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In some instances, the mining will cause the drainage area to change <br />• during the life of the sediment structure. When the pit moves into the <br />watershed, runoff is intercepted by the pit and diverted away from the <br />structure. In these cases,'a conservative procedure was used; the <br />structure was analyzed for the largest anticipated drainage area that <br />will contribute runoff to the structure. This condition usually occurs <br />at the start of mining and again during the reclamation period. <br />Following is a summary of the SEDIMOT II input values used in the Design <br />Report and the As-Built Report (see the Design Report for the derivaticn <br />of the input values): <br />10-Year, 24-Hour = 1.60 inches <br />25-Year, 24-Hour = 1.80 inches <br />100-Year, 24-Hour = 2.40 inches <br />SCS Type II Storm <br />CN = 81 <br />k = 0.25 <br />Disturbed Hydrograph (No. 1) <br />tc = 0.064 hr. <br />(1) MUSLE = 0.035 ac-ft. or 65.46 tons <br />Specific Gravity = 2.5 <br />Submerged Bulk S.G. = 1.25 <br />LS = 4.10 <br />CP = 1.0 <br />The particle size distribution for this sediment pond was taken from <br />Simons, Li and Associates (Design of Sediment Control Measures for Small <br />Areas in Surface Coal Mining). This distribution is representative of a <br />sandy loam soil similar to those described in Tab 9 of the current Nucla <br />Mine Plan. <br />• <br />3 <br />