# Investigating Effects of Landfill Soil Gases on Landfill Elevated Subsurface Temperature
## 4 Data Collection  
This research used archived data relating to the abovementioned factors collected for the Bridgeton Sanitary Landfill, Missouri. The landfill was permitted to operate in 1985 and is regulated under the Missouri Department of Natural Resources' Solid Waste Management Program (SWMP). It stopped receiving waste in 2004, when the refuse mass covered almost 210,436.5 square meters at a depth of approximately 73.2 m beneath the surface with a total 97.54 m waste thickness. The landfill first notified the SWMP about the SET events along with smoldering and odor concerns in some gas-extraction wells in 2010. Since 2013, public access was granted for commonly requested data files and reports related to subsurface smoldering events and odors in and around Bridgeton Landfill [55].  
The box in the upper left-hand corner in Figure 3 shows a geographical site overview of the Bridgeton Landfill and the locations of the gas-extraction wells used to collect subsurface gas samples. The three other boxes show the names of the gas-extraction wells within the A, B and C areas outlined in the overview box. Weekly and monthly sample data are available for these gas-extraction wells and were used in this study for in-depth analysis. Weekly gas-well data comprise the concentrations of the basic gas parameters (CO\({}_{2}\), CH\({}_{4}\), O\({}_{2}\), and balance gas) and temperature data, but the monthly data contains only CH\({}_{4}\), CO\({}_{2}\), O\({}_{2}\), N\({}_{2}\), hydrogen (H\({}_{2}\)), and CO without the wellhead temperature data. We used weekly available datasets for the time period of June 2013 to October 2016 since the temperature is the most important parameter for our data analysis. We collected 18,469 observations from the gas-interceptor wells, gas-collection wells, and temperature monitoring probes. Table 3 shows a sample of the collected data.  
As discussed in Section 2, RN\({}_{2}\) and the CH\({}_{4}\)-to-CO\({}_{2}\) ratio are two significant gas parameters to predict gas-well temperatures and can be calculated using the collected gas data. RN\({}_{2}\) is the percentage of N\({}_{2}\) during aerobic decomposition that stays unused. The overpulling of gas due to air infiltration through a gas collection system can cause there to be excess N\({}_{2}\). The O\({}_{2}\) in the intruded air pulled by the vacuum in the gas-collection system kills methanogens and initiates aerobic conditions. O\({}_{2}\) is consumed during the decomposition process and the N\({}_{2}\) present in the air remains in the landfill. A report provided by the SWANA considers O\({}_{2}\), CH\({}_{4}\), and CO\({}_{2}\) as crucial parameters to estimate the concentration of the balance gas, which primarily indicates the amount of N\({}_{2}\), and emphasizes that the usual ratio of N\({}_{2}\) to O\({}_{2}\) is approximately 3.76 [52]. Using a simple gas equilibrium equation, we estimated the RN\({}_{2}\) concentration--e.g., if a gas-well measures CO\({}_{2}\) (28.1%), CH\({}_{4}\) (32.5%), O\({}_{2}\) (3.7%), then the balance gas would be the rest of the gas portion (\(100-32.5-28.1-3.7=35.7\%\)). The normal N\({}_{2}\) was measured by multiplying the typical ratio (3.76) with the oxygen composition (3.7%), 3.76 * 3.7 = 13.912%. The RN\({}_{2}\) was then calculated by subtracting the normal N\({}_{2}\) composition (13.912%) from the balance gas (35.7%) which yields an RN\({}_{2}\) composition of 21.8% [52].  
Figure 2: Step-by-step research procedures and outputs.