Salt/sea water intrusion: Assessing methods for identifying natural background levels of groundwater aquifers

In order to study the anthropogenic impacts on groundwater quality we will need to identify the natural conditions or Natural background levels (NBLs) within the aquifer, which are used as references to assess the evolution of the contamination status. This information, in addition to the threshold values (TV) for different potential water uses, is required for an appropriate assessment of the chemical status of groundwater in accordance with the Water Framework Directive (WFD, 2000) and to analyses potential program of measures where they are required. 

In the literature we find general methodologies to assess NBL and reference TV for different geochemical substances. Nevertheless, those methods have weak points to study some specific impacts on groundwater depending on the conditions. In the framework of WP5 of TACTIC project and in cooperation with colleagues from HOVER WP3, we are working on a paper that analyses the applicability of different methods to identify natural background levels and reference values to assess salt/sea water intrusion dynamics. The challenge is to identify a general approach that could be applied to any aquifer affected by sea/saltwater intrusion in Europe. We will test it in different environments (southern /northern European / Mediteranean/ North Sea and Baltic Sea comparison) and aquifer typologies (detrital, karstic, fissured aquifers) and management issues (overexploitation, land use and land cover changes, etc) (Figure 1). It may provide insight to understand the groundwater salinization processes within the aquifers. The paper will be submitted to the Special Issue ” Natural Background Levels in Groundwater” 

Figure: Left- Overview of pilot areas across Europe. Right – First example of different NBL methods for four pilots.


Hinsby K, Condesso de Melo MT, Dahl M. European case studies supporting the derivation of natural background levels and groundwater threshold values for the protection of dependent ecosystems and human health. Sci Total Environ. 2008 Aug 15;401(1-3):1-20. doi: 10.1016/j.scitotenv.2008.03.018. Epub 2008 May 16. PMID: 18486193.

Müller D, Blum A, Hart A, Hookey J, Kunkel R, Scheidleder A, et al. Final proposal of a methodology to set up groundwater threshold values in Europe. www.wfd-bridge.net2006.

Walter, T., Beer, A., Brose, D., Budziak, D., Clos, P., Dreher, T., Fritsche, H., Hübschmann, M., Marczinek, S., Peters, A., Poeser, H., Schuster, H., Wagner, B., Wagner, F., Wirsing, G., & Wolter, R. (2012). Determining natural background values with probability plots.