In the present study, the impact of the construction of the sewerage network (2014) on groundwater quality was studied on the example of a middle-sized settlement in the Great Hungarian Plain and changes in water quality were assessed using GIS and multivariate statistical analysis. As a result of the pollution that has been going on for decades, the groundwater supply of the municipality has become heavily polluted. In the period before sewerage (2011–2013), clear spatial differences were shown in the degree of contamination in the area of the settlement: the degree of contamination increased in the direction of local groundwater flow. Based on our results, the construction of the sewerage network resulted in marked changes in the quality of groundwater wells. Our studies showed a clear decrease in the concentrations of inorganic pollutants (NH4+
). In the fifth year of the post-sewerage period (2019), the clear spatial difference between wells was eliminated. We have observed a strong descent (1.5 to 2 m) in groundwater levels in the post-sewerage period, the reason for that is clearly due to that wastewater outflow was eliminated. On this basis, it can be declared that the purification processes in the area have started, but at the same time, our results show that pollutants entering environment undergo a number of transformations and remain in the system for a long time.
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