Applied numerical modeling of saturated / unsaturated flow and ...

Abstract
Applied numerical modeling of saturated /
unsaturated flow and reactive contaminant transport -
evaluation of site investigation strategies
and assessment of environmental impact
CHRISTOF BEYER
In this thesis numerical models of variably saturated flow and reactive transport
processes in porous media are employed as assessment tools in two different fields of
application.
The first thematic complex studied is the computer based evaluation of investigation
strategies for contaminated soils and aquifers. For this purpose the “Virtual Aquifer”
(VA) concept is introduced and demonstrated by an assessment of the so called center
line method for contaminant plume investigation. Errors and uncertainties in the
estimation of contaminant degradation rates from center line data, which is often
collected at field sites, are analysed. This is done by application at synthetic
contaminated aquifers models, which are generated in the computer by numerical
simulation of contaminant spreading. Monte Carlo simulations and sensitivity studies
are performed to quantify the influences of sampling error magnitude, aquifer
heterogeneity and model parameterisation on the estimated rate constants. In a second
application example, the VA concept is used for the development and testing of a new
approach for biodegradation parameter estimation. The performance of this method is
studied in heterogeneous synthetic aquifers. Also, the propagation of errors and
uncertainties from estimated rate parameters to a prognosis of the contaminant plume
lengths is studied to obtain an indicator for the significance of the estimated degradation
potential. The performance of the new parameter estimation method is assessed by
comparison to frequently used approximations by first order kinetics.
The second thematic complex addressed in this thesis is the evaluation of environmental
impact of contaminant emissions from road constructions by type scenario modelling.
Two general concepts for modelling of flow and transport, i.e. the Eulerian and the
Lagrangian points of view, are combined in this study to assess the extent of leaching
from contaminated demolition waste within road structures to the groundwater surface.
Transport simulations are performed for a number of typical subsoil units of Germany
to analyse the sensitivity of contaminant transport behaviour on subsoil properties. The
relevant contaminant transport and attenuation processes in road constructions and the
different subsoils are identified. The study allows to draw important conclusions on how
these mechanisms could be used or enhanced to reduce contaminant leaching to groundwater.
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