Monitoring of emerging organic contaminants (EOCs) in Krško aquifer (Slovenia) by integrating passive and grab sampling

The Krško aquifer in southeast Slovenia is a Quaternary intergranular system composed of highly permeable carbonate and silicate gravels. Due to its geological vulnerability and the surrounding land use that ranges from intensive agriculture to urban and industrial centres, the aquifer is susceptible to contamination. This study presents a comprehensive monitoring campaign initiated in September 2025 to capture seasonal variations in groundwater quality during the 2025-2026 winter recharge cycle. To characterize the chemical status of the aquifer, a multi-proxy analytical framework was implemented. The baseline characterization included a broad suite of physical and chemical parameters with major ions (e.g., NO₃^-, SO₄^2-, Cl^-, TOC, redox sensitive metals such as Fe and Mn, etc.). They were coupled with targeted quantitative grab sampling for a wide array of contaminants that include pesticides and metabolites, persistent organic contaminants such as Per- and Polyfluoroalkyl Substances (PFAS) and Volatile Halogenated Hydrocarbons (VHHs), pharmaceuticals and hormones. Parallel to grab sampling, Chemcatcher passive samplers were installed to provide time-weighted average concentrations of specific organic compounds. By comparing the validated quantitative laboratory results (LC-MS) with the results from the passive samplers, this research and integrated approach aim to refine groundwater vulnerability models and improve the reliability of chemical status assessments in porous alluvial systems.