Proposition d'un support d'aide à la décision pour l'amélioration de l'accès à une eau souterraine de meilleure qualité dans un contexte de contamination géogénique au fluorure au Bénin, Afrique de l'Ouest

Abstract

High concentrations of fluoride (up to 7 mg/L) are observed in the hard crystalline aquifers in the central part of Benin (Department of Collines) while the WHO recommended standard is 1.5 mg/L. The drinking of water with high fluoride contents affects human heath as dental fluorosis which already occurs frequently in the region. The hydrogeochemical investigations in the area reveal that the origin of fluoride in groundwater is geogenic with an important contribution of ferromagnesian minerals, mainly biotite. This work aims to carry out a double cartography at the scale of the Department of Collines for: (i) an estimation map of the fluoride concentration in the groundwater by ordinary kriging and (ii) a probability map to exceed the WHO guideline value of fluoride in water (1.5 mg/L) by indicator kriging. Beside the cartography, analysis of the spatial structure of the data (groundwater fluoride content) through variograms calculation was also carried out. This analysis shows a strong link between spatial structure of fluoride contents in groundwater and the dominant geological layer structures, corroborating the geogenic origin of fluoride. The proposed maps could be useful as decision support for policymakers and water resources managers for the appropriate locations of further groundwater extraction wells to limit or avoid fluoride risk areas