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<br />TOPSOIL STOCKPILE SAE <br />Topsoil stockpiles are located at various places at the Y'oast mine and are planned at various places in the <br />Sage Creek area. The locations of the planned topsoil stockpiles are shown on Exhibit 12-1, Operations <br />Plan. IL is estimated tha[ the lar¢est s[ockpile planned wtll encompassed about 5.5 acres. Once topsoil is <br />placed in the stockpile. it is seeded with the previously approved intertm seed mixture. Therefore, the <br />topsoil stockpiles are in a disturbed condition for a relatively short time. Due to the small area affected by <br />the topsoil stockpiles, Seneca believes that conventional drainage and sediment control measures are not <br />necessary. <br />Seneca proposes alternative sediment control measures to contain runoff from the topsoil stockpile areas. <br />A 2.5 Foot berm will be constructed completel}• around the stockpiles. The down-gradient portion of the <br />berm will contain the entire runoff volume from a 10-year, ?4-hour (1.7 in.) storm event. Diversion ditches <br />will be constructed (up-gradient), as necessary, to divert runoff away From the stockpiles. <br />The following calculations demonstrate that a 2.5 foot containment berm constructed down-gradient of the <br />stockpile will contain the runoff from the design storm. <br />Hvdroloev Inputs <br />The cun~e number (CN) assigned to the topsoil stockpiles was indicative of a one year reclaimed condition <br />using approved interim seed mi.x. <br />Reclaimed <br />• <br />Sod Type: B <br />Ground Cover: One year ineerim reclamation (Fair >709n) <br />Cover Type: Interim seed mix <br />CN: 71 <br />All other hydrology inputs are shown on the attached SEDCAD4 computer printouts. <br />Hvdroloev Results <br />Runoff volume: <br />Berm Desion <br />0.07 ac. ft. (3.136 cu. Ct.) <br />.4 2.5 ft high berm will be constructed on the down-gradient side of the stockpile alone the contour for its <br />full length. The length of a typical stockpile is estimated to be 300 ft. The slope of the land is estimated <br />to be 209c. on averaee. The storage volume was calculated as follows: <br />Cross-sectional area (containment area): berm (?H:1 V) ?.5 ft. (use 2 R.): <br />Length, using ?09c averaee slope, ?09c= I 1 degrees. L = 2ft.(pan 1 I = I Oft <br />Area (A) = Qft X I OfU/2 = 10 sy.ft. <br />Storage Volume: 10 sq. ft. X 400 ft = 4.000 cu. ft. = U.09 ac. ti. <br />Since 0.07 ac. fl. is required. the containment volume is adequate. <br />• <br />