Hydrogeochemical characterization and determination of natural background levels (NBL) in groundwater within the main lithological units in Slovenia

Groundwater represents a vast and highly important source of drinking water. As a part of the hydrological cycle, it can only be managed by understanding the components that make up its vulnerability profile. These are referenced with anthropogenic influences related to pressures connected with land use and the ever-increasing conversion of land surface for urban use. The quality of groundwater can be assessed and expressed using a number of different chemical parameters. In this paper, we focus on the analysis of groundwater's physico-chemical field parameters and the major ions present in Slovenian aquifers. Several statistical methods were applied to outline the relevant criteria involved in determining the groundwater's natural background. Additionally, a graphical method was applied to evaluate the source of major ions distribution in the groundwater. The most common BRIDGE methodology used to determine background values is based on upper percentile values. It turns out that this methodology might be relevant for chemical parameters mainly affected by geogenic sources, while the "anthropogenic" parameters have to be treated with a different approach e.g., probability plot method.