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<br /> <br /> <br />Memorandum <br />February 26, 2025 <br />Page 3 <br />21202-23 North County Landfill_Noise DRAFT <br />Term Definition <br />Ambient Noise Level The existing level of environmental noise at a given location from all sources <br />near and far. <br />Vibration Decibel (VdB) A unit describing the amplitude of vibration on a logarithmic scale. <br />Peak Particle Velocity <br />(PPV) <br />The maximum instantaneous peak of a vibration signal. <br />Root Mean Square (RMS) <br />Velocity <br />The average of the squared amplitude of a vibration signal. <br />Sources: Charles M. Salter Associates, Inc., 1998. Acoustics – Architecture, Engineering, the Environment, William <br />Stout Publishers. <br />Federal Transit Administration, 2018. Transit Noise and Vibration Impact Assessment Manual, FTA Report No.0123, <br />September. <br /> <br />A typical method for determining a person’s subjective reaction to a new noise is by comparing <br />it to existing conditions. The following describes the general effects of noise on people: <br />• A 3-dBA increase is considered barely noticeable. <br />• A 5-dBA increase is considered clearly noticeable, but not dramatic. <br />• A 10-dBA increase is perceived as a doubling in loudness. <br />Traffic noise levels are often expressed in terms of the hourly dBA. The noise levels generated <br />by vehicular sources mainly depend on traffic volume, the speed, and the percent of trucks <br />within the fleet. Increases in these three factors will lead to higher noise levels. Doubling the <br />number of sources, such as traffic volume, increases the noise level by approximately 3 dBA due <br />to the logarithmic nature of noise levels.1 <br />In an unconfined space, such as outdoors, noise attenuates with distance. Noise levels at a <br />known distance from point sources are reduced by 6 dBA for every doubling of that distance for <br />hard surfaces (e.g., asphalt) and by 7.5 dBA for every doubling of distance for soft surfaces (e.g., <br />vegetative areas). <br />General Information on Vibration <br />Vibration is an oscillatory motion through a solid medium in which the motion’s amplitude can <br />be described in terms of displacement, velocity, or acceleration. Typically, ground-borne <br />vibration generated by human activities attenuates rapidly with distance from the source of the <br />vibration. Vibration amplitudes are usually expressed as either Peak Particle Velocity (PPV) or as <br />Root Mean Square (RMS) velocity. The PPV is defined as the maximum instantaneous peak of <br /> <br />1 Federal Highway Administration (FHWA), 2018. Techniques for Reviewing Noise Analyses and Associated Noise <br />Reports.