USING GEOSTATISTICS TO ASSESS INDUSTRIAL CONTAMINATION IN A FLUVIAL ENVIRONMENT, PATAGONIA, ARGENTINA

In order to assess the environmental situation of a Sodium Hydroxide, Polyvinyl chloride (PVC) and DDT plant in the artificial island of Cinco Saltos, Province of Rio Negro, Argentina, the results of more than 10 years of geochemical survey and sampling in water table and sediments were analyzed. The samples were collected in more than 50 monitoring wells and fixed surveying locations. Geochemical analysis results, were interpolated by the ordinary Kriging geostatistical method for the Hg, 1,2-dichloroethane, HCH alpha and HCH beta variables, among others. The results were compared with field analysis to validate the pollution maps generated by geostatistics. The lithological constitution of the island subsoil, with a high permeability and physical nature of the island, made the remediation of the soil extremely difficult. The island is surrounded by two channels, which differ in depth from each other, as they were originally designed for a small hydroelectric dam operating on the western channel. To avoid pollutant mobility, an asphalt layer was used for capping critical locations. To prevent water table circulation from the eastern irrigation channel to the island subsoil, a physical barrier was built around it, 6 m deep and 0.6 m thick. Through the temporary series of pollution maps generated during the study, it was possible to confirm the continue mobility of mercury and the clays present in the pebble gravel soil due normal water circulation. Because of this, the values of Hg in the period analyzed in this study decreased beyond the safety limits established by local regulations and WHO guidelines. The effectiveness of traditional physical barriers in this kind of pebble gravel soil is questionable. The use of a geographic information system (GIS) was a determining factor in understanding the dynamics of the Cinco Saltos contamination plume.