CHEMFRONTS:: a coupled geochemical and transport simulation tool

A computer program to calculate coupled mass transport and fluid rock interactions has been developed. CHEMFRONTS is based on the quasi-stationary state approximation and it uses a kinetic expression to describe mineral dissolution and precipitation rates. It simulates the chemical evolution of the mineral and aqueous phases over time along a streamline. For fast kinetics, local equilibrium conditions are approached. In the aqueous phase, complexation and redox reactions are included. Reactions with gas phases such as carbonation may also be handled by the program in some special cases. The quasi-stationary state approximation makes it possible to solve problems that would require an extremely large computer effort with conventional models. Such problems arise when the mass of minerals is large compared to the concentrations in the water. The program is especially suited to handle sharp reaction fronts. As the program does not use spatial discretization, the separation between closely located fronts can be resolved and the movements of the fronts may be computed with high spatial resolution. Sharp fronts are usual in the ground and typical examples an redox fronts and dissolution and precipitation fronts. The capabilities of the program are shown in the interpretation of two field-scale processes. (C) 1999 Elsevier Science B.V. All rights reserved.