Replacement Terminal Environmental Assessment
10. What noise studies are proposed for the Terminal Environmental Assessment?
The EA analysis includes conducting a noise analysis using the most recent version of FAA's AEDT 2D to generate DNL noise contours for the “no build” and “build” scenarios. The noise contours will be superimposed on a land use map depicting existing and future land uses. The results of the two scenarios will be compared and contrasted. The build scenario, and its difference relative to the no build scenario, will be evaluated to determine if the "threshold of significance" is exceeded.
Previous requests have been made regarding the implementation of a Noise Compatibility Study (FAR Part 150). A Part 150 Study is a process initiated by an airport to develop, evaluate, and recommend actions that the airport, local municipalities, airlines, and/or the FAA could take to help reduce the land use incompatibility due to aircraft noise in communities surrounding an airport. FAA acceptance of an airport’s Noise Exposure Map (NEM) and approval of a Noise Compatibility Program (NCP) allows an airport operator to become eligible to receive Federal funding to develop and implement the recommended programs within the NCP that have been designed to help mitigate aircraft noise. The primary use of a Part 150 Study is to determine where noise impacts facilities on and off the airport, define the eligibility of residential properties for sound insulation or purchase through FAA funded programs, or to identify other measures that can be undertaken related to air traffic procedures or other operations based functions.
Land use compatibility is defined by the FAA in FAR Part 150, as the “use of land that is identified as normally compatible with the outdoor noise environment or an adequately attenuated noise reduction level for the indoor activities at the location.” The goal of the FAA’s noise compatibility guidelines is to discourage the development of incompatible land uses around airports. The FAA guidelines specify that DNL is the noise metric used in defining land-use compatibility. Both the U.S. Department of Housing and Urban Development (HUD) and the FAA define a Day-Night Average Sound Level (DNL) value of 65 dB as the threshold of incompatibility with residential land uses.
The outdoor noise environment, in relation to airport noise compatibility, is measured in terms of the yearly Day-Night Sound Level (DNL) metric. The DNL represents noise as it occurs over a 24-hour period, with one important note: DNL treats nighttime noise differently from daytime noise. In determining DNL, it is assumed that the sound levels occurring at night (defined as 10 p.m. to 7 a.m.) are 10 dB louder than they really are. This 10 dB penalty is applied to account for greater sensitivity to nighttime noise, and the fact that events at night are often perceived to be more intrusive because nighttime ambient noise is less than daytime ambient noise. FAA has published guidelines which include a table describing compatible land use information for several land uses as a function of yearly DNL values and a matrix that identifies what types of land uses are incompatible with certain levels of noise exposure; for example, residences, schools, and outdoor music shells or amphitheaters are incompatible land uses where noise exposure levels are greater than DNL 65 dB. While noise from airport operations may be experienced in areas beyond the DNL 65 dB noise contour, only those areas with noise levels of DNL 65 dB or higher are considered to be incompatible. It is the intent of a FAR Part 150 Study to find ways to reduce incompatible land uses and prevent future incompatible land uses in these areas first, while still addressing noise exposure and evaluating methods to reduce noise exposure in all areas surrounding the airport. The 65 dB noise contour at TTN is largely on airport or within Airport or County owned property and TTN and the County are addressing issues where residences are within the 65 dB noise contour.