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5.ENVIRONMENTAL CHECKLIST MOUNTAIN HOUSE NEIGHBORHOODS K AND L INITIAL STUDY 11. NOISE Table 5.11.1 EXISTING NOISE ENVIRONMENT IN PROJECT SITE VICINII y Recorded Noise u Location Time Period Levels Noise Sources 55 feet from center Wednesday,July 13 to 24-Hour Ldn:84 Unidentified. of Byron Road(long- Thursday,July 14, Hourly Average (Unattended noise term measurement) 2011 Leq(Decibel) measurements do not Range,70-79 specifically identify noise , _ sources. _ 50 feet from center Wednesday,July 13, 5-Minute Average Noise from traffic on of Byron Road 2011, Noise Levels,Leq Byron Roadlwind causing (short-term 1:32-1:47 PM (decibels): high background levels. measurement) 74,74,72 Semi truck,85 dBA Car,80 dBA e All noise levels measured in decibels(dBA).Noise measurement data presented here using a Metrosonics dB-308 sound level meter,calibrated prior to use. Source:ESA,2011 The railroad is used only a few times per year. Noise levels are typically dominated by truck and automobile traffic on Byron Road. The measured 24- hour average day/night noise level (Ldn)'was 84 dB2 at this location. It should be noted that weather conditions included high winds during this time period.These �f winds contributed to an increased ambient noise level,especially during the nighttime hours,which create an inflated Ldn calculation, This shows that weather conditions in the area can dominate the noise environment at times. `r General aviation aircraft flyovers associated with the Byron Airport,which is located to the west in Contra Costa County, are occasionally audible in the area. (I� However,aircraft noise is not significant. The Contra Costa Airport Land Use I Compatibility Plan(prepared December 13,2000)shows that the annual average Community Noise Equivalent Level (CNEL) in the Mountain House community due to Byron Airport activity is less than 55 dB everywhere within the community. Noise Standards and Regulations I The 1994 MEIR and the Mountain House Master Plan require that noise levels in ; primary outdoor use areas in new residential developments, schools,and other noise-sensitive land uses must not exceed 65 dB. The Master Plan further I states that community walls should be no more than 7 feet high whenever possible. Specifically,the Development Title for Mountain House requires the following(San Joaquin County, 1992): a4 9-1025.9M NOISE The regulations concerning noise shall be as specified in the development title with the following modifications: J i Day/Night Noise Level,Ldn,is 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. I 2 Decibel,dB,is a unit describing the amplitude of sound,equal to 20 times the logarithm to the J base 10 of the ratio of the pressure of the sound measured to the reference pressure,which is 20 micropascals(20 micronewtons per square meter). ii NJ 5-136 7