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ALUC Minutes Page 2 January 15, 2004 CONTINUED BUSINESS: 2. City of Santa Ana - Geneva Commons - MacArthur Place Zone Chanee (JW A AELUP) Gtem continued from December 18,2003): Executive Officer Golding explained that no replies have been received to the letters sent to ALP A and the FAA, although a verbal contact with the FAA's 7460 specialist revealed that the project is 60S' outside ofthe "flight envelope" for instrument approaches to JW A Runway 19R, per the question asked by Commissioner Propst. Ms. Golding next introduced the JW A noise consultant, Mr. Vince Mestre, who presented a noise tutorial at the Commission's request, including the issues of noise impacts at ground level vs. atop high-rise buildings and the effect of proximity to aircraft. Mr. Vince Mestre, of Mestre-Greve Associates, the contract acoustical consultant for JW A, identified the buildings site at MacArthur Place in relation to the AELUP noise contours from the 1985 JW A Master Plan, as well as its distance to aircraft arriving on straight-in and turning approaches to Runway 19R. He next described the slant ranges from the ground and from the top of a 250' proposed building perpendicular to an aircraft on a 30 final approach, and he explained the physics of sound decreasing with distance from the source, such that noise would be .5 dB louder atop the building. However, as described below, he noted that there are numerous other factors which contribute to the actual real world result. When all factors are considered, the noise from a source at a sideline slant range to a site results in a higher noise level at the ground level of the building. Replying to Commissioners Webb and H. Beverburg, Mr. Mestre noted that the human ear detects a difference of about 3 dB, such that the difference just described is not detectable, adding that other factors affect sound propagation such as ground reflection and bending by temperature inversion and by wind and temperature gradients. He added that empirical data from actual measurements answer such questions. Mr. Mestre described the reflective qualities of various hard and soft landscape surfaces, noting that research is ongoing into sideline sound propagation as pertains to the FAA's Integrated Noise Model, adding that these issues complicate the correlating of noise model results with actual measurements that are undertaken by airports and aircraft manufacturers. He related the various factors that affect the lateral attenuation and spreading effect vis a vis the ground reflection of noise such as distance, angle to the aircraft, and aircraft size and type, including tail-mounted vs. wing-mounted engines. Mr. Mestre described the results of calculations for an observer at ground level and on the roof of a 250' building, perceiving noise along the slant distances to commercial aircraft arriving straight in to Runway 19R, and his conclusion that it will be noisier on the ground due to the diverse factors affecting sound propagation. He next described the situation of General Aircraft (GA) arriving to 19R by flying directly over the building, in which case it would be noisier at the roof than on the ground. The differences for the examples being 3.5 to 4.5 dB respectively, although he opined that actual measurements would likely be less than the model's calculations. Replying to Commissioner H. Beverburg, regarding such GA operations above the site, Mr. Mestre confirmed that his calculations were all based on A-weighted decibels, to reflect the range of human hearing, and he related the results for various models of GA aircraft affecting a ground level observer. He added that a top-floor observer would, in such examples, likely hear 3 dB more, after describing and comparing the various noise levels to human conversation levels. 75C-165