***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

1

III. Appropriate and Necessary Finding

A. Summary of EPA’s Finding that it is Appropriate and 

Necessary to Regulate EGUs to Address Public Health and 

Environmental Hazards Resulting from Emissions of Hg and 

Non-Hg Hazardous Air Pollutants (HAP) from EGUs

In the preamble to the proposed rule, we confirmed our 

December 2000 finding that it is appropriate to regulate 

emissions of Hg and other HAP from EGUs because emissions 

of those pollutants pose hazards to public health and the 

environment, and EGUs are the largest or among the largest 

contributors of many of those HAP. We also confirmed that 

it is necessary to regulate EGUs under section 112 for a 

variety of reasons, including that hazards to public health 

and the environment posed by HAP emissions from EGUs remain 

after imposition of the requirements of the CAA. Our 

confirmation of the December 2000 finding was supported in 

part by several new analyses of the hazards to public 

health posed by both mercury and non-mercury HAP.

Congress did not define the phrase “appropriate and 

necessary” in section 112(n)(1)(A). Rather, Congress 

expressly delegated to the Agency the authority to 

interpret and apply those terms. Courts have interpreted 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

2

the terms “appropriate” and “necessary” in other provisions 

of the CAA and other statutes, and concluded that those 

terms convey upon the Agency a wide degree of discretion. 

We evaluate the terms “appropriate” and “necessary” within 

the statutory context in which they appear to determine the 

meaning of the words.

In this context, we interpret the statute to require 

the Agency to find it appropriate to regulate EGUs under 

CAA section 112 if the Agency determines that the emissions 

of one or more HAP emitted from EGUs pose an identified or 

potential hazard to public health or the environment at the 

time the finding is made. The hazard to public health or 

the environment may be the result of HAP emissions from 

EGUs alone or the result of HAP emissions from EGUs in 

conjunction with HAP emissions from other sources. In 

addition, EPA must find that it is appropriate to regulate 

EGUs if it determines that any single HAP emitted by 

utilities poses a hazard to public health or the 

environment. We further interpret the term “appropriate” to 

not allow for the consideration of costs in assessing 

whether HAP emissions from EGUs pose a hazard to public 

health or the environment. Finally, we may conclude that it 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

3

is appropriate, in part, to regulate EGUs if we determine 

that there are controls available to address HAP emissions 

from EGUs.

The Agency must find it necessary to regulate EGUs 

under section 112 if the identified or potential hazards to 

public health or the environment will not be adequately 

addressed by the imposition of the requirements of the CAA.

Moreover, it may be necessary to regulate utilities under 

section 112 for a number of other reasons, including, for 

example, that section 112 standards will assure permanent 

reductions in EGU HAP emissions, which cannot be assured 

based on other requirements of the CAA. We maintain that we 

must find it necessary based on such a finding even if 

regulation under section 112 will not fully resolve the 

identified hazard to public health or the environment. We 

may also find it necessary to regulate EGUs under section 

112 to further the policy goal of supporting international 

efforts to reduce HAP emissions, including Hg.

In this section, we summarize the finding as reported 

in the preamble to the proposed rule. Specifically, we 

address the Agency’s determination that it is appropriate 

and necessary to regulate coal- and oil-fired EGUs under 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

4

CAA section 112. The extensive analyses summarized in the 

preamble to the proposed rule and documented in several 

Technical Support Documents1,2 confirmed that it remains 

appropriate and necessary today to regulate EGUs under 

section 112. The analyses demonstrated that 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 are still the largest domestic source of U.S. 

Hg, HCl, and HF emissions, and a significant source of 

other HAP emissions; 4) Hg emissions from individual EGUs 

leads to excess local deposition in areas directly 

surrounding those individual EGUs (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 

 

1 U.S. EPA. 2011a. National-Scale Assessment of Mercury Risk to 

Populations with High Consumption of Self-caught Freshwater Fish In 

Support of the Appropriate and Necessary Finding for Coal- and OilFired Electric Generating Units. Office of Air Quality Planning and 

Standards. November. EPA-xxx-xx-xxx.

2 U.S. EPA. 2011b. Supplement to Non-Hg Case Study Chronic Inhalation 

Risk Assessment for the Utility MACT Appropriate and Necessary 

Analysis. Office of Air Quality Planning and Standards. November.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

5

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 concluded 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 concluded 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 concluded that 

non-Hg HAP emissions from U.S. EGU are a public health 

hazard because they contribute to elevated cancer risks. 

Finally, EPA concluded that U.S. EGU’s HCl and HF emissions 

contribute to acidification in sensitive ecosystems and, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

6

therefore, pose a risk of adverse effects on the 

environment. 

The analyses demonstrated that it is necessary to 

regulate emissions from coal- and oil-fired EGUs under CAA 

section 112 because 1) Hg emissions from EGUs remaining in 

2016 still pose a hazard to public health and the 

environment in the absence of regulations under Section 112 

that would be required to be implemented at that time, 2) 

U.S. EGU emissions of Hg after imposition of the 

requirements of the CAA are projected to be 29 tons per 

year in 2016, the same as the level of Hg emitted today, 3) 

EGUs are the largest source of Hg in the U.S. and thus 

contribute to the risk associated with exposure to MeHg, 4) 

we cannot be certain that the identified cancer risks 

attributable to EGUs will be addressed through imposition 

of the requirements of the CAA, 5)the environmental hazards 

posed by acidification will not be fully addressed through 

imposition of the CAA, 6) regulation under section 112 is 

the only way to ensure that HAP emissions reductions that 

have been achieved since 2005 remain permanent, 7) direct 

control of Hg emissions affecting U.S. deposition is only 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

7

possible through regulation of U.S. emissions; we are 

unable to control global emissions directly.

a. Finding that U.S. EGU Hg Emissions Continue to Pose a 

Hazard to Public Health and the Environment

In support of the finding that U.S. EGU mercury 

emissions are a hazard to public health, in the preamble to 

the proposed rule, EPA reported the results of a national 

scale assessment of mercury risk to populations with high 

consumption of self-caught freshwater fish, which is the 

population most likely to experience elevated risk from 

U.S. EGU mercury emissions. This assessment was based on 

detailed emissions, air quality, exposure, and risk 

modeling, which provided estimates of the watersheds in 

which populations with high levels of fish consumption 

experience the potential for risk due to deposition of 

mercury. The national scale mercury risk assessment (“the 

mercury risk assessment”) of the hazard to public health 

posed by U.S. EGU Hg emissions focused on comparisons to 

the RfD of exposures caused or contributed to by U.S. EGU 

Hg emissions. In the mercury risk assessment, almost all 

(98 percent) of the more than 2,400 watersheds for which we 

identified fish tissue data, exceeded the RfD, above which 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

8

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. 

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 to result in potential MeHg exposures above the 

RfD, regardless of the additional deposition from other 

sources of Hg deposition. This approach is likely to 

understate risk because any contribution of Hg to 

watersheds where potential exposures to MeHg exceed the RfD 

poses a public health hazard. Thus, because we found a 

large percentage of watersheds with populations potentially 

at risk even using this approach, we have confidence that 

emissions of Hg from U.S. EGUs are causing a hazard to 

public health, as there are additional watersheds that have 

contributions at lower percent benchmarks.

In total, the mercury risk assessment found an 

estimated 28 percent of sampled watersheds with populations 

that are potentially at risk from exposure to MeHg based on 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

9

the contribution of U.S. EGUs. This total includes 

watersheds that are potentially at risk either because U.S. 

EGU attributable deposition is sufficient to cause 

potential exposures to exceed the reference dose even 

excluding 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. 

We found that at the 99th percentile fish consumption 

level for subsistence fishers, 22 percent of sampled 

watersheds where total potential exposures to MeHg exceed 

the RfD received at least 5 percent of Hg deposition from 

U.S. EGUs. Although the most complete estimate of potential

risk is based on total exposures to Hg, including 

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 excluding consideration of the 

deposition from other non-U.S. EGU sources. Based on these 

considerations, we found that at the 99th percentile fish 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

10

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 

excluding consideration of the additional deposition from 

other sources.

In addition, we highlighted in the preamble to the 

proposed rule that 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 that we were able to identify for the 

mercury risk assessment was 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. In addition, due to 

limitations in our models and available data, we did not 

estimate risks in near-coastal waters, and some of these 

waters, such as the Chesapeake Bay, could have substantial 

EGU-attributable Hg deposition.

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 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

11

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 by 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 affecting 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, 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 

contribute to that global pool. Controlling Hg emissions 

from U.S. EGUs helps to reduce the potential for 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

12

environmental hazard from Hg now and in the future. The 

findings described above independently support a 

determination that it is appropriate to regulate HAP 

emissions from EGUs.

b. Finding that U.S. EGU Non-Hg HAP Emissions Continue to 

Pose a Hazard to Public Health and the Environment

In addition to the mercury risk assessment, EPA also 

reported in the preamble to the proposed rule the results 

of 16 case studies of inhalation risks of cancer for 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. 

The results of that analysis showed that of the 16 

facilities modeled (4 facilities, 3 coal-fired facilities 

and 1 oil-fired facility), have estimated risks of greater 

than 1 in 1 million for the most exposed individual. 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, risks above that level represent a hazard to 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

13

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 acidification 

affects many sensitive ecosystems across the country, it is

appropriate to reduce emissions of this magnitude, which 

may aggravate acidification. The Administrator concluded 

that, in addition to the regulation of non-Hg HAP that 

cause elevated cancer risks, it is appropriate to regulate 

those HAP that 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 supported the 

determination that it remains appropriate to regulate HAP 

emissions from EGUs.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

14

c. Finding that 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, fabric filters, and wet FGD scrubbers are 

all effectively remove Hg; the degree of effectiveness 

depends on the specific characteristics of the EGU and fuel 

types. Additionally, these devices all effectively remove 

Non-Hg metal HAP. Activated carbon injection is the most 

successfully demonstrated Hg-specific control technology. 

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 

supported 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’s Finding 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 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

15

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 evaluated 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 emission reductions 

anticipated from the proposed Transport Rule (finalized in 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

16

June 2011 as the Cross State Air Pollution Rule3); 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. However, we did notconduct an 

analysis to determine whether the state requirements 

arebased on requirements of the CAA. As such, 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 the CAA as 

contemplated under section 112(n)(1)(A). To the extent 

that these non-federal actions do not result in permanent 

reductions in Hg emissions, their inclusion in the baseline 

 

3 Since the time of the analyses conducted in support of the appropriate 

and necessary finding, EPA has finalized the CSAPR. Compared to the 

proposed Transport Rule, the final CSAPR is expected to achieve greater 

reductions in criteria pollutants, and also to have a slightly greater 

impact on U.S. EGU Hg emissions. The current projection is that after 

implementation of CSAPR in 2016, there will be 27 tons of Hg emitted by 

U.S. EGU, as compared to the 29 tons we modeled for the national scale 

mercury risk assessment. We do not expect that the 2 tons less of Hg 

will substantially change the mercury risks that we reported in the 

preamble to the proposed rule, as this represents less than a 10 

percent reduction in Hg emissions.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

17

Hg emissions estimates for the national scale mercury risk 

analysis will result in an underestimate of the risks 

associated with U.S. EGU Hg emissions. We did not include 

in our analysis any state-only requirements or voluntary 

actions to reduce HAP emissions because there is no Federal 

backstop for those requirements and actions.

Our analysis confirmed 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 

estimated that U.S. EGU emissions of Hg after imposition of 

the requirements of the CAA will be 29 tons per year in 

2016, the same as the level of Hg that we estimated at the 

time of proposal would be emitted by U.S. EGUs 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, we 

determined it is necessary to regulate EGUs.

It is necessary to regulate HAP emissions from EGUs, 

even though the hazards from Hg will not be fully resolved 

through regulation under section 112. EPA finds that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

18

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. Real reductions between 2005 and 2010 are 

attributable to state Hg regulations and to the Clean Air 

Interstate Rule (CAIR) and Federal enforcement actions that 

achieve Hg reductions as a co-benefit of controls for PM, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

19

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, it is likely that such emissions have 

also decreased between 2005 and 2010. Thus, the 

Administrator finds it necessary to regulate HAP emissions 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

20

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 the 

finding, as reported in the preamble to the proposed rule, 

that it is necessary to regulate U.S. 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 confirmed in the preamble 

to the proposed rule its decision to include coal- and oilfired EGUs on the list of source categories regulated under 

CAA section 112(c).

B. Peer Review of the National-Scale Mercury Risk 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

21

Assessment Supporting the Appropriate and Necessary Finding 

for Coal and Oil-Fired EGUs and EPA Response

In the preamble to the proposed rule, EPA stated that 

“in making the finding that 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, EPA determined that the NationalScale Mercury Risk Analysis supporting EPA’s 2011 review of 

U.S. EGU health impacts should be peer-reviewed.”4 We also 

indicated that due to the court-ordered schedule for the 

final rule, we would conduct the peer review as 

expeditiously as possible after issuance of the proposed 

rule, and that the results of the peer review and any EPA 

response would be published before the final rule.

We have completed the peer-review of the national 

scale mercury risk analysis, which is fully documented in 

the revised Technical Support Document (TSD): NationalScale Assessment of Mercury Risk to Populations of High 

Consumption of Self-Caught Fish In Support of the 

Appropriate and Necessary Finding for Coal and Oil-Fired 

Electric Generating Units. The following sections describe 

 

4 76 FR 25012
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

22

the peer-review process that we followed, provide the peerreview charge questions presented to the peer-review panel, 

summarize the key recommendations from the peer-review, and 

summarize our responses to those recommendations.

1. Summary of Peer Review Process

Peer review is consistent with EPA’s routine open and 

transparent process to ensure that the Agency’s scientific 

assessments and rulemakings are based on the best science 

available. This regulatory action was supported by the 

National-Scale Mercury Risk Assessment, which is a highly 

influential scientific assessment. Therefore, EPA conducted 

a peer review in accordance with OMB’s Final Information 

Quality Bulletin for Peer Review5 as described below. The 

peer review report is located in the docket for today's 

action. 

EPA commissioned the peer review through EPA’s Science 

Advisory Board (SAB), which provides independent advice and 

peer review to EPA's Administrator on the scientific and 

technical aspects of environmental issues. The SAB formed a 

22-member peer-review committee, which included a diverse 

 

5 Office of Management and Budget (OMB). 2004. Final Information 

Quality Bulletin for Peer Review. December. Available on the Internet 

at http://www.whitehouse.gov/omb/memoranda_fy2005_m05-03. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

23

mix of experts from industry, states and academia. The SAB 

process for selecting the panel began with two Federal 

Register Notices requesting nominations for the Mercury 

Review Panel6. Based on nominations received, a list of 

potential panel members, along with bio-sketches, was 

posted for public comment on the SAB website on April 15, 

2011. The final members of the Mercury Review Panel were 

announced on May 24, 2011. The membership of the panel 

included members representing 16 academic institutions, 4 

state health or environmental agencies, 1 federal agency, 

and 1 utility industry organization7. The charge to the 

panel was provided on May 23, 2011. The panel met at a 

public meeting in Research Triangle Park, NC on June 15-17, 

2011, which included the opportunity for public comment on 

the March Mercury Risk TSD and the peer review process8. At 

the June 15-17 public meeting, the panel completed a draft 

peer review report. The minutes of that meeting and the 

 

6 76 FR 10896 and 76 FR 17649. The first notice requested nominations to 

a Clean Air Science Advisory Committee (CASAC) panel. Upon review of 

the scope of the CASAC charter (resulting from a public comment 

received in response to the first notice), the SAB determined that it 

would be more appropriate to form a panel under the SAB, rather than 

CASAC. The second notice announced this change and requested 

nominations for the SAB panel.

7 The full list of panel members is documented at 

http://yosemite.epa.gov/sab/sabproduct.nsf/0/9F048172004D93BB8525783900

503486/$File/Determination%20memo%20with%20addendum-05.24.11.pdf

8 76 FR 29746
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

24

draft peer review report were posted to the SAB public 

website within the public comment period for the proposed 

rule. The panel discussed the draft report at a public 

teleconference on July 12, 2011, during which additional 

opportunities for public comment were provided9, and 

submitted a revised draft for quality review by the 

Chartered SAB. The Chartered SAB held a public 

teleconference on September 7, 2011 to conduct a quality 

review of the draft report; this teleconference also 

included a final opportunity for public comment10. The SAB

submitted its final peer-review report to EPA on September 

29, 201111. All of the materials discussed at the SAB 

meetings, including technical documents, presentations, 

meeting minutes, and draft reports were posted for public 

access on the SAB website and were added to the docket for 

the final rule on October 14, 2011.12

2. Peer Review Charge Questions

EPA asked the SAB to comment on the risk assessment, 

 

9 76 FR 39102

10 76 FR 50729

11 U.S. Environmental Protection Agency-Science Advisory Board (U.S. 

EPA-SAB). 2011. Peer Review of EPA’s Draft National-Scale Mercury Risk 

Assessment. EPA-SAB-11-017. September. Available on the internet at 

http://yosemite.epa.gov/sab/sabproduct.nsf/BCA23C5B7917F5BF8525791A0072

CCA1/$File/EPA-SAB-11-017-unsigned.pdf.

12 See http://yosemite.epa.gov/sab/sabpeople.nsf/WebCommittees/BOARD
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

25

including the overall design and approach, as well as the 

use of specific models and key assumptions. EPA also asked 

the SAB to comment on the extent to which specific facets 

of the assessment are well characterized in the March 

Mercury Risk TSD. The specific charge questions are listed 

below: 

Question 1. Please comment on the scientific 

credibility of the overall design of the mercury risk 

assessment as an approach to characterize human health 

exposure and risk associated with U.S. EGU mercury 

emissions (with a focus on those more highly exposed). 

Question 2. Are there any additional critical health 

endpoint(s) besides IQ loss, which could be quantitatively 

estimated with a reasonable degree of confidence to 

supplement the mercury risk assessment (see section 1.2 of 

the Mercury Risk TSD for an overview of the risk metrics 

used in the risk assessment)? 

Question 3. Please comment on the benchmark used for 

identifying a potentially significant public health impact 

in the context of interpreting the IQ loss risk metric 

(i.e., an IQ loss of 1 to 2 points or more representing a 

potential public health hazard). Is there any 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

26

scientifically credible alternate decrement in IQ that 

should be considered as a benchmark to guide interpretation 

of the IQ risk estimates (see section 1.2 of the Mercury 

Risk TSD for additional detail on the benchmark used for 

interpreting the IQ loss estimates)?

Question 4: Please comment on the spatial scale used 

in defining watersheds that formed the basis for risk 

estimates generated for the analysis (i.e., use of 12-digit 

hydrologic unit code classification). To what extent do 

[Hydrologic Unit Code] HUC12 watersheds capture the 

appropriate level of spatial resolution in the relationship 

between changes in mercury deposition and changes in MeHg 

fish tissue levels? (see section 1.3 and Appendix A of the 

Mercury Risk TSD for additional detail on specifying the 

spatial scale of watersheds used in the analysis).

Question 5: Please comment on the extent to which the 

fish tissue data used as the basis for the risk assessment 

are appropriate and sufficient given the goals of the 

analysis. Please comment on the extent to which focusing on 

data from the period after 1999 increases confidence that 

the fish tissue data used are more likely to reflect more 

contemporaneous patterns of mercury deposition and less 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

27

likely to reflect earlier patterns of mercury deposition. 

Are there any additional sources of fish tissue MeHg data 

that would be appropriate for inclusion in the risk 

assessment? 

Question 6: Given the stated goal of estimating 

potential risks to highly exposed populations, please 

comment on the use of the 75th percentile fish tissue MeHg 

value (reflecting targeting of larger but not the largest 

fish for subsistence consumption) as the basis for 

estimating risk at each watershed. Are there scientifically 

credible alternatives to use of the 75th percentile in 

representing potential population exposures at the 

watershed level? 

Question 7: Please comment on the extent to which 

characterization of consumption rates and the potential 

location for fishing activity for high-end self-caught fish 

consuming populations modeled in the analysis are supported 

by the available study data cited in the Mercury Risk TSD. 

In addition, please comment on the extent to which 

consumption rates documented in Section 1.3 and in Appendix 

C of the Mercury Risk TSD provide appropriate 

representation of high-end fish consumption by the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

28

subsistence population scenarios used in modeling exposures 

and risk. Are there additional data on consumption behavior 

in subsistence populations active at inland freshwater 

water bodies within the continental U.S.? 

Question 8: Please comment on the approach used in the 

risk assessment of assuming that a high-end fish consuming 

population could be active at a watershed if the “source 

population” for that fishing population is associated with 

that watershed (e.g. at least 25 individuals of that 

population are present in a U.S. Census tract intersecting 

that watershed). Please identify any additional alternative 

approaches for identifying the potential for population 

exposures in watersheds and the strengths and limitations 

associated with these alternative approaches (additional 

detail on how EPA assessed where specific high-consuming 

fisher populations might be active is provided in section 

1.3 and Appendix C of the Mercury Risk TSD). 

Question 9: Please comment on the draft risk 

assessment’s characterization of the limitations and 

uncertainty associated with application of the Mercury Maps 

approach (including the assumption of proportionality 

between changes in mercury deposition over watersheds and 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

29

associated changes in fish tissue MeHg levels) in the risk 

assessment. Please comment on how the output of CMAQ 

modeling has been integrated into the analysis to estimate 

changes in fish tissue MeHg levels and in the exposures and 

risks associated with the EGU-related fish tissue MeHg 

fraction (e.g., matching of spatial and temporal resolution 

between CMAQ modeling and HUC12 watersheds). Given the 

national scale of the analysis, are there recommended 

alternatives to the Mercury Maps approach that could have 

been used to link modeled estimates of mercury deposition 

to monitored MeHg fish tissue levels for all the watersheds 

evaluated? (additional detail on the Mercury Maps approach 

and its application in the risk assessment is presented in 

section 1.3 and Appendix E of the Mercury Risk TSD). 

Question 10: Please comment on the EPA’s approach of 

excluding watersheds with significant non-air loadings of 

mercury as a method to reduce uncertainty associated with 

application of the Mercury Maps approach. Are there 

additional criteria that should be considered in including 

or excluding watersheds? 

Question 11: Please comment on the specification of 

the concentration-response function used in modeling IQ 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

30

loss. Please comment on whether EPA, as part of uncertainty 

characterization, should consider alternative 

concentration-response functions in addition to the model 

used in the risk assessment. Please comment on the extent 

to which available data and methods support a quantitative 

treatment of the potential masking effect of fish nutrients 

(e.g. omega-3 fatty acids and selenium) on the adverse 

neurological effects associated with mercury exposure, 

including IQ loss. (detail on the concentration-response 

function used in modeling IQ loss can be found in section 

1.3 of the Mercury Risk TSD). 

Question 12: Please comment on the degree to which key 

sources of uncertainty and variability associated with the 

risk assessment have been identified and the degree to 

which they are sufficiently characterized. 

Question 13: Please comment on the draft Mercury Risk 

TSD’s discussion of analytical results for each component 

of the analysis. For each of the components below, please 

comment on the extent to which EPA’s observations are 

supported by the analytical results presented and whether 

there is a sufficient characterization of uncertainty, 

variability, and data limitations, taking into account the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

31

models and data used: mercury deposition from U.S. EGUs , 

fish tissue methyl mercury concentrations, patterns of Hg 

deposition with HG fish tissue data, percentile risk 

estimates, and number and frequency of watersheds with 

populations potentially at risk due to U.S. EGU mercury 

emissions. 

Question 14: Please comment on the degree to which the 

final summary of key observations in Section 2.8 is 

supported by the analytical results presented. In addition,

please comment on the degree to which the level of 

confidence and precision in the overall analysis is 

sufficient to support use of the risk characterization 

framework described on page 18.

3. Summary of Peer Review Findings and Recommendations

The SAB peer review panel was generally supportive of 

EPA’s approach.13 SAB concluded, “In summary, based on its 

review of the draft Technical Support Document and 

additional information provided by EPA representatives 

during the public meetings, the SAB supports the overall 

design of and approach to the risk assessment and finds 

that it should provide an objective, reasonable, and 

 

13 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

32

credible determination of the potential for a public health 

hazard from mercury emitted from U.S. EGUs.”

14 SAB further 

concluded, “The SAB regards the design of the risk 

assessment as suitable for its intended purpose, to inform 

decision-making regarding an “appropriate and necessary 

finding” for regulation of hazardous air pollutants from 

coal and oil-fired EGUs, provided that our recommendations 

are fully considered in the revision of the assessment.”15

The SAB report contained many recommendations for 

improving the Mercury Risk TSD, which SAB organized into 

three general themes: (1) improve clarity of the Mercury 

Risk TSD regarding methods and presentation of results, (2) 

expand discussion of sources of variability and 

uncertainty, and (3) de-emphasize IQ loss as an endpoint. 

In the following sections, we describe each of the specific 

recommendations along with EPA’s response to these 

recommendations.

4. EPA Responses to Specific Peer Review Recommendations

In response to the peer review, EPA has substantially 

revised the TSD as part of the final rulemaking and has 

 

14 Id.

15 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

33

made that revised Mercury Risk TSD available in the rule 

docket. The revised Mercury Risk TSD addresses all of the 

recommendations from the SAB peer review panel and includes 

a detailed list of the specific revisions made to the 

Mercury Risk TSD. Revisions in response to the main 

recommendations are summarized below. Italicized statements 

are the SAB’s recommendations, followed by EPA’s response.

 The watershed-focus of the risk assessment should be 

clearly stated early in the introduction to the 

document. We have stated clearly in the introduction 

to the revised Mercury Risk TSD that the focus of the 

analysis is on scenarios of high fish consumption by 

subsistence level fishing populations, assessed at 

watersheds where there is the potential for this type

of subsistence fishing activity. Specifically, we are 

modeling risk for a set of subsistence fisher 

scenarios at those watersheds where (a) we have 

measured fish tissue Hg data and (b) it is reasonable 

to assume that subsistence-level fishing activity 

could occur. We emphasize the point that the analysis 

is not a representative population-weighted assessment 

of risk. Rather, it is based on evaluating these 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

34

potential exposure scenarios.

 Because IQ does not fully capture the range of 

neurodevelopmental effects associated with Hg 

exposure, analysis of this endpoint should be 

deemphasized (and moved to an appendix) and primary 

focus should be placed on the MeHg RfD-based hazard 

quotient metric. We modified the structure of the 

Revised Mercury Risk TSD accordingly.

 Clarify the rationale for using an [Hazard Quotient] 

HQ at or above 1.5 as the basis for selecting 

potentially impacted watersheds. We revised this 

discussion accordingly. Reflecting precedent in 

interpreting HQ estimates, we clarified that exposures 

above the RfD (i.e., an HQ above one) to represent a 

potential public health hazard. We further clarified 

that the HQ is calculated to only one significant 

digit, based on the precision in the underlying RfD 

calculations. As a result, rounding convention 

requires that any values at or above 1.5 be expressed 

as an HQ of 2, while any values below 1.5 (e.g. 1.49) 

will be rounded to an HQ of 1. Thus, exposures at or 

above 1.5 are considered above the RfD and represent a 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

35

potential public health hazard.

 Regarding the fish tissue dataset used in the risk 

assessment, clarify which species of Hg is reflected 

in the underlying samples and discuss the implications 

of differences across states in sampling protocols in 

introducing bias into the analysis. We clarified that

in most cases, the fish tissue is measured for total 

Hg. Furthermore, based on the literature, it is 

reasonable to assume that more than 90 percent of fish 

tissue Hg is methylmercury (MeHg). Therefore, we 

incorporated a Hg conversion factor into our exposure 

calculations to account for the fraction of total Hg 

that is MeHg in fish. We also expanded the discussion 

of uncertainty to include the potential for different 

sampling protocols across states to introduce bias 

into the risk assessment. 

 Additional detail should be provided on the 

characteristics of the fish tissue Hg dataset, 

including its derivation and the distribution of 

specific attributes across the dataset (e.g., number 

of fish tissue samples and number of different 

waterbodies in a watershed, number of species 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

36

reflected across watersheds). We included additional 

figures and tables describing the derivation of the 

watershed-level fish tissue Hg dataset, including the 

filtering steps applied to the original water body 

level data and the additional steps to generate the 

watershed-level fish tissue Hg percentile estimates. 

In addition, we included tables summarizing the 

distribution of key attributes within that dataset 

highlighted by the SAB (e.g., distribution of fish 

tissue sample size and number of species across the 

watershed-level estimates). 

 Determine whether there is additional (more recent) 

fish tissue data for key states including 

Pennsylvania, Jew Jersey, Kentucky and Illinois where 

U.S. EGUs Hg deposition may be more significant. We 

expanded the fish tissue dataset by incorporating 

additional fish tissue data from the National Listing 

of Fish Advisories (NLFA), which included additional 

data for four states (MI, NJ, PA, and MN). We also 

obtained additional data for Wisconsin. This 

additional data expanded the number of watersheds in 

the analysis from 2,317 to 3,141, an increase of 36 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

37

percent. The increase in watersheds provides greater 

coverage of areas with high levels of U.S. EGU Hg 

deposition.

 Include additional discussion of the potential that 

the low sampling rates reflected across many of the 

watersheds may low-bias the 75th percentile fish tissue 

Hg estimates used in estimating potential exposures. 

In addition, the SAB recommended including a 

sensitivity analysis using the 50th percentile 

estimates to provide a bound on the risk assessment. 

The SAB expressed support for the use of the 75th

percentile fish tissue Hg value in the risk 

assessment, while recommending additional discussion 

of the issue. We provided additional description of

the fish tissue dataset, including distribution of 

sample sizes and fish species across the watersheds, 

which includes an improved discussion of uncertainty 

and potential bias resulting from estimation of the 

75th percentile fish tissue levels. We also included a 

sensitivity analysis that used the 50th percentile 

watershed-level fish tissue Hg level. This sensitivity 

analysis showed that using the 50th percentile 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

38

estimates resulted in a decrease in the number and 

percentage of watersheds identified as having 

populations potentially at risk from U.S. EGUattributable MeHg exposures, from 29 percent to 26 

percent.

 Expand the discussion of caveats associated with the 

fish consumption rates used in the analysis. The SAB 

was generally supportive of the consumption rates 

used, while recommending additional discussion of 

caveats. We expanded the discussion of uncertainty 

related to the fish consumption rates to address the 

caveats identified by the SAB. The uncertainty 

discussion now describes 1) how high-end consumption 

rates for South Carolina reflect small sample sizes, 

and therefore may be more uncertain, 2) that the 

consumption surveys underlying the studies are older 

and behavior may have changed, and 3) that consumption 

rates used in the risk analysis are annualized rather 

than seasonal rates and thus contribute little to 

overall uncertainty. None of these sources of 

uncertainty are associated with a particular 

directional bias (e.g., neither systematically higher 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

39

nor lower risk).

 Verify whether the consumption rates are daily values 

expressed as annual averages and whether they are “as 

caught” or “as prepared.” These factors have important 

implications for the exposure calculations. We 

carefully reviewed the studies underlying the fish 

consumption rates used in the risk assessment and 

verified that the rates are annual-average daily 

consumption rates and that they represent as prepared 

estimates. We also expanded the explanation of the 

exposure calculations to more completely describe the 

exposure factors and equation used to generate the 

average daily MeHg intake estimates for the 

subsistence scenarios. 

 Explain the criteria for exclusion of fish less than 7 

inches in length from analysis. We provided the 

rationale for the 7-inch cutoff for edible fish used 

in the risk analysis. Seven inches represents a 

minimum size limit for a number of key edible 

freshwater fish species established at the state 

level. For example, Pennsylvania establishes 7 inches 

as the minimum size limit for both Trout and Salmon 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

40

(other edible fish species such as Bass, Walleye and 

Northern Pike have higher minimum size limits). The 

impact of the 7-inch cutoff is likely to be quite 

small, as only 6 percent of potential fish samples 

were excluded due to this criterion.

 Identify the number of watersheds excluded from the 

analysis due to the criterion for excluding watersheds 

with less than 25 members of a source population. The 

SAB was generally supportive of the approach used for 

identifying watersheds with the potential for 

subsistence activity, while recommending additional 

information on the results of applying the approach. 

We added a figure to illustrate the number of 

watersheds with fish tissue Hg data used to model risk 

for each of the subsistence fisher scenarios. For all 

scenarios except the female subsistence scenario, 

there were significant limitations to the number of 

watersheds where the exposure scenario was applied. 

Because this scenario represents female subsistence 

fishers without differentiation with regard to 

ethnicity or socio-economic status(SES), we applied 

this scenario to all regions of the country and to all 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

41

watersheds with fish tissue Hg data. This reflects our 

assumption that, given the generalized nature of this 

subsistence scenario, it is reasonable to assume that 

it could potentially occur at any watershed with fish 

tissue Hg data. The female subsistence scenario 

included in the revised risk assessment is similar to 

the high consuming female scenario included in the 

Mercury Risk TSD.16 However, the female subsistence 

scenario is applied without consideration for a source 

population, while in the scenario for the highconsuming low-income female angler, we considered a 

source population based on poverty. The female 

subsistence scenario provides greater coverage 

geographically than the high-consuming low-income 

female scenario from the March assessment that was 

only applied to watersheds with fish tissue Hg data 

and at least 25 members of the source population 

(individuals living below the poverty line). This also 

helps to address the concern raised by the SAB that 

more remote water bodies are fished by subsistence 

 

16 In the Revised Mercury Risk TSD, this population is also referred to 

as the “typical female subsistence consumer”.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

42

anglers as well, and exclusion of those more remote 

watersheds could lead to underestimation of the 

percent of watersheds where Hg exposure from U.S. EGU 

sources is a risk.

 Enhance the discussion of the assumption of a linear 

relationship between changes in Hg deposition and 

changes in fish tissue Hg at the watershed level, 

including providing citations to more recent studies 

supporting the proportional relationship between 

changes in Hg deposition and changes in MeHg fish 

tissue levels. The SAB supported the assumption of a 

linear relationship between changes in Hg deposition 

and changes in fish tissue Hg at the watershed level, 

while recommending additional supporting language. We 

expanded our discussion of the scientific basis for 

the proportionality assumption and added citations for 

the more recent studies supporting the assumption. We 

also expanded the discussion of uncertainties 

associated with this assumption, including 

uncertainties related to the potential for sampled 

fish tissue Hg level to reflect previous Hg 

deposition, and the potential for non-air sources of 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

43

Hg to contribute to sampled fish tissue Hg levels. 

Each of these sources of uncertainty may result in 

potential bias in the estimate of exposure associated 

with current deposition. If the fish tissue Hg levels 

are too high due to either previous Hg deposition or 

non-air sources of Hg, then the absolute level of 

exposure attributed to both total Hg deposition and 

U.S. EGU-attributable Hg deposition will be biased 

high. However, the percent contribution from U.S. EGUs 

will not be affected as it depends entirely on 

deposition. EPA took steps to minimize the potential 

for these biases by 1) only using fish tissue Hg 

samples from after 1999, and 2) screening out 

watersheds that either contained active gold mines or 

had other substantial non-U.S. EGU anthropogenic 

releases of mercury. The SAB commented that EPA’s 

approach to minimizing the potential for these biases 

to affect the results of the risk analysis appears to 

be sound. In addition, we conducted several 

sensitivity analyses to gauge the impact of excluding 

watersheds with the potential for non-U.S. EGU Hg 

releases, and we found that the results were largely 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

44

insensitive to these exclusions.

 Additional sources of variability should be discussed 

in terms of the degree to which they are reflected in 

the design of the risk assessment and the impact that 

they might have on risk estimates. These include: 1) 

the geographic patterns of populations of subsistence 

fishers, including how this factor interacts with the 

limited coverage we have for watersheds with our fish 

tissue Hg data, 2)the protocols used by states in 

collecting fish tissue Hg data, 3) body weights for 

subsistence fishing populations and the impact that 

this might have on exposure estimates, and 4) 

preparation and cooking methods which affect the 

conversion of fish tissue Hg levels (as measured) into 

“as consumed” values. We expanded the discussion of 

sources of variability in the revised TSD to more 

fully address these sources of variability as 

recommended. 

 Additional sources of uncertainty should be discussed 

in terms of their potential impact on risk estimates. 

These include: 1) emissions inventory used in 

projecting total and U.S. EGU-attributable Hg 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

45

deposition, including the projection of reductions in 

U.S. EGU emissions for the 2016 scenario, 2) air 

quality modeling with CMAQ including the prediction of 

future air quality scenarios, 3) ability of the 

Mercury Maps-based approach for relating Hg deposition 

to MeHg in fish to capture Hg hotspots, 4) the limited 

coverage that we have with fish tissue Hg data for 

watersheds in the U.S. and implications for the risk 

assessment, 5) the preparation factor used to estimate 

“as consumed” fish tissue Hg levels, 6) the 

proportionality assumption used to relate changes in 

Hg deposition to changes in fish tissue Hg levels at 

the watershed-level, 7)characterization of the spatial 

location of subsistence fisher populations (including 

degree to which these provide coverage for highconsuming recreational fishers), and 8) application of 

the RfD to low SES populations and concerns that this 

could low-bias the risk estimates. We expanded the 

discussion of sources of uncertainty presented in the 

revised TSD to more fully address these sources of 

uncertainty and the potential impact on risk 

estimates. Regarding these eight additional sources of 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

46

uncertainty, we have 1) evaluated the uncertainty in 

the preparation factor and determined that the level 

of uncertainty is low, and as such would have minimal 

impact on the risk estimates, 2) focused the risk 

estimates on female subsistence fishing populations, 

which are assumed to have the potential to fish in all 

watersheds, reducing uncertainties about the coverage 

of the risk estimates for other populations, 3) 

continued to include the sensitivity analyses designed 

to test whether removing watersheds that would 

potentially violate the proportionality assumption 

would significantly affect the results (they do not), 

4) supplemented the coverage of watersheds by 

obtaining additional fish tissue Hg samples for areas 

heavily impacted by U.S. EGU deposition. We have also 

assessed the potential impact of the uncertainty in 

application of the RfD to low SES populations, and 

have determined that due to the method used in 

calculating the RfD (which includes an uncertainty 

factor to capture pharmacokinetic variability across 

the population), concerns that the RfD may not provide 

coverage for low SES populations is reduced.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

47

Uncertainty in emissions and air quality modeling is 

an important source of uncertainty which is not 

quantified in the risk analysis, however, the models 

of emissions and air quality are based on peerreviewed science, and represent the best available 

method for predicting mercury deposition in the U.S.

 Expand the sensitivity analyses (over those included 

in the original risk assessment) to address 

uncertainty related to the use of the 75th percentile 

fish tissue Hg value (at each watershed) as the core 

risk estimate. We added a sensitivity analysis using 

the median fish tissue Hg estimate (at the watershed 

level). This sensitivity analysis showed that use of 

the median fish tissue Hg concentration instead of the 

75th percentile resulted in only a small change in the 

estimates of risk.

C. Summary of Results of Revised National Scale 

Assessment of Risks to Populations with High Levels of 

Self-Caught Fish Consumption

Based on the recommendations we received from the SAB, 

we revised the quantitative analysis of risk to subsistence 

fishing populations with high levels of fish consumption. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

48

Our revision to the quantitative risk results reflects 

three key recommendations from the SAB, including 1) 

addition of 824 watersheds based on additional fish tissue 

Hg sample data we obtained from states and the National 

Listing of Fish Advisories, 2) application of a 0.95 

adjustment factor to the reported fish tissue Hg 

concentrations to account for the fraction that is MeHg, 

and 3) inclusion of all watersheds with fish samples that 

meet the filtering criteria in representing potential risks 

for low income female subsistence fishing populations. 

Based on these changes, our estimates of the number and 

percent of watersheds where populations may be at risk from 

exposure to EGU-attributable MeHg changed from those 

presented in the preamble to the proposed rule. For the 99th

percentile consumption scenario, the number of watersheds 

with fish tissue Hg samples where subsistence fishing 

populations may be at risk from exposure to EGUattributable MeHg increased from 672 to 917 (an increase of 

36 percent). For this same scenario, the percent of 

watersheds where subsistence fishing populations may be at 

risk increased from 28 percent to 29 percent. For the 95th

percentile consumption scenario, the percent of watersheds 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

49

where subsistence fishing populations may be at risk has 

increased from 22 percent to 24 percent. The increase in 

the percent of watersheds at risk using the expanded 

geographic coverage of watersheds provides additional 

confidence that emissions of Hg from U.S. EGUs are a hazard 

to public health.

The additional sensitivity analyses conducted as a 

result of the SAB peer review showed that the estimates of 

the percent of watersheds where subsistence fishing 

populations may be at risk are robust to alternative 

assumptions about both the watersheds included in the 

analysis and the selection of the 50th percentile or 75th

percentile fish tissue Hg level. Sensitivity analyses 

excluding entire states with the potential for historical 

loadings of Hg from non-air sources17 resulted in an 

increase in the percent of watersheds with populations at 

risk, from 29 percent to 33 percent. Including only 

watersheds in the top 25th percentile of U.S. EGU deposition 

resulted in an increase in the percent of watersheds with 

 

17 The SAB noted that areas with substantially elevated fish tissue Hg 

levels could also be characterized by lakes and rivers with high 

natural methylation rates, and thus some of the states we excluded for 

this sensitivity analysis might not have fish tissue Hg levels that 

reflect non-U.S. EGU Hg loadings.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

50

populations at risk, from 29 percent to 30 percent. Using 

the 50th percentile fish tissue Hg level resulted in a 

decrease in the percent of watersheds with populations at 

risk, from 29 percent to 26 percent. None of these 

sensitivity analyses result in reductions in the percent of 

watersheds with populations at risk that would challenge 

the finding that Hg emissions from U.S. EGUs are a hazard 

to public health.

D. Peer Review of the Approach for Estimating Cancer Risks 

Associated with Chromium and Nickel Emissions in the U.S. 

EGU Case Studies of Cancer and Non-Cancer Inhalation Risks 

for Non-Hg HAP and EPA Response

In the preamble to the proposed rule, EPA determined 

that the characterization of the chemical speciation for 

the emissions of Cr and Ni used in the non-Hg HAP 

inhalation risk case studies should be peer-reviewed. The 

Agency determined that the remaining aspects of the non-Hg 

HAP case study risk assessments used methods that have 

already been subject to adequate peer-review. The 

methodologies used to conduct those risk assessments are 

consistent with those used to conduct inhalation risk 

assessments under the EPA’s Risk and Technology Review 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

51

(RTR) program. Because the RTR assessments are considered 

to be highly influential science assessments, the 

methodologies used to conduct them were subject to a peer 

review by EPA’s Science Advisory Board (SAB) in 2009. The 

SAB issued its peer review report in May 2010.18 The report 

generally endorsed the risk assessment methodologies used 

in the program.

The EPA’s case studies identified chromium and nickel 

emissions as the key drivers of the estimated inhalation 

cancer risks for EGUs. Because these results hinged on 

specific scientific interpretations of data used to 

characterize EGU emissions of chromium and nickel, EPA 

conducted a letter peer review of its analysis and 

interpretation of those data relative to the inhalation 

risks associated with EGU HAP emissions. The following 

sections describe the peer-review process that we followed, 

enumerate the peer-review charge questions presented to the 

peer-review panel, summarize the key recommendations from 

 

18 U.S. Environmental Protection Agency – Science Advisory Board (U.S. 

EPA-SAB). 2010. Review of EPA’s draft entitled, “Risk and Technology 

Review (RTR) Risk Assessment Methodologies: For Review by the EPA’s 

Science Advisory Board with Case Studies – MACT I Petroleum Refining 

Sources and Portland Cement Manufacturing”. EPA-SAB-10-007. May. 

Available on-line at: 

http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F0066

8381/$File/EPA-SAB-10-007-unsigned.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

52

the peer-review, and summarize our responses to those 

recommendations.

1. Summary of Peer Review Process

EPA asked three independent, external peer reviewers 

representing government, academic and the private sector to 

review of the methods for developing inhalation cancer risk 

estimates associated with emissions of chromium and nickel 

compounds from coal- and oil-fired EGUs in support of the 

appropriate and necessary finding. The approaches and 

rationale for the technical and scientific considerations 

used to derive inhalation cancer risks were summarized in 

the draft document entitled, “Methods to Develop Inhalation 

Cancer Risk Estimates for Chromium and Nickel Compounds.” 

The peer reviewers were given approximately a month to 

respond to a series of charge questions on the technical 

and scientific relevance of the approaches used to develop 

the inhalation unit risk estimates. These estimates were 

based on the speciation data available from selected source 

categories and on the available unit risk estimates (UREs) 

reflecting the dose that corresponds to a specific level of 

cancer risk. EPA also provided information on chromium 

speciation profiles for different industrial sources, as 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

53

well as information on the nickel speciation of particulate 

matter from oil-fired power plants to the peer reviewers.

2. Peer Review Charge Questions

Below we present the charge questions posed to the 

peer reviewers to help guide their review and development 

of recommendations to the EPA on key issues relevant to the 

characterization of risks from EGU emissions containing 

either chromium or nickel compounds. 

EPA asked three questions regarding chromium and 

chromium compounds:

Question 1: Do EPA’s judgments related to speciated 

chromium emissions adequately take into account the 

available chromium speciation data? 

Question 2: Has the EPA selected the species of 

chromium (i.e., hexavalent chromium) that accurately 

represents the toxicity of chromium and chromium compounds? 

Question 3: Are the assumptions used in past analysis 

scientifically defensible, and are there alternatives that 

the EPA should consider for future analysis? 

EPA asked two questions regarding nickel and nickel 

compounds:

Question 1: Do EPA's judgments related to speciated 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

54

nickel emissions adequately take into account available 

speciation data, including recent industry spectrometry 

studies?

Question 2: Based on the speciation information 

available and on what we know about the health effects of 

nickel and nickel compounds, and taking into account the 

existing Unit Risk Estimates (URE) values (i.e., values 

derived for EPA’s Integrated Risk Information System 

(IRIS), California Environmental Protection Agency (Cal 

EPA) and Texas Commission on Environmental Quality (TCEQ)), 

the EPA has provided several approaches19 to derive unit 

risk estimates that may be more scientifically defensible 

than those used in past analyses. Which of the options 

presented would result in more accurate and defensible 

characterization of risks from exposure to nickel and 

nickel compounds? Are there alternative approaches that the 

EPA should consider?

3. Summary of Peer Review Findings and Recommendations

Regarding chromium and chromium compounds, all three 

reviewers considered hexavalent chromium as the species 

 

19 See section 3.3 of U.S. Environmental Protection Agency (U.S. EPA). 

2011c. Methods to Develop Inhalation Cancer Risk Estimates for Chromium 

and Nickel Compounds. Office of Air Quality Planning and Standards.

October.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

55

likely to be driving cancer risks based on solid evidence 

from the health effects database for chromium and chromium 

compounds. All three authors also considered EPA’s use of 

the average of the range of the available speciation data 

(i.e., 12 percent and 18 percent hexavalent chromium 

contained in coal- and oil-fired EGUs, respectively) as a 

reasonable approach for the derivation of default 

speciation profiles to be used when there is no speciation 

data available. All reviewers agreed that there is high 

uncertainty associated with the variability in the 

speciation data available for chromium (e.g., range of 

approximately 4 to 23 percent chromium hexavalent from 

coal-fired units). One of the reviewers recommended several 

additional studies for EPA’s consideration. 

Regarding nickel and nickel compounds, two of the 

reviewers agreed with the views of the international 

scientific bodies, which consider nickel compounds 

carcinogenic as a group. Nickel and nickel compounds have 

been classified as human carcinogens by national and 

international scientific bodies including the International 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

56

Agency for Research on Cancer ,20 the World Health 

Organization,21 and the European Union’s Scientific 

Committee on Health and Environmental Risks22. In their 12th

Report of the Carcinogens, the National Toxicology 

Program(NTP) has classified nickel compounds as known to be 

human carcinogens based on sufficient evidence of 

carcinogenicity from studies in humans showing associations 

between exposure to nickel compounds and cancer, and 

supporting animal and mechanistic data.23 More specifically, 

this classification is based on consistent findings of 

increased risk of cancer in exposed workers, and supporting 

evidence from experimental animals that shows that exposure 

to an assortment of nickel compounds by multiple routes 

causes malignant tumors at various organ sites and in 

multiple species. The 12th Report of the Carcinogens states 

 

20 International Agency for Research on Cancer (IARC), 1990. IARC 

monographs on the evaluation of carcinogenic risks to humans. Chromium, 

nickel and welding. Vol. 49. Lyons, France: International Agency for 

Research on Cancer, World Health Organization Vol. 49:256.

21 International Labour Organization/United Nations Environment 

Programme, World Health Organization (WHO). 1991. Nickel. In 

Environmental Health Criteria No 108 Geneva.

22 European Commission, Scientific Committee on Health and Environmental 

Risks (SCHER). 2006. Opinion on: Reports on Nickel, Human Health part. 

SCHER, 11th plenary meeting of 04 May 2006 

[http://ec.europa.eu/health/ph_risk/committees/04_scher/docs/scher_o_03

4.pdf].CHER 2006.

23 National Toxicology Program (NTP). 2011. Report on Carcinogens, 

Twelfth Edition. Research Triangle Park, NC: U.S. Department of Health 

and Human Services, Public Health Service, National Toxicology Program. 

499 pp.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

57

that the “combined results of epidemiological studies, 

mechanistic studies, and carcinogenesis studies in rodents 

support the concept that nickel compounds generate nickel 

ions in target cells at sites critical for carcinogenesis, 

thus allowing consideration and evaluation of these 

compounds as a single group”. The third reviewer 

recommended that the EPA review several manuscripts on 

nickel speciation profiles showing that sulfidic nickel 

compounds (which the reviewer considered as the most potent 

carcinogens within the group of all nickel compounds) are 

present at low levels in emissions from EGUs. In addition, 

this reviewer pointed out that some authors believe that 

water soluble nickel, such as nickel sulfate, should not be 

considered a human carcinogen.

4. EPA Responses to Peer Review Recommendations

After considering the comments of all the peer 

reviewers, EPA revised the document as appropriate to 

create the final version of “Methods to Develop Inhalation 

Cancer Risk Estimates for Chromium and Nickel Compounds”.24

We summarize EPA’s basic responses to the peer review 

 

24 U.S. EPA, 2011c.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

58

comments below, first for chromium-related issues, and 

second for nickel-related issues.

a. Chromium and chromium compounds:

The EPA concluded that based on the health effects 

information available for chromium there is high confidence 

in the assumption that hexavalent chromium is the 

carcinogenic species driving the risk of chromium-emitting 

facilities and thus considered the derivation of default 

speciation profiles based on the mass of hexavalent 

chromium contained in the emissions from chromium-emitting 

facilities is a reasonable approach. As suggested by one of 

the reviewers, the EPA reviewed two potentially relevant 

studies, one of which showed coal combustion emissions 

containing as much as 43 percent hexavalent chromium25, 

which suggests that EPA's quantitative approach could, in 

fact, underestimate hexavalent chromium inhalation risks. 

However, the other study reviewed by the EPA on speciation 

of chromium in coal combustion showed hexavalent chromium 

percentage levels close to detection limits (i.e., 3 to 5 

percent of total chromium, which was close to limit of 

 

25 Galbreath KC, Zygarlicke CJ. 2004. “Formation and chemical speciation 

of arsenic-, chromium-, and nickel-bearing coal combustion PM2.5,” Fuel 

Process Technol 85:701-726.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

59

detection in this study).26 Thus, the more recent speciation 

data available is unlikely to reduce the uncertainty of the 

chromium speciation analyses used by EPA as the bases for 

risk characterization analysis.

In agreement with the peer reviewers, the EPA also 

recognizes that the confidence in the default speciation 

profiles is low because the profiles are based on a limited 

data set with a wide range of percentages of hexavalent 

chromium across the different samples. 

b. Nickel and nickel compounds:

Based on the views of the major scientific bodies 

mentioned above and expert peer reviewers that commented on 

EPA’s approaches to risk characterization of nickel 

compounds, the EPA considers all nickel compounds to be 

carcinogenic as a group and does not consider nickel 

speciation or nickel solubility to be strong determinants 

of nickel carcinogenicity. One of the reviewers suggested 

we consider different views by some authors that believe 

that water soluble nickel, such as nickel sulfate, should 

not be considered a human carcinogen This notion is based 

 

26 Huggins FE, Najih M, Huffman GP. 1999. “Direct speciation of chromium 

in coal combustion by-products by X-ray absorption fine structure 

spectroscopy,” Fuel Process Technol 78:233-242.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

60

primarily on a negative nickel sulfate 2-year NTP rodent 

bioassay (which is different than the positive 2-year NTP 

bioassay for nickel subsulfide).27,28,29 One review article 

identifies the discrepancies between the animal and human 

data (i.e., from studies of cancers in workers inhaling 

certain forms of nickel versus inhalation studies 

suggesting different carcinogenic potential in rodents with 

different nickel compounds) and states that the 

epidemiological data available clearly supports an 

association between nickel and increased cancer risk, 

although the article acknowledges that the data are weakest 

regarding water soluble nickel. In addition, the EPA 

identified a recent review30 that highlights the robustness 

and consistency of the epidemiological evidence across 

several decades showing associations between exposure to 

 

27 Oller A. 2002. “Respiratory carcinogenicity assessment of soluble 

nickel compounds.” Environ Health Perspect. 110:841-844.

28 Heller JG, Thornhill PG, Conard BR. 2009. “New views on the hypothesis 

of respiratory cancer risk from soluble nickel exposure; and 

reconsideration of this risk's historical sources in nickel 

refineries.” J Occup Med Toxicol. 4:23.

29 Goodman JE, Prueitt RL, Thakali S, and Oller AR. 2011. “The nickel 

iron bioavailability model of the carcinogenic potential of nickelcontaining substances in the lung.” Crit Rev Toxicol 41:142-174.

30 Grimsrud TK and Andersen A. “Evidence of carcinogenicity in humans of 

water-soluble nickel salts.” J Occup Med Toxicol. 2010. 5:1-7. 

Available online at http://www.ossup-med.com/content/5/1/7.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

61

nickel and nickel compounds (including nickel sulfate) and 

cancer. 

Regarding the second charge question on nickel 

compounds, two reviewers suggested using the URE derived by 

the TCEQ31 for all nickel compounds as a group, rather than 

the one derived by the Integrated Information System (IRIS, 

1991)32 specifically for nickel subsulfide. The third 

reviewer did not comment on an alternative approach. The 

EPA decided to continue using 100 percent of the current 

IRIS URE for nickel subsulfide (rather than assuming that 

65 percent of the total mass of emitted nickel might be of 

nickel subsulfide, as used in previous analyses) because 

IRIS values are at the top of our hierarchy with respect to 

the dose-response information used in EPA’s risk 

characterizations, and because of the concerns about the 

potential carcinogenicity of all forms of nickel raised by 

the major national and international scientific bodies. 

Nevertheless, taking into account that there are potential 

 

31 Texas Commission on Environmental Quality (TCEQ). 2011. Development 

Support Document for nickel and inorganic nickel compounds. Available 

online at 

http://www.tceq.state.tx.us/assets/public/implementation/tox/dsd/final/

june11/nickel_&_compounds.pdf

32 U.S. EPA, 1991. Integrated Risk Information Service (IRIS) assessment 

for nickel subsulfide. Available at: 

http://www.epa.gov/iris/subst/0273.htm.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

62

differences in toxicity and/or carcinogenic potential 

across the different nickel compounds, and given that two 

URE values have been derived for exposure to mixtures of 

nickel compounds that are 2 to 3 fold lower than the IRIS 

URE for nickel subsulfide, the EPA also considers it 

reasonable to use a value that is 50 percent of the IRIS 

URE for nickel subsulfide for providing an estimate of the 

lower end of a plausible range of cancer potency values for 

different mixtures of nickel compounds.

Although this report focused primarily on cancer risks 

associated with emissions containing nickel compounds, it 

is important to note that comparative quantitative analyses 

of non-cancer toxicity of nickel compounds indicate that 

nickel sulfate is as toxic or more toxic than nickel 

subsulfide or nickel oxide which does not support the 

notion that the solubility of nickel compounds is a strong 

determinant of its toxicity.33,34

E. Summary of Results of Revised U.S. EGU Case Studies of 

 

33 Haber LT, Allen BC, Kimmel CA. 1998. “Non-Cancer Risk Assessment for 

Nickel Compounds: Issues Associated with Dose-Response Modeling of 

Inhalation and Oral Exposures.” Toxicol Sci. 43:213-229.

34 National Toxicology Program (NTP). 1996. Technical Report Series No. 

454, Toxicology and carcinogenesis studies of nickel sulfate 

hexahydrate. July. Available online at 

http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr454.pdf.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

63

Cancer and Non-Cancer Inhalation Risks for Non-Hg HAP 

Based on the results of the peer review and public 

comments on the non-Hg case study chronic inhalation risk 

assessment, we made several changes to the emissions 

estimates, dispersion modeling, and risk characterization 

for the modeled case study facilities. Key changes include 

1) changes in emissions, 2) changes in stack parameters for 

some facilities based on new data received during the 

public comment period, 3) updated versions of AERMOD and 

its input processors (AERMAP, AERMINUTE, and AERMET) were 

used, and 4) 100 percent of the current IRIS URE for nickel 

subsulfide was used to calculate nickel-associated 

inhalation cancer risks (rather than assuming that the 

nickel might be 65 percent as potent as nickel subsulfide). 

Based on estimated actual emissions, the highest 

estimated individual lifetime cancer risk from any of the 

sixteen case study facilities was 20 in a million, driven 

by nickel emissions from the one case study facility with 

oil-fired EGUs. Of the facilities with coal-fired EGUs, 

five facilities had maximum individual cancer risks 

greater than 1 in a million (the highest was five in a 

million), four were driven by emissions of hexavalent 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

64

chromium and one was driven by emissions of nickel. There 

were also two facilities with coal-fired EGUs that had 

maximum individual cancer risks equal to 1 in a million. 

All of the facilities had non-cancer Target Organ Specific 

Hazard Index (TOSHI) values less than one, with a maximum 

TOSHI value of 0.4 (also driven by nickel emissions from 

the one case study facility with oil-fired EGUs).

Since these case studies do not cover all facilities 

in the category, and since 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 for 

the source category.

F. Public Comments and Responses to the Appropriate and 

Necessary Finding

1. Legal Aspects of Appropriate and Necessary Finding

a. History of Section 112(n)(1)(A)

Comment: One commenter provided a detailed history of 

EPA’s regulatory actions concerning EGUs and implementation 

of section 112(n)(1)(A). The same commenter implies that 

the EPA’s December 2000 appropriate and necessary finding 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

65

and listing of EGUs was flawed because the Agency did not 

comply with CAA section 307(d) rulemaking process. The 

commenter sought review of the December 2000 notice in the 

U.S. Court of Appeals for the District of Columbia Circuit, 

which was dismissed by the D.C. Circuit. Utility Air 

Regulatory Group v. EPA, No. 01-1074 (D.C. Cir. July 26, 

2001). The commenter then characterizes at length the 2005 

EPA action that revised the interpretation of section 

112(n)(1)(A) and illegally removed EGUs from the section 

112(c) list of sources that must be regulated under section 

112. See New Jersey v. EPA, 517 F.3d 574 (D.C. Cir. 2008). 

The commenter notes that the D.C. Circuit did not rule on 

the legal correctness or the sufficiency of the factual 

record supporting EPA’s December 2000 listing decision or 

on the factual correctness of EPA’s later decision to 

reverse its 112(n)(1)(A) determination. The commenter noted 

further that the D.C. Circuit indicated that the listing 

decision could be challenged when the Agency issued the 

final section 112(d) standards pursuant to section 

112(e)(4). The commenter concluded by asserting that the 

Agency could not ignore the history associated with the 

regulation of EGUs under section 112 and that two earlier 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

66

dockets - Docket ID. No. A-92-55 and Docket ID. No. EPA-HQOAR-2002-0056 – are also part of this long rulemaking 

effort and must be accounted for in conjunction with Docket 

No. EPA-HQ-OAR-2009-0234 if all pertinent material and 

comments are to be part of the rulemaking record.

Response: The commenter characterizes the regulatory 

history of the rule EPA proposed on May 3, 2011. To the 

extent that characterization is inconsistent with the 

lengthy regulatory history EPA provided in the preamble to 

the May 3, 2011 rule, we disagree. We address several of 

the statements in more detail below.

The commenter makes much of the fact that EPA did not 

go through CAA section 307(d) notice and comment rulemaking 

when making the appropriate and necessary finding and 

listing decision in December 2000. However, the commenter’s 

complaint is without foundation. The CAA does not require 

307(d) rulemaking for listing decisions. In fact, section 

112(e)(4) specifically provides that listing decisions may 

only be challenged “when the Administrator issues emission 

standards for such . . . [listed] category.” The commenter 

challenged the listing decision in the U.S. Court of 

Appeals for the District of Columbia Circuit (Court) and, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

67

on July 26, 2001, the Court granted EPA’s motion to dismiss 

that action based on the plain language of section 

112(e)(4). EPA clearly articulated its basis for listing 

EGUs in this proposed rule, which is consistent with CAA

section 307(d), and the commenter was provided an ample 

opportunity to comment. 

Finally, the commenter asserts that the rulemaking 

docket for this action is incomplete because the Agency did 

not include two earlier dockets - Docket ID. No. A-92-55 

and Docket ID. No. EPA-HQ-OAR-2002-0056 - for the Section 

112(n) Revision Rule, 70 F.R. 15994 (March 29, 2005), and 

the reconsideration of the Section 112(n) Revision Rule, 71 

F.R. 33388 (June 9, 2006), respectively. Commenter is 

incorrect because EPA incorporated by reference the two 

dockets at issue. See EPA-HQ-OAR-2009 -0234-3056. 

Comment: One commenter states that the EPA has 

assessed the public health risks posed by HAP emissions 

from coal- and oil-fired EGUs for the last 40 years. 

According to the commenter throughout that time, EPA has 

come to a single repeated conclusion the HAP emissions from 

EGUs pose little or no risk to public health. Based on this 

conclusion, EPA has properly chosen not to require EGUs to 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

68

install expensive, new pollution control equipment to 

control HAP emissions. The commenter asserts that in this 

proposed rule, the EPA shifts its opinion on the health 

impacts of EGU HAP emissions 180 degrees and now seeks to 

impose sweeping regulatory requirements on all power 

plants. Again, according to the commenter the EPA’s 

newfound concern about HAP emissions from EGUs is not based 

on new and different assessments of the public health 

consequences of EGU HAP emissions but instead on health 

benefits from the reduction of non-hazardous air 

pollutants, primarily PM, that the Agency is required to 

regulate under other provisions of the CAA. One commenter 

states that for decades the EPA set primary ambient air 

quality standards that protect public health with an 

adequate margin of safety, CAA 109(b)(1), and set secondary 

standards that are [sic] “requisite to protect the public 

health from any known or anticipated adverse effects 

associated with the presence of such air pollutant in the 

ambient air,” CAA 109(b)(2). The commenter notes that even 

if EPA now views those past PM standards as inadequate, the 

EPA has ongoing regulatory proceedings in which it can 

address any perceived health concerns. The commenter 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

69

concludes that regulation of EGU HAP emissions under 112 is 

an unlawful way to address those concerns. 

Response: The commenter is incorrect in its assertion 

that the Agency has consistently concluded that HAP 

emissions from EGUs do not present a hazard to public 

health. In the December 2000 Finding, the Agency concluded 

that HAP emissions from coal- and oil-fired EGUs do pose a 

hazard to public health and determined that it was 

appropriate and necessary to regulate such units under 

section 112 of the CAA. As a result of that finding, EPA 

added coal- and oil-fired EGUs to the CAA section 112(c) 

list of source categories for which emission standards are 

to be established pursuant to section 112(d). Further, in 

support of the proposed rule published in the Federal 

Register on May 3, 2011, EPA conducted additional extensive 

quantitative analyses, which confirm that it remains 

appropriate and necessary to regulate EGUs under CAA 

section 112. Among other things, those analyses demonstrate 

that emissions from coal- and oil-fired EGUs continue to 

pose a hazard to public health. The commenter also fails to 

note that EPA found that HAP emissions from EGUs pose a 

hazard to the environment as well.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

70

The commenter seems confused about the basis for the 

Agency’s appropriate and necessary finding because it 

maintains that EPA made the appropriate and necessary 

finding based on the health co-benefits attributable to PM 

reductions that will be achieved as a result of the 

Agency’s regulation of HAP emissions from EGUs. Nowhere in 

the May 2011 proposal does EPA state that it based the 

appropriate and necessary finding on hazards to public 

health attributable to PM emissions. The commenter’s 

allegation simply lacks foundation. The proposal 

unmistakably focuses on the hazards to public health 

associated with HAP emissions from EGUs.

Comment: One commenter states that section 112, added 

to the CAA in 1970, required the EPA to make a risk-based 

determination in order to regulate substances as HAPs. The 

EPA may regulate substances “reasonably ... anticipated to 

result in an increase in mortality or increase in serious 

illness,” to a level that protects public health with an 

“ample margin of safety.” CAA 112(a)(1). Under this 

provision, EPA regulated a number of HAPs emitted from 

industrial source categories other than EGUs. See 40 C.F.R. 

Part 63.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

71

As for EGUs, according to the commenter, the EPA found 

that the combustion of fossil fuels produces extremely 

small releases of a broad variety of substances that are 

present in trace amounts in fuels and that are removed from 

the gas stream by control equipment installed to satisfy 

other CAA requirements. The EPA, in past reviews, found 

that these HAP releases did not pose hazards to public 

health. See 48 Fed. Reg. 15,076, 15,085 (1983) 

(radionuclides). In the case of mercury specifically, EPA 

found that “coal-fired power plants ... do not emit mercury 

in such quantities that they are likely to cause ambient 

mercury concentration to exceed” a level that “will protect 

public health with an ample margin of safety.” 40 Fed. Reg. 

48,297-98 (Oct. 19,1975) (mercury); 52 Fed. Reg. 8724, 8725 

(Mar. 19, 1987) (reaffirming mercury conclusion).

In the late 1980s, the EPA was concerned that its 

prior risk assessments of individual HAP emissions from 

fossil-fuel-fired power plants may not reflect the total 

risks posed by all HAPs emitted by those sources. The EPA 

modeled the risks posed by all HAPs emitted by power plants 

(very much like the analyses the Agency would conduct for 

the Utility Study ten years later). The commenter asserts 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

72

that the modeling again failed to identify threats to 

public health that warranted regulation under an “ample 

margin of safety” test.

Response: The commenter’s statements concerning the 

pre-1990 CAA are not relevant to the current action. As the 

commenter notes, Congress enacted CAA section 112(n)(1) as 

part of the 1990 amendments to the Act. That provision 

requires, among other things, that the Agency evaluate the 

hazards to public health posed by HAP emissions from 

fossil-fuel fired EGUs. Had Congress concluded as commenter 

appears to assert that HAP emissions from EGUs did not pose 

a hazard to public health or the environment, it defies 

reason that Congress would have required EPA to conduct the 

three studies at issue in section 112(n)(1) (titled 

“Electric utility steam generating units”) and regulate 

EGUs under section 112 if the Administrator determined in 

her discretion that it was appropriate and necessary to do 

so. The Agency complied with the statutory mandates in 

section 112(n)(1) in conducting the studies and reasonably 

exercised its discretion in making the appropriate and 

necessary finding. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

73

We acknowledge, however, that Congress treated 

radionuclide emissions from EGUs differently. For 

radionuclides from EGUs (and certain other sources), 

Congress included CAA section 112(q)(3), which authorizes 

but does not require the Agency to maintain the regulations 

of radionuclides in effect prior to the 1990 amendments. 

The fact that Congress made an exception for radionuclides 

and no other HAP from EGUs further demonstrates that the 

HAP-related actions EPA took with regard to EGUs prior to 

the 1990 amendments to the CAA were not germane. 

As for the commenter’s statements about mercury 

emissions from EGUs, we find their conclusions wholly 

inconsistent with CAA section 112(n)(1). That provision is 

titled “Electric utility steam generating units,” and it 

directs EPA to conduct two mercury specific studies. See 

CAA sections 112(n)(1)(B) and 112(n)(1)(C). Commenter’s 

suggestion that EPA could or should rely on assessments of 

mercury from EGUs conducted prior to the 1990 amendments is 

not tenable. 

Finally, one commenter states that EPA conducted a 

risk assessment of all HAP from EGUs prior to the 1990 

amendments and that the Agency did not identify any HAP 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

74

that failed the “ample margin of safety” test. The 

commenter does not cite the study or provide any 

information to support the statements so we are unable to 

respond to the alleged study directly; however, the risk 

assessment conducted in support of the proposed rule did 

identify hazards to public health and the environment.

b. Interpretation of “Appropriate” and “Necessary”

Comment: One commenter states that in the preamble to 

the proposed rule, the EPA sets out its “interpretation of 

the critical terms in CAA 112(n)(1),” arguing that this 

latest interpretation is “wholly consistent with the CAA” 

and with the Agency’s earlier “December 2000 Finding.” See 

76 Fed. Reg. 24,976, 24,986/2 (May 3, 2011). The commenter 

states that throughout the proposal the EPA tries to 

suggest that it is returning to some earlier, “correct” 

interpretation of CAA section 112(n)(1) set forth in its 

December 2000 action. See, e.g., 76 Fed. Reg. at 24,989/1-2 

(“The Agency’s interpretation of the term ‘appropriate’... 

is wholly consistent with the Agency’s appropriate finding 

in December 2000”); id. at 24,992/1 (“Our interpretation of 

the necessary finding is reasonable and consistent with the 

December 2000 Finding”). According to the commenter, the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

75

EPA did not provide in December 2000 any interpretation of 

what it now characterizes as the “critical terms” of 

section 112(n)(1). See, e.g., 70 Fed. Reg. at 15,999 n.13 

(the “December 2000 finding does not provide an 

interpretation of the phrase ‘after imposition of the 

requirements of the Act”); id. at 16,000/2 (in December 

2000, EPA “did not provide an interpretation of the term 

‘appropriate’”); 76 Fed. Reg. at 24,992/1 (the “Agency did 

not expressly interpret the term necessary in the December 

2000 Finding”). The commenter believes that for that reason 

alone, it is impossible to credit EPA’s assertion that it 

“appropriately concluded that it was appropriate and 

necessary to regulate hazardous air pollutants . . . from 

EGUs” in December 2000, and that it is today merely 

“confirm[ing] that finding and conclud[ing] that it remains 

appropriate and necessary to regulate these emissions...”35

Response: The commenter disagrees with certain 

statements in the proposed rule that provide that the 

Agency’s interpretation of section 112(n)(1) is reasonable 

and consistent with the December 2000 Finding. It is 

difficult to decipher the exact complaint that the 

 

35 Id. at 24,977/3.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

76

commenter has with EPA’s proposed rule in this regard, but 

the commenter does assert that “the Agency did not provide 

in December 2000 any interpretation of what it now 

characterizes as the “critical terms” of CAA 112(n)(1).”

Commenter’s assertion lacks foundation. While the 2000 

finding did not provide detailed interpretations of the 

regulatory terms at issue, it discussed the types of 

considerations relevant to the A and N inquiry. For 

example, it is clear that the Agency was concerned with the 

then current hazards to public health and the environment 

when assessing whether it was appropriate to regulate EGUs 

under section 112. 65 FR 79830. In addition, when 

evaluating whether it was necessary to regulate utilities, 

the Agency specifically noted that “section 112 is the 

authority intended to address” hazards to public health and 

the environment posed by HAP emissions. Id. The detailed 

interpretation set forth in the proposed rule is consistent 

with the 2000 Finding, but EPA does not assert that the 

interpretation is in any way necessary to support the 

factual conclusions reached in that notice. Instead, we 

noted in the proposed rule that our interpretation is 

consistent with the 2000 Finding because in 2005 we 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

77

interpreted the statute in a manner that was not consistent 

with the 2000 finding. If anything, making an 

interpretation that directly contradicted a prior factual 

conclusion was improper. At least one commenter that takes 

issue with the interpretation in the proposed rule 

participated in the 2005 action and it did not complain at 

that time about the Agency establishing an express 

interpretation that obviously was in conflict with a prior 

Finding. We are confused by the inconsistent approach to 

evaluating EPA actions. In any case, the commenter has 

provided no legal support for its position that the Agency 

erred in interpreting the statute in a manner that is 

consistent with a prior factual finding. 

Comment: Several commenters state that a finding that 

HAP regulation is “appropriate” for a single HAP does not 

indicate that it is “appropriate” to regulate all HAPs. 

According to the commenters the sponsor of the House bill 

that became § 112(n)(1)(A) provides an explanation that 

contradicts EPA’s approach. “Pursuant to section 112(n), 

the Administrator may regulate fossil fuel fired electric 

utility steam generating units only if the studies 

described in section 112(n) clearly establish that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

78

emissions of any pollutant, or aggregate of pollutants, 

from such units cause a significant risk of serious adverse 

effects on the public health. Thus, . . . he may regulate 

only those units that he determines – after taking into 

account compliance with all provisions of the act and any 

other Federal, State, or local regulation and voluntary 

emission reductions – have been demonstrated to cause a 

significant threat of serious adverse effects on the public 

health.” 136 Cong. Rec. H12,934 (daily ed. Oct. 26, 1990) 

(statement of Rep. Michael Oxley).

The commenters state that the EPA position is premised 

on the assumption that “regulation under section 112” 

necessarily means “regulation under 112(d)” and falsely 

premised on the assumption that source categories listed by 

operation of § 112(n)(1)(A) cannot be regulated 

differently. The language of § 112(n)(1)(a) reflects 

Congress’ intent that “regulation of HAPs from EGUs was not 

intended to operate under § 112(d) but was instead intended 

to be tailored to the findings of the utility study 

mandated by §112(n)(1)(A).” 

Response: The commenter maintains that the Agency’s 

interpretation of CAA section 112(n)(1) is flawed in many 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

79

respects. The primary support for commenter’s arguments 

against EPA’s interpretation, including in the comment 

above, is legislative history in the form of statements 

from one Congressman, Representative Oxley. In the May 3, 

2011, proposed rule, EPA did not give much consideration 

to, and in fact did not even mention, the legislative 

history cited by the commenter because the Supreme Court 

has repeatedly stated that the statements of one 

Congressperson alone should not be given much weight. See 

Brock v. Pierce County, 476 U.S. 253, 263 (1986) (finding 

that “statements by individual legislators should not be 

given controlling effect, but when they are consistent with 

the statutory language and other legislative history, they 

provide evidence of Congress’ intent.”) (emphasis added) 

(citation omitted); Garcia, et. al., v. U.S., 469 U.S. 70, 

78 (1984), citing Zuber v. Allen, 396 U.S. 168, 187 (1969) 

(reiterating its prior findings the Court indicated that 

isolated statements “are ‘not impressive legislative 

history.’”); Weinberger, et. al., v. Rossi et. al., 456 

U.S. 25, 35 (declining to make a ruling based on “one 

isolated remark by a single Senator”); Consumer Product 

Safety Comm., et. al. v. GTE Sylvania, Inc., et. al., 447 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

80

U.S. 102, 117-118 (1980) (declining to give much weight to 

isolated remarks of one Representative); Chrysler Corp. v. 

Brown, et. al., 441 U.S. 281, 311 (1979) (finding that

“[t]he remarks of a single legislator, even the sponsor, 

are not controlling in analyzing legislative history.”); 

Zuber, 396 U.S. at 186 (concluding that “[f]loor debates 

reflect at best the understanding of individual 

Congressmen.”); and U.S. v. O’Brien, 391 U.S. 367, 384 

(1968) (in evaluating the statements of a handful of 

Congressmen, the Court concluded that “[w]hat motivates one 

legislator to make a speech about a statute is not 

necessarily what motivates scores of others to enact 

it...”).36 As these cases show, the Supreme Court does not 

 

36 The D.C. Circuit has similarly refused to rely on such limited 

legislative history, as evidenced by NRDC v. EPA in which that Court 

stated:

It is true . . . that we 'may examine the statute's legislative 

history in order to "shed new light on congressional intent, 

notwithstanding statutory language that appears superficially 

clear."'" Consumer Elecs. Ass'n v. FCC, 358 U.S. App. D.C. 180, 

347 F.3d 291, 298 (D.C. Cir. 2003) (quoting NRA of Am., Inc. v. 

Reno, 342 U.S. App. D.C. 231, 216 F.3d 122, 127 (D.C. Cir. 2000)

(quoting Natural Res. Def. Council, Inc. v. Browner, 313 U.S. 

App. D.C. 37, 57 F.3d 1122, 1127 (D.C. Cir. 1995))). But "'the 

bar is high,'" id. (quoting Williams Cos. v. FERC, 358 U.S. App. 

D.C. 109, 345 F.3d 910, 914 (D.C. Cir. 2003)), and "only rarely 

have we relied on legislative history to constrict the otherwise 

broad application of a statute indicated by its text," id. Here, 

EPA cannot clear the high bar relying solely on the isolated 

remarks of a few senators. Cf. Davis County Solid Waste Mgmt. v. 

EPA, 322 U.S. App. D.C. 107, 101 F.3d 1395, 1407 (D.C. Cir. 1996)

(finding contradictory comments of individual [**23] senators 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

81

give any weight to the statements of an individual 

Congressperson, except when the statements are supported by 

other legislative history and the clear intent of the 

statute. The Commenter has cited no case law that would 

support any reliance on such limited legislative history. 

We could not find, and the commenter has not cited, 

any other legislative history to support Representative 

Oxley’s statement, and the lack of additional support makes 

the statement of little utility or import under the case 

law we reviewed. In fact, there does not appear to be 

anything in the House, Senate, or Committee Reports that 

supports Oxley’s statement. We find the lack of support for 

the Oxley’s statement in the Committee Report particularly 

telling since, as the commenter notes, the House and Senate 

bills required different approaches to regulating EGUs 

under section 112, with the Senate bill requiring EGUs be 

 

during section 129 debates "too 'meager [a] record'" to rely on 

"'given the clear statutory language' to the contrary") (quoting 

Engine Mfrs. Ass'n v. EPA, 319 U.S. App. D.C. 12, 88 F.3d 1075, 

1091 (D.C. Cir. 1996)). In any event, the remarks that EPA cites, 

when viewed in the context of the express and unambiguous 

provisions in the statute, show only that when the Congress 

wanted to exempt a particular kind of solid waste combustor from 

section 129's coverage--based on the desirability of resource 

recovery or any other interest--it knew how to accomplish this 

through an express statutory exception and in fact did so for 

four specific classes of combustion units. See 42 U.S.C. § 

7429(g)(1)

489 F.3d 1250, 1259 (D.C. Cir. 2007).
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

82

regulated prior to the Utility Study. In fact, legislative 

statements from Senator Durenberger, a supporter of the 

Senate version, demonstrate that others would almost 

certainly not have agreed with Oxley’s interpretation. For 

example, Senator Durenberger stated: “It seems to me 

inequitable to impose a regulatory regime on every industry 

in America and then exempt one category, especially a 

category like power plants which are a significant part of 

the air toxics problem.”

Senator Durenberger discussed the negotiations with 

the Administration and the industry push to avoid 

regulation, including industry arguments for not regulating 

mercury from EGUs: “[t]he utility industry continued to 

adamantly oppose [regulation under section 112]. First, 

they argued that mercury isn’t much of an environmental 

problem. But as the evidence mounted over the summer and it 

became clear that mercury is a substantial threat to the 

health of our lakes, rivers and estuaries and that power 

plants are among the principal culprits, they changed their 

tactic. Now they are arguing that mercury is a global 

problem so severe that just cleaning up U.S. power plants 

won’t make enough of a difference to be worth it. They’ve 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

83

gone from “we’re not a problem” to “you can’t regulate us 

until you address the whole global problem.” Recasting an 

issue that way is not new around here. So, it is not a 

surprise. But it does suggest the direction in which this 

debate will be heading in the next few years.”

Senator Durenberger also explained why the House 

version was adopted: “[g]iven that a resolution of the 

difficult issues in the conference were necessary to 

conclude work on this bill, the Senate proposed to recede 

to the House provision which was taken from the original 

administration bill. It provides for a 3-year study of 

utility emissions followed by regulation to the extent that 

the Administrator finds them necessary.”

Senator Durenberger’s statements indicate that it is 

unlikely that he would agree with Oxley’s interpretation of 

section 112(n)(1), a provision that is inarguably ambiguous 

and that clearly provides the Agency with considerable 

discretion; and nothing indicates that others in the Senate 

(or for that matter anyone else in the House) would agree 

with that interpretation. Given this disparity, EPA 

reasonably declined to discuss the legislative history in 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

84

the proposed rule and we think it would be unreasonably to 

ascribe Oxley’s statements to the entire Congress.37

Moreover, Oxley’s statement directly conflicts with 

the statutory text. Oxley states that “[the Administrator 

may regulate only those units that he determines – after 

taking into account compliance with all provisions of the 

act and any other Federal, State, or local regulation and 

voluntary emission reductions - have been demonstrated to 

cause a significant threat of serious adverse effects on 

the public health.” 136 Cong. Rec. H12934 (daily ed. Oct. 

26, 1990), reprinted in 1 1990 Legis. Hist. at 1416-17 

(emphasis added). But the Utility Study required under 

section 112(n)(1)(A) directs the Agency to consider the 

hazards to public health reasonably anticipated to occur 

after “imposition of the requirements of [the Clean Air 

Act].” EPA was not required to consider state or local 

regulations or voluntary emission reduction programs in the 

 

37 Though we in no way relied on Senator Durenberger’s statement 

concerning regulation of EGUs under section 112, we find his statements 

somewhat prophetic given the arguments of industry commenters and the 

fact that EGUs have avoided proper regulation under section 112 for 

almost a decade.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

85

Utility Study, and that study is the only condition 

precedent to making the appropriate and necessary finding.38

For all these reasons, we maintain that our 

interpretation is reasonable and consistent with the 

statute and, for those reasons, should be afforded 

deference. In addition, we believe that any arguments 

against our interpretation that rely on Congressman Oxley’s 

statements are without merit. 

Comment: One commenter states that the EPA does 

acknowledge that, in many significant respects, its new 

interpretation of CAA 112(n)(1) “differs from that set 

forth” in the Agency’s 2005 rulemaking, but argues that its 

change of position is permissible. See 76 Fed. Reg. at 

24,988/1 (“[T]o the extent our interpretation differs from 

that set forth in the 2005 Action, we explain the basis for 

that difference and why the interpretation, as set forth in 

this preamble, is reasonable.”). In support, the EPA cites 

National Cable & Telecommunication Ass’n v. Brand X 

 

38 In addition, EPA only considered CAA requirements in the Utility 

Study and this was the correct approach because Congress knew how to 

require consideration of non-Federal requirements when directing EPA to 

conduct a study or assessment. See CAA section 112(n)(5) (Congress 

required EPA to conduct an assessment of hydrogen sulfide from oil and 

gas extraction activities and provided that the assessment “shall 

include review of existing State and industry control standards, 

techniques and enforcement.”).
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

86

Internet Services, 545 U.S. 967 (2005). It is true that, in 

Brand X Internet Services, the Supreme Court explained 

that, if an agency “adequately explains the reasons for a 

reversal of policy,” such change is “not invalidating,” 

since the “whole point of Chevron is to leave the 

discretion provided by the ambiguities of a statute with 

the implementing agency.” 545 U.S. at 981 (internal 

quotations omitted). But all Brand X Internet Services was 

saying is that “[a]gency inconsistency is not a basis for 

declining to analyze the agency’s interpretation under the 

Chevron framework.” Id.

According to the commenter it is not enough that EPA 

has purported to “explain” why it has abandoned the 

interpretation of CAA 112(n)(1) which it adopted in 2005. 

Under the first step of Chevron, the Agency’s latest 

interpretation must still be consistent with congressional 

intent. See Chevron v. NRDC, 467 U.S. at 842-43. Under the 

second step of Chevron, if there is discretion for EPA to 

exercise in interpreting the “critical terms” of CAA 

112(n)(1), the Agency must properly define the range of 

that discretion and then act reasonably in exercising that 

discretion. See Chevron, 467 U.S. at 843; see also Village 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

87

of Barrington, Ill. v. Surface Transportation Bd., No. 09-

1002 (D.C. Cir. Mar. 15, 2011). As discussed below, EPA has 

failed to do so here. In each instance, the Agency has 

departed from the correct interpretation of CAA 112(n)(1) 

that it adopted in 2005, seizing instead upon a new 

approach that is contrary to the plain language of the CAA 

itself.

Response: Commenter here appears to argue that EPA’s 

interpretation of section 112(n)(1) is not consistent with 

the plain language of the statute, implying that the 

statute is clear and must be evaluated under step one of 

Chevron. See Chevron v. NRDC, 467 U.S. 837 842-42 (1984) 

(finding that when the legislative intent is clear no 

additional analysis is required). However, much of the 

commenter’s argument against EPA’s interpretation is based 

on the flawed legislative history discussed above. As 

explained in the preamble to the proposed rule, the statute 

is subject to multiple interpretations, and we provided a 

reasoned basis for all the changes made to the 2005 

interpretation. Furthermore, we properly considered the 

scope of our discretion in interpreting the statute. We 

believe the interpretation set forth in the proposed rule 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

88

is a more natural and reasonable interpretation of the Act 

and, therefore, the Agency should be afforded deference 

pursuant to National Cable & Telecommunication Ass’n v. 

Brand X Internet Services, 545 U.S. 967 (2005). 

Comment: One commenter asserts that the EPA’s ultimate 

motivation for rejecting its prior interpretation of CAA 

112(n)(1) and embracing this flawed new approach is made 

clear from the very outset of the proposal. According to 

the commenter the EPA touts the fact that “one consequence” 

of the MACT rule would be that the “market for electricity 

in the U.S. will be more level” and “no longer skewed in 

favor of the higher polluting units that were exempted from 

the CAA at its inception on Congress’ assumption that their 

useful life was near an end.” See 76 Fed. Reg. at 24,979/2. 

The MACT rule would “require companies to make a decision –

control HAP emissions from virtually uncontrolled sources” 

or else “retire these sometimes 60 year old units and shift 

their emphasis to more efficient, cleaner modern methods of 

generation, including modern coal-fired generation.” Id.

The commenter states that this remarkably forthright 

statement establishes is that the underlying basis for the 

EPA’s proposal to regulate EGUs under CAA 112 is not to 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

89

address any “hazards to public health” that might be 

attributed to the emission by EGUs of HAPs listed under CAA 

§ 112(b). Rather, according to commenter, the EPA is 

utilizing the regulation of EGUs under CAA 112 as a means 

to an entirely different end: i.e., to force the imposition 

of controls that will also have the result of reducing nonHAP emissions (primarily PM) or force the shutdown those 

units for which the cost of such controls would be 

prohibitive. At the same time, the EPA tacitly acknowledges 

that it cannot hope to make out a case that the regulation 

of EGU HAP emissions is “appropriate and necessary” within 

the meaning of CAA 112(n)(1). The commenter asserts that 

the only HAP whose health-related benefits the EPA 

quantifies is mercury. Elsewhere, the commenter states EPA 

contends that there are “additional health and 

environmental effects” attributable to HAPs other than 

mercury, but admits that it has “not quantified” those 

risks due supposedly to “insufficient information.” See 76 

Fed. Reg. at 24,999/2. With respect to mercury the 

commenter states that the benefits are so questionable and 

miniscule, some $4 million to $6 million (given a 3% 

discount rate), that compared to the total social costs of 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

90

the rule (i.e., nearly $11 billion) the rule cannot be 

justified were EPA properly to interpret CAA 112(n)(1) and 

undertake the sort of regulatory analysis Congress 

intended. The commenter states that the reason that the EPA 

touts in this rulemaking the health benefits the EPA 

attributes to the reduction of non-hazardous air pollutants 

(again, primarily PM), the regulation of which is 

authorized under provisions of the CAA apart from CAA 112, 

is to elide the inconvenient truth regarding the truly 

trivial nature of the benefits attributable to HAP 

regulation itself. The commenter concludes that the EPA 

distorts CAA 112(n)(1)(A) “beyond all recognition.” 

One commenter states that the EPA is directed by CAA 

112(n)(1)(A) to study the “hazards to public health 

anticipated to occur as a result of emissions” by EGUs of 

“pollutants listed under subsection (b) of this section” –

i.e., HAPs and HAPs alone. Thereafter, EPA is authorized to 

regulate EGU HAP emissions if, and only if, they determine 

that “such regulation” of HAP emissions is “appropriate and 

necessary” to address the “hazards to public health” that 

may be attributable to HAP emissions. According to the 

commenter, by contrast, in this rulemaking, the EPA has 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

91

seized upon the fact that the control of EGU HAP emissions 

will also control non-HAPs (such as PM), and then seeks to 

justify the regulation of HAP emissions based almost 

entirely on the health benefits of the reductions in nonHAP emissions that would be coincidentally achieved. The 

commenter believes that this “regulatory sleight-of-hand” 

runs afoul of congressional intent and is unlawful. Apart 

from EPA’s fundamentally unlawful attempt to use the CAA 

112(n)(1) process to impose controls on EGUs to regulate 

non-HAP pollutants, a number of other legal errors pervade 

EPA’s proposal. 

Response: The commenter alleges that the healthrelated benefits to regulating HAP emissions from EGUs are 

“questionable and miniscule,” and that the only real 

benefits stem from non-HAP emissions, such as PM. The 

commenter also implies that regulation of HAP is nothing 

more than a straw man and that the Agency’s ultimate goal 

is to regulate other pollutants, and specifically PM. These 

allegations are wholly without merit. The Agency has 

conducted comprehensive technical analyses that confirm 

that HAP emissions from EGUs pose a hazard to public 

health. The analyses are discussed at length elsewhere in 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

92

this final rule, and a review of the proposed and final 

rules utterly refutes commenter’s assertion that PM 

reductions form the basis for the appropriate and necessary 

finding. PM benefits are only discussed in the Regulatory 

Impact Analysis accompanying the rule

In addition, the commenter appears to ignore the 

Agency’s findings concerning the hazards to public health 

and the environment posed by HAP emissions simply because 

the Agency is not able to quantify the benefits associated 

with reductions of HAP emissions from EGUs or because the 

benefits that are quantified are small in relation to the 

co-benefits achieved through reductions in non-HAP air 

pollutants. What the commenter conveniently omits is the 

fact that the Agency is not required to quantify any

benefits under the CAA before regulating HAP emissions from 

EGUs. The statute does not require any consideration of 

costs or benefits and the commenter has not shown that such 

considerations are required under section 112. As explained 

below, EPA does not consider costs when determining whether 

to regulate EGUs under section 112.

Comment: One commenter states that EPA has ignored the 

language and intent of CAA §112(n)(1)(A) and its 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

93

interpretation of this provision violates step one of 

Chevron. Under Chevron where the “intent of Congress is 

clear,” that is the “end of the matter,” for both the 

implementing agency and a reviewing court “must give effect 

to the unambiguously expressed intent of Congress.” 

Chevron, 467 U.S. at 842-43. The commenter asserts that the 

legislative history of CAA §112(n)(1)(A) “sheds 

considerable light on Congress’ unique approach to 

regulation of EGUs under CAA §112.” According to the 

commenter on April 3, 1990, the Senate passed S. 1630. The 

Senate bill would have required EPA to list EGUs under CAA 

§112(c) and to regulate them under the MACT provisions of 

CAA §112(d). See S. 1630 §301, 3 1990 Legis. Hist. at 4407. 

Thereafter, the House of Representatives passed a modified 

version of S. 1630 on May 23, 1990. This House version 

substantially changed the provisions of CAA §112 as they 

applied to EGUs. See 1 1990 Legis. Hist. at 572-73 The 

House version was virtually identical to the current CAA 

§112(n)(1)(A), and was ultimately adopted by the conference 

committee, enacted by Congress and signed into law. 

According to the commenter Congress expressly rejected the 

“list-under-(c)-and-regulate-under-(d)” approach that S. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

94

1630 would have applied to EGUs, and which Congress did 

choose to apply to other source categories. Commenter 

states that EPA’s interpretation that the Agency is 

“required to establish emission standards for EGUs 

consistent with the requirements set forth in section 

112(d)” (Id. at 24,993/3) fails to take the legislative 

history into account.

Response: For the reasons stated above, we believe 

commenter’s reliance on the single statement of one 

Representative is flawed. In addition, in a footnote 

commenter states that EPA did recognize a “need to address” 

the legislative history in its 2005 action. Commenter cites 

no case law to support this “need to address” unpersuasive 

legislative history argument. Further, in the 2005 action, 

EPA relegated to a footnote the Oxley statement that 

commenter relies on so heavily even though the statement 

supported the interpretation we provided in that rule. We 

recognized what the commenter fails to, that the Agency 

cannot argue that the meaning of section 112(n)(1)(A) is 

clear based on the statements of one Congressman. 

Commenter is incorrect when it asserts that EPA’s 

opinion is of no moment. The Agency tasked with 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

95

implementing an ambiguous statute is given considerable 

deference in interpreting the provision. Commenter’s 

assertion that Congress unambiguously defined the factors 

to consider in making the appropriate determination is 

wholly without merit. We explain in the proposed rule the 

basis for the Agency’s interpretation, and we are not 

revising that interpretation based on the comments 

received.

c. Consideration of Both Public Health and Environmental 

Effects

Comment: Several commenters state that EPA misreads 

CAA §112(n)(1)(B) and (C) to inject environmental effects 

in the CAA§112(n)(1)(A) determination. According to one 

commenter the plain language of CAA§112(n)(1) establishes 

that regulation of EGUs is to be predicated solely on 

“hazards to public health” attributable to HAP emissions. 

The legislative history providing that the EPA “may 

regulate [EGUs] only if the studies described in section 

112(n) clearly establish that emissions of any pollutant... 

from such units cause a significant risk of serious adverse 

risk to the public health” confirms that plain language. 

See Oxley Statement at 1416-17. The commenter further 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

96

states that nothing on the face of (n)(1)(A) indicates that 

Congress intended that EPA should (or must) take into 

account any additional information that might be developed 

through the other studies mentioned in subparagraphs 

(n)(1)(B) and (C) (i.e., the Mercury Study and the NAS 

Study).

Response: Commenter again relies on the statements of 

one Representative to attack EPA’s reasoned interpretation 

of an ambiguous statute. To the extent the commenter’s 

arguments rely on this paltry evidence, and they rely on it 

to a significant degree, we need not address them as we 

have explained above. Because we have established that we 

are interpreting ambiguous statutory provisions, EPA’s 

interpretation, not commenter’s, is entitled to 

considerable deference because it is a reasonable reading 

of the statute. Chevron, 467 U.S. at 843-44. The Agency 

directs attention to section III.A. of the proposed rule 

for responses to commenter’s arguments as we are not 

revising our interpretation.

Commenter appears to maintain that EPA must interpret 

the scope of the appropriate and necessary finding in the 

context of the section 112(n)(1)(A) Utility Study, such 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

97

that only hazards to public health and only EGU HAP 

emissions may be considered. The commenter incorrectly 

conflates the requirements for the Utility Study with the 

requirement to regulate EGUs under section 112 if EPA 

determines it is appropriate and necessary to do so. The 

commenter concedes that the Agency may consider information 

other than that contained in the Utility Study, but only to 

the extent it relates specifically to hazards to public 

health directly attributable to HAP emissions from EGUs. We 

agree that we may consider additional information other 

than that contained in the Utility Study, as we stated in 

the proposed rule, because courts do not interpret phrases 

like “after considering the results of” in a manner that 

precludes the consideration of other information. See 

United States v. United Technologies Corp., 985 F.2d 1148, 

1158 (2nd Cir. 1993) (“based upon” does not mean “solely)39; 

see also 76 FR 24988. We further explained in the proposed 

rule that it was reasonable to interpret the scope of the 

 

39 Several commenters have taken issue with our citation to United 

States v. United Technologies Corp. because the language at issue in 

that case was “based upon” and the language of section 112(n)(1)(A) is 

“after considering the results of.” We believe that, if anything, 

“based upon” is more prescriptive than “after considering the results 

of” such that the case supports the Agency’s interpretation that 

additional information other than the Utility Study may be considered 

in making the appropriate and necessary finding. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

98

appropriate and necessary finding in the context of all 

three studies required under section 112(n)(1) because the 

provision is title “Electric utility steam generating 

units.” 76 FR 24986-87. Commenter has provided nothing of 

significance to support its stunted interpretation of our 

authority. Id. 

The commenter also argues that the statute clearly 

prohibits the Agency from considering adverse environmental 

effects or the cumulative effects of HAP emissions from 

EGUs and other sources based on its claim that the statute 

is clear when one properly considers the legislative 

history. Again commenter has provided no support for its 

contention other than the statements of one Representative 

and the improper conflation of the section 112(n)(1)(A) 

direction on the conduct of the Utility Study and the 

appropriate and necessary finding. Congress left it to the 

Agency to determine whether it is appropriate and necessary 

to regulate EGUs under section 112 and the statute does not 

limit the Agency to considering only hazards to public 

health and only harms directly attributable to EGUs. 

Commenter does state that Congress specifically told EPA 

when it wanted EPA to consider adverse environmental 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

99

effects in section 112 and cites to several provisions of 

the Act that require consideration of adverse environmental 

effects. Commenter conveniently ignores section 

112(n)(1)(B), which requires consideration of adverse 

environmental effect, and all of the other provisions have 

purposes that are distinguishable from section 112(n)(1). 

Furthermore, EPA rightly concluded that we should protect 

against identified or potential adverse environmental 

effects absent clear direction to the contrary. Concerning 

the consideration of the cumulative effect of HAP emissions 

from EGUs and other sources, we provided a reasonable 

interpretation of the statute and noted that our 

interpretation, unlike commenters, does not “ignore the 

manner in which public health and the environment are 

affected by air pollution. An individual that suffers 

adverse health effects as the result of the combined HAP 

emissions from EGUs and other sources is harmed, 

irrespective of whether HAP emissions from EGUs alone would 

cause the harm.” 76 FR 24988. 

d. Finding for all HAPs to be Regulated

Comment: Several commenters state that for those EGU 

HAPs for which the Agency makes no Section 112(n)(1)(A) 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

100

determination, their regulation under CAA §112 is not 

authorized. Accordingly, to the extent that the EPA reads 

CAA § 112, as construed by National Lime Ass’n, as 

compelling it to regulate all HAPs emitted by EGUs, should 

the Agency make an “appropriate and necessary” 

determination under CAA § 112(n)(1)(A) with respect to a 

single HAP (e.g., mercury), the EPA stands poised to commit 

a fundamental legal error that will condemn the final rule 

on review. Cf., e.g., PDK Laboratories, Inc., 362 F.3d at 

797-98; Holland v. Nat’l Mining Ass’n, 309 F.3d at 817 

(where an agency applies a Court of Appeals “interpretation 

... because it believed that it had no choice” and that it 

“was effectively ‘coerced’ to do so,” then the agency 

“cannot be deemed to have exercised its reasoned 

judgment”).

Response: We do not agree with commenter’s assertion 

that Congress intended EPA to regulate only those EGU HAP 

emissions for which an appropriate and necessary finding is 

made, and commenter has cited no provision of the statute 

that states a contrary position. EPA reasonably concluded 

that we must find it “appropriate” to regulate EGUs under 

section 112 if we determine that a single HAP emitted from 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

101

EGUs poses a hazard to public health or the environment. If 

we also find that regulation is necessary, the Agency is 

authorized to list EGUs pursuant to section 112(c) because 

listing is the logical first step in regulating source 

categories that satisfy the statutory criteria for listing 

under the statutory framework of section 112. See New 

Jersey, 517 F.3d at As we noted in the preamble to the 

proposed rule, D.C. Circuit precedent requires the Agency 

to regulate all HAP from major sources of HAP emissions. 

National Lime Ass’n v. EPA, 233 F.3d 625, 633 (D.C. Cir. 

2000). 76 FR 24989.

Commenter does not explain its issues with our 

interpretation of how regulation under section 112 works –

i.e. making a determination that a source category should 

be listed under section 112(c), listing the source category 

under section 112(c), regulating the source category under 

section 112(d), and conducting the residual risk review for 

sources subject to MACT standards pursuant to section 

112(f). Instead it asserts that our decision is flawed 

because the interpretation we provided does not account for 

all the alternatives for regulating EGUs under section 112, 

thus we have not properly exercised our discretion and that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

102

is a fatal flaw. But what commenter has not done is 

provided an alternative theory for regulating EGUs under 

section 112, other than to blithely state that EPA could 

regulate under section 112(n)(1), and we have been unable 

to identify one absent clear statutory direction. However, 

even if we were to determine that we could issue standards 

pursuant to section 112(n)(1), or some other alternative, 

we would decline to do so for several reasons. First, 

section 112(n)(1) provides no guidance on how to establish 

standards and any mechanism we devised, absent explicit 

statutory support, would likely receive less deference than 

a section 112(d) standard issued in the same manner in 

which the Agency issues standards for other listed source 

categories. Second, Congress did provide a mechanism for 

establishing emission standards for HAP emissions from 

stationary sources and it is reasonable to use that 

mechanism to regulate HAP emissions from EGUs. Third, we do 

not believe that Congress intended to treat EGUs different 

from other sources, except in the manner in which they are 

listed. Finally, we believe section 112(d) standards 

provide the best chance of addressing the hazards to human 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

103

health and the environment posed by HAP emissions from 

EGUs. 

e. Considering Cost in Finding

Comment: Two commenters state that a natural reading 

of the term “appropriate” would include the consideration 

of costs. According to the commenters something may be 

found to be “appropriate” where it is “specially suitable,” 

“fit,” or “proper.” See Webster’s Third New International 

Dictionary at 106 (1993). The term “appropriate” carries 

with it the connotation of something that is “suitable or

proper in the circumstances.” See New Oxford American 

Dictionary (2d Ed. 2005) Considering the costs associated 

with undertaking a particular action is inextricably linked 

with any determination as to whether that action is 

“specially suitable” or “proper in the circumstances.” 

Commenter notes that in 2005 (70 Fed. Reg. 15,994, 16,000 

(Mar. 29, 2005)) the EPA used the dictionary definition of 

“appropriate,” as being “especially suitable or compatible” 

and that it would be difficult to fathom how a regulatory 

program could be either “suitable” or “compatible” for a 

given public health objective without consideration of 

cost.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

104

Response: Commenters first take issue with EPA’s 

explanation of why the Agency determined that costs should 

not be considered in making the appropriate determination. 

What commenters do not identify is an express statutory 

requirement that the Agency consider costs in making the 

appropriate determination. Congress treated the regulation 

of HAP emissions differently in the 1990 CAA amendments 

because the Agency was not acting quickly enough to address 

these air pollutants with the potential to adversely affect 

human health and the environment in such small amounts. See 

New Jersey, 517 F.3d at 578. For this reason alone, it is 

reasonable to make the listing decision, including the 

appropriate determination, without considering costs. 

Congress could easily have required the Agency to consider 

costs, and, because it did not, commenter’s assertion that 

the Agency’s conclusion does not withstand scrutiny are 

unfounded. 

Commenters next argues that the Agency is compelled by 

the statute to consider costs based on a dictionary 

definition of “appropriate” and the section 112(n)(1)(A) 

direction to consider alternative control strategies for 

regulating HAP emissions in the Utility Study. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

105

Concerning the definition of “appropriate”, Commenters 

state: “Not only is it “reasonable” for EPA to consider 

costs in determining whether it is “appropriate” to 

regulate EGU HAP emissions, a natural reading of the term 

indicates that excluding the consideration of costs would 

be entirely unreasonable. Something may be found to be 

“appropriate” where it is “specially suitable,” “fit,” or 

“proper.” See Webster’s Third New International Dictionary 

at 106 (1993). The term “appropriate” carries with it the 

connotation of something that is “suitable or proper in the 

circumstances.” See New Oxford American Dictionary (2d Ed. 

2005) at 76. Considering the costs associated with 

undertaking a particular action is inextricably linked with 

any determination as to whether that action is “specially 

suitable” or “proper in the circumstances.”

EPA believes the definition of “appropriate” 

commenters provide wholly support our interpretation and 

nothing about the definition compels a consideration of 

costs. It is appropriate to regulate EGUs under section 112 

because EPA has determined that HAP emissions from EGUs 

pose hazards to public health and the environment and 

section 112 is “specially suitable” for regulating HAP 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

106

emissions, and, furthermore, Congress specifically 

designated section 112 as the “proper” authority for 

regulations HAP emissions from stationary sources, 

including EGUs. Section 112 is “suitable [and] proper in 

the circumstances” because EPA has identified a hazard to 

public health and the environment and Congress directed the 

Agency to regulate HAP emissions from EGUs under that 

provision if we make such a finding. Cost does not have to 

be read into the definition of “appropriate” as commenter 

suggests.

Commenters’ argument that costs must be considered 

based on the section 112(n)(1)(A) requirement to “develop 

and describe alternative control strategies” in the Utility 

Study is equally flawed. The argument is flawed because 

Congress did not direct the Agency to consider in the 

Utility Study the costs of the controls when evaluating the 

alternative control strategies. In addition, EPA did not in 

fact consider the costs of the alternative controls in the 

Utility Study. In a footnote, commenter attempts to refute 

EPA’s statement in the proposed rule that EPA did not 

consider costs in the 2000 Finding by pointing to the only 

two mentions of cost in that notice. But EPA did not say 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

107

that costs were not mentioned in the 2000 Finding and a 

review of the regulatory finding will show that costs were 

not considered in the regulatory finding. 65 FR 79830 

(December 20, 2000) (“Section III. What is EPA’s Regulatory 

Finding?”).

f. Considering requirements of the CAA in “Necessary”

Comment: Several commenters disagree with EPA’s 

position that it need consider “only those requirements 

that Congress directly imposed on EGUs through the CAA as 

amended in 1990,” for which “EPA could reasonably predict 

HAP emission reductions at the time of the Utility Study.” 

According to the commenters the statutory language of 

112(n)(1) requires that EPA consider the scope and effect 

of EGU HAP emissions after the imposition of all of the 

“requirements” of the CAA, not just the Acid Rain program. 

It would have been easy enough for Congress in subparagraph 

(n)(1)(A) to specify “after imposition of the requirements 

of Title IV of this chapter,” but Congress did not. 

Commenters further add that the legislative history 

confirms that Congress meant something much broader than 

that, providing that EPA is authorized to regulate EGUs 

under CAA § 112 only after “taking into account compliance 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

108

with all provisions of the act and any other Federal, 

State, or local regulation and voluntary emission 

reductions.” The commenters provides that the CAA’s 

“requirements” include the submission by states of ozone 

and fine PM attainment demonstrations, as well as SIP 

provisions needed to reach attainment of the NAAQS because 

such provisions could include controls on EGUs to reduce 

SO2 and NOx, which controls could also result in a 

reduction in mercury emissions.

Response: Commenter’s characterization of the facts is 

flawed and its reliance on legislative history that is in 

direct conflict with the express terms of the statute is 

unfounded. 

On the facts, EPA explained in the proposed rule its 

interpretation of the phrase “after imposition of the 

requirements of [the Act]” as it related to the conduct of 

the Utility Study. 76 FR 24990. We reasonably concluded 

that since Congress only provided three years after 

enactment to conduct the study that the phrase referred to 

requirements that were directly imposed on EGUs through the 

CAA amendments and for which the Agency could reasonably 

predict co-benefit HAP emission reductions. Id. EPA did not 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

109

state that the phrase only applied to the Acid rain program 

as commenter asserts and the Utility Study in fact 

discussed other regulations, including the NSPS for EGUs 

and revised NAAQS. With regard to the latter, EPA 

ultimately determined that it could not sufficiently 

quantify the reductions that might be attributable to the 

NAAQS because states are tasked with implementing those 

standards. See Utility Study, pages ES-25, 1-3, 2-32. 

Conversely, commenter’s position is that EPA must consider 

implementation of all the requirements of the CAA, but it 

does not indicate how in conducting the Utility Study the 

Agency could have possibly considered co-befit HAP 

reductions attributable to all future CAA requirements. 

In the proposed rule, EPA recognized that we could 

consider requirements beyond those considered in the 

Utility Study, and we did consider a number of requirements 

that we maintain far exceed what Congress contemplated when 

enacting section 112(n)(1)(A). 76 FR 24991. We maintain 

that we have reasonably interpreted the requirement to 

consider the hazards to public health and the environment 

reasonably anticipated to occur after imposition of the 

requirement of the Act as explained in the proposed rule. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

110

76 FR 24990. In addition, as stated above, we also believe 

it would be reasonable to find it necessary to regulate HAP 

emissions from EGUs based on our finding that such 

emissions pose a hazard to public health and the 

environment today. 

With regard to the legislative history, as stated 

above, Representative Oxley’s supposedly authoritative 

statement is not even consistent with the express terms of 

section 112(n)(1)(A) on this issue, and commenter here 

relies on that misstatement as support for its attack on 

the Agency’s reasonable interpretation of the statute. 

Specifically, Representative Oxley stated that EPA was to 

take “into account compliance with all the provisions of 

the act and any other Federal, State, or local regulation 

and voluntary emission reductions,” but section 

112(n)(1)(A) directed the Agency to consider only 

“imposition of the requirements of [the CAA].” We need not 

address this argument further. (See also Response to 

Comment 1F above)

Finally, commenter implies that EPA’s position is that 

the Agency will only consider requirements of the Act that 

directly regulate HAP emissions. EPA never stated or 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

111

suggested that interpretation and a fair reading of the 

proposed rule will demonstrate that EPA considered 

requirements that achieve co-benefit HAP emission 

reductions, for example the Transport Rule.

Comment: One commenter continues stating under CAA 

§112 regulating EGUs is permissible only insofar as it is 

focused, targeted, and predicated on concrete findings by 

the Agency that such regulation is indeed “necessary.” 

According to the commenter the EPA construes CAA § 

112(n)(1)(A) as permitting it to find that it is 

“necessary” to regulate EGUs even where the Agency does not 

actually know whether it is “necessary” to regulate EGUs. 

Citing the D.C. Circuit, EPA suggests that “‘there are many 

situations in which the use of the word ‘necessary,’ in 

context, means something that is done, regardless of 

whether it is indispensible,’” in order to “‘achieve a 

particular end.’” 76 Fed. Reg. at 24,990, quoting Cellular 

Telecommunications v. FCC, 330 F.3d 502, 510 (D.C. Cir. 

2003). The commenter states that in the “context” of CAA § 

112(n)(1)(A), as informed by the relevant legislative 

history, it is clear that regulation of EGU HAP emissions 

can be considered “necessary” only if EPA were to “clearly 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

112

establish” that such regulation was effectively 

“indispensible” to address the identified harm. As EPA 

concedes that it has made no such determination here, its 

proposal is fatally flawed for that reason alone.

Response: Commenter again relies on the legislative 

statements of one Representative and asserts that the 

statements are controlling. It is commenter’s legal 

analysis that is flawed, not EPA’s interpretation of the 

statute. 76 FR 24990-92 (Section III.A.2.b of the proposed 

rule contains EPA’s interpretation of the term 

“necessary”). Commenter also, in a footnote, implies that 

EPA based the appropriate and necessary finding on non-HAP 

air pollution. Commenter is wrong.

Further, the Commenter appears to argue that EPA’s 

interpretation authorizes the Agency to find it necessary 

to regulate EGUs when we are uncertain it is necessary, but 

that misconstrues our interpretation and makes no sense. 

Instead, EPA reasonably interprets the statute to authorize 

the Agency to find that it is necessary to regulate if we 

are unable to determine that imposition of the requirements 

of the Act will address identified hazards to public health 

and the environment. The statute does not prohibit this 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

113

interpretation and it is a legitimate exercise of our 

discretion to err on the side of regulation in the face of 

uncertainty concerning the level of protection necessary to 

protect public health and the environment. Particularly in 

a determination such as the necessary finding that is based 

on modeled projections of emissions four years into the 

future. The CAA requires EPA to exercise its discretion in 

determining whether regulation under section 112 is 

necessary, and the D.C. Circuit has stated that “there are 

many situations in which the use of the word ‘necessary,’ 

in context, means something that is done, regardless of 

whether it is indispensible, to achieve a particular end.” 

See Cellular Telecommunications & Internet Association, et. 

al. v. FCC, 330 F.3d 502, 510 (D.C. Cir. 2003). EPA’s 

interpretation of “necessary” is reasonable in the context 

of section 112(n)(1)(A)

Commenter states that EPA concedes that the Agency has 

not “clearly established” that regulation of HAP emissions 

under section 112 is “indispensible.” EPA has conceded 

nothing but, more importantly, the supposed standard that 

commenter presents for evaluating whether it is necessary 

to regulate HAP emissions from EGUs is not required by the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

114

statute and even the limited legislative history on which 

the commenter incorrectly relies does not espouse such a 

standard. 

Commenter takes issue with EPA’s statement that the 

Agency may find it is necessary to regulate EGUs under 

section 112 if we are “uncertain whether imposition of the 

other requirements of the CAA will sufficiently address the 

identified hazards.” 76 Fed. Reg. at 24,990. But commenter 

has again misinterpreted the Agency’s position by stating 

that “EPA construes CAA 112(n)(1)(A) as permitting it to 

find that it is “necessary” to regulate EGUs even where the 

Agency does not actually know whether it is “necessary” to 

regulate EGUs.” Instead, EPA maintains that it may be 

necessary to regulate EGUs under section 112 if we identify 

a hazard to public health or the environment that is 

appropriate to regulate today and our projections into the 

future do not clearly establish that the imposition of the 

requirements of the CAA will address the identified hazard 

in the future. Making a prediction about future emission 

reductions from a source category is difficult when there 

are no statutory provisions that mandate direct control of 

the given source category or pollutants of concern. We 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

115

maintain that erring on the side of caution is appropriate 

when the protection of public health and the environment 

are not assured by our modeling of future emissions, and it 

is troubling that commenter does not. Furthermore, as we 

stated in the proposed rule, we believe it would be 

reasonable to find it appropriate and necessary today based 

on a determination that HAP emissions from EGUs pose a 

hazard to public health and the environment without 

considering future HAP emission reductions. 76 FR 24991, 

n.14. We maintain this is reasonable because “Congress 

could not have contemplated in 1990 that EPA would have 

failed in 2011 to have regulated HAP emissions from EGU’s 

where hazards to public health and the environment remain.” 

Id. The phrase “after imposition of the requirements of 

[the Act]” as contemplated section 112(n)(1)(A) could be 

read to apply only to those requirements clearly and 

directly applicable to EGUs under 1990 CAA amendments, all 

of which have been implemented and still hazards to public 

health and the environment remain.

Finally, commenter does not address all of the bases 

on which the necessary finding is made. Specifically, EPA 

found in the May 3, 2011 proposed rule that it was 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

116

necessary to regulate HAP emissions from EGUs because the 

modeling showed that the hazards to public health [and the 

environment?] would not be addressed through imposition of 

the requirements of the Act. 

g. Listing EGUs under 112

Comment: One commenter states that even if the EPA 

were to establish under CAA 112(n)(1)(A) that it is 

“appropriate and necessary” to regulate HAP emissions from 

EGUs – and the Agency has not done so – regulating those 

emissions in the form of a MACT standard established 

pursuant to CAA 112(d) is contrary to the plain language of 

the Act. Accordingly if EPA proceeds to finalize the 

proposal and adopts such a standard, the rule will for this 

reason alone be dead-on-arrival. According to the commenter 

the EPA apparently believes that its only option in 

regulating EGU HAP emissions is establishing a MACT 

standard under CAA 112(d). In the preamble to its proposal, 

the EPA contends that, “once the appropriate and necessary 

finding is made,” EGUs are then “subject to section 112 in 

the same manner as other sources of HAP emissions” – i.e., 

by “listing” EGUs under CAA 112(c) and adopting a MACT 

standard under CAA 112(d). See 76 Fed. Reg. at 24,993/2 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

117

(emphasis added). Given that Congress “directed the Agency 

to regulate utilities ‘under this section’ [i.e., CAA 

112],” The EPA continues, it follows that “EGUs should be 

regulated in the same manner as other categories for which 

the statute requires regulation.” Id. (emphasis added). As 

EPA sees it, because “Congress did not exempt EGUs from the 

other requirements of section 112,” once EGUs were “listed” 

under CAA 112(c), the Agency was “required to establish 

emission standards for EGUs consistent with the 

requirements set forth in section 112(d).” Id. at 24,993/3 

(emphasis added).

In support of this reading of the CAA, the EPA invokes 

the decision of the U.S. Court of Appeals for the D.C. 

Circuit in New Jersey v. EPA, 517 F.3d 574 (D.C. Cir. 

2008). According to EPA, the D.C. Circuit has “already held 

that section 112(n)(1) ‘governs how the Administrator 

decides whether to list EGUs.’” See 76 Fed. Reg. at 

24,993/2-3, quoting 517 F.3d at 583. EPA construes that 

holding as indicating that, “once listed, EGUs are subject 

to the requirements of section 112” – including, EPA 

presumes, CAA 112(d). Id. (The commenter states that 

elsewhere, the EPA construes CAA 112(n)(1) (A) as 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

118

“govern[ing] how the Administrator decides whether to list 

EGUs for regulation under section 112,” and quotes the D.C. 

Circuit’s observation in New Jersey that “Section 112(n)(1) 

governs how the Administrator decides whether to list EGUs; 

it says nothing about delisting EGUs.” See 76 Fed. Reg. at 

24,981/2, quoting 517 F.2d at 582.

The commenter asserts that the EPA misinterprets the 

“under this section” language of CAA 112(n)(1); overstates 

the significance of the New Jersey decision; and, as a 

consequence, misapprehends the scope of its own discretion 

to formulate regulatory standards for EGUs under CAA 112. 

In light of these errors, EPA should withdraw the proposed 

MACT rule.

One commenter states that if Congress had intended 

that EPA regulate EGU HAP emissions only through a MACT 

standard, Congress could have – and presumably would have –

directed the Agency to regulate EGU emissions “under CAA 

112(d).” Congress did not do so. The EPA’s authority to 

regulate EGU HAP emissions is not derived from any 

particular subsection of CAA 112. Rather, EPA is authorized 

to regulate “under this section” – i.e., CAA 112 generally 

– as may be “appropriate and necessary.” There is nothing 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

119

on the face of CAA 112(n)(1)(A) that specifies that 

regulation of EGUs must occur under CAA 112(d). To the 

contrary, a plain reading of CAA 112(n)(1)(A) indicates 

that establishing a MACT standard for EGUs under CAA 112(d) 

is not what Congress had in mind at all.

Response: We do not agree with the commenter. EPA 

interpreted section 112(n)(1)(A) in a manner that gives 

meaning to all the words used in the provision. See NRDC v. 

EPA, 489 F.3d 1364, 1373 (D.C. Cir. 2007) (admonishing EPA 

for an interpretation of CAA section 112(c)(9) that ignored 

certain words and the context in which they were used the 

Court stated that “EPA’s interpretation would make the 

words redundant and one of them ‘mere surplusage,’ which is 

inconsistent with a court's duty to give meaning to each 

word used by Congress.”) (citing TRW Inc. v. Andrews, 534 

U.S. 19, 31, 122 S. Ct. 441, 151 L. Ed. 2d 339 (2001)). 

Specifically, in the proposed rule, we stated: “ The 

statute directs the Agency to regulate EGUs under section 

112 if the Agency finds such regulation is appropriate and 

necessary. Once the appropriate and necessary finding is 

made, EGUs are subject to section 112 in the same manner as 

other sources of HAP emissions. Section 112(n)(1)(A) 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

120

provision provides, in part, that: ‘[t]he Administrator 

shall perform a study of the hazards to public health 

reasonably anticipated to occur as a result of emissions by 

electric utility steam generating units of pollutants 

listed under subsection (b) of this section after 

imposition of the requirements of this chapter... The 

Administrator shall regulate electric utility steam 

generating units under this section, if the Administrator 

finds such regulation is appropriate and necessary after 

considering the results of the study required by this 

subparagraph.’” Emphasis added.

In the first sentence, Congress described the study 

and directed the Agency to evaluate the hazards to public 

health posed by HAP emissions listed under subsection (b) 

(i.e., section 112(b)). The last sentence requires the 

Agency to regulate under this section (i.e., section 112) 

if the Agency finds such regulation is appropriate and 

necessary after considering the results of the study 

required by this subparagraph (i.e., section 112(n)(1)(A)). 

The use of the terms section, subsection, and subparagraph 

demonstrates that Congress was consciously distinguishing 

the various provisions of section 112 in directing the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

121

conduct of the study and the manner in which the Agency 

must regulate EGUs if the Agency finds it appropriate and 

necessary to do so. Congress directed the Agency to 

regulate utilities “under this section,” and accordingly 

EGUs should be regulated in the same manner as other 

categories for which the statute requires regulation. See 

76 FR 24993.

We maintain that our interpretation of the statute 

gives meaning to all the word, and commenter’s 

interpretation does not give any particular meaning to the 

requirement to “regulate under this section [112]”. 

Commenter is correct that Congress could have in section 

112(n)(1)(A) directed EPA to regulate HAP from EGUs under 

section 112(d) after making the appropriate and necessary 

finding, but commenter presumes too much when it states 

that Congress would have directed the Agency to regulate 

HAP emissions from EGUs in such a manner if that is what 

Congress wanted. It is equally true that Congress could 

have directed EPA to regulate HAP emissions from EGUs under 

subparagraph 112(n)(1)(A) if that is what it wanted, but it 

did not. As we explained in the section II.A. of the 

proposed rule, section 112 establishes a mechanism to list 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

122

and regulate stationary sources of HAP emissions. 76 FR 

24,980-81. Regulation under section 112 generally requires 

listing under section 112(c), regulation under section 

112(d), and, for sources subjected to MACT standards, 

residual risk regulations under section 112(f) (as 

necessary to protect human health and the environment with 

an ample margin of safety). It is not inconsistent with the 

plain language of section 112(n)(1)(A) to conclude that EPA 

should list EGUs once the prerequisite appropriate and 

necessary finding is made, and listed sources must be 

regulated under section 112(d). See section 112(c)(2). 

Furthermore, the flaws in commenter’s interpretation 

are highlighted by other section 112 provisions wherein 

Congress provided specific direction as to the manner of 

regulation. For example, section 112(m)(6) requires the 

Administrator to determine “whether the other provisions of 

this section [112] are adequate” and also indicates that 

“[a]ny requirements promulgated pursuant to this paragraph

. . .shall only apply to the coastal waters of the States 

which are subject to [section 328 of the CAA].” (emphasis 

added). In addition, section 112(n)(3) provides that when 

the Agency is “promulgating any standard under this section 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

123

[112] applicable to publicly owned treatment works, the 

Administrator may provide for control measures that include 

pretreatment of discharges causing emissions of hazardous 

air pollutants and process or product substitutions or 

limitations that may be effective in reducing such 

emissions.” Finally, section 112(n)(5) directs the Agency 

to assess hydrogen sulfide emissions from oil and gas 

extraction and “develop and implement a control strategy 

for emissions of hydrogen sulfide to protect human health 

and the environment . . . using authorities under [the CAA] 

including [section 111] of this title and this section 

[112].” (emphasis added). We believe these provisions 

provide ample evidence that Congress knew how to alter or 

caveat regulation under section 112 when that was its 

intent. For these reasons, we believe commenter’s argument 

is without merit.

Comment: Two commenters state that Section 

112(n)(1)(A) does not specify that regulation of EGUs must 

proceed under section 112(d). An argument could be made, 

therefore, that the CAA accords EPA with the discretion to 

regulate EGUs using strategies other than emission 

standards in section 112(d). Section 112(n)(1)(A) requires 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

124

that the EPA “develop and describe” alternative control 

strategies for emissions which may warrant regulation under 

section 112. According to the commenters if Congress meant 

for EPA to have one sole regulatory option, i.e., 

regulation of EGUs only under section 112(d), then the 

development of alternative control strategies would be 

rendered meaningless because under CAA § 112(d)(3), EPA is 

required to determine the level of control that is achieved 

by the best performing existing units for which it has data 

and then to impose that level of control on all existing 

units. The development of “alternative control strategies” 

has no role to play in this process. One commenter does 

note that the consideration of “alternative” controls 

becomes relevant, if at all, only in those circumstances 

where EPA might seek to establish a “Beyond-the-Floor” MACT 

standard pursuant to CAA § 112(d)(2).

Response: The Commenters are correct that section 

112(n)(1)(A) directed the Agency to develop alternative 

control strategies for regulating HAP emissions from EGUs 

that may warrant regulation in the Utility Study, but the 

commenters’ interpretation of and conclusion based on that 

language are both factually and legally inaccurate. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

125

The commenters appear to interpret the word 

“alternative control strategies” to mean something other 

than the traditional control technologies and control 

measures that are used to control HAP emissions from EGUs. 

We do not believe that is a realistic or reasonable 

interpretation of the statute, and the Agency did not 

interpret the statute in that manner when it conducted the 

Utility Study. In Chapter 13 of the Utility Study, EPA 

considered a range of control measures that would reduce 

the different types of HAP emitted from EGUs. 

http://www.epa.gov/ttn/atw/combust/utiltox/eurtc1.pdf. EPA 

considered pre-combustion controls such as coal washing, 

fuels switching, and gasification; combustion controls such 

as boiler design; post-combustion controls such as fabric 

filters, scrubbers, and carbon absorption; and alternative 

controls strategies such as demand side management, energy 

conservation, and use of alternative fuels (e.g. biomass) 

or renewable energy. The options discussed in the Utility 

Study for controlling HAP emissions from EGUs are almost 

universally available to comply with a section 112(d) 

standard. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

126

Given the manner in which the Agency conducted the 

Utility Study, EPA obviously interpreted the statutory 

direction as a requirement to set forth the control options 

available to EGUs to comply with section 112 standards in 

the event the Agency determined regulation was appropriate 

and necessary. EPA’s development and discussion in the 

Utility Study of alternative control strategies for 

complying with the standards would help prepare EGUs to 

comply with the standards if promulgated. Further, our 

interpretation is consistent with the direction in section 

112(n)(1)(A) to develop the control strategies for HAP 

“emissions which may warrant regulation under this 

section.” Thus, the statute only directed the Agency to 

develop alternative control strategies for the HAP the 

Agency determined may warrant regulation under section 112, 

and, tellingly, the Agency developed alternative control 

strategies for all manner of HAP emissions. Commenters’ 

interpretation finds no support under the statute and we 

reject it. 

Furthermore, EPA establishes section 112(d) standards 

for stationary sources and it is the responsibility of the 

sources to comply with the standards using any mechanism 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

127

available, including pre-combustion and post combustion 

measures. Also, the establishment of a MACT standard under 

section 112(d)(2) and (3) is a two-step process. In the 

first step, the Agency establishes a floor based on the 

performance of the best controlled unit or units. Section 

112(d)(3). In the second step, the Agency must consider 

additional measures that may reduce HAP emissions and adopt 

such measures if reasonable after considering costs and 

non-air quality health and environmental effects. Section 

112(d)(2). Under the second step, the Agency can consider 

any measure that reduces HAP emissions even if no source in 

the category is employing the option under consideration. 

So, even under the commenter’s flawed interpretation of 

“alternative control strategies”, the direction in section 

112(n)(1)(A) is not a “pointless exercise” for the 

development of section 112(d) standards.

Comment: One commenter does not agree with EPA’s 

finding that the word “subsection” in the first sentence of 

CAA §112(n)(1)(A) demonstrates that Congress was 

consciously distinguishing between the various provisions 

of section 112 in directing the conduct of the study and 

the manner in which the Agency must regulate EGUs,” were 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

128

EPA to “find[] it appropriate and necessary to do so.” See 

76 Fed. Reg. at 24,993/2. According to the commenter the 

only evident reason that the word “subsection” is used in 

the first sentence of CAA § 112(n)(1)(A) is because 

reference is made to the “pollutants” which the Utility 

Study is to address – i.e., the “pollutants” that are 

emitted by EGUs and which are “listed under subsection (b)” 

of CAA § 112. Similarly, the word “subparagraph” is used in 

the last sentence of CAA § 112(n)(1)(A) to identify “the 

study” which EPA is directed to undertake by subparagraph 

(A) of CAA § 112(n)(1) – i.e., the Utility Study. That the 

last sentence of subparagraph (n)(1)(A) also states that 

EPA “shall regulate electric utility steam generating units 

under this section” does not even imply – much less 

expressly communicate – that regulation “under this 

section” must mean “regulation under section 112(d).” The 

commenter states that Congress was “consciously 

distinguishing” between the “various provisions of section 

112” for the sake of clarity in the drafting of CAA § 

112(n).

Response: Commenter here makes a number of arguments 

that appear to take issue with EPA’s determination that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

129

EGUs should be regulated under section 112(d) if the Agency 

determines that regulation of HAP emissions from such units 

is appropriate and necessary. The commenter implies that 

EPA erred because alternative mechanisms for regulation of 

EGUs under section 112 might exist. We do not agree.

Commenter’s argument that EPA erred because we did not 

explain why section CAA section 307(d)(1)(C) contemplates 

regulations under section 112(n) is without merit. It is 

correct that the Agency believes EGUs should be regulated 

in the same manner as other sources if the appropriate and 

necessary finding is made because of the structure of 

section 112. Nothing in section 112(n)(1) requires or 

implies that the Agency should or must establish standards 

for EGUs under that provision. Furthermore, unlike sections 

112(n)(3) and 112(n)(5) that commenter cites, section 

112(n)(1)(A) does not provide any guidance concerning the 

manner in which EPA is authorized or required to regulate 

sources under section 112. See section 112(n)(3) 

(specifically authorizing identified control measures and 

other requirements for consideration in issuing standards 

under section 112); see also section 112(n)(5) (directing 

the Agency to develop and implement a control strategy for 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

130

emissions of hydrogen sulfide using any authority available 

under the CAA if regulation is appropriate). For these 

reasons, we disagree that any error occurred because we did 

not specifically discuss in this proposed rule whether we 

could or should regulate EGUs under section 112(n)(1) 

instead of section 112(d). The Agency validly listed EGUs 

in 2000 and listed sources must be regulated pursuant to 

section 112(d). 

Even if we agreed that regulation under section 

112(n)(1) was a viable option prior to the listing, we 

would still list and regulate EGUs like other sources 

because section 112(d) provides a statutory framework for 

regulating HAP emissions from sources and section 112(n)(1) 

does not. Even if section 112(n)(1) were available to 

regulate EGUs, there is sufficient uncertainty about the 

legally vulnerability of such an approach to caution 

against employing it. This is particularly true given that 

we have identified hazards to public health and the 

environment from HAP emissions from EGUs that warrant 

regulation.

Commenter also takes issue with our statement in the 

proposed rule that the use of the words “section”, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

131

“subsection”, and “subparagraph” in section 112(n)(1)(A) 

“demonstrates that Congress was consciously distinguishing 

the various provisions of section 112 in directing the 

conduct of the study and the manner in which the Agency 

must regulate EGUs.” See 76 Fed. Reg. at 24,993. Commenter 

appears to make much of our use of the word “must” in that 

sentence and also states that our interpretation of the 

significance of the use of the three terms in section 

112(n)(1)(A) is flawed because Congress only used the three 

terms for purposes of clarity. The commenter is wrong on 

both points. In regard to commenter’s concern with the use 

of the word “must” in the sentence quoted above, we note 

that in the next sentence we state that “Congress directed 

the Agency to regulate utilities ‘under this section,’ and 

accordingly EGUs should be regulated in the same manner as 

other categories for which the statute requires 

regulation.” Id. (emphasis added). Clearly we were not 

foreclosing the possibility of any alternative 

interpretation and our use of the term “must” should not 

detract from the point we were trying to make - a point 

that undermines commenter’s argument that EPA should not 

regulate EGUs under section 112(d). Specifically, we 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

132

believe that Congress would have directed us to regulate 

EGUs under section 112(n)(1)(A) if that was its intent and, 

absent that mandate, the best reading of the statute is the 

one we provided in the proposed rule.

Commenter also states that EPA relied on section 

112(c)(6) to support a conclusion that EGUs must be 

regulated under section 112(d). Commenter takes EPA’s 

statements out of context. The statement in whole read: 

“Furthermore, the D.C. Circuit Court has already held that 

section 112(n)(1) “governs how the Administrator decides 

whether to list EGUs” and that once listed, EGUs are 

subject to the requirements of section 112. New Jersey, 517 

F.3d at 583. Indeed, the D.C. Circuit Court expressly noted 

that “where Congress wished to exempt EGUs from specific 

requirements of section 112, it said so explicitly,” noting 

that “section 112(c)(6) expressly exempts EGUs from the 

strict deadlines imposed on other sources of certain 

pollutants.” Id. Congress did not exempt EGUs from the 

other requirements of section 112, and once listed, EPA is 

required to establish emission standards for EGUs 

consistent with the requirements set forth in section 

112(d), as described below.” See 76 Fed. Reg. at 24,993
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

133

As can be seen from this passage, EPA did not rely on 

112(c)(6), instead the Court used that provision as an 

example of Congress’ intent regarding regulating EGUs under 

section 112. The commenter cited the last clause of the 

last sentence of the paragraph quoted above without 

including the prefatory clause “once listed,” and, without 

that clause, the statement is not fairly characterized. The 

point EPA was making in that paragraph is that EGUs are a 

listed source category and listed sources must be regulated 

under section 112(d) unless EPA delists the source 

category.

Comment: One commenter states that EPA overstates the 

significance of the D.C. Circuit’s holding in New Jersey by 

suggesting that the decision mandates EGU regulation under 

CAA §112(d) because EGUs “remain listed” under CAA §112(c), 

See New Jersey, 517 F.3d at 582. According to the commenter 

the court declined to address the lawfulness of EPA’s 

having “listed” EGUs under CAA §112(c), leaving that matter 

to be decided if and when EPA adopted standards for EGUs 

under CAA §112. Nowhere in the decision did the D.C. 

Circuit indicate that EPA must regulate EGUs under CAA 

§112(d).
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

134

Response: Commenter’s arguments are circular and it is 

difficult to fully determine exactly what its issue is with 

EPA’s listing; however, it appears that commenter believes 

that EPA incorrectly relied on the New Jersey decision to 

justify the listing of EGUs. Commenter also appears to 

argue that the Agency has never explained why it has the 

authority to list EGUs at all. We disagree.

As we stated in the proposed rule, section 

112(n)(1)(A) requires EPA to conduct a study of HAP 

emissions from EGUs and regulate EGUs under section 112 if 

we determine that regulation is appropriate and necessary, 

after considering the results of the study. 76 FR 24981, 

24986, and 24998. The only condition precedent to 

regulating EGUs under section 112 is a finding that such 

regulation is appropriate and necessary (after conducting 

and considering the Utility Study), and once that finding 

is made the Agency has the authority to list EGUs under 

section 112(c) as the first step in the process of 

establishing regulations under section 112. The D.C. 

Circuit agrees with that interpretation of the statute as 

evidenced by its finding in New Jersey that “section 

112(n)(1)(A) governs how the Administrator decides whether 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

135

to list EGUs for regulation under section 112,” 517 F.3d at 

582, and the Court’s finding directly contradicts the 

commenter’s position. 

EPA did not rely on the New Jersey decision to justify 

the appropriate and necessary finding as the commenter 

suggests. We based the finding in 2000 on the extensive 

information available to the Agency at the time and we 

reaffirmed the Finding in the proposed rule based on new 

information. Commenter had ample opportunity to comment on 

the appropriate and necessary finding, and it may challenge 

the basis of the listing (i.e. the appropriate and 

necessary finding) when EPA issues the final standards.

Comment: One commenter believes that as a result of 

EPA’s “misapprehension” that upon making an “appropriate 

and necessary” finding, the Agency is compelled by the CAA 

to adopt a regulatory standard for EGUs under CAA § 112(d) 

the D.C. Circuit will condemn the final rule. According the 

commenter a regulation will be invalid if the regulation 

“‘was not based on the [agency’s] own judgment’” but 

“‘rather on the unjustified assumption that it was 

Congress’ judgment that such [a regulation] is desirable’ 

or required.” See Transitional Hospitals Corp. v. Shalala, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

136

222 F.3d 1019, 1029 (D.C. Cir. 2000), quoting Prill v. 

NLRB, 755 F.2d 941, 948 (D.C. Cir. 1985). Similarly, the 

D.C. Circuit has held that, where an agency wrongly 

construes a judicial decision as compelling a particular 

statutory interpretation, and thereby unduly limits the 

scope of its own discretion, the agency’s action cannot be 

sustained. See, e.g., Phillips Petroleum Co. v. FERC, 792 

F.2d 1165, 1171 (D.C. Cir. 1986). Because the commenter 

believes the rule is bound to be rejected, the EPA should 

“reconsider the legal interpretations on which it purports 

to base its rule.”

Response: We do not agree that we have improperly 

interpreted the statute as limiting our discretion in the 

manner suggested by the commenter. The commenter makes only 

one specific allegation in this comment and that concerns 

the Agency’s conclusion that it must establish section 

112(d) standards for EGUs in light of the New Jersey

decision. The commenter does not explain why that 

conclusion is incorrect, but as we state above and in the 

proposed rule, because EGUs are a section 112(c) listed 

source category, the Agency must establish section 112(d) 

standards or delist EGUs pursuant to section 112(c)(9). See 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

137

New Jersey, 517 F.3d at 582-83 (holding that EGUs remain 

listed under section 112(c)); see also section 112(c)(2) 

(requiring the Agency to “establish emission standards 

under subsection [112] (d)” for listed source categories 

and subcategories); 76 FR 24998-99. We concluded in the 

proposed rule that we could not delist EGUs because our 

appropriate and necessary analysis showed that EGUs did not 

satisfy the 112(c)(9)(B)(i) delisting criteria. Id. We did 

not address in the proposed rule whether EGUs satisfied the 

112(c)(9)(B)(ii) criteria because EGUs failed the first 

prong of the delisting provisions. Id. We reach the same 

conclusion in the final rule and also address the delisting 

petition submitted by this commenter. Because we cannot 

delist EGUs, we must regulate them under section 112(d). 

Commenter has provided no legitimate argument to rebut this 

conclusion.

Comment: One commenter alleges that EPA impermissibly 

relied on CAA §112(c)(9) to interpret “hazards to public 

health”, and argues that the “residual risk” provisions in 

CAA § 112(f)(2) are more appropriate for the establishment 

of standards for EGUs. The commenter states that by using 

112(c)(9)(B)(i) in defining “hazards to public health”, the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

138

Agency has seized on the one interpretation of the phrase 

that is surely contrary to congressional intent and, thus, 

falls out the permissible range of its interpretative 

discretion. The “delisting” criteria of CAA § 112(c)(9) are 

simply irrelevant to the decision whether EGU HAP emissions 

will present any “hazards to public health” sufficient to 

warrant regulation of those emissions under CAA § 112.

The commenter also argues that Congress intended that 

EGUs be treated differently from all other “major sources” 

to which “listing” provisions of CAA § 112(c)(9), and the 

standard-setting provisions of CAA §112(d) necessarily and 

automatically apply. Therefore, EPA’s proposal to utilize 

the criteria of CAA § 112(c)(9) to inform its findings 

under CAA § 112(n)(1)(A) treats EGUs exactly the same as 

all other major source categories, is contrary to 

congressional intent, and thus unlawful. The commenter goes 

on to state that in exercising its discretion to define 

“hazards to public health” as the phrase is used in CAA § 

112(n)(1)(A), EPA would be better served to consider the 

“residual health risk” provisions of CAA § 112(f)(2). Those 

provisions provide a better analogy to the establishment of 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

139

standards for EGUs under CAA § 112 than do the “de-listing” 

criteria of CAA § 112(c)(9).

The commenter believes the category-specific criteria 

of paragraph (c)(9) are a poor fit for an evaluation of 

“hazards to public health” that should reasonably include 

such factors as the affected population, the 

characteristics of exposure, the nature of the health 

effects, and the uncertainties associated with the data. 

While CAA § 112(n)(1)(A) does not expressly include any 

requirement that EGU emissions be regulated with an “ample 

margin of safety,” that standard is more appropriate than 

the “one-in-a-million” cancer risk standard of CAA § 

112(c)(9)(B)(i) that EPA proposes to employ. 

Response: Commenter acknowledges that EPA has broad 

discretion to interpret the phrase “hazard to public 

health” but that the one thing we cannot do is use the 

section 112(c)(9)(B) delisting provisions as a guide. 

Commenter asserts that the use of the delisting standard is 

clearly contrary to Congressional intent but it does not 

provide any substantive rebuttal to our conclusion that the 

section 112(c)(9) standards reflects the level of hazard 

which Congress concluded warranted continued regulation. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

140

Instead, the commenter reverts to its argument that the 

statute treated EGUs differently. EPA apparently views the 

disparate treatment of EGUs in a different light than 

commenter. We maintain that the only difference applies to 

the manner in which EGUs are added to the list of source 

categories subject to regulation. We do not interpret 

section 112(n)(1)(A) as a Congressional license to ignore 

risks that Congress determined warranted regulation for all 

other source categories. Because section 112(c)(9) defines 

that level of risk, it is reasonable to consider it when 

evaluating hazards to public health. 

Commenter also suggests that the “ample margin of 

safety standard” of section 112(f)(2) is a better fit than 

the one-in-a-million standard set forth in section 

112(c)(9)(B)(1) for evaluating hazards to public health. 

Commenter asserts that an evaluation of “hazards to public 

health” should include such factors as the affected 

population, the characteristics of exposure, the nature of 

the health effects, and the uncertainties associated with 

the data. But EPA did not rely solely on the delisting 

provisions for evaluating hazards to public health as 

commenter suggests. In fact, EPA considered all of the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

141

factors the commenter suggests in making our finding. 76 FR 

24992. We decline to adjust our approach to evaluating 

hazards to public health and the environment based on this 

comment.

h. December 2000 Finding (and 2005 Reversal)

Comment: Several commenters generally support the 

EPA’s 2000 finding that regulating HAPs emissions from EGUs

under CAA section 112 is “appropriate and necessary.”

According to the commenters, the 2000 finding was proper 

under the CAA and within EPA’s discretion, well-supported 

based on sound science available to the Agency at the time 

on the harm from HAPs emitted by EGUs, and no additional 

information makes the finding invalid. Several commenters 

cited the conclusions of the Utility Study and Mercury 

Study, which they assert well-supported the finding and 

satisfied the only prerequisite for the finding. One 

commenter specifically asserted that the 2000 finding was 

well-supported by the Utility Study’s conclusions that (1) 

there was a link between anthropogenic mercury emissions 

and methylmercury found in freshwater fish, (2) mercury 

emissions from coal-fired utilities were expected to worsen 

by 2010, and (3) methylmercury in fish presents a threat to 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

142

public health from fish consumption. One commenter noted 

that the CAA does not require a conclusive link between HAP 

emissions and harm. One commenter stated that the CAA

grants the Administrator discretion in her finding, and 

that discretionary decision should not be overly 

scrutinized, citing court opinion.40

The commenters who generally supported the 2000 

finding also commented on specific aspects of the finding. 

Several commenters asserted that while the evidence on 

mercury alone supports the finding, the potential harm from 

non-Hg HAP further supported the 2000 finding. Several 

commenters noted that new science continues to support the 

2000 finding. Several commenters also stated that the 

“appropriate” finding was further supported because 

numerous control options were available at the time of the 

finding that would reduce HAP emissions. One commenter 

concurred with EPA that regulating natural gas-fired EGUs

was not appropriate and necessary because the impacts due 

 

40 “Where a statute is precautionary in nature, the evidence difficult 

to come by, uncertain, or conflicting because it is on the frontiers of 

scientific knowledge, the regulations designed to protect the public 

health, and the decision that of an expert administrator, [courts] will 

not demand rigorous step-by-step proof of cause and effect.” Ethyl 

Corp. v. EPA, 541 F.2d 1, 28 (Ct. App. D.C. Circ. 1978)
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

143

to HAP emissions from such units are negligible based on 

the results of the Utility Study. 

Several commenters addressed the 2005 reversal of the 

2000 finding. While one commenter stated that the attempted 

2005 reversal of the 2000 finding was properly rejected by 

the U.S. Court of Appeals, another commenter asserted that 

the 2005 action was reasoned and proper and that EPA 

reverted back to the 2000 finding without adequate 

explanation or support. Several commenters cited EPA in 

2005 as invalidating the 2000 finding, specifically that 

EPA concluded that “no hazards to public health” remained 

after accounting for emission reductions under CAIR, and 

that because EPA took the exact opposite position on the 

interpretation of the term “necessary” in its 2005 

reversal, the commenters assert that EPA’s current position 

is illegal and eliminates any deference to the Agency. One 

commenter stated that in 2005 EPA recognized the potential 

for excessive regulation created by section 112 and 

determined that the December 2000 finding lacked 

foundation. 

Several commenters generally disagreed with the 2000 

finding, with two commenters stating that the EPA did not 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

144

have a rational justification for it and another claiming 

that it was fraught with misinformation and overestimating 

assumptions. One commenter claimed that EPA did not explain 

the terms “appropriate” and “necessary” in the 2000 finding 

and that the emission control analysis was inadequate. Two 

commenters stated that the 2000 finding was based on data 

that was more than 10 years old, which causes serious 

concern regarding the validity of the findings because 

technology, the regulatory environment, and economic 

climate have evolved. Furthermore, because the Utility 

Report underestimated emissions controls that EGUs would 

install by 2010 and additional controls that would be later 

required by the Cross State Air Pollution Rule (CSAPR), the 

basis for EPA‘s 2000 finding has changed. Several 

commenters state that a “plausible link” between 

anthropogenic mercury and methylmercury in fish is not an 

adequate reason for the 2000 finding. Several commenters 

claim that EPA only identified health concerns for mercury 

(and potentially nickel) not other HAPs from coal-fired 

EGUs in the 2000 finding, and thus cannot regulate HAPs

other than mercury because the 2000 finding authorizes only 

the regulation of mercury. One commenter questioned the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

145

mercury emissions underlying the 2000 finding, specifically 

the fraction of total deposition attributable to U.S. EGUS 

and the fact that EPA projected an increase in U.S. EGU 

emissions from 1990 to 2010 though emission actually 

declined. 

Several commenters raised procedural issues related to 

the 2000 finding. Several commenters stated that the 2000 

finding failed to provide public notice and comment. 

According to the commenters, the CAA requires that any 

decision made under section 112(n) must go through public 

notice and comment. The commenters further stated that the 

failure to provide public notice and comment means that 

this MACT is outside EPA’s statutory authority. One 

commenter stated that because the 2000 finding was never

“fully ventilated” in front of the D.C. Circuit, EPA’s 

authority to regulate EGUs under Section 112(d) is directly 

at issue. Commenters claimed that specific issues did not 

undergo public notice and comment, specifically least-cost 

regulatory options, the impact of regulation on electricity 

reliability, and EPA’s interpretation of the requirements 

under section 112(n)(1)(A). One commenter claimed that EPA 

attempted to provide after-the-fact support for its 2000 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

146

finding with new legal analysis and new factual 

information, which is contrary to New Jersey v. EPA which 

held that the EPA may not revisit its 2000 finding except 

through delisting under Section 112(c)(9). One commenter

stated that the EPA’s 2000 Finding should be reviewed when 

EPA issues the actual NESHAP.

41 One commenter stated that 

the 2000 finding ignored Executive Order 12866.

Response: EPA agrees with the commenters that the 

December 2000 finding was reasonable and disagrees with the 

commenters asserting that the December 2000 finding was 

unreasonable or failed to follow proper procedural 

requirements. 

EPA agrees that reviewing Courts defer to the reasoned 

scientific and technical decisions of an Agency charged 

with implementing complex statutory provisions such as 

those at issue in this case. As EPA stated in the proposed 

rule, EPA maintains that the December 2000 finding was 

reasonable based on well-supported evidence available at 

the time, including the Utility Study, the Mercury Study, 

and the NAS study, which all showed the known and potential 

 

41 See UARG v. EPA, 2001 WL 936363, No. 01-1074 (D.C. Cir. July 26, 

2001).
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

147

hazards to public health and the environment. New technical 

analyses conducted by EPA confirm that it remains 

appropriate and necessary to regulate HAP emissions from 

EGUs. Furthermore, EPA agrees with the commenters on 

several points raised, specifically that EGUs were and 

remain the largest anthropogenic source of several HAP in 

the U.S., that risk assessments supporting the December 

2000 finding indicated potential concern for several nonmercury HAP, and that several available control options 

would effectively reduce HAP emissions from U.S. EGUs.

EPA agrees with the commenters that Congress did not 

exempt EGUs from HAP emission limits while simultaneously 

limiting emissions at other sources with less HAP

emissions. Congress simply provided EPA with a separate 

path for listing EGUs by requiring that the Agency evaluate 

HAP emissions from EGUs and determine whether regulation 

under section 112 was appropriate and necessary. Since 

1990, EPA has promulgated regulations requiring the use of 

available control technology and other practices to reduce 

HAP emissions for more than 50 industrial sectors. U.S. 

EGUs are the most significant source of HAP in the country 

that remains unaddressed by Congress’s air toxics program. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

148

EPA listed EGUs in 2000 because the considerable amount of 

available data supported a conclusion that regulation of 

EGUs under section 112 was appropriate and necessary. That 

finding was valid at the time and EPA reasonably added EGUs

to the section 112(c) list of sources that must be 

regulated under section 112.

EPA acknowledges that we did not expressly define the 

terms appropriate and necessary in the 2000 finding, but 

the finding is instructive in that it shows that EPA 

considered whether HAP emissions from EGUs posed a hazard 

to public health and the environment and whether there were 

control strategies available to reduce HAP emissions from 

EGUs when determining whether it was appropriate to 

regulated EGUs.

42 When concluding it was necessary, the 

Agency stated that imposition of the requirements of the 

Act would not address the identified hazards to public 

health or environment from HAP emissions and that section 

112 was the proper authority to address HAP emissions.43 EPA 

explained in the proposed rule the conclusion that the 2000 

finding was fully supported by the information available at 

 

42 65 FR 79830.

43 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

149

the time and EPA stands by the conclusions in that notice. 

Furthermore, EPA provided an interpretation of the terms 

appropriate and necessary that is wholly consistent with 

the 2000 finding. EPA does not agree with the commenters

that a quantification of emissions reductions or a specific 

identification of the available controls was necessary to 

support the 2000 finding and listing. EPA considered the 

Utility Study when making the finding and that study 

clearly articulated the various alternative control 

strategies that EGUs could employ to control HAP

emissions.44 As to emission reductions, the level of HAP

emission reductions cannot be estimated until the Agency 

proposes a section 112(d) standard after a source category 

is listed.

EPA further disagrees with commenters that suggest 

that it was not “rational” to determine that it was 

appropriate to regulate HAP emissions from EGUs due to the 

cancer risks identified in the Utility Study or the 

potential concerns associated with other HAP emissions from 

EGUs. Nothing in section 112(n)(1)(A) suggest that EPA must 

determine that every HAP emitted by EGUs poses a hazard to 

 

44 See Chapter 13 of the Utility Study. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

150

public health or the environment before EPA can find it 

appropriate to regulate EGUs under section 112. In fact, 

EPA maintains that it must find it appropriate and 

necessary to regulate EGUs under section 112 if it 

determines that any one HAP emitted from EGUs poses a 

hazard to public health or the environment that will not be

addressed through imposition of the requirements of the 

Act. EPA disputes the commenters’ conclusion that the 2000 

finding was limited to mercury and nickel emissions, but, 

even if it was, EPA reasonably concluded that EGUs should 

be listed pursuant to section 112(c) based on the mercury 

and nickel finding. Source categories listed for regulation 

under section 112(c) must be regulated under section 

112(d), and the D.C. Circuit Court has stated that EPA has 

a “clear statutory obligation to set emission standards for 

each listed HAP”. See Sierra Club v. EPA, 479 F.3d 875, 883 

(D.C. Cir. 2007), quoting National Lime Association v. EPA, 

233 F.3d 625, 634 (D.C. Cir. 2000). Therefore, even if EPA 

concluded that section 112(n)(1) authorized a different 

approach for regulating HAP emissions from EGUs, which we 

question, the chosen course (i.e. listing under section 

112(c)) requires the Agency to regulate under section 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

151

112(d) consistent with the statute and case law 

interpreting that provision. 

EPA disagrees that there is any concern regarding the 

validity of the December 2000 finding or that the emissions 

information provided in the December 2000 finding makes the 

finding “questionable” as stated by some of the commenters. 

EPA maintains that the December 2000 finding was sound and 

fully supported by the record available at the time, 

including the future year emissions projections. Therefore,

the listing of EGUs is valid based on that finding alone. 

Even though mercury emissions have decreased since the 

December 2000 finding instead of increasing as projected, 

the new technical analyses confirm that mercury emissions 

from EGUs pose known and potential hazards to public health 

and the environment. EPA also stated in 2000 that 

uncertainty associated with the potential risk from HAP

emissions justified regulation of HAP emissions from EGUs. 

This is true because it is well established that even small 

amounts of HAP can cause significant harm to human health 

and the environment. 

EPA agrees with the commenters that assert that the 

2005 action was in error and disagrees with the commenters 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

152

that the 2005 action invalidated the 2000 finding. As fully 

described in the preamble to the proposal, EPA erred in the 

2005 action by concluding that the December 2000 finding 

lacked foundation. The 2005 action improperly conflated the 

“appropriate” and “necessary” analyses by addressing the 

“after imposition of the requirements of the Act” in the 

appropriate finding as well as the necessary finding. EPA 

also indicated that it was not reasonable to interpret the 

necessary prong of the finding as a requirement to scour 

the CAA for alternative authorities to regulate HAP

emissions from stationary sources, including EGUs, when 

Congress provided section 112 for that purpose. EPA asserts 

that the December 2000 finding was sound and fully 

supported by the record available at the time for all the 

reasons stated in this final rule and the proposed 

rule. The 2005 action interpreted the statute in a manner 

wholly inconsistent with the 2000 finding and attempted to 

delist EGUs without complying with the mandates of section 

112(c)(9)(B). See New Jersey, 517 F.3d at 583 (vacating the 

2005 “delisting” action). EPA set forth a revised 

interpretation of section 112(n)(1) that is consistent with 

the statute and the December 2000 finding and, as explained 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

153

in the preamble to the proposed rule, the December 2000 

finding was sound and fully supported by the record 

available at the time. EPA also explained in the proposed 

rule why the 2005 action was not technically or 

scientifically sound. EPA specifically addressed the errors 

associated with the 2005 action in the proposed rule and 

commenter’s assertions do not cause us to revisit those 

finding in the final rule. The commenter is also incorrect 

in suggesting that a change in interpretation is per se 

invalid and the commenter has provided no support for that 

position. See National Cable & Telecommunications Ass’n, 

et. a., v. Brand X Internet Services, et. al., 545 U.S. 

967, 981 (Discussing the deference provided to an Agency 

changing interpretations the Court stated “change is not 

invalidating, since the whole point of Chevron deference is 

to leave the discretion provided by ambiguities of a 

statute with the implementing Agency.”) (Internal citations 

and quotations omitted).

EPA disagrees with the commenters who raise concerns 

about the validity of the 2000 finding because the data on 

which that finding was based in more than 10 years old. EPA 

made the finding at that time based on the scientific and 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

154

technical information available, and that finding is wholly 

supported by that information. In addition, even though 

EPA was not required to do so, EPA conducted new technical 

analyses utilizing the best information available since 

several years have passed since the December 2000 finding. 

These new analyses confirm that HAP emissions from EGUs

continue to pose a hazard to public health and the 

environment, even after incorporating emission reductions 

that have occurred since 2000 from promulgated rules, 

settlements, consent decrees, and closures. 

Commenters are also incorrect regarding procedural 

requirements associated with the 2000 listing. EPA did not 

violate CAA section 307(d) by not providing notice and 

comment opportunity before making the appropriate and 

necessary finding. Commenter UARG challenged EPA’s 2000 

finding and listing on the same grounds and the D.C. 

Circuit dismissed the case because CAA section 112(e)(4) 

clearly states that listing decisions cannot be challenged 

until the Agency issues final emission standards for the 

listed source category. See UARG v. EPA, 2001 WL 936363, 

No. 01-1074 (D.C. Cir. July 26, 2001). EPA has provided the 

public an opportunity to comment on both the 2000 finding 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

155

and the 2011 analyses that support the appropriate and 

necessary determination as part of the proposed rule, and 

anyone may challenge the listing in the D.C. Circuit in 

conjunction with a challenge to this final rule. Commenters

could have also commented on the section 112(n)(1) studies 

as they were included in the docket, but EPA is not aware 

of any comments on those studies. In any case, the studies 

were peer reviewed and considered the best information 

available at that time. EPA has fully complied with the 

rulemaking requirement of section 307(d). EPA also 

disagrees with commenters’ characterization of the New 

Jersey case. The D.C. Circuit did not say as commenter

suggests that EPA is not able to consider additional 

information that is collected after the 2000 finding; 

instead, the Court stated that EPA could not just revise 

its appropriate and necessary finding and remove EGUs from 

the section 112(c) list without complying with the 

delisting provisions of section 112(c)(9). See New Jersey, 

517 F.3d at 582-83. EPA also disagrees with the commenter’s

assertion that EPA disregarded Executive Order 12866 when 

making the 2000 finding. The 2000 finding did not impose 

regulatory requirements or costs, and the finding was 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

156

reviewed by the Office of Management and Budget in 

accordance with the EO.

2. New Technical Analyses

a. General comments on new technical analyses

Comment: Several commenters state that the new 

analyses confirm that it remains appropriate and necessary 

to regulate U.S. EGU HAP under Section 112 of the CAA. 

These commenters state that the new analyses provide even 

more support than the information available at the time the 

2000 finding was made, including further developed 

emissions control technology, proven and cost-effective 

control of acid gases using trona and dry sorbent

injection, stabilized natural gas prices that makes fuel 

switching and switching dispatch to underutilized combined 

cycle plants more feasible, more information on ecosystem 

impacts from HAPs, “hotspots” from the deposition of 

mercury around EGUs, the potential for re-emission of 

mercury, updated emissions data and future projections of 

HAP emissions, and modern air pollution modeling tools. One 

commenter states that a uniform federal requirement that 

levels the playing field is even more of an imperative 

today than in 2000.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

157

Several commenters claim that regulating U.S. EGUs is 

necessary to protect public health based on information 

provided in the new technical analyses. These commenters 

acknowledge the substantial reductions in HAPs from this 

regulation and new studies that confirm serious health 

risks from HAP exposure. One commenter stated that new 

studies show higher risks to fetuses than previously 

estimated, increasing the potential for neurodevelopmental 

effects in newborns. One commenter notes that EGUs are a 

major source of HAPs, including HCl, HF, arsenic, antimony, 

chromium, nickel, and selenium, all of which adversely 

affect human health. The commenter states that because of 

these health effects, EPA has ample evidence to support a 

determination that non-Hg HAP emissions present a risk to 

human health.

One commenter believes that industry data support 

emissions standards at least as stringent as those proposed 

by EPA, effective and affordable control technology has 

been in use in this sector for 10 to 40 years, and studies 

on EGU-related mercury hazard has undergone two in-depth 

EPA reviews, as well as a review by the National Academy of 

Sciences. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

158

One commenter agrees that EPA may supplement its 

finding with subsequent information, analyses and arguments 

to reaffirm that earlier finding until it issues emissions 

standards. The commenter notes that the CAA does not freeze 

the finding. However, another commenter argues that EPA 

does not have the authority to rely on new technical 

analyses because the CAA requires EPA to make the finding 

on the basis of the Utility Study alone. According to the 

commenter, EPA unreasonably stretched the language of 

section 112 by considering new technical analyses.

Other commenters disagree that the new analyses

confirm that it remains appropriate and necessary to 

regulate U.S. EGUs. One commenter claims that EPA tried to 

use the new technical analyses to provide justification for 

the 2000 finding, which only found “plausible links” of 

health effects and “potential concerns” of health effects 

of certain metal emissions, dioxins and acid based 

aerosols. The commenter asserts that none of these new 

analyses demonstrate that EGU regulation under section 112 

is necessary and appropriate.

One commenter questions whether acid gas emissions 

limits for oil-fired units are “appropriate” or “necessary” 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

159

because EPA’s new technical analyses do not indicate a 

health concern from acid gas emissions from oil-fired 

units. According to the commenter, EPA identifies nickel as 

the main HAP of concern from oil-fired units, even though 

cancer-related inhalation risks were well below the 

reference concentrations and EPA admits that significant 

uncertainty remains as to whether those emissions present a 

health concern. 

Citing a report from Dr. Willie Soon that was 

submitted to the SAB Mercury Review Panel, one commenter

states that the proposed rule does not conform to the 

Information Quality Act, which requires that information 

relied on by the EPA be accurate, reliable, unbiased, and 

presented in a complete and unbiased manner. 

Response: EPA agrees with the commenters that state 

that the new technical analyses (e.g., the Mercury Risk 

Assessment and the Non-Hg Case Study Chronic Inhalation 

Risk Assessment) confirm the 2000 finding and disagree with 

the commenters that state otherwise. EPA also agrees with 

the commenters that the 2000 finding was valid at the time 

it was made based on the section 112(n)(1) studies and 

other information available to the Agency at that time. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

160

Furthermore, EPA agrees with commenters that the final rule 

will lead to substantial reductions in HAP emissions from 

EGUs, that control of the HAP will lead to public health 

and environmental benefits as discussed in the RIA, that 

mercury emissions from EGUs pose a hazard to public health, 

and that non-mercury HAP emissions from EGUs pose a hazard 

to public health that warrants regulation under section 

112.

Although these new analyses were not required, EPA 

agrees with the commenters that stated that EPA is 

authorized to conduct additional analyses to confirm the 

December 2000 finding. EPA disagrees with the commenter’s 

assertion that the Agency is not authorized to consider new 

information and at the same time unable to use the 

information available in 2000 because according to the 

commenter that information because it is “stale.” Under 

this theory, the Agency could not ever make an appropriate 

and necessary finding prospectively, thus the Agency would 

be excused from its obligations to protect public health 

and the environment because EPA did not diligently act in 

undertaking its statutory responsibility to establish 

section 112(d) standards within two years of listing EGUs. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

161

See section 112(c)(5). This is an illogical result that 

finds no basis in the statute. EPA also disagrees with the 

commenter's assertion that EPA may only consider the 

Utility Study in determining whether it is appropriate and 

necessary to regulate EGUs under section 112 for the 

reasons set forth in the proposed rule.45

The Mercury Risk TSD was peer reviewed by EPA’s 

independent Science Advisory Board during the public 

comment period, and the panel assigned to review the 

assessment concluded “the design of the risk assessment 

[w]as suitable for its intended purpose, to inform a 

decision-making regarding an “appropriate and necessary 

finding” for regulation of hazardous air pollutants from 

coal and oil-fired EGUs.”46 The risk assessment methodology 

for the non-Hg case studies was consistent with the 

methodology that EPA uses for assessments performed for 

Risk and Technology Review rulemakings, which underwent 

peer review by the SAB in 2009.47 During the public comment 

period, EPA also completed a letter peer review of the 

methods used to develop inhalation cancer risk estimates 

 

45 76 FR 24988.

46 U.S. EPA-SAB, 2011.

47 U.S. EPA-SAB, 2010.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

162

for chromium and nickel compounds, and those reviews were 

generally supportive. EPA has revised both TSDs documenting 

the two risk assessments consistent with recommendations 

from the peer reviewers and in response to some public 

comments as part of the final rulemaking and has made those 

revised TSDs available in the rule docket. 

EPA disagrees with the commenter’s implication that 

EPA conducted the new appropriate and necessary analysis 

because of alleged flaws in the 2000 finding. As explained 

in detail in the proposed rule, the 2000 finding was wholly 

valid and reasonable based on the information available to 

the Agency at that time, including the Utility Study. 

Further, EPA maintains that had it complied with the 

statutory mandate to issue section 112(d) standards within 

2 years of listing EGUs EPA would likely have declined to 

conduct new analyses. EPA conducted new analyses because 

over 10 years had passed since the December 2000 finding, 

and EPA wanted to evaluate EGUs on the most accurate 

information available, even though the Agency maintains 

that it was not required to reevaluate the 2000 finding. In 

conducting the new analyses, EPA corrected errors that 

affected the 2005 analysis finding that it was neither 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

163

appropriate nor necessary to regulate EGUs under section 

112 and used updated information to support the finding.

Under EPA’s interpretation of section 112(n)(1) set 

forth in the proposed rule, the Agency concludes that it 

may list EGUs under section 112(c) if it determines that 

even one HAP emitted from EGUs poses a hazard to public 

health or the environment that will not be addressed 

through imposition of the requirements of the CAA.

48 Once 

the Agency lists EGUs under section 112(c), it must 

regulate such units under section 112(d) unless the Agency 

can delist such sources, which EPA’s risk analyses 

demonstrates is not possible. The D.C. Circuit has stated 

that EPA has a “clear statutory obligation to set emission 

standards for each listed HAP.” See Sierra Club v. EPA, 479 

F.3d 875, 883 (D.C. Cir. 2007), quoting National Lime 

Association v. EPA, 233 F.3d 625, 634 (D.C. Cir. 2000). 

Concerning the acid gas HAP, EPA disagrees with the 

notion that each emitted HAP requires its own separate 

appropriate and necessary finding before the Agency may 

list and regulate EGUs under section 112. Furthermore, in 

the inhalation case study assessments, EPA was only able to 

 

48 76 FR 24988.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

164

quantify the portion of the acid gas risks, which might be

attributable to hydrogen chloride and hydrogen fluoride 

emissions. While these estimated risks (which are 

associated with chronic non-cancer impacts, not cancer) by 

themselves were not very high, EPA noted that they carry 

the potential to combine with other respiratory irritants 

from other nearby sources to create cumulative exposures of 

concern to nearby residents. EPA also noted the sheer 

tonnage of hydrogen chloride emitted by all EGUs nationally 

as a potential concern, and indicated that these emissions 

had the potential to exacerbate the acidification of the 

natural environments. Additionally, EPA was not able to get 

quantitative emission information about the other acid 

gases (including chlorine and hydrogen cyanide), some of 

which are more potent respiratory irritants than hydrogen 

chloride. As a result, EPA continues to be concerned about 

the potential impacts of acid gas emissions from EGUs.

Furthermore, EPA reasonably concluded that it was 

appropriate and necessary to regulate oil-fired EGUs in 

2000 and EPA confirmed that conclusion was proper with the 

analysis set forth in the proposed rule. Commenters appear 

to take issue with the determination based on its view of 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

165

how the Agency can and should exercise its discretion. EPA 

disagrees and stands by the determination for the reasons 

set forth in the proposed rule. EPA also stands by the 

determination that the maximum cancer risks posed by 

emissions of oil-fired EGUs are greater than 1 in a 

million, owing primarily to emissions of nickel compounds, 

and based on our analysis we are unable to delist oil-fired 

EGUs. 

EPA strongly disagrees with the commenter that state 

that EPA failed to conform to the Information Quality Act. 

EPA used peer-reviewed information and quality assured data 

in all aspects of the technical analyses used to support 

the appropriate and necessary finding supporting the MATS. 

In addition, EPA submitted the national-scale mercury risk 

analysis to the SAB, which “supports the overall design of 

and approach to the risk assessment and finds that it 

should provide an objective, reasonable, and credible 

determination of the potential for a public health hazard 

from mercury emitted from U.S. EGUs.”49 The SAB received the 

comments from Dr. Willie Soon, and had those comments 

available for consideration in their deliberations 

 

49 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

166

regarding the mercury risk analysis. The SAB specifically 

supported elements of the analysis criticized by Willie 

Soon regarding the use of the EPA RfD as a benchmark for 

risk and the connection between mercury emissions from U.S. 

EGUs and mercury concentrations in fish.

b. Mercury Emissions

1. Mercury emissions from EGUs

Comment: Commenters addressed the 2005 and 2016 

emissions estimates for mercury and expressed concern that 

inaccuracies in these emissions result in overestimates of 

risks from mercury deposition. Further, commenters compared 

EPA’s 2010 estimate and 2016 estimate, noting that it is 

not possible for 29 tons to be a correct inventory total 

for mercury emissions in both years given expected 

reductions from the Cross-State rule. In addition, 

commenters made specific comments on assumptions included 

in the Integrated Planning Modeling (IPM), including a 

concern that mercury speciation factors used by IPM are 

resulting in overestimates of emissions in 2016. Other 

commenters noted that EGU sources are the predominant 

source of U.S. anthropogenic mercury emissions, and in 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

167

particular the oxidized and particulate forms of mercury 

that are of concern for mercury deposition.

Response: EPA disagrees with commenters assertions 

that emissions estimates result in overestimates of risk. 

While EPA agrees that the 2005 Hg emissions may be an 

overestimate, such an overestimate in 2005 would lead to an 

underestimate of risk in 2016 and not an overestimate of 

risk as claimed by the commenter because the ratio approach 

used by EPA to scale fish tissue data would underestimate 

risk if 2005 Hg estimates were overestimated. Since the 

2005 emissions are not used as a starting point for 2016 

emissions from IPM, any 2005 overestimate does not affect 

the 2016 emissions levels. The 2016 emissions are computed 

by IPM based on forecasts of demand, fuel type, Hg content 

of the fuel, and the emissions reductions resulting from 

each unit’s configurations. See IPM Documentation for 

further information. No commenter has provided any evidence 

that the IPM 2016 emissions projection methodology result 

in an overestimate.

EPA acknowledges that the current Hg emissions 

estimate should not be the same as the 2016 Hg emissions 

estimate given that compliance with CSAPR is expected to 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

168

lead to some Hg emission reduction co-benefits. For this 

reason, EPA has included those reductions in the futureyear modeling used for the final rule mercury risk 

analysis. EPA estimates that current mercury emissions are 

28 tons, replacing the estimated 2010 value of 29 tons 

reported at proposal. EPA has also revised the 2016 base 

estimate to 27 tons. Finally, any remaining inconsistency 

in EPA’s revised values is not relevant to the Hg national 

risk analysis since the 2010 emissions are not used in any 

of the risk calculations, which depend only on the modeled 

2005 and 2016 Hg emissions. 

EPA disagrees with the commenter’s assertion that 

incorrect mercury emission factors result in incorrect 2016 

emissions. The 2016 projected mercury emissions are not 

based on emissions factors. The 2016 mercury emissions are 

computed by the Integrated Planning Model (IPM) based on 

forecasts of demand, fuel type, Hg content of the fuel, and 

the emissions reductions resulting from each unit’s

configurations. The speciation factors referenced by the 

commenter provide a basis for the speciation of total 

projected mercury emissions into particulate, divalent 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

169

gaseous, and elemental species, and do not impact the total 

amount of mercury emissions.

EPA agrees with commenters who noted that EGU sources 

are the predominant source of U.S. anthropogenic mercury 

emissions, and in particular the oxidized and particulate 

forms of mercury that are of greater concern for mercury 

deposition.

2. Global Mercury emissions

Comment: Several commenters state that predicted 

mercury deposition relies heavily on the amount of gaseous 

elemental mercury used to define the boundary and initial 

conditions of a model, e.g. the mercury that enters the 

U.S. from outside the U.S. boundaries. Commenters assert 

that this is especially important because mercury emissions 

from Asia—the region immediately upwind of North America 

that affects U.S. mercury deposition significantly and also 

affects it the most compared to other regions—are expected 

to continue to increase.50,51,52,53,54,55 This will have 

 

50 Jaffe D., Prestbo E., Swartzendruber P., Weiss-Penzias P., Kato S., 

Takami A., Hatakeyama S., Kajii Y., 2005. “Export of Atmospheric 

Mercury from Asia,” Atmospheric Environment, 39, 3029–3038.

51 Jaffe D., Strode S., 2008. “Fate and Transport of Atmospheric Mercury 

from Asia,” Environmental Chemistry, 5, 121. 

52 Pacyna E.G., Pacyna J.M., Sundseth K., Munthe J., Kindbom K., Wilson 

S., Steenhuisen F., Maxson P., 2010. ‖Global Emission of Mercury to the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

170

implications for the amount of mercury in the boundary and 

initial conditions. The commenters feel that these emission 

changes have not been accounted for in EPA‘s model 

exercise, thus leading to an overestimate of U.S. EGUattributable deposition in 2016.

Multiple commenters note that U.S. EGU mercury 

emissions are small when compared to global mercury 

emissions totals and natural sources within the U.S. These 

commenters use a variety of information to support 

alternative conclusions about the necessity to control U.S. 

EGU emissions to reduce mercury risk: global mercury 

emissions inventories, global and regional photochemical 

modeling research, and observation based assessments. A 

commenter states that the EPA has not acknowledged the 

dramatic decline in mercury emissions from U.S. EGUs since 

 

Atmosphere from Anthropogenic Sources in 2005 and Projections to 2020,‖

Atmospheric Environment, 44, 2487–2499.

53 Pirrone N., Cinnirella S., Feng X., Finkelman R.B., Friedli H.R., 

Leaner J., Mason R., Mukherjee A.B., Stracher G.B., Streets D. G., 

Telmer K., 2010. “Global Mercury Emissions to the Atmosphere from 

Anthropogenic and Natural Sources,”‖ Atmospheric Chemistry and Physics, 

10, 5951–5964.

54 Streets, D.G., Zhang, Q., Wu, Y., 2009. “Projections of Global 

Mercury Emissions in 2050.” Environmental Science & Technology 43, 

2983-2988.

55 Weiss-Penzias P., Jaffe D., Swartzendruber P., Dennison J.B., Chand 

D., Hafner W., Prestbo E., 2006. “Observations of Asian Air Pollution 

in the Free Troposphere at Mt. Bachelor Observatory in the Spring of 

2004,” Journal of Geophysical Research, 110, D10304.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

171

the late 1990s (approximately 50 percent) to the current 

level and also does not consider the relative magnitude of 

EGU mercury emissions compared to other sources, natural 

(such as fires) and human-caused.

Response: EPA disagrees that boundary condition inflow 

needs adjustment. The first 10 days of the modeling 

simulation are not used in the analysis, which is beyond 

the number of days necessary to remove the influence of 

initial conditions on mercury deposition estimates.56

Accurate characterization of speciated ambient mercury 

inflow is problematic due to the lack of observation data 

near the boundaries of the large continental-scale modeling 

domain. EPA has determined that the perturbations applied 

by Pongprueksa et al (2008), of 1 ng/m3 are not realistic 

boundaries of global speciated mercury concentrations and 

do not provide directly applicable information about 

uncertainty related to boundary conditions. The boundary 

inflow for the CMAQ mercury modeling used in the mercury 

deposition modeling are based on a global model GEOS-CHEM 

 

56 Pongprueksa, P., Lin, C.J., Lindberg, S.E., Jang, C., Braverman, T., 

Bullock, O.R., Ho, T.C., Chu, H.W., 2008. “Scientific uncertainties in 

atmospheric mercury models III: Boundary and initial conditions, model 

grid resolution, and Hg(II) reduction mechanism.” Atmospheric 

Environment 42, 1828-1845.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

172

simulation using a 2000 based global inventory.57 A 

comparison of global mercury emissions by continent for 

2000 and 2006 was recently published by Streets et al. 

(2009).58 Total mercury emissions from Asia (and Oceania) 

total 1,306 Mg/yr in 2000 and 1,317 Mg/yr in 2006.59 EPA has 

determined that these estimates are consistent and there is 

no discernable change in mercury emissions from Asia 

between 2000 and 2006 and any adjustments to the boundary 

conditions or adjustments to modeled mercury deposition 

would be invalid and inappropriate. Recent research has 

shown that ambient mercury concentrations have been 

decreasing in the northern hemisphere since 2000.60 Since 

emissions from Asia have not appreciably changed between 

2000 and 2006 and ambient mercury concentrations have been 

decreasing, ENVIRON’s analysis presents information with 

incorrect assumptions and we need not address them further. 

For these reasons and the large uncertainties surrounding 

 

57 Selin, N.E., Jacob, D.J., Park, R.J., Yantosca, R.M., Strode, S., 

Jaegle, L., Jaffe, D., 2007. “Chemical cycling and deposition of 

atmospheric mercury: Global constraints from observations.” Journal of 

Geophysical Research-Atmospheres 112.

58 Streets et al., 2009.

59 Streets et al., 2009.

60 Slemr, F., Brunke, E.G., Ebinghaus, R., Kuss, J., 2011. “Worldwide 

trend of atmospheric mercury since 1995.” Atmospheric Chemistry and 

Physics 11, 4779-4787.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

173

projected mercury global inventories EPA asserts that the 

most appropriate technical choice is to keep the mercury 

boundary conditions the same between the 2005 and 2016 

simulations.

EPA disagrees with the commenter’s assertion that EPA 

has not acknowledged the dramatic decline in mercury 

emissions for the U.S. EGUs since the late 1990s. EPA 

analyzed historical, current, and future projected mercury 

emissions from the power generation sector, as cited in the 

proposed regulatory preamble. EPA also disagrees with the 

commenters’ assertion that EPA failed to consider the 

relative magnitude of EGU mercury emissions compared to 

other sources. As noted in the Mercury Risk TSD, EPA 

modeled mercury emissions from U.S. and non-U.S. 

anthropogenic and natural sources to estimate mercury 

deposition across the country. EPA also determined the 

contribution of U.S. EGU Hg emissions to total Hg 

deposition in the U.S. by running modeling simulations for 

2005 and 2016 with U.S. EGU Hg emissions set to zero. Based 

on the analysis done for this rule EPA finds that total 

mercury deposition from EGUs do significantly impact human 

health.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

174

Commenters suggest that U.S. EGU Hg emissions 

represent a limited portion of the total mercury emitted 

worldwide, including anthropogenic and natural sources. 

While EPA acknowledges that U.S. EGU Hg emissions are a 

small fraction of the total mercury emitted globally, it 

views the environmental significance of mercury emissions 

from U.S. EGUs and other domestic sources as a more germane 

consideration. Mercury is emitted from EGUs in three forms. 

Each form of mercury has specific physical and chemical 

properties that determine how far it travels in the 

atmosphere before depositing to the landscape. While 

gaseous oxidized mercury and particle bound mercury are 

generally local/regional mercury deposition concerns, all 

forms of mercury have the potential to deposit to local or 

regional watersheds. U.S. coal-fired power plants account 

for over half of the U.S. controllable emissions of the 

quickly depositing forms of mercury. Although emissions 

from mercury sources outside the U.S. contribute to mercury 

deposition in the United States, the peer reviewed 

scientific literature shows that EGU mercury emissions in 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

175

the U.S. significantly enhance mercury deposition and the 

response of ecosystems in the U.S.61,62,63,64

c. Mercury Deposition Modeling

1. General Comments on Deposition Modeling

Comment: Several commenters state that according to 

the ENVIRON report the EPA overestimated U.S. EGU mercury 

deposition by 10 percent on average (and up to 41 percent 

in some areas). The commenters feel this overestimation is 

the result of boundary condition treatment, the exclusion 

of U.S. fire emissions,65 and mercury plume chemistry 

approach. In addition, one commenter references the same 

ENVIRON report and states that before implementation of 

controls required by the proposed rule, areas with 

relatively high EGU-attributable mercury deposition (onefifth or more of total deposition) in 2016 constitute less 

 

61 Caffrey et al., 2010.

62 Driscoll, C. T., Han, Y.-J., Chen, C. Y., Evers, D. C., Lambert, K. 

F., Holsen, T. M., et al. (2007). “Mercury Contamination in Forest and 

Freshwater Ecosystems in the Northeastern United States.” BioScience, 

57(1).

63 Keeler, G.J., Landis, M.S., Norris, G.A., Christianson, E.M., Dvonch, 

J.T., 2006. “Sources of mercury wet deposition in Eastern Ohio, USA.” 

Environmental Science & Technology 40, 5874-5881.

64 White, E.M., Keeler, G.J., Landis, M.S., 2009. “Spatial Variability 

of Mercury Wet Deposition in Eastern Ohio: Summertime Meteorological 

Case Study Analysis of Local Source Influences.” Environmental Science 

& Technology 43, 4946-4953.

65 Finley, B.D., Swartzendruber, P.C., Jaffe, D.A., 2009. “Particulate 

mercury emissions in regional wildfire plumes observed at the Mount 

Bachelor Observatory.” Atmospheric Environment 43, 6074-6083.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

176

than 0.25 percent of the continental U.S. area and only 

three grid cells have EGU contributions exceeding half of 

total deposition. 

Another commenter suggests that current research shows 

that models of mercury atmospheric fate and transport 

overestimate the local and regional impacts of some 

anthropogenic sources, such as U.S. EGUs. Thus, calculated 

contributions to mercury deposition and fish tissue 

methylmercury levels from these sources represent upper 

bounds of actual contributions66,67 and EPA should present 

results as estimates of lower and upper bound limits.

Response: EPA disagrees with the information presented 

by ENVIRON. The work by ENVIRON is based on the 

misapplication of multiple incommensurate modeling studies 

and false premises which include the incorrect idea that 

the boundary conditions are over-estimated and the idea 

that EPA should use in-plume chemistry that has not been 

explicitly characterized and peer reviewed. Reactions that 

 

66 Seigneur, C., Lohman, K., Vijayaraghavan, K., Shia, R.L., 2003. 

“Contributions of global and regional sources to mercury deposition in 

New York State.” Environmental Pollution 123, 365-373.

67 Seigneur, C., Vijayaraghavan, K., Lohman, K., Karamchandani, P., 

Scott, C., 2004. “Modeling the atmospheric fate and transport of 

mercury over North America: power plant emission scenarios.” Fuel 

Processing Technology 85, 441-450.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

177

may reduce gas phase oxidized mercury in plumes have not 

been explicitly identified in literature. Recent studies in 

central Wisconsin and central California suggest the 

opposite may happen; elemental mercury may be oxidized to 

Hg(II) in plumes.68,69 Better field study measurements and 

specific reaction mechanisms need to be identified before 

making conclusions about potential mercury in-plume 

chemistry or applying surrogate reactions in regulatory 

modeling. The possibility that Hg(0) is oxidized to Hg(II) 

in plumes suggests coal-fired power plant mercury 

contribution inside the United States may be underestimated 

in the EPA modeling. 

EPA asserts that the numbers suggested by the 

commenter are inaccurate as it is not appropriate to adjust 

EPA estimated deposition estimates based on previous 

mercury modeling done with older mercury chemistry, inplume reactions that have not been explicitly identified, 

and erroneous adjustments to mercury boundary inflow. 

 

68 Kolker, A., Olson, M.L., Krabbenhoft, D.P., Tate, M.T., Engle, M.A., 

2010. “Patterns of mercury dispersion from local and regional emission 

sources, rural Central Wisconsin, USA.” Atmospheric Chemistry and 

Physics 10, 4467-4476.

69 Rothenberg, S.E., McKee, L., Gilbreath, A., Yee, D., Connor, M., Fu, 

X.W., 2010. “Wet deposition of mercury within the vicinity of a cement 

plant before and during cement plant maintenance.” Atmospheric 

Environment 44, 1255-1262.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

178

Recent research has shown that ambient mercury 

concentrations have been decreasing in the northern 

hemisphere since 2000.70 Since emissions from China have not 

appreciably changed between 2000 and 200671 and ambient 

mercury concentrations have been decreasing, inappropriate 

mixing and matching of older out of date mercury modeling 

simulations with EPA results has been included, and the 

fact that ENVIRON’s analysis has not undergone any 

scientific peer review and presents information with 

incorrect assumptions as noted in this response, we decline 

to revise our analysis as commenter suggests.

EPA also disagrees with the commenter’s interpretation 

of the applicability of wildfire mercury emissions to this 

assessment. Finley et al. (2009)72 suggests caution when 

using their field data to make assumptions about Hg(p) 

emissions from wildfires; the estimated particulate Hg 

emissions from wildfires is based on one field site with a 

limited sample size and the assumptions made (such as the 

observed Hg(p) to carbon monoxide ratios at this location) 

 

70 Slemr et al., 2011.

71 Streets et al., 2009.

72 Finley et al. 2009.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

179

may not be valid on a broader scale.73 Mercury emissions 

from wildfires are a re-volatilization of previously 

deposited mercury.

74 Given that electrical generating power 

plants are currently and have historically been a large 

mercury-emitting source the inclusion of wildfire emissions 

in a modeling assessment would necessarily increase the 

contribution from this emissions sector.

EPA disagrees with the assertion that EPA failed to 

consider the relative magnitude of U.S. EGU mercury 

emissions compared to other sources and disagrees with the 

interpretation of EGU deposition presented in the ENVIRON 

report. As noted in the Mercury Risk TSD, EPA modeled 

mercury emissions from U.S. and non-U.S. anthropogenic and 

natural sources to estimate mercury deposition across the 

country. EPA also determined the contribution of U.S. EGU 

Hg emissions to total Hg deposition in the U.S. by running 

modeling simulations for 2005 and 2016 with U.S. EGU Hg 

emissions set to zero. Based on the analysis done for this 

rule EPA finds that total mercury deposition from EGUs do 

 

73 Id.

74 Wiedinmyer, C., Friedli, H., 2007. “Mercury emission estimates from 

fires: An initial inventory for the United States.” Environmental 

Science & Technology 41, 8092-8098.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

180

significantly impact human health. The ENVIRON report 

provides no risk analysis of EGU contribution. 

EPA disagrees that research75,76 presented by the 

commenter shows that U.S. EGU impacts are over-estimated. 

The commenter’s references do not support this statement. 

The references provided by the commenter are based on 

mercury modeling that uses models that are no longer 

applied and that are based on out-dated mercury chemistry 

and deposition assumptions. Given the advances in mercury 

modeling since the early 2000s EPA does not feel an upper 

and lower bound estimate is necessary.

2. Chemical reactions

Comment: Several commenters state that the CMAQ 

modeling fails to account for the chemical reduction of 

gaseous ionic mercury to elemental mercury that may occur 

in EGU plumes. The commenters note that the EPA did not use 

the Electric Power Research Institute’s (EPRI) Advanced 

Plume-in-Grid Treatment, which includes a surrogate 

reaction to reduce gaseous ionic mercury to elemental 

mercury inside plumes. Multiple commenters contend that the 

 

75 Seigneur et al., 2003.

76 Seigneur et al., 2004.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

181

reduction of reactive gaseous mercury to gaseous elemental 

mercury has been reported in power plant plumes and 

supporting data include atmospheric concentrations of 

speciated mercury measured downwind of power plant stacks 

at ground level monitor sites and dispersion model 

predictions.77,78 A detailed description of various plume 

measurement studies is provided in EPRI Comments, Section 

3.4: Plant Bowen, Georgia, Plant Pleasant, Wisconsin, and 

Plant Crist, Florida. One commenter felt the impact of grid 

resolution (12 km sized grid cells) on the CMAQ modeling 

was not appropriately addressed by EPA. Their concerns due 

to grid resolution include the idea that a source‘s 

emissions will be averaged over the entire grid cell and 

such averaging causes an artificially fast dilution and may 

result in smoothing out areas of high and low deposition 

and decrease model ability to simulate smaller areas of 

localized high deposition. This commenter felt that using 

the APT would address these issues. 

 

77 Edgerton, E.S., Hartsell, B.E., Jansen, J.J., 2006. “Mercury 

speciation in coal-fired power plant plumes observed at three surface 

sites in the southeastern U.S.” Environmental Science & Technology 40, 

4563-4570.

78 Lohman, K., Seigneur, C., Edgerton, E., Jansen, J., 2006. “Modeling 

mercury in power plant plumes.” Environmental Science & Technology 40, 

3848-3854.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

182

Response: EPA disagrees with the commenters’ 

suggestions. Reactions that may reduce gas phase oxidized 

mercury in plumes have not been explicitly identified in 

literature. The references cited by the commenters are from 

non-peer-reviewed reports and conference proceedings. EPA 

does not consider information presented at conferences or 

industry reports to be peer reviewed literature and 

consideration of oral presentation material would be 

inappropriate. Still, the references supplied by the 

commenter do not contain any explicit mercury reactions. 

These references suggest that oxidized gas phase mercury 

may be reduced and postulate a possible pathway, but never 

describe the specific chemical reaction mechanism. 

Recent studies in central Wisconsin and central 

California suggest the opposite may happen; elemental 

mercury may be oxidized to Hg(II) in plumes.79,80 Better 

field study measurements and specific reaction mechanisms 

need to be identified before making conclusions about 

potential mercury in-plume chemistry or applying surrogate 

reactions in regulatory modeling. Currently, models such as 

 

79 Kolker et al., 2010.

80 Rothenberg et al., 2010.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

183

Advanced Plume Treatment (APT) use a surrogate reaction for 

the potential reactive gas phase mercury reduction that may 

or may not occur in plumes.

81 Reactions that may reduce gas 

phase oxidized mercury in plumes have not been explicitly 

identified in literature. The application of potentially 

erroneous in-plume chemistry that is a fundamental 

component of APT would be inappropriate. In addition, the 

APT is not available in the most recent version of CMAQ. It 

would be inappropriate for EPA to apply an out of date 

photochemical model with in-plume chemistry that has not 

been shown to exist.

EPA agrees with the commenter that the CMAQ modeling 

with 12 km grid resolution may provide a lower bound 

estimate on EGU contribution as higher impacts using finer 

grid resolution are possible. The commenter’s assertion 

that EGU impacts are likely higher further supports the 

final conclusions of the exposure modeling assessment. EPA 

would like to point out that the application of a 

photochemical model at 12 km grid resolution for the entire 

continental United States is more robust in terms of grid 

 

81 Vijayaraghavan, K., Seigneur, C., Karamchandani, P., Chen, S.Y., 

2007. “Development and application of a multipollutant model for 

atmospheric mercury deposition.” Journal of Applied Meteorology and 

Climatology 46, 1341-1353.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

184

resolution and scale that anything published in literature 

and represents the most advanced modeling platform used for 

a national mercury deposition assessment.

3. Modeled deposition compared to measured deposition

Comment: Multiple commenters expressed dissatisfaction 

related to EPA’s model performance evaluation of CMAQ 

estimated mercury deposition. Commenters state that EPA 

failed to evaluate the CMAQ model against real-world 

measurements and that EPA fails to provide first-hand 

information on wet and dry deposition processes. Commenters 

also state EPA needs to assess how predicted values of

deposition compare to Mercury Deposition Network (MDN) data 

and how predicted values of ambient speciated mercury 

concentrations compare to measurement networks like AMNet 

and SEARCH. In addition, commenters state that the EPA used 

highly aggregated performance metrics comparing model 

estimates to observations that they felt result in a 

degraded and lenient operational evaluation of the modeling 

system. A commenter suggests EPA’s model performance 

provides no confidence for the intended purpose of 

estimating deposition near point sources. One commenter 

simply noted that EPA’s model over-estimated total mercury 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

185

wet deposition at MDN monitors. Finally, several commenters 

note that EPA presented a negative modeled wet deposition 

total in the air quality modeling TSD, which is physically 

impossible.

Response: The model predicted wet deposition in the 

air quality modeling TSD was incorrectly calculated during 

post-processing of model and observation pairs. This error 

only influenced the calculation of model performance 

metrics. The error has been fixed and the model performance 

metrics in the revised air quality modeling TSD have been 

updated. In response to comments, EPA has provided 

additional model performance evaluation by season to the 

air quality modeling TSD. In addition, EPA has now included 

model performance evaluation for total mercury wet 

deposition for the 36 km modeling domain at the suggestion 

of the commenters. 

EPA disagrees that an assessment comparing CMAQ total 

mercury wet deposition estimates to MDN data was not done. 

The air quality modeling TSD clearly shows a comparison of 

CMAQ estimated total mercury wet deposition with MDN data 

for the entire length of the modeling period. The 

characterization of wet and dry deposition processes 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

186

relating to speciated mercury in global and regional scale 

photochemical models should be continually evaluated by the 

academic community and improved when appropriate. CMAQ wet 

deposition of mercury has been and will continue to be 

extensively evaluated against Mercury Deposition Network 

sites.82 There is no dry deposition monitoring network and 

the CMAQ dry deposition processes will be evaluated when 

measurement data sets become available. EPA disagrees an 

evaluation of ambient speciated mercury against routine 

monitor networks such as AMNet or SEARCH would be useful 

for the purposes of this particular modeling application. 

The AMNet mercury network did not exist in 2005, which 

matches EPA’s baseline model simulation time period. The 

SEARCH network just started making preliminary measurements 

of mercury at one or two sites in 2005. In addition, 

measurement artifacts related to gaseous oxidized mercury 

are difficult to quantify and make direct comparison to 

 

82 Bullock, O.R., Atkinson, D., Braverman, T., Civerolo, K., Dastoor, 

A., Davignon, D., Ku, J.Y., Lohman, K., Myers, T.C., Park, R.J., 

Seigneur, C., Selin, N.E., Sistla, G., Vijayaraghavan, K., 2009. “An 

analysis of simulated wet deposition of mercury from the North American 

Mercury Model Intercomparison Study.” Journal of Geophysical ResearchAtmospheres 114.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

187

model estimates problematic.83 Given the problems associated 

with TEKRAN measurements of ambient mercury and the sparse 

nature of routine measurements in the United States, 

ambient mercury was not compared against model estimates. 

EPA disagrees that the model performance presented in 

the air quality TSD is insufficient. EPA asserts that the 

model performance evaluation is generally similar to the 

level of model performance presented in literature. One 

commenter presents the results of several mercury modeling 

studies as providing information they believe to be 

relevant for this assessment in terms of model performance 

metric estimation and the level of model performance 

evaluation shown for assessments modeling mercury near 

point sources. For example, one cited study titled 

‘Modeling mercury in power plant plumes’ models near-source 

EGU mercury chemistry, but provides absolutely no 

information about model performance evaluation.84 A 

commenter identifies two studies as supposedly having 

 

83 Lyman, S.N., Jaffe, D.A., Gustin, M.S., 2010. “Release of mercury 

halides from KCl denuders in the presence of ozone.” Atmospheric 

Chemistry and Physics 10, 8197-8204.

84 Lohman et al., 2006.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

188

mercury modeling results that are applicable to EPA’s 

analysis.85,86

These studies present similar model performance 

metrics as EPA, and also aggregated the metrics across many 

monitor locations similar to U.S. EPA; however, these 

articles make long term annual averages of modeled and 

observed total mercury wet deposition before performance 

metrics are estimated, which presents a more favorable 

evaluation. The Seigneur et al. paper87 employs a less 

stringent approach for matching observations and model 

estimates of total mercury wet deposition in that this 

paper makes annual averages of both before comparison to 

make model performance seem optically better. It is common 

practice to pair modeled estimates and observations in 

space and time (weekly in this case) and estimate 

performance metrics, then average all the metrics together. 

The latter is the approach taken by U.S. EPA and should 

have been taken by the studies presented by the commenter. 

 

85 Seigneur, C., Lohman, K., Vijayaraghavan, K., Jansen, J., Levin, L., 

2006. “Modeling atmospheric mercury deposition in the vicinity of power 

plants.” Journal of the Air & Waste Management Association 56, 743-751.

86 Vijayaraghavan, K., Karamchandani, P., Seigneur, C., Balmori, R., 

Chen, S.-Y., 2008. “Plume-in-grid modeling of atmospheric mercury.” 

Journal of Geophysical Research-Atmospheres 113.

87 Seigneur et al., 2006.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

189

EPA finds the performance evaluation presented in the 

modeling TSD consistent with and in the case of one study,88

far beyond what is presented in published articles deemed 

relevant by the commenter. In addition to the evaluation 

presented by EPA in the air quality modeling TSD, CMAQ 

model performance for total mercury wet deposition has been 

compared with other mercury models.89

EPA agrees that the commenter accurately restates 

total wet deposition model performance information provided 

by EPA in the Air Quality Modeling TSD. To provide context, 

other mercury modeling studies show a positive bias for 

annual total mercury wet deposition.90,91 An annual mercury 

modeling application done by ENVIRON92 and the Atmospheric 

and Environmental Research for Lake Michigan Air Directors 

Consortium show seasonal average normalized bias between 70 

and 158 percent and seasonal average normalized error 

 

88 Lohman, K., Seigneur, C., Edgerton, E., Jansen, J., 2006. Modeling 

mercury in power plant plumes. Environmental Science & Technology 40, 

3848-3854.

89 Bullock et al., 2009.

90 Id.

91 Vijayaraghavan et al., 2007.

92 Yarwood, G, Lau, S., Jia, Y., Karamchandani, P., Vijayaraghavan, K. 

2003. Final Report: Modeling Atmospheric Mercury Chemistry and 

Deposition with CAMx for a 2002 Annual Simulation. Prepared for 

Wisconsin Department of Natural Resources. 

http://www.gypsymoth.wi.gov/air/toxics/mercury/hg_X97579601_appB.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

190

between 72 and 503 percent.93 These results indicate a very 

large over-estimation tendency. The model performance shown 

by EPA is consistent with other long-term mercury modeling 

applications.

4. Excess Local Deposition from U.S. EGU Hg Emissions 

(Deposition Hotspots)

Comment: One commenter states that reducing mercury 

will benefit local environments. The commenter states that 

a 2007 study confirmed the presence of mercury “hotspots” 

downwind from coal-fired power plants, and confirmed that 

coal-fired power plants within the United States are the 

primary source of mercury to the Great Lakes and the 

Chesapeake Bay.94 The commenter also states that the study 

is consistent with a major mercury deposition study 

conducted by EPA and the University of Michigan that 

concluded that approximately 70 percent of mercury wet 

deposition resulted from local fossil fuel emissions in the 

region.95

 

93 Yarwood et al., 2003.

94 Evers, David C. et al. 2007. “Biological Mercury Hotspots in the 

Northeastern United States and Southeastern Canada,” Bioscience. Vol. 

57 No. 1. p. 29.

95 Cohen, et al. 2004. “Modeling the Atmospheric Transport and 

Deposition of Mercury to the Great Lakes,” Environmental Research 95, 

(247-265).
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

191

One commenter agrees with the Agency’s assessment of 

potential for deposition “hotspots” that shows that Hg 

deposition near EGUs can be three times as large as the 

regional average. The commenter states that this excess Hg 

deposition would substantially increase the health and 

environmental risks associated with emissions at these 

sites. The same commenter also states that the methodology 

applied by EPA to quantify near-source Hg deposition is 

conservative. The commenter states maximum excess local Hg 

deposition may be significantly underestimated by averaging 

high deposition sites downwind of an EGU in the direction 

of prevailing winds with lower excess deposition at 

locations close to but frequently upwind of the facility. 

The same commenter suggests that had EPA used CMAQ and 

individual 144 km2 grid cells to quantify local deposition 

the model could increase the excess Hg deposition at these 

locations significantly and place them at even greater risk 

of adverse health and environmental effects of HAP from 

U.S. EGUs. 

One commenter states that the Hubbard Brook Research 

Foundation issued a report in 2007 that confirmed five 

mercury hotspots, one of which was in the Adirondack Park, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

192

along with four suspected hotspots.96 The commenter states 

that this study also provides a good description of the 

impacts of mercury on the Common Loon, which is a symbol of 

a healthy Adirondack environment.

One commenter states that there is there is no 

evidence of mercury hotspots due to local deposition 

associated with coal-fired power plants. According to the 

commenter EPA‘s use of a 50km radius to calculate hotspots 

is flawed. The commenter states that modeling studies show 

that deposition of mercury emitted from power plants is not 

confined to a 50-km radius around the plants and that most 

emissions from power plants travel beyond 50 km.97

Several commenters state that the EPA does not 

adequately define hotspots in this proposed rule. Those 

same commenters cite a previous EPA definition of hotspots 

as “a waterbody that is a source of consumable fish with 

methylmercury tissue concentrations, attributable solely to 

utilities, greater than the EPA‘s methylmercury water 

 

96 Driscoll, C.T., D. Evers, K.F. Lambert, N. Kamman, T. Holsen, Y-J. 

Han, C. Chen, W. Goodale,T. Butler, T. Clair, and R. Munson. Mercury 

Matters: Linking Mercury Science with Public Policy inthe Northeastern 

United States. 2007. Hubbard Brook Research Foundation. Science Links 

Publication. Vol. 1, no. 3.

97 Seigneur et al., 2006.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

193

quality criterion of 0.3 mg/kg” (milligrams per kilogram)98. 

The same commenters state that it is unclear why the EPA 

changed from defining a hotspot by fish tissue 

methylmercury concentration to defining a hotspot by 

depositional excess. Two commenters suggest that a mercury 

hotspot is a specific location that is characterized by 

elevated concentrations of mercury exceeding a wellestablished criterion, such as a reference concentration 

(RfC) when compared to its surroundings. Those same 

commenters state that identifying mercury hotspots should 

not be constrained to locations where concentrations can be 

attributed to a single source or sector99. One of those two 

commenters notes that others have defined “hotspots as a 

spatially large region in which environmental 

concentrations far exceed expected values, with such values 

(i.e. concentrations) being 2 to 3 standard deviations 

above the relevant mean”.100

 

98 U.S. EPA, 2005. 40 CFR Part 63 [OAR–2002–0056; FRL–7887–7] RIN 2060–

AM96. Revision of December 2000 Regulatory Finding on the Emissions of 

Hazardous Air Pollutants From Electric Utility Steam Generating Units 

and the Removal of Coal- and Oil-Fired Electric Utility Steam 

Generating Units From the Section 112(c). Final rule, March 29.

99 Evers et al., 2007.

100 Sullivan T., 2005. “The Impacts of Mercury Emissions from coal-fired

Power Plants on Local Deposition and Human Health Risk.” Presented at 

the Pennsylvania Mercury Rule Workgroup Meeting, October 28.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

194

One commenter states that mercury concentrations are 

not always highest at sites closest to a major source. The 

commenter refers to a study by Kolker, et al. (2010)101 that 

demonstrated that concentrations of atmospheric reactive 

gaseous mercury, gaseous elemental mercury, and fine 

particulate mercury were lower when measured 25 km from a 

1114 MW coal-fired EGU than when measured 100 km away. The 

commenter states that these findings contradict the idea, 

implicit in EPA‘s hotspot analysis, that reactive gaseous 

mercury decreases with distance from a large point source.

One commenter states that wet deposition measurements 

were taken between November 2004 through December 2007 at 

three sites located downwind from the coal-fired power 

plant Crist in Pensacola, FL. The commenter states that 

during this period, Plant Crist emitted about 230 pounds of 

mercury annually, about 85 percent of which was reactive 

gaseous mercury.102 The commenter cites a study by Landing 

et al. (2010)103 that estimated that 22–33 percent of wet-

 

101 Kolker, et al., 2010.

102 EPRI, 2010. Atmospheric Deposition of Mercury, Trace Metals and Major 

Ions to a Watershed Around a Coal-Fired Power Plant. Palo Alto, CA: 

1021566.

103 Landing W.M., Caffrey J.M., Nolek S. D., Gosnell K. J., and Parker W. 

C., 2010 “Atmospheric Wet Deposition of Mercury and Other Trace 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

195

deposited mercury at these sites came from coal combustion, 

including regional and local sources while the remaining 

67–78 percent came from the global background. The 

commenter states that using the same data from these same 

wet deposition sites, Caffrey et al. (2010)104 found that 

mercury deposition and concentrations did not differ in a 

statistically significant manner among these three sites 

and that the concentrations values were similar to those 

from Mercury Deposition Network (MDN) sites that are more 

than 50 km away from Plant Crist located along the Northern 

Gulf of Mexico coast. 

Another commenter states that Plant Crist installed a 

wet scrubber and has operated that scrubber continuously 

since December 2009. The commenter states that the scrubber 

reduces total mercury emissions by about 70 percent, but 

reduces emissions of reactive gaseous mercury by about 85 

percent. According to the commenter, using mercury to trace 

metal (arsenic and selenium) ratios in precipitation 

 

Elements in Pensacola, Florida,” Atmospheric Chemistry and Physics, 10, 

4867–4877.

104 Caffrey, J.M., Landing, W.M., Nolek, S.D., Gosnell, K.J., Bagui, 

S.S., Bagui, S.C., 2010. “Atmospheric deposition of mercury and major 

ions to the Pensacola (Florida) watershed: spatial, seasonal, and 

inter-annual variability.” Atmospheric Chemistry and Physics 10, 5425-

5434.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

196

collected in the same MDN in (post-scrubber) 2010, 

Krishnamurthy, et al. (2011)105 reported that mercury 

deposition due to local and regional sources had changed 

between -10 to +6 percent at these sites, relative to 

historic measurements. The commenter states that these 

changes were thought to represent upper bound estimates, 

since the researchers assumed that all mercury, arsenic, 

and selenium measured in wet deposition was from local and 

regional coal combustion sources although this is not the 

case. The commenter states that, taken collectively, these 

findings show that increased local deposition, possibly due 

to EGUs, and deposition changes due to changes in EGU 

emissions, are small and within the range of natural 

variability.

Two commenters state that a study by the Department of 

Energy (DOE) that collected and analyzed soil and 

vegetation samples for mercury near three U.S. coal-fired 

power plants – one in North Dakota, one in Illinois, and 

one in Texas – found no strong evidence of “hotspots” 

around these three plants. 

 

105 Krishnamurthy N., Landing W.M, Caffrey J.M., 2011. “Rainfall 

Deposition of Mercury and Other Trace Elements to the Northern Gulf of 

Mexico.” Presented at the 10th International Conference on Mercury as a 

Global Pollutant, Halifax, Nova Scotia, Canada, July 27.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

197

Two commenters state that analysis of long-term trends 

in coal-fired EGU mercury emissions and wet deposition in 

Florida concluded that statistical analysis does not show 

evidence of a significant relationship between temporal 

trends in coal-fired EGU Hg emissions in Florida and Hg 

concentrations in precipitation during 1998-2010. According 

to the commenters these observational studies are supported 

by and consistent with evidence that oxidized mercury 

emitted from coal-fired power plants rapidly converts to 

elemental mercury, significantly reducing the potential for 

“local” or nearby deposition.

Two commenters state that the Mercury Risk TSD 

presents no information, summary statistics, and/or actual 

calculations showing how excess deposition within 50 km of 

an EGU source is obtained. The commenters state that by 

assessing only mercury deposition attributable to EGUs, EPA 

fails to provide a context for all other sources of mercury 

deposition. The commenters state that the Agency does not 

explain why deposition from the top 10 percent of EGU 

mercury emitters does not decline, despite substantial 

reductions in modeled mercury emissions from those sources 

between 2005 and 2016. According to the commenters this 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

198

implies that the top 10 percent EGUs may have approximately 

as much of a regional effect as a local effect. 

Two commenters state that the CMAQ model has 

limitations when used to predict local deposition and tends 

to overestimate local deposition. The commenters state that 

modeling studies using either a plume model or an Eulerian 

model predict that 91 to 96 percent of the mercury emitted 

by an EGU travels beyond 50 km.106

Response: EPA agrees with the commenters that stated 

that mercury emissions from EGUs deposit locally and 

regionally and contribute to excess local deposition near 

U.S. EGUs. EPA acknowledges additional studies107 cited by 

those commenters that corroborate EPA’s conclusions. 

However, EPA disagrees with those commenters’ 

characterization of the methodology used to calculate the 

potential for excess local deposition. In response, EPA has 

clarified the methodology in the new TSD entitled, 

“Technical Support Document: Potential for Excess Local 

Deposition of U.S. EGU Attributable Mercury in Areas near 

U.S. EGUs”, which is available in the docket.

 

106 Edgerton et al., 2006.

107 Driscoll et al., 2007.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

199

EPA agrees that there is no generally agreed upon 

absolute definition of “hotspot”. As discussed in the 

preamble and TSD, for the purposes of the appropriate and 

necessary finding, EPA determined that information on the 

potential for excess deposition of mercury in areas 

surrounding power plants would be useful in informing the 

finding. EPA disagrees with some commenters who 

misinterpreted the intent of the mercury deposition hotspot 

analysis. Specifically, the analysis is not of “mercury 

hotspots” but rather of mercury deposition hotspots, 

defined as excess local mercury deposition around power 

plants, as clarified in the new Local Deposition TSD. 

EPA disagrees that the analysis assumes that 

deposition of mercury is confined to a 50-km radius around 

power plants. The purpose of the EPA analysis was to 

evaluate whether there existed “excess deposition of Hg in 

nearby locations within 50 km of EGUs that might result in 

Hg deposition ‘hotspots’.” As explained further in the new 

TSD, EPA calculated the average EGU-attributable deposition 

(based on CMAQ modeling of mercury deposition) in the area 

500 km around each plant and the average EGU-attributable 

deposition in the area 50 km around each plant. The 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

200

difference between those two values is the excess local 

deposition around the plant. 

EPA disagrees with some commenters’ interpretation of 

the analysis as being focused on local deposition from all 

sources. In fact, the focus was on excess local deposition, 

rather than all local deposition. EPA agrees that all EGUs 

add to local deposition, however, not all EGUs have local 

deposition that greatly exceeds regional deposition, which 

is the relevant question. EPA disagrees that the DOE study 

referenced by the commenters attempted to assess the same 

analytical question as EPA’s analysis. The DOE study 

focused on comparisons of total deposition near and far 

from power plants. EPA’s analysis was not of total mercury 

deposition, because as EPA acknowledges throughout its 

analysis, global sources of mercury deposition account for 

a large fraction of total mercury deposition, and including 

those global sources of deposition would simply be adding 

noise to the comparison of local and regional U.S. EGU 

sourced mercury deposition. Because of regional deposition 

from both domestic and global sources of mercury, total 

mercury deposition at any location is unlikely to be highly 

correlated with local sources. However, EPA’s analysis 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

201

focused on U.S. EGU sourced mercury deposition, and 

demonstrates that for some plants (especially those with 

high mercury emissions), there is local deposition of 

mercury that exceeds the average regional deposition around 

the plant. 

EPA’s analysis shows there is heterogeneity in the 

amount of excess local deposition around plants, and Figure 

1 in the new Local Deposition TSD shows that some plants 

actually have local deposition that is less than the 

regional average deposition, suggesting that most of the 

mercury from those plants is transported regionally, or 

that other EGUs in the vicinity of those plants dominate 

the deposition of mercury near the plants. This does not 

detract from the overall finding that around some power 

plants with high levels of mercury emissions, there is 

excess local deposition that is on average 3 times the 

regional EGU-attributable deposition around those plants. 

EPA has clarified the purpose of the excess local 

deposition analysis in the new TSD.

EPA disagrees that the Mercury Risk TSD did not 

provide sufficient information regarding the excess local 

deposition calculation. Nonetheless, EPA has further 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

202

clarified the methodology in the new Local Deposition TSD, 

including further descriptions of the method used to 

calculate the local and regional deposition around power 

plants along with maps and tables of results.

EPA disagrees with the commenters that stated that the 

discussion of local deposition in the Mercury Risk TSD did 

not demonstrate that mercury deposition from the top 10 

percent of EGU mercury emitters declines. Table 1 of the 

new Local Deposition TSD clearly shows that mean local 

deposition (within 50km of a plant) for the top 10 percent 

of emitters declines from 4.89 μg/m3 to 1.18 μg/m3. What 

does not change is the percent local excess for EGUattributable mercury deposition. This implies that while 

mercury deposition from EGUs is declining, there is still 

an excess contribution to local deposition relative to 

regional deposition, e.g. because of dispersion, the 

contribution to average deposition outside 50km from the 

plant is lower than the contribution to average deposition 

within 50km of the plant.

EPA disagrees with commenters with respect to 

interpretation of the literature related to the spatial 

extent of deposition of mercury emitted by U.S. EGUs. EPA 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

203

also disagrees that the CMAQ model has limitations for this 

application or “overestimates” local deposition. The 

commenter does not provide any credible support for the 

idea that grid based models typically overestimate “local” 

deposition surrounding EGUs. EPA maintains that the CMAQ 

photochemical model represents the best science currently 

available in simulating atmospheric chemistry, transport, 

and deposition processes. EPA does not suggest mercury 

emissions from power plants stop at 50 km from the source. 

Some portion of EGU emissions deposit before 50 km, and 

some portion travels beyond 50 km. In addition, mercury 

disperses as it transports, so the average EGU contribution 

can be lower in areas beyond 50km relative to areas within 

50km even though mercury emissions from EGUs are depositing 

into U.S. watersheds.

The study108 cited by the commenter supporting the 

notion that 91-96 percent of mercury emitted from power 

plants travels beyond 50 km is based on a photochemical 

transport model that does not employ current state of the 

science (TEAM model) and that is not actively developed or 

updated. The modeling is based on grid cells that are 20 km 

 

108 Seigneur et al., 2006.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

204

in size which limits generalizability to EPA modeling 

performed at 12 km grid resolution using a state of the 

science photochemical grid model. The cited modeling study 

ignores dry deposition of elemental mercury from all 

sources which is an assumption that will clearly limit the 

regional impacts from sources109. This study cited by the 

commenter is critically flawed in methodology in that no 

results are presented where single mercury emission sources 

are removed and the difference between the zero out 

simulation and baseline model simulations are directly 

compared. Finally, the cited modeling study presents an 

illustration of gridded TEAM model total annual Hg 

deposition for the eastern United States that clearly shows 

elevated annual total mercury deposition in the vicinity of 

coal-fired power plants in the Ohio River Valley and 

northeast Texas.

The information provided by a commenter based on the 

EPRI, 2010 reference, is not relevant to the analysis of 

excess local deposition from EGUs alone, as it is based on 

wet deposition alone. It is not expected that changes to 

wet deposition over a fairly short time frame such as a 

 

109 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

205

year (the part of the study where the coal-fired power 

plant (Crist) emitting mercury installed controls) will 

provide a meaningful evaluation about the effectiveness of 

control technology since this study is based on ground 

level measurements of wet precipitation which is highly 

variable from year to year in addition to varying 

meteorological wind patterns from year to year. A more 

appropriate observation based assessment would be to 

evaluate both wet and dry deposition.

d. National-Scale Mercury Risk Analysis

1. Assumption of Linear Proportionality in Relationship 

between Changes in Hg Deposition and Changes in Fish Tissue 

Hg Concentrations (Mercury Maps)

Comment: Several commenters are critical of EPA’s 

assumption that changes in deposition resulting from U.S. 

EGU emissions of Hg will result in proportional changes in 

fish tissue Hg concentrations at the watershed level, as 

supported by the Mercury Maps modeling exercise. According 

to one commenter, the Mercury Maps (MMaps) model has 

limited capability to adequately determine bioaccumulation 

in fish. The same commenter states that the Mercury Cycling 

Model (MCM) developed by EPRI is a more rigorous model that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

206

was developed expressly to evaluate the relationship 

between changes in atmospheric mercury deposition to 

waterbodies and changes in fish tissue methylmercury 

levels.

Several commenters state that the Mercury Maps model 

has many deficiencies. Those commenters state that Mercury 

Maps is a static model unable account for the dynamics of 

ecosystems that affect mercury bioaccumulation is fish, 

cannot consider non-air mercury inputs to watersheds, and 

assumes reductions in airborne mercury lead to proportional 

reductions in fish mercury concentrations. Another 

commenter states that data that demonstrate a steady-state 

linear reduction in fish tissue MeHg in response to a 

reduction in atmospheric mercury deposition within 

watersheds do not exist, providing several references they 

state show non-linear responses to changes in mercury 

deposition110,111. 

 

110 Harris., R. C., John W. M. Rudd, Marc Amyot, Christopher L. Babiarz, 

Ken G. Beaty, Paul J. Blanchfield, R. A. Bodaly, Brian A. Branfireun, 

Cynthia C. Gilmour, Jennifer A. Graydon, Andrew Heyes, Holger 

Hintelmann, James P. Hurley, Carol A. Kelly, David P. Krabbenhoft, 

Steve E. Lindberg, Robert P. Mason, Michael J. Paterson, Cheryl L. 

Podemski, Art Robinson, Ken A. Sandilands, George R. Southworth, 

Vincent L. St. Louis, and Michael T. TateRudd, J. W. M., Amyot M., et 

al., Whole-Ecosystem study Shows Rapid Fish-Mercury Response to Changes 

in Mercury Deposition. Proceedings of the National Academy of Sciences 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

207

The same commenter disagrees with EPA’s interpretation 

of Figure 2-17 in the March TSD, and states that a U.S. 

Geological Survey national waterway study112 showed that 

sheet flow and drainage, not deposition, dominated input to 

the waterbodies it surveyed. The commenter states that 

sheet flow and drainage could well contain mercury, 

complicating the relationship that EPA claims is linear and 

direct. Another commenter cited Figure 2-17 in the Mercury 

TSD as showing that there is no well-defined relationship 

between mercury deposition and MeHg concentrations in fish 

tissue on a national basis. 

Several commenters provided comments related to the 

assumption that fish tissue Hg levels used in the analysis 

represent a steady state. One commenter stated that given 

the demonstrated lag time in response to deposition change, 

it is logical to conclude that a lag time needs to be 

incorporated in MMaps to adjust the estimation of how much 

 

Early Edition, PNAS 2007 104 (42) pp. 16586-16591; (published ahead of 

print September 27, 2007).

111 Orihel D.M., Paterson M.J., Blanchfield P.J., Bodaly R.A., Gilmour 

C.C., Hintelmann H., 2007. “Temporal Changes in the Distribution, 

Methylation, and Bioaccumulation of Newly Deposited Mercury in an 

Aquatic Ecosystem,” Environmental Pollution, 154, 77–88. 

112 Scudder B.C., Chasar L.C., Wentz D.A., Bauch N.J., Brigham M.E., 

Moran P.W., Krabbenhoft D.P., 2009. Mercury in fish, bed sediment, and 

water from streams across the United States, 1998–2005: U.S. Geological 

Survey Scientific Investigations Report 2009–5109, 74 p.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

208

fish tissue methylmercury levels decrease in response to 

decreases in mercury deposition attributable to U.S. EGUs. 

According to the same commenter, the METAALICUS study show 

that there is a lag time (and a non-proportional response) 

after 3–4 years. The same commenter notes that there are 

numerous factors that influence lag time including (1) 

watershed characteristics113, (2) watersheds may act as 

legacy sources releasing mercury when disturbed114, (3) the 

magnitude of emission reductions and subsequent changes in 

atmospheric deposition need to be weighed against the 

amount of mercury already in an ecosystem115, (4) the 

distance of an ecosystem from mercury sources116, and (5) 

mercury deposited to aquatic ecosystems becomes less 

available for uptake by biota over time117. Another 

 

113 Grigal D.F., 2002. “Inputs and Outputs of Mercury from Terrestrial 

Watersheds: A Review,” Environmental Review, 10, 1–39. 

114 Yang H., Rose N.L., Battarbee R.W., Boyle J.F., 2002. “Mercury and 

Lead Budgets for Lochnagar, a Scottish Mountain Lake and Its 

Catchment,” Environmental Science & Technology, 36, 1383–1388.

115 Krabbenhoft D.P., Engstrom D., Gilmour C., Harris R., Hurley J., 

Mason R., 2007. Monitoring and Evaluating Trends in Sediment and Water 

Indicators. In Harris R., Krabbenhoft D., Mason R., Murray M.W., Reash 

R., Saltman T. (Eds.), Ecosystem Responses to Mercury Contamination: 

Indicators of Change. New York: Society of Environmental Toxicology and 

Chemistry (SETAC) North America Workshop on Mercury Monitoring and 

Assessment, CRC, pp. 47–87.

116 Lindberg S. et al. 2007. “A synthesis of progress and uncertainties 

in attributing the sources of mercury in deposition.” Ambio 36(1): 19-

32.

117 Orihel D.M., Paterson M.J., Blanchfield P.J., Bodaly R.A., Hintelmann 

H., 2008. “Experimental Evidence of a Linear Relationship between
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

209

commenter stated that there are additional Mercury Maps 

assumptions that do not allow for considerations of lag in 

response to changes in: (1) deposition; (2) legacy sources 

of mercury such as mining; (3) historical mercury 

deposition; (4) natural mercury levels in fish; (5) 

ecosystem dynamics over time; or (6) the relative source 

contributions over time. Another commenter stated that lag 

times would need to be included in the modeling and be able 

to vary from watershed to watershed and sometimes even from 

waterbody to waterbody within a watershed. Several 

commenters stated that the emission rates of mercury due to 

U.S. sources have been decreasing for more than a decade, 

while emissions due to sources outside the U.S. have been 

increasing. Therefore, the commenter asserts that the 

system is not at steady-state, a basic premise of the 

model. Another commenter states that while the time lag for 

deposition to reach a waterbody is mentioned in the Mercury 

Risk TSD, there is no discussion of that fact that a 

portion of the deposition is unlikely to reach the water at 

all. 

 

Inorganic Mercury Loading and Methylmercury Accumulation by Aquatic 

Biota,” Environmental Science & Technology, 41, 4952–4958.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

210

One commenter believes EPA is incorrect in implying 

that its EGU risk estimates using Mercury Maps are 

underestimated because they do not account for legacy EGUattributable deposition, which EPA assumes to be higher. 

One commenter states that while EPA properly screened 

out watersheds with significant current non-air sources of 

Hg, EPA has not adequately screened out watersheds with 

significant Hg contributions from non-air sources, 

specifically, EPA does not screen out watersheds with 

historic mercury or gold mining or other industrial Hg 

discharges. The same commenter stated that EPA’s study was 

not geographically balanced, and was dominated by rivers in 

the coastal region of the southeast that has numerous 

wetlands, which are favorable locations for methylation, 

and that the conditions in the southeast are not typical of 

much of the rest of the U.S.

Response: EPA disagrees with the commenters asserting 

that the assumption of a linear proportional relationship 

between changes in U.S. EGU deposition and fish tissue Hg 

levels. EPA specifically asked SAB to evaluate EPA's 

assumption of linear proportionality in the relationship 

between mercury deposition and fish tissue methylmercury 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

211

concentrations, supported by the Mercury Maps analysis. The 

SAB peer review committee provided the following overall 

response, which generally supports EPA’s approach:

“The SAB agrees with the Mercury Maps approach used in 

the analysis and has cited additional work that 

supports a linear relationship between mercury loading 

and accumulation in aquatic biota. These studies 

suggest that mercury deposited directly to aquatic 

ecosystems can become quickly available to biota and 

accumulated in fish, and reductions in atmospheric 

mercury deposition should lead to decreases in 

methylmercury concentrations in biota. The SAB notes 

other modeling tools are available to link deposition 

to fish concentrations, but does not consider them to 

be superior for this analysis or recommend their use. 

The integration of Community Multiscale Air Quality 

Modeling System (CMAQ) deposition modeling to produce 

estimates of changes in fish tissue concentrations is 

considered to be sound. Although the SAB is generally 

satisfied with the presentation of uncertainties and 

limitations associated with the application of the 

Mercury Maps approach in qualitative terms, it 

recommends that the document include quantitative 

estimates of uncertainty available in the existing 

literature.”118

The SAB peer review committee specifically addressed 

the Mercury Cycling Model suggested by the commenter, and 

had the following response:

“The SAB agrees with the application of Mercury Maps 

in this assessment. There are other modeling tools 

capable of making a national scale assessment, such as 

the Regional Mercury Cycling Model (R-MCM). However, 

the R-MCM is more data intensive and the results 

produced by the two model approaches should be 

equivalent.

 

118 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

212

“The R-MCM, a steady-state version of the timedependent Dynamic Mercury Cycling Model, has been 

publicly available to and used by the EPA (Region 4, 

Athens, Environmental Research Laboratory) for a 

number of years. R-MCM requires more detail on water 

chemistry, methylation potential, etc., and yields 

more information as well. Substantial data support the 

Mercury Maps and the R-MCM steady-state results, so 

that the results of the sensitivity analysis and the 

outcomes from using the alternative models would be 

equivalent between the two modeling approaches. Though 

running an alternative model framework may provide 

additional reassurance that the Mercury Maps “base 

case” approach is a valid one, it is unlikely that 

substantial additional insight would be gained with 

the alternative model framework.”119

In addition, the SAB states, “Since the Mercury Maps 

approach was developed, several recent publications have 

supported the finding of a linear relationship between 

mercury loading and accumulation in aquatic biota.120,121,122

These studies suggested that mercury deposited directly to 

aquatic ecosystems can become quickly available to biota 

and accumulated in fish, and that reductions in atmospheric 

mercury deposition should lead to decreases in 

methylmercury concentrations in biota. These results 

substantiate EPA’s assumption that proportionality between 

air deposition changes and fish tissue methylmercury level 

 

119 U.S. EPA-SAB, 2011.

120 Orihel et al., 2007. 

121 Orihel et al., 2008.

122 Harris et al., 2007. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

213

changes is sufficiently robust for its application in this 

risk assessment.”123

Based on the responses of the SAB peer review 

committee, EPA’s use of the linear proportionality 

assumption, supported by the Mercury Maps analysis, is 

well-supported.

EPA also disagrees with commenters’ interpretation of 

Figure 2-17. As stated in the Mercury Risk TSD, while this 

figure is useful in demonstrating the lack of correlation 

across watersheds between total deposition of mercury and 

MeHg concentrations in fish tissue, it is not indicative of 

the likely correlation between changes in mercury 

deposition at a given watershed and changes in MeHg 

concentrations in fish tissue from that watershed. The SAB 

peer review panel agreed with this interpretation, noting 

the importance of Figure 2-17 demonstrating that “spatial 

variability of deposition rates is only one major driver of 

spatial variability of fish methylmercury and that 

variability of ecosystem factors that control methylation 

 

123 U.S. EPA-SAB, 2011. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

214

potential (especially wetlands, aqueous organic carbon, pH, 

and sulfate) also play a key role.”124

In response to recommendations from the SAB, we 

expanded the discussion of uncertainties associated with 

the linearity assumption, including uncertainties related 

to the potential for sampled fish tissue Hg level to 

reflect previous Hg deposition, and the potential for nonair sources of Hg to contribute to sampled fish tissue Hg 

levels. Each of these sources of uncertainty may result in 

potential bias in the estimate of exposure associated with 

current deposition. EPA took steps to minimize the 

potential for these biases by 1) only using fish tissue Hg 

samples from after 1999, and 2) screening out watersheds 

that either contained active gold mines or had other 

substantial non-U.S. EGU anthropogenic releases of mercury. 

The SAB commented that EPA’s approach to minimizing the 

potential for these biases to affect the results of the 

risk analysis appears to be sound, and that additional 

criteria that could be applied are unlikely to 

substantially change the results. As a result, EPA 

disagrees with the commenter that EPA’s screening process 

 

124 U.S. EPA-SAB, 2011. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

215

is inadequate. In addition, we conducted several

sensitivity analyses to gauge the impact of excluding 

watersheds with the potential for non-U.S. EGU Hg releases, 

and found that the results were robust to these exclusions.

In response to specific comments regarding the use of 

the Mercury Maps model, EPA clarifies that the national 

scale mercury risk analysis did not directly use the 

Mercury Maps model. Instead, EPA is applying an assumption 

of linear proportionality between changes in mercury 

deposition and changes in MeHg concentrations in fish that 

is supported by the Mercury Maps modeling. By assuming 

steady-state conditions in apportioning fish tissue Hg 

levels and risk, EPA does not attempt to project lag times. 

Recent research cited by the SAB125,126,127 identifies 

relatively rapid response of fish tissue Hg to changes in 

Hg loading, which suggests that fish tissue Hg levels could 

react more quickly to reductions in Hg deposition than 

previously thought. This finding reduces concern that fish 

tissue Hg levels could be linked to older patterns of Hg 

 

125 Orihel et al., 2007.

126 Orihel et al., 2008.

127 Harris et al., 2007.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

216

deposition and strengthens the approach used in the Revised 

Mercury Risk TSD. 

2. Characterization of Subsistence Fishing Populations and 

Exposure Scenario

Comment: Several commenters state that the EPA 

provides no clear definition of subsistence, near 

subsistence, or high-end fish consumption, instead assuming 

that poverty is a direct indication of subsistence fishing 

and high-end fish consumption. One commenter states that 

there is no documentation supporting these assumptions.

Another commenter states that EPA’s definitions of

subsistence fishers in the Mercury Risk TSD are not 

consistent with earlier EPA documents, and are used 

inconsistently throughout the Mercury Risk TSD. Several 

commenters state that while subsistence fishing can be 

associated with poverty, poverty does not indicate 

subsistence fishing. One commenter states that by including 

watersheds with as few as 25 members of individuals living 

in poverty, EPA overstates risks.

One commenter states that it is unclear what 

literature the Agency says “generally supports the 

plausibility of high-end subsistence-like fishing ... to some 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

217

extent across the watersheds” and states that if other 

studies exist, then the EPA should provide the values for 

comparison.

One commenter states that the EPA combined two 

parameters with differing scales to establish the 

geographic unit used in the Mercury Risk TSD risk 

assessment. HUC watersheds are based on average about 35 

square miles in size, while U.S. census tracts used to 

identify watersheds relevant for subpopulations of 

interest—cover a few tenths to hundreds of square miles. 

Several commenters stated that it is unclear how 

differences in geographic resolution between watersheds and 

census tracts were handled in the analyses.

One commenter states that procedure for assigning 

census tracts could bias exposure outcomes. For example, a 

single influential census tract in a watershed could drive 

risk, even if the watershed had only a minimal number of 

fish samples. The commenter states that this possibility is 

a concern in urban areas, which account for the majority of 

census tracts, because these census tracts are more likely 

to be included in a risk analysis because they have more 

than 25 people living in poverty. The commenter states that 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

218

these census tracts may drive the extremes of the 

distribution without regard to the actual number of highlevel, self-caught fish consumers within their boundaries. 

The commenter stated that they could not assess the 

potential bias and noted that the EPA did not test the bias 

by sensitivity analyses.

Several commenters state that EPA was not clear 

whether the poverty criteria were applied in all scenarios 

or just for the high-end female fish consumer scenario. One 

commenter states that EPA should apply the minimum 25 

source population criteria only to populations of women of 

childbearing age. One commenter states that the EPA 

assumption would result in any densely populated urban 

census tract with a single fish tissue sample being 

assigned to a potentially at risk watershed, regardless of 

the actual degree of recreational or subsistence fishing 

taking place there.

Response: EPA agrees with the comments that 

subsistence fish consumption was not clearly defined, and 

we have provided a clearer definition in the revised 

Mercury Risk TSD, however, this clarification does not 

result in any changes to the quantitative analysis. In the 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

219

Revised Mercury Risk TSD, EPA clarifies that “subsistence 

fishers” are defined as individuals who rely on 

noncommercial fish as a major source of protein (U.S. EPA, 

2000).128 This definition is reflected in the range of fish 

consumption rates used in estimating risk. The likely 

presence of this type of subsistence fish consumer is 

supported by available peer-reviewed literature (see Table 

1-5 of the Revised Mercury Risk TSD). These studies clearly 

show that a subset of surveyed fishers consumes self-caught 

fish at the rates that were cited in the Mercury Risk TSD. 

The SAB peer review concluded that the consumption rates 

and locations for fishing activity are supported by the 

data presented in the Mercury Risk TSD, and are generally 

reasonable and appropriate given the available data.129

EPA notes that there is some confusion in the comments 

related to the size of the watersheds modeled. Several 

commenters stated that HUC watersheds are 35 km on a side. 

The commenters appear to be referring to HUC8 

classifications. HUCs are defined for varying spatial 

 

128 U.S. EPA, U.S. Environmental Protection Agency. 2000. Guidance for 

Assessing Chemical Contaminant Data for Use in Fish Advisories, Volume 

3: Overview of Risk Management. Office of Science and Technology, 

Office of Water, U.S. Environmental Protection Agency, Washington, DC. 

EPA 823-B-00-007.

129 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

220

resolutions. The geographic unit used as the basis for 

generating risk estimates is the HUC12 scale, which is 

about 10 km on a side, which is consistent with the size of 

the CMAQ grid cells, which are 12km2. EPA has also clarified 

that the specific unit of analysis for this assessment is 

at the watershed, not enumerated subpopulations. 

The U.S. Census tracts are only used to determine 

whether there are populations in the vicinity of a given 

watershed, which could increase the potential for a 

category of subsistence fishers to be active at that 

watershed. In the Revised Mercury Risk TSD, EPA modified 

the female subsistence scenario to be applied equally to 

all watersheds with fish tissue Hg data based on the 

likelihood that these populations have the potential to 

fish at most watersheds. Thus, concerns regarding the use 

of census data to select watersheds with the potential for 

subsistence fishing are no longer applicable for this 

scenario. However, for the remaining subsistence scenarios, 

EPA continues to use U.S. Census tract-level data to 

evaluate the presence of a “source population” in the 

vicinity of the watershed being modeled for risk. In this 

context, the U.S. Census data are being used to assess 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

221

whether a SES-differentiated group similar to the 

particular type of subsistence fisher being modeled (e.g., 

poor Hispanics) are located in the vicinity of the 

watershed. If a source population is nearby, then this 

increases the potential that subsistence fishing activity 

could occur for that population scenario.

EPA continues to model risk for white and black 

subsistence fishers active in the southeast and for 

Hispanics assessed nationally. In this case, EPA links 

poverty with subsistence fishing in that these populations 

are only modeled for locations with poor source 

populations. However, in modeling these three populations,

EPA asserts that the presence of a poor source population 

is an indicator of the potential for subsistence fishing 

activity, rather the presence of such activity. The linkage 

between poverty and higher rates of subsistence fish 

consumption is supported by the Burger et al. study,130

which identified substantially higher consumption rates for 

poor individuals (see Table 5 of the study). EPA 

acknowledges that subsistence fishing activity by specific 

 

130 Burger, J., 2002. “Daily Consumption of Wild Fish and Game: Exposures 

of High End Recreationists," International Journal of Environmental 

Research and Public Health, 12 (4), 343–54.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

222

subpopulations might only be present across a subset of the 

watersheds EPA modeled for risk. However, given the stated 

goal of the analysis of determining the percent of 

watersheds where the potential exists for exposures to U.S. 

EGU-attributable Hg to represent a public health hazard, 

identifying a set of watersheds with the potential for the 

type of high fish consumption that leads to high Hg 

exposure is appropriate. EPA notes that a relatively small 

fraction (less than 4 percent) of watersheds has fish 

tissue Hg data, thereby allowing them to be included in the 

risk assessment. Consequently, while there is the potential 

for including in the analysis some watersheds that may not 

have currently active subsistence fishing activity, there 

is also the very real possibility that EPA excluded other 

watersheds from the analysis where this type of subsistence 

fishing activity occurs, due to a lack of fish tissue Hg 

data.

EPA agrees with the comment that it is likely that 

exposure to total MeHg through commercial fish consumption 

represents a more significant risk for the general 

population than consumption of freshwater fish obtained 

through self-caught fishing activity. However, subsistence 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

223

fishers active at inland freshwater watersheds are likely 

to experience the highest levels of individual risk as a 

result of exposure to U.S. EGU-sourced mercury. Therefore, 

EPA focuses on this group of subsistence fishers in the 

risk assessment and do not evaluate exposure for the 

general population related to mercury exposure through 

seafood.

3. Cooking Loss Adjustment Factor

Comment: Several commenters state that the EPA did not 

justify the selection of a cooking loss factor of 1.5 that, 

according to one commenter, increases estimated intake by 

50 percent, thus increasing the daily methylmercury intake 

rate by a constant factor of 33 percent and also increasing 

any resulting (HQ) risk estimate by a similar factor. 

Several commenters state that the source of the EPA’s 

selected loss factor131 reported a range of cooking losses 

from 1.1 to 6. Several commenters cite several studies that 

report no or highly variable changes in MeHg levels as a 

 

131 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.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

224

result of cooking fish132,133,134,135,136. One commenter suggests 

that the EPA cooking loss adjustment factor of 1.5 is at 

the high-end of the values supported by the literature. 

Another commenter stated that EPA has used other adjustment 

factors in previous documents, and that the adjustment 

factor should not be fixed across different populations 

given potential differences in cooking practices. Several 

commenters noted that the cooking loss adjustment factor 

should only be applied to estimates of consumption rates 

for prepared fish, and that some sources of consumption 

rates are based on raw fish.

Response: EPA disagrees with the commenters that the 

selection of the cooking loss factor of 1.5 is not 

justified by the literature. EPA also disagrees with the 

 

132 Armbruster G., Gerow K.G., Lisk D.J., 1988. “The Effects of Six 

Methods of Cooking on Residues of Mercury in Striped Bass,” Nutrition 

Reports International, 37, 123–126.

133 Gutenmann, W.H. and Lisk D.J., 1991. “Higher Average Mercury 

Concentration in Fish Fillets after Skinning and Fat Removal,” Journal 

of Food Safety, 11, 99–103. 

134 Farias L.A., Favaro, D.I., Santos J.O., Vasconcellos M.B., et al., 

2010. “Cooking Process Evaluation on Mercury Content in Fish,” Acta 

Amazonia, 40 (4), 741–748.

135 Perelló G., Martí-Cid R., Llobet J.M., Domingo J.L., 2008. “Effects 

of Various Cooking Processes on the Concentrations of Arsenic, Cadmium, 

Mercury, and Lead in Foods,” Journal of Agricultural and Food 

Chemistry, 156 (22), 11262–11269. 

136 Torres-Escribano S., Ruiz A., Barrios L., Vélez D., Montoro R., 2011. 

“Influence of Mercury Bioaccessibility on Exposure Assessment 

Associated with Consumption of Cooked Predatory Fish in Spain,” Journal 

of the Science of Food and Agriculture, 91 (6), 981–6.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

225

comment that the cooking loss adjustment factor of 1.5 is 

at the high-end of the range of values in the literature. 

EPA selected the Morgan (1997) study as the basis for the 

food preparation/cooking adjustment factor because it 

focused on the types of freshwater fish species 

representative of what might be consumed by subsistence 

fishing populations (i.e., walleye and lake trout). The 

Morgan (1997) study provides a range of adjustment factor 

for each fish type including 1.1 to 1.5 for walleye and 1.5 

to 2.0 for lake trout. Given these two ranges, EPA 

determined it to be reasonable to take an intermediate 

value between the two ranges (i.e., 1.5), rather than focus 

on either the highest or lowest values. The Morgan (1997) 

study explains that preparation/cooking of fish results in 

an increase in MeHg levels per unit fish because Hg 

concentrates in the muscle, while preparation/cooking tends 

to reduce non-muscle elements (e.g., water, bone, fat). 

Regarding the alternative studies identified by the 

commenters, EPA makes the following observations. Regarding 

the first study,137 the study suggests that the authors may 

have included measurement of non-fish components added to 

 

137 Farias et al., 2002. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

226

dishes (e.g., onions, heavy breading etc.) in measuring Hg 

concentrations post-cooking. These non-fish elements could 

dilute the post-cooking Hg measurements giving the 

appearance of a cooking loss, even while actual fish tissue 

Hg levels could have increased due to preparation. 

In the second study,138 the three fish species 

considered are saltwater and not freshwater which decreases 

the relevance of this study compared with another study139

that focused on freshwater species of the type reflected in 

the risk modeling. Furthermore, this study140 notes that the 

absolute content of Hg in fish does not decrease during 

cooking and instead, it is the reduction of water and fat 

that result in an increase in the concentration (but not a 

change in content), which is conceptually consistent with 

EPA’s cooking loss factor. 

The third study raises an interesting issue with its 

focus on measurement of bioaccessible mercury in raw and 

cooked fish.141 Their analysis shows that the concentration 

of bioaccessible mercury appears to significantly decrease 

in cooked fish compared with raw fish and they suggest that 

 

138 Perelló et al., 2008. 

139 Morgan et al., 1997.

140 Perelló et al., 2008.

141 Torres-Escribano et al., 2011
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

227

this needs to be factored in when measuring risk. However, 

in order to factor in (quantitatively) measurements of 

bioaccessible mercury into the risk assessment, the risk 

model would have to be parameterized to work with this 

category of mercury. However, available information 

currently allows us to specify the risk model in terms of 

total mercury intake (and not bioaccessible mercury). 

Specifically, the factor linking mercury intake to hair 

mercury level (which is then used as the exposure metric to 

estimate risk) is based on intake of total Hg. 

Consequently, while this article provides information that 

is potentially informative for guiding future research and 

methods development, it does not directly impact the 

current risk assessment. In addition, in terms of total 

mercury (not differentiated as bioaccessible), the TorresEscribano study shows a substantial increase in unit fish 

concentration following cooking (see Table 1 in the 

article). 

The Armbruster et al. study142 focused on the issue of 

whether cooking of fish decreased Hg levels, as can be the 

case with lipophilic chemicals. Their study found instead, 

 

142 Armbruster et al., 1988.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

228

a modest, but non-statistically significant increase in Hg 

levels for most of the cooking methods assessed, which is 

directionally consistent with the values used in the risk 

assessment. The Gutenmann et al. study focuses on the 

relationship between fish size and sex and mercury 

concentration (specifically for brown trout) and only 

addresses the issue of mercury concentration in relation to 

cooking and preparation in a qualitative manner.143

Specifically, while the article does provide results for 

skin on versus skin off (noting a non-statistically 

significant increase in mercury concentration with the 

latter), it qualitatively discusses the potential of fat 

removal (which could occur through preparation and cooking) 

to increase mercury concentration given that mercury is 

associated with protein elements of the fish. Because the 

article does not provide substantial empirical data 

regarding preparation/cooking adjustment, it is of little 

use in informing the food preparation/cooking adjustment 

factor used in the risk assessment. 

When considered collectively, EPA disagrees that the 

additional studies identified by the commenter contradict 

 

143 Gutenmann et al., 1991.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

229

the cooking loss factor used in the risk assessment and 

maintains that the Morgan study144 remains the most 

applicable for characterizing cooking/preparation effects 

on Hg concentrations in fish, given the fisher scenarios 

assessed in this study.

EPA agrees that application of the cooking loss 

adjustment factor is appropriate if the fish consumption 

rates are for as cooked or as consumed and not for raw 

fish. Careful review of the three studies used in the risk 

assessment to identify subsistence fisher consumption rates 

suggests that all three represent annual-average daily 

intakes (g/day) of as consumed or as cooked fish. One study 

states that they used models of portion or meal size 

servings (the size of the serving the respondent regularly 

eats).145 Therefore, EPA interprets the fish consumption 

rates provided in the Burger et al. study as representing 

as cooked/prepared and not for raw fish and for that 

reason, application of a preparation/ cooking adjustment 

factor is required. The Shilling et al., (2010) study146

 

144 Morgan et al., 1997. 

145 Burger et al., 2002.

146 Shilling, Fraser, Aubrey White, Lucas Lippert, Mark Lubell (2010). 

Contaminated fish consumption in California’s Central Valley Delta. 

Environmental Research 110, p. 334-344.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

230

used different sized models of cooked fish filets and 

therefore these consumption rates are also interpreted as 

represented as cooked/prepared and not raw fish. One 

study147, based on personal communication with the author,148

did query survey responders for meal portion or serving 

size and therefore, the consumption rates do represent as 

cooked/prepared. Because all three studies provide 

consumption rates based on as cooked/prepared or as 

consumed, it is appropriate to apply the cooking loss 

adjustment factor in modeling exposure.

4. Fish Consumption Rates and Fish Tissue Hg 

Characterization

Comment: One commenter stated that in the past the 

Agency has recommended various default consumption rates 

(in the general range of 130 to <150 g/day) to provide 

default intakes for subsistence fishers under the Risk 

Assessment Guidance for Superfund (RAGS) or the Fish 

Advisory Guidance.

149,150 The commenter states that these 

 

147 Dellinger JA. 2004. “Exposure assessment and initial intervention 

regarding fish consumption of tribal members of the Upper Great Lakes 

Region in the United States.” Environ Res 95:325–340.

148 Personal communication, Dr. Dellinger, September 27, 2011

149 U.S. EPA. 1991. Risk Assessment Guidance for Superfund (RAGS). Part C 

1991 EPA/9285.7-01C. October.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

231

default consumption rates are derived from various studies 

and generally are based on 90th or 99th percentile 

distribution estimates. Another commenter states that EPA’s 

use of the 99th percentile fish consumption for its risk 

analysis is inconsistent with the Agency’s risk assessment 

guidelines, which recommend evaluating a reasonable maximum 

exposure (“RME”) scenario,151 which equates to about a 95th 

percentile fish consumption value. The same commenter 

states that EPA applies the 99th percentile to a “small 

survey of 149 South Carolina female anglers” to calculate 

an ingestion rate of 373 g/day. The commenter states that 

if the 95th percentile is use the ingestion rate would be 

173 g/day and if the default ingestion rate for determining 

ambient water standards is used the ingestion rate would be 

142 g/day.

Several commenters state that EPA bases its fish 

consumption rates used in the risk analysis on a limited 

number of studies, and that those studies are poorly 

documented. 

 

150 U.S. EPA. 2000. National Guidance: Guidance for Assessing Chemical 

Contaminant Data for Use in Fish Advisories, Volume 2. EPA 823-B-00-

008, November.

151 U.S. EPA. 1989. Risk Assessment Guidance for Superfund (RAGS).

EPA/540/1-89/002. December.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

232

Another commenter states that the EPA should summarize 

available supporting studies by basic study content, 

characteristics, design, size, demographics, dietary recall 

period, and fish intake rates by demographic variables. 

According to the commenter this summary would support the 

scientific validity of the assessment, and better 

illustrate the potential variability and uncertainty 

involved in extrapolating data from small populations to 

the national scale, noting that the three studies actually 

used to provide subsistence population estimates, which 

were extrapolated to the national scale, included a limited 

number of individuals living in diverse and localized 

areas.

One commenter stated that the assumption with the 

greatest impact is the fish consumption rate. That same 

commenter stated that there is a dramatic effect of 

increased HQs and loss of IQ depending on the ingestion 

rate considered going from the 50th percentile ingestion 

rate to the 99th percentile ingestion rate. The commenter 

states that when an estimate of the 95th percentile 

ingestion rate of the 15-44 year old female population is 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

233

considered, the HQ is a tenth of the value computed with 

the 99th percentile high-end female fisher.

One commenter states that EPA provides broad summary 

statistics of its fish tissue data in Table 5-2 of the 

Regulatory Impact Analysis (RIA), but the summary does not 

allow an assessment of the representativeness and 

robustness of the underlying data for the risk assessment, 

especially at the tails of the distribution. The commenter 

states that the table does not include a median statistic 

and does not provide any information on the number of lakes 

and river segments in each watershed. According the 

commenter an analysis of EPA’s database by the SAB peer 

review panel indicated that 60 percent of the watersheds 

with fish mercury data from rivers have risks calculated 

based upon a sample size of one or two fish. The commenter 

states that it is not reasonable to base a significant 

policy and regulation decision on watersheds whose exposure 

is based on a single fish sample in a single water body 

within it.

Several commenters criticized EPA’s use of the 75th

percentile fish tissue MeHg level in a watershed. One 

commenter states that EPA provides no rationale for its 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

234

decision to choose the highest of the 75th percentile for 

fish mercury levels among rivers and lakes within the HUC. 

Several commenters stated that subsistence fishers are less 

likely to target larger fish relative to recreational 

fishers. Several commenters suggested that EPA include a 

sensitivity analysis using the mean or median fish MeHg 

level in a watershed. One commenter also stated that EPA 

arbitrarily inflates the risk estimates by assuming 

consumption of only fish greater than 7 inches and choosing 

the largest of the 75th percentile of fish mercury levels 

from these larger fish (i.e., larger than 7 inches) for 

rivers and lakes. That same commenter suggests using the 

median of all size fish, not just those over 7 inches. 

One commenter states that EPA should quantify adverse 

effects from the ingestion of MeHg in seafood in addition 

to ingestion of MeHg from self-caught freshwater fish. 

According to the commenter, recent studies demonstrate that 

were EPA to take into account consumption of seafood, MeHg 

consumption in the U.S. is of even greater concern.

Response: EPA acknowledges that the focus of the 

national scale risk assessment is characterizing risk for 

the group likely to experience the greatest U.S. EGU-
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

235

sourced mercury risk, which is subsistence fishing 

populations active at inland freshwater lakes and rivers. 

Specifically, within that subsistence fishing population, 

EPA is interested in those individuals who are most at 

risk, which includes those who consume the most fish. For 

that reason, EPA included consideration for a range of 

high-end fish consumption rates including the 99th

percentile representing the most highly-exposed 

individuals. In responding to the SAB peer review, EPA has 

clarified this focus in the introduction to the Revised 

Mercury Risk TSD, and have changed the full title to 

“Revised Technical Support Document: National-Scale 

Assessment of Mercury Risk to Populations with High 

Consumption of Self-caught Freshwater Fish.” This focus for 

the risk assessment (including modeling of the 99th

percentile fish consumption rate by subsistence fishers) 

reflects consideration for the provisions of the Clean Air 

Act addressing the appropriate and necessary determination 

for U.S. EGUs, and is consistent with treatment of other 

HAP under Section 112 of the CAA, which focuses on 

maximally exposed individuals. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

236

EPA agrees that the fish consumption rate is an 

important factor in calculating risk from exposure to 

methylmercury in fish. EPA acknowledges that the 

distribution of fish consumption rates is positively 

skewed, which means that at higher percentiles (e.g., 90th, 

95th and 99th) there is a substantial increase in ingestion 

rates relative to the mean or median. The Revised Mercury 

Risk TSD includes a reasonableness check on the amount of 

fish consumed (as a daily value) reflected in the different 

rates. While the 99th percentile consumption rates for the 

subsistence female fisher (373 g/day) is substantially 

higher than the 90th or 95th percentile values (123 and 173 

g/day respectively) the 99th percentile value translates 

into a 13-ounce meal. While this does represent a large 

serving, it is still reasonable if representing an 

individual who receives all of their meat protein from 

self-caught fishing (and the 13 ounces per day does not 

have to be eaten all at one meal). The larger rates of 

consumption (values in the 250+ g/day range) are supported 

by all three studies used in the risk assessment and 

therefore, there is support across studies for near 

bounding consumption rates in this range. EPA acknowledges 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

237

uncertainty associated with estimation of high-end 

percentile values in these studies due to relatively low 

samples sizes for some of the population groups. However, 

even if a few individuals provided these high self-caught 

fish consumption rates, making it difficult to characterize 

the population percentiles they represent, the values still 

suggest the existence of these levels of high fish 

consumption among surveyed individuals. In the context of 

determining whether a public health hazard could exist, EPA 

asserts that it is reasonable to include these consumption 

rates as representative of the most at risk populations. In 

these cases, however, it is important to highlight 

uncertainty associated with characterizing the specific 

population percentile that these ingestion rates represent, 

and EPA has done so in the Revised Mercury Risk TSD.

EPA disagrees with the comment that high consumption 

rates are poorly documented. Evidence of these high fish 

consuming populations can be found in surveys152 and 

specialized studies.

153,154,155,156,157 Several studies identified 

 

152 Burger et al., 2002.

153 Burger, J., K. Pflugh, L. Lurig, L. Von Hagen, and S. Von Hagen. 

1999a. “Fishing in Urban New Jersey: Ethnicity Affects Information 

Sources, Perception, and Compliance.” Risk Analysis 19(2): 217-229.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

238

additional fishing populations with subsistence or near 

subsistence consumption rates, including urban fishing 

populations (including low-income populations),158,159,160

Laotian communities,161 and Hispanics. EPA participated in 

1999 in a project investigating exposures of poor, minority 

communities in New York City to a number of contaminants 

including Hg, which found these populations can have very 

high fish consumption rates.162 The SAB peer review 

concluded that the consumption rates and locations for 

fishing activity are supported by the data presented in the 

Mercury Risk TSD, and are generally reasonable and 

appropriate given the available data.

163

 

154 Burger, J., Stephens, W. L., Boring, C. S., Kuklinski, M., Gibbons, 

J. W., Gochfeld M. 1999b. “Factors in Exposure Assessment: Ethnic and 

Socioeconomic Differences in Fishing and Soncumption of Fish Caught 

along the Savannah River.” Risk Analysis, Vol. 19, No. 3, p. 427.

155 California Environmental Protection Agency (CalEPA). 1997. 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, 

July.

156 Tai, S. 1999. “Environmental Hazards and the Richmond Laotian 

American Community: A Case Study in Environmental Justice.” Asian Law 

Journal 6: 189.

157 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).

158 Burger et al., 1999a.

159 Burger et al., 1999b.

160 CalEPA, 1997.

161 Tai, 1999..

162 Corburn, 2002.

163 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

239

EPA agrees that the Mercury Risk TSD would be improved 

by clarifying that the literature review focused on 

identifying studies characterizing subsistence fish 

consumption for groups active at freshwater locations 

within the U.S., and EPA has revised the Mercury Risk TSD 

accordingly. In the Mercury Risk TSD, EPA provided a 

summary of important study attributes for the source 

studies used to obtain fish consumption rates. This 

information was provided in Table C-1 in an appendix. To 

improve clarity, EPA has moved the summary table to the 

main body in the Revised Mercury Risk TSD. In identifying 

these studies, EPA focused on surveys for subsistence 

fishers that were applicable at the broader regional or 

national level. In the Mercury Risk TSD, EPA acknowledged 

the lower sample sizes for some of the subsistence fisher 

groups, and in several cases did not use the 99th percentile 

consumption rates because the sample sizes were too low to 

support this level of resolution.

EPA disagrees with the comment that it did not provide 

a rationale for choosing the highest 75th percentile fish 

tissue concentration across lakes and rivers in a 

watershed. However, EPA has modified the methodology based 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

240

on evaluation of the number of samples within each 

watershed (responding to a recommendation from the SAB). In 

the revised methodology, EPA computes the 75th percentile 

value at each sampling site within a watershed. EPA then 

computed the average of the site-specific 75th percentile 

fish tissue Hg values within a given watershed. This 

approach does not differentiate between rivers and lakes 

and reflects an improved treatment of behavior, allowing 

for fishers to choose among multiple fishing sites within a 

watershed. 

EPA generally agrees with the comment that some 

fraction of subsistence fishers likely consume fish without 

consideration for size (given dietary necessity), however, 

it is reasonable to assume that a subset of subsistence 

fishers could target larger fish to maximize the potential 

consumption per unit of fishing effort. It is this subset 

of subsistence fishers targeting larger fish, which is 

represented by the 75th percentile fish tissue value used in 

the risk assessment. In addition, the female subsistence 

fishing population that is included in the analysis is also 

likely to provide coverage for high-end recreational 

anglers who could target larger freshwater fish. The SAB 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

241

commented that: “Using the 75th percentile of fish tissue 

values as a reflection of consumption of larger, but not 

the largest, fish among sport and subsistence fishers is a 

reasonable approach and is consistent with published and 

unpublished data on predominant types of fish consumed.”164

The SAB suggested that EPA include a sensitivity analysis 

based on use of the median value, and EPA has done so in 

the Revised Mercury Risk TSD. This sensitivity analysis 

showed that using the median estimates had only a small 

impact on the number and percent of watersheds identified 

as having populations potentially at risk from U.S. EGUattributable MeHg exposures. Regarding the 7-inch criteria, 

for the Revised Mercury Risk TSD, EPA clarified that this 

cutoff represents a minimum size limit for a number of key 

edible freshwater fish species established at the Statelevel. For example, Pennsylvania establishes 7 inches as 

the minimum size limit for both Trout and Salmon (other 

edible fish species such as Bass, Walleye and Northern Pike 

have higher minimum size limits).165

 

164 U.S. EPA-SAB, 2011.

165 Pennsylvania Fish and Boat Commission. 2011. Summary Book: 2011 

Pennsylvania Fishing Laws & Regulations available at: 

http://fishandboat.com/fishpub/summary/inland.html.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

242

EPA disagrees with the comment that it is not 

reasonable to use watersheds where only a single fish 

sample is available. While it is preferred to have multiple 

samples, if anything, based on the comments of the SAB peer 

review panel, using a single sample is likely to 

underestimate the 75th percentile fish MeHg concentration 

and is therefore likely to underestimate the risk estimates 

for those watersheds. The SAB peer review panel provided 

EPA with several suggested analyses of the fish tissue MeHg 

data that have been undertaken and are included in the 

Revised Mercury Risk TSD. The Revised Mercury Risk TSD 

includes information on the number of watersheds modeled in 

the risk assessment with various fish tissue Hg samples 

sizes (e.g., 1, 2, 3-5, 6-10 and >10 measurements).

5. Reference Dose (RfD) for Methylmercury

Comment: Several commenters state that the EPA’s RfD166

is based on sound science, which was supported by the 

findings of the National Academy of Sciences’ Study on 

Mercury,167 and EPA applied an appropriate RfD in the 

mercury risk assessment. The commenters also state that 

 

166 U.S. Environmental Protection Agency – Integrated Risk Information 

System (U.S. EPA-IRIS). 2001. Methylmercury (MeHg) (CASRN 22967-92-6). 

Available at http://www.epa.gov/iris/subst/0073.htm

167 NAS, 2000.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

243

recent studies find clear associations between maternal 

blood Hg levels and delayed child development, 

cardiovascular effects, and potential effects due to 

exposure to pollutant mixtures including lead. 

However, many commenters expressed concerns regarding 

EPA’s use of the Methylmercury RfD as a benchmark for 

health risk. Several commenters raised concerns claiming 

that EPA has not incorporated the best available mercury 

toxicological data into the RfD, which results in a flawed 

analysis and an overestimate of the impact of mercury 

emissions on human health.

Several commenters state that, when deriving the RfD, 

the EPA relied on the flawed Faroe Islands’ children study 

and ignored the Seychelles Islands study,168 which did not 

confirm any harm on children due to MeHg exposure. 

According to the commenters, application of the Faroe 

Island study is suspect because (1) the raw data from the 

study have never been made available for independent 

analysis and scrutiny, (2) confounding by polychlorinated 

biphenyls (PCBs) and lead, (3) population exposure to MeHg 

 

168 Budtz-Jorgensen E, Debes F, Weihe P, Grandjean P. 2005. “Adverse 

Mercury Effects in 7-Year-Old Children Expressed as Loss in “IQ”.” EPAHQ-OAR-2002-0056-6046.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

244

through consumption of highly contaminated pilot whale 

meats and blubbers, and (4) exposure levels in the U.S. 

remain lower than those observed in the primary study. One 

commenter also notes that (1) Seychelles Islanders consume 

far more fish than do Americans; (2) the amount of MeHg in 

the U.S. population is 10 to 20 times below that of the 

Seychelles islanders; and (3) all ocean fish throughout the 

world contain about the same amount of MeHg, so per fish 

meal MeHg intake is similar between Americans and 

Seychelles Islanders. According to one commenter, EPA’s 

reliance on the statistical analysis performed by the Faroe 

Island researchers at the request of the NAS169 failed to 

address the question of why study failed to observe any 

significant effects from PCBs. However, another commenter 

states that industry arguments against using the Faroe

Islands study in deriving the RfD due to PCB confounding 

and the differences in the diets of Faroe Islanders fails 

to acknowledge that the study results were consistent with 

 

169 NAS, 2000.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

245

studies in the Seychelles Islands, New Zealand170, and 

Poland171. 

One commenter criticized EPA for using a linear doseresponse model for both the RfD-based HQ metric and the IQ 

metric without supporting explanation beyond the 

interpretation that this is NAS‘s preference, and that it 

was “easier to quantify IQ loss.” One commenter states that 

the RfD assumes a threshold dose below which an appreciable 

risk of adverse effects is unlikely, NAS did not evaluate 

whether methylmercury exposure data from the Faroe Islands 

were better fit by a linear or non-linear model, or by a

threshold or non-threshold model. 

Several commenters state that EPA’s mercury RfD is 

more conservative than “safe” levels determined by the U.S. 

Food And Drug Administration, the World Health 

Organization, and the U.S. Agency for Toxic Substances and 

Disease Registry. Several commenters claim that EPA 

assigned unusually high uncertainty factors, including 

 

170 Kjellstrom, T; Kennedy, P; Wallis, S; et al. (1986) Physical and 

mental development of children with prenatal exposure to mercury from 

fish. Stage 1: Preliminary test at age 4. Natl Swed Environ Protec Bd, 

Rpt 3080 (Solna, Sweden).

171 Wieslaw Jedrychowski et al., 2006. “Effects of Prenatal Exposure to 

Mercury on Cognitive and Psychomotor Function in One-Year-Old Infants: 

Epidemiologic Cohort Study in Poland,” 16 Annals of Epidemiology 439.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

246

accounting for pharmacokinetic variability and 

toxicodynamic variability. According to the commenter, much 

of pharmacokinetic variability results from EPA selecting a 

one-compartment model instead of the Psychologically Based 

Pharmcokinetic Model (PBPK) model suggested by the NAS 

(2000).172 Another commenter questions why EPA added an 

uncertainty factor to address toxicodynamic variability 

when such a factor was considered unnecessary in previous 

RfDs. One commenter states that the EPA noted that research 

demonstrates that the 10 percent risk level of benchmark 

dose roughly correlates with the NOAEL (“no observed 

adverse effects level”) in EPA’s 1995 RfD. According to the 

commenter, the EPA departed from this approach and used a 5

percent risk level for the benchmark dose and this results 

in a benchmark dose that is six times more stringent than 

the traditional 10 percent risk level benchmark dose (BMD) 

or NOAEL approach.

Several commenters state that the EPA's use of the 

1999 NHANES data is outdated and National Health and 

Nutrition Examination Survey (NHANES) blood mercury levels 

 

172 NAS, 2000.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

247

show a downward trend since 1999 and the levels have been 

below the EPA RfD since 2001. 

One commenter states that a study by Texas Department 

of State Health Services (DSHS, 2004)173 determined that 

even when subsistence fishers are eating fish from Caddo 

Lake with elevated methylmercury, women of child-bearing 

years did not have blood mercury levels greater than the 

RfD. Thus, according to the commenter, the connection 

between methylmercury in fish and adverse health effects in 

the U.S. is not fully understood and could involve other 

factors, including the protective effects of fatty acids 

and selenium in fish, in populations that eat large amounts 

of fish, which were not taken into account in the EPA's 

assessment. 

Two commenters claim that EPA uses the RfD as if it 

were an absolute threshold for health risk in the risk 

assessment even though the RfC/RfD methodology was 

developed as a screening tool for deciding when risks 

clearly do not exist. 

 

173 DSHS. 2005. Health Consultation: Mercury Exposure Investigation Caddo 

Lake Area-Harrison County Texas. Agency for Toxic Substances and 

Disease Registry. 

http://www.tceq.state.tx.us/assets/public/comm_exec/pubs/sfr/085.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

248

Several commenters recommend adding qualitative 

discussion about the uncertainty to the Mercury Risk TSD, 

including the RfD, extrapolating a dose-response 

relationship between methylmercury exposure and change in 

IQ, extrapolating the dose-response relationship from 

marine fish and marine mammals to freshwater fish, and 

confounding due to PCBs in marine species.

Several commenters raised concerns regarding the 

relationship between methylmercury exposure and IQ loss. 

Two commenters state that changes in IQ are not a welldefined health consequence of methylmercury exposure. One 

commenter states that SAB had reservations about EPA’s use 

of IQ loss as a second risk measure. One commenter stated 

that this rulemaking would have little impact on IQ (e.g., 

only a fraction of an IQ point gain for the most exposed 

individuals). Two commenters questioned whether IQ impacts 

would even occur because in Japan and Korea, where the 

maternal blood mercury levels are higher than in the U.S., 

there is no evidence of harm to child development or IQs. 

Another commenter cited a study174 that found verbal IQ 

 

174 Hibbeln JR, Davis JM, Steer C, Emmett P, Rogers I, Williams C, et al. 

2007. “Maternal seafood consumption in pregnancy and neurodevelopmental 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

249

scores for children from mothers with no seafood intake 

were 50 percent more likely to be in the lowest quartile. 

One commenter questions using an IQ risk metric threshold 

of >1 or >2 points because of variation in IQ measures and 

the intra-individual variation in IQ is higher than the 

threshold, and EPA should described the reasoning behind 

this threshold in the Mercury Risk TSD. One commenter 

states that none of the IQ studies measured full IQ, and 

EPA relied on summary data results that introduced some 

uncertainty in the low-dose linear response.

Several commenters question the relationship between 

cardiovascular effects and methylmercury exposure. 

According to a commenter, EPA cites a workshop report as 

support for a causal relationship between methylmercury 

exposure and cardiovascular effects, but other studies 

report no increased risk for cardiovascular events. One 

commenter states that the two major studies used by EPA to 

show cardiovascular effects are flawed in design and the 

results are simply not applicable to U.S. public health. 

One commenter cited several studies examining the 

 

outcomes in childhood (ALSPAC study): an observational cohort study. “ 

Lancet 369:
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

250

relationship between methylmercury exposure and 

cardiovascular effects,175,176,177,178,179,180 but concluded that 

it seems premature to use these studies to establish a 

dose-response relationship. 

Several commenters mention that the risks from eating 

seafood are low relative to the benefits, fish advisories 

can limit the beneficial aspects of fish consumption, and 

fish advisories are often unsuccessful.181,182 One commenter 

noted the important role of dietary selenium’s protective 

effects against MeHg toxicity because the binding affinity 

of Hg to Se is up to a million times higher than for sulfur 

– mercury’s second-best binding partner.

 

175 Roman HA, Walsh TL, Coull BA, Dewailly É, Guallar E, Hattis D, et al. 

2011. Evaluation of the Cardiovascular Effects of Methylmercury 

Exposures: Current Evidence Supports Development of a Dose–Response 

Function for Regulatory Benefits Analysis. Environ Health Perspect 

119:607-614.

176 Guallar E, Sanz-Gallardo MI, van't Veer P, et al. 2002. “Mercury, 

fish oils, and the risk of myocardial infarction.” N Engl J 

Med.;347:1747.

177 Virtanen JK, Voutilainen S, Rissanen TH, et al. 2005. “Mercury, fish 

oils, and risk of acute coronary events and cardiovascular disease, 

coronary heart disease, and all-cause mortality in men in eastern 

Finland.” Arterioscler Thromb Vasc Biol. 2005;25:228.

178 Yoshizawa, Rimm, Morris, Spate, Hsieh, Spiegelman, Stampfer, Willett.

“Mercury and the Risk of Coronary Heart Disease in Men,” N Engl J Med

2002; 347:1755-1760.

179 Hallgren CG, Hallmans G, Jansson JH, et al. 2001. Markers of high 

fish intake are associated with decreased risk of a first myocardial 

infarction. Br J Nutr: 86:397.

180 Mozaffarian, Dariush. 2011. “Mercury Exposure and Risk of 

Cardiovascular Disease in Two U.S. Cohorts,” N Engl J Med 364: 1116-

1125.

181 Hibbeln et al. 2007.

182 Mozaffarian, et al., 2011
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

251

Response: EPA agrees with the commenter that the MeHg 

RfD is the appropriate health value for determining 

elevated risks from MeHg exposure and disagrees with 

commenters that state otherwise. At this time, U.S. EPA is 

neither reviewing nor revising its 2001 RfD for MeHg. The 

2001 RfD for MeHg is EPA’s current peer-reviewed RfD, which 

is the value EPA uses in all its risk assessments. EPA’s 

RfD is based on multiple benchmark doses and RfDs were 

calculated on various endpoints using the three extant 

large studies of childhood effects of in utero exposure: 

Faroe Islands, New Zealand, and an integrative measure 

including data from Seychelles. EPA did not choose to base 

its MeHg RfD solely on results from the Seychelles Island, 

as both the NAS183 and an independent scientific review 

panel convened as part of the IRIS process184 advised 

strongly against using results from a study that at the 

time had not shown an association between MeHg exposure and 

adverse effects. Further, EPA disagrees with the commenter 

that EPA based the MeHg RfD solely on results from the 

Faroe Islands population. EPA disagrees that the 

 

183 NAS, 2000.

184 U.S. EPA. 2001b. Responses to Comments of the Peer Review Panel and 

Public Comments on Methylmercury. Available on the Internet at 

http://www.epa.gov/iris/supdocs/methpr.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

252

information underlying the RfD is “poorly explained”. EPA 

has provided detailed documentation for the choices 

underlying calculation of the RfD.185,186,187 To correct the 

statement by the commenter, the data underlying the Faroe 

Islands study has been previously published in the peerreviewed literature.

EPA disagrees that it did not incorporate the latest 

mercury data to support the “appropriate and necessary” 

finding. It is the policy of EPA to use the most current 

peer-reviewed, publicly available data and methodologies in 

its risk assessments. However, EPA noted in the preamble to 

the proposed rule that “data published since 2001 are 

generally consistent with those of the earlier studies that 

were the basis of the RfD, demonstrating persistent effects 

in the Faroe Island cohort, and in some cases associations 

of effects with lower MeHg exposure concentrations than in 

the Faroe Islands. These new studies provide additional 

 

185 U.S. EPA, 2001a. Water Quality Criterion for the Protection of the 

Human Health: MethylmercuryEPA-823-T-01-001, available at 

http://water.epa.gov/scitech/swguidance/standards/criteria/aqlife/pollu

tants/methylmercury/index.cfm

186 U.S. Environmental Protection Agency – Integrated Risk Information 

System (U.S. EPA-IRIS). 2001. Methylmercury (MeHg) (CASRN 22967-92-6). 

Available at http://www.epa.gov/iris/subst/0073.htm

187 Rice D, Schoeny R, Mahaffey K. 2003. “Methods and Rationale for 

Derivation of a Reference Dose for Methylmercury by the U.S. EPA.” Risk 

Analysis 23(1)107-115.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

253

confidence that exposures above the RfD are contributing to 

risk of adverse effects, and that reductions in exposures 

above the RfD can lead to incremental reductions in risk.” 

However, EPA has not completed a comprehensive review of 

the new literature, and as such, it would be premature to 

draw conclusions about the overall implications for the 

RfD. Several of the commenters refer to old calculations 

based on the science available at the time, which have been 

superseded by advances in knowledge and best practices used 

by risk assessors. 

EPA agrees that EPA’s RfD is not the same as the 

levels used by FDA, WHO, or ATSDR. In their advice to the 

U.S. EPA on the appropriate bases for a MeHg RfD, NAS 

specifically recommended that EPA use neither the study nor 

the uncertainty factor employed by ATSDR in the calculation 

of their minimal risk level.188

EPA disagrees that the uncertainty factor is 

“unusually high”. The uncertainty factor used in 

calculation of the RfD is small (10 fold); half of this 

factor is to account for measured variability in human 

pharmacokinetics. This uncertainty factor considered advice 

 

188 NAS, 2000.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

254

of NAS189 and an independent panel of scientific peer 

reviewers convened as part of the IRIS process190. Both 

groups of scientists felt at that time that the available 

PBPK model had not undergone sufficient scientific scrutiny 

to be used in the derivation of the MeHg RfD. The 

uncertainty factor was applied to multiple calculated 

effect levels; that is, statistical lower limits on 

benchmark doses for a 5 percent response level. These 

methods, including use of benchmark dose and data-derived 

uncertainty factors, result in more precise and accurate 

estimates with decreased uncertainty. 

It is important to clarify that EPA did not model low 

dose extrapolation for the RfD; rather, an uncertainty 

factor of 10 was applied to the chosen points of departure 

(lower limit on a BMD05 for multiple endpoints). IRIS makes 

this statement regarding a threshold for MeHg: “It is also 

important to note that no evidence of a threshold arose for 

methylmercury-related neurotoxicity within the range of 

exposures in the Faroe Islands study. This lack [of a 

threshold] is indicated by the fact that, of the K power 

 

189 Id.

190 U.S. EPA, 2001b.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

255

models, K = 1 provided a better fit for the endpoint models 

than did higher values of K.”191 This remains a factual 

statement. 

It is the best practice of EPA when the data support 

it, to use benchmark dose modeling (BMD), rather than a 

point estimate derived from inspection or a pair-wise 

comparison. EPA is not obliged to use any particular 

benchmark response level (BMR) in calculation of the BMD. 

The choice of the BMR for the MeHg RfD was guided by the 

advice of the NAS192 and an independent scientific peer 

review panel193. Scientists conversant in the tests and 

neurobehavioral endpoints to be modeled found that a 5 

percent BMR was most appropriate and congruent with 

practice in the field. 

EPA disagrees that it is using the MeHg RfD as an 

absolute bright line for health effects in the risk 

assessment. As stated in the preamble to this proposed 

rule, the RfD is an estimate of a daily exposure to the 

human population that is likely to be without an 

appreciable risk of deleterious effects during a lifetime. 

 

191 U.S. EPA-IRIS, 2001.

192 NAS, 2000.

193
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

256

EPA disagrees that exposure levels in the U.S. are lower 

than in the Faroe Islands study. Exposure to MeHg in the 

U.S. has been reported at the same levels as those 

published in the Faroe Islands.194 Mahaffey et al.195 note 

that in the NHANES data (1999-2004), the highest five 

percent of women’s blood mercury exceeded 8.2 μg/L in the 

Northeast U.S. and 7.2 μg/L in coastal areas. Higher levels 

have been reported among subjects known to consume fish. 

For example, Hightower and Moore (2003)196 reported mean 

blood mercury for women aged 27 to 87 in their study to be 

15 μg/L; range for men and women was 2 to 89.5 μg/L. Note 

that some publications have reported mercury effects in 

U.S. populations near the current U.S. RfD.197,198

 

194 Schober Susan E, Sinks Thomas H, Jones Robert L, Bolger P Michael, 

McDowell Margaret, Osterloh John, Garrett E Spencer, Canady Richard A, 

Dillon Charles F, Sun Yu, Joseph Catherine B, Mahaffey Kathryn R. Blood 

mercury levels in U.S. children and women of childbearing age, 1999-

2000. JAMA. 2003 Apr 2; 289(13):1667–1674.

195 Mahaffey, K.R., R.P. Clickner and R.A. Jeffries. 2009. Adult Women’s 

Blood Mercury Concentrations Vary Regionally in the U.S.: Association 

with Patterns of Fish Consumption (NHANES 1999–2004). Environ. Health 

Perspect., 117: 47-53.

196 Hightower Jane M, Moore Dan. Mercury levels in high-end consumers of 

fish. Environ Health Perspect. 2003 Apr;111(4):604–608. 

197 Oken, E., Radesky, J.S., Wright, R.O., Bellinger, D.C., 

Amarasiriwardena, C.J., Kleinman, K.P., Hu, H., Gillman, M.W. 2008. 

Maternal fish Intake during Pregnancy, Blood Mercury Levels, and Child 

Cognition at Age 3 Years in a U.S. Cohort. American Journal of 

Epidemiology, 167(10), 1,171-1,181.

198 Lederman, Sally Ann Robert L. Jones, Kathleen L. Caldwell, Virginia 

Rauh, Stephen E. Sheets, Deliang Tang, Sheila Viswanathan, Mark Becker, 

Janet L. Stein, Richard Y. Wang, and Frederica P. Perera. 2008. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

257

The commenter stating that of MeHg in the U.S. 

population is 10 to 20 times below that of the Seychelles 

islanders and all ocean fish throughout the world contain 

about the same amount of MeHg is in error. McKelvey et 

al.199 report that NYC residents have mean blood mercury 

levels of 2.7 μg/L, and women of childbearing age had a 

mean of 2.64 μg/L, nearly at the 90th percentile in NHANES; 

ethnic Asians had even higher blood mercury levels. 

Furthermore, marine fish in commerce differ widely in 

mercury concentration by species, and fish within the same 

species but caught at different locations have variable 

amounts of mercury in their tissues200,201. 

EPA disagrees that the dose-response relationship 

between mercury and IQ was developed for marine fish

because the dose-response function was actually calculated 

for exposure to MeHg rather than for fish consumption. 

 

Relation between Cord Blood Mercury Levels and Early Child Development 

in a World Trade Center Cohort. Environmental Health Perspectives

118(8) 1085 -1091.

199 McKelvey et al., 2007.

200 Hisamichi Y, Haraguchi K, Endo T. 2010. “Levels of mercury and 

organochlorine compounds and stable isotope ratios in three tuna 

species taken from different regions of Japan.” Environ Sci Technol 

44(15):5971-8.

201 Sunderland EM. 2007. “Mercury exposure from domestic and imported 

estuarine and marine fish in the U.S. seafood market.” Environ Health 

Perspect. 115(2):235-42. Epub 2006 Nov 20.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

258

Recent studies202,203,204 and analyses point to the potential 

for nutrients in fish (particularly marine fish) to 

ameliorate some of the observed adverse effects of MeHg 

when co-exposure occurs. There was no correction for 

potential confounding by nutrients in marine fish and 

mammals in calculation of the benchmark doses used in the 

RfD derivation; these benchmark doses may, thus, be 

underestimates. 

EPA disagrees that there is a statistically 

discernible downward trend in the NHANES data on blood 

mercury. EPA is unaware that a formal statistical analysis 

for temporal trends has been completed for NHANES data on 

blood mercury levels for the period 1999 to 2008. Mahaffey 

et al., evaluating NHANES data collected 1999 to 2004 for 

women at child-bearing age, could “not support the 

conclusion that there was a general downward trend in blood 

mercury concentrations over the 6-year study period.”205

 

202 Oken et al., 2008.

203 Choi AL, Cordier S, Weihe P, Grandjean P. 2008a. “Negative 

confounding in the evaluation of toxicity: the case of methylmercury in 

fish and seafood.” Crit Rev Toxicol. 2008;38(10):877-93.

204 Choi AL, Budtz-Jørgensen E, Jørgensen PJ, Steuerwald U, Debes F, 

Weihe P, Grandjean P. 2008b. “Selenium as a potential protective factor 

against mercury developmental neurotoxicity.” Environ Res. 

May;107(1):45-52. Epub 2007 Sep 12.

205 Mahaffey, K.R., R.P. Clickner and R.A. Jeffries. 2009. Adult Women’s 

Blood Mercury Concentrations Vary Regionally in the U.S.: Association 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

259

However, the same publication noted that “there was a 

decline in the upper percentiles reflecting the most highly 

exposure women” having blood mercury concentration greater 

than established levels of concern. Visual observations of 

the data show a slight decrease in mercury blood level 

concentrations from 1999-2008 at the geometric mean. This 

decrease may not be statistically significant based on 

overlapping confidence intervals. A decrease in mercury 

blood level concentrations is also observed at the 95th

percentile. Except for differences observed between 1999 

and 2008, the temporal decrease may not be statistically 

significant. Conclusions cannot be drawn without further 

and more formal statistical analysis of the data. EPA 

remains concerned that substantial numbers of women of 

childbearing age in the U.S. may have blood mercury levels 

that are equivalent to exposures at or above the RfD. Mean 

and 95th percentiles from recent NHANES data are below 5.8 

μg/L (a blood mercury concentration equivalent to the RfD). 

However, blood levels for some portions of the population 

(high consumers of fish, for example) may be indicative of 

 

with Patterns of Fish Consumption (NHANES 1999–2004). Environ. Health 

Perspect., 117: 47-53.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

260

exposures above the RfD. EPA did not find data for NHANES 

blood distributions above the 95th percentile. Modeled data 

from Tran et al. 206 provided estimates showing high blood 

mercury levels at the 99th percentile for females of childbearing age (i.e., 24.41 μg/L at the 99th percentile). 

Mahaffey et al. showed that 2.4 percent of women of childbearing age had blood mercury values above 5.8 μg/L.207

Other published studies have shown that various population 

groups can have high blood mercury levels.208,209,210,211,212 For 

example, one study found that Asian populations had mercury 

exposures greater than 5.8 μg/L in 83 percent of the Asian 

population compared to 12 percent for the total survey 

population.213

 

206 Tran, N. L., L. Barraj, et al. 2004. "Combining food frequency and 

survey data to quantify long-term dietary exposure: a methyl mercury 

case study." Risk Anal 24(1): 19-30.

207 Mahaffey, K. R. 2005. "Mercury exposure: medical and public health 

issues." Trans Am Clin Climatol Assoc 116: 127-153.

208 Id.

209 Miranda, M. L., S. Edwards, et al. 2011. "Mercury levels in an urban 

pregnant population in Durham County, North Carolina." Int J Environ 

Res Public Health 8(3): 698-712.

210 Hightower and Moore, 2003.

211 Hightower, J. M., A. O'Hare, et al. (2006). "Blood mercury reporting 

in NHANES: identifying Asian, Pacific Islander, Native American, and 

multiracial groups." Environ Health Perspect 114(2): 173-175.

212 McKelvey, W., R. C. Gwynn, et al. 2007. "A biomonitoring study of 

lead, cadmium, and mercury in the blood of New York city adults." 

Environ Health Perspect 115(10): 1435-1441.

213 Hightower et al., 2006.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

261

EPA disagrees with the commenter regarding confounding 

by PCBs and lead because the commenter makes several 

misstatements. PCB congeners were measured in cord tissue 

for the first Faroese cohort recruited in 1986 and 1987 and 

in maternal serum in the cohort recruited in 1994 –

1995.214,215 Exposure to MeHg in the Faroe Islands was largely 

from consumption of pilot whale meat; exposure to PCBs was 

found in the portion of the population who also consume 

whale blubber. The lipophilic PCBs are found in the fat 

compartment of the pilot whales; MeHg, by contrast is bound 

covalently to protein in the whale meat. Numerous analyses 

have shown neurobehavioral effects of PCBs; however, the 

effects of MeHg and PCB in the Faroe Islands study are 

separable.216 EPA also documented the independence of PCB 

and MeHg effects in the Faroe Islands population.217 NIEHS 

 

214 Grandjean P, Bjereve K, Wihe P, and Sterewald u. 2001a. “Birthweight 

in a fishing community: significance of essential fatty acids and 

marine food contaminants.” In. J. Epidemiol. 30:1272-1278. 

215 Grandjean, Philippe, Pal Weihea, c, Virlyn W. Bursed, Larry L. 

Needhamd, Eva Storr-Hansene, Birger Heinzowf, Frodi Debesc, Katsuyuki 

Muratag, Henrik Simonsenh, Peter Ellefsenc, Esben Budtz-Jørgenseni, 

Niels Keidingi, Roberta F. White 2001b. “Neurobehavioral deficits 

associated with PCB in 7-year-old children prenatally exposed to 

seafood neurotoxicants.” Neurotoxicology and Teratology 23:305– 317.

216 NAS, 2000.

217 U.S. EPA, 2001a.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

262

concluded that both PCB and mercury had adverse effects. 218

NAS concluded that there was no empirical evidence or 

theoretical mechanism to support the opinion that in utero 

Faroese exposure to PCBs exacerbated the reported 

methylmercury effect.219 A second set of analyses found that 

the effect of prenatal PCB exposure was reduced when the 

data were sorted into tertiles by cord PCB 

concentrations.220 These analyses support a conclusion that 

there are measurable effects of methylmercury exposure in 

the Faroese children that are not attributable to PCB 

toxicity. We also note that the Faroe Island population was 

not exposed to lead.

EPA disagrees with the commenter’s assertion that the 

connection between methylmercury in fish and observed 

health effects is not understood due to evidence from the 

cited Texas study221. This is an exposure study rather than 

a study on measures of neurobehavioral or any other health 

 

218 National Institute of Environmental Health Sciences (NIEHS). 1998. 

Scientific issues relevant to assessment of health effects from 

exposure to methylmercury. Workshop organized by Committee on 

Environmental and Natural Resources (CENR) Office of Science and 

Technology Policy (OSTP), The White House, November 18-20, 1998, 

Raleigh, NC.

219 NAS, 2000.

220 Budtz-Jørgensen, E., N. Keiding, and P. Grandjean. 1999. Benchmark 

modeling of the Faroese methylmercury data. Final Report to U.S. EPA.

221 DSHA, 2005.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

263

endpoint. TCEQ noted that none of the Caddo Lake study 

participants had blood mercury levels above the BMDL of 5.8 

μg/L (one of the several used by EPA in the calculation of 

the MeHg RfD). The BMDL is not a “no effect” level. Rather 

it is an effect level for a percentage of the population. 

EPA has noted in correspondence with TCEQ that, as an 

exposure study, the Caddo Lake study may be representative 

of the surrounding population; however, the sample size is 

very small. It is not appropriate to extrapolate from Caddo 

Lake to larger regional or national populations.

EPA is aware of the possibility of both interactions 

among environmental contaminants and cumulative effects of 

pollutants that produce the same adverse endpoint. EPA 

guidance exists for dealing with such scenarios.222,223,224,225

The Agency’s concern with the likelihood of human exposure 

 

222 U.S. EPA. 1986. Guidelines for the Health Risk Assessment of Chemical 

Mixtures. U.S. Environmental Protection Agency, Office of Research and 

Development, Washington, DC. September. EPA/630/R-98/002. Available at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=2256

223 U.S. EPA. 1999. Guidance for Performing Aggregate Exposure and Risk 

Assessments. U.S. Environmental Protection Agency, Office of Pesticide

Programs, Washington, DC. October. Available at 

http://www.pestlaw.com/x/guide/1999/EPA-19991029A.html

224 U.S. EPA. 2000a. Supplementary Guidance for Conducting Health Risk 

Assessment of Chemical Mixtures. U.S. Environmental Protection Agency, 

Risk Assessment Forum, Washington, DC. EPA/630/R-00/002. Available at 

http://www.epa.gov/ncea/raf/pdfs/chem_mix/chem_mix_08_2001.pdf

225 U.S. EPA. 2003a. Framework for Cumulative Risk Assessment. Risk 

Assessment Forum, U.S. Environmental Protection Agency. Washington, DC. 

EPA/630/P-02/001F. EPA/600/P-02/001F. Available at 

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=54944
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

264

to multiple contaminants is reflected in the multi-chemical 

scope of the rulemaking. However, EPA focused the technical 

analyses supporting the proposed regulation on effects of 

individual pollutants rather than cumulative effects. 

Further, SAB “agreed that EPA’s calculation of a 

hazard quotient for each watershed included in the 

assessment is appropriate as the primary means of 

expressing risk,” and that “because the RfD from which the 

HQ is calculated is an integrative metric of 

neurodevelopmental effects of methylmercury, it constitutes 

a reasonable basis for assessing risk.”226

EPA disagrees that the “appropriate and necessary 

finding” was based on the IQ analysis in the Mercury TSD. 

As fully described in the preamble, EPA made its finding in 

part on the HQ-based risk metrics derived from comparisons 

of MeHg exposure to the RfD. EPA’s Mercury Risk TSD 

evaluated the potential public health hazard on several 

high-risk subpopulations, specifically high-consuming 

subsistence fishers. This assessment was not designed to 

characterize the full range of risk associated with 

exposure to Hg emitted from U.S. EGUs. For this rulemaking, 

 

226 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

265

EPA did not conduct an analysis of risks and benefits of 

fish consumption. Rather EPA conducted an analysis of the 

risks of exposure to mercury and the benefits accruing to 

consumers of freshwater fish from reduction in mercury 

emissions from EGUs.

EPA agrees that additional qualitative discussion 

about uncertainty would improve the Revised Mercury Risk 

TSD. The SAB recommended that the IQ analyses be retained 

but de-emphasized in the documentation underlying the final 

regulation. In their report they stated the following: “The 

Panel does not consider it appropriate to use of IQ loss in 

the risk assessment and recommended that this aspect of the 

analysis be de-emphasized, moving it to an appendix where 

IQ loss is discussed along with other possible endpoints 

not included in the primary assessment. While the Panel 

agreed that the concentration-response function for IQ loss 

used in the risk assessment is appropriate, and no better 

alternatives are available, IQ loss is not a sensitive 

response to methylmercury and its use likely underestimates 

the impact of reducing methylmercury in water bodies.”227

EPA is following up on the SAB recommendation by 

 

227 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

266

deemphasizing the IQ analysis and placing that analysis in 

an appendix to the revised TSD. The SAB panel also 

recommended that EPA revise the Mercury Risk TSD “to better 

explain the methods and choices made in the analysis, and 

analytical results, and where the uncertainties lie.” The 

SAB panel noted several uncertainties related to the RfD, 

and EPA is preparing a revised TSD that will address the 

SAB recommendations, including a more complete discussion 

of uncertainties including those related to the RfD.

EPA disagrees that the IQ metric threshold is 

“questionable”. The SAB concluded that it was reasonable to 

consider a loss of >1 or >2 IQ points a public health 

concern. The executive summary of their report says the 

following: “The Panel agreed that if IQ loss is retained in 

the risk assessment despite these reservations, a loss of 1 

or 2 points would be an appropriate benchmark.”228 The SAB 

further comments in their report: “The consensus is that if 

IQ were to be used, then a loss of 1 or 2 points as a 

population average is a credible decrement to use for this 

risk assessment. This metric seems to be derived from the 

lead literature and was peer-reviewed by the Clean Air 

 

228 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

267

Scientific Advisory Committee (U.S. EPA CASAC 2007) [

229]. 

While its applicability to methylmercury is questionable, 

the size of the decrement is justified based on the 

extensive analyses available from the literature reviewed 

by CASAC.”230 As noted in other studies,231,232 a decrease of 

1-2 points at the mean results in a much larger decrease on 

those with IQs that are much lower or higher than the mean. 

Although EPA disagrees that the IQ results too 

uncertain to rely upon, EPA acknowledges that IQ is not the 

most sensitive neurodevelopmental endpoint affected by MeHg 

exposure, as also noted by SAB. The SAB recommended that 

“the appropriate approach would be to mention the IQ 

analysis in the body of the TSD and to discuss the 

uncertainties involved with the use of the analysis, 

offering the conclusion that it would be a less sensitive 

 

229 U.S. Environmental Protection Agency – Science Advisory Board (U.S. 

EPA-SAB). 2007. Clean Air Scientific Advisory Committee’s (CASAC) 

Review of the 1st Draft Lead Staff Paper and Draft Lead Exposure and 

Risk Assessments. EPA-CASAC-07-003. March. Available on the internet at 

http://yosemite.epa.gov/sab/sabproduct.nsf/989B57DCD436111B852572AC0079

DA8A/$File/casac-07-003.pdf

230 U.S. EPA-SAB, 2011.

231 Axelrad, D. A.; Bellinger, D. C.; Ryan, L. M.; Woodruff, T. J. 2007. 

“Dose-response relationship of prenatal mercury exposure and IQ: an 

integrative analysis of epidemiologic data.” Environmental Health 

Perspectives, 115, 609–615.

232 Bellinger DC. 2005. Neurobehavioral Assessments Conducted in the New 

Zealand, Faroe Islands, and Seychelles Islands Studies of Methylmercury 

Neurotoxicity in Children. Report to the U.S. Environmental Protection 

Agency. EPA-HQ-OAR-2002-0056-6045.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

268

endpoint than the Hazard Quotient (HQ), which is based on 

the current reference dose (RfD) for methylmercury”.233 The 

SAB, however, supported the use of the IQ dose-response 

function calculated by EPA in support of the proposed 

regulation. They note, “The function used came from a paper 

by Axelrad and Bellinger (2007) that seeks to define a 

relationship between methylmercury exposure and IQ. A 

whitepaper by Bellinger (Bellinger, 2005)[234] describes the 

sequence of steps in relating methylmercury exposure to 

maternal hair mercury and then that to IQ. The Mercury Risk 

TSD furthers notes that IQ has shown utility in describing 

the health effects of other neurotoxicants. These are 

appropriate bases for examining a potential impact of 

reducing methylmercury on IQ, but the SAB does not consider 

these compelling reasons for using IQ as a primary driver 

of the risk assessment.”235

EPA disagrees with the commenter’s implication that 

the MATS rule would not have public health benefits. As

shown in the RIA accompanying the rule, the public health 

 

233 U.S. EPA-SAB, 2011.

234 Bellinger, 2005.

235 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

269

benefits are substantial, and the monetized benefits exceed 

the costs by a substantial margin. 

EPA disagrees that EPA has overstated or failed to 

review the scientific literature on cardiovascular effects 

from MeHg exposure. As summarized in the preamble to the 

proposal, EPA stated that the NAS study concluded that 

“Although the data base is not as extensive for 

cardiovascular effects as it is for other end points (i.e., 

neurologic effects) the cardiovascular system appears to be 

a target for MeHg toxicity in humans and animals.”236 EPA 

also stated that additional cardiovascular studies have 

been published since 2000. EPA did not develop a 

quantitative dose response assessment for cardiovascular 

effects associated with MeHg exposures, as there is no 

consensus among scientists on the dose-response functions 

for these effects, and there is inconsistency among 

available studies as to the association between MeHg 

exposure and various cardiovascular system effects. In the 

future, EPA may update the MeHg RfD and will review all of 

the relevant scientific literature available at that time, 

including data on all relevant endpoints, and weight of 

 

236 76 FR 25001
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

270

evidence for likelihood that MeHg produces specific effects 

in humans.

EPA acknowledges the research regarding the 

effectiveness of fish advisories. However, the proposed 

regulation does not address the subject of fish advisories, 

consumer advice on fish or efficacy of such advice. EPA 

rejects the commenter’s speculation regarding whether the 

estimated IQ impacts for the regulation are real. Adverse 

effects of in utero mercury exposure have been reported in 

populations in the U.S.237,238 In another study on 

neurobehavioral effects of prenatal exposure to 

methylmercury through maternal consumption of seafood, 

adverse effects are observed for MeHg even without 

controlling for fish consumption.239 That study suggests 

that at normal Japanese dietary intake of MeHg and fish 

nutrients, the overall effect is adverse. While Japanese 

fish consumption and mercury exposure are both somewhat 

 

237 Oken et al., 2008,

238 Lederman et al., 2008.

239 Suzuki, K., Nakai, K., Sugawara, T., Nakamura, T., Ohba, T., Shimada, 

M., Hosokawa, T., Okamura, K., Sakai, T., Kurokawa, N., Murata, K., 

Satoh, C., and Satoh, H. 2007. “Neurobehavioral effects of prenatal 

exposure to methylmercury and PCBs, and seafood intake: neonatal 

behavioral assessment scale results of Tohoku study of child 

development.” Environ Res 110, 699-704.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

271

higher than the mean U.S. exposure, these levels are still 

within the distribution of U.S. consumers. 

Moreover, many studies show that beneficial effects of fish 

on both cardiovascular and neurodevelopmental health are 

decreased by concomitant exposure to MeHg. Several studies 

describe one or more aspects of exposure to fish nutrients 

and MeHg.240,241,242,243244,245,246 Note that in the Hibbeln et al. 

study247 cited by the commenter, there were self-reported 

levels of fish consumption, but no measures of mercury 

exposure; no biomarker data such as blood, hair or urine 

mercury were reported. Daniels et al. (2004)248 reporting on 

the same population noted that no significant increase was 

seen in umbilical cord mercury (the biomarker used) as 

seafood consumption increased from one meal per 2 weeks to 

four or more per week. Consequently, no methylmercury-

 

240 Grandjean et al., 2001a.

241 Budtz-Jorgensen, E.; Grandjean, P.; Weihe, P. 2007. “Separation of 

risks and benefits of 16 seafood intake.” Environmental Health 

Perspectives. Vol. 115, 323-327.

242 Choi et al., 2008a. 

243 Choi et al., 2008b.

244 Oken et al., 2008.

“

245 Strain, J.J. et al. 2008. Associations of maternal long chain 

polyunsaturated fatty acids, methyl mercury, and infant development in 

the Seychelles Child Development Nutrition Study.” Neurotoxicology. 

29(5): 776–782.

246 Suzuki, et al., 2007.

247 Hibbeln et al., 2007.

248 Daniels JL, Longnecker MP, Rowland AS, Golding J. 2004. Fish intake 

during pregnancy and early cognitive development of offspring.

Epidemiology;15:394–402.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

272

associated suboptimum performance outcomes would be 

expected in the ALSPAC population.

EPA recognizes the potential for confounding of the 

effects of mercury on the developing nervous system by a 

range of nutrients (including long-chain poly-unsaturated 

fatty acids) and we discuss this in the uncertainty 

characterization section of the Revised Mercury Risk TSD. 

Regarding selenium, SAB commented that ”one SAB member 

suggests the use of blood markers of selenium-dependent 

enzyme function, noting that methylmercury irreversibly 

inhibits selenium-dependent enzymes that are required to 

support vital-but-vulnerable metabolic pathways in the 

brain and endocrine system. Impaired selenoenzyme 

activities would be observed in the blood before they would 

be observed in brain, but the effect is also expected to be 

transitory. The use of these measures is a minority view 

among the SAB members.”249 The SAB did not express a 

consensus recommendation on adjustments to the risk 

estimates for exposure to selenium or other nutrients, 

noting that “there is not enough known about their 

 

249 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

273

quantitative impact to support a recommendation of a reanalysis.”250

6. General comments on Mercury Risk Assessment

Comment: Several commenters generally supported the 

mercury risk assessment, but several other commenters 

generally disagreed with the mercury risk assessment. One 

supporter stated that EPA reasonably determined that 

mercury emissions pose a public health hazard, correctly 

requested peer-review of mercury risk analysis and 

correctly concluded EGU-attributable MeHg poses a hazard to 

public health at watersheds when considering all sources of 

Hg deposition and U.S. EGUs alone. Two commenters noted 

that the contribution of U.S. EGUs to total Hg deposition 

can significantly contribute to hundreds of watersheds, and 

U.S. EGU deposition alone may endanger sensitive 

populations near many of these watersheds. 

Several commenters claimed that overly conservative 

assumptions in the risk analysis render the results flawed 

and unreliable, including using CMAQ to model deposition, 

MMAPs, fish consumption rate and fish methylmercury 

concentrations, overly stringent RFD, national-scale model, 

 

250 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

274

using poverty as a surrogate for subsistence fishing, 

assuming a subsistence fisher resides in most watersheds 

with fish tissue data, fishers only eat larger fish with 

high mercury concentrations, cooking loss adjustment, 

unrealistically high fish ingestion rates (a large fish 

meal every day), focused on the extremes of the 

distributions, cast many assumptions as an underestimate of 

the effect despite evidence to the contrary, and created 

inappropriate metrics for risk that show no improvement 

despite significant mercury emissions reductions in the 

U.S. 

Several commenters cite Tetra Tech’s analysis that 

assessed mercury risk using different consumption rates, 

cooking factor, mean fish tissue concentrations, and EGUattributable mercury deposition only, which showed 

considerably fewer watersheds that exceed an HQ of 1 at 

2016 deposition levels. 

Several commenters claim that this regulation would 

not significantly reduce mercury exposure via fish 

consumption because EGU-attributable deposition is a small 

fraction of total deposition. One commenter states that 

EPA’s data shows U.S. EGU mercury emissions have little 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

275

influence on fish mercury concentrations despite reduction 

of 41 tons of Hg in U.S. between 2005 and 2016. One 

commenter requested that EPA accurately describe the low 

health risks posed by utility hazardous air pollutant 

emissions. One commenter states that the EPA did not 

consider scientific information showing that there is no 

straightforward connection between mercury emissions from 

EGUs to the mercury level in fish, which is dependent upon 

many environmental factors, such as sunlight and organic 

matter, pH, water temperature, sulfate, bacteria, and 

zooplankton present in the ecosystem. One commenter states 

that there is not any demonstrable evidence that anyone in 

the U.S. has suffered adverse health problems as a result 

of mercury emissions from coal-fired EGUs. One commenter 

states that EPA’s findings are similar to the 2000 findings 

where the EPA found a plausible link between anthropogenic 

releases of Hg from sources in the U.S. and MeHg in fish, 

and “plausible” is a euphemism for unproven.

Several commenters had recommendations for the mercury 

risk analysis. One commenter stated that more data from 

Florida should have been included because Florida is known 

to have a rich data set on fish mercury concentrations. One 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

276

commenter states that the EPA should characterize general 

recreational angler fishers instead of subsistence fishers. 

One commenter claims that EPA made math errors in the 

Mercury Risk TSD regarding the deposition in watersheds at 

specific percentiles. One commenter questioned EPA’s policy 

metrics used to characterize mercury risk. One commenter 

states that EPA should state that lags occur in the 

response of aquatic ecosystems to changes in mercury 

deposition, and that some Hg deposition is unlikely to 

reach the water at all.

Several commenters state that the Mercury TSD is 

unclear and lacks detail, as noted by SAB. One commenter 

states that the SAB is critical of EPA’s efforts, stating 

that SAB found it difficult to evaluate the risk assessment 

based solely upon Mercury Risk TSD and recommended that EPA 

transparently explain the methods and uncertainties. One 

commenter states that because of insufficient review time 

and the lack of detail in the TSD, they could not assess 

key questions, such as the nation-wide representativeness 

of the fish tissue data. 

One commenter states the subset of watersheds 

considered in the analysis (i.e., with fish tissue data) 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

277

have clearly higher U.S. EGU-attributable deposition than 

the distribution of all watersheds. 

One commenter states the EPA's reporting of IQ point 

loss is erroneous and not relevant to informing policy, and 

the U.S. EGU contribution to risk is marginal as evidenced 

by the null values for the 50th percentile watershed.

One commenter notes that U.S. EGU-attributable 

emissions of mercury have decreased significantly between 

2005 and 2016, but claims that this decrease does not 

appear to affect the risk results. 

One commenter questions why the EPA has departed from 

the Clean Air Act (CAA) 112(n) risk comparison to the 1 in 

1 million to use the RfD for mercury.

Response: The purpose of the mercury risk assessment 

is not to assess the magnitude of risk reduction under the 

proposed rule, but rather to estimate the magnitude of 

absolute risk attributable to U.S. EGUs currently and 

following implementation of other applicable Clean Air Act 

requirements. That said, any potential risk reductions 

following implementation of the MACT rule itself would 

likely reflect a number of factors besides the national 

average U.S. EGU deposition value cited by the commenter. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

278

These additional factors include: (a) spatial gradients in 

the magnitude of absolute U.S. EGU-attributable Hg 

deposition, (b) spatial gradients in the magnitude of 

reductions in Hg deposition linked to the rule, (c) 

availability of measured fish tissue Hg levels in the 

vicinity of U.S. EGUs experiencing larger Hg emission 

reductions to support risk modeling, and (d) the potential 

for subsistence fishing activity at watersheds in the 

vicinity of U.S. EGUs experiencing larger reductions in Hg 

emissions (also required to support risk modeling). It is 

also important to point out that while the national average 

U.S. EGU-attributable mercury deposition (for the 2016 

scenario – see Revised Mercury Risk TSD) is 2 percent, 

values range up to 11 percent for the 99th percentile 

watershed. This illustrates the substantial spatial 

variation in U.S. EGU-attributable Hg deposition, which 

translates into spatial variation in the magnitude of U.S. 

EGU-attributable subsistence fisher risk.

The SAB conducted a comprehensive peer review of all 

of EPA’s assumptions in the Mercury Risk TSD, and concluded 

that “the SAB supports the overall design of and approach 

to the risk assessment and finds that it should provide an 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

279

objective, reasonable, and credible determination of the 

potential for a public health hazard from mercury emitted 

from U.S. EGUs.”251 Furthermore, SAB concluded, “The SAB 

regards the design of the risk assessment as suitable for 

its intended purpose, to inform decision-making regarding 

an “appropriate and necessary finding” for regulation of 

hazardous air pollutants from coal and oil-fired EGUs, 

provided that our recommendations are fully considered in 

the revision of the assessment.”

252 While the SAB did 

indicate difficulty in evaluating the risk assessment based 

solely on the Mercury Risk TSD, the panel was able to 

obtain enough additional information through the peer 

review process to make the determination that “the overall 

design of and approach to the risk assessment and finds 

that it should provide an objective, reasonable, and 

credible determination of the potential for a public health 

hazard from mercury emitted from U.S. EGUs.”253 The primary 

advice of the SAB panel was that EPA should “revise the 

Technical Support Document to better explain the methods 

and choices made in the analysis, and analytical results, 

 

251 U.S. EPA-SAB, 2011.

252 Id.

253 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

280

and where the uncertainties lie.”254 EPA has revised the 

Mercury Risk TSD as part of the final rulemaking to address 

the SAB’s recommendations and has made that revised TSD 

available in the rule docket. 

SAB concurred with EPA’s analytical assumptions and 

overall study design for the Mercury Risk TSD, including 

the RfD-based HQ approach, fish tissue data, 75th percentile 

size fish, MMAPs assumption, and consumption rates. Based 

on the SAB peer review, EPA strongly disagrees with 

commenter statements that the results reported in the 

Mercury TSD are unreliable, overly conservative, extreme, 

inconsistent with EPA risk guidelines, or severely 

overstate risk based on the stated objectives of the 

analysis. EPA has specifically addressed each of these 

assumptions in the previous sections of the preamble, thus, 

does not repeat those responses here. Based on the review 

by the SAB, EPA has accurately described the health risks 

posed by utility hazardous air pollutant emissions and 

disagrees with the commenter’s statement that EPA has not 

provided any demonstrable evidence to show that adverse 

health risks exist. EPA has applied peer reviewed modeling 

 

254 Id.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

281

to estimate the deposition of Hg attributable to U.S. EGUs. 

EPA asserts that these metrics demonstrate a clear hazard 

to public health from U.S. EGU Hg emissions.

EPA thoroughly evaluated the Tetra Tech analysis. EPA 

does not agree that the analysis by Tetra Tech uses 

assumptions that are “more reasonable”, as the SAB agreed 

that all of EPA’s assumptions are reasonable and 

appropriate. EPA asserts that the Tetra Tech analysis does 

not provide coverage for subsistence fishers likely to 

experience elevated U.S. EGU-related Hg exposure. 

Specifically, the risk estimated cited in the comment 

reflects application of a number of behavioral assumption 

that provide significantly less coverage for higher risk 

subsistence fishers. Fish consumption surveys cited in the 

Revised Mercury Risk TSD, suggest that higher percentile 

subsistence fishers eat more than twice the level of fish 

assumed by Tetra Tech. The Tetra Tech analysis also used 

the median fish tissue levels, but it is reasonable to 

assume that subsistence fishers would target somewhat 

larger fish to maximize the volume of edible meat per unit 

time spent fishing. The Tetra Tech assumed that cooking 

fish did not concentrate mercury, but a number of studies 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

282

discussed in the Revised Mercury Risk TSD explicitly 

provide adjustment factors involving a higher unit 

concentration following preparation. Taken together, Tetra 

Tech’s analysis does not address the stated goal of the 

risk assessment to assess the nature and magnitude of risk 

for those individuals likely to experience the greatest 

risk associated with exposure to U.S. EGU-attributable 

mercury. 

EPA disagrees with the commenter’s assertion that this 

rule will not affect risks associated with mercury 

exposure. Mercury from U.S. EGUs is a contributor to the 

levels of methylmercury in fish across the country and 

consumption of contaminated fish can lead to increased risk 

of adverse health effects. EPA has shown in the RIA Chapter 

5 that this rule will reduce mercury levels in fish. 

EPA acknowledges that U.S. EGUs contribute only a 

small fraction of total mercury deposition in the U.S. 

However, U.S. EGUs remain the largest emitter of mercury in 

the U.S., and the revised risk analysis shows that U.S. 

EGU-attributable Hg deposition results in up to 29 percent 

of modeled watersheds having the potential for subsistence 

level freshwater fish consumers with total mercury 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

283

exposures exceeding the RfD to have at least 5 percent of 

total mercury risk contributed by U.S. EGUs, and up to 10 

percent of modeled watersheds having the potential for 

subsistence level freshwater fish consumers to have mercury 

exposures exceeding the RfD due to mercury emissions from 

U.S. EGUs even before considering mercury exposures due to 

other sources. Mercury risk is increasing for exposures 

above the RfD, and as a result, any reductions in mercury 

exposures in locations where total exposures exceed the RfD 

can result in reduced risks. While these reductions in risk 

may be small for most populations and locations, in some 

watersheds and for some populations, reductions in risk may 

be greater. 

The SAB also directly addressed the question of the 

nation-wide representativeness of the fish tissue MeHg data 

in the national mercury risk assessment. The SAB panel 

concluded, “Although the SAB considers the number of 

watersheds included in the assessment adequate, some 

watersheds in areas with relatively high mercury deposition 

from U.S. EGUs were under-sampled due to lack of fish 

tissue methy[l]mercury data. The SAB encourages the Agency 

to contact states with these watersheds to determine if 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

284

additional fish tissue methylmercury data are available to 

improve coverage of the assessment.”255 In response to the 

SAB recommendations, EPA obtained additional fish tissue 

sample data from several states, particularly Pennsylvania, 

Wisconsin, Minnesota, New Jersey, and Michigan. This 

additional data increased the total number of watersheds 

assessed in the analysis by 33 percent nationally. In 

Florida, EPA assessed the mercury-related health risk for 

40 watersheds. Because EPA did not find any fish tissue 

data for new watersheds in Florida that could be 

incorporated into the analysis, the total number of 

watersheds in Florida assessed in the Revised Mercury Risk 

TSD remains the same as proposal. 

EPA disagrees with the commenter that there were 

errors in the Mercury Risk TSD. Instead, the commenter has 

misinterpreted how EPA calculated the percentiles. The 

percentile (and mean) values presented in Table ES-1 for 

total and U.S. EGU-attributable Hg deposition are not 

matched by watershed. In other words, EPA queried for the 

percentiles (and mean) provided for total Hg deposition and 

presented those percentiles and then separately estimated 

 

255 U.S. EPA-SAB, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

285

the percentiles for U.S. EGU-attributable Hg. Therefore, 

the total and U.S. EGU-attributable values for the 99th

percentile do not necessarily occur at the same watershed. 

EPA has provided additional clarification in the Revised 

Mercury Risk TSD. 

EPA agrees with the commenter that MeHg levels in fish 

depend on a complicated set of environmental factors, and 

EPA acknowledged this in the Revised Mercury Risk TSD. 

Furthermore, EPA acknowledges that total Hg fish tissue 

levels are not correlated with levels of total Hg 

deposition when looking across watersheds because this 

relationship is highly dependent on the methylation 

potential at the specific waterbody, which is affected by 

pH, sulfate deposition, turbidity, etc. However, several 

recent studies (Orihel et al., 2007, Orihel et al., 2008 

and Harris et al., 2007) show, and the SAB agrees, that it 

is appropriate for EPA to assume that changes in mercury 

deposition are linearly associated with changes in fish 

tissue concentration. In addition, EPA agrees that the 

subset of watersheds in the risk analysis have somewhat 

higher U.S. EGU deposition than the distribution of all 

watersheds, but EPA disagrees that oversampling of high 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

286

deposition watersheds is inappropriate. EPA also 

acknowledges in the Revised Mercury Risk TSD that MMAPS 

does not account for a time lag in ecosystem response to 

reductions in mercury emissions. 

EPA does not agree that there is no improvement in 

fish mercury concentrations between 2005 and 2016, or that 

there will be no further improvement from decreasing U.S. 

EGU mercury emissions from the baseline in 2016. While 

total risk from all mercury exposures will remain elevated 

in much of the U.S., much of that risk is associated with

global, non-U.S. mercury emissions. U.S. EGUs remain the 

largest source of Hg emissions in the U.S., and reductions 

in those emissions will result in reduced Hg deposition in 

many highly impacted watersheds. Based on the mercury risk 

assessment, average EGU-attributable fish tissue Hg 

concentrations will be decreased by 65 percent. Likewise, 

the number of watersheds identified as having populations 

potentially at risk from U.S. EGU Hg emissions will decline 

from 62 percent in 2005 to 28 percent in 2016. Emissions 

reductions due to regulation of Hg under section 112 should 

result in additional reductions in U.S. EGU-attributable 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

287

fish tissue Hg concentrations and watersheds with 

populations at risk.

EPA disagrees that IQ loss is erroneous or irrelevant 

to informing policy, but EPA has moved that analysis to an 

appendix in the Revised Mercury Risk TSD, per SAB 

recommendation. EPA disagrees that the IQ effects at the 

50th percentile watershed are useful in determining that 

there is not a hazard to public health because EPA’s stated 

goal of the risk assessment was to focus on populations 

likely to experience relatively higher exposures to U.S. 

EGU-attributable mercury. 

The commenter is referring to cancer risk (i.e., a 1 

in 1 million probability of developing cancer over a 

lifetime due to a specific chemical exposure). For mercury, 

EPA focused on the potential for neurodevelopmental effects 

in the children born to mothers exposed to MeHg during 

pregnancy through fish consumption. This health endpoint is 

a non-cancer endpoint, and risk in this context is assessed 

by comparing an estimate of daily exposure to MeHg for the 

mother to the MeHg RfD. Values greater than one (i.e., 

exposures that exceed the RfD) are considered to represent 

an exposure that could represent a public health hazard, 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

288

this reflecting the methodology and underlying 

epidemiological data used in deriving the MeHg RfD.

We also disagree with those commenters that point to 

the SAB statements concerning the clarity of the Mercury 

Risk TSD to suggest that the public did not have an ample 

opportunity to comment on the mercury risk assessment.

While it is correct that the SAB said the Mercury Risk TSD 

was difficult to evaluate until EPA staff explained it at 

the public meeting in June 2011, we note that the 

commenters that assert that this issue amounts to a 

violation of section 307(d) notice requirements made 

detailed technical comments, including many of the same 

comments as the SAB. Furthermore, EPA provided notice of 

the peer review in the proposed rule and a number of 

Federal Register notices advised the public of the peer 

review process and all the meetings were open to the public 

for comment and participation and the minutes of those 

meetings were posted on the SAB website. The minutes for 

the June 2011 meeting, during which EPA provided clarifying 

information, were available well within the public comment 

period for the proposed rule. For these reasons, we 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

289

maintain that the public was provided adequate opportunity 

to comment on the mercury risk assessment.

e. Non-Mercury HAP Case Studies

1. Emissions for non-mercury case studies 

Comment: Commenters raised concerns about a wide 

variety of aspects of EPA’s approach for emissions used for 

the non-Hg case studies, including the use of an arithmetic 

mean for computing emission factors for representing 

emissions of untested units, the suggestion of statistical 

outliers in the chromium test data, the claim that metals 

content of the fuel is a indicator of flawed test data, the 

statistical approaches used by EPA to create emission 

factors, the absence in EPA’s approach of an equation that 

commenters claim better represents emissions values, that 

EPA’s approach to estimate hexavalent chromium is flawed, 

and the lack of coal rank as a delineating factor for

emission factor calculation. Commenters also suggested that 

EPA should revise stack parameters used for the case 

studies based on better available data.

Response: In response to the comments on the emission 

factors, EPA has undertaken additional analysis to address 

all commenter concerns. EPA disagrees with commenter’s 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

290

criticisms of emission factors based on arithmetic means, 

and EPA demonstrates that the use of an arithmetic mean 

provides the most representative result. EPA agrees with 

commenters’ recommendations to use statistical outlier 

tests, but has applied tests different from those suggested 

by the commenters. This approach did not eliminate the 

chromium test data from the chromium emission factors used 

for some of the case study emissions.

EPA disagrees with commenters’ assertions that the 

metal content of the coal is a basis for invalidating the 

test results of high chromium emissions. The identification 

of sources whose measured emissions do not match the 

commenters’ preconceived idea of emissions behavior is not 

surprising. There are many possible explanations for these 

differences. For example, the inconsistency between the 

test data and the coal analysis could be due to any number 

of reasons including unrepresentative coal sampling, 

control device problems, degradation of the refractory, or 

sampling contamination. The idea that test data should be 

discarded because it does not match initial expectations is 

unfounded.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

291

EPA disagrees with the commenter recommendations for 

using an equation from AP-42, developed in part by the 

commenters. EPA conducted regression analyses between 

metals emissions measured at the site and predicted from 

the equations and demonstrates the poor predictive 

capability of these equations, concluding that emission 

test data is a more accurate predictor of actual emissions, 

and emission factors based on the arithmetic mean when test 

data are not available. 

EPA also disagrees with commenters concerns about the 

assumption that 12 percent of the chromium will be Cr+6 for 

every coal-fired unit. EPA disagrees with the commenter’s 

assertion that any impact of scrubbers will impact the case 

study analyses. In EPA’s final case study analysis, 6 

facilities have risk greater than 1 in 1 million, and of 

these, four facilities have chromium as the risk driver 

(James River, Conesville, TVA Gallatin, and Dominion –

Chesapeake Bay). For these facilities, none of the units 

contributing the bulk of the chromium emissions have 

scrubbers according to the data provided to EPA by those 

facilities, so scrubber impacts on chromium speciation is 

not relevant to EPA’s conclusions based on the non-Hg case 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

292

studies. In any case, EPA disagrees with the commenter’s 

conclusions about the impacts of scrubbers on chromium 

speciation and provides evidence that impacts of scrubbers 

on chromium speciation can have the opposite effect on Cr+6 

fractions, concluding that EPA’s 12 percent assumption is 

somewhat conservative.

EPA also disagrees that coal rank must be a factor in 

computing chromium emission factors for use in the case 

studies. EPA’s analysis has demonstrated that coal rank 

appears to play no role in metals emissions. EPA’s newly 

revised emissions factor development procedures can isolate 

and compare subgroups based on control device type or coal 

rank; the ICR data were subjected to these tests and no 

statistical significance was found between coal rank 

groups.

Finally, EPA agrees with commenters recommendations on 

revised stack parameters for the case studies and has 

included these revisions in the case study modeling for the 

final rule.

2. General Comments on Non-Hg Risk Case Study 

Comment: One commenter stated that the EPA’s case 

study assessment reaffirms the need to regulate HAP emitted 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

293

by both coal and oil-fired EGUs. The commenter noted that 

over 40 percent of the case studies conducted by EPA to 

quantify health hazards associated with the inhalation of 

non-Hg HAP indicated a cancer risk greater than or equal to 

the one in one million threshold level required to delist a 

source category under section 112 of the Clean Air Act.

One commenter stated that the EPA’s case study 

assessment might be flawed by the use of “beta” tests 

versions of the AERMOD meteorological preprocessors 

(AERMINUTE and AERMET). The commenter obtained from EPA the 

meteorological data used for the EPA’s assessment of the 

Conesville facility and processed these data with the EPA’s 

current regulatory versions of these preprocessors, which 

differ from the beta version. According to the commenter, a 

comparison of the hourly wind speed and hourly wind 

direction data produced by the beta preprocessor and by 

current EPA preprocessors revealed numerous and often 

substantial disparities.

One commenter stated that the EPA’s finding that only 

three coal-fired facilities and one oil-fired facility out 

of roughly 440 coal-fired facilities and 97 oil-fired 

facilities in the U.S. indicated risk greater than one-in-
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

294

a-million supports a finding that it is “appropriate” to 

regulated those four and not the other 537. Another 

commenter stated that EPA found only a “few” facilities 

that have estimated maximum cancer risks in excess of one 

in a million, and that this does not justify regulating all 

non-Hg HAPs for all sources in this category.

One commenter stated that the EPA’s discussion in the 

proposed rule misleads the reader into believing that nonHg HAP emissions from EGUs are associated with serious 

human health effects. According to the commenter, EPA’s 

discussion of the effects associated with excessive 

exposure to an individual HAP would lead the reader to 

believe that those effects inevitably occur from EGU 

emissions because EGU emissions have trace amounts of nonHg HAPs. 

One commenter stated that with the assumptions in the 

Utility RTC, both in terms of conservative scientific 

estimates and overestimated amounts of oil burned by these 

units, EPA concluded that the risks from oil-fired units 

would result in only one new cancer case every five years.

The commenter does not believe that this level of risk 

warrants regulation under Section 112(n)(1)(A) of the CAA. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

295

Several commenters state that even if the additional 

studies EPA performed were accurate, they hardly 

demonstrate that it is necessary and appropriate to 

regulate coal-fired EGU HAPs under Section 112 because 

three sites nationwide show risks greater that one in one 

million, with the highest at eight in one million.

One commenter stated that the highest cancer risk 

estimated for coal-fired EGUs is still within the 

acceptable range used by EPA in other programs and is also 

far less than the background exposure risks the average 

person experiences. The background risk of developing 

cancer in a lifetime is approximately 1 in 3 (0.33). 

According to EPA's own data, the predicted added cancer 

risk of exposure to HAPs from U.S. EGUs would change the 

background risk from 0.33 to 0.330001. This level of change 

is so minimal that it could not be observed in any health 

effects study that might be conducted.

One commenter stated that EPA conducted a health risk 

assessment on a limited number of facilities and found a 

“few” facilities that have estimated maximum cancer risks 

in excess of one in a million. The commenter stated that, 

based on this limited health risk assessment, EPA 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

296

apparently decided that they were justified to regulate all 

non-Hg HAPs for all sources in this category. 

Several commenters stated that EPA’s assumption that 

implies that a person stays exactly at the center of a 

census tract for 70 years and that a unit will operate in 

exactly the same manner for 70 years is unrealistic. The 

commenters suggest that Tier 3 risk assessment is warranted 

or a lifetime exposure adjustment is needed.

One commenter asserts that because the alleged health

benefits are derived from total exposure, EPA should 

explain how its numerical emission limit units, which would 

not directly restrict total exposure if heat inputs 

increase, redress this health concern. In its preamble, EPA 

simply notes that its emission limit units are consistent 

with, and allow for simple comparison to, other 

regulations.

Response: EPA agrees with the commenter that the nonHg HAP risk assessment confirms the appropriate and 

necessary finding.

EPA disagrees that EPA’s case study assessment is 

flawed by the use of beta versions of AERMET and AERMET. 

EPA remodeled the case study facilities using the current 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

297

versions of AERMINUTE (version 11059), AERMET (version 

11059), and AERMOD (version 11103). While there were 

differences in the number of calm and missing winds in the 

current AERMINUTE/AERMET output compared to the beta 

version, the resulting risks differed by less than two 

percent, on average. For Conesville, which had the largest 

difference in calms between the beta and current versions 

of AERMINUTE/AERMET, the risks differed by three percent. 

For the final rule, the case study facilities have been 

modeled with the current available versions of AERMINUTE, 

AERMET, and AERMOD.

The EPA disagrees with the commenter that only a few 

case study facilities exceeding 1 in a million risk 

invalidates the “appropriate finding”. The sixteen 

facilities EPA selected as case studies for assessment may 

not represent the highest-emitting or highest-risk sources. 

Although case study facility selection criteria included 

high estimated cancer and non-cancer risks using the 2005 

NEI data, high throughput, and minimal emission control, 

another necessary criterion was the availability of 

Information Collection Request (ICR) data for the EGUs at 

those facilities (or for similar EGUs at other facilities). 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

298

Because the ICR data were collected for the purpose of 

developing the MACT standards, the ICR was targeted towards 

better performing sources for non-mercury metal HAP, acid 

gas HAP, and organic HAP, with a smaller set of random 

recipients. Therefore, facilities for which ICR data were 

available may not represent the highest-emitting sources. 

EPA’s assessment of the case study facilities for the 

proposed rule concluded that three coal-fired facilities 

and one oil-fired facility had estimated lifetime cancer 

risks greater than one in a million. For the final rule, 

revisions were made to the 16 case studies based on 

comments received, and the results indicate that five coalfired facilities and one oil-fired facility had estimated 

lifetime cancer risks greater than one in a million. EPA 

maintains that its finding that more than 30 percent of the 

case study facilities had a cancer risk greater than one in 

one million is sufficient to support the appropriate 

finding. Furthermore, EPA did not base the appropriate 

finding on just the case study analysis as explained in the 

proposed rule.

The EPA disagrees with the commenter's assertion that 

the health effects associated with exposures to non-Hg HAP 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

299

from U.S. EGUs are mischaracterized in the preamble to the 

proposed rule. The discussion of the health effects of nonHg HAP provided in the preamble includes general 

information on the potential health effects associated with 

a broad range of exposure concentrations (from low to high 

levels) of the various non-Hg HAP (some of which have been 

determined to be carcinogenic to humans) based on peer 

reviewed scientific information extracted from priority 

sources such as IRIS, Cal EPA and ATSDR health effects 

assessments

The EPA disagrees with the commenter’s 

characterization of the Utility RTC. The Utility RTC 

represented the highest-quality factual record of 

information available at the time regarding EGU emissions 

and risks. Further, EPA’s recent risk assessments of 16 EGU 

case studies, performed with more recent data and refined 

scientific methods, indicate that there are still multiple 

EGU facilities that pose estimated inhalation cancer risks 

greater than one in a million. EPA maintains that the 

findings of the case studies are one element that 

independently supports our determination that it remains 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

300

appropriate and necessary to regulate EGUs under section 

112.

EPA does not agree with the commenter suggesting that 

EPA should interpret the results of the non-Hg HAP risk 

analysis in the context of background cancer risk. As 

explained in the proposed rule, EPA reasonably looked to 

the cancer risk threshold established under section 

112(c)(9)(B)(1) for delisting a source category as an 

indicator of the level of cancer risk that was appropriate 

to regulate under section 112. Commenters comparison of the 

cancer risk from EGUs as compared with the risk of 

contracting cancer from unknown sources is not the standard 

Congress established for evaluating HAP emission risk and 

the commenter has provided no support for its contention 

that the Agency should evaluate risk in that manner. EPA 

maintains that the analysis was reasonable. 

EPA does not agree with the commenter’s implication 

that EPA must make a facility-specific finding for each HAP 

for each source and then only regulate individual EGU 

facilities for the individual HAP that identified as 

causing an identified hazard to public health or the 

environment. That approach is not required under section 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

301

112(n)(1) or anywhere under section 112, and it would be 

virtually impossible to undertake such an effort. For these 

reasons, EPA does not agree with the commenter and maintain 

that the appropriate and necessary finding is reasonably 

supported by the record and consistent with the statute for 

all the reasons set forth in the proposed rule and this 

final action.

The EPA disagrees that an exposure adjustment is 

needed to account for conditions changing over 70 years 

because it runs counter to the long-standing approach that 

EPA has taken to estimate the maximum individual risk, or 

MIR. The MIR is defined by the EPA’s Benzene NESHAP 

regulation of 1989256 and codified by CAA 112(f) as the 

lifetime risk for a person located at the site of maximum 

exposure 24 hours a day, 365 days a year for 70 years (e.g. 

census block centroids). The MIR is the metric associated 

with the determination of whether or not a source category 

may be delisted from regulatory consideration under section 

112 (112(c)(9)). The MIR is the risk metric used to 

characterize the inhalation cancer risks associated with 

the case study facilities. EPA used the annual average 

 

256 54 FR 38044
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

302

ambient air concentration of each HAP at each census block 

centroid as a surrogate for the lifetime inhalation 

exposure concentration of all the people who reside in the 

census block. The EPA has used this approach to estimate 

MIR values in all of its risk assessments to support riskbased rulemakings under section 112 of the CAA to date.

EPA disagrees with the commenter’s assertion that the 

numerical emission limits being promulgated in today's 

final rule must be justified on their ability to redress 

the health concerns that were identified as the basis for 

regulating EGUs. The emission limits in today's rule are 

technology-based, as prescribed under section 112, and do 

not need to be justified based on their ability to protect 

public health. Regarding potential health concerns, EPA has 

up to 8 years after the promulgation of the technologybased emission limits for EGUs to determine whether they 

protect public health with an ample margin of safety. If 

they do not, EPA will promulgate additional more stringent 

standards (within the prescribed 8 years) to achieve the 

appropriate level of public health protection.

The commenter claims that prior studies provide no support 

for establishing standards for non-mercury HAP metals.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

303

3. Nickel Risk

Comment: Several commenters stated that the 

assumptions regarding the speciation and carcinogenic 

potential of nickel compounds used in EPA’s inhalation risk 

assessment of the case study facilities are overly 

conservative and likely to overstate the risks. With 

respect to nickel speciation, the commenters stated that 

there are substantial uncertainties regarding the species 

of nickel being emitted and the risk of such emissions, and 

that EPA has made ultraconservative assumptions aimed at 

overestimating the risk. The commenters stated that 

assigning the same carcinogenic potency of nickel 

subsulfide to other forms of nickel is overly conservative 

and inconsistent with the best available evidence.

Response: The EPA disagrees with the commenters’ 

assertion that it is impossible to give an accurate 

assessment of the risks to human health from nickel 

emissions from EGUs, and maintains that its assessment of 

the potential inhalation risks from EGU emissions of nickel 

compounds is scientifically valid, reasonable, and based on 

the best-available current scientific understanding. To 

that end, in July 2011, EPA completed an external peer 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

304

review (using three independent expert reviewers) of the 

methods used to evaluate the risks from nickel and chromium 

compounds emitted by EGUs.257 There were two charge 

questions relating to nickel in that review. First, do 

EPA's judgments related to speciated nickel emissions 

adequately take into account available speciation data, 

including recent industry spectrometry studies? Second, 

based on the speciation information available and what is 

known about the health effects of nickel compounds, and 

taking into account the existing URE values (i.e., values 

derived by the Integrated Risk Information System258, 

California Department of Health Services259, and the Texas 

Commission on Environmental Quality260), which of the 

following approaches to derive unit risk estimates would 

result in a more accurate and defensible characterization 

of risks from exposure to nickel compounds?

 

257 U.S. EPA, 2011c.

258 U.S. EPA, 1998. Integrated Risk Information Service (IRIS) 

assessment for hexavalent chromium. Available at:

http://www.epa.gov/ncea/iris/subst/0144.htm.

259 California Department of Health Services (CDHS) 1991. Health Risk 

Assessment for Nickel. Air

Toxicology and Epidemiology Section, Berkeley, CA. Available online at 

http://oehha.ca.gov/air/toxic_contaminants/html/Nickel.htm.

260 Texas Commission on Environmental Quality (TCEQ), 2011. Development 

Support Document for nickel and inorganic nickel compounds. Available 

online at 

http://www.tceq.state.tx.us/assets/public/implementation/tox/dsd/final/

june11/nickel_&_compounds.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

305

1. To continue using the same approach as that developed 

for use in the 2000 NATA, which consists of using the 

IRIS URE for nickel subsulfide and assuming that 

nickel subsulfide constitutes 65 percent of the mass 

emissions of all nickel compounds.

2. To consider a more health-protective approach, based 

on the consistent views of the most authoritative 

scientific bodies (i.e., NTP in their 12th ROC, IARC, 

and other international agencies) that consider nickel 

compounds to be carcinogenic as a group.

3. To make the same assumptions as in option 2, but 

considering alternative UREs derived by the CDHS or 

TCEQ.

In responding to these peer review questions, two of 

the reviewers agreed with the views of the most 

authoritative scientific bodies, which consider nickel 

compounds carcinogenic as a group. These reviewers, 

therefore, did not focus on the availability of nickel 

speciation profile data. The third reviewer recommended 

that the EPA review several manuscripts on nickel 

speciation profiles showing that sulfidic nickel compounds 

(which the reviewer considered as the most potent 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

306

carcinogens) are present at low levels in emissions from 

EGUs.

Nickel and nickel compounds have been classified as 

human carcinogens by national and international scientific 

bodies including the IARC,261 the World Health 

Organization262, and the European Union’s Scientific 

Committee on Health and Environmental Risks263. In their 12th 

Report of the Carcinogens, the NTP has classified nickel 

compounds as known to be human carcinogens based on 

sufficient evidence of carcinogenicity from studies in 

humans showing associations between exposure to nickel 

compounds and cancer, and supporting animal and mechanistic 

data. More specifically, this classification is based on 

consistent findings of increased risk of cancer in exposed 

workers, and supporting evidence from experimental animals 

that shows that exposure to an assortment of nickel 

 

261 International Agency for Research on Cancer (IARC), 1990. IARC 

monographs on the evaluation of carcinogenic risks to humans. Chromium, 

nickel and welding. Vol. 49. Lyons, France: International Agency for 

Research on Cancer, World Health Organization Vol. 49:256.

262International Labour Organization/United Nations Environment 

Programme, World Health Organization (WHO), 1991. Nickel. In 

Environmental Health Criteria No 108 Geneva.

263European Commission, Scientific Committee on Health and Environmental 

Risks (SCHER), 2006. Opinion on: Reports on Nickel, Human Health part. 

SCHER, 11th plenary meeting of 04 May 2006 

http://ec.europa.eu/health/ph_risk/committees/04_scher/docs/scher_o_034

.pdf
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

307

compounds by multiple routes causes malignant tumors at 

various organ sites and in multiple species. The 12th Report 

of the Carcinogens states that the “combined results of 

epidemiological studies, mechanistic studies, and 

carcinogenesis studies in rodents support the concept that 

nickel compounds generate nickel ions in target cells at 

sites critical for carcinogenesis, thus allowing 

consideration and evaluation of these compounds as a single 

group”.264 Although the precise nickel compound (or 

compounds) responsible for the carcinogenic effects in 

humans is not always clear, studies indicate that nickel 

sulfate and the combinations of nickel sulfides and oxides 

encountered in the nickel refining industries cause cancer 

in humans. There have been different views on whether or 

not nickel compounds, as a group, should be considered as 

carcinogenic to humans. Some authors believe that water 

soluble nickel, such as nickel sulfate, should not be 

considered a human carcinogen, based primarily on a 

negative nickel sulfate 2-year NTP rodent bioassay (which 

is different than the positive 2-year NTP bioassay for 

 

264 NTP, 2011.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

308

nickel subsulfide).265,266,267 Although these authors agree 

that the epidemiological data clearly supports an 

association between nickel and increased cancer risk, they 

sustain that the data are weakest regarding water soluble 

nickel. A recent review268 highlights the robustness and 

consistency of the epidemiological evidence across several 

decades showing associations between exposure to nickel and 

nickel compounds (including nickel sulfate) and cancer. 

Based on the views of the major scientific bodies 

mentioned above, and those of expert peer reviewers that 

commented on EPAs approaches to risk characterization of 

nickel compounds, the EPA considers all nickel compounds to 

be carcinogenic as a group and does not consider nickel 

speciation or nickel solubility to be strong determinants 

of nickel carcinogenicity. With regards to non-cancer 

effects, comparative quantitative analysis across nickel 

 

265 Oller A. Respiratory carcinogenicity assessment of soluble nickel 

compounds. Environ Health Perspect. 2002, 110:841-844.

266 Heller JG, Thornhill PG, Conard BR. New views on the hypothesis of 

respiratory cancer risk from soluble nickel exposure; and 

reconsideration of this risk's historical sources in nickel refineries. 

J Occup Med Toxicol . 2009, 4:23.

267 Goodman JE, Prueitt RL, Thakali S, and Oller AR. The nickel iron 

bioavailability model of the carcinogenic potential of nickelcontaining substances in the lung. Crit Rev Toxicol . 2011, 41:142-174.

268 Grimsrud TK and Andersen A. Evidence of carcinogenicity in humans of 

water-soluble nickel salts. J Occup Med Toxicol. 2010. 5:1-7. Available 

online at http://www.ossup-med.com/content/5/1/7.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

309

compounds indicates that nickel sulfate is as toxic or more 

toxic than nickel subsulfide or nickel oxide.269,270

Regarding the second charge question, two of the 

reviewers suggested using the URE derived by TCEQ for all 

nickel compounds as a group, rather than the one derived by 

IRIS specifically for nickel subsulfide. The third reviewer 

did not comment on alternative approaches. The EPA decided 

to continue using 100 percent of the current IRIS URE for 

nickel subsulfide because IRIS values are at the top of the 

hierarchy with respect to the dose response information 

used in EPA’s risk characterizations, and because of the 

concerns about the potential carcinogenicity of all forms 

of nickel raised by the major national and international 

scientific bodies. Nevertheless, taking into account that 

there are potential differences in toxicity and/or 

carcinogenic potential across the different nickel 

compounds, and given that there have been two URE values 

derived for exposure to mixtures of nickel compounds that 

are 2-3 fold lower than the IRIS URE for nickel subsulfide, 

the EPA also considers it reasonable to use a value that is 

 

269 Haber LT, Allen BC, Kimmel CA. Non-Cancer Risk Assessment for Nickel 

Compounds: Issues Associated with Dose-Response Modeling of Inhalation 

and Oral Exposures. Toxicol Sci. 1998. 43:213-229.

270 NTP, 1996.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

310

50 percent of the IRIS URE for nickel subsulfide for

providing an estimate of the lower end of a plausible range 

of cancer potency values for different mixtures of nickel 

compounds.

4. Chromium Risk

Comment: One commenter stated there are several 

problems with EPA's analysis related to the fact that 

chromium emissions were evaluated as being entirely 

chromium (VI). The commenter stated that not all of the 

emitted chromium will remain in the hexavalent form by the 

time it reaches the target population, and that some may be 

converted to the much less toxic (and noncarcinogenic) 

trivalent species. The commenter also stated that the 

concentration levels considered in the case study 

assessment are far below occupational levels. The commenter 

concluded that EPA’s cancer estimates should, therefore, be 

looked on with some skepticism. Another commenter stated 

that EPA’s estimate of 12 percent chromium (VI) from coalfired EGUs is unsupported, and that EPA failed to recognize 

that chromium (VI) is highly water-soluble and is easily 

reduced to chromium (III) in the presence of S02 in a low pH 

environment. The resulting chromium (III) would be expected 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

311

to precipitate out in a FGD. The commenter stated that the 

actual amount of chromium (VI) that would be present in the 

emissions from an EGU with a wet scrubber is likely to be 

far lower than the 12 percent estimate made by EPA.

Several commenters questioned the validity of the 

chronic inhalation study by the EPA because of (1) the use 

of surrogate speciated chromium emissions data instead of 

actual emissions data, (2) the assumption that units were 

run 100 percent of the time which is impossible, (3) 

dispersion modeling was used that is biased towards over 

predicting downwind impacts, and (4) estimated ambient 

concentrations were utilized as substitutes for real 

exposure concentrations for all people within a census 

block.

Response: EPA disagrees with the commenters’ assertion 

that all chromium was considered to be hexavalent. As 

discussed in “Methods to Develop Inhalation Cancer Risk 

Estimates for Chromium and Nickel Compounds”271, existing 

test data for utility and industrial boilers indicate that 

hexavalent chromium is, on average, twelve percent of total 

chromium from coal-fired boilers. The methods document 

 

271 U.S. EPA, 2011c.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

312

underwent peer review by three external reviewers, and all 

three reviewers considered EPA’s use of the values to be 

reasonable given the limited data available for chromium 

speciation profiling. The EPRI inhalation study for coalfired boilers also used the twelve percent value.

EPA also disagrees that units were assumed to operate 100 

percent of the time. The dispersion modeling performed for 

the case study facilities used hourly heat input as a 

temporalization factor for estimating hourly emissions, and 

in some cases hourly heat inputs (and emissions) were zero 

or very low. The commenter provided no data or information 

to support their claim that the dispersion modeling EPA 

used is biased towards overestimating downwind impacts.

EPA disagrees with the commenters’ assertion that 

“real exposure concentrations for all people within a 

census block” must be considered because it runs counter to 

the long-standing approach that EPA has taken to estimate 

the maximum individual risk, or MIR. The MIR is defined by 

the EPA’s Benzene NESHAP regulation of 1989 272 and codified 

by CAA 112(f) as the lifetime risk for a person located at 

the site of maximum exposure 24 hours a day, 365 days a 

 

272 54 FR 3804
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

313

year for 70 years (e.g. census block centroids). The MIR is 

the metric associated with the determination of whether or 

not a source category may be delisted from regulatory 

consideration under section 112 (112(c)(9)). The MIR is the 

risk metric used to characterize the inhalation cancer 

risks associated with the case study facilities. EPA used 

the annual average ambient air concentration of each HAP at 

each census block centroid as a surrogate for the lifetime 

inhalation exposure concentration of all the people who 

reside in the census block. EPA has used this approach to 

estimate MIR values in all of its risk assessments to 

support risk-based rulemakings under section 112 of the CAA 

to date.

5. Acid Gas Risk 

Comment: One commenter stated that acid gas emissions 

from oil-fired EGUs are not of the magnitude that triggered 

EPA's decision to regulate EGUs in general, raising the 

question of whether reduction (or even total elimination) 

of acid gas emissions from oil-fired EGUs could have any 

significant effect on EPA's goals of reducing non-cancer 

health risk or acidification of sensitive ecosystems in the 

U.S.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

314

Several commenters stated that acid gas concentrations 

estimated in the case study facility assessment and the 

Utility RTC do not exceed human health thresholds of 

concern. Two commenters stated that HCl emissions are 

negligible compared to other primary emissions (such as SO2) 

that can lead to potential acidification of ecosystems.

Response: Consistent with the proposed rule, EPA is 

not adopting an emissions standard based on its authority 

under section 112(d)(4) in the final rule. EPA first notes 

that the Agency’s authority under section 112(d)(4) is 

discretionary. That provision states that EPA ”may” 

consider established health thresholds when setting 

emissions standards under section 112(d). By the use of the 

term “may,” Congress clearly intended to allow EPA to 

decide not to consider a health threshold even for 

pollutants that have an established threshold. As explained 

in the preamble to the proposed rule, it is appropriate for 

EPA to consider relevant factors when deciding whether to 

exercise its discretion under section 112(d)(4), and the 

language of that provision does not prevent the Agency from 

considering factors not specifically enumerated. To 

interpret the statute as commenters suggest, would 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

315

effectively require the Agency to establish section 

112(d)(4) standards whenever there is an established health 

threshold for a HAP. EPA has considered the public comments 

received and is not adopting an emissions standard under 

section 112(d)(4) for the reasons explained below and in 

the proposed rule.

First, as explained in the preamble to the proposed 

rule, EPA maintains that the potential cumulative public 

health and environmental effects of acid gas emissions from 

EGUs and other acid gas sources located near EGUs supports 

the Agency’s decision not to exercise its discretion under 

section 112(d)(4). EPA did not receive information 

regarding facility-specific emissions of all the acid gases 

from EGUs as well as sources that may be co-located with 

EGUs or nearby such sources. Additional data were also not 

provided during the comment period, and the data already in 

hand regarding these emissions are not sufficient to 

support the development of emissions standards for any of 

the EGU subcategories under section 112(d) that take into 

account the health threshold for acid gases, particularly 

given that the Act requires EPA’s consideration of health 

thresholds under section 112(d)(4) to protect public health 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

316

with an ample margin of safety. Commenters’ assertions that 

EPA has sufficient data, even for HCl, are incorrect, and 

it appears that they believe that EPA can establish a 

section 112(d) standard for HCl and ignore the other acid 

gas HAP, a belief that is also incorrect. Second, the 

concerns expressed by EPA in the proposal regarding the 

potential environmental impacts and the cumulative impacts 

of acid gases on public health were not assuaged by the 

comments received.

As explained in the preamble to the proposed rule, EPA 

also considered the co-benefits of setting a conventional 

MACT standard for HCl. EPA considered the comments received 

on this issue and maintains that the co-benefits are 

significant and provide an additional basis for the 

Administrator to conclude that it is not appropriate to 

exercise her discretion under section 112(d)(4). EPA 

disagrees with the commenters who stated that it is not 

appropriate to consider non-HAP benefits in deciding 

whether to invoke section 112(d)(4). Although MACT 

standards may directly regulate only HAPs and not criteria 

pollutants, Congress did recognize, in the legislative 

history to section 112(d)(4), that MACT standards would 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

317

have the collateral benefit of controlling criteria 

pollutants as well and viewed this as an important benefit 

of the air toxics program.273 EPA consequently does not 

accept the argument that it cannot consider reductions of 

criteria pollutants, for example in determining whether to 

take or not take certain discretionary actions, such as 

whether to adopt a risk-based standard under section 

112(d)(4). There appears to be no valid reason that, where 

EPA has discretion in what type of standard to adopt, EPA 

must ignore controls which further the health and 

environmental outcomes at which section 112(d) of the Act 

is fundamentally aimed because such controls not only 

reduce HAP emissions but emissions of other air pollutants 

as well.

Thus, the issue being addressed is not whether to 

regulate non-HAP under section 112(d) or whether to 

consider other air quality benefits in setting section 

112(d)(2) standards—neither of which EPA is doing—but 

rather whether to make the discretionary choice to regulate 

certain HAP based on the MACT approach and whether EPA must 

put blinders on and ignore collateral environmental 

 

273 See S. Rep. No. 101–228, 101st Cong. 1st sess. at 172.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

318

benefits when choosing whether or not to exercise that 

discretion. EPA knows of no principle in law or common 

sense that precludes it from doing so.

6. EPRI Risk Analysis

Comment: Two commenters stated that a comprehensive 

tiered inhalation risk assessment (the EPRI study) using 

EPA-prescribed methods with improved emission factors, fuel 

data, and confirmed stack parameters did not identify 

significant health risks (cancer or non-cancer) among U.S. 

coal-fired power plants (as they existed in 2007). The 

commenters noted that these results contrast with those 

presented by EPA for its non-mercury case studies on 16 (15 

coal-fired) power plants. The commenters state that several 

issues appear to underlie these differences, indicating the 

need for EPA to reevaluate its assessment and to undertake 

more refined (Tier 3) risk assessment for any facility of 

concern. Several commenters stated that for non-mercury 

HAPs the EPA produced one study on chronic inhalation risk 

assessment that identified three sites with cancer risks 

greater that one in one million for hexavalent chromium, 

which was authored by EPA staff and not peer reviewed. One 

commenter stated that the EPA study is based on 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

319

misinformation and overestimates assumptions, and that the 

EPA has no data demonstrating health impacts from EGU 

emissions of non-mercury HAPs, or the benefit from reducing 

such emissions. Two commenters stated that no benefits will 

be derived from the non-mercury HAP emission reductions 

associated with the proposed rule because no non-mercury 

HAP health risks were proven, and that no showing was made 

that EGU non-mercury HAP emission levels reach levels 

associated with adverse health effects. Another commenter 

stated that EPA must complete a comparable and separate 

national scale risk assessment in order to determine 

appropriateness of proposing emissions standards for nonmercury metals.

Response: The commenters are incorrect in the 

assertion that EPA’s case studies were performed with less 

rigor than the EPRI analysis. The EPRI analysis used a 

tiered approach to risk assessment, beginning with Tier 1 

using EPA’s SCREEN3 dispersion model on all 470 coal-fired 

power plants in the U.S., and following with Tier 2 with 

EPA’s Human Exposure Model (which uses the AERMOD 

dispersion model) for plants with higher risks from the 

Tier 1 modeling. Although tiered risk assessment is an 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

320

appropriate approach, the Tier 2 modeling could have been 

more refined. For example, more meteorological data could 

have been used and building downwash could have been 

considered. The EPRI analysis ostensibly concluded that the 

Tier 2 modeling with HEM was conservative, and that because 

the modeled risks did not exceed certain thresholds, no 

further refinement was necessary. However, such refinements 

could result in higher modeled risks than those from the 

commenter’s Tier 2 modeling.

EPA’s dispersion modeling of the case study facilities 

was actually performed with a greater degree of refinement 

than the EPRI analysis, and was consistent with EPA’s 

Guideline on Air Quality Models.274

In contrast to the approach used in the EPRI analysis, 

EPA used:

1) 5 years of recent meteorological data from the 

weather station nearest to each facility, rather 

than 1 year of meteorological data. This is more 

representative of long-term (i.e., lifetime) 

exposures and risks.

 

274 Appendix W to 40 CFR 51
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

321

2) Temporally-varying emissions based on continuous 

emissions monitoring data, rather than assuming a 

constant emission rate for each facility throughout 

the entire simulation.

3) Building downwash, where appropriate.

4) The latest version of AERMOD [version 11103]

EPA’s assessment of the case study facilities for the 

proposed rule concluded that three coal-fired facilities 

and one oil-fired facility had estimated lifetime cancer 

risks greater than one in a million. For the final rule, 

revisions were made to the case studies based on comments 

received, and the results indicate that five coal-fired 

facilities and one oil-fired facility had estimated 

lifetime cancer risks greater than one in a million.

Regarding peer review, the risk assessment methodology 

used by EPA for the case studies was consistent with the 

method that EPA uses for assessments performed for Risk and 

Technology Review rulemakings, which underwent peer review 

by the Science Advisory Board in 2009.275 The SAB issued its 

peer review report in May 2010. The report generally 

endorsed the risk assessment methodologies used in the 

 

275 U.S. EPA-SAB, 2010. 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

322

program. In addition, in July 2011, EPA completed a letter 

peer review of the methods used to develop inhalation 

cancer risk estimates for chromium and nickel compounds.

f. Ecosystem Impacts from HAPs

Comment: Two commenters assert that EPA is not 

justified in regulating acid gases based on concern about 

the potential that acid gases contribute to ecosystem 

acidification rather than concerns about hazards to public 

health. The commenters further claim that HCl’s 

contribution to ecosystem acidification is de minimis. The 

commenters point out that EPA acknowledges uncertainty in 

quantification of acidification and EPA relies on recently 

published research276 that is irrelevant to the question 

since it is based on research conducted in the peat bog 

ecosystem in the United Kingdom. Another commenter calls 

attention to several new studies published in a special 

issue of the journal Ecotoxicology devoted to the effects 

of methylmercury on wildlife.

Response: While EPA agrees that quantification of 

acidification effects has remaining uncertainty, the 

 

276 Evans, Chris D., Don T. Monteith, David Fowler, J. Neil Cape, and 

Susan Brayshaw. 2011. “Hydrochloric Acid: An Overlooked Driver of 

Environmental Change.” Environmental Science & Technology 45 (5), 1887-

1894.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

323

science and methodology has progressed in recent years. 

Based on recent peer-reviewed research including Evans et 

al.277, acid gases can significantly contribute to 

acidification. EPA published a comprehensive risk 

assessment of acidification effects of nitrogen and sulfur 

deposition278 and a policy assessment279. Given the extent 

and importance of the sensitive ecosystems evaluated in the 

review of nitrogen and sulfur deposition any substance that 

contributes to further acidification must be considered to 

be affecting the public welfare. EPA disagrees that the 

peer-reviewed study mentioned by commenter by Evans et al. 

(2011) is not relevant to U.S. ecosystems. The paper 

presents experimental results that show 1) that HCl is 

highly mobile in the environment, transferring acidity 

easily through soils and water, 2) that HCl can transport 

 

277 Id.

278 U.S. Environmental Protection Agency (U.S. EPA). 2009. Risk and 

Exposure Assessment for Review of the Secondary National Ambient Air 

Quality Standards for Oxides of Nitrogen and Oxides of Sulfur (Final). 

EPA-452/R-09-008a. Office of Air Quality Planning and Standards, 

Research Triangle Park, NC. September. Available on the Internet at 

<http://www.epa.gov/ttn/naaqs/standards/no2so2sec/data/NOxSOxREASep2009

MainContent.pdf>.

279 U.S. Environmental Protection Agency (U.S. EPA). 2011. Policy 

Assessment for the Review of the Secondary National Ambient Air Quality 

Standards for Oxides of Nitrogen and Oxides of Sulfur. EPA-452/R-11-

005a. Office of Air Quality Planning and Standards, Research Triangle 

Park, NC. February. Available on the Internet at 

<http://www.epa.gov/ttnnaaqs/standards/no2so2sec/data/20110204pamain.pd

f>.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

324

longer distances than previously thought (given its 

presence in remote ecosystems, and 3) that it can be a 

larger driver of acidification than previously thought. The 

fact that this study took place in the U.K. is itself 

irrelevant. The chemical interactions of HCl in water are 

the same the world over and sensitive ecosystems exist in 

the U.S. as well as in Europe as illustrated in the risk 

assessment for NOx and SOx (U.S. EPA, 2009). Furthermore, 

the commenter is factually incorrect that EPA is justifying 

that it is appropriate and necessary to regulate HAP 

emissions from EGUs based on this one study. EPA agrees 

with the commenter that mercury exposure in wildlife is 

responsible for various adverse health effects in many 

species across the U.S. and recognizes that research is 

ongoing in this area. As discussed in the preamble to the 

proposed rule, EPA agrees that there are potential 

environmental risks from exposures of ecosystems through Hg 

and non-Hg HAP deposition. EPA cited relevant articles from 

the special edition of Ecotoxicology280 mentioned by the 

commenter in the ecosystem effects section on Chapter 5 of 

the RIA for this rule, which is available in the docket.

 

280 Ecotoxicology 17:83-91, 2008
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

325

G. EPA Affirms the Finding that it is Appropriate and 

Necessary to Regulate EGUs to Address Public Health and 

Environmental Hazards Associated with Emissions of Hg and 

Non-Hg HAP from EGUs

In response to peer reviews of both the Hg and non-Hg 

HAP risk analyses, and taking into account public comments, 

we conducted revised analyses of the risks associated with 

U.S. EGU emissions of Hg and non-Hg HAP. These revised 

analyses demonstrated that the risk results reported in the 

preamble to the proposed rule are robust to the revisions 

made to the risk analyses. 

Specifically, with regards to the revised national 

scale assessment of mercury risk to populations with high 

consumption of self-caught freshwater fish, the revised 

results show that up to 29 percent of modeled watersheds 

have populations that are potentially at risk from exposure 

to Hg resulting from U.S. EGU Hg emissions. Up to 24 

percent of modeled watersheds have potential total Hg 

exposure greater than the RfD and U.S. EGU-attributable Hg 

deposition accounts for 5 percent or more of total 

deposition. Up to 10 percent of modeled watersheds have 

exposure that exceeds the RfD based on U.S. EGU-
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

326

attributable deposition even excluding consideration of 

other non-U.S. EGU sources of Hg deposition. In the 

preamble to the proposed rule, we reported that up to 28 

percent of modeled watersheds had populations potentially 

at risk from exposure to Hg resulting from U.S. EGU 

emissions. Given that 1) the percent of modeled watersheds 

has increased from 28 to 29 percent in the revised risk 

assessment, and 2) the revised analysis includes 36 percent 

more watersheds covering a much larger part of the U.S., we 

conclude that the finding that emissions of Hg from U.S. 

EGUs are a hazard to public health is affirmed by the 

revised risk analysis.

With regards to the revised non-Hg inhalation case 

studies, the highest estimated individual lifetime cancer 

risk for the one case study facility (out of 16) with oilfired EGUs is estimated to be 20 in a million, driven by 

nickel emissions. For the facilities with coal-fired EGUs, 

there were five (out of 16) with maximum individual cancer 

risks greater than 1 in a million (the highest was five in 

a million), four of which were driven by emissions of 

hexavalent chromium, and one which was driven by emissions 

of nickel. There were also two facilities with coal-fired 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

327

EGUs with maximum individual cancer risks at 1 in a 

million. In the preamble to the proposed rule, we reported 

that the maximum individual lifetime cancer risk for the 

one facility with oil-fired EGUs was estimated to be 10 in 

a million, and that there were three coal-fired EGU 

facilities with maximum individual cancer risks greater 

than 1 in a million (the highest was eight in a million), 

and one coal-fired EGU facility with maximum individual 

cancer risks equal to 1 in a million. Given that 1) the 

lifetime cancer risk for the oil-fired EGU facility has 

increased from 10 to 20 in a million, 2) the number of 

coal-fired EGU facilities with cancer risks greater than 1 

in a million has increased from three to five, and 3) the 

highest risk coal-fired facility still has cancer risks of 

five in a million, which is substantially greater than the 

1 in a million benchmark, we conclude that the finding that 

emissions of non-Hg HAP from U.S. EGUs are a hazard to 

public health is affirmed by the revised risk analysis.

We have affirmed that emissions of Hg and non-Hg HAP 

are a hazard to public health. We also reiterate that 1) 

U.S. EGU Hg emissions are a hazard to the environment, 

contributing to adverse impacts on fish-eating birds and 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

328

mammals, 2) Hg is a persistent bioaccumulative 

environmental contaminant, and as a result, 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.; controlling Hg emissions from U.S. EGUs helps to 

reduce the potential for environmental hazard from Hg now 

and in the future, 3) 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 Hg and non-Hg HAP emissions from 

EGUs. In addition, we have identified effective controls 

available to reduce Hg and Non-Hg HAP emissions.

Our revised analyses still show 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, 

based on evaluation of the regulations required by the Clean 

Air Act, including the recent Cross State Air Pollution Rule 

(CSAPR), it is necessary to regulate EGUs under section 112 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

329

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. While CSAPR is projected to achieve some Hg 

reductions due to co-control of mercury provided by controls 

put in place to achieve required reductions in SO2 

emissions, our national scale mercury risk assessment shows 

that there are still a substantial percent of watershed 

where populations will remain at risk from U.S. EGU Hg 

deposition after implementation of CSAPR. While we modeled 

slightly higher U.S. EGU Hg emissions of 29 tons in our risk 

analysis compared to the most recent estimate of 27 tons, we 

do not expect that this small change would affect our 

finding that U.S. EGU Hg emissions are a hazard to public 

health. In addition, the actual reductions in mercury that 

will occur due to application of controls to meet the SO2 

emissions requirements of CSAPR may differ from those 

projected to occur, due to differences in the technologies 

that individual EGU sources choose to install. The only way 

to ensure reductions in Hg, including those modeled as 

resulting from the CSAPR, is to directly regulate Hg 

emissions under section 112.
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

330

We reiterate that it is necessary to regulate HAP 

emissions from EGUs because 1) even though the hazards from 

Hg will not be resolved through regulation under section 

112, incremental reductions in Hg are important because as 

exposure above the RfD increases the likelihood and severity 

of adverse effects increases, 2) we cannot be certain that 

the identified cancer risks attributable to EGUs will be 

addressed through imposition of the requirements of the CAA, 

3) the environmental hazards posed by acidification will not 

be fully addressed through imposition of the CAA, 4) 

regulation under section 112 is the only way to ensure that 

HAP emissions reductions that have been achieved since 2005 

remain permanent, and 5) direct control of Hg emissions 

affecting U.S. deposition is only possible through 

regulation of U.S. emissions as we are unable to control 

global emissions directly.

All of these findings independently support a finding 

that it is necessary to regulate EGUs under section 112. 

Therefore, the agency affirms its finding that it remains 

appropriate and necessary to regulate coal- and oil-fired 

EGUs under CAA section 112, and the inclusion of coal- and 

oil-fired EGUs on the section 112(c) list of source 
***E.O. 12866 Review – Draft (10/17/2011) – Do Not Cite, 

Quote or Release During Review***

EO12866 NESHAP MACT & NSPS for Utilities (Mercury and Air 

Toxics Standard) Appropriate and Necessary Finding RIN 

2060-AP52 Final Rule 20111017

331

categories regulated under CAA section 112.