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Chapter II <br />concentration of 70 milligrams per liter (mg/I) nor a 30 consecutive-day average of more <br />.than 35 mg/I (snow melt or precipitation event /wet conditions = .5 mg/I settleable <br />• solids -- See Chapter I~. <br />Each sedimentation pond is designed to detain the peak flow of a 10 year/24 hour <br />storm event for a minimum of 24 hours. Embankments are designed fora 1.0 foot <br />freeboard during a 25-year/24-hour event (App. II-B-7). <br />The sedimentation pond storage volumes have been designed using the Universal Soil <br />Loss Equation and a standard 0.1 acre-foot for each acre disturbed (App. II-B-7) <br />The dam widths have been designed in accordance with the equation (H = 35)/5 where <br />H is the height in feet from the upstream toe to the top. Slopes where the combined <br />upstream and downstream slope is less than iv:5h are stabilized by vegetation. <br />The spillways have been designed to safely convey the runoff event from a <br />25-year/24-hour storm and constructed with a 1.0 foot freeboard above the principal <br />spillway. The principal spillway is designed to function only when the storm event <br />exceeds the 10-year/24-hour storm. <br />The embankments of the ponds were constructed using the following procedures: <br />- material placed in the fill has been kept free of <br />detrimental amounts of rock, roots and debris; <br />• <br />- backfill material around culverts and antiseep collars <br />had been placed at approximately the same rate in <br />order to prevent uneven loading; <br />- keyways have been constructed in accordance with <br />sound engineering practices; <br />- fill material has been placed and spread in 12" horizontal <br />layers, started from the lowest point of the foundation, <br />and up. The ma~dmum compaction, acxording to <br />engineering consultant recommendations, was done for <br />each layer; <br />- to improve compaction the moisture content of the fill <br />was optimized. <br />Principal spillways are constructed of corrugated metal pipe and conform to federal <br />specifications W. W-P-402. The pipe was firmly and uniformly embedded throughout <br />the impounding structure, anti-seep collars have been placed around the pipe. <br /> <br />29 <br />