## 2 Materials and Methods
### Methodology  
The Environmental Risk Assessment (ERA) methodology was used to evaluate the environmental risks associated with the chosen metals and other pollution components in the groundwater in the vicinity of the municipal landfills in Tychy. Data from the monitoring of groundwater quality near pollution sources from 1995-2021 were analyzed. The years 1995, 2003, 2010, and 2021 were selected from this period. The choice of the years for which the assessment was carried out was not accidental:  
* 1995 was the year that the monitoring system started;
* 2003 was the last year before the activation of the first site of the new landfill;
* 2010 was the year with the largest number of monitoring points near the landfills;
* 2021 was the last year for which year-round research is available. The following parameters were used in the analysis: Pb, Cd, Ni, Cu, Fe, Zn, and the content of chlorides, sulphates, and NH\({}_{4}\). The research took into account the data from all existing piezometers located in the observation network around the inactive waste landfill in a given year. The results for the individual pairs of P17/P17A and P19/P19A nested piezometers were both presented. Three indicators were calculated under the ERA, i.e., the Horizontal ratio [17], the Nemerow Pollution, and the enrichment factor [47]. Figure 3: Contour map of the study area (based on [44]). Due to the fact that the long-term monitoring of groundwater quality in the vicinity of an active landfill does not indicate water pollution, and that the landfill has a liner system, the analyses did not take into account the data from piezometers belonging to the observation network of this facility. The values of individual components in the water were assessed using the Horizontal ratio (H\({}_{\text{R}}\)) in the direction of groundwater flow at a certain distance from the P16 piezometer (located up stream) to the individual piezometers from the observation network of the closed landfill, i.e., P1, P2, P8, P9, P10, P17, P18, and P19 piezometers. The Horizontal ratio was calculated using the following formula:  
\[\text{H}_{\text{R}}=\frac{\text{Cf}_{\text{A}}}{\text{Cf}_{\text{B}}} \tag{1}\]  
where:  
Cf\({}_{\text{A}}\)--is the concentration of the parameter on site A (in this case, the value from the P16 piezometer). Cf\({}_{\text{B}}\)--is the concentration of the parameter on site B. An index value greater than 1 for a single parameter suggests that the water would be treated after passing through the landfill, an index value of less than 1 for a single parameter suggests an impact of landfill leachate on groundwater, and a value of 1 suggests no impact. The article takes into account the total values of the index. If more parameters are taken into account, each result should be multiplied by the number of parameters. The Nemerow Pollution Index (NPI) is a measure that takes into account the relationship between the measured value of a given parameter and the limit value [48]. The value of this index was calculated using the formula:  
\[\text{NPI}=\frac{\text{C}_{\text{i}}}{\text{L}_{\text{i}}} \tag{2}\]  
where:  
C\({}_{\text{i}}\)--is the measured value of the ith parameter. L\({}_{\text{i}}\)--is the allowable limit of the ith parameter. The values for groundwater quality class III were adopted as the limit value for the good state of water quality on the basis of the Regulation of the Minister of Maritime Economy and Inland Navigation of 11 October 2019, on the criteria and method of assessing the state of groundwater bodies (Journal of Laws 2019 item 2148). As L\({}_{\text{i}}\) in the formula above, the following values were adopted (Table 1):  
An index value < 1 suggests low contamination, a value between 1 and 3 suggests moderate contamination, a value between 3 and 6 indicates considerable contamination, and a value > 6 indicates very high contamination [49]. The enrichment factor (EF) is another measure that takes into account the relationship between the measured concentration of a given parameter, but this time in relation to the