facilities renewal master plan - National Zoo - Smithsonian Institution

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FACILITIES MASTER PLAN ENVIRONMENTAL ASSESSMENT The National Zoo is proposing an incentive for employees to use public transportation that could result in reduced vehicle trips by employees to the Zoo and therefore, reduce emissions. Overall, Alternatives A, B, and C would have minor short-term adverse impacts from construction activities associated with exhibit and facilities renewal. Implementation of Alternatives A, B, or C would not be expected to generate an increase in vehicular traffic, change land use, or affect employment patterns at the National Zoo; therefore, no longterm impact on air quality would occur. Mitigation for the Preferred Alternative Best management practices will be utilized during construction of individual projects to avoid and/or minimize the release of airborne pollutants. Such practices could include, but would not be limited to, the use of water to control airborne dust in active grading areas and material stockpiles, and the use of temporary vegetative cover and/or barriers on inactive areas. To the extent possible, commercial power will be used over portable generators during construction of projects to reduce temporary impacts to air quality. More detailed air quality mitigation will be prepared during the conceptual design phase of individual projects. A.6 Noise The extent to which individuals are affected by noise is controlled by several factors, including: The duration and frequency of sound; The distance between the sound source and the receptor; The intervening natural or man-made barriers or structures; and The ambient environment. The “A-weighted” decibel (dBA) is a unit of measure used to express the relative loudness of sounds in the air as perceived by the human ear. The dBA scale deemphasizes the very low and the very high frequencies and emphasizes the middle frequencies, thereby closely approximating the frequency response of the human ear. Common noise sources and their sound levels are described in the table below. SMITHSONIAN INSTITUTION – NATIONAL ZOOLOGICAL PARK 58 | P a g e
FACILITIES MASTER PLAN ENVIRONMENTAL ASSESSMENT Table 2. Common Noise Sources and Their Sound Levels Source Sound Level (dBA) Near large jet at takeoff 140 Air-raid siren 130 Threshold of pain 120 Thunder or sonic boom 110 Garbage or trailer truck at roadside 100 Power lawn mower at 5 feet 90 Alarm clock or vacuum cleaner 80 Freeway traffic at 50 feet 70 Conversational speech 60 Average residence 50 Bedroom 40 Soft whisper at 15 feet 30 Rustle of leaves 20 Breathing 10 Threshold of hearing 0 Source: Adapted from U.S. National Bureau of Standards Handbook 119, 1976. Human ability to perceive change in noise levels varies widely from person to person, as do responses to perceived changes. Generally, a three dBA change in noise level would be barely perceptible to most listeners, whereas a ten dBA change is normally perceived as doubling (or halving) of noise levels and is considered a substantial change. These thresholds permit direct estimation of an individual’s probable perception of changes in noise levels. Section 5 of the Washington, DC Noise Control Act of 1977 permits noise resulting from construction or demolition (excluding pile drivers) activity between 7:00 am and 7:00 pm on any weekday. Noise levels are not permitted to exceed 80 dBA unless granted variance. FHWA has established noise abatement criteria (NAC) that define limits beyond which noise abatement measures must be considered. Since the proposed action is not a FHWA project, these standards are not directly applicable. However, they provide a convenient benchmark to assess the level at which noise becomes a marked source of annoyance. Thresholds vary depending on the type of land use in an area. These are summarized in the table below. Land use Category B, which represents moderately sensitive land uses, including residents, churches, and hospitals, best characterizes land uses near National Zoo. The NAC for Category B land uses is a Leq(1) of 67 dBA. SMITHSONIAN INSTITUTION – NATIONAL ZOOLOGICAL PARK 59 | P a g e
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