory interior noise levels are defined as 45 dba CNEL or less. According to CEQA, a significant noise impact would result if noise levels increase substantially over a permanent basis at existing noise-sensitive land uses (e.g., residences) as a result of the project. A substantial increase would be defined as an increase of 3 dba L dn or greater. Significant noise impacts would result from construction if noise levels are sufficiently high to interfere with speech, sleep, or normal residential activities. Construction activities would substantially increase ambient noise levels over a temporary basis if noise levels resulting from these activities exceeds 60 dba L eq(hr), is at least 5 dba L eq(hr) above ambient noise levels, and the duration of the construction exceeds one year. Impact 1: Noise and Land Use Compatibility. Future residential uses developed at the project site would be exposed to exterior noise levels greater than 60 dba CNEL, which exceeds the exterior noise and land use compatibility standard presented in the City of Antioch s General Plan. Interior noise levels would be expected to exceed 45 dba CNEL without the incorporation of noise insulation features into the project s design. This is a less-than-significant impact with the incorporation of mitigation. Future Exterior Noise Environment Two alternative site plans were provided for this project (Alternatives A and B). Site plan Alternative A shows Prewett Ranch Drive connecting through the project site to Heidorn Ranch Road. Site plan Alternative B would not connect Prewett Ranch Drive from its existing terminus west of the site through to Heidorn Ranch Road. The future noise environment at the project site is anticipated to increase as a result of cumulative growth forecast under the current General Plan. Cumulative plus project traffic volumes were used to assess the compatibility of the proposed residential project with respect to the noise environment expected at the site. Future noise levels were calculated for receivers positioned 105 feet from the center of Heidorn Ranch Road (nearest residential rear yard areas). The results of these calculations indicate that exterior noise levels in the rear yard of the residential units nearest Heidorn Ranch Road would be approximately 65 dba CNEL under Alternative A and 64 dba CNEL under Alternative B. Under Alternative A, future noise levels are calculated to reach 54 dba CNEL at rear yard areas adjacent to Prewett Ranch Drive 10
assuming the connection from Heidorn Ranch Road to the existing subdivision west of the site. Under Alternative B, future noise levels are calculated to reach 52 dba CNEL at rear yard areas adjacent to Prewett Ranch Drive assuming the future roadway does not connect to the existing subdivision west of the site. Noise levels in outdoor use areas that are affected by transportation noise are required to be maintained at or below 60 dba CNEL to be considered acceptable for residential development. Under Alternatives A and B, overall CNEL noise levels in outdoor use areas of residential uses adjacent to Heidorn Ranch Road would be 64 to 65 dba CNEL and would exceed the City s exterior noise standard by 4 to 5 dba CNEL. Under Alternatives A and B, CNEL noise levels are calculated to remain below 60 dba CNEL at rear yard areas adjacent to Prewett Ranch Drive. Noise barriers could be constructed to reduce noise levels in the yards of homes adjacent to Heidorn Ranch Road. Preliminary barrier calculations indicate that a six-foot noise barrier, relative to the residential pad elevation, would be required to reduce exterior noise levels at residential outdoor use areas proposed adjacent to Heidorn Ranch Road to 60 dba CNEL or less. A preliminary barrier design is shown for Alternatives A and B in Appendix 2. Interior Noise Environment The City of Antioch requires that interior noise levels within new residential units not exceed 45 dba CNEL. Residential units proposed along Heidorn Ranch Road would be exposed to exterior noise levels ranging from 64 to 65 dba CNEL. Residential receiver proposed along Prewett Ranch Drive would be exposed to future exterior noise levels ranging from 52 to 54 dba CNEL depending on the selected alternative. In buildings of typical construction, with the windows partially open, interior noise levels are approximately 15 dba lower than exterior noise levels. With the windows closed, standard residential construction typically provides 20 to 25 decibels of exterior to interior noise reduction. Where exterior noise levels range from 60 to 65 dba L dn the interior noise level can typically be maintained below City standards (45 dba CNEL) assuming standard construction methods and the incorporation of forced air mechanical ventilation systems in residential units. These systems allow the occupant the option of controlling noise by maintaining the windows shut. Given the anticipated noise levels at exterior facades adjacent to Heidorn Ranch Road, it may also be necessary to provide sound-rated building elements (e.g., windows and doors) to maintain interior noise levels at or below 45 dba CNEL. Preliminary calculations suggest that residential units nearest Heidorn Ranch Road would require sound rated windows and exterior doors with ratings ranging from STC 26-28 to assure that the interior average noise level guideline is met. Interior noise levels vary depending on the final design of the units (relative window area to wall area) and construction materials and methods. The remaining units on the site would achieve interior noise levels of 45 dba CNEL assuming standard California construction methods. 11
Mitigation 1: The following mitigation measure would reduce the significant impact to a less-than-significant level: A six-foot noise barrier shall be constructed to reduce noise levels at private use areas along Heidorn Ranch Road to 60 dba CNEL or less (Alternatives A and B). To be effective, the barriers should be constructed solidly over the entire surface and at the base. Openings or gaps between barrier materials or the ground decrease the reduction provided by a noise barrier. Suitable materials for barrier construction should have a minimum surface weight of 3 lbs./ft 2. (such as one-inch thick wood, masonry block, concrete, or metal). A preliminary barrier design is shown in Appendix 2. Project-specific acoustical analyses are required by the City of Antioch to ensure that interior noise levels will be reduced to 45 dba CNEL or lower. Building sound insulation requirements would need to include the provision of forced-air mechanical ventilation for residential units adjacent to Heidorn Ranch Road, satisfactory to the local building official, so that windows could be kept closed to control noise. Results of project specific analyses, including the description of the necessary noise control treatments, will be submitted to the City along with the building plans and approved prior to issuance of a building permit. Feasible construction techniques such as these would adequately reduce interior noise levels to 45 dba CNEL or lower. Impact 2: Project-Generated Traffic Noise. The proposed project would generate a substantial permanent noise level increase at residential land uses in the vicinity. This is a less-than-significant impact with the incorporation of mitigation. Project-generated traffic noise level increases were calculated for both access alternatives by comparing existing plus project traffic volumes to existing traffic volumes to determine the noise level increase attributable to the project. Access Alternative A shows a full connection of Prewett Ranch Drive between Summerfield Drive and Heidorn Ranch Road. Prewett Ranch Drive would terminate in a bulb intersection at lots 17 and 18, where it would turn to the south and continue to Sand Creek Road under Access Alternative B. The proposed project could be the one of many future projects that will contribute to substantial increases in ambient noise levels expected in the future and the first project to change the character of the noise environment at rural residences east of the site. Noise levels at recently constructed residential land uses to the north and west include extensive noise mitigation, such as open space buffers and noise barriers that shield private outdoor use areas from traffic noise. It is apparent that future increases in noise were taken into account in the design of these subdivisions. Noise levels resulting from the project generated traffic would be partially mitigated by the existing noise mitigation, but noise levels are predicted to substantially increase above existing levels. 12
Access Alternative A Substantial increases in traffic noise are expected in the near term at single-family residences located west of Heidorn Ranch Road north of Lone Tree Plaza Drive. Single-family residential receivers west of Heidorn Ranch Road appear to have been developed recently enough to factor in future noise level increases from the surrounding area. A seven foot noise barrier was constructed along the backyards of homes along Heidorn Ranch Road. Future noise levels in the private outdoor use areas of homes along the roadway are not anticipated to exceed 60 dba CNEL. Although traffic noise levels are estimated to increase 7 dba CNEL as a result of project-generated traffic, the impact is less than significant because these recently constructed residences were designed to accommodate such a noise increase as the area transitions from rural residential to suburban residential. Substantial increases in traffic noise levels are also expected in the near-term along Heidorn Ranch Road opposite from the site. There are two large-lot rural residential parcels east of Heidorn Ranch Road in the City of Brentwood that have been located there for a number of years. Traffic noise levels at the front yard areas of these residential land uses are calculated to increase 5 dba CNEL as a result of project-generated traffic assuming that the roadway would be widened to three lanes (two southbound lanes and one northbound lane) and away from the existing residential land uses located east of Heidorn Ranch Road. Existing noise levels at the westernmost portions of these front yard areas, approximately 40 feet from the center of the existing roadway, are calculated to increase from an existing noise level of 57 dba CNEL to a near-term plus project noise level of 62 dba CNEL. Traffic noise levels would exceed the City of Brentwood s maximum allowable noise level limit for residential outdoor activity areas by 2 dba. Traffic noise levels near the façade of the residences are calculated to increase from an existing noise level of 55 dba CNEL to a near-term plus project noise level of 60 dba CNEL. Recognizing that future traffic noise levels in the area were not planned and designed for when these residences were constructed, the near term, substantial traffic noise increases would be considered significant. Substantial increases in traffic noise levels are also expected in the near-term at residential land uses along Prewett Ranch Drive between Hillcrest Avenue and the west entrance to the project site. Under site plan Alternative A the project would connect to the existing subdivision at Prewett Ranch Drive and Summerfield Drive. Through traffic would pass existing residential uses where traffic did not pass before. The character of the noise environment at these adjacent residential uses would change because each vehicle passby would be audible over the existing background noise environment resulting from distant vehicular traffic. Maximum instantaneous noise levels resulting from a vehicle passby would range from 55-65 dba L max at 50 feet. Based on site visits it appears that Prewett Ranch Drive was intended to be extended in the future to accommodate future growth in the area. Private outdoor use areas of residential uses along the roadway are located in side yards that are shielded by existing six-foot noise barriers or behind the residential units themselves. Although noise levels are expected to increase along the existing section of Prewett Ranch Drive in the future as a result of the project, noise levels are not anticipated to exceed 60 dba CNEL at the adjacent residences, and the impact is less than significant recognizing that these noise increases have been accounted for in the design of these recently constructed residential units. 13
Access Alternative B Traffic noise impacts would not occur at existing large-lot rural residential parcels east of Heidorn Ranch Road under Access Alternative B. The majority of traffic associated with the project would enter and exit the subdivision via the northernmost access point. Near-term plus project traffic volumes along the segment of Heidorn Ranch Road adjacent to the residential properties east of the site would continue to be low, similar to existing conditions, and near-term noise levels would remain similar to existing noise conditions. Traffic noise impacts would not occur at single-family residences located west of Heidorn Ranch Road north of Lone Tree Plaza Drive or at residential land uses along Prewett Ranch Drive between Hillcrest Avenue and the west entrance to the project site recognizing that these noise increases have been accounted for in the design of the mitigation implemented at these newer residential units. Mitigation 2: Noise reduction methods for Access Alternative A include either of the following: Pave Heidorn Ranch Road with quiet pavement such as Open-Grade Asphalt Concrete. Case studies have shown that the replacement of dense grade asphalt (standard type) with open-grade or rubberized asphalt can reduce traffic noise levels along residential-type streets by 2 to 3 dba. A possible noise reduction of 2 dba would be expected using conservative engineering assumptions. Exterior noise levels with mitigation would be expected to be 60 dba L dn /CNEL or less throughout the residential outdoor activity areas west of existing Heidorn Ranch Road residences and exterior noise levels at the residential facades would be approximately 58 dba L dn /CNEL. Interior noise levels within the affected residences would be expected be 43 dba L dn /CNEL or less. Opportunities to lower noise levels through pavement surface treatments could only be identified after an assessment of the current roadway surface with respect to noise. Alternatively, institute traffic calming measures to reduce noise levels expected under the near-term plus project traffic scenario. Each 5 mph reduction in average speed provides approximately 1 dba of noise reduction on an average basis (L eq / CNEL). For example, reducing the posted speed from 45 mph to 35 mph would yield 2 dba of noise reduction. Traffic calming measures that regulate speed improve the noise environment by smoothing out noise levels. Exterior noise levels with mitigation would be expected to be 60 dba L dn /CNEL or less throughout the residential outdoor activity areas west of existing Heidorn Ranch Road residences and exterior noise levels at the residential facades would be approximately 58 dba L dn /CNEL. Interior noise levels within the affected residences would be expected be 43 dba L dn /CNEL or less. The implementation of either mitigation measure, as presented above, would reduce the nearterm plus project noise impact to a less than significant level. Impact 3: Cumulative Traffic Noise. The proposed project would not substantially contribute to cumulative noise levels anticipated with the build-out of the General Plan. This is a less-than-significant impact. 14
Traffic noise levels in the area are calculated to increase substantially over the long-term as the area transitions from a rural land use pattern to a suburban area. Cumulative traffic noise levels increases were calculated by comparing cumulative plus project traffic volumes to cumulative no project volumes. The project s contribution to cumulative noise level increases would be less than 1 dba CNEL in the long-term. This increase in noise would not be substantial. The project would not make a cumulatively considerable contribution to increased noise levels resulting from the build-out of the area. Mitigation Measures: None Impact 4: Construction Noise. The project site is bordered by existing residential land uses to the north, east, south, and west. Noise generated by construction activities at the site would not be expected to adversely affect adjacent land uses provided standard construction noise controls are implemented at the site and the cumulative duration of significant noise-producing activities is limited to one year or less. This is a less-than-significant impact with the incorporation of mitigation. Construction activities generate considerable amounts of noise. Construction-related noise levels are normally highest during the demolition phase and during the construction of project infrastructure. These phases of construction require heavy equipment that normally generates the highest noise levels over extended periods of time. Typical hourly average construction generated noise levels are about 81 dba to 88 dba L eq 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.) Construction-related noise levels are normally less during building erection, finishing, landscaping phases. There would be variations in construction noise levels on a dayto-day basis depending on the actual activities occurring at the site. Construction generated noise levels drop off at a rate of about 6 dba per doubling of distance between the source and receptor. The nearest existing residential receivers are about 40 feet from the project site. Hourly average noise levels would range from 79 to 86 dba L eq during the busiest construction periods along the perimeter of the site. Shielding by barriers or buildings would provide an additional 5 to 10 decibels of attenuation at distant receptors. Noise impacts resulting from construction depend on 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 receptors. Construction noise impacts primarily occur when construction activities occur during noise-sensitive times of the day (early morning, evening, or nighttime hours), the construction occurs in areas immediately adjoining noise sensitive land uses, or when construction durations last over extended periods of time. Where noise from construction activities exceeds 60 dba L eq and exceeds the ambient noise environment by at least 5 dba L eq at noise-sensitive uses in the project vicinity for a period greater than one year, the impact would be considered significant. Grading and the construction of project infrastructure would be completed first. Residential units would then be constructed. The project would be built in two phases, each consisting of several releases of homes that are scheduled to be constructed together. Each release proposes to 15
build between 8 and 14 homes. The project would be built in approximately 3 years. As construction moves away from noise-sensitive receptors, or indoors, noise levels generated by heavy construction will be lower. Noise generated by grading, infrastructure improvements and the construction of units nearest perimeter of the project site would not be expected to exceed ambient noise levels at receivers to the north, east, and south by more than 5 dba L eq for a period greater than one year provided the order in which homes are constructed as shown in the preliminary phasing plan is altered. Significant noise impacts do not normally occur when standard construction noise control measures are enforced at the project site and when the duration of the noise generating construction period at a particular receiver or group of receivers is limited to one construction season (typically one year) or less. Construction noises associated with projects of this type are disturbances that are necessary for the construction or repair of buildings and structures in urban areas. Reasonable regulation of the hours of construction, as well as regulation of the arrival and operation of heavy equipment and the delivery of construction material, are necessary to protect the health and safety of persons, promote the general welfare of the community, and maintain the quality of life. Mitigation Measures: The following controls, as identified in the General Plan and Municipal Code, shall be implemented at the construction site: Per Section 5-17.04 of the City s Municipal Code, construction activities shall be limited to the hours of 7:00 AM to 6:00 PM on weekdays. Construction within 300 feet of occupied dwelling units and the Heritage Baptist Academy and athletic fields shall be further limited to the hours between 8:00 AM to 5:00 PM on weekdays. On weekends and holidays, irrespective of the distance from dwelling units, construction activity shall be limited to the hours between and 9:00 AM to 5:00 PM. Require proposed development adjacent to occupied noise sensitive land uses to implement a construction-related noise mitigation plan. This plan would depict the location of construction equipment storage and maintenance areas, and document methods to be employed to minimize noise impacts on adjacent noise sensitive land uses. Require that all construction equipment utilize noise reduction features (e.g., mufflers and engine shrouds) that are no less effective than those originally installed by the manufacturer. Prior to the issuance of any grading plans, the City shall condition approval of subdivisions and non-residential development adjacent to any developed/occupied noisesensitive land uses by requiring applicants to submit a construction-related noise mitigation plan to the City for review and approval. The plan should depict the location 16
of construction equipment and how the noise from this equipment will be mitigated during construction of the project through the use of such methods as: o The construction contractor shall use temporary noise-attenuation fences, where feasible, to reduce construction noise impacts on adjacent noise sensitive land uses. Temporary noise barrier fences would provide a 5 dba noise reduction if the noise barrier interrupts the line-of-sight between the noise source and receiver and if the barrier is constructed in a manner that eliminates any cracks or gaps. o o During all project site excavation and grading on-site, the construction contractors shall equip all construction equipment, fixed or mobile, with properly operating and maintained mufflers, consistent with manufacturers standards. The construction contractor shall place all stationary construction equipment so that emitted noise is directed away from sensitive receptors nearest the project site. The construction contractor shall limit all construction-related activities that would result in high noise levels to between the hours of 7:00 a.m. and 7:00 p.m. Monday through Saturday. No construction shall be allowed on Sundays and public holidays. The construction-related noise mitigation plan required shall also specify that haul truck deliveries be subject to the same hours specified for construction equipment. Additionally, the plan shall denote any construction traffic haul routes where heavy trucks would exceed 100 daily trips (counting those both to and from the construction site). To the extent feasible, the plan shall denote haul routes that do not pass sensitive land uses or residential dwellings. Lastly, the construction-related noise mitigation plan shall incorporate any other restrictions imposed by the city. The following additional controls shall be considered to reduce construction noise levels as low as feasible and minimize annoyance at residential land uses in the project vicinity: Construct units at the perimeter of the site and immediately adjacent to existing residences as early as possible so that the completed buildings will provide acoustical shielding for existing residences to the north and west. Constructing units in Releases 6-10 would provide approximately 10 db of noise reduction during the remainder of project construction activities. Unnecessary idling of internal combustion engines should be strictly prohibited. Located stationary noise generating equipment such as air compressors or portable power generators as far as possible from sensitive receptors. Construct temporary noise barriers to screen stationary noise generating equipment when located near adjoining sensitive land uses. Temporary noise barriers could reduce construction noise levels by 5 dba. Utilize quiet air compressors and other stationary noise sources where technology exists. 17
Control noise from construction workers radios to a point where they are not audible at existing residences bordering the project site. Designate a disturbance coordinator who would be responsible for responding to any local complaints about construction noise. The disturbance coordinator will determine the cause of the noise complaint (e.g., starting too early, bad muffler, etc.) and will require that reasonable measures warranted to correct the problem be implemented. Conspicuously post a telephone number for the disturbance coordinator at the construction site and include in it the notice sent to neighbors regarding the construction schedule. With the incorporation of these standards measures, the noise impact resulting from project construction would be considered less-than-significant. 18
Appendix 1: Daily Trend in Noise Levels at LT-1
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Appendix 2: Preliminary Barrier Design (Alternatives A and B) 6-foot Noise Barrier 21