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

Fig. 9: Influence of dispersivity parameterization on estimated degradation rate constants for
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method 4 (and method 3 with �T = 0) of Tab. 1 and four degrees of aquifer heterogeneity � Y
(Bauer et al., 2006a [EP 2]). Symbols represent ensemble medians of 100 realizations.
Extensive monitoring networks
For the previous studies, linearly arranged
center line observation wells have been
used for the VA investigation (compare Fig.
6). Contaminant plumes in natural heterogeneous
aquifers may however show a
substantial amount of meandering (Wilson
et al., 2004) resulting in non-linear center
line orientations. As documented, an
inappropriate assumption of a linear center
line may result in misplacement of the
observation wells and in significant overestimation,
if degradation rate constants are to
be derived. Moreover, only measurements
in observation wells located on the plume
axis are evaluated and additional information
possibly at hand (i.e. well data downgradient
from the source but not on the
center line) is not explicitly accounted for
in the rate estimation. Therefore the performance
of methods 1, 3 and 4 of Tab. 1 was
Fig. 10: Site investigation for degradation
rate constant evaluation by (A) non-linearly
positioned center line wells and (B) using
all observation wells of the monitoring
network (Beyer et al., 2007a [EP 5]). Small
dark squares show observation well
locations, larger squares show presumed
center line well locations, contour lines are
concentrations calculated analytically with
the approach of Stenback et al. (2004).
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