Aim of the study:
Groundwater quality monitoring tests in the area of pollution sources are one of the elements of the assessment of groundwater vulnerability. The aim of the article is to indicate a good index for the assessment of water quality and the selection of an appropriate value of the hydrochemical background.

Material and methods:
The quality of groundwater in the region of the municipal landfills in Dabrowa Gornicza (southern Poland) was assessed in the context of the content of ammonium, chlorides, sulphates, iron and electric conductivity values . The level of the contamination of groundwater was determined on the basis of the monitoring data from 2016-2020. The research used the Landfill Water Pollution Index (LWPI) and the Nemerow index (NI). In order to determine the reliability of the methods used, three different values of the hydrochemical background were taken into account.

Results and conclusions:
The results of the analyses show that the values of the Nemerow index are definitely higher than the LWPI index. Additionally, the highest values of the indicators were obtained when comparing the obtained results to the hydrochemical background from the 1980s. The maximum values of the indicators were approx. 156 (LWPI) and approx. 721 (NI) for the PZ4 piezometer located east of the landfills. The differentiated results of the index values depending on the selection of the background value and the assignment of individual weights indicate that for such a transformed area it is difficult to indicate the value of the hydrochemical background for which the index values would be representative.