A local natural background level concept to improve the natural background level: a case study on the drainage basin of the Venetian Lagoon in Northeastern Italy

This study analyzes a problem related to the definition of a natural background level (NBL) for naturally occurring contaminants. Specifically, it considers the definition of an arsenic NBL in groundwater because arsenic in alluvial aquifers is a worldwide problem that causes issues in human health. Currently, the European Union (through the BRIDGE project) has suggested several methods to estimate NBLs based on the quantity and quality of the available data, providing a unique NBL value for an investigated study area. This study suggests an improvement of the NBL concept by introducing the local NBL (LNBL). LNBLs are estimated considering an indicator geostatistical approach, which takes into account both the spatial distribution of arsenic and the geochemical relationships occurring inside the aquifer. The LNBL concept aims to provide detailed spatial information of the natural background level and prevents one from defining uncontaminated water sources as contaminated water sources, and vice versa. In this study, an application of the LNBL in the drainage basin of the Venetian Lagoon is proposed.