Integrated Hydrogeochemical Characterization and Drinking Water Quality Assessment of the Terminal Complex Aquifer in El Oued Region (Southeastern Algeria) Based on Multivariate Analysis and Water Quality Index

Abstract

Groundwater from the Terminal Complex aquifer is a principal water resource in the El Oued region of southeastern Algeria, where the region relies heavily on deep aquifers for domestic supply. This study investigates the hydrochemical characteristics and drinking suitability of this groundwater using Pearson correlation analysis, Principal Component Analysis (PCA), Hierarchical Cluster Analysis (HCA), hydrochemical facies diagrams, and the Water Quality Index (WQI). A total of 36 groundwater wells and 15 physicochemical parameters were analyzed across the study area. The results show marked spatial variability in mineralization and distinguish two main groups of wells; one characterized by higher mineralization and the other by lower mineralization. Multivariate analysis grouped the chemical variables into three clusters associated with hardness-related ions, salinity and secondary anthropogenic indicators, and carbonate-buffered parameters. The Piper and Schoeller-Berkaloff diagrams indicate an evolution from calcium-magnesium sulfate waters toward sulfate-sodic facies, controlled mainly by evaporite dissolution and ion-exchange processes. Correlation analysis shows that salinity is closely linked to Na⁺ and SO₄²⁻, whereas total hardness is mainly governed by Mg²⁺. The WQI values, ranging from 222.55 to 339.13, classify most samples as very poor to unsuitable for drinking. Overall, the groundwater is highly mineralized and hard, and it is not suitable for direct domestic use without treatment. These findings provide a useful basis for future softening and treatment strategies in the El Oued region.