Assessment of changes in the Water Quality Index followingthe establishment of a sewage system

In the present Eastern-Hungarian case study the effects of the establishment of a sewagesystem on groundwater quality are evaluated using the Water Quality Index (WQI).The WQI was calculated via the weighted arithmetic index method using the following parameters: pH, EC, NH₄⁺, NO₂⁻, NO₃⁻, PO₄³⁻,CODps, Na⁺. The Water Quality Status (WQS) of the monitoring wells was determined according to the WQI values. In 2013 30%of the water samples were categorised as being in the poor (51 WQI 75) and very poor WQS categories (75 WQI 100),70% were unsuitable for any usage (WQI 100),and in none of the monitoring wells did the WQI range between25-50 (good WQS) and0-25 (excellent WQS). In 2017, 3 years after the establishment of a sewage network, there was a significant increase in the water quality. The average WQI values decreased from 147.8 to 78.9. The number of wells with a WQS which was unsuitable for any usage had dropped to one third, while the number of wells with good WQS had increased from 0 to12. However, in 201770% of the monitoring wells still had a WQS which was poor, very poor, or unsuitable for any usage, which can be explained by the fact that the cleaning process takes a long time, and by the existence of contaminant discharge of households not connected to the sewage system (approx. 10%), and other local contaminant sources which have not been eliminated.Based on the above, it can be concluded that the cleaning process has obviously started, but could take several years to complete, and further environmental measures may be necessary.