Calibration and Reliability in Groundwater
Modelling: Credibility of Modelling
(Proceedings of ModelCARE 2007 Conference, held in
Denmark, September 2007). IAHS Publ. 320, 2008, 203-209.
A module for the
MT3DMS solute transport model for simulating redox processes
M. VAN CAMP
& K. WALRAEVENS
Laboratory
for Applied Geology and Hydrogeology, Ghent University, Krijgslaan 281, 9000
Gent, B-Belgium
Abstract A
module for the widely used solute transport model MT3DMS (Zheng & Wang,
1999) is presented which allows for the simulation of redox processes. Redox
reactions are rewritten as hydrogen producing oxidation half-reactions and
hydrogen consuming reduction half-reactions. The model uses the concept of a
Òvirtual hydrogen poolÓ which includes all the hydrogen that has been produced
so far by oxidation reactions. The model incorporates three reaction
mechanisms: instantaneous reactions are used for oxygen reduction, kinetic rate
expressions describe the hydrogen producing oxidation reactions and redox
equilibria relate oxidant and reductant concentrations with hydrogen levels in
solution. A direct relation exists between hydrogen levels in solution, the
occurrence of redox species and the size of the virtual hydrogen pool. Using an
iterative scheme based on the Newton-Raphson method, the hydrogen and redox
component concentrations can be derived from the size of the virtual hydrogen
pool. For describing the kinetics of the hydrogen producing oxidation
half-reactions, the model uses RPN like instructions defined in a data file,
which act upon a LIFO based stack and are translated into binary code as the
data are read. This easily allows the redefinition of kinetic reaction
networks, without the need to alter the simulator code. The model has fast
calculation times.
Key words modelling; reactive transport; redox; MT3DMS