PRINCIPLE COMPONENT ANALYSIS AND ISOTOPIC DETERMINATION AS INVESTIGATION TOOLS FOR UNDERGROUND WATERS CONTAMINATION IN CASE OF MIXING AND EXCHANGE PROCESSES

Underground and surface water samples taken near an old landfill have been investigated by using statistical methods of classification based on Principal Component Analysis (PCA). PCA has turned out to be a very useful tool when investigation methods based only on concentration trigger values are difficult to apply due to waters of different origin that contain the same contaminants typical of leachate, e.g. Chlorides. PCA enabled us to highlight a methanogenic area located SSW from the landfill. Moreover, some important water-clay interactions have been discovered, which led to an enrichment of waters in Ca and a loss of Na in many water samples. D and O-18 isotopic abundance determination helped to understand that upstream and downstream samples from the nearby S. Rocco Canal have a very different chemical and isotopic composition, that can be explained only by hypothesizing that downstream waters are formed by a mix of upstream waters with waters richer in Chlorides, that may come from the landfill.