TITLE:
Groundwater Geochemistry and Saltwater Intrusion in the Dakar Coastal Area, Senegal
AUTHORS:
Ousmane Coly Diouf, Lutz Weihermüller, Mathias Diedhiou, Edgar Y. Terence Benam Beltoungou, Ndeye Maguette Dieng, Seynabou Cissé Faye, Harry Vereecken, Serigne Faye
KEYWORDS:
Coastal Groundwater, Major Ions, Hydrochemical Facies, Anthropogenic Activities, Nitrate Pollution
JOURNAL NAME:
Journal of Geoscience and Environment Protection,
Vol.10 No.12,
December
8,
2022
ABSTRACT: 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-> SO42-> 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.