306-7 An Integrated Critical Zone Perspective on Groundwater Dynamics and Hydrogeochemical Evolution in Guwahati City, India

Abstract:

Groundwater dynamics and hydrogeochemical processes within the Critical Zone govern the availability, quality, and sustainability of freshwater resources. This study integrates hydrogeological and hydrogeochemical investigations of the shallow aquifer system in Guwahati City, Assam, India, to evaluate groundwater dynamics and the processes controlling groundwater quality within the Critical Zone. Hydrogeological characterization based on borehole lithology and groundwater-level monitoring revealed heterogeneous aquifer conditions dominated by clay, sand, and granular deposits. Spatial variations in water-table depth and groundwater flow reflect the combined influence of topography, aquifer heterogeneity, and localized groundwater abstraction, with regional flow toward the Brahmaputra River. Trend analyses using the Mann–Kendall test and Sen's slope identified both declining and rising groundwater levels, while the absence of significant long-term rainfall trends suggests that local hydrogeological conditions and anthropogenic activities primarily govern groundwater dynamics. Hydrogeochemical analyses indicate that groundwater evolution is controlled by rock–water interactions, including silicate weathering, carbonate dissolution, and cation exchange, producing predominantly Ca–HCO₃-type waters. Elevated concentrations of As, Al, Ba, Cu, F⁻, Fe, Mn, and Pb exceeding World Health Organization and Bureau of Indian Standards guideline values, together with Water Quality Index and Heavy Metal Pollution Index assessments, reveal widespread groundwater quality deterioration and the need for targeted interventions. Integrating groundwater flow with hydrogeochemical evolution provides new insights into the hydrological and geochemical processes regulating contaminant distribution in shallow urban aquifers and offers a scientific basis for sustainable groundwater resource management in rapidly urbanizing regions.

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