Experts in acoustics, noise and vibration To: Hyoksang Kwon, COBE Construction hyoksang@cobeinc.com From: Joshua Marcley, josh@mei-wu.com Mei Wu, meiwu@mei-wu.com Date: May 24, 2016 Subject: Cal Water Construction Noise Study MWA Project - 16044 is providing acoustical consulting services to COBE Construction for the demolition and construction of the Cal Water Facility located at 341 North Delaware Street, San Mateo, CA. The project site is situated among residential uses. 1. Project Criteria The project must adhere to the San Mateo General Plan and San Mateo Municipal Code. The relevant excerpts from the two documents are included below: a. San Mateo General Plan Noise Element GOAL 2: Minimize unnecessary, annoying, or unhealthful noise. POLICIES: N 2.1: Noise Ordinance. Continue implementation and enforcement of the City's existing noise control ordinance: a) which prohibits noise that is annoying or injurious to neighbors of normal sensitivity, making such activity a public nuisance, and b) restricts the hours of construction to minimize noise impact. Implementation of N 2.1: Noise Ordinance. Noise nuisances, as defined in the City's Municipal Code, are abated through a standardized enforcement process, which includes referral to the Housing and Advisory Appeals Board. This includes noise generated by building construction and equipment at unauthorized times. Enforcement of a noise control ordinance can reduce nuisance noise generated by commercial uses or from residential sources such as amplified music, parties, leaf blowers, or barking dogs. Construction activities also generate substantial short-term noise impacts, which can be limited to specified hours and days of the week. b. San Mateo Municipal Code Title 7: Health, Sanitation, and Public Nuisances Chapter 7.30 Noise Regulations 7.30.060 Special Provisions (e) Construction. Construction, alteration, repair or land development activities which are authorized by a valid city permit shall be allowed on weekdays between the hours of seven a.m. and seven p.m., on Saturdays between the hours of nine a.m. and five p.m., and on Sundays and holidays between the hours of noon and four p.m., or at such other hours as may be authorized or restricted by the permit, if they meet at least one of the following noise limitations: 1
(1) No individual piece of equipment shall produce a noise level exceeding 90 db at a distance of 25 feet. If the device is housed within a structure or trailer on the property, the measurement shall be made outside the structure at a distance as close to 25 feet from the equipment as possible. (2) The noise level at any point outside of the property plane of the project shall not exceed 90 db. (3) The operation of leaf blowers shall additionally comply with Chapter 10.80, Operation of Leaf Blowers. (Ord. 2013-13 9; Ord. 2004-16 1) c. Summary of Noise Codes The General Plan requires that the hours allowed for construction in the Municipal code be followed, but does not provide specific regulations regarding the limitation of construction noise. The Municipal Code allows construction activities to occur between 7AM and 7PM on weekdays, between 9AM and 5PM on Saturdays, and between 12PM and 4PM on Sundays and Holidays. Other hours may be permitted or restricted according to the exact language of the construction permit. We assume the hours defined herein as the expected hours of construction of this project. Additionally, the noise level during construction activities from any piece of equipment may not exceed 90 dba at a distance of 25 feet or the noise level due to construction activities must not exceed 90 dba at any point outside the property plane. 2
2. Site Plan The project calls for the construction of the new Cal Water Facility before the demolition of the existing building. The site demolition plan is shown below. Figure 1: Site demolition plan (paving removal in hatched area, new building in green, buildings scheduled for demolition in orange, southeast property line in blue) Construction activities are expected to include the following: Remove existing pavement (in pavement removal area), Excavate below the new building pad area to 5 feet deep and re-compact to rebuild the subbase, Place new concrete footings and slab on grade, Construct a new wood/steel framed building structure, Demolish two existing buildings, and Make site improvements, consisting of new fencing, pavement and driveway. The nearest neighboring property line to the construction activities is to the southeast (blue line in Fig. 1). It is approximately 100 ft to the new building (green outline Fig. 1) and 35 ft to the nearest building to be demolished (orange outline Fig. 1). There is a paved area to the southeast (right side of Fig. 1 / outlined in yellow Fig. 2) of the paving removal area that is part of the Cal Water property. This area is approximately 17 ft wide and runs the length of the southeast side of the property. This area is not scheduled for construction activities. 3
Figure 2: Aerial photo of project area (property outlined in red and area in yellow is not planned for demolition) 4
3. Construction Noise Analysis The San Mateo Municipal Code limits the noise level from any piece of equipment to 90 dba at a distance of 25 ft or 90 dba at the property line. The table below contains the sound level information for various pieces of construction equipment 1, also included in the table are sound levels from previous MWA construction/demolition noise studies. Equipment Noise Level at 25 ft [dba] Air Compressor 87 Backhoe 86 Ballast Equalizer 88 Ballast Tamper 89 Compactor 88 Concrete Mixer 91 Concrete Pump 88 Concrete Vibrator 82 Dozer 91 Generator 87 Grader 91 Impact Wrench 91 Jack Hammer 94 Loader 91 Pneumatic Tool 91 Pump 82 Roller 80 Scarifier 89 Scraper 95 Shovel 83 Truck 82 Excavator 87 Table 1: Noise levels at 25 ft for various pieces of construction equipment If/when the highlighted equipment is used, the level at the property line must not exceed 90 dba. This must be achieved through the use of an acoustic barrier or shielding the equipment such that the noise level at 25 ft is less than 90 dba. Any combination of the equipment not highlighted in the table may be used at any location on the property for the construction or demolition. 1 Traffic Noise and Vibration Impact Assessment. Federal Transit Administration, May 2006 (report number FTA-VA-90-1003-06) 5
4. Recommended Mitigation The distance from the construction area to all property lines except the southeast are large enough such that noise levels from construction activities will not exceed the Code requirements. Due to the distance from the new building site to the property line, there is no required mitigation from any piece of equipment. Stationary equipment should be placed far from the southeast property line wherever possible. The demolition of the southeast building and paving on the southeast of the property are the activities most at risk of causing noise levels exceeding Code limits. The equipment listed in Table 2 may be used at distances greater than those listed without mitigation. Equipment Minimum Distance to Property Line [ft] Concrete Mixer 28 Dozer 28 Grader 28 Impact Wrench 28 Jack Hammer 39 Loader 28 Paver 44 Pneumatic Tool 28 Scraper 44 Table 2: Minimum distance for various pieces of equipment to achieve 90 dba at the southeast property line If equipment must be used at distances closer to the southeast property line than the prescribed distances in Table 2, then a barrier must be utilized. The barrier should be at least 80 ft long if installed along the yellow line in Figure 3, or 50 ft long if installed along the orange line, and be centered perpendicular to the equipment. The barrier must be moved to remain centered, if the equipment moves. 6
Figure 3: Two possible locations where barriers may be utilized As an example the barrier shown in Figure 4 shows what a barrier installation intending to mitigate noise from a jack hammer operating at the closest edge of the pavement removal area to the southeastern property line. The yellow barrier is 50 ft and the orange barrier is 80 ft. 7
Figure 4: Example barriers for a jackhammer operating at the edge of the pavement removal area. The recommended barrier may be constructed with any solid material with a density no less than 2 lb. per square foot. Materials meeting this requirement include ½-inch thick wood, ½ inch outdoor plywood and 16 gauge steel sheet, masonry, or CMU blocks. For a moveable barrier, plywood sheets meeting the density requirements may be placed along the existing chain link fence and should be moved as construction activities move laterally along the property line. Sheets should overlap and have their faces flush with each other to prevent air gaps between sheets. The barrier should be at least 6 ft in height. Additional strategies to mitigate noise include: Construction of the new building before the demolition of the existing buildings (already planned). Demolition of the existing buildings from the northwest and proceeding in a southeast direction (toward the residential property line). This will allow the existing buildings to block noise from construction/demolition activities. As stated before, the closest building should be demolished from the far side first and proceeding toward the southeast property line and wherever, possible equipment should be placed as far as possible from the property line. Trucking and loading should be routed away from the southeast property line wherever possible. Construction activities may only occur during the hours allowed in the San Mateo Municipal Code. 8
Note, that the above bulleted recommendations are not required to meet the Code, except those regarding construction hours, but will further reduce the noise level from construction activities to the most sensitive noise receptors. * * * The information contained in this document is intended only for the subject project and the person(s) or entity(ies) to which it is addressed, and may contain confidential and/or privileged material. Any review, re-transmission, dissemination, modification, copy or other use of, or the taking of any action in reliance upon this information for uses other than the subject project or by persons or entities other than the intended recipient is prohibited. This document is 9 pages long and should not be distributed in any lesser or modified form. 9