# Investigating Effects of Landfill Soil Gases on Landfill Elevated Subsurface Temperature
## 5 Results
### Testing the Effect of Each Variable on Temperature  
In the absence of CO data for the Bridgeton Landfill, we analyzed the other available gas parameters. First, we determined how individual gas conditions can affect the temperature. Figure 4 demonstrates the temperature ranges in boxplots, when the four factors (CH\({}_{4}\), O\({}_{2}\), RN\({}_{2}\), CH\({}_{4}\)-to-CO\({}_{2}\) ratio) meet the criteria for safe and unsafe conditions (safe = 0 and unsafe = 1). The boxplot shows the distribution of temperature datapoints with five measures: the minimum, median, maximum, first and third quartile. The middle quartile marks the median value (midpoint of the data) and is indicated by the middle line dividing the box into two. The samples within the first to third quartiles contain 50% of the total samples and is represented as the interquartile range (shown as the colored boxes in Figure 4). A total of 25% of the total datapoints fall below the first quartile, while the remaining 25% fall above the third quartile. The data points considered as outliers are located above the third quartile and below the first quartile, 1.5 times outside the interquartile range and are shown as open circles in the figure. Three factors other than O\({}_{2}\) were observed to have a high median and third quartile values for temperature in the unsafe condition than in the safe condition. We noticed that the safe O\({}_{2}\) range recommended by the EPA was associated with higher temperature values typically referred to as an unsafe temperature range, which contrasts with the literature described above. To summarize Figure 4, when the gas conditions are unsafe, the temperature should be higher. [PERSON] et al. [56] observed O\({}_{2}\) concentrations of 15 to 21.2% _v/v_ (more than double the reference O\({}_{2}\) volume of 5%) in gas-wells, whereas the gas-well temperature ranged from 24.9 to 48.9 \({}^{\circ}\)C and the fire probability ratio decreased by 0.836 with an increase in the CH\({}_{4}\)-to-CO\({}_{2}\) ratio concentrations. Another study [16] also found similarly high O\({}_{2}\) levels (15-21.2% _v/v_) corresponding with gas-wells in both cool temperature and SET areas. The reason for this difference in O\({}_{2}\)'s impact on temperature could be the categorization of O\({}_{2}\) with reference to the recommended range by the US EPA, or its relationship to other parameters, or the operational status of this particular landfill. O\({}_{2}\)'s effect on temperature should be reexamined in light of its categorization levels of varying ranges. Its reference value (5%vol) by the US EPA should also be reevaluated.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Rules of categorization** & **Category** & **Reference** \\ \hline \multirow{2}{*}{Methane} & Safe range: 45 to 60\% & safe & \\  & Unsafe range: \textless{} 45\% and \textgreater{}60\% & unsafe & \\ \hline \multirow{2}{*}{Ratio (CH\({}_{4}\):CO\({}_{2}\))} & Safe range: \textgreater{}1 & safe & \\  & Unsafe range: \textless{}1 & unsafe & \\ \hline \multirow{2}{*}{Oxygen} & Safe range: \textless{}5\% & safe & \\  & Unsafe range: \textgreater{}5\% & unsafe & \\ \hline \multirow{2}{*}{Temperature} & Safe range: \textless{}176\({}^{\circ}\)F (80 \({}^{\circ}\)C) & safe & \\  & Unsafe range: \textgreater{}176 \({}^{\circ}\)F (80 \({}^{\circ}\)C) & unsafe & \\ \hline \multirow{2}{*}{Residual Nitrogen} & Safe range: \textless{}20\% & safe & \\  & Unsafe range: \textgreater{}20\% & unsafe & \\ \hline \hline \end{tabular}
\end{table}
Table 4: Categorization rules for the parameters based on the selected standards.