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• Soth the Rion NA-29 and the RTA Sound Logging Meter were operated within their stated factory <br />calibration periods. In addition, the Rion was field-calibrated using a CEL Model 282 calibrator befom <br />and after each measurement. The RTA was field calibrated with the CEL calibrator prior to and after <br />operation. No adjustments to the units or the data were requirzd after the first calibration. <br />6.0 MEASUREMENT RESULTS <br />As described in Section 5.2, the L90 is the acoustic metric most commonly used to quantify <br />ambient noise. Table 1 shows the L90 measured at each location during both daytime and nighttime <br />periods. Also shown is the average hourly L90 measured by the monitor for daytime and nighttime <br />periods. The continuous monitor data is shown graphically in Figure 2. Measured data has been <br />included in Appendices A and 8. <br />TABLE 1 <br />MEASURED L90 LEVELS (d BA) <br />• <br />Loom Description Dav time L90 Nighttime L90 <br />1 Somerset 48 d1 <br />2 Residence i3 53 47 <br />3 Property Line 35 38 <br />3 Monitor 39 39 <br />4 Pesidence D 41 42 <br /> <br />Locations 3 and 4 experienced the lowest ambient noise {evets, with L90s ranging from about 35 to <br />42 dBA for both handheld and continuous monitor data. These ambient levels were controlled <br />exclusively by noise from the Gunnison River. As discussed in Section 4.0, highway and train traffic <br />noise was too intermittent to appreciably affect the L90, which is evident from the tact that daytime L90s <br />were lower than those measured at night. This diurnal variation is most likely due to slightly greater wind <br />at night, which produced low levels of noise in nearby trees and bushes. Note: wind levels were <10 <br />mph, which is considered adequate conditions for noise measurements. <br />6 <br />