A Broad-Scale Method for Estimating Natural Background Levels of Dissolved Components in Groundwater Based on Lithology and Anthropogenic Pressure

Analysis of the geological control on the spatial distribution of potentially toxic concentrations of As and F- in groundwater on a Pan-European scale

The distribution of the high concentrations of arsenic (As) and fluoride (F^-) in groundwater on a Pan-European scale could be explained by the geological European context (lithology and structural faults). To test this hypothesis, seventeen countries and eighteen geological survey organizations (GSOs) have participated in the dataset. The methodology has used the HydroGeoToxicity (HGT) and the Baseline Concentration (BLC) index. The results prove that most of the waters considered in this study are in good conditions for drinking water consumption, in terms of As and/or F^- content. A low proportion of the analysed samples present HGT≥ 1 levels (4% and 7% for As and F^-, respectively). The spatial distribution of the highest As and/or F^- concentrations (via BLC values) has been analysed using GIS tools. The highest values are identified associated with fissured hard rock outcrops (crystalline rocks) or Cenozoic sedimentary zones, where basement fractures seems to have an obvious control on the distribution of maximum concentrations of these elements in groundwaters.

A systematic approach to derive natural background levels in groundwater: Application to an aquifer in North Lebanon perturbed by various pollution sources

Several efforts have recently emerged to develop methods capable of determining groundwater natural background levels (NBLs) due to their utmost importance in assessing water quality. A recently developed systematic approach to derive NBLs is the Khadra-Stuyfzand (KS) scheme. It has a clear and standardized flow with multi-steps to eliminate biased or contaminated samples, and hence it is capable of dealing with different pollution sources as well as saltwater intrusion. This method was applied to the Koura-Tripoli-Zgharta (KTZ) Miocene aquifer of coastal North Lebanon. It derived baseline conditions for 2 physical, 16 chemical, and 3 bacteriological parameters in addition to 8 trace elements, and 83 pesticides, polynuclear aromatic hydrocarbons, and volatile organic compounds. The results revealed the extent of anthropogenic shift from background levels, and delineated the main contaminated spots. In fact, the established groundwater baseline composition is typical of limestone aquifers with oligohaline-fresh, moderate alkalinity, calcium bicarbonate water, under freshening conditions. Nonetheless, this quality is locally degraded by microbial contamination due to wastewater disposal sites, saltwater intrusion, and minor nutrient loading from agricultural activities and/or urban development. The measured concentrations of major water ions and a variety of drinking water contaminants (e.g. nutrients, pesticides, hydrocarbons, and heavy metals) are below human health benchmarks, but the microbiological content at several spots has exceeded the permissible limits which renders the water unsuitable for domestic use, and calls for prompt mitigation measures.

Linking local natural background levels in groundwater to their generating hydrogeochemical processes in Quaternary alluvial aquifers

Calculating natural background levels (NBLs) in groundwater is vital for supporting a sustainable use of groundwater resources. Although NBLs are often assessed through a unique concentration value per groundwater body, where hydrogeochemical features are highly variable, spatial heterogeneity needs to be accounted for, leading to the calculation of so-called "local" NBLs. Despite much research devoted to the identification of the best performing techniques for local NBLs spatialization, a deep understanding of the link between local NBL values and their generating hydrogeochemical processes is often lacking and so is addressed here for the redox-sensitive species As, NH₄, Fe and Mn in the groundwater bodies of Lombardy region, N Italy. Local NBLs were calculated by a tired approach involving the hybridization of preselection and probability plot methods. Since the spatial variability of the target species depends mainly on redox conditions, a redox zonation was performed using multivariate statistical analysis. A conceptual model was developed and improved combing factor and cluster analysis. Results showed that NBLs for arsenic were up to 291 μg/L, reached in groundwaters under methanogenesis, a condition related to the prolonged degradation of peat buried in aquifer sediments. Ammonium NBLs up to 6.62 mg/L were generated by the upwelling of fluids from deep sediments hosting petroleum systems; ammonium NBLs up to 4.48 mg/L were generated as the accumulation of by-products of peat degradation. Iron and manganese NBLs up to, respectively, 6.0 and 1.51 mg/L were generated by the oxidation of younger and less stable Mn and Fe oxides within river valleys, mostly the Po River valley. The evaluation of local NBLs, and their association to generating natural hydrogeochemical processes/conditions, achieves a step forward from the commonly used approach of a single NBL per groundwater body, improving decision-support tools for sustainable groundwater management and protection.

Assessment of chloride natural background levels by applying statistical approaches. Analyses of European coastal aquifers in different environments

Estimated natural background levels (NBLs) are needed to assess groundwater chemical status according to the EU Groundwater Directive. They are commonly derived for different substances by applying statistical methodologies. Due to the complexity of the sea water intrusion process, some of those methods do not always provide appropriate assessment of chloride NBLs. This paper analyzes the applicability of different NBL estimation methods in five EU coastal aquifers with significant differences in available datasets and hydrogeological settings. A sensitivity analysis of results to different constraints was performed to remove samples with anthropogenic impacts. A novel statistical approach combining different methods to identify the range of chloride NBLs is proposed. In all pilots the estimated NBLs were below 85 mg/L and fitted well with previous studies and expert judgment, except Campina del Faro aquifer (the maximum being 167.5 mg/L). Although this approach is more time consuming, it provides a more robust solution.