Index-Based Evaluation (IBE) and Geospatial Mapping of Heavy Metal Contamination in Groundwater of an Industrially Influenced Peri-Urban Area of Guwahati, Assam; India

This study evaluates the geospatial variability of heavy metal contamination in groundwater within an industrially influenced peri-urban area spanning parts of Guwahati, Assam, and Meghalaya, India. The region is experiencing rapid population and industrial growth, driven by its proximity to the state capital and rising urban costs, often with limited consideration for groundwater sustainability. Groundwater was sampled across the study area during both the pre- and post-monsoon seasons and analysed for heavy metal concentrations using Atomic Absorption Spectroscopy (AAS). Index-Based Evaluation (IBE), comprising Metal Index (MI) and Heavy Metal Pollution Index (HPI), was employed to assess cumulative contamination levels. The results revealed significantly elevated concentrations of Lead, Cadmium, Nickel, and Manganese in several locations, particularly during the pre-monsoon season. Notably, Lead exceeded permissible limits in over 90% of the samples. MI and HPI values confirmed widespread contamination, with 21 locations during pre-monsoon and 7 locations during post-monsoon falling into the ‘seriously affected’ category (MI ≥ 6). Kernel Density Estimation (KDE) and box plots further supported the temporal patterns of contamination. The geospatial maps generated using GIS and Inverse Distance Weighting (IDW) interpolation techniques clearly illustrated contamination hotspots and seasonal dilution effects, with improved water quality observed post-monsoon due to natural recharge. High contamination is not uniform across the aquifer but concentrated near industrial clusters, indicating point-source or localized anthropogenic inputs rather than widespread geogenic leaching. The methodological framework and outcomes of this study offer a transferable model for industrially stressed aquifers, enabling early detection, spatial prioritization, and timely remediation of heavy metal contamination at a global scale.