Hydrochemical controls and irrigation suitability of groundwater in northwest Riyadh, Saudi Arabia: an integrated multivariate assessment

Groundwater in the Al Hisy-Thadiq sector, northwest of Riyadh, is strategic for agriculture and local development, yet its quality and controlling processes remain unclear. This study evaluated 25 groundwater samples using physicochemical parameters, major ions, nutrients, trace elements, irrigation indices, and multivariate statistics. Groundwater is neutral to slightly alkaline (pH 7.48–8.10; mean 7.74), mineralised, with EC of 2800–7230 µS/cm, TDS of 1804–4600 mg/L and total hardness of 925–2675 mg/L as CaCO3. Chemistry is dominated by Na+, Mg2+, Ca2+, Cl− and SO42−, and Piper facies are mainly Na+ + K+-Cl− and Mg2+-Cl−. Some samples have screening values of EC, TDS, hardness, Cl− and SO42−, whereas NO3− and F− remain acceptable. Trace elements are generally low. SAR and KR indicate a low sodicity hazard, whereas Na%, PI, and especially MR indicate irrigation restrictions. Cross-consistency among facies, spatial maps, correlations, PCA, K-means, and HCA identifies a salinity-mineralisation axis and one outlier. The groundwater is suitable for irrigation and requires quality-based allocation, salinity management, crop selection, leaching control, and soil monitoring.