## 3 Results and Discussion  
### Municipal Landfill with Liners Installed-Leakage Investigation  
The first case study--municipal solid waste (MSW) disposal--is located in the central part of Poland. The thickness of the quaternary deposits varies from 11 to 60 m. The deposits consist of glacial tilts, river sand, and gravels of the Mazovian interglacial. The investigation was performed due to the EC and TOC (total organic carbon) present in groundwater samples, collected from a selected piezometer. The piezometer was located where groundwater was discharged from the landfill (south western part). The changes of EC and TOC with ground water table fluctuations over time, are presented in Figures 2 and 3. From the monitoring results, it was determined that the leakage had appeared in 2005 and had been most intensive in the following three years. The later drop in EC and TOC values was achieved by applying remediation solutions at the site (purifying pumping). The results of selected indicators of a groundwater quality assessment, are presented in Table 1. According to Polish standards, the salinity parameters indicate a IV and V quality class [34]. Figure 1: Correlation between EC and hydrocarbons (\(\blacktriangleright\) set of 194 data points), sulfate (\(\blacktriangleright\) set of 380 data points), chlorate (\(\blacktriangleright\) set of 392 data points), ammonium (\(\vartriangle\) set of 248 data points). Figure 2: Electrical conductivity (EC) and ground water table changes over time. For the site investigation purposes, geophysical investigation was performed to identify the leakage zones. The electrical resistivity method was used to distinguish the top of the less permeable layers of clay in the landfill's subsoil. The purpose of the tests was also to investigate the depth of the groundwater table and to confirm the direction of the groundwater flow in the south eastern part, where the leakage had occurred. The distance between testing points allowed an investigation of the subsoil as deep as 35 m below the ground level. The quantity interpretation gave a full picture of the resistivity characteristics, which are listed in Table 2. The interpretation and testing results are presented in Figure 4.  
The proposed solutions for remedial works at the landfill site consisted of: \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Indicator** & **Unit** & **Amount** & **Water Class \({}^{*}\)** \\ \hline Nitrate & mg \(\text{NO}_{3}/\text{dm}^{3}\) & 56 & IV \\ Phosphate & mg \(\text{PO}_{4}/\text{dm}^{3}\) & 3,1 & IV \\ Sulphate & mg \(\text{SO}_{4}/\text{dm}^{3}\) & 344 & V \\ Chloride & mg \(\text{Cl}/\text{dm}^{3}\) & 819 & V \\ \hline \hline \end{tabular} \({}^{*}\) Regulation of the Minister of Environment [34].  
\end{table} 
Table 1: The results of a groundwater quality assessment for a selected piezometer. Figure 3: Total organic carbon (TOC) and ground water table changes over time. * The pumping of contaminated water from piezometer P-2 and the redirecting to the pumping station on the landfill;
* A depression well construction of enough discharge to transmit the leachate from the landfill, to a sewage treatment plant;
* A landfill solution sealing in the area where leakage was detected, with the use of injecting methods. The changes of EC, the mass of sewage sludge, and the amount of pumped water, is present in Figure 5.  
Figure 4: Geoelectrical cross-section of the landfill subsoil. Figure 5: Changes of EC, dry residues, and the amount of pumped water at the landfill site (daily and in total). Due to the high values of EC, tests of the residual dry mass were also performed for collected water samples. This is a water class indicator that is used in hydrogeology and is determined in the laboratory.