Coupling Transport Codes with Geochemical Models

Abstract

Multi-dimensional reactive transport models are needed for understanding the fate and transport of the metal contaminants in groundwater aquifers. The goal of this research is to develop a framework for coupling the MINTEQ family of geochemical equilibrium models with the public domain reactive transport code RT3D. In this research effort, a suite of one-dimensional reactive transport models were built by coupling MICROQL, MINEQL and MINTEQA2 equilibrium geochemistry modules with a fully implicit, finite-difference, advection-dispersion solver. The one-dimensional reactive transport models were tested by solving four benchmark problems, which were identified as a part of this study. These benchmark problems simulate four distinct equilibrium-controlled processes that involve ion-exchange, surface-complexation, precipitation-dissolution, and redox reactions. The modular framework developed for coupling the one-dimensional codes with the equilibrium codes was used to implement the USEPA code MINTEQA2 within RT3D to develop a prototype model. The prototype model was also tested by solving several benchmark problems. Finally, a scalable numerical model was developed to describe the reactive transport of arsenic in MnO2(s) containing soils. The model performance was validated by reproducing a set of column-scale data using scaled parameters obtained from the batch experiments.