Quantifying Uncontrolled Landfill Gas Emissions from Two Florida ...

ecoveries for the total mercury samples were 98.2 percent. Total mercury concentrations in the
landfill gas at Site #2 ranged from 36 to 47 ng/m 3 with an average of 43 ng/m 3 for all of the
samples. Spike recoveries for the total mercury samples were not performed at Site #2.
During the October 2007 field campaign, total mercury concentrations in the landfill gas at Site
#1 ranged from 21,700 to 25,800 ng/m 3 with an average of 24,500 ng/m 3 for all of the samples.
Spike recoveries for the total mercury samples were 102 percent. Total mercury concentrations
in the landfill gas at Site #2 ranged from 109 to 526 ng/m 3 with an average of 352 ng/m 3 for all of
the samples.
There is almost 5 times difference in the total mercury results for Site 1 between the February
and October sampling dates (5,022 in February versus 25,400 ng/m 3 in October). For site 2, the
difference in total mercury results between February and October is about 6 times higher (43
versus 270 ng/m 3 ). The collection technique and equipment were the same during both sampling
campaigns. Spike recoveries for total mercury during both sampling periods were acceptable and
showed no degradation or loss of mercury.
There was a difference in the analytical method that was used to evaluate the samples between
February and the October 2007. The February matrix spike analysis was performed by adding a
known amount of mercury to the sample after sampling and leaching (i.e., Method 1631). This
post-leaching type of spiking does not assess any potential losses of mercury from sampling,
matrix interferences, or the wet leaching procedure.
To account for potential mercury losses from sampling or matrix interferences, EPA developed
EPA Method 30B, “Determination of Mercury from Coal-Fired Combustion Sources using
Carbon Sorbent Traps”. This method requires additional replicates and QA/QC that helps to
account for any potential losses of mercury from sampling and matrix interferences. Method
30B is being used for power plants and other mercury sources to demonstrate performance of
mercury continuous emission monitors. Therefore, in the October 2007 field sampling
campaign, the thermal decomposition mercury analysis technique. Sampling included a prespiked
iodated carbon tube traps spiked with elemental mercury and were used to assess matrix
recovery at Site #1. Results for the thermal decomposition mercury analysis matrix spike
recovery were 102%. The results for total mercury analysis from the October sampling are
thought to be more reliable because of the additional QA/QC requirements to account for
mercury loss during sampling and analysis.
Dimethyl mercury concentrations in the landfill gas at Site #1 ranged from 1.22 to 2.65 ng/m 3
with an average of 1.91 ng/m 3 . Dimethyl mercury concentrations in the landfill gas at Site #2
ranged from 0.69 to 9.19 ng/m 3 with an average of 5.66 ng/m 3 . Spike recoveries for the dimethyl
mercury traps were 13.9 percent for Site #1 and 1.9 percent for Site #2. Un-sampled spike traps
had recoveries from 87.4 to 89.9 percent with an average of 88.7 percent. Recoveries for the
spiked/sampled traps were significantly lower than the acceptance criteria of 50 to 150 percent
established in the project QAPP. This is possibly due to the presence of an unknown interfering
compound either destroying or masking the detection of the dimethyl mercury. For this reason,
all of the dimethyl mercury results from this campaign must be labeled as suspect. Oversampling
was performed by the ARCADIS personnel performing the sampling. Sampling was
performed at approximated 10 times the necessary volume to collect a valid sample.
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