Numerical modelling of fate and transport of heavy metal contaminant in an open dumping yard, South India

Leachate from unsanitary landfills is a complex mixture of organic and inorganic pollutants, posing a major threat to groundwater due to its high concentration of heavy metals. This study models the fate and transport of heavy metal contaminants in groundwater using Visual MODFLOW, based on field data from the open dumpsite at Saduperi, Vellore, Tamil Nadu, which has existed for over a decade. Open dumping has caused severe groundwater and soil contamination, with leachate showing high TDS (21,854 mg/L), BOD (2850 mg/L), COD (18,570 mg/L), and heavy metals Cr (3.2 mg/L), Pb (0.69 mg/L), Cd (0.98 mg/L), and Ni (0.97 mg/L). The 19.14 km² study area comprises three aquifer layers and 18 wells. The MODFLOW model, calibrated with 2021–2022 data (R² = 0.98, RMSE = 4.69 m, Normalized RMS = 7.11%), and validated with May 2023 data, simulated contaminant migration using MT3DMS. Results showed Ni, Cd, and Cr plumes migrating 1.1 km, 1.15 km, and 1.3 km eastward, reaching 0.858, 0.428, and 0.60 mg/L, respectively. The eastern wells are most vulnerable. The study demonstrates the effectiveness of numerical modelling in predicting contaminant transport and supports sustainable groundwater management.