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' RISC User's Manual Version 4 0 <br /> • <br />' L (A-30) <br /> Q(L,,,t) = q C(LL,t) �1000cm2 <br /> 1 where <br /> Q(L.,t) = mass flux at the water table as a function of time <br /> [g/CM2/dl <br /> — <br /> C(L,,,t) dissolved phase concentration of contaminant at the <br /> water table as a function of time [mg/L] <br /> the distance from the source to the water table [cm] <br /> q — net infiltration rate [cm/d] <br /> The mass flux, Q, is used as the time-varying source for the saturated zone model <br /> ' described in Appendix B <br /> ' A 6 2 Retardation <br /> The retardation factor for the unsaturated zone,R, is estimated using <br /> i * R = 1+ PbF.K,,, (A-31) <br /> 0. <br /> where <br /> F„, = fraction organic carbon in dry soil [gig] <br /> &, = organic carbon normalized partition coefficient [ml/g] <br /> This retardation equation is assumed to be valid when F,, > 0 001 [Below values of <br /> 0 001 the retardation is estimated to be equal to 1 --essentially non-retarded) <br /> tA 6.3 Degradation <br /> Degradation is assumed to be a first-order reaction occurring only in the aqueous <br /> phase as the leachate is carried from the source to the water table <br /> A-'18 <br />