Evaluation of the cleaning process of groundwater following the establishment of a sewage system

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Abstract
The countries of the European Union are required to establish a sewage system in every settlement which has a population over 2000. In this Eastern-Hungarian case study the effects of the establishment of a sewage system on groundwater quality are evaluated. It was concluded that due to the contamination, which lasted several decades, the groundwater is heavily contaminated, in 85% of the wells included in the study, the concentration of NO3 − was above the contamination limit of 50 mgdm−3. Three years after the establishment of the sewage system the NO3 − values significantly decreased, in 50% of the investigated wells the measured NO3 − concentrations were below the limit value. The average value of 213 mgdm−3 measured in 2013 decreased to 137 mgdm−3, and in certain wells the rate of decrease was above 80%. By performing the Wilcoxon test (p = 0.008) it was confirmed that the decrease was not accidental but was the result of the project. In 25% of the groundwater wells was not found a decrease in the concentration, a fact which is explained by the contaminant discharge of households not connected to the sewage system, and other local contaminant sources which have not been eliminated. Based on the trends observed, the cleaning process may last for years, and as such should be supported by environmental protection measures.

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