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<br /> <br />Delta Sand & Gravel Mining Area Expansion Noise <br /> <br />occurs for less than 30 minutes per hour, a six foot high noise reduction berm in the vicinity <br />of the work area shown in Figure 2 will be enough to ensure compliance with the DEQ noise <br />limits. <br /> <br />It is our understanding that Delta Sand & Gravel plans to construct a 10 foot high berm along <br />the length of the aquaclude work area prior to excavating and hauling any material from the <br />aquaclude trench. If that is the case, then excavation operations can occur without time <br />constraints anywhere in the aquaclude work area and meet the DEQ noise regulations. <br /> <br />You indicated during a recent call that the construction of the aquaclude will occur on an "as <br />needed" basis and that the aquaclude may be constructed in 300 to 500 foot segments. If that <br />is the case, noise reduction berms may be constructed on an "as needed" basis. In addition, it <br />should be pointed out that a noise reduction berm does not have to extend the full length of <br />the trench to effectively mitigate the trench excavation noise. If excavation will occur more <br />than 30 minutes per hour, to be effective, a noise reduction berm needs only to extend 50 feet <br />beyond the line of sight between all portions of a work area and any residence located within <br />475 feet of the work area. If excavation will occur less than 30 minutes per hour, noise <br />reduction berms can be constructed to extend 50 feet beyond the line of sight between the <br />work area and any residence within 250 feet of the work area. <br /> <br />137045-M2.doc <br /> <br />October 27, 2006 <br /> <br />Page 3 of 3 <br />