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Mr. Mike Murlowski <br />SelAir Excavating . <br />May 14, 2009 <br />Page 2 of 2 <br />As shown above, the tailgate "bang" sound will be reduced by 8 dBA by installation of <br />the new berm. To put this reduction in perspective, most people judge a sound level <br />reduction of 10 dBA as "half as loud". <br />It should be noted that this extrapolation is very conservative and does not account for <br />additional reduction due to atmospheric attenuation, ground absorption, vegetative <br />shielding and ambient noise generated by wind. An estimate of the additional reduction <br />due to atmospheric attenuation and ground absorption is 12 dBA. <br />Thank you for the opportunity to provide this addendum. If you have any questions,. <br />please contact me at 763-479-4236. <br />Sincerely, <br />WENCK ASSOCIATES, INC. <br />T <br />Timothy J. Colliton, PE, CIH <br />Project Engineer <br />encl <br />• <br />TA2284101 \Addendum #2 to Sound Mitigation Lettmdoc <br />