Groundwater vulnerability based on four different assessment methods and their quantitative comparison in a typical North European Lowland river catchment (the Pliszka River catchment, western Poland)

The assessment of groundwater vulnerability is a crucial part of planning and water management because it can identify areas where aquifers are more susceptible to contamination. Depending on the vulnerability assessment method, the results can differ significantly. Consequently, different methods can provide ambiguous information that could further influence decision-making processes in planning or water management. For the Pliszka River catchment, the intrinsic groundwater vulnerability of the uppermost aquifer was estimated using four different methods: DRASTIC, GOD, and two methods that are based on empirical formulas of water residence time in an unsaturated zone. The input data include a series of thematic maps supplemented by 1,322 shallow borehole profiles and laboratory tests of samples collected in the course of fieldwork. The collected data were processed in GIS software, and the results of each method were mapped in high resolution. The resulting maps of groundwater vulnerability were then quantitatively compared to validate their applicability for the assessment of groundwater vulnerability in a typical North European Lowland river catchment. The maps generated by the DRASTIC and GOD methods are dominated by areas with moderately high (54.6 and 48.4%, respectively) and moderate groundwater vulnerability (32.7 and 32.3%, respectively). No areas of high groundwater vulnerability are present. One of the water residence time methods provides results similar to the previous methods at the catchment scale, and one method yields high groundwater vulnerability values for the majority of area.