## 3 Results and Discussion  
### Relationship with Leachate Water Quality  
Figure 4 shows the long-term trends in rainfall and temperature at the landfill site, as well as the water quality of the leachate flowing into the treatment facility, including water temperature, pH, and transparency. While leachate quality is considered one of the potential causes of equipment failures within the treatment facility, the leachate generated at this landfill remained relatively stable, with water temperatures ranging from 10 to 30 \({}^{\circ}\)C and pH values between 6 and 8. Transparency refers to the maximum depth at which objects can be distinguished from the water surface, and is an indicator of water clarity. The higher the transparency, the closer the water is to being colorless, and the lower the transparency, the more turbid the water becomes. The transparency meter used in this facility has a maximum detectable depth of 30 cm, and transparency values above this are denoted as \(>\)30 cm. Transparency was generally maintained above 30. A few days of turbidity were observed over the 17-year period. The leachate was consistently clear. It was free of suspended solids (SSs).  
While it is known that malfunctions of equipment within the leachate treatment facility can be caused by foreign substances such as sludge and fine particles, the water quality data suggest that these factors are unlikely to be the direct cause in this case. This is because the transparency consistently remained above 30, indicating that SSs were rarely visible to the naked eye. Additionally, the pH stayed within a neutral range, which is not conducive to significant calcium precipitation. Given these conditions, it is reasonable to conclude that the operational environment of the equipment was favorable, and that the observed failures were likely due to aging and mechanical wear of the equipment itself.  
\begin{table}
\begin{tabular}{l c c c c c} \hline  & **Operating** & \multicolumn{3}{c}{**Standby**} & \\ \hline  & **Normal** & **Noise** & **Normal** & **Noise** & **Failure** & **Total Events** \\ \hline Sludge scraper & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Sludge dewatering machine & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Caustic soda injection pump & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Sulfuric acid injection pump & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Phosphoric acid injection pump & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Dewatering agent injection pump & 1981 & 0 & 0 & 0 & 0 & 1981 \\ Miscellaneous wastewater pump & 1975 & 0 & 0 & 0 & 8 & 1983 \\ Sludge feed pump & 1983 & 0 & 0 & 0 & 0 & 1983 \\ Groundwater pump & 1981 & 0 & 0 & 0 & 0 & 1981 \\ Adjustment tank pump No. 1 & 946 & 0 & 1036 & 0 & 0 & 1982 \\ Adjustment tank pump No. 2 & 1097 & 0 & 881 & 0 & 0 & 1978 \\ Leachate water pump No. 1 & 1977 & 0 & 6 & 0 & 0 & 1983 \\ Leachate water pump No. 2 & 1974 & 0 & 9 & 0 & 0 & 1983 \\ Backwash blower No. 1 & 1981 & 0 & 2 & 0 & 0 & 1983 \\ Backwash blower No. 2 & 1981 & 0 & 2 & 0 & 0 & 1983 \\ Blower No. 1 & 1015 & 0 & 968 & 0 & 0 & 1983 \\ Blower No. 2 & 1047 & 0 & 935 & 1 & 0 & 1983 \\ Rotating disk device No. 1 & 1086 & 3 & 5 & 154 & 767 & 2015 \\ Rotating disk device No. 2 & 1091 & 428 & 3 & 343 & 150 & 2015 \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._  
\begin{table}
\begin{tabular}{l c c c c} \hline  & **Checking** & **Cleaning** & **Calibration** & **Total Events** \\ \hline pH meter for neutralization tank & 1995 & 33 & 7 & 1996 \\ pH meter for flocculation mixing tank & 1993 & 34 & 6 & 1994 \\ \hline \end{tabular}
\end{table}
Table 2: Summary of maintenance history for pH meters at the leachate treatment facility. Includes frequency of checking, cleaning, and calibration events over a 17-year period.