Assessing Chemical Status of Shared Groundwater Resources: A Crucial Political, Regulatory and Management Issue

摘要

According to the EU Water Framework Directive 2000/60/EU (WFD, 2000) and the project of the Daughter Groundwater Directive (GWD, 2003), water chemical status should be assessed for all usable groundwater bodies (GWBs) or group of bodies to identify any significant and sustained upward trend of concentrations of pollutants found in these bodies of groundwater, and define the starting point for trend reversals. Groundwater is a resource at risk, thus correct assessment of its chemical status and identification of risk, in particular in shared groundwater bodies is of a vital importance and has significant political dimension as a potential source of conflicts. The presented studies carried out on two selected objects within the EU 5FP BASELINE and 6FP BRIDGE projects were aimed to contribute to evaluating natural baseline quality in European Aquifer and to establishing reliable common approach for assessing groundwater chemical status based on the criteria set by WFD (2000) and GWD (2003), and with using also national regulations and threshold values (RMS, 2004). Assessment of groundwater chemical status performed in parallel in the point and spatial mode based on aggregation with use of median values proved this procedure to be the most appropriate. Application of the point method enables visualization of areas (within the drainage basin or groundwater bodies) of different groundwater chemical status for a correct decision-making, early identification of a risk and timely undertaking interception/reversal actions for restoration of good groundwater status. Spatial assessment of groundwater chemical status on the basis of concentration data aggregated with use of either mean or median values was proved to cause over- or underestimation of risks that lead to wrong decisions resulting in considerable economic losses, possible damage to human health and the environment, and to unavoidable conflicts in case of shared groundwater resources. The spatial assessment was found to be more reliable if performed on the basis of median values, and not of arithmetic mean, as recommended by WFD (2000) and GWD (2003). This results from the fact that chemical constituents of groundwater usually display log-normal distribution, and in this case median is not susceptible to a deformation to such extent as mean value. In GWBs of multilayer structure, assessing groundwater chemical status should be accomplished separately for groundwater of shallow and deeper circulation due to different exposure to contamination sources.