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i The sound levels from the proposed concrete recycling operation that were projected for <br />, each of these locations would be lower than their respective measured sound levels of <br />� weekday background noises, with the exception of the detention facility. For reference, <br />, 50 dBa sounds about like being in a quiet restaurant, 60 dBa sounds like the inside of an <br />s active office or a normal restaurant, and 70 dBa sounds like a passenger car passing about <br />�'� 20 feet away. Noise level projections were made assuming flat land with no obstructions, <br />- so the actual sound levels experienced at the residential receptor sites should be lower <br />� due to the sound barrier effect of gravel stockpiles, bez�zs, and vegetation. <br />�r fi.5 The MPCA's daytime residential standard indicates that continuous noises are acceptable <br />i�. when their sound levels remain below 60 d�3a for more than 50% of their duration or <br />� � remain below 65 d�a for more than 90% of their duration. <br />�° 6.� During the May 3, 2006 public hearing related to a similar recycling operation to be <br />i� located in the Twin Lakes area, a contractor specializing in concrete recycling explained <br />i � that vibrations from crushing operations are typically not felt beyond 150 feet. And the <br />i k City Planner was able to confirm the limited range of the noticeable vibrations after <br />P�'07-013 TtCA 032507 <br />Page 3 of 4 <br />