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The background noise level at Location 2 was also controlled exclusively by the Gunnison River. <br />• The measured L90s ranged from 47 to 53 dBA. During the daytime, noise from traffic on Highway SH- <br />133 was clearly audible. <br />The L90s measured at Location 1 ranged from 41 to 48 dBA. At night, the background noise level <br />was controlled by a ventilation fan located about 3,000 feet west of Somerset on the north side of SH~ <br />133 (not owned or operated by MCC). This fan exhausts in the direction of Somerset. In comparison, <br />the proposed fan site is located about 6,500 feet from Somerset. <br />As shown in Figure 2, the L90s measured by the continuous monitor ranged from 37 to 42 deA. <br />This demonstrates the constant nature of the ambient noise level in the study area. The Gunnison River <br />provides a steady baseline noise level. Traffic and other intermittent sources have little eftact. <br />Note that there is good correlation between the handheld and continuous monitor data measured ai <br />Location 3. For the daytime measurement at 10:15 a.m. on April 27, the L90 measured using the <br />handheld meter was 41 dBA. The continuous monitor rtreasured 37 dB.4 far the period of 10:00 to 11:00 <br />a.m. The handheld meter has an accuracy of t1 dB, and the continuous monitor has an accuracy of ±2 <br />dB. This leaves only 1 dB of variability. There was a difference of only 2 d6 in the nighttime <br />• measurements at Location 3. <br />7.0 CONCLUSIONS <br />Ambient noise levels in the study area are controlled mainly by the Gunnison River. At any <br />location, the background noise level is dependent on the proximity and topographical relationship to the <br />river. The lowest L90 levels measured ranged from 35 to 42 dBA. These levels are representative of <br />the acoustic environment of Residences A and D. <br />Noise from traffic and trains was observed to be too intermittent to appreciably affect the <br />background noise level. <br />Ambient noise levels in the center of the Town of Somerset were controlled by mining activities <br />close to and to the east of town. The dominant noise source, particularly at night, was the ventilation fan <br />located about 3,000 feet west of Somerset along SH-133 (not owned or operated by MCC). <br /> <br />8 <br />