Spatio-temporal variation in hydrogeochemical characteristics and trace elements occurrence in groundwater in parts of Lakhimpur district, Uttar Pradesh

This study focuses on evaluating the seasonal variations in physicochemical parameters and trace element concentrations, along with the associated hydrogeochemical processes and human health risks, in parts of Lakhimpur district, Uttar Pradesh, India. Groundwater samples (n = 140) were strategically collected and subsequently analyzed during the Pre-monsoon (Pre-M) and Post-monsoon (Post-M) seasons of 2023. Ca 2+ Mg 2+ HCO 3 – is the dominant facies, as identified by the Piper trilinear diagram, reflecting the dominance of alkaline earth over alkalis and weak acids over strong acids. Gibbs plots indicate that major ionic composition is mainly controlled by rock-water interaction. Bivariate plots of different molar ratios suggest that groundwater chemistry is primarily controlled by silicate weathering and ion exchange processes, while a few Post-M samples also reflect the influence of carbonate dissolution. PHREEQC-based geochemical modeling shows that groundwater is oversaturated with magnesium-bearing silicate minerals and carbonate minerals but remains undersaturated in relation to sulfate minerals during both seasons. The majority of analyzed trace elements remain within the desirable limits of the BIS and WHO in both seasons, except for As and Mn, which exceed the BIS limits in 7% and 67% of samples, respectively. Moreover, seasonal comparison shows that most trace elements have decreased concentration in Post-M samples due to monsoonal recharge, whereas redox-sensitive elements such as As and Mn exhibit higher concentrations, likely resulting from mobilization from alluvial sediments. Principal Component Analysis (PCA) and Hierarchical Cluster Analysis (HCA) results show that groundwater chemistry is influenced by both natural and human-induced factors. Health Risk Assessment (HRA) reveal that As is the major contaminant, posing the highest non-carcinogenic and carcinogenic health risks, with children being more vulnerable than adults.