LIABILITY OF GROUNDWATER AND DEPTH OF SOIL TO CONTAMINATION BY PESTICIDES AND OTHER ORGANIC XENOBIOTICS - 2 CASE-HISTORIES

We discuss the penetration of organic pollutants into the depth of soi l and into groundwater under different environmental and geological co nditions. In one case a field study was conducted on the impact of pro longed irrigation by effluents on groundwater and vadose zone contamin ation. 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 efflue nt irrigated site, where the pollution increased markedly while descen ding from the top soil into the unsaturated zone, compared to the two control sites, where the extent of pollution decreased strongly with t he depth. It seems that detergents and other surfactants present in th e effluents strongly enhance the transport of organic components via t he unsaturated zone. The second case study deals with the transport of organic pollutants in a site where the subsoil is interspaced with cl ay layers. In this case groundwater pollution derived from the chemica l waste of a pesticides plant. A long term follow up of groundwater po llution indicates that the typical contaminant distribution pattern re mained unchanged during the years. The pollutants distribution indicat es that in this area the penetration of organic pollutants does not oc cur vertically but rather by horizontal flow, due to inhibition of ver tical migration by a thick clay layer present in this area.