Evaluation of Groundwater Quality in the Deep Maastrichtian Aquifer of Senegal Using Multivariate Statistics and Water Quality Index-Based GIS

Abstract

A regional groundwater quality evaluation was conducted in the deep Maas-trichtian aquifer of Senegal through multivariate statistical analysis and a GIS-based water quality index using physicochemical data from 232 boreholes distributed over the whole country. The aim was to 1) identify the water types and likely factors influencing the hydrochemistry, and 2) determine the suitability of groundwater for drinking and irrigation. Results showed that sodium, chloride, and fluoride are highly correlated with electrical conductivity (EC) reflecting the significant contribution of these elements to groundwater mineralization. The principal component analysis evidenced: 1) salinization processes (loaded by Na + , K + , EC, Cl − , F − and 3 HCO − ) controlled by water/rock interaction, seawater intrusion and cation exchange reactions; 2) dolomite dissolution loaded by the couple Ca 2+ and Mg 2+ and 3) localized mixing with upper aquifers and gypsum dissolution respectively loaded by 3 NO − and 24 SO − . The hierarchical clustering analysis distinguished four clusters: 1) freshwater (EC = 594 µs/cm) with mixed-HCO 3 water type and ionic contents below WHO standard; 2) brackish (Na-mixed) water type with moderate mineralization content (1310 µs/cm), 3) brackish (Na-Cl) water