MULTICOMPONENT TRANSPORT WITH COUPLED GEOCHEMICAL AND MICROBIOLOGICALREACTIONS - MODEL DESCRIPTION AND EXAMPLE SIMULATIONS

A reactive transport code (FEREACT) has been developed to examine the coupled effects of two-dimensional steady-state,groundwater flow, equi librium aqueous speciation reactions, and kinetically-controlled inter phase reactions. The model uses an iterative two-step (SIA-1) solution algorithm to incorporate the effects of the geochemical and microbial reaction processes in the governing equation for solute transport in the subsurface. This SIA-1 method improves upon the convergence behavi or of the traditional sequential iterative approach (SIA) through the inclusion of an additional first-order term from the Taylor Series exp ansion of the kinetic reaction rate expressions. The ability of FEREAC T to simulate coupled reactive processes was demonstrated by modeling the transport of a radionuclide (cobalt, Co-60(2+)) and an organic lig and (ethylenediaminetetraacetate, EDTA(4-)) through a column packed wi th an iron oxide-coated sand. The reaction processes considered in thi s analysis included equilibrium aqueous speciation reactions and three types of kinetic reactions: adsorption, surface dissolution, and biod egradation. (C) 1998 Elsevier Science B.V. All rights reserved.