WTC site damage assessment map, Sept 21, 2001

NYC 9/11 Public Portal Document

heard over a specific period by assuming it had been a steady, unchanging sound. For this descriptor, called the equivalent sound level, Leq, can be computed. The Leq is the constant soimd level that, in a given situation and period, conveys the same sound energy as the actual time-varying sound.

In order to describe the fluctuating noise over a specific period, statistical sound level descriptors are used. The most commonly used statistical noise levels .^re the Lio, L90, and Leq. The Lio is defined as the maximum one-hour sound level exceeded 10 percent of the time and is appropriate to describe traffic noise assessments. The L90 is defined as the sound level that is exceeded 90 percent of the time and is taken as the background noise level. The Leq is the equivalent steady-state sound level that contains the same acoustic energy as the time-varying sound level during a stated time period. As required by New York City criteria, Lio is used to assess the impact caused by project-generated traffic. The equivalent noise level, Leq, is used for stationary source evaluation.

The U.S. EPA’s guidelines (and those of many Federal agencies) state that outdoor sound levels in excess of 65dB DNL are “normally unacceptable” for noise-sensitive land uses such residences, schools, and hospitals. At unacceptable levels, noise can disrupt activities, particularly those associated with noise sensitive receptors, which can include parks, hospitals, residences, schools, museums, and houses of worship, among others. Although sound levels are subjective. Federal and local governments have established noise guidelines and regulations to protect people from adverse effects associated with noise. In general, residential units and other noise-sensitive land uses are "clearly unacceptable" in areas where the noise exposure exceeds 75dB DNL, "normally imacceptable" in areas where noise falls between 65dB to 75dB DNL, and "normally acceptable" in areas where the DNL is 65dB or below. « The City of New York has developed a local ordinance for noise control, a.k.a., the New York City Noise Code (DEP Code Title 24), dated March 1998. General provisions include prohibition against unreasonable noise. Constmetion activities are limited to weekdays between the hours of 7 a.m. and 6 p.m. imless urgent necessity in the interest of public safety exists. Rapid transit railroad, railroads, air compressors, paving breaker are restricted to allowable sound levels. Ambient noise quality zones, criteria and standards for various zoning and land uses have been developed based on the Leq Subchapter 7 of the Noise Code, Certificates and Tunneling Permits, describes requirements for tunneling permits and stipulated standards or requirements for tunneling operations. Noise levels in the study area are consistent with other urban areas. Traffic is a significant source of noise and is particularly heavy during the morning and evening rush hours.

The noise statutes, regulations, and guidance potentially applicable to the WTC redevelopment project include:

• New York City Noise Code—Title 24 • New York State Department of Public Service Noise Guidelines

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