environment

Vol. 11 No. 1 2004
Figure 3: The geological profile along a vertical cross-section based upon information from soundings and borings.
isolated area. So, there is less dilution and far less time
available for biodegradation in the shallow aquifer. The
result is a higher emission to the deeper aquifer for the
current situation. Therefore, remedial measures need to
address this aspect in the near future in order to reduce
Figure 4: Back tracing along flow lines. The flow lines
(light blue lines) end at the depth of the observation
well at which the concentration level exceeds more
than five times the Dutch intervention level for
cyanide. The flow line starts at the groundwater table
where replenishment with infiltrating rainwater takes
place.
this emission.
Conclusions
The geological origin of the investigated location of
the former Gasworks facility in The Hague is a key factor
in assessing the risk of contaminant migration. The
presence of a continuous layer consisting of peat and
clay is dominant not only in the local groundwater flow
pattern. Especially the peat layer also is a major source
of carbon and of nutrients necessary for microbiological
activity. The result of this activity is biodegradation or
transformation of contaminants. A disadvantage of the
peat layer is consolidation when extraction of
groundwater is involved. Therefore, it is important to
gain a thorough knowledge of the geological origin of a
site in order to be able to construct a reliable Conceptual
Site model. Subsequently, soundings, borings and other
measurements are used to verify the CSM.
Literature
Clement, T.P. 1997, RT3D - A Modular Computer Code
for Simulating Reactive Multi-Species Transport in 3-
Dimensional Groundwater Aquifers. Pacific Northwest
National Laboratory, Richland, Washington. PNNL-
11720.
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