Modeling biogeochemical processes in leachate-contaminated soils: A review

During subsurface transport, reactive solutes are subject to a variety of h ydrological, physical and biochemical processes. The major hydrological and physical processes include advection, diffusion and hydrodynamic dispersio n, and key biochemical processes are aqueous complexation, precipitation/di ssolution, adsorption/desorption, microbial reactions, and redox transforma tions. The addition of strongly reduced landfill leachate to an aquifer may lead to the development of different redox environments depending on facto rs such as the redox capacities and reactivities of the reduced and oxidise d compounds in the leachate and the aquifer. The prevailing redox environme nt is key to understanding the fate of pollutants in the aquifer. The local hydrogeologic conditions such as hydraulic conductivity, ion exchange capa city, and buffering capacity of the soil are also important in assessing th e potential for groundwater pollution. Attenuating processes such as bacter ial growth and metal precipitation, which alter soil characteristics, must be considered to correctly assess environmental impact. A multicomponent re active solute transport model coupled to kinetic biodegradation and precipi tation/dissolution model, and geochemical equilibrium model can be used to assess the impact of contaminants leaking from landfills on groundwater qua lity. The fluid flow model can also be coupled to the transport model to si mulate the clogging of soils using a relationship between permeability and change in soil porosity. This paper discusses the different biogeochemical processes occurring in leachate-contaminated soils and the modeling of the transport and fate of organic and inorganic contaminants under such conditi ons.