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Chapter II <br /> concentration of 70 milligrams per liter (mg/1) 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 IV). <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 for a 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 1v: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 /> — 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 maximum compaction, according 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 /> 29 <br />