Response to Comment 191: The EPA disagrees with the commenter for all the reasons set forth in the preamble to the proposed rule. As the EPA explained, the 2005 action interpreted the statute in a manner inconsistent with the 2000 Finding, and the EPA provided a revised interpretation that is fully consistent with the CAA and that finding. The commenter is also incorrect in suggesting that a change in interpretation is per se invalid and the commenter has provided no support for that position. See National Cable & Telecommunications Ass'n  v. Brand X Internet Services, 545 U.S. 967, 981 (2005) (discussing the deference provided to an Agency changing interpretations the Court stated "change is not invalidating, since the whole point of Chevron deference is to leave the discretion provided by ambiguities of a statute with the implementing Agency.") (Internal citations and quotations omitted).
Comment 192: Commenters 17689 and 17712 state that the EPA did not have a rational justification for its 2000 decision that it was appropriate and necessary to regulate EGU emissions as hazardous. The commenters state that addressing non-Hg metal HAP, the EPA found that although cancer risks are not high, they are not low enough to be eliminated as a potential public health concern, and regarding dioxins, HCl, and HF, the agency found them to be of "potential concern."
Response to Comment 192: The EPA asserts that the 2000 Finding was sound and fully supported by the record available at the time. The analysis accompanying this rule fully addresses all of commenters contentions and need not fully revisit the analysis in response to this comment; however, the EPA disagrees that it was not "rational" to determine that it was appropriate to regulate HAP emissions from U.S. EGUs due to the cancer risks identified in the Utility Study or the potential concerns associated with other HAP emissions from U.S. EGUs. The EPA maintains that uncertainty favors a finding that it is appropriate and necessary to regulate HAP emissions because even small amounts of HAP can cause significant harm to human health and the environment. The EPA is charged with interpreting the statute and evaluating the scientific and technical information to determine whether regulation of HAP emissions from U.S. EGUs is appropriate and necessary, and the agency is afforded considerable discretion when making such decisions. In the case of the 2000 Finding, the EPA identified a risk from Hg and some non-Hg metal HAP and a potential concern for other HAP emitted from U.S. EGUs. The EPA considered all the available information and concluded regulation was appropriate and necessary. Based on that valid finding, the EPA listed EGUs for regulation and listed sources must be regulated under CAA section 112(d).
Comment 193: Several commenters (17383, 17689, 17877, and 17885) state that the EPA found a "plausible link" between anthropogenic Hg (from EGU and all other man-made emissions) and MeHg in fish, thus concluding that EGU Hg emissions are considered a threat to public health. According to the commenters, potential concerns and "plausible links" are not adequate reasons to regulate EGU emissions under CAA section 112.
Response to Comment 193: The commenter appears in this comment to be referring to the 2000 Finding and listing of EGUs. The commenter implies that the agency was required to have made a specific finding like those made in this action before making the Appropriate and Necessary Finding. The commenter is wrong. CAA section 112(n)(1)(A) does not require such a finding and the agency reasonably concluded in 2000 that it was appropriate and necessary to regulate HAP emissions from U.S. EGUs based on the considerable amount of information available to the agency. The EPA explained in the preamble to the proposed rule why the 2000 Finding was valid at the time it was made.
Further, the EPA conducted new analyses in conjunction with the development of the CAA section 112(d) standards and found that HAP emissions from U.S. EGUs continue to pose a hazard to public health and the environment. As shown in the revised Hg Risk TSD and the Non-Hg Case Study Chronic Inhalation Risk Assessment, HAP emissions from U.S. EGUs pose a hazard to public health. These peer reviewed assessments, as well as the previous Utility Study, Hg Study, and NAS study, all lead to the same conclusion that HAP emissions from U.S. EGUs pose hazards to public health and the environment.
Comment 194: Commenter 18034 states that the 2000 Finding is questionable because the Hg emissions upon which the finding was made were inaccurate. According to the commenter, in 2000 the EPA estimated that about 60% of total Hg deposited in the U.S. came from U.S. anthropogenic air emission sources, and the EPA further said that of that 60%, approximately 30% was from U.S. EGU Hg emissions, which translated into about 18% of total deposition in the U.S. at that time. According to the commenter, in 2000, the EPA also estimated that EGU Hg emissions would increase from 46 tons in 1990 to over 60 tons in 2010. However, states the commenter, U.S. Hg emissions did not increase, but actually decreased to less than 30 tons a year and that according to the EPA EGUs, on average contribute about 2% of total Hg deposition across the country.
Response to Comment 194: The EPA disagrees that the emissions information provided in the 2000 Finding makes the finding "questionable" as stated by the commenter. The information upon which the EPA based the finding in 2000 was the best information available and the agency must make decisions based on the information they have, not on information that will not be available for many years. The 2000 Finding was sound and fully supported by that record, including the future year emissions projections. Even though Hg emissions have decreased since the 2000 finding instead of increasing as projected, the new technical analyses confirm that Hg emissions from U.S. EGUs pose a hazard to public health. Moreover, Hg emissions from U.S. EGUs also pose a hazard to the environment. The EPA also notes that the commenter's average deposition estimates fail to accurately characterize the Hg deposition problem in the U.S. As shown in Table 2-2 of the revised Hg Risk TSD, the EPA found that U.S. EGUs account for up to 11% of total Hg deposition for the 99[th] percentile watersheds in 2016.
Comment 195: Commenter 18429 notes that the EPA's decision that it is appropriate and necessary to regulate is based on the 2000 Finding that is over a decade old and since that time there have been decreases in HAP from EGUs.
Response to Comment 195: The EPA maintains that the 2000 listing was valid at the time it was made based on the information available to the agency. Because the EPA is still unable to delist EGUs pursuant to CAA section 112(c)(9)(B), the agency is required to regulate EGUs under CAA section 112(d). Furthermore, the EPA reaffirmed that it is appropriate and necessary to regulate HAP emissions from EGUs in the notice of proposed rulemaking.
c. Comments stating that the 2000 Finding only supports Hg regulation.
Comment 196: Commenters 17696 and 18477 state that, under the 2000 Finding, Hg is the only HAP emitted by EGUs for which the EPA made a specific finding of significant hazards to public health to support a determination that regulation under CAA section 112(n)(1)(a) is "appropriate and necessary." According to the commenters, in the 2000 Finding the EPA noted the uncertainty with respect to HAP emissions from oil-fired units. The EPA later clarified that, based on the record before the agency in 2000, its stated concern with the uncertainties of health impacts from oil-fired HAP emissions from U.S. EGUs emissions was limited to nickel emissions. 69 FR 4652, 4656, 4683-84 (Jan. 30, 2004). Subsequently, based on new information concerning diminished nickel emissions, the EPA decided that regulating nickel emissions from oil-fired EGUs was not warranted. 70 FR 28606, 28611 (May 18, 2005).
Comment 197: Commenters 17724 and 17799 state that the 2000 Final Report concluded that Hg is the HAP of greatest potential concern emitted from coal-based EGUs but never made an affirmative finding with respect to other HAP. According to the commenters, since the Final Report is the factual basis for the proposed rule, the EPA will exceed its statutory authority if it promulgates a final rule regulating HAP not identified in the Final Report. The commenters state that in the event that the EPA determines that it is "appropriate and necessary" to regulate EGUs under CAA section 112 after notice and comment rulemaking, the EPA must amend the proposed rule and limit its scope only to the HAP for which a factual foundation to regulate has been established in the Final Report.
Comment 198: Commenters 17774 and 18020 state that the EPA cannot regulate HAP other than Hg because the 2000 Finding authorizes only the regulation of Hg.
Comment 199: Commenter 18428 states that the EPA's 2000 determination identified health concerns only with Hg emissions from coal-fired power plants and potentially nickel from oil-fired units. Although the EPA did not find health concerns related to non-Hg HAP, states the commenter, the agency has decided to propose regulating a large number of HAP from U.S. EGUs despite the lack of data to support it.
Response to Comments 196 - 199: Nothing in CAA section 112(n)(1)(A) suggests that the EPA must determine that every HAP emitted by EGUs poses a hazard to public health or the environment before the EPA can find it appropriate to regulate EGUs under CAA section 112. In fact, the EPA maintains that it must find it appropriate and necessary to regulate EGUs under CAA section 112 if it determines that any one HAP emitted from U.S. EGUs poses a hazard to public health or the environment that will not be addressed through imposition of the requirements of the CAA. The EPA disputes the commenters' conclusion that the 2000 Finding was limited to Hg and nickel emissions, but, even if it was, the EPA reasonably concluded that EGUs should be listed pursuant to CAA section 112(c) based on the Hg and nickel finding. As stated in the 2000 finding, cancer risks from some non-Hg metal HAP (including arsenic, chromium (Cr), nickel, and cadmium) were not low enough to be eliminated as potential concern. 76 FR 79827. Source categories listed for regulation under CAA section 112(c) must be regulated under CAA section 112(d), and the D.C. Circuit Court has stated that the 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 Ass'n v. EPA, 233 F.3d 625, 634 (D.C. Cir. 2000). Therefore, even if the EPA concluded that CAA section 112(n)(1) authorized a different approach for regulating HAP emissions from U.S. EGUs, the chosen course, which is supported by the CAA (i.e., listing under CAA section 112(c)) requires the agency to regulate under CAA section 112(d) consistent with the statute and case law interpreting that provision. In any case, the EPA disputes that the 2000 Finding was limited as commenters suggest for the reasons set forth in the preamble to the proposed rule and, furthermore, the agency has conducted new analyses of HAP emissions from HAP emissions from U.S. EGUs that demonstrate it remains appropriate and necessary to regulate EGUs under CAA section 112.
d. Comments stating that the 2000 Finding was required to go through notice and comment.
Comment 200: Commenters 17840 and 17931 state that the EPA's 2000 determination has never been "fully ventilated" in front of the D.C. Circuit and therefore the EPA's authority to regulate EGUs under CAA section 112(d) is directly at issue in the preamble to the proposed rule.
Comment 201: Multiple commenters (17724, 17728, 17656, 17740, 17876, 17383, 17712, 17877) state that the 2000 Finding that it was appropriate and necessary to regulate EGUs under CAA section 112 failed to go through public notice and comment. According to the commenters, CAA section 307(d)(1)(C) together with CAA section 112(n)(1)(A) requires that any decision made under CAA section 112(n) must go through public notice and comment. The commenters further stated that the failure to undertake this non-discretionary requirement means that final promulgation of this MACT is outside the EPA's statutory authority.
Comment 202: Commenter 17730 states that the 2000 Finding ignored the plain English directive from Congress and the administrative guidance set out in the Clinton Administration's EO 12866.
Comment 203: Commenter 17689 states that the 2000 rule did not provide an opportunity for interested parties to comment on a rule having immense implications on the utility industry from at least cost and reliability standpoints.
Comment 204: Commenters 18034 and 18023 state that in the 2000 Finding the EPA did not allow for public comment and did not define their interpretation of the terms "appropriate and necessary" in making the finding under CAA section 112(n)(1)(A). According to the commenters, the EPA's attempts to provide after the fact support for its 2000 Finding with new legal analysis and new factual information is contrary to New Jersey v. EPA which held that the EPA may not revisit its 2000 Finding except through delisting under CAA section 112(c)(9).
Comment 205: Commenters 17885 and 17383 state that interested parties had no opportunity to comment on at least three major and critical issues posed in the 2000 final rulemaking: first, whether the EPA's interpretation of CAA section 112(n)(1)(A) regarding the specific requirements of the mandatory study provisions was correct, or at least not arbitrary; second, whether the EPA's scientific conclusions of the hazardous associated with HAP emissions from U.S. EGUs was correct, or at least not arbitrary; and third, whether the EPA's interpretation of "necessary and appropriate" requisite under CAA section 112(n)(1)(A) to regulating HAP emissions from U.S. EGUs under CAA section 112 was correct; or at least not arbitrary.
Comment 206: Commenter 17909 states that the EPA failed to meet its statutory obligations under CAA section 307(d)(1)(c) in issuing the 2000 Finding and the current proposed rule does not remedy the EPA's failure to provide the public an opportunity to comment on it and the underlying data and methodology. According to the commenter, in contrast to the 2000 Finding, the 2005 Finding concluding it was not "appropriate" to regulate U.S. EGUs under CAA section 112, was reasoned and proper; this proposed rule reverts back to the 2000 Finding without adequate explanation or support.
Comment 207: Commenter 14368 states that the EPA's 2000 Finding should be reviewed once again when the EPA issues actual NESHAP.
Response to Comments 200 - 207: Commenters are incorrect in their assertions of certain procedural requirements associated with the 2000 listing. The EPA did not violate CAA section 307(d) by not providing notice and comment opportunity before making the Appropriate and Necessary Finding. Commenter UARG challenged the EPA's 2000 Finding and listing on the same grounds and the D.C. Circuit dismissed the case because CAA section 112(e)(4) clearly states that listing decisions cannot be challenged until the agency issues final emission standards for the listed source category. See UARG v. EPA, 2001 WL 936363, No. 01-1074 (D.C. Cir. July 26, 2001). The EPA 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 with a challenge to this final rule. Commenters could have also commented on the CAA section 112(n)(1) studies (e.g., the Utility Study and the Mercury Study) as they were included in the docket, but the EPA is not aware of any comments on those studies. In any case, these studies were peer reviewed and considered the best information available at that time. The EPA fully complied with the rulemaking requirement of CAA section 307(d).
The EPA also disagrees with commenters' characterization of the New Jersey case. The D.C. Circuit did not say as one commenter suggested that the EPA is not able to consider additional information that is collected after the 2000 Finding; instead, the Court stated that the EPA could not just revise its Appropriate and Necessary Finding and remove EGUs from the CAA section 112(c) list without complying with the delisting provisions of CAA section 112(c)(9). See New Jersey, 517 F.3d at 582-83. The EPA also disagrees with the commenter's assertion that the EPA disregarded EO 12866 when making the 2000 Finding. As stated in the Federal Register notice, the 2000 Finding did not impose regulatory requirements or costs, and the finding was reviewed by the Office of Management and Budget (OMB) in accordance with the EO. 65 FR 79831. In any case, noncompliance with the EO would not invalidate the EPA action under the CAA.

1C - New Technical Analyses: General Comments
1. Agreement that new analyses confirm that it remains appropriate and necessary to regulate HAP emissions from U.S. EGUs under CAA section 112 of the CAA.
Commenters: 17620, 17648, 19536, 19537, 19538
Comment 1: Commenter 17620 believes that the data obtained from the most recent round of industry testing support emissions standards at least as stringent as those proposed by the EPA. The commenter notes that the technology needed to meet these standards has been in use in this sector for 10 to 40 years, and has been shown to be effective and affordable. The commenter also points out that the determination of whether Hg emissions from this sector should be regulated has been the subject of two in-depth EPA reviews, as well as a review by the National Academy of Sciences (NAS).
Comment 2: Commenter 17648 agrees that regulating EGUs under CAA section 112 on the basis of today's facts remains appropriate and necessary. The commenter notes that it is particularly appropriate to regulate EGUs under the facts in existence today because emissions control technology has been further developed. According to the commenter, use of Trona and dry sorbent injection has provided proven and cost-effective control of acid gases, and the stabilization of natural gas prices over the last decade due to the development of abundant shale gas supplies has made fuel switching and switching dispatch to underutilized combined cycle plants more feasible. Moreover, the commenter states, imposition of toxics controls by increasing numbers of stated makes a uniform federal requirement that levels the playing field even more of an imperative today than in 2000.
Commenter 17648 notes that environmental effects from Hg emissions, the creation of "hotspots" from the deposition of Hg in concentrated areas around individual EGUs, and the potential for re-emission of Hg all bolster the basis for regulating HAP emissions from U.S. EGUs under CAA section 112.
Comment 3: Several commenters (19536, 19537, 19538) state that the new technical analyses reaffirm the 2000 Finding that regulation of toxic air pollution from U.S. EGUs under CAA section 112 is appropriate and necessary. One commenter states that the new technical analyses incorporate present and future projections of HAP emissions, modern air pollution modeling tools, current control technologies, and updated pollutant emissions regulations. According to the commenter, the results clearly demonstrate that not only was the 2000 decision justified at the time, but that 11 years later, the science shows that it is even more critical to regulate HAP emissions from U.S. EGUs.
The commenter goes on to state that the EPA's 2000 Finding and contemporaneous listing decision were fully supported at the time they were made, and new studies performed since 2000 provide further support for the decision to regulate HAP emissions from this industry. According to the commenter, because the CAA makes clear that listing a source category is not judicially reviewable until issuance of final CAA section 112 emissions standards (section 7412(e)(4)), the EPA clearly may augment and supplement its original 2000 Appropriate and Necessary Finding with subsequent information, analysis and arguments to support and reaffirm that earlier finding. The commenter states that there is nothing in the CAA that freezes in time the Appropriate and Necessary Finding made in 2000, nor is there any prohibition on the EPA's ability to supplement and update that finding up until the time that it issues final emissions standards for EGUs. Indeed, states the commenter, the natural reading of CAA sections 112(n)(1)(A) and 112(e)(4) together make clear that the D.C. Circuit will review both the Appropriate and Necessary Finding and the related listing decision based upon the administrative record associated with issuance of final MACT emissions standards for EGUs.
Response to Comments 1 - 3: The EPA agrees that the new technical analyses (e.g., the risk assessments and the technology assessment) confirm the 2000 Appropriate and Necessary Finding. The Hg Risk TSD was peer reviewed by the EPA's independent Science Advisory Board (SAB) during the public comment period, and the panel assigned to review the assessment concluded "the design of the risk assessment [w]as suitable for its intended purpose, to inform a decision-making regarding an "appropriate and necessary finding" for regulation of HAP from coal- and oil-fired EGUs" (U.S. EPA-SAB, 2011). The risk assessment methodology for the non-Hg case studies was consistent with the methodology that the EPA uses for assessments performed for Risk and Technology Review rulemakings, which underwent peer review by the SAB in 2009. During the public comment period, the EPA also completed a letter peer review of the methods used to develop inhalation cancer risk estimates for Cr and nickel compounds, and those reviews were supportive. The EPA revised both TSDs documenting the two risk assessments consistent with recommendations from the peer reviewers as part of the final rulemaking and has made those revised TSDs available in the rule docket. Although these new analyses were not required, the EPA agrees that it was authorized to conduct additional analyses to confirm the 2000 Finding. The EPA also agrees with the commenters that the 2000 Finding was valid at the time it was made based on the CAA section 112(n)(1) studies and other information available to the agency at that time. The public has been provided a fair opportunity to evaluate both the 2000 Finding and the new assessment, each of which independently support the listing of coal- and oil-fired EGUs.
Comment 4: Commenter 17620 states that the substantial reductions in Hg, HCl, PM2.5 and SO2 that are projected by the Integrated Planning Model (IPM) analyses are needed to protect public health and to improve the environment.
Response to Comment 4: The EPA agrees that the final rule will lead to substantial reductions in HAP emissions from U.S. EGUs and that control of the HAP will lead to public health and environmental benefits as discussed in the RIA.
Comment 5: Commenter 17648 notes that the EPA's Hg Risk TSD confirms that the risk from Hg emitted from U.S. EGUs at 2010 levels that deposits in watersheds, bio-accumulates in fish tissue, and is consumed by humans, thereby threatening public health. The commenter also states that other studies conducted since the Finding confirm that there are serious health risks to the developing fetus from MeHg exposure and that more MeHg is distributed to the fetus than was previously estimated, increasing the prospect for neurological deficiencies in newborns. According to the commenter, this risk to human health alone justifies regulating EGUs under CAA section 112.
Response to Comment 5: Based on the results of the Hg risk assessment set forth in the Hg Risk TSD, the EPA agrees that Hg emissions from U.S. EGUs pose a hazard to public health that warrants regulation under CAA section 112. The revised Hg Risk TSD provides analyses that increase our confidence in the results presented in the Hg Risk TSD.
Comment 6: Commenter 17648 also states that non-Hg HAP emissions from poorly controlled EGUs present a risk to human health and the environment warranting regulation under CAA section 112. The commenter notes that EGUs are the predominant sources of HCl and HF emissions in the U.S., as well as the leading or a major source of other non-Hg HAP, including arsenic, antimony, Cr, nickel, and Se which adversely affect human health. The commenter also notes that emissions of HF, HCl, and toxic metals such as antimony, arsenic, beryllium, cadmium, Cr, cobalt, lead, manganese, nickel, and Se, which are contained in PM2.5, cause severe respiratory problems, cancer, neurological and organ damage, and adverse reproductive effects. In addition, the commenter points out that HCl exposure has been shown to irritate and restrict the airways of asthmatics, and both HCl and HF irritate and damage eye tissue, nasal passages, and lungs; that fine PM, which includes most non-Hg metals emitted by coal-fired EGUs, are smaller than the width of a human hair and, when inhaled, may deposit along the respiratory tract or penetrate deeply into the lungs from where they can enter the bloodstream; that as a result, inhalation of fine PM is recognized to cause cardiovascular effects, including heart attacks, and can cause inflammation of lung tissue; that more generally, studies demonstrate that people living in cities with higher fine particle pollution levels have lower life expectancies than people living in cities with cleaner air; and that studies of individuals exposed to fine PM reflect that exposure to PM2.5 correlates with markers of cardiovascular damage, including irregular heartbeat and pulmonary and systemic inflammation. The commenter stated that because of these health effects, the EPA has ample evidence to support a determination that non-Hg HAP emissions present a risk to human health.
Response to Comment 6: Based on the results of the Non-Hg Case Study Chronic Inhalation Risk Assessment and other analyses, the EPA agrees non-Hg HAP emissions from U.S. EGUs pose a hazard to public health that warrants regulation under CAA section 112. Moreover, HAP from U.S. EGUs pose a hazard to the environment.
Comment 7: Several commenters (19536, 19537, 19538) note that three distinct quantitative and qualitative technical analyses were conducted by the EPA that determined HAP emissions from U.S. EGUs contributed to the risk of adverse effects to public health or the environment; these were: (i) EPA's revised Hg Risk TSD; (ii) EPA's case studies of cancer and non-cancer inhalation risks for non-Hg HAP; and (iii) EPA's qualitative assessment of potential environmental risks from deposition of HAP. One commenter states that the results from all three risk analyses conducted indicate that HAP from U.S. EGUs pose hazards to public health and the environment.
Response to Comment 7: The EPA agrees that HAP emissions from U.S. EGUs pose a hazard to public health that warrants regulation under CAA section 112. Moreover, HAP from U.S. EGUs pose a hazard to the environment.
2. Disagreement that new analyses confirm that it remains appropriate and necessary to regulate HAP emissions from U.S. EGUs under CAA section 112 of the CAA.
Commenters: 17712, 17834, 17877, 18443, 18023
Comment 8: Commenter 17712 states that in EPA's 2000 decision they found "plausible links" of health effects of all man-made sources of Hg, and "potential concerns" of health effects of certain metal emissions, dioxins and acid based aerosols. According to the commenter, the EPA may have realized that this finding did not provide justification to regulation EGUs under CAA section 112 and therefore the EPA provided a new analysis. The commenter asserts that none of these evaluations demonstrates that EGU regulation under CAA section 112 is necessary and appropriate.
Response to Comment 8: The EPA disagrees with the commenter's implication that the EPA conducted the new appropriate and necessary analysis 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 at that time. Further, the EPA maintains that had it complied with the statutory mandate to issue CAA section 112(d) standards within 2 years of listing EGUs, no additional analysis would have likely been conducted to support the listing. The EPA conducted the new analyses because the agency recognized that given the considerable lag in time between listing EGUs and proposing standards it was reasonable to confirm that it remains appropriate and necessary to regulate EGUs under CAA section 112. In conducting the new analysis, the EPA corrected errors that affected the 2005 analysis finding that it was neither appropriate nor necessary to regulate EGUs under CAA section 112 and used updated information to support the finding.
Comment 9: Commenters 17712 and 18443 state that for acid gases, especially HCl and HF, the EPA identified no study or rational basis to demonstrate concrete health concerns associated with these types of emissions. According to the commenters, the fact that the EPA Administrator "remains concerned" about potential effects of these acid gases falls far short of any reasonable appropriate and necessary basis to regulate them under CAA section 112. The commenters state that for non-Hg HAP, the EPA produced one study on chronic inhalation risk assessment that identified three sites with cancer risks greater that one in one million for hexavalent Cr; the study was authored by EPA staff, has not been peer reviewed, and raised numerous critical issues fundamental to its validity. For example, state the commenters, surrogate speciated Cr emissions data were used at the study sites instead of actual emissions information, emissions factors were derived where site unit data was unavailable, in some cases the units were assumed to run 100% of the time which is impossible, dispersion modeling was used that is biased towards over-predicting downwind impacts, and estimated ambient concentrations were utilized as substitutes for real exposure concentrations for all people within a census block. In short, state the commenters, the study was nothing more than a rough synthetic attempt at ascertaining the EPA-desired individual risk information.
Commenter 17712 concludes that the EPA's conclusions appear inconsistent with other research efforts and are highly suspect, especially considering the study's shortfalls as cited above. Even if taken as accurate representation, the commenter believes the results hardly demonstrate that it is necessary and appropriate to regulate HAP emissions from coal-fired U.S. EGUs under CAA section 112 because three sites nation-wide show risks greater that one in one million with the highest at eight in one million.
Response to Comment 9: The commenter makes much of the fact that the EPA identified at proposal only three coal-fired EGU facilities that had a maximum cancer risk greater than 1 in a million, the level below which sources may petition to delist under CAA section 112(c)(9)(B)(i), but the commenter fails to note that the finding was based on an analysis of only sixteen case study facilities and the total number of facilities with risks greater than 1 in a million was four. Furthermore, an additional four of the 16 case study facilities showed maximum cancer risks equal to 1 in a million. In these assessments, the EPA only quantified the risk attributable to the EGU facility itself without considering the location of the facility and the other HAP-emitting facilities that may be located in sufficiently close proximity to exacerbate the cancer risks for the exposed population. Cumulative HAP inhalation risks for the population near these facilities could be substantially greater. As stated at proposal, the EPA concludes it is unreasonable and unrealistic to view HAP emissions from U.S. EGUs emissions as if they occur in a bubble because that is not the manner in which the public is exposed to HAP emissions. In sum, the EPA maintains that the level of risk from non-Hg metallic HAP from U.S. EGUs alone makes it appropriate and necessary to regulate such sources under CAA section 112(d) and that is before even considering the total HAP risk for affected populations. This determination is consistent with the valid interpretation of CAA section 112(n)(1) set forth in the preamble to the proposed rule.
Concerning the acid gas HAP, the EPA disagrees with the notion that each HAP emitted by U.S. EGUs requires its own separate Appropriate and Necessary Finding. Furthermore, in the inhalation case studies, the EPA was only able to quantify the portion of the acid gas risks that might be attributable to hydrogen chloride and HF emissions. While these estimated risks (which are associated with chronic non-cancer impacts, but not cancer) by themselves were not very high, the EPA noted that they carry the potential to combine with other respiratory irritants from other nearby sources to create cumulative exposures of concern to nearby residents. The EPA also noted the sheer tonnage of HCl emitted by all EGUs nationally as a potential concern, as there was the potential for these emissions to acidify natural environments. Additionally, the EPA was not able to get quantitative emission information about the other acid gases (including chlorine and HCN), some of which are more potent respiratory irritants than HCl. As a result, the EPA continues to be concerned about the potential impacts of acid gas emissions from U.S. EGUs.
The EPA disagrees that the case study analysis for non-Hg HAP is not valid. The EPA's dispersion modeling of the case study facilities was performed consistent with EPA's Guideline on Air Quality Models, and used:
   1)    5 years of recent meteorological data from the weather station nearest to each facility, rather than 1 year of meteorological data. This is more representative of long-term (i.e., lifetime) exposures and risks.
   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]
The EPA's assessment of the case study facilities for the proposed rule concluded that, out of the 16 case studies, 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 partly based on comments received, and the results indicate that five coal-fired facilities and one oil-fired facility had estimated lifetime cancer risks greater than one in a million.
Regarding peer review, the risk assessment methodology for the case studies was consistent with the methodology that the EPA uses for assessments performed for Risk and Technology Review rulemakings, which underwent peer review by the SAB in 2009. Also, in July 2011, the EPA completed a letter peer review of the methods used to develop inhalation cancer risk estimates for Cr and nickel compounds, and the reviews were supportive. The EPA also disagrees that units were assumed to operate 100% of the time. The dispersion modeling performed for the case study facilities used hourly heat input as a temporalization factor for estimating hourly emissions, and in some cases hourly heat inputs (and emissions) were zero or very low.
The 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 the EPA took to estimate the maximum individual risk (MIR). The MIR is defined by EPA's Benzene NESHAP regulation of 1989 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). 54 FR 38044. The MIR is the risk metric associated with the determination of whether or not a source category may be delisted from regulatory consideration under CAA section 112 (112(c)(9)). The MIR is the risk metric used to characterize the inhalation cancer risks associated with the case study facilities. To evaluate the MIR, the EPA used the estimated 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 that census block. The EPA used this approach to estimate MIR values in all of its risk assessments to support risk-based determinations and rulemakings under CAA section 112 of the CAA to date.
Comment 10: Commenter 18023 questions whether acid gas emissions limits proposed for oil-fired units are "appropriate" or "necessary." The commenter asserts that the EPA's preamble and the health studies referenced in it do not provide any compelling evidence of a health concern arising from acid gas emissions from oil-fired units. Rather, states the commenter, the EPA's entire discussion of the possible health concerns associated with the emissions from oil-fired units focuses solely on nickel emissions, and the EPA admits that significant uncertainty remains as to whether those emissions present a health concern as well. The commenter goes on to say that nickel emissions from oil-fired EGUs contributed most to the potential cancer-related inhalation risks, but those risks were not high. According to the commenter, the non-cancer risk assessment due to inhalation exposure indicated exposures were well below the reference levels. The commenter states that in discussing its findings (in the 2000 Appropriate and Necessary Finding), the EPA also noted that uncertainties remained concerning the extent of the public health impact from HAP emissions from oil-fired units.
Response to Comment 10: The EPA does not agree with the commenter's implication that the EPA must make a separate appropriate and necessary finding for each HAP emitted by U.S. EGUs before the agency may list and regulate EGUs under CAA section 112. The EPA's interpretation of CAA section 112(n)(1) is set forth in the preamble to the proposed rule and it is reasonable. Under that interpretation, the agency concludes that it may list EGUs under CAA section 112(c) if it determines that even one HAP emitted from U.S. EGUs poses a hazard to public health or the environment that will not be addressed through imposition of the requirements of the CAA. 76 FR 24988. Once the agency lists EGUs under CAA section 112(c), it must regulate such units under CAA section 112(d) unless the agency can delist such sources, which the EPA's risk analyses demonstrates is not possible. The D.C. Circuit Court has stated that the 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).
Furthermore, the EPA reasonably concluded that it was appropriate and necessary to regulate oil-fired EGUs in 2000 and the EPA confirmed that conclusion was proper with the analysis set forth in the preamble to the proposed rule. The commenter appears to take issue with the determination based on its view of how the agency can and should exercise its discretion. The EPA disagrees and stands by the determination for the reasons set forth in the preamble to the proposed rule. The EPA's determination that the maximum cancer risks posed by emissions of oil-fired EGUs are greater than 1 in a million, owing primarily to emissions of nickel compounds, is well-founded based on the available information. See discussion of the peer review of the methods for estimating nickel and Cr risks below.
Concerning the acid gas HAP, in the EPA's inhalation case study assessments, the EPA was only able to quantify the portion of the acid gas risks which might be attributable to HCl and HF emissions. While these estimated risks (which are associated with chronic non-cancer impacts, not cancer) by themselves were not very high, the EPA noted that they carry the potential to combine with other respiratory irritants from other nearby sources to create cumulative exposures of concern to nearby residents. The EPA also noted the sheer tonnage of HCl emitted by all EGUs nationally as a potential concern, as was the potential for these emissions to acidify natural environments. Additionally, the EPA was not able to get quantitative emission information about the other acid gases (including chlorine and HCN), some of which are more potent respiratory irritants than HCl. As a result, the EPA continues to be concerned about the potential impacts of acid gas emissions from U.S. EGUs.
Comment 11: Commenter 17834 argues that the EPA does not have the authority to rely on "additional technical analyses." The commenter states that CAA section 112 is clear: the agency is to make the "appropriate and necessary" finding on the basis of the Utility Study alone. The decision to consider additional technical analyses is one of many ways in which the EPA unreasonably stretched the language of CAA section 112. The commenter also points out that the EPA highlights the "very strict deadlines" Congress provided in CAA section 112 as justification for their current imposition of the Utility MACT rule. According to the commenter, the EPA's justification is belied by the fact that the studies upon which the proposed rule relies were ordered more than 20 years ago and were finally completed more than 10 years ago. The commenter states that promptness was necessary not only to get the HAP issue resolved but also to make certain that costly regulation of power generators was undertaken only in light of timely, accurate information. According to the commenter, imposing costly regulation upon the power generating industry on the basis of stale data that does not account for the current regulatory landscape is unreasonable and will not withstand legal challenge.
Response to Comment 11: The EPA disagrees with the commenter's assertion that the EPA may only consider the Utility Study in determining whether it is appropriate and necessary to regulate EGUs under CAA section 112 for the reasons set forth in the preamble to the proposed rule. Commenter provides no legal basis that would cause us to reconsider the conclusion concerning the consideration of information when evaluating whether it is appropriate and necessary to regulate HAP emissions from U.S. EGUs. The EPA also disagrees with the commenter's interpretation of the basis for the Finding to the extent the commenter believes the Finding was at all based on "very strict deadlines" in CAA section 112. The EPA's 2000 and 2011 findings are based on the hazards to public health that HAP emissions from U.S. EGUs pose. The EPA notes the strict deadlines as an indication that Congress expected prompt action to evaluate and, if appropriate and necessary, regulate HAP emissions from U.S. EGUs and that the agency has not fulfilled that directive. The EPA does not agree with the commenter's characterization of why Congress wanted prompt action and it provided no support for its conclusion so the EPA need not address it further.
As the EPA stated in the preamble to the proposed rule, the 2000 finding was valid at the time it was made based on the information available to the agency at that time, including the Utility Study. The EPA conducted new analyses because over 10 years had passed since the 2000 Finding, and the EPA wanted to evaluate HAP emissions from U.S. EGUs based on the most accurate information available, though the agency was not required to reevaluate the 2000 Finding. This conclusion based on the new data is that it remains appropriate and necessary to regulate HAP emissions from U.S. EGUs. Finally, the EPA disagrees with the commenter's assertion that the agency is not authorized to consider new information and at the same time unable to use the information available because it is "stale." Under this theory, the agency could not ever make an Appropriate and Necessary Finding prospectively, thereby excusing the agency from its obligations to protect public health and the environment because it did not diligently act in undertaking its statutory responsibilities. This is an illogical result that finds no basis in the statute.
Comment 12: Commenter 17877 notes that the 2000 decision only found "plausible links" of health effects of all man-made sources of Hg, and "potential concerns" of health effects of certain metal emissions, dioxins and acid based aerosols. The commenter states that even assuming there is validity in these findings, none of these findings individually or in combination is adequate justification to regulate EGU emissions under CAA section 112. The commenter also states that none of the analyses performed for acid gases, non-Hg HAP and Hg demonstrate that EGU regulation under CAA section 112 is necessary and appropriate.
Response to Comment 12: The EPA disagrees with the commenter's interpretation of the information available that supported the 2000 Finding for the reasons set forth in the preamble to the proposed rule, and the EPA is not revising these conclusions. The EPA has considerable discretion when evaluating hazards to public health and the environment and we decline to adopt commenter's view of the information. The EPA also disagrees with commenter's conclusions to the extent they are directed at the new technical analyses. The Hg Risk TSD and the Non-Hg Case Study Chronic Inhalation Risk Assessment were both peer reviewed during the public comment period and both showed that HAP emissions from U.S. EGUs pose a hazard to public health. Moreover, HAP from U.S. EGUs pose a hazard to the environment. The EPA revised both TSDs documenting the two risk assessments consistent with recommendations from the peer reviewers as part of the final rulemaking and has made those revised TSDs available in the rule docket.
3. Adequacy of data quality and documentation for new technical analyses.
Commenters: 17751, 10167, 10569, 6543
Comment 13: Commenter 17751 states that the proposed rule does not conform to the Information Quality Act (IQA) or the EPA's guidelines implementing the IQA. According to the commenter, objectivity related standards of the IQA require that information relied on by the EPA be accurate, reliable, unbiased, and presented in a complete and unbiased manner. The commenter notes that the report by Willie Soon supports a finding that the data upon which the EPA relies is "incomplete and inaccurate." See Willie Soon, PhD, A Scientific Critique of the Environmental Protection Agency's "National Emission Standards for HAP [NESHAP] from Coal- and Oil-fired Electric Utility Steam Generating Units and Standards of Performance for Fossil-Fuel-Fired Electric Utility, Industrial-Commercial-Institutional, and Small Industrial- Commercial-Institutional Steam Generating Units" Proposed Rule (March 16, 2011)  -  Focusing on the Hg Emission Issues, June 2011.
Response to Comment 13: The EPA strongly disagrees with the commenter. The 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 this regulation. In addition, the EPA submitted the Hg Risk TSD to the SAB, which reviewed the analysis and "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 Hg emitted from U.S. EGUs" (U.S. EPA-SAB, 2011). The SAB received the comments from Willie Soon, and had those comments available for consideration in their deliberations regarding the Hg Risk TSD. The SAB provided substantial comments and recommendations, however, none of the comments or recommendations challenged the fundamental information relied upon by the EPA, and in fact, the SAB specifically supported a number of the elements of the analysis that were the subject of criticisms by Willie Soon. Two of these are discussed here as examples. One of Willie Soon's major criticisms is the use of the EPA's RfD for MeHg as a benchmark for risk. On this matter, the SAB specifically "agrees that EPA's calculation of a hazard quotient for each watershed is appropriate as the primary means of expressing risk because it is based on an established RfD for MeHg that reflects a range of potential neurobehavioral effects" (U.S. EPA-SAB, 2011). A second major criticism from Willie Soon is that "EPA proposal neglects key scientific knowledge and many peer reviewed papers that suggest there is no straightforward connection between Hg emissions from power plants or other man-made sources to the Hg level in fish." Again, the SAB specifically "agrees with the Hg Maps approach used in the analysis and has cited additional work that supports a linear relationship between Hg loading and accumulation in aquatic biota. These studies suggest that Hg deposited directly to aquatic ecosystems can become quickly available to biota and accumulated in fish, and reductions in atmospheric Hg deposition should lead to decreases in MeHg concentrations in biota." The EPA thus rejects the commenters' statements that the data used in the Hg Risk TSD is "incomplete and inaccurate" and therefore rejects the statement that the proposed rule does not conform to the IQA.
In addition, the risk assessment methodology for the non-Hg case studies is consistent with the methodology that the EPA uses for assessments performed for Risk and Technology Review rulemakings, which underwent peer review by the SAB in 2009 (U.S. EPA-SAB, 2010). During the public comment period, the EPA also completed a letter peer review of the methods used to develop inhalation cancer risk estimates for Cr and nickel compounds, and those reviews were supportive. For the final rulemaking, the EPA revised both risk assessments consistent with recommendations from the peer reviewers. The EPA relies on the SAB's review of the quality of the information supporting the analytical results. Accordingly, contrary to the commenters' assertions, the EPA acted consistently with the Information Quality Act as well as EPA and OMB's peer review requirements.
Comment 14: Commenters 10167 and 10569 state that the agency has not provided information on risk assessment, which is a key component to the proposal.
Response to Comment 14: The EPA disagrees that it has not provided information on the risk assessments. Although the commenters do not specify which risk assessment they are referencing, both the Hg and Non-Hg risk assessments were fully documented on the EPA's website and the docket including all underlying datasets.
Comment 15: Commenters 6543 and 10943 state the following files should be provided and then additional time given for review and comment:
From the ICR
a. The original contractor test reports associated with the Part II ICR data;
b. Additional ICR Part III documentation, such as the complete contractor test reports and the laboratory reports appended to the ERT.
Items related to the Hg Risk TSD, the RIA, and the Air Quality Modeling TSD
a. All input and surface layer output files and analyses of all CMAQ simulations performed as part of this rule;
b. Data summaries similar to those presented on pages 31 to 58 of the Hg Risk TSD for the 2005 EGU zero-out case, the 2016 base case, the 2016 zero-out case, and the 2016 rule case;
c. Underlying data sets, extractions thereof, and spreadsheets from which the EPA calculated and prepared the following summary tables and figures:
   i. Within the Hg Risk TSD:
               *          Tables ES-1 to ES-5,
               *          Tables 2-1 to 2-15,
               *          Figures 2-1 to 2-18,
               *          Figures G-1 and G-2 and Table G-1
   ii. Within the RIA:
               *          Figures 4.2 to 4.6,
               *          Tables 5-2 to 5-19,
               *          Figures 5-11 to 5-13
   iii. Within the Air Quality Modeling TSD:
               *          Tables 111-1 to 111-3,
               *          Integrated 12-km model output Hg deposition file,
               *          HUC-12 Hg deposition file.
Commenters 6543 and 10943 add that there are numerous key endpoints that use the information in different ways; therefore, it would also be critical to include a step-by-step description of the process and spreadsheets leading to each endpoint, including the following:
* Maps and tables showing projected annual PM2.5, daily PM2.5, and ozone design values for the 2016 base and 2016 rule case
Items related to EPA's Integrated Planning Model (IPM)
* IPM parsed files for the ToxR Base Case illustrating the assigned emission controls and emission rates for each unit;
*  IPM parsed files for the ToxR Policy Case illustrating the assigned emission controls and emission rates for each unit;
Item related to EPA's Beyond the Floor Determination for new source IGCC
* EPA's analysis that takes into account costs, energy, and non-air quality health and environmental impacts relating to going beyond the floor for new source IGCC.
Commenter 17627 recommends that the EPA reset the 60-day comment period when revised data or additional supporting information is made publicly available. The commenter adds that the posting of support documents during the comment period does not provide commenters with sufficient time to evaluate the impact of the support documents on the rule. The commenter gives the following examples:
a. Air Quality Modeling Technical Support Document: Point Source Sector Rules, posted June 16, 2011;
b. List of facility/unit Hg stack emission averages from the EU MACT ICR Parts II and III, posted June 30, 2011;
c. Clarification and updating of Hg deposition maps provided in the Hg Risk TSD, posted July 1, 2011.
Response to Comment 15: The EPA disagrees with the commenters that the data underlying the proposed rule were not made sufficiently available. Below we identify the docket identification number for each requested dataset, all of which were either posted at proposal or with more than 30 days remaining in the public comment period.
* Original contractor test reports associated with the Part II ICR data: All docketed separately by company name with multiple docket entries for each EGU's ICR data submittals, posted in February and March 2011.
* Additional ICR Part III documentation, such as the complete contractor test reports and the laboratory reports appended to the ERT: EPA-HQ-OAR-2009-0234-10827, posted on 05/23/11. Although this information posted to the docket after proposal, this documentation simply reformatted data already available in the docket in the individual data submittals provided by the companies through the ERT; these individual ICR/ERT submittals are in the docket under multiple entries (by unit) for each company and were made available prior to proposal.
* Input and surface layer output files and analyses of all CMAQ simulations: Docket EPA-HQ-OAR-2009-0234-2989, posted on 5/3/2011.
* Data summaries for the 2005 EGU zero-out case, the 2016 base case, the 2016 zero-out case, and the 2016 policy case Hg Risk TSD: EPA only generated these specific data summaries for the 2005 and 2016 base case because these specific data summaries were not relevant to the Hg Risk TSD. However, these data summaries can be generated from the data in EPA-HQ-OAR-2009-0234-3079, posted on 5/3/2011. The 2005 and 2016 base case summaries are provided in the Hg Risk TSD.
* Underlying data sets for the Hg Risk TSD: Docket EPA-HQ-OAR-2009-0234-3074 and EPA-HQ-OAR-2009-0234-3079, both posted on 5/3/2011.
* Underlying data sets for the Air Quality Modeling and Hg Benefits in the RIA: AQ modeling data in Docket EPA-HQ-OAR-2009-0234-2989 on 5/3/2011. Hg benefits data mostly consistent with Hg Risk TSD data in Dockets EPA-HQ-OAR-2009-0234-3074 and EPA-HQ-OAR-2009-0234-2989, both posted on 5/3/2011. Additional RIA-specific information in Docket EPA-HQ-OAR-2009-0234-13662, posted on 6/7/11. Although the RIA-specific information was posted to the docket after proposal, it did not contain data relevant to the Hg Risk TSD. Underlying data sets for the Air Quality Modeling TSD: Can be generated from CMAQ output files in Docket EPA-HQ-OAR-2009-0234-2989, posted on 5/3/2011.
* Maps and tables of projected PM2.5 and ozone design values: Can be generated from CMAQ output files in Docket EPA-HQ-OAR-2009-0234-2989, posted on 5/3/2011, in conjunction with publically available data and software. Because absolute design values were not relevant to the rulemaking, EPA did not generate these absolute estimates, only the change in design values between the baseline and policy scenario presented in the RIA. Note: IPM does not estimate ambient levels of pollution or design values.
* IPM parsed files for the ToxR Base Case: Docket EPA-HQ-OAR-2009-0234-3032, posted on 5/3/2011.
* IPM parsed files for the ToxR Policy Case: Docket EPA-HQ-OAR-2009-0234-3033, posted on 5/3/2011.
* Air Quality Modeling Technical Support Document: Point Source Sector Rules: Docket EPA-HQ-OAR-2009-0234-2988, posted on 5/3/2011, but also posted on EPA website (http://www.epa.gov/ttn/atw/utility/utilitypg.html) on 6/30/11.
* List of facility/unit Hg stack emission averages from the EGU MACT ICR Parts II and III: EPA-HQ-OAR-2009-0234-15896 on 7/7/2011, but also posted on EPA website (http://www.epa.gov/ttn/atw/utility/utilitypg.html) on 6/30/2011. Although this information posted to the docket after proposal, this documentation simply reformatted data already available in the docket in the individual data submittals provided by the companies through the ERT; these individual ICR/ERT submittals are in the docket under multiple entries (by unit) for each company and were made available prior to proposal.
* Clarification and updating of Hg deposition maps provided in the Hg Risk TSD: Docket EPA-HQ-OAR-2009-0234-15522, posted on 7/5/2011, also posted on SAB website (http://yosemite.epa.gov/sab/sabproduct.nsf/MeetingCal/4A60092A413F56608525783F0050F148?OpenDocument) on 7/1/2011, and discussed at SAB teleconference on 7/20/2011. Although these documents were posted to the docket after proposal in response to questions raised during the SAB meeting on 6/15/2011, the use of intermediate maps in the Hg Risk TSD did not affect the risk calculations.
As noted in the preamble to the proposed rule, the EPA has no information on the costs and non-air quality health, environmental, and energy impacts of setting the new source limits for new IGCC units, and EPA solicited comment, including data on costs, emissions data, or engineering analyses. However, the EPA did not receive any data as requested, and, thus, the EPA does not have any datasets as implied by the commenter.
1D - Hg Emissions
1. Hg Emissions from U.S. EGUs.
Commenters: 17627, 17770, 17771, 17775, 18421, 19536, 19537, 19538, 18023
Comment 1: Commenter 17627 states that the 2005 base year did not include emission reductions that have already occurred as a result of many enforceable federal and state programs and that the 2016 emissions are predicated off the IPM related NODA dated October 2010 and do not include results from two subsequent NODAs. According to the commenter, if the emission estimates were corrected the benefits would not be overstated, and it is possible that the rule could not be justified on cost considerations.
Response to Comment 1: The EPA disagrees with the commenter's implication that either the baseline risks or the benefits are overstated based on a 2005 base year. While the EPA agrees that the 2005 Hg emissions may be overestimated, 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 approach used by the EPA to scale fish tissue data would underestimate risk if 2005 Hg estimates were overestimated. Since the 2005 emissions are not used as a starting point for 2016 emissions from IPM, any 2005 overestimate does not affect the 2016 emissions levels. The 2016 emissions are computed by IPM based on forecasts of demand, fuel type, Hg content of the fuel, and the emissions reductions resulting from each unit's configurations. See IPM Documentation for further information. No commenter has provided any evidence that the IPM 2016 emissions projection methodology resulted in an overestimate. The benefits CAA section of the RTC addresses the portion of this comment regarding benefits.
Comment 2: Commenters 17771 and 17775 state that there are questions about the Hg emission estimates used in the Hg TSD for the 2005 and 2016 cases. According to the commenters, the 2005 HAP emission estimates come from the 2005 National Emissions Inventory (NEI) and U.S. coal-fired EGUs emitted 53 tons of Hg in 2005, and the EPA used this estimate as in input to the IPM run that predicted 2016 Hg emissions from U.S. EGUs to be 29 tons per year after implementation of all CAA rules (including the then-proposed Transport Rule) but not the requirements of the EGU MACT. The commenters state that if the 2005 NEI estimate of 53 tons is an over estimate of Hg emissions that would lead to an overestimation of the remaining risk attributable to U.S. EGUs in 2016. In addition, according to the commenters, the EPA's estimate for 2010 Hg emissions from U.S. EGUs based on the 2010 ICR data is 29 tons. The commenters suggest that the 2016 estimate of 29 tons must be incorrect because it is not lower than the 2010 estimate and the installation of scrubbers from the CSAPR would result in lower Hg emissions in the future. The commenters further claim that the EPA has not included the 2010 emissions estimation approach in the public record.
Response to Comment 2: The EPA acknowledges that the current Hg emissions estimate would not be the same as the 2016 Hg emissions estimate given that compliance with CSAPR is anticipated to have some Hg co-benefits. For this reason, the EPA included reflected emission reductions from CSAPR in the mercury deposition modeling for 2016 in the Hg Risk TSD.
The EPA disagrees with the commenters' overall conclusion that the Hg Risk TSD overestimates the risk from U.S. EGUs from Hg for several reasons as follows. The commenter incorrectly assumes that the EPA's 2016 Hg estimate is based on the 2005 Hg estimate that the commenter claimed is an overestimate. The commenter incorrectly concludes that a 2005 overestimate in Hg emissions would overestimate the risk in the 2016 analysis. The commenter improperly questions the EPA's choice of a 2005 modeling year, when this is based on the mid-point of the available fish tissue data. The commenter incorrectly calls into question the EPA's 2016 Hg estimate based on the EPA's 2010 estimate, providing no specific comments on the 2016 IPM emissions approach but rather including speculation of problems. The commenter incorrectly stated that the 2010 Hg calculations were not provided, since these data were provided in the docket on 5/3/2011 through EPA-HQ-OAR-2009-0234-3035. While the EPA agrees that the 2005 Hg emissions may be an overestimate, such an overestimate in 2005 would lead to an underestimate of risk in 2016 and not an overestimate of risk as claimed by the commenter because the ratio approach used by the EPA to scale fish tissue data would underestimate risk if 2005 Hg estimates were overestimated. Furthermore, the commenters provide no alternative emissions data that could be used for 2005 in place of the EPA's approach, so the EPA continued its conservative approach of using a 2005 value that may be somewhat too high. The EPA also agrees that the 2010 and 2016 Hg estimates of 29 tons may seem inconsistent given known expected reductions in emissions, but disagrees that this inconsistency impacts its conclusions on risk from Hg since the 2010 data were not used in the Hg Risk TSD.
The commenters incorrectly assume that the 2016 Hg emissions are an overestimate because they are tied to the 2005 NEI Hg values, which the commenter claimed is an overestimate. This assumption is incorrect, and therefore any overestimates in 2005 emissions would not lead to an overestimate in 2016 emissions. The 2016 emissions are computed by the IPM based on forecasts of demand, fuel type, Hg content of the fuel, and the emissions reductions resulting from each unit's configurations. See IPM Documentation for further information. No commenter has provided any evidence that the IPM 2016 emissions projection methodology result in an overestimate.
Further, the EPA disagrees with the commenters' central assertions that any 2005 overestimate would lead to an overestimate in risk. The 2005 emissions and modeling predict 2005 Hg deposition, and the 2016 base emissions and modeling predict 2016 Hg deposition. The EPA used the ratio of the 2016 deposition to the 2005 deposition to scale the fish tissue Hg levels from the best available data from 2000-2009. Thus, any overestimate of the 2005 Hg emissions would lead to an underestimate of the 2016 Hg fish tissue levels because a smaller 2005 emissions and deposition estimate would give a smaller reduction of the Hg fish tissue data to 2016.
The EPA disagrees with the commenters' assumption that the EPA used a 2005 modeling episode as a representative case for present emissions. The 2005 model year is the midpoint of the fish tissue data (2000-2009) used for the scaling of fish tissue Hg levels.
The EPA agrees with the commenters' claim that the 2005 Hg estimate of 53 tons/year may be an overestimate, but maintains that the 2005 Hg estimate is the best available comprehensive estimate needed for performing the type of modeling needed for this rule. In response to this comment, the EPA reviewed its methodology for estimating the 2005 inventory and has concluded that there could be a modest overestimate. This is because the approach to compute 2005 emissions did not consider changes in control configurations between 1999 and 2005, but rather has scaled the 1999 emissions rates based on changes to unit-level throughput from 1999 to 2005. As another check on the EPA's estimate, the EPA reviewed the Toxics Release Inventory (TRI) data for 2005 and has found that industry-reported emissions of Hg in 2005 were 48 tons/year. As described above, an overestimate in 2005 is a more conservative approach for the overall Hg Risk TSD because of the deposition scaling approach used.
However, the EPA disagrees that a trend from 2010 to 2016 due to the Cross-State Rule should necessarily be evident. As previously mentioned, these were estimated using different methods for different purposes, these estimates have different uncertainties and therefore are difficult to compare when the numbers are relatively close. One important difference is that the 2010 emissions included state Hg rules that lower 2010 emissions, but the 2016 total does not include state Hg rules. The EPA excluded state Hg regulations because the CAA directs the EPA to consider only federal CAA requirements in estimating future risks associated with EGUs. In addition, the significant decrease in demand observed in the industry in 2009 and 2010 will tend to depress the emissions in 2010 relative to the 2016 projections, all else constant, simply as a result of the higher future electricity demand assumed in IPM, which is identical to AEO 2010 projections of net energy for load.
In response to this comment, the EPA further improved its "current base" estimate labeled at proposal as "2010," but representing a 2007-2009 average throughput using current-year facility configuration and emission rates. This estimate is 29 tons/year, which is consistent with the estimate at proposal. The average throughput approach helps to account for the decrease in EGU activity that started in 2008 to allow the EPA to create a representative value for a current-year best estimate. This revised current base Hg estimate represents final emission rates based on the ICR data (i.e., the latest facility configurations), and actual throughputs from the Acid Rain CEMS program rather than the maximum heat inputs and capacity factors used at proposal. In addition to the revised current base, the EPA also computed alternative estimates using the same emission rates (present-day controls) but different throughputs. Using only 2010 throughputs results in an estimate of 27 tons/year, and using 2002 through 2010 average throughputs results in 29 tons/year. The EPA found that from 2007 to 2010, the Hg decreases associated with decreased demand alone is 3.8 tons and from 2007 to 2009 is 5 tons, which supports the EPA's position that even the revised current base estimate using 2007-2009 includes impacts of depressed demand which is not expected to continue at the same low levels and is therefore not reflected in the 2016 estimate.
Further, the EPA disagrees with the commenters' assertion that the IPM Hg emissions estimates in 2016 are "thrown into doubt" by the 2010 emissions estimate. The reason these numbers are inconsistent with expected trends is that different emission estimation methods were used for each inventory. In addition to the different assumption about state rules, it is not possible for the future-year estimation to rely on stack test data because it is forecasting the future, whereas the 2010 method relies a great deal on stack test data. In any case, this inconsistency is not relevant to the core of the Hg Risk TSD since the 2010 emissions are not used in calculating the 2016 to 2005 deposition ratios. Concerns about the 2005 estimates have already been addressed above. Any meaningful comments on the validity of the 2016 Hg estimates need to specifically address concerns with the IPM Hg estimation methods. The EPA addressed all comments on the IPM predictions and has revised emissions estimates accordingly.
In the final rule, the EPA revised the estimate of Hg emissions remaining from U.S. EGUs in 2016, which includes additional emission reductions anticipated from the final CSAPR. The revised estimate shows that U.S. EGUs would emit 27 tons of Hg in 2016.This new IPM modeling for the final rule continues the methodology excludes state Hg regulations. The revised current base estimate is 29 tons/year and does not exclude state Hg regulations. Even given the difficulty comparing these estimates as described above, these revised estimates show a 1 ton decrease, even though the current base estimate reflectsstate Hg regulations in the current base but not 2016 estimate does not. Conclusions about the trend between current emissions and emissions in 2016 are limited by the fact that different methods were used to compute the two estimates, as fully explained in the revised Emissions Overview memo in the docket.
In addition, the EPA considered other data sources to help assess the validity of its 2005 and 2010 emissions estimates. The TRI data submitted by industry includes estimates for 2005 through 2010. The 2005 TRI Hg emissions are 48 tons/year, supporting the EPA's conclusion that its 2005 estimate may be somewhat too high. The EPA notes that the 2010 emissions cited for this rule proposal were actually an average of 2007-2009 throughputs with emission rates from the ICR data. To have a comparable value, the EPA averaged the 2007, 2008, and 2009 TRI Hg emissions from U.S. EGUs (46.9, 44.8, and 35.6 tons/year, respectively), resulting in an estimate of 42 tons/year. Furthermore, the TRI national Hg emissions estimate in 2010 is 31 tons/year, and this value is expected to be an underestimate since the final numbers have not yet been compiled to include emissions from all facilities.
Finally, the EPA disagrees with the comment that the calculations for the 2010 annual emissions were not provided. These calculations were provided in an Excel spreadsheet to the docket on 5/3/2011 [EPA-HQ-OAR-2009-0234-3035]. The spreadsheet lists each unit included in the calculations, the throughput assumed, the emission factor bin, the emission factor, and the resulting Hg emissions for each unit. A readme tab included in the spreadsheet provided additional information about the approach.
Comment 3: Commenter 18421 states that coal-fired power plants were responsible for 72% of Hg air emissions in 2008 and 50 percent of total Hg in the U.S. According to the commenter, by 2005 hospital and medical waste incinerators and municipal waste combustors had reduced their Hg emissions by over 95 percent. In contrast, coal-fired power plants had reduced Hg emissions by only 10% and, today, they persist as the single largest anthropogenic source of Hg air pollution in our nation. The commenter notes that the top 25 emitters of Hg from coal-fired power plants accounted for only eight percent of the country's electric generation in 2008
Response to Comment 3: The EPA agrees with the commenter's assertion that coal-fired power plants are a major source of Hg air emissions in 2008 and that other sectors such as hospital and medical waste incinerators and municipal waste incinerations have reduced their Hg significantly based on other EPA rules. The EPA appreciates the data provided showing that coal-fired power plants have reduced Hg emissions only 10% since 2005, however, other data sources such as industry-provided TRI data show greater reductions (2005: 48 tons; 2009: 36 tons is a 25% reduction). Nevertheless, even larger reductions were considered as part of the EPA's Hg Risk TSD and the EPA concluded that risk still exists from coal-fired power plants.
Comment 4: Commenter 17775 states that there is no indication how the EPA derived emission factors used by the EPA in its IPM runs to estimate future Hg emissions. According to the commenter, Appendix A to CAA section 3 of the RIA contains a detailed list of emissions factors for the three species of Hg (elemental, gaseous ionic and particulate) depending on the control equipment installed on a given unit, and these included factors for control configurations that are fairly rare in the utility industry (such as units equipped with DSI) and the factors included four significant figures. The commenter suggests that without further explanation these factors could result in an overstating Hg emissions and remaining Hg risks in 2016 following full implementation of the existing CAA rules.
Response to Comment 4: The 2016 projected Hg emissions are not based on emissions factors. The 2016 Hg emissions are computed by the IPM based on forecasts of demand, fuel type, Hg content of the fuel, and the emissions reductions resulting from each unit's configurations. See IPM Documentation for further information on demand assumptions, coal supply and Hg content, and Hg emissions reductions.
The speciation factors in the RIA, Chapter 3 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. The data used for the MATS proposal and final rule are the same as the data used for the Clean Air Hg Rule. More information is available in the docket under Hg speciation for EGUs in the "Hg_speciation_summary_CAMR.pdf" and associated spreadsheet.
Comment 5: Several commenters (19536, 19537, 19538) state that EGUs remain the largest source of Hg in the U.S., accounting for approximately half of U.S. anthropogenic emissions and Hg emissions from U.S. EGUs are projected to remain relatively unchanged through 2016. According to the commenters, even in 2016 Hg emissions from U.S. EGUs will be over six times larger than those from the second largest contributing source. Additionally, state the commenters, the significant fractions of oxidized and particulate Hg in Hg emissions from U.S. EGUs make these emissions more relevant to local and regional deposition than natural emissions comprised of elemental Hg.
Response to Comment 5: The EPA agrees with the commenter's statement that EGUs remain the largest source of Hg in the U.S. and that significant fractions of oxidized and particulate Hg in Hg emissions from U.S. EGUs make these emissions more relevant to local and regional deposition than natural emissions comprised of elemental Hg.
Comment 6: Commenter 18023 states that the EPA's indication (on page 31 of the Hg TSD) that "current" or 2010 EGU Hg emissions were 29 tons and would be the same amount in 2016 after full implementation of other existing regulations, in particular CSAPR, cannot be true because neither program would be fully implemented in 2010. Similarly, the commenter notes that page 15 of the Hg TSD the EPA noted "[f]urther modeling of future emissions indicates that in the absence of binding federal regulations U.S. EGU emissions are not likely to be substantially reduced between 2010 and 2016..." According to the commenter, it is unreasonable to conclude that EGU Hg emissions will not decrease further as a co-benefit of other regulations. The confusion over the level of current emissions makes meaningful comment difficult.
Response to Comment 6: See response to Comment 2 above regarding the comparability of the 2010 and 2016 emissions estimates.
The EPA disagrees with the commenter's assertion that the "confusion over the level of current emissions makes meaningful comment difficult." The reason these numbers are inconsistent with expected trends is that different emission estimation methods were used for each inventory. However, this inconsistency is not relevant to the core of the Hg Risk TSD since the 2010 emissions are not used in calculating the 2016 to 2005 deposition ratios. Meaningful comment is therefore relevant only for comments on 2005 and 2016 emissions values and approaches. Comments on the 2005 estimates have already been addressed above. The EPA also addressed all comments on IPM estimation methods and the resulting updated Hg emissions are 27 tons/year, and this value is 2 tons less than the revised current-base ("2010") estimate of 29 tons/year. While uncertainties exist about all emissions estimates, the EPA considered all comments on its estimates and has revised its methods to reflect the best available estimates in both years. The EPA maintains that the commenters are well aware of uncertainties associated with emissions estimation and that such uncertainties are not cause for avoiding review or comment, as evidenced by the numerous relevant comments received by the EPA on emissions values used at proposal.
Comment 7: Commenter 17770 states that the EPA TSDs include an assumption that two of We Energies' plants, the Oak Creek Power Plant and the Valley Power Plant, will be retired in 2015. The commenter states that this assumption is incorrect and should be changed; We Energies has no current plans to retire either of these plants.
Commenter 17770 further states that the EPA's utility sector modeling analyses includes an estimate of unit retirements that will occur as a result of the proposed rule. According to the commenter, the EPA assumes that two of We Energies' plants, the Oak Creek Power Plant and the Valley Power Plant, will be retired in 2015. Again, the commenter states that this assumption is incorrect and should be changed, as We Energies has no current plans to retire either of these plants.
Response to Comment 7: Contrary to commenter's statement, the EPA does not assume that the units referenced by the commenter will retire in 2015. The EPA's IPM modeling represents a national perspective of least-cost electricity dispatch throughout the modeled regions to meet electricity demand, in both base case projections as well as projections with policy constraints (such as the proposed MATS emission rate limitations). The EPA is not making any determination of future unit-level compliance based on these modeling projections; individual unit owners will make their own economic determination of how they wish to comply with the regulation. Unit owners and operators should consider compliance options with the proposed emission rate standards and are advised to weigh the economic merit of each compliance option to minimize costs while achieving compliance in the future.
The EPA's IPM modeling relies on assumptions regarding future electricity demand and available generating capacity in each modeled region. The parsed file disaggregates model results to a unit level and does not necessarily capture all of the relevant unit-level details that a unit owner may account for in the future when determining compliance planning and economic operations. IPM projections represent a least-cost system-wide pattern of generation allowing the agency to determine the overall cost impacts of a potential regulation. In the future, the decision to continue operation with emissions controls, or to cease operation, will be made by each facility according to that owner's determination of economic operation potential.
2. Global Hg emissions.
Commenters: 17254, 17620, 17621, 17756, 17807, 17877, 18014, 18033, 18023
Comment 8: Commenter 17620 states that mandatory Hg emission reductions from the international community are essential if the Hg problem in this country is to be effectively addressed. The commenter states that the U.S. is currently engaged in international efforts to reduce global Hg emissions and that the third session of the United Nations Environment Programme (UNEP) Intergovernmental Negotiating Committee will be held in November 2011 to attempt to prepare a global legally binding instrument for the control of Hg. The UNEP negotiation schedule calls for an agreement to be reached by February 2013. According to the commenter, if the U.S. fails to require Best Available Technology (BAT) levels of controls of its EGU sector, the prospects for an international agreement will be substantially diminished. For this reason, states the commenter, effective Hg regulation of U.S. EGUs, while not sufficient in and of itself, is nonetheless a necessary component of the larger program that is needed to effectively address excess Hg exposure of sensitive U.S. populations, including U.S. children and pregnant women.
Response to Comment 8: The EPA agrees with the commenter that the regulation of Hg from EGU in the U.S. would enable the U.S. to serve as a model of effective policies and technologies to reduce Hg. Such leadership could provide confidence to other countries that they can succeed in meeting their commitments to reduce Hg, including Hg from EGU's. The regulation would also demonstrate the U.S. commitment to addressing the global Hg problem by decreasing the largest remaining man-made source of Hg emissions in the U.S. and serve to encourage other countries to reduce Hg emissions from their own sources.
Comment 9: Commenter 17621 states that predicted Hg deposition relies heavily on the amount of gaseous elemental Hg used to define the boundary and initial conditions of a model. For example, Pongprueksa, et al. (2008) demonstrated this effect while simulating atmospheric Hg on a regional scale; they found that increasing the amount of gaseous elemental Hg in the boundary condition by 1 nanogram per cubic meter (ng/m[3]) caused the predicted monthly deposition of total Hg to increase by 1270 nanograms per square meter (ng/m[2]) in the continental U.S. Model initial conditions have a similar, but weaker effect. The commenter states that Pongprueksa, et al. (2008) found that increasing the amount of gaseous elemental Hg in the initial condition by 1 ng/m[3] increased predicted deposition in the continental U.S. by 250 ng/m[2]. According to the commenter, similar sensitivity analyses have not been provided by the EPA, but need to be reported, most appropriately as part of a more comprehensive model performance evaluation. This is especially important, states the commenter, 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 (Jaffe et al., 2005; Jaffe et al., 2008; Pacyna et al., 2010; Pironne et al., 2010; Streets et al., 2009; Weiss-Penzias et al., 2006). According to the commenter, this will have implications for the amount of Hg in the boundary and initial conditions; however, these emission changes have not been accounted for in the EPA's model exercise, thus leading to an overestimate of U.S. EGU-attributable deposition in 2016.
Response to Comment 9: The EPA disagrees with the commenter that additional sensitivity analysis is needed for this Hg assessment. The EPA also disagrees that boundary and initial conditions inflow needs adjustment for several reasons. First, the EPA does not use the first 10 days of the modeling simulation are not used in the analysis, which is more than sufficient to remove the influence of initial conditions on Hg deposition estimates (Pongprueksa et al., 2008). Second, it is difficult to accurately characterize the speciation of Hg the flows into the U.S. from other countries due to the lack of data near the boundaries of the modeling domain.  Without appropriate observational constraints characterizing lateral boundary concentrations from the surface to upper troposphere, it is difficult to design meaningful sensitivity scenarios. The EPA does not consider the perturbations applied in Pongprueksa et al.2008 of 1 ng/m[3] are realistic boundaries of global speciated Hg concentrations and do not provide directly applicable information.
The boundary inflow for the CMAQ Hg modeling used to predict Hg deposition for the Hg Risk TSD are based on a global model GEOS-CHEM simulation using a 2000 based global inventory as described in (Selin et al., 2007) . A recently published comparison of global Hg emissions by continent for 2000 and 2006 found that total Hg emissions from Asia (and Oceania) total 1,306 megagrams per year (Mg/yr) in 2000 and 1,317 Mg/yr in 2006 (Streets et al., 2009). The EPA determined that because the Asian Hg emissions estimated in this study are nearly constant between 2005 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 2000 (Slemr et al., 2011). Since emissions from Asia have not appreciably changed between 2000 and 2006 and ambient Hg concentrations have been decreasing, ENVIRON's analysis contains information with incorrect assumptions and will be disregarded. For these reasons and the large uncertainties surrounding projected Hg global inventories the EPA concludes that the most appropriate technical choice is to keep the Hg boundary conditions the same between the 2005 and 2016 simulations.
Comment 10: Commenter 17621 states that considering the relatively small contribution of U.S. EGUs, defining boundary and initial conditions accurately and correctly is even more important. According to the commenter, anthropogenic sources of Hg to the atmosphere have been extensively studied, with the most recent global estimates of about 2,500 megagrams (Mg) emitted annually. The commenter states that about 18% of these global anthropogenic emissions come from U.S. EGUs, with U.S. EGUs making up approximately 2.5 and 1.2% of this global anthropogenic total in 2005 and 2010, respectively (Pacyna et al., 2010; Pironne et al., 2010; Streets et al., 2009; U.S. EPA, 2011).
Response to Comment 10: The EPA agrees with the comment that boundary conditions need to be appropriately characterized and has done so in the air quality modeling TSD. The EPA asserts that the boundary conditions used for this analysis fairly represent global inflow.
Comment 11: Commenter 17621 states that global modeling studies show that only 20 - 33% of all the Hg deposited within the continental U.S. comes from North American anthropogenic sources. According to the commenter, Seigneur et al. (2004)  used a global chemical transport model and a continental chemical transport model (TEAM) to calculate the contribution of North American anthropogenic sources to total Hg deposition for low, average, and high Hg emission scenarios, and their calculations yielded a range of 25 - 32%, which they defined as the upper and lower bounds of U.S. anthropogenic contribution to Hg deposition within the country. In another global modeling study, states the commenter, Travnikov (2005) found that 30 - 33% of Hg deposited in North America is of North American origin, while 21 - 24% comes from Asia. Using the GEOS-CHEM model, Selin and Jacob (2008) found that North American anthropogenic emissions contributed, on average, 20% of the total Hg deposited within the continental U.S., corroborating previous findings by Selin, et al. (2007).
Response to Comment 11: The EPA agrees that Hg is a global problem, but disagrees about the nature of EGU impacts. The complex chemical nature of the pollutant means it is also important on a local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010, Keeler et al., 2006; White et al., 2009).
Comment 12: Commenter 17621 states that most of the reactive gaseous Hg deposited by wet processes originates in the global atmospheric Hg pool. The commenter states that in their GEOS-CHEM study, Selin and Jacob (2008) found that 60% of reactive gaseous Hg deposited by wet processes within the U.S. comes from scavenging Hg (removing it from the gas stream) in the free troposphere; the rest of the reactive gaseous Hg deposited by wet processes comes from scavenging within the U.S. atmospheric boundary layer, where oxidation of gaseous elemental Hg is the principal source of reactive gaseous Hg.
Response to Comment 12: The EPA does not agree that the cited study is relevant to the analysis for this rule. The EPA examined contribution to total Hg deposition of all forms of speciated Hg through wet and dry deposition pathways, not just wet deposition of reactive gas phase Hg.
Comment 13: Commenter 18014 states that under the EGU MACT, the agency estimates that the deposition of Hg in the U.S. would be reduced by only about 1% since most of the Hg deposition is related to natural or international industrial sources (i.e., U.S. Hg deposition is not significantly impacted by EGU emissions).
Response to Comment 13: The EPA corrected the statement in the RIA. While the percentage of total Hg deposition attributed to EGUs on a national-scale is a small amount, the absolute amount of total Hg deposition attributable to EGU emissions will go down significantly. In certain parts of the country, the percentage reduction is much larger than 1%. As shown in the revised Hg Risk TSD, 11% of Hg deposition in the 99[th] percentile watershed comes from U.S. EGUs in 2016.
Comment 14: Commenter 17877 states that the proposed rule emphasizes global emissions of Hg and overall atmospheric deposition of Hg as critical factors for Hg concentrations in fish, but the EPA's proposed rule would only reduce U.S. atmospheric levels by 1/1000. According to the commenter, this fact "leads away" from a finding that it is necessary and appropriate to regulate U.S. EGUs.
Response to Comment 14: The EPA disagrees that the EGU MACT would only reduce U.S. ambient concentrations of Hg by 1/1000. Further, it is important to keep in mind the impacts on total Hg deposition are evaluated for the purposes of this rule, not changes to ambient concentrations of Hg. As noted in the Hg Risk TSD, the EPA modeled Hg emissions from U.S. and non U.S. anthropogenic and natural sources to estimate Hg deposition across the country. The 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 the EPA finds that total Hg deposition from U.S. EGUs do significantly impact human health.
Comment 15: Commenter 17807 states that Hg emissions from U.S. coal-fired power plants have decreased considerably over the past 10 years, from a national total of approximately 60 tons per year to the current level of approximately 29 tons, and they will continue to fall even without the utility MACT as a result of other regulations, such as the current CAIR, the recently finalized CSAPR, and changes resulting from NAAQS reductions. According to the commenter, the 29 tons per year from U.S. EGUs is a relatively small amount compared to the more than 1,200 tons per year arriving from Asia and the approximately 2,500 tons per year that are emitted worldwide from natural sources of Hg (half of all Hg emissions are from natural sources such as the soil and volcanoes). The commenter states that compared to these numbers the EPA's estimate of 35 tons per year contributed from global sources is extremely low. According to the commenter, the EPA should re-evaluate and compare its data with other independent sources to test its conclusions and determine the necessity of proceeding with this costly proposed rule in light of the most current information.
Response to Comment 15: The EPA disagrees that Hg emissions reductions from other rules will result in the same level of decrease expected from the EGU MACT. The commenter provides no technical support for that statement. The EPA agrees that Hg is a global problem, but disagrees about the nature of EGU impacts. The complex chemical nature of the pollutant means it is also important on a local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010 , Keeler et al., 2006; White et al., 2009).
Comment 16: Commenter 18033 states that the EPA's conclusions in the 2005 rulemaking are bolstered by the continuing Hg emission trends in the U.S. According to the commenter, power plants emit an estimated 41-48 tons of Hg per year. However, states the commenter, U.S. forest fires emit at least 44 tons per year; cremation of human remains discharges 26 tons; Chinese power plants eject 400 tons; and volcanoes, subsea vents, geysers and other sources spew out 9,000-10,000 additional tons per year. In short, states the commenter, the U.S. releases less than 5% of the 2,400 tons of Hg emitted per year due to human activities. U.S. coal-based power plants emit less than 2% of the global total of human-caused Hg emissions. The commenter states that taking into account natural emissions, U.S. power plants contribute less than 1% of total Hg emissions to the global pool.
Response to Comment 16: The EPA disagrees with the commenter's characterization of the nature of EGU impacts. The complex chemical nature of the pollutant means it is important on a global, local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents and other regional sources contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010; Keeler et al., 2006; White et al., 2009).
Comment 17: Commenter 18033 states that the EPA ignores the fact that over 75% of the Hg that deposits in the U.S. comes from sources outside the country. The commenter states that once Hg is released, it accumulates in the atmosphere resulting in deposition long distances from the actual source exacerbating the lack of causal relationship between the need for regulation and the risk posed by Hg emissions from U.S. EGUs. According to the commenter, EPRI has documented in recent studies the critical role that intercontinental Hg transport from Asia and other nations play in determining U.S. Hg deposition. According to the commenter, direct measurements have revealed significant levels of Hg exiting mainland Asia and crossing the Pacific to the U.S. In 2001 and 2002, EPRI, in cooperation with the National Center for Atmospheric Research, the National Aeronautics and Space Administration, the National Oceanographic and Atmospheric Administration, and other agencies used aircrafts to measure Hg in air plumes exiting China near the city of Shanghai, following them over the Pacific for 400 miles. The commenter states that a later set of flights over the Pacific between southern California and Oregon found evidence of the same plume crossing the California coast.
Commenter 18033 concludes that because Hg is emitted and transported globally, reductions of U.S. Hg emissions from U.S. EGUs would have a negligible impact on Hg deposition in the U.S. For all of these reasons, states the commenter, the factual record does not support a finding that Hg emissions from U.S. EGUs pose a meaningful health risk, and it is therefore not "appropriate" to regulate EGU Hg emissions under CAA section 112(n)(1)(A).
Response to Comment 17: The EPA agrees that Hg is a global problem, but disagrees about the nature of EGU impacts. The complex chemical nature of the pollutant means it is also important on a local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010; Keeler et al., 2006; White et al., 2009).
Comment 18: Commenter 17254 states that studies from Cambridge University have been ignored. According to the commenter, the studies estimate that 9,100 pounds of Hg are put into the air from volcanoes alone; most of those emissions are going into the water as a result of volcanic activity underwater and so there is no way to control it. The commenter compares this amount to the amount from all industrial sources and compares that amount to the 4,400 tons from forest fires. According to the commenter, that is roughly 0.5% of what volcanoes put in the air. The commenter states that power plants in the south supposedly emit 24 tons per year and the U.S. total is 50 tons, and if you combine the power plants and the forest fires, you get perhaps 1% of the Hg in the air that could be controlled if we stopped all forest fires and stopped all Hg in all power plants. According to the commenter, that means that in 20 years, the detectable amount of Hg in the air will not change.
Response to Comment 18: The EPA agrees that Hg is a global problem but disagrees about the nature of EGU impacts. The complex chemical nature of the pollutant means it is also important on a local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010; Keeler et al., 2006; White et al., 2009). As noted in the Hg Risk TSD, the EPA modeled Hg emissions from U.S. and non U.S. anthropogenic and natural sources to estimate Hg deposition across the country. The 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 the EPA finds that total Hg deposition from U.S. EGUs do significantly impact human health.
Comment 19: Commenter 17756 states that the EPA's purported basis for regulating EGUs is rooted in nothing more than assertions of broad discretion delegated to it by Congress. The commenter states that such assertions do nothing to supplement the findings set forth in the EPA's 1998 "Utility Study," which shows that utility emissions of Hg are dwarfed by emissions from natural and other man-made sources around the globe, and that totally eliminating utility emissions of Hg will not advance the public health in any meaningful way.
Response to Comment 19: As noted in the Hg Risk TSD, the EPA modeled Hg emissions from U.S. and non U.S. anthropogenic and natural sources to estimate Hg deposition across the country. The 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 Hg Risk TSD, the EPA finds that Hg deposition from U.S. EGUs can cause a public health hazard.
Comment 20: Commenter 18023 states an alternative analysis performed by ENVIRON found that "The highest Hg deposition fluxes simulated in the U.S. in 2005 are at locations with EGU-attributable deposition less than 5% of total deposition. Before implementation of controls required by the proposed rule, areas with relatively high EGU-attributable Hg deposition (one-fifth or more of total deposition) in 2016 constitute less than 0.25% of the continental U.S. area and only 3 grid cells of the over 55000 twelve-km grid cells in the EPA's integrated CMAQ domain (or less than 0.006% of the total continental U.S. area) have EGU contributions exceeding half of total deposition."
Response to Comment 20: The EPA finds the fundamental approach taken by ENVIRON to match and adjust CMAQ-estimated Hg for the A&N Finding with older Hg modeling done with Hg chemistry that is not considered state-of-the-science and with in-plume Hg chemistry that has not been explicitly characterized and may not happen at all is inappropriate and the findings thus provide no useful information. The EPA also disagrees with the commenter's assertion that the EPA failed to consider the relative magnitude of EGU Hg emissions compared to other sources. As noted in the Hg Risk TSD, the EPA modeled Hg emissions from U.S. and non U.S. anthropogenic and natural sources to estimate Hg deposition across the country. The 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 Hg Risk TSD, the EPA finds that total Hg deposition from U.S. EGUs can cause a public health hazard.
Comment 21: Commenter 17621 states that the origin of atmospheric Hg that is deposited to watersheds in the U.S. is still poorly understood. According to the commenter, the relative contributions of local, regional, and global anthropogenic sources -- as well as natural sources -- of Hg are likely to vary across the U.S. The commenter states 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, and thus, calculated contributions to Hg deposition and fish tissue MeHg levels from these sources represent upper bounds of actual contributions (Seigneur et al., 2003; Seigneur et al., 2004) According to the commenter, the EPA fails to provide a detailed discussion of its results based on currently available scientific data; these results should be presented as estimates of lower and upper bound limits.
Response to Comment 21: The EPA disagrees that recent research 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 2000's the EPA does not believe an upper and lower bound estimate is necessary.
Comment 22: Commenter 18034 states that U.S. EGUs do not contribute significantly to the current risk to public health resulting from all natural and anthropogenic sources of Hg worldwide. According to the commenter, any Hg reductions resulting from the proposed utility NESHAP rule would result in an insignificant change in the overall risk from Hg from all sources.
Response to Comment 22: The EPA agrees that Hg is a global problem, but disagrees about the nature of EGU impacts. The complex chemical nature of the pollutant means it is also important on a local and regional scale. Coal-fired power plants emit three forms of Hg: one form transports regionally and globally and the other forms deposit very quickly near the sources impacting local and 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. While emissions from other continents contribute to Hg deposition in the U.S., published research shows that U.S. coal-fired power plants significantly enhance local and regional Hg deposition (Caffrey et al., 2010 , Keeler et al., 2006; White et al., 2009). Based on the Hg Risk TSD, the EPA finds that Hg deposition from U.S. EGUs can cause a public health hazard.

1E - Hg Deposition Modeling
Commenters: 17681, 17775, 17807, 17777, 18023
1. General comments on deposition modeling.
Comment 1: Commenters 17775 and 18023 state that the boundary conditions used in the CMAQ modeling are based on a global emissions estimate for 2000. Global emissions have changed significantly in the last 10 years. For example, state the commenters, between 2000 and 2005, Hg emissions from China alone increased 38%. The commenters state that the Hg TSD does not contain any type of sensitivity analysis that evaluates the effects of variable boundary conditions. According to the commenters, the change in boundary conditions results in a 1% or more over prediction of EGU-attributable deposition on average across the U.S.
Response to Comment 1: The EPA disagrees with the commenters. The CMAQ Hg modeling used in the Hg Risk TSD are based on a global model GEOS-CHEM simulation using a 2000 based global inventory as described in (Selin et al., 2007). A recently published comparison of global Hg emissions by continent for 2000 and 2006 found that total Hg emissions from Asia (and Oceania) total 1,306 Mg/yr in 2000 and 1,317 Mg/yr in 2006 (Streets et al., 2009). The EPA determined that because the Asian Hg emissions estimated in this study are nearly constant between 2000 and 2006, any adjustments to the boundary conditions or adjustments to modeled Hg deposition would be invalid and inappropriate.
Comment 2: Commenter 17621 states that the AQ Modeling TSD fails to include detailed context and background information on the effect of grid size on CMAQ model results. The commenter states that the EPA used a 36-km grid resolution (i.e., 36 x 36 km) to establish incoming air quality concentrations (boundary conditions) along the boundaries of 12 x 12 km grids (144 km[2]) but used only the 12 x 12 km grids in determining the impact of changes in Hg emissions on changes in Hg deposition. According to the commenter, this choice raises numerous concerns.
   1. First, CMAQ predicts only an average Hg concentration for an entire grid cell. For example, if there is only one Hg source in a grid cell, then that source's emissions will be averaged over the entire grid cell. Such averaging causes an artificially fast dilution and may result in smoothing out areas of high and low deposition. APT (see EPRI Comments, CAA section 3.2.3) resolves this problem.
   2. Second, although the ability to identify large areas of localized high deposition is important in the current proposed rulemaking, using a 12 x 12 km grid provides a resolution that is too coarse for pinpointing smaller areas of localized high deposition.
   3. Third, anglers are likely to catch fish from several water bodies. Thus, a grid larger than the current 12 x 12 km would better account for such common fishing patterns. Conversely, a larger grid would also decrease model ability to simulate smaller areas of localized high deposition.
   4. Finally, the EPA needs to provide detailed and rigorous background information regarding the effects of grid size on CMAQ model results, in the context of over- and underestimation of predicted changes in deposition.
Response to Comment 2: The EPA disagrees with the commenter's claim. 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 (Vijayaraghavan et al., 2007). Reactions that may reduce gas phase oxidized Hg in plumes have not been explicitly identified in literature. The application of potentially erroneous in-plume chemistry that is a fundamental component of APT would be inappropriate. In addition, APT is not available in the latest state-of-the-science version of CMAQ.
The EPA agrees with the commenter that the CMAQ modeling with 12 km grid resolution is likely a lower bound estimate on EGU contribution as higher impacts using finer grid resolution are possible. The commenter's assertion that EGU impacts are likely higher further supports the final conclusions of the exposure modeling assessment.
The EPA notes that the application of a photochemical model at 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 platform used for a national Hg deposition assessment.
Comment 3: Commenter 18023 states that the EPA provides no underlying information about the CMAQ Hg deposition results associated with the 2005 and 2016 zero-out and the 2016 proposed rule simulations. According to the commenter, a full review of the EPA's analysis is difficult because the EPA failed to provide full and complete documentation of its analysis.
Response to Comment 3: The EPA disagrees that the EPA provided no information about the CMAQ Hg deposition results, these results are clearly shown in the air quality modeling TSD. However, the EPA provided additional information in the Air Quality Modeling TSD to answer questions raised by the commenter. For example, in response to comments, the EPA now included model performance evaluation for total Hg wet deposition for the 36 km modeling domain at the suggestion of ENVIRON.
Comment 4: Commenter 18023 states that according to the ENVIRON report the EPA overestimated U.S. EGU Hg deposition by 10% on average (and up to 41% in some areas).
Response to Comment 4: The EPA disagrees with the information presented by ENVIRON for Southern Company. The ENVIRON report is based on the misapplication of multiple incommensurate modeling studies and false premises which include the incorrect notion that the boundary conditions are over-estimated and the notion that the EPA should use in-plume chemistry that has not been explicitly 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 (Kolker et al., 2010; Rothenberg et al., 2010). 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 the EPA modeling. The EPA asserts that the numbers suggested by the commenter are inaccurate as it is not appropriate to adjust the EPA estimated deposition estimates based on previous Hg modeling done with older Hg chemistry and in-plume reactions that have not been explicitly identified. Recent research has shown that ambient Hg concentrations have been decreasing in the northern hemisphere since 2000 (Slemr et al., 2011). The 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 (Streets et al., 2009) and ambient Hg concentrations have decreased, of the commenter inappropriately comingled out - of- date Hg modeling simulations with the EPA results, and ENVIRON's analysis has not undergone any scientific peer review and presents information with incorrect assumptions as noted in this response.
Comment 5: Commenter 18023 states that the EPA's use of highly aggregated (spatially and temporally) metrics to compare against similarly aggregated observations obscures errors and biases and is a highly degraded and lenient approach to operational evaluation. According to the commenter, the EPA did not provide any diagnostic evaluation in any of its modeling for regulatory purposes and as a result not only can the model performance conducted not determine if the model is getting the right answer for the right reasons (i.e., no diagnostic evaluation), it cannot tell if it is getting the right answer (degraded operational evaluation).
Response to Comment 5: The EPA disagrees that the model performance presented in the air quality TSD is insufficient. The EPA also disagrees that the Agency used "highly aggregated performance metrics" that result in degraded and lenient model evaluation.The EPA asserts that the model performance evaluation is generally similar to the level of model performance presented in literature. The commenter presents the results of several Hg modeling studies as providing information they believe to be appropriate and relevant for this assessment. (Lohman et al., 2006) model near-source Hg chemistry from U.S. EGUs, but provide absolutely no information about model performance evaluation. Results from (Seigneur et al., 2006; Vijayaraghavan et al., 2008) are identified by the commenter as supposedly having Hg modeling results that are applicable to the EPA's analysis. These studies present similar model performance metrics as the EPA, and aggregate the metrics across many monitor locations; however, these articles calculate long-term annual averages or model estimates and observations total Hg wet deposition before estimating performance metrics, which presents a more favorable evaluation. It is common practice to pair modeled estimates and observations in space and time (weekly in this case) and estimate performance metrics, then average all the metrics together. The latter is the approach taken by the EPA and should have been taken by the studies presented by the commenter. The EPA finds the performance evaluation presented in the modeling TSD consistent with and in the case of (Lohman et al., 2006) far beyond what is presented in published articles deemed relevant by the commenter. In addition to the evaluation presented by the EPA in the modeling TSD, CMAQ model performance for total Hg wet deposition has been compared with other Hg models (Bullock et al., 2009) .
Comment 6: Commenter 18023 states that instead of establishing specific performance goals, the EPA judges acceptance of model performance if "the mean bias (bias) and mean error (error) statistics...are within the range or close to that found by other groups in recent applications."
Response to Comment 6: The EPA disagrees that the model performance presented in the air quality TSD is insufficient or that it differs from the model performance presented in literature. The model performance reported for the CMAQ Hg modeling done by the EPA is consistent or better than applications the commenter finds relevant for this type of analysis. This includes journal articles cited by the commenter including (Lohman et al., 2006; Seigneur et al., 2006; Vijayaraghavan et al., 2008). None of these articles establishes specific model performance goals and, in particular, the Lohman et al. (2006) paper presents absolutely no model performance evaluation of any kind.
Comment 7: Commenter 18023 states that the results of the modeling are extracted and used in the Hg Risk TSD at a highly specific geographic scale (i.e., census tracts, [Hydrologic Unit Code] HUC-12s, and 50 km to 500 km circles to calculate ratios) to calculate the relative contribution of Hg emissions from U.S. EGUs and changes in deposition resulting from Hg emission reductions. According to the commenter, the EPA's approach to model performance provides no confidence in the models' estimates for such purposes, especially around point sources where the EPA assumes significant gradients exist.
Response to Comment 7: The EPA disagrees. The EPA's approach to model performance is consistent or better than the journal articles referenced by the commenter for such purposes: Lohman et al., 2006; Seigneur et al., 2006; and Vijayaraghavan et al., 2008. In fact, the Lohman et al. (2006) study is titled "Modeling Mercury in power plant plumes" and provides no model performance of any kind. The Seigneur et al., 2006 paper is titled `Modeling atmospheric mercury deposition in the vicinity of power plants' and employs a less stringent approach for matching observations and model estimates of total Hg wet deposition in that this paper makes annual averages of both before comparison to make model performance seem optically better. The EPA's model performance evaluation is at a minimum consistent with and in some cases better than what is employed in journal articles supplied by the commenter.
Comment 8: Commenter 17807 states that the EPA has not conducted an adequate model performance evaluation and no diagnostic evaluation was conducted to ensure the results were attributable for the reasons the EPA assumed. According to the commenter, the EPA used inappropriate operational performance test to confirm it correlates with actual observations; a review of actual historical emissions data and contemporaneous deposition monitoring data does not support the EPA's modeling conclusions. For example, states the commenter, statistical analysis of available data conducted on behalf of the Florida Electric Power Coordinating Group does not show evidence of a statistically significant relationship between temporal trends in coal-fired EGU Hg emissions in Florida and Hg concentrations in rain during 1998-2010 (Vijayaraghavan et al., 2011). The commenter states that using a Theil-Sen (TS) slope analysis to determine statistically significant trends, Florida EGU reductions of 83% between 1997 and 2010 were compared to publicly available monitoring data (SEARCH, MDN, FSU-WDF) from the same timeframe, and the analysis showed a poor correlation (R2 = 0.10) with total Hg deposition remaining essentially flat during a period of substantial Hg emission reductions.
Response to Comment 8: The EPA's approach to model performance is consistent or better than the journal articles for similar purposes: Lohman et al., 2006; Seigneur et al., 2006; and Vijayaraghavan et al., 2008. In fact, the Lohman et al. (2006) study is titled "Modeling Mercury in power plant plumes" and provides no model performance of any kind. The EPA's model performance evaluation is at a minimum consistent with and in some cases better than what is employed in journal articles supplied by the commenter. The EPA used actual historical emissions representing 2005 and compared model estimates of total Hg wet deposition to monitors that collected that data in 2005. No other routinely available measurements are available in 2005. The 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. However, the EPA does not necessarily expect an analysis of a single EGU with monitor located near the ocean to be representative of the entire sector.
Comment 9: Commenters 17775 and 18023 state that the EPA overestimated EGU-attributable Hg deposition by 11% across the U.S., and by even higher percentages, deposition in the vicinity of coal-fired EGUs where ionic Hg reduction has a stronger effect as well as in regions with frequent wildfires or prescribed burns because fire emissions have not been accounted for in the CMAQ modeling. The commenters rely on a report by ENVIRON that provides that that Hg emissions from biomass fires are not included in EPA CMAQ modeling inventory. According to the commenters, Hg emissions from fires in the continental U.S. in 2005 were approximately 28 Mg/y (Wiedinmyer and Friedli, 2007)  and, hence, are significant compared to the U.S. anthropogenic emissions 2005 emissions total of 105 tons (EPA, 2011d). The commenters state that unlike many natural sources, fires have large Hg(p) emissions (EPA, 2011d; Finley et al., 2009) which deposit locally and regionally.
Response to Comment 9: The EPA disagrees with the information presented by ENVIRON for Southern Company. The work by ENVIRON is based on the misapplication of multiple incommensurate modeling studies and false premises which include the incorrect notion that the boundary conditions are over-estimated and the notion that the EPA should use in-plume chemistry that has not been explicitly 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 (Kolker et al., 2010; Rothenberg et al., 2010). 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 the EPA modeling. The EPA asserts that the numbers suggested by the commenter are inaccurate as it is not appropriate to adjust the EPA-estimated deposition estimates based on previous Hg modeling done with older Hg chemistry and in-plume reactions that have not been explicitly identified. Recent research has shown that ambient Hg concentrations have been decreasing in the northern hemisphere since 2000 (Slemr et al., 2011). Since emissions from China have not appreciably changed between 2000 and 2006 (Streets et al., 2009) and ambient Hg concentrations have been decreasing, inappropriate mixing and matching of older out of date Hg modeling simulations with the EPA results has been included, and the fact that ENVIRON's analysis has not undergone any scientific peer review and presents information with incorrect assumptions as noted in this response, it will be disregarded.
The EPA also disagrees with the commenters' interpretation of the applicability of wildfire Hg emissions to this assessment. Finley et al., 2009, suggests caution when using their field data to make assumptions about Hg(p) emissions from wildfires; the estimated particulate Hg emissions from wildfires is based on one field site with a limited sample size and the assumptions made (such as the observed Hg(p) to carbon monoxide (CO) ratios at this location) may not be valid on a broader scale (Finley et al., 2009). Hg emissions from wildfires are a revolatilization of previously deposited Hg (Wiedinmyer and Friedli, 2007). Given that electrical generating power plants are currently and have historically been a large Hg emitting source the appropriate inclusion of wildfire emissions in a modeling assessment would increase the contribution from this emissions sector.
Comment 10: Commenter 17681 states that the EPA has not acknowledged the dramatic decline in Hg emissions from U.S. EGUs since the late 1990s (approximately 50%) to the current level of approximately 29 tons. The commenter notes that in Florida specifically, a recent study shows that EGU Hg emissions have declined 83% between 1997 and 2010. According to the commenter, the EPA also fails to consider the relative magnitude of EGU Hg emissions compared to other sources, natural and human-caused. The commenter states that the current U.S. EGU Hg emissions (approximately 29 tons) represents about 1% of worldwide human-caused emissions, and about 0.5% of total Hg emissions (approximately two-thirds of Hg emissions are from natural sources, such as volcanic events and forest fires).
Response to Comment 10: The EPA disagrees with the commenter's assertion that the EPA has not acknowledged the decline in Hg emissions for the U.S. EGUs since the late 1990s. The EPA analyzed historical, current, and future projected Hg emissions from the power generation sector, as stated in the preamble to the proposed rule. Because the commenter's assertion is based on a conference presentation which is not part of the peer reviewed scientific literature, the EPA is unable to further consider the merits of that work.
The EPA also disagrees with the commenter's assertion that the 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, the EPA modeled Hg emissions from U.S. and non U.S. anthropogenic and natural sources to estimate Hg deposition across the country. The 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 the EPA finds that total Hg deposition from U.S. EGUs do significantly impact human health.