Seasonal Hydrochemical Assessment of Groundwater from Agricultural Fields in Bengaluru Rural District, India

Groundwater quality in agricultural areas of Bengaluru Rural District, Karnataka, was examined to assess seasonal hydrochemical variation and suitability for drinking and irrigation. The study reports 52 groundwater samples collected during the pre- and post-monsoon periods. Major physicochemical parameters were analysed using descriptive statistics and seasonal comparisons. Drinking-water quality was evaluated through the Water Quality Index (WQI), irrigation suitability through the Sodium Adsorption Ratio (SAR) and Wilcox classification, and hydrochemical characteristics through the Hill–Piper diagram. Geographic information system techniques were used to examine spatial variability. Following the monsoon, mean concentrations of total dissolved solids, sodium, chloride, bicarbonate, sulphate and nitrate decreased, whereas magnesium and alkalinity increased. The mean WQI changed only marginally, from 55.81 ± 26.14 before the monsoon to 55.95 ± 26.39 afterwards, with no statistically significant seasonal difference (p = 0.72). Mean SAR decreased from 8.21 to 7.70, indicating a modest improvement in sodium-related irrigation suitability. The predominant Ca–Mg–HCO₃ facies was consistent with mineral weathering and groundwater–rock interaction within the region's granitic and gneissic terrain. Spatial differences indicated that groundwater quality was not uniform across the sampled agricultural areas. Seasonal recharge appeared to influence dissolved constituents, while lithological conditions and possible agricultural inputs remained relevant. The findings support location-specific groundwater monitoring and management rather than reliance on district-wide averages alone.