Abstract
Study Region: Hail in northwestern Saudi Arabia is a hyper-arid, groundwater-dependent region where the regional Saq sandstone aquifer is hydraulically and geochemically influenced by Paleozoic cover rocks, Precambrian basement, local volcanic units and Quaternary wadi deposits. Salinity and geogenic trace constituents constrain the safe use of water. Study Focus: Thirty regional water samples collected in December 2025 (28 groundwater wells and two surface-water reference sites) were evaluated for pH, electrical conductivity (EC), total dissolved solids (TDS), turbidity, major ions, nutrients and trace/metalloid elements. Parameter-specific guideline screening, sodium adsorption ratio (SAR), GIS-based regional screening maps, Pearson correlation and principal component analysis (PCA) were integrated to identify hydrochemical domains and management priorities. New hydrological insights for the region: The regional samples were neutral to alkaline (pH 7.29–10.32) and ranged from weakly mineralized to brackish (EC 90–9225 µS/cm; TDS 111–7600 mg/L). Twelve samples exceeded 1000 mg/L TDS and two exceeded the FAO severe irrigation-salinity threshold of 3.0 dS/m. SAR ranged from 0.15 to 18.31; 29 samples were S1 and GW-29 was S3. EC-TDS-Ca-Mg-Sr-Na-SO4 associations and PC1 (44.1%) define a robust salinity-hardness pathway driven by evaporation, carbonate/gypsum dissolution, ion exchange, and residence-time variation. PC2 (18.5%) separates reported Se-Sn-Sb-Si behavior from bulk salinity.