DOI: 10.11648/j.ajwse.20261202.13 ISSN: 2575-1875

Analysis of Water Chemical Quality Evolution in the Quaternary Aquifer of the Samba Dia Area (Central-western Senegal)

Amadou Sarr, Seyni Ndoye, Jean Ndiaye, Serigne Faye, Philippe Coustumer, Arnaud Gauthier
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The Quaternary sand aquifer of the Samba Dia lens is a critically important water reserve for the municipalities of Fimela, Djilass, and Diofior, located near the Atlantic Ocean and hypersaline waters of the Saloum estuary in central-western Senegal. To assess the influence of this environment on groundwater quality, two water sampling campaigns were carried out in March 2021 and January 2024 on 33 wells. The objective of this study is to evaluate the evolution of groundwater chemical quality during this period. Data interpretation was performed using a multidisciplinary approach based on descriptive statistics of physicochemical parameters, identification of chemical facies using Piper's diagram, analysis of the mineralization process, the use of the hydrochemical facies evolution diagram (HFE-D) to measure the impact of recharge and basic ion exchange processes, and Stuyfzand classification to identify water types. A study of the suitability of water for various uses was also conducted to assess the evolution of water suitability between the two periods. The results indicate that this aquifer consists mainly of chloride facies. Four facies were identified in 2021: NaCl (72.72%), CaCl (12.12%), CaHCO 3 (9.09%) and NaHCO 3 (6.07%) increasing to five in 2024: NaCl (66.66%), CaHCO 3 (24.24%), NaHCO 3 (3.03%), CaCl (3.03%), MgCl (3.03%) with the emergence of a new magnesian facies. This evolution is marked by a generalized increase in seawater intrusion, which rises from 33.33% in 2021 to 66.66% in 2024. Several wells located in the center of the area, which were characterized in 2021 by a softening process, find themselves under the influence of saline water intrusion after three years. The Stuyzand classification indicates an increase in the representativeness of salt water in the aquifer, varying from 24.24% to 30.30% over three years. However, the suitability of the water for drinking and irrigation is not yet affected by the increase in salinity. This widespread increase in water salinity is the result of saltwater intrusion due to excessive pumping of the Quaternary aquifer, leaching of saline soils from the surface in coastal areas, reduced recharge in the center between the two periods, and a reverse ion exchange process in which Ca 2+ and Mg 2+ ions replace Na + ions.

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