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BlNJ.lDIHI'.D'L RBVIJIf SIL"'J'1at BIGHr AIRFua" JtmS'.Im PIAN SM1~, ~ This section provides a brief evaluation of potential adverse envj.ronmenta1 impacts resulting from the proposed airport development. AltlDlgh no major improvements have been proposed that would require a full envi.J:aunental assessment, this review does address the long term deve.lopment at San Marcos Municipal .Ai.rport. adse The potential for adverse noise levels produced by existing and projected aircraft operations is present at all airports and must be accurately assessed to effectively determine the actual impact on the environment. There are a number of methodologies or descriptors available for use in airport noise analyses. The most recent tecbnique, the FAA Integrated Noise Model (INM), permits a variety of data to be developed for the determination of the extent of noise exposure on and around the airPOrt site. In Figures 8.1, 8.2, and 8.3, noise ocntours generated by the INM oomputer program is based on air traffic projected for the years 1986, 1995, and 2005. These noise contours can be defined as lines of equal noise exposure in terms of day-night sound level (um). '!be day-night sound level (:Wn) is the equivalent A-weighted sound level during a 24-hour time period, with a 10 decibel weighting applied. to the equivalent sound level durinq the night-time hours of 10 p.m. to 7 a.m.; a 5 decibel weighting is applied during the evening hours of 7 p.m. to 10 p.m. With these Idn noise ocntours, cxmununity response to aircraft noise f%all future operations can be estimated to evaluate present and future land use compatibility. Generally, the FAA and EPA interpretation of zones defined by the Mn contours for land use guidelines are as follows: ZOne 1 tama ~ Idn 65): '!his area has no restrictions as to the type of development due to sound levels. 8.1