We discuss the penetration of organic pollutants into the depth of soil and into groundwater under different environmental and geological conditions. In one case a field study was conducted on the impact of prolonged irrigation by effluents on groundwater and vadose zone contamination. The studied site was rich in sandy soil which allowed vertical penetration of pollutants into the depth. A significant difference has been observed in the distribution of organic pollutants in the effluent irrigated site, where the pollution increased markedly while descending from the top soil into the unsaturated zone, compared to the two control sites, where the extent of pollution decreased strongly with the depth. It seems that detergents and other surfactants present in the effluents strongly enhance the transport of organic components via the unsaturated zone.

The second case study deals with the transport of organic pollutants in a site where the subsoil is interspaced with clay layers. In this case groundwater pollution derived from the chemical waste of a pesticides plant. A long term follow up of groundwater pollution indicates that the typical contaminant distribution pattern remained unchanged during the years. The pollutants distribution indicates that in this area the penetration of organic pollutants does not occur vertically but rather by horizontal flow, due to inhibition of vertical migration by a thick clay layer present in this area.

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