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RISC User's Manual Version .4 0 <br /> I IA <br /> B <br /> RAN PQ TIOjNSANDPROCESSES�, _ _ <br /> The model considers the following fate and transport processes <br /> • one-dimensional flow <br /> • three-dimensional dispersion <br /> • retardation(adsorption) <br /> • degradation <br /> This model is identical to the AT123D code (Yeh, 1981) with the exception of <br /> allowing the user to input a source concentration rather than a mass loading (The <br /> model in RISC automatically calculates the mass loading from the source <br /> concentration input) The three-dimensional dispersion equation for a uniform flow <br /> field is given by <br /> a C a2Cy a2C a2C' aC, _r (18-1) <br /> at x aX, y ay2 r aZ2 aX B <br /> where <br /> C. = concentration of component in the aqueous phase([g/l or <br /> g/m3] <br /> x = distance in the direction of groundwater flow [m] <br /> y = cross-gradient distance(from centerline of plume)[m] <br /> z = vertical distance positive downwards from water table <br /> [m] <br /> Dx = dispersion coefficient in the direction of groundwater <br /> flow [m2/d] <br /> Dy = transverse dispersion coefficient [M2/d] <br /> Dz = vertical dispersion coefficient [M2/d] <br /> v — seepage velocity [m/d] <br /> µ — first-order decay coefficient for chemical [1/d] <br /> t = time [d] <br /> B-2 <br />