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<br /> <br />April 6, 2001 <br />Steve O'Brian <br />Environment, Inc. <br />7985 Vance Drive, Suite 205A <br />Arvada, Colorado 80003 <br />RE: S&H Mine <br />Platteville, Colorado <br />PEI No. O1-006/14.0 <br />Deaz Mr. O'Brian: <br />-~- <br />PICKETT <br />ENGINEERING, INC. <br />i III IIIIIIIIIIIIIIII <br />999 <br />RECEIVED <br />APR 1 Z 2001 ' . <br />Division of Minerals and Geology <br />You forwarded to me a portion of a letter that you received from the Division of Minerals <br />and Geology, regarding information they require in reviewing the application that has <br />been presented to them. Question pumber 9 asks what specific measures will be taken to <br />mitigate the impacts of flooding. I offer recommendations based upon my review of the <br />available data, specifically,. the South Platte River Basin Flood Study prepared by the <br />U.S. Army Corps of Engineers, Omaha District, dated April 1977. <br />The following chart reflects the flood event, the expected velocities, the flow rates and <br />the depths of flow as they impact the site. <br />STORM ESTIMATED,FLOW ESTIMATED AVG. ESTIMATED <br />FREQUENCY RATE DEPTH OF FLOW VELOCITY <br /> cfs ~ feet s <br /> South End North End South North South North <br /> Of Site• Of Site End• End End• End <br />100- ear 28 000 33 000 2.2 3.0 1.5 fo 2.0 3.6 <br />500- ear 49,000 57 500 4.4 4.7 ~ 1.6 to 2.5 5.0 <br />• South end and all but the porthernmost end of the site. <br />Based upon this information, it would be my recommendation that the mitigation <br />measures utilized would include the following, in order of priority: <br />1. Keeping the dry pit slopes at a maximum slope of 1:1 <br />808 8th Street <br />Phone (970) 356-6362 <br />Greeley, CO 80631 <br />- Fax (970) 356-6486 <br />