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1 **III. Appropriate and Necessary Finding**
In the preamble to the proposed rule 1 , EPA determined that that it is appropriate and necessary to regulate emissions of mercury ( Hg ) and other Hazardous Air Pollutants ( HAP ) from U.S. EGUs , confirming the finding
made in 2000 . As discussed fully in the preamble to the proposed rule, EPA interpret s the Clean Air Act (CAA) to require the Agency to find it appropriate to regulate U.S. EGUs under section 112 if the Agency determines that the emissions of one or more HAP emitted from U.S. EGUs pose an identified or potential hazard to public health or the environment . The Agency must find it necessary to regulate EGUs under section 112 if the imposition of other requirements of the CAA would not adequately address the identified or potential hazards to public health or the environment . 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

1 76 FR 24986***E.O. 12866 Review

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2 reduction s in EGU HAP emissions, which cannot be assured based on other requirements of the CAA. In this section, we describe revisions to the technical analyses that accompanied the proposed rule and the responses to public comments on legal, technical, and policy aspects of the finding. We first summarize the elements of the appropriate and necessary finding, as discussed in the preamble to the proposed rule. We then discuss the results of the peer reviews of our national
scale mercury risk assessment (hereafter referred to as the Hg Risk TSD) and non - Hg HAP risk assessment . In this discussion, we describe the peer review processes, the
charges provided to the peer review panels, the findings and recommendations from the peer review panels, and EPA’s responses to those peer reviews. We also summarize the results of revisions to the Hg Risk TSD and the case studies of non
- Hg HAP inhalation risks and compare these results to those reported in the preamble to the proposed rule. In the next subsection, we summarize and respond to the major categories of comments on the legal, technical, and policy aspects of the appropriate and necessary***E.O. 12866 Review

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3 finding. The first portion of the response to comments subsection addresses legal aspects of the appropriate and necessary finding. This subsection includes comments on the history of Section 112(n)(1)(a), the definition and interpretation of the terms “appropri ate” and “necessary”, regulation of all HAP, consideration of both health and environmental effects in making the appropriate finding, consideration of costs in making the appropriate finding, consideration of CAA requirements in making the necessary findi ng, listing of U.S. EGU under section 112, and the 2000 finding. The second portion of the response to comments subsection addresses comments related to the new technical analyses confirm that HAP emissions from U.S. EGUs remain a hazard to public health. This includes comments on the inputs, methods, and assumptions used in Hg Risk TSD , the
non - Hg inhalation risk case studies, and the assessment of excess local deposition due to U.S. EGU Hg emissions. Comments on the Hg risk analysis included comments on the modeling of Hg emissions (both global and U.S.) and deposition, the reference dose (RfD) for methylmercury (MeHg), fish tissue Hg concentrations, the assumed linear***E.O. 12866 Review

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4 relationship between changes in Hg deposition and changes in fish tissue Hg concentrati ons, the behavior of subsistence fishing populations, and fish consumption rates. Comments on the non - Hg inhalation risk case studies included comments on non
- Hg HAP emissi ons, modeling parameters , estimating nickel (Ni) and chromium (Cr) risk, and an alte rnative risk analysis . Comments on the assessment of excess local deposition addressed the definition of hotspots, evidence for local Hg deposition from U.S. EGU emissions, documentation of methods, and limitations of deposition modeling. We also received comments related to ecosystem impacts from HAP, focused on the adverse impact of acid gases on ecosystems. Based on our review of the comments and our updated analyses in response to the peer reviews, we affirm 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 . The revised analyses for Hg and non - Hg risk, which fully addresses the advice we received from the peer reviews, confirm that emissions of both Hg and non - Hg HAP from U.S. EGUs are a hazard to public health. These results, along with the***E.O. 12866 Review

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5 other elements of the finding, confirm that it remains appropriate and necessary to regulate EGUs under CAA section 112 and that such units are properl y listed pursuant to section 112(c). 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 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 2000 finding was supported in part by several new analyses of the hazards to public health posed by both Hg and non - Hg HAP.***E.O. 12866 Review

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6 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 CAA section 112. The extensive analyses summarized in the preamble to the proposed rule and documented in several Technical Support Documents 2 , 3 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 unde r 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 large st 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

2 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 Oil
Fired Electric Generating Units . Office of Air Quality Planning and Standards. November. EPA- 452/R
- 11
- 009 . 3 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. Novembe r.***E.O. 12866 Review

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7 surrounding those individual EGUs (not solely the result of regionally transported emissions), and would not be adequately addressed through re ductions in regional levels of Hg emissions, requiring controls to be in place at all U.S. EGU sources that emit Hg; 5) Hg emissions from EGUs affect not only deposition, exposures, and risk today, but may contribute to future deposition, exposure and risk due to the processes of reemission of Hg that occur given the persistent nature of Hg in the environment and that Hg will remain part of the global burden of Hg; in fact, the delay in issuing Hg regulations under section 112 has already resulted in seve ral hundred additional tons of Hg being emitted to the environment, 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 reference dose ( RfD ) . EPA also concluded that Hg emissions from U.S. EGUs contribute to environmental concentrations of Hg that are harmful to wildlife and can affect production of important ecosystem services, including recreational hunting, fishing, and wildlife viewing. EPA***E.O. 12866 Review

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8 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 HCl and HF emissions from U.S. EGUs contribute to acidification in sensitive ecosystems and, 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 regulati ons 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 were projected to be 29 tons per year in 2016, similar to level s 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***E.O. 12866 Review

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9 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 possible through regulation of U.S. emissions; we are unable to control global emissions directly. a. Finding that Hg Emissions from U.S. EGUs Continue to Pose a Hazard to Public Health and the Environment In support of the finding that Hg emissions from U.S. EGUs are a hazard to public health, EPA assessed the Hgrelated risk to populations with high consumption of self
caught freshwater fish, which is the population most likely to experience elevated risk from Hg emissions from U.S. EGUs . This Hg Risk TSD incorporated 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 Hg . The Hg Risk TSD assessed the hazard to public health posed by Hg emissions from U.S. EGUs focused on comparisons of the RfD to exposures caused or contributed to by Hg emissions from U.S. EGUs . In the Hg risk assessment, almost all (98 percent) of the more than 2,400 watersheds for which we identified fish tissue data,***E.O. 12866 Review

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10 exceeded the RfD, above which there is the potential for an increased risk of adver se 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 wat ersheds (where U.S. EGU- attributable deposition alone result ed in potential MeHg exposures above the RfD,
re gardless of the additional deposition from other sources of Hg deposition , and where U.S. EGU- attributable deposition contributed at least 5 percent of the total 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 modeled watersheds with populations potenti ally 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 where U.S. EGU s contribut e to mercury risk at lower percent benchmarks. In total, the Hg risk assessment found an estimated 28 percent of mode led watersheds with populations with***E.O. 12866 Review

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11 potentially at - risk from exposure to MeHg based on 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 RfD 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 RfD . We found that at the 99 th 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 es timate 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 Hg emissions from U.S. EGUs is large enough in some watersheds that per sons consuming contaminated fish would have exposures that exceed the RfD even without additional deposition from other sources. Based on these considerations, we found that at the 99 th percentile fish consumption level for***E.O. 12866 Review

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12 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 modeled watersheds with populations potentially at - risk from U.S. EGU- attributable Hg deposition is likely understated because the data on fish tissue MeHg con centrations that we were able to identify for the Hg risk assessment was limited in some regions of the U.S., such as Pennsylvania, with very high U.S. EGU attributable Hg deposition . Thus , it is possible that watersheds with potentially high MeHg exposures were excluded from the Hg Risk TSD . 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 great snowy egrets. Studies have also shown adverse effects***E.O. 12866 Review

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13 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 d that EGUs are contributing to the identified adverse environmental effects. Hg 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 res ult 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 po ol. Controlling Hg emissions from U.S. EGUs helps to reduce the potential for environmental hazard from Hg now and in the future.***E.O. 12866 Review

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14 In the preamble to the proposed rule, we concluded that all of the se findings independently support a determination that it is appropriate to regulate Hg emissions from EGUs. b. Finding that U.S. EGU Non
- Hg HAP Emissions Continue to Pose a Hazard to Publi c Health and the Environment In addition to the Hg 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 rela tively higher emissions of non
- Hg HAP compared to other U.S. EGUs. The results of that analysis showed that of the 16 facilities modeled , four facilities ( three coal - fired facilities and one oil
- fired facility ) have estimated risks of greater than one in 1 million 4 for the most exposed individual. Given Congress’ determination that categories of sources which emit HAP resulting in a lifetime cancer risk greater than one in 1 million should not be removed

4 A risk level of 1 in a million implies a likelihood that up to one person, out of one million equally exposed people would contract cancer if exposed continuously (24 hours per day) to the specific concentration over 70 years (an assumed lifetime). Th is would be in addition to those cancer cases that would normally occur in an unexposed population of one million people.***E.O. 12866 Review

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15 from the section 112(c) source category li st and should continue to be regulated under 112, we concluded that risks above that level from U.S. EGUs represent a hazard to public health such that it is appropriate to regulate EGUs under section 112. Although our case studies did not identify significant chronic non
- cancer risks from acid gas emissions from the specific EGUs assessed, the Administrator remains concerned about the potential for acid gas emissions to add to already high atmospheric level s 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. 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.***E.O. 12866 Review

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16 These findings independently supported the determination that it remain s appropriate to regulate HAP emissions from EGUs. 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 s econdary PM control devices. Electrostatic precipitators, fabric filters, and wet f lue gas desulfurization ( 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 (o r 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.***E.O. 12866 Review

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17 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 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 Utility Study 5
. Nonetheless, the Agency recognizes that it has discretion to look beyond the Utility Study in

5 U . S . EPA. Study of Hazardous Air Pollutant Emissions from Electric Utility Steam Generating Units

—Final Report to Congress. EPA

– 453/R

– 98

– 004a. February 1998.***E.O. 12866 Review

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18 determining whether it is necessary to regulate EGUs under section 112. Because several years have passed since the 2000 Finding, we conducted an additi onal, updated analysis, examining a broad array of diverse requirements. Specifically, we analyzed HAP emissions from U.S. EGUs remaining in 2016. The baseline for our analysis included emission reductions anticipated from the proposed Transport Ru le (finalized in June 2011 as the Cross - State Air Pollution Rule (CSAPR) 7 ); CAA section 112(g); the Acid Rain Program ; settlements of 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 not conduct an

7
. Since the time of the analyses conducted in support of the appropriate and necessary finding, EPA has updated IPM modeling to reflect to the most recently available information, including public comments and the final CSAPR (see IPM Documentation for further details on these updates , which is available in the docket ) . Compared to the modeling conducted at proposal, these updates are projected to result in greater reductions in criteria pollutants, and also to have a slightly greater impact on U.S. EGU Hg emissions. The current projection in 2016, there will be 27 tons of Hg emitted by U.S. EGU, as compared to the 29 tons we modele d for the Hg Risk TSD. 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

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19 analysis to determine whether the state requirements are based 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 may be based solely in state law and not be 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 Hg emissions estimates for the Hg Risk TSD would underestimate the risks associated with Hg emissions from U.S. EGUs . 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***E.O. 12866 Review

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20 time of proposal would be emitted by U.S. EGUs today. As 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 concluded in the preamble to the propos ed rule that incremental reductions in Hg are important because as exposure above the RfD increases , the likelihood and severity of adverse effects increases. In the preamble to the propos ed rule , we also found that it is necessary to regulate EGUs under section 112 based on non - Hg HAP emissions because we could not 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 would not be fully addressed through imposition of the CAA.***E.O. 12866 Review

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21 In the preamble to the propos ed rule , we also found 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 reducti ons 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, NOX, and SO 2 emissions. However, there are no nati onal, 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 HCl and HF emissions U.S. EGUs 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***E.O. 12866 Review

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22 lesser extent, state regul ations. 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 U.S. EGUs, it is likely that such emissions have also decreased between 2005 and 2010. Thus, the Administrator found it necessary to regulate HAP emissions from U.S. 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 ed the finding that it is necessary to regulate U.S. EGUs under section 112.***E.O. 12866 Review

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23 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 rul e its decision to include coal
- and oil
fired EGUs on the list of source categories regulated under CAA section 112(c). B. Peer Review of the Hg Risk TSD 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 Hg Risk TSD supporting EPA’s 2011 review of U.S. EGU health impacts should be peer - reviewed.” 8 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.

8 76 FR 25012***E.O. 12866 Review

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24 We have completed the peer review of the Hg Risk TSD , which is fully documented in the revised Technical Support Document (TSD): National
-Scale Assessment of Hg 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 . 9 The following sections describe the peer review process that we followed, provide the peer review 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 Hg Risk TSD , which is a highly influential scientific assessment. Therefore, EPA conducted a peer review in accordance with OMB’s Final Information Qual ity Bulletin

9 U.S . EPA, 2011a.***E.O. 12866 Review

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25 for Peer Review10 as described below. All the materials related to the peer review , including the SAB’s final report , can be found in the docket for this rulemaking . 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 convened a 22
-member peer review committee . The SAB process for selecting the panel began with two Federal Register Notices requesting nominations for the Mercury Review Panel 11 . 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 members of the Mercury Review Panel were announced on May 24, 2011. The membership of the panel included represent at ives of 16 academic institutions, four st ate health or environmental agencies, one federal agency, and one utility industry

10 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 . 11 76 FR 10896 and 76 FR 17649. The first notice requested nominations to a Clean Air Scien tifi c Advisory Committee (CASAC) panel. Upon review of the scope of the CASAC charter (resulting from a publi c 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.***E.O. 12866 Review

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26 organization 12 . The panel held a public meeting in Research Triangle Park, NC on June 15
- 17, 2011, which included the opportunity for public comment on the Hg Risk TSD and the peer review process 13 . At the June 15
- 17 public meeting, the panel completed a draft peer review report. The minutes of that meeting and the 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 provided 14 , 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 te leconference also included a final opportunity for public comment 15 . The SAB submitted its final report to EPA on September 29, 2011 16
. All of the materials discussed at the SAB meetings,

12 The full list of panel members is documented at http://yosemite.epa.gov/sab/sabproduct.nsf/0/9F048172004D93BB8525783900 503486/$File/Determination%20memo%20with%20addendum
- 05.24.11.pdf 13 76 FR 29746 14 76 FR 39102 15 76 FR 50729 16 U.S. Environmental Protection Agency
- Science Advisory Board (U.S. EPA- SAB). 2011. Peer Review of EPA’s Draft National
- Scale Mercury Risk Assessmen t. EPA- SAB - 11
- 017. September. Available on the internet at http://yosemite.epa.gov/sab/sabproduct.nsf/BCA23C5B7917F5BF8525791A0072 CCA1/$File/EPA
- SAB - 11
- 017
- unsigned.pdf .***E.O. 12866 Review

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27 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. 17 2. Peer Review Charge Questions EPA asked the SAB to comment on the Hg Risk TSD , including the overall design and approach and 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 were well characterized in the Hg 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

17 See http://yosemite.epa.gov/sab/sabpeople.nsf/WebCommittees/BOARD***E.O. 12866 Review

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28 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 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***E.O. 12866 Review

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29 fish tissue data used as the bas is 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 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***E.O. 12866 Review

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30 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 wh ich 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 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 populati ons might be active is provided in section***E.O. 12866 Review

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31 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 associated changes in fish tissue MeHg levels) in the risk assessment. Please comment on how the output of CMAQ [Community Multiscale Air Quality] modeli ng 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***E.O. 12866 Review

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32 excluding watersheds with sign ificant 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 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 as sociated with the risk assessment have been identified and the degree to which they are sufficiently characterized.***E.O. 12866 Review

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33 Question 13: Please comment on the draft Mercury Risk TSD’s discussion of analytical results for each component of the analysis. For each o f 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 models and data used: mercury deposition from U.S. EGUs , fish tissue MeHg 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***E.O. 12866 Review

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34 The SAB was generally supportive of EPA’s approach. 18 The SAB concluded, “ [i] n 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 credible determination of the potential for a public health hazard from mercury emitted from U.S. EGUs. ” 19 The SAB further concluded, “ [t] he SAB regards the design of the risk assessment as suitable for its intende d 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.” 20 The SAB report contained many recommendations for improving the Hg Risk TSD, which the SAB organized into three general themes: (1) improve the clarity of the Hg Risk TSD regarding methods and presentation of results, (2) expand the discussion of sources of variability and

18 U.S. EPA- SAB, 2011. 19 Id. 20 Id.***E.O. 12866 Review

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35 uncertainty, and (3) de
- emphasize IQ loss as an endpoint. In the following section, we provide EPA’s response to these recommendations. 4. EPA Responses to Peer Review Recommendations In response to the peer review, EPA has substantially revised the Hg Risk TSD . The revised Hg 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 Hg Risk TSD. Revisions in response to the main recommendations are summarized below. Italicized statemen ts are the SAB’s recommendations, followed by EPA’s response.

 The watershed- focus of the Hg Risk TSD should be clearly stated early in the introduction to the document . We have stated clearly in the introduction to the revised Hg 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 such subsistence fishing activity. Specifically, we model ed 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***E.O. 12866 Review

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36 subsistence
- level fishing activity could occur. We emphasize the point that the analysis is no t a representative population
-weighted assessment of risk. Rather, it is based on evaluating these potential exposure scenarios.

 Because IQ does not fully capture the range of neurodevelopmental effects associated with Hg exposure, analysis of this endpoin t 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 Hg 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. The SAB fully supported using HQ as the risk metric, but we revised the discussion in the Hg Risk TSD to clarify why we selected 1.5 as the benchmark . Reflecting precedent in interpreting HQ estimates, we clarified that exposures above the RfD (i.e., an HQ above one) represent a***E.O. 12866 Review

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37 potential public health hazard . 21 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) be rounded to an HQ of 1. Thus, exposures at or above 1.5 are considered above the RfD and represent a potential public health hazard.

 Regarding the fish tissue dataset used in the Hg Risk TSD , 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 22 , it is reasonable to assume that more than 90 percent of fish tissue Hg is MeHg . Therefore, we incorporated an Hg

21 As stated in the preamble to the proposal, based on the current literature, exposures above the RfD contribut e to risk of adverse effects. 22 See the literature summary in Chapter 4 of U.S. EPA. 2000. Guidance for Assessing Chemical Contaminant Data for Use in Fish Advisories . Office of Science and Technology, Office of Water, Washington, DC. EPA 823
- B - 00
- 007.***E.O. 12866 Review

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38 conversion factor 23 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 address the potential for different sampling protocols across states to introduce bias into the Hg Risk TSD .
 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 reflected across watersheds). We included additional figures and tables describing the deriva tion of the watershed- level fish tissue Hg dataset, including the filtering steps applied to the original water body level data and the additional steps taken to generate the watershed- level fish tissue Hg percentile estimates. In addition, we included tables summarizing

23 In the March Hg Risk TSD, we assumed that 100 percent of Hg in fish was MeHg. We derived the 0.95 conversion factor for the Revised Hg Risk TSD to reflect that most studies show that more than 90 percent of total Hg in fish is MeHg. See Chapter 4 of U.S. EPA, 2000.***E.O. 12866 Review

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39 key attributes of the dataset (e.g., distribution of fish tissue sample size and number of species a cross the watershed- level estimates).

 Determine whether there is additional (more recent) fish tissue data for key states including Pennsylvania, New Jersey, Kentucky and Illinois where U.S. EGUs Hg deposition may be more significant. We expanded the f ish 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 percent. The additional watersheds improve coverage in areas with high levels of U.S. EGU
- attributable Hg deposition , and thus increase our confidence in the overall results of the Hg Risk TSD .
 Include additional discussion of the potential that the low sampling rates reflected across many of the watersheds may low-bias the 75 th percentile fish tissue Hg estimates used in estimating potential exposures.***E.O. 12866 Review

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40 In addition, include a sensitivity analysis using the 50 th percentile estimates to provide a bound on the risk . The SAB expressed support for the use of the 75 th percentile fish tissue Hg value in the Hg Risk TSD , 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, and an improved discussion of uncertainty and potential low bias resulting from estimation of the 75 th percentile fish tissue levels. We also included a sensitivity analysis that used the 50 th percentile watershed
- level fish tissue Hg level. This sensitivity analysis showed that using the 50 th percentile estimates resulted in a decrease in the number and percentage of modeled watersheds with populations potentially at - risk f rom U.S. EGU- attributable MeHg exposures, from 29 percent in the revised Hg Risk TSD to 26 percent in the sensitivity analysis in the revised Hg Risk TSD .
 Expand the discussion of caveats associated with the fish consumption rates used in the analysis. The SAB was generally supportive of the consumption rates***E.O. 12866 Review

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41 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 explains 1) that 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 (i.e., mostly based on survey data f rom the 1990s) and behavior may have changed (i.e., consumption rates may have changed since the surveys were conducted) , and 3) that consumption rates used in the Hg Risk TSD are annualized rather than seasonal rates and thus contribute litt le to overall uncertainty. None of these sources of uncertainty is associated with a particular directional bias (e.g., neither systematically higher nor lower risk).

 Verify whether the consumption rates are daily values expressed as annual averages and whether they are “as caught” or “as prepared.” We carefully reviewed the studies underlying the fish consumption rates used in the Hg Risk TSD and verified that the rates are annual***E.O. 12866 Review

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42 average s of the daily consumption rates and that they represent as prepared estimates. We also expanded the explanation of the exposure calculations to describe more completely 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 Hg Risk TSD . 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 t rout and s almon (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***E.O. 12866 Review

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43 SAB was generally supportive of the approach used for identifying waters heds 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 subsis tence fish ing scenarios. For all scenarios except the female subsistence fishing scenario, the exposure scenario s significant ly limit ed the number of watersheds . Because the female subsistence fish ing scenario does not differentiate with regard to ethnicity or socio
- economic status(SES), we applied this scenario to all regions of the country and to all watersheds with fish tissue Hg data. This reflects our assumption that, given the generalized nature of the female subsistence fishing scenario, it is reasonable to assume that it could potentially occur at any watershed with fish tissue Hg data. The female subsistence fis hing scenario included in the revised risk assessment is similar to the high
consuming female scenario included in the Hg Risk***E.O. 12866 Review

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44 TSD. 24 However, the female subsistence fishing scenario is applied to all watersheds , while in the scenario for the high
- consuming low
- income female angler , we only evaluated watersheds with a population of at least 25 low
- income females . The female subsistence fishing scenario provides greater coverage geographically than the high
- consuming low
- income female scenario .
 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

24 In the Revised Mercury Risk TSD, this population is also referred to as the “typical female subsistence consumer”.***E.O. 12866 Review

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45 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 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 b y 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 emissions of Hg . The SAB concluded that EPA’s approach***E.O. 12866 Review

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46 to minimizing the potential for these biases to affect the results of the Hg Risk TSD is sound. In addition, we conducted several sensitivity analyses to gauge the impact of excluding watersheds with the poten tial for
non - EGU Hg emissions . We found that the estimates of the percent of modeled watersheds with populations potentially at
- risk were largely insensitive to these exclusions , suggesting that any potential biases from including watersheds with potential non
- air Hg loadings are likely to be small .
 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 colle cting 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***E.O. 12866 Review

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47 conversion of fish tissue Hg levels (as measured) into “as con sumed” values. We expanded the discussion of sources of variability in the revised Hg Risk TSD to more fully address these sources of variability . The Hg Risk TSD quantitatively reflected many aspects of variability, including spatial and temporal variabil ity in Hg emissions, Hg deposition, fish tissue Hg levels, and subsistence behavior. We do not believe that the aspects of variability assessed qualitatively in the Hg Risk TSD such as temporal response in fish tissue would substantially change the risk results given the stated goal of the analysis.

 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 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***E.O. 12866 Review

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48 coverage that we have with fish tissue Hg data for watersheds in the U.S. and implications for the Hg Risk TSD , 5) the preparation factor used to estimate “as consumed” fish tissu e 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 the degree to which these provide coverage for high
consuming 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 i n the revised TSD to address more fully these sources of uncertainty and the potential impact on risk estimates. Regarding these eight additional sources of uncertainty, we have 1) evaluated the uncertainties in the emissions and determined that wh ile an important source of uncertainty, we are not able to quantify emissions uncertainty in the risk analysis, but have determined that the emissions inventories and emissions models represent the best available methods***E.O. 12866 Review

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49 for predicting Hg emissions in the U.S., 2) evaluated the uncertainties in the Hg deposition predictions and determined that while an important source of uncertainty, we are not able to quantify uncertainty in Hg deposition in the Hg Risk TSD , but the CMAQ model used to estimate deposition is based on peer reviewed science and represents the best available method for predicting Hg deposition in the U.S., 3) evaluated the ability of the Mercury Maps
-based approach for relating Hg deposition to MeHg in fish to capture Hg hotspots and determine d that while finer resolution deposition modeling might reveal additional areas with elevated deposition, the 12 km deposition modeling matches well with the watershed size selected for the analysis, and thus the use of 12 km deposition estimates with the Mercury Maps based approach will not be a large source of uncertainty, 4)evaluated the limited coverage that we have with fish tissue Hg data for watersheds in the U.S. and implications for the Hg Risk TSD and based on the SAB ’s recommendations, we supplemented the coverage of watersheds by obtaining additional fish tissue Hg samples for areas heavily***E.O. 12866 Review

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50 impacted by U.S. EGU deposition, thus reducing the uncertainty in the analysis 5) 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, 6) evaluated the uncertainty resulting from the proportionality assumption used to relate changes in Hg deposition to changes in fish tissue Hg levels at the watershed- level , and determined, based both on quantitative sensitivity analyses and qualitative assessments, that this source of uncertainty is not likely to greatly influence the results, and is not likely to have a specific directional bias, 7) evaluated the uncertainty related to characterization of the spatial locations of subsistence populations and determined that uncertainty could be reduced by focusing the risk estimates on female subsistence fishing populations, which are assumed to have the potential to fish in all watersheds, and 8) evaluated the potential impact of the uncertainty in application of the RfD to low SES populations, and determined that due to the method used in calculating the RfD , have***E.O. 12866 Review

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51 confidence that the RfD may coverage for low SES populations .
 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. Based on the SAB’s recommendation, 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 75 th percentile resulted in only a small decrease in the estimates of risk. C. Summary of Results of Revised Hg Risk TSD 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 l evels of fish consumption. 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***E.O. 12866 Review

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52 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 25 in representing potential risks for low income female subsistence fishing populations. Based on these revisions , our estimates of the number and percent of modeled watersheds with populations potentially at - risk from exposure to EGU- attributable MeHg changed from those presented in the preamble to the proposed rule. For the 99 th percentile consumption scenario, the number of watersheds with fish tissue Hg samples where subsistence fishing populations may be at - ri sk from exposure to EGU- attributable MeHg increased from 672 to 917 (an increase of 36 percent). For this same scenario, the percent of modeled watersheds with populations potentially at - risk increased from 28 percent to 29 percent. For the 95 th percentile consumption scenario, the percent of modeled watersheds with populations potentially at - risk has
25 The watersheds were filtere d to exclude watersheds that: (a) were not freshwater, (b) did not have fish sampling data since 2000, (c) did not have fish larger than 7 inches in length, (d) contained active gold mines or (e) had substantial non
- air Hg loading.***E.O. 12866 Review

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53 increased from 22 percent to 24 percent. The increase in the percent of modeled watersheds with populations potentially 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 in response to the SAB peer review showed that the estimates of the percent of modeled watersheds with populations potentially at - risk are robust to alternative assumptions about both the watersheds included in the analysis and the selec tion of the 50 th percentile or 75 th percentile fish tissue Hg level. Sensitivity analyses excluding entire states with the potential for historical loadings of Hg from non - air sources 26 resulted in an increase in the percent of modeled watersheds with populations potentially at - risk , from 29 percent to 33 percent. Including only watersheds in the top 25 th percentile of U.S. EGU deposition resulted in an increase in the percent of modeled watersheds with populations potentially at - risk , f rom 29

26 The SAB noted that are as 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 reflec t non - U.S. EGU Hg loadings.***E.O. 12866 Review

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54 percent to 30 percent. Using the 50 th percentile fish tissue Hg level resulted in a decrease in the percent of modeled watersheds with populations potentially at - risk , from 29 percent to 26 percent. On balance, these sensitivity analyses do not substantially reduce the percent of modeled watersheds with populations potentially at - risk , and thus confirm the finding that Hg emissions from U.S. EGUs are a hazard to public health. In fact, given the broader coverage of modeled watersheds in the revised analysis, we have greater confidence in our finding that U.S. EGU Hg emissions result in deposition that causes a hazard to public health. D. Peer Review of the Approach for Estimating Cancer Risks Associated with Cr and Ni Emissions in the U.S. EGU Case Studies of Cancer and Non
- Cancer Inhalation Risks for Non
Hg HAP and EPA Response As explained in the preamble to the proposed rule, EPA determined to peer review its characterization of the chemical speciation for the emissions of Cr and Ni used in the non - Hg HAP inhalation risk case studies . The Agency determined that the remaining aspects of the non - Hg HAP case study risk assessments used methods that were already***E.O. 12866 Review

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55 been subject to adequate peer review. The methodologies used to conduct those risk assessments were consistent with those used to conduct inhalation risk assessments under EPA’s Risk and Technology Review (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 the SAB in 2009 . The SAB issued its peer review report in May 2010. 27 The report endorsed the risk assessment methodologies used in the program , and made a number of technical recommendations for EPA to consider as the RTR program evolves . EPA’s case studies identified Cr and Ni 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 Cr and Ni , EPA conducted a letter peer review of its analysis and interpretation of those data relative to the quantification of inhalation risks associated with

27 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

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56 Cr and Ni emissions from U.S. EGU s . The following sections describe the peer review process , enumerate the peer review 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 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 Cr and Ni 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 received several charge questions (three questions on Cr and two questions on Ni , which are provided below ) on the technical and scientific relevance of the approaches used to develop the inhalation unit risk estimates. EPA also provided information on C r speciation profiles for different industrial sources, as well as***E.O. 12866 Review

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57 information on the Ni speciation of particulate matter from oil
- fired power plants . 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 EPA on key issues relevant to the characterization of risks from EGU emissions containing either Cr or Ni compounds. EPA asked three questions regarding Cr and Cr compounds: Question 1: Do EPA’s judgments related to speciated chromium emissions adequately take into account the available chromium speciation data? Question 2: Has 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 EPA should consider for future analysis? EPA asked two questions regarding Ni and Ni compounds: Question 1: Do EPA's judgments related to speciated nickel emissions adequately take into account available***E.O. 12866 Review

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58 speciation data, including recent industry spectrometry studies? Question 2: Base d 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)), EPA has provided several approaches 28 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 EPA should consider? 3. Summary of Peer Review Findings and Recommendations Regarding Cr and Cr compounds, all three reviewers considered hexavalent Cr as the species likely to be driving cancer risks based on solid evidence from the
28 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

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59 health effects database for Cr and Cr 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 Cr 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 Cr (e.g., range of approximatel y 4 to 23 percent hexavalent Cr from coal - fired units). One of the reviewers recommended several additional studies for EPA’s consideration ; EPA considered these in finalizing the report . Regarding Ni and Ni compounds, the reviewers agreed with the views of the international scientific bodies, which consider Ni compounds carcinogenic as a group. One reviewer recommended that EPA review several additional Ni speciation data that suggests that sulfidic Ni compounds (which the reviewer considered as the most potent carcinogens within the group of all Ni compounds) are present at low levels in emissions from EGUs. In addition, this reviewer pointed out that there is a recently proposed***E.O. 12866 Review

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60 model that may explain the differences in carcinogenic potential across Ni compounds . 4. EPA Responses to Peer Review Recommendations We summarize EPA’s basic responses to the peer review comments below, first for Cr - related issues, and second for Ni
- related issues , which are reflecte d in the revised document . 34
a. Cr and Cr compounds: In agreement with the peer reviewers and based on the health effects information available for Cr , EPA assigns high confidence in the assumption that hexavalent Cr is the carcinogenic species driving the risk of Cr - emitting facilities . In agreements with the reviews, EPA considers derivation of default speciation profiles ba sed on the mass of hexavalent Cr a reasonable approach. As suggested by one of the reviewers, EPA reviewed two potentially relevant studies, one of which showed coal combustion emissions containing as much as 43 percent hexavalent Cr 35 , which suggests that EPA's quantitative approach could actually underestimate hexavalent Cr inhalation risks. However, the
34 U.S. EPA, 2011c. 35 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

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61 other study reviewed by EPA on speciation of Cr in coal combustion showed hexavalent Cr percentage levels close to detection limits (i.e., three to five percent of total Cr , which was close to limit of detection in this study). 36 Thus, the more recent speciation data available is unlikely to reduce the uncertainty of the Cr speciation analyses used by EPA as the bases for risk characterization analysis. In agreement with the peer reviewers, 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 Cr across the different samples. b. Ni and Ni compounds: Based on the views of the major scientific bodies mentioned above and the peer reviewers that commented on EPA’s approaches to risk characterization of Ni compounds, EPA considers all Ni compounds to be carcinogenic as a group and , contrary to the point of view expressed by representatives of oil
- fired EGUS, EPA does not consider Ni

36 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

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62 speciation or Ni solubility to be strong determinants of Ni carcinogenicity. These scientific bodies also recognize that ba sed on the data available, the precise Ni compound(s) responsible for the carcinogenic effects in humans is not always clear, and that there may be differences in the potential toxicity and carcinogenic potential across Ni compounds. Nevertheless, studies in humans indicate that various mixtures of Ni compounds (including Ni sulfate, sulfides and oxides, alone or in combination) encountered in the Ni refining industries may cause cancer in humans , and there is no reason to expect anything different from thi s for mixtures of nickel compounds from other emission sources . One of the reviewers suggested we consider views by some authors that believe that water soluble Ni , such as Ni sulfate, should not be considered a human carcinogen . This view is based primarily on a negative Ni sulfate 2
- year NTP rodent bioassay (which is different from the positive 2
- year NTP bioassay for Ni subsulfide). 37 , 38 , 39 One review article identifies the

37 Oller A. 2002. “Respiratory carcinogenicity assessment of soluble nic kel compounds.” Environ Health Perspect . 110:841
- 844. 38 Heller JG, Thornhill PG, Conard BR. 2009. “New views on the hypothesis of respiratory cancer risk from soluble nickel exposure; and***E.O. 12866 Review

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63 discrepancies between the animal and human data (i.e., from studies of cancers in workers inhaling certain forms of Ni versus inhalation studies suggesting different carcinogenic potential in rodents with different Ni compounds) and states that the epidemiological data available clearly support an association between Ni and increased cancer risk, although the article acknowledges that the data are weakest regarding water soluble Ni . In addition, EPA identified a recent review 40 that highlights the robustness and consistency of the epidemiological evidence across several decades showing associations between exposure to Ni and Ni compounds (including Ni sulfate) and cancer. Regarding the second charge question on Ni compounds, two reviewers suggested using the URE derived by the TCEQ 41 for all Ni compounds as a group, rather than the one derived by the Integrated Risk Information System (IRIS,
reconsideration of this risk's historical sources in nickel refineri es.” J Occup Med Toxicol. 4:23. 39 Goodman JE, Prueitt RL, Thakali S, and Oller AR. 2011. “The nickel iron bioavailability model of the carcinogenic potential of nickel
containing substances in the lung.” Crit Rev Toxicol 41:142
- 174. 40 Grimsrud TK and Ander sen 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. 41 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

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64 1991) 42 specifically for Ni subsulfide. The third reviewer did not comment on an alternative approach. Considering this, EPA decided to use a health protective approach by applying 100 percent of the current IRIS URE for Ni subsulfide , rather than assuming that 65 percent of the total mass of emitted Ni might be Ni subsulfide, as used in previous analyses . We used the IRIS URE value because IRIS values are preferred given the conceptual consiste ncy with EPA risk assessment guidelines and the level of peer review that such values receive . We used 100 percent of the IRIS value because of the concerns about the potential
car cinogenicity of all forms of Ni raised by the major national and international scientific bodies , and recommendations of the peer reviewers . Nevertheless, taking into account that there are potential differences in toxicity and/or carcinogenic potential across the different Ni compounds, and given that two URE values have been derived for exposure to mixtures of Ni compounds that are two to three fold lower than the IRIS URE for Ni subsulfide, EPA also considers it reasonable to use a value

42 U.S. EPA, 1991. Integrated Risk Information Service (IRIS) assessment for nickel subsul fide . Available at: http://www.epa.gov/iris/subst/0273.htm.***E.O. 12866 Review

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65 that is 50 percent of the IRIS URE for Ni subsulfide for providing an estimate of the lower end of a plausible range of cancer potency values for different mixtures of Ni compounds. Although this report focused primarily on cancer risks associated with emissions containing Ni compounds, it is important to note that comparative quantitative analyses of
non - cancer toxicity of Ni compounds indicate that Ni sulfate is as toxic or more toxic than Ni subsulfide or Ni oxide which does not support the notion that the solubility of Ni compounds is a strong determinant of its toxicity. 43 , 44 E. Summary of Results of Revised U.S. E GU Case Studies of Cancer and Non - Cancer Inhalation Risks for Non
- Hg HAP Based on the results of the peer review and public comment s 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

43 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. 44 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

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66 1) changes in emissions, 2) changes in stack parameters for some facilities based on new data received during the public comment period, 3) use of updated versions of AERMOD and its input processors (AERMAP, AERMINUTE, and AERMET ), and 4) use of 100 percent of the current IRIS URE for Ni subsulfide to calculate Ni
- associated inhalation cancer risks (rather than assuming that the Ni might be 65 percent as potent as Ni subsulfide). Based on estimated actual emission s, the highest estimated individual lifetime cancer risk from any of the sixteen case study facilities was 20 in a million, driven by Ni emissions from the one case study facility with oil
fired EGUs. Of the facilities with coal
- fired EGUs, five faci lities had maximum individual cancer risks greater than
one in a million (the highest was five in a million), with the risk from four due to emissions of hexavalent Cr and the risk from one due to emissions of Ni . There were also two facilities with coal
- fired EGUs that had maximum individual cancer risks equal to one in a million. All of the facilities had non
- cancer T arget Organ Specific Hazard Index (TOSHI) values less than one, with a maximum TOSHI***E.O. 12866 Review

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67 value of 0. 4 (also driven by Ni 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. Based on the fact that six EGUs were estimated to meet
or exceed the CAA 112(c)(9) criterion of one in a million, EGUs cannot be removed from the list of source categories to be regulated under CAA 112. 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 EPA’s 2000 appropriate and necessary finding and listing of EGUs was flawed because the Agency did not comply with CAA***E.O. 12866 Review

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68 section 307(d) rulemaking process. The commenter sought review of the 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 , which the D.C. Circuit concluded 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 2000 listing decision or on the factual correctness of EPA’s later decision to reverse its section 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 dockets - Docket ID. No. A- 92
- 55 and Docket ID. No. EPA- HQ -***E.O. 12866 Review

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69 OAR- 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 propose d 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. First, 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 2000 . However, the commenter’s complaint is without foundation. The CAA does not require section 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.” Second, the commenter challenged the listing decision in the U.S. Court of Appeals for the District of Columbia Circuit (Court) and, on July 26, 2001,***E.O. 12866 Review

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70 the Court granted EPA’s motion to dismiss that action based on the plain language of section 112(e)(4). EPA clea rly 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. Third , 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) Revi sion Rule, 71 F.R. 33388 (June 9, 2006), respectively. The commenter is incorrect because EPA incorporated by reference the two dockets at issue. See EPA
- HQ - OAR- 2009
- 0234
- 3056. Comment: One commenter state d that 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 that 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 install expensive, new pollution control equipment to***E.O. 12866 Review

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71 control HAP emissions. The commenter asserts that in this proposed rule, 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. According to the commenter , 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, which the Agency is required to regulate under other provisions of the CAA. One commenter state d that for decades , EPA set primary ambient air quality standards that protect public health with an adequate margin of safety, CAA section 109(b)(1), and set secondary standards that are [sic] “requisite to protect the public welfare 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, EPA has ongoing regulatory proceedings in which it can address any perceived health concerns. The commenter concludes that regulation of EGU***E.O. 12866 Review

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72 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 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

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73 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 state d that section 112 required EPA to make a risk
-based determination in order to regulate HAP. According to the commenter, 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.” According to the commenter , EPA has regulated a number of HAP emitted from industrial source categories other than EGUs.***E.O. 12866 Review

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74 As for EGUs, according to the commenter, EPA found that the combustion of fossil fuels produces extremely small emissions 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. EPA, in past reviews, found that these HAP emissions did not pose hazards to public health. See 48 Fed. Reg. 15,076, 15,085 (1983) (radionuclides). In the case of Hg specifical ly, 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 (Oc t. 19,1975) (mercury); 52 Fed. Reg. 8724, 8725 (Mar. 19, 1987) (reaffirming mercury conclusion). In the late 1980s, EPA was concerned that its prior risk assessments of individual HAP emissions from fossil
fuel - fired power plants may not reflect the to tal risks posed by all HAP emitted by those sources. EPA modeled the risks posed by all HAP emitted by power plants (very much like the analyses the Agency would conduct for the Utility Study ten years later). The commenter asserts that the***E.O. 12866 Review

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75 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 appropri ate 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

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76 We acknowledge 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 prio r 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 Hg 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 Hg- spec ific studies. See CAA sections 112(n)(1)(B) and 112(n)(1)(C). The commenter ’s suggestion that EPA could or should rely on assessments of Hg from EGUs conducted prior to the 1990 amendments is not tenable. Finally, one commenter state d 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 that failed the “ample margin of safety” test. The***E.O. 12866 Review

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77 commenter did not cite the study or provide any information to suppo rt the statements so we are unable to respond to the alleged study directly; however, the risk assessment s conducted in support of the appropriate and necessary finding, as well as the 2000 finding, demonstrate that HAP emissions from EGUs pose hazards to public health and the environment. b. Interpretation of “Appropriate” and “Necessary” Comment: One commenter state d that in the preamble to the proposed rule, 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 “ 2000 Finding.” See 76 Fed. Reg. 24,976, 24,986/2 (May 3, 2011). The commenter state d that throughout the proposal EPA tries to suggest that it is returning to some earlier, “correct” interpretation of CAA section 112(n)(1) set forth in its 2000 action. See, e.g., 76 Fed. Reg. at 24,989/1
- 2 (“The Agency’s i nterpretation of the term ‘appropriate’... is wholly consistent with the Agency’s appropriate finding in 2000 ”); id. at 24,992/1 (“Our interpretation of the necessary finding is reasonable and consistent with the 2000 Finding”). According to the***E.O. 12866 Review

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78 commenter, EPA did not provide in 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 “ 2000 finding does not provide an interpretation of the phrase ‘after imposition of the requirements of the Act”); id. at 16,000/2 (in 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 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 2000 , and that it is today merely “confirm[ing] that finding and conclud[ing] that it remains appropriate and necessary to regulate these emissions...” 45 Response: The commenter disagrees with certain statements in the preamble to the proposed rule that provide that the Agency’s interpretation of section 112(n)(1) is reasonable and consistent with the 2000 Finding. It is difficult to decipher the exact complaint

45 Id. at 24,977/3.***E.O. 12866 Review

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79 that the commenter has with EPA’s proposed rule in this regard, but the commenter does assert that “the Agency did not provide in 2000 any interpretation of what it now characterizes as the “critical terms” of CAA 112(n)(1).” The 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 . 46 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 preamble to 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 the 2000 finding . Instead, we noted in the preamble to the

46 65 FR 79830.***E.O. 12866 Review

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80 proposed rule that our interpretation is consistent with the 2000 Finding because in 2005 we interpreted the statute in a manner that was not consistent with the 2000 finding. If anything, making an interpretation in 2005 that directly contradicted a prior factual conclusion was improper. At least one commenter who takes issue with the interpretation in the preamble to 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. 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 d that a finding that HAP regulation is “appropriate” for a single HAP does not indicate that it is “appropriate” to regulate all HAP . According to the commenters the spons or of the House bill that became section 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***E.O. 12866 Review

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81 described in section 112(n) clearly establish that 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 d that 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 section 112(n)(1)(A) cannot be regulated differently. The commenters conclude that the language of section 112(n)(1)(a) reflects Congress’ intent that “regulation of HAP from EGUs was not intended to operate under section 112(d) but was instead intended to be tailored to the findings of the utility study mandated by section 112(n)(1)(A).”***E.O. 12866 Review

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82 Response: The commenter maintains that the Agency’s interpretation of CAA section 112(n)(1) is flawed in many 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. The Supreme Court has repeatedly stated that the statements of one legislator 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 U.S. 102, 117
- 118 (1980) (declining to give much weight to***E.O. 12866 Review

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83 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 legislato r, 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 evaluat ing 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...”). 47 As these cases show, the Supreme Court does not

47 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. 200 3)) , 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 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,***E.O. 12866 Review

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84 give any weight to the statements of an individual legislator , except when the statements are supported by other legislative history and the clear intent of the statute. The c ommenter s cited no case law that would support any re liance 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 . In fact, there does not appear to be anything in the House, Senate, or Committee Reports that supports Oxley’s statement. The lack of support for 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 regulated prior to the Util ity Study. In fact, legislative statements from
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 whe n 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 USC section 7429(g)(1) 489 F.3d 1250, 1259 (D.C. Cir. 2007).***E.O. 12866 Review

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85 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 Hg from U.S. 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 p lants 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 gone from “we’re not a prob lem” to “you can’t regulate us***E.O. 12866 Review

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86 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 Oxle y’s interpretation of section 112(n)(1), a provision that 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 the Supreme Court’s views on the use of such limited legislative history , EPA reasonably declined to consider (or even discuss ) the legislative history in the preamble to the proposed rule and we believe it would be improper to***E.O. 12866 Review

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87 ascribe Representative Oxley’s statements to the entire Congress . Moreover, Representative Oxley’s statement directly conflicts with the statutory text. Representative Oxley state d that “[the Administrator may regulate only those units that he determines

– after taking into account compliance with all provisions of the ac t 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). However, 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 Utility Study, and that study is the only condition precedent to making the appropriate and necessary finding. 49

49 In addition, EPA only considered CAA requirements in the Utility Study and this was the correct approach because Congress knew how to***E.O. 12866 Review

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88 Our interpretation , not commenters’ , should be afforded deference because the legislative history the commenters rely on is not controlling . In addition, commenters often cite Representative Oxley’s statements as support for alternative interpretations of section 112(n)(1). We believe that any arguments that rely such limited legislative history are without merit. Comment: One commenter state d that 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, commenters note that EPA cites National Cable & Telecommunication Ass’n v. Brand X Internet Services , 545 U.S. 967 (2005). The commenter s agree that i t is true that, in Brand X require consideration of non
- Federal requirements when directing EPA to conduct a study or assessment. See CAA section 11 2(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

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89 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). The commenter s maintain that 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) adopted in 2005. The commenter states that under the first step of Chevron , the Agency’s latest interpretation must still be consi stent with congressional intent . See Chevron v. NRDC, 467 U.S. at 842
- 43. The commenter s state that 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 of Barrington,***E.O. 12866 Review

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90 Ill. v. Surface Transportation Bd ., No. 09
- 1002 (D.C. Cir. Mar. 15, 2011). The commenter s allege that EPA failed to properly define and exercise the scope of its discretion . In each instance, the commenter maintains that 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 , as interpreted after considering the statements of Representative Oxley . Response: The c ommenter appears to argue that EPA’s interpretation of sec tion 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, as noted above, much of the commenter’s argument that the plain language of the statute precludes 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.***E.O. 12866 Review

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91 Furthermore, we properly considered the scope of our discretion in interpreting the statute as explained in detail in the preamble to the proposed rule . We believe the interpretation set forth in the preamble to the proposed rule is consistent with 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 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 , 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

– contro l HAP emissions from virtually uncontrolled sources” or else “retire these sometimes 60 year old units and shift***E.O. 12866 Review

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92 their emphasis to more efficient, cleaner modern methods of generation, including modern coal
- fired generation.” Id. The commenter state d that this remarkably forthright statement establishes that the underlying basis for EPA’s proposal to regulate EGUs under CAA 112 is not to address any “hazards to public health” that might be attributed to the emission by EGUs of HAP listed under CAA section 112(b). Rather, according to commenter, EPA is utilizing the regulation of EGUs under CAA 112 as a means to an entirely different end: to force the imposition of controls that will also have the result of reducing non
- HAP emissions (primarily PM) or force the shutdown of those units for which the cost of such controls would be prohibitive. At the same time, according to commenter, EPA tacitly acknowledges that it cannot hope to make out a case that the regulation of EGU HAP emissi ons is “appropriate and necessary” within the meaning of CAA 112(n)(1). The commenter asserts that the only HAP whose health - related benefits EPA quantifies is Hg . Elsewhere, the commenter stated that EPA contends there are “additional health and environmental effects” attributable to HAP other than Hg , but admits that it has “not quantified” those risks due***E.O. 12866 Review

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93 supposedly to “insufficient information.” See 76 Fed. Reg. at 24,999/2. With respect to Hg the commenter state d 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 the rule (i.e., nearly $11 billion) the rule cannot be justified were EPA properly to interpret section 112(n)(1) and undertake the sort of regulatory analysis Congress intended. The commenter state d that the reason that EPA touts in this rulemaking the health benefits EPA attributes to the reduction of non
- hazardous air poll utants (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
c oncludes that EPA distorts CAA 112(n)(1)(A) “beyond all recognition.” One commenter state d that 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., HAP and HAP alone. Thereafter, EPA is authorized to***E.O. 12866 Review

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94 regulate EGU HAP emissions if, and only if, they determine that “such regulation” of HAP emissions is “appropriate and necessary” to address the “haz ards to public health” that may be attributable to HAP emissions. According to the commenter, by contrast, in this rulemaking, EPA has seized upon the fact that the control of EGU HAP emissions will also control non - HAP (such as PM), and then seeks to justify the regulation of HAP emissions based almost entirely on the health benefits of the reductions in non
HAP emissions that would be coincidentally achieved. The commenter believes that this “regulatory sleight
- of - hand” runs afoul of congressional intent and is unlawful. Response: The commenter alleges that the health related 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 publ ic***E.O. 12866 Review

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95 health. The analyses are discussed at length elsewhere in 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 on ly 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 ab le 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 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 a re required under section 112. As explained below, EPA does not consider costs when determining whether to regulate EGUs under section 112.***E.O. 12866 Review

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96 Comment : One commenter state d that EPA has ignored the language and intent of section 112(n)(1)(A ) , as interpreted based on Representative Oxley’s statements, and that the Agency’s 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 section 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 section 112(c) and to regulate them under the MACT provisions of CAA s ection 112(d). See S. 1630 section 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 section 112 as they applied to EGUs. See 1 1990 Legis. Hist. at 572
- 73 The House version was virtually identical to the current CAA section***E.O. 12866 Review

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97 112(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. 1630 would have applied to EGUs, and which Congress did choose to apply to other source categories. The commenter stated 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 , and in a footnote, the commenter states that the Agency erred by not addressing the legislative history as it did in the 2005 action . Response: For the reasons stated above, we believe commenter’s reliance on the single statement of one legislator is flawed. In addit ion, in a footnote the commenter state d that EPA recognize d “ that it had to address” the legislative history in its 2005 action , and that EPA erred in this case because we did not address the legislative history . The c ommenter cites no case law to support its contention that an Agency must “ address” unpersuasive legislative history . Further, in the 2005***E.O. 12866 Review

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98 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 n commenter fails to recognize
now , that the Agency cannot argue that the meaning of section 112(n)(1)(A) is clear based on the statements of
one legislator . The commenter is incorrect when it asserts that EPA’s opinion is of no moment. The Agency tasked with implementing an ambiguous statute is given considerable deference in interpreting the provision. The c ommenter’s assert ion that Congress unambiguously defined the factors to consider in making the appropriate determination is wholly without merit. We explain in the preamble to 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 d that EPA misreads CAA section 112(n)(1)(B) and (C) to inject environmental effects in the CAA section 112(n)(1)(A) determination.***E.O. 12866 Review

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99 According to one commenter the plain language of CAA section 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 E PA “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 Stat ement at 1416
- 17. The commenter further state d 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 50 and the NAS Study 51 ). The commenter also identified other provisions of section 112 that specifically require consideration of environmental effects and states that Congress would have requires such consideration in section 112(n)(1) if it had wanted EPA to consider environmental effects.

50 U.S . EPA. 1997. Mercury Study Report to Congress . EPA
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100 Response: The c ommenter again relies on the statements of one legislator to attack EPA’s reasoned interpretation of an ambiguous statute. To the extent the commenter’s arguments rely on this paltry evidence, we need not address them as we have explained above. As we stated above, section 112(n)(1) is an ambiguous statutory provision ; thu s , 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. The commenter appears to maintain that EPA must interpret the scope of the app ropriate and necessary finding in the context of the section 112(n)(1)(A) Utility Study, such 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***E.O. 12866 Review

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101 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 preamble to 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 (2 nd Cir. 1993) (“based upon” does not mean “solely) 52 ; see also 76 FR 24988. We further explained in the preamble to the proposed rule that it was reasonable to interpret the scope of the appropria te and necessary finding in the context of all three studies required under section 1 12(n)(1) because the provision is title “Electric utility steam generating units .” 53 The commenter has provided little more than unpersuasive

52 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. 53 76 FR 24986
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102 legislative history to support its restrictive 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 , the 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 haz ards to public health and only harms directly attributable to EGUs. The c ommenter state d that Congress specifically told EPA when it wanted EPA to consider adverse environmental effects in section 112 and cites to several provisions of the Act that require consideration of adverse environmental effects. The c ommenter ignores section 112(n)(1)(B), which***E.O. 12866 Review

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103 requires consideration of adverse environmental effect, and all of the other provisions of section 112 that specifically require consideration of environmental effects have purposes that are distinguishable from section 11 2(n)(1). Furthermore, the lack of a requirement to consider environmental effects in section 112(n)(1) does not equate to a prohibition on the consideration of environmental effects as the commenter concludes. EPA maintains that it reasonably 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 i nterpretation 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,***E.O. 12866 Review

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104 irrespective of whether HAP emissions from EGUs alone would cause the harm .” 54 d. Finding for all HAP to be Regulated Comment: Several commenters state d that for those EGU HAP for which the Agency makes no s ection 112(n)(1)(A) determination, their regulation under CAA section 112 is not authorized. For example, the commenter maintains that the Agency could regulate HAP emissions from EGUs under section 112(n). Accordingly, to the extent that EPA reads CAA section 112, as construed by National Lime Ass’n , as compelling it to regulate all HAP emitted by EGUs, should the Agency make an “appropriate and necessary” determination under CAA section 112(n)(1)(A) with respect to a single HAP (e.g., Hg ), 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”).

54 76 FR 24988.***E.O. 12866 Review

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105 Response: We do not agre e 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 con cluded that we must find it “appropriate” to regulate EGUs under section 112 if we determine that a single HAP emitted from EGUs poses a hazard to public health or the environment. If we also find that regulation is necessary, the Agency is authorized to l ist 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 582 (stating that “[s]ection 112(n)(1) governs how the Administrator decides whether to list EGUs...”) . 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 once a source catego ry is added to the list of categories under section 112(c) . National Lime Ass’n v. EPA, 233 F.3d 625, 633 (D.C. Cir. 2000 ). 55

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106 The 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 sub ject 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, and that we have not properly exercised our discretion leading to a fatal flaw in our rulemaking . The commenter has not provided an alternative theory for regulating EGUs under section 112, other than to state that EPA could regulate under section 1 12(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***E.O. 12866 Review

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107 a section 112(d) standard issued in the same manner in which the Agency i ssues standards for other listed source categories. Second, Congress did provide a mechanism under sections 112(d) and (f) for establishing emission standards for HAP emissions from stationary sources and it is reasonable to use that mechanism to regulate HAP emissions from EGUs. Finally , we do not believe that Congress intended to treat EGUs different ly from other source categories for purposes of establishing standards once they are listed . 56 e. Considering Cost in Finding Comment: Two c ommenters state d 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

56 Congress defined EGUs is section 112(a)(8). That definition defines the EGU source category and it includes both major and area sources.***E.O. 12866 Review

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108 with undertaking a particul ar action is inextricably linked with any determination as to whether that action is “specially suitable” or “proper in the circumstances.” The commenter notes that in 2005 (70 Fed. Reg. 15,994, 16,000 (Mar. 29, 2005)) 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. Response: The commenter s 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 . See New Jersey, 517 F.3d at 578. For this reason alone, it is reasonable to make the listing decision, including the appropriate determination,***E.O. 12866 Review

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109 without considering costs. Congress could easily have required the Agenc y to consider costs, and, because it did not, commenter’s assertion that the Agency’s decision not to consider costs does not withstand scrutiny are unfounded. The c ommenters next argue that the Agency is compelled by the statute to c onsider 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. Concerning the definition of “appropriate”, c ommenters stated : “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 unreas onable. 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 o r proper in the circumstances.” See New Oxford American Dictionary (2d Ed. 2005) at 76. Considering the costs associated with***E.O. 12866 Review

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110 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” that the 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 emissions, and 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 re gulate 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. The commenter s’ 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***E.O. 12866 Review

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111 Study is equally flawed. The argument is flawed because Congress did not direct the Agency to cons ider in the Utility Study the costs of the controls when evaluating the alternative control strategies. In addition, EPA did not consider the costs of the alternative controls in the Utility Study , as implied by the commenter . In a footnote, the c ommenter attempts to refute EPA’s statement in the preamble to 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. However , EPA did not say 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 “Necess ary” 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***E.O. 12866 Review

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112 section 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 p rogram. It would have been easy enough for Congress in subparagraph 112 (n)(1)(A) to specify “after imposition of the requirements of Title IV of this chapter,” but Congress did not. The commenter s 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 section 112 only after “taking into account compliance with all provisions of the act and any other Federal, State, or local regulation and voluntary emission reductions.” The commenters stated 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 Hg emissions. Response: The commenter ’s characterization of the facts is flawed and its reliance on legislative history***E.O. 12866 Review

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113 that is in direct conflict with the express terms of the statute is unfounded. On the facts, EPA explained in the preamble to the proposed rule its interpretation of the phra se “after imposition of the requirements of [the Act]” as it related to the conduct of the Utility Study . 57 We reasonably concluded that , since Congress only provided three years after enactment to conduct the study , the phrase referred t o 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 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

57 76 FR 24990.***E.O. 12866 Review

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114 does not indicate how in conducting the Utility Study the Agency could have possibly considered co
-bene fit HAP reductions attributable to all future CAA requirements. In the preamble to the proposed rule, EPA recognized that we could consider requirements beyond those c onsidered in the Utility Study, and we did consider a number of requirements that 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 s of the Act as explained in the preamble to the proposed rule . 58 In addition, as stated above, we also believe it would be re asonable 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

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115 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. Finally, commenter implies that EPA’s position is that the Agency will only consider requirements of the Act that directly re gulate HAP emissions. EPA never stated or 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 (known as CSAPR) . Comment: One commenter stat ed that, under CAA section 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 , EPA construes CAA section***E.O. 12866 Review

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116 112(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 state d that in the “context” of CAA section 112(n)(1)(A), as informed by the relevant legislative history from Representative Oxley , it is clear that regulation of EGU HAP emissions can be considered “necessary” only if EPA were to “clearly establish” that such regulat ion 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: The c ommenter 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***E.O. 12866 Review

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117 the statute. 76 FR 24990
- 92 (Section III.A.2.b of the proposed rule contains EPA’s interpretation of the term “necessary”). The c ommenter also, in a footnote, implies that EPA based the appropriate and necessary finding on
non - HAP air pollution. The commenter is wrong as explained in more detail above . Further, the c ommenter 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 . 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 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. This is particul arly true 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***E.O. 12866 Review

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118 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 & Intern et 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 ) . The c ommenter stated 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 statute . Even the limited legislative history on which the commenter incorrectly relies does not espouse such a standard. The c ommenter 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***E.O. 12866 Review

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119 identified hazards.” 76 Fed. Reg. at 24,990. The commenter has aga in 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 for statutory provisions that do not mandate direct control of the given sou rce category or pollutants of concern. We maintain that erring on the side of caution is appropriate when the protection of public health and the environment from HAP emissions is not assured based on our modeling of future emissions . Furthermore, as we stated in the preamble to 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***E.O. 12866 Review

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120 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 still remain. Finally, the commenter doe s not address all of the bases on which the necessary finding is made. Specifically, EPA found in the preamble to the proposed rule that it was necessary to regulate HAP emissions from EGUs because 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 state d that even if EPA were to establish under CAA 112(n)(1)(A) that it is “appropriate***E.O. 12866 Review

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121 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 cont rary to the plain language of the Act. According to the commenter, 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 , 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 commenter states that 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 (emphasis added). The commenter further stated that, given that Congress “directed the Agency to regulate utilities ‘under this section’ [i.e., CAA 112],” 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). The commenter asserts that a s EPA sees it, because “Congress***E.O. 12866 Review

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122 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). The commenter stated that, i n support of this reading of the CAA, 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). The commenter further alleged that,
a ccording 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. The commenter stated that 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 state d that elsewhere, EPA construes CAA 112(n)(1) (A) as “govern[ing] how the Administrator decides whether to list EGUs for regulation under section 112,” and quotes the D.C. Circuit’s observat ion in New Jersey that “Section 112(n)(1) governs how the Administrator decides whether to list EGUs;***E.O. 12866 Review

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123 it says nothing about delisting EGUs.” See 76 Fed. Reg. at 24,981/2, quoting 517 F.2d at 582. The commenter asserts that 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, the commenter maintains that EPA should withdraw the proposed MACT rule. One commenter state d 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 t o regulate EGU emissions “under CAA 112(d).” Thus, the commenter maintained that EPA’s authority to regulate EGU HAP emissions is not derived from any particular subsection of CAA 112. Rather, the commenter stated that EPA is authorized to regulate “under this section”

– i.e., CAA 112 generally

– as may be “appropriate and necessary.” The commenter stated that there is nothing on the face of CAA 112(n)(1)(A) that specifies that regulation of EGUs must occur under CAA 112(d). To the contrary, according to the commenter, a plain reading of***E.O. 12866 Review

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124 CAA 112(n)(1)(A ) , as interpreted based on the Oxley statement, indicates that establishing a MACT standard for EGUs under CAA 112(d) is not what Congress had in mind at all. Respons e: 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 1 12(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
wo rd 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 preamble to 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) provision provides, in part, that:***E.O. 12866 Review

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125 ‘[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 conduct of the study and the manner in which***E.O. 12866 Review

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126 the Agency must regulate EGUs if the Agency finds it appropr iate 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 words , and the commenter’s interpretation does not give any particular meaning to the requirement to “regulate under this section [112]”. The
c ommenter 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 the commenter presumes too much when it state d 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 and regulate stationary sources of HAP emissions. 76 FR***E.O. 12866 Review

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127 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 fully consistent 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 the 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 [112] applicable to publicly owned***E.O. 12866 Review

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128 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 c ommente rs state d 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 that EPA “develop and describe” alternative control***E.O. 12866 Review

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1 29 strategies for emissions which may warrant regulation under section 112. According to the commenters if Congress meant for EPA to have one sole regu latory 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 section 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 considera tion 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 section 112(d)(2). Response: The c ommenters 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

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130 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 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 wa shing, fuel 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

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131 Given the manner in which the Agency conducted the Utility Study, EPA obviously interpreted the statutory direction as a requirement to set forth the potential alternative 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 different types of HAP emitted from U.S. EGUs . The c ommenters’ 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***E.O. 12866 Review

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132 sources to comply with the standards using any mechanism 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 s tep, 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 section 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***E.O. 12866 Review

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133 the manner in which the Agency must regulate EGUs,” were 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 section 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 section 112. Similarly, the word “subparagraph” is used in the la st sentence of CAA section 112(n)(1)(A) to identify “the study” which EPA is directed to undertake by subparagraph (A) of CAA section 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 state d that Congress was “consciously distinguishing” between the “various provisions of section 112” for the sake of clarity in the drafting of CAA section 112(n).***E.O. 12866 Review

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134 Response: The c ommenter makes a number of arguments that appear to take issue with EPA’s determination that EGUs should be regulated under section 112(d) if the Agency determines that regulation of HAP emissions from such units is appropriate and neces sary. The commenter implies that EPA erred because alternative mechanisms for regulation of EGUs under section 112 might exist. We do not agree. The c ommenter’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 guidan ce 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***E.O. 12866 Review

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135 in issuing standards under section 1 12); see also section 112(n)(5) (directing the Agency to develop and implement a control strategy for 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.***E.O. 12866 Review

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136 The c ommenter also takes issue with our statement in the preamble to the proposed rule that the use of the words “section”, “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 manne r in which the Agency must regulate EGUs.” See 76 Fed. Reg. at 24,993. The c ommenter 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 s ection 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 d 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). 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
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137 that undermines commenter’s argument that EPA should not regulate EGUs under section 112(d). Specifically, we 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 preamble to the proposed rule. The c ommenter also state d that EPA relied on section 112(c)(6) to support a conclusion that EGUs must be regulated under section 112(d). The 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***E.O. 12866 Review

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138 consistent with the requirements set forth in section 11 2(d), as described below.” See 76 Fed. Reg. at 24,993 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 cite d 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 li sted source category and listed sources must be regulated under section 112(d) unless EPA delists the source category. Comment: One commenter state d 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 section 112(d) because EGUs “remain listed” under CAA section 112(c), See New Jersey, 517 F.3d at 582. Acco rding to the commenter , the court declined to address the lawfulness of EPA’s having “listed” EGUs under CAA section 112(c), leaving that matter to be decided if and when EPA adopted standards for EGUs under CAA section 112. Nowhere***E.O. 12866 Review

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139 in the decision did the D.C. Circuit indicate that EPA must regulate EGUs under CAA section 112(d). Response: The c ommenter’s arguments are circular and it is difficult to fully determine exactly what its issue is with EPA’s listing; however, it appears that the
commenter believes that EPA incorrectly relied on the New Jersey decision to justify the listing of EGUs. The
c ommenter also appears to argue that the Agency has never explained why it has the authority to list EGUs at all. We disagree. As stated in the preamble to 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.***E.O. 12866 Review

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140 Circuit agrees with that interpretation of the statute as evidenced by its statement in New Jersey that “section 112(n)(1)(A) governs how the Administrator decides whether to list EGUs for regulation under section 112,” 517 F.3d at 582, and the Court’s statement 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 preamble to the proposed rule based on new information. The 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 the D.C. Circuit will condemn the final rule 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 section 112(d ). According to the commenter , a regulation will be***E.O. 12866 Review

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141 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, 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 agen cy 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, 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***E.O. 12866 Review

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142 conclusion is incorrect . As we state above and in the preamble to 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 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 preamble to the proposed rule that we could not delist E GUs 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 preamble to 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). The c ommenter has provided no legitimate argument to rebut this conclusion.***E.O. 12866 Review

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143 Comment: One c ommenter alleges that EPA impermissibly relied on CAA section 112(c)(9) to interpret “hazards to public health”, and argues that the “residual risk” provisions in CAA section 112(f)(2) are more appropriate for the establishment of standards for EGUs. The commenter state d that by using 112(c)(9)(B)(i) in defining “hazards to public health”, the Agency has seized on the one interpretation of the phrase that is surely con trary to congressional intent and, thus, falls out side the permissible range of its interpretative discretion. The “delisting” criteria of CAA section 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 section 112. The commenter also argues that Congress intended that EGUs be treated differently from all other “major sources” to which “listing” provisions of CAA section 112(c)(9), and the standard- setting provisions of CAA section 112(d) necessarily and automatically apply. Therefore, EPA’s proposal to utilize the criteria of CAA section 112(c)(9) to inform its findings under CAA section 112(n)(1)(A)***E.O. 12866 Review

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144 treats EGUs exactl y 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 section 112(n)(1)(A ), EPA would be better served to consider the “residual health risk” provisions of CAA section 112(f)(2). Those provisions provide a better analogy to the establishment of standards for EGUs under CAA section 112 than do the “de
- listing” criteria of CAA section 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 expo sure, the nature of the health effects, and the uncertainties associated with the data. While CAA section 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 section 112(c)(9)(B)(i) that EPA proposes to employ.***E.O. 12866 Review

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145 Response: The c ommenter acknowledge d that EPA has broad discretion to interpret the phrase “hazard to public health” but argues that the one thing we cannot do is use the section 112(c)(9)(B) delisting provisions as a benchmark in making that interpretation . The c ommenter assert ed 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 wa rranted continued regulation. Instead, the commenter revert ed to its argument that the statute treated EGUs differently. EPA 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.***E.O. 12866 Review

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146 The c ommenter 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. The commenter asserts that an evaluation of “hazards to public health” should include such factors as the affected population, the characteri stics of exposure, the nature of the health effects, and the uncertainties associated with the data. However, 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 factors the commenter suggests in making our finding . 59 Thus, our approach to evaluating hazards to public health and the environment based on this comment. h. 2000 Finding (and 2005 Reversal) Comment **:** Several commenters generally support EPA’s 2000 finding that regulating HAP 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

59 76 FR 24992 .***E.O. 12866 Review

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147 harm from HAP emitted by EGUs, and no additional information makes the finding invalid. Several commenters cited the conclusions of the Utility Study 60 and Mercury Study 61 , which they assert 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 anthropogen ic Hg emissions and MeHg found in freshwater fish, (2) Hg emissions from coal
fired utilities were expected to worsen by 2010, and (3) MeHg in fish presents a threat to 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. 62 In support of the finding, one commenter stated that it would not make sense for Congress to limit HAP emissions from

60 U.S. EPA, 1998. 61 U.S. EPA, 1997. 62 “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

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148 small businesses such as dry cleaners but to exempt U.S. EGUs, which are the largest sources of many HAP emissions. One commenter agreed that finding was further supported because numerous control options were available to reduce HAP emissions. One commenter agreed with the 200 finding that the Agency lacked sufficient evidence to conclude that
non - Hg HAP from EGUs posed no hazard . The commenters who generally supported the 2000 finding also commented on specific aspects of the finding. Several commenters assert ed that while the evidence on Hg 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 to HAP emissions from such units are negligible based on the results of the Utility Study .***E.O. 12866 Review

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149 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 the 2005 action as invalidating the 2000 finding, specifically noting that EPA concluded that “no hazards to public health” remained after accounting for emission reductions under CAIR . These commenters assert that EPA’s current position is illegal because EPA took the exact opposite position on the interpretation of the term “necessary” in its 2005 reversal, and thus deserves no judicial deference . One commenter stated that in 2005 EPA recognized the potential for excessive re gulation created by section 112 and determined that the 2000 finding lacked foundation. Several commenters generally disagreed with the 2000 finding, with two commenters stating that EPA did not 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***E.O. 12866 Review

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150 the terms “appropriate” and “necessary” in the 2000 finding and that the emission control analysis was inadequate. Two commenters state d that the 2000 finding was based on data that wa s more than 10 years old, which causes serious concern regarding the validity of the findings because technology, the regulatory environmen t, and the 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 CSAPR , the basis for EPA‘s 2000 finding has changed. Several commenters state d that a “plausible link” between anthropogenic Hg and MeHg in fish is not an adequate reason for the 2000 finding. Several commenters claim that EPA only identified health concerns for Hg (and potentially Ni ) but not other HAP from coal - fired EGUs in the 2000 finding, and thus cannot regulate HAP other than Hg because the 2000 finding authorizes only the regulation of Hg **.** One commenter questioned the Hg 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 s actually declined.***E.O. 12866 Review

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151 S everal commenters raised procedural issues related to the 2000 finding. Several commenters state d 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 state d 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 200 0 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. The commenter s claim that specific issues did not undergo public notice and comment, including 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 claims that EPA attempted to provide after
- the - fact support for its 2000 finding with new legal analysis and new factual information, contrary to New Jersey v. EPA that held that EPA may not revisit its 2000 finding except through delisting under Section 112(c)(9). One commenter state d that EPA’s 2000 Finding should be reviewed when EPA issues***E.O. 12866 Review

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152 the actual NESHAP . 63 One commenter state d that the 2000 finding ignored Executive Order 12866. Response **:** EPA agrees with the commenters that the 2000 finding was reasonable and disagrees with the commenters asserting that the 2000 finding was unreasonable or failed to follow proper procedural requirements. EPA agrees that reviewing c ourts defer to the reasoned scientific and technical decisi ons of an Agency charged with implementing complex statutory provisions such as those at issue in this case. As EPA stated in the preamble to the proposed rule, EPA maintains that the 2000 finding was reasonable and based on well - supported evidence available at the time , including the Utility Study, the Mercury Study 64 , and the NAS study 65 , which all showed the known and potential 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
63 See UARG v. EPA, 2001 WL 936363, No. 01
- 1074 ( D.C . Cir. July 26, 2001). 64 U.S. EPA, 1997. 65 NAS, 2000.***E.O. 12866 Review

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153 of severa l HAP in the U.S. , that risk assessments supporting the 2000 finding indicated potential concern for several non - Hg HAP , and that several available control options would effectively reduce HAP emissions from U.S. EGUs . EPA agrees with the c ommenters 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. EPA listed EGUs in 2000 because the considerable amount of available data supported the conclusion that regulation of EGUs under section 112 was appropriate and necessary. That finding was valid at the time , and EPA reasonably added***E.O. 12866 Review

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154 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 strategi es available to reduce HAP emissions from EGUs when determining whether it was appropriate to regulated EGUs . 66 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 emi ssions. 67 EPA explained in the preamble to the proposed rule its conclusion that the 2000 finding was fully supported by the information available at the time , 68 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

66 65 FR 79830. 67 Id . 68 65 FR 24994
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155 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 clearl y articulated the various alternative control strategies that EGUs could employ to control HAP emissions. 69 As to emission reductions, EPA cannot estimate the level of HAP emission reductions cannot until the Agency proposes a section 112(d) standard after a source category is listed. EPA disagrees with commenters that suggest 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 s that EPA must determine that every HAP emitted by EGUs poses a hazard to 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

69 See Chapter 13 of the Utility Study (U.S. EPA, 1998) .***E.O. 12866 Review

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156 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 Hg and Ni emissions, but, even if it were , EPA reasonably concluded that EGUs should be listed pursuant to section 112(c) based on the Hg and Ni finding. As stated in the 2000 finding, cancer risks from some non
- Hg metal HAP (including arsenic, chromium, nickel, and cadmium) were not low enough to be to eliminate as potential concern. 70 Source categories listed for regulation under section 112(c) must be regulated under section 112(d), and 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). Therefore, even if EPA concluded that section 112(n)(1) authorized a different approach for regulating HAP emissions from EGUs , with which
we disagree , the chosen course which is supported by the CAA ( i.e . listing under section 112(c)) requires the Agency

70 76 FR 79827.***E.O. 12866 Review

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157 to regulate under section 112(d) consistent with the statute and case law interpreting that provision. EPA disagrees that there is any concern regarding the validity of the 2000 finding or that the emissions information provided in the 2000 finding makes the finding “questionable” as stated by some of the commenters . EPA maintains that the 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 Hg emissions have decreased since the 2000 finding instead of increasing as projected, the new technica l analyses confirm that Hg 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 emission s 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 who assert that the 2005 action was in error and disagrees with the commenters that the 2005 action invalidated the 2000 finding. As fully***E.O. 12866 Review

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158 described in the preamble to the proposal, EPA erred in the 2005 action by concluding that the 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 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). In the preamble to the proposed rule, EPA set forth a revised interpretation of section 112(n)(1) that is consistent with the statute and the 2000 finding . EPA also explained in the preamble to the proposed rule why the 2005***E.O. 12866 Review

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159 action was not technically or scientifically sound. EPA specifically addressed the errors associated with the 2005 action in the preamble to the proposed rule , and commenter s ’ assertions do not cause us to revisit these issues . The commenter is also incorrect in suggesting that a change in interpretation is per se invalid and 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 defe rence 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 were more than 10 years old. EPA made the finding at that time based on the scientific and technical information available, and the finding is whol ly supported by that information. In addition, even though not required to do so, EPA has since conducted new technical analyses utilizing the best information available***E.O. 12866 Review

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160 in 2010 as several years have passed since the 2000 finding. These new analyses confirm that HAP emissions from EGUs continue to pose a hazard to public health and the environment, even after taking into account emission reductions that have occurred since 2000 from promulgated rules, settlements, consent decrees, and closures. Some c ommenters are also incorrect regarding their assertion of certain 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. One
c ommenter 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, 200 1). EPA has provided the public an opportunity to comment on both the 2000 finding 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***E.O. 12866 Review

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161 with a challenge to this final rule. The commenter s could have also commented on the section 112(n)(1) (e.g., the Utility Study and the Mercury Study) studies in 2000 as they were included in the docket, but EPA is not awa re of any comments on those studies. In any case, the se 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
one commenter suggest ed , that EPA is not able to consider additional information that is collected after the 2000 finding; instead, the Court stated that EPA could not 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 (EO) 12866 when making the 2000 finding. As stated in the Federal Register notice, the 2000 finding did not impose***E.O. 12866 Review

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162 regulatory requirements or costs and was reviewed by the Office of Management and Budget in accordance with the EO . 71 2. New Technical Analyses a. General comments on new technical analyses Comment: Several commenters state d that the new analyses , including the risk assessments and technology assessments, confirm that it remains appropriate and necessary to regulate U.S **.** EGU HAP under Section 112 of the CAA . These commenters state d that the new analyses provide even more support than the risk and technology information available at the time the 2000 finding was made, including information on 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 HAP , “hotspots” from the deposition of Hg around EGUs , the potential for re
emission of Hg , updated emissions data and future projections of HAP emissions, and modern air pollution model ing tools. One commenter states affordable control

71 65 FR 79831.***E.O. 12866 Review

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163 technology has been in use in this sector for 10 to 40 years, and studies on EGU
- attributable Hg hazard has undergone two in
- depth EPA reviews, as well as a revi ew by the NAS. Several commenters claimed that regulating U.S. EGUs is appropriate and necessary to protect public health based on information provided in the new technical analyses. These commenters acknowledge d the substantial reductions in HAP from recent regulation s 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 note d that EGUs are a major source of HAP , including HCl, HF, arsenic, antimony, Cr , Ni , and selenium, all of which adversely affect human health. The commenter state d 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. Other commenters disagree d 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 retroactive***E.O. 12866 Review

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164 justification for the 2000 finding, which only found “plausible links” of health effects and “potential concerns” of health effects of certain metal emi ssions, dioxins and acid based aerosols. The commenter also asserted that none of these new analyses demonstrate that EGU regulation under section 112 is necessary and appropriate. One commenter agreed that EPA may supplement its finding with new information, analyses and arguments to
re affirm the 2000 finding up until EPA issues final emissions standards. The commenter noted that the CAA does not freeze the finding. However, another commenter argue d that EPA does not have the authority to rely on new technical analyses because the CAA re quires EPA to make the finding on the basis of the Utility Study alone. According to that commenter, EPA unreasonably stretched the language of section 112 by considering new technical analyses. Citing a report from Dr. Willie Soon that was submitted to the SAB , one commenter state d that the new technical analyses supporting the proposed rule do not conform to the Information Quality Act , which requires that***E.O. 12866 Review

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165 information relied on by 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 r isk a ssessment s and technology assessment ) confirm the 2000 finding and disagree s 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. 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 environment al benefits as discussed in the RIA, that Hg emissions from EGUs pose a hazard to public health, and that non
- Hg 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 2000 finding. EPA disagrees with the commenter’s assertion that the Agency is not authorized to consider new***E.O. 12866 Review

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166 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, thereby excus ing the Agency from its obligations to protect public health and the environment because it did not diligently act in undertaking its statutory responsibility to establish section 112(d) standards within two years of list ing EGUs. 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 not consider new analyses conducted after the Utility Study in determining whether it is app ropriate and necessary to regulate EGUs under section 112 for the reasons set forth in the preamble to the proposed rule. 72 EPA disagrees with the commenter’s implication that EPA conducted the new analys e s because of alleged flaws in the 2000 finding. As explained in detail in the preamble to the proposed rule, the 2000 finding was wholly valid and reasonable based on the information available to the Agency

72 76 FR 24988.***E.O. 12866 Review

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167 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 two 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 2000 finding, and EPA wanted to evaluate HAP emissions from U.S. EGUs based on the most accurate information available, though the Agency not required t o reevaluate the 2000 finding. In conducting the new analyses, EPA used this updated information to further support the finding. E PA strongly disagrees with the commenter that state d 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 th is regulation . In addition, EPA submitted the Hg Risk TSD 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***E.O. 12866 Review

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168 from U.S. EGUs.” 76 The SAB received the comments from Dr. Willie Soon, and had those comments available for consideration in their deliberations regarding the Hg risk analysis. The SAB specifically supported elements of the analysis criticized by Willie Soon regarding the use of EPA RfD as a benchmark for risk and the connection between Hg emissions from U.S. EGUs and MeHg concentrations in fish. In addition, the risk assessment methodology for the non
- Hg case studies i s 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. 77 During the publ ic comment period, EPA also completed a letter peer review of the methods used to develop inhalation cancer risk estimates for Cr and Ni compounds, and those reviews were generally supportive. For the final rulemaking, EPA revised both risk assessments
con sistent with recommendations from the peer reviewers. EPA relies on the SAB’s review of the quality of the information supporting the analytical results. b. Hg Emissions Estimates

76 U.S. EPA- SAB, 2011. 77 U.S. EPA- SAB, 2010.***E.O. 12866 Review

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169 1. Hg emissions from EGUs Comment : The commenter s addressed the 2005 and 2016 emissions estimates for Hg and expressed concern that inaccuracies in these emissions estimates result in overestimates of risks from Hg deposition. Further, commenters compared EPA’s 2010 estimate and 2016 estimate, and stated that it is not possible for 29 tons to be a correct inventory total for Hg emissions in both years given expected reductions from CSAPR . In addition, commenters specific ally comment ed on assumptions included in the Integrated Planning Modeling (IPM), including a concern that Hg speciation factors used by IPM overestimate
emissions in 2016. Other commenters noted that EGU sources are the predominant source of U.S. anthropogenic Hg emissions, particular ly the oxidized and particulate forms of Hg that are of primary concern for Hg depositi on. Response : EPA disagrees with commenters ’ assertions that emissions estimates overestimate risk. While EPA agrees that the 2005 Hg emissions may be overestimate d , such an overestimate in 2005 would actually lead to an underestimate of risk in 2016 and not an overestimate of risk , as claimed by the commenter , because the ratio***E.O. 12866 Review

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170 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 reducti ons 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 ed in an overestimate. EPA acknowledges that the current Hg emissi ons estimate should not be the same as the 2016 Hg emissions estimate given that compliance with CSAPR is expected to lead to some Hg emission reduction co
-benefits. For this reason, EPA has included those reductions in the future
year modeling used for the Hg risk analysis. EPA estimates that current Hg 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. Any remaining inconsis tency in EPA’s revised values is not relevant to the Hg national risk analysis since the 2010***E.O. 12866 Review

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171 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 Hg emission factors result in incorrect 2016 emissions. The 2016 projected Hg emissions are not based on emissions factors. The 2016 Hg 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 Hg emissions into particulate, divalent gaseous, and elemental species, and do not impact the total amount of Hg emissions. EPA agrees with commenters who noted that EGU sources are the predominant source of U.S. anthropogenic Hg emissions, and in particular the oxidized and particulate forms of Hg that are of primary concern for Hg deposition. 2. Global Hg emissions Comment : Several commenters state d that predicted Hg deposition relies heavily on the amount of gaseous***E.O. 12866 Review

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172 elemental Hg used to define the boundary and initial conditions of a model, e.g. the Hg that enters the U.S. from outside the U.S. boundaries. The commenter s assert ed that this is especially important because Hg emissions from Asia

—the region immediately upwind of North America that affects U.S. Hg deposition significantly and also affects it the most compared to other regions

—are expected to continue to increase. 78 , 79 , 80 , 81 , 82 , 83 This wou l d affect the amount of Hg in the boundary and initial conditions. The
c ommenters claim that EPA‘s modeling did not account for these emission changes , thus leading to an overestimate of U.S. EGU- attributable deposition in 2016.

78 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. 79 Jaffe D., Strode S., 2008. “Fate and Transport of Atmospheric Mercury from Asia,” Environmental Chemistry, 5, 121. 80 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 Atmosphere from Anthropogenic Sources in 2005 and Projections to 2020 , ” Atmospheric Environment , 44, 2487

– 2499. 81 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., Te lmer K., 2010. “Global Mercury Emissions to the Atmosphere from Anthropogenic and Natural Sources ,” Atmospheric Chemistry and Physics , 10, 5951

– 5964. 82 Streets, D.G., Zhang, Q., Wu, Y., 2009. “Projections of Global Mercury Emissions in 2050.” Environmen tal Science & Technology 43, 2983
- 2988. 83 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

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173 Several commenters note d that Hg emissions from U.S. EGUs are small when compared to global Hg emissions totals and natural sources within the U.S. These commenters use d a variety of information to support alternative conclusions about the necessity to control U.S. EGU emissions to reduce Hg risk: global Hg emissions inventories, global and regional photochemical modeling research, and observation
based assessments. A commenter state d that EPA has not acknowledged the dramatic decline in Hg emissions from U.S. EGUs since the late 1990s (approximately 50 percent) to the current level or consider the relative magnitude of Hg emissions from U.S. EGUs 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 Hg deposition estimates. 84 Accurate characterization of speciated ambient Hg inflow is

84 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
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174 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 Hg concentrations and do not provide directly applicable information about uncertainty related to boundary conditions. The boundary inflow for the CMAQ Hg modeling used in the Hg deposition modeling are based on a global model GEOS - CHEM simulation using a 2000 based global inventory. 85 A recently published comparison of global Hg emissions by continent for 2000 and 2006 was found that t otal Hg emissions from Asia (and Oceania) total 1,306 Mg/yr in 2000 and 1,317 Mg/yr in 2006. 87 EPA has determined that because the Asian Hg emissions estimate d in this study are nearly constant between 200 5 and 2006 , any adjustments to the boundary conditions or adjustments to modeled Hg deposition would be invalid and inappropriate. Recent research has shown that ambient Hg concentrations have been decreasing in the northern hemisphere since

85 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 co nstraints from observations.” Journal of Geophysical Research
-Atmospheres 112. 87 Streets et al., 2009.***E.O. 12866 Review

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175 2000. 88 Since emissions from Asia have not appreciably changed between 2000 and 2006 and ambient Hg concentrations have been decreasing, ENVIRON’s analysis contains incorrect assumptions and we need not address them further. For these reasons and the large uncertainties surrounding projected Hg global inventories , EPA concludes that the most appropriate technical choice is to keep the Hg 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 Hg emissions for the U.S. EGUs since the late 1990s. EPA analyzed historical, current, and future projected Hg emissions from the power generation sector, as cited in the preamble to the propo sed rule . EPA also disagrees with the commenters’
a ssertion s that EPA failed to consider the relative magnitude of Hg emissions from U.S. EGUs compared to other sources. As noted in the Hg Risk TSD, EPA modeled Hg emissions from U.S. and non
- U.S. anthropogenic and natural sources to estimate Hg deposition across the country. EPA also determined the contribution of Hg emissions from U.S.

88 Slemr, F., Brunke, E.G., Ebinghaus, R., Kuss, J., 2011. “Worldwide trend of atmospheric mercury since 1995.” Atmospheric Chemistry and Physics 11, 4779
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176 EGUs to total Hg deposition in the U.S. by running modeling simulations for 2005 and 2016 with Hg emissions from U.S. EGUs set to zero. Based on the Hg Risk TSD, EPA finds that total Hg deposition from EGUs do significantly impact human health. The commenter s suggest that Hg emissions from U.S. EGUs represent a limited portion of the total Hg emitted worldwide, including anthropogenic and natural sources. While EPA acknowledges that Hg emissions from U.S. EGUs are a small fraction of the total Hg emitted globally, it views the environmental significance of Hg emissions from U.S. EGUs and other domestic sources as a more germane consideration. Hg is emitted from EGUs in three forms. Each form of Hg has specifi c physical and chemical properties that determine how far it travels in the atmosphere before depositing to the landscape. While gaseous oxidized Hg and particle
-bound Hg are generally local/regional Hg deposition concerns, all forms of Hg may 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 Hg . Although emissions from international Hg sources contribute to Hg deposition in the***E.O. 12866 Review

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177 U.S. , the peer reviewed scientific literature shows that Hg emissions from U.S. EGUs in the U.S. significantly enhance Hg deposition and the response of ecosystems in the U.S. 89 , 90 , 91 , 92
c. Hg Deposition Modeling 1. General Comments on Deposition Modeling Comment : Several commenters state d that according to the ENVIRON report , EPA overestimated U.S. EGU
- attributable Hg deposition by 10 percent on average (and up to 41 percent in some areas). The commenters claim this overestimation is the result of boundary condition treatment, the exclusion of U.S. fire emissions, 93 and Hg plume chemistry approach. In addition, one commenter reference d the same ENVIRON report and state d that before implementation of controls required by the proposed rule,

89 Caffrey et al., 2010. 90 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 State s.” BioScience, 57 (1). 91 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. 92 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. 93 Finley, B.D., Swartzendruber, P.C., Jaffe, D.A., 2009. “P articulate mercury emissions in regional wildfire plumes observed at the Mount Bachelor Observatory.” Atmospheric Environment 43, 6074
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178 areas with relatively high EGU
- attributable Hg deposition (one - fifth or more of total deposition) in 2016 constitute less 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 suggest e d that current research shows that models of Hg atmospheric fate and transport overestimate the local and regional impacts of some anthropogenic sources, such as U.S. EGUs. Thus, according to the commenter, calculated contributions to Hg deposition and fish tissue MeHg leve ls from these sources represent upper bounds of actual contributions , 96 , 97 and EPA should present results as estimates of lower and upper bound limits. Response : EPA disagrees with the information presented by ENVIRON. The ENVIRON report is based on the misapplication of multiple incommensurate modeling studies and false premises which include the incorrect notion that

96 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. 97 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
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179 the boundary conditions are over
- estimated and the idea that EPA should use in
-plume chemistry that has not been expli citly characterized and peer reviewed. Reactions that may reduce gas phase oxidized Hg in plumes have not been explicitly identified in literature. Recent studies in central Wisconsin and central California suggest the opposite may happen; elemental Hg may be oxidized to Hg(II) in plumes. 98 , 99 Better field study measurements and specific reaction mechanisms need to be identified before making conclusions about potential Hg 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 Hg contribution inside the U.S. may be underestimated in EPA mode ling. EPA asserts that the numbers suggested by the commenter are inaccurate , as it is not appropriate to adjust EPA ’s deposition estimates based on previous Hg modeling done with older Hg chemistry, in
-plume reactions

98 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. 99 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
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180 that have not been explicitly identified, and erroneous adjustments to Hg boundary inflow. Recent research has shown that ambient Hg concentrations have been decreasing in the northern hemisphere since 2000. 100 EPA declines to revise this analysis as commenter suggests for several reasons, including available evidence indicates that emissions from China have not appreciably changed between 2000 and 2006 101 and ambient Hg concentrations have decreas ed , the commenter inappropriate ly comingled out
– of date Hg modeling simulations with EPA results , and ENVIRON’s analysis has not undergone any scientific peer review and presents information with incorrect assumptions as noted in this response , . EPA also disagrees with the commenter’s interpretation of the applicability of wildfire Hg emissions to this assessment. Finley et al. (2009) 102 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

100 Slemr et al., 2011. 101 Streets et al., 2009. 102 Finley et al. 2009.***E.O. 12866 Review

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181 observed Hg(p) to carbon monoxide ratios at this location) may not be valid on a broader scale. 103 Hg emissions from wildfires are a re
-volatilization of previously deposited Hg . 104 Given that electrical generating power plants are currently and hi storically have been a large Hg- 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 Hg emissions from U.S. EGUs compared to other sources and disagrees with the interpretation of EGU deposition presented in the ENVIRON report. As noted in the Hg Risk TSD, EPA modeled Hg emissions from U.S. and non
- U.S. anthropogenic and natural sources to estimate Hg deposition across the country. EPA also determined the contribution of Hg emissions from U.S. EGUs to total Hg deposition in the U.S. by running modeling simulations for 2005 and 2016 with Hg emissions from U.S. EGUs set to zero. Based on the analysis done for this rule EPA finds that total Hg deposit ion from EGUs do
103 Id. 104 Wiedinmyer, C., Friedli, H., 2007. “Mercury emission estimates from fires: An initial inventory for the United States.” Environmental Science & Technology 41, 8092
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182 significantly impact human health. The ENVIRON report provides no risk analysis of EGU contribution. EPA disagrees that research 105 , 106 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 Hg modeling that uses models that are no longer applied and that are based on out - dated Hg chemistry and deposition assumptions. Given the advances in Hg modeling since the early 2000s , EPA does not feel an upper and lower bound estimate is necessary. 2. Chemical reactions Comment : Several commenters state d that the CMAQ modeling fails to account for the chemical reduction of gaseous ionic Hg to elemental Hg that may occur in EGU plumes. The commenters note d that 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 Hg to el emental Hg inside plumes. Multiple commenters claimed that the reduction of reactive

105 Seigneur et al., 2003. 106 Seigneur et al., 2004.***E.O. 12866 Review

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183 gaseous Hg to gaseous elemental Hg has been reported in power plant plumes and that supporting data include atmospheric concentrations of speci ated Hg measured downwind of power plant stacks at ground
- level monitor sites and dispersion model predictions. 107 , 108 A detailed description of various plume measurement studies is provided in EPRI Comments, Section 3.4: Plant Bowen, Georgia, Plant Ple asant, Wisconsin, and Plant Crist, Florida. One commenter felt the impact of grid resolution (12 km sized grid cells) on the CMAQ modeling was not appropriatel y addressed by EPA. Their concerns due to grid resolution include the notion that a source‘s emissions will be averaged over the entire grid cell . According to the commenter, such averaging causes an artificially fast dilution that smoothe s out areas of high and low deposition , which may limit the ability of the model to simulate smaller areas of localized high deposition. This

107 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. 108 Lohman, K., Seigneur, C., Edgerton, E., Jansen, J., 2006. “Modeling mercury in power plant plumes.” Environmental Science & Technology 40, 3848
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184 commenter felt that using the APT would address these issues. Response: EPA disagrees with the commenters’ claims that oxidized Hg chemically reduces to elemental mercury within the plume. There is no evidence of these chemical reactions in the scientific literature. The references cited by the commenters are from non
-peer reviewed repo rts 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. Further, even these cited references do not provide sufficient information for incorporating the supposed reactions into the modeling (e.g., specific chemical reactions, reaction rates, etc.); rather, the cited references only suggest that oxidized gas phase Hg could be reduced and postulate a possible pathway . Recent studies in central Wisconsin and central California suggest the opposite may happen; elemental Hg may be oxidized to Hg(II) in plumes. 109 , 110 Better field study

109 Kolker et al., 2010. 110 Rothenberg et al., 2010.***E.O. 12866 Review

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185 measurements and specific reaction mechanisms need to be identified before making conclusions about potential Hg in
plume chemistry or applying surrogate reactions in
re gulatory modeling. Currently, models such as Advanced Plume Treatment (APT) use a surrogate reaction for the potential reactive gas phase Hg reduction that may or may not occur in plumes . 111 Reactions that may reduce gas phase oxidized Hg in pl umes 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 c ontribution as higher impacts using finer grid resolution are possible. The commenter’s assertion that EGU impacts are likely higher further supports the
111 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
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186 final conclusions of the exposure modeling assessment. EPA notes that the application of a photochemical model at a 12 km grid resolution for the entire continental U.S. is more robust in terms of grid resolution and scale that anything published in literature and represents the most advanced modeling plat form used for a national Hg deposition assessment. 3. Modeled deposition compared to measured deposition Comment : Multiple commenters expressed dissatisfaction related to EPA’s model performance evaluation of CMAQ estimated Hg deposition. The commenter s stated 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. The commenter s also stated that EPA needs to assess how predicted values of deposition compare to Mercury Deposition Network (MDN) data and how predicted values of ambient speciated Hg concentrations compare to measurement networks like AMNet and SEARCH. In addition, commenters st ate d that EPA used highly aggregated performance metrics comparing model estimates to observations that they felt result in a degraded and lenient operational evaluation of***E.O. 12866 Review

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187 the modeling system. A commenter suggested that 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 Hg wet deposition at MDN monitors. Finally, several commenters note d that EPA presented a negative modeled wet deposition total in the air quality modeling TSD, which is physically impossible. Response : The 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 per formance metrics in the revised air quality modeling TSD have been updated. In response to comments, EPA provided additional model performance evaluation by season to the air quality modeling TSD. In addition, in response to comments, EPA has now included model performance evaluation for total Hg wet deposition for the 36 km modeling domain . EPA disagrees that it did not conduct an assessment comparing CMAQ total Hg wet deposition estimates to MDN data . The air quality modeling TSD clearly shows a***E.O. 12866 Review

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188 comparison of CMAQ estimated total Hg wet deposition with MDN data for the entire length of the modeling period. The characterization of wet and dry deposition processes relating to speciat ed Hg in global and regional scale photochemical models should be continually evaluated by the academic community and improved when appropriate. CMAQ wet deposition of Hg has been and will continue to be extensively evaluated against Mercury Deposition Network sites. 112 There is no dry deposition monitoring network , and the CMAQ dry deposition processes will be evaluated when measurement data sets become available. EPA disagrees that an evaluation of ambient speciated Hg against routine monitor networks such as AMNet or SEARCH would be useful for this particular modeling application. The AMNet Hg network did not exist in 2005, which is EPA’s baseline model simulation time period , and the SEARCH network started making preliminary measurements of Hg at one or two sites in 2005. In addition, measurement artifact s related to gaseous oxidized Hg are difficult to quantify and make

112 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 Research
Atmospheres 114.***E.O. 12866 Review

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189 direct comparison to model estimates problematic. 113 Considering the problems associated with TEKRAN measurements of ambient Hg and the sparse nature of routine measurements in the U.S. , EPA did not compare ambient Hg 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 present ed the result s of several Hg modeling studies as providing information that the commenter believe s to be relevant for this assessment in terms of model performance metric estimation and the level of model performance evaluation shown for assessments modeling Hg near point sources. For example, one cited study titled

”Modeling Mercury in Power P lant P lumes ” models near - source Hg chemistry from U.S. EGUs , but provides absolutely no information about model performance evaluation. 114 Another

113 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. 114 Lohman e t al., 2006.***E.O. 12866 Review

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190 commenter identifie d two studies as supposedly having Hg modeling results that are applicable to EPA’s analysis. 115 , 116 These studies present similar model performance metrics as EPA and aggregate the metrics across many monitor locations as did EPA; however, these articles calculate long term annual averages of modeled and observed total Hg wet deposition before estimating performance metrics , which presents a more favorable evaluation. The Seigneur et al. paper 117 employs a less stringent approach for matching observations and model estimates of total Hg wet deposition by calculating 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 ) , estimate performance metrics, then average all the metrics together. The latter is the approach take n by U.S. EPA and should have been taken by the studies presented by the commenter. EPA finds the performance evaluation presented

115 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. 116 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. 117 Seigneur et al., 2006.***E.O. 12866 Review

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191 in the modeling TSD consistent with and far beyond what is presented in published articles 119 deemed relevant by the commenter. In addition to the evaluation presented by EPA in the air quality modeling TSD, CMAQ model performance for total Hg wet deposition has been compared with other Hg models. 120 EPA agrees that the commenter accurately restat e d total wet deposition model performance information provided by EPA in the Air Quality Modeling TSD. To provide context, other Hg modeling studies show a positive bias for annual total Hg wet deposition. 121 , 122 An annual Hg modeling application done by ENVIRON 123 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 between 72 and 503 percent. 124 These results indicate a very

119 Lohman, K., Seigneur, C., Edgerton, E., Jansen, J., 2006. Modeling mercury in power plant plumes. Environmental Science & Technology 40, 3848
- 3854. 120 Bullock et al., 2009. 121 Id. 122 Vijayaraghavan et al., 2007. 123 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 124 Yarwood et al., 2003.***E.O. 12866 Review

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192 large over - estimation tendency. The model performance shown by EPA is consistent with other long
- term Hg modeling applications. 4. Excess Local Deposition from Hg Emissions from U.S. EGUs (Deposition Hotspots) Comment **:** One commenter state d that reducing Hg will benefit local environments. The commenter state d that a 2007 study confirmed the presence of Hg “hotspots” downwind from coal - fired power plants and confirmed that coal
- fired power plants within the U.S. are the primary source of Hg to the Great Lakes and the Chesapeake Bay. 125 The commenter also state d that the study is consistent with a major Hg deposition study conducted by EPA and the University of Michigan that concluded that approximately 70 percent of Hg wet deposition resulted from local fossil fuel emissions in the region. 126 One commenter agree d 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

125 Evers, David C. et al. 2007. “Biological Mercury Hotspots in the Northeastern United States and Southeas tern Canada,” Bioscience . Vol. 57 No. 1. p. 29. 126 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

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193 regional average. The commenter state d that this excess Hg deposition would substantially increase the health and environmental risks associated with emissions at these sites. The same commenter also state d that EPA applied a conservative methodology to quantify near
- source Hg deposition is conservative. The commenter state d that 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 12x12 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 state d that the Hubbard Brook Research Foundation issued a report in 2007 that identified five Hg hotspots, one of which was in the Adirondack Park, along with four suspected hotspots. 127 The commenter state d that

127 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***E.O. 12866 Review

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194 this study also provides a good description of the impacts of Hg on the Common Loon, which is a symbol of a healthy Adirondack environment. One commenter state d that there is there is no evidence of Hg hotspots due to local deposition a ssociated with coal
- fired power plants. According to the commenter , EPA‘s use of a 50 km radius to calculate hotspots is flawed. The commenter state d that modeling studies show that deposition of Hg 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. 128 Several commenters state d that EPA does not adequately define hotspots in this proposed rule. Those same
commenters cite d a previous EPA definition of hotspots as “a waterbody that is a source of consumable fish with MeHg tissue concentrations, attributable solely to utilities, greater than EPA‘s MeHg water quality criterion of 0.3 mg/kg” (milligrams per kilogram) 129 . The same commenters
Matters: Linking Mercury Science with Public Policy inthe Northeastern United States. 2007. Hubbard Brook Research Foundation. Science Links Publication. Vol. 1, no. 3. 128 Seigneur et al., 2006. 129 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***E.O. 12866 Review

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195 state d that it is unclear why EPA changed from defining a hotspot by fish tissue MeHg concentration to defining a hotspot by depositional excess. Two commenters suggest ed that a Hg hotspot is a specific location that is characterized by elevated concentrations of Hg exceeding a well - established criterion, such as a reference concentration (RfC) when compared to its surroundings. Those same commenters state d that identifying Hg hotspots should not be constrained to locations where concentrations can be attributed to a single source or sector 130 . One of those two commenters note d that others have defined “hotspot s as a spatially large region in which environmental concentrations far exceed expected values, with such values (i.e. concentrations) being 2 to three standard deviations above the relevant mean”. 131 One commenter state d that Hg concentrations are not always highest at sites closest to a major source. The commenter refer red to a study by Kolker, et al. (2010) 132

and the Removal of Coal - and Oil
-Fired Electric Utility Steam Generating Units From the Section 112(c) . Final rule, March 29. 130 Evers et al., 2007. 131 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. 132 Kolker, et al., 2010.***E.O. 12866 Review

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196 that demonstrated that concentrations of atmospheric reactive gaseous Hg , gaseous elemental Hg , and fine particulate Hg were lower when measured 25 km from a 1114 MW coal - fired EGU than when measured 100 km away. The commenter state d that these findings contradict the idea, implicit in EPA‘s hotspot analysis, that reactive gaseous Hg decreases with distance from a large point source. One commenter state d 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 state d that during this period, Plant Crist emitted about 230 pounds of Hg annually, about 85 percent of which was reactive gaseous Hg . 133 The commenter cite d a study by Landing et al. (2010) 134 that estimated that 22

– 33 percent of wet - deposited Hg 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

133 EPRI, 2010. Atmospheric Deposition of Mercury, Trace Metals and Major Ions to a Watershed Around a Coal -Fired Power Plant. Palo Alto, CA: 1021566. 134 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 Elements in Pensacola, Florida,” Atmospheric Chemistry and Physics, 10, 4867

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197 state d that using the same data from these same wet deposition sites, Caffrey et al. (2010) 135 found that Hg 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 state d that Plant Crist installed a wet scrubber and has operated that scrubber continuously since December 2009. The commenter state d that the scrubber reduces total Hg emissions by about 70 percent and reduces emissions of reactive gaseous Hg by about 85 percent. According to the commenter, using Hg to trace metal (arsenic and selenium) ratios in precipitation collected in the same MDN in (post
- scrubber) 2010, Krishnamurthy, et al. (2011) 136 reported that Hg deposition due to local and

135 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. 136 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

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198 regional sources had changed between
- 10 to +6 percent at these sites, relative to historic measurements. The commenter state d that these changes were thought to represent upper bound estimates, since the researchers assumed that all Hg , arsenic, and selenium measured in wet deposition was from local and regional coal combustion
sources even though measured deposition can also include global emission sources . The commenter state d 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 d that a study by the Department of Energy (DOE) that collected and analyzed soil and vegetation samples for Hg 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. Two commenters state d that analysis of long
- term trends in Hg emissions from coal - fired EGUs and wet deposition in Florida concluded that statistical analysis does not show evidence of a significant relationship***E.O. 12866 Review

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199 between temporal trends in Hg emissions from coal - fired EGUs 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 Hg emitted from coal
- fired power plants rapidly converts to elemental Hg , significantly reducing the potential for “local” or nearby deposition. Two commenters state d that the Hg 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 d that by assessing only Hg deposition attributable to EGUs, EPA fails to provide a context for all other sources of Hg deposition. The commenters state d that the Agency does not explain why deposition from the top 10 percent of EGU Hg emitters does not decline, despite substantial reductions in modeled Hg emissions from those sources between 2005 and 2016. According to the commenters this implies that the top 10 percent EGUs may have approximately as much of a regional effect as a local effect. Two commenters state d that the CMAQ model has limitations when used to predict local deposition and tends***E.O. 12866 Review

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200 to overestimate local deposition. The commenters state d that modeling studies using either a plume model or an Eulerian model predict that 91 to 96 percent of the Hg emitted by an EGU travels beyond 50 km. 137 Response **:** EPA agrees with the commenters that stated that Hg emissions from EGUs deposit locally and regionally and contribute to excess local deposition near U.S. EGUs. EPA acknowledges additional studie s 138 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 i n 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. EPA agrees that there is no generally agreed- upon definition o f “hotspot”. As discussed in the preamble and TSD, for the purposes of the appropriate and necessary finding, EPA determined that information on the potential

137 Edgert on et al., 2006. 138 Driscoll et al., 2007.***E.O. 12866 Review

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201 for excess deposition of Hg in areas surrounding power plants would be useful in informing the finding. EPA disagrees with some commenters who misinterpreted the intent of the Hg deposition hotspot analysis. Specifically, the analysis is not of “ Hg hotspots” but rather of Hg deposition hotspots, defined as excess local Hg deposition around power plants, as clarified in the new Local Deposition TSD. EPA disagrees that the analysis assumes that deposition of Hg is confined to a 50
- km radius around power plants. The purpose of 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 Hg deposition) in the area 500 km around each plant and the average EGU - attributable deposition in the area 50 km around each plant. The difference between those two values is the excess local deposition around the plant. EPA does not suggest Hg emi ssions from power plants stop at 50 km from the source. Some portion of EGU emissions deposit before 50 km, and***E.O. 12866 Review

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202 some portion travels beyond 50 km. In addition, Hg disperses as it transports, so the average EGU contribution can be lower in areas beyond 50km relative to areas within 50km even though Hg emissions from EGUs are depositing into U.S. watersheds. EPA disagrees with some commenters’ interpretation of the analysis as being focused on local deposition from all sources. In fact, the focus was on exces s local deposition, rather than all local deposition. EPA has clarified the purpose of the excess local deposition analysis in the new TSD. 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 did not focus on total Hg deposition, because as EPA acknowledges throughout its analysis, global sources of Hg deposition account for a large percentage of total Hg deposition . In addition , including global sources of Hg deposition would obscure to***E.O. 12866 Review

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203 the comparison of local and regional U.S. EGU
- attributable Hg deposition. Because of regional deposition from both domestic and global sources of Hg , total Hg deposition at any location is unlikely to be highly correlated with local
sources. EPA’s analysis focused on U.S. EGU
- attributable Hg deposition and demonstrates that for some plants (especially those with high Hg emissions), there is local deposition of Hg that exceeds the average regional deposition around the plant. EPA’s analysis shows heterogeneity in the amount of excess local deposition around plants . The new Local Deposition TSD shows that some plants can have local deposition that is less than the regional average deposition, suggesting that most of the Hg from those plants is transported regionally or that other EGUs in the vicinity of those plants dominate the deposition of Hg near the plants. This does not detract from the overall finding that around some power plants with high levels of Hg emissions that excess local deposition is on average three times the regional EGU
- attributable deposition around those plants.***E.O. 12866 Review

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204 EPA disagrees that the Hg Risk TSD did not provide sufficient information regarding the excess local deposition calculation. Nonetheless, EPA has further 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 Hg Risk TSD did not demonstrate that Hg deposition from the top 10 percent of EGU Hg 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 EGU
- attributable Hg deposition. Th is implies that while Hg 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.***E.O. 12866 Review

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205 EPA disagrees with the commenter regarding the interpretation of the literature related to the spatial extent of deposition of Hg emitted by U.S. EGUs. EPA 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 assertion 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. The study 139 cited by the commenter to support the notion that 91 to 96 percent of Hg emitted from power plants travels beyond 50 km is based on a photochemical transport model ( the TEAM model) that does not employ current state - of - the - science and is not actively developed or updated. Furthermore, the modeling is base d on grid cells that are 20 km 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 Hg from

139 Seigneur et al., 2006.***E.O. 12866 Review

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206 all sources , an assumption that clearly limit s the regional impacts from sources 140
. The methodology of this study cited by the commenter is critically flawed in that it presents no results where individual Hg emission sources are removed and the difference between the zero out simulation and baseline model simulations are directly compared. Finally, the modeling study cited by the commenter presents an illustration of gri dded tota l annual Hg deposition from the TEAM model for the eastern U.S. that clearly shows elevated annual total Hg deposition in the vicinity of coal
- fired power plants in the Ohio River Valley and northeast Texas. The information 141 provided by a commenter is not relevant to the analysis of excess local deposition from EGUs , as it is based on ground level measurements of wet deposition alone. Changes to wet depo sition over a fairly short time frame such as a year (the part of the study where the coal - fired power plant (Crist) emitting Hg installed controls) are not expected to provide a meaningful information about the effectiveness of control technology . Wet deposition is highly variable from year to

140 Id. 141 EPRI, 2010.***E.O. 12866 Review

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207 year and is subject 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. Hg Risk TSD 1. Assumption of Linear Proportionality in Relationship between Changes in Hg Deposition and Changes in Fish Tissue Hg Concentrations (Mercury Maps) Comment: Several commenters critic ized 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 state d that the Mercury Cycling Model (MCM) developed by EPRI is a more rigorous model that was developed expressly to evaluate the relationship between changes in atmospheric Hg deposition to waterbodies and changes in fish tissue MeHg levels. Several **c**ommenters state d that the Mercury Maps model has many deficiencies. Those commenters state d that Mercury***E.O. 12866 Review

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208 Maps is a static model unable account for the dynamics of ecosystems that affect Hg bioaccumulation i n fish, cannot consider non
- air Hg inputs to watersheds, and assumes reductions in airborne Hg lead to proportional re ductions in fish MeHg concentrations **.** Another commenter claimed that data that demonstrate a steady- state linear reduction in fish tissue MeHg in response to a reduction in atmospheric Hg deposition within watersheds do not exist and provided several references that they claimed show non - linear responses to changes in Hg deposition 142 , 143
. The same commenter disagree d with EPA’s interpretation of Figure 2
- 17 in the March TSD and state d that a U.S. Geological Survey national waterway study 144 showed that

142 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 Early Edition, PNAS 2007 104 (42) pp. 16586
- 16591; (published ahead of print September 27, 2007). 143 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. 144 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 Scie ntific Investigations Report 2009

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209 sheet flow and drainage, not deposition, dominated input to the waterbodies it surveyed. The commenter state d that sheet flow and drainage could contain Hg and thus complicat e the relationship that EPA asserts is linear and direct. Another commenter cited Figure 2
- 17 in the Hg Risk TSD as showing that there is no well
- defined relations hip between Hg 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 demonstrat ed 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 fish tissue MeHg levels decrease in response to decreases in Hg deposition at tributable to U.S. EGUs. According to the same commenter, the METAALICUS study show s that there is a lag time (and a non
-proportional response) after 3

– 4 years. The same commenter note d that there are numerous factors that influence lag time including (1) watershed***E.O. 12866 Review

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210 characteristics 145 , (2) the fact that watersheds may act as legacy sources releasing Hg when disturbed 146 , (3) the magnitude of emission reductions and subsequent changes in atmospheric deposition need to be weighed against the amount of Hg already in an ecosystem147 , (4) the distance of an ecosystem from Hg sources 148 , and (5) the fact that Hg deposited to aquatic ecosystems becomes less available for uptake by biota over time 149 . Another commenter stated that additional Mercury Maps assumptions do not allow for considerations of lag in response to changes in: (1) deposition , (2) legacy sources of Hg such as mining , (3) historical Hg deposition , (4) natural Hg levels in fish , (5) ecosystem dynamics over time , or (6) the rel ative

145 Grigal D.F., 2002. “Inputs and Outputs of Mercury from Terrestrial Watersheds: A Review,” Environmental Review, 10, 1

– 39. 146 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. 147 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. 148 Lindberg S. et al. 2007. “A synthesis of progress and uncertainties in attributing the sources of mercury in deposition.” Ambio 3 6(1): 19
- 32. 149 Orihel D.M., Paterson M.J., Blanchfield P.J., Bodaly R.A., Hintelmann H., 2008. “Experimental Evidence of a Linear Relationship between Inorganic Mercury Loading and Methylmercury Accumulation by Aquatic Biota,” Environmental Science & Techn ology, 41, 4952

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211 source contributions over time. Another commenter stated that lag times need to be included in the modeling and be able to vary from watershed to watershed and sometimes even from waterbody to waterbody withi n a watershed. Several commenters stated that the emission rates of Hg 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. For this reason , the commenter ass ert ed that the system is not at steady
- state, a basic premise of the model. Another commenter state d that while the time lag for deposition to reach a waterbody is mentioned in the Hg Risk TSD, there is no discussion of the fact that a portion of the deposition is unlikely to reach the water at all. One commenter believes EPA incorrect ly impli ed 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 state d that while EPA properly screened out watersheds with significant current non
- air sources of Hg, EPA did not adequately screened out watersheds with significant Hg contributions from non
- air sources, specifically watersheds with historic Hg or gold mining or***E.O. 12866 Review

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212 other industrial Hg discharges. The same commenter stated that EPA’s study was not geographically balanced and was dominated by rivers i n the coastal region of the southeast that has numerous wetlands, which are favorable locations for methylation and have conditions are not typical of much of the rest of the U.S. Response **:** EPA disagrees with the commenters who challenged the assumption of a linear proportional relationship between changes in U.S. EGU deposition and fish tissue Hg levels. EPA specifically asked the SAB to evaluate EPA's assumption of linear proportionality in the relationship be tween Hg deposition and fish tissue MeHg 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 aquati c 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 deposit ion to fish concentrations, but does not consider them to be superior for this analysis or recommend their use. The integration of Community***E.O. 12866 Review

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213 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.” 150 The SAB peer review committee specifically addressed the Mercury Cycling Model suggest ed 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 appro aches should be equivalent. “The R-MCM, a steady- state version of the time
dependent 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 addit ional insight would be gained with the alternative model framework.” 151

150 U.S. EPA- SAB, 2011. 151 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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214 In addition, the SAB state d , “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. 152 , 153 , 154 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 changes is sufficiently robust for its application in this risk assessment.” 155 Ba sed 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 Hg Risk TSD, while this
152 Orihel et al., 2007. 153 Orihel et al., 2008. 154 Harris et al., 2007. 155 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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215 figure is useful to demonstrat e the lack of correlation across watersheds between total deposition of Hg and MeHg concentrations in fish tissue, it is not indicative of the likely correlation between changes in Hg deposition at a given watershed and changes in MeHg concentrations in fish tissue from that watershed. The SAB 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 potential (especially wetlands, aqueous organic carbon, pH, and sulfate) also play a key role.” 156 In response to recommendations from the SAB, EPA expanded the discussion of uncertainties associated with the linearity assumption, including uncertainties related to the potential for sampled f ish tissue Hg level to reflect previous Hg deposition and the potential for non
air 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

156 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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216 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 emissions of Hg . 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 is inadequate. In addition, we conducted several sensitivity analyses to gauge the impact of excluding watersheds with the potential for non
- EGU Hg emissions , 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 Hg Risk TSD did not directly use the Mercury Maps model. Instead, EPA applied an assumption of linear proportionality between changes in Hg deposition and changes in MeHg concentrations in fish that is supported by the Mercury Maps modeli ng. By assuming steady
- state conditions in apportioning fish***E.O. 12866 Review

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217 tissue Hg levels and risk, EPA does not attempt to project lag times. Recent research cited by the SAB 157 , 158 , 159 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 deposition and strengthens the approach used in the Revised Hg Risk TSD. 2. Characterization of Subsistence Fishing Populations and Exposure Scenario Comment: Several commenters state d that 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 stated no documentation exists to support s these assumptions. Another commenter state d that EPA’s definitions of subsistence fishers in the Hg Risk TSD are not consistent with earlier EPA documents and are used inconsistently throughout the Hg Ris k TSD.

157 Orihel et al., 2007. 158 Orihel et al., 2008. 159 Harris et al., 2007.***E.O. 12866 Review

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218 Several commenters state d that while subsistence fishing can be associated with poverty, poverty does not indicate subsistence fishing. One commenter state d that by including watersheds with as few as 25 members of individuals living in poverty, EPA overstates risks. One commenter state d that it is unclear what literature the Agency says “generally supports the plausibility of high
- end subsistence
- like fishi ng ... to some extent across the watersheds” and state d that if other studies exist, EPA should provide the values for comparison. One commenter state d that EPA combined two parameters with differing scales to establish the geographic unit us ed in the Hg 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 the analysis handled differences in geographic resolution between watersheds and census tracts were . One commenter state d that procedure for assigning census tracts could bias exposure outcomes. For example,***E.O. 12866 Review

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219 the commenter stated that a single influential census tract in a watershed could drive risk, even if the watershed had only a minimal number of fish samples. The comment er state d 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 state d that these census tracts may drive the extremes of the distribution without regard to the actual number of high
- level, self - caught fish consumers within their boundaries. The commenter stated that they could not assess the potential bias and noted that EPA did not test the bias by sensitivity analyses. Several commenters state d 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 state d that EPA should apply the minimum 25 source population criteria only to populations of women of childbearing age. One commenter state d that EPA assumption would result in any densely populated urban census tract with a single fish tissue sample being assigned to a
mo deled watershed with populations potentially at - risk ,***E.O. 12866 Review

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220 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 Hg Risk TSD, however, this clarification does not result in any changes to the quantitative analysis. In the Revised Hg 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). 160 This definition is reflected in the range of fish consumption rates used in estimating risk. The l ikely presence of this type of subsistence fish consumer is supported by available peer reviewed literature (see Table 1
- 5 of the Revised Hg Risk TSD). These studies clearly show that a subset of surveyed fishers consumes self
- caught fish at the rates that were cited in the Hg Risk TSD. The SAB peer review concluded that the consumption rates and locations for fishing activity are supported by the data presented in the Hg Risk

160 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 Agen cy, Washington, DC. EPA 823
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221 TSD, and are generally reasonable and appropriate given the available data. 161 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 fo r varying spatial resolutions. The geographic unit used as the basis for generating risk estimates is HUC12 , which are watersheds about 10 km on a side, which is comparable with the size of the 12 km2 grid cells in CMAQ , which are 12km2 . EPA has also clarified that the specific unit of analysis for this assessment is at the watershed, not enumerated subpopulations. EPA only used the U.S. Census tracts 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 Hg Risk TSD, EPA modified the female subsistence scenario to appl y equally to all wat ersheds with fish tissue Hg data based on the likelihood

161 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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222 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 no longer appl y to 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, EPA uses the U.S. Census data assess whether a SES - differentiated group similar to the particular type of sub sistence 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 , as EPA only modeled locations with poor source populations. However, in modeling these three populations, EPA asserts that the presence of a poor source population indicates the potential for subsistence fishing activity, rather the***E.O. 12866 Review

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223 presence of such activity. The linkage between pove rty and higher rates of subsistence fish consumption is supported by the Burger et al. study, 162 which identified substantially higher consumption rates for poor individuals (see Table 5 of the study). EPA acknowledges that subsistence fish ing activity by specific subpopulations might only be present across a subset of the watersheds EPA modeled for risk. However, given the stated goal of the analysis to determine 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 relatively few water sheds (less than 4 percent) have fish tissue Hg data, thus can be included in the risk assessment. Consequently, while there is the potential for including some watersheds in the analysis that may no t have currently active subsistence fishing activity, there is also the very real possibility that EPA excluded other watersheds from the analysis where this type

162 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

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224 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, subsist ence 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 - attributable Hg . Therefore, EPA focuses on this group of subsistence fishers in the risk assessment and did not evaluate exposure for the general population related to Hg exposure through seafood. 3. Cooking Loss Adjustment Factor Comment **:** Several commenters stat e d that 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 MeHg intake rate by a constant factor of 33 percent and also increasing any resulting (HQ) risk estimate by a similar factor. Several commenters state d that the source of EPA’s selected loss***E.O. 12866 Review

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225 factor 163 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 result of cooking fish 164 , 165 , 166 , 167 , 168
. One commenter suggest ed that EPA ’s cooking loss adjustment factor of 1.5 is at the hi gh 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

163 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. 164 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. 165 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. 166 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. 167 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. 168 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

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226 for prepared fish, and that some sources of consumption rates are based on raw fish. Response **:** EPA disagrees with the c ommenters that the selection of the cooking loss factor of 1.5 is not justified by the literature. EPA also disagrees with the 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 te nds to reduce non -muscle elements (e.g., water, bone, fat).***E.O. 12866 Review

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227 Regarding the alternative studies identified by the commenters, EPA disagrees that these studies considered collectively contradict the cooking loss factor in the analysis . Specifically, the first study 170 may have included measurement of non - fish components added to dishes (e.g., onions, heavy breading etc .) , which could dilute the post
cooking Hg measurements and give the appearance of a cooking loss even as actual fish t issue Hg levels could have increased . In the second study, 171 the fish species are saltwater and not freshwater , and the authors note that the reduction of water and fat could increase in the Hg concentration without changing absolute content. The third study focus ed on measurement of bi oaccessible Hg in raw and cooked fish. 174 However, available information currently allows us to specify the risk model in terms of total Hg intake , not bioaccessible Hg , thus, this article is potentially informative for guiding future research and methods development , not the current risk assessment. The fourth study 176 found a modest but statistically in significant increase in Hg levels for most of the cooking
170 Farias et al., 2002. 171 Perelló et al., 2008. 174 Torres - Escribano et al., 2011 176 Armbruster et al., 1988.***E.O. 12866 Review

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228 methods assessed, which is directionally consistent with EPA’s cooking loss adjustment. The fifth study 178 only addressed the issue qualitatively, thus cannot be used for the cooking loss factor. When considered collectively, EPA disagrees that the additional studies identified by the commenter contradict the cooking loss factor used in the risk assessment and maintains that the Morgan study 179 remains the most applicable for characterizing cooking/preparation effects on Hg concentrations in fish . 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 state d that they used models of portion or meal size servings (the size of the serving the respondent regularly eats). 180 Therefore, EPA interprets the fish consumption rates provided in the Burger et al. study as representing

178 Gutenmann et al., 1991. 179 Morgan et al., 1997. 180 Burger et al., 2002.***E.O. 12866 Review

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229 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) study 181 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 study 184 , 185 queried 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

181 Shilling, Fraser, Aubrey White, Lucas Lippert, Mark Lubell (2010). Contaminated fish consumption in California’s Central Valley Delta. Environmental Research 110, p. 334
- 344. 184 Dellinger JA. 2004. “Exposure asses sment and initial intervention regarding fish consumption of tribal members of the Upper Great Lakes Region in the United States.” Environ Res 95:325

– 340. 185 Personal communication, Dr. Dellinger, September 27, 2011***E.O. 12866 Review

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230 Assessment Guidance for Superfund (RAGS) or the Fi sh Advisory Guidance . 186 , 187 The commenter state d that these default consumption rates are derived from various studies and generally are based on 90 th or 99 th percentile distribution estimates. Another commenter state d that EPA’s use of the 99 th 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, 188 which equates to about a 95 th percentile fish consumption value. The same comme nter state d that EPA applie d the 99 th percentile to a “small survey of 149 South Carolina female anglers” to calculate an ingestion rate of 373 g/day. The commenter state d that if the 95 th percentile is use d 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.

186 U.S. EPA. 1991. Risk Assessment Guidance for Superfund (RAGS). Part C 1991 EPA/9285.7
- 01C. October. 187 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. 188 U.S. EPA. 1989. Risk Assessment Guidance for Superfund (RAGS). EPA/540/1
- 89/002. December.***E.O. 12866 Review

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231 Several commenters state d that EPA base d its fish consumption rates used in the risk analysis on a limited number of studies and that those studies are poorly documented. Another commenter state d that 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 popu lations to the national
scale . The commenter also not ed 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 on risk is the fish consumption rate. That same commenter stated that using 99th percentile ingestion rate dramatically increases HQ and IQ loss compared to the 50th percentile ingestion rate . The commenter state d that***E.O. 12866 Review

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232 when an estimate of the 95 th percentile ingestion rate of the 15
- 44 year old female population is considered, the HQ is a tenth of the value computed with the 99th percentile high
- end female fisher. One commenter state d 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 state d 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 indicated that 60 pe rcent of the watersheds with fish Hg data from rivers have risks calculated based upon a sample size of one or two fish. The commenter state d that it is not reasonable to base a significant policy and regulation decision on watersheds whe re expos ure is based on a single fish sample in a single water body within it. Several commenters criticized EPA’s use of the 75 th percentile fish tissue MeHg level in a watershed. One***E.O. 12866 Review

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233 commenter state d that EPA provide d no rationale for its decision to choose the highest of the 75th percentile for fish Hg 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 inflate d the risk estimates by assuming consumption of only fish greater than 7 inches and choos ing the largest of the 75 th percentile of fish Hg levels from these larger fish ( i.e. , larger than 7 inches) for rivers and lakes. That same commenter suggest ed using the median of all size fish, not just those over 7 inches. One commenter state d 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 sea food, MeHg consumption in the U.S. is of even greater concern. Response : EPA acknowledges that the focus of the Hg Risk TSD is characterizing risk for the group s likely to***E.O. 12866 Review

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234 experience the greatest U.S. EGU
- attributable Hg risk, which are 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 considered a range of high
- end fish consumption rates including the 99 th percentile representing the most highly
- exposed individuals. In responding to the SAB peer review, EPA clarified this focus in the introduction to the Revised Hg Risk TSD and 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 . The focus on the most highly
- exposed individuals is consistent with the appropriate and necessary finding and the treatment of other HAP under Section 112 . EPA agrees that the fish consumption rate is an important factor in calculating risk from exposure to MeHg in fish. EPA acknowledges that the distribution of fish consumption rates is positively skewed, which means that at higher percentiles ( e.g., 90 th , 95 th and 99 th ) there is a***E.O. 12866 Review

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235 substantial increase in ingestion rates relative to the mean or median. The Revised Hg Risk TSD includes a reasonableness check on the amount of fish consumed (as a daily value) reflected in the different rates. While the 99 th percentile consumption rates for the subsistence female fisher (373 g/day) is substantially higher than the 90 th or 95 th percentile values (123 and 173 g/day respectively ) , the 99 th percentile value translates into a 13
- ounce meal. While this represent s 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 do not have to be eaten all at one meal . The higher consumption rates ( i.e., greater than 250 g/day ) are supported by all three studies used in the risk assessment , and therefore, there is support across studies near the upper bound of likely consumption rates in this range. EPA acknowledges uncertainty associated with estimati ng high
end percentile values in these studies due to relatively low sample sizes for some population groups. However, even if a few individuals reported these high self
- caught fish consumption rates, making it difficult to characterize the population percentiles they represent, the values still***E.O. 12866 Review

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236 suggest that these levels of high fish consumption exist among surveyed individuals. To determine 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, EPA acknowledges that 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 Hg 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 surveys 189 and specialized studies . 190 , 191 , 192 , 193 , 194 Several studies identified

189 Burger et al., 2002. 190 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. 191 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. 192 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 T oxicology Section, Office of Environmental Health Hazard Assessment, July. 193 Tai, S. 1999. “Environmental Hazards and the Richmond Laotian American Community: A Case Study in Environmental Justice.” Asian Law Journal 6: 189. 194 Corburn, J. 2002. “Combining community
-based research and local knowledge to confront asthma and subsistence
- fishing hazards in***E.O. 12866 Review

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237 additional fishing populations with subsistence or near subsistence consumption rates, including urban fishing populations (including low
- income populations), 195 , 196 , 197 Laotian communities, 198 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. 199 The SAB concluded that the consumption rates and locations for fishing activity are supported by the data presented in the Hg Risk TSD, and are generally reasonable and appropriate given the available data . 200 EPA agrees that the Hg Risk TSD would be improved by clarifying that the literature review focused on identifying studies that characteriz e subsistence fish consumption for groups active at freshwater locations within the U.S., and EPA has revised the Hg Risk TSD accordingly. In the Hg Risk TSD, EPA summar ized important Greenpoint/Williamsburg, Brooklyn, New York.” Environmental Health Perspectives 110(2). 195 Burger et al., 1999a. 196 Burger et al., 1999b. 197 CalEPA, 1997. 198 Tai , 1999.. 199 Corburn, 2002. 200 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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238 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 moved the summary table to the main body in the Revised Hg 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 Hg Risk TSD, EPA acknowledged the smaller sample sizes for some of the subsistence fisher groups, and in several cases EPA did not use the 99 th 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 choos ing the highest 75 th percentile fish tissue concentration across lakes and rivers in a watershed. However, EPA modified the methodology based on evaluation of the number of samples within each watershed (responding to a recommendation from the SAB). In the revised methodology, EPA computes the 75 th percentile value at each sampling site within a watershed. EPA then computed the average of the site
- specific 75 th percentile fish tissue Hg values within a given watershed. This approach does not differentiate between rivers and lakes and reflects an***E.O. 12866 Review

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239 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, EPA considers it reasonable to assume that a subset of subsistence fishers could target larger fish on order to maximize the potential consumption per unit of fishing effort. EPA u ses this subset of subsistence fishers targeting larger fish, which is represented by the 75 th percentile fish tissue value , in the risk assessment. In addition, including the female subsistence fishing population in the analysis also provide s coverage for high
end recreational anglers who target larger freshwater fish. The SAB 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.” 201 The SAB suggested that EPA include a
s ensitivity analysis based on use of the median value, and

201 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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240 EPA has done so in the Revised Hg Risk TSD. This sensitivity analysis showed that using the median estimates had only a small impact on the number and percent of modeled watersheds with populations potentially at - risk from U.S. EGU- attributable MeHg exposures. Regarding the 7
- inch criteria, for the Revised Hg Risk TSD, EPA clarified that this cutoff 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 t rout and s almon (other edible fish species such as bass , walleye and
northern p ike have higher minimum size limits). 202 EPA disagrees with the comment that it is not reasonable to use watersheds where only a single fish sample is available. While it is generally preferred to have multiple samples, the SAB noted that using a single sample is likely to underestimate the 75 th percentile fish MeHg concentration and is therefore likely to underestimate the risk estimates for those watersheds. The SAB suggested that EPA conduct additional analyses of the fish tissue

202 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

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241 MeHg data , which EPA has done and included in the Revised Hg Risk TSD. The Revised Hg 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 MeHg and Hg Health Effects Studies Comment: Several commenters state d that EPA’s RfD 203 is based on sound science, which was supported by the findings of the NAS Study , 204 and that EPA appropriate ly applied the RfD in the Hg risk assessment. The commenters also state d that recent studies find clear associations between maternal blood Hg levels and delayed child development and cardiovascular effects, as well as potential for effects due to exposure to pollutant mixtures including lead. However, many commenters expressed concerns regarding EPA’s use of the MeHg RfD as a benchmark for health risk. Several commenters raised concerns claiming that EPA has not incorpo rated the best available Hg toxicological data

203 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 204 NAS, 2000.***E.O. 12866 Review

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242 into the RfD, which results in a flawed analysis and an overestimate of the impact of Hg emissions on human health. Several commenters state d that, when deriving the RfD, EPA relied on the flawed Faroe Islands’ children study and ignored the Seychelles Islands study, 205 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) there is potential for confounding by polychlorinated biphenyls (PCBs) and lead, (3) population exposure to MeHg was 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 Americans do ; (2) the amount of MeHg in the U.S. population is much lower than the Seychelles islanders; and (3) all ocean fish contain about the same amount of MeHg, so MeHg intake per fish meal is similar between Americans and

205 Budtz - Jorgensen E, Debes F, Weihe P, Grandjean P. 2005. “Adverse Mercury Effects in 7
- Year - Old Children Expressed as Loss in “IQ”.” EPA
HQ - OAR- 2002
- 0056
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243 Seychelles Islanders. However , another commenter state d that industry arguments against using the Faroe Islands study fail to acknowledge that the study results were consistent with studies in the Seychelles Islands, New Zealand207 , and Poland208
. One commenter criticized EPA for using a linear dose
response model for the RfD -based HQ metric and the IQ metric . Another commenter state d that the RfD assumes a threshold dose below which an appreciable risk of adverse effects is unlikely, and NAS did not evaluate whether MeHg exposure data were better fit by a linear or non
- linear model or by a threshold or non - threshold model. Several commenters state d that EPA’s MeHg RfD is more conservative than “safe” levels determined by other federal agencies and claim that EPA assigned unusually high uncertainty factors . Several commenters stated that EPA's use of the 1999 National Health and Nutrition Examination

207 Kjellstrom, T; Kennedy, P; Wallis, S; et al. 1 986 . 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). 208 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

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244 Survey (NHANES) blood Hg levels show a downward trend since 1999 , and the levels have been below the RfD since 2001. One commenter state d that a study by Texas Department of State Heal th Services (DSHS, 2004) 210 determined that among subsistence fishers who eat fish from Caddo Lake with elevated MeHg , women of child
-bearing years did not have blood Hg levels greater than the RfD. Thus, according to the commenter, the connection between MeHg 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, which EPA did not taken into account . 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 RfD methodology is a screening tool for deciding when risks clearly do not exist. Several commenters recommended adding qualitative discussion s to the Hg Risk TSD regarding several aspects of uncertainty , including uncertainty in the RfD, uncertainty in extrapolating a dose
- response relationship between MeHg
210 DSHS. 2005. Health Consultation: Mercury Exposure Investigat ion 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

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245 exposure and change in IQ, uncertainty in extrapolating the dose - response relationship from marine fish and marine mammals to freshwater fish, and uncertainty due to potential confounding by PCBs in marine species. Several commenters raised concerns regarding the relationship between MeHg exposure and IQ loss. Two commenters state d that changes in IQ are not a well
- defined health consequence of MeHg exposure. One commenter state d that the SAB had reservations about EPA’s use of IQ loss . Two commenters questioned whether IQ impacts would even occur because in Japan and Korea, where the maternal blood Hg levels are higher than in the U.S., there is no evidence of adverse effects . Another commenter cited a study211 that found verbal IQ 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 variation in IQ measures and the intra
- individual variation in IQ are higher than the threshold .

211 Hibbeln JR, Davis JM, Steer C, Emmett P, Rogers I, Williams C, et al. 2007. “Maternal seafood consumption in pregnancy and neurodevelopmental outcomes in childhood (ALSPAC study): an observational cohort study. “ Lancet 369:***E.O. 12866 Review

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246 Several commenters question the relationship between cardiovascular effects and MeHg exposure. Two commenter s cited studies examining the relationship between MeHg exposure and cardiovascular effects, 212 , 213 , 214 , 215 , 216 , 217 but concluded that it seems premature to use these studies to establish a dose
- response relationship. Several commenters assert that the risks from eating seafood are low relative to the benefits, that fish advisories can limit the beneficial aspects of fish consumption, and that fish advisories are often unsuccessful in changing behavior . 218 , 219 One commenter noted the important protective role of dietary selenium against

212 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. 213 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. 214 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. 215 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. 216 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. 217 Mozaffarian, Dariush. 2011. “Mercury Exposure and Risk of Cardiovascular Disease in Two U.S. Cohorts,” N Engl J Med 364: 1116
- 1125. 218 Hibbeln et al. 2007. 219 Mozaffarian, et al., 2011***E.O. 12866 Review

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247 MeHg t oxicity because the binding affinity of Hg to Se is much higher than binding to sulfur . 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 the MeHg RfD solely on results from the Seychelles Islands , as both the NAS 220 and an independent sc ientific review panel convened as part of the IRIS process 221 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
220 NAS, 2000. 221 U.S. EPA. 2001b. Responses to Comments of the Pe er Review Panel and Public Comments on Methylmercury. Available on the Internet at http://www.epa.gov/iris/supdocs/methpr.pdf***E.O. 12866 Review

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248 that EPA base d the MeHg RfD solely on results from the Faroe Islands population and disagrees that the information underlying the RfD is “poo rly explained”. EPA has provided detailed documentation for the choices underlying calculation of the RfD. 222 , 223 , 224 To correct a misunderstanding by the commenter, the data underlying the Faroe Islands study have been previously published in the peer reviewed literature. EPA disagrees that it did not incorporate the latest Hg 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 a re 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

222 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 223 U.S. Environmental Protection Agency

– I ntegrated Risk Information System (U.S. EPA- IRIS). 2001. Methylmercury (MeHg) (CASRN 22967
- 92
- 6). Available at http://www.epa.gov/iris/subst/0073.htm 224 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
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249 effects with lower MeHg exposure concentrations than in the Faroe Islands. These new studies provide additional 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. EPA agrees that EPA’s RfD is not the same as the levels used by other federal agencies . 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 Agency for Toxic Substances Disease Registry ( ATSDR ) in the calculation of the minimal risk level. 225 EPA disagrees that the uncertainty fa ctor 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

225 NAS, 2000.***E.O. 12866 Review

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250 pharmacokinetics , which is based on advice of the NAS 226 and an independent panel of scientific peer reviewers convened as part of the IRIS process 227
. IRIS makes this statement regarding a threshold for MeHg , “It is also important to note that no evidence of a thresho ld 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 models, K = 1 provided a better fit for the endpoint models than did higher values of K.” 228 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. EPA also stated that no RfD defines an exposure level corresponding to zero risk . EPA disagrees that exposure levels in the U.S. are lower than those in the Faroe Islands study. Exposure to

226 Id. 227 U.S. EPA, 2001b. 228 U.S. EPA- IRIS, 2001.***E.O. 12866 Review

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251 MeHg in the U.S. has been reported at the same levels as those published in the Faroe Islands. 231 One study note s that in the NHANES data (1999
- 2004), the highest five percent of women’s blood Hg exceeded 8.2 μg /L in the Northeast U.S. and 7.2 μg/L in coastal areas . 233 Higher levels have been reported among subjects known to consume fish. For example, one study reported mean blood Hg for adult women to be 15 μg /L; range for men and women was 2 to 89.5 μg/L . 235 Note that some publications have reported Hg effects in U.S. populations near the current U.S. RfD. 236 , 237 Also, EPA disagrees with the commenter stating all ocean fish throughout the world contain about the same amount of

231 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. 233 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. 235 Hightower Jane M, Moore Dan. Mercury levels in high
- end consumers of fish. Environ Health Perspect. 2003 Apr;111(4):604

– 608. 236 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. 237 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. Relation be tween Cord Blood Mercury Levels and Early Child Development in a World Trade Center Cohort. Environmental Health Perspectives 118(8) 1085
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252 MeHg . Marine fish in commerce differ widely in Hg concentration by species, and fish within the same species but caught at different locations have variable amounts of Hg in their tissues . 244 , 245 EPA disagrees that there is a statistically discernible downward trend in the NHANES data on blood Hg . EPA is unaware that a formal statistical analysis for temporal trends has been completed for NHANES data on blood Hg 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 Hg concen trations over the 6
- year study period.” 246 However, the same publication noted that “there was a decline in the upper percentiles reflecting the most highly expos e d women” having blood Hg concentration greater than established levels of concern. Visual observations of the data show a

244 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. 245 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. 246 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
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253 slight decrease in Hg blood level concentrations from 1999
- 2008 at the geometric mean , but this decrease may not be statistically significant . EPA remains concerned that substantial numbers of women of childbearing age in the U.S. may have blood Hg levels that are equivalent to exposures at or above the RfD. While mean and 95 th percentiles from recent NHANES data are below the blood Hg concentration equivalent to the RfD , blood levels for some portions of the population (high consumers of fish, for example) show exposures above the this level . One study estimated very high blood Hg levels at the 99 th percentile for females of child
-bearing age . 249Other published studies have shown that various population groups can have high blood Hg levels. 250 , 251 , 252 , 253 , 254 For example, one study found

249 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. 250 Id. 251 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. 252 Hightower and Moore, 2003. 253 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. 254 McKelvey, W., R. C. Gwynn, et al. 2007. "A biomonitor ing study of lead, cadmium, and mercury in the blood of New York city adults." Environ Health Perspect 115(10): 1435
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254 that 83 percent of the NHANES Asian population exceeded the RfD - equivalent blood mercury level . 255 EPA disagrees with the commenter regarding confounding by PCBs and lead . 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. Numerous analyses have shown neurobehavioral effects of PCBs; however, the effects of MeHg and PCB in the Faroe Islands study are separable. 258 EPA also documented the independence of PCB and MeHg effects in the Faroe Islands population. 259 NIEHS concluded that both PCB and Hg had adverse effects. 260 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 MeHg effect. 261 A second set of analyses found that the effect of prenatal PCB exposure was reduced when the data were sorted into

255 Hightower et al., 2006. 258 NAS, 2000. 259 U.S. EPA, 2001a. 260 National Institute of Environmental Health Sciences (NIEHS). 1998. Scientifi c 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. 261 NAS, 2000.***E.O. 12866 Review

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255 tertiles by cord PCB concentrations. 262 These analyses support a c onclusion that there are measurable effects of MeHg exposure in the Faroese children that are not attributable to PCB toxicity. We also note that the re was no report of lead exposure in the Faroe Islands population . EPA disagrees with the commenter’s assertion that the connection between MeHg in fish and observed health effects is not understood due to evidence from the cited Texas study263 . This is an exposure study rather than a study on measures of neurobehavioral or any other health endpoint. TCEQ noted that none of the Caddo Lake study participants had blood Hg 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” leve l. 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 i s not appropriate to extrapolate from Caddo Lake to larger regional or national populations.

262 Budtz - Jørgensen, E., N. Keiding, and P. Grandjean. 1999. Benchmark modeling of the Faroese methylmercury data. Final Report to U.S. EPA. 263 DSHA, 2005.***E.O. 12866 Review

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256 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. 264 , 265 , 266 , 267 The Agency’s concern with the likelihood of human exposure to multiple contaminants is reflected in the multi
- chemical scope of the rulemaking. However, EPA focused the technical analyses supporti ng the proposed regulation on effects of individual pollutants rather than cumulative effects. EPA disagrees with commenters suggesting that the RfD
based HQ is inappropriate. The 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
264 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 265 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 266 U.S. EPA. 20 00a. 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 267 U.S. EPA. 2003a. Framework for Cumulative Risk Assessment. Risk Assessment Forum, U.S. Environmental Protection Agen cy. 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

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2 57 neurodevelopmental effects of methylmercury, it constitutes a reasonable basis for assessing risk.” 268 EPA agrees that additional qualitative discussion about uncertainty would improve the Revised Hg Risk TSD. The SAB also recommended that EPA revise the Hg Risk TSD “to better explain the methods and choices made in the analysis, and analytical results, and where the uncert ainties lie.” The SAB noted several uncertainties related to the RfD, and EPA is preparing a revised TSD that will address the SAB ’s recommendations, including a more complete discussion of uncertainties including the RfD. EPA disagrees that the IQ metric thre shold is questionable . The SAB concluded that it was reasonable to consider a loss of >1 or >2 IQ points a public health
concern. The SAB stated, “The Panel agreed that if IQ loss is retained in the r isk assessment despite these reservations, a loss of one or two points would be an appropriate benchmark.” 270 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

268 U.S. EPA- SAB, 2011. 270 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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258 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 Scientific Advisory Committee (U.S. EPA CASAC 2007) [ 271 ]. 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.” 272 As noted in other studies, 273 , 274 a decrease of 1
- 2 points at the mean results in a much larger decrease i n those with IQs that are much lower or higher than the mean. Although EPA disagrees that the IQ results are too uncertain to rely upon, EPA acknowledges that IQ is not the most sensitive neurodevelopmental endpoint affected by MeHg exposure, as also noted by the SAB. The SAB recommended that the IQ analyses be retained but be de - emphasized in

271 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 272 U.S. EPA- SAB, 2011. 273 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. 274 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
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259 the documentation underlying the final regulation. The SAB concluded, “The Panel does not consider it appropriate to use 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.” 276 EPA is following up the SAB ’s recommendation by deemphasizing the IQ analysis and placing that analysis in an appendix to the revised TSD. The SAB, however, supported the use of the IQ dose response function calculated by EPA in the Hg Ris k TSD . The SAB note d , “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)[ 277 ] describes the sequence of

276 U.S. EPA- SAB, 2011. 277 Bellinger, 2005.***E.O. 12866 Review

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260 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 re ducing methylmercury on IQ, but the SAB does not consider these compelling reasons for using IQ as a primary driver of the risk assessment.” 278 EPA disagrees that EPA has overstated or failed to review the scientific literature on cardiovascular effe cts 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 cardiova scular system appears to be a target for MeHg toxicity in humans and animals.” 279 EPA also stated that additional cardiovascular studies have been published since 2000. EPA did not develop a quantitative dose response assessment for cardiovascular effects as sociated with MeHg exposures, as there is no

278 U.S. EPA- SAB, 2011. 279 76 FR 25001***E.O. 12866 Review

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261 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 effec ts. 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 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 rega rding whether the estimated IQ impacts for the regulation are real. Adverse effects of in utero Hg exposure have been reported in populations in the U.S. 280 , 281 In another study on neurobehavioral effects of prenatal exposure to MeHg through maternal consumption of seafood, adverse effects are observed for MeHg even without controlling for fish

280 Oken et al., 2008, 281 Lederman et al., 2008.***E.O. 12866 Review

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262 consumption. 282 That study suggests that at normal Japanese dietary intake of MeHg and fish nutrients, the overall effect is adverse. While Japanese fish consumption and Hg exposure are both somewhat 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. 283 , 284 , 285 , 286 287 , 288 , 289 Recent studies 292 , 293 , 294

282 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 i ntake: neonatal behavioral assessment scale results of Tohoku study of child development.” Environ Res 110, 699
- 704. 283 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. 284 Budtz - Jorgensen, E.; Grandjean, P.; Weihe, P. 2007. “Separ ation of risks and benefits of 16 seafood intake.” Environmental Health Perspectives . Vol. 115, 323
- 327. 285 Choi et al., 2008a. 286 Choi et al., 2008b. 287 Oken et al., 2008. “ 288 Strain , J.J. et al. 2008. Associations of maternal long chain polyunsaturated fatt y acids, methyl mercury, and infant development in the Seychelles Child Development Nutrition Study.” Neurotoxicology . 29(5): 776

– 782. 289 Suzuki, et al., 2007. 292 Oken et al., 2008. 293 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
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263 and analyses indicate the potential for nutrients in fish (particularly marine fish) to mask some of the observed adverse effects of MeHg. Because EPA did not adjust for potential confounding by nutrients in marine fish and mammals , the benchmark doses us ed in the RfD derivation may be underestimate d . EPA recognizes the potential for confounding of the effects of Hg on the developing nervous system by a range of nutrients and discuss es this uncertainty in the Revised Hg Risk TSD. Regarding selenium, the 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.” 295 The

294 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. 295 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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264 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 quantitative impact to support a recommendation of a re - analysis.” 296 6. General comments on Hg Risk Assessment Comment **:** Several commenters generally supported the Hg risk assessment, but several other commenters generally disagreed with the Hg risk assessment. One supporter stated that EPA reasonably determined that Hg emissions pose a public health hazard, correctly requested peer review of Hg
r isk 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 s ignificantly 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

296 Id.***E.O. 12866 Review

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265 and unreliable, including using CMAQ to model deposition, MMAPs, fish consumption rate and fish MeHg concentrations, overly stringent RFD, national
- scale model, 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 Hg concentration s, 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 Hg emissions reductions in the U.S. Several commenters cite Tetra Tech’s analysis that assessed Hg risk using different consumption rates, cooking factor, mean fish tissue concentrations, and EGU
attributable Hg 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 Hg exposure vi a fish consumption because EGU- attributable deposition is a small fraction of***E.O. 12866 Review

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266 total deposition. One commenter state d that EPA’s data shows Hg emissions from U.S. EGUs have little influence on fish Hg 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 c ommenter state d that EPA did not consider scientific information showing that there is no straightforward connection between Hg emissions from U.S. EGUs to the Hg level in fish, which is dependent upon many environmental factors, such as sunlight and organic mat ter, pH, water temperature, sulfate, bacteria, and zooplankton present in the ecosystem. One c ommenter state d that there is not any demonstrable evidence that anyone in the U.S. has suffered adverse health problems as a result of Hg emissions from coal - fired EGUs. One commenter state d that EPA’s findings are similar to the 2000 findings where EPA found a plausible link between anthropogenic emissions of Hg from sources in the U.S. and MeHg in fish, and “plausible” is a euphemism for unp roven. Several commenters had recommendations for the Hg risk analysis. One commenter stated that more data from Florida***E.O. 12866 Review

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267 should have been included because Florida is known to have a rich data set on fish Hg concentrations. One commenter state d that EPA should characterize general recreational angler fishers instead of subsistence fishers. One commenter claims that EPA made math errors in the Hg Risk TSD regarding the deposition in watersheds at specific percentiles. One commenter questioned EPA’s policy metrics used to characterize Hg risk. Several commenters state d that the Hg TSD is unclear and lacks detail, as noted by the SAB. One commenter state d that the SAB is critical of E PA’s efforts, stating that the SAB found it difficult to evaluate the risk assessment based solely upon Hg Risk TSD and recommended that EPA transparently explain the methods and uncertainties. One commenter state d that because of insufficient revi ew time and the lack of detail in the Hg Risk TSD, they could not assess key questions, such as the nation
-wide representativeness of the fish tissue data. One commenter state d the subset of watersheds considered in the analysis ( i.e ., with fish tissue data) have clearly higher U.S. EGU
- attributable deposition than the distribution of all watersheds.***E.O. 12866 Review

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268 One commenter stated 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 c ommenter notes that U.S. EGU - attributable emissions of Hg have decreased significantly between 2005 and 2016, but claims that this decrease does n ot appear to affect the risk results. One c ommenter questions why EPA has departed from the Clean Air Act (CAA) 112(n) risk comparison to the 1 in 1 million to use the RfD for Hg . Response **:** The purpose of the Hg 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. These additional factors include: (a) spatia l gradients in the magnitude of absolute U.S. EGU
- attributable Hg***E.O. 12866 Review

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269 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 experien cing 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 al so important to point out that while the national average U.S. EGU- attributable Hg deposition (for the 2016 scenario

– see Revised Hg Risk TSD) is two percent, values range up to 11 percent for the 99 th 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 Hg 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 objective, reasonable, and credible determination of the po tential for a public health hazard from Hg emitted from***E.O. 12866 Review

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270 U.S. EGUs.” 297 Furthermore, the 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. ” 298 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 approa ch 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.” 299 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, and where the uncertainties lie.” 300 EPA has revised the Hg Risk TSD as part of the final rulemaking to address the
297 U.S. EPA- SAB, 2011. 298 Id. 299 Id. 300 Id.***E.O. 12866 Review

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271 SAB’s recommendations and has made that revised TSD available in the rule docket. The SAB concurred with EPA’s analytical assumptions and overall study design for the Hg Risk TSD, including the RfD -based HQ approach, fish tissue data, 75 th percentile size fish, Mercury Maps assumption, and consumption rates. Based on the SAB peer review, EPA strongly disagrees with commenter statements that the results reported in the Hg 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 to estimate the deposition of Hg attributable to U.S. EGUs. EPA asserts that these metrics demonstrate a clear hazard to public health from Hg emissions from U.S. EGUs .***E.O. 12866 Review

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272 EPA thoroughly evaluated the Tetra Tech analysis. EPA does not agree that the analysis by Tetra Tech uses assumptions that are “more reasonable”, and the SAB agreed that all of EPA’s assumptions are reasonable and appropriate. EPA asserts that the Tetra Tech analysis does not fully cover 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 subsis tence fishers. Fish consumption surveys cited in the Revised Hg 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 Hg , but a number of studies discussed in the Revised Hg Risk TSD explicitly provide adjustment factors involving a higher unit concentration following preparation. Taken together, Tetra Tech’s analysis does not***E.O. 12866 Review

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273 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 Hg . EPA disagrees with the commenter’s assertion that this rule will not affect risks associated with Hg exposure. Hg from U.S. EGUs contribut es to the levels of MeHg 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 Hg levels in fish. EPA acknowledges that U.S. EGUs contribute only a small fraction of total Hg deposition in the U.S. However, U.S. EGUs remain the largest emitter of Hg 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 Hg exposures exceeding the RfD to have at least 5 percent of total Hg 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 Hg exposures exceeding***E.O. 12866 Review

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274 the RfD due to Hg emissions from U.S. EGUs even before considering Hg exposures due to other sources. Hg risk is increasing for exposures above the RfD, and as a result, any reductions in Hg 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 repre sentativeness of the fish tissue MeHg data in the national Hg risk assessment. The SAB 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 additional fish tissue methylmercury data are available to improve coverage o f the assessment.” 301 In response to the SAB ’s recommendations, EPA obtained additional fish tissue sample data from several states, particularly Pennsylvania,

301 U.S. EPA- SAB, 2011.***E.O. 12866 Review

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275 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 Hg- 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 ana lysis, the total number of watersheds in Florida assessed in the Revised Hg Risk TSD remains the same as proposal. EPA disagrees with the commenter that there were errors in the Hg 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 fo r the percentiles (and mean) provided for total Hg deposition and presented those percentiles and then separately estimated the percentiles for U.S. EGU
- attributable Hg. Therefore, the total and U.S. EGU- attributable values for the 99 th percentile do not necessarily occur at the same watershed. EPA has provided additional clarification in the Revised Hg Risk TSD.***E.O. 12866 Review

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276 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 Hg 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 Hg 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 deposition watersheds is inappropriate. EPA does not agree that there is no improvement in fish Hg concentrations between 2005 and 2016, or that there will be no further improvement from decreasing Hg emissions from U.S. EGUs from the baseline in 2016. While total risk***E.O. 12866 Review

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277 from all Hg exposures will remain elevated in much of the U.S., much of that risk is associated with global, non
- U.S. Hg 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 Hg risk assessment, average EGU- attributable fish tissue Hg concentrations will be decreased by 65 percent. Likewise, the number of modeled watersheds with populations po tentially at - risk from Hg emissions from U.S. EGUs 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 fish tissue Hg concentrations and modeled watersheds with populations potentially 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 Hg Risk TSD, per the SAB ’s 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***E.O. 12866 Review

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278 likely to experience relatively higher exposures to U.S. EGU- attributable Hg . Regarding the commenter who questioned the alleged change in risk metrics to use the RfD approach, 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 Hg , 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, 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 ’s statements concerning the clarity of the Hg Risk TSD to suggest that the public did not have an ample opportunity to comment on the Hg risk assessment. While it is correct that the SAB said the Mercury Risk TSD was***E.O. 12866 Review

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279 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 preamble to 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 provi ded clarifying information, were available well within the public comment period for the proposed rule. For these reasons, we maintain that the public was provided adequate opportunity to comment on the Hg risk assessment. e. Non - Hg HAP Case Studies 1. Emissions for non
- Hg case studies Comment : The commenter s 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***E.O. 12866 Review

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280 emissions of untested units, the suggestion of statistical outliers in the Cr test data, the claim that metals conte nt 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 Cr is flawed, and the lack of coal rank as a delineating factor for emission factor calculation. The commenter s 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 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 Cr test data from the Cr emission factors used for some of the case study emissions.***E.O. 12866 Review

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281 EPA disagrees with commenters’ assertions that the metal content of the coal is a basis for invalidating the test results of high Cr 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. 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 equat ions 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.***E.O. 12866 Review

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282 EPA also disagrees with commenters concerns about the assumption that 12 percent of the Cr will be Cr (VI) 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 Cr 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 Cr emissions have scrubbers according to the data provided to EPA by those facilities, so scrubber impacts on Cr speciation is not relevant to EPA’s conclusions based on the non
- Hg case studies. In any case, EPA disagrees with the commenter’s conclusions about the impacts of scrubbers on Cr speciation and provides evidence that impacts o f scrubbers on Cr speciation can have the opposite effect on Cr (VI) fractions, concluding that EPA’s 12 percent assumption is somewhat conservative. EPA also disagrees that coal rank must be a factor in computing Cr 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***E.O. 12866 Review

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283 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 commenter ’ s 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 EPA’s case study assessment reaffirms the need to regulate HAP emitted 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 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 E PA the meteorological data***E.O. 12866 Review

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284 used for EPA’s assessment of the Conesville facility and processed these data with 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 c ommenter stated that 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
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 HAP for all sources in th is category. One commenter stated that EPA’s discussion in the preamble to the proposed rule misleads the reader into believing that non
- Hg HAP emissions from EGUs are associated with serious human health effects. According to the commenter, EPA’s discussion of the effects associated***E.O. 12866 Review

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285 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
non - Hg HAP . One c ommenter stated that with the assumptions in the Utility Study , 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. Several commenters state d that even if the additional studies EPA performed were accurate, they hardly demonstrate that it is necessary and appropriate to regulate coal - fired EGU HAP under Section 112 because three sites nationwide show risks greater that one in one million, with the highest at eight in one million. One c ommenter stated that the highest cancer risk estimated for coal
- fired EGU s 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***E.O. 12866 Review

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286 cancer in a lifetime is approximately one in three (0.33). According to EPA's own data, the predicted added cancer risk of exposure to HAP 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 c ommenter 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 apparently decided that they were justified to regulate all
non - Hg HAP 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
censu s 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 c ommenter asserts that because the al leged health benefits are derived from total exposure, EPA should explain how its numerical emission limit units, which would***E.O. 12866 Review

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287 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. One commenter questioned whether acid gas emissions limits for oil
- fired units are “appropriate” or “necessary” 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 Ni as the main HAP of concern from oil
- fired units, even though
cancer - related inhalation risks were well below the reference concentrations and EPA states that significant uncertainty remains as to whether those emissions present a health concern. Response : EPA agrees with the commenter that the non
Hg 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 versions of AERMINUTE (version 11059), AERMET (version***E.O. 12866 Review

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288 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. EPA disagrees with the commenter that having only a few case study facilities exceeding one 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). Because the ICR data were collected for the purpose of***E.O. 12866 Review

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289 developing the MACT standards, the ICR was targeted towards better performing sources for non
- Hg 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 coal
fired 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 preamble to the proposed rule. EPA disagrees with the commenter's assertion that the health effects associated with exposures to non
- Hg HAP from U.S. EGUs are mischaracterized in the preamble to the***E.O. 12866 Review

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290 proposed rule. The discussion of the health effects of non
Hg 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 EPA disagrees with the commenter’s characterization of the Utility Study . The Utility Study 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 appropr iate and necessary to regulate EGUs under section 112.***E.O. 12866 Review

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291 EPA does not agree with the commenter who suggest ed that EPA should interpret the results of the non
- Hg HAP risk analysis in the context of background cancer risk. As explained in the preambl e to 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. The commenter s 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 contenti on 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 112(n)(1) or anywhere under section 112, and it would be***E.O. 12866 Review

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292 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 preambl e to the proposed rule and this final action. 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 EPA’s Benzene NESHAP regulation of 1989 302 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 centroi ds). 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 associ ated with the case study facilities. EPA used the annua l average ambient air concentration of each HAP at each census block

302 54 FR 38044***E.O. 12866 Review

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293 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. 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 justifie d based on their ability to protect public health. Regarding potential health concerns, EPA has up to 8 years after the promulgation of the technology
based emission limits for EGUs to determine whether the regulations protect public health with an amp le margin of safety. If the regulations do not, the CAA directs EPA to promulgate additional more stringent standards (within the prescribed 8 years) to achieve the appropriate level of public health protection. Furthermore, EPA reasonably concluded that it was appropriate and necessary to regulate oil
- fired EGUs in***E.O. 12866 Review

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294 2000, and EPA confirmed that conclusion was proper with the analysis set forth in the preamble to the proposed rule. Certain commenters question the determination based on their views of how the Agency can and should exercise its discretion. EPA disagrees with these commenters and stands by the determination for the reason s set forth in the preamble to the proposed rule. EPA also stands by the determination that the maximum cancer risks posed by emissions of oil
- fired EGUs are greater than one in a million, due primarily to emissions of Ni compounds. Based on our analysis, we are unable to delist oil
- fired EGUs. 3. Ni Risk Comment : Several commenters stated that the assumptions regarding the speciation and carcinogenic potential of Ni compounds used in EPA’s inhalation risk assessment of the case study facilitie s are overly conservative and likely to overstate the risks. With respect to Ni speciation, the commenters stated that there are substantial uncertainties regarding the species of Ni being emitted and the risk of such emissions, and that EPA ha s made ultraconservative assumptions aimed at overestimating the risk. The commenters stated that***E.O. 12866 Review

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295 assigning the same carcinogenic potency of Ni subsulfide to other forms of Ni is overly conservative and inconsistent with the best available evidence. Response **:** EPA disagrees with the commenters’ assertion that it is impossible to give an accurate assessment of the risks to human health from Ni emissions from EGUs, and
maintains that its assessment of the potential inhalation risks from EGU emissions of Ni 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 review (using three independent expert reviewers) of the methods used to evaluate the risks from Ni and Cr compounds emitted by EGUs. 303 There were two charge questions relating to Ni in that review. First, do EPA's judgments rel ated to speciated Ni 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 Ni compounds, and taking into account the existing URE values (i.e., values derived

303 U.S. EPA, 2011c.***E.O. 12866 Review

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296 by the Integrated Risk Information System304 , California Department of Health Services 305 , and the Texas Commission on Environmental Quality 306 ), 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? 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.

304 U.S. EPA, 1998. Integrated Risk Information Service (IRIS) assessment for hexavalent chromium. Available at: http://www.epa.gov/ncea/iris/subst/0144.htm. 305 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. 306 Texas Commission on Environmental Quality (TCEQ), 2011. Development Support Document for ni ckel 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

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297 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 Ni speciation prof ile data. The third reviewer recommended that EPA review several manuscripts on Ni speciation profiles showing that sulfidic Ni compounds (which the reviewer considered as the most potent carcinogens) are present at low levels in emissions from EGUs. Ni and Ni compounds have been classified as human carcinogens by national and international scientific bodies including the IARC, 307 the World Health Organization 308 , and the European Union’s Scientific Committee on Health and

307 International Agency for Research on Cancer (IARC), 1990. IARC monographs on the evaluation of c arcinogenic risks to humans. Chromium, nickel and welding . Vol. 49. Lyons, France: International Agency for Research on Cancer, World Health Organization Vol. 49:256. 308 International Labour Organization/United Nations Environment Programme, World Health Organization (WHO), 1991. Nickel. In Environmental Health Criteria No 108 Geneva.***E.O. 12866 Review

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298 Environmental Risks 309 . In their 12 th Report of the Carcinogens , the NTP has classified Ni compounds as known to be human carcinogens based on sufficient evidence of carcinogenicity from studies in humans showing associations between exposure to Ni 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 expo sure to an assortment of Ni compounds by multiple routes causes malignant tumors at various organ sites and in multiple species. The 12 th 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”. 310 Although the precise Ni compound (or compounds) responsible for the carcinogenic effects in

309European 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 310 NTP, 2011 .***E.O. 12866 Review

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299 humans is not always clear, studies indicate that Ni sulfate and the combinations of Ni sulfides and oxides encountered in the Ni refining industries cause cance r in humans. There have been different views on whether or not Ni compounds, as a group, should be conside red as carcinogenic to humans. Some authors believe that water soluble Ni , such as Ni sulfate, should not be considered a human carc inogen, based primarily on a negative Ni sulfate 2
- year NTP rodent bioassay (which is different than the positive 2
- year NTP bioassay for Ni subsulfide). 311 , 312 , 313 Although these authors agree that the epidemiological data clearly supports an association between Ni and increased cancer risk, they sustain that the data are weakest regarding water soluble Ni . A recent review 314 highlights the robustness and consistency of the epidemiological evidence across several decades showing associations

311 Oller A. Respiratory carcinogenicity assessment of soluble nickel compounds. Environ Health Perspect. 2002, 110:841
- 844. 312 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. 313 Goodman JE, Prueitt RL, Thakali S, and Oller AR. The nickel iron bioavailability model of the carcinogenic potential of nickel
containing substances in the lung. Crit Rev Toxicol . 2011, 41:142
- 174. 314 Grimsrud TK and Andersen A. Evidence of carcinogenicity in humans of water - soluble nickel salts. J Occup Med Tox icol. 2010. 5:1
- 7. Available online at http://www.ossup
-med.com/content/5/1/7.***E.O. 12866 Review

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300 between exposure to Ni and Ni compounds (including Ni sulfate) and cancer. Based on the views of the major sc ientific bodies mentioned above, and those of expert peer reviewers that commented on EPA ’ s approaches to risk characterization of Ni compounds, EPA considers all Ni compounds to be carcinogenic as a group and does not consider Ni speciation
or Ni solubility to be strong determinants of Ni carcinogenicity. With regards to non
- cancer effects, comparative quantitative analysis across Ni compounds indicates that Ni sulfate is as toxic or more toxic than Ni subsulfide or Ni oxide. 315 , 316 Regarding the second charge question, two of the reviewers suggested using the URE derived by TCEQ for all Ni compounds as a group, rather than the one derived by IRIS specifically for Ni subsulfide. The third reviewer did not comment on alternative approaches. EPA decided to continue using 100 percent of the current IRIS URE for Ni subsulfide because IRIS values are at the top of the hierarchy with respect to the dose response information
315 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. 19 98. 43:213
- 229. 316 NTP , 1996.***E.O. 12866 Review

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301 used in EPA’s risk characterizations, and because of the concerns about the potential carcinogenicity of all forms of Ni raised by the major national and international scientific bodies. Nevertheless, taking into account that there are potential differences in toxicity and/or carcinogenic potential ac ross the different Ni compounds, and given that there have been two URE values derived for exposure to mixtures of Ni compounds that are 2
- 3 fold lower than the IRIS URE for Ni subsulfide, EPA also considers it reasonable to use a val ue that is 50 percent of the IRIS URE for Ni subsulfide for providing an estimate of the lower end of a plausible range of cancer potency values for different mixtures of Ni compounds. 4. Cr Risk Comment : One commenter stated there are several problems with EPA's analysis related to the fact that Cr emissions were evaluated as being entirely Cr (VI). The commenter stated that not all of the emitted Cr 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***E.O. 12866 Review

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302 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 Cr (VI) from coal - fired EGUs is unsupported, and that EPA fail ed to recognize that Cr (VI) is highly water
soluble and is easily reduced to Cr (III) in the presence of S O 2 in a low pH environment. The resulting Cr (III) would be expected to precipitate out in a FGD. The commenter stated that the actual amount of Cr (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 EPA because of (1) the use of surrogate speciated Cr 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.***E.O. 12866 Review

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303 Response **:** EPA disagrees with the commenters’ assertion that all Cr was considered to be hexavalent. As discussed in “Methods to Develop Inhalation Cancer Risk Estimates for Chromium and Nickel Compounds” 317 , existing test data for utility and industrial boilers indicate that hexavalent Cr is, on average, twelve percent of total Cr from coal - fired boilers. Th is document 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 Cr speciation profiling. The EPRI inhalation study for coal
- fired 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 emis sions, 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.

317 U.S. EPA, 2011c.***E.O. 12866 Review

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304 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 EPA’s Benzene NESHAP regulation of 1989 318 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 a ssociated 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 fac ilities. 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.

318 54 FR 3804***E.O. 12866 Review

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305 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
- fire d 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. Several commenters stated that acid gas concentrations estimated in the case study facility assessment and the Utility Study do not exceed human health thresholds of concern. Two commenters stated that HCl emissions are negligible compared to other primary emissions (such as SO 2 ) that can lead to potential acidification of ecosystems. Response **:** As explained in the preamble to 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 provisi on states that EPA ”may” consider established health thresholds when setting emissions standards under section 112(d). By the use of the***E.O. 12866 Review

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306 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 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 preamble to 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***E.O. 12866 Review

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307 from EGUs as well as sources that may be co - located with EGUs or nearby such sources. Additional data were also no t 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 with an ample margin of safety. The commenter s’ 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 preamble to the propo s ed rule 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***E.O. 12866 Review

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308 significant and provide an additional basis for the Administrator to conclude that it is not appropriate to exercise her discret ion 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 HAP and not criteria poll utants, Congress did recognize, in the legislative history to section 112(d)(4), that MACT standards would have the collateral benefit of controlling criteria pollutants as well and viewed this as an important benefit of the air toxics program. 319 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). The re 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

319 See S. Rep. No. 101

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309 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

—ne ither 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 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
- Hg case studies on 16 (15 coal - fired) power plants. The commenters state d that***E.O. 12866 Review

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310 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 - Hg HAP EPA produced one study on chronic inhalation risk assessment that identified three sites with cancer risks greater that one in one million for hexavalent Cr , which was authored by EPA staff and not peer reviewed. One commenter stated that EPA study is based on misinformation and overestimates assumptions, and that EPA has no data demonstrating health impacts from EGU emissions of non
- Hg HAP , or the benefit from reducing such emissions. Two commenters stated that no benefits will be derived from the non - Hg HAP emission reductions associated with the proposed rule because no non - Hg HAP health risks were proven, and that no showing was made that EGU non
- Hg 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 for
non - Hg metals in order to determine appropriateness of proposing emissions standards for non
- Hg metals.***E.O. 12866 Review

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311 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 appropriate approach, the T ier 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 be cause 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 faci lities was actually performed with a greater degree of refinement***E.O. 12866 Review

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312 than the EPRI analysis, and was consistent with EPA’s Guideline on Air Quality Models. 320 In contrast to the approach used in the EPRI analysis, EPA used: 1) 5 years of recent meteorological dat a from the weather station nearest to each facility, rather than one year of meteorological data. This is more representative of long
- term (i.e., lifetime) exposures and risks. 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

320 Appendix W to 40 CFR 51***E.O. 12866 Review

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313 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 assessme nts performed for Risk and Technology Review rulemakings, which underwent peer review by the Science Advisory Board in 2009. 321 The SAB issued its peer review report in May 2010. The report generally endorsed the risk assessment methodologies used in the pro gram. In addition, in July 2011, EPA completed a letter peer review of the methods used to develop inhalation cancer risk estimates for Cr 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

321 U.S. EPA- SAB, 2010.***E.O. 12866 Review

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314 published research 322 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 MeHg on wildlife. Response : While E PA agrees that quantification of acidification effects has remaining uncertainty, the science and methodology has progressed in recent years. Based on recent peer reviewed research including Evans et al. 323 , acid gases can significantly contribute to acidification. EPA published a comprehensive risk assessment of acidification effects of nitrogen and sulfur deposition 324 and a policy assessment 325 . Given the extent

322 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. 323 Id. 324 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>. 325 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***E.O. 12866 Review

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315 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 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
<http://www.epa.gov/ttnnaaqs/standards/no2so2sec/data/201 10204pamain.pd f>.***E.O. 12866 Review

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316 with the commenter that Hg 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 Ecotoxicology326 mentioned by the commenter in the ecosystem effects sec tion on Chapter 5 of the RIA for this rule, which is available in the docket. 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.

326 Ecotoxicology 17:83
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317 Specifically, the revised Hg Risk TSD shows that up to 29 percent of modeled watersheds have populations potentially at - risk from exposure to Hg from U.S. EGUs . 327 In the revised Hg Risk TSD, 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 to those watersheds . In the revised Hg Risk TSD, U.S. EGUs contribute to potential exposure greater than the RfD in 10 percent of modeled watersheds , even excluding consideration of other U.S. and non - U.S. sources of Hg deposition. Given that 1) the percent of modeled watersheds with populations potentially at - risk increased from 28 to 29 percent in the revised risk assessment, and 2) the revised analysis includes 36 percent more watersheds , which significantly expands the coverage in several states , we conclude that the finding that emissions of Hg from U.S. EGUs are a hazard to public health is con f irmed by the revised Hg Risk TSD .

327 This corresponds to 28 percent of modeled watersheds with populations potentially at
- risk in the analysis reported in the preamble to the proposed rule .***E.O. 12866 Review

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318 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 oil
fired EGUs is estimated to be 20 in a million, driven by Ni emissions. For the facilities with coal
- fired EGUs, there were five (out of 16) with maximum individual cancer risks greater than one in a million (the highest was five in a million), four of which were driven by emissions of hexavalent Cr , and one of which was driven by emissions of Ni . There were also two facilities with coal
- fired EGUs with maximum individual cancer risks at one in a million , for a total of six facilities that meet or exceed the criterion for EGUs to be regulated under section 112 . 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 one in a million (the highest was eight in a million), and one coal - fired EGU facility with maximum individual cancer risks equal to one in a million. Given that 1) the lifetime cancer risk for the oil
- fired EGU facility has***E.O. 12866 Review

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319 increased from 10 to 20 in a million, 2) the number of coal - fired EGU facilities with cancer risks greater than
one 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 above the one 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
con f irmed by the revised non - Hg risk inhalation case studies . While we did not do new analyses on these topics, we also reiterate that 1) Hg emissions from U.S. EGUs are a hazard to the environment, contributing to adverse impacts on fish
- eating birds and 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 environmenta l 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, and 3) it is appropriate t o regulate those HAP which are not known to cause cancer but are known to contribute to chronic non
- cancer toxicity and***E.O. 12866 Review

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320 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 emission s from EGUs will not be addressed by other sections of the CAA ; therefore, it is necessary to regulate EGUs under section 112. In addition, based on evaluation of the regulations required by the CAA , including the recent CSAPR , 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. While CSAPR is projected to achieve some Hg reductions due to co - control of Hg provided by controls put in place to achieve required reductions in SO 2 emissions, the Hg Risk TSD shows that a substantial percent of modeled watersheds with populations potentially at - risk from U.S. EGU- attributable Hg deposition would remain after implementation of CSAPR. While we modeled slightly higher Hg emissions from U.S. EGUs***E.O. 12866 Review

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321 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 Hg emissions from U.S. EGUs are a hazard to public health. In addition, the actual reductions in Hg 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 instal l. 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. 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 identifie d 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***E.O. 12866 Review

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322 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 categories regulated under CAA section 112.