Assessment of Soil and Groundwater Heavy Metal Contamination by Finite Element Modelling with Freundlich Isotherm Adsorption Parameters in Waste Landfill Kieu Ky in Hanoi, Vietnam

Abstract World research results indicate that untreated leachate contains high contents of heavy metals that are likely to pollute the soil and groundwater (GW) environment. Most studies have shown that soil and GW in the waste landfill sites and adjacent areas are not polluted by heavy metals at levels greater than those allowable levels for agricultural land. However, studies have shown that waste and leachate contribute to the increase of heavy metals in soil and GW. The concentrations of some heavy metals (HMs) in waste leachate and soil samples at Kieu Ky landfill site, Hanoi, Vietnam exceed the allowable levels in Vietnam national standards. The local geochemical background (LGB) had been determined for the soil in the study soil. The reference soil isotherm adsorption parameters have been determined based on the published works. Finite element (FE) modelling of advection-dispersion transport of HMs by GW movement along with Freundlich isotherm adsorption parameters has been applied to evaluate the HMs’ concentrations in soil skeleton and pore water. The Freundlich’s adsorption isotherm parameters have been calibrated giving a good fitting with a relative error less than 7%. The model results show that the soil and soil water would be contaminated by such HMs at levels higher than the allowable limits only if the HM concentrations are high and sufficiently exceeding the soil adsorption capacity at equilibrium concentration with pore water contamination. For Kieu Ky landfill site, a surface soil layer has concentrations of Cr, Pb and Zn higher than the allowable limits for agricultural land and the leachate has concentrations of Cr, Pb and As higher than the allowable limits for treated industrial wastewater. The soil, soil water and GW are vulnerable to contamination with Cr, Pb and Zn.