Geospatial and Numerical Modeling Framework for Spatio-Temporal Assessment of Groundwater Contamination in Ranchi Urban Agglomeration, Jharkhand, India

Abstract

Groundwater quality and contamination have become major concerns in several parts of Jharkhand, India. The principal contributors to groundwater contamination are rapid urbanisation, industrial effluents, the increased use of chemicals in agricultural practices, and uncontrolled groundwater extraction. In this context, the present study proposes an integrated framework combining a Geographical Information System (GIS), MODFLOW (Modular Finite-Difference Groundwater Flow Model), and MT3DS (Modular Three-Dimensional Multi-Species Transport Model) to evaluate the spatio-temporal dynamics of groundwater flow and contaminant transport in the Ranchi Urban Agglomeration. Hydrogeological, geological, geomorphological, land-use/land-cover, drainage, rainfall, borehole, and groundwater-level data were used as inputs to simulate groundwater flow and contaminant-plume migration under steady-state and transient conditions. The groundwater-flow model was calibrated under steady-state conditions by comparing simulated hydraulic heads with observed groundwater-level data. A model error of less than 2% indicated close agreement between the simulated and observed heads. The numerical simulations were based on a hydrogeologically representative conceptual model incorporating spatially distributed recharge, river–aquifer interaction, evapotranspiration, groundwater abstraction, and regional groundwater exchange through appropriate MODFLOW packages. The results indicate that groundwater flows predominantly towards the south-eastern and eastern parts of the study area. These areas were also characterised by declining groundwater levels and contaminant-plume migration and were therefore more susceptible to groundwater contamination. Although natural recharge contributes to the localised dilution of contaminants, it is insufficient to compensate for groundwater depletion in areas experiencing substantial discharge. The integration of GIS with MODFLOW and MT3DS provides a process-based framework for simulating groundwater flow, predicting contaminant transport, and generating spatial groundwater-contamination risk maps. The modelling framework may serve as a practical decision-support tool for groundwater monitoring, contamination-risk assessment, and sustainable groundwater-resource management. It may also assist in identifying priority areas for future field validation and water-quality monitoring.