Quantifying Uncontrolled Landfill Gas Emissions from Two Florida ...

Chapter 3
Results and Discussion
The results from the measurement campaign are presented in the following subsections,
including the calculated methane flux values from each landfill cell, total site methane emission
rates, data on VOC constituents in the landfill gas from each site, and data on total, elemental
and organo-mercury (including methyl- and dimethyl- mercury) collected in the vicinity of the
gas header pipes at the sites. The methane concentrations used to calculate methane flux values
from each cell are presented in Appendix C of this document.
As mentioned previously, background methane concentration measurements were collected at
each site to establish a background methane concentration value. Although measurements were
collected at Site #1 in an area upwind of the measurement cells, the measurement location was
still within the boundaries of the landfill facility. The average methane concentration found from
the background survey at Site #1 was 3.1 ± 1.68 ppm. The fact that the standard deviation of the
measurement is high (almost equal to the expected atmospheric background value of 1.7 ppm)
indicates that there were methane sources captured by the background measurement
configuration. Therefore, the background data collected at Site #1 does not represent a true site
background measurement. Due to this, we used an accepted global methane background value of
1.7 ppm. The average methane concentration from the background survey performed at Site #2
was 1.7 ± 0.376 ppm. The background values from each site were subtracted from all raw
methane concentrations prior to calculating methane flux values from the sites.
During the Site #1 measurement campaign, an inter-comparison study was performed between
the OP-FTIR and OP-TDLAS instruments. The objective of the study was to assess the
comparability of the two instruments by deploying them along the same optical path and
comparing the measured path-averaged methane concentrations. Due to project time constraints,
the inter-comparison study was not performed over an adequate period of time to obtain reliable
data. Ideally this should have been done during the study at each site. However, for the
reporting of this data and based on previous studies where both instruments were compared over
adequate time periods, it is assumed that the two instruments provide identical results for
methane concentration measurements. Further information is presented in Section 5.
3.1 Landfill Site #1
3.1.1 Control Cell
ORS measurements were collected in the control cell on February 20. A schematic of the ORS
measurement configuration from this cell can be found in Figure 2-1. Although measurements
were collected in this cell for several hours, problems were encountered with the alignment of
the OP-TDLAS beams on the retro-reflecting mirror targets, as the synthetic liner on the surface
of the cell did not provide a firm surface to deploy the OP-TDLAS scanner. After the instrument
3-1