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velocity relationship, the settling efficiency of the ponds is more likely to be underestimated versus overestimated. In addition to choosing a conservative relationship for particle size versus settling velocity, the density of the suspended particles was assumed to be 2.2 gmlcm'. representing the lower range of density associated with sediments composed of SiO,' , The lower density also translates to a more conservative, less rapid settling velocity. . Assumption: The density of the suspended sediment particles is 2.2 glcm'. This assumption results in a more conservative, less rapid settling rate as it represents the lower density range for sediments composed of SiO,. Particle Surface Area Distribution Versus Settling Velocity The distribution of the particles' total surface area versus particle size can be combined with the settling velocity unique to each particle size to produce, for a specific drainage, a distribution of particle surface area versus settling velocity as shown in Figure 5. This surface area versus settling velocity rating can be used in estimating the fraction of actinide that settles to the bottom of a detention pond (since Pu and Am are assumed to be evenly distributed on all surface areas) given the physical parameters of the given detention pond system. Figure 5. Re/ationship Between Cumulative Surface Area f Percent Remaining Pluto;;!u", a;;~ Settling Velocity for North and South Walnut Creek (A- and B-Series, respectively) Remaining Plutonium and Settling Velocity 100' 80' ;; ~ <~ ~c ~ .~ '\:E , ~ '" (J)a: ;;; , 00. 1-- _c o B c - B~ - ~ lf~ tOt ~.!!! ~ ~ ~ , "5() E , () lOt " o 05 1.5 2 Settling VeloCIty (ftlsec) " " , Si02 compounds. as listed in the CRC Handbook of Chemistry and Physics. range in density from 2.2 glcm' to 2.6 gI em'. The lower value in this range was used for this model.