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Mr. Mark Heffner - 2 - May 25, 1989 <br />Drainage Crossing Culverts <br />Culverts at the two drainage crossings will be designed to safely pass <br />the 25-year, 24-hour precipitation event with an additional 2 feet of <br />freeboard provided at the culvert headwalls. Riprap or other materials <br />will be provided in the design to establish stable channel conditions at <br />the culvert inlet and outlet. <br />Silt Fences <br />Silt fences will be utilized and constructed at the border of the mining <br />area along the setback from the drainage course. The setback will be <br />defined as a 6-foot minimum vertical elevation rise between the channel <br />bottom and the adjacent land. Silt fences will be placed prior to <br />disturbance of upgradient drainage area, and removed after success of <br />revegetation has been established. <br />Topsoil Stockpile Berm <br />A berm of 1-foot vertical height will be placed around the temporary <br />topsoil stockpile. <br />In developing the designs for submittal to the Division, please include all of <br />the hydrologic design parameters, calculations and any assumptions used in the <br />analysis. This will assist in the review and provide documentation for the <br />file. <br />If you, or a consultant retained to complete the designs, have any ouestions <br />on appropriate design methodologies please feel free to contact me at any time. <br />Sincerely, <br />John T. Doerfer <br />Reclamation Specialist <br />JTD/eke <br />cc: Daniel I. Hernandez <br />H. Bruce Humphries <br />6539E <br />