Investigating the Effects of Mercury Emissions in the Four Corners Area on Local Deposition Levels and Ambient Concentrations
Abstract
In 2005, the United States Environmental Protection Agency (EPA) issued the
Clean Air Mercury Rule (CAMR) as a means for regulating mercury emissions from
coal-fired utility boilers in the United States. However, there is concern that this
rule
may result in local ‘hot spots’ of increased mercury in the environment surrounding
these
facilities. Citizens of the Four Corners region in the southwest are particularly
concerned
about this rule due to the presence of two of the highest mercury-emitting facilities
in the
country. While studies have shown that an increase in atmospheric levels of mercury
lead to a global increase in mercury deposition, little is known on the effects air
emissions from point sources on local mercury levels in the environment.
In this study, mercury emissions from the Four Corners Power Plant and the San
Juan Generating Station of New Mexico were investigated for their possible impacts
on
local mercury levels in the environment. The analysis included statistical and back
trajectory analysis of deposition data at a nearby monitoring site, as well as SCREEN
dispersion modeling of mercury emissions to calculate mercury concentrations in the
ambient air.
Results of the statistical analysis of the deposition data showed a relationship
between precipitation and deposition levels, with higher deposition associated with
higher precipitation. However, season was also shown to have an effect, with summer
having the highest levels of deposition in the area, despite having only the second
highest
level of precipitation, suggesting complexity in the relationship that was infeasible
to
fully evaluate with the available data. The results of the back trajectory analysis
suggested an association between high deposition and trajectories coming from the
southwest and passing within 50 kilometers of the facilities. However, the small sample
size of dates available for back trajectory analysis leads to caution in interpreting
the
results. More extensive monitoring schemes are proposed in order to perform more
elaborate back trajectory analysis. With the proposed monitoring scheme it is believed
that source attribution analysis may be performed to determine the contribution of
the
Four Corners and San Juan facilities to local mercury deposition levels.
Results from the SCREEN dispersion model of the facilities’ emissions were
compared to EPA and California Office of Environmental Health Hazard Assessment
(OEHHA) reference levels to assess possible health risks due to inhalation. Results
from
the dispersion analysis showed maximum ambient concentrations of 0.030 µg/m3 of
elemental mercury and 0.032 µg/m3 of total mercury. Neither of these concentrations
exceeds either the EPA or OEHHA reference levels. However, given that they are on
the
same order of magnitude of the OEHHA reference level, more extensive modeling may
be required with more detailed emissions estimates.
Type
Master's projectPermalink
https://hdl.handle.net/10161/407Citation
Weidner, Kristin (2007). Investigating the Effects of Mercury Emissions in the Four Corners Area on Local Deposition
Levels and Ambient Concentrations. Master's project, Duke University. Retrieved from https://hdl.handle.net/10161/407.Collections
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