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U.S. Environmental Protection Agency
Office of Inspector General
At a Glance
2006-P-00025
May 15, 2006
Why We Did This Review
In support of its Clean Air
Mercury Rule (CAMR), the
Environmental Protection
Agency (EPA) conducted a
detailed analysis of mercury
emissions and deposition.
EPA concluded that "utility-
attributable" hotspots would
not occur after implementation
of CAMR's mercury trading
program. This evaluation
assesses the basis for EPA's
conclusion.
Background
About 40 percent of U.S.
man-made airborne mercury is
emitted from coal-fired
utilities. EPA revised a
previous finding that mercury
emissions from coal-fired
utilities be regulated with a
Maximum Achievable Control
Technology standard. Instead,
EPA adopted a cap-and-trade
program to reduce mercury
emissions. Several State
agencies and environmental
groups objected to these
actions. One concern was that
a cap-and-trade program could
result in localized areas with
unacceptably high levels of
mercury, or "hotspots."
For further information,
contact our Office of
Congressional and Public
Liaison at (202) 566-2391.
To view the full report,
click on the following link:
www.epa.qov/oiq/reports/2006/
20060515-2006-P-00025.pdf
Catalyst for Improving the Environment
Monitoring Needed to Assess Impact of EPA's
Clean Air Mercury Rule on Potential Hotspots
What We Found
EPA brought significant scientific, technical, and modeling expertise to bear in
developing a specific methodology to consider the potential for mercury hotspots.
Several uncertainties associated with key variables in the analysis could affect the
accuracy of the Agency's conclusion that the Clean Air Mercury Rule (CAMR)
will not result in "utility-attributable" hotspots. We noted:
•	gaps in available data and science for mercury emissions estimates,
•	limitations with the model used for predicting mercury deposition,
•	uncertainty over how mercury reacts in the atmosphere, and
•	uncertainty over how mercury changes to a more toxic form in waterbodies.
Two recent studies support the need for additional monitoring to ensure that EPA's
analysis has properly estimated the contribution of local, regional, and global
sources on U.S. deposition. These studies are "Mechanisms of Mercury Removal
by Oi and OH in the Atmosphere, " published in Atmospheric Environment in June
2005; and "Sources of Mercury Wet Deposition in Eastern Ohio, USA," submitted
for publication in a scientific journal in February 2006. Results of both studies
were not available until after EPA issued CAMR in March 2005, and thus could
not have been considered in EPA's deliberations on CAMR. Although EPA
indicated in CAMR that it would monitor the impact of the cap-and-trade rule on
mercury deposition, the Agency has not yet developed a monitoring plan for this
purpose. Without field data from an improved monitoring network, EPA's ability
to advance mercury science will be limited and "utility-attributable" hotspots that
pose health risks may occur and go undetected.
Based on our interpretation of CAMR, EPA could not take action to mitigate a
mercury hotspot unless the Agency first determined that the hotspot was solely
"utility-attributable." Therefore, EPA could not require additional utility emission
reductions if utilities contributed significantly, but not solely, to a mercury
hotspot. This could limit EPA's ability to mitigate human health hazards by
reducing potentially harm fill levels of mercury in waterbodies and fish tissue.
This could also limit EPA's ability to reduce the number of waterbodies with fish
consumption advisories.
What We Recommend
We recommend that EPA develop and implement a mercury monitoring plan to
(1) assess the impact of CAMR, if adopted, on mercury deposition and fish tissue;
and (2) evaluate and refine mercury estimation tools and models. Further, if
CAMR is adopted after the rule reconsideration process is complete, we
recommend that EPA clarify in the final rule that the "utility-attributable" hotspot
definition does not establish a prerequisite for making future revisions to CAMR.
In response to the draft report, the Agency agreed that additional mercury
monitoring is needed and explained that CAMR does not establish the "utility-
attributable" hotspot definition as a prerequisite for future changes to CAMR.

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