Modeling of long-term chromium migration from the Rajbandh open landfill: a case study

Data were collected to develop MODFLOW groundwater flow and MT3DMS contamination models, then calibrated, validated, and visualized. Groundwater contaminated by landfill leachate is a critical environmental and public health concern, especially in developing nations. This study presents the first calibrated contaminant transport model evaluating long-term chromium (Cr) transport from the Rajbandh open landfill located in the urban fringe of Khulna. A MODFLOW-2005 model was assembled and run for the period 2010–2050 to simulate groundwater flow, while contaminant transport was simulated using MT3DMS for 2017–2050. The model was developed for a 50 km2 area with five layers of geologic formation. Conservative advection–dispersion assumptions were applied, and model outputs were visualized in ArcGIS 10.8. The strong model evaluation statistics showed satisfactory correlation between observed and modeled concentrations of Cr with R2 = 0.89. The results showed Cr-contaminated areas above WHO drinking water standards expanding from 0.15 to 0.66 km2. The plume migration pattern was advection-dominated along the groundwater flow path from south to north. The natural clay layer breakthrough time was determined as 20 years for the WHO drinking water limit of Cr to be exceeded in the sand aquifer. The study visualizes the long-term groundwater contamination risk from the landfill leachate in Khulna's urban fringe.