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86. Section 8.12 Noise, Projected Noise impacts -need reference(s) to: nearest residence (1 mile), 55 db(A) at 0.3 mile, <45 db(A) at 1 mile, <or-80db(A) at 300 feet (construction activity) The distances to the nearest residences from the Piceance Site and the Parachute Site were estimated by Steigers Corporation staff. According to Table 8-2 of the Mine Plan, the tnaxirnum noise level at a distance of 50 feet from heavy-duty truck travel is 85 decibels fdb(A)]. This noise level will be attenuated by approximately 6 db(A) each time the original distance from the source (50 feet) is doubled. Attenuation of the 85 db(A) noise level to the permissible Residential Zone Levels of 55 db(A) (see Table 8-3 of the Mine Plan) requires a 30 db(A) reduction. Therefore, the original distance from the source (50 feet) must be doubled five times (30/6 = 5). The new distance from the source at which the noise level is attenuated to 55 db(A) is 50 x 25 = 1,600 feet = approximately 0.3 mile. Note that the attenuation rate of 6 dB(A) for each doubling of the distance was estimated from empirical measurements of sound levels at the Healy Clean Coal Project (HCCP) site using a technique known as a "walk-away test." It was observed that sound levels decreased at a rate of approximately 6 dB(A) with a doubling of the distance from Healy Unit No. 1, an existing coal fired power plant that was the dominant source of noise at the HCCP site. Alaska Industrial Development and Export Authority (AIDEA). 1992. Permit, Application for Air Oualitu Control Prevention of Significant Deterioration Permit to Operate. Prepared by Stone £> Webster Engineering Corporation for the Healy Clean Coal Project. April. To further attenuate the noise level from heavy-duty truck travel to a background noise level of 45 db(A), the 55 db(A) at 1,600 feet would have to be reduced by 10 db(A). This attenuation would occur between one and two doubling distances from 1,600 feet, or between 3,200 feet C6 db(A) reduction to 49 db(A)] and 6,400 feet (12 db(A) reduction to 43 db(A)]. Interpolating between these two attenuation points, the 10 db(A) reduction to 45 db(A) would occur at approximately 1.0 mile. At a distance of 50 feet from construction activity, the maximum noise level is 100 db(A). Attenuation of this 100 db(A) noise level to the permissible Industrial Zone Levels of 80 db(A) requires a 20 db(A) reduction. This attenuation would occur between three and four doubling distances from 50 feet, or betzueen 400 feet (18 db(A) reduction to 82 db(A)] and 800 feet (24 db(A) reduction to 76 db(A)]. Interpolating between these two attenuation points, the 20 db(A) reduction to 80 db(A) would occur at approximately 500 feet. Note that the lest sentence of the paragraph in the Projected Noise Irnpncts section of the Commercial Mine Plnn should be modified to read as follows: 33