The contaminant introduced into the soil-rock-groundwater system will spread within the system only if a transport mechanism is available, for example, a flowing liquid. As soon as the contaminant reaches the subsurface water in the unsaturated or saturated zone, various processes (physical, geochemical and bio- chemical) determine its fate [14]. The physical processes include advection, dis- persion, evaporation, filtration, and degassing while those of geochemical are ac- id-base reactions, adsorption-desorption, ion exchange, oxidation-reduction, pre- cipitation-dissolution, retardation and complexation. The biochemical processes include amongst others transpiration, bacterial respiration, decay and cell syn- thesis (Figure 4). The movement of a chemical pollutant within an aquifer is described by the “transport equation” (Equation (1)): where C is the concentration of the contaminant, t is time, x is the distance in the flow path, v is the average water flow velocity in the porous media, D is the hydrodynamic dispersion coefficient and q is a coefficient regarding to processes affecting the concentration.This equation considers mass conservation over an elemental volume of the aquifer and it is also known as the advection-dispersion equation as these are the two main processes controlling solute transport in a porous media. It includes (from left to right) an advection term, a dispersion term and a source/sink term that describes different processes affecting the concentration. Thus this equation considers the multiple ways in which a contaminant could move within an aqui- fer. Overall, advection is by far more relevant for contaminant transport than diffusion in sedimentary aquifers, whereas diffusion is the most relevant process in aquitards (i.e., geological materials of low hydraulic conductivity).