Integrating water quality indices and multivariate statistics for groundwater assessment in a Mediterranean coastal aquifer, Northeast Algeria

Study region: The Wadi Djendjen alluvial plain, located within a Mediterranean coastal aquifer in northeastern Algeria. Study focus: In April 2021, thirty-one groundwater samples were collected to assess the hydrogeochemical characteristics and overall quality of the aquifer. An integrated methodological approach was employed, combining multivariate statistical analyses (Principal Component Analysis and Hierarchical Cluster Analysis), hydrochemical diagrams, and water quality indices. Electrical conductivity (EC) ranged from 325 to 1896 μS/cm, while total dissolved solids (TDS) ranged from 208 to 1213 mg/L, indicating slightly to moderately mineralized water. Two dominant hydrochemical facies were identified: Ca2⁺-Mg2⁺-Cl⁻ and Ca2⁺-HCO3⁻ (84% and 16% of samples, respectively), reflecting the combined effects of freshwater recharge and seawater intrusion. Principal Component Analysis revealed that groundwater chemistry is primarily controlled by geogenic processes (mineral dissolution, dedolomitization, and ion exchange) together with anthropogenic inputs from agricultural return flows and domestic effluents. New hydrological insights: Drinking water quality assessment based on the water quality index (WQI) revealed pronounced spatial variability. Approximately 50 % of samples were classified as excellent to good quality (WQI ≤ 50), while the remaining samples ranged from poor to unsuitable for human consumption (50 < WQI < 100), with one sample (P8) deemed non-potable (WQI =138). Similarly, the Irrigation Water Quality Index (IWQI) delineated three distinct irrigation suitability zones, including a high-restriction zone associated with industrial and port- related activities. These findings pinpoint critical zones of groundwater degradation and provide a robust scientific basis for targeted groundwater management strategies aimed at protecting public health and ensuring agricultural sustainability.