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City of San Leandro 2824 Halcyon Drive Residential Project 82  Construction activities shall be restricted to the daytime hours of between 7:00 a.m. and 7:00 p.m. on weekdays, or between 8:00 a.m. and 7:00 p.m. on Sunday and Saturday.  Prior to the start of construction activities, the construction contractor shall: Maintain and tune all proposed equipment in accordance with the manufacturer’s recommendations to minimize noise emission. Inspect all proposed equipment and fit all equipment with properly operating mufflers, air intake silencers, and engine shrouds that are no less effective than as originally equipped by the manufacturer. Post a sign, clearly visible at the site, with a contact name and telephone number of the City of San Leandro’s authorized representative to respond in the event of a noise complaint. Place stationary construction equipment and material delivery in loading and unloading areas as far as practicable from the residences. Limit unnecessary engine idling to the extent feasible. Use smart back-up alarms, which automatically adjust the alarm level based on the background noise level, or switch off back-up alarms and replace with human spotters. Use low-noise emission equipment. Limit use of public address systems. Minimize grade surface irregularities on construction sites. Noise Noise is defined as unwanted sound that disturbs human activity. Noise level (or volume) is generally measured in decibels (dB) using the A-weighted sound pressure level (dBA). The A- weighting scale is an adjustment to the actual sound power levels to be consistent with human hearing response, which is most sensitive to frequencies around 4,000 Hertz (similar to the highest note on a piano) and less sensitive to frequencies below 100 Hertz (similar to a transformer hum). Sound pressure level is measured on a logarithmic scale with the 0 dB level based on the lowest detectable sound pressure level that people can perceive (an audible sound that is not zero sound pressure level). Based on the logarithmic scale, a doubling of sound energy is equivalent to an increase of 3 dB, and a sound that is 10 dB less than the ambient sound level has no effect on ambient noise. Because of the nature of the human ear, a sound must be about 10 dB greater than the reference sound to be judged as twice as loud. In general, 5 dBA change is a readily perceivable change in noise levels, a 3 dBA change noise levels is barely perceivable, while 1-2 dBA changes generally are not perceivable outside a laboratory environment. Quiet suburban areas typically have noise levels in the range of 40-50 dBA, while those along arterial streets are in the 50-60+ dBA range. Normal conversational levels are in the 60-65 dBA range, and ambient noise levels greater than 65 dBA can interrupt conversations. Noise levels typically attenuate (drop off) at a rate of 6 dB per doubling of distance from point sources such as industrial machinery. Noise from heavily traveled roads typically attenuates at about 3 dB per doubling of distance. The time period in which noise occurs is important since noise that occurs at night tends to be more disturbing than that which occurs during the day. The DNL (also referred to as Ldn) is a commonly used noise metric– that recognizes changes in human sensitivity by weighting nighttime hourly average noise. The DNL is a 24-hour equivalent noise level that adds 10 dBA to actual nighttime (10 p.m. to 7 a.m.). One of the other most frequently used noise metrics that considers both duration