1 NATIONAL EMISSIONS STANDARDS FOR HA ZARDOUS AIR POLLUTANTS: PRIMARY ALUMINUM REDUCTION PLANTS

SUMMARY OF PUBLIC COMMENTS AND RESPONSES

U.S. Environmental Protection Agency Office of Air Quality Planning and Standards Sector Policies and Programs Division Research Triangle Park, North Carolina 27711

September, 20152 The primary contact regarding questions or comments on this document is:
David Putney U.S. Environmental Protection Agency OAQPS/Sector Policies and Programs Division Metals and Inorganic Chemicals Group (D243-02) Research Triangle Park, North Carolina 27711
Email: putney.david@epa.gov3 TABLE OF CONTENTS
Section Page No.

1.0 Introduction .................................................................................................................. ....... 7 2.0 List of Commenters............................................................................................................. 7 3.0 Summary of Public Comments ........................................................................................... 9 3.1 Comment Period Extension Request .................................................................................. 9 3.2 Residual Risk Findings and Requirements ......................................................................... 9 3.2.1 General .................................................................................................................... 9 3.2.2 Data Collection ..................................................................................................... 13

a. Allowable Emissions ................................................................................. 13 b. Total Facility Emissions ........................................................................... 14

c. Other Data Collection ............................................................................... 16 3.2.3 Gap Filling ............................................................................................................ 20 3.2.4 Health Risks .......................................................................................................... 22

a. Cancer, Chronic and Acute Health Risks ................................................. 22 b. Cancer ....................................................................................................... 26

c. Acute ......................................................................................................... 29 d. Chronic Non-Cancer ................................................................................. 33 3.2.5 Risk Assessment Methodology ............................................................................. 35

a. Multipathway Exposures ........................................................................... 35 b. Risk for Children ....................................................................................... 37

c. Environmental Justice ............................................................................... 40 d. Cumulative Risk ........................................................................................ 45

e. Margin of Safety ........................................................................................ 48 3.2.6 Environmental Effects .......................................................................................... 52 3.2.7 Modeling Data ...................................................................................................... 56 3.3.1 General .................................................................................................................. 59 3.3.2 Affirmative Defense .............................................................................................. 63 a. Proposal Comments Received ........................................................................... 63 b. Supplemental Proposal Comments Received .................................................... 66 c. Response to Affirmative Response Comments ................................................... 71 3.4 MACT Review and Rulemaking ...................................................................................... 73 3.4.1 General .................................................................................................................. 73 3.4.2 POM Requirements ............................................................................................... 82 3.4.3 COS Requirements ................................................................................................ 86 3.4.4 PM Requirements.................................................................................................. 88 a. Anode Bake Furnace ......................................................................................... 88 b. Paste Production Plant ..................................................................................... 88 3.4.5 UPL Methodology ................................................................................................ 89 3.5 Monitoring, Recordkeeping and Reporting ...................................................................... 95 3.5.1 General .................................................................................................................. 95 3.6 Work Practice Standards ................................................................................................. 104 3.7 Changes to General Provisions Monitoring Requirements ............................................. 106 3.8 Other Corrections and Revisions .................................................................................... 1074 3.9 Incorporation of Other Comments .................................................................................. 1095 List of Acronyms and Abbreviations

Acronyms ATSDR Agency for Toxic Substances and Disease Registry CAA Clean Air Act CDC Centers for Disease Control and Prevention CEMS Continuous Emissions Monitoring System CERCLA Comprehensive Environmental Respons e, Compensation, and Liability Act of 1980 COS Carbonyl Sulfide CSEFH Child-Specific Exposure Factors Handbook CTE Central Tendency Exposure D/F Dioxins and Furans EFH Exposure Factors Handbook EJ Environmental Justice EO Executive Order EPA U.S. Environmental Protection Agency FR Federal Register HAP Hazardous Air Pollutant HAPEM Hazardous Air Pollutant Exposure Model HEM Human Exposure Model HF Hydrogen Fluoride HI Hazard Index HON Hazardous Organic NESHAP HQ Hazard Quotient IRIS Integrated Risk Information System LOAEL Lowest Observable Adverse Effect Level MACT Maximum Achievable Control Technology MEI Maximum Exposed Individual MIR Maximum Individual Risk MRL Minimum Risk Level NAAQS National Ambient Air Quality Standards NEI National Emissions Inventory NESHAP National Emission Standard s for Hazardous Air Pollutants NOAEL No Observable Adverse Effect Level OAQPS Office of Air Qualit y Planning and Standards OHEA Office of Health and Environmental Assessment PAH Polycyclic Aromatic Hydrocarbons PB-HAP Persistent Bioaccumulative Hazardous Air Pollutant PCB Polychlorinated Biphenyls PM Particulate Matter POM Polycyclic Organic Matter PSD Prevention of Significant Deterioration RCRA Resource Conservation and Recovery Act REL Recommended Exposure Limit6 Acronyms RfC Reference Concentrations RME Reasonable Maximum Exposure RQ Reportable Quantity (CERCLA) RTR Residual Risk and Technology Review SAB Scientific Advisory Board SCAQMD South Coast Air Qual ity Management District SIC Standard Industrial Classification SIP State Implementation Plan SOP Standard Operating Procedure SSM Startup, Shutdown, and Malfunction TEF Toxic Equivalency Factor TEQ Toxicity Equivalence TF Total Fluoride THC Total Hydrocarbon TOSHI Target Organ Specific Hazard Index TRI Toxic Release Inventory UPL Upper Predictive Limit URE Unit Risk Exposure WHO World Health Organization7 1.0 Introduction
On November 4, 2011, the EPA proposed revisions to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for primary aluminum reduction plants. On December 8, 2014, the EPA published a supplemental proposal and requested comme nts on the additional revisions proposed at that time. Some significant comments and responses appear in the preamble to the final rule. This document contains summaries of the public comments that the EPA received on both the 2011 proposal and the 2014 supplemental proposal, and responses to those comm ents that are not summarized and addressed in the preamble to the final rule. Copies of all comme nts submitted are available at the EPA docket Center Public Reading Room. The pub lic comments are also available electronically through http://www.regulations.gov by searching Docket ID No. EPA-HQ-OAR-2011-0797.

2.0 List of Commenters
The EPA received 6 comment letters on the propose d RTR revisions in 2011 and 9 comment letters on the supplemental proposal in 2014 fo r the primary aluminum reducti on plants NESHAP. The initial proposal comment period closedon February 1, 2012 and the suppl emental proposal comment period closed on February 6, 2015. All comments are c ontained in Docket ID No. EPA-HQ-OAR-2011-0797. The commenters, affiliations and item numbers in Docket ID No. EPA-HQ-OAR-2011-0797 are listed in Table 2-1 for the 2011proposal and Tabl e 2-1 for the 2014supplemental proposal .
Table 2-1. Public Comments Received by February 1, 2012 for NESHAP: Primary Aluminum Reduction Plants, Proposed Rule Docket ID No. EPA-HQ-OAR-2011-0797

Docket ID Commenter ID Code Commenter and Affiliation

EPA-HQ-OAR-2011-0797-0158 0158 A.R. Baluch, unaffiliated

EPA-HQ-OAR-2011-0797-0162 0162 Charles D. Johnson, Vice President, Environmental Health & Safety, The Aluminum Association

EPA-HQ-OAR-2011-0797-0163 0163 Matthew Todd, Chair, The Residual Risk Coalition (R2C)

EPA-HQ-OAR-2011-0797-0164 0164 Michael A. Palazzolo, Manager Air Services, EHS Services North America, Alcoa Inc.

EPA-HQ-OAR-2011-0797-0165 0165 G. Vinson Hellwig, Michigan, Co-Chair, andRobert H. Colby, Chattanooga, Tennessee, CoChair, Air Toxics Committee, National Association of Clean Air Agencies (NACAA)8 Docket ID Commenter ID Code Commenter and Affiliation

EPA-HQ-OAR-2011-0797-0166 through EPA-HQ-OAR-2011-0797-0172 0166 Emma Cheuse, Earthjustice, on behalf of Sierra Club (Parts 1 through 7)

Table 2-2. Public Comments Received by February 6, 2015 for NESHAP: Primary Aluminum Reduction Plants, Supplemental Proposed Rule Docket ID No. EPA-HQ-OAR-2011-0797

Docket ID Commenter ID Code Commenter and Affiliation

EPA-HQ-OAR-2011-0797-0362 0362 L. Nelson

EPA-HQ-OAR-2011-0797-0369 0369 G. Vinson Hellwig, Michigan, Co-Chair andRobert H. Colby, Chattanooga, Tennessee, CoChair, National Association of Clean Air Agencies (NACAA)

EPA-HQ-OAR-2011-0797-0370 0370 Sean O. Alteri, Director, Energy and Environment Cabinet, Department for Environmental Protection on behalf of the Commonwealth of Kentucky

EPA-HQ-OAR-2011-0797-0371 0371 Matt Owens, Health Safety and Environmental Director, Century Aluminum North America Operations

EPA-HQ-OAR-2011-0797-0372 0372 Charles D. Johnson, Vice President, Policy, The Aluminum Association

EPA-HQ-OAR-2011-0797-0373 0373 Emma C. Cheuse, Sierra Club & California Communities Against Toxics

EPA-HQ-OAR-2011-0797-0374 0374 SSM Coalition

EPA-HQ-OAR-2011-0797-0375 0375 Michael A. Palazzolo, Director, Global Environmental Affairs and Henk J. van der Meyden, Sr. Environmental Consultant, Alcoa Inc.9 Docket ID Commenter ID Code Commenter and Affiliation

EPA-HQ-OAR-2011-0797-0376 0376 Michael A. Palazzolo, Director, Global Environmental Affairs and Henk J. van der Meyden, Sr. Environmental Consultant, Alcoa Inc.

3.0 Summary of Public Comments
Comments received on both proposed (2011 proposal and 2014 supplemental proposal) amendments to the primary aluminum reduction plant rule that are not presented in the preamble to the final rule are summarized in the following sections along with the EPA’s responses. In some instances, commenters provided additional documents as background information or otherwise in support of their comments. Those documents are contained in the docket to this rulemaking but are not summarized here.
3.1 Comment Period Extension Request

Comment: Two docket items (EPA-HQ-OAR-2011- 0797-0159 and EPA-HQ-OAR-2011-0797-0161) contained requests for an extension to the initial comment period for the 2011 proposal.
Response: The EPA extended the comment period by 12 days.

Comment: One docket item (EPA-HQ-OAR -2011-0797-0361) contained a re quest for an extension to the comment period for the supplemental proposal.
Response: The EPA extended the comment period by 15 days.

3.2 Residual Risk Findi ngs and Requirements
We note that most of the comments and responses pr esented in section 3.2 a ddress the risk assessment associated with the 2011 proposal. That risk assessment is superseded by the risk assessment associated with the 2014 supplemental proposal and most of th e comments and responses addressing the 2014 risk assessment are presented in the preamble to the final rule.

3.2.1 General

Comment: One commenter (0166) states that the EPA’s re sidual risk assessment analysis under section 112(f)(2) failed to consider or assess types of pollutant emissions , exposures, health risk, and the increased vulnerability for partic ular individuals and communities, including children. The commenter states that the EPA must fully assess each of these f actors and consider the context of the residual risk posed by exposure to HAP emissions from this source category, including: (1) the communities affected, (2) the greater risk to children who are more vulnera ble to harm when exposed to toxic air pollution, and (3) the total cumulative impacts to people and commun ities who are exposed to multiple sources of toxic air pollution, multiple pollutants, and through multiple pathways, including but not limited to ingestion,10 dermal, as well as inhalation. The commenter further as serts that the EPA’s failure to consider, at step one, the full extent of the risk of harm experience d by the most exposed and vulnerable people in local communities is unlawful, arbitrary, and capricious. The commenter’s extended arguments on these points are summarized in sections below.
Response: We disagree with the comment that the risk assessment for this source category does not consider the groups that may be mo st at-risk (e.g., children). When the EPA derives exposure reference concentrations and unit risk estimates for hazardous air pollutants, it also considers the most sensitive populations identified in the availabl e literature, and importantly, these are the values used in our risk
assessments. 1
We acknowledge that population subgroups, including ch ildren, may have a potential for risk that is greater than the general popul ation due to greater relative exposure and/or greater susc eptibility to the toxicant. The assessments we undertake to estimate risk account for this potential vulnerability. With respect to exposure, the risk asse ssments we perform implicitly account for this greater potential for exposure by assuming lifetime exposure, in which populations are conservatively presumed to be exposed to airborne concentrations at their residence c ontinuously, 24 hours per day for a full lifetime, including childhood. With regard to ch ildren’s potentially greater suscepti bility to non-cancer toxicants, the assessments rely on the EPA (o r comparable) hazard identification and dose-response values which have been developed to be prot ective for all subgroups of the ge neral population, in cluding children.
For example, a review 2 of the chronic reference value proce ss concluded that the EPA’s reference concentration (RfC) derivation proc esses adequately considered poten tial susceptibility of different subgroups with specific consideratio n of children, such that the result ant RfC values pertain to the full human population “including sensi tive subgroups,” a phrase which is inclusive of childhood. With respect to cancer, the EPA uses the age-dependent adju stment factor, but limits the use of those factors only to carcinogenic pollutants that are known to act via mutagenic m ode of action (MOA). In lieu of chemical-specific data on which age or life-stage speci fic risk estimates or poten cies can be determined, default age dependent adjustment factors can be applied when assessing cancer risk for early-life exposures to chemicals which cause cancer thro ugh a mutagenic MOA. With regard to other carcinogenic pollutants for which early-life susceptibil ity data are lacking, it is the Agency’s longstanding science policy position that us e of the linear low-dose extrapolation approach (without further adjustment) provides adequate public health conservatism in the ab sence of chemical-specific data indicating differential early-life susceptibility or when the mode of action is not mutagenicity. 3 The basis for this methodology is provided in the 2005 Supplemental Guidance. 4

1 U.S. EPA. A Review of the Reference Dose and Referenc e Concentration Processes. U. S. Environmental Protection Agency, Risk Assessment Forum, Washington, DC, EPA/630/P-02/002F, 2002. Available online at http://www.epa.gov/raf/publications/pdfs/rfd-final.pdf 2 Ibid. 3 Ibid. 4 U.S. EPA. (2005). Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens

. EPA/630/R-03/003F. Washington, DC. Available online at : http://www.epa.gov/cancerguide lines/guidelines-carcinogensupplement.htm.11 The estimated risks must also be considered in the context of the full set of assumptions used for this risk assessment. Our unit risk estimates for HAP are considered a plausibl e upper-bound estimate with an appropriate age dependent adjustment; actual potency is likely to be lower and some of which could be as low as zero. Our chronic noncancer reference va lues have been derived considering the potential susceptibility of different subgroups, with specific consideration of children. In addition, a more protective adjustment, as suggested by the commen ter, is not needed in the RfC/RfD methodology because the currently available factors are consider ed sufficient to account for uncertainties in the database from which the reference values are deri ved. After considering these and other factors, we continue to consider the risks base d on existing emissions from this s ource category to provide an ample margin of safety (consistent with the Benzene NESHAP framework).
We disagree with the comment that we failed to consider or account for cumulative risk. The EPA modeled whole-facility risks for both chronic cancer and non-cancer impacts to understand the risk contribution of the sources within the primary alumin um source category. The individual cancer risks for the source category were aggregated for all carc inogens. In assessing noncancer hazard from chronic exposures for pollutants that have similar modes of action or (where this information is absent) that affect the same target organ, we aggregated the h azard quotients (HQ). This process creates, for each target organ, a Target Organ-Specific Hazard Index (T OSHI), defined as the sum of hazard quotients for individual HAP that affect the same organ or orga n system. All TOSHI calculations presented here were based exclusively on effects occurrin g at the “critical dose” (i.e., the lowest dose that produces adverse health effects).
We also disagree with the commente r’s assertion that additional qua ntitative assessment of risks from sources outside the source category is required. The statute requires the EPA to provide the quantitative risk information necessary to inform RTR regulator y decisions, and to this end, the EPA conducts a comprehensive assessment of the risk s associated with exposure to th e hazardous air pollutants emitted by the source category and supplements that with a dditional information that is available about other possible concurrent and releva nt risks, as appropriate.
For the primary aluminum source category, the EPA conducted an assessment of the cumulative cancerrisks from emitted carcinogens and the cumulative noncancer hazard indices from all emitted noncarcinogens affecting the same target organ syst em for both the source category emissions and the facility-wide emissions. While the incorporation of additional bac kground concentrations from the environment in our risk assessments (including thos e from mobile sources a nd other industrial and area sources) could be technically challenging, they are neither mandated nor barred from our analysis. In developing the decision framework in the Benzene NESHAP currently used for making residual risk decisions, the EPA rejected approaches that would ha ve mandated consideration of background levels of pollution in assessing the acceptability of risk, conc luding that comparison of acceptable risk should not be associated with levels in polluted urban air (54 FR 38044, 38061, September 14, 1989). Background levels (including natural background) are not barred from the EPA’s ample margin of safety (AMOS) analysis, and the EPA may consider them, as appropriate and as available, along w ith other factors, such as cost and technical feasibility, in the second step of its section 112(f) analysis. This assessment excludes background contributions because the availabl e data are of insufficient quality upon which to base a meaningful analysis.12 Comment: One commenter (0165) states th at the emissions of particulat e fluoride from the 14 (at that time) primary aluminum reduction faci lities ranges from 50 to 250 tons per year and was not accounted for in the Residual risk and Technology Review (RTR ) analysis because fluoride itself is not a HAP.
Response: Total fluoride (TF) is made up of hydrogen fl uoride (HF) and particulate fluoride. Limited data are available on the relative cont ributions of these fractions. Test data suggest that typically about 50% of the TF is made up of HF, and this was assu med in cases where no data were available for HF emissions. Total fluoride was adopted as a surrogat e for HF in the original 1997 NESHAP for primary aluminum reduction plants because of the uncertainty in analyses of HF. The co mmenter is correct that we did not assess the risks due to ex posures to particulate fluoride be cause particulate fluoride is not a HAP. We believe this approach is appropriate for this specific acti on since section 112(f) of the CAA directs the EPA to assess the risks due to exposure to HAP emissions. We believe assessing risks due to exposure to non-HAPs is outside the scope of this specific action.

Comment: Commenter (0372) stated that th e EPA’s residual risk conclusi ons are reasonable, but that the risk assessment calculations likely significantly overstate actual risk from the operation of primary aluminum reduction facilities. Commenter (0372) provi ded seven examples of how the risk assessment was likely overestimated. Commenter (0372) stated that they are in conc urrence with the EPA’s determinations that there are “acceptable” risks and more than an “ample margin of safety” in establishing the HAP emission limits as contained in the proposed rule.
Response: Uncertainty and the potential for bias are inhe rent in all risk assessments, including those performed for this rulemaking. Although uncertainty ex ists, our approach, which uses conservative tools and assumptions, ensures that our decisions are appropria tely health protectiv e and environmentally protective. A brief discussion of the uncertainties in the RTR emissions datasets, dispersion modeling, inhalation exposure estimates and dose-response relationships can be found in the proposal for this rulemaking [79 FR 72914]. A more thorough discussion of these uncertainties is included in the Residual Risk Assessment for the Primar y Aluminum Production Source Category in Support of the September 2015 Risk and Technology Review Final Rule, which was available in the docket for this action.

Comment: Commenter (0373) stated that the EPA’s revised risk assessment and supplemental proposal on risk for primary aluminum contains the same se rious problems in underest imating health risks and failing to satisfy the 42 U.S.C. § 7412(f)(2) requirements as Commenters already addressed in their 2012 Comments, all of which are reincorporated into these comments.
Response: This compilation of suggestions for improving th e perceived deficiencies in our residual risk assessment have been addressed in other respons es in section 3.2 of this document. Further, it is important to note that the EPA’s approach to perf orming risks assessments in support of residual risk program has been reviewed and supported by the Science Advisory Board (SAB) several times over the past 17 years. First, in 1998 they examined our analytical and policy approach for assessing residual risk from hazardous air pollutants emitted from stationary sources, followed by a second review in 2000 to verify that ou r application to a specific source category was consistent with the approved approach. A third SAB consultation in 2006 focused on development of emissions inventories for source categories and updated methods for characterizing human exposure and risks. Again in 2009, the SAB reviewed and supported our updated and expanded air toxics risk assessment13 methods, including our multipathway assessment, refine ment of acute risk screening, and the methods of assessing potential environmental risk. We will continue to seek SAB consultation as our risk assessment methods develop and revise our approach as appropriate.

3.2.2 Data Collection

a. Allowable Emissions

Comment: One commenter (0163) states th at the EPA does not have author ity to consider hypothetical “MACT allowable” emissions in conducting residual ri sk assessments. The commenter states that the EPA cannot lawfully use MACT allowable emissions in the proposed risk assessments and residual risk determinations because the Agency has failed to provide any reasoned ex planation for why risk assessments based on actual emissions estimates are inadequate. The commenter notes that section 112(f)(1)(A) required the EPA to report to Congress on “methods of calculating the risk to public health remaining, or likely to remain , from sources subject to regulation unde r this section after the application of standards under subsection (d) of this section” (emphasis added). The commenter further notes that section 112(f)(1)(B) required the EPA also to report on “the actual health effects with respect to persons living in the vicinity of affect ed sources” (emphasis added). The commenter concludes that these requirements clearly signal that Congress expected the EPA to focus on actual risk and not hypothetical risk in implementing the requirements of section 112(f), and it is not re asonable in the first instance for the EPA to construe section 112(f) as authorizi ng the Agency to conduct risk assessments based on hypothetical “MACT allowable” emissions.
The commenter provides several examples of inst ances in the Agency’s risk assessment methodology that already reflect conser vative assumptions and concludes that in light of the conservatism that already is inherent to the EPA’s risk assessment methodology , it makes no sense to apply yet another layer of conservatism – this time based on the hypothetical assu mption that affected sources should be expected to emit more than the actual dataindicate – to section 112(f) ri sk assessments. Furthermore, the commenter states that the EPA has provided no data or analyses indicating th at its current methodology results in negative bias. The commenter asserts that the EPA has provided no da ta demonstrating that affected sources actually do emit at levels signifi cantly higher than the actual data show for any significant period of time, or should reasonably be expected to do so. The commenter states that the EPA has failed to provide a reasoned explan ation as to why this approach is justified or any record evidence supporting the use of MACT allowable emissions, rendering this proposal in supportable under the law.
Response: Consistent with previous ri sk assessments, the EPA considers both allowable and actual emissions in assessing chronic ri sks under section 112(f)(2) for the primary aluminum source category (see e.g., National Emission Standards for Coke Oven Batteries [70 FR 19998-19999, April 15, 2005] and the proposed and final National Emission Standards for Organic Hazardous Air Pollutants from the Synthetic Organic Chemical Manufacturing Industry [71 FR 34428, June 14, 2006, and 71 FR 76603, December 21, 2006]). In those previous actions, we noted that modeling the allowable levels of emissions (i.e., the highest emission levels that could be emitted while still complying with the NESHAP requirements) is inherent ly reasonable since they reflect the maximum level sources could emit and still comply with the national emission st andards. This is in acc ord with the statutory requirement that the EPA evaluate “standards promul gated pursuant to subsect ion (d)” and if those14 standards “do not reduce lifetime excess cancer risk to the individual most exposed” the EPA must promulgate standards under section 112(f). This langua ge most naturally refers to allowable emissions, since those are what the standards allow. Quite simp ly, in determining whethe r unacceptable residual risk remains after promulgation of section 112(d) technology-based standard s, it is reasonable to consider the emission allowed by th e standards. In addition, the Ben zene NESHAP looked to allowable emissions in assessing residual ri sk, and section 112(f) specifically preserves (indeed, mandates) the Benzene NESHAP decision framework. But we also expl ained that it is reasonabl e to consider actual emissions, where such data are available, in the accep table risk and ample margin of safety analyses. Sources typically emit lower than MACT allowable levels on most days (the EPA in fact assumes the cost facilities expend to r each a design level of control, typically about 70% of the allowed standard) and, if so, overall risk incidence is probably less than the maximum estim ated levels. Failure to consider available data on actual emissions in risk estimates could unrealistically inflate risk levels. (See National Emission Standards for Coke Oven Ba tteries, 70 FR 19992, 19998 (April 15, 2005)).

Comment: Three commenters (0165, 0369 and 0166) agree with the EPA’s use of MACT-allowable emissions to evaluate residual hea lth risks, stating that the use of allowable emissions appropriately takes into account the emissions that may legally occur under th e existing standard.
Commenter (0165 and 0369) believes an analysis base d on actual emissions from a single point in time could underestimate the residual risk from a source category. This commenter further argues that the major source HAP thresholds are based on maximum potential-to-emit, as opposed to actual emissions, and air agencies issue permits based on potential emissions. The commenter believes that limiting the scope of a risk evaluation to actual emissions would be inconsistent with the appl icability section of Part 63 rules. The commenter is pleased to see that the EPA used allowable emissions in parts of the risk assessment but is concerned about th e fact that the EPA continues to use actual emissions in other parts of its risk assessment. The commenter encourages th e agency to use allowable emissions in the future, including in assessing acute health risks.
Response: The EPA acknowledges the commenter’s support for our use of MACT-allowable emissions to evaluate residual health risks. However, we disagree with the comment suggesting the use of allowable emissions in the assessment of acute healtheffects. The use of allowable emissions for our acute risk assessment is not consid ered appropriate due to the conser vative assumptions used to gauge worst-case potential acute health effects. The conser vative assumptions built into the acute health risk screening analysis include: (1) us e of peak 1-hour emissions; (2) th at all emission points experience peak emissions concurrently; (3) worst-case meteor ology (from 1 year of local meteorology); and (4) that a person is located downwind at the point of maximum impact during this same 1-hour period. Thus, performing an acute screen based on allowabl e emissions would be ove rly conservative and at best, of questionable uti lity to decision makers.
b. Total Facility Emissions

Comment: One commenter (0163) states that the EPA does not have au thority to consider “total facility” emissions in conducting the residual risk assessments for a given source category. The commenter states that the EPA is without authorit y to consider facility-wide risks because the CAA requires residual risk determinations to be conduc ted on a category-by-category basis. The commenter15 notes that section 112(f)(2)(A) una mbiguously requires the EPA, with in eight years after adopting a MACT standard for a given source category or subcat egory, to “promulgate standards for such category or subcategory if promulgation of such standards is required in order to provide an ample margin of safety to protect public health,” and further dictat es that, “Emissions standa rds promulgated under this subsection shall provide an ample margin of safety to protect public health.” The commenter argues that it is not reasonable to construe thes e provisions as authorizing the EPA to consider emissions from entire facilities in conducting risk asse ssments and potentially revising the underlying rule for the simple reason that the Congress clearly en visioned that full implementation of the MACT program would take longer than eight years and it woul d be impossible for the EPA to fu lfill its unambiguous obligation for section 112(f) standards to protect pu blic health with an ample margin of safety in cases where facilities contain sources in a category where the eight-year deadline for conducting the section 112(f) risk review precedes the adoption of MACT standards for other sources at the facilities.
The commenter also notes that the language of sec tion 112(f)(2)(A) specifical ly requires the section 112(f) risk assessment to be focused exclusivel y on “emissions from a source in the category or subcategory,” and thus, the EPA does not have author ity to consider emissions from any sources other than those in the source category or subcategory under review at that time.
Response: We disagree that examining f acility-wide risk in a risk a ssessment conducted under section 112(f) exceeds the EPA’s authority. The development of facility-wide risk estimates provides additional information about the potential cumulative risks in the vicinity of the RTR sources, as one means of informing potential risk-based de cisions about the RTR source categor y in question. While we recognize that, because these risk estimates were derived from facility-wide emissions estimates which have not generally been subjected to the same level of engineering review as the source category emission estimates, they may be less certain than our risk estimates for the s ource category in question, but they remain important for providing context as long as th eir uncertainty is taken in to consideration in the process. Section 112(f)(2) of the CAA expr essly preserves our use of the two-step process for developing standards to address residual risk and interpret “acceptable risk” and “ample margin of safety” as developed in the Benzene NESHAP (54 FR 38044, September 14, 1989). In the Benzene NESHAP, the EPA rejected approaches that would have mandated consideration of background levels of pollution in assessing the acceptability of risk, concluding that“...comparison of acceptab le risk should not be associated with levels in polluted urban air. With respect to considering othe r sources of risk from benzene exposure and determining the acceptable risk level for all exposures to benzene, the EPA considers this inappropriate becaus e only the risk associated with th e emissions under consideration are relevant to the regulation being established and, consequently, the decision being made.” (54 FR 38044, 38061, September 14, 1989).
Although not appropriate for consid eration in the determination of acceptable risk, we note that background risks or contributions to risk from sources outside the source category under review could be one of the relevant factors considered in the ample margin of safety determination, along with cost and economic factors, technological f easibility, and other factors. Bac kground risks and contributions to risk from sources outside the facilities under review were not considered in th e ample margin of safety16 determination for this source category, mainly because of the significant uncertainties associated with emissions estimates for such sources. Our approach here is consistent with the approach we took regarding this issue in the Hazardous Organi c NESHAP (HON) RTR (71 FR 76603, December 21, 2006), which the court upheld in th e face of claims that the EPA had not adequately considered background (NRDC v. EPA, 529 F.3d 1077, 1086 (D.C. Cir. 2008)).
With respect specifically to the primary aluminumrisk assessment, a facility-wide analysis was performed for most primary aluminum facilities. Most primary aluminum facilities are collocated with secondary aluminum facilities and a facility-wide assessment was performe d for this RTR and as part of the secondary aluminum risk assessment (see the ri sk assessment document, which is available in the docket, and the response to the next comment for more detail).

Comment: One commenter (0166) objects that the EPA has not performed a facility-wide risk assessment or considered combined emissions and ri sk posed by this source category and other sources. The commenter sees no reason to wa it to do a facility-wid e risk assessment when the EPA needs this information to decide how best to address high fa cility-wide risk for the primary aluminum source category. The commenter observes that an SAB re port addressing the EPA’s RTR methodologies (May 2010 (EPA-SAB-10-007) response to the EPA Administrator) stated that “the Pane l recommends that the Agency perform a sensitivity analysis to identify th e major uncertainties in both the human health and ecological risk assessments. The Agency should then proceed to: (1) explain them clearly in the risk characterization section and (2) take steps to reduce them.” The co mmenter argues that uncertainties require more conservative assessment and mo re protective action, rather than inaction.
Response: Most of the primary aluminum reduction facilities (9 of the 11 subject reduction facilities) are collocated with secondary alumin um production facilities. As a result , the facility-wide analysis that was conducted as part of the residual risk assessme nt for this RTR and for the secondary aluminum source category provides a facility-wide analysis for most of the primary aluminum production facilities. We note that facility-wide risk results (i.e., results considering primary and secondary aluminum operations) had a cancer MIR of 70-in-1 million, whic h is the same as the MIR from the primary aluminum source category risk assessment. Thus, cons ideration of facility-wide risks did not change the conclusions reached in this rulemaking. The secondary aluminum source category risk assessment is available at http://www.regulations.gov in docket number EPA-HQ- OAR-2010-0544-0146. With respect to describing the major uncertainties associatedwith the risk assessment, we note that major uncertainties are thoroughly described in the Residual Risk Assessment for the Primary Aluminum Production Source Category in Support of the September 2015 Risk and Technology Review Final Rule

. c. Other Data Collection

Comment: One commenter (0162) states that the 70 yearlifetime exposure assumes no shutdowns or partial curtailments in operation inthe risk analysis. The commente r notes that this assumption, in addition to not including the short and long term activity patterns and indoor/outdoor exposure differences, also assumes that facilities will not experience partial or full curtailments of operations. The commenter observes that this leads to additional overestimates of long term cumulative risk estimates, because as seen since the early 1990’s, many primary aluminum plants have experienced short and multi-year curtailments, including intermittent part ial and complete plant shutdowns. The commenter17 points out that if these trends continue, it is like ly that the EPA assessment will further overestimate cumulative risks as curtailments occur.
Response: The commenter is correct that the EPA assume s no curtailment of operations over the 70 year period, and that short or long term activity patterns were not considered in th is assessment. Regarding exposure times and the consideration of time-activity pa tterns, we do not believe that such consideration would significantly lower the general estimates of indi vidual risks. In assessing risk, we estimate the maximum individual risk (MIR) or the maximum hazar d index (HI), which are de fined as the risk (or hazard) associated with a lifetime of exposure at the highest concentration. For this assessment, we used the annual average ambient air conc entration of each HAP at each census block centroid as a surrogate for the lifetime inhalation exposure concentration of all the people who reside in the census block. Basing exposure estimates at census block centroids may underestimate or overestimate actual exposure concentrations at some residences. Further reduc ing exposure estimates for the most highly exposed residents by modeling their short-term behavior could add a systematic low bias to these results. This risk analysis did not consider th e short-term human activity patterns and their potential influence on exposure. Our experience with the National-Scale Ai r Toxics Assessments (which modeled daily activity using the EPA’s HAPEM model) suggests that, gi ven our current understanding of microenvironment concentrations and daily activities, modeling short-term activity would, on average, reduce risk estimates about 25 percent for particulate HAP; it w ill also reduce risk estimates for gaseous HAP, but typically by much less. Moreover, we note that the risk assessment also contains assumptions that would lead to an underestimation of risk; for exampl e the assessment does not take into account population growth over the 70 year period. A disc ussion of activity patter ns and of uncertainties associated with the risk assessment are described in the Residual Risk Assessment for the Primary Aluminum Production Source Category in Support of th e September 2015 Risk and T echnology Review Final Rule

. Comment: One commenter (0162) states that the EPA om its consideration of indoor versus outdoor exposures in the assessment, and assumes that ou tdoor concentrations ar e equivalent to indoor exposures. The commenter notes that for particulate ty pes of emissions, including POM, this differential is significant, with the EPA estimates of indoor exposures for particulate types of emissions that may be reduced by a value of 25 to 30 percent. The comm enter concludes that ri sks projected for POM emissions are overestimat ed by 25 to 30 percent.
Response: As noted in the previous response, while co nsideration of time-activ ity patterns (i.e., indoor versus outdoor exposures) may minimally effect our risk estimates, we do notanticipate that the maximum individual risk would si gnificantly change such as to alter our risk-b ased decision.

Comment: In response to the 2011 proposal, one comme nter (0166) stated that the EPA’s risk assessment is not sufficiently protective of public hea lth due to the data that the EPA used for the rule. The commenter’s concerns were: (1) the EPA collected some emission data but had little actual test data, using emissions estimates instead; (2) the EPA usedindustry-supplied estimates from the NEI; (3) the EPA used a limited amount of test data from 1994, which the commenter is concerned may not be representative; and (4) the EPA estimated allowable emissions by multiplying its original estimates by 1.5 for most facilities. The commenter concluded that the EPA had not demonstrat ed that the data used in the proposed rulemaking are an appropriate substitute for actual emission test data.18 The commenter recommended collecti ng actual emissions data, as itcould identify any additional pollutants of which the EPA is not aware. The co mmenter recommended that the EPA collect emission measurements from the roof vents, from the storage tanks, and from other emission points for this source category. The commenter noted that NEI data woul d not provide information on any HAPs of which the EPA is not already aware. The commenter was al so concerned that relying only on the NEI and estimated data is unlikely to provide even estimate s of the actual HAP emissions coming from a facility that has installed control devices and has never measured the amountor types of HAPs coming from those control devices. The commenter stated that not co llecting actual test data is likely to lead the EPA to ignore some HAPs emitted by control devices. The commenter remarked that the EPA has not explained how use of the NEI data accounts for emissions created by control devices. The commenter recommended the EPA collect emission test data from state agencies.

The commenter asserted that the EPA did not provide a reasoned expl anation of why its inventory is representative or why its rule is sufficiently prot ective in view of these da ta concerns. The commenter further asserted that it also has not adequately expl ained its decision not to co llect or use actual emission test data from all emission points in this rulemaking. The commenter as serts that the EPA’s choice of data must be rational, supported by a reasoned explanation, and consistentwith the statutory requirement to provide an “ample margin” to protect public hea lth. The commenter suggests that to strengthen and finalize its rule proposal, the EPA must set a stronge r rule to account for the likelihood that its data concerns have led it to underestimate health risk.
Response: This comment was in response to the November 2011 proposal. We agree that at that time we had limited data. The dataset used fo r the 2011 proposal was based on li mited data and other information we received in April 2013 through an Information Coll ection Request (ICR) from 11 of the 15 facilities in the source category at that time. These ICR datawere then used along with the 2005 NATA inventory data to develop the emissions dataset for this s ource category for the 2011 proposal, which included our best estimates of actual emissions of HAP for the fac ilities at that time. However, after considering comments received in 2012 (such as the comment describe d above), we agreed that our 2011 dataset was limited. For example, we lacked emissions test data for several HAP, including HAP metals and dioxins and furans. We also had limited test data for some other important HAP such as POM from prebake potlines, and we decided it was appropriate to collect a dditional emissions test data for multiple HAP from multiple sources in the category. Therefore, in March 2013 we sent a comprehensive information request to the primary aluminum companies pursuant to section 114 of the CAA to gath er a substantial amount of additional relevant emissions test data. In response to this request, selected facilities provided the following data:

 Additional emission test data for PO M emissions from prebake potlines;

 Additional emission test data for PM emissions from prebake potlines, Soderberg potlines (which have subsequently shut down), anode bake furnaces and paste production plants;

 Additional emission test data for speciated P AH, speciated HAP metals (including mercury, nickel, arsenic, chromium, cadmium, lead, manga nese, etc.), speciated PCBs and speciated polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofur ans from potlines, anode bake furnaces and paste production plants.19 Additional information regarding the emissions data and emissions estimates used for the RTR are described in the Revised Draft Development of the RTR Emissions Dataset for the Primary Aluminum Production Source Category, which is available in the docket for this action (Docket ID No. EPA-HQOAR-2011-0797). The EPA believe the data set used for the 2014 supplemental proposal and final rule are robust and are the best informat ion available with regard to estim ating actual emissions of HAP from this source category. With regard to allowable emissi ons, the emissions estimates used for assessment of risk associated with allowable emissions provides a conservative ap proach to the risk estimation.

Furthermore, the public comment period for the 201 1 and 2014 proposed rules provided an opportunity for submission of any additional available emissions information or submission of corrections to the data we already had. We believe that the EPA has provide d multiple opportunities for third party review of: data the EPA’s risk assessment included; an evaluati on of facilities contained in the source category; the emissions units expected to be included for the pr ocesses in the source category; coordinates and stack parameters; and the HAP compounds and emissions levels typically seen. Therefor e, we believe the data set used in this rulemaking is sufficiently accurate and complete and constitutes the best information the EPA has concerning the emissions and risk fromthis source category for conducting the RTR.

Comment: One commenter (0166) asks thatthe EPA consider the control efficiency for the control devices when analyzing risk in the case of the co ntrol equipment’s failure. The commenter provides as an example that in the case of failure of a control device with 99 percent efficiency, the resulting emissions will increase by a factor of 100.
Response: The most important control devices in use in the primary aluminum industry, dry alumina scrubbers, are integral to the operatio n of the reduction process and in the event of fail ure it would be impossible to continue producing aluminum and emitti ng pollutants. Other control devices such as dry coke scrubbers would be unlikely to fail catastrophically. A decline in control efficiency would result in an increase in emissions, but such an increase woul d be far less than one hundred fold. Fabric filters, used as part of the control system are designed w ith multiple compartments. Failure of the components in a single compartment would not increase emissions by a significant amount. The NESHAP for primary aluminum reduction plants, and additional re quirements imposed as part of the title V permit program, require monitoring of parameters to confirm that day-to-day control device efficiencies are comparable to control efficiencies during periodic performance tests.
Furthermore, in a case where a control device fails to the extent described by the commenter, we expect this would be characterized as a ma lfunction or a violation of the standard. As we discuss in more detail in another response below, we disagree with the comm enter that emissions that exceed standards and are violations, whether or not they are caused by malfuncti on events, should be considered as part of the risk analysis. The purpose of the risk review is to eval uate whether the emission limits – the “standards promulgated pursuant to subsection (d)” not th e non-compliance with those standards (section 112(f)(2)(A)) -- should be made more stringent to reduce the risk posed after compliance with the underlying MACT standard. Therefore, we disagree that this type of control device failure scenario should be included in the RTR risk analysis.20 Comment: One commenter (0166) states that because the EPA’s analysis is based primarily on modeling and estimates, its risk asse ssment starts with a significant amount of uncertainty and the EPA’s modeling has underestimated or co mpletely missed emissions. The commenter provides the following examples: (1) to create an emission estimate for some of these emission points, the EPA assumed that facilities are using a control devi ce, without providing a basis; a nd (2) without explanation the EPA decided to equally divide emissions from potlines be tween the control device outlet stacks, and to divide roof vent emissions equally. The commenter propos es proportioning emissions to specific emission points in cases where plants had non-identical (length, number of pots, aluminum capacity) potlines. The commenter concludes that the EPA’s an alysis uses assumptions and estima tes that have an unclear basis.
Response: Control devices are in use at all facilities to limit emissi ons from potrooms, anode bake furnaces and paste plants. As explained in a response above, we have a substa ntial amount of emissions data for this source category and overall we believe that the data set used in this rulemaking is sufficiently accurate and complete and constitute s the best information the EPA has concerning the emissions and risk from this source category for c onducting the RTR. Neverthele ss, there are still some uncertainties and data gaps. For example, no data are available to characterize pitch storage tank emissions because the EPA has not identified a suitable test method for this emission stream because of its low flow rate and intermittent nature. At most f acilities potroom vent lengths are identical; in some cases the lengths vary slightly. All estimated emissions from each facility are ac counted for within that facility, even if the precise al location of estimated emissions ca nnot be confirmed. Notwithstanding these technical difficulties, as statedabove, we believe the data set used in this rulemaking is sufficiently accurate and complete and constitutes the best in formation the EPA has concerning the emissions and risk from this source category for conducting the RTR and we do not believe that the emissions proportioning method employed introduced signifi cant error to the estimated risk results.
3.2.3 Gap Filling

Comment: One commenter (0166) states th at under section 112( f)(2) the EPA must assess health risk for all emission points in order to ensure emissions ar e reduced to a safe level and to provide an “ample margin of safety to protect public health.” The co mmenter asserts that the pr omulgation of any section 112(d) standard for a source category is what trigge rs the EPA’s obligation to conduct a complete section 112(f)(2) rulemaking for the enti re source category (or subcategor y), and all HAP emissions and emission points, including but not limited to any emission points that the s ection 112(d) standard previously covered. The commenter quotes, “A [s ection 112] program which deliberately and consistently under-regulates in th e technology-based phase will lead to more, and more stringent, regulation as the Agency moves to reduce residual risks.” (S. Rep. No. 101-228, at 143 (1989), reprinted in 1990 U.S.C.C.A.N. 3385, 3555). The commenter conti nues that according to the Senate report, the EPA is required during the residual risk rulemaking to compare the existing MACT limit with stronger emissions limitations which would eliminate the a dverse health and environm ental effects caused by a source category. The commenter states that if the section 112(d) standard still allows harmful or risky levels of emissions, then the EPA is required to set a more stringent st andard to aim to eliminate those effects and provide an ample margin of safety.21 The commenter asks that the EPA assess whethe r the other HAPs listed (i .e., chromium, cadmium, arsenic, biphenyl, chlorine, ethyl benzene, hydrochloric acid, lead, ma nganese, nickel, carbon disulfide, and toluene) in a title V air permit in the rulemaking record for the Mt. Holly, SC, primary aluminum facility are coming from the primary aluminum faci lity or a collocated facility from another source category (such as secondary aluminum). The commenter notes that assuming that these are emitted from the primary aluminum portion of this facility, the EPA must address these and all other emissions from this source category. The commenter recommends the EPA perform a full assessment of the health risk for the entire source category, including all emitted HAPs.
The commenter also notes that although the EPA’ s emissions inventory document includes 0.772 tons per year of naphthalene, the EPA does not propose to set any limit to control naphthalene. The commenter observes that an IRIS review is curre ntly in process to update the EPA’s 1998 toxicity information for naphthalene. The commenter recommends that the EPA use the best available scientific information from the IRIS review during the current rulemaking, otherwise, the EPA must take a more protective approach due to the out-dated health risk referenc e information that it is using.
The commenter observes that failing to assess and reduce the health risk fo r all HAPs emitted from the source category is unlawful under section 112(f)(2), wh ich requires a full assessm ent of the health risk for the entire source category, and is also arbitrary and capricious.
Response: The primary aluminum risk assessment takes into account all HAP emissions that we are aware of at facilities in the sour ce category and for which we are able to estimate emissions of, including several HAP metals (e.g., nickel, arsenic, beryllium, l ead, cadmium, chromium, manganese, mercury, etc.), POM, D/F, HF, PCBs and COS. Regarding the HAP listed by the commenter associated with the Alumax facility in Mt. Holly, SC; the EPA has emi ssions data for several of these HAP (chromium, cadmium, arsenic, lead, manganese, and nickel) a nd the EPA has included these HAP in the risk assessment (for more information see the risk assessment document, which is available in the docket). However, for the other HAP associated with the Alumax facility listed above (biphenyl, chlorine, ethyl benzene, hydrochloric acid, carbon disulfide) the EPA does not have any recent quality-assured measurements of these HAP obtained by EPA refere nce methods. Furthermore, we have no emissions estimates for these HAP and therefore these HAP were not included in our risk assessment.
With regard to naphthalene, the final rule include s MACT emissions standards for POM from all known emissions sources (potlines, paste pl ants, pitch storage tanks and anode bake furnaces). Naphthalene is a POM. Therefore, from a regulatory perspective, th e POM MACT standards serve as surrogates for the regulation of napthalene emissions. Napthalene emissions are subject to MACT standards for this source category. With regard to the risk assessment, emissions of naphthalene were included in the risk assessment; however, both cancer and chronic, non-cancer health risks were found to be very low.

Comment: One commenter (0166) notes thatthe EPA appears not to have analyzed the Ormet Primary Reduction Corp facility in Burnside, Louisiana, which announced its reopening on May 16, 2011. The commenter remarks that the EPA must assess this f acility and cover all emissions from all facilities before finalizing action on this source category. Another facility mentioned by the commenter is the22 Columbia Falls facility in Montana, which is locate d on the Flathead River justa few miles from Glacier National Park. The commenter notes that the Colu mbia Falls facility wa s idled in 2009, but has negotiated a new power agreement that should start in April 2012.
Response: The Ormet Primary Reduction Corp facility in Burnside, Louisiana is a bauxite-to-alumina plant which is not subject to re gulation under the NESHAP for primary aluminum reduction plants. In addition, it is not a major source of HAP. With regard to the Columbia Falls facility, at the time we developed the supplemental proposal, th is facility was idle, but still had a permit. Therefore, for the supplemental proposal, since the plant was not operating, we did not assess act ual emissions. However, we estimated allowable emissions and included th ese emissions in the primary aluminum risk assessment for allowable emissions in the 2014 supplem ental proposal. However, after publication of the 2014 supplemental proposal, we learned that the nego tiations for a new power agreement referenced by the commenter were not successful and the Columbia Falls facility is now permanently shut down (see March 3, 2015 article in the FlatheadBeacon, available in the docket). Th erefore, for the final rule, as we described in the preamble, we did not include the Columbia Falls facility in our final risk results.

Comment: One commenter (0166) states th at the EPA proposes to set stan dards to control POM that the existing standard does not control. The commenter states that it is not clear from the record whether the EPA’s health risk assessment includes the curren tly uncontrolled emission points for which the EPA proposes to set standards and asserts thatthese emission points must be included.
Response: The EPA’s health risk assessment did include estimated HAP emissions from these currently unregulated emission points.

3.2.4 Health Risks

Comment: Commenter (0373) supported the EPA’s pr oposal to find risk unacceptable from the Soderberg subcategory of primary aluminum reduc tion plants based on the risk the EPA has found. Commenter (0373) cited the reasons that itagrees with the unacceptable risk finding.
Response: We acknowledge the commenter’s support for th e finding of our residual risk review for Soderberg plants for the 2014 supplemental proposal. Ho wever, as we explain in the preamble, since this facility is now permanently shut down, we dete rmined that the risk due to HAP emissions from this source category are now acceptable.
a. Cancer, Chronic and Acute Health Risks

Comment: One commenter (0166) states th at by ignoring risk from malf unctions, other violations and higher emissions during startup period s, the EPA’s proposal fails to cons ider the full cancer and chronic non-cancer health risk from this source category. The commenter observes that the CAA specifically requires the EPA to base its risk an alysis on the highest potential risk “to the individual most exposed to emissions from a source in the category or subcategory.” The commenter states that it is necessary for the EPA to analyze risk based on what emissions ma y indeed occur during a malfunction and other types of violations, even with the MACT standard in pl ace. The commenter notes that these events increase HAP emissions and thereby pose increased health risks which the EPA must consider.23 The commenter argues that the “allowable” emissions limit represents the maximum level of emissions to which an individual may legally be exposed froma given facility under th e existing MACT, but that analysis is incomplete because facilities may violat e that standard and emit HAPs at a level beyond what is “allowable” under the rule. The commenter asserts that the EPA knows that there is additional risk from malfunctions and violations and it cannot ignore that risk. The commenter asks that the EPA should account for the heightened risk from exceedances of the MACT in its risk calculation, using data regarding the use of th e malfunction exemption and enforcemen t actions in the past and other information it has regarding the hist ory or likelihood of ma lfunctions or other viol ations. The commenter points to the EPA’s use of a worst case scenario used to calculate acute health risk and suggests that the EPA should create a factor that would account for the potential for malfunctions and violations of the standard and then assess health ri sk accordingly for acute, cancer a nd non-cancer risk when emissions spike above the allowable leve l under the existing standard.
Response: We disagree with the commenter that emissi ons that exceed standards and are violations, whether or not they are caused by malfunction events, s hould be considered as part of the risk analysis. The purpose of the risk review is to evaluate wh ether the emission limits – the “standards promulgated pursuant to subsection (d)” not the non-compliance w ith those standards (secti on 112(f)(2)(A)) -- should be made more stringent to reduce the risk posed after compliance with the underlying MACT standard. To the extent that a source is violating the underl ying MACT standard, no tightening of the emission standard under the residual risk rule will avoid or mitigate against such violations. In other words, a source that is violating the MACT emissions standard promulgated und er section 112(d) would not be any more likely to be able to avoid such violatio ns and comply with a different, presumably more stringent, standard promulgated under section 112(f). Such events are violations and subject to enforcement by the EPA, the States or citizens, and an action for injunctive relief is the most effective means to address such violations, whether or not th ey are caused by malfunctions if an emissions event poses a significant health or environmental risk.
Although we disagree that emissions that result in a violation should be considered as part of the risk assessment, malfunction events do no t contribute significantly to cancer or chronic non-cancer risks for the source category in this rulemaking because ma lfunction events are inherently short-term and infrequent relative to an nual operations and emissions.
The EPA further disagrees that it should create an emissions factor that w ould account for the potential for malfunctions and violations of the standard. The EPA has no info rmation on which to base such a factor. With respect to the sugge stion of using emissions data from malfunction exemption and enforcement actions to create such a factor, we note that the commenter did not provide any such data. We further note that the accuracy of estimates of malfunction emissions provided by sources to regulatory authorities is questionabl e (e.g., they are not obtained via the EPA’s reference test methods) and we believe that these emission estimates are no t suitable for use in a risk assessment. The EPA believes that increases in emissions over a short tim e period associated with malfunction events would have minimal effect on the EPA’s estimates of actual annual emissions. Further, the acute risk assessment procedures incorporate a multiplier wh ich would account for excursions of this type.24 Comment: One commenter (0166) expresses concern that some of the HAPs emitted from this source have no reference values and the EPA has failed to assess risk for these pollutants, resulting in a potential understatement of risks. The commenter st ates that the EPA has not explained whether or how the uncertainty resulting from this understatement has been factored into the risk assessment. The commenter notes that the EPA has not stated which pollutants have no referen ce values nor has it sought information it could use to address the gaps.
The commenter states that the EPA may not treat risk as zero for a given HAP simply because it has no reference value for the health risk from that HAP. The commenter notes that section 112 requires the EPA to address all emitted HAPs in its regulation and, in the absence of an available reference dose for a given HAP, the EPA must, at minimum, add an uncertain ty factor to account for the additional risk that the subject HAP likely causes, until such time as the EPA does have a reference value to use. The commenter further emphasizes thatthe absence of a reference value means that the EPA does not know by how much it is underestimating risk to human health, it merely knows th at its health risk assessment is an underestimation.
The commenter points to section 11 2(f)(2) of the CAA as creating a critical duty and opportunity for the EPA to conduct a comprehensive and protective analysis of residual risk to public health and the environment, but asserts that over twenty years after the CAA was amended, the Integrated Risk Information System (IRIS) review process is bogged down for many pollutants and sufficient studies for some HAPs have not been conducted to allow calculation of reference doses, re ference concentrations, or potency values. The commenter asserts that the EPA should prevent the dela y in this process from undermining its residual risk analys is for this and other source cat egories. The commenter recommends that if the EPA determines that it must wait until these reassessments are complete to use the newly available scientific information, then the EPA must take a more protective approach due to the out-dated health risk reference information that it is using.
The commenter suggests that to account for the delay a nd lack of reference values for some pollutants, and the fact that it is still updati ng the toxicity information for othe r pollutants, the EPA must set a regulatory deadline no later th an eight years from the finalization of these rules, to review the current residual risk analysis and again perform a residual risk rulemaking once additional data on reference values become available.
Response: This issue was addressed by the EPA’s SAB in its May 7, 2010 response to the EPA Administrator. 5 In that response, the Science Advisory Board (SAB) panel recommended that, for HAP that do not have dose-response values from the EPA’ s list, the EPA should consider and utilize, as appropriate, additional sources for suchvalues that have undergone adequa te and rigorous scientific peer review. The SAB panel further recommended that the inclusion of additional sources of dose-response values into the EPA’s list should be adequately docu mented in a transparent manner in any residual risk assessment case study. We agree with this approach and have considered other sources of dose-response

5 The SAB peer review of RTR Risk Assessment Methodologies is available at: http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F00668381 /$File/EPA-SAB-10-007-unsigned.pdf

.25 data when conducting our risk determinations under RTR. However, in some instances no sources of information beyond the EPA’ s list are available.
The EPA agrees that we should ultimately develop toxi city values for all HAP u tilizing all credible and relevant toxicity information. The need to update a ssessments with newly available data as well as the need to complete toxicological assessments for all HAP lacking dose-response assessments further increases the importance of Agency activities to streamline and fully utilize the EPA’s already overloaded IRIS program. To that end, the EPA has alwa ys prioritized for future IRIS assessments those HAP without dose-response values but with the greatest potential for public exposure. As a result of this prioritization, while not all HAP may have scientifically accepted dose- response values that can be used in residual risk assessments, it is clear that the vastmajority of HAP which might carry the potential to significantly impact the results of residual risk assessments do, in fact, have credible dose-response values. Thus, while we are not yet at the point where all HAP have dose-response values, we are generally capable of deriving reasonable risk es timates for those HAP which dominate the risks from any one source category. In the course of each re sidual risk assessment, should we encounter HAP without dose-response values which carry the potential to create significa nt risks, we shall clearly point those out as uncertainties and target them for fu ture IRIS assessments. Moreover, as additional doseresponse values become available, the EPA will incor porate these dose-response values into future risk
assessments. The EPA disagrees that with the commenter that we did not state which HAPs currently have no reference value. Table 3.1-1 in the Residual Risk Assessment for the Primary Aluminum Production Source Category in Support of the 2014 Supplemental Proposal lists all the HAP emitted by the source category, as well as whether there is an availabl e cancer, chronic noncancer, and/or acute dose-response value.

Comment: One commenter (0166) argues that even if a chronic, non-cancer hea lth risk number below the EPA’s safety HQ threshold of 1 might be accept able in some circumstances, the EPA has failed to justify how it could be acceptable when combined with all of the other kinds of health risks that the EPA has found, including high cancer risk (that is, above 1-in-1 million), multipathway risk that is 7,000 times the EPA’s screening threshold, and acute risk that is 10 times the EPA’s threshold. The commenter notes that these health risks are not happening independently, but are combining together for the same individual people who are most expos ed to this source category. The co mmenter states that the EPA may not permit a single source covered by this rulemaki ng to consume the entire non-cancer risk safety factor, and the EPA must achieve a lower level of risk from this source category to ensure acceptable risk for the most exposed person in a community where ther e is a history of exposures from multiple sources. The commenter concludes that the EPA should find this category’s total health risk to be unacceptable.
Response: We note that the commenter is referring to the 2011 risk assessment, which is superseded by the 2014 risk assessment. Pollutant-specific reference c oncentrations (RfCs) are not absolute thresholds, but estimates of chronic inhalation e xposures at or below which health effects would not be expected to occur after a lifetime of exposure, including in sensitive subgroups. These RfCs are developed using a health-protective approachand TOSHI values of 1 or less ar e generally considered to carry no appreciable risk of adverse health effects. We gene rally draw no bright lines of acceptability regarding26 cancer or noncancer risks from source category HAP emi ssions. It is always im portant to consider the specific uncertainties of the emissi ons and health effects information regarding the source category in question when deciding exactly what level of cancer and noncancer risk should be considered acceptable. In addition, the source cate gory-specific decision of what c onstitutes an acceptable level of risk should be a holistic one; thatis, it should simultaneously consid er all potential h ealth impacts - chronic and acute, cancer and noncancer, and multip athway - along with thei r uncertainties, when determining the acceptable level of source category risk. The Benzene NESHAP decision framework of 1989 acknowledged this; in today’s world, such flexib ility is even more imperative, because new information relevant to the question of risk accep tability is being developed all the time, and the accuracy and uncertainty of each piece of informati on must be considered in a weight-of-evidence approach for each decision. This relevant body of info rmation is growing fast (and will likely continue to grow faster and faster), necessitating a flexib le weight-of-evidence approach that acknowledges both complexity and uncertainty in the simplest and most transparent way possible. While this challenge is formidable, it is nonethele ss the goal of the EPA’s RTR decision-making, and it is the goal of the risk assessment to provide the information to support the decision-making process.
In this case, after considering all th e available risk information and the uncertainties associated with that risk information, risk was found to be acceptable. However, as is the case all RTR reviews, as part of the second step ample margin of safety analysis, we considered additiona l controls and process improvements that might further reduce risks in a cost -effective, technically feasible manner. In the case of the prebake primary aluminum sources, we did not find any such controls. However, as explained in the preamble, we are finalizing standards for Soderb erg potlines under section 1 12(f) under step two of the risk decision framework to ensure an ample margin of safety.
With respect to the potential for multipathway risk, the results referenced by the commenter were from a worst-case screening scenario and do not indicate that adverse multipathway effects are expected to occur. The screening assessment used highly conservati ve assumptions designed to ensure that facilities with results below the screening threshold values di d not have the potential for multipathway impacts of concern. The screening scenario is a hypothetical scenario, and due to the theoretical construct of the screening model, exceedances of the thresholds are not directly translatable into estimates of risk or hazard quotients for these faciliti es. Rather, the results of the sc reening multipathway assessment only indicate that we cannot rule out th e potential for multipathway effects.

b. Cancer

Comment: One commenter (0162) states that the EPA divides POM compounds into a number of separate groups with similar URE values, assign ing each group the URE of the most potent compound in the group. The commenter notes that th is approach tends to overestimate risk.
Response: The commenter is incorrect. The emissions in ventory for this sour ce category contained individual POM and those pollutants were not assi gned to a group. For each POM, a chemical-specific URE was applied in conduc ting the risk assessment.

Comment: One commenter (0162) states that the EPA’s POM dose response model is a likely worst case estimate of carcinogenic risk. The commenter observes that in general this model assumes that27 every molecule of exposure has added risk, without physiological defense mechanisms to protect against or repair damage to cells or genetic material, and it assumes that low doses of POM are potent in linear proportion to the responses seen of high doses. The commenter asserts that gi ven the wide-spread and common occurrence of POM compounds in nature, it is not likely that there are no defense mechanisms in the human body to protect against POM impacts, nor is it likely that low dose exposures are as potent molecule-for-molecule as high dose exposures. The commenter concludes that the EPA dose-response model likely overestimates risk for POM compounds especially at low exposure levels, but the quantification of the overestimate is not possible at this time.
Response: We disagree that the EPA should considerthat the human body has natural defense mechanisms against health effects associated withPOM exposure and note that, the commenter provided no evidence as to the extent of these defenses. Re gardless, in general the development of UREs and RfCs considers results from animal toxicological studies where an effect has been observed despite whatever natural defenses (if indeed there are an y) from HAP are present in the species tested.

Comment: One commenter (0166) expresses concern that 41,000 people face lifetime cancer risk of 1- in-1 million or more with estimated incidence of 0.005 per year based on inhalation alone, because they live near primary aluminum facilities, based on allo wable emissions. The commenter disagreed with the EPA’s reliance on the 1989 Benzene Rule’s presumpti on that a 100-in-1 million lifetime cancer risk is acceptable today, as this fails to account for evol ving science and societal standards. The commenter states that this analysis is arbitrar y and capricious for th e following reasons:

 The CAA requires an up-to-date contemporary asse ssment, section 112(f)(2) directs the EPA to assess and address risk remaining to public heal th and the environment 8 years after the MACT standard is in place, an inherent direc tion to take account of new circumstances;

 There is significant new information on the factor s the EPA discussed in its old rulemaking that should influence its analysis of what level of risk is currently “acceptable;”

 Scientific research has evolved dramatically since the EPA set that presumption. The commenter cites risk assessment studies and guidance, stud ies on children’s exposure to toxics, and CDC reports as providing evidence of the EPA and other federal funded research and developments in health effects of chemicals (examples are provid ed as attachments to the commenter’s letter);

 The EPA’s commitment to environmental justice mu st inform its considera tion of what level of risk is “acceptable” as re quired by the 1994 Environmental Justice Executive Order and 2010 guidance (i.e., Interim Guidance on Considering Environmental Justice During the Development of an Action) to direct all federal agencies to take environmental justice into consideration; and

 American values and policies have evolved to tolerate less hea lth risk from industrial pollution since the 1988 Survey of Societal Risk , and Congress amended the CAA after the 1988 study to reduce deaths and human health risks from air pollution, presumably because it did not consider the risk of death from air pollution at that time to be acceptable.28 Response: As an initial matter, we note that in 1990 C ongress codified in section 112(f)(2)(B) of the Clean Air Act the approach we use for our residual risk analyses. Under that approach, the 100-in-1 million cancer risk is not a bright line indicating that ri sk is “acceptable.” Rather, we consider this health metric in conjunction with a variety of health fact ors and their associated un certainties to determine whether the risk is acceptable. Wher e we conclude that the risk is notacceptable, we cannot and do not consider costs in requiring controls to bring risks down to an acceptable level. However, the analysis of whether risk is acceptable is not th e endpoint. Once we determine that c ontrols are sufficient to ensure that risk is acceptable, we again review the health metrics (e.g., cancer and chronic non-cancer risks) and their associated uncertainties in c onjunction with the costs of controls , technical feasibility, and other relevant factors, to determine whether additional contro ls should be required to provide an ample margin of safety.
We generally draw no bright lines of acceptability regarding cancer or noncancer risks from source category HAP emissions. It is always important to consider the specific uncertainties of the emissions and health effects information regarding the sour ce category in question when deciding exactly what level of cancer and noncancer risk should be cons idered acceptable. In addition, the source categoryspecific decision of what constitutes an acceptable level of risk should be a holistic one; that is, it should simultaneously consider all potential health impa cts – chronic and acute, cancer and noncancer, and multipathway -- along with all their uncertainties, when determining the acceptable level of source category risk. The Benzene NESHAP decision frame work of 1989 acknowledged this; in today’s world, such flexibility is even more imperative, because new information relevant to the question of risk acceptability is being developed all the time, a nd the accuracy and uncerta inty of each piece of information must be considered in a weight-of-evidence approach fo r each decision. This relevant body of information is growing fast (and it will continue to grow faster and faster), necessitating a flexible weight-of-evidence approach that acknowledges both co mplexity and uncertainty in the simplest and most transparent way possible. While this challenge is formidable, it is nonethe less the goal of the EPA’s RTR decision-making, and it is the goal of the risk assessment to provide the in formation to support the decision-making process.
Moreover, the commenter does not support its conten tion that people are now unwilling to accept a level of risk that was acceptable at the time the Clean Air Act was amended in 1990. Nor does the commenter support how science has evolved in a way that would undermine the stat utorily codified framework for determining risk acceptability. Al so, for purposes of this rulemaking, we performed a demographic analysis to inform our risk-based decision proce ss and that analysis is available in the docket.

Comment: One commenter (0166) states th at the EPA should reduce the thre shold of what cancer risk is presumed to be acceptable, and find the estimated can cer risk in the proposed rule to be unacceptable. The commenter observes that although the HON d ecision found that the EPA was not required to achieve a lifetime cancer risk of 1- in-1 million, that decision recognize s that the EPA has full authority to protect public health by reduci ng risk to a lower level, and the d ecision did not authorize the EPA to continue presuming forever that any lifetime cancer risk between 1-in-1 million and 100-in-1 million is acceptable.29 Response: As stated in prior responses, we do not consid er the 1-in-1 million MIR level as a bright line mandated level of protection for esta blishing residual risk standards. In determining the ample margin of safety (i.e., setting the level of the standard), health risk is one factorthat we must consider, along with other factors such as cost and technological feasibili ty. Balancing these and other factors with the ability to achieve meaningful risk reduction is a critical component of the residual risk rulemaking process.
As noted above, considering all the available risk information and the associated uncertainties, risk was found to be acceptable. However, as is the case in a ll RTR reviews, as part of the second step ample margin of safety analysis, we considered additio nal controls and process improvements that might further reduce risks in a cost-effective, technically feasible manner. For th e primary aluminum source category, we didn't find any such cost-effective controls other than the controls and standards for Ni, As and POM from Soderberg potlines which are described in the preamble.

c. Acute

Comment: One commenter (0162) states that the EPA cal culates the acute healthrisk of exposures using a combination of worst case factors, which ex aggerates risk as it requires the extremely small probability of all these factors occurring together at the exact same time. Still, the commenter observes, the EPA concludes that the acute level health risk from the primary aluminum source category is within acceptable bounds. The commenter emphasizes that the acu te risk estimates the EPA calculates are very conservative and have a low probability of occurring.
Response: The commenter is correct that the accuracy of the acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emission rates, meteorology and human activity pa tterns. The EPA conservatively assumes that individuals remain for 1 hour at th e point of maximum ambient concentration (as determined by the cooccurrence of peak emissions and worst-case mete orological conditions) and these assumptions would tend to result in worst-case estimates of actual exposur es as it is unlikely that a person would be located at the point of maximum exposure during the time when peak emissi ons and worst-case meteorological conditions occur simultaneously.

Comment: In response to the 2011 proposal, one comment er (0162) disagrees with the EPA’s use of hourly emission rates estimated from long term emissi on averages and then used for short term acute health concerns. The commenter disagr ees with the EPA’s use of a safety factor applied to the estimated hourly maximum for short term acute health concer ns. The commenter notes that the EPA proposed a factor of 5, instead of a default factor of 10, for alumin um facilities citing data in the preamble that demonstrates peak hourly emissions are less variable than many other source types, due to the nature of the multiple pots in the potline and the individual pots wh ich operate in cycles that are not in phase with each other. The commenter observes that the EPA conduc ted a statistical analysis of available data and established a factor of 4.5 times the mean fo r estimating maximum hourly concentrations. The commenter states that the EPA uses a conservative f actor of 5 times the average hourly emissions rate, rather 4.5, in the acute screening a ssessment. The commenter agrees thatthe factor of five is more realistic than the default value the EPA commonly uses of 10, but states that th e factor of 5 is still a conservative factor that will also lead to an overestimate of risk for acute exposures.30 Response:
To develop screening estimates of acute exposures in the absence of hourly em issions data, we develop estimates of maximum hourly emissions rates by multip lying the estimated average actual annual hourly emissions rates by a default factor to cover routinely variable emissi ons or by a source category specific factor developed based on source cat egory specific information. We choose the factor based on process knowledge and engineering judgment reflecting, where appropriate, circumstan ces of the particular source category. The default factor reflects the fi ndings of the Texas study of short-term emissions variability, which showed that most peak emission events in a heavily-industrialized were less than twice the annual average hourly emissions rate. 6
For the primary aluminum reduction source category, information was available to determine processspecific factors. The processes in this source category are typically equipped with controls which will not allow startup of the emission source until the associated control device is operating and will automatically shut down the emission source if the associated controls malfunction. The potline processes typically operate continuously, so there are no significant spikes in emissions. Consistent with this information, the EPA believes emissions from th e potlines are relatively consistent over time with minimal fluctuation.

The EPA estimated that the maximum allowable emi ssions for potlines are about 1.5 times higher than the average long-term actual emissions for these sour ces. Therefore, the EPA also assumes that hourly emissions rates from potlines could occasionally in crease by a factor of up to 1.5 times the average hourly emissions. The EPA believes this is a valid mu ltiplier to estimate maximum acute emissions from potlines. Paste production and anode baking processes ma y have specific cycles with peak emissions occurring for a part of that cycle. The EPA believes these peak emissions could be as high as 2 times the average emissions for paste plants and bake furnaces.

Comment: One commenter (0166) disagrees with the EPA’ s approach to calculating a multiplying factor to calculate the maximum acute health risk based on a worst case scenario. The commenter objects to the use of a single facility’s data for two potlines to calculate the multiplying factor for the source category and disagrees with the EPA’s decision to us e a multiplying factor of 4.5 to estimate worst case HQ values when the referenced dataset indicated a maximum emission rate of 5.6 times the average rate of routine operations.
Response: See response to comment preceding this one.

Comment: One commenter (0166) asks whether the EPA’ s acute health risk worst case analysis accounts for the higher level of emissions that may occur during startup periods . The commenter cites a comment letter from the National Park Service (NPS) on the Columbia Falls Aluminum Company (CFAC) power sales agreement (included as an atta chment to the comment letter) stating that startup emissions have caused a serious co ncern around primary aluminum plants in the past because “fluoride levels spike far beyond those typically observed during routine plant operations.” The commenter states

6 See http://www.tceq.state.tx.us/compliance/field_ops/eer/index.html or the docket to access the source of these data.31 that the EPA must assess the higher risk that is associated with startup periods and set a residual risk standard to ensure acceptable risk, and provide an ample margin of safe ty to protect public health during these times. The commenter is concerned that although emissions are known to be higher for this industry during startup periods and the EPA even proposes an unlawful exemption for startup periods under section 112(d), the EPA does notaddress higher startup emissions at all under section 112(f)(2). The commenter argues that this is a significant oversight that the EPA s hould correct, and it must finalize a more protective standard accordingly.
Response: We believe startup events do not contribute si gnificantly to chronic cancer or noncancer risks for the source category. Startup events for this sour ce category are inherently s hort-term and infrequent relative to continuous annual operations and emissions. Affected sources in this industry often go for years between startups. The commenter did not supply any data to the contrary that would change the acute multipliers calculated for this source category that would lead us to believe that peak modeled hour events are underestimated. Further, no specific data on the alleged spiked startup emissions of fluoride were provided by the commenter or NPS.

Comment: One commenter (0166) recommends that the EP A should at least use a factor of ten to calculate and assess the worst case s cenario of what acute health risk the existing MACT would allow, as it has done for other rulemakings. The commenter pr oposes that even a factorof ten, however, is not necessarily high enough to assess th e true risk to the most-exposed individual and community, such as when a facility’s emissions could spike to 100 times or more its usual emissions due to control device failure. The commenter concludes that in view of this, even a 10x margin simply does not make sense, and is arbitrary and capricious.
Response: Primary aluminum potroom emissions are expectedto be less variable than typical industrial sources because they are composedof contributions from numerous individual pots which are operated continuously and are not synchronizedwith regard to anode changes, crust breaking and other events that may affect emissions. Based on a substantial data set, as well as the proce ss characteristics, the EPA concluded that primary aluminum s ource category emissions were gene rally consistent and therefore a lower acute risk multiplier should be used instead of the typical default value. The commenter did not supply any specific data that woul d indicate that the EPA should cha nge the acute multipliers used to estimate acute peak emissions for this source category.

Comment: One commenter (0166) questions why the EP A has failed to justify not requiring the reduction of acute health risk below 1 after finding a le vel of acute risk that is 10 times the EPA’s safety threshold. The commenter disagrees with the EPA’s determination that the acute hea lth risk could be safe or acceptable, based on concerns that the EPA did notconsider the combined acute health risk for multiple pollutants; did not assess the acute health risk based on allowable emissions; did not calculate or provide any information on facility-wide acute heal th risk; is not accounting for health risk due to malfunctions; and did not consider the Columbia Fa lls Aluminum Company facility because it was not operational. The commenter asserts that the EPA’s ri sk screening cannot be considered conservative and the acute risk number is not the worst-case scenario.
Response: As noted above, the acute risk screen is a wo rst-case screening scenario. It assumes worstcase meteorology, peak emissions for all emission poi nts occurring concurrently, and an individual being32 located at the site of maximum c oncentration for an hour. The screen provides us information that for those facilities where the hazard quotients are less th an 1, we do not expect acute effects, and for those situations where the hazard quotient s are greater than 1, the potential for acute effects exists. For those situations where the acute hazard quotients are great er than 1 based on our screening assessment, the fact that it is a screeni ng-level assessment is taken into cons ideration in the decision. The finding of unacceptable risks is not based on any one risk me tric (e.g., acute hazard quotients), but rather considering all of the health information available and the degree of uncertainty associated with that information. Considering these factors, the EPA does not believe that in all RTR reviews, HQ values must be less than or equal to 1 in order for source category risk to be considered acceptable. Rather, the EPA finds that acute risks must be judged on a case by case basis in the cont ext of all the available health evidence and risk analyses, including the re sults of the chronic, non- cancer and cancer risk analyses. Using this holistic approach, the EPA consider s the overall health risk to be acceptable for this source category. Additional information regarding the finding of acceptable risk can be found in section IV.C. of the proposal preamble as well as section IV.A. of the promulgation preamble.

Comment: Two commenters (0165, 0369 and 0166) object to the use of Acute Exposure Guideline Levels (AEGL) or Emergency Response Planning Guide lines (ERPG) values to address acute exposures in the residual risk assessments, asserting that they were created for emergency exposure scenarios, not to define “acceptable” lifetime risk for a person living near an industria l facility, and would be expected to underestimate risk. Commenter (0165 and 0369) refers to the December 2002 EPA document, “A Review of the Reference Dose and Reference Concen tration Processes,” where the EPA stated that the primary purpose of the AEGL program is to deve lop guidelines for once-in -a-lifetime short-term exposures to airborne concentratio ns of acutely toxic chemicals. Commenters (0165 and 0369) observes that they are not meant to evaluate the acute impacts from routine emi ssions that occur over the life of a facility. Further, commenter (0165 a nd 0369) asserts that, unlike the refe rence concentrations (RfCs) for chronic exposures, the AEGLs and ERPGs do not incl ude adequate safety and uncertainty factors and cannot be relied upon to protect the p ublic from the adverse effects of exposure to toxic air pollutants. The commenter concludes that use of AEGLs or ERPG s in residual risk assessm ents is not appropriate and does not ensure that public heal th is adequately protected from the acute impacts of HAP exposure.
Commenters (0165, 0369 and 0166) support the EPA’s use of the California Reference Exposure Levels (RELs) to address acute exposures in the residual risk assessments and continue to urge the EPA to use these RELs for these assessments.
Response: The EPA does not rely exclusively upon AEGL or ERPG values for assessment of acute exposures. Rather, the EPA’s approach is to consider various acute health effect reference values (see 79 FR 37857), including the California REL, in assessing the potential for risks from acute exposures. To better characterize the potential heal th risks associated with estimatedacute exposures to HAP, and in response to a key recommendation from the SAB’s p eer review of the EPA’s RTR risk assessment methodologies, 7 we generally examine a wider range of available acute health metrics (e.g., RELs, AEGLs) than we do for our chronic risk assessments . This is in response to the SAB’s acknowledgement

7 The SAB peer review of RTR Risk Assessment Methodologies is available at: http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966 E263D943A85257 71F00668381/$File/EPA-SA B-10-007-unsigned.pdf

.33 that there are generally more data gaps and inconsistencies in acute reference values than there are in chronic reference values. In some cases, when Reference Value Arrays 8 for HAP have been developed, we consider additional acute valu es (i.e., occupational and international values) to provide a more complete risk characterization. As discussed in the preamble to the proposedrule (79 FR 72914), the exposure guidelines the EPA considers depends on which exposure guidelines are available for the various hazardous air pollutants emitted. The EPA us es AEGL and ERPG values (when available) in conjunction with REL values (again, when available) to characterize potential acute health risks. However, it is often the case that HAP do not have all of these acute reference benchmark values. In these instances, the EPA describes the potential acute he alth risk in relation to the acute health values that are available. Importantly, when interpreting th e results, we are careful to identify the benchmark being used and the health implications associ ated with any specific benchmark being exceeded.

d. Chronic Non-Cancer

Comment: One commenter (0166) states thatfailing to look at the potentia l for spikes in emissions over a person’s lifetime may underestimate th e amount of chronic risk based on pollutants that persist in the environment, including POM, which is one of the pr imary risk drivers for the primary aluminum source category. The commenter asserts that the failure to account for greater risk due to malfunctions violates section 112(f)(2) and is arbitrary and capricious.
Response: We disagree with the commenter that emissi ons that exceed standards and are violations, whether or not they are caused by malfunction events, s hould be considered as part of the risk analysis. The purpose of the risk review is to evaluate wh ether the emission limits – the “standards promulgated pursuant to subsection (d)” not the non-compliance w ith those standards (secti on 112(f)(2)(A)) -- should be made more stringent to reduce the risk posed after compliance with the underlying MACT standard. To the extent that a source is violating the underl ying MACT standard, no tightening of the emission standard under the residual risk rule will avoid or mitigate against such violations. In other words, a source that is violating the MACT emissions standard promulgated und er section 112(d) would not be any more likely to be able to avoid such violatio ns and comply with a different, presumably more stringent, standard promulgated under section 112(f). Such events are violations and subject to enforcement by the EPA, the States or citizens, and an action for injunctive relief is the most effective means to address such violations, whether or not th ey are caused by malfunctions if an emissions event poses a significant health or environmental risk.
Primary aluminum potlines are typi cally operated in continuous mode. Some batch processing of anode baking and paste production occurs, however the bake furnaces and pa ste plants, when operating, are in operation 24 hours per day, and do not produce widely varying emissions. Further, all actual emissions data for potlines and anode bake furnaces are ba sed on performance tests which are conducted during maximum periods of production. Furthermore, we believ e SSM events do not contribute significantly to

8 U.S. EPA. (2009) Chapter 2.9 Chemical Specific Reference Values for Formaldehy de in Graphical Arrays of ChemicalSpecific Health Effect Reference Values for Inhalation Exposures (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R–09/061, and available on-line at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003

.34 cancer or chronic noncancer risks for the source categ ory in this rulemaking because SSM events are inherently short-term and infrequent re lative to annual operations and emissions.

Comment: One commenter (0166) disagrees with the EP A’s acceptability determination for chronic non-cancer health risk. The commenter urges the EPA to not assume that 1 is an accept able level of chronic non-cancer risk from a single major air toxi cs source category. The commenter states that by finding that a non-cancer TOSHI of 1 or below is nota human health concern, the EPA has arbitrarily ignored its staff’s past scientific assessment of this issue, in th e 2002 internal memo Residual Risk Program: Selection of Hazard Index Li mits, where the EPA stated that the default HI limit for chronic non-cancer risks should be well under 1.0 for individual sources. Specifically, staff then recommended that it should be no higher than 0.2. The comme nter recommends that the EPA reduce the TOSHI presumptive acceptability threshold to 0.2 or below to ensure that the EPA is fully protecting the mostexposed people in local communitie s exposed to multiple sources and types of toxic air pollution.

The commenter also notes that the EPA has not ev aluated other nearby sources of HAPs (beyond this source category) (except in its facil ity-wide risk assessment), and has failed to consider the interaction of multiple health risks found for affected communities.
The commenter expresses concern that the EPA c oncedes that the TOSHI itself “may have been underestimated,” in a statement, conf using to the commenter, that only says that “impacts on organs or systems that occur above the critical dose have no t been included in the TO SHI calculations.” The commenter observes that this is a dramatic way of underestimating ris k, in that if the EPA takes out impacts that are occurring above th e critical dose, the EPA is ignori ng health risk that has already reached an unacceptable level. The commenter states that this has no rational basis and demonstrates that the EPA must reduce the TOSHI.
Response: The EPA disagrees with the commenter thatTOSHI value greater than 0.2 should be considered unacceptable. Pollutant-specific reference c oncentrations (RfCs) are not absolute thresholds, but estimates of chronic inhalation e xposures at or below which health effects would not be expected to occur after a lifetime of exposure, including in sensitive subgroups. These RfCs are developed using a health-protective approac h, and TOSHI values of 1 or less ar e generally considered to carry no appreciable risk of adverse health effects. Theref ore, there is no need to compound this protection by suggesting that a source category maximum TOSHI va lue would need to be at or below 0.2 to be considered acceptable. The commenter’s source for its statement that default HI limit should be established at 0.2 rest on an internal EPA staff me mo (from 2002) which was never adopted as agency policy (and never reviewed by the public or by any peer review body) and c onsequently carries no precedential weight.
We generally draw no bright lines of acceptability regarding cancer or noncancer risks from source category HAP emissions, and that it is always important to consider the specific uncertainties of the emissions and health effects information regardi ng the source category in question when deciding exactly what level of cancer and nonc ancer risk should be considered acceptable. In addition, the source category-specific decision of what constitutes an acceptable level of risk should be a holistic one; that is, it should simultaneously consider al l potential health impact s - chronic and acute, cancer and noncancer, and multipathway - along with their uncertainties, when determining the acceptable level of source35 category risk. The Benzene NESHAP decision frame work of 1989 acknowledged this; in today’s world, such flexibility is even more imperative, because new information relevant to the question of risk acceptability is being developed all the time, a nd the accuracy and uncerta inty of each piece of information must be considered in a weight-of-evidence approach fo r each decision. This relevant body of information is growing fast (and it will continue to grow faster and faster), necessitating a flexible weight-of-evidence approach that acknowledges both co mplexity and uncertainty in the simplest and most transparent way possible. While this challenge is formidable, it is nonethe less the goal of the EPA’s RTR decision-making, and it is the goal of the risk assessment to provide the in formation to support the decision-making process.
With respect to TOSHI values pote ntially underestimating risk, and the confusion over the statement that “impacts on organs or systems that occur above the cr itical dose have not been included in the TOSHI calculations” the Residual Risk Assessment for the Primary Aluminum Production Source Category in Support of the 2014 Supplemental Proposal document states insection 2.7.2:
All TOSHI calculations presented here were ba sed exclusively on effects occurring at the “critical dose” (i.e., the lowest dose that pr oduces adverse health effects). Although HQs associated with some pollutants have been aggr egated into more than one TOSHI, this has been done only in cases where the critical dose affects more than one target organ. Because impacts on organs or systems that occur above the critical dose have not been included in the TOSHI calculations, some TOSHIs may have been underestimated.
This paragraph means that the EPA only calculates TO SHI values from multiple HAP that have the same target organ identified as the basis for the quantitative reference concentrati on (e.g., RfC) for that HAP. This means that if a HAP has a reference concentra tion based on kidney effects, it will be included in TOSHI calculations with other HAP whose reference c oncentration is based on kidney effects. Thus, the above statement is meant to acknowledge that it is possible that a HAP whose re ference concentration is based on for example, kidney effects, would not be included in TOSHI calculations for respiratory effects even though it may have some effect on the respiratory system. This is because reference concentrations are based on a specific target organ and are not transferrable to other organs that HAP effects (e.g., in the example above, the quantitative re ference concentration for kidney effects would not be the same as if a reference concentration had be en developed for respiratory effects). Importantly however, the TOSHI should not be interpreted as a probabi lity of adverse effects, or as strict delineation of “safe” and “unsafe” levels. Rather, the TOSHI is an other measure of the potential for adverse health outcomes associated with pollutant exposure, and need s to be interpreted carefu lly by health scientists and risk managers.
3.2.5 Risk Assessment Methodology
a. Multipathway Exposures

Comment: One commenter (0162) disagrees with the EPA’s statement that there may be some risk from multipathway exposures based on the EPA’s screening an alysis, stating that the EPA should also include in the preamble discussion that the small annual POM emissions for the entire s ource category (91 tpy) is minuscule compared to other sources. The commenter states that the EPA s hould note in the preamble36 that the contribution of primary al uminum facilities to this universe of multipathway POM exposures is too insignificant to merit further review and the pote ntial impacts are too small to determine and likely infinitesimal.
Response: We do not believe that multipathway risk can be dismissed based on the results of the risk analysis. In addition to the quantity of emissions from a source, the pr oximity of a source to a receptor also affects the associated impacts.

Comment: One commenter (0166) states that the EPA’s choi ce to restrict multipathway risk screening to only contaminants that are identifie d in the 2003 Risk Assessment Guid ance as being both persistent and bioaccumulative in the environment is not support ed by the 2003 Guidance and underestimates risks from HAPs emitted by this source category. The commenter specifically names naphthalene, chromium, cadmium, arsenic, manganese, and nickel as pollutant s that require a full multipathway risk assessment, but also states that any and all metals should have a full multipathway risk assessment. The commenter recommends using the California OEHHA risk assessment guidelines. The commenter concludes that the EPA may not assume that the ingestion risks are ze ro for these pollutants, a nd asserts that doing so when science shows otherwise is arbitrary and capri cious. The commenter states that to not assess multipathway risk from exposure to these HAPs vi a incidental ingestion, both individually and cumulatively, results in an underestimate of the risks of HAP emissions from this source category.
Response: We acknowledge we do not have screening valu es for some of the PB-HAP but we disagree that the multipathway assessment is inadequate. In the Air Toxics Risk Assessment Reference Library, we developed the current PB-HAP list considering a ll of the available information on persistence and bioaccumulation (see http://www2.epa.gov/fera/air-toxics -risk-assessment-refere nce-library-volumes-1- 3), specifically Volume 1 Appendix D). (The Air T oxics Risk Assessment Reference Library provides information on the fundamental principles of risk-basedassessment for air toxics and how to apply those principles in different settings (e.g., facility-specific) as we ll as strategies for re ducing risk at the local level.) This list considered HAP identified as PB-HAP by other EPA Program Offices (e.g., the Great Waters Program), as well as information from the persistent, bioaccumulative and toxic (PBT) profiler (see http://www.pbtprofiler.net/). This list was peer-reviewed by th e SAB and found to be acceptable, and therefore we consider it to be reasonable fo r use in the RTR program. Based on these sources and the limited available information on the persiste nce and bioaccumulation of other HAP, we do not believe that the potential for multipathway risk fro m other HAP rises to the level of the PB-HAP currently on the list. However, in th e future we may add more pollutant s to the multipathway analysis if we determine it is appropriate to do so.

Comment: One commenter (0166) disagrees with the EPA’s basing its multipathway assessment on actual PAH emissions instead of allowable PAH emissions. The commenter maintains that the EPA’s analysis is likely to be an underestimate of the h ealth risks from multipathway routes of exposure. The commenter notes that the EPA has recognized the need to use allowable emissions to assess inhalation risk, and should do the same for multipathway risk. Th e commenter also notes that intermittent or short spikes of PB-HAPs can represent a significant hea lth risk because the contaminants stay in the environment and small amounts can accumulate into larger amounts over time. The commenter states that failing to account for the full multipathway risk th at the EPA’s existing standard allows, or for risk37 due to violations from that standard, violates the section 112(f)(2) re quirement to protect the individuals most exposed to this source category.
Response: Regarding the commenter’s assertion that we did not base the multipathway risk assessment on allowable emissions, we believe it is reasonable for the multipathway risk assessment to be based on actual emissions for this source category, and not the allowable level of emissi ons that facilities are permitted to emit. As discussed in the preamble, the uncertainties associated with the multipathway screen combined with the uncertain ties associated with the allowabl e emissions estimates, would make a multipathway risk assessment based on allowable emissions highly uncertain. Such an assessment would be too uncertain to support a regul atory decision. We also note that in our inhalation assessment, these allowable emissions estimates were used and did not show significant inhalation risk, and therefore, we did not focus on the uncertainty in the emissions.
b. Risk for Children

Comment: One commenter (0166) states th at the residual risk assessment underestimates risk to the developing child and fetus. The commenter observes th at biological differences in the developing child and fetus can result in increased cancer and non-ca ncer risk due to both increased exposure and increased vulnerability, and emphasizes that the EPA must account for the increased susceptibility of children to HAP emissions from this source category in the risk assessment. The commenter states that the most recent review of the EPA risk assessmen t practices by the National Academy of Sciences (NAS) explicitly advises the EPA to include in utero exposures as a period of increased sensitivity to carcinogens, and the commenter cites evidence from th e most recent California draft risk assessment guidelines recommending assessment of health risk due to breast milk exposure as well as dermal and other ingestion exposures.
Response: We disagree with the comment that the risk assessment for this source category does not consider the groups that may be mo st at-risk (e.g., children). When the EPA derives exposure reference concentrations and unit risk estimates for hazardous air pollutants, it also considers the most sensitive populations identified in the availabl e literature, and importantly, these are the values used in our risk
assessments. 9
We acknowledge that population subgroups, including ch ildren, may have a potential for risk that is greater than the general popul ation due to greater relative exposure and/or greater susc eptibility to the toxicant. The assessments we undertake to estimate risk account for this potential vulnerability. With respect to exposure, the risk asse ssments we perform implicitly account for this greater potential for exposure by assuming lifetime exposure, in which populations are conservatively presumed to be exposed to airborne concentrations at their residence c ontinuously, 24 hours per day for a full lifetime, including childhood. With regard to ch ildren’s potentially greater suscepti bility to non-cancer toxicants, the assessments rely on the EPA (o r comparable) hazard identification and dose-response values which have been developed to be prot ective for all subgroups of the ge neral population, in cluding children.

9 U.S. EPA. A Review of the Reference Dose and Referenc e Concentration Processes. U. S. Environmental Protection Agency, Risk Assessment Forum, Washington, DC, EPA/630/P-02/002F, 2002. Available online at http://www.epa.gov/raf/publications/pdfs/rfd-final.pdf38 For example, a review 10 of the chronic reference value proce ss concluded that the EPA’s reference concentration (RfC) derivation proc esses adequately considered poten tial susceptibility of different subgroups with specific consideratio n of children, such that the result ant RfC values pertain to the full human population “including sensi tive subgroups,” a phrase which is inclusive of childhood. With respect to cancer, the EPA uses the age-dependent adju stment factor, but limits the use of those factors only to carcinogenic pollutants that are known to act via mutagenic mode of action. In lieu of chemicalspecific data on which age or life-s tage specific risk estimates or pot encies can be determined, default age dependent adjustment factors can be applied when assessing cancer risk for early-life exposures to chemicals which cause cancer through a mutagenic M OA. With regard to othe r carcinogenic pollutants for which early-life suscep tibility data are lacking, it is the Agency’s long-standing science policy position that use of the linear lo w-dose extrapolation approach (w ithout further adjustment) provides adequate public health conservati sm in the absence of chemical-spe cific data indicating differential early-life susceptibility or when the mode of action is not mutagenicity. 11 The basis for this methodology is provided in the 2005 Supplemental Guidance. 12

The estimated risks must also be considered in the context of the full set of assumptions used for this risk assessment. Our unit risk estimates for HAP are considered a plausibl e upper-bound estimate with an appropriate age dependent adjustment; actual potency is likely to be lower and some of which could be as low as zero. Our chronic noncancer reference va lues have been derived considering the potential susceptibility of different subgroups, with specific consideration of children. In addition, a more protective adjustment, as suggested by the commen ter, is not needed in the RfC/RfD methodology because the currently available factors are consider ed sufficient to account for uncertainties in the database from which the reference values are deri ved. After considering these and other factors, we continue to consider the risks base d on existing emissions from this s ource category to provide an ample margin of safety (consistent with the Benzene NESHAP framework).

Comment: One commenter (0166) suggest s that the EPA should adopt the Office of Environmental Health Hazard Assessment (OEHHA ) of the California Environmental Protection Agency childprotective scientific appr oach on cancer and other po llutants, and use at leas t an additional 10-fold uncertainty factor to protect childre n in addition to the uncertainty fa ctors it already uses, when a childspecific reference value or vulnerability information is not available.

The commenter states that the EPA must follow the lead of OEHHA by using ag e-dependent adjustment factors for all carcinogens emitted by this source, including naphthalene, PAHs and arsenic; should account for prenatal suscep tibility to POM; and use the OEHHA factors for pren atal susceptibility and exposures. The commenter recommends using a 10X adjust ment factor to address early life exposure in its risk assessment.

10 Ibid. 11 Ibid. 12 U.S. EPA. (2005). Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens

. EPA/630/R-03/003F. Washington, DC. Available online at : http://www.epa.gov/cancerguide lines/guidelines-carcinogensupplement.htm.39 The commenter suggests that the EPA use the OEHHA child-specific reference doses to assess chronic noncancer and acute health risk, where they are available.

The commenter recommends that the EPA consult with multiple scientific bodies on the scientific basis of the proposed rulemaking, and the commenter provides multiple citations in support of the commenter’s assertions about risk s from POM, PAHs and arsenic.
The commenter observes that Congress recognized this science in toxics legisl ation in 1996 (i.e., in the Food Quality Protection Act (FQPA) for pesticide ch emical residue) wherein C ongress used a ten-fold margin of safety for infants and children.
The commenter provides a table of comparisons between OEHHA child-health reference values and those of the EPA.
Response: The EPA disagrees with the commenter’s assertion that the chronic noncancer health benchmarks used for the assessment are not protective of children. The EPA uses RfC values and chronic REL values that are expres sly derived with the intention of protecting sensitive subpopulations, including children (see document EPA/630/P-02/002F: A Review of the Reference Dose and Reference Concentration Processes; which was prepared for the Risk Assessment Forum, Washington DC, and is available online at http://www.epa.go v/raf/publications/pdfs/rfd-final.pdf ). With respect to cancer, the EPA uses the age-dependent adjustment factor, but limits the use of those factor s only to carcinogenic pollutants that are known to act vi a mutagenic mode of action, in c ontrast to the OEHHA approach which uses them across the board for all carcinogen s regardless of mode of action. The EPA believes the OEHHA approach is unwarranted and overly conser vative, and provides a le ngthy rationale for its approach in the 2005 Supplemental Guidance, as refe rred to by the commenter. With respect to the commenter’s recommendation for the EPA to use the California benchmarks developed explicitly for protecting children, we note that the EPA is currently evaluating whether or not itis appropriate to use the CalEPA child-specific reference doses, and further notes that there are curren tly no such values for HAP inhalation, so their current util ity would be limited to PB-HAP which may be associated with nonnegligible ingestion exposures. Th at is, before using these child-sp ecific reference doses, the EPA wants to evaluate whether they have been appropriately derived.
The dose-response values that were used in this risk assessment are based on the current peer reviewed IRIS values, as well as other similarly peer-revie wed values. Our approach, which uses conservative tools and assumptions, ensures that our decisions are appropr iately health protective and environmentally protective. The approach for selecti ng appropriate health benchm ark values, in general, places greater weight on the EPA derived health be nchmarks than those from other agencies (see http://www.epa.gov/ttn/atw/nata1999/ 99pdfs/healtheffectsinfo.pdf). This approach has been endorsed by the SAB. The SAB further recommended that the EPA sc rutinize values that emerge as drivers of risk assessment results and the Agency has incorporat ed this recommendation into our risk assessment process. This may result in the EPA determining that it is more appropriate to use a peer-reviewed doseresponse value from another agency even if an IRIS value exists. For example, this is the case for manganese. In our RTR assessments, the EPA curr ently relies on the ATSDR Minimal Risk Level40 (MRL) for manganese, published in 2012 13 rather than the IRIS Re ference Concentration (RfC) published in 1993 14 . Both of these values were based on the same study (Roels et al., 1993); however, in developing their assessment, ATSDR used updated dose-response modeling methodology (benchmark dose approach) and considered recent pharmacokine tic findings to support their MRL derivation.
We disagree that the EPA should adopt California OEHHA’s approach to deriving reference concentrations to protect children. A review of the EPA’s chronic reference value process 15 concluded that the EPA’s reference concentration (RfC) derivation processes adequately cons idered potential susceptibility of different subgroups with specific consideration of children, such that the resultant RfC values pertain to the full human population “including sensitive s ubgroups,” a phrase which is inclusive of childhood. With respect to cancer, the EPA uses the age-depende nt adjustment factor approach referred to by the commenter, but limits the use of thos e factors only to carcinogenic pol lutants that are known to act via mutagenic mode of action, in contra st to the OEHHA approach, which uses them across the board for all carcinogens regardless of mode of action (MOA). In li eu of chemical-specific data on which age or lifestage specific risk estimates or potencies can be determined, default age dependent adjustment factors can be applied when assessing cancer risk for earl y-life exposures to chem icals which cause cancer through a mutagenic MOA. With regard to other car cinogenic pollutants for wh ich early-life susceptibility data are lacking, it is the Agency’s long-standi ng science policy position th at use of the linear lowdose extrapolation approach (without further adjustment) provides adeq uate public health conservatism in the absence of chemical-specific data indicating di fferential early-life susceptibility or when the mode of action is not mutagenicity. 16 The basis for this methodology is provided in the 2005 Supplemental Guidance. 17

c. Environmental Justice

Comment: One commenter (0163) states th at the EPA does not have author ity to consider demographics in conducting residual risk assessments. The comment er notes that the EPA evaluated HAP-related risks across different social, demographic, and economic groups within the popul ations living near the facilities of this source category in order to examine the potential fo r any environmental justice issues, but that the proposal (appropriately ) does not suggest that the demographic risk analysis must (or may) be considered in satisfying the requirements of section 112(f).
The commenter argues that the term “public heal th” cannot reasonably be interpreted to include consideration of environmental justi ce in the section 112(f) context, and that the term “public health” refers to all people, not partic ular demographic segments. The co mmenter states that the EPA’s established approach to assess ing potential impacts on public h ealth under the NAAQS program is

13 Agency for Toxic Substances & Disease Registry T oxicological Profile for Manganese (2012) available at http://www.atsdr.cdc.gov/toxpro files/tp.asp?id=102&tid=23 14 USEPA Integrated Risk Information System Review of Manganese (1993) available at http://www.epa.gov/iris/subst/0373.htm 15 U.S. EPA. A Review of the Reference Dose and Reference Concentration Processes. U.S. Environmental Protection Agency, Risk Assessment Forum, Washington, DC, EPA/630/P-02/002F, 2002. 16 Id. 17 U.S. EPA. (2005), Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens

. EPA/630/R-03/003F. Washington, DC. Available online at: http://www.epa.gov/cancerguidelines/guidelines-carcinogensupplement.htm.41 consistent with this meaning. The commenter agrees with the EPA’s interpretation of the term “public health” to include c onsideration not only of potential impacts to the population as a whole, but also to sensitive subpopulations, but notes that sensitive subpopulations are identified according to their particular health-based sensitivities ra ther than demographic classifications.
The commenter further states that the EPA’s proposal would unreasonably inject racial, ethnic, and other policy considerations into a program designed to provide protection for the public at large. The commenter asserts that injecting “environmental justice” considerations into section 112(f) standard setting would inappropriately cause arbitrary policy and political considerations to trump objective scientific analysis. The commenter believes that this would be patently unreas onable and, as such, would not be a supportable interp retation of section 112(f).
Response: Executive Order (EO) 12898 directs the EPA to the greatest extent practicable and permitted by law, to make environmental justice (EJ) partof their mission by identi fying and addressing, as appropriate, disproportionately hi gh and adverse human health or environmental effects of their programs, policies, and activitie s on minority populations and low-income populations in the United States. Consistent with EO 12898 and the Presidentia l Memorandum that accompanies it, the EPA’s EJ policies promote EJ by focusing attention and Agency efforts on addressing the types of environmental harms and risks that are prevalent among minor ity, low-income, and indigenous populations. The Agency’s EJ policies and EO 12898 do not mandate particular outcomes from an action, but they demand that decisions involving the action be informed by a consideration of EJ issues. Consistent with EO 12898 and the EPA’s EJ policy, it is appropriate to inform decisions makers, through risk analysis, of the impacts on minority, low-income, and indigenous populations. This information provides a better understanding of whether any popula tion groups may be experiencing disproportionate impacts. In addition, the EPA notes that there ar e many factors, in addition to heal th-based sensitivities, that may influence whether a population expe riences disproportionate impacts as a result of an Agency action. These include: proximity and exposure to environmental hazards, unique exposure pathways, multiple and cumulative effects, ability to participate in the decision-making pr ocess and physical infrastructure.
As stated in the Benzene NESHAP, in determining the need for residual risk standards, we strive to limit to no higher than approximately 1-in-10 thousand ( 100 in a million) the estimated cancer risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years and, in the ample margin of safety decision, to protect the greatest number of persons possible to an individual lifetime risk level of no higher than approximately 1-in-1 million. These considerations are made for all people regardle ss of racial or socioeconomic status. However, in determining whether to require addi tional standards under section 112(f), these levels are not considered rigid lines, and we weigh the cancer risk values with a series of other health m easures and factors in both the decision regarding risk acceptabi lity and in the ample margin of safety determination. We also consider cost of controls in the ample margin of safety determination. While we analyzed the demographic makeup of the at-risk populations surr ounding the facilities with in the source category addressed by this rule making, we ultimately conc luded that the risks were acceptable and protected public health with an ample margin of safety. Thus, while the results of our demographic analyses served to provide information about th e demographic makeup of the populations exposed to the source category, as noted by the commenter, the EPA did not base its deci sion on these analyses.42 The EPA disagrees that the term “ public health” cannot include consider ation of EJ. The EPA defines EJ to mean fair treatment and meaningful involvement of allpeople, and this definition represents a commitment to ensuring that the EPA works to impr ove conditions affecting th e public health of all Americans so that everyone has access to clean water, clean air, and healthy communities.

Comment: One commenter (0166) notes th at while the EPA recognizes that the primary aluminum source category disproportionately exposes Native Americans and people living below the poverty level, among others, to a high level of cancer risk, the EP A does not assess the disproportionate impact of chronic non-cancer and acute health ri sk, but its demographic analysis su ggests that the disproportionate nature of these risks would be similar. The commenter notes that the EPA states that the proposed rule will have no disproportionate effects because the risks are within an acceptable range.
The commenter states that for this source category, the EPA’s data show that the maximum exposed individual is more likely to be a Native American individual or a pe rson who may be more vulnerable to the impacts of pollution due to socioeconomic status. The commenter adds that the EPA must also assess the starting point or baseline of “overall health” status of the affected individuals and communities using the best available data at a local and national level, including the baseline cancer and other health levels. The commenter states that the EPA should also fo llow the recommendations of the EPA’s own interim guidance and presented in the Environmental Justi ce Strategic Enforcement Assessment Tool (EJSEAT), and include other relevant EJ factors.

The commenter recommends that the EPA must incorporate the improved EJ assessment fully into the policy decision it chooses in the final rule, by recognizing that it is not fair or ac ceptable for particular individuals or communities to have this type of disproportionate imp act. The commenter asserts that the fact that the EPA’s proposed rule reduces the risk for all communities is not enough to make a no-impact finding under EO 12898. The commenter suggests that the EPA recognize that there is still disproportionate impact from this source category that remains.
Response: The commenter has not accurately characterized the EPA’s statements about disproportionate impacts. The preamble notes that the proposed rule will not have disproportio nately high and adverse human health or environmental effects on minority or low-income populations. We disagree with the comment that the EPA states Native Americans and people below the poverty le vel have a high level of risk. In the demographics analysis, the EPA noted th at the percentage of Native Americans living within 50 km of these facilities with a cancer risk greater than or equal to 1-in-1 million is higher than the corresponding national pe rcentage of Native Americans. With respec t to cancer risk greater than or equal to 1-in-1 million, this analysis also noted that those ages 65 and up, below the poverty level, over 25 without a high school diploma, and working age with disability were somewhat higher than their respective national percentages. That being said, we importantly note that overall risk was found to be acceptable for all populations living within 50 km of th e facilities in this source category. Moreover, the demographic results do not indicate that the individual who represents the MIR is Native American (or any of the other demographic groups mentioned above). The demographics analysis simply identifies the percent of individuals in different demographic groups with a cancer risk greater than or equal to 1-in-1 million. While it is possible that the individua l representing the MIR is Native American, the43 demographics analysis is not meant to make this determination. Rather, the purpose of the demographics analysis is to identify demographic groups that may be impacted by the proposed rule.
With respect to chronic, noncancer effects, the EPA only performs a demographics analysis if the maximum target organ specific hazard index (TOSHI) value for the source category is greater than 1. For this source category no TOSHI values were greater than 1 and, therefore, the EPA did not perform this additional analysis.
With respect to the EJSEAT tool, we disagree th at it should be used in our demographic analyses because EJSEAT is currently a draft tool in develo pment, whose intended use is to provide information relevant to the EPA’s enforcement activities.
The EPA disagrees that it did not follow its interim guidance on EJ a nd the Action Development Process. In addition to proximity and exposure to environm ental hazards, susceptible populations, and multiple and cumulative effects – which were addressed via the procedures described above (e.g., via the TOSHI and RfCs) – the EPA also assessed possible dispro portionate impacts due to unique exposure pathways, ability to participate in the decision making process, and physical infrastructure. However, no disproportionate impacts due to unique exposure pathwa ys, ability to participate in the decision making process, or physical infrastructure were identif ied by the EPA and no information was provided by the commenter to the contrary.

Comment: One commenter (0166) is concerned that after finding that cancer risk falls disproportionately on Native Americans, the EPA di d not describe which tribal communities are affected, where they are located, or which sources in the source cate gory create this disproportionate risk. The commenter believes that this makes it difficult for local community members who may wish to be aware of this health risk and to comment on this rule proposal. The commenter asserts that the EPA should provide more specific information, as described above, for public review.
Response: As noted in the proposal preamble and de mographics analysis, the purpose of the demographics analysis was to ge nerally identify demographic groups that may be impacted by the proposed rule. For this purpose, the EPA believes that a source-category wide demo graphics analysis is a reasonable approach. Note that the emissions dataset provided in the docket for this proposed rule did include the addresses of the prim ary aluminum reduction facilities.

Comment: One commenter (0166) asks that as part of providing sufficient information to affected local communities, the EPA should publish a plain-language st atement of the health ri sks and benefits from the EPA’s final action, and in future rule proposals. The commenter stat es that although it provides the MIR and chronic and risk numbers, these are noteasily understandable by the general public. The commenter asks for expanded discussion of health disord ers or other adverse effect s, stating that without a full discussion of health impacts a nd risks, it is difficult for the publ ic to provide meaningful comment on the impact this proposal will have on their lives, which is an EJ issue.

The commenter also asks that the EP A provide a statement and analysis in this residual risk rulemaking (and all others) on the real world impacts of the EPA’s rulemaking, so that the public has a clear understanding of what the risk is , and precisely what types of ha rm to public health the EPA is44 determining are “acceptable” and “unacceptable.” This is needed to inform the EPA’s and the public’s consideration of what level of ri sk is acceptable or unacceptable, a nd what standard is required to provide an ample margin of safety.
Response: It is the EPA’s goal to provide all rule text and risk assessment documents in plain language and understandable to the general pu blic. As future risk assessment documents and rulemakings are written, we will consider the comments provided and c ontinue to strive to make them thorough and clear to the interested public.

Comment: Three commenters (0165, 0369 and 0166) assert that in addition to the demographic analysis conducted for communities within 50 km of the sour ces, the EPA must also an alyze those who are the most exposed, within 5 km of primary aluminum plants, regardless of pr ojected risk, consistent with the approach used for the Hard and Decorative Chro mium Electroplating and Chromium Anodizing Tanks source category. Commenter 0166 recommends that the EPA analyze communities within a 2 km radius of each facility for sites locatedin urban or higher density popul ation areas. Comm enters (0165 and 0369) observes that the EPA’s socioeconomic analysis fo r this rule did not evalua te potential disparities within 5 km for cancer risk at maximum allowable emission levels, which is especially important in instances where a facility is located in a minority and low-income community . Commenters (0165 and 0369) states that in the proposal th e EPA only evaluated the risk to th e population within a 50-km radius, which could dilute the results by including populations not in the demographic groups most at risk, a concern if the source is located in or next to a minority or low-in come population. Both commenters state that failing to perform the 5 km analysis may cause the EPA to overlook EJ impacts if there is a minority or low-income community located adjace nt to the facility. Commenters (0165 and 0369) recommends that the EPA conduct the demographic an alysis on individuals proj ected to experience a risk greater than 1-in-1-million.
Response: As noted in the preamble and demographics analysis, the purpose of the demographics analysis was to generally identify demographic gr oups that may be impacted by the proposed rule. For this purpose, identifying groups within 50 km with a cancer risk greater than 1-in-1 million or a TOSHI value greater than 1 is a reasonabl e approach. Also, selecting 50 km is a reasonable approach given that we modeled cancer and chronic, nonc ancer risk out to 50 km. It is also possible, especially around facilities with larger stacks, that those with a can cer risk greater than 1-in-1 million are located at distances greater than 5 km. Thus, selecting a 50 km radius ensures that we account for all populations located in the modeling domain with a can cer risk greater than 1-in-1 million.

Comment: Commenters (0165 and 0369) recommend that the rule writers work with the EPA Office of Environmental Justice to develop criteria and specific guidance on how to interpret and apply the outcome of these types of analyses in the rule making process. Commenters 0165 and 0166 suggest that the EPA update the poverty statistics used to identify low-income communities to include 2010 census data, rather than relying on older information, becau se the number of people in poverty in 2010 is the largest number in the 52 years for which poverty estimates have been published.
Response: We agree with the commenter and we work closely with the EPA Office of Environmental Justice to develop criteria and spec ific guidance on how to interpre t and apply the outcome of these types of analyses in the rulemaking process. With respect to the 2010 census da ta, these data were not45 available at the time the demographics analysis was performed for this source category. However, future risk and demographic analyses will incorporate 2010 census data.

Comment: One commenter (0166) notes th at the EPA released the Plan EJ 2014 to direct ways the agency intends to address environmental justice imp acts, and it includes the development of scientific tools on cumulative impacts. The commenter sugge sts that the EPA use this and other similar rulemakings to inform the implementation of Plan EJ 2014.
Response: The EPA appreciates the commenter’s reco mmendation to use this and other similar rulemakings to inform the implementation of Pl an EJ 2014. The EPA is co llecting feedback across offices and is examining various rulemakings to assi st in the creation of scientific tools on cumulative impacts.

d. Cumulative Risk

Comment: One commenter (0166) maintains that for cancer, chronic and acu te health risks, the EPA has not appropriately assessed cumulativ e risk. The commenter provides exte nsive citations, attached to the comment letter, in support of the commenter’s statements. More detailed comments from this commenter are presented in this document, below.
Response: Section 112(f) of the Clean Air Act directs th e EPA to evaluate the risks associated with emissions of hazardous air pollutants listed under section 112 (b)(1) or those added to this list under section 112(b)(2). The EPA conducted an assessment of the cumulative cancer risks from all emitted carcinogens and the cumulative noncancer hazard i ndices from all emitted non-carcinogens that are HAP affecting the same target organ system for both the source category emissions and the facility-wide emissions. To address the effect of mixtures of carcinogens, the indi vidual cancer risks for the source category were aggregated for all carcinogens. In asse ssing noncancer hazard from chronic exposures for pollutants that have similar modes of action or that affect the same target organ, we aggregated the hazard quotients (HQ) to provide a target organ- specific hazard index (TOSHI). We further modeled whole-facility risks for both chronic cancer and n on-cancer impacts to understa nd the risk contribution of the sources within the prim ary aluminum source category.

Comment: One commenter (0166) asserts that the EPA has failed to assess the cumulative impact of exposure by not including past b ackground exposure as part of the health risk assessment. The commenter states that section 112(f) includes recognition of b ackground levels, including background levels of past exposures and past pollution. The commenter reminds the EPA that the Scientific Advisory Board has urged the EPA to incorporate cumulative ri sks into its residual risk analysis as section 112(f)(2) requires, including a full a ssessment of background and new risk.
Response: For the primary aluminum source category, the EPA conducted an assessment of the cumulative cancer risks from emitted carcinogens and th e cumulative noncancer hazard indices from all emitted non-carcinogens affecting the same target or gan system for both the source category emissions and the facility-wide emissions. While the incorpor ation of additional background concentrations from the environment in our risk assessments (including those from mobile sources and other industrial and area sources) could be technically ch allenging, they are neither mandate d nor barred from our analysis.46 In developing the decision framework in the Benzen e NESHAP currently used for making residual risk decisions, the EPA rejected approaches that would ha ve mandated consideration of background levels of pollution in assessing the acceptability of risk, conc luding that comparison of acceptable risk should not be associated with levels in polluted urban air (54 FR 38044, 38061, September 14, 1989). Background levels (including natural background) are not barred from the EPA’s ample margin of safety (AMOS) analysis, and the EPA may consider them, as appropriate and as available, along with other factors, such as cost and technical feasibility, in the second step of its secti on 112(f) analysis. This assessment excludes background contributions because the availabl e data are of insufficient quality upon which to base a meaningful analysis. See also NRDC v. EPA, 529 F.3d 1077, 1086 (D.C . Cir. 2008) (rejecting similar arguments).

Comment: One commenter (0166) expre sses concern that the EPA ha s not combined risks from multiple HAP and pathways, thus not assessing cumu lative impacts and health risk appropriately. The commenter notes that the EPA shoul d assess the synergistic, carcinogeni c (and other) effects of different pollutants; create a combined acute risk number th at would represent the to tal acute risk for all pollutants that act in a similar way on the same organ system or systems, similarly to the chronic TOSHI; perform a cumulative risk assessment that co mbines inhalation and multipathway risk for each pollutant, such as POM, that causes both risks; and create a metric to assess the total, combined health risk that could be used to assess the cumulative impact of all of the types of risks, including synergistic effects. The commenter emphasizes that the EPA’s failure to assess and address cumu lative health risk is unlawful, arbitrary, and caprici ous, and it undermines the EPA’s acceptability determination.
Response: We disagree with the commenter that the EP A should create a combined acute risk number that would represent the total acute risk for all poll utants that act in a similar way on the same organ system or systems (similar to the chronic TOSHI). As noted in previous responses, the worst-case acute screen is already a conservative scenario. That is, the acute screening scenario assumes worst-case meteorology, peak emissions for all emission points o ccurring currently and an individual being located at the site of maximum concentration for an hour. Because of the conservative nature of the acute screening assessment and the variable nature of emissions and potential exposures, acute impacts are screened on an individual pollutant basi s rather than using a TOSHI approach.

Comment: One commenter (0166) suggests th at in order to appropriately conduct the risk assessment, the multipathway risks should be combined with the inhalation risks before pr oceeding with the required section 112(f)(2) analysis to determine whether or not that total level of risk is acceptable and, if not, what standards are needed to reach an acceptable leve l and also to provide an ample margin of safety. The commenter states that by not adding the multipathway and inhalation risk, the EPA failed to adequately assess or address the fu ll risk to the most-exposed person from the combined impact of both inhalation and other ro utes of exposure.
Response: We have combined risk assessment results to th e extent that it is appropriate to do so. We consider the effect of mixtures of carcinogens and use a target or gan-specific hazard index (TOSHI) approach for our chronic noncancer assessments. We do not use a TOSHI approach for our acute analyses nor do we combine the results of our inhalation and multipathway assessments. The multipathway risk assessment conducted for all the prebake facilities for the proposals and final rule47 were screening-level assessments (Tier 1 and Tier 2 screens). (We note that we conducted a more refined multipathway analysis for one Soderberg facili ty, as described in the risk assessment documents, which are available in the docket. However, that one Soderberg facil ity is now permanently shut down. In fact, all Soderberg facilitie s are now shut down. So, those re sults are now less relevant.)
The screening assessments used highly conservative assu mptions designed to ensure that facilities with results below the screening threshold values did not have the potential for multipathway impacts of concern. The screening scenario is a hypothetical scenario, and due to the theoretical construct of the screening model, exceedances of the thresholds are not directly translatable into estimates of risk or hazard quotients for these facilities. In situations where we have previously summed the inhalation and multipathway assessment results (e.g., secondary leadsmelters), it was for two refined assessments conducted for an operating facility, and still serves as a conservativ e overestimate of potential risks given that it is highly unlikely that the same receptor has the maximum results in both assessments.

Comment: One commenter (0166) states thatcumulative impacts an alysis is a routine consideration that is also required under other provisions of the CAA and other environmental statutes ( see e.g., Clean Air Act New Source Review program, 42 U.S.C. sec tions 7475 and 7503 (requiring a localized, cumulative assessment of whether or not a new or modified s ource’s additional emissions will cause an attainment area to deteriorate, or will make it difficult for a nonattainment area to make progress toward achieving the national ambient air quality standards); and New York v. EPA, 443 F.3d 880, 883 n.1 (D.C. Cir. 2006) (citing New York I, 413 F.3d 3, 11-14 (D.C. Cir. 2005))).

The commenter recommends that the EPA should co mbine current baseline emissions, exposures, and health impacts in addition to those of the specific s ource category the EPA is reviewing and suggests that the EPA aggregate or add the emissions for the most-exposed communities coming from the source category (including all indivi dual sources within it); facility-wide risk from collocated sources outside of this category; and all other sources of toxic air pollu tion in the area.

The commenter states that the EPA has failed to combine the risks and determine whether the cumulative impact of all of the health risks is una cceptable and that, thus, th e current acceptability determination is incomplete, and therefore arbitrar y and capricious. The commenter argues that the EPA must combine the health risks and address them together to satisfy its legal duty under section 112(f)(2) to consider all health risks, combined, from this source category to the most-exposed person.
Response: First, as noted in previous responses, we note that our assessment of cancer risks is, in fact, cumulative, summing the risks associated with all car cinogens emitted by a facility. Similarly, the use of the TOSHI for chronic non-cancer ef fects evaluates the cumulative effects of HAPs on a given target organ. Further, our assessment is cumulative in that it considers all emission points within the fence line that are covered by the NESHAP for primary aluminum reduction plants. With respect to a facility-wide risk analysis, we note that most (9 of 11) of the primary alumin um reduction facilities (i.e., those facilities with potlines and anode bake furnaces) ar e collocated with secondary aluminum production facilities. As a result, the facility-wide analysis thatwas conducted as part of the risk assessment for the secondary aluminum source category provides a faci lity-wide analysis for most of the primary aluminum production facilities. The f acility-wide risk assessment and re sults are also described in the risk assessment document for the primary aluminum source category, which is available in the docket48 for this action. As mentioned in a response above, the faci lity-wide risks (i.e., facility-wide results including those associated with primary aluminum operations) did not ch ange the conclusions reached in this rulemaking. With respect to “al l other sources of toxic air polluti on in the area,” the commenter did not provide any information as to what other so urces they suggest should be taken into account.

Comment: Commenter (0373) stated that the EPA also should be evaluating the cumulative risks from all nearby toxics sources in multiple source categories, not looking only at multiple sources in the same category, and different sources at the same facility . Commenter (0373) stated that the EPA has said it recognizes the need to put risk in context, but sti ll has not even attempted to evaluate the bigger picture of health risks by looking at all nearby sources (from various source categories, including those collocated and those not collocated). Commenter ( 0373) stated that that would likely lead to recognizing that the individual most -exposed to each of these source categories is also experiencing significant risks from other source s, providing even more evidence as to why the EPA should reduce risks from the primary and secondary aluminum s ource categories, as discu ssed in the 2012 Comments and reincorporated here by reference.
Response: We also disagree with the commenter’s asserti on that additional quant itative assessment of risks from sources outside the source category is requi red under the statute. The statute requires the EPA to provide the quantitative risk in formation necessary to inform RTR regulatory decisions, and to this end, the EPA conducts a comprehensive assessment of the risks associated with exposure to the hazardous air pollutants emitted by the source category and supplements that with additional information that is available about other possible concurrent and relevant risks, as appropriate. We also point out that, as noted above, the risk assessment fo r primary aluminum facilities did take into account emissions from collocated sec ondary aluminum facilities.
e. Margin of Safety

Comment: One commenter (0166) asserts th at the EPA’s ample margin of safety determination does not consider the full range of control options available and ar bitrarily relies on uns upported assumptions for the options it does consider. The commenter states that the EPA’s cost-baseddetermination is not supported in the record, providing no explanation for why a cost of $140,000 per ton of HAP reduction is too high, when for the Secondary Lead NESH AP, a cost of $1.5 million per ton was found to be reasonable. The commenter concludes that without adequate support or a reasoned rationale for its assumptions, the EPA’s analysis of the additional m easures it does evaluate is arbitrary and capricious.
Response: As stated in the Benzene NESHAP, in determin ing the need for residual risk standards, we strive to limit to no higher than approximately 1-in -10 thousand (100 in a million) the estimated cancer risk that a person living near a pl ant would have if he or she were exposed to the maximum pollutant concentration for 70 years and, in th e ample margin of safety decision, to protect the greatest number of persons possible to an individual lifetime risk level of no higher than approximately 1-in-1 million. We also strive to minimize noncancer risks as appropriate. We performed an ample margin of safety analysis to determine whether additional controls are warranted considering health risks, costs and technical feasibility. We have determined that the controls require d in this final rule include all of the controls that are technically and economically feasible to reduc e risks due to HAP emissions from this source category. These requirements will protect the pub lic health with an ample margin of safety.49 Comment: One commenter (0166) states thatthe EPA fails to set a residual risk standard that provides the requisite “ample margin of safety to protect p ublic health” pursuant to CA A section 112(f)(2). The commenter argues that the EPA fails to analyze the emission reductions needed to provide an ample margin of safety for public health and fails to asse ss whether its proposed standard fully protects public health. The commenter refers to the EPA’s “ample margin” analysis for POM that does not center on health protection but on cost, which the commenter fi nds to be flawed. The commenter observes that the EPA’s neglect of health criteria is illustrated in the Agency’s approach to its cost analysis in which the EPA uses a ton-based and investment cost-basedmetric. The commenter states that assuming arguendo that cost is a factor that the EPA may consider in an “ample margin” analysis, the EPA may not make cost its sole factor, and may notsubjugate health interests and objectives to cost. The commenter observes that the EPA fails to consid er what the “margin” of safety is for the rule it has proposed, or what margin would provide “ample” protection, as th e EPA’s proposal would st ill expose people to a cancer risk significantly higher than the 1-in-1 million target of section 112(f)(2), and the EPA has failed to justify this or explain why there is an “am ple margin of safety” under its proposed rule. The commenter asserts that the EPA has not considered th e uncertainty that has likely led it to underestimate health risk; the combination of can cer, non-cancer chronic, acute, a nd multipathway health risks; the cumulative health impacts; or children’s health, multiple source exposure, and environmental justice factors needed to provide an “ample margin of safe ty.” The commenter states that the EPA includes no discussion or analysis regarding what the maximu m feasible protection would be, or how many people could be protected from a greater level of risk an d whether they are the greatest number. The commenter objects to setting the standard withou t finding or explaining how the pro posal provides more than bare minimum protection for public health, and claims th at this action would re nder the phrase “ample margin of safety to protect public health” superfluous and violat e section 112(f)(2).
The commenter states that the EPA may not lawfully consider cost in deci ding what is the “ample margin of safety to protect public health,” rather th ere is only an authoriza tion to consider cost in determining whether additional standards are neededto prevent environmental harm. The commenter states that although the D.C. Circ uit previously allowed the agency to consider cost in the HON decision, that case was wrongly decided and the EPA s hould not rely on it as just ification to evade the statute. The commenter notes that in section 112(f )(2), the clause “taking into consideration costs, energy, safety, and other relevant factors” only m odifies the environmental effect prong of the EPA’s duty. The commenter further notes that the statemen t in section 112(f)(2)(B) is not a clear statement authorizing the consideration of co st and it does not enshrine the EPA’s prior Benzene rule analysis forever in all instances. The commenter further asse rts that the purpose of citing the Benzene Rule was not to enshrine that rule or its st atutory interpretations for all time, but rather to prevent back-sliding by the Agency after the 1990 Amendments. The commenter concludes that the statut e prohibits the agency from considering cost in its “ample margin” analysis.
Response: This comment was in response to the 2011 proposal. We considered whether the existing NESHAP provided an ample margin of safety (AMO S). Under the AMOS analysis, we evaluated the cost and feasibility of available control technologi es and other measures (i ncluding developments in practices, processes and control technologies assessed under the sec tion 112(d)(6) technology review) that could be applied in this so urce category to further reduce the ri sks (or potential risks) due to50 emissions of HAP identified in our risk assessment, along with all of the healthrisks and other health information considered in the risk acceptability determination described above. We believe it is appropriate to consider costs, f easibility and health risks under the ample margin of safety analysis.
In the 2011 proposal (76 FR 76260, December 6, 2011) we provided an ample margin of safety analysis which was largely focused on Soderberg facilities, becau se at that time one Sode rberg facility was still operating and another Soderberg facil ity was idle and the Soderberg faci lities posed the highest potential risks for the source category at that time. At that time, we proposed tighter POM limits based on that analysis. (See pages 76277-78 of the 2011 FR Noti ce, 76 FR 76260). However, as explained in the preamble to the final rule, all Soderberg plants are now shutdown and it is very unlikely that any Soderberg facilities will reopen, due to the less effi cient and higher emitting nature of the Soderberg technology compared to prebake technology.
With regard to the 2014 supplemental proposal (7 9 FR 72914, December 8, 2014), after gathering additional data and conducting additional risk analys es, we provided a revised ample margin of safety analysis and explained our decisions based on the ample margin of safe ty analysis. The ample margin of safety analysis in the supplemental proposal was largely focused on possible op tions to reduce emissions from prebake facilities (see pages 72 947-72948 of the December 8, 2014 FR Notice).
For example, under the ample margin of safety anal ysis (AMOS) in the 2014 supplemental proposal, we evaluated possible options to re duce HAP metal and POM emissions from the prebake potline roof vents. The main option we evaluated was based on requi ring most prebake faciliti es to install wet roof scrubbers to reduce secondary HAP metals emissions fr om their potline roof vents. Under this option we estimated that post-control cancer MIR would be 40- in-1 million for prebake f acilities (down from 70- in-1 million). We estimated that under this option chronic non-cancer hazards would be below 1. The As maximum acute HQ would be reduced from 10 down to 7. With regard to the acute As exposures, we estimated that about 60 people could be exposed to concentrations leading to an acute HQ of 7, about 154 people could be exposed to a con centration leading to an acute HQ greater than 5, and that about 3,600 people could be exposed to a con centration leading to an acute HQ greater than 1. This assessment still assumed, in order to reach an HQ greater than 1, peak emissions from the source category and worst-case meteorological conditions co-occur. We e xpect that this would happen for very few hours of the 8,760 hours that are in a year. For HF, the maximu m off-site HQ would be reduced from 3 to 2 and is at a location where we would notexpect people to be for 1 hour.
We estimated that the total capital costs would be at least $415 million ($46 million per facility), annualized costs would be at least $133 million ($15 million pe r facility), with cost effectiveness (CE) of $6 million per ton HAP metals and $130,000 per ton POM or higher. This option would also achieve 715 tpy PM 2.5 reductions with CE of $185,000 per ton PM 2.5 . We believe these costs are substantial. Furthermore, based on our economic analysis , we projected that this option would pose a significant economic burden on the companies and that seve ral facilities would be at risk of closure under this option. The option would also be associated w ith potentially adverse environmental effects (more wastewater discharge), and increased energy usag e (with attendan t carbon pollution), although these are not the most significant factors in the EPA’s propos ed decision. Therefore, given all the factors descri bed above, we did not propose this option in 2014. In the final rule, we arrived at the same conclusions and therefore51 did not promulgate tighter standa rds for prebake facilities based on the AMOS. However, as described in the final rule preamble, we did promulgate st andards for As, Ni, and POM for Soderberg potlines based on the AMOS analysis.
In accordance with the approach es tablished in the Benzene NESHAP, the EPA weighed all health risk measures and information considered in the risk acceptability determination, along with the costs and economic impacts of emissions controls, technologi cal feasibility, uncertainties and other relevant factors in our ample margin of safety determinati on. Considering the health risk information and the costs of the options iden tified, we found that the existing MACT standards along with the amendments promulgated in the 2015 final rule for the primary aluminum production source category will provide an ample margin of safety to protect public health.

Comment: One commenter (0166) suggests th at the EPA incorporate a margin of safety (or uncertainty) factor to account for a history of exposure or exposure to additional emissions beyond the source category under review. The commenter states that the total risk that is accep table for the most-exposed person must be less for each source category to whic h that person is exposed than the total acceptable amount. As an example, the commenter recommends adjusting the acceptable level of cancer, noncancer chronic and acute risk based on the number of other HAP emitting facilities, reducing the source category’s contribution to a commen surate fraction of the threshold. The commenter further suggests a case-by-case determination of whethe r stronger emission limits are needed.

The commenter asserts that the EPA ha s full authority to address the full public health risk faced by the affected individuals and community before deciding what emission limits to set for this source category. The commenter states that under s ection 112(f)(2), the EPA is requi red to decide whether to set a standard for a given source category if the cancer risk from that spec ific source catego ry is 1-in-1 million or more. The commenter observes that if the ri sk associated with a source category’s emissions are between 1-in-1 million and the presumptive li mit on acceptability (currently 100-in-1 million) and that source category is contributing risk along with numerous other sour ce categories, then the EPA has the authority under section 112(f)(2) to decide both that the total, cumulative risk is unacceptable and that the specific risk contributed by the source category is unacceptable.
The commenter suggests that the EPA could draw on its experience with a si milar contribution-based approach in the Clean Air Act’s prevention of sign ificant deterioration prog ram, where a source’s contribution or increment of new pollution is analyzed to see wh ether it would cause too much deterioration of air quality based on na tional ambient air quality standards.
Response: We disagree with the commenter that the EP A should incorporate a margin of safety (or uncertainty) factor to account for a history of exposure or exposure to additional emissions beyond the source category under review. To provide the quantit ative risk information necessary to inform RTR regulatory decisions, the EPA conducts a comprehens ive assessment of the ri sks associated with exposure to the HAPs emitted by the source category (i.e ., those emissions that can actually be affected by the specific rulemaking) and supplements that with additional available information about other possible concurrent and relevant ri sks, as appropriate. In some cases, we have additional information about HAP emissions that are outside the scope of the particular rulemaking but w ithin the boundaries of the subject facilities. In other case s, we may have ambient HAP monito ring data that can be considered52 as part of the regulatory decision-making process. In still other cases, we may have very little additional risk information that can be considered. In all cas es, however, when we consider additional information about risks, we also consider its attendant uncertainties, and info rmation which carries significant uncertainties generally carries much less we ight in the overall regulatory decision.
All of the quantitative risk assessment informati on about HAP emissions from the source category under consideration is also considered in the manner pr escribed by the decision framework set forth by the CAA for residual risk decision-making (i.e., the Benzene NESHAP deci sion framework), and this means that the general guidelines of risk acceptability have been develope d in a way that they already take into account the impossibility of accurate ly quantifying the health risks posed by outside forces on every individual in the population. This acknowledgment allows the EPA to make risk-based decisions by focusing on the risks posed by the so urce category under consideration.

3.2.6 Environmental Effects

Comment: One commenter (0166) states that the EPA has failed to provide a determination of the environmental effects from this source category and may not rationally or lawfully assume there is no potential for environmental effects based on the h ealth assessment. The commenter expresses concern that the EPA’s proposed rule preamble contains no proposed determination rega rding whether there is currently a risk of an “adverse environmental effect” from this source category, or whether its proposed rule provides an ample margin of safety to “preve nt an adverse environmental effect.” The commenter notes that only in the multipathway risk assessment is there any disc ussion of ecological exposure, but only in general terms, and this document contains no determination that the proposed rule would “prevent an adverse environmental effect.” The co mmenter also notes that the EPA has provided no environmental determination for commenters to evaluate. The commenter, citing the Residual Risk Assessment for the Primary Aluminum Production Source Category in Support of the 2014 Supplemental Proposal , and stating that the potential for multipathway risk exceeds the EPA’s own safety threshold by 7,000 times, (see the comments on multipathway risk) argue s that when there is such a high risk for people, there is likely to be a parallel high risk due to ingestion and other non-inhalation pathways of exposure for wildlife and other impacts to natural resources.
Response: We conducted a screening-level evaluation of the potential adverse environmental risks associated with emissions of the following enviro nmental HAP from the Primary Aluminum Production source category: cadmium, PAHs, dioxins, methyl mercury and hydrogen fluor ide. In our Tier 1 analysis, emissions of dioxins and methyl mercury di d not exceed the threshold emission rates for any of the ecological benchmarks for any f acility in the source category. In our Tier 1 analysis, emissions of cadmium and PAHs exceeded some ecological benchmarks for one facility, therefore, a Tier 2 analysis was performed. In the Tier 2 analysis, emissions of cadmium did not exceed the threshold emission rates for any of the ecological benchmarks for any facil ity in the source category. In the Tier 2 analysis, emissions of PAHs exceeded the NOAEL sediment benchmark for one lake by 2 times, but did not exceed the threshold effect level. For hydrogen fluor ide, the average modeled concentration around each facility (i.e., the average concentr ation of all off-site data points inthe modeling domain) did not exceed the ecological benchmarks. Additional details on the environmental risk screen methodology and results are located in the Residual Risk Assessment for the Primar y Aluminum Production Source Category in53 Support of the September 2015 Risk and Technology Review Final Rule which can be found in the docket.

Comment: One commenter (0166) recommended that th e EPA review comments from the National Park Service (NPS) regarding the Columbia Falls Aluminum Company (CFAC) plant (comments were attached labeled “National Park Service comments on CFAC Glacier BPA 2011”); consider ecological risks from the primary aluminum source category, particularly from plants near Class I Areas and other national parks; and seek further comment from the NPS and the Department of Interior. The commenter notes that the NPS’ particular c oncerns included PAH concentrations in the environment, the use of control technologies, and fluoride emission spikes during startup.
Response: With respect to assessing ecological risk fr om startup, we note thatthe commenter did not provide any such data. We did analyze ambient tota l fluoride concentration data for Glacier National Park provided by the NPS for the period in 2002 during which the potlines were re started (there were no PAH data available relevant to this startup period). The NPS data do indicate an increase in ambient total fluoride concentrations for 2002 when the startup took place, over the ambient co ncentrations measured in 2001 or 2004. The CFAC/Glacier National Park repor ts refer to a “Previous State Standard of 1 ppb Total Fluoride”. On average, the 2002 ambient total fluoride concentrations measured at Glacier Park were 4 percent of this standard.

The EPA also reviewed limited data from the Alco a Wenatchee facility from March and April of 2011, during which one of their three potlines (line 2) was in startup mode and the other two potlines (line 1 and line 5) were presumably operating normally. TF emissions were estimated by adding HF emissions measured at the roof monitors to an estimate of particulate fluoride emissions. In March 2011, line 2 averaged aluminum production of 70 tons per day and estimated TF emissions of 2.6 lb TF per ton of aluminum produced (TAP). The 3 potlines taken together emitted an estimated 1.4 lb TF/TAP. The associated emission limit is 1.9 lb TF/TAP.
In April 2011, line 2 averaged aluminum production of 96 tons per day and estimated TF emissions of 1.9 lb/TAP. The steady state production of line 2 is likely to be between 130 and 165 tons of aluminum per day (i.e., the production of lines 1 and 5, resp ectively, during this time). The emissions on a mass basis do not appear to be str ongly related to the production. Betw een March and April 2011, when production in line 2 increased by 36%, the estimated TF emissions were unchanged at 181 lbs/day (the HF emissions went down slightly and the particulate F emissions went up slightly).
These limited data suggest that at this plant, there is not an incr ease in TF emissions on a mass basis during startup. Line 2 emitted sligh tly more HF than the lines operati ng at steady state and slightly less particulate matter (and presumably s lightly less particulate F) than th e lines operating at steady state.
As mentioned previously, we conducted a screen ing-level evaluation of the potential adverse environmental risks that included hydrogen fluoride a nd PAHs. In our Tier 1 analysis, we did find that emissions of PAHs exceeded some ecological benchmarks for one facility, theref ore, a Tier 2 analysis was performed. In the Tier 2 analysis, we found th at emissions of PAHs exceeded the NOAEL sediment benchmark for one lake by 2 times, butdid not exceed the threshold ef fect level. For hydrogen fluoride, the average modeled concentration ar ound each facility (i.e., the averag e concentration of all off-site54 data points in the modeling domain) did not exceed the ecological benchmarks. Based on the results of the environmental risk screening analysis, we do not expect adverse environmental effects as defined in CAA section 112(a)(7) as a result of HAP emissi ons from primary aluminum production facilities. Additional details on the environmental risk scre en methodology and result s are located in the Residual Risk Assessment for the Primar y Aluminum Production Source Category in Support of the September 2015 Risk and Technology Review Final Rule which can be found in the docket.

Comment: One commenter (0166) disagrees with the EPA’s use of healthrisk numbers, stating that these numbers are above the threshol d and that the EPA’s reference doses apply to rodents, but are not necessarily sufficient for protec ting more sensitive wildlife or other environmental receptors. The commenter notes that the SAB has stated “[t]he assu mption that ecological receptors will be protected if human health is protected is incorrect.” The commen ter observes that risks include inhalation risk for wildlife and persistent or bioaccumu lative chemicals in the environment. The commenter asks that the EPA perform an appropriate ecological assessment.
Response: The EPA has developed a scre ening approach to examine the potential for adverse environmental effects as required under section 112(f)(2 )(A) of the CAA that focuses on the following seven environmental HAP:

 Five persistent bioaccumulative HAP (PB-HAP) – cadmium, dioxins/furans, polycyclic organic matter (POM), mercury (both inorganic me rcury and methyl mercury), and lead.

 Two acid gases - hydrogen chloride (HCl) and hydrogen fluoride (HF).
With the development of the environmental risk screen we no longer make the assumption “that ecological receptors will be protectedif human health is protected.” In the environmental risk screen, we evaluate four exposure media: terre strial soils, surface water bodies, fish consumed by wildlife, and air. Within these four exposure media, we evaluate a to tal of nine Generic Ecol ogical Assessment Endpoints (GEAEs) that reflect the overall “health” of aquati c and terrestrial ecosystems and any important biota or community types that could be exposed in thos e ecosystems. For each HAP and GEAE we screen for adverse environmental effects using ecological benchm arks. Ecological benchmarks represent a level of exposure to a chemical in the enviro nmental that has been linked to a particular environmental effect level (e.g., a no-effect level or a thre shold effect level) through scien tific study. Additi onal details on the environmental risk screen methodology, the ecological benchmarks used, and the screening results are located in the Residual Risk Assessment for the Primar y Aluminum Production Source Category in Support of the September 2015 Risk and Technology Review Final Rule which can be found in the docket.

Comment: One commenter (0166) observes that the EPA does not mention an Endangered Species Act (ESA) consultation, which provides further evidence that it has not consid ered or addressed its duty to prevent adverse environmental effects, as recognized by the D.C. Circuit, (based on Sierra Club v. EPA, 353 F.3d at 992, explaining that ESA consultation is requ ired to occur as part of the section 112(f)(2) rulemaking).55 Response: Because our analysis shows that we do not expect an environmental effect from this source category even at a national level, we disagree with the commenter’s st atement that the EPA must engage in consultations ( e.g. , with the U.S. Fish & Wildlife Service and the National Marine Fisheries Service) under 16 U.S.C. 1536(a)(2). See, e.g., Ground Zero Center for Non-Violent Action v. U.S. Dept. of Navy, 383 F. 3d 1082, 1091-92 (9th Cir. 2004) (where the like lihood of jeopardy to a species from a federal action is extremely remote, ESA does not require consultation).

Comment: Commenter (0369) stated that the baseline environmental risk screening for emissions of gaseous hydrogen fluoride (HF) is based on an assessm ent of actual emissions, but they believe the risk screening for gaseous HF should include an assessmen t of allowable emissions on plant life and indicate which specific fluoride standard is being applied (i.e., 24-hour or 30-day av erage). Commenter (0369) stated the ecological assessment should also indicate how close the predicted modeled concentrations for each facility are to the standard as a percentage (e.g., facility X that modeled concentration of gaseous fluoride is 90 percent of the 24-hour average standard). Commenter (0369) stated that this information will strengthen the conclusion that adverse effect s on grazing wildlife and grazing domestic animals are not expected to occur.
Commenter (0165) notes that fluoros is in grazing ruminants has been shown to occur with continuing low level fluoride ingestion and is the direct result of livesto ck grazing (ingestion) on fluoride contaminated forage. The commenter cites concer ns regarding fluoride and vegetation damage and human health. The commenter states that a review of aerial photography shows that most of the primary aluminum production plants have active farm land su rrounding the identified fac ilities and the potential for animal grazing should be a concern. The comm enter expresses concern that the RTR fails to recognize this welfare effect and th e important exposure pathway of inge stion needs to be accounted for in addition to direct inhalation exposure for all mammals
Response: The commenter is correct that we did not ba se the ecological screening risk assessment on allowable emissions, and instead based it on actual emissions. The uncertainties associated with the ecological screen along with uncertainties in the allowable emi ssions estimates would make an ecological risk assessment based on allowable emissi ons too uncertain for use in making a regulatory decision. We also note that in our inhalation assessm ent, these allowable emissions estimates were used and did not show significant inhalati on risk, and therefore, we did notfocus on the uncertainty in the emissions.
In our environmental risk screening analysis we determined that for hydrogen fluoride, the average modeled concentration around each facili ty (i.e., the average concentratio n of all off-site data points in the modeling domain) did not exceed the ecological benchmarks. In the risk assessment document we indicate that as a category, onl y 0.2% of the modeled area exceededthe ecological benchmarks. The facility with the highest average concentration of HF ove r the modeling domain had a concentration of 0.0472 ug/m 3 . This concentration is approximately 10 tim es lower than the ecological benchmark or 12% of the benchmark value.
For HF, the environmental risk screen evaluates th e potential phytotoxicity a nd reduced productivity of plants due to chronic exposure to HF. The environmental risk screen compares the modeled ambient air concentrations in the modeling domain around each f acility to the ecological benchmark for HF. The56 Environment Canada benchmark that was used for HF (0.4 ug HF/m 3 ) represents a lowest observed effect level (LOEL), which is defined as:

" ”The level above which there are demonstr ated effects on human health and/or the environment. It is scient ifically based and de fines the boundary between the LOAEL and the NOAEL. It is considered to be the level of exposure just below that most likely to result in a defined and identifiable but minimal effect." ” (CCME 1999)

The Environment Canada criteria was developed using data from 13 inves tigations into the effects of HF on plants that represented 32 sepa rate effects results. The data se t included 18 effects results from studies using plants of horticultura l importance, 10 from studies using agricultural species, and 4 from studies of effects on forest (conife r) species. We agree with the commen ter, that high concentrations of HF in the air have been linked to fluorosis in li vestock. However, the HF concentrations at which fluorosis in livestock occur are hi gher than those at which plant damage begins. Therefore, the HF benchmark that was used for the screen is protective of both plants and livestock.
3.2.7 Modeling Data

Comment: One commenter (0162) states that the AERMOD model used by the EPA to calculate downwind HAP emission concentrations severely over- predicts ambient pollutant concentrations for primary aluminum facilities, especially for short-term concentration estimates. The commenter notes that AERMOD and other regulatory models are cons ervative by design. The commenter further notes that AERMOD is designed as a point, area or volu me source model and does not specifically address line sources of emissions, such as aluminum potline s, thus not adequately accounting for heat release (and associated plume rise) within these types of facilities; the effect of numerous merged buoyant plumes; and/or the impact of downwash from larg e or long buildings. As an example the commenter provides data (see table titled Over Predic tions Using Modeling, below) comparing AERMOD predictions with two years of ambient SO 2 measurement data for one US aluminum smelter, showing that the model over-predicts short-term SO 2 monitored concentration by a factor of 30 to 70 (3000 to 7000%). The commenter believes that over predictions are also likely for HAP emissions modeled using AERMOD as part of the residual risk assessment.
Over Predictions Using Modeling

Facility Monitoring Period Measured 99 th Percentile 1-hr SO 2 ug/m 3 AERMOD Predicted* 99 th Percentile 1-hr SO 2 ug/m 3 Over Prediction

Plant No. 1 Station PS2 2009 99.56 3112 3126%

Station PS2 2010 47.16 3472 7362%
* Modeling performed with actual SO 2 emissions for 2009 or 2010.57 Response: The EPA disagrees that the AERMOD model ove restimates concentrations for sources like potroom roof monitors, and that th e BLP model needs to be used to correctly model such sources. An analysis performed by the EPA to compare the m odeled estimates from AERMOD and the BLP model for a typical Primary Aluminum facility indicated th at the maximum modeled concentrations were only twenty percent different. 18 The EPA concluded that this differen ce was not significant enough to warrant changing the RTR modeling methodology it uses for all source categories, which includes the use of AERMOD and meteorological data generated by AERMET.
With respect to the comment regarding comparis ons between modeled and measured short-term concentrations of SO 2 , we note that in this assessment we are primarily modeling annual HAP concentrations and therefore a comparison between m odeled and measured short-term concentrations is of questionable utility. Moreover, the use of AERMOD and HEM has been the EPA’s SAB-approved approach for estimating chronic maximum individua l exposures and risks throughout the RTR program.
With respect acute health risks, which do take in to account 1-hour maximum HAP concentrations, the data provided with respect to SO 2 are again of questionable utility. Other than stating that AERMOD was run with “regulatory default assumptions to primary control de vice stacks,” the commenter provides little additional detail about the analysis, thus making it diffic ult to assess (e.g., the commenter did not state the name of the facility usedin this analysis, where the facility was located, or the source of the monitoring data that was compared to the modeling data). Moreover, we again note that in this case we are measuring short-term concentrations of HAP and not SO 2 . That all being said, we do agree that our worst-case acute health screen is conservative in nature because it assumes worst-case meteorology, peaking of all emission points concurrently, and assumes that an individual will be at the site of maximum concentration for at least an hour.

Comment: One commenter (0162) states thata flaw in the risk assessment is that the risk assessment does not include short or long term population mobility. The commente r expresses concern that the EPA assumes full-exposures of 70 years outdoors and full-ti me at the census blocks modeled in HEM3, and that omission of a mobility/activity analysis is es timated by the EPA to overestimate risk by 25 percent for particulate HAPs (such as POM) based only on short term mobility patterns. The commenter concludes that the inclusion of l ong term activity patterns, such as moving residences and job locations, would result in even lower risk estimates.
Response: Refer to the response to the following comment, below.

Comment: Three commenters (0165, 0369 a nd 0166) disagree with the EPA’s modeling assumption that estimates the impact of emissions at the census block centroid rather than the facility fence or property line for cancer and other chronic health risk.
Commenter 0166 expresses concern that the EPA’s analysis fails to consid er the actual level of risk for the “individual most exposed to emissions” as re quired by section 112(f). Commenter 0166 notes that the EPA adjusted receptor points in the HEM-AERM OD system to estimate acute health risks for

18 September 27, 2010, Memo to the EPA from EC/R Incorporated; “Draft Modeling Comparison of BLP and AERMOD for Primary Aluminum” available in the docket at http://www .regulations.gov/#!documentDetail;D=EPA-HQ-OAR-2011-0797- 017558 residents living on the fence line. Co mmenter 0166 concludes that failing to assess risk at the fence line would be unlawful, arbitrary, and capr icious as such an approach fails to assess risk for the person “most exposed” to the source category’s emissions.
Additional concerns of Commenters (0165 and 0369) include development over time as homes and businesses locate closer to the facility and assu mptions that the population distribution is homogenous. Based on the power and ability of the HEM-3 model, Commenters (0165 and 0369) suggests that the EPA abandon its use of the predicted chronic exposure s at the census block centroid as surrogates for the exposure concentrations for all people living inthat block. Instead, Co mmenters (0165 and 0369) recommend that the EPA use the trul y maximum individual risk, irrespec tive of its location in the census block, in its section 112(f)(2) risk assessments.
Response: As we have noted in the development of previ ous residual risk regulatio ns in a national-scale assessment of lifetime inhalation exposures and health risks from facilities in a source category, it is appropriate to identify exposure lo cations where it may be reasonably expected that an individual will spend a majority of his or her lifetime. Further, indetermining chronic risks, it is appropriate to use census block information on where people actually resi de, rather than points on a fence line, to locate the estimation of exposures and risks to individuals living near such facilities. Census blocks are the finest resolution available as part of the nationwide population data (as developed by the US Census Bureau); each is typically comprised of approxima tely 40 people or about 10 households. In the EPA risk assessments, the geographic centroid of each census block containing at least one person is used to represent the location where all the people in that census block live. The census block centroid with the highest estimated exposure then becomes the locati on of maximum exposure, and the entire population of that census block is assumed to experience the maximum individua l risk. In some cases, because actual residence locations may be closer to or farther from facility emission points, this may result in an overestimate or underestimate of the actual annual concentrations (althoug h there is no systematic bias for average levels). Given the relatively small dime nsions of census blocks in densely-populated areas, there is little uncertainty introduced by using the ce nsus block centroids. There is more uncertainty when census blocks are larger, although there is still no syst ematic bias. Thus, the EPA concludes that the most appropriate locations at which to estimate chronic exposures and ri sks are the census block centroids because (1) census blocks are the fine st resolution available in the natio nal census data, (2) facility fence lines do not typically represent locations where chronic exposures are li kely (i.e., people do not typically live at the fence line of facilities), and (3) as described abov e, there is no systematic bias with respect to using census block centroids as an exposure surroga te for all individuals re siding in that block.
Assessing risk at the geographic centroid of each censu s block containing at least one person has been the EPA’s approach for estimating chronic maximum individual exposures a nd risks throughout the RTR program. In addition, in its peer revi ew of the methodologies used to es timate risks as part of the RTR rulemaking efforts, the EPA’s SAB endorsed this approach.
In addition, the commenter is corr ect that the EPA does not considerin its model that homes and businesses may locate closer to faci lities over time (i.e., population gr owth over time). While this could result in an underestimation of risk, there are also modeling assu mptions that could lead to an overestimation of risk. Thus, we do not believe that th ere is a significant bias inthe risk results in any59 one direction. Notably, uncertainties are described in section 4.1 of the Residual Risk Assessment for the Primary Aluminum Production Source Categor y in Support of the 2014 Supplemental Proposal . In part, this section states:
If anything, the population exposure estimates are bias ed high by not accounting for short- or long-term population mobility, and by neglecti ng processes like deposition, plume depletion, and atmospheric degradation. Additionally, estimates of the maximum individual ri sk (MIR) contain uncertainty, because they are derived at census block cen troid locations rather than actual residences. This uncertainty is known to create potential unde restimates and overestimates of th e actual MIR values for individual facilities, but, overall, it is not thought to have a significant impact on the estimated MIR for a source category. Finally, we did not factor in the possibili ty of a source closure o ccurring during the 70-year chronic exposure period, leading to a potential upward bias in both the MIR and population risk estimates; nor did we factor in the possibility of population growth during the 70-year chronic exposure period, leading to a potential dow nward bias in both the MIR and population risk estimates.

Comment: Commenter (0369) appreciated the development of the Summ ary Data Facility, Maximum Achievable Control Technology, Hazardous Air Pollu tants and Emissions Data Access database to evaluate the emissions inventory from each prim ary aluminum facility included in the proposal’s analysis. Commenter stated that this is an extremely useful tool to cross check the emissions inventories for the individual facilities and that this increases the transparency of the proposal and should be used in the development of all future RTR standards.
Response: The EPA acknowledges the commenter's support for the Summary Data Facility, Maximum Achievable Control Technology, Hazardous Air Po llutants and Emissions Data Access database.
3.3 Startup, Shutdown and Malfunction

3.3.1 General

Comment: One commenter (0162) agrees that work pract ices provide an appropriate basis for potline startup standards. The commenter suggests specific revisions to the work practices for potline startup proposed in section 63.854(a).
First, in proposed section 63.854(a)(6 )(iii) – the commenter suggests dele ting the phrase “but in no case more than 24 hours from the time the crust was br oken” from this provision. The commenter believes that the proposed restriction to re seal pot crust within “no more than 24 hours from the time the crust was broken” would be counter-productive or even inf easible for some pots in startup and for some pot types. The commenter provides the examples of (1) an unstable or hot pot may take more than 24 hours to develop a stable crust, and trying to reseal th e pot within 24 hours will introduce excess alumina into the bath, further destabilizing the pot, and (2) star tup of side-worked pots re quires clamshell scooping at each individual anode over a period of 48 hours to remove the baking resister coke or graphite. Trying to reseal the cell during this 48 hour period would introduce excess alumina, again increa sing the risk of pot instability. The commenter suggest s a revised provision to read as fo llows: “(iii) Re seal pot crusts that have been broken as often and as soon as practicable; and”60 Second, in proposed section 63.854(a)(6)(ii) – the co mmenter recommends revi sing this provision to read as follows: “(ii) Reduce cell temperatures to as low as practicable, and follow the written operating plan described in paragraph (a)(7) of this section if cell temperature exceeds the specified high temperature limit.” The commenter believes that setting a temperature limit that triggers corrective action would ensure better control of pot operation and emissions than establishing a never to exceed “maximum temperature” limit and suggests that sucha “maximum temperature” limit would have little meaning if established to cover the full range of operating conditions that may be encountered during potline startup.
Response: The EPA acknowledges the commenter’s support for potline work pract ice standards during startup periods and agrees with th e commenter’s suggested revisions a nd has changed these sections in the final rule. In addition, a provisi on has been added to the final rule requiring that the written operating plan include a specified pot temperatur e that will trigger corrective action.

Comment: One commenter (0162) notes that the proposeddefinition for anode bake furnace startup does not capture the full range of star tups typical for an anode bake furnace. The commenter states that the EPA’s proposed definition for “startup of an anode bake furnace.” implies that anode bake furnace “startups or restarts” only occur when a furnace has cooled all the way down to ambient temperature. The commenter disagrees, because there are situati ons, such as maintenance events or brief power outages, where a furnace must be shutdown (burners turned off) for a short enough time that the furnace does not reach ambient temperature before a re-start is initiated (burners turned back on). The commenter states that in these situations, the bake furnace is returned to normal operation as soon as possible, rather than delaying re-start until ambient te mperatures have been reached in all sections of the furnace. The commenter proposes a revised definition that reads:
“Startup of an anode bake furnace means the process of initiating heating to the anode baking furnace where all sections of the furnace have previously been at ambient temperature. The startup or re-start of the furnace begins when the heating begins. The startup or re-start concludes at the start of the second anode bake cycle if the furnace was at ambient temp erature upon startup or when the anode bake cycle resumes if the furnace was not at ambient temperature.”
During the supplemental proposal, Commenters (0372 and 0375) suggested further revisions to the definition, respectively:

 Startup of an anode bake furnace means the proce ss of initiating heating to the anode baking furnace where all sections of the furnace have previ ously been at ambient temperature. The startup or re-start of the furnace begins when the heating begins. The startup or re-start concludes at the start of the second anode bake cycle if the fu rnace was at ambient temperature upon startup or when the anode bake cycle resumes if the furnace was not at ambient temperature.

 Startup of an anode bake furnace means the proce ss of initiating heating to the anode baking furnace where all sections of the furnace have previ ously been at ambient temperature. The startup or re-start of the furnace begins when the heating begins. The startup concl udes at the start of the second anode bake cycle if the furnace was at ambient temperature upon startup. The re-start61 concludes when the anode bake cycle resumes if the furnace was not at ambient temperature upon re-start.
Response: The EPA agrees with the commenter and has re vised the final definition to capture the full range of startups typical fo r an anode bake furnace.

Comment: One commenter (0162) asks that the EPA cl arify the provisions of section 63.847(l) as follows:

 Delete the word “first” from section 63.847(l)(1) because it is not clear what the term “first anode bake furnace” means;

 Clarify the language in section 63.847(l)(2) to say “Reco rds of time, date, and duration of anode bake furnace startup and records of any nonroutine actions taken during startup;” and

 Add the following sentence to the end of section 63.847(l)(4) to clarify that there is no requirement to cool the furnace to ambi ent temperature again before restart:
“(4) A requirement to shut down the anode bake furnaces immediately if the associated emission control system is off line at any tim e during startup. The anode bake furnace restart may resume once the associated emission control system is back on line and operating within normal parametric limits.”
Response: The EPA has clarified section 63.847 (l)(1) in the final rule to r ead “A requirement to develop an anode bake furnace startup schedule.” The EPA ha s clarified section 63.847(l)(2) and (4) as suggested by the commenter.

Comment: One commenter (0166) assert s that the EPA’s proposed 6- month startup practices for potlines is unlawful, by creating new provisions th at would perpetuate the problem of the SSM exemption. The commenter agrees with the proposedremoval of the SSM exemption, but does not agree with the proposed new startup requirements for potlines, which include only work practices. The commenter also objects to the require ment for an initial compliance test six months after startup of a potline or potroom group, and questions the lack of a definition of “startup” for potlines.
The commenter states that the EPA fails to satisfy th e test it must meet to promulgate work practice standards “in lieu of” numerical emission standards set by section 112( h), observing that the EPA has not provided any evidence or reasoned explanation for th e statements, “it is economically and technically infeasible to measure emissions du ring these startup periods,” and “[t]hese long startup periods for potlines are recognized as part of the normal operations during which emissions testing is not feasible.” The commenter argues that the record suggests that it should be feasible both to control and test emissions during startup. Since the work practice standards require thatthe primary capture and control system is operating at all times during startup, the co mmenter asserts, emission testing from the control device is also feasible. The commenter notes th at technology is available to perform continuous emission monitoring for HF and asserts that, ther efore, under section 112( h), the EPA cannot avoid setting a numerical standard that applies du ring startup.62 The commenter notes that in an attached document, the National Park Service expresses serious concern about fluoride level spikes during st artups at primary aluminum plants . The commenter asserts that the EPA should not create a startup ex emption loophole that would allo w high levels of emissions to continue to occur during startup peri ods, without any numerical limitation.
Response: The commenter has misinterpreted the 180 da y period following startup as an exemption. This refers to the deadline fo r conducting initial performance test s or performance tests following a restart. Prior to any startup, the operator is required to start the control device and ope rate the fans directing potline emissions to the control device, as well as comply with other provisions of the rule. Startup of potlines, as defined in the General Provisions , is the setting in operation of an affected source, or any part of an affected source, for any purpose.
Potroom testing to determine secondary emissions t ypically utilizes sampling equipment located at a fixed position within the potroom. During normal operation, this provides a sample that is representative of the overall secondary emissions from the potroom. Du ring startup, this sample is not representative as it is largely representative of the status of the pot s that are located close to the sampling equipment. Further since emissions rates are normalized by pr oduction rates, during peri ods when production is zero, calculated production based emi ssion rates are not meaningful. It may be feasible to determine emission rates from the primary control system duri ng startup, however these rates would be variable depending on the phase of the startup, and thus would not be useful for compliance purposes. We did consider ambient data provided by th e National Park Service and emissions data from a potline startup at the Alcoa facility in Wenatchee, WA (see section 3.2.6, above). These data suggested that an increase in the mass emission rate may occur duri ng periods of startup, but that those increases in emissions would have minimal effect on the EPA’s estimates of actual annual emissions.
Concerning continuous emission monito ring for HF, the fluoride emission standard is expressed in terms of total fluoride (TF), which includes both HF and particulate fluoride. Reliab le continuous emission monitors may not be available for measurement of TF.

Comment: One commenter (0166) states th at the EPA must implement strong enforcement provisions to prevent emission spikes, malfunctions and other violations in a way that will be enforceable by citizens in the title V permits for this source category. Th e commenter suggests that the EPA consider example violation and malfunctions that have occurred in the past, based on Enforcement and Compliance History Online (ECHO) repor ts for existing facilities.
Response: The EPA believes that the enforcement provisions of the final rule are enforceable by citizens. A citizen suit claim under section 304 allo ws citizens to commence a civil action against any person alleged to be in violation of “an emission sta ndard or limitation under th is chapter.” In exercising its authority under se ction 112 to establish emission standards at a level that m eets the stringency requirements of section 112, the EPA necessarily define s conduct that constitutes a violation. If there is a violation of the emission standard and the source demonstrates that all the elements of the affirmative defense are met, only injunctive reli ef is available. All other violations of the emission standard are subject to injunctive relief and penalties.63 Comment: One commenter (0166) recommends further ac tions in the case of an exceedance or malfunction as follows:

 The EPA must require automatic s hut off of the malfunctioning equipment or process for the time needed to take correctiv e action, whenever an exceedance or malfunction occurs.

 The EPA must assign responsibility and liability to th e plant manager or a high-up staff member to allow only that person to restart the equipment or process.

 The EPA must require specific corrective measur es to be taken immediately, to remedy and prevent recurrence of the malfunction or violation.

 For a facility that has had 1 or more malfunction, exceedance, or other violation incident in the prior month, written authorization by the EPA must be required to restart e quipment or processes. The EPA should only authorize restart after making a public determination that provides information on the corrective measures that the EPA is requiring. The EPA should release this public determination on the Internet and requi re its Regional office to communicate this determination to all interested members of the pu blic, including local comm unity representatives.

 If a facility has more than 4 exceedances or ma lfunctions during the same quarter, then the EPA must require automatic shut dow n of the operation for a period of time needed to conduct and publish a full investigation and ensure systematic correction of the problem/s.

 The EPA should create a community complaint mech anism in the standards that ensure that a citizen complaint of air pollution incidents or health concerns receiv e an immediate response from the EPA’s enforcement division within 7 days, in which the EPA commits to initiate an investigation and provide a publicly available report of the result of the investigation, including whether it leads to an enforcement outcome.
Response: It is not feasible to instantaneously shut of f the affected sources within this source category in the event of a malfunction and au tomatic shut off of malfunctioni ng equipment may not ensure that emissions are minimized. Owners or operators must, atall times, operate and maintain any affected source, including associated air pollution control e quipment, in a manner consistent with safety and good air pollution control practic es for minimizing emissions.

3.3.2 Affirmative Defense
The affirmative defense was vacated by the courts in NRDC v. EPA, 749 F. 2d 1055, 1064 (D.C. Cir. April 18, 2014). As such, comments for and against th e affirmative defense no longer apply. A summary of the comments provided from the proposal and the supplemental proposal are provided below. A general response to these issues is provided in section 3.3.2(c).
a. Proposal Comments Received

Comment: One commenter (0166) states that the EPA’s own proposal addressing malfunctions and violations creates a loophole thatreduces the incentive to comply and may make malfunction-based64 violations more likely. While the commenter agrees with the EPA’s proposal to remove the malfunction exemption from the MACT standard, the commenter asse rts that the EPA also pr oposes to create a new loophole in the form of an “affirmative defense to civil penalties” for malfunctions. The commenter expresses concern that the new “affirmative defense” may make it more likely that malfunctions happen by giving industry a way to evade penalties if facili ties can show a violation was due to a malfunction. The commenter recommends that the EPA collect information on major sources’ malfunction and violation history.

Comment: One commenter (0166) states that the proposed affirmative defense to penalties due to malfunction is unlawful. The commenter argues that Congress, in CAA section 304(b)(1)(B), plainly intended citizens to be able to enforce emission st andards under the CAA usi ng the full range of civil enforcement mechanisms available to the government and, in the HAP context, subject only to the limitation that government not be “diligently prosecuting” its own civil enforcement action.
The commenter asserts that Congress expressed a clear intent as to how judges should determine the size of civil penalties whenever they are sought and th us Congress flatly barred the EPA from limiting when civil penalties can be assessed, and th at in this proposal the EPA acts outsi de of its delegated authority to limit civil penalties available in citizen suits or its own enforcement actions. Further, the commenter argues, the proposal will impermissibly chill citizen pa rticipation and the ability to win an effective, deterrent remedy in CAA enforcement actions.
The commenter states that the CAA grants th e EPA minimal discretion that only applies to administrative penalties which may be imposed unde r section 113(d) and th at there is no similar authority to compromise, modify or limit civil pena lties that a court may impose under sections 113(e) or 304. Rather, the commenter argues, it is improper for a court to fail to make its own determination of what civil penalties are “appropria te” under CAA section 304(a), and th e EPA should not ask a court to ignore its legal duty. The commenter not es that it is improper for the EP A to fail to consider the section 113(e)(1) factors in situations in which it is setting the penalty. (CAA section 113(e)(1)).
The commenter believes that citizen participation in CAA enforcement also will be hindered, in violation of citizens’ rights to pr otect themselves from pollution and indirect conflict with congressional intent. The commenter expresses concern that the af firmative defense would likely be used on a routine basis by polluters seeking to avoid penalties, just as the malfunction exemption was, and as a result, citizens who seek the assessment of civil penalties against polluters inorder to protect themselves and achieve the Clean Air Act’s goals could be forced to engage in fact-intensive disputes over the cause of emission violations and adequacy of responsive meas ures – an outcome Congre ss intended to prevent with the simple straightforward enforcement and penalty provisions in the Clean Air Act. The commenter concludes that enforcement of the Clean Air Act could suffer, for civil penalties provide a powerful deterrent to violat ors as Congress intended.
The commenter expresses concern that if a local community group sued a covered facility for a violation of the emission standards, the owner could argue that it is exempt from paying civil pena lties so long as the owner satisfied the requirements set forth in the EPA’s proposed affirmative defense regulations, and continues that the owner must not be able to evade civil penalties that apply wh en the congressionally mandated (see 42 U.S.C. section 7413(e)) factors are met. The commenter believes that the proposed65 exemption would also be barred under Chevron step two or found to be arbitr ary and capricious since, even if there exists some slight ambiguity, it is unreasonable to construe the statute as permitting the EPA to short-circuit the consideration of specifica lly listed factors. (See Chevron, 467 U.S. at 843) (explaining that if the statute does not answer the question at issue, “the question for the court is whether the agency’s answer is based on a permissible construction of the statute”); S. Coast Air Quality Mgmt. Dist. v. EPA, 472 F.3d 882, 895 (D.C. Cir. 2006) (“We fu rther hold that the EPA’s interpretation of the Act in a manner to maximize its own discretion is unr easonable because the clear intent of Congress in enacting the 1990 Amendments was to the contrary.”); see also Gen. InstrumentCorp. v. F.C.C., 213 F.3d 724, 732 (D.C. Cir. 2000) (explaining that “an arbi trary and capricious claim and a Chevron step two argument overlap”); Motor Vehicle Mfrs. Ass’n of U.S., Inc. v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 43 (1983) (explaining that the Agency acts in an arbitrary and capricious manner if it fails to consider “relevant factors” or “entirely fail[s] to consider an important aspect of the problem”). By “upset[ting] the statutory balance struck by Congress,” argues that commenter, the affirmative defense is unreasonable under Chevron step two. Int’l Alliance of Theatrical & Stage Employees v. N.L.R.B, 334 F.3d 27, 35 (D.C. Cir. 2003).

Comment: One commenter (0166) states th at the affirmative defense also runs counter to two clearly expressed intentions of Congress: (1) the burden it places on citizens makes it less likely that they will enforce the Act; and (2) several of the factors at issue in the affi rmative defense undercut Congress’s intent that citizen suit enforcemen t should avoid re-delving into “technol ogical or other considerations.” The commenter proposes that both result from the tech nical burden the EPA imposes on citizens with the affirmative defense, and both render the defense impermissible.

Comment: One commenter (0166) asserts that the EPA has not demonstrated any need or rational justification for an affirmative de fense to penalties to be written into the regulations. The commenter asserts that affirmative defense allows facilities to escape penalties due to malfunctions if they meet factors that the EPA defines, reducing the deterren t value of the MACT standard and undermining the ability of people living near facilities that violate the standard to receive effective relief from unlawful emissions. The commenter states that polluters are likel y to claim that any violation of the standard is due to a malfunction in order to evade the requireme nts. The commenter observes that allowing polluters to evade financial penalties through this type of measur e is likely to lead to po lluters simply ignoring or factoring potential standard violations into their co st of doing business. The commenter states that the EPA has provided no evidence that an affirmative de fense for malfunctions would serve the purpose of section 112 (that is, to protect people from toxic air pollution).

Comment: One commenter (0166) asserts th at, assuming that the EPA had authority to promulgate any type of affirmative defense to penalties for malfun ctions, the EPA should also promulgate the following provisions:

 The commenter suggests that the EPA apply a speci fic amount of compensatory penalties to each reported malfunction (consistent with the CAA) , and these funds should be dedicated to enforcement, inspections, and monitoring in the local community around the specific facility, to create greater assurance that malfunctions will not happen again.66  The commenter proposes that the EPA modify the regulations so that the affirmative defense cannot be used by a specific facil ity or company more than once within a set period of time, such as 10 years. The commenter further proposes that affirmative defense should become automatically unavailable to a facility that ha s previously had a malfunction within the last 10 years, to ensure that this defense does not swallow the value of the standards.
b. Supplemental Proposal Comments Received

Comment: Commenters (0372 and 0375) are concerned th at with the removal of the “Affirmative Defense” provisions (DC Ci rcuit Court ruling in NRDC v. EPA , 749 F. 3d1055 2014) that there will be a regulatory expectation that emission limits mu st be complied with dur ing malfunction periods. Commenters stated that the Agen cy’s proposed approach of only offering case-by-case enforcement discretion in the event malfunction ev ents occur does not provide an ad equate regulatory framework for managing them. Commenters stated that malfunctions are by defin ition sudden, unavoidable events and an approach of treating these even ts as violations of emission limit s that were established for normal operations is unreasonable for owners and operators working diligently to maintain compliance. Commenter (0375) stated that that the EPA needs to reconsider this position and establish reasonable standards, rather than leaving a vague regulatory framew ork that could allow bi ased agency action or third party litigation for unavoidable events. Commenter (0375) stated that due to the number and nature of potential malfunctions, establishing numerical emission limits is not technically feasible or practicable.
Commenter (0372) requested that th e final rule and/or its accomp anying preamble contain clear and unambiguous language indicating that there is not an expectation th at the final emission limits be complied with during periods of malfunction. Comment er (0372) stated that in the absence of an “Affirmative Defense” provision in the final rule , the EPA provide guidance on the factors and framework for the implementation of appropriate ma lfunction response activity in lieu of applying numerical emissions limits that were developed for normal operating conditions during periods of malfunction events. Commenter (0372) requested that the EPA provide guidance on how it will determine the appropriate level of enforcement acti on to be taken in response to malfunction events. Commenter (0375) recommended that the EPA develop a malfunction work practice standard (such as a written malfunction response plan ) in place of numerical emi ssion limits developed for normal operating conditions.

Comment: Commenter (0374) stated that the EPA is withdrawing from the Proposed Rule a provision that would have accorded primary aluminum plants anaffirmative defense to civil penalties for excess emissions associated with malfunc tion events, provided the malfunction meets certain criteria and the operator complies with reporting requi rements. Commenter (0374) stated that there is no indication that the EPA has reconsidered, however, whether the Proposed Standards are appropriate (i.e., are consistent with congressional directives) in the absence of an affirmative defense for malfunctions.
Commenter (0374) stated that simply eliminating the affirmative defense provision without assessing the need for some other adjustment in the Proposed St andards in light of that change does not comply with the CAA. Commenter (0374) st ated that the affirmative defense was something that the EPA considered necessary when the EPA initially pr oposed revised emission standards for primary67 aluminum plants, and it was part of the statement of basis and purpose for the proposed standards that the EPA was required to publish under CAA section 307(d)(3). Commenter ( 0374) stated that the supplemental notice does not explai n at all why the remai nder of the proposed st andards does not need to be revised in light of that elimination. Commenter(0374) stated that the EP A cannot delete a critical piece of a proposed rule without at least analyzing and explaining to the public why the proposed rule still is appropriate and consistent with statutory requirements in the absence of that critical piece. Commenter (0374) stated that the EPA must publis h a new or supplemental statement of basis and purpose for the proposed rule that explains and allows for public co mment on the appropriateness of the entire proposed primary aluminum emission sta ndards without an affirmative defense provision.
Commenter (0374) stated that the supplemental notice seems to imply that the affirmative defense was not really a necessary part of the standards but was nevertheless included in the standards “to provide a more formalized approach and mo re regulatory clarity.” 79 FR 72950. Commenter (0374) stated that this statement does not excuse the EP A’s failure to reconsiderentirely its statemen t of basis and purpose for the Proposed Rule with the affirmative defens e for malfunctions removed. Commenter (0374) stated that the affirmative defense was a key element of the EPA’s explanation for why it was lawful for the Agency to promulgate MACT standards that apply dur ing malfunctions, but that do not reflect what is achievable with available technol ogy during malfunctions. See propos ed rule, 76 FR 76280. Commenter (0374) stated that the Agency believed at the time that an affirmative defense provision was necessary to effectuate the congressional directive that MA CT standards be based on what is achievable with available technology; otherwise, the EPA would have had no statutory author ity to promulgate the affirmative defense.
Commenter (0374) stated that the EPA staff almost in evitably had to have consid ered the effect of the affirmative defense on compliance obligations whenthey were deriving the Proposed Standards. Commenter (0374) stated that in the Response to Comments docume nt for MACT standards for the recently promulgated MACT standard for boilers and process heaters, the EPA stated: “EPA agrees with the commenter that the malfunction periods do not qualify for affirmative defense and should be factored into the MACT floor calculation since thes e flagged ‘malfunctions’ occur too often. We revised the analysis of the CO CEMS datato include the flagged malfunction periods. The final rule contains the revised emission limits.” EPA-HQ-OAR- 2002-0058-3846 p. 259. See also EPA-HQ-OAR-2002- 0058-3877 p. 11 (“CO CEMS data from periods of malfunction were included in the analysis. This change was due to the fact that when facilities comply with the am ended final Boiler MACT frequent periods of malfunction cannot qualify for the Affirmat ive Defense provisions in the amended final rule and these data will need to be included in the ro lling averages. It would thus not be appropriate to exclude them from the calculations.”). Commenter (0374 ) stated that in that rulemaking, whether or not excess emissions associated withunavoidable equipment failures would qualify for the affirmative defense dictated whether the EPA wo uld factor those emissions into se tting the standard, or would rely instead on the affirmative defense to address those emissions.
Commenter (0374) stated that havi ng taken the affirmative defense into account when deciding what emission standards to include in the Proposed Rule, the EPA cannotnow eliminate the affirmative defense from the proposal withou t reassessing the appropriateness of those emission standards and how they will affect primary aluminum plants if the standards are no longer mitigated by the68 affirmative defense. Commenter (0374) stated that the EPA must then publis h its analysis and seek public comment on it before promulgating a final ru le that makes emission limitations based on data from normal operations applicable even during malfunctions but dele tes any affirmative defense for malfunctions.
Commenter (0374) stated that the EPA cannot simply eliminate the af firmative defense for malfunctions without considering its effect on the r easonableness of the emission standards.

Comment: Commenter (0374) stated that the EPA is requ ired, before eliminating SSM provisions in the original MACT standards for Primary Aluminum Produc tion, to demonstrate that the resulting standards will be consistent with CAA section 112 and cong ressional intent that those standards must be achievable with available technology, and that they must be at least as stringent as the actual emissions of the best performers. Commenter (0374) stated that the supplemental notice esse ntially just restates the EPA’s inadequate statement in the Proposed Ruleaddressing the EPA’s pu rported authority to promulgate technology- based standards under se ction 112 without taking the inevitability of malfunctions of the technology into account.
Commenter (0374) stated that the co urt decision that the EPA cites as the reason for eliminating the affirmative defense provisions of the current sta ndards said nothing about (a) whether the EPA must consider the effect of malfunctions when it sets emission standards that apply at all tim es (except during some startup and shutdown periods); or (b) whether it is appropriate for the emission standards themselves to contain an alternativ e emission standard that applies du ring malfunction events that meet certain criteria. Commenter (0374) st ated that the only basis for the court striking down the affirmative defense in that case was that it dictated to the federal district courts whether a civil penalty was appropriate for a particular violation, whereas the statute gives th e authority to determine an appropriate penalty for a violation to the court. See 749 F.3d at 1063-64. Commenter (0374) st ated that because the affirmative defense in the Portland Cement MACT standards at issue in that case, as with the affirmative defense provision that was included in the Proposed Rule for primary aluminum plants, applied after a violation occurre d, rather than being part of how a violation is determined, the affirmative defense intruded into the sole discretion of the district courts. Comm enter (0374) stated that thus, while the court decision is grounds for the EP A eliminating the affirmative defense as it was written in the Proposed Rule, it in no way authori zes the EPA to remove the affirmative defense from the emission standards for prim ary aluminum plants without s ubstituting some other provision addressing malfunctions. Commenter (0374) stated that nor does it allow the EPA to remove the affirmative defense without even considering whether/how the remainder of the emission standards must be revised in light of the removal of the affirmative defense.
Commenter (0374) stated that the statutory language is clear: section 112(d) requires the EPA to create standards that are achievable based on identified emission reduction measures or the demonstrated emission performance of existi ng sources, and to limit emissions only “where achievable.” Commenter (0374) stated that section 112(d)(3) requires the st andards at minimum to reflect actual achievements in the field by best performers. Comment er (0374) stated that for new sources, section 112(d)(3) sets this “floor” for what is “ach ievable” as “the emissions control that is achieved in practice by the best controlled similar source” (emphasis added). Commenter (0374)69 stated that for existing sources, it requires that the MACT standard refl ect at least the average level of control “achieved” by the top class of best-performing existing sources. Commenter (0374) stated that in both cases, where, as here, the EPA based MACT standards on the “floor,” section 112(d) thus requires the EPA to ground its decisi ons on actual performance. Comme nter (0374) stated that when the EPA ignores emissions that even best- perf orming sources experience during malfunctions, the EPA breaches its duty to set standards on the basi s of real-world performance. Commenter (0374) stated that it fails to take into account how sources actually operate a nd unlawfully prohibits emissions that cannot be avoided. See, e.g., Sierra Club v. EPA , 167 F.3d 658, 665 (D.C. Cir. 1999) (a best-performing source should not vi olate a standard supposed to be based on what it “achieve[s] in practice”); see also 76 FR 15628 (re jecting a comment as “inappropriate” because it “would result in emission limits that even the best performing so urces would be expected to exceed”). Commenter (0374) stated that the EPA's position — that the st atute requires it to set section 112-compliant emission standards that apply at a ll times, but that the EPA can meet this mandate by setting emission standards based on what is achieve d and achievable only part of th e time — simply makes no sense.
Commenter (0374) stated that every court that has addressed the issu e, both under the CAA section 111 requirement that new source performance standard s be based on the best demonstrated control technology and under the similar tec hnology-based requirements of CAA section 112(d) and (h), has indicated that the EPA must take the effect of ma lfunctions on emissions into account when establishing such technology-based emission standards. See Portland Cement Ass’n v. Ruckelshaus , 486 F.2d 375, 398-99 (D.C. Cir. 1973); Essex Chemical Corp. v. Ruckelshaus , 486 F.2d 427, 432 (D.C. Cir. 1973); Nat’l Lime Ass’n v. EPA , 627F. 2d 416, 431 (D.C. Cir. 1980); Cement Kiln Recyclin g Coalition v. EPA
, 255 F.3d 855, 872 (D.C. Cir. 2001); Nat’l Ass’n of Clean Water Agencies v. EPA , 734 F.3d 1115, 1158 (D.C. Cir. 2013).
Commenter (0374) stated that the EPA may be implying in the supplemental notice that the “flexibility” the EPA has to consider the effect of a malfunction on the ability of the source to comply in determining an appropriate enforcement response, and the opportunity that a source would have to argue to a court in an enforcement action that a malfunction justifies a reduced or no penalty, is a satisfactory means of accommodating th e effect of malfunctions on what standards are achievable with available technology. See 79 FR 72950. Commenter (0374 ) stated that the stat ute directs the EPA to set standards based on what the ava ilable technology can do or, in the case of MACT floor standards, based on what the best performers are actually do ing. Commenter (0374) statedthat nothing in the statutory language or legislative history indicates that Congress inte nded the EPA to establish MACT standards that apply at all time s, but that even best performe rs cannot meet during unavoidable malfunctions, and then have penalties poten tially mitigated in an enforcement action.
Commenter (0374) stated that the co urts agree with this analysis, st ating repeatedly that relying on enforcement discretion is no substitute for setting technology-based standards that reflect the performance of that technology dur ing all reasonably an ticipated conditions (s uch as malfunctions, which the EPA expects will occur, see id .). See, e.g., Portland Cement , 486 F.2d at 398 n.91; Nat’l Lime , 627 F. 2d at 431 n.46; Marathon Oil Co. v. EPA , 564 F.2d 1253, 1273 (9th Cir. 1977). Commenter (0374) stated that the enforcement di scretion approach does not satisfy the purpose of CAA section 112 — reducing HAP emissi ons. Commenter (0374) stated that a post-hoc case-by-case70 evaluation of emission circumstances, as the EPA intends to handle all malfunction periods, will not prevent or reduce emissions of HAPs. Commenter ( 0374) stated that rather than the starting point being affirmative steps to prevent emissions as Congress intended (including steps that would have been encouraged by the conditions specified in th e affirmative defense), th e starting point for the approach in the supplemental no tice is the post-emission presum ption of wrongdoing by the source operator. Commenter (0374) stated that the EPA is required to take malfunctions into account when setting MACT standards.

Comment: Commenter (0374) stated that the EPA has t ools for accounting for malfunctions in the standards once the affirmative defe nse is eliminated. Commenter (0374 ) stated that the supplemental notice repeats the EPA’s conclusory statements in the Proposed Rule that it would be too difficult for the EPA to consider malfunctions when establishing em ission standards and that doing so would result in standards that are too lenient. S ee 79 FR 72,949. Commenter (0374) statedthat the court decision that the EPA cites as its reason for applying emission standards based on normal operations to periods of malfunctions, Sierra Club v. EPA , 551 F.3d 1019 (D.C. Cir. 2008), specifically acknowledged that the EPA has authority under the CAA to se t different standards that apply at different times, so long as some CAA section 112 compliant standard applies at all times. See 551 F.3d at 1021, 1027. Commenter (0374) stated that the EPA has used that authority in numerous rulema kings to set alternative emission standards that apply duri ng startup and shutdown periods. Commen ter (0374) stated that the EPA may well have sufficient data on emi ssions from primary aluminum plants and/or on the performance of processes and control equipment to set alternative emission standards that appl y during malfunctions, at least during certain types of malf unctions whose effect on emissions may be predicted. Commenter (0374) stated that nothing in the EPA’s mandate to set emission standards th at are achievable with available technology and, in the case of MACT floor st andards, are actually achieved in practice by best performers allows the EPA to decline to even as sess whether it has sufficient data, or can obtain sufficient data, to set numerical limitations that apply during malfunction events.
Commenter (0374) stated that they have never suggested that the EPA establish numerical limitations that apply during normal operations at a leve l that would assure those limitations would not be exceeded even during malfunction events, as the EPA describe s in its straw-man argument in the supplemental notice (see 79 FR 72949). Commenter (0374) stated th at establishing alternative emission standards for malfunction events, whether numerical limitations or work practice st andards, would (based on how the EPA defines “malfunctions”) by defi nition not allow excess emissions th at could be avoided with proper design, operation, and maintenance of the facility. Comm enter (0374) stated that it is not advocating an approach to standard setting that “could l ead to standards that are not reflective of (and significantly less stringent than) levels that are achieved by a well-performing non- malfunctioning source.” Id

. Commenter (0374) stated that since the EPA defi nes “malfunction” in 40 CFR §63.2 not to include negligent operation, much less deliberate malf easance, the EPA’s suggestion that accounting for malfunctions in standard-setting woul d excuse excess emissions associat ed with “operator intoxication” or the source’s negligent choice to continue to operate during a strike, see 79 FR 72949, is groundless.
Commenter (0374) stated that the EPA also can use the authority Congress gave it in CAA sections71 112(h) and 302(k) to substitute a design, equipment, work practice, or operational standard for a numerical emission limitation. Commen ter (0374) stated that the use of such “work practices” will in most cases be more practicable and more comprehens ive than trying to establish numerical standards to address all malfunctions. Commenter ( 0374) stated that given the wide range of events that meet the EPA’s definition of “malfunction” and can result in excess emissions, and given that by definition the source cannot reasonably be designe d or operated to avoid malfunctions , it is eminently reasonable to address malfunctions through requirements that the s ource take all reasonably available measures to reduce the frequency, magnitude, and duration of th e malfunction. Commenter (0374) stated that one approach that has proven effective in the past is to specify the elements and objectives of a plan that the source must develop, follow, and review to assure thatthe source is taking the appropriate steps before, during, and after a malfunction to minimize excess emissions. Commenter (0374) stated that the EPA would no doubt find that most if not all or the sources identified as “best performers” have such plans and follow them to responsibly address malfunctions.
Commenter (0374) stated that the EPA has already s hown that it can use work practices to address the effect on emissions when a source is operating in other than normal steady- state operation, when the EPA established work practice stan dards in lieu of numerical emissi on limitations for numerous source categories that apply duri ng startup or shutdown. Commenter (0374) stated that the EPA also often has recognized that conditions during st artup and shutdown are not amenable to monitoring compliance with a numerical standard (see, e.g., 79 FR 72874, 72,904), and that is true even more so with respect to malfunctions. Commenter (0374) stated that the EPA regulations long ha ve specified that malfunctions are not representative conditions fo r purposes of monitoring emissions and determining compliance. See, e.g., 40 CFR §§ 60.8(c) and 63.7(e)(1). Commenter (0374) stated that before the EPA promulgates revised emission standards for primary aluminum plan ts that apply even duri ng malfunctions but that contain no affirmative defense or other provision a ddressing malfunctions, the EPA should determine an appropriate set of work practices, or a combination of work practices and alternative numerical emission limitations, that address higher emissions associat ed with malfunctions of properly designed and operated MACT technology, and the EPA must offer its analysis for public comment before finalizing the deletion of the affirmative defense and the adoption of the a lternative standards.

Comment: Commenter (0374) urged the EPA to withdraw its proposal, as reflected in the supplemental notice, to remove the affirmative defense provi sion of the Proposed Rule without evaluating the reasonableness of the Proposed Standards in lightof the deletion of the affirmative defense. Commenter (0374) stated that the EPA must consider the variety of options, as described in these comments, that it has for addressing excess emissi ons during malfunction events, rather than setting standards that do not comply with CAA section 112 b ecause they do not reflect th e effect of process or equipment malfunctions on what emissions the id entified technology can achieve at all times.

Comment: Commenter (0373) supported the EPA’s remova l of the originally proposed affirmative defense for civil penalties in the event of a malfunction. Commenter (0373) stated that such provisions are unlawful, as the D.C. Circuit has held, and the EPA appropriately determined that the EPA’s original proposals on such a defense should be withdrawn.
c. Response to Affirmative Response Comments72 Response: In the 2012 proposed rule, the EPA proposed to include an affirmative defense to civil penalties for violations caused by ma lfunctions in an effort to create a system that incorporates some flexibility, recognizing that there is a tension, inherent in many type s of air regulation, to ensure adequate compliance while simultaneously recognizing th at despite the most diligent of efforts, emission standards may be violated under circumstances entirely beyond the control of the source. Although the EPA recognized that its case-by-case enforcement di scretion provides sufficient flexibility in these circumstances, it proposed the affirmative defense to provide a more formalized approach and more regulatory clarity. See Weyerhaeuser Co. v. Co stle, 590 F.2d 1011, 1057-58 (D.C. Cir. 1978) (holding that an informal case-by-case enforcement discretion ap proach is adequate); but see Marathon Oil Co. v. EPA, 564 F.2d 1253, 1272-73 (9th Cir. 1977) (requiring a more formalized approach to consideration of “upsets beyond the control of the permit holder.”) . Under the EPA’s regulatory affirmative defense provisions, if a source could demonstrate in a judici al or administrative proceeding that it had met the requirements of the affirmative defense in the regulat ion, civil penalties would not be assessed. After the 2012 proposal, the United States Court of Appeals fo r the District of Columbia Circuit vacated an affirmative defense in one of the EPA’s secti on 112 regulations. NRDC v. EPA, 749 F.3d 1055 (D.C. Cir., 2014) (vacating affirmative defense provisions insection 112 rule establishing emission standards for Portland cement kilns). The court found that the EPA lacked authority to establish an affirmative defense for private civil suits and held that under the CAA, the authority to determine civil penalty amounts in such cases lies exclusiv ely with the courts, not the EPA. Specifically, the Court found: “As the language of the statute makes clear, the courts determine, on a case-by-case basis, whether civil penalties are ‘appropriate.’” See NRDC, 749 F. 3d at 1063 (“[U]nder this statute, deciding whether penalties are ‘appropriate’ in a given private ci vil suit is a job for the courts, not EPA.”). 19 In light of NRDC, the EPA in the 2014 supplemental proposal w ithdrew the proposed affirmative defense and is not including a regulatory affirmative defense provision in the final rule. As expl ained above, if a source is unable to comply with emissions standards as a result of a malfunction, the EPA may use its case-bycase enforcement discretion to provide flexibility, as appropriate. Further, as the D.C. Circuit recognized, in an EPA or citizen en forcement action, the court has the discretion to consider any defense raised and determine whether pena lties are appropriate. Cf. NRDC, 749 F. 3d at 1064 (arguments that violation were caused by unavoidable t echnology failure can be made to the courts in future civil cases when the issue arises). The same is true for the presiding officer in EPA administrative enforcement actions.20
In light of the courts vacating the affirmative defe nse and the EPA’s decision not to include the affirmative defense in the final rule, we are not respondin g to the comments opposing or supporting the addition and removal of the affirmative defense.

19 The court’s reasoning in NRDC focuses on civil judicial actions. The Court noted that “EPA's ability to determine whetherpenalties should be assessed for Clean Air Act violations extends only to administrative penalties, not to civil penalties imposed by a court.” Id. 20 Although the NRDC case does not address the EPA’s authority to estab lish an affirmative defense to penalties that is available in administrative enforcement acti ons, the EPA is not including such an affirmative defense in the final rule. As explained above, such an affirm ative defense is not necessary, and in the 2014 supplemental pr oposal we withdrew the proposed affirmative defense. Moreover, assessment of penalties for violations caused by malfunctions in administrative proceedings and judicial pro ceedings should be consistent. Cf. CAA section 11 3(e) (requiring both the Administrator and the court to take specified criteria into account when assessing penalties).73 3.4 MACT Review and Rulemaking

3.4.1 General

Comment: One commenter (0158) is in favor of the pr oposed regulation of POM and COS, especially in consideration of these two pollutants potential harm to human health and the environment.
Response: The EPA acknowledges the commenter’s support for these provisions.

Comment: One commenter (0166) states th at to satisfy section 112(d)(6 ) the EPA must recalculate the MACT floor and perform a beyond-the- floor analysis to determine whatemissions reductions are being “achieved” and are now “achievable” under sections 112(d)(2) and (3), and assess emission reduction “developments” in current industry “practices, proce sses, and technologies” under section 112(d)(6) to ensure that it does not miss “achievable” emission reductions. The commenter a sserts that the EPA did not perform these actions and did not recalculate th e MACT floor to address greater emission reductions now achievable. The commenter believes that the EP A interpreted the term “d evelopments” too narrowly and as a result, did not adequately assess all “developments” that have occurred that are relevant to the emission reductions now achievable. The commenter recommends seeking information from all of the states with existing facilities, and by considering the use of stronger limits such as those included in the permit for the Alumax of South Carolina facility in Mt. Holly, SC.
Response: The commenter is incorrect in asserting that the EPA mustrecalculate MACT floors under CAA sections 112(d)(2) and (3). As explained in prior RTR rulemakings, the EPA does not read section 112(d)(6) as requiring a reanalysis or recalculation of MACT floors. See National Emission Standards for Coke Oven Batteries (70 FR 19998-19999, April 15, 2005 ).). We read section 112(d)(6) as providing the EPA with substantial latitude in weighing a variety of factors and arriving at an appropriate balance in considering revisions to stan dards promulgated under section 112( d)(2) & (3). Nothing in section 112(d)(6) expressly or implicitly requi res that the EPA recalculate the MA CT floor as part of the section 112(d)(6) review. This position has been upheld by th e D.C. Circuit, repeatedly. NRDC v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008). Notwithstandi ng this clear holding, the comme nter has persisted with the argument, and been told twice more by the D.C. Circuit that their argument has been rejected. Ass’n of Battery Recyclers v. EPA , 716 F. 3d 667 (D.C. Cir. 2013); Nat’l Ass’n for Surface Finishing v. EPA , 2015 U.S. App. LEXIS 12530 (D.C. Cir. July 21, 2015).
The EPA reviewed other potential developments in practices, processe s and control tec hnologies for the primary aluminum reduction source category and evalua ted costs of potentially mo re stringent standards reflecting any such developments. The EPA believes th is review and the revisions finalized in this rulemaking satisfy the EPA’s obligations under CA A section 112(d)(6) for the primary aluminum reduction source category.

Comment: One commenter (0166) supports the EPA’s decision to set limits for previously uncontrolled sources of emissions in this proposed rule, incl uding POM from prebake potlines, COS from potlines and POM from existing storage tanks. However, th e commenter has expressed numerous concerns about the data inventory used in the RTR rulemaking and a lack of emission test data in the record for the proposed rule. The commenter urges the EPA to ensure these are strong limits that reflect what has been74 “achieved” by the best performing sources and what is “achievable” as required by CAA sections 112(d)(2) and (3).
Response: The EPA conducted an information request in support of the December 2014 supplemental proposal. The emissions data set for previously unregul ated emissions has been increased to the extent possible. New data were collected for PM, HAP me tals, POM, D/F, PCB, and speciated organics. MACT floors, emission limits, and the RTR analysis we re revised based on the best available data and, where data were not available, reasonable estimates of emissions. The EPA believes that this new data set and our analyses of the data (described in the emissions and MA CT technical memoranda, which are available in the docket) adequately demons trates what has been and is achievable.

Comment: One commenter (0163) states th at the EPA is not authorized by CAA sections 112(d)(2) or (d)(3) to fill “gaps” in existing MACT standards. The commenter as serts that the EPA does not have unfettered discretion to revisit a prior MACT determination once that determin ation has been issued. Rather, the commenter states, the EPA may revise a pr ior determination only “as necessary” according to explicit statutory criteria. Cf. New Jersey v. EPA, 517 f.3d 574, 582 (D.C. Cir. 2008). The commenter concludes that the EPA can point to no persuasive evidence suggesting that[the statute’s] plain text is ambiguous, and is therefore bound by [the statute] becau se “for EPA to avoid a literal interpretation at Chevron step one, it must show either that, as a matte r of historical fact, Congr ess did not mean what it appears to have said, or that, as a matter of logic a nd statutory structure, it almo st surely could not have meant it,” Engine Mfrs. Ass’n v. EPA, 88 F.3d 1 075, 1089 (D.C. Cir. 1996), showings the EPA has failed to make.
The commenter notes that in the proposal, the EPA e xplains that “pursuant to CAA sections 112(d)(2) and 112(d)(3)” it is proposing MA CT standards for POM emissions no t specifically currently regulated by the NESHAP for primary aluminum reduction plan ts. 76 FR at 76267. The commenter points to this statement to show that the EPA is not invoking sec tion 112(d)(6) as the aut hority for the new proposed standards, as the preamble provides no analysis of “developments in practices, processes, and control technologies” to justify the proposedstandards, as would be required if the EPA were relying on section 112(d)(6). The commenter further notes that there is no mention of section 112( d)(6) in relation to the proposed new standards, instead, the Agency is invoki ng sections 112(d)(2) and (3) directly, as if a MACT standard for this source category does not already exist.
The commenter emphasizes that section 112(d)(6) pr ovides the only authority for the Agency to later review and possibly revise the dete rmination, which forecloses the Agen cy’s ability to directly invoke sections 112(d)(2) and (3) for a given source cate gory when a MACT determination has already been issued for the source category.
Response: In Medical Waste Institute v. EPA , 645 F. 3d 420, 425-27 (D.C. Cir. 2011), the D.C. Circuit held that the EPA may permissibly amend improperMACT determinations, including amendments to improperly promulgated floor determinations, using it s authority under section 112(d)(2) and (3). (The lack of a remand on these issues here is a distincti on without a difference.) Th e absence of standards for these HAPs is not proper. National Lime, 233 F. 3d at 633-34; see also Medical Waste Incinerator, 645 F. 3d at 426 (resetting MACT floor, based on post-comp liance data, is permissible when originallyestablished floor was improperly established, and pe rmissibility of the EPA’s action does not turn on75 whether the prior standard was remanded or vacate d). The D.C. Circuit’s December 9, 2011 decision in Portland Cement Ass’n v. EPA, 665 F. 3d 177, 189) conf irms that the EPA is not constrained by section 112(d)(6) and it may reassess its standards more often, including revising existing floors if need be. If the EPA did not adopt a proper MACT standard init ially, it is not amending a MACT standard but adopting one for the first time. That is the case he re for POM from prebake potlines and COS and PM from all potlines. In the case of primary alumi num reduction, the EPA has not previously adopted MACT standards at all for these HAP, an approach soundly rejected by the D.C. Circuit in National Lime, 233 F. 3d at 633-34. Consequently, the EPA is not barred from making MACT floor determinations and issuing MACT standards pursuant to section 112(d)(2) and (3) here.

Comment: One commenter (0166) states that the EPA’s method of considering variability seeks to assure that none of the sources among those identifi ed as best performers would ever exceed the floor level. The commenter states that the EPA’s approach ignores the reality that sources’ emission levels are largely within their control and that a great deal of variability may be statistically conceivable if the EPA chooses a high enough prediction limit (in this case th e 99th percentile) does not mean that a well-run source actually would experience such variability. The commenter continues that one of the main points of having emission standards is to ensure that sour ces not only deploy the appr opriate control measures but use those control measures properly and consistently to minimize emissions.
Response: Generally sources conduct performance tests under conditions that reflect representative operations and performance. Sources establish m onitoring parameters duri ng performance tests and maintain these parameters to ensure that capture and control systems continue to operate at the level of efficiency at which they were ope rating during the performance tests. A source’s emission levels with a particular process configuration a nd control device may not be “largely within their c ontrol” beyond the necessity to maintain the equipment and monitor para meters to ensure a con tinuing level of control. Given that there is inhere nt variability associated with EPA Reference Test Methods, if the MACT floor level of control were established with no allowance fo r variability, the facility that established the floor would have a significant chance of failing a subsequent performance test, even if its process and control system were operating identically to their performance during the perfor mance test that established the MACT floor.
The EPA must exercise its judgment, based on an evalua tion of the relevant factor s and available data, to determine the level of emissions control that has been achieved by the best performing sources under variable conditions. It is recognizedin the case law that the EPA may consider variabi lity in estimating the degree of emissions reduction achieved by best-per forming sources and in setting MACT floors. See Mossville Envt’l Action Now v. EPA
, 370 F.3d 1232, 1241–42 (D.C. Cir 2004) (holding that the EPA may consider emissions variability in estimating pe rformance achieved by best-performing sources and may set the floor at a level that a best-performi ng source can expect to meet “every day and under all operating conditions”).
See also the response to the following comment.

Comment: One commenter (0166) asserts th at (citing dicta in a D.C. Ci rcuit decision) industry groups have argued that the EPA must set weak sta ndards to accommodate sources’ worst reasonably foreseeable performance. The commenter argues that those dicta have no precedential value, and do not76 bind the EPA’s rulemaking in any way. The commenter notes that even if they constituted a holding – which they do not – they do not apply to the EPA’ s floors for existing sources. The commenter asserts that the underlying assumption – that if a particular standard reflects what a given source achieves in practice, that source will never violate the standard– is plainly flawed. The commenter further argues that no matter what level a given source normally ach ieves in practice, that source may emit far higher levels if it is not run properly. Th e commenter states that the high emi ssions that occur when a source is poorly operated must be treated as exceedances or viol ations of the emission standards, even though it is “foreseeable” that periods of sloppy or negligent operation may occur even at the source with the lowest emission tests. The commenter maintains that floors s hould not be set at a level that the best performers could never exceed even when they operate poorly or fail to maintain their control equipment. Indeed, such an approach violates section 112(d)(3) and frus trates its intent. The commenter argues that, rather, floors must be set at the average emission level achiev ed by the best performers when they are operating properly – i.e., in the way that identified them as the best performers. The co mmenter states that using an “upper prediction limit” to set standards reflecti ng the worst performance these sources could have in a purely statistical sense does not yiel d an accurate picture of the best sources’ actual performance, and it is especially arbitrary in the abse nce of any explanation of why the EP A thinks that the relevant best sources’ performance would ever be so bad, other th an the fact that it is statistically possible.
Response: The MACT floor limits were developed by inco rporating variability, as has been done in other MACT standards. In determining the MACT fl oor limits, we first determine the floor, which, for existing sources in a category or subcategory with fewer than 30 sources, is the emissions limitation achieved in practice by the average of the top 5 exis ting sources, or the level achieved in practice by the best controlled similar source for new sources. In setting emission limits, the EPA used the lowest emissions rate as the measure of best performance. We then assessed variability of the best performers by using a statistical formula design ed to estimate a MACT floor level based on the average of the best performing sources using the expecteddistribution of future compliance tests. We used the UPL because for a future observation, the UPL will, with a specifie d degree of confidence, contain the next (or some other pre-specified) randomly selected observation from a popul ation. In other words, the prediction interval estimates what future values will be, based on present or past background samples taken. For this source category, where there is a limited sampli ng of the source category, the UPL was used to determine variability. Because the UPL represents the value which we can expect the mean (i.e., average) of future observations (e .g. a 3-run average) to fall below, based upon the results of the independent sample size from the same population, the UPL reflects average emissions. We maintain that the MACT floor analyses conducted in this rulemaking are appropriate and are consistent with section 112(d) of the CAA.
See also the response to th e previous comment above.

Comment: One commenter (0166) states th at the EPA must set a standard to limit all HAP emissions, including naphthalene and the HAPs lis ted in the permit for the Alumax of South Carolina facility in Mt. Holly, SC. The commenter further states that the EPA has not justified failing to set a specific limit to control hydrogen fluoride (HF), as th e existing standards are based on an approach that uses total fluorides (TF) as a surrogate for HF. The commenter disagrees with the EPA’s conclusion that TF is a77 reasonable surrogate for HF, and di sagrees with the EPA’s setting of standards that allegedly use a surrogate without meeting the conditions for a surrogate.
Response: Naphthalene is a polycyclic organic compound and is included in POM. POM emissions are regulated under the NESHAP for primary alumin um reduction plants and are measured during performance tests (as methylene ch loride extractable material - MC EM). Speciation of samples of MCEM from primary aluminum potroom emissions confirms the presence of naphthalene. Also, currently available performance test methods do not reliably distinguish HF from particulate fluoride, as opportunities exist within the sampling train for transf ormation between these forms. As an alternative to attempting to account for inaccuracy in measuremen t of HF, the EPA has selected total fluoride as a surrogate for HF. The EPA believes that TF is a reasonable surrogate for HF because: (1) HF is a component of TF, (2) HF emissions are correlated with TF emissions (it is believed that somewhere between 50 and 75% of TF is composed of HF) a nd (3) emission limits established to achieve good control of TF will also achieve good control of HF (good capture of particulat e is associated with good capture of HF - in the primary control system good c ontrol of HF is achievedthrough reaction with dry alumina and good control of particulate is achieved by the particulate control device downstream of the dry alumina scrubber, typically a baghouse).

Comment: One commenter (0166) states that there is ev idence in the record showing that, due to improvements in technology, sources have “achieved” a level of “actual” HAP emissions that is not only below the existing MACT standard, but also below the standards proposed by the EPA in the proposed rule. The commenter observes that the EPA’s own m odeling shows that the leve l the existing standard allows is 1.5 times higher than the EPA’s estimated “actual” emissions for most facilities, and is 1.9 times higher for the Columbia Falls Aluminum Company facility (CFAC - which has the highest potential for emissions of all the facilities). The commenter asserts that unde r section 112(d)(6) this information should lead the EPA to revise the exis ting MACT standards for the source category to meet the requirements of sections 112( d)(2) and (3), by setting standards lower than what the EPA has proposed in this rulemaking.
Response: The estimated actual emissions of POM from prebake potlines were multiplied by 1.5 to estimate “allowable emissions” for risk modeling. For Soderberg potlines, the estimated actual emissions were multiplied by 1.5 or 1.9 to represent a level of “allowable emissions” that reflected our estimate of what the potlines could actually emit and still be in compliance with the emission limit from the 2005 amendments to the NESHAP for primary al uminum reduction plants. The revised potline POM emissions limits being promulgated reflect a recogn ition that these affected sources have, in fact, achieved a level of “actual” HAP emissions that is below the associated MACT standards in the 2005 amendments to the NESHAP for primary aluminum reduction plants.
As described in the MACT floor memorandum, whic h is available in the docket, the MACT floor emissions limits promulgated today for HAP emi ssions (e.g., POM and PM) from prebake potlines, anode bake furnaces and paste produc tion plants reflect the achieved le vel of “actual” HAP emissions of the best performing sources. The POM limit promulga ted today for Soderberg facilities, under section 112(f) of the CAA, is three times lower than th e limit in the 1997 NESHAP. Based on our analyses, this limit is lower than the level “ach ieved” by those sources and refl ects the assumption that if any78 Soderberg potline ever reopened in the U.S., it would n eed to install roof top wet scrubbers to comply with the revised POM limit for Soderb erg potlines (see 79 FR 72914, December 8, 2015).
Prior to the December 2011 proposal, only Soderberg potlines had POM limits for the HSS, VSS1, and VSS2 sub-categories. There are currently no operational HSS, VSS1, or VSS2 potlines. The HSS and VSS1 subcategories are being removed from the final ru le and were not included in the risk analysis, as the facilities associated with these sub-categories were confirmed to be shutdown. At the time of the 2014 risk analysis, the EPA still beli eved that the VSS2 sub-category (specifically, Columbia Falls) may re-open. After the December 2014 supplemental proposal , the EPA received information confirming the permanent shut down of Columbia Fa lls. In spite of this information, the EPA is promulgating POM, As and Ni emission limits for existing VSS2 potlines to en sure that risks would be acceptable in the very unlikely event that a new Soderberg type facility is ever built.
Pursuant to sections 112(d)(2) a nd (3), the EPA is additionally promulgating MACT limits for emissions of POM from new and existing preb ake potlines and existing pitch stor age tanks, which were previously unregulated. These MACT limits were set using data gathered via an information request sent to the primary aluminum production industry in March of 2013 and data received during the comment period (ending on February 6, 2015) of the supplemental propos al. Additional information is available in the Final MACT Analysis for the Primary Aluminum Production Source Category memo, which can be found in the docket.

Comment: One commenter (0166) states th at the section 112(d)(6) text plainly requires that the EPA review and revise as necessary th e existing section 112(d)(2) MACT st andards, and it also explicitly requires that the EPA take account of new technologi cal or industrial developments. The commenter argues that to give meaning to the phrase “as necessary” as it is used in section 1 12(d)(6), it must be read in the context of the rest of section 112(d). The commenter observes that sect ion 112(d)(2) by its plain language applies to “emission standards promulgated unde r this subsection,” and thus explicitly requires any section 112(d) standard to meet the section 112(d)(2) requirements, including those standards set under section 112(d)(6). The commenter argues that the essentia l thrust of section 11 2(d)(2) is to require technology-based standards that reflect the ma ximum achievable degree of emission reduction.

The commenter continues that all national emission st andards for hazardous air pollutants must satisfy the requirements of sections 112(d) (2) and (3), both when set initia lly and when they are revised. The commenter states that the CAA does not invite the EPA to improvise in determining what revisions, if any, are “necessary” under section 1 12(d)(6), rather, the subs tantive provisions in sections 112(d)(2) and (3) (and section 112(d )(5), if applicable) continue to govern.
Response: The EPA previously determined that section 112(d)(6) does not require MACT floors to be recalculated, and why the EPA’s interpretation that no further floor analysis is required was reasonable. See 70 FR at 20008 (April 15, 2005).The EPA is not reopening that issue here, or otherwise reconsidering its in terpretation. Moreover, the argument was rejected by the D.C. Circuit in the HON opinion. See 529 F. 3d at 1084 (“It is argued that EPA was obliged to completely recalculate the maximum achievable control techno logy-in other words, to start from scratch. We do not think the words ’review, and revise as necessary’ can be cons trued reasonably as imposi ng any such obligation.”). We thus disagree with the asser tion that the HON Court’s ruling that CAA section 112(d)(6) does not79 require re-calculation of MACT floors was limited to instances in which there have not been developments in practices, processes, or control technologies. In fact, the Court was quite clear on this point, and declined to rule only on whether it was appropriate for the EP A to consider costs and risks in conducting CAA section 112(d)(6) reviews, as the i ssue was rendered moot by the litigants’ failure to preserve it. As noted above, the commenter’s argu ment has been twice more rejected by the D.C. Circuit.

Comment: One commenter (0166) asserts th at a revision of the existing standard is necessary under section 112(d)(6) if the prior st andard was not established in a manner that complies with the requirements of the CAA. The commenter states th at since the adoption of the primary aluminum reduction plants MACT, the D.C. Circuit has specif ically rejected a number of practices employed by the EPA to set MACT limits including but not limited to: (1) requiring that MACT limits be achievable by all sources; (2) basing the standard on an evalua tion of control technology performance rather than plant performance; (3) adopting “no control” MACT limits where activ e pollution controls were not in use in a subcategory; (4) employing regulatory limits where actual perf ormance data are available; (5) rejecting MACT floor technologies a nd limits based on cost or feasibility; and (6) rejecting the use of a surrogate where not supported. (The commenter pr ovides citations of court cases.) Further, the commenter notes, the EPA has recogni zed its obligation to reconsider earlier-set standards where its prior approach resulted in “no control” MACT floors.
The commenter argues that the situation here is di stinguishable from the fact s in NRDC v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008), in which the court ex plained that recalculat ing the floors was not necessary because “petitioners ha ve not identified any post-1994 tec hnological innovations that EPA has overlooked.” In the case of the proposed rule here, the commenter asserts, there have been developments in practices, processes, a nd control technologies that obligate the EPA to recalculate MACT floors. The commenter argues that even if the EPA’s section 112( d)(6) holding were relevant here, section 112(d)(6) requires the EPA to recalculate the MACT floor when there have been advances in technology, practices, and processes, and when there is information s howing that greater emission reductions have been “actually achieved.” The commenter stat es that based on the information the EPA has in the record, it is “necessary” for the EPA to strengthen the existing MA CT floor and to appropriately set a beyond-thefloor standard to ensure that th e MACT standards for primary alumin um reduction plants comply with sections 112(d)(2), (3) and (6). Th e commenter observes that if the EP A were not required at the very least to address and update the sta ndard when significant improvements are made in practice, consistent with the overall purpose and requireme nts of sections 112(d)(2) and (3), it would be unclear what the standard of review actually is fo r an action taken under section 112(d) (6). The commenter claims that the court’s job is to determine whether the Administra tor has made a lawful determination of whether or not it is “necessary” to update the MACT standards established pursuant to section 112(d). The commenter argues that this requires the court to deci de whether, just as sec tion 112(d)(6) requires the EPA to satisfy section 112(d)(2), the Administra tor has made a decision consistent with section 112(d)(3), which gives defin ition to section 112(d)(2).
The commenter states that the EPA interprets the te rm “developments” too narrowly, and that the EPA needs to consider an increase in acceptance and utilization of a techno logy or process within a category as a “development” warranting consideration during a review. The commenter asserts that the EPA is80 obliged during the eight-year review to determine whether the facts underlying those earlier assessments have changed and to revise the limit accordingly.
The commenter concludes that the EPA has no justif ication for failing to recalculate the MACT floors and set revised beyond-the-floor standards for primary aluminum reduction plants.
Response: We disagree with the assertion that the HON Court’s ruling that CAA section 112(d)(6) does not require recalculation of MACT floors was limite d to instances in which there have not been developments in practices, processes, or control technologies. In fact, the Court was quite clear on this point, and declined to rule only on whether it was appropriate for the EP A to consider costs and risks in conduction CAA section 112(d)(6) reviews, as the i ssue was rendered moot by the litigants’ failure to preserve it. See NRDC v. EPA, 529 F.3d at 1084. We do not believe that the words “review, and revise as necessary” can be construed reasonably as imposing th e obligation to recalculate MACT floors. Further, the commenter has not identified an y applicable technological innovatio ns that the EPA has overlooked.

Comment: One commenter (0166) states that the EPA’s ei ght-year MACT review fails to consider all relevant emission reduction developments in the primary aluminum source category. The commenter asks that the EPA consider control practices, pr ocesses, and technologies that are achieving HAP emission levels well below the existing and proposed standards and that the EP A look to jurisdictions with the most stringent standards for HAP emissions to gather data from facili ties and information about control systems that are attaining the highest control efficiencies. Th e commenter notes that the title V permit for the Alumax of South Carolina facility in Mt. Holly, SC has more stringent limits on potlines for TF than those considered by the EPA. The comme nter notes that the EPA has not provided a review of other air permits to see whethe r any other facilities are also mee ting more stringent limits for TF, POM or other pollutants.
The commenter provides examples of gaps in the EPA’s evaluation:

 The EPA recognized that COS emissions can be decreased by using coke with a lower sulfur content for anode preparation, however the EPA did not consider requiring emission reductions based on this, which the commenter finds to be arbitrary and capricious;

 The EPA found that most pitch storage tanks are uncontrolled, but that co ndensers and activated carbon adsorbers would reduce emissions, yet th e EPA failed to consid er requiring emission reductions based on the use of these devices, wh ich the commenter finds to be arbitrary and capricious;

 Prebake is a new technology that has lower emissions than Soderberg, the commenter recommends that the EPA require all facilities to meet the level of HAP emissions achievable by prebake potlines; and

 The EPA should also assess whether it is possibl e to reduce the existing emission standard for anode bake furnaces based on the level of emission reduction now achieved and achievable by anode bake furnaces.81 Response: The amendments being promulgated, do in fact include COS standards representative of the MACT floor. It is anticipated that sources will comply with these standards by selecting coke with a low enough sulfur content to meet the limit. Requiring reductions beyond the floor were considered, but rejected for various reasons (e.g., th e availability of suitable low sulf ur anode coke and the cost of incineration or scrubbing of COS - see 76 FR at 76275).
The amendments being promulgated do in fact include requirements for installation of emission control systems designed and operated to reduce emissions of POM by 95% or greater from all pitch storage tanks (see 76 FR at 76275 – 76276).
There is presently one existing Soderberg facility that is shut down. This facility will be required to meet the MACT floor standards for its subcategory and the Ni, As and POM standards for Soderberg potlines (described above) should it decide to ever re-open. All new potlines of either Soderberg or prebake technology will need to meet th e standards for new potlines promulgated in the final rule.

Comment: One commenter (0166) asserts th at the EPA’s section 112(f) an alysis of control options is cursory, arbitrary, and capricious. The commenter finds that the control options considered in the section 112(d)(6) analysis was limited and dismisses opti ons with little or no analysis or grounds. The commenter submits information from the recent haze assessment in Washington regarding control devices for the primary aluminum plants there for th e EPA’s consideration in this rulemaking (attached to comment letter - see Nat’l Park Service Comm ents to Stuart Clark, WA Dep’t of Ecology, on Washington’s revised haze implementation plan, at 2-3 (Oct. 6, 2010), under docket ID No. EPA-HQOAR-2011-0797-0168 labeled “Letter re garding regional haze plan”).
Response: The letter from the National Parks Service to Stuart Clark referred to scrubbing technologies to control SO 2 emissions. The commenter provided no data regarding the efficiency of this process to control of HAP. Further, wet scrubbers were c onsidered as beyond-the-floor control options for secondary emissions from potlines and determinednot to be cost effective (see 76 FR at 76274).

Comment: Commenter (0373) supported th e EPA’s recognition of the ne ed to propose and finalize standards for HAPs and emissions points that are cu rrently unregulated, in view of the requirements under USC § 7412(d)(2)-(3) and National Lime Association . Commenter (0373) supported the EPA’s proposal to set emission limits for POM from pr ebake potlines, COS from prebake and Soderberg potlines, POM from existing pitch storage tanks, and HAP metals from potlines, anode bake furnaces, and paste plants. Commenter (0373) stated that this is legally required by USC § 7412(d)(2)-(3) and (d)(6), and it would also be arbi trary and capricious for the EPA notto set standards for HAPs and emission points that are currently unrestricted.
Response: The EPA acknowledges the commenter's support for the newly established MACT emissions limits for POM, COS and metallic HAP.

Comment: Commenters (0372 and 0375) stated that the EPA has in appropriately conflated the emissions testing results from the CWPB1 and SWPB subcategories to arrive at a set of new source emissions limits for which it would be impossible for any single new source facility to comply with. Commenters explained how the EPA recognizes ( by calculating different limits for each existing82 potline subcategory) that different configurations generate inherently different emissions profiles, but does not apply this methodology to the ne w source emission limits. Commenters supported using data from the ‘best existing plant’ to set the new source potline emissions limits, but stated that this is not what the new source emission standards pr opose. Commenters stated that the EPA has proposed a POM limit from the CWPB1 subcategory and a PM limit from the SWPB subcategory. Commenters stated that the POM limits for the SWPB category (19 lbs POM/ton Al) are almost 20 times higher than the POM limits for the CWPB 1 category (1.1 lbs POM/ton Al). Commenters stated that the proposed new source performance st andard ensures that no single new facility could ever be constructed absent costly add-on emission control systems (i.e . wet roof scrubb ers) that the EPA has already found in the supplem ental rule analysis to not be cost-effective. Commenters stated that this essentially guarantees that no new prim ary reduction capacity will ever be constructed in the US, even though the EPA’s own assessments of technology and risk considerations indicate that the operation of such of a facility would be pr otective of human health and the environment.
Commenters proposed that the EPA select the best overall performing existing CWPB1 facility as the facility upon which to base the new source emissions limits. Co mmenters stated that CWPB1 is the most common existing facility type, is a facility type that presents an overall well-performing emission profile, and is the facility type that th e commenters believe is the most likely to be constructed in the US if such new construction we re to occur. Response: The EPA disagrees with the commenter’s position that no single new facility could ever be constructed, absent costly add-on emission control systems, th at could meet both the new source POM and PM standards. The new source standard for POM was set using the best performing source in the prebake group (Alumax - Mt. Holly; CWPB1). While it is true that POM emissions for the SWPB subcategory are almost 20 times higher than the POM limits for the CWPB1 category, this is not the case for PM. See “Final MACT Floor Analysis for th e Primary Aluminum Production Source Category” (EPA-HQ-OAR-2011-0797) for more detail.
Based on data provided by industry, Alumax - Mt. Ho lly (CWPB1) is the best performing source for PM based on the average emissions of three test runs. Howe ver, the data provided for this facility is limited, resulting in a situation where the 99% UPL for this source was higher than the 99% UPL for the second best performing source, which is Alcoa – Intalco (SWPB).
The EPA has established its authority to use discreti on when evaluating limited data sets. Please refer to the “Approach for Applying the Upper Prediction Limit to Limited Datasets for the Primary Aluminum Production Source Category” memorandum (EPA -HQ-OAR-2011-0797-0344) for more detail.
The EPA used its discretion in evaluating limited dataand set the new source PM limit using data from Alcoa – Intalco (SWPB). Alcoa – Intalco (SWPB) had twelve PM test runs compared to three from Alumax - Mt. Holly (CWPB1). The final standards for POM and PM for new source potlines are 1.1 lb POM/ton Al and 4.9 lb PM/ton Al. Based on the data provided by industry, f our CWPB1 facilities are already in compliance with the ne w source standard. As such, the EP A believes that newly constructed sources can meet these limits.
3.4.2 POM Requirements83 Comment: One commenter (0162) asks that the EPA re-e valuate the proposed PO M emission limits for the SWPB and CWPB1 subcategories. The commenter expresses concern that the underlying technical assumptions used by the EPA to predict current PO M emissions for existing prebake potlines, and to develop the proposed POM emission limits for exis ting and new prebake potlines, based on ratios of POM emissions to TF emissions, are not supported by sufficient data. The commenter asserts that the MACT floor analysis was based on very limited emissi ons data collected prior to implementation of the original 1997 NESHAP for primary aluminum reduction plants and prior to promulgation of the current POM reference test method (i.e., Method 315).
The commenter disagrees with the EPA’s estimation of emissions for currently operating potlines that assumed a fixed “estimated” ratio of POM emissions to TF emissions (0.3 for CWPB1 and SWPB and 0.5 for CWPB2 and CWPB3). The commenter argues that there is no underlying da ta or technical basis to demonstrate that the ratio of POM emissions to TFemissions is the same for different potlines or pot types (e.g. CWPB1 and SWPB), or to expect this rati o to be a constant. The commenter observes that the primary source of POM emitted from a potroom is th e consumption of anode material while fluoride emissions can come from numerous sources, some tie d to production and others tied to pot design and operating practices. The commenter concludes that th e assumption that POM emissions will increase or decrease proportionally with actual TF increases and decreases is erroneous.
Response: The EPA conducted an information request in support of the December 2014 supplemental proposal. New POM emissions test da ta were received for prebake potlines and as a result, new MACT floors and emission limits were established for preb ake potlines. As such, the comment above no longer applies to the current data set.

Comment: One commenter (0162) states th at Equation 3 in the proposed ru le is based on an assumption that the ratio of concentra tion of POM to TF in secondary roof em issions is that same as the ratio of concentration of POM to TF at the primary contro l device exit (Cpp1/CpF1). The commenter observes that the POM to TF concentration ratio changes substantially across the c ontrol device, and when performance of the TF control device is optimized, the ratio Cpp1/CpF1 (and, th erefore, the calculated POM secondary emission rate) increases rapidly. The commenter concludes that Equation 3 is not a viable compliance option for any prebake smelter and should be deleted for the proposed rule.
Response: The EPA conducted an information request in support of the December 2014 supplemental proposal. New POM emissions test datawere received for prebake potlines. Based on this new data, the EPA is finalizing POM emission standards for pr ebake potlines and requiring annual and semi-annual POM testing for the primary and se condary potline emission sources, re spectively. Equa tion 3 has been revised to remove the provisions re garding the ratio of TF to POM.

Comment: One commenter (0162) states th at actual data on POM emissi ons from prebake potlines is needed to validate whether the POM emission limits proposed by the EPA can actually be achieved by operating prebake potlines. The commenter’s association member companies were unable to generate sufficient POM data for multiple facilities within the time allotted by the EPA for public comment on the proposed rule. The commenter states that prelimin ary POM tests completed on the only existing SWPB facility (i.e., the Intalc o Aluminum Corporation fac ility in Ferndale, WA) demonstrate that the proposed POM emission limit for this category is not achievable , with measured emissions from limited testing of84 1.05 pounds of POM per ton of aluminum produced as opposed to the proposed SWPB standard of 0.65 pounds of POM per ton of aluminum produced.
The commenter states that preliminary data from so me facilities suggest that the proposed POM limits for CWPB1 and CWPB3 may be achievable. The commenter states that preliminary results of POM tests conducted at the Rio Tinto Alcan CWPB1 facility in Sebree, KY indicates emissions of 0.48 pounds of POM per ton of aluminum produced as oppos ed to the proposed standard of 0.62 pounds of POM per ton of aluminum produced, and preliminary data from a the Alcoa Inc. CWPB1 facility in Warrick, IN indicates 0.55 pounds of POM per ton of aluminum produced from the primary control device only. (The commenter note s that POM contribution from se condary emissions could not be measured as this facility uses Method 14A casse ttes for secondary emissions sampling.) The commenter plans to provide further comment to the EPA on ach ievability of the proposed prebake POM emission limits when sufficient test data become available.
The commenter expresses concern that POM standard s may not be achievable fo r each of the prebake subcategories because the commenter is not aware of cost-effective m easures available to reduce POM emissions. The commenter believes that the EPA needs to identify demonstrated control alternatives that can be implemented to meet the final POM limits and provide an analysis of th e cost and impact that such standards will have on aluminum potlines impacted by the standards.
Response: The EPA conducted an information request in support of the December 2014 supplemental proposal. New POM emissions test da ta were received for prebake potlines and as a result, new MACT floors and emission limits were established for preb ake potlines. As such, the comment above no longer applies to the current data set. The EPA believes that this new data set and our analyses of that data adequately demonstrates what has been and is achievable.

Comment: One commenter (0164) offered to provide the EPA with additional POM emissions data and requested that the EPA use that data to establish a SWPB limit that can be achieved by the only existing SWPB facility (i.e., the Intalco Aluminum Corp. f acility in Ferndale, WA). The commenter included results from testing of the primary control system (dry scrubbers) and the secondary control system (wet scrubbers applied to roof vent emi ssions). Additional performance test da ta were provided after the close of the comment period.
Response: The EPA conducted an information request in support of the December 2014 supplemental proposal. New POM emissions test da ta were received for prebake potlines and as a result, new MACT floors and emission limits were established for preb ake potlines. As such, the comment above no longer applies to the current data set. The EPA believes that this new data set and our analyses of that data adequately demonstrates what has been and is achievable.

Comment: One commenter (0162) requests that the EPA provide a POM compliance option for prebake potlines that use EPA Method 14A for fluoride testing. The commenter notes that neither of the options for demonstrating compliance with the prebake POM emission limits in the proposed rule (i.e., testing via Method 14 and Equation 3) provide s a viable alternative for alumi num production facilities that have installed Method 14A cassette sampling systems to determine total fluoride emissions.85 The commenter observes that at l east four operating primary aluminum facilities utilize Method 14A sampling systems, rather than Method 14 sampling manifolds, to determine compliance with the NESHAP for primary aluminum reduction plants. Th e commenter notes that each of these facilities operates multiple potlines using Method 14A for TF compliance testing and the decision to install Method 14A systems was largely based on cost. The co mmenter states that the installation of Method 14 sampling manifolds at these exis ting facilities today would cost $400,000 or $500,000 per potline, which is not economically feasible for POM roof sampling.
The commenter states that the EPA has not propo sed or promulgated a Reference Test Method for POM sampling that is compatible with a Method 14A cassette sampling system, but it may be feasible to develop and promulgate a cassette method for determining POM secondary emissions. The commenter is investigating a test method based on the principles of Method TO-10 cartridges. The commenter urges the EPA to provide an approved ca ssette-based method for POM sampling as part of final RTR rule.
Commenters (0372 and 0375) stated that reference to only Method 14A in §63.849(a)(7), (9), and (11) is not sufficient. Commenters stated that the requirements do not include the use of a Method 14 downcomer and only specify the use of the Meth od 14A cassette method. Commenters stated that facilities with Method 14 downcomer s installed need to be able to use their Method 14 downcomers for the collection of PM, POM and metal HAP samples. Commenters stated that an y facility that uses a Method 14 downcomer to sample is not able to use the manifold for Me thod 315 sampling and would therefore also be required to install Method 14A casse ttes to be able to sample for Method 315. Commenters stated that they believe that it was not the in tent of the proposed re gulatory language to require both systems. Commenter s recommended changing §63.849(a)(7), (9), and (11) to include reference to Method 14 sampling using a manifold as being acceptable in addition to Method 14A sampling using cassettes.
Response: The EPA agrees with the Commenters that th e intent of the supplemental proposal was to allow the use of the Method 14 (man ifold/downcomer) or Method 14A (cassette method) to demonstrate POM compliance. We have modified the final te xt to clarify that both methods are allowed.

Comment: One commenter (0165) agrees with the EPA’s proposal to address em issions of POM from Soderberg potlines and from other previously unre gulated emission points. Commenter 0158 also agrees with the new proposed POM regulation.
Response: The EPA acknowledges the commenter’s support for these provisions.

Comment: One commenter (0166) cites a dditional technologies adaptable to achieve lower emissions found in the EPA’s technology review:

 Overall POM and TF emissions could be reduced by retrofit of a control device to treat the high volume, low concentration secondary emissions from the potroom roof vents;

 POM and TF capture can be improved by increa sing the flow rate through the dry alumina scrubber; and86  Conversion of existing Soderberg potlines to prebake potlines would result in decreased emissions of POM and TF.
The commenter objects to the EPA’s decision to no t require emission reductions based on these methods under section 112(d)(6).
Response: The commenter provided no data to indicate that POM and TF capture would be improved by increasing the flow through the dry alumina scrubber. This is possible, but the reduced gas residence time in the scrubber might result in decreased control efficiency. Furthe r, the design and operation of the dry alumina scrubber is integral to the operation of the asso ciated potline and it is not clear that the gas flow could be increased without affecting the alumina feed rate.

The use of wet scrubbers for contro l of secondary emissions from roof vents was evaluated as a beyondthe-floor control option for some sources and not found to be cost effective. The commenter has not identified other control de vices for consideration.
The commenter is correct that conversion of existing Soderberg potlines to prebake potlines would result in decreased emissions. Nevertheless, as mentioned previously, all Soderberg facilities are now shut down. Furthermore, the final rule includes emissions limits for POM, Ni and As for Soderberg potlines that will ensure risks would be acceptable if such a facility decided to open, and the rule will provide an ample margin of safety.
3.4.3 COS Requirements

Comment: One commenter (0162) agrees with the EPA’s conclusions regarding th e significant cost and challenges associated with measuring potline COS emissions. The commenter also supports the massbalance calculation approach proposed in section 63.847(g). (The correct citation for the mass-balance calculation approach is section 63.847(j)).
The commenter requests the EPA to clarify or revi se the definition of parameter “Y” in the COS equation to say “tons of anode consumed”, rather than “tons of anode used”. The commenter observes that only anode material actually consumed in the potline has the potential to release COS emissions, and the term “anode used” could be interpreted mo re broadly to include a node material (e.g., scrap anodes or butt material) that does not actually get consumed to produce aluminum.
Response: The definition of Y has been clarified in acco rdance with the commenter’s suggestion in the final amendments.

Comment: One commenter (0162) agrees with the EPA’s de cision to reject beyond-the-floor options for COS based on the substantial potential cost impacts. The commenter has signifi cant concerns about the future availability and cost of lower-sulfur anode grade coke.
Response: The EPA acknowledges the commenter’s support for these provisions.

Comment: One commenter (0162) asks for cl arification of the facility si te-wide COS limit for facilities that have both new and existing potlines. The comment er explains that all anode s made at an aluminum production facility are produced in a single paste plant and anode bake furnace, and it would typically87 not be feasible to produce lower sulfur anodes for only a new potline. Given that COS emissions are to be calculated on a site-wide basis, the commenter requ ests that the final rule allow calculation of a production-weighted average COS limit for facilities th at have both new and existing potlines, using the production weighted average calculated for each month based on the actual amount of aluminum produced by each potline:

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Where: E COS = The facility-wide production weightedCOS emission limit for a calendar month in pounds of COS per ton of aluminum produced;

ଷ.ଽ	௟௕	஼ைௌ
்஺௉ = The proposed COS emission limit for existing potlines;

Z Existing = The tons of aluminum produced at the faci lity in existing potlines during the calendar month;

ଷ.ଵ	௟௕	஼ைௌ
்஺௉ = The proposed COS emission limit for new potlines; and

Z New = The tons of aluminum produced at the facility in new potlines during the calendar month.
Response: The proposed amendments to the primary al uminum NESHAP include MACT floor level standards for COS emissions from potlines. The propos ed limit for COS emissions from new potlines is more stringent than the proposed emission limit for existing potlines. Compliance is based on the average sulfur content of the coke used to produce paste for anodes.
The affected sources have previously been established as each individual potline at a facility. The commenter suggests an approach th at permits emissions averaging between existing sources and new sources, which is not permitted. The EPA believes that th e affected facilities (i.e ., those facilities that install new potlines) could generate anodes capable of meeting the new source COS limit (i.e., anodes with lower coke sulfur content) eith er in a separate dedicated paste plan t or in batches in the paste plant used to produce anodes for the existing potlines.

Comment: One commenter (0165) agrees with the EPA’s proposal to address em issions of COS from previously unregulated emission poi nts. Another commenter (0158) also agrees with the new proposed COS regulation.
Response: The EPA acknowledges the commenter’s support for these provisions.

Comment: Commenter (0375) stated thatthe supplemental proposed rule revises parameter “Y” in §63.847(j) for calculating the COS emissions rate from each Potline from what originally was proposed in 2011. Commenter (0375) agreed with this revision because it correctly refl ects the fact that only anode material actually consumed in the potlin e has the potential to release COS emissions.
Response: The EPA acknowledges the commenter’s support for the revision to the revised parameter88 “Y” in §63.847(j).
3.4.4 PM Requirements

a. Anode Bake Furnace

Comment: Commenter (0371) stated that Century Aluminum cannot consiste ntly meet the proposed PM limits of 0.068 lb/ton and 0.036 lb/ton for existing and new anode bake furnaces (ABFs), respectively. Commenter (0371) stated that Century Aluminum cannot consistently meet the proposed PM limits of 0.068 lb/ton and 0.036 lb/ton for existing and new a node bake furnaces (ABFs), respectively. Commenter (0371) stated that the PM emissions da ta set sent to the EPA in the 2013 ICR for ABFs shows that the proposed PM emissions limit cannot be met consistently. Commenter (0371) stated that supplemental PM emissions data was sent to the EP A providing historical PM emissions that further illustrates that the proposed PM limit cannot be met. Commenter (0371) stated that this data shows a wide range of variability in PM emissions from year to year, some of which ar e higher than the proposed PM limit for ABFs.
Response: New PM test data for anode bake furnaces was provided by six facilities in response the supplemental proposal. This data has been incorporat ed and both the new and existing PM standards for anode bake furnaces have been re-calculated. The EP A is promulgating final standards based on this new information. Further information regarding the final emission limits can be found in the docket for this source category (Final MACT Floor Analysis fo r the Primary Aluminum Production Source Category).

Comment: Commenter (0371) stated that the current proposal allows the use of an alternative emission limit for TF and POM for certain co-controlled new and existing ABFs to demonstrate compliance. Commenter (0371) requested adding an alternative production weighted average emission limit for PM testing (similar to TF and POM) to fu rther simplify compliance demonstration.
Response: In this final action, the EPA is setting exis ting and new source standards for COS, POM, and PM. For the purpose of compliance w ith these final standards, the EPA is amending the final rule to specify what constitutes a new source. Based on thes e new source dates, all cu rrently constructed anode bake furnaces will be considered existing sources fo r compliance with the PM standards established in this rule making. As such, the EPA does not believe that an altern ative production weighted average emission limit for PM testing (similar to TF and POM) is needed.

b. Paste Production Plant

Comment - Commenters (0372 and 0375) requested a revision to th e definition of P b in equation 3 utilized for the calculation of paste plant PM emissions. Commen ters stated that the proposed definition of P b is “quantity of green anode material pl aced in the anode bake furnace, mg/hr (ton/hr)”. Commenters statedthat this is an inappropriate value to use in calculating the denominator of Equation 3 as there is not a co rrelation between anodes in the bake furnace and PM emissions from the paste plant. Commenters also stated that the quantity of green anode material produced by a paste production plant is not always the same as the quantity of green anode materi al placed in the anode bake furnace.89 Commenters stated that operati on of the paste plant necessarily involves some amount of green anodes produced that are scrappedas unusable prior to baking, placedin inventory for future baking, etc. Commenters stated that the scenario may ex ist where the anode bake furnace is offline for maintenance yet the paste plant is still operating and placing inventory into storage for future baking. Commenters stated that according to the current proposed equation 3, the P b value would be zero and thus result in an i ndivisible equation.
Commenter (0372) requested that the definition of P b in equation 3 be revised to read as follows, “quantity of green anode material exiting the paste plant, mg/hr (ton/hr), during the test”. Commenter (0372) stated that the actual throughput of the paste plant should be utilized as the denominator of the paste plant PM emission calculation because it correctly accounts for scrapped or inventoried anodes that may be formed in the paste plant but not immediately placed into the bake furnace.
Commenter (0375) suggested that the definition of Pb in equation 3 be revised to read as follows, “Ppp = quantity of green anode material produced fr om the paste production plant”. Commenter (0375) stated that this change will require adding a defini tion on how the paste plant production rate, Ppp, is to be determined. Commenter (0375) recommended that §63.847(e) is revised by adding subparagraph (10):
(10) Determine the rate of green anode material produced from the paste production plant (Ppp) by dividing the number of operating hours of the paste production plant into the total weight of green anode material produced by the paste production plant on the day of the performance test.
Response: The EPA agrees that the current definition of Pb in Equation 3 in not appropriate. The definition of Pb will be revised to clarify that the “quantity” is th at which is produc ed from the paste production plant. We do not believe th at it is necessary to prescribe a specific method for determining the rate of green anode produced duri ng a testing event. It is the respons ibility of the f acility conducting the test event to accurately determine and report Pb.
3.4.5 UPL Methodology

Comment: Commenter (0373) stated thatwhen setting standards, the EPA must follow the Act’s requirements to assure that such standards are at l east as stringent as the emission limitation achieved by the best-performing sources, under § 7412(d)(3), a nd that the EPA assures the maximum achievable degree of emission reduction, as required by § 7412(d)(2 ). Commenter (0373) stat ed that instead of following the Act’s requirements, the EPA has propos ed weaker standards through use of its “Limited Dataset Memo” and “upper prediction limit” (“UPL”). Commenter (0373) stated that local communities near these sources need emissions reductions, and the EPA has not provided the protection the Act requires they receive.
Commenter (0373) stated that the EPA proposes to use an “upper prediction limit” (“UPL”) to set floor standards, even after the D.C. Circu it remanded the EPA’s use of that method in NACWA v. EPA , 734 F.3d 1115, 1139-45 (D.C. Cir. 2013). Commenter (0373) stated that the EPA’s use of the UPL in this rule is unlawfu l, arbitrary, and capricious.90 Commenter (0373) stated that the D.C. Circu it in 2013 addressed the ag ency’s upper prediction approach in the context of anot her air toxics rule that the EP A had issued for sewage sludge incinerators under the virtually id entical floor language of Clean Air Act § 7429(a)(2). Commenter (0373) stated that the Court found that the EPA s eemed to have interpreted “‘average emissions limitation achieved by the best performing 12 percent’ . . . [to] refe r to the future average of a 3-run test that EPA predicts a source in the best-perfo rming 12 percent will fall below with 99 percent confidence.” Commenter (0373) stat ed that the co urt then held:

 Although the EPA may be able to justify its novel interpretation that “average” means the average of a future 3-run compliance test, on e sentence in the Fede ral Register is not enough of a basis to uphold the EPA’s new appr oach to incorporati ng variability against arbitrary and capricious review. Accordingly, on remand, we expect the EPA to clarify how the upper prediction limit represents the “averag e emissions limitation achieved by the best performing 12 percent.”
Commenter (0373) stated that the Court also noted that the upper prediction limit produces an “apparently illogical result.” Commenter (0373) stated that the EP A predicted a “higher MACT floor for an incinerator with raw test data ranging from 0.31 to 2.26 than for a group of incinera tors with raw test data ranging from 0.31 to 40.32 and a mean of 9.38.” Commenter (0373) stated that the Court remanded on this issue as well, observing “[w]e are hesitant to rubber-stamp EPA’s invocation of statistics without some explanation of the underlyi ng principles or reasons why its formulas would produce an accurate result, particularly when the ‘f acts found’ – the MACT floor datasets – demonstrate flaws in the formula.”
Commenter (0373) stated that in this rulemaking, th e EPA may not evade the re quirement to follow the plain text of § 7412(d)(3) to se t standards based on the “average emission limitation achieved.” Commenter (0373) stated that Clean Air Act § 7412( d)(3) requires that floo rs reflect the “average” emission level “achieved in practice” by the best-per forming units. Commenter (0373) stated that the EPA has failed to justify its interpretation of the statute’s direction for this “average,” 42 U.S.C. § 7412(d)(3), that is “achieved in practice,” and has fa iled to provide the necessary factual support to use the approach it chooses even if it could be considered to meetthe statutory test.
Commenter (0373) stated that although § 7412(d)(3 ) unambiguously requires floors to reflect the “average” emission level actually “achieved” by th e best-performing 12 percent of units, the EPA proposes to use a floor in this rule based on th e upper prediction limit, notbased on the “average emission limitation” achieved. Commenter (0373) stat ed that as the EPA itsel f made clear, the upper prediction limit is the level the EPA expects any “future” test by any source in the top 12 percent to “fall below” during 99 out of 100 performance tests. Commenter (0373) stated that i t is the level that a source or sources “would be expected to meet a specifiedpercent of the time that the source is operating” based on the EPA’s calculation of hypothe tically higher emissions at some (unmeasured) times. Commenter (0373) stated that it is neither the re quired “average” nor evenany measure of what units have actually “achieved.”
Commenter (0373) stated that the EP A’s claim that it has discretion to set standards using a UPL is91 unlawful under the Act, per Chevron . Commenter (0373) stated that the statute is clear and the EPA may not read ambiguity into the statute where it does notexist, nor ignore the us e of the unambiguous term “average emission limitation.” Commenter (0373) stated that the UPL is simply not the same thing as the achieved average. Commenter (0373) stated that ju st because it uses an “average of the short- term emissions test data” at some step of its calculatio n, does not make the UPL an accurate reflection of the “average emission limitation” actual ly achieved. Commenter (0373) stat ed that these numbers are not and cannot be considered comparable or equivalent and the UPL is not a lawful substitute for the statutorily required average.
Commenter (0373) stated that the EPA has failed to demonstrate with substantial evidence that its floors reflect the average emission levels actually achieved by the best-performing units. Commenter (0373) stated that record evidence strongly indicates that they do notreflect these levels. Commenter (0373) stated that the EPA’s new rationale fails to clarify how the estimated number it comes up with for the floors “represents the ‘average emissions lim itation achieved’” by the re levant best-performers, as the law requires.
Commenter (0373) stated that in regard to the Limited Datasets and UPL Memos and the analysis that relies on them in this record, the EPA also has not clearly explained what it is doing. Commenter (0373) stated that the results the EP A reached for certain pollutants are higher than the test data it has. Commenter (0373) stated that in NACWA , the “facts found,” i.e. , the test data, suggest that the EPA’s limit is just too high, however it got there. Commenter (0373) stated that a number above what sources have achieved is not the “average emissi on limitation” that they have achieved.
Commenter (0373) highlighted se veral issues, in particular:

 Commenter (0373) stated that the use of the 99% confidence level in the UPL results in a proposed floor with a greater than average level of emissions achieved in practice, which is unlawful under CAA § 7412(d)(3). Commenter (0373) stated that rather than setting a limit at the average achieved, the EPA sele cts a confidence level for calcu lating the UPL to reasonably assure that the limit calculated can be met at al l times by the best performing source or sources. Commenter (0373) stated that in establishing the floor, the EPA states that the 99 percent UPL is the emissions level that a source woul d be predicted to meet during 99 out of 100 performance tests. Commenter (0373) stated that the use of this confidence le vel reflects the failure of the UPL to calculate the average of the best pe rforming units, because it guarantees that all of the best performing units will perform below the limit calculated in the UPL 99% of the time. Commenter (0373) stat ed that it is not based on actual performance, but on hypothetically much higher emission levels thatthe EPA has made up and that are unsupported by the data before the EPA in the record. Commen ter (0373) stated that the EPA admits that a lower confidence level would lower emissions limits. Commenter (0373) stated that the EPA is unable to justify the use of the UPL rather than the use of an average, as the law directs.

 Commenter (0373) stated that the use of the UP L as a method for accounting for variability is just as likely to create a weaker standard due to sources operating improp erly as it is to account for any other causes of variability. Commenter ( 0373) stated that the EPA does not explain how92 this use will avoid that problem, and thus its use is unlawful and arbi trary. Commenter (0373) stated that the EPA may not lawf ully account for malfunctions in setting standards, and thus it may not use a method for accounting for variabil ity that builds in poten tial malfunction-caused higher emissions as a potential driver of the floor. Commenter (0373) stated that the record demonstrates that the floors the EPA is proposin g, after applying the 99% UPL, are substantially higher than the true averages. Commenter (0373) stated that if a source malfunction created variability that the EPA then accounts for in its UPL approach (as this approach makes no distinction between any causes of variability) then the EPA is setting a floor impermissibly high because it does not reflect the average emission of the best performing units operating properly. Commenter (0373) stated that the EPA has failed to show how using the UPL does not unlawfully account for malfunctions in setting sta ndards or otherwise allo w sources to get away with emission exceedances resulting from malf unctions, which is counter to the Act.

 Commenter (0373) stated that the proposed fl oors differ significantly from the average emissions achieved by existing sources. Commenter ( 0373) stated that as the EPA’s memo (Tables 2-3) shows, the MACT floors the EPA has proposed for POM and PM are much higher in each instance than the average em issions limitations achi eved. Commenter (0373) provided a table of data that showed how many times higher the MACT limit was over the average of the MACT floor data set for the PM and POM standards; in all cases, the MACT limit is higher. Commenter (0373 ) stated that none of thes e floors reflects the “average emission limitation” achieved – and many are ov er 2 times higher. Commenter (0373) stated that the EPA’s approach turns the statute on it s head. Commenter (0373) stated that the EPA may not call something an average when it is tw o or more times the average of the data the EPA has.

 Commenter (0373) stated that the Act directs the EPA to set standards based on the average emission limitation achieved by the best perf orming 12% of sources “for which the Administration has emissions information” (if there are at least 30 sources) or based on the best performing 5 sources “forwhich the Administrator has or could reasonably obtain emissions information.” Commenter (0373) stated that if the EPA believes that it does not have accurate information on emissions, it can and should collect more data to assess a source’s actual, variable emissions over time . Commenter (0373) stat ed that the EPA may not, however, justify setting a standard based on what is not much more than the agency’s speculative guess that units’ emissions could rang e as high as 2-5 times what the “average” is of the data the EPA actually has collected. Commenter (0373) stated that that contradicts the statute’s direction to us e emissions information it has (or could reasonably obtain). Commenter (0373) stated thatrecognizing that the EPA may do some calculations and modeling to evaluate the data ithas, it cannot justify distorti ng the emission data as far as its UPL approach does: to make the emission inventory look dramatica lly higher than what the numbers show. Commenter (0373) stated that that is like creating a whole new emission inventory from scratch, and the EPA can provi de no valid justifica tion for discounting the actual test and emission data th at it has. Commenter (0373) st ated that these are the “facts found” that the EPA may not lawfully or rationally di stort or ignore.93 Commenter (0373) stated that the EPA has failed to justify its us e of its proposed mathematical calculations based on the scien ce, record, or the clear te xt of the law to follow what has been “achieved,” rather than a speculative guess by the agency regarding emissions that is inconsistent with the actual data before it on what units have achieved. Commenter ( 0373) stated that the terms “average” and “achieved in practice” are clearly defined te rms and concepts that cannot be reconciled with the UPL approach, which adds uncertainty and unreliability, and fall s far from the achieved average. Commenter (0373) stated that by using a floor higher than the aver age emissions actually achie ved by the best performing units, the EPA fails to meet the Act’s requirements and fails to propose the le gally required, necessary, and appropriate protection for communities living near Primary Aluminum Reduction Plants.
Commenter (0373) stated that by using the UPL, th e EPA is increasing the limit above the average of what data in the record show is actually achieved. Commenter (0373) stat ed that as a result, the emission limits the EPA proposes to set are higher and weaker than the statute directs an d higher and weaker than communities need to protect their health. Commenter (0373) stated that the EPA may not redefine what “average emission limitation” means when its meaning is clear. Commenter (0373) stated that it also may not distort the text “achie ved” beyond its meaning. Commenter (0373) stated that if the EPA believes test data it is us ing does not accurately reflect what has been achieved, then it should collect better test data. Commenter (0373) stated that the EPA may not collect test data and then suggest that it does not actually reflect what has been achieved. Commenter (0373) st ated that in essence, the EPA makes up new math to try to reach the result it pref ers in terms of the limit, instead of using the data before the agency to set the emission limits as directed by law.
Commenter (0373) stated that using the larger values the EPA has chosen (instead of the statutorily required averages) has led the EPA to propose high er emission limits that increase the amount of pollution allowed to go into the air and harm th e health of neighboring communities. Commenter (0373) stated that this proposal also runs directly contrary to the textand Congressional intent of the § 7412(d)(2)-(3) and (d)(6) provisions, which were designed to ensure mi nimum levels of protection for communities from hazardous air poll ution, based on pollution control ach ievements, that would also update and become stronger over time, following what sources have achieved.
Response: As stated in the memorandum entitled “Use of the Upper Prediction Limit for Calculating MACT Floors” (Docket No. EPA-HQ-OAR-2011-0797- 0353) (“UPL memorandum”), in “the context of development of MACT floors, the UPL is a value, calculated from a dataset, which identifies the average emissions level that a source or group of s ources is meeting and would be expected to meet a specified percent of the time that the source is operating. That percent of time is based on the confidence level used in the UPL equation, as expl ained in more detail below. For a single best controlled emission source that serves as the basi s for a new source MACT floor, the 99 percent UPL is the emissions level that the source would be pr edicted to be below during 99 out of 100 performance tests, including emissions tests condu cted in the past, present, and fu ture, based on the short term stack test data available for that source. It is importa nt to note that the UPL does not represent the worst emissions performance of the best performing units atany time, but rather the average level expected to have been achieved over time, as the first elem ent of the UPL equation is the average of the shortterm emissions test data from the best performing units.94 In other words, the 99 percent UPL is the level of emissions that we are 99 percent confident is achieved by the average source represented in a data set (in the case of MACT standards, the dataset representing the performance of th e best performers as specified in the CAA) over a long-term period based on its previous, measured performance history as reflected in short-te rm stack test data.” Contrary to the commenter’s assertion, the NACWA court did not find the UPL to be an arbitrary approach, but simply asked for a better explanat ion from the Agency. The UPL memorandum provides the explanation of what the UPL represents sough t by the NACWA Court. It also explains why the UPL is representative of the level of performance achieved by the best performing unit or units. The court did not state that the “average emissions lim itation achieved by the best performing 12 percent” must be equal to the mean of the available data, as sugge sted by the commenter, and in past decisions the court has upheld that it is appropriate for th e EPA to account for variability when establishing numeric MACT standards. See Mossville Envi ronmental Action Now v. EPA, 370 F.3d 1232, 1241-42 (D.C. Cir. 2004).
We also refer the commenter to the “Approach fo r Applying the Upper Prediction Limit to Limited Datasets for the Final Rule for Primary Aluminum Production Source Category” memorandum (EPAHQ-OAR-2011-0797), which is in th e rulemaking docket. This memorandum provides a detailed discussion of the EPA’s authority to consider variability, especially give n that MACT and other technology-based standards are necessari ly derived from short term emissions test data and such data are not representative of the range of operating conditions that the best-p erforming facilities face on a dayto-day basis. In statistical terms, each test produces a limited data sample, not a complete enumeration of the available data for performance of the unit over a l ong period of time. The EPA, therefore, often needs to adjust the short-term data to account for these varying conditions in order to properly estimate these sources’ performance over time. The types of variab ility that the EPA accounts for include variability between and within tests at the same unit as well as between units in the pool of “best performing units.” This memo also describes the EPA’s selection of the UPL methodology to addre ss such variability and details all small data set issues in the final MACT floor limits. Please refer to that memo for a detailed discussion of each.

Comment: Commenter (0373) stated that the EPA has not shown how its analysis of the UPL for PM could satisfy both the test for a surrogate and the § 7412(d)(3) floorrequirements. Commenter (0373) stated that the EPA’s cursory statemen t regarding surrogacy is insufficient to satisfy the legal test to use a surrogate. Commenter (0373) stated that a surrogate might possibly be reasonable only if it meets three conditions: (1) the target pollu tant(s) must invariably be presen t in the surrogate ; (2) the control technology used to control the surroga te must indiscriminately capture both the surrogate and the target pollutant(s); and (3) control of the surrogate mustbe “the only means by which facilities achieve reductions in the target pollutant.” Commenter (0373) stated that the EPA has not shown that reducing PM will reduce all of the HAP metals as well, or provided any evidence of the % of each HAP metal reductions that will occur based on a % reduction in PM. Commenter (0373) stated that the EPA has not described what evidence on which it is basing its proposed use of PM as a surrogate, or shown why this is scientifically supported. Commenter (0373) st ated that the EPA has not shown that it has met the surrogacy test and thus has not shown that contro lling PM will also control the emitted HAP metals effectively.
Commenter (0373) stated that whatever UPL the EPA comes up with for PM, even if there were some95 appropriate correlation between PM and the HAP metals for which the EPA is proposing to use PM as a surrogate, the EPA has not shown that the UPL for PM reflects the “average emission limitation achieved” for each of the HAP metals. Commenter (0373) stated that even assuming a surrogatetargeted regulation were otherwis e appropriate, the EPA may not set that standard using a UPL – it must set that standard based on the average emission limitation achieved for the actual HAPs that the EPA is required to regulate. Commenter (0373) stat ed that the EPA has not shown and cannot show that the UPL has any relationship atall to average emission limitations achieved for the HAPs that the EPA is required to restrict pursuant to § 7412(d)(2)-(3).
Response: The rule does meet the tests for using PM as a surrogate. First, metal HAP emissions were measured during the stack tests and in fabric filter dust. Second, the particulate matter control devices used in the industry (fabric filt ers and scrubbers) achieve broad sp ectrum control of PM emissions and the associated metal HAP. In a similar fashion, the EPA identified PM as a surrogate for metal HAP emissions in establishing MACT standard s for Iron and Steel F oundries (Foundry MACT). When promulgating the Foundry MACT standard, the EPA explained that PM is a reasonable surrogate in this context because the ‘technologies currently used by foundries that reduce metal HAP emissions are those specifically designed to cont rol PM.’ Foundry metal HAP emissions, particularly those associated with melting proc esses, include PM emissions in th e exhaust stream. Thus, the use of control devices (e.g., fabric filters and wet scrubbers) to reduce meta l HAP emissions to comply with the Foundry MACT will also resu lt in the control of PM.
The commenter’s argument that the EPA is legall y barred from using the UPL, or some other statistical method, for calculating a MACT floor for a valid surrogate is just a backdoor argument that variability cannot be considered in establishing MA CT floors. This argument has been rejected, as noted above. Best performing sources do not perform da y-in, day-out at one cons tant level, and this variability is an aspect of the best performance. Moreover, the commenter’s argument is factually dubious. In this source category, non-Hg HAP meta ls and PM are captured and controlled by the same capture and control system, and the variability of that control is reflected in both HAP and PM emission levels. Further, non-Hg HA P metals are present as a compone nt of PM. The UPL statistical tool reasonably incorporates that degree of variability.
3.5 Monitoring, Recordkeeping and Reporting

3.5.1 General

Comment: One commenter (0162) requests that the final rule include an alternative method for determining sulfur content of anode coke. The comm enter states that the pr oposed method (i.e., ASTM Method D-3177-02) is not the predominant method usedfor anode coke sulfur analysis. Instead, the commenter suggests that ASTM Method D6376-06 is commonly used by the aluminum industry and suppliers of calcined petroleum coke for coke sulf ur analysis. The commenter requests that the rule either incorporate ASTM Method D6376- 06 as an alternative method for c oke sulfur analysis, or include it as the required method in lieu of ASTM Method D-3177-02.
Response: The final rule has been revi sed to allow for the use of either ASTM D4239-14 or ASTM D6376-10 method.96 Comment: One commenter (0162) asks thatthe EPA revise the proposed ru le to allow testing of one prebake potline to represent the POM releases of other similar potlines at a facility. The commenter suggests this option because it woul d reduce the overall cost of POM compliance testing by a factor of two or three, and may help reso lve the secondary POM sampling issu e for facilities using Method 14A because a Method 14 manifold would only be required in one of multiple potlines. The commenter notes that some primary aluminum facilities that use Me thod 14A already have a Me thod 14 manifold in one of their potlines to allow sampli ng for pollutants other than TF.
Response: The final rule has been revised to clarify that testing of POM and PM emissions from a representative existing prebake potline to represen t emissions of all existing prebake potlines of the same type at the facility is permitted, provided that a shared or similar control device is used for these potlines and the applicable requirements of 40 CFR section 63.848(d) are satisfied. Similarly, the final rule has been revised to clarify that testing of POM and PM emi ssions from a representative new prebake potline to represent emission s of all new prebake potlines of th e same type at the facility is permitted, provided that a shared or similar control de vice is used for these potlines and the applicable requirements of 40 CFR secti on 63.848(d) are satisfied.

Comment: One commenter (0166) states that the EPA must require periodic monitoring that will demonstrate to the EPA, states and the public whet her or not the facilities are in compliance. The commenter suggests that the EPA require performan ce tests every year instead of every 5 years.
Response: We have finalized new performance test requ irements for all numerical MACT standards. Primary emissions from all potlines for all MACT st andards will be required to test annually. Secondary emissions from all potlines for all MACT standards will be required to test semi-annually, with the exception of Arsenic and Nickel from VSS2 potlines , which are required annually. Emissions from all bake furnaces and potlines for all MACT st andards will be required to test annually.

Comment: One commenter (0166) states th at the EPA must require cont inuous monitoring of emissions from this source category. The commenter recommends that the EPA should re quire the use of CEMS technology for HF, particularly due to the issue with alleged high st artup emissions, and should require immediate reporting on the Internet of all monitoring reports.
Response: HF CEMS are not in common use, and it is no t clear that they could be applied in all potrooms. In addition, the emission limits in the NESHAP for primary aluminum reduction plants are expressed in terms of TF and there are very limited data available on which to set a limit for HF. Finally, potline startups are very infrequent and in some cases facilities operate for a decade between startups.

Comment: One commenter (0166) asks that the EPA promulgate specific public reporting and notification requirements for malfun ctions or any other emission exceedances. The commenter states that the proposed malfunction repor ting is not adequate and proposes telephone reporting by the facility no later than 24 hours after the malfunction or exceedan ce. The commenter further proposes that when a facility provides the EPA with telephone notificat ion of a malfunction or emission exceedance under the regulations, this notice be made publicly availabl e on the EPA’s website and through Enforcement and Compliance History Online (ECHO) within 24 hours. Then, the commenter continues, the EPA should require that the Administrator pr ovide this information to the Re gional Office within 24 hours of97 receiving notificati on, and direct the Regional Office to notif y the local community on the Internet, by direct communication, and through all av ailable means, by the next day.

The commenter further states that the EPA must promulgate the require ment that when such notification is made, the facility must also provide for co mmunity notification of th e malfunction or emission standard exceedance within 24 hours, through an appr opriate public forum thatis designed to reach residents who live near the facility , including but not limited to a notice on the facility’s own website (if it has one), a written notice to the lo cal municipality and local school district, a press release to the local newspaper, radio and TV news station that contai ns any information community members may need to try to protect themselves and their fa milies from the addi tional air pollution.

The commenter also recommends that the EPA shoul d also require a written report to be submitted within 7 days, and use the same distribution me thod as outlined above, including publication on ECHO, the EPA’s Regional Office websites, and sending th is to active local community members who are interested (such as throu gh setting up an email list, a local lists erv, Twitter, and other media). In the written report, the commenter states, the EPA should require the facility to include: (1) th e nature of the event; (2) the duration of the even t; (3) estimate of emissions rele ased during the event; and (4) a description and timing of corrective actions that were taken and any planned to be taken.
Response: Malfunction reporting provisions are establis hed in part 63, subpart A (i.e., General Provisions) and these final amendments do not alter those provisions. Any such reports submitted to the EPA are publicly available pursuant to CAA section 1 14. Further, the General Pr ovisions specify that submittal of a report to a State that has been delegate d the authority to implement the provisions of part 63, constitutes submittal of a report to the Administrator.

Comment: One commenter (0166) states that the EPA should not allow emissions averaging under section 112(f)(2) or section 112(d), as the EPA pr ovides no justification a nd this is an unlawful compliance loophole that the EPA should not finalize. The commenter asserts that section 112(f)(2) requires the EPA to set stronger standards, if need ed, to protect public health, and the EPA may not provide an “alternative” compliance option under which sources could exceed the very emissions limits it has found necessary to achieve “acceptable” risk.
The commenter also argues that the EPA may not justify this proposal based on cost. Section 112(f)(2), the commenter notes, does not allow the EPA to us e cost as a basis for cr eating a loophole in the standard. The commenter further argues that the EP A cannot justify the use of emissions averaging under section 112(d), because that provision requires th e EPA to set and ensure compliance with emission standards that meet the requirement s of sections 112(d)(2) and (3).
Response: The final rule includes an emissions aver aging compliance alternative because emissions averaging represents an equivalent , more flexible, and less costly alternative to controlling certain emission points to MACT levels. We recognize that we must ensure that any emissions averaging option can be implemented and enforced, will be clear to sources, and most importan tly, will achieve no less emissions reductions than unit by unit impl ementation of the MACT requirements.
In general, the EPA has concluded that it is pe rmissible to establish within a NESHAP a unified98 compliance regimen that permits averaging across af fected units subject to the standard under certain conditions. Averaging across affected units is permitte d only if it can be demonstrated that the total quantity of any particular HAP that may be emitted by that portion of a contiguous major source that is subject to the NESHAP will not be greater under the averaging mech anism than it would be if each individual affected unit complied se parately with the applicable sta ndard. Under this rigorous test, the practical outcome of averaging is eq uivalent in every respect to comp liance by the discrete units, and the statutory policy embodied in the MACT floor provisions is, therefore, fully effectuated.
The EPA has generally imposed certain limits on the scope and nature of emi ssions averaging programs. These limits include: (1) no averaging between different types of pollutants (e.g., TF and PM), (2) no averaging between sources that are not part of the same major source, (3) no averaging between sources within the same major source that are not subject to the same NESHAP, and (4) no averaging between different types of emissions units (e .g., potlines and anode bake furnaces).
Emission averaging provisions incl uded in the 2005 amendments to the NESHAP for primary aluminum reduction plants included a “discount factor” to ensure that emission averaging resulting in compliance with a more stringent limit. The emission averaging provisions included in the proposal did not properly reflect this discount. The final amendments include a revised table of emission li mits that reflects the same degree of emissions reductions (i.e., the same “discount factor ”) as the 2005 amendments to the NESHAP for primary aluminum reduction plants.

Comment: Commenter (0370) stated thatdecreasing the frequency to three times each semiannual period would not provide a practical means of demonstrating conti nuous compliance with the emission standards for total fluorides (TF), polycyclic orga nic matter (POM), and particulate matter (PM) from roof vents. Commenter (0370) stat ed that a reduced testing freque ncy may allow unidentified problems to persist for significant periods of time before disc overy and result in substa ntial exceedances of the standards. Commenter (0370) stated that within the past 4 years in Kentucky, exceedances of 40 CFR 63, Subpart LL standards revealed atthe current testing frequency re sulted in identific ation and quick correction of substantial issues causing the excess emissions. Commenter (0370) stated that the issues included sick pots, fan failures, st orage routines, shielding practices and maintenance, material purity, furnace temperature variation, broken dust collector bags, pitch buildup, and others. Commenter (0370) stated that the current requirement of three test runs per month provides more sufficient continuous compliance assurance than the proposal affords.
Response: The EPA disagrees with the commenters assessment of PM and POM from potlines. The current NESHAP (prior to promulgation of the 2015 amendments) only included standards for POM emissions from Soderberg potlines and included no PM standards for any potlines. There are currently no operational Soderberg potlines in the United Stat es. As such, the commenter’s statement regarding decreased testing frequency for POM and PM from r oof vents is without basis and requires no further response. Based on the consistency of previous test results and considering the pot line work practices included in the final rule, the EPA believes that a reduced tes ting frequency for TF is appropriate and would be adequate in determining compliance with the sec ondary TF emission limits. Commenter (0370) pointed out that decreasing the testing frequency would not provide a practical means of demonstrating99 compliance. The commenter stated that the current testing frequency aided in the identification and quick correction of substantial issues causing exce ss emissions. The EPA reached out to the commenter for more detail regarding the exact nature of these exceedances to determine the following:

 The number of exceedances and the specific issues that led to these exceedances.

 The corrective actions that were im plemented to correct the issues.

 Whether or not the issues leading to the exceed ance were a chronic problem or an acute issue that was not likely to occur again.
Commenter (0370) provided no further detail regarding the nature of th ese issues. Based on the TF data received as part of the information request, it appears th at the majority of facilities that we have data for are sampling monthly because they exceed the thres holds in the rule that allow for decreasing the frequency to quarterly, but do not exceed the TF emission limit. Feedback from industry and available test data support the EPA’s posi tion that a reduced testing freque ncy for TF from roof vents is appropriate. The EPA is promulgating the final sec ondary TF potline testing at three times each semiannual period.

Comment: Commenter (0372) raised several is sues related to §63.848(a) and (b). Commenter (0372) stated that they believe the appropriate testing fr equency to include in the final rule for secondary potline TF is semi-annual. Commente r (0372) stated that the sampli ng frequencies for secondary POM and PM emissions should be set annually to alig n with their corresponding primary control system sampling events.
Commenter (0372) stated that their review of POM data in the 2013 ICR dataset against that found in the 2011 dataset finds thatparticularly for the most common CWPB1 category, POM emissions were higher, yet similar, to those estimated in 2011. Commenter (0372) stated that the 2011 data was estimated based on a ratio of POM emissions to TF emissions and it has since been determined by the EPA that this is not a defensible approach for determining POM emissions. Commenter (0372) stated that using a comparison against a now discredited dataset as justification for setting the testing frequency for secondary potline POM emissions is inappropriate. Commenter (0372) stated that member experience indicat es that the variability in secondary POM emissions is low (lower, for example, than for secondary TF emissions which is more significantly influenced by ongoing variables in pot operation).
Commenter (0372) stated that impl ementation of many of the work practices proposed in §63.854 have the effect of minimizing secondary PM emissions, which based on member co mpany experience are not as variable as sec ondary TF emissions.
Commenters (0372 and 0375) stated concern that POM emission compliance sampling run time is set at 8 hours in §63.848(b), however, the testing that was provided to th e EPA under the 2 013 ICR request was between 2.5 and 4 hours to comp lete a run (minimum volume of 3 dscm per run). Commenters stated the duration of a test run has a direct impact on the acc uracy and detection limits of the sample analytical results and in order for a consistent and fair comparison of future performance test results to the established emission limits, the performance test runs should be of a similar duration as the test runs100 that were used to establish the emission limits. Co mmenters stated that the run time for testing the primary capture and control system should be specified in the site-specific test plan in consideration of the site-specific conditio ns and operations to ensure that that a sufficient amount of sample is collected. Commenters stated that since the regulatory authority has to approve the testplan, there is no added benefit for specifying a test run duration in the regulation. Comme nters stated this is also consistent with the proposed emission monitoring requirements for TF and PM emissions from potlines under §63.848(a) which do not specify a test run durati on for sampling the primary control system.
Commenters recommended changes to §63.848 as follows:

 (a)TF and PM emissions from potlines . Using the procedures in §63.847 and in the approved test plan, the owner or operator shall monitor emissions of TF and PM from each potline by conducting annual performance tests on the primary contro l system, and semiannual performance tests on the sec ondary TF emissions, and annua l performance tests on the secondary PM emissions....The owner or opera tor must include all valid runs in the semiannual or annual average....

 (b) POM emissions from potlines . Using the procedures in §63.847 and in the approved test plan, the owner or operator must monitor emissions of POM from each potline stack annually and secondary potline POM emissions semiannually annually. The owne r or operator must compute and record the semiannual average from at least three runs per ye ar for secondary emissions and at least three runs per year fo r the primary control systems to determine compliance with the applicable emission limit. The ow ner or operator must include all valid runs in the semiannual annual average.
The duration of each run for secondary emissions must represent a complete operating cycle. The primary control system must be sampled over an 8-hour period, unless site-s pecific factors dictate an alternative sampling time subject to the approval of the regulatory authority. Potline emissions shall be recorded as the sum of the average of at least three runs from the primary control system and the average of at least th ree runs from the r oof monitor or secondary control device.
Commenter (0375) stated that (in the event that the semi-annual requirement is retained) the second sentence of the proposed rule requires “[t]he owner or operator must compute and record the semiannual average from at least three runs per year [ emphasis added] for secondary emissions and at least three runs per year for the primary control systems to dete rmine compliance with the applicable emission limit.” Commenter (0375) stated that the reference to three runs per year for secondary emissions is incorrect since the rule requires semiannual testing (not a nnual testing) and the words “per year” need to be deleted.
Commenter (0371) requested that se condary emissions testing be aligned with the primary control emissions testing frequency for PM, polycyclic organic matter (POM), and total fluoride (TF). Commenter (0371) proposed that all emissions testi ng (primary and secondary) be required once per year so that all testing can be conducted simultaneously for each po llutant at the required sources.
Response: Commenters have not provided sufficient emissions data for secondary POM and PM from101 prebake potlines to supp ort their position that annual testi ng would be adequate to demonstrate compliance with the standard. The EPA retains its original position that se mi-annual testing of POM and PM for secondary roof vent emissions from prebake potlines is appropriate.
In regards to the sampling run time (8 hours) specified in §63.848( b), the EPA recognizes that the regulatory authority has to approve the test pla n. However, the proposed language makes allowance for reduced sample duration, subject to approval of th e regulatory authority and the EPA does not believe the suggested modification is necessary.
The EPA will amend §63.848(b) to rem ove the per year reference relate d to the semi-annual average as follows: “The owner or operator must compute and reco rd the average from at least three runs per semiannual period for secondary emissions and at least th ree runs per year for the primary control systems to determine compliance with the applicable emission limit.

Comment: Commenter (0375) stated that they disagree with the EPA' s opinion that POM emissions were higher than expected for all subcategories, based on a comparison of previous data to the 2013 ICR data. Commenter (0375) stat ed that the POM re sults obtained for the CWPB1 and CWPB3 subcategories were similar to t hose initially estimated. Commenter (0375) stated that the one CWPB2 facility is currently shut down and there is only one SWPB faci lity. Commenter (0375) stated that the EPA should consider separate POM testing frequenc ies based on potline subcategories that takes into consideration the approximate orde r of magnitude difference in POM emissions from different potline subcategories.
Commenter (0375) stated that alternatively, the EPA should consider a redu ced testing option that would allow facilities to change th e secondary emissions testing freque ncy for a subsequent test from semi-annual to annual if the combined primary and secondary POM emissions tested below a threshold level. Commenter (0375) stated that POM emissions above the threshold level would result in reverting back to semi-annual te sting of the secondary emissions.
Response: As stated previously, commenters have not provided sufficient emissions data for POM from prebake potlines to justify c onsideration of separate POM testing frequencies for the individual sub-categories. The EPA retains its original pos ition requiring semi-annual testing of POM for secondary roof vent emissions a nd annual testing of PO M from the prebake potline primary emission control device.

The EPA does not have sufficient data to establis h appropriate thresholds for allowing a reduced testing frequency, nor does the EPA have enough information to determine if such an option is appropriate. Therefore, the final rule does not allow for a reduced sampling frequency option (of less than semi-annual) for secondary POM emissions from prebake potlines.

Comment: Commenter (0162, 0372, and 0375) provided multiple comments regarding the provisions of 63.847(c).

Commenters stated that the curr ent rule under §63.847( c) allows for the use of results from performance tests cond ucted on the primary control system for potlines or for the anode bake furnace within the 12 months prior to the compliance date to demonstrate initial compliance. Commenters102 stated that this provision was ava ilable in 1999 for the perf ormance testing done to determine initial compliance with TF and POM em ission limits. Commenters stated that the EPA should provide facilities with this same flexibil ity to schedule and conduct performanc e tests in advance of the initial compliance date to determine initial compliance w ith POM emission limits for prebake potlines and existing pitch storage tank controls (where appl icable), and PM emission limits for potlines, anode bake furnaces, and pa ste production plants.

Commenters stated that the EP A’s November 2, 2005 final rule to amend Subpart LL established performance test dates for a new or reconstructed anode bake furnace and for an existing anode bake furnace that was shut do wn at the time complianc e would have otherwise been required and is subsequently restarted (see 40 CFR §63.847(c)(2)(ii) and (3)(ii), respectively). Commenters stated that the test date for both is “by the 45 day from the start of the second a node bake cycle (but no later than the 180 day from the startup of the anode bake furnace).” Comment ers stated that the current proposed rule deletes the performance test date for anode bake furnaces and instea d requires the initial anode bake furnace performance test to be conducted “[d]uri ng the first month following the compliance date for an existing ... anode bake furnace”. Commenters stated that the 2005 performance test dates were specified to ensure th at the initial annual performance test on a new anode bake furnace is conducted after the furnace achieves normal operati on. Commenters stated that, as noted in the final preamble to these amendments, fu rnace firing rates are retarded during the initial operating cycle of an anode bake furnace to dry and cure the refractory. Commenters stated that this drying/curing cycle, which may take from 45 to 120 days, is typi cally performed with baked or partially-baked anodes. Commenters stated that conditions during th is period will likely produce POM emissions that are lower than normal at the contro l device inlet, and clearly do not represent normal operation. Commenters stated that si milar conditions exist during the st artup of an existing anode bake furnace that was shut down for more than one year. Commen ters stated that results of such testing would not provide useful data for either evaluating the condition of the control device or determining continuous compliance with the ap plicable MACT emission limits.
Commenters stated that the propos ed rule establishes additional performance testing requirements for new or reconstructed and exis ting paste production pl ants and, as an option, for existing pitch storage tanks. Commenters statedthat the proposed rule appears to inadvertently have removed the initial performance test date provis ion for a new or rec onstructed potline.
Commenters suggested revisions to §63.847(c).
Response: The EPA agrees with the commenters that perf ormance tests conducted within the 12 months prior to the compliance date can be used to demonstrate initial compliance for existing sources. Additionally, the EPA agrees that equipment specific te st provisions were inadvertently removed in some cases and left out in other cases. S ection 63.847(c) is being ame nded in the final rule to clarify test date requirements.
3.5.2 Electronic Reporting

Comment: One commenter (0162) asks the EPA to clarify that the propos ed electronic test reporting requirement does not apply to potline performance testing. The commenter disagrees with the EPA’s103 proposed requirement to submit performance test re ports for aluminum potlines using the Electronic Reporting Tool (ERT) because the ERT is not compatible with secondary roof emission test methods or the compliance calculation procedur e required for potlines in the NESHAP for primary aluminum reduction plants. The commenter e xplains that monthly fluoride co mpliance the NESHAP for primary aluminum reduction plants is determined based on a monthly test for secondary emissions (Methods 14 or 14A), an annual control device test for primary emissions and the monthly aluminum production for a given potline. The commenter notes that ERT is desi gned to report compliance from tests conducted in a single test campaign, does not have the capability to combine resu lts from monthly tests with results from a prior annual test, and does not have the cap ability to accept and ca lculate secondary roof emissions from Methods 14 and 14A. In addition, th e commenter notes that th e requirement to submit monthly test reports through the ERT would impose a significant added burden on owners and operators of aluminum smelters because most facilities us e in-house staff for secondary potline emission test reporting and reporting of monthly fluor ide test results is cu rrently only required as part of semiannual or quarterly NESHAP reports to the state or local permitting authorities. The commenter states that because submittal of data to the ERT will not suppla nt these other periodic NESHAP and title V SIP reports and only adds a new monthl y burden to facility personnel, th e commenter requests that the EPA clarify that the ERT reporting requirements do not apply to the monthly potline performance tests.
The commenter agrees that annual anode bake furn ace tests using Method 13 and 315 could readily be submitted through ERT, and supports submission of these test reports through the ERT. The commenter notes that these annual compliance tests are performed in a single te st campaign and are frequently completed by outside test contractors.
Commenters (0372 and 0375) stated concern that the current proposed rule retains the requirement to submit performance test data electronically to th e EPA through the use of the ERT and the Compliance and Emissions Data Reporting Interface (CED RI) in CDX under §63.850(b)(1) and additionally proposes to add a requirement under §63.850(b)(2) to submit results of perf ormance tests directly to the Regional Administrator when performance test data are obtained us ing test methods that are not supported by the ERT at the time of the test. Commenters stated thatbased on a recent review of the ERT Web site, all the test methods specified in proposed §63.849(a) ar e supported by the ERT with the exception of Methods 14 and 14A.
Commenters stated that this is problematic because it would require that perfor mance test results that require summation (of primary control system emissions and secondary roof ventemissions) to calculate compliance with an applicable emission limit be su bmitted via two different means (electronic and hardcopy) across different entities within Federal and State agencies. Commenter s stated that emissions testing of the potline primary c ontrol system does not involve Met hod 14 or 14A and the resulting performance test data could be submitted using the ERT, whereas testing of the secondary emissions for the same pollutants does require the use of Method 14 or 14A and the results curr ently would not have to be submitted via ERT. Commenters stated that this will present recordkeeping and compliance evaluation challenges for regulatory ag encies as well as the facilities.
Commenter (0372) stated that a less confusing and more efficient appr oach is to allow the hardcopy submittal of both existing non-ERT supported test methods as well as existing ERT supported test104 methods when the sum of both th e non-ERT and ERT supported methods must be used to make a compliance evaluation.
Commenter (0375) recommended that the EPA provide a single approach in the final rule for submitting potline performance test results from the primary control system and the roof monitors. Commenter (0375) stated that that this can be accomplished through clarifying that the use of the ERT does not apply to the reporting of potline performance test data (primary control and secondary emissions) as we had originally commented on in 2011.
Response: Performance test reports must be reported thr ough the ERT to the extent that the system will accommodate them. The ERT does not accommodate Methods 14 and 14A. The owner operator will be required to submit hard copy results of Methods 14 a nd 14A performance tests to the Administrator. For data that requires summation of results from both ERT and non-ERT supported te st methods in order to demonstrate compliance with an emission limit, the ow ner operator will only be required to submit hard copy results of the performance te sts to the Administrator. This has been clarified in the final amendments.

Comment: One commenter (0166) supports the EPA’s proposal for electr onic reporting. The commenter notes that as the public has a righ t to all collected repor ts under the CAA, it is important that the EPA ensure immediate disclosure of thes e reports to the public on the Internetwithin 7 days of receipt of a report, without the need for any person to submit a FOIA request.
Response: We acknowledge the commenter’s support fo r the proposed electronic reporting. The electronic reports will be submitted to the EPA via th e Central Data Exchange and will be available to the public via the Internet within the time frame suggested by the commenter at http://cfpub.epa.gov/webfire/index.cfm ?action=fire.searchERTSubmission.

3.6 Work Practice Standards

Comment: Commenter (0371, 0372 and 0375) re lated several concerns regarding the proposed work practice standards under §63.854(a).
Commenters stated that when the propos ed requirements §63.854(a)(1) and (2) are read literally, it would mean that any electrical trips or other unexpected brief ope rational interruptions/maintenance would be considered viol ations of the work pract ice standards when the re gulation already contains parametric limits (63.848(f)) along with excursion/exceedance reportin g, if needed, for these units. Commenters stated that operation of the potline dry alumina control devices in accordance with the approved parametric monitoring plan already establis hes the appropriate work practices for the potline primary control system and that proposed §63.854(a)(1) and (2) are notneeded and should be removed. Commenters stated that additionally placing these re quirements in the work practices section creates a ‘double jeopardy’ situation wherein the same excursion/exceedance w ould be enforceable against two different parts of the regulation.
Commenters stated that §63.854(a)(4)(i) requires th at unstable pots be identi fied. Commenters stated that the term ‘stability’ is normally related to the ability of a pot to produce metal, not its ability to give off emissions. Commenters stated th at an ‘unstable’ pot may not give off any more or less emissions105 than a stable pot and therefore the commenter does not support its continued inclusion in the work practices section. Commenters statedthat in the absence of a clear definition of what constitutes an ‘unstable pot’ and how this relates to increased emi ssions, the requirement of (4)(i) should be removed.
Commenters stated that §63.854(a) (4)(ii) and (4)(iii) have the potential to actually increase TF emissions if not done at the correct time, which may not be th e time that is ‘as soon as practicable’. Commenters stated that reducing pot temperature to as low as practicable redu ces the solubility of the alumina in the bath, puts alumina sludge on the bottom, makes the pot mo re unstable, and causes higher fluoride emissions. Commenters stated that premature attempts to rese al the pot crust by raking alumina and bath into open cracks and holes can put additiona l sludge on the bottom of th e pot and that this will lead to further instability and in creased emissions. Commenters statedthat the requirements of (4)(ii) and (4)(iii) should be removed.
Commenters stated that they agree that hooding of the pots is importantto capturing emissions. Commenters stated that differen t pot activities require a differen t number of hoods to be removed. Commenters stated that the NSPS preamble addre sses specific hooding expect ations that are more comprehensive than what the EPA has proposed. Co mmenters suggested removing the work practices proposed in §63.854(a) completely and replacing them with applicable potlin e work practices as contained in the 1980 NSPS Preamble (45 FR 44202). Commenters provided brief description of why the standards are a better alte rnative. Commenters recommen d that §63.854(a) is revised.
Response: The EPA has reviewed the commenter’s positio n regarding the proposed work practices and the suggested work practices. The EPA agrees with th e commenters that certain work practices should be modified where there is reasonable suspicion that implementation of said practices will increase emissions. However, the EPA does not agree with th e commenters that all proposed work practices will result in increased emissions. The EPA has finalized work practice standards that are a combination of proposed and newly suggested practices. Standards that appear to increase emissions when/if implemented have been removed.

Comment: Commenter (0375) supported the in clusion of work practice requi rements for the startup of anode bake furnaces and paste production plants unde r §63.847(l) and (m), respectively, in the proposed supplemental rule. Commenters (0372 and 0375) st ated concern about th e requirements in §63.847 (l)(4) and (m)(3) that require shutdown of the anode bake furnace or paste product plant “immediately if the associated emissions control system is off line at any time during startup.” Commenter (0375) stated that the terms “off line” and i mmediate” are unclear and not defined.

Commenters stated that the best course of action to minimize em issions may not be the immediate shutdown of the anode bake furnace or paste producti on. Commenters stated that responding to a simple electrical problem involving an exhaust fan, rotary feeder, air compressor or computer that can be corrected through a simple re-setand re-start may result in fe wer emissions than an immediate shutdown of the anode bake furnace (which could involve venting the fu rnace to prevent an explosion) or the paste production plant (whichcould involve dumping th e initial mixer contents of hot green mix).
Commenters stated that the propos ed requirement for immediate shutdow n of the source could actually result in actions that are in conflict with th e proposed general compliance requirements of §63.843(f)106 and §63.844(f). Commenters stated that the decision on what actions to take during the startup of anode bake furnace or paste production pl ant when its associated control de vice goes off line should be left to the operator and that the written st artup plans should include a require ment to operate the source and its emissions control device in a manner that is consistent with sa fety and good air pollution control practices for minimizing emissions. Commenters recommended that the EPA revise §63.847.
Response: The EPA agrees with the Commenters’ position that the proposed requirement for immediate shutdown of the source could conflic t with the general compliance requi rements and in some cases lead to higher emissions. We agree that the operators should employ the approp riate corrective actions for off line emission control systems, based on site specifi c conditions. The EPA has finalized text clarifying that operators have discretion in implementing the be st corrective action in accordance with the general compliance requirements.
3.7 Changes to General Provisions Monitoring Requirements

Comment: One commenter (0162) states th at the proposed rule preamble does not justify, explain or seek public review and comment for planned changes in the General Provision monitoring requirements. The commenter states that the EPA made substantive changes to “Appendix A to Subpart LL of Part 63 – Applicability of General Provisions.” The commente r expresses concern that although these changes were explained in the preamble to be limited to removal of the startup, shutdown and malfunction (SSM) exemption, the EPA also made changes in Appe ndix A to the applicability of several monitoring requirements under the General Provisions, includi ng provisions related to continuous parametric monitoring systems (CPMS) and continuous monitori ng systems (CMS). The commenter notes that the Agency proposes changing some of these requirement s from being inapplicable to sources regulated under subpart LL to being applicable to these sources in the proposed rule. The commenter states that these changes are not discussed or explained in the preamble to al low public review and comment of these significant changes. The commenter cited th e Quality Control Program required under section 63.8(d), currently not applicable und er subpart LL, as an example.
Response: The revisions to the General Provision were addressed in a separate action which included provisions for public notice and comment. Changes to th e monitoring requirements included in this final rule were made to conform to the amendments to th e General Provisions. The fina l rule has been revised to correct an error in th e proposal changing the app licability of 63.8(d). This provision does not apply to this subpart. In addition, the Ge neral Provisions table has been updated to reflect the reserved paragraphs are not applic able to this subpart.

Comment: Commenters (0372 and 0375)) stated that the section §63.7 of the general provisions establishes the performance testing requirements fo r the NESHAP regulations. Commenters stated that the proposed Appendix A to subpart LLlists both the applicable and n on-applicable requirements of the general provisions to subpart LL a nd indicates that §63.7(e)(1) is not applicable to subpart LL, and that the conduct of performance tests is defined in §63.847(d). Commenters st ated that in order to avoid potential conflict between the performance test requirements of §63.847(d) and §63.7(e), that §63.847(d) should be revised.
Response: We agree with the commenter’s position and ha ve added clarifying text to the final rule.107 Comment: Commenters (0372 and 0375) stat ed that the rule-specific prov isions contained in Appendix A of the current subpart LL rule we re not correctly incorporated into Appendix A of the proposed rule and that some additional requireme nts of proposed subpart LL are not correctly reflected in proposed Appendix A. Commenters highlighted the following deficiencies:

 There are no area sources subject to subpart LL, §63.1(c)(2) does not apply.

 The rule-specific definition of “reconstruction” contained in §63.84 1 of current subpart LL is not incorporated in §63.2 of proposed Appendix A.

 The rule-specific provisions of §63.850(a)(9) regardi ng a notification of re-start of a previously shutdown existing source are not addre ssed in the comments of proposed §63.9(b).

 Rule- specific provisions regarding notification of performance test, noti fication of VE/opacity test, and addition CMS notifications are not correctly in corporated in §63.9(e) , (f) and (g) of proposed Appendix A.

 The requirements for reporting performance test results of proposed §63.850(b) are not correctly reflected in applicability of the re porting requirements of §63.10(d)(2).
Commenters (0372 and 0375) both provided revised versions of Appendix A and suggested that it be utilized in the final rule to address the above-noted items as well as other minor corrections and typographical errors.
Response: The EPA agrees with the Commenters position regarding the proposed Appendix A. We have reviewed Appendix A and added text to clarify the applicability requirements and to address typographical errors.

3.8 Other Corrections and Revisions

Comment: One commenter (0162) pr ovides other corrections to the proposed rule:

 Table 2 of the proposed rule lists Potline POM Limits for Emissions Averaging. The commenter notes that values listed for HSS type potlines are all greater than the proposed HSS POM limit of 3.0 pounds of POM per ton of aluminum produced. The commenter asks if the EPA intended the HSS limit to be higher than 3.0 pounds of POM per ton of aluminum produced or do the HSS values in Table 2 need to be revised lower?

 The commenter recommends revising 63.844(a) by a dding “(a)(3)” to the list. The commenter’s recommended revised text would read “...any emi ssion limits in paragraphs (a)(1), (a)(2) and (a)(3).”
Response: Table 2 of the proposed rule included erro rs. Table 2 has been revised in the final amendments to reflect the EPA’s intention to maintain the discount factor fo r emissions averaging. The entries in Table 2 have been adjusted to reflect the revised standards and incorporate the reduction in emission limit for averaging to the same extent as the 2005 amendments to the NESHAP for primary aluminum reduction plants.

The final amendments have been revised in accord ance with the commenter’s suggestion to read “...any emission limits in paragraphs (a)(1), (a)(2) and (a)(3).”108 Comment: Commenter (0370) requested th at through the process of updati ng the testing frequency for roof vents that the EPA further de fine the "increase in the amount of total fluoride emitted into the atmosphere" currently used in the definition of "Modified potroom group" located in 40 CFR 63.842. Commenter (0370) stated that the definition should include a defined averaging period, increase in lb/ton limit, or defined testi ng that must be completed.
Response: The current rule indicates that any physical change in, or change in the method of operation that results in an increase in the amount of tota l fluoride (TF) emitted would meet the definition of “modified potroom group.” The EPA does not agree that an averaging period, lb/ton limit, or testing is required to confirm an increase in emissions b ecause any increase would meet the definition. The current definition will be retained.

Comment: Commenter (0372) stated that the Tables 1, 2 and 3 provided fo r Potline PM, TF, and POM averaging require revi sion to account for the fact that the supplemental rule requires testing frequencies that do not match up with the testing frequencies f ound in the Tables (e.g., Table 1 reflects a monthly TF limit when the sampling is proposed for semi-annually). Commenter (0372) requested that the EPA ensure cons istency of the emissions averaging tables with whatever frequency is ultimately selected for inclusion in the final rule for each HAP.
Response: The EPA agrees with the Commenter that the headings for Tables 1, 2 and 3 were inadvertently not updated to reflect the proposed samp ling frequency. We have revised the headings of Tables 1, 2, and 3 to reflect th e final sampling frequencies.

Comment: Commenter (0375) stated that63.847(d) (1) has missing refere nces to regulated pollutants that need to be included:

 TF, POM and PM emissions from potlines. For each potline, the owner or operator shall measure and record the emission rates of TF, POM and PM exiting the outlet of the primary control system for each potline and the rate of secondary emissions exiting through each roof monitor, or for a plant with roof scrubbers, exiting through the scrubbers. Using the equation in paragraph (e)(1) of this sect ion, the owner or operator shall compute and record the average of at least three runs semiannua lly for secondary emissions and at least three runs each year for the primary control system to determine co mpliance with the applicable emission limit. Compliance is demonstrated when the emission ra tes of TF, POM and PM is are equal to or less than the applicable TF, POM a nd PM emission limits in §63.843, §63.844, or §63.846.
Response: The EPA agrees with the Commenter regard ing missing references to POM and PM in 63.847(d)(1). The final text has been revise d to include reference to POM and PM.

Comment: Commenter (0375) stated thatthe COS limit for existing potline sources as currently proposed under §63.843(e) should be re- numbered as §63.843(a)(6) in order to have all existing potline emission limits in one subsection. Commenter ( 0375) stated that this also would require that Change in subcategory be renumbered as §63.843(a )(7). Commenter (0375) stated that the same comment applies to new or recons tructed source potlines under §63.844(e).
Response: The rule citation for the COS limit inthe final rule will not be changed.109 Comment: Commenter (0375) stated that the EPA is proposing the use of Equation 1 for computing the emission rate of TF, POM or PM from each potline a nd streamlining this into a single requirement under §63.847(e)(1). Commenter (0375) stated support for this . Commenter (0375) stated that the EPA should also remove the current requirement under §63.847(e )(2) for computing potline POM emissions since it will be covered under §63.847(e)(1).
Response: The EPA acknowledges the commenter’s suppo rt for the revision to §63.847(e)(1) and agrees that §63.847(e)(2) is no longer required. The final rule has been amended to remove §63.847(e)(2).

Comment: Commenter (0370) requested th at the delineat ion between subcategories be distinctly established in regard to 40 CFR 63.843(a)(6), Change in subcategory. Commenter (0370) stated that a definition of "very high purity aluminum" would be help ful when any facility, pr eviously subject to the limits of a CWPB3 potline, changes processes, feed mate rials, or customer base such that the facility no longer produces "very high purity aluminum." Commente r (0370) stated that this definition is necessary for the permitting agency to appropriately classi fy sources and establish the appropriate emission limitations.
Response: The EPA agrees with the commenter that a de finition of “high purity aluminum” is required to appropriately classify sources. The final rule has been amended to include a definition for “high purity aluminum”.
3.9 Incorporation of Other Comments
Commenter 0164 (Alcoa Inc.) inco rporates by reference the comm ents of 0162 (The Aluminum Association).
Response: The EPA has responded to these comments referenced as having been submitted by Commenter 0162.

Comment: Commenter (0372) incorporated by reference th e comments submitted to this docket by the Commenter (0374) concerning remo val of the “Affirmative Defense” provision and SSM event compliance more generally.
Response: The EPA has responded to these comments referenced as having been submitted by Commenter 0374.