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

Applied numerical modeling of saturated / unsaturated
flow and reactive contaminant transport –
evaluation of site investigation strategies and assessment
of environmental impact
1. Introduction
In the field of subsurface hydrology, mathematical
models are used to simulate fluid
flow and solute transport by translating
physical and biogeochemical processes into
mathematical equations, which can be
solved by either analytical or numerical
methods. Understanding of individual processes
in domains of simple geometry is
already a challenging task for itself. In large
scale applications, however, we are faced
with heterogeneous environments and interactions
of many different types of spatially
and temporally variable processes, which
leave the numerical treatment of such complex
coupled problems often as the only
way to reach meaningful conclusions
(Zheng and Bennett, 1995). As a benefit of
the rapid development of computational capabilities
(e.g. high performance parallel
computing, specialized software implementation
methods, data pre- and post-processing
tools, graphical display routines) the
numerical simulation of complex coupled
problems in subsurface hydrology is continuously
advanced. In general, numerical
models of flow and transport in geosystems
are used as tools for
� qualitative and quantitative analysis of
single or coupled processes
� identification of relevant parameters
� parameter estimation / inverse modeling
� sensitivity and uncertainty analysis
� prediction of system response to changes
in initial or boundary conditions
These capabilities as well as the spectrum
of application would not have been
achieved without the ever growing demand
for groundwater resources and the concern
about its quality. Groundwater is one of the
main drinking water supplies and increasingly
used for agricultural field irrigation
(Morris et al., 2003). At the same time
pollution from industrial activities, waste
disposal, agricultural use of fertilizers or
pesticides and urban waste waters (Scheidleder
et al., 1999) poses a serious threat to
our groundwater resources.
In this thesis numerical modeling is used in
three applications within the context of contaminant
hydrology. The term applied numerical
modeling here emphasizes the field
scale application of computational methods
to obtain solutions to systems of partial differential
equations describing flow and
reactive transport process interactions in
porous media. Application 1 introduces the
“Virtual Aquifer” (VA) concept, in which
numerical modeling is used as a tool for the
evaluation of investigation and remediation
strategies for contaminated soils and aquifers.
The concept is demonstrated by an
assessment of the so called center line method
for site investigation. In application 2
the VA concept is applied for the development
and testing of a new approach for biodegradation
parameter estimation. Both
applications make use of the GeoSys /
Rockflow code (Kolditz et al., 2006) for the
numerical simulations. In application 3 the
Eulerian and Lagrangian concepts for contaminant
transport modeling are combined.
GeoSys / Rockflow is coupled with the
SMART model (Finkel et al., 1998) and
used for type scenario modeling to assess
the environmental impact of recycling
materials in road constructions.
This synthesis is organized as follows:
Chapter 2 presents the mathematical process
models and numerical schemes used
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