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The following runoff coefficient "C" values obtained from Table <br /> 11-15 of the Pitkin County Regulations (11) were used: <br /> Buildings (assume metal roofs, steep slopes) : .90 <br /> Unpaved Parking Lots: .60 <br /> Spoil Piles (good permeability) : .25 <br /> Coal Storage (good permeability) : .25 <br /> These values were weighted according to the percentage of area <br /> covered by each land use. for insertion in the Rational Method <br /> formula. - <br /> Table 4 shows the computations of peak- discharges for the eight <br /> drainage sub-basins of the Preparation Plant Area. <br /> Sedimentation Pond Design. The required volumes of storage in the <br /> -sedimentation ponds were computed to meet federal, state and county <br /> regulations given in References 6, 10 and 11 which specify design <br /> fora 10-year/24-hour precipitation event. In addition, sediment <br /> storage volumes of 0.2 acre-foot for each acre of disturbed drainage <br /> i <br /> area were added as specified in the regulations (3) . Disturbed areas <br /> for the Preparation Plant Area are defined as the total drainage area <br /> less the area covered by buildings. <br /> • 11 <br /> ;I - <br />