Abstract
<title>Abstract</title> <p>Groundwater quality in semi-arid Mediterranean aquifers reflects the joint action of geogenic mineralization and anthropogenic contamination, yet few studies statistically separate the two. This study addresses that gap in the shallow alluvial aquifer of Tébessa (NE Algeria) using a multi-temporal dataset (2005–2018) from wells, boreholes, springs, and surface water. Measured electrical conductivity ranged from 442 to 9120 μS cm⁻¹, whereas nitrate concentrations varied between 1.52 and 117.97 mg L⁻¹, with several groundwater samples exceeding the WHO drinking-water guideline of 50 mg L⁻¹. Because raw hydrochemical variables were non-normally distributed, logarithmic transformation was applied before Principal Component and Hierarchical Cluster Analyses. This step proved decisive: nitrate consistently separated from mineralization-related variables (TDS, Cl⁻, Na⁺, SO₄²⁻) only after transformation, confirming its anthropogenic origin. Carbonate and evaporite dissolution govern natural mineralization, whereas nitrate enrichment is principally associated with agricultural return flow and wastewater infiltration affecting shallow recharge zones. GIS mapping further identifies the recharge zones most exposed to contamination. This log-transformation-based framework offers a replicable diagnostic pathway for distinguishing natural evolution from pollution in comparable semi-arid aquifers.</p>