DEVELOPMENT AND DEMONSTRATIVE APPLICATION OF A 3-D NUMERICAL-MODEL OFSUBSURFACE FLOW, HEAT-TRANSFER, AND REACTIVE CHEMICAL-TRANSPORT - 3DHYDROGEOCHEM

This paper presents the development of a 3-D coupled model of subsurfa ce flow, heat transfer, and reactive chemical transport where the loca l equilibrium assumption is applied. Strong coupling is used for stead y-state simulations, while weak coupling may be employed for transient simulations to save computation time. Four types of boundary conditio ns and a complete suite of geochemical reactions are taken into accoun t. The flow equation is discretized by the Galerkin finite element met hod. Both the reactive chemical transport and heat transfer equations are solved by either the hybrid Lagrangian-Eulerian or the conventiona l Eulerian finite element method. Two approaches are considered to com pute the transport of aqueous components. The Picard method is used to handle non-linearity in both reactive chemical transport and unsatura ted subsurface flow, while the Newton-Raphson method is employed to ca lculate chemical equilibrium. Two realistic, albeit hypothetical examp le problems are used to demonstrate the capability of the model. (C) 1 998 Elsevier Science B.V. All rights reserved.