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Source height, 6 ft. <br />Height above ground of the fan end of the loader or back hoe <br />d at engineering <br />, dynamics <br />incorporated <br />B. Electric Generator <br />The Electric Generator is a diesel driven unit delivery about 350 KW of power which is equal to about <br />250 shaft horsepower of the diesel engine. The generator will be located at the south boundary of the pit <br />area and the distance to the nearest residential property line is 300 ft. At this distance the direct line - of- <br />sight noise level will be 57.5 dB(A) or 2.5 dB(A) above the 55 dB(A) noise limit for residential properties. <br />This means that the generator must be located either below grade level or shielded with a noise wall. <br />There is the possibility that a smaller generator will be used at the pit because 350 KW is about twice the <br />electrical power required. An engine /generator of about 200 KW would be 3 dB(A) quieter then the 350 <br />KW unit and the noise level at 300 ft. would be 54.5 dB(A). This dB(A) level is too high because of the <br />additive effect of all the other equipment operating in the pit. Also, a wind from the south would increase <br />the noise level by as much as 5 dB(A). A 10 ft. high noise wall or setting the unit 15 ft. below grade level <br />would provide a minimum of a 5 dB(A) reduction. An additional reduction can be achieved by having the <br />cooling fan end of the engine pointing towards the south, which would reduce the noise going towards <br />the north by 2 or 3 dB(A). <br />C. Track Hoe and Loader <br />Both the Track Hoe and the Front End Loader produce 58 dB(A) at 100 ft. when at maximum power with <br />the fan end (the rear end) pointing towards the north. When the loader or track hoe is right at the <br />northern pit boundary and on the surface, the distance to the closest residential property line is 100 ft. <br />and the direct Tine -of -sight noise level would be 58 dB(A) which is in excess of the 55 dB(A) limit. <br />This situation is very typical for many surface mining operations when the mobile equipment such as <br />loader and dozer are working at the surface during mine development. When mine development is <br />occurring the noise emission limits are those presented in Colorado Revised Statutes, CRS -25 -12 -103 § <br />(5) which allows the noise emissions to be those for industrial zones which is 80 dB(A) at 25 ft. beyond <br />the property line. Mine development at the Destiny Gravel Pit would consist of moving the thin layer of <br />top soil to the edge of the pit and forming a berm around the pit. This berm would be no more than 3 ft. <br />in height and is not high enough to reduce the noise from the loader and track hoe. Top soil scrapping <br />and construction of the berm around the pit will take about one week at the most, after which the noise <br />level according to the BLM requirements must not exceed 55 dB(A). This can be accomplished by <br />starting mining at the southern portion of the pit and getting the loader and track hoe at least 25 ft. below <br />grade level. The noise reduction calculations using the Maekawa Barrier Equation are: <br />Barrier Height, 25 ft. <br />Height of the face of the pit when starting the mining process. This area of the mine would be <br />the first to be excavated. <br />Receptor Height, 30 ft. <br />Ground elevation at pit boundary, same as height of mine face, 25 ft. plus 5 ft. The mine face <br />slope is 1 to 1. <br />Source to Barrier Distance, 25 ft. <br />Distance between mine face and loader or back hoe. This is the height above grade on which <br />the noise monitor would be positioned. <br />Distance from Mine Face to Pit Boundary — 200 ft. <br />Barrier noise reduction — 16 dB <br />Line -of -Sight Noise Level at Pit Boundary — 52 dB <br />Resulting noise level at Pit Boundary — 36 dB(A) <br />E.D.I. Job # C3864 <br />Page 9 of 11 <br />3925 S. Kalamath St., Englewood, Colorado 80110 • voice: 303 - 761 -4367 • fax: 303 - 761 -4379 <br />