Predictive simulation of groundwater contamination due to landfill leachate: A case study on the Robinson Deep Landfill, Johannesburg, South Africa

Groundwater contamination from municipal solid waste landfills is a global issue, including South Africa. The Robinson Deep landfill (RDL) in Johannesburg lacks necessary leachate collection and handling facilities, has a shallow groundwater table, and no groundwater quality forecast tool. This situation poses a risk of groundwater contamination. This study aimed to construct groundwater flow and contaminant transport models to predict contamination from leachate migration at RDL. Visual MODFLOW Flex software was used for model construction and verification. Heavy metal concentration observations (Al, Cd, Mn, and Pb) from boreholes BH-1, BH-2, BH-3, and BH-H near the RDL were used to calibrate and validate the contaminant transport model (CTM). The result of the CTM predictive simulations for 2030 show Mn and Pb concentrations in the BH-H groundwater could reach 4.28 mg/L and 6.85 mg/L, respectively, exceeding permissible limits of 0.01 mg/L for Pb and 0.4 mg/L for Mn. The simulations indicate that the RDL threatens groundwater quality, especially in the northern areas of the landfill. Based on these findings, a recommendation is made for future studies on assessment and modelling of groundwater quality to focus on areas where increased concentrations of Pb and Mn are predicted. Further, it is recommended that precautionary preventive measures be implemented to mitigate possible contamination of groundwater in the northern areas of the landfill.