Abstract
This paper presents a reaction-based water quality transport model in
subsurface flow systems. Transport of chemical species with a variety of
chemical and physical processes is mathematically described by M partial
differential equations (PDEs). Decomposition via Gauss-Jordan column reduction
of the reaction network transforms M species reactive transport equations into
two sets of equations: a set of thermodynamic equilibrium equations representing
NE equilibrium reactions and a set of reactive transport equations of M-NE
kinetic-variables involving no equilibrium reactions (a kinetic-variable is a
linear combination of species). The elimination of equilibrium reactions from
reactive transport equations allows robust and efficient numerical integration.
The model solves the PDEs of kinetic-variables rather than individual chemical
species, which reduces the number of reactive transport equations and simplifies
the reaction terms in the equations. A variety of numerical methods are
investigated for solving the coupled transport and reaction equations.
Simulation comparisons with exact solutions were performed to verify numerical
accuracy and assess the effectiveness of various numerical strategies to deal
with different application circumstances. Two validation examples involving
simulations of uranium transport in soil columns are presented to evaluate the
ability of the model to simulate reactive transport with complex reaction
networks involving both kinetic and equilibrium reactions.
