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• A value of 30 _f or the average Annual R value and a period of seven years was used. <br /> Sedcad+ determined the required Sediment Storage for the seven year period to be 3.01 <br /> ec-ft. The amount of availabl e sediment storage is 3.01 ac-ft (elevation 7081.9). <br /> Therefore, when 60 percent. of the sediment storage capacity has been consummed (1.8 <br /> ec•f t), the pond wi ll be cleaned out. <br />Since the sediment storage capacity is greeter than three years, Peabody Coal Company wilt <br />periodically monitor the sediment storage capacity to ensure enough capacity is available. <br />The estimated design storm sediment volume is based on a worst-case disturbance in the <br />watershed. This worst case will not occur until approximately 1995. Therefore the <br />construeted sediment storage capacity should be adequate for at least a seven year period. <br />Particle Size Distributions. The particle size distribution for this sedimentation pond <br />was based on sieve end hydrometer analysis of various soil types in the Seneca II permit <br />area. This distribution is representative of the watershed for Pond 009 and based on a <br />weighted average. The specific gravity and the submerged bulk specific gravity of the <br />soil ere estimated to be 2.50 end 1.25, respectively. <br />• <br />TABLE 13-SA-4 <br />Sedimentology Size Analysis _- <br />weighted Average ~- <br /> Percent <br /> Size (mm) Passing <br /> <br /> 12.7 100 <br /> 11.2 97 <br /> 2.0 91 <br /> 1.0 87 <br /> 0.5 84 <br /> 0.25 82 <br /> 0.106 79 <br /> 0.045 56 <br /> 0.02 40 <br /> 0.01 31 <br /> 0.005 24 <br />• ..., , .. 0.002.... .. 17 <br /> 0.001 14 <br />13-SA-6 Revised 08/17/92 <br />