The unsaturated zone is the medium through which pollutants move from the soil surface to groundwater. Polluting substances are subjected to complex physical, chemical and biological transformations while moving through the unsaturated zone and their displacement depends on the transport properties of the water-air- porous medium system. Pollution caused by human activities, agriculture, and industry, has brought about a growing interest in the role of the unsaturated zone in groundwater pollution. Due to the complexity and the multidisciplinary nature of the subject, it is being investigated...