Projet 689 - Etudier la recharge des aquifères d'Ali-Sabieh (Rép. de Djibouti)

Bref résumé du projet

The sulphate and nitrate concentrations of the Ali-Sabieh aquifer groundwater, which are up to 1800 ppm and 245 ppm respectively, lie well above the maximum permissible values prescribed by the World Health Organization for drinking water (i.e. 250 ppm for sulphate and 50 ppm for nitrate). Therefore, the origin of these high sulphate and nitrate concentrations should be deciphered for a better management of this aquifer. To that end, detailed geochemical investigations will be carry out on all boreholes groundwater from the Ali-Sabieh volcanic aquifer system. The strategy developed for the study of this hydro-system is a multi-tracer approach combining stable and radiogenic isotopes (δ2H, δ18O, δ18O-SO42−, δ34S-SO42−, δ13C, 14C, 87Sr/86Sr, δ11B, δ15N(NO3− ), and δ18O(NO3−)) as well as major, minor, and trace ion chemistry. For the first time, the complex Ali-Sabieh volcanic aquifer will be study to improve understanding of the recharge conditions of this aquifer that supplies drinking water to the second most populated city of the republic of Djibouti. Furthermore, the main geochemical process that explain the water geochemistry of the Ali-Sabieh volcanic aquifer system will be characterized and its geochemical evolution will be understood. Finally, a conceptual model for this aquifer system will be proposed.

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