Hydrogeochemistry of the Turonian-Coniacian aquifer was studied over the northern part of the Benin-Togo Coastal Sedimentary Basin to enhance groundwater facies knowledge, mineralization processes, and probable interactions between groundwater and surface water. The study employed geochemical analyses and hydrochemical diagrams which revealed that groundwater chemistry changes seasonally and differs between Benin and Togo. In Benin, bicarbonate-type waters dominated during the dry season, while chloride-type waters were more common during the rainy season. Sodium chloride waters dominated in the dry season in Togo, whereas bicarbonate waters were more prevalent in the rainy season. Three main processes controlling water mineralization were identified in this study as follows: dissolution/concentration, impacts from human activities, and ion exchange mechanisms. Hierarchical Cluster Analysis (HCA) further showed evidence of probable interconnection between groundwater and surface water in both seasons. Ultimately, the study improved understanding of the aquifer system and provided useful information for a sustainable water resource management in the Benin-Togo Coastal Sedimentary Basin, while highlighting the need for further lithostratigraphic and isotopic studies.
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