the potential for higher bioaccumulation. The use of the 75th
percentile fish tissue MeHg value as the basis for risk
characterization reflects our overall goal of modeling realistic high-
end fishing behavior; in this case, reflecting individuals who target
somewhat larger fish for purposes of supplementing their diets (the
average fisher may eat a variety of different sized fish, but in order
to capture higher potential MeHg exposure scenarios, it is realistic to
assume that some fishers may favor somewhat larger fish).
---------------------------------------------------------------------------

    \97\ http://water.epa.gov/scitech/swguidance/fishshellfish/fishadvisories/.
---------------------------------------------------------------------------

    Deposition of Hg for the continental U.S. was estimated using the
Community Multiscale Air Quality model v4.7.1 (http://www.cmaq-model.org), applied at a 12 km grid resolution.
    The CMAQ modeling was used to estimate total annual Hg deposition
from U.S. and non-U.S. anthropogenic and natural sources over each
watershed. In addition, CMAQ simulations were conducted where U.S. EGU
Hg emissions were set to zero to determine the contribution of U.S. EGU
Hg emissions to total Hg deposition. U.S. EGU-related Hg deposition
characterized at the watershed-level for 2005 and 2016 is summarized in
Table 6 of this preamble for the complete set of 88,000 HUC12
watersheds.
    Table 6 is intended to demonstrate the wide variation across
watersheds in the contribution of EGU emissions to deposition. The
percentiles of total Hg deposition and U.S. EGU-attributable deposition
are not linked, e.g., the 99th percentile of the percent of total
deposition attributable to U.S. EGUs is based on the distribution of
total Hg deposition, and the 99th percentile of U.S. EGU-attributable
Hg deposition is based on the distribution of U.S. EGU-attributable
deposition. These percentiles do not occur at the same watershed.

   Table 6--Comparison of Total and U.S. EGU-Attributable Hg Deposition ([micro]g/m\2\) for the 2005 and 2016
                                                   Scenarios *
----------------------------------------------------------------------------------------------------------------
                                                                       2005                       2016
                                                           -----------------------------------------------------
                                                                           U.S. EGU-                  U.S. EGU-
                         Statistic                            Total Hg   attributable    Total Hg   attributable
                                                             deposition       Hg        deposition       Hg
                                                                          deposition                 deposition
----------------------------------------------------------------------------------------------------------------
Mean......................................................        19.41          0.89        18.66          0.34
Median....................................................        17.25          0.24        16.59          0.15
75th percentile...........................................        23.69          1.07        22.83          0.46
90th percentile...........................................        30.78          2.38        29.90          0.85
95th percentile...........................................        36.85          3.60        35.16          1.18
99th percentile...........................................        58.32          7.77        56.23          2.41
----------------------------------------------------------------------------------------------------------------
* Statistics are based on CMAQ results interpolated to the watershed-level and are calculated using all ~88,000
  watersheds in the U.S.

    To give a better idea of the relationship between total deposition
and U.S. EGU-attributable deposition, we also summarize the percent of
total Hg deposition attributable to U.S. EGUs (by percentile) in Table
7. Table 7 shows the high variability in the percent contribution from
U.S. EGU Hg emissions. Tables 6 and 7 cannot be directly compared, as
the watershed with the 99th percentile U.S. EGU-attributable deposition
is not the same watershed as the watershed with the 99th percentile
U.S. EGU-attributable fraction of total Hg deposition. A watershed can
have a high U.S. EGU-attributable fraction of total deposition and
still have overall low Hg deposition.

  Table 7--Comparison of Percent of Total Hg Deposition Attributable to
                      U.S. EGUs for 2005 and 2016 *
------------------------------------------------------------------------
                                         2005         2016
             Statistic                (percent)    (percent)
-------------------------------------------------------------
Mean...............................            5            2
Median.............................            1            1
75th percentile....................            6            3
90th percentile....................           13            5
95th percentile....................           18            6
99th percentile....................           30           11
------------------------------------------------------------------------
* Values are based on CMAQ results interpolated to the watershed-level
  and reflect trends across all ~88,000 watersheds in the U.S.

    U.S. EGUs are estimated to contribute up to 30 percent of total Hg
deposition in 2005 and up to 11 percent in 2016.
    EPA estimates the relationship between the EGU-attributable Hg
deposition and EGU-attributable fish tissue MeHg concentrations using
an assumption of linear proportionality based on the agency's MMaps
approach. The MMaps assumption specifies that, under certain conditions
(e.g., Hg air deposition is the primary source of Hg loading to a
watershed and near steady-state conditions have been reached), a
fractional change in Hg deposition to a watershed will ultimately be
reflected in a matching proportional change in the levels of MeHg in
fish.98 99 This assumption holds in watersheds where air
deposition is the primary source of Hg loadings, and as a result,
watersheds where this is not the case are removed from the risk
analysis. The practical application of the MMaps approach is that U.S.
EGUs will account for the same proportion of fish tissue MeHg in a
watershed as they do for Hg deposition. MMaps is discussed in greater
detail in section 1.3 and Appendix E of the National Scale Mercury Risk
Assessment TSD. Patterns of U.S. EGU-attributable fish tissue MeHg
concentrations are summarized in Table 8 of this preamble. Table 8 of
this preamble compares total and U.S. EGU-attributable fish tissue MeHg
concentrations for the 2005 and 2016 scenarios by watershed percentile.
---------------------------------------------------------------------------

    \98\ The MMaps approach implements a simplified form of the IEM-
2M model applied in EPA's Mercury Study Report to Congress (Mercury
Maps--A Quantitative Spatial Link Between Air Deposition and Fish
Tissue Peer Reviewed Final Report. U.S. EPA, Office of Water, EPA-
823-R-01-009, September, 2001). By simplifying the assumptions
inherent in the freshwater ecosystem models that were described in
the Report to Congress, the MMaps model showed that these models
converge at a steady-state solution for MeHg concentrations in fish
that are proportional to changes in Hg inputs from atmospheric
deposition (e.g., over the long term fish concentrations are
expected to decline proportionally to declines in atmospheric
loading to a watershed). This solution only applies to situations
where air deposition is the only significant source of Hg to a water
body, and the physical, chemical, and biological characteristics of
the ecosystem remain constant over time. EPA recognizes that
concentrations of MeHg in fish across all ecosystems may not reach
steady state and that ecosystem conditions affecting Hg dynamics are
unlikely to remain constant over time. EPA further recognizes that
many water bodies, particularly in areas of historic gold and Hg
mining in western states, contain significant non-air sources of Hg
(note, however, that as described below, we have excluded those
watersheds containing gold mines or with other non-EGU related
anthropogenic Hg releases exceeding specified thresholds).
    \99\ The risk assessment is not designed to track the detailed
temporal profile associated with changes in fish tissue MeHg levels
following changes in Hg deposition. Rather, we are focusing on
estimating risk in the future, assuming that near steady state
conditions have been reached (following a simulated change in Hg
deposition). Additional detail regarding the temporal profile issue
and other related factors (e.g., methylation potential across
watersheds) is discussed in Section 1.3 and in Appendix E of the
National Scale Mercury Risk Assessment TSD).

    Table 8--Comparison of Total and U.S. EGU-Attributable Fish Tissue MeHg Concentrations for 2005 and 2016
----------------------------------------------------------------------------------------------------------------
                                                                    Fish tissue MeHg concentration (ppm)
                                                           -----------------------------------------------------
                                                                       2005                       2016
                         Statistic                         -----------------------------------------------------
                                                                           U.S. EGU-                  U.S. EGU-
                                                               Total     attributable     Total     attributable
----------------------------------------------------------------------------------------------------------------
Mean......................................................         0.31         0.024         0.29         0.008
50th Percentile...........................................         0.23         0.014         0.20         0.005
75th Percentile...........................................         0.39         0.032         0.36         0.011
90th Percentile...........................................         0.67         0.056         0.63         0.019
95th Percentile...........................................         0.91         0.079         0.87         0.026
99th Percentile...........................................         1.34         0.150         1.29         0.047
----------------------------------------------------------------------------------------------------------------

    Because the focus of this analysis is on higher-consumption self-
caught fisher populations active at inland freshwater locations, we
identified surveys of higher consumption fishing populations active at
inland freshwater rivers and lakes within the continental U.S. to
inform the selection of consumption rate scenarios.\100\

Information on the studies used to develop the high end fish
consumption scenarios for the risk analysis is provided in the National
Scale Mercury Risk Assessment TSD.
---------------------------------------------------------------------------

    \100\ A number of criteria had to be met for a study to be used
in providing explicit consumption rates for the high-end fisher
populations of interest in this analysis. For example, studies had
to provide estimates of self-caught fish consumption and not
conflate these estimates with consumption of commercially purchased
fish. Furthermore, these studies had to focus on freshwater fishing
activity, or at least have the potential to reflect significant
contributions from that category, such that the fish consumption
rates provided in a study could be reasonably applied in assessing
freshwater fishing activity. Studies also had to provide statistical
estimates of fish consumptions (i.e., means, medians, 90th
percentiles, etc). Given our interest in higher-end consumption
rates, the studies also had to either provide upper percentile
estimates, or support the derivation of those estimates (e.g.,
provide medians and a standard deviations). Studies of activity at
specific watersheds (e.g., creel surveys), while informative in
supporting the presence of higher-end consumption rates, could not
be used as the basis for defining our high-end consumption rates
since there would be greater uncertainty in extrapolating activity
at a specific river or lake more broadly to fishing populations in a
region. Therefore, we focused on studies characterizing fishing
activity more broadly than at a specific fishing location.
---------------------------------------------------------------------------

    Generally all of the studies identified high-end percentile
consumption rates (90th to 99th percentiles for the populations
surveyed) ranging from approximately one fish meal every few days to a
fish meal a day (i.e., 120 grams per day (g/day) to greater than 500 g/
day fish consumption). We used this trend across the studies to support
application of a generalized female high-end fish consumption scenario
(high-end female consumer scenario) across most of the 2,461
watersheds.\101\
---------------------------------------------------------------------------

    \101\ Reflecting the fact that higher levels of self-caught fish
consumption (approaching subsistence) have been associated with
poorer populations, we only assessed this generalized high-end
female consumer scenario at those watersheds located in U.S. Census
tracts with at least 25 individuals living below the poverty line
(this included the vast majority of the 2,461 watersheds and only a
handful were excluded due to this criterion).
---------------------------------------------------------------------------

iv. Risk Related to Exposure to MeHg in Fish and Assessment of
Contribution of U.S. EGUs to MeHg Exposure and Risk
    For the scenario representing high-end female fish consumption, we
estimated total exposure to MeHg at each of the 2,461 watersheds.\102\
Estimates of total Hg exposure were generated by combining 75th
percentile fish tissue values with the consumption rates for female
subsistence fishers. A cooking loss factor (reflecting the fact that
the preparation of fish can result in increased Hg concentrations) was
also included in exposure calculations.\103\
---------------------------------------------------------------------------

    \102\ As noted earlier, each high-end fish consuming female
population included in the analysis was assessed for a subset of
these watersheds, depending on which of those watersheds intersected
a U.S. Census tract containing a ``source population'' for that fish
consuming population. Of the populations assessed, the low-income
female subsistence fishing population scenario was assessed for the
largest portion (2,366) of the 2,461 watersheds.
    \103\ Morgan, J.N., M.R. Berry, and R.L. Graves. 1997. ``Effects
of Commonly Used Cooking Practices on Total Mercury Concentration in
Fish and Their Impact on Exposure Assessments.'' Journal of Exposure
Analysis and Environmental Epidemiology 7(1):119-133.
---------------------------------------------------------------------------

    Our estimates of total percent of watersheds where female
subsistence fishing populations may be at risk from exposure to U.S.
EGU-attributable MeHg are as high as 28 percent. The upper end estimate
of 28 percent of watersheds reflects the 99th percentile fish
consumption rate for that population, and a benchmark of 5 percent U.S.
EGU contribution to total Hg deposition in the watershed. Any
contribution of Hg emissions from EGUs to watersheds where potential
exposures from total Hg deposition exceed the RfD is a hazard to public
health, but for purposes of our analyses we evaluated only those
watersheds where we determined EGUs contributed 5 percent or more to
deposition to the watershed. EPA believes this is a conservative
approach given the increasing risks associated with incremental
exposures above the RfD. Of the total number of watersheds where
populations may be at risk from exposure to EGU-attributable MeHg, we
estimate that up to 22 percent of watersheds included in this analysis
could potentially have populations at risk based on consideration of
the U.S. EGU attributable fraction (e.g., 5, 10, 15, or 20 percent) of
total Hg deposition over watersheds with total risk judged to represent
a public health hazard (MeHg total exposure greater than the RfD).\104\
Of the total number of watersheds where populations may be at risk from
exposures to U.S. EGU-attributable MeHg, we estimate that up to 12
percent of watersheds included in this analysis could potentially have
populations at risk because the U.S. EGU incremental contribution to
exposure is above the RfD, even before consideration of contributions
to exposures from U.S. non-EGU and non-U.S. sources. In other words,
for this 12 percent of watersheds, even if there were no other sources
of Hg exposure, exposures associated with deposition attributable to
U.S. EGUs would place female high-end consumers above the MeHg RfD. The
upper end estimate of 12 percent of watersheds reflects a scenario
using the 99th percentile fish consumption rate.
---------------------------------------------------------------------------

    \104\ Because of the MMaps assumption of linear proportionality
between deposition and exposures, a 5 percent U.S. EGU contribution
to deposition will produce an equivalent 5 percent U.S. EGU
contribution to MeHg exposures.
---------------------------------------------------------------------------

    The two estimates of percent of watersheds where populations may be
at risk from EGU-attributable Hg do not sum to the total estimates of
28 percent because some watersheds where U.S. EGUs contribute greater
than 5 percent to total Hg deposition also have U.S. EGU attributable
exposures that exceed the RfD without consideration of exposures from
other U.S. and non-U.S. Hg sources.
    Exposures based on the 99th percentile consumption rate represent
close to maximum potential individual risk estimates. These consumption
rates are based on data reported by fishers in surveys, and, thus,
represent actual consumption rates in U.S. populations. There are also
a number of case studies in other locations, such as poor urban areas,
which provide additional evidence that high fish consumption occurs in
a number of locations throughout the U.S.105 106 107 108
However, EPA does not have sufficiently complete data on the specific
locations where these high self-caught fish consuming populations
reside and fish, and as a result, there is increased uncertainty about
the prevalence of populations who are high-end consumers of fish caught
in the set of watersheds included in the analysis. Populations matching
the high-end fish consumption scenario could be restricted to a subset
of these watersheds, or could be more heavily focused at watersheds
with higher or lower U.S. EGU-attributable fish tissue MeHg (and
consequently higher or lower U.S. EGU-attributable risk).
---------------------------------------------------------------------------

    \105\ Burger, J., K. Pflugh, L. Lurig, L. Von Hagen, and S. Von
Hagen. 1999. Fishing in Urban New Jersey: Ethnicity Affects
Information Sources, Perception, and Compliance. Risk Analysis
19(2): 217-229.
    \106\ Burger, J., Stephens, W., Boring, C., Kuklinski, M.,
Gibbons, W.J., & Gochfield, M. (1999). Factors in exposure
assessment: Ethnic and socioeconomic differences in fishing and
consumption of fish caught along the Savannah River. Risk Analysis,
19(3).
    \107\ Chemicals in Fish Report No. 1: Consumption of Fish and
Shellfish in California and the United States Final Draft Report.
Pesticide and Environmental Toxicology Section, Office of
Environmental Health Hazard Assessment, California Environmental
Protection Agency, July 1997.
    \108\ Corburn, J. (2002). Combining community-based research and
local knowledge to confront asthma and subsistence-fishing hazards
in Greenpoint/Williamsburg, Brooklyn, New York. Environmental Health
Perspectives, 110(2).
---------------------------------------------------------------------------

    With regard to the other fisher populations included in the full
risk assessment described in the TSD (Vietnamese, Laotians, Hispanics,
blacks and whites in the southeast, and tribes in the vicinity of the
Great Lakes), our risk estimates suggests that the high-end female
consumer assessed at the national-level generally provides coverage (in
terms of magnitude of risk) for all of these fisher populations except
blacks and whites in the southeast.109 110
---------------------------------------------------------------------------

    \109\ Specifically, upper percentile risk estimates for the
high-end female consumer assessed at the national level were notably
higher than matching percentile estimates for the Hmong, Vietnamese,
Hispanic, and Tribal populations. By contrast, risk estimates for
whites in the southeast were somewhat higher than the high-end
female consumer, while risk estimates for blacks in the southeast
were notably higher (see summary of risk estimates in the TSD
supporting this finding).
    \110\ The National Scale Mercury Risk Assessment TSD discusses
the greater uncertainty in characterizing the magnitude of high-end
fish consumption for these specialized populations due, in
particular, to the lower sample sizes associated with the survey
data (see Appendix C, Table C-1).

---------------------------------------------------------------------------

v. Variability and Uncertainty (Including Discussion of Sensitivity
Analyses)
    There are some uncertainties in EPA's analyses which could lead to
under or over prediction of risk to public health from U.S. EGU Hg
emissions. Based on sensitivity analyses we have conducted, we conclude
that even under different assumptions about the applicability of the
MMaps proportionality assumption, Hg from U.S. EGUs constitutes a
hazard to public health due to the percent of watersheds where U.S.
EGUs cause or contribute to exposures to MeHg above the RfD.
    Key sources of uncertainty potentially impacting the risk analysis
include: (1) Uncertainty in predicting Hg deposition over watersheds
using CMAQ; (2) uncertainty in predicting which watersheds will be
subject to high-end fishing activity and the nature of that activity
(e.g., frequency of repeated activity at a given watershed and the
types/sizes of fish caught); (3) uncertainty in using MMaps to
apportion exposure and risk between different sources, including U.S.
EGUs, and predicting changes in fish tissue MeHg levels for future
scenarios; and (4) potential under-representation of watersheds highly
impacted by U.S.-attributable Hg deposition due to limited MeHg
sampling. In the National Scale Mercury Risk Assessment TSD, we
describe in greater detail key sources of uncertainty impacting the
risk analysis, including their potential impact on the risk estimates
and the degree to which their potential impact is characterized as part
of the analysis.
    As part of the analysis, we have also completed a number of
sensitivity analyses focused on exploring the impact of uncertainty
related to the application of the MMaps approach in apportioning
exposure and risk estimates between sources (U.S. EGU and total) and in
predicting changes in fish tissue MeHg levels.\111\ These sensitivity
analyses evaluated: (1) The effect of including watersheds that may be
disproportionately impacted by non-air Hg sources; \112\ and (2) the
representativeness of the MMaps approach, which was tested for lakes,
when applied to streams and rivers (in the analysis, the MMaps was
applied to watersheds including a mixture of streams, rivers, and
lakes). The results of the limited sensitivity analyses we were able to
conduct suggest that uncertainties due to application of MMaps would
not affect our finding that U.S. EGU-attributable Hg deposition poses a
hazard to public health.
---------------------------------------------------------------------------

    \111\ The sensitivity analyses completed for the risk assessment
focused on assessing sources of uncertainty associated with the
application of the MMaps approach, because this was a critical
element in the risk assessment and identified early on as a key
source of potential uncertainty. Given the schedule of the analysis,
we did not have time to complete a full influence analysis to
identify those additional modeling elements that might introduce
significant uncertainty and therefore should be included in a
sensitivity analysis. Appendix F, Table F-2 of the Mercury Risk TSD
provides a qualitative discussion of key sources of uncertainty and
their potential impact on the risk assessment.
    \112\ In addition to non-air Hg sources of loadings, some
regions of concern may also have longer lag period associated with
the linkage between Hg deposition such that the fish tissue MeHg
levels we are using are actually associated with older historical Hg
deposition patterns.
---------------------------------------------------------------------------

    We also examined the potential for under-representation of
watersheds highly impacted by U.S.-attributable Hg deposition due to
limited MeHg sampling, by identifying watersheds that did not have fish
tissue MeHg samples, but had U.S. EGU-attributable Hg deposition at
least as high as watersheds that were identified as being at risk of
potential exposures greater than the RfD. Comparing the pattern of U.S.
EGU-attributable Hg deposition across all watersheds with that for
watersheds containing fish tissue MeHg data shows that while we have
some degree of coverage for watersheds with high U.S. EGU-attributable
deposition, this coverage is limited, especially in areas of
Pennsylvania which have high levels of U.S. EGU-attributable
deposition. For this reason, we believe that the actual number of
watersheds where populations may be at risk from exposures to U.S. EGU-
attributable MeHg could be substantially larger than the number
estimated based on the available fish tissue MeHg sampling data.
d. U.S. EGU Case Studies of Cancer and Non-Cancer Inhalation Risks for
Non-Hg HAP
    EPA conducted 16 case studies to estimate the potential for human
health impacts from current emissions of HAP other than Hg from EGUs. A
refined chronic inhalation risk assessment was performed for each case
study facility. The results of this analysis were that 4 (out of 16)
facilities posed a lifetime cancer risk of greater than 1 in 1 million
(the maximum was 10 in 1 million) and 3 more posed a risk at 1 in 1
million. Risk was driven by Ni (the oil-fired unit) and Cr+6
(the coal-fired units).
i. Case Study Selection
    An initial set of eight case study facilities was selected based on
several factors. First, we considered facilities with the highest
estimated cancer and non-cancer risks using the 2005 National Emissions
Inventory (NEI) data and the Human Exposure Model (HEM). The 2005 NEI
data were used because the initial set of case study facilities was
selected before we received the bulk of the emissions data from the
2010 ICR. Other factors considered in the selection included whether
facilities had implemented emission control measures since 2005, and
their proximity to residential areas. After the receipt of more data
through the 2010 ICR, additional case study facilities were selected,
based on the magnitude of emissions, heat input values (throughput),
and level of emission control. There were a total of 16 case study
facilities, 15 that use coal as fuel, and 1 that uses oil.
ii. Methods
    Annual emissions estimates for each EGU (including those in the
initial set of case study facilities) were developed using data from
the 2010 ICR. The results for the initial set indicated that Ni,
Cr+6, and As were the cancer risk drivers, and that non-
cancer risks did not produce any hazard index (HI) estimates exceeding
one. Although the non-cancer risks were low (the maximum chronic
noncancer HI was 0.4), they were driven by emissions of Ni, As, and
HCl. For the reasons discussed above, emissions were estimated only for
Ni, Cr+6, and As for the additional case study facilities.
Additional details on the emissions used in the modeling are provided
in a supporting memorandum to the docket for this action (Non-Hg Case
Study Chronic Inhalation Risk Assessment for the Utility MACT
``Appropriate and Necessary'' Analysis) (Non-Hg Memo). For each of the
16 case study facilities, we conducted refined dispersion modeling with
EPA's AERMOD modeling system (U.S. EPA, 2004) to calculate annual
ambient concentrations. Average annual concentrations were calculated
at census block centroids.
    We calculated the MIR for each facility as the cancer risk
associated with a continuous lifetime (24 hours per day, 7 days per
week, and 52 weeks per year for a 70-year period) exposure to the
maximum concentration at the centroid of an inhabited census block,
based on application of the unit risk estimate from EPA's IRIS, which
is a human health assessment program that evaluates quantitative and
qualitative risk information on effects that may result from exposure
to environmental contaminants. For Ni compounds, we

used 65 percent of the IRIS URE for nickel subsulfide. The
determination of this value is discussed in the Non-Hg Memo, and the
value is receiving peer review as discussed in section later. To assess
the risk of non-cancer health effects from chronic exposures, following
the approach recommended in EPA's Mixtures
Guidelines,113 114 we summed the HQs for all HAP that affect
a common target organ system to obtain the HI for that target organ
system (target-organ-specific HI, or TOSHI). The HQ for chronic
exposures is the estimated chronic exposure (again, based on the
estimated annual average ambient concentration at each nearby census
block centroid) divided by the chronic non-cancer reference level,
which is usually the EPA reference concentration (RfC). In cases where
an IRIS RfC is not available, EPA utilizes the following prioritized
sources for chronic dose-response values: (1) The Agency for Toxic
Substances and Disease Registry (ATSDR) Minimum Risk Level (MRL), and
(2) the California Environmental Protection Agency chronic Reference
Exposure Level (REL). In this assessment, we used the IRIS RfC values
for Cr+6 and HCl, the ATSDR MRL for Ni compounds, and the
California Environmental Protection Agency REL for As.
---------------------------------------------------------------------------

    \113\ U.S. EPA, 1986, Guidelines for the Health Risk Assessment
of Chemical Mixtures, EPA-630-R-98-002. http://www.epa.gov/NCEA/raf/pdfs/chem_mix/chemmix_1986.pdf.
    \114\ U.S. EPA, 2000. Supplementary Guidance for Conducting
Health Risk Assessment of Chemical Mixtures. EPA-630/R-00-002.
http://www.epa.gov/ncea/raf/pdfs/chem_mix/chem_mix_08_2001.pdf.
---------------------------------------------------------------------------

iii. Results
    The highest estimated lifetime cancer risk from any of the 16 case
study facilities was 10 in 1 million (1 x 10-5), driven by
Ni emissions from the 1 case study facility with oil-fired units. For
the facilities with coal-fired units, there were 3 with maximum cancer
risks greater than 1 in 1 million (the highest was 8 in 1 million), all
driven by Cr+6, and there were 4 with maximum cancer risks
at 1 in 1 million. All of the facilities had non-cancer TOSHI values
less than one, with a maximum HI value of 0.4 (also driven by Ni
emissions from the one case study facility with oil-fired units). The
maximum chronic impacts of HCl emissions were all less than 10 percent
of its chronic RfC. Because of uncertainties in their emission rates,
other acid gases (Cl2, HF, and HCN) were not included in the
assessment of noncancer impacts. Because EGUs are not generally co-
located with other source categories, facility-wide HAP emissions and
risks are equal to those associated with the EGU source category.
    The cancer risk estimates from this assessment indicate that the
EGU source category is not eligible for delisting under CAA section
112(c)(9)(B)(i), which specifies that a category may be delisted only
when the Administrator determines ``* * * that no source in the
category (or group of sources in the case of area sources) emits such
HAP in quantities which may cause a lifetime risk of cancer greater
than one in one million to the individual in the population who is most
exposed to emissions of such pollutants from the source * * *'' We note
that, because these case studies do not cover all facilities in the
category, and because our assessment does not include the potential for
impacts from different EGU facilities to overlap one another (i.e.,
these case studies only look at facilities in isolation), the maximum
risk estimates from the case studies may underestimate true maximum
risks.
e. Peer-Review of Quantitative Risk Analyses
    The Agency has determined that the National-Scale Mercury Risk
Analysis supporting EPA's 2011 review of U.S. EGU health impacts should
be peer-reviewed. In addition, the Agency has determined that the
characterization of the chemical speciation for the emissions of Cr and
Ni should be peer-reviewed. The Agency has evaluated the other
components of the analyses supporting this finding and determined that
the remaining aspects of the case study analyses for non-Hg HAP use
methods that have already been subject to adequate peer-review. As a
result, the Agency is limiting the peer-review to the National-Scale
Mercury Risk Analysis and the speciation of emissions for Cr and Ni.
Due to the court-ordered schedule for this proposed rule, EPA will
conduct these peer reviews as expeditiously as possible after issuance
of this proposed rule and will publish the results of the peer reviews
and any EPA response to them before the final rule.
4. Qualitative Assessment of Potential Environmental Risks From
Exposures of Ecosystems Through Hg and Non-Hg HAP Deposition
    Adverse effects on fish and wildlife have been observed to be
occurring today which are the result of elevated exposures to MeHg,
although these effects have not been quantitatively assessed.
    Elevated MeHg concentrations in fish and wildlife can occur not
only in areas of high Hg deposition. Elevated MeHg concentrations can
also occur in diverse locations, including watersheds that receive
average or even relatively low Hg deposition, but are particularly
sensitive to Hg pollution, for example, they have higher than average
methylation rates due to high levels of sulfur deposition. Such
locations are characterized by moderate deposition levels that have
generated high Hg concentrations in biota compared to the surrounding
landscape receiving a similar Hg loading. These Hg-sensitive watersheds
readily transport inorganic Hg, convert the inorganic Hg to MeHg, and
bioaccumulate this MeHg through the food web. Areas of enhanced MeHg in
fish and wildlife are not constrained to a single Hg source, because
ecosystems respond to the combined effects of Hg pollution from
multiple sources.
    A review of the literature on effects of Hg on reproduction in
fish\115\ reports adverse reproductive effects for numerous species
including trout, bass (large and smallmouth), northern pike, carp,
walleye, salmon, and others from laboratory and field studies. Mercury
also affects avian species. In previous reports \116\ much of the focus
has been on large fish-eating species, in particular the common loon.
Breeding loons experience significant adverse effects including
behavioral (reduced nest-sitting), physiological (flight feather
asymmetry) and reproductive (chicks fledged/territorial pair)
effects.\117\
---------------------------------------------------------------------------

    \115\ Crump, Kate L., and Trudeau, Vance L. Mercury-induced
reproductive impairment in fish. Environmental Toxicology and
Chemistry. Vol. 28, No. 5, 2009.
    \116\ U.S. Environmental Protection Agency (EPA). 1997. Mercury
Study Report to Congress. Volume V: Health Effects of Mercury and
Mercury Compounds. EPA-452/R-97-007. U.S. EPA Office of Air Quality
Planning and Standards, and Office of Research and Development.
    U.S. Environmental Protection Agency (U.S. EPA). 2005.
Regulatory Impact Analysis of the Final Clean Air Mercury Rule.
Office of Air Quality Planning and Standards, Research Triangle
Park, NC., March; EPA report no. EPA-452/R-05-003. Available on the
Internet at http://www.epa.gov/ttn/ecas/regdata/RIAs/mercury_ria_final.pdf.
    \117\ Evers, David C., Savoy, Lucas J., DeSorbo, Christopher R.,
Yates, David E., Hanson, William, Taylor, Kate M., Siegel, Lori S.,
Cooley, John H. Jr., Bank, Michael S., Major, Andrew, Munney,
Kenneth, Mower, Barry F., Vogel, Harry S., Schoch, Nina, Pokras,
Mark, Goodale, Morgan W., Fair, Jeff. Adverse effects from
environmental mercury loads on breeding common loons. Ecotoxicology.
17:69-81, 2008.
---------------------------------------------------------------------------

    Other fish-eating bird species such as the white ibis and great
snowy egret experience a range of adverse effects due to exposure to
Hg. The white ibis has been observed to have decreased foraging
efficiency \118\ and decreased

reproductive success and altered pair behavior.\119\ These effects
include significantly more unproductive nests, male/male pairing,
reduced courtship behavior and lower nestling production by exposed
males. In egrets, Hg has been implicated in the decline of the species
in south Florida \120\ and studies show liver and possibly kidney
effects.\121\ Insectivorous birds have also been shown to suffer
adverse effects due to Hg exposure. Songbirds such as Bicknell's
thrush, tree swallows and the great tit have shown reduced
reproduction, survival, and changes in singing behavior. Exposed tree
swallows produced fewer fledglings,\122\ lower survival,\123\ and had
compromised immune competence.\124\ The great tit has exhibited reduced
singing behavior and smaller song repertoire in areas of high
contamination.\125\
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    \118\ Adams, Evan M., and Frederick, Peter C. Effects of
methylmercury and spatial complexity on foraging behavior and
foraging efficiency in juvenile white ibises (Eudocimus albus).
Environmental Toxicology and Chemistry. Vol 27, No. 8, 2008.
    \119\ Frederick, Peter, and Jayasena, Nilmini. Altered pairing
behavior and reproductive success in white ibises exposed to
environmentally relevant concentrations of methylmercury.
Proceedings of The Royal Society B. doi: 10-1098, 2010.
    \120\ Sepulveda, Maria S., Frederick, Peter C., Spalding,
Marilyn G., and Williams, Gary E. Jr. Mercury contamination in free-
ranging great egret nestlings (Ardea albus) from southern Florida,
USA. Environmental Toxicology and Chemistry. Vol. 18, No.5, 1999.
    \121\ Hoffman, David J., Henny, Charles J., Hill, Elwood F.,
Grover, Robert A., Kaiser, James L., Stebbins, Katherine R. Mercury
and drought along the lower Carson River, Nevada: III. Effects on
blood and organ biochemistry and histopathology of snowy egrets and
black-crowned night-herons on Lahontan Reservoir, 2002-2006. Journal
of Toxicology and Environmental Health, Part A. 72:20, 1223-1241,
2009.
    \122\ Brasso, Rebecka L., and Cristol, Daniel A. Effects of
mercury exposure in the reproductive success of tree swallows
(Tachycineta bicolor). Ecotoxicology. 17:133-141, 2008.
    \123\ Hallinger, Kelly K., Cornell, Kerri L., Brasso, Rebecka
L., and Cristol, Daniel A. Mercury exposure and survival in free-
living tree swallows (Tachycineta bicolor). Ecotoxicology. Doi:
10.1007/s10646-010-0554-4, 2010.
    \124\ Hawley, Dana M., Hallinger, Kelly K., Cristol, Daniel A.
Compromised immune competence in free-living tree swallows exposed
to mercury. Ecotoxicology. 18:499-503, 2009.
    \125\ Gorissen, Leen, Snoeijs, Tinne, Van Duyse, Els, and Eens,
Marcel. Heavy metal pollution affects dawn singing behavior in a
small passerine bird. Oecologia. 145:540-509, 2005.
---------------------------------------------------------------------------

    In mammals, adverse effects from Hg including mortality have been
observed in mink and river otter, both fish eating species. Other
adverse effects may include increased activity, poorer maze
performance, abnormal startle reflex, and impaired escape and avoidance
behavior.\126\ EPA is also concerned about the potential impacts of HCl
and other acid gas emissions on the environment. When HCl gas
encounters water in the atmosphere, it forms an acidic solution of
hydrochloric acid. In areas where the deposition of acids derived from
emissions of sulfur and NOX are causing aquatic and/or
terrestrial acidification, with accompanying ecological impacts, the
deposition of hydrochloric acid would further exacerbate these impacts.
Recent research\127\ has, in fact, determined that deposition of
airborne HCl has had a greater impact on ecosystem acidification than
anyone had previously thought, although direct quantification of these
impacts remains an uncertain process.
---------------------------------------------------------------------------

    \126\ Scheuhammer, Anton M., Meyer Michael W., Sandheinrich,
Mark B., and Murray, Michael W. Effects of environmental
methylmercury on the health of wild birds, mammals, and fish. Ambio.
Vol.36, No.1, 2007.
    \127\ Evans, Chris D., Monteith, Don, T., Fowler, David, Cape,
J. Neil, and Brayshaw, Susan. Hydrochloric Acid: An Overlooked
Driver of Environmental Change, Env. Sci. Technol., DOI: 10.1021/
es10357u.
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5. Potential for Deposition ``Hotspots'' in Areas Near U.S. EGUs
    Although it has been characterized and addressed as a global issue,
Hg from U.S. EGUs is shown to deposit in higher quantities close to
emission sources, and around some sources can be as high as 3 times the
regional average deposition. EPA evaluated the potential for ``hot
spot'' deposition near U.S. EGU emission sources on a national scale,
based on the CMAQ modeled Hg deposition for 2005 and 2016.\128\ We
calculated the excess deposition within 50 km of U.S. EGU sources by
first calculating the average U.S. EGU attributable Hg deposition
within a 500 km radius around the U.S. EGU source. This deposition
represents the likely regional contribution around the EGU. We then
calculated the average U.S. EGU attributable Hg deposition within 50 km
of the U.S. EGUs to characterize local deposition plus regional
deposition near the EGU facility. Excess local deposition is then the
50 km radius average deposition minus the 500 km radius average
deposition. Summary statistics for the excess local deposition are
provided in Table 9 of this preamble. Table 9 of this preamble shows
both the mean excess deposition around all U.S. EGUs, and the mean
excess deposition around just the top 10 percent of Hg emitting U.S.
EGUs. Table 9 of this preamble also shows the excess Hg deposition as a
percent of the average regional deposition to provide context for the
magnitude of the local excess deposition. In 2005, for all U.S. EGU,
the excess was around 120 percent of the average deposition, while for
the top 10 percent of Hg emitting U.S. EGU, local deposition was around
3.5 times the regional average. By 2016, although the absolute excess
deposition falls, the local excess still remains around 3 times the
regional average for the highest 10 percent of Hg emitting U.S. EGUs.
---------------------------------------------------------------------------

    \128\ More details are provided in the National Scale Mercury
Risk Assessment TSD.

  Table 9--Excess Local Deposition of Hg Based on 2005 CMAQ Modeled Hg
                               Deposition
------------------------------------------------------------------------
                                       50 km-Radius-average excess local
                                        deposition values ([mu]g/m\2\)
                                     -----------------------------------
                                         Mean across EGUs (percent of
                                         regional average deposition)
                                     -----------------------------------
                                            2005              2016
------------------------------------------------------------------------
All U.S. EGU sites with Hg emissions       1.65 (119%)        0.36 (93%)
 > 0 (672 sites)....................
Top ten percent U.S. EGU in Hg             4.89 (352%)       1.18 (302%)
 emissions (67 sites)...............
------------------------------------------------------------------------

    This analysis shows that there is excess deposition of Hg in the
local areas around EGUs, especially those with high Hg emissions.
Although this is not necessarily indicative of higher risk of adverse
effects from consumption of MeHg contaminated fish from waterbodies
around the U.S. EGUs, it does indicate an increased chance that Hg from
U.S. EGUs will impact local waterbodies around the EGU sources, and not
just impact regional deposition.
6. Emissions Controls for Emissions of Hg and Non-Hg HAP Are Available
and Effective
    Analyses of currently available control technologies for Hg, acid
gases,

and non-Hg metal HAP show that significant reductions in these
pollutants can be achieved from EGUs with significant coincidental
reductions in the emissions of other pollutants as well.
a. Availability of Hg Emissions Control Options
    The control of Hg in a coal combustion flue gas is highly dependent
upon the form (or species) of the Hg. The Hg can be present in one of
three forms: as Hg\0\, as a vapor of Hg+\2\ (e.g., mercuric
chloride, Hg(Cl2)), or as HgP (e.g., adsorbed on
fly ash or unburned carbon). The specific form of the Hg in the flue
gas will strongly influence the effectiveness of available control
technology for Hg control. The form (or ``speciation'') of the Hg is
determined by the flue gas chemistry and by the time-temperature
profile in the post combustion environment. During coal combustion, Hg
is released into the exhaust gas as Hg\0\. This vapor may then continue
through the flue gas cleaning equipment and exit the stack as gaseous
Hg\0\ or it may be oxidized to Hg+\2\ compounds (such as
HgCl2) via homogeneous (gas-gas) or heterogeneous (gas-
solid) reactions. The primary homogeneous oxidation mechanism is the
reaction with gas-phase chlorine (Cl radical or possibly, HCl) to form
HgCl2. Although this mechanism is thermodynamically
favorable, it is thought to be kinetically limited due to rapid cooling
of the flue gas stream. Heterogeneous oxidation reactions occur on the
surface of fly ash and unburned carbon. It is thought that in-duct
chlorination of the surface of the fly ash, unburned carbon, or
injected activated carbon sorbent is the first step to heterogeneous
oxidation and surface binding of vapor-phase Hg\0\ in the flue gas
stream (i.e., the formation of HgP).
    Mercury control can occur as a ``co-benefit'' of conventional
control technologies that have been installed for other purposes.
Particulate Hg can be effectively removed along with other flue gas PM
(including non-Hg metal HAP) in the primary or secondary PM control
device. For units using electrostatic precipitators (ESPs), the
effectiveness will depend upon the amount of HgP entering
the ESP. Units that burn coals with higher levels of native chlorine
and that produce more unburned carbon can see good Hg removal in the
ESP. Fabric filters (FF) have been shown to provide very high levels of
control when there is adequate halogen to convert the Hg to the
oxidized form. Units with wet FGD scrubbers can achieve high levels of
Hg control--provided that the Hg is present in the oxidized (i.e., the
soluble) form. A selective catalytic reduction (SCR) catalyst can
enhance the Hg removal by catalytically converting Hg\0\ to
Hg+\2\, making it more soluble and more likely to be
captured in the scrubber solution. Halogen additives (usually bromide
salts, but chloride salts may also be used) can also be added directly
to the coal or injected into the boiler to enhance the oxidation of Hg.
    Activated carbon injection (ACI) is the most successfully
demonstrated Hg-specific control technology. In this case, a powdered
AC sorbent is injected into the duct upstream of the primary or a
secondary PM control device. The carbon is injected to maximize contact
with the flue gas. Mercury binds on the surface of the carbon to form
HgP, which is then removed in the PM control device.
Conventional (i.e., non-halogenated) AC is effective when capturing Hg
that is already predominantly in the oxidized state or when there is
sufficient flue gas halogens to promote oxidation of the Hg on the AC
surface. Pre-halogenated (i.e., brominated) AC has been shown to be
very effective when used in combination with low chlorine coals (such
as U.S. western subbituminous coals). Activated carbons can suffer from
poor performance when used with high sulfur coals. Firing high sulfur
coals (especially when an SCR is also used) can result in sulfur
trioxide (SO3) vapor in the flue gas stream. The
SO3 competes with Hg for binding sites on the surface of the
AC (or unburned carbon) and limits the effectiveness of the injected
AC. An SO3 mitigation technology--such as dry sorbent
injection (DSI, e.g., trona or hydrated lime)--applied upstream of the
ACI can minimize this effect.
    Mingling of AC with the fly ash can affect the viability for use of
the captured fly ash as an additive in concrete production. Use of the
TOXECONTM configuration can keep the fly ash and the AC
separate. This configuration consists of the primary PM control device
(ESP or FF) followed by a secondary downstream pulsejet FF. The AC is
injected prior to the secondary FF. The fly ash is captured in the
primary PM control device and the AC and Hg are captured in the
downstream secondary FF.
b. Availability of PM or Metal HAP Emissions Control Options
    Electrostatic precipitators and FFs are the most commonly applied
PM control technologies in U.S. coal-fired EGUs. Newer units have
tended to install FFs, which usually provide better performance than
ESPs. An existing facility that wants to upgrade the PM control may
choose to replace the current equipment with newer, better performing
equipment. The facility may also consider installation of a downstream
secondary PM control device--such as a secondary FF. A wet ESP (WESP)
can be installed downstream of a wet FGD scrubber for control of
condensable PM.
c. Availability of Acid Gas Emissions Control Options
    Acid gases are likely to be removed in typical FGD systems due to
their solubility or their acidity (or both). The acid-gas HAP--HCl, HF,
and HCN (representing the ``cyanide compounds'')--are water-soluble
compounds, more soluble in water than is SO2. This indicates
that HCl, HF, and HCN should be more easily removed from a flue gas
stream in a typical FGD system than will SO2, even when only
plain water is used. Hydrogen chloride is also a strong acid and will
react easily in acid-base reactions with the caustic sorbents (e.g.,
lime, limestone) that are commonly used in FGD systems. Hydrogen
fluoride is a weaker acid, having a similar acid dissociation constant
as that of SO2. Cyanide is the weakest of these acid gases.
In the slurry streams, composed of water and sorbent (e.g., lime,
limestone) used in both wet-scrubber and dry spray dryer absorber FGD
systems, acid gases and SO2 are absorbed by the slurry
mixture and react to form alkaline salts. In fluidized bed combustion
(FBC) systems, the acid gases and SO2 are adsorbed by the
sorbent (usually limestone) that is added to the coal and an inert
material (e.g., sand, silica, alumina, or ash) as part of the FBC
process. Hydrogen chloride and HF have also been shown to be
effectively removed using DSI where a dry, alkaline sorbent (e.g.,
hydrated lime, trona, sodium carbonate) is injected upstream of a PM
control device. Chlorine in the fuel coal may also partition in small
amounts to Cl2. This is normally a very small fraction
relative to the formation of HCl. Limited testing has shown that
Cl2 gas is also effectively removed in FGD systems. Although
Cl2 is not strictly an acidic gas, it is grouped here with
the ``acid gas HAP'' because it is controlled using the same
technologies.
d. Expected Impact of Available Controls on HAP Emissions from EGUs
    In 2016, EGUs are projected to account for an estimated 45 percent
of anthropogenic Hg (excluding fires) in the continental U.S.
Application of available Hg controls in 2016 that would be required
under section 112 reduces

Hg emissions from 29 down to 6 tons, achieving a 23 tpy reduction of Hg
from EGUs, which results in a 79 percent reduction in U.S. EGU
emissions, and a 36 percent reduction of total anthropogenic Hg
emissions nationally.
    In 2016, EGUs are projected to account for 53 percent of total U.S.
anthropogenic HCl. Application of available HCl controls in 2016 that
would be required under section 112 achieves a 68,000 tpy reduction in
HCl emissions (a 91 percent reduction in EGU emissions), resulting in a
49 percent reduction of anthropogenic emissions nationally.
    Metal HAP emissions are a component of PM, and are expected to be
reduced along with PM as a result of application of PM controls. In
2016, application of controls required under section 112 is expected to
provide an average reduction in PM for the continental U.S. of 38
percent. Although no specific projection of metals is available for
2016, applying the 38 percent reduction in PM to the 2010 ICR emissions
levels of anthropogenic metals,\129\ results in reductions of
approximately 430 tons of metals per year.\130\
---------------------------------------------------------------------------

    \129\ It is generally assumed that the same types of controls
that reduce PM will also reduce metals, because they are components
of the PM.
    \130\ This value is 38 percent of 1,140 tons, which is the total
tonnage of the metals listed in Table 5, based on the 2010 ICR
emissions data.
---------------------------------------------------------------------------

    EPA believes these projected reductions in Hg, acid gases, and
metal HAP emissions demonstrate the effectiveness of available
controls.
6. Consideration of the Role of U.S. EGU Hg Emissions in the Global
Effort To Decrease Hg Loadings in the Environment
    This would allow the U.S. to demonstrate effective technologies to
reduce Hg; such leadership could provide confidence to other countries
that they can succeed in meeting their commitments. Mercury pollution
is a significant international environmental challenge, and it is well
understood that efforts that reduce Hg emissions in other countries
will reduce Hg that impacts U.S. public health and the environment.
Recognizing this, EPA and others in the U.S. Government are actively
involved in international efforts to reduce Hg pollution. These efforts
include global negotiations aimed at concluding a legally-binding
agreement to reduce Hg that were initiated in February 2009 under the
UNEP.\131\ Negotiation of the agreement is not expected to be completed
until early 2013. Once the international process is complete, the
agreement must be ratified domestically before the agreement will
become binding in the U.S. The agreement is expected to cover major
man-made sources of air Hg emissions, including coal-fired EGUs.
Current negotiations are considering the application of best available
technologies and practices to reduce air Hg emissions significantly.
Regulations such as the proposed rule demonstrate the U.S. commitment
to addressing the global Hg problem by decreasing the largest source of
Hg emissions in the U.S. and serve to encourage other countries to
address Hg emissions from their own sources.
---------------------------------------------------------------------------

    \131\ Governing Council of the United Nations Environment
Programme http://www.unep.org/hazardoussubstances/Mercury/Negotiations/Mandates/tabid/3321/language/en-US/Default.aspx.
---------------------------------------------------------------------------

7. It Remains Appropriate and Necessary To Regulate EGUs To Address
Public Health and Environmental Hazards Associated With Emissions of Hg
and Non-Hg HAP From EGUs
    The extensive analyses summarized above confirm that it remains
appropriate and necessary today to regulate EGUs under section 112. It
is appropriate to regulate emissions from coal- and oil-fired EGUs
under CAA section 112 because: (1) Hg and non-Hg HAP continue to pose a
hazard to public health, and U.S. EGU emissions cause and/or contribute
to this hazard; (2) Hg and some non-Hg HAP pose a hazard to the
environment; (3) U.S. EGU emissions, accounting for 45 percent of U.S.
Hg emissions, are still the largest domestic source of U.S. Hg
emissions (by 2016, EPA projects that U.S. EGU Hg emissions will be
over 6 times larger than the next largest source, which is iron and
steel manufacturing), as well as the largest source of HCl and HF
emissions, and a significant source of other HAP emissions; (4) Hg
emissions from individual EGUs leads to hot spots of deposition in
areas directly surrounding those individual EGUs, and, thus, deposition
is not solely the result of regionally transported emissions, and will
not be adequately addressed through reductions in regional levels of Hg
emissions, requiring controls to be in place at all U.S. EGU sources
that emit Hg; (5) Hg emissions from EGUs affect not only deposition,
exposures, and risk today, but may contribute to future deposition,
exposure and risk due to the processes of reemission of Hg that occur
given the persistent nature of Hg in the environment--the delay in
issuing Hg regulations under section 112 has already resulted in
several hundred additional tons of Hg being emitted to the environment,
and that Hg will remain part of the global burden of Hg; and (6)
effective controls for Hg and non-Hg HAP are available for U.S. EGU
sources.
    EPA concludes that Hg emissions from U.S. EGUs are a public health
hazard today due to their contribution to Hg deposition that leads to
potential MeHg exposures above the RfD. EPA also concludes that U.S.
EGU Hg emissions contribute to environmental concentrations of Hg that
are harmful to wildlife and can affect production of important
ecosystem services, including recreational hunting and fishing, and
wildlife viewing. EPA further concludes that non-Hg HAP emissions from
U.S. EGU are a public health hazard because they contribute to elevated
cancer risks.
    Finally, EPA concludes that U.S. EGU's HCl and HF emissions
contribute to acidification in sensitive ecosystems and, therefore,
pose a risk of adverse effects on the environment.
a. U.S. EGU Hg Emissions Continue To Pose a Hazard to Public Health and
the Environment
    The CAA does not define what constitutes a hazard to public health.
As noted earlier, the agency must use its scientific and technical
expertise to determine what constitutes a hazard to public health in
the context of Utility Hg emissions. Congress did provide guidance as
to what it considered an important benchmark for public health hazards,
particularly in regard to Hg. In section 112(n)(1)(C), Congress
required the NIEHS to determine ``the threshold level of Hg exposure
below which adverse human health effects are not expected to occur.''
This threshold level is represented by the RfD, and as such, the RfD is
the benchmark for determining hazards to public health that is most
consistent with Congress's interpretation of adverse health effects. As
a result, our assessment of the hazard to public health posed by U.S.
EGU Hg emissions is focused on comparisons to the RfD of exposures
caused or contributed to by U.S. EGU Hg emissions.
    As described above, almost all (98 percent) of the more than 2,400
watersheds for which we have fish tissue data exceed the RfD, above
which there is the potential for an increased risk of adverse effects
on human health. U.S. EGU-attributable deposition of Hg contributes to
a large number of those watersheds in which total potential exposures
to MeHg from all sources exceed the RfD and, thus, pose a hazard to
public health. For our analysis, we focused on the watersheds to which
EGUs contributed at least 5 percent of the total Hg deposition and
related

MeHg exposures at a watershed, or contributed enough Hg deposition
resulting in potential MeHg exposures above the RfD, regardless of the
additional deposition from other sources of Hg deposition. We believe
this is a conservative approach because any contribution of Hg to
watersheds where potential exposures to MeHg exceed the RfD poses a
public health hazard. Thus, because we are finding a large percentage
of watersheds with populations potentially at risk even using this
conservative approach, we have confidence that emissions of Hg from
U.S. EGUs are causing a hazard to public health, as we believe that
there are additional watersheds that have contributions at lower
percent benchmarks.
    In total, 28 percent of sampled watersheds have populations that
are potentially at risk from exposure to MeHg based on the contribution
of U.S. EGUs, either because U.S. EGU attributable deposition is
sufficient to cause potential exposures to exceed the reference dose
even before considering the deposition from other U.S. and non-U.S.
sources, or because the U.S. EGU attributable deposition contributes
greater than 5 percent of total deposition and total exposure from all
sources is greater than the reference dose. At the 99th percentile fish
consumption level for subsistence fishers, 22 percent of sampled
watersheds where total potential exposures to MeHg exceed the RfD have
a contribution from U.S. EGUs of at least 5 percent of Hg deposition.
    Although the most complete estimate of potential risk is based on
total exposures to Hg, including that due to deposition from U.S. EGU
sources, U.S. non-EGU sources, and global sources, the deposition
resulting from U.S. EGU Hg emissions is large enough in some watersheds
that persons consuming contaminated fish would have exposures that
exceed the RfD even before taking into account the deposition from
other sources. At the 99th percentile fish consumption level for
subsistence fishers, in 12 percent of the sampled watersheds, U.S. EGUs
are responsible for deposition that causes the RfD to be exceeded, even
before considering the additional deposition from other sources.
    In addition, we believe the estimate of where populations may be at
risk from U.S. EGU-attributable Hg deposition is likely understated
because the data on fish tissue MeHg concentrations is limited in some
regions of the U.S., such as Pennsylvania, with very high U.S. EGU
attributable Hg deposition, and it is possible that watersheds with
potentially high MeHg exposures were excluded from the risk
analysis.\132\ In addition, due to limitations in our models and
available data, we have not estimated risks in near-coastal waters, and
some of these waters, including the Chesapeake Bay, have EGU-
attributable Hg deposition.
---------------------------------------------------------------------------

    \132\ An analysis of the impact of sampling location limitations
on coverage of high U.S. EGU deposition watersheds is provided in
the National Scale Mercury Risk Assessment TSD.
---------------------------------------------------------------------------

    Further, scientific studies have found strong evidence of adverse
impacts on species of fish-eating birds with high bird-watching value,
including loons, white ibis, and great snowy egrets. Studies have also
shown adverse effects on insect-eating birds including many songbirds.
Adverse effects in fish-eating mammals, such as mink and otter, include
neurological responses (impaired escape and avoidance behavior) which
can influence survival rates. Because EGUs contribute to Hg deposition
in the U.S., we reasonably conclude that EGUs are contributing to the
identified adverse environmental effects.
    Mercury emitted into the atmosphere persists for years, and once
deposited, can be reemitted into the atmosphere due to a number of
processes, including forest fires and melting of snow packs. As a
result, Hg emitted today can have impacts for many years. In fact, Hg
emitted by U.S. EGUs in the past, including over the last decade, is
still having impacts on concentrations of Hg in fish today. Failing to
control Hg emissions from U.S. EGU sources will result in long term
environmental loadings of Hg, above and beyond those loadings caused by
immediate deposition of Hg within the U.S. Although we are not able to
quantify the impact of U.S. EGU emissions on the global pool of Hg,
U.S. EGUs do contribute to that global pool. Controlling Hg emissions
from U.S. EGUs helps to reduce the potential for environmental hazard
from Hg now and in the future. These findings independently support a
determination that it is appropriate to regulate HAP emissions from
EGUs.
b. U.S. EGU Non-Hg HAP Emissions Continue To Pose a Hazard to Public
Health and the Environment
    EPA recently conducted 16 case studies of U.S. EGUs for which we
had 2007 to 2009 emissions data (based on the 2010 ICR) and that we
anticipated would have relatively higher emissions of non-Hg HAP
compared to other U.S. EGUs. Of the 16 facilities modeled, 4
facilities, 3 coal and 1 oil facility, have estimated risks of greater
than 1 in 1 million for the most exposed individual. Although section
112(n)(1)(A) does not specify what constitutes a hazard to public
health for the purposes of the appropriate and necessary finding, CAA
section 112(c)(9) is instructive. As explained in section III.A above,
for carcinogenic HAP, section 112(c)(9) contains a test for delisting
source categories based on lifetime risk of cancer. That test reflects
Congress' view as to the level of health effects associated with HAP
emissions that Congress thought warranted continued regulation under
section 112. Specifically, section 112(c)(9) provides that a source
category can be delisted only if no source emits HAP in quantities
which may cause a lifetime risk of cancer greater than 1 in 1 million
to the most exposed individual. As noted above, the results of the case
study risk analysis confirm that sources in the EGU source category
emit HAP in quantities that cause a lifetime risk of cancer greater
than 1 in 1 million. Given Congress' determination that categories of
sources which emit HAP resulting in a lifetime cancer risk greater than
1 in 1 million should not be removed from the section 112(c) source
category list and should continue to be regulated under 112, we believe
risks above that level represent a hazard to public health such that it
is appropriate to regulate EGUs under section 112.
    Although our case studies did not identify significant chronic non-
cancer risks from acid gas emissions from the specific EGUs assessed,
the Administrator remains concerned about the potential for acid gas
emissions to add to already high atmospheric levels of other chronic
respiratory toxicants and to environmental loading and degradation due
to acidification. EGUs emit over half of the nationwide emissions of
HCl and HF, based on 2010 emissions estimates. In addition, given that
many sensitive ecosystems across the country are experiencing
acidification, it is appropriate to reduce emissions of this magnitude
which carry the potential to aggravate acidification. The Administrator
concludes that, in addition to the regulation of non-Hg HAP which cause
elevated cancer risks, it is appropriate to regulate those HAP which
are not known to cause cancer but are known to contribute to chronic
non-cancer toxicity and environmental degradation, such as the acid
gases.
    These findings independently support a determination that it is
appropriate to regulate HAP emissions from EGUs.

c. Effective Controls Are Available To Reduce Hg and Non-Hg HAP
Emissions
    Particle-bound Hg can be effectively removed along with other flue
gas PM (including non-Hg metal HAP) in primary or secondary PM control
devices. Electrostatic precipitators, FF, and wet FGD scrubbers are all
effective at removing Hg, with the degree of effectiveness depending on
the specific characteristics of the EGU and fuel types. These devices
are all effective in removing metal HAP as well. Activated carbon
injection is the most successfully demonstrated Hg-specific control
technology, although performance may be reduced when used with high
sulfur coals. Acid gases are readily removed in typical FGD systems due
to their solubility or their acidity (or both). The availability of
controls for HAP emissions from EGUs supports the appropriate finding
because sources will be able to reduce their emissions effectively and,
thereby, reduce the hazards posed by HAP emissions from EGUs.
d. The Administrator Finds That It Remains Necessary To Regulate Coal-
and Oil-Fired EGUs Under CAA Section 112
    EPA determined that in 2016 the hazards posed to human health and
the environment by HAP emissions from EGUs will not be addressed;
therefore, it is necessary to regulate EGUs under section 112. In
addition, it is necessary to regulate EGUs under section 112 because
the only way to ensure permanent reductions in U.S. EGU emissions of
HAP and the associated risks to public health and the environment is
through standards set under section 112.
    The Agency first evaluates whether it is necessary to regulate HAP
emissions from EGUs ``after imposition of the requirements of the
CAA.'' As explained above, we interpret that phrase to require the
Agency to consider only those requirements that Congress directly
imposed on EGUs through the CAA as amended in 1990 and for which EPA
could reasonably predict HAP emission reductions at the time of the
Study. Nonetheless, the Agency recognizes that it has discretion to
look beyond the Utility Study in determining whether it is necessary to
regulate EGUs under section 112. Because several years have passed
since the December 2000 Finding, we conducted an additional, updated
analysis, examining a broad array of diverse requirements.
    Specifically, we analyzed EGU HAP emissions remaining in 2016. Our
analysis included the proposed Transport Rule; CAA section 112(g); the
ARP; Federal, state, and citizen enforcement actions related to
criteria pollutant emissions from EGUs; and some state rules related to
criteria pollutant emissions. We included state requirements and
citizen and state enforcement action settlements associated with
criteria pollutants because those requirements may have a basis under
the CAA. We did not, however, conduct an analysis to determine whether
the requirements are, in fact, based on requirements of the CAA. As
such, we believe there may be instances where we should not have
considered certain state rules or state and citizen suit enforcement
settlements in our analysis, because those requirements are based
solely in state law and are not required by Federal law. We did not
include in our analysis any state-only requirements or voluntary
actions to reduce HAP emissions because we knew there was no Federal
backstop for those requirements and actions.
    Our analysis confirms that Hg emissions from EGUs remaining in 2016
still pose a hazard to public health and the environment and, for that
reason, it remains necessary to regulate EGUs under section 112.
Specifically, we estimate that U.S. EGU emissions of Hg after
imposition of the requirements of the CAA will be 29 tpy in 2016, the
same as the level of Hg emitted today. As we stated above, we evaluated
the hazards to public health and the environment from Hg based on the
estimated Hg emissions in 2016 and found that a hazard exists. Because
a hazard remains after imposition of the requirements of the CAA, it is
necessary to regulate EGUs.
    It is necessary to regulate HAP emissions from EGUs, even though
the hazards from Hg will not be resolved through regulation under
section 112. EPA finds that incremental reductions in Hg are important
because as exposure above the RfD increases the likelihood and severity
of adverse effects increases.
    EGUs are the largest source of Hg in the U.S. and, thus, contribute
to the risk associated with exposure to MeHg. By reducing Hg emissions
from U.S. EGUs, this proposed rule will help to reduce the risk to
public health and the environment from Hg exposure.
    We also find that it is necessary to regulate EGUs under section
112 based on non-Hg HAP emissions because we cannot be certain that the
identified cancer risks attributable to EGUs will be addressed through
imposition of the requirements of the CAA. In addition, the
environmental hazards posed by acidification will not be fully
addressed through imposition of the CAA.
    We also find it necessary to regulate EGUs because regulation under
section 112 is the only way to ensure that HAP emissions reductions
that have been achieved since 2005 remain permanent.
    The difference between the 53 ton 2005 estimate and the 2010 ICR-
based estimate of total EGU emissions may be overstated. While EPA has
estimated 2010 total EGU Hg emissions of 29 tons based on data from the
2010 ICR database, this may underestimate total 2010 EGU Hg emissions
due to the fact that emission factors used to develop the estimates may
not accurately account for larger emissions from units with more poorly
performing emission controls. The 2010 ICR by which the data used to
develop the factors was collected was designed to provide the agency
the data to determine the appropriate MACT levels and was not designed
to collect data to fully characterize all units' Hg emissions,
particularly those that might have poorly performing controls. EPA
tested only 50 randomly selected units that were not selected for
testing as best performing units (the bottom 85 percent of units), and
we used that small sample to attempt to characterize the lower
performing units. Because the 50 units were randomly selected, we do
not believe we have sufficiently characterized the units that have
poorly performing controls. In addition, the methodology for estimating
the 2005 and 2010 emission estimates are not the same. The 2005
estimate is based on control configurations as of 2002, therefore, it
does not reflect reductions due to control installations that took
place between 2002 and 2005. As a result, the apparent difference
between 2005 and 2010 is overstated. There are real factors that
explain why Hg reductions would have occurred between 2005 and 2010.
The actual reductions between 2005 and 2010 are attributable to state
Hg regulations and to CAIR and Federal enforcement actions that achieve
Hg reductions as a co-benefit of controls for PM, NOX, and
SO2 emissions. However, there are no national, Federally
binding regulations for Hg. State Hg regulations can potentially change
or be revoked without EPA approval, and reductions that occur as a co-
benefit of criteria pollutant regulations can also change. Furthermore,
companies can change their criteria pollutant compliance strategies and
use methodologies that do not achieve the same level of Hg or other HAP
co-benefit (e.g., purchasing allowances in a trading program instead of
using add-on controls).

    As with Hg, the most recent data on U.S. EGU HCl and HF emissions
show a significant reduction between 2005 and 2010. These reductions in
HCl and HF are the co-benefit of controls installed to meet other CAA
requirements, including enforcement actions, and to a lesser extent,
state regulations. There is no guarantee other than regulation under
section 112 that these significant decreases in HCl and HF emissions
will be permanent. Although we do not have estimates for the remaining
HAP emitted from EGUs, we believe it is likely that such emissions have
also decreased between 2005 and 2010. Thus, the Administrator finds it
necessary to regulate HAP emissions from EGUs to ensure that HAP
emissions reductions are permanent.
    Finally, direct control of Hg emissions affecting U.S. deposition
is only possible through regulation of U.S. emissions; we are unable to
control global emissions directly. Although the U.S. is actively
involved in international efforts to reduce Hg pollution, the ability
of the U.S. to argue effectively in these negotiations for strong
international policies to reduce Hg air emissions depends in large part
on our domestic policies, programs and regulations to control Hg.
    All of these findings independently support a finding that it is
necessary to regulate EGUs under section 112.
    Therefore, given the Agency's finding that it remains appropriate
and necessary to regulate coal- and oil-fired EGUs under CAA section
112, EPA is confirming its inclusion of coal- and oil-fired EGUs on the
list of source categories regulated under CAA section 112(c).
8. Implications of Hazards to Public Health for Children and
Environmental Justice Communities
    Children are at greatest risk of adverse health effects from
exposures to Hg, and this risk is amplified for children in minority
and low income communities who subsist on locally-caught fish. Today's
proposed rule is therefore an important step in addressing disparate
impacts on children and environmental justice (EJ) communities.
    Children are more vulnerable than adults to many HAP, because of
differences in physiology, higher per body weight breathing rates and
consumption, rapid development of the brain and bodily systems, and
behaviors that increase chances for exposure. Even before birth, the
developing fetus may be exposed to HAP through the mother that affect
development and permanently harm the individual. Infants and children
breathe at much higher rates per body weight than adults, with infants
under one year of age having a breathing rate up to five times that of
adults.\133\ In addition, children breathe through their mouths more
than adults and their nasal passages are less effective at removing
pollutants, which leads to a higher deposition fraction in their
lungs.\134\ Crawling and frequent hand-to-mouth activity lead to
infants' higher levels of ingestion of contaminants deposited onto soil
or in dust. Infants' consumption of breast milk can pass along high
levels of accumulated persistent bioaccumulative pollutants from their
mothers. Children's dietary intake also exceeds that of adults, per
body weight, posing a potential added risk from persistent HAP that
accumulate in food. In addition to the greater exposure, the less-well
developed detoxification pathways and rapidly developing systems and
organs put children at potentially greater risk.
---------------------------------------------------------------------------

    \133\ U.S. Environmental Protection Agency. 2006. Revision of
the metabolically-derived ventilation rates within the Exposure
Factors Handbook. (External review draft) Washington, DC: Office of
Research and Development. EPA/600/R-06/129A. http://oaspub.epa.gov/eims/eimscomm.getfile?p_download_id=460261.
    \134\ Foos, B., M. Marty, J. Schwartz, W. Bennett, J. Moya, A.
M. Jarabek, and A. G. Salmon. 2008. Focusing on children's
Inhalation Dosimetry and Health Effects for Risk Assessment: An
Introduction. J Toxicol Environ Health 71A: 149-165.
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    Mercury is the HAP from EGUs of most concern to early life stages.
The adverse affects of Hg on developing neuropsychological systems is
well-established and permanent. The prenatal period of development has
been established to be the most sensitive lifestage to the
neurodevelopmental effects of MeHg.\135\ Children who are exposed to
low concentrations of MeHg prenatally are at increased risk of poor
performance on neurobehavioral tests, such as those measuring
attention, fine motor function, language skills, visual-spatial
abilities, and verbal memory.136 137 Impaired cognitive
development from exposures to MeHg prenatally and in early childhood
affect the individual into adulthood, by affecting learning and
potential future earnings, and contributing to behavioral problems.
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    \135\ National Academy of Sciences. 2000. Toxicological Effects
of Methylmercury. Washington, DC: National Academy Press. http://books.nap.edu/catalog/9899.html?onpi_newsdoc071100.
    \136\ P. Grandjean, P. Weihe, R.F. White, F. Debes, S. Araki, K.
Yokoyama, K. Murata, N. Sorensen, R. Dahl and P.J. Jorgensen. 1997.
Cognitive deficit in 7-year-old children with prenatal exposure to
methylmercury. Neurotoxicology and Teratology 19 (6):417-28.
    \137\ T. Kjellstrom, P. Kennedy, S. Wallis and C. Mantell. 1986.
Physical and mental development of children with prenatal exposure
to mercury from fish. Stage 1: Preliminary tests at age 4. Sweden:
Swedish National Environmental Protection Board.
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    Other HAP related to EGU emissions present greater risks to
children as well. For example, mutagenic carcinogens such as
Cr+6 have a larger impact during young lifestages, given the
rapid development of the corporal systems.\138\ Exposure at a young age
to these carcinogens could lead to a higher risk of developing cancer
later in life.
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    \138\ U.S. Environmental Protection Agency. 2005. Supplemental
Guidance for Assessing Susceptibility from Early-Life Exposure to
Carcinogens. Washington, DC: Risk Assessment Forum. EPA/630/R-03/
003F http://www.epa.gov/raf/publications/pdfs/childrens_supplement_final.pdf
---------------------------------------------------------------------------

    The adverse effects of individual non-Hg HAP may be more severe for
children, particularly the youngest age groups, than adults. A number
of epidemiologic studies suggest that children are more vulnerable than
adults to lower respiratory symptoms associated with
PM.139 140 Non-Hg metal HAP may behave similarly to
particulate matter, at least in terms of the deposition fraction that
reaches children's lungs. As with Hg, Pb and Cd are known to affect
children's neurologic development. A meta-analysis of seven studies has
shown an association between exposure to formaldehyde, another HAP of
concern, and development of asthma in children.\141\
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    \139\ Pope, C.A. and D.W. Dockery. 1992. Acute health effects of
PM10 pollution on symptomatic and asymptomatic children. Am Rev
Respir Dis 145: 1123-1128.
    \140\ Gauderman, W.J., R. McConnell, F. Gilliland, S. London, et
al. 2000. Association between air pollution and lung function growth
in Southern California children. Am J Respir Crit Care Med 162:
1283-1390.
    \141\ McGwinn, G. Jr., J. Lienert, and J.I. Kennedy Jr. 2010.
Formaldehyde Exposure and Asthma in Children: A Systematic Review.
Environ Health Perspect 118: 313-317.
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    Within communities overburdened with environmental exposures, the
youngest lifestages are likely the most vulnerable. Looking at the
health effects for children in those communities can be an important
part of appropriately assessing community risks.
    EPA has also considered the effects of this rule on EJ communities.
The nature of exposures to Hg is such that populations with high levels
of self-caught fish consumption are likely to be disproportionately
affected. EPA's risk analysis identified many EJ communities, including
Laotian, Vietnamese, Hispanic, African-American, tribal, and low income
communities, as having higher levels of subsistence fishing activities.
Consequently, individuals in these

communities are potentially exposed to levels of MeHg in fish that may
result in these individuals' exposure exceeding the RfD. These EJ
populations are thus at higher risk for the health effects associated
with exposures to MeHg, which include impacts on neurological functions
that can cause children to struggle in school. In EJ populations which
often face numerous other stressors that can result in lower
educational performance, the additional burdens imposed by exposure to
Hg may cause significant and long-lasting impacts on children that
continue into adulthood, affecting learning potential and measures of
IQ, including future earnings and indicators of quality of life.
9. The Analysis Supporting the 2005 Action Was Subject to Technical
Limitations and These Flaws Undermine the Basis for the 2005 Action
    In 2005, EPA conducted a set of technical analyses to support a
revision to the 2000 appropriate and necessary finding.\142\ In those
analyses, EPA made several assumptions that were not justified based on
scientific or technical grounds, and which we have corrected in our
technical analysis supporting our current confirmatory finding that it
is appropriate and necessary to regulate coal- and oil-fired EGUs under
section 112.
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    \142\ U.S. EPA. 2005. Technical Support Document: Methodology
Used to Generate Deposition, Fish Tissue Methylmercury
Concentrations, and Exposure for Determining Effectiveness of
Utility Emission Controls.
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a. Interpretation of the MeHg Reference Dose and Incremental U.S. EGU-
Attributable Exposures
    In the 2005 analysis, EPA made the following statement:
    The RfD provides a useful reference point for comparisons with
measured or modeled exposure. The Agency defines the RfD as an exposure
level below which the Agency believes exposures are likely to be
without an appreciable risk over a lifetime of exposure. For the
purposes of assessing population exposure due to EGUs, we create an
index of daily intake (IDI). The IDI is defined as the ratio of
exposure due solely to EGUs to an exposure of 0.1 [mu]g/kg bw/day. The
IDI is defined so that an IDI of 1 is equal to an incremental exposure
equal to the RfD level, recognizing that the RfD is an absolute level,
while the IDI is based on incremental exposure without regard to
absolute levels. Note that an IDI value of 1 would represent an
absolute exposure greater than the RfD when background exposures are
considered.\143\
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    \143\ U.S. EPA. 2005. Technical Support Document: Methodology
Used to Generate Deposition, Fish Tissue Methylmercury
Concentrations, and Exposure for Determining Effectiveness of
Utility Emission Controls.
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    Upon further consideration, EPA concludes that it did not have a
scientific or technical justification for creating a metric other than
the HQ \144\ to compare U.S. EGU-attributable exposures to the RfD. As
EPA recognized in 2005, the RfD is an absolute level above which the
potential risks of exposures increase, based on total exposures to
MeHg. The concept of the IDI was created by EPA in 2005 solely to
support its interpretation that it must assess hazards to public health
solely based on U.S. EGU emissions with no consideration of exposures
to MeHg arising from other sources of Hg deposition. As noted above,
nothing in section 112(n)(1)(A) prohibits consideration of HAP
emissions from U.S. EGUs in conjunction with HAP emissions from other
sources of HAP, including sources outside the U.S. Indeed, such an
approach would ignore the manner in which the public is actually
exposed to HAP emission. By focusing on whether incremental exposures
attributable to U.S. EGU Hg emissions exceeded the RfD without
consideration of other exposures, EPA implied that U.S. EGU Hg
emissions were not causing a hazard to public health even though such
emissions were increasing risks in locations where the RfD was already
exceeded due to total exposures from all Hg sources, including U.S. EGU
emissions. This is a serious flaw in EPA's 2005 assessment, due to
reasons we discuss below.
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    \144\ The HQ is the ratio of observed or modeled exposures to
the RfD.
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    Ninety-eight percent of watersheds with fish tissue MeHg samples
have Hg deposition levels such that total potential exposure to MeHg
exceeds the RfD, and many have exposures that are many times the
RfD.\145\ As a result, in almost all watersheds with fish tissue MeHg
samples, any additional Hg will increase potential risk. Thus, U.S.
EGU-attributable Hg deposition is contributing to increased potential
risk. The Agency believes the assessment of potential risk due to Hg
emissions from U.S. EGUs must consider both the extent to which U.S.
EGUs contribute to such risk along with other sources, and the extent
to which U.S. EGU-attributable deposition leads to exposures that
exceed the RfD even before considering the contributions of other
sources of Hg. The Agency has conducted such an evaluation in the
national-scale MeHg risk analysis presented above. In 2005, as a result
of relying on a flawed, non-scientific approach for comparing MeHg
exposures to the RfD, and a failure to consider cumulative risk
characterization metrics, EPA incorrectly determined that U.S. EGU
emissions of Hg did not constitute a hazard to public health. As
discussed above, EPA has revised this determination and concluded that
U.S. EGU Hg emissions are a hazard to public health because they cause
exposures to exceed the RfD or contribute to exposures in watersheds
where total exposures to MeHg exceed the RfD.
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    \145\ See the National Scale Mercury Risk Assessment Technical
Support Document.
---------------------------------------------------------------------------

b. Interpretation of Populations Likely To Be at Risk and Conclusions
Regarding Acceptable Risk
    In addition to developing a flawed exposure indicator based on only
U.S. EGU attributable exposure (the IDI), EPA also erred in finding
that exposures above the RfD (an IDI greater than 1) did not pose an
``unacceptable risk'' (e.g., did not pose a hazard to public health).
EPA cited three reasons for the finding in 2005: (1) Lack of confidence
in the risk estimates; (2) lack of seriousness of the health effects of
MeHg; and (3) small size of the population at risk and low probability
of risks in that population. EPA was not justified in making its
determination based on these three factors.
    In the 2005 Action, EPA cited the underpinnings of the RfD as
introducing a degree of conservatism. In fact, however, as discussed
above, EPA has stated consistently, including in the RfD issued in
2001, that the RfD for Hg is a level above which there is the potential
for increased risk. Only at levels at or below the RfD does the Agency
maintain that exposures are without significant risk. EPA's
interpretation in 2005 was a departure from prior EPA policy as it
concerns exposures to Hg and was in error.
    In the 2005 Action, EPA identified risk of poor performance on
neurobehavioral tests, such as those measuring attention, fine motor
function, language skills, visual-spatial abilities (like drawing), and
verbal memory as the primary health effects of MeHg exposures. Although
not stated explicitly, it is implicit in the 2005 Action that EPA did
not consider these health effects to be serious. The Agency did not,
and could not have, provided any scientific or policy rationale for
dismissing these serious public health effects. For example, as
mentioned

above, there are potentially serious implications of the identified
effects on learning potential and measures of IQ, including future
earnings and indicators of quality of life. EPA was not justified in
dismissing these health effects as not serious without providing
evidence or justification, which it could not do based on the
information available at the time or today.
    In the 2005 Action, EPA made several statements in the technical
analysis suggesting that the probability that an IDI of 1 would be
exceeded (e.g., that U.S. EGU attributable exposures would be greater
than the RfD) was low due to the rare occurrence of high consumption
rate populations in high deposition watersheds. The 2005 analysis
showed that 15 percent of watersheds would have U.S. EGU-attributable
potential exposures that were twice the RfD for the highest fish
consumption rates. EPA dismissed this high percent of watersheds by
stating that those high fish consumption rates would only occur in
Native American populations, and that those populations lived in
locations that were not heavily impacted by U.S. EGU Hg deposition.
    Information was available at the time of the 2005 analysis
indicating that other populations besides Native Americans engaged in
subsistence fishing activities that would result in consumption rates
similar to Native Americans. EPA chose to selectively use information
only on Native American consumption rates and erroneously concluded
that subsistence fishing activities would not occur in a wider set of
locations. This choice was in error, as EPA should have investigated
whether other subsistence populations could fish in locations heavily
impacted by U.S. EGU emissions (e.g., watersheds with the top 15
percent of U.S. EGU-attributable fish tissue MeHg levels). A search of
the literature available in 2005 reveals several studies that
identified additional fishing populations with subsistence or near
subsistence consumption rates, including urban fishing populations
(including low-income populations),146 147 148 Laotian
communities,\149\ and Hispanics. In fact, EPA participated in 1999 in a
project investigating exposures of poor, minority communities in New
York City to a number of contaminants including Hg, and should thus
have been aware that these populations can have very high consumption
rates.\150\ If EPA had conducted a thorough investigation in 2005, it
should have concluded that populations with the potential for
subsistence-level fish consumption rates occur in many watersheds, and,
thus, could not have concluded that exposures above the RfD (IDI
greater than 1) were not likely.
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    \146\ Burger, J., K. Pflugh, L. Lurig, L. Von Hagen, and S. Von
Hagen. 1999. Fishing in Urban New Jersey: Ethnicity Affects
Information Sources, Perception, and Compliance. Risk Analysis
19(2): 217-229.
    \147\ Burger, J., Stephens, W., Boring, C., Kuklinski, M.,
Gibbons, W.J., & Gochfield, M. (1999). Factors in exposure
assessment: Ethnic and socioeconomic differences in fishing and
consumption of fish caught along the Savannah River. Risk Analysis,
19(3).
    \148\ Chemicals in Fish Report No. 1: Consumption of Fish and
Shellfish in California and the United States Final Draft Report.
Pesticide and Environmental Toxicology Section, Office of
Environmental Health Hazard Assessment, California Environmental
Protection Agency, July 1997.
    \149\ Tai, S. 1999. ``Environmental Hazards and the Richmond
Laotian American Community: A Case Study in Environmental Justice.''
Asian Law Journal 6: 189.
    \150\ Corburn, J. (2002). Combining community-based research and
local knowledge to confront asthma and subsistence-fishing hazards
in Greenpoint/Williamsburg, Brooklyn, New York. Environmental Health
Perspectives, 110(2).
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    Thus, based on the errors EPA made in the 2005 Action related to
evaluating the risks from MeHg exposures attributable to U.S. EGUs,
EPA's technical determination in 2005 that risks were acceptable based
on that analysis was not justified. As a result the technical
determination in 2005 which supported the finding of no public health
hazard, and the determination that it was not appropriate or necessary
to regulate HAP from U.S. EGUs was in error.

IV. Summary of This Proposed NESHAP

    This section summarizes the requirements proposed in this proposed
rule. Our rationale for the proposed requirements is provided in
Section V of this preamble.

A. What source categories are affected by this proposed rule?

    This proposed rule affects coal- and oil-fired EGUs.

B. What is the affected source?

    An existing affected source for this proposed rule is the
collection of coal- and oil-fired EGUs within a single contiguous area
and under common control. A new affected source is a coal- or oil-fired
EGU for which construction or reconstruction began after May 3, 2011.
    CAA section 112(a)(8) defines an EGU as:

    a fossil fuel-fired combustion unit of more than 25 megawatts
electric (MWe) that serves a generator that produces electricity for
sale. A unit that cogenerates steam and electricity and supplies
more than one-third of its potential electric output capacity and
more than 25 MWe output to any utility power distribution system for
sale is also an electric utility steam generating unit.

    If an EGU burns coal (either as a primary fuel or as a
supplementary fuel), or any combination of coal with another fuel
(except as noted below), the unit is considered to be coal fired under
this proposed rule. If a unit is not a coal-fired unit and burns only
oil, or oil in combination with another fuel other than coal (except as
noted below), the unit is considered to be oil fired under this
proposed rule. As noted below, EPA is proposing a definition to
determine whether the combustion unit is ``fossil fuel fired'' such
that it is an EGU for purposes of this proposed rule. The unit must be
capable of combusting more than 73 megawatt-electric (MWe) (250 million
British thermal units per hour, MMBtu/hr) heat input (equivalent to 25
MWe electrical output) of coal or oil. In addition, using the construct
of the definition of ``oil-fired'' from the ARP, we are proposing that
the unit must have fired coal or oil for more than 10.0 percent of the
average annual heat input during the previous 3 calendar years or for
more than 15.0 percent of the annual heat input during any one of those
calendar years to be considered a ``fossil fuel fired'' EGU subject to
this proposed rule. If a new or existing EGU is not coal- or oil-fired,
and the unit burns natural gas exclusively or natural gas in
combination with another fuel where the natural gas constitutes 90
percent or more of the average annual heat input during the previous 3
calendar years or 85 percent or more of the annual heat input during
any 1 of those calendar years, the unit is considered to be natural
gas-fired and would not be subject to this proposed rule. As discussed
later, we believe that this definition will address those situations
where either an EGU fires coal or oil on only a limited basis or co-
fires limited amounts of coal or oil with other non-fossil fuels (e.g.,
biomass).
    To the extent a unit combusts solid waste, that unit is not an EGU
under section 112, but rather would be subject to CAA section 129.
    The Small Entity Representatives (SERs) serving on the Small
Business Advocacy Review Panel (SBAR) established under the Small
Business Regulatory Enforcement Fairness Act (SBREFA) suggested that
EPA consider developing an area-source (i.e., those EGUs emitting less
than 10 tpy of any one HAP or less than 25 tpy of any combination of
HAP) vs. major-source (i.e., those EGUs emitting 10 tpy or more of any
one HAP or 25 tpy of more of any

combination of HAP) distinction for this source category. The proposed
rule treats all EGUs the same and proposes MACT standards for all
units.
    Nothing in the CAA requires that we issue GACT standards for area
sources. Indeed, here, the data show that similar HAP emissions and
control technologies are found on both major and area sources greater
than 25 MWe. In fact, because of the significant number of well-
controlled EGUs of all sizes, we believe it would be difficult to make
a distinction between MACT and GACT. Moreover, EPA believes the
standards for area source EGUs should reflect MACT, rather than GACT,
because there is no essential difference between area source and major
source EGUs with respect to emissions of HAP. There are EGUs that are
physically quite large that are area sources, and EGUs that are small
that are major sources. Both large and small EGUs are represented in
the MACT floor pools for acid gas, Hg, and non-Hg metal HAP. Finally,
given that EPA is regulating both major and area source EGUs at the
same time in this rulemaking, a common control strategy consequently
appears warranted for these emissions.
    If area sources tend to be very different from major sources and
the capacity to control those sources is different, we could exercise
our discretion under section 112(d)(5) to set GACT standards for area
sources. But, as explained above, that is not the case here.
Accordingly, we believe it is appropriate to set MACT standards for
both major and area source EGUs. EPA solicits comment on its proposed
approach. Specifically, we solicit comments on whether there would be a
basis for considering area sources to be significantly different from
major sources with respect to issues relevant to standard setting.
Commenters should also explain the basis of their suggested approach
and how that approach would lead to similar health and environmental
benefits, including data that would underpin a GACT analysis.\151\
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    \151\ As we have explained in other rules, determining what
constitutes GACT involves considering the control technologies and
management practices that are generally available to the area
sources in the source category. We also consider the standards
applicable to major sources in the same industrial sector to
determine if the control technologies and management practices are
transferable and generally available to area sources. In appropriate
circumstances, we may also consider technologies and practices at
area and major sources in similar categories to determine whether
such technologies and practices could be considered generally
available for the area source category at issue. Finally, in
determining GACT for a particular area source category, we consider
the costs and economic impacts of available control technologies and
management practices on that category.
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C. Does this proposed rule apply to me?

    This proposed rule applies to you if you own or operate a coal- or
oil-fired EGU as defined in this proposed rule.

D. Summary of Other Related DC Circuit Court Decisions

    In March 2007, the DC Circuit Court issued an opinion (Sierra Club
v. EPA, 479 F.3d 875 (DC Cir. 2007)) (Brick MACT) vacating and
remanding CAA section 112(d) NESHAP for the Brick and Structural Clay
Ceramics source categories. Some key holdings in that case were:
     Floors for existing sources must reflect the average
emission limitation achieved by the best-performing 12 percent of
existing sources, not levels EPA considers to be achievable by all
sources (479 F.3d at 880-81);
     EPA cannot set floors of ``no control.'' The DC Circuit
Court reiterated its prior holdings, including National Lime Ass'n. v.
EPA (233 F.3d625 (DC Cir. 2000)) (National Lime II), confirming that
EPA must set floor standards for all HAP emitted by the source,
including those HAP that are not controlled by at-the-stack control
devices (479 F.3d at 883);
     EPA cannot ignore non-technology factors that reduce HAP
emissions. Specifically, the DC Circuit Court held that ``EPA's
decision to base floors exclusively on technology even though non-
technology factors affect emissions violates the Act.'' (479 F.3d at
883.) The DC Circuit Court also reiterated its position stated in
Cement Kiln Recycling Coalition v. EPA, 255 F.3d 855 (DC Cir. 2001)
that CAA section 112(d)(3) ``requires floors based on the emission
level actually achieved by the best performers (those with the lowest
emission levels).''
    Based on the Brick MACT decision, we believe a source's performance
resulting from the presence or absence of HAP in fuel materials must be
accounted for in establishing floors (i.e., a low emitter due to low
HAP fuel materials can still be a best performer). In addition, the
fact that a specific level of performance is unintended is not a legal
basis for excluding the source's performance from consideration.
National Lime II; 233 F.3d at 640.
    The Brick MACT decision also stated that EPA may account for
variability in setting floors. The DC Circuit Court found that ``EPA
may not use emission levels of the worst performers to estimate
variability of the best performers without a demonstrated relationship
between the two.'' 479 F.3d at 882.
    A second DC Circuit Court opinion is also relevant to this
proposal. In Sierra Club v. EPA, 551 F.3d 1019 (DC Cir. 2008), the DC
Circuit Court vacated the portion of the regulations contained in the
General Provisions which exempt major sources from NESHAP during
periods of startup, shutdown and malfunction (SSM). The regulations (in
40 CFR 63.6(f)(1) and 63.6(h)(1)) provided that sources need not comply
with the relevant CAA section 112(d) standard during SSM events and
instead must ``minimize emissions * * * to the greatest extent which is
consistent with safety and good air pollution control practices.'' As a
result of the DC Circuit Court decision, sources must comply with the
emission standards at all times and we are addressing SSM in this
proposed rulemaking. Discussion of this issue may be found later in
this preamble.
    A third relevant DC Circuit Court opinion is National Lime II (233
F.3d 625), where, in considering whether EPA may use PM, a criteria
pollutant, as a surrogate for metal HAP, the DC Circuit Court stated
that EPA ``may use a surrogate to regulate hazardous pollutants if it
is `reasonable' to do so'' and laid out criteria establishing a three-
part analysis for determining whether the use of PM as a surrogate for
non-Hg metal HAP was reasonable. The DC Circuit Court found that PM is
a reasonable surrogate for HAP if: (1) ``HAP metals are invariably
present in * * * PM;'' (2) ``PM control technology indiscriminately
captures HAP metals along with other particulates;'' and (3) ``PM
control is the only means by which facilities `achieve' reductions in
HAP metal emissions.'' 233 F.3d at 639. If these criteria are satisfied
and the PM emission standards reflect what the best sources achieve--
complying with CAA section 7412(d)(3)--``EPA is under no obligation to
achieve a particular numerical reduction in HAP metal emissions.'' We
have considered this case in evaluating whether the surrogate standards
we propose to establish in this proposed rule are reasonable.

E. EPA's Response to the Vacatur of the 2005 Action

    After the vacatur of the Revision Rule, EPA evaluated the HAP and
other emissions data available to establish CAA section 112(d)
standards for coal- and oil-fired EGUs and determined that additional
HAP emission data were required. EPA initiated an information
collection effort entitled ``Electric Utility Steam Generating Unit
Hazardous Air Pollutant Emissions Information

Collection Effort'' (OMB Control Number 2060-0631). This information
collection (2010 ICR) was conducted by EPA's Office of Air and
Radiation (OAR) pursuant to CAA section 114 to assist the Administrator
in developing emissions standards for coal- and oil-fired EGUs pursuant
to CAA section 112(d). CAA section 114(a) states, in pertinent part:

    For the purpose of * * * (iii) carrying out any provision of
this Chapter * * * (1) the Administrator may require any person who
owns or operates any emission source * * * to * * * (D) sample such
emissions (in accordance with such procedures or methods, at such
locations, at such intervals, during such periods and in such manner
as the Administrator shall prescribe); (E) keep records on control
equipment parameters, production variables or other indirect data
when direct monitoring of emissions is impractical * * *; (G)
provide such other information as the Administrator may reasonably
require * * *

    Prior to issuance of the information collection effort, information
necessary to identify all coal- and oil-fired EGUs as defined in CAA
section 112(a)(8) was publicly available for EGUs owned and operated by
publicly-owned utility companies, Federal power agencies, rural
electric cooperatives, investor-owned utility generating companies, and
nonutility generators (such units include, but may not be limited to,
independent power producers (IPPs), qualifying facilities, and combined
heat and power (CHP) units). The most recent information available was
for 2005, and the available information generally did not include any
information on permitted HAP emission limits; or monitoring,
recordkeeping, and reporting requirements for HAP emissions; and we did
not have complete HAP emissions data for any EGU. Additionally, we had
little current information on the fuel amounts received, fuel sources,
fuel shipment methods, or results of previously conducted fuel analyses
for coal- and oil-fired EGUs, or for results from tests conducted since
January 1, 2005. We did not have emissions test results that would
provide data for emissions of a variety of pollutants, including: PM,
PM with an aerodynamic diameter equal to or less than 2.5 micrometers
(PM2.5); SO2; HCl/HF/HCN; metal HAP (including
compounds of Sb, As, Be, Cd, Cr, Co, Pb, Mn, Ni, and Se); Hg; total
organic hydrocarbons (THC); volatile organic compounds (VOC); and
carbon monoxide (CO).
    To obtain the information necessary to evaluate coal- and oil-fired
EGUs, EPA developed a two-phase ICR and published the first notice in
the Federal Register for comment consistent with the requirements of
the PRA. 74 FR 31725 (July 2, 2009). We received comments from industry
and other interested parties. We also met with industry and other
interested parties, and published a revised ICR in the Federal Register
for another round of comments consistent with the PRA. 74 FR 58012
(November 10, 2009). OMB approved the ICR on December 24, 2009, and we
sent the ICR to owners and operators of EGUs on December 31, 2010.
    As stated above, the ICR contained two phases or components. The
first component solicited information from all potentially affected
units. EPA provided the survey in electronic format; however, written
responses were also accepted. The survey was submitted to all coal- and
oil-fired EGUs listed in the 2007 version of the DOE's Energy
Information Administration's (EIA) Forms 860 and 923, ``Annual Electric
Generator Report,'' and ``Power Plant Operations Report,''
respectively.
    The second component required the owners/operators of a limited
number of coal-and oil-fired EGUs to conduct stack testing in
accordance with an EPA-approved protocol. Some coal-fired units were
selected to be tested because we determined based on the information
available that the units were among the top performing 15 percent of
sources in the coal subcategory for certain types of HAP. Best-
performing coal-fired units to be tested were selected to cover three
groups of HAP that may be regulated through the use of surrogate
standards: (1) Non-Hg metallic HAP (e.g., As, Pb, Se); (2) acid gas HAP
(e.g., HCl, HF, HCN); (3) and non-dioxin/furan organic HAP. We also
required the non-Hg metallic HAP sources to test for Hg even though Hg
is to be regulated separately and not covered by any non-Hg metallic
HAP surrogacy. Fifty coal-fired units were also selected at random from
the entire population of coal-fired EGUs to test for dioxin/furan
organic HAP. An additional 50 coal-fired units were selected at random
from among those units not selected as being ``top performing'' units
to represent those coal-fired units not comprising the top-performing
units in the three HAP surrogate groups; these 50 randomly selected
units were required to test for all HAP except dioxin/furan organic
HAP. Data from this last grouping was collected so we could estimate
the HAP emission reductions associated with the proposed standards.
Oil-fired units to be tested were also selected at random to test for
HAP in all three groups of HAP noted above, in addition to testing for
Hg and dioxin/furan.
    The testing consisted of three runs at the sampling location and
was in accordance with a specified emission test method. The owner/
operator of each selected EGU was also required to collect and analyze,
in accordance with an acceptable procedure, three fuel samples from the
fuel fed to the EGU during each stack test. Additional details of the
required sampling may be found in Docket entry EPA-HQ-OAR-2009-0234-
0062.
    In phase one, all coal- and oil-fired EGUs identified by EPA as
being potentially subject sources under the definition in CAA section
112(a)(8), including all integrated gasification combined cycle (IGCC)
EGUs and all EGUs fired by petroleum coke, were required to submit
information to EPA. The sources were required to provide information on
the current operational status of the unit, including applicable
controls installed, along with emissions information from the preceding
5 years. This information was necessary for EPA to fully characterize
the category and update our database of coal- and oil-fired EGUs.
    Phase two was the testing phase. As stated above, coal-fired units
to be tested were selected to cover five HAP or groups of HAP, three of
which may be regulated through the use of surrogate pollutant standards
and were chosen because EPA determined the units were best performing
units for one or more of the three HAP surrogate groups. In the stack
testing, each facility was required to test after the last control
device or at the stack if the stack is not shared with other units
using different controls. In this way, the facility would test before
any ``dilution'' by gases from a separately-controlled unit. Under
certain circumstances, however, testing after a common control device
or at the common stack was allowed.
    EPA selected for testing the sources that the Agency believed,
based on a variety of factors and information available to the Agency
at the time, were the best performing sources for the three HAP
surrogate groups for which they were required to test. In targeting the
best performing sources, EPA required testing for approximately 15
percent of all coal-fired EGUs for the 3 HAP surrogate groups--non-Hg
metal HAP and PM; non-dioxin/furan organic HAP, total hydrocarbon, CO,
and VOC; and acid gas HAP and SO2. As we stated in response
to comments on the proposed 2010 ICR, we targeted the best performing
coal-fired sources for certain HAP groups because the statute requires
the Agency to set the MACT floor at the ``average emission limitation
achieved by the best performing 12 percent of the

existing sources (for which the Administrator has information)'' in the
category. By targeting the best performing 15 percent of coal-fired
EGUs for testing in the 3 HAP groups, we concluded that we would have
emissions data on the best performing 12 percent of all existing coal-
fired EGUs. In this proposed rule, we used data from sources
representing the best performing 12 percent of all sources in any
category or subcategory to establish the CAA section 112(d) standards
for the 3 HAP groups because we believe we have identified the best
performing 12 percent of sources for those subcategories with 30 or
more sources. For Hg from coal-fired units, we used the top 12 percent
of the data obtained because, even though we required Hg testing for
the units testing for the non-Hg metallic HAP, we did not believe those
units represented the top performing 12 percent of sources for Hg in
the category at the time we issued the ICR and we made no assertions to
that effect. For oil-fired units, we also used the top 12 percent of
the data obtained because we were unable, based on the information
available, to determine the best performing oil-fired units. The
primary reason for our inability to identify best performing oil-fired
units is that such units are generally uncontrolled or controlled only
with an ESP. The approach for both coal- and oil-fired EGUs was
discussed with, and agreed upon by, several industry and environmental
organization stakeholders prior to finalizing the ICR.
    The acid-gas HAP, HCl and HF, are water-soluble compounds and are
more soluble in water than is SO2. (Cyanide, representing
the ``cyanide compounds,'' and Cl2 gas are also water-
soluble and are considered ``acid-gas HAP'' in this proposal.) Hydrogen
chloride also has a large acid dissociation constant (i.e., HCl is a
strong acid) and it, thus, will react easily in an acid-base reaction
with caustic sorbents (e.g., lime, limestone). The same is true for HF.
This indicates that both HCl and HF will be more rapidly and readily
removed from a flue gas stream than will SO2, even when only
plain water is used. In FBC systems, the acid gases and SO2
are adsorbed by the sorbent (usually limestone) that is added to the
coal and an inert material (e.g., sand, silica, alumina, or ash) as
part of the FBC process.
    Hydrogen chloride and HF have also been shown to be effectively
removed using DSI where a dry, alkaline sorbent (e.g., hydrated lime,
trona, sodium carbonate) is injected upstream of a PM control device.
    Chlorine in the fuel coal may also partition in small amounts to
Cl2. This is normally a very small fraction relative to the
formation of HCl. Limited testing has shown that Cl2 gas is
also effectively removed in FGD systems. Although Cl2 is not
strictly an acidic gas, it is grouped here with the ``acid gas HAP''
because it is controlled using the same technologies.
    Because the technologies for removal of the acid gases are
primarily those that are also used for FGD, we consider emissions of
SO2, a commonly measured pollutant, as a potential surrogate
for emissions of the acid-gas HAP HCl, HF, HCN, and Cl2.
Although use of SO2 as a surrogate for acid gas HAP has not
been used in any CAA section 112 rules by EPA, it has been used in a
number of state permitting actions (see Docket entry EPA-HQ-OAR-2009-
0234-0062). Hydrogen chloride has been used as a surrogate for the acid
gas HAP in other Agency actions (e.g., Portland Cement NESHAP, 75 FR
54970, September 9, 2010 (final rule); major and area source
Industrial, Commercial, and Institutional Boilers and Process Heaters
NESHAP (collectively, Boiler NESHAP), 75 FR 32005, June 4, 2010; 75 FR
31895, June 4, 2010 (proposed rules; the final rules were signed on
February 21, 2011)), and we propose to use HCl as a surrogate for all
the acid gas HAP, with an alternative equivalent standard using
SO2 as a surrogate. In addition, we gathered sufficient data
on HCl, HF, and HCN \152\ to establish individual emission limitations
if warranted.
---------------------------------------------------------------------------

    \152\ Although the combination of extended sampling times and
stack chemistry for many units in this source category rendered the
test method for HCN unreliable, yielding suspect HCN results, we
still consider SO2 or HCl emissions to be adequate
surrogates for HCN emissions.
---------------------------------------------------------------------------

    EPA identified the units with the newest FGD controls installed for
testing of acid gas HAP based on our analysis that FGD controls are the
best at reducing acid gas HAP emissions. EPA also believes that the
units with the newest FGD systems represent those units having to
comply with the most recent, and, therefore, likely most stringent,
emission limits for SO2. We determined that efforts by units
to comply with stringent SO2 limits would also likely
represent the top performers with regard to acid gas HAP emissions.
Specifics of the required testing may be found in Docket entry EPA-HQ-
OAR-2009-0234-0062.
    Dioxin/furan emissions data were obtained in support of the 1998
Utility Report to Congress. However, approximately one-half of those
data were listed as being below the minimum detection level (MDL) for
the given test. Dioxin/furan emissions from coal-fired EGUs are
generally considered to be low, presumably because of the insufficient
amounts of available chlorine. As a result of previous work conducted
on municipal waste combustors (MWC), it has also been proposed that the
formation of dioxins and furans in exhaust gases is inhibited by the
presence of sulfur.\153\ Further, it has been suggested that if the
sulfur-to-chlorine ratio (S:Cl) in the flue gas is greater than 1.0,
then formation of dioxins/furans is inhibited.154 155 The
vast majority of the coal analyses provided through the 1999 ICR effort
indicated S:Cl values greater than 1.0. As a result, EPA expected that
additional data gathering efforts would continue the trend of data
being at or below the MDL. Even so, EPA believed it necessary to
collect some additional data so that the trend could be affirmed or
rejected for EGUs. If the trend were rejected, then EPA would be able
to establish an emission limit for dioxin/furan; however, if the trend
were affirmed, then EPA would need to seek alternatives to an emissions
limit, such as a work practice standard. The latter approach might
become necessary because measurements made at or below MDL generally
indicate the presence, but not the exact quantity, of a substance. In
addition, measurements made at or below the MDL have an accuracy on the
order of plus or minus 50 percent, whereas other environmental
measurements used by EPA in other rulemakings exhibit accuracies of
plus or minus up to 15 percent. Sampling and analytical methods for
dioxins/furans have improved since the 1990's work, so their MDLs are
expected to have decreased. Moreover, for this sampling effort, we
required sampling periods to be extended up to eight times longer than
normal to collect more sample volume, thus, hopefully improving
detection capability. Note that although longer sampling periods can be
obtained during short term emissions testing, maintaining such longer
sampling times

becomes impractical, if not infeasible, for continuous monitoring.
---------------------------------------------------------------------------

    \153\ Gullett, BK, et al. Effect of Cofiring Coal on Formation
of Polychlorinated Dibenzo-p-Dioxins and Dibenzofurans during Waste
Combustion. Environmental Science and Technology. Vol. 34, No.
2:282-290. 2000.
    \154\ Raghunathan, K, and Gullett, BK. Role of Sulfur in
Reducing PCDD and PCDF Formation. Environmental Science and
Technology. Vol. 30, No. 6:1827-1834. 1996.
    \155\ Li., H, et al. Chlorinated Organic Compounds Evolved
During the combustion of Blends of Refuse-derived Fuels and Coals.
Journal of Thermal Analysis. Vol. 49:1417-1422. 1997.
---------------------------------------------------------------------------

    For these reasons, we selected 50 units at random from the entire
coal-fired EGU population to conduct emission testing for dioxins/
furans. EPA has identified AC as a potential control technology for
dioxin/furan control based on results of previous work done on MWC
units, and several of the units that were selected for testing have ACI
systems that had been installed for Hg control. Specifics of the
required testing may be found in Docket entry EPA-HQ-OAR-2009-0234-
0062.
    Emissions of CO, VOC, and/or THC have, in the past, been used as
surrogates for the non-dioxin/furan organic HAP based on the theory
that efficient combustion leads to lower organic emissions (Portland
Cement NESHAP--THC (75 FR 54970; September 9, 2010); Boiler NESHAP--CO
(75 FR 32005, June 4, 2010; 75 FR 31895, June 4, 2010 (proposed rules;
the final rules were signed on February 21, 2011)); Hazardous Waste
Combustor NESHAP--CO (64 FR 52828; September 30, 1999)). Although
indications are that organic HAP emissions are low (and perhaps below
the MDL), there were very few emissions data available for these
compounds from coal-fired EGUs and we determined that it was necessary
to obtain additional information on which to establish standards for
these HAP. EPA identified the newest units as being representative of
the most modern, and, thus, presumed most efficient units. The 170
newest units were selected and were required to test for CO, VOC, and
THC; specifics of the required testing may be found in Docket entry
EPA-HQ-OAR-2009-0234-0062.
    Emissions of certain non-Hg metallic HAP (i.e., Sb, Be, Cd, Cr, Co,
Pb, Mn, and Ni) have been assumed to be well controlled by PM control
devices. However, Hg and other non-Hg metallic HAP (i.e., As and Se),
have the potential to exist in both the particulate and vapor phases,
and, therefore, may not be well controlled by PM control devices alone.
Also, it has been shown through recent stack testing that certain of
these HAP (i.e., As and Se) may condense on (or as) very fine PM in the