## 3 Results and Discussion  
The newest results of the monitoring carried out since 1995 indicate that the closed municipal waste landfill in Tychy remains a source of groundwater pollution. Electrical conductivity (EC) is a parameter used to indirectly assess the mineralization of water. In shallow groundwater exposed to anthropogenic pollution, an EC value of over 1000 uS/cm indicates water pollution [58]. Leakage from municipal landfills has an EC of up to approx. 20,000 uS/cm. The EC of the tested samples in 2021 was within a wide range, from 543 uS/cm (in October in P2) to 29,900 uS/cm (in June in P18) [44]. In 2021, the water with the lowest mineralization was recorded in the P2 piezometer (366-396 mg/L), located east of the landfill, and in P16 (707-623 mg/L), located north of the landfill in the water inflow zone. The most highly mineralized water (>2000 mg/L) occurred under the landfill (P18) and in its southern foreland in piezometers P19A and P17A (measuring the bottom of the aquifer), in P17 (measuring the top of the aquifer), and in P10, on water outflow. The highest pH in 2021 was found in the most heavily polluted water under the landfill (in the P18 piezometer--7.94) and in its immediate vicinity in the direction of water outflow. The lowest pH values were found east of the landfill (5.67 in P2). Current research results indicate the permanent or periodic occurrence of transitional conditions in water in the vast majority of the tested piezometers, taking into account the results of Eh. In the analyzed water, the Eh value ranged from 49 mvolts in P19 and 52 mvolts in P19A, to 339 mvolts in P2, and up to 312 mvolts in P16. The total organic carbon (TOC) content in uncontaminated groundwater usually does not exceed 10 mg/L [59]. In the studied water, these values range from 2.9-3.4 mg C/L (in P2) and 5.1-5.9 mg C/L (in P16) to 1400-1917 mg C/L in P18. High concentrations of TOC were also found in P19A (81-100 mg C/L), in P19 (50-53 mg C/L), in P10 (up to 44-48 mg C/L), in P17A (up to 36-43 mg C/L), and in P1 (32-35 mg C/L). The results of research from 2021 in the area clearly show increased concentrations of ammonium ions (NH4+). The content of this ion varied from <0.13 mg/L periodically in the P16 piezometer to an extremely high value of 2282 mg/L in the water sampled from the P18 piezometer. Increased concentrations of these ions were recorded in practically all the tested piezometers. High values were recorded in P10 (89-142 mg/ L), in P1 (19-56 mg/L), and in nested piezometers monitoring deep parts of the aquifer, i.e., in P17A (146-152 mg/L) and in P19A (89-226 mg/L). Lower concentrations were recorded in P16 and in the P2 piezometer. \begin{table}
\begin{tabular}{c c} \hline \hline
**Parameter** & **RfD [mg/kg/day]** \\ \hline Pb & 14 \\ Cd & 0.5 \\ Ni & 20 \\ Cu & 40 \\ Fe & 0.7 \\ Zn & 300 \\ NH4 & 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: RfD values for analyzed parameters [56]. The nitrate content was significantly lower and ranged from <0.89 mg/L in P1, P10, P18, P19, and P19A to 56-62 mg/L in P17, and up to 55-62 mg/L in P2. High levels of nitrates were recorded in the water in the P16 piezometer (20 mg/L). Extremely high levels of these ions were found in piezometers representing oxidizing groundwater conditions: in P2 (55-62 mg/L) and in P17 (56-62 mg/L). The highest Eh values, a high content of sulphates, and the lowest TOC content and amount of ammonium ions were also found in these piezometers. Chloride content in the tested water varied from 32 mg/L in P16 and 42 mg/L in P2 to 4760 mg/L in P18. Concentrations above 1000 mg/L were not found in any piezometer (apart from P18). Values greater than 100 mg/L were recorded in the vast majority of the piezometers (except for P2, P16, and P19). In four of the piezometers, apart from the already mentioned P18 (in P1, P10, P17, and P17A), the chloride content exceeded 500 mg/L. The content of sulphates in the monitored water varied within a range from <10.0 mg/L in P18 and P19, to 168-190 mg/L in P1, and 170 mg/L in P17.