## 4 Conclusions  
In this study, 32 groundwater samples from 1995, 2003, 2010, and 2021 were analyzed for various physicochemical parameters to assess their quality using four indices, i.e., the Horizontal ratio (HR), the Nemerow Pollution Index (NPI), the enrichment factor (EF), and the Hazard Index (HI). The calculations include not only metals such as Pb, Cd, Ni, Cu, Fe, and Zn, but also chlorides, sulphates, and NH\({}_{4}\). The values of the three additional parameters had a significant impact on the final values of the indicators. Despite the fact that most of the existing indices are very helpful in assessing the risk to groundwater and human health in the vicinity of pollution sources, the improper selection of background parameters or piezometers as a reference can lead to misinterpretation of the situation. The long-term monitoring of groundwater in the vicinity of the closed landfill in Tychy clearly indicates the migration of leachate from the landfill and the contamination of groundwater in this area. However, if the results for HR are taken into account, it appears that the landfill is not the main pollution source. Performing the isolines with the use of software using algorithms indicates that the greatest pollution is generated in the P19 region. In this study, the NPI turned out to be the least resistant to the choice of background, indicator parameter, or reference point. In this case, it seems most reasonable to use legal acts to determine the relationship between the individual parameter values measured in the piezometers and the limit values for groundwater quality class III. The assessment of human health, even on the basis of general statistical data on Poles, indicates that consuming groundwater from this region exposes drinkers to the harmful effects of substances contained within it. This indicator also suggests that the high value depends primarily on the concentration of chloride and ammonium ions. From the point of view of the use of monitored groundwater as drinking water, the most important problem is the water quality in front of the landfill, i.e., in the outflow zone, e.g., in the vicinity of the P17 and P17A piezometers, which are located approximately 200 m from the landfill. In this context, it is worth mentioning the vertical differentiation of the flow of pollutants. Taking into account the HI index, the water from the shallow piezometer P17 indicates no risk (index \(<1\)), and that of the deeper one (P17A) indicates high risk (index of several dozen). In this case, if we only had a single shallow piezometer (P17), we could conclude that the groundwater quality in this observation well is not negatively affected by the nearby landfill and could even be used as drinking water. Due to the advantages of the selected proposed indices in groundwater risk assessment, it is suggested that the NPI index and artificial neural network methods be used for long-term observations in future studies on other landfills. Conceptualization, D.D. and A.J.W. ; methodology, D.D. ; writing--original draft preparation, D.D. and A.J.W. ; writing--review and editing, D.D. and A.J.W. All authors have read and agreed to the published version of the manuscript. This research received no external funding. **Data Availability Statement:** Not applicable. **Conflicts of Interest:** The authors declare no conflict of interest. **Appendix A**  
**Table A1. ** Partial values of HR, NPI and EF indices.