Author(s)

Ousmane Coly Diouf^1*, Lutz Weihermüller², Mathias Diedhiou¹, Edgar Y. Terence Benam Beltoungou¹, Ndeye Maguette Dieng¹, Seynabou Cissé Faye¹, Harry Vereecken², Serigne Faye¹

¹Geology Department, Faculty of Sciences and Techniques, Cheikh Anta Diop University of Dakar, Dakar, Senegal.
²Forschungszentrum Jülich GmbH, Agrosphere Institute IBG-3, Jülich, Germany.

Groundwater levels and water samples were collected from 20 drinking water pumping and piezometer wells in the urban area of Dakar coastal region in the year 2019. The pH-value, electrical conductivity, as well as calcium, magnesium, sodium, potassium, chloride, sulfate, bicarbonate, and nitrate concentrations were measured to assess the hydrochemical quality of the infrabasaltic aquifer in the area. The present work carried out a hydrochemical analysis to interpret the groundwater chemistry of the aquifer. The results of this chemical analysis indicate that Na⁺ > Mg²⁺ > Ca²⁺ > K⁺ was the most dominant cation sequence in the groundwater, while Cl^- > HCO₃^- > SO₄^2- > NO₃^- was the most dominant one for anions. The chemical analysis of our samples showed, that the Cl-Ca-Mg facies was dominant in the aquifer, while Cl-Na-K and HCO₃-Na-K facies represent 20% and 10% of the groundwater sampled, respectively. A comparison of the measured groundwater quality in relation to WHO drinking water quality standards revealed that 80% of the water samples are suitable for drinking purposes. Ca enrichment, Simpson ratio, ratio of sodium chloride, and calculating Base Exchange (BEX) indices for the samples revealed that the groundwater is mainly affected by three factors: seawater intrusion due to aquifer overexploitation on one hand, and freshening processes and nitrate pollution, on the other, mainly caused by the groundwater flow from the unconfined aquifer.

Coastal Groundwater, Major Ions, Hydrochemical Facies, Anthropogenic Activities, Nitrate Pollution

Diouf, O. , Weihermüller, L. , Diedhiou, M. , Beltoungou, E. , Dieng, N. , Faye, S. , Vereecken, H. and Faye, S. (2022) Groundwater Geochemistry and Saltwater Intrusion in the Dakar Coastal Area, Senegal. Journal of Geoscience and Environment Protection, 10, 45-64. doi: 10.4236/gep.2022.1012004.