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| Titel |
A hydrogeological study of the confined aquifers below the Boom Clay in NE-Belgium: combining a piezometric analysis with groundwater modelling |
| VerfasserIn |
Katrijn Vandersteen, Matej Gedeon |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250074405
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| Zusammenfassung |
| For more than 35 years, SCKCEN has been investigating the possibility of high-level and/or
long-lived radioactive waste disposal in the Boom Clay in north-eastern Belgium. This
research, defined in the long term management programme for high-level and/or long-lived
waste of ONDRAF/NIRAS, includes studying the regional hydrogeology of the aquifer
systems surrounding the Boom Clay. In this context, a hydrogeological study of the confined
aquifers below the Boom Clay was performed. To properly address the conceptual
uncertainties related to the poorly characterized domain featuring large uncertainty in the
forcing data, a combination of a piezometric data analysis and hydrogeological modelling
was used.
The study area represents the confined part of the groundwater system located
stratigraphically below the Boom Clay in NE-Belgium. This so-called deep aquifer system
includes, with increasing depth, parts of the Oligocene aquifer, the Bartoon aquitard system
and the Ledo-Paniselian-Brusselian aquifer. Due to the considerable pumping from these
aquifers in combination with a limited recharge to the deep aquifer system, a gradual
decrease in groundwater levels has been observed in more than 30-year piezometric
records.
The analysis of the piezometry of the confined deep aquifer system allowed gaining more
insight on the system response to the intensive pumping. Since the Oligocene aquifer has a
significantly lower permeability compared to the Ledo-Paniselian-Brusselian aquifer, the
Oligocene pumping triggers only local effects on groundwater levels. Hence, the
regional effects (constant decrease of groundwater levels) in the Oligocene aquifer are
presumably caused by pumping in the Ledo-Paniselian-Brusselian aquifer, whereby the
hydraulically isolating Maldegem Formation (Bartoon aquitard) dampens these effects.
The amount of this dampening is given by the spatial distribution of the hydraulic
properties of the Maldegem Formation and/or its variable thickness. For the piezometers
located in the Ledo-Paniselian-Brusselian aquifer, we see that although the pumping
is concentrated in the south, it causes the water level to decrease far northwards,
which implies a higher hydraulic conductivity of this aquifer than the Oligocene
aquifer.
A transient hydrogeological model was constructed for the area in order to
confirm the findings of the piezometric analysis and to analyze the regional flow
processes occurring in the deep aquifer system. Since groundwater pumping is the most
important process affecting the groundwater flow in the deep aquifer system, we
reconstructed the pumping history in the Oligocene aquifer, the Bartoon aquitard
system and the Ledo-Paniselian-Brusselian aquifer as far as possible into the past.
The detailed geometry of the Oligocene aquifer and Bartoon aquitard system was
introduced in the model, implying a variable thickness of the clay layers in these
formations.
The model was calibrated using an automated calibration algorithm and is able to
reproduce satisfactorily the general trends in the observed groundwater level data. The most
sensitive parameters of the model are the pumping amount, the hydraulic conductivity of the
Ledo-Paniselian-Brusselian aquifer and the vertical hydraulic conductivity of the clay
layers in the Oligocene aquifer and the Bartoon aquitard system. The outcome of the
hydrogeological modelling confirms the results of the piezometric data analysis and
is further used for assessment of the regional flows in the deep aquifer system. |
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