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Staff Recommendation <br /> Docket #SU-81-20 <br /> November 13, 1981 <br /> Page Five <br /> operations from a noise standpoint. In the worst case, the boundary of <br /> Stage 4 of the revised plan is only 700 feet from the nearest mobile home <br /> in the Coliday Mobile Home Park. The maximum level of 64dBA to be received <br /> at the trailer park exceeds the L ambient level ny 17 dBA. From standards <br /> previously cited, this would genMte widespread complaints and threats of <br /> legal action and more than double perceived loudness. Noise levels would <br /> be especially critical at the start of mining of the phase due to a lack <br /> of difference in elevation (lowered level of pit) and a lack of overburden <br /> stockpiles. <br /> An item that hasn' t been mentioned is that all noise calculations have been <br /> based on outdoor noise levels. Noise levels inside structures with the <br /> windows closed can be reduced by anywhere from 20dBA for light frame con- <br /> struction with ordinary sash windows to 35dBA for masonry structures with <br /> double-glazed windows (USDOT Report No. FHWA-HHI-HEV-73-7976-1, 1973). In <br /> winter months when windows are likely to be closed and outdoor activities <br /> are minimized, higher outdoor noise levels can be acceptable. A constant <br /> noise level of 65 dBA would typically be reduced by 20dBA to 45dBA indoors <br /> in a light frame construction residence with the windows closed. In fact, <br /> the standard EPA equation for noise attenuation over distance assumes a <br /> 20dBA reduction for being indoors with closed windows. <br /> Staff's recommendation is that, over the course of mining all phases, the <br /> initial mining in any phase be scheduled so as to occur in winter months <br /> in order to offset the initial lack of overburden stockpiles and pit walls <br /> as noise barriers. In addition, overburden should be stripped and stockpiled <br /> between the mining area and the nearest residences as quickly as possible. <br /> This can usually provide a 5-10 dBA reduction in noise levels. <br /> It should be noted that noise level problems in the initial stages of <br /> mining a phase will be temporary in nature. In the worst case of the mobile <br /> home park, mining noise levels at the far side of the stage will be attenuated <br /> by distance alone by an additional 6 decibels to a maximum level of 58dBA <br /> which is lower than the 65dBA maximum level recommended by staff. An additional <br /> 5-10 dBA reduction through pit walls and overburden stockpiles would bring <br /> the noise well within acceptable levels. <br /> A final noise concern with mining operations is the noise associated with <br /> operating and loading trucks in the pit areas. Empty trucks will tend to <br /> rattle on the rougher pit surfaces and the noise of dumping pit run into <br /> the trucks has been cited in previous public hearings. If these noises <br /> prove to be excessively annoying and/or in violation of recommended noise <br /> standards, the Special Use will need to be reviewed to consider requiring <br /> the use of conveyors to transport pit run to the processing plant. Short <br /> of requiring conveyors, this impact, like many others, can be at least <br /> partially mitigated by sensible methods of operation, including slower <br /> truck speeds in pit areas, maintenance of commonly traveled areas in the <br /> pits and loading near the pit walls and overburden stockpiles to make the <br /> most effective use of these noise barriers.. <br /> Hauling <br /> The noise from diesel trucks is the item of greatest concern with respect <br /> to hauling. Diesel trucks are generally 8-10 dB noisier than gasoline <br />