Pollutant transport and chemical effects

This paper focuses on the issue of pollutant transport in soils: An overview of the problem is first presented before considering pollutant transport in saturated soils, pollutant transport in unsaturated soils and finally two examples. Causes of pollution, types of pollutants, commonly used remediation techniques, the importance of risk assessment and waste disposal facilities are discussed. Pollutant transport in the saturated zone is briefly covered, via the derivation of the governing differential equations, together with a discussion of available software. Pollutant transport in the unsaturated zone is considered in much greater detail. The formulation developed by the authors is presented, together with the numerical solution scheme achieved (COMPASS). An application of COMPASS to an isothermal problem is then considered involving both advection-diffusion of 2 chemical species, including geochemical reactions with the soil particles. The coupled flow and geochemical model is then compared with the transport model alone, to demonstrate the effect of the coupled model on the attenuation of chemicals due to the geochemical interactions with the soil particles. In the second application results of research on the modelling of lead transport in partly saturated soil are presented. Comparisons of numerical results with experimental observations are given, for a range of soil leaching experiments, covering a variety of conditions. Good agreement was achieved in this case, lending confidence in the approach proposed. It is however acknowledged that considerable further work is required to fully explore and develop the model's capabilities