Hydrogeochemical assessment of groundwater quality in the Midyan Basin, northwest Saudi Arabia: implications for irrigation use in an arid region

Purpose This study presents a comprehensive hydrogeochemical assessment of groundwater in the Midyan Basin, northwest Saudi Arabia, with the goal of evaluating its suitability for irrigation and drinking in a hyper-arid environment. Design/methodology/approach A total of 72 groundwater samples were collected from shallow wells and analyzed for major ions and trace metals using ion chromatography and ICP-MS. Hydrochemical facies were determined through Piper and Gibbs diagrams. Water quality indices, including Sodium Adsorption Ratio (SAR), Electrical Conductivity (EC), and Residual Sodium Carbonate (RSC), Sodium Percentage (Na%), Magnesium Ratio (MR)and Chloro-Alkaline Indices (CAI) were used to assess irrigation suitability. Findings Groundwater is dominated by Ca2+–SO42−–Cl− and Na+–SO42−–Cl− facies, reflecting evaporite dissolution, carbonate weathering and ion exchange. EC ranged from 1,106 to 14,290 µS/cm and TDS from 545 to 7,027 mg/L. About 29% of samples exceeded the WHO TDS limit, and 95% exceeded sodium limits (200 mg/L). Magnesium ranged from 18.8 to 899.3 mg/L, and calcium from 144.6 to 1869.0 mg/L, both often exceeding guideline values. Nitrate exceeded the 50 mg/L limit in 29% of samples, while fluoride concentrations ranged from 0.98 to 2.10 mg/L. Most trace metals were within safe limits, though slightly elevated levels of Mn, Cr, Zn, and As were detected in a few locations, likely due to anthropogenic inputs. Based on EC and SAR values, nearly 40% of samples are unsuitable for irrigation, though 91% fall within acceptable zones for salt-tolerant crops based on the Wilcox diagram. Originality/value This is the first systematic hydrogeochemical investigation of the Midyan Basin. It reveals significant geogenic and anthropogenic influences on groundwater quality and provides essential data to guide sustainable water management and agricultural planning in arid regions.