Groundwater environmental objectives in Europe are defined by the Water Framework Directive (2000/60/EC) and the Groundwater Directive (2006/118/EC), based on contaminant thresholds and considering Natural Background Levels (NBL) when appropriate. NBL represents the boundary between natural processes and anthropic impact, and defines the targets for remediation in polluted sites.
The Sacco River Basin (1530 km², Latium, Italy) includes a contaminated “Site of National Interest”, 72.35 km² wide. Anthropic pressures are widespread within the basin (e.g. industrial sites, transport infrastructures, landfills). Geogenic arsenic (As), iron (Fe), and manganese (Mn) can be mobilized in anoxic conditions into groundwater by biogeochemical processes.
This research aims to define the NBL for As, Fe, and Mn in the different lithologies (alluvial deposits, volcanic rocks, travertines) using a multidisciplinary approach. The currently ongoing groundwater sampling targets the low-impact areas to get a set of concentration values associable exclusively to geogenic processes. Groundwater levels, chemical-physical parameters, inorganics, dissolved organic carbon, isotopes (δ18O, δ2H, δ13C, and 87Sr/86Sr), and microbial properties were analyzed.
Preliminary results show that the highest Fe (201-1988 μg/L), As (38-55 μg/L), and Mn (55-406 μg/L) levels are related to reducing conditions in peat-rich alluvial sediments and, to a minor extent, to volcanic formations. Cell abundance is in the range of 10^3-10^4 cells/mL with predominance of cells with low nucleic acid content, as reported in oligotrophic environments. Furthermore, microbial respiration suggests higher metabolism and functional diversity of microbial communities in the alluvial facies. Our findings contribute to a more accurate assessment of natural versus anthropogenic influences, ultimately supporting the development of effective groundwater management and remediation strategies in contaminated sites.