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Hydrochemical borehole logs characterizing fluoride contamination in a crystalline aquifer (Maheshwaram, India)
Abstract : Hydrochemical borehole-loggings with a submersible Idronaut Ocean Seven 302 multiparameter probe equipped of F- and NO3-ion-selective electrodes in combination with EC, pH and dissolved oxygen, were applied for characterizing fluoride (F) contamination in a crystalline (hard-rock) aquifer of a small Indian agricultural watershed where groundwater is intensively abstracted for rice irrigation. A high accuracy of F concentrations determined in-situ—shown by comparing with laboratory analyses—was obtained through using conductivity logs for ionic strength consideration. Large variations in chemical composition and particularly of F-concentration were observed inside boreholes, though restricted to the weathered/fractured layer down to 30–35 m depth. This conforms to the hydrogeological model of a crystalline aquifer where most groundwater flow occurs in the shallow part of the fractured zone. The general trend of increasing F content with depth results from F accumulation through water–rock interaction, but the shape of the F profile depends on the connectivity of the fracture network close to the borehole. The concentrations seen within the water-table fluctuation zone locally suggest F input from fertilizers in groundwater, in addition to the earlier-demonstrated role of evaporation from irrigation return flow. It is also likely that, locally, the deepening of boreholes has contributed to increasing the population’s vulnerability by tapping F-enriched groundwater at depth.
https://hal-brgm.archives-ouvertes.fr/hal-01357897
Contributeur : Anne-Marie Pouget Connectez-vous pour contacter le contributeur
Soumis le : mardi 30 août 2016 - 15:47:18
Dernière modification le : lundi 11 octobre 2021 - 13:02:10
Contributeur : Anne-Marie Pouget Connectez-vous pour contacter le contributeur
Soumis le : mardi 30 août 2016 - 15:47:18
Dernière modification le : lundi 11 octobre 2021 - 13:02:10