2008-04-15_REVISION - M1980244 (336)

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r /1 ?/? efi e ? _. 1J 1 ./?? jEXISTING NOISE ENVIRONMENT A. Assessment Considerations The accepted procedure when considering an'impact assessment of any environmental factors such as noise, air quality, etc. is first to determine by analysis or measurement the existing environmental conditions. Of all of the environmental factors, noise can have the greatest variability, especially in those areas where there is human activity. This is especially true in the Cripple Creek and Goldfield areas where the noise from vehicle traffic and other cultural activities can vary hourly, daily and weekly. Thus, a single noise sample in a residential area may not be a true measure of the existing noise environment. For this reason it was decided to conduct long-term noise measurements at several locations adjacent the CC&V mine. Noise measurements were conducted in 2004 as part of the East Cresson Mine Expansion (ECME) project, which is currently approved under the Office of Mined Land Reclamation Permit M-1980-244. Most of these measurements were taken in the Goldfield area. The results of this work conducted by E. D. I. in 2004 are summarized in Section II-B of this report. Additional noise measurements were conducted in 2007 in and around the City of Cripple Creek as part of the proposed MLE Project. These results are presented in Section II-C of this report. B. 2004 Measurement - Methodology and Results In February of 2004, the existing noise environment was measured using five (5) noise monitors. These instruments consist of an accurate (Type II) sound level meter and a data storage unit all incorporated in the same physical package. The five instruments were Quest Model M39 and they measured the average sound level every minute during the entire time of operation. These one-minute averages were then stored in a computer memory chip for printout at a later time. The computer in the instrument also determined the average maximum and percentile for each hour and for the entire period of operation. In addition, the instrument computes the statistical distribution in 1 percent (1 %) increments for 1 % to 99% exceedance value. The decibel number and the % exceedance can be compared to the familiar "class average" numbers. The 50% decibel value means that half of the time the noise was either greater or less than that decibel level. On the other hand, the 10% exceedance level means that only 10% of the time did the noise exceed the decibel levels. During the measurement interval from 2/2/04 to 2/3/04, the temperature ranged from a low of about 5 deg. F to a high of about 25 deg. F, the wind was variable with occasional gusts as high as 15 mph, the sky was clear and there was no precipitation. At distances of less than one mile, the most significant meteorological factor is wind, other factors such as precipitation, cloud cover or temperature become contributing factors at greater distances. Also, at altitudes above about 7500 ft., temperature inversions do not occur. At distances of about one mile, a change in sound level at the receptor of plus or minus 10 dB(A) can occur. At several hundred feet the wind effect is plus or minus 5 dB(A). Table 1 presents the statistics of the baseline noise levels measured at the five sites in 2004. The columns titled 1, 10, 50 and 90 are the exceedance levels. At measurement Site 1 for example, 1 % of the time the noise was greater than 45 dB(A), 10% of the time greater than 39 dB(A), 50% of the time greater than 36 dB(A) and 90% of the time greater than 35 dB(A). The average noise level at Site 1 was 36 dB(A). Table 1 Goldfield Area - 2004, Noise Exceedance Levels - dB(A) Exceedance Percentile Measurement Site 1 10 50 90 Average 1 - Cabin 45 39 36 35 36 2 - Corral 47 41 38 37 38 3 - City Hall 47 42 40 38 41 4 - Independence and 8 48 44 44 41 44 5 - Independence and 12 49 40 31 28 35 Rev # EDI Job No. C3616 Page 6 of 17 3925 S. Kalamath St., Englewood, Colorado 80110 • voice: 303-761-4367 9 fax: 303-761-4379