MODELING OF MULTICOMPONENT REACTIVE TRANSPORT IN GROUNDWATER .1. MODEL DEVELOPMENT AND EVALUATION

MINTRAN is a new model for simulating transport of multiple thermodyna mically reacting chemical substances in groundwater systems. It consis ts of two main modules, a finite element transport module (PLUME2D), a nd an equilibrium geochemistry module (MINTEQA2). Making use of the lo cal equilibrium assumption, the inherent chemical nonlinearity is conf ined to the chemical domain. This linearizes the coupling between the physical and chemical processes and leads to a simple and efficient tw o-step sequential solution algorithm. The advantages of the coupled mo del include access to the comprehensive geochemical database of MINTEQ A2 and the ability to simulate hydrogeological systems with realistic aquifer properties and boundary conditions under complex geochemical c onditions. The model is primarily targeted toward groundwater contamin ation due to acidic mine tailings effluents but is potentially also ap plicable to the full range of geochemical scenarios covered by MINTEQA 2. The model is tested with respect to ion exchange chemistry and with respect to precipitation/dissolution chemistry involving multiple sha rp fronts. The companion paper presents two-dimensional simulations of heavy metal transport in an acidic mine tailings environment, focusin g on environmental implications.