3 - The Bowery_PUBLIC COMMENT_RAMSEY

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5.0 Environmental Analysis 5.6 Noise Avion Project SEIR Page 5.6-3 described in terms of hertz, abbreviated hertz (Hz). The normal frequency range of most groundborne vibration that can be felt generally starts from a low frequency of less than 1 Hz to a high of about 200 Hz. While people have varying sensitivities to vibrations at different frequencies, in general they are most sensitive to low-frequency vibration. Vibration in buildings caused by construction activities may be perceived as motion of building surfaces or rattling of windows, items on shelves, and pictures hanging on walls. Vibration of building components can also take the form of an audible low-frequency rumbling noise, which is referred to as groundborne noise. Groundborne noise is usually only a problem when the originating vibration spectrum is dominated by frequencies in the upper end of the range (60 to 200 Hz), and when the structure and the construction activity are connected by foundations or utilities, such as sewer and water pipes. Although groundborne vibration is sometimes noticeable in outdoor environments, groundborne vibration is almost never annoying to people who are outdoors (Federal Transit Administration [FTA] 2006). The primary concern from vibration is the ability to be intrusive and annoying to local residents and other indoor vibration sensitive land uses. Vibration energy spreads out as it travels through the ground, causing the vibration level to diminish with distance away from the source. High frequency vibrations reduce much more rapidly than low frequencies, so that low frequencies tend to dominate the spectrum at large distances from the source. Discontinuities in the soil strata can also cause diffractions or channeling effects that affect the propagation of vibration over long distances. When vibration encounters a building, a ground-to- foundation coupling loss will usually reduce the overall vibration level. However, under certain circumstances, the ground-to-foundation coupling may also amplify the vibration level due to structural resonances of the floors and walls. Vibration levels are usually expressed as single-number measure of vibration magnitude, in terms of velocity or acceleration, which describes the severity of the vibration without the frequency variable. The peak particle velocity (PPV) is defined as the maximum instantaneous positive or negative peak of the vibration signal, usually measured in inches per second (in/sec). Since it is related to the stresses that are experienced by buildings, PPV is often used in monitoring of blasting vibration. Vibration-sensitive receivers are generally considered the same as noise-sensitive receivers, but may also include historical structures, laboratories, research facilities, and similar facilities. All vibration- sensitive receivers in the vicinity of the project are typical residential uses. There are no special uses or historic structures affected by the project. 5.6.3 Regulatory Framework 5.6.3.1 Vibration The threshold for blasting vibration impacts, as established by the U.S. Bureau of Mines, is 2.0 in/sec PPV at the closest structure. Additionally, as required by the County of San Diego Fire Code, pre- and post-blast inspections for building damage would be conducted by the blasting contractor prior to the first blast.