Multicomponent groundwater transport with chemical equilibrium and kinetics: model development and evaluation

Abstract

A multicomponent reactive transport model, MIN3KIN, has been developed. MIN3KIN handles both multiple chemical equilibrium and multiple component chemical kinetic reactions. A two-dimensional transport code has been coupled with a chemical equilibrium code and a chemical kinetic subroutine. A finite element method is used to solve the transport equations. Different coupling methods between transport and equilibrium calculations are evaluated and chemical equilibrium may be solved sequentially or iteratively. MIN3KIN has been evaluated against an analytical solution and applications for different coupling schemes and temporal discretization. It is shown that the chemical kinetic flux should not exceed 10% of the mass depletion for a given time step. Systems with both chemical equilibrium and irreversible chemical kinetics reach a condition, where the concentration quotient does not correspond with the equilibrium constant. The model is finally applied to a two-dimensional case study to illustrate the presence of an intermediate aqueous state governed by transport and irreversible chemical kinetics.