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East and West Topsoil /Coverfill Stockpiles <br />Gob Pile #3 <br />Alternate Sediment Control <br />Straw Log substitute for Silt Fences <br />The following table summarizes the peak water stage, trap efficiency and silt <br />fence length for the topsoil and coverfill stockpiles at gob pile #3. <br />Description <br />Peak Water Stage <br />Trap Efficiency <br />Length <br />Feet <br />% <br />Feet <br />Coverfill Stockpile- <br />0.37 <br />58.58 <br />100 <br />Gob Pile #3 <br />Topsoil Stockpile- <br />0.24 <br />60.96 <br />65 <br />Gob Pile #3 <br />The design flow rate for the silt fence is 10 gallons per minute per square foot. <br />The peak water stage for the coverfill stockpile is 0.37 feet or 4.44 ". <br />The peak water stage for the topsoil stockpile is 0.24 feet or 2.88 ". <br />The key factor in sediment control is the trap efficiency. According to data <br />published by American Excelsior Company, its 12" Curlex sediment log has a trap <br />efficiency (% Soil Retained) of 70.3% and a flow rate of 37.5 gallons per minute <br />per square foot. Its 6 and 9 inch sediment logs have a trap efficiency of 53.9% <br />at 42.5 gallons per minute per square foot. <br />The high flow rates of the sediment logs in relation to the silt fence design would <br />indicate run -off will not overtop the straw logs. The straw logs will filter the run- <br />off faster that the sediment fences. The favorable trap efficiency of the straws <br />logs indicate they are as good as or better than the designed silt fence. The 6 <br />and 9 inch straw logs have a slightly lower trap efficiency that is not considered <br />significant. <br />Straw logs will be keyed into the natural soil at the low point of the topsoil <br />stockpiles as shown on Map 21 -3. The total length of the straw logs will be <br />comparable to the length indicated in the approved silt fence designs including <br />tie back distances. The straw logs will be overlapped to prevent flow bypass <br />when pieces are joined to achieve the appropriate total linear footage. Flo ORA130 t/� <br />from the straw logs will then be directed to the Clean Water Diversion di **AE STO•F ?s�, <br />iOz 43402 <br />12 Z'V ►moo: <br />�Q <br />ss�o /0 <br />TR -91 Volume XI, App. B -80 12/14 <br />