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| Titel |
Dating tools applied to mineralized Eocene groundwater, for a sustainable management of the Entre-deux-Mers drinking water, Aquitaine Basin, South western France. |
| VerfasserIn |
Eline Malcuit, Philippe Négrel, Christophe Innocent, Emmanuelle Pételet-Giraud, Pierre Durst |
| Konferenz |
EGU General Assembly 2011
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 13 (2011) |
| Datensatznummer |
250054763
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| Zusammenfassung |
| In the south-west of France, the Eocene aquifer is one of the main resources for
irrigation, thermo-mineral water, and mainly for drinking water in the Bordeaux
region.
This aquifer is characterized by the presence of a large mineralized area, centered on the
Entre-deux-Mers region, between the Garonne and the Dordogne rivers, where the
groundwaters show strong mineralization and anomalous levels of critical elements, such as
sulphates and fluoride, leading to difficulties of resource exploitation for drinking water
supply.
Initiated early 2009, the CARISMEAU 2 project, focuses on the geochemical,
multi-isotopic and hydrogeological characterization of this mineralized groundwater sector of
the Entre-deux-Mers area. The main objectives of this project are to improve the
understanding of the origin of the salinity of this mineralized area and to investigate how
these mineralized waters circulate in the Eocene aquifer and/or in this multi-layer aquifer
system.
The deposit sequences characterizing the Eocene aquifer system are progradational
westward, from detrital deposits to carbonates. The Eocene sands and the Eocene limestones
are hydraulically connected, the limit of their extension is located under the city of Bordeaux.
The groundwater recharge may occur through the Eocene outcrops located in the north and
north-east of this mineralized area of the Entre-deux-Mers, and also by vertical leakage from
the Oligocene aquifer.
Furthermore, the second aspect to consider in this saline area concerns the piezometric
evolution of the Eocene aquifer years after years. In fact, a trough in the potentiometric
surface is noticeable for the Eocene Aquifer, centred under the city of Bordeaux.
For years, the decline of the piezometric surface is roughly one meter per year
in the center. The cone of pressure relief in this confined aquifer stretches to the
east year after year in the same direction, toward the Garonne and the Dordogne
rivers.
In autumn 2009, the first investigation of over 50 wells and springs gave preliminary
characterizations of the aquifer. Groundwaters from more than 50 boreholes have been
sampled. Others groundwater samples come from continuously monitoring, in 2010 - 2011,
during long-term pumping of several boreholes for drinking water.
Combined geochemical analysis (major and trace elements) and classical isotopic
methods using δ18OH20 and δ2HH20, δ34SSO4 and δ18OSO4is carried out. In addition, an
innovative set of isotopic methods using strontium isotopes and more exploratory isotopic
methods like boron, lithium, uranium/thorium and radium isotopes are applied on the
mineralized area. U/Th results are compared to former 14C results. Moreover several 3H
analyses have been performed on 11 samples, including one spring which age and original
aquifer were unknown.
These dating tools may help to better understand the complex circulations in the Eocene
aquifer, of primary importance for drinking water, and its connections to the others aquifer
layers. The results of this dating approach coupled with hydrodynamics models,
hydrogeological knowledge and a better understanding of the deposit conditions and
mineralization may help to better manage this strategic resource of drinking water. |
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