Hydrochemical characterization and irrigation suitability mapping of groundwater in Pashupathihal subwatershed,...

This study comprehensively evaluated irrigation suitability of groundwater in the Pashupathihal Sub-watershed using GIS by examining thirteen strategically selected locations for key physicochemical parameters and established irrigation water quality indices. Hydrochemical facies were identified using Piper diagrams and irrigation suitability was classified using Wilcox and USSL plots in line with national and international standards. Results showed water table depths from 10.50 to 17.00 mbgl, while pH values (7.12-8.44, mean 7.62) indicated mildly alkaline conditions typical of semi-arid aquifers. EC varied from 1.27 to 5.98 dS/m (mean 2.75 dS/m), with 23.08% of samples falling into the saline category. SAR values ranged between 4.15 and 14.48 (mean 9.84), with nearly half of samples presenting moderate sodicity risk. All RSC values were below 1.25 mmol/L, signifying absence of carbonate hazards for irrigation. TH (19.25-60.63 mg/L) and TDS (812.80-3824.64 mg/L) corroborated elevated salinity in some samples. IWQI, 30.7 7% of samples qualified as Excellent and 53.85% as Good for irrigation, demonstrating overall suitability, with 15.38% of samples were classified as poor or unsuitable demonstrating well-balanced water chemistry with manageable risks. Hydrochemical facies (Piper) analysis identified Ca²⁺-Mg²⁺-SO₄^2-Cl^- as the dominant type, indicated geochemical evolution with increasing sulphate and chloride from mineral dissolution. Wilcox and USSL diagrams revealed that half samples had salinity and sodicity problem. Durov and Schoeller diagrams showed groundwater was predominantly of Ca²⁺-Mg²⁺-HCO₃^- type, reflecting fresh recharge water controlled by carbonate weathering and rock-water interaction. PCA indicated dominant control of salinity and hardness, with PC1 explaining 47.1% of variance through EC, TDS, Ca²⁺, Mg²⁺, SO₄^2-, Cl^- and TH, while five PCs together accounted for 93.18% variance, highlighting roles of alkalinity, sodium hazard, localized inputs, bicarbonate buffering and boron. Correlation heatmap and parameter index analyses confirmed strong interrelationships among major salinity ions, identifying TH, Ca²⁺, SO₄^2- and Na⁺ as key contributors to groundwater quality variability. Spatial IWQI mapping showed 73.43 % of the area under moderate irrigation water quality, with poorer zones in central and downstream areas, and regression analysis revealed strong negative impacts of pH (R² = 0.794) and SAR (R² = 0.605), moderate influence of TH (R² = 0.448) and weak contribution of TDS (R² = 0.249) on irrigation water suitability. The Charge Balance Error (CBE) values (-6.61 to 7.80%, mean 1.09%) were within acceptable limits, confirming the analytical accuracy and reliability of the dataset, thereby supporting the validity of hydrochemical interpretations and emphasizing the need for appropriate management strategies.