10.4122/1.1000000507
CATA, CRISTINA
CRISTINA
CATA
cata@ifh.uka.de
MOHRLOK, ULF
ULF
MOHRLOK
mohrlok@ifh.uka.de
CATA, CRISTINA
CRISTINA
CATA
cata@ifh.uka.de
A random-walk approach for simulating transport and transformations in the unsaturated zone
XVI International Conference on Computational Methods in Water Resources
2006
2006
A new reactive transport modelling approach and its applications are presented,
dealing with the impact of the transformation processes, e.g. redox-reactions, on
the spreading of solutes, e.g. wastewater, in unsaturated zone. This method is based
on the random walk approach, balancing the water and associated mass transport in
the unsaturated zone. It allows the quantification of the mass transfer between
different phases (i.e. mobile fluid phase, immobile solid phase) and of the reactive
processes. It is applied for investigating the plume development from a point
source, e.g. sewer leak, in unsaturated zone and its impact on groundwater. One
advantage of the model is that the water and the solute transport are simultaneous
calculated, without having to first run a flow model and then a transport model,
saving simulation effort.
Transport of dissolved solutes in the unsaturated soil zone depends on the
unsaturated water flow, which is usually described by the Richardâ€™s equation. As the
Richardâ€™s equation is reformulated as a Fokker-Planck equation for the water
transport, the random walk approach can be used for balancing the water flow in the
unsaturated zone by moving particles representing a defined water volume. Also,
defining mass loadings for each particle represents the mass transport. Thus, the
unsaturated water transport and mass transport are computed together. When a
particle moves, it represents the mobile fluid phase and brings the solute mass from
one location to another one. At the same time it exchanges mass with the immobile
solid phase (i.e. the cell). This approach is implemented in the numerical model
Water and Solute Transport Model (WSTM), where this exchange takes place between
individual particles and the respective cell. The method was applied to simulate a
sewer leak infiltration in unsaturated soils considering conservative and reactive
solutes. The distributions of the water content and the solutes concentration are
well represented.
For the complete assessment of the wastewater impact on soils and groundwater
detailed understanding of migration and transformation of solutes in the subsurface
is required. The implementation of the relevant transformation processes (e.g. redox-
reactions) into the numerical model enables detailed investigation of their
interactions on transport. Simulation results considering transformation processes
will be validated by the use of the experimental results in order to provide a tool
with predictive capability.