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Pessac, France

Malcuit E.,CFG Services | Atteia O.,ENSEGID IPB | Larroque F.,ENSEGID IPB | Franceschi M.,ENSEGID IPB | Pryet A.,ENSEGID IPB
Journal of Contaminant Hydrology | Year: 2014

Fluoride (F-) commonly threatens groundwater quality. This is the case around the city of Bordeaux (France), where numerous wells tapping the thick and complex Eocene aquifer are contaminated by fluoride, which presents an issue for drinking water supply. The joint analysis of the spatial distribution of fluoride with other species like sulfate suggests that concentrations are mainly related to the occurrence of low-permeability layers containing evaporites or fluorite deposits. In order to identify the origin of the observed concentrations, a radial flow and transport model is implemented at the borehole scale. The hydraulic conductivity of the low-permeability layers and the vertical dispersivity of the aquifer were optimized to match the observed values of sulfate and fluoride concentrations. Interestingly, each of these parameters influences differently the simulated concentrations. This model has been successfully implemented to a neighboring well with the same parameter values, which tests the approach. The major conclusions drawn are: (i) the contamination in fluoride originates from the low-permeability layers, (ii) every low-permeability layer intercepted by the well releases fluoride (iii) Contamination not only originates from pore water of low-permeability layers, but may persist with long-term pumping due to mineral dissolution. As a consequence, fluoride contamination is likely to persist for a long time and the only solution to reduce fluoride concentration in abstracted water is to seal well screens facing low-permeability layers. © 2014 Elsevier B.V.

Malcuit D.E.,CFG Services | Atteia O.,ENSEGID IPB | Negrel P.,Bureau de Recherches Geologiques et Minieres | Franceschi M.,ENSEGID IPB | And 2 more authors.
Techniques - Sciences - Methodes | Year: 2013

Groundwaters in the north of the Aquitaine Basin are mainly used to supply drinking water to the population of the Gironde département *. Among the various aquifers exploited, the Eocene aquifer has concentrations of sulfates and fluorides naturally excessive by comparison with the standard defined for the drinking water supply. Indeed, some drilling have too mineralized waters to be distributed without treatment. So far, the solution to lower these excessive contents in sulfates and/or fluorides in the water has consisted in diluting them with another less mineralized resource, so as to pass below the value of drinking water standard, when it was possible. If the municipality, the association of communes had no other water resource, the well should be abandoned. This research project has allowed understanding the origin of the mineralization in sulfates and fluorides of the Eocene groundwaters in the mineralized Entre-Deux-Mers area and suggests new perspectives of research to improve the sustainable management of water resources in Gironde.

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