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nnr. Kex rsurns <br />Page Six <br />May 1, 1998 <br />Construction of the grade control structure will not be necessary until mining comes within 440 <br />feet of the river at the north end of the proposed gravel pit. There are many options available <br />regarding the type and construction of the grade control structure. The applicant favors use of <br />concrete rubble. Other alternatives include articulated concrete blocks, riprap, and soil cement. <br />We have assumed uniform erosion across the width of the gravel pit. In reality, there is potential <br />for concentrations of flow that may cause more localized erosion in some areas. We <br />recommend that when mining comes within 600 feet of the river on the north end of the pit, the <br />applicant have an emergency plan in place that will mitigate this localized erosion that may <br />occur. <br />If you need additional information, please don't hesitate to call me. <br />Sincerely, <br />en Ayr s & Associates, Inc. <br />Scott Que n, P.E. <br />Civil Engineer <br />SQ:sp <br />Enclosure <br />BURNS-4A.LTR <br />34-0648.00 <br />