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1J J BENDER READY -MIX CONCRETE MANUFACTURING PROJECT Initial'Study /Mitigated Negative Declaration obsolete octave -band sound pressure levels in the 600 -1200, 1200 -2400, and 2400 -4800 Hz octaves. At the present time, Speech Interference Level, based upon the octave band levels at the preferred frequencies of 500, 1000, 2000, and 4000 Hz, is considered to provide a better estimate of the masking ability of a noise. As Speech Interference Level does not take the actual speech level into account, the associated masking effect depends upon vocal effort and speaker -to- listener distance. Speech spoken with slightly more vocal effort can be understood well, when the noise level is 65 dBA. A typical building can reduce noise levels by 20 dBA with the windows closed.2 This noise reduction could be maintained only on a temporary basis in some cases, since it assumes windows would remain closed at all times. Therefore, this analysis utilizes an interior level of 65 dBA as a criterion level for determining significance for construction related activities, in the absence of an adopted specific construction noise related threshold by the City. The project involves the construction of aesthetic, drainage /water quality, and safety improvements at the project site. Table 4.12 -5, Average Construction Noise Levels, provides the anticipated construction noise levels during specific construction stages. The average noise levels presented in Table 4.12 -5 are based on the quantity, type, and acoustical use factor for each type of equipment that would be used during each construction phase. Table 4.12 -5 Average Construction Noise Levels 2 United States Department of Housing and Urban Development, The Noise Guidebook, undated, page 14. ' JULY 2011 4.12 -5 NOISE 31A-79