Identification of the natural background levels in the Phlaegrean fields groundwater body (Southern Italy)

The paper deals with the identification of Natural Background Levels (NBLs) in a groundwater body located in a volcanic area. NBLs were assessed through spatial analysis adopting both the probability plot and the pre-selection methods. They were performed on 33 sampling points, focusing on F, Fe, Mn and As ions. The approach is discussed adopting the groundwater body of Phlaegrean Fields as relevant case study. The area is an active volcanic caldera, hosting a geothermal system superimposed on the regional groundwater flow and characterized by hydrogeochemical anomalies. The results, especially referred to As, suggest a local geogenic contamination or concentrated volcano-related phenomena, as fluids upwelling along faults, in the most active portion of the caldera. The application of the probability maps generated by the indicator kriging, resulted effective to distinguish within the same groundwater body areas characterized by peculiar geochemical anomalies.