1 

NATIONAL EMISSIONS STANDARDS FOR HAZARDOUS 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, 2015 
2 

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.gov 
3 

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 .................................................................................... 107
4 

3.9 Incorporation of Other Comments .................................................................................. 109
5 

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 Response, 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 Standards for Hazardous Air Pollutants 

NOAEL No Observable Adverse Effect Level 

OAQPS Office of Air Quality 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 Limit 
6 

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 Quality 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 Organization 
7 

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 comments 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 comments that are not summarized and addressed in 

the preamble to the final rule. Copies of all comments submitted are available at the EPA docket Center 

Public Reading Room. The public 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 proposed RTR revisions in 2011 and 9 comment letters on 

the supplemental proposal in 2014 for the primary aluminum reduction plants NESHAP. The initial 

proposal comment period closed on February 1, 2012 and the supplemental proposal comment period 

closed on February 6, 2015. All comments are contained 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 Table 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, and 

Robert 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 and 

Robert 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 request 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 Findings and Requirements 

We note that most of the comments and responses presented in section 3.2 address 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 the 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 residual 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 particular individuals and communities, including children. The commenter 

states that the EPA must fully assess each of these factors 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 vulnerable to harm when exposed to toxic air pollution, and 

(3) the total cumulative impacts to people and communities 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 asserts that the EPA’s failure to consider, at step 

one, the full extent of the risk of harm experienced 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 most 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 available literature, and importantly, these are the values used in our risk 

assessments.1

We acknowledge that population subgroups, including children, may have a potential for risk that is 

greater than the general population due to greater relative exposure and/or greater susceptibility to the 

toxicant. The assessments we undertake to estimate risk account for this potential vulnerability. With 

respect to exposure, the risk assessments 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 continuously, 24 hours per day for a full lifetime, 

including childhood. With regard to children’s potentially greater susceptibility to non-cancer toxicants, 

the assessments rely on the EPA (or comparable) hazard identification and dose-response values which 

have been developed to be protective for all subgroups of the general population, including children. 

For example, a review2

 of the chronic reference value process concluded that the EPA’s reference 

concentration (RfC) derivation processes adequately considered potential susceptibility of different 

subgroups with specific consideration of children, such that the resultant RfC values pertain to the full 

human population “including sensitive subgroups,” a phrase which is inclusive of childhood. With 

respect to cancer, the EPA uses the age-dependent adjustment factor, but limits the use of those factors 

only to carcinogenic pollutants that are known to act via mutagenic mode of action (MOA). In lieu of 

chemical-specific data on which age or life-stage specific risk estimates or potencies 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 MOA. With regard to other 

carcinogenic pollutants for which early-life susceptibility data are lacking, it is the Agency’s longstanding science policy position that use of the linear low-dose extrapolation approach (without further 

adjustment) provides adequate public health conservatism in the absence 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 Reference 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/cancerguidelines/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 plausible 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 values 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 commenter, is not needed in the RfC/RfD methodology 

because the currently available factors are considered sufficient to account for uncertainties in the 

database from which the reference values are derived. After considering these and other factors, we 

continue to consider the risks based on existing emissions from this source 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 aluminum source category. The individual cancer risks for 

the source category were aggregated for all carcinogens. 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 hazard quotients (HQ). This process creates, for each 

target organ, a Target Organ-Specific Hazard Index (TOSHI), defined as the sum of hazard quotients for 

individual HAP that affect the same organ or organ system. All TOSHI calculations presented here were 

based exclusively on effects occurring at the “critical dose” (i.e., the lowest dose that produces adverse 

health effects). 

We also disagree with the commenter’s assertion that additional quantitative 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 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. 

For the primary aluminum source category, the EPA conducted an assessment of the cumulative cancer 

risks from emitted carcinogens and the cumulative noncancer hazard indices from all emitted noncarcinogens affecting the same target organ system for both the source category emissions and the 

facility-wide emissions. While the incorporation 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 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 have mandated consideration of background levels of 

pollution in assessing the acceptability of risk, concluding 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 section 112(f) analysis. This assessment 

excludes background contributions because the available data are of insufficient quality upon which to 

base a meaningful analysis. 
12 

Comment: One commenter (0165) states that the emissions of particulate fluoride from the 14 (at that 

time) primary aluminum reduction facilities 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 fluoride (HF) and particulate fluoride. Limited 

data are available on the relative contributions of these fractions. Test data suggest that typically about 

50% of the TF is made up of HF, and this was assumed in cases where no data were available for HF 

emissions. Total fluoride was adopted as a surrogate for HF in the original 1997 NESHAP for primary 

aluminum reduction plants because of the uncertainty in analyses of HF. The commenter is correct that 

we did not assess the risks due to exposures to particulate fluoride because particulate fluoride is not a 

HAP. We believe this approach is appropriate for this specific action 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 the EPA’s residual risk conclusions are reasonable, but that 

the risk assessment calculations likely significantly overstate actual risk from the operation of primary 

aluminum reduction facilities. Commenter (0372) provided seven examples of how the risk assessment 

was likely overestimated. Commenter (0372) stated that they are in concurrence 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 inherent in all risk assessments, including those 

performed for this rulemaking. Although uncertainty exists, our approach, which uses conservative tools 

and assumptions, ensures that our decisions are appropriately health protective 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 Primary 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 serious problems in underestimating 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 the perceived deficiencies in our residual 

risk assessment have been addressed in other responses in section 3.2 of this document. Further, it is 

important to note that the EPA’s approach to performing 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 our 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 assessment 
13 

methods, including our multipathway assessment, refinement 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 that the EPA does not have authority to consider hypothetical 

“MACT allowable” emissions in conducting residual risk 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 explanation 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 under 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 affected 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 reasonable in the first instance for 

the EPA to construe section 112(f) as authorizing the Agency to conduct risk assessments based on 

hypothetical “MACT allowable” emissions. 

The commenter provides several examples of instances in the Agency’s risk assessment methodology 

that already reflect conservative 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 assumption that affected sources should be expected 

to emit more than the actual data indicate – to section 112(f) risk assessments. Furthermore, the 

commenter states that the EPA has provided no data or analyses indicating that its current methodology 

results in negative bias. The commenter asserts that the EPA has provided no data demonstrating that 

affected sources actually do emit at levels significantly 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 explanation as to why this approach is justified or any record evidence 

supporting the use of MACT allowable emissions, rendering this proposal insupportable under the law. 

Response: Consistent with previous risk assessments, the EPA considers both allowable and actual 

emissions in assessing chronic risks 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 inherently reasonable since they reflect the maximum level sources could 

emit and still comply with the national emission standards. This is in accord with the statutory 

requirement that the EPA evaluate “standards promulgated pursuant to subsection (d)” and if those 
14 

standards “do not reduce lifetime excess cancer risk to the individual most exposed” the EPA must 

promulgate standards under section 112(f). This language most naturally refers to allowable emissions, 

since those are what the standards allow. Quite simply, in determining whether unacceptable residual 

risk remains after promulgation of section 112(d) technology-based standards, it is reasonable to 

consider the emission allowed by the standards. In addition, the Benzene NESHAP looked to allowable 

emissions in assessing residual risk, and section 112(f) specifically preserves (indeed, mandates) the 

Benzene NESHAP decision framework. But we also explained that it is reasonable to consider actual 

emissions, where such data are available, in the acceptable 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 reach a design level of control, typically about 70% of the allowed standard) 

and, if so, overall risk incidence is probably less than the maximum estimated levels. Failure to consider 

available data on actual emissions in risk estimates could unrealistically inflate risk levels. (See National 

Emission Standards for Coke Oven Batteries, 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 health risks, stating that the use of allowable emissions appropriately 

takes into account the emissions that may legally occur under the existing standard. 

Commenter (0165 and 0369) believes an analysis based 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 applicability 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 the fact that the EPA continues to use actual emissions in other parts 

of its risk assessment. The commenter encourages the 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 health effects. The use of allowable emissions for our 

acute risk assessment is not considered appropriate due to the conservative assumptions used to gauge 

worst-case potential acute health effects. The conservative assumptions built into the acute health risk 

screening analysis include: (1) use of peak 1-hour emissions; (2) that all emission points experience 

peak emissions concurrently; (3) worst-case meteorology (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 allowable emissions would be overly conservative and at 

best, of questionable utility to decision makers. 

b. Total Facility Emissions 

Comment: One commenter (0163) states that the EPA does not have authority to consider “total 

facility” emissions in conducting the residual risk assessments for a given source category. The 

commenter states that the EPA is without authority to consider facility-wide risks because the CAA 

requires residual risk determinations to be conducted on a category-by-category basis. The commenter 
15 

notes that section 112(f)(2)(A) unambiguously requires the EPA, within eight years after adopting a 

MACT standard for a given source category or subcategory, 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 dictates that, “Emissions standards 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 these provisions as authorizing the EPA to consider emissions from entire 

facilities in conducting risk assessments and potentially revising the underlying rule for the simple 

reason that the Congress clearly envisioned that full implementation of the MACT program would take 

longer than eight years and it would be impossible for the EPA to fulfill its unambiguous obligation for 

section 112(f) standards to protect public 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 section 112(f)(2)(A) specifically requires the section 

112(f) risk assessment to be focused exclusively on “emissions from a source in the category or 

subcategory,” and thus, the EPA does not have authority 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 facility-wide risk in a risk assessment 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 decisions about the RTR source category 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 source category in question, but they 

remain important for providing context as long as their uncertainty is taken into consideration in the 

process.

Section 112(f)(2) of the CAA expressly 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 acceptable risk should not be 

associated with levels in polluted urban air. With respect to considering other sources of risk from 

benzene exposure and determining the acceptable risk level for all exposures to benzene, the EPA 

considers this inappropriate because only the risk associated with the 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 consideration 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 feasibility, and other factors. Background risks and contributions to 

risk from sources outside the facilities under review were not considered in the ample margin of safety 
16 

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 Organic NESHAP (HON) RTR (71 FR 76603, December 21, 

2006), which the court upheld in the 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 aluminum risk 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 performed for this RTR and as part of 

the secondary aluminum risk assessment (see the risk 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 risk posed by this source category and other sources. 

The commenter sees no reason to wait to do a facility-wide risk assessment when the EPA needs this 

information to decide how best to address high facility-wide risk for the primary aluminum source 

category. The commenter observes that an SAB report addressing the EPA’s RTR methodologies (May 

2010 (EPA-SAB-10-007) response to the EPA Administrator) stated that “the Panel recommends that the 

Agency perform a sensitivity analysis to identify the 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 commenter argues that uncertainties 

require more conservative assessment and more protective action, rather than inaction. 

Response: Most of the primary aluminum reduction facilities (9 of the 11 subject reduction facilities) 

are collocated with secondary aluminum production facilities. As a result, the facility-wide analysis that 

was conducted as part of the residual risk assessment 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, which is the same as the MIR from the primary 

aluminum source category risk assessment. Thus, consideration 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 associated with 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 year lifetime exposure assumes no shutdowns or 

partial curtailments in operation in the risk analysis. The commenter 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 partial and complete plant shutdowns. The commenter 
17 

points out that if these trends continue, it is likely that the EPA assessment will further overestimate 

cumulative risks as curtailments occur. 

Response: The commenter is correct that the EPA assumes no curtailment of operations over the 70 year 

period, and that short or long term activity patterns were not considered in this assessment. Regarding 

exposure times and the consideration of time-activity patterns, we do not believe that such consideration 

would significantly lower the general estimates of individual risks. In assessing risk, we estimate the 

maximum individual risk (MIR) or the maximum hazard index (HI), which are defined 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 concentration of each HAP at each census block centroid as a surrogate 

for the lifetime inhalation exposure concentration of all the people who reside in the census block. 

Basing exposure estimates at census block centroids may underestimate or overestimate actual exposure 

concentrations at some residences. Further reducing 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 the short-term human activity patterns and their potential influence on 

exposure. Our experience with the National-Scale Air Toxics Assessments (which modeled daily activity 

using the EPA’s HAPEM model) suggests that, given 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 will 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 example the assessment does not take into account population 

growth over the 70 year period. A discussion of activity patterns 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 the September 2015 Risk and Technology Review Final Rule. 

Comment: One commenter (0162) states that the EPA omits consideration of indoor versus outdoor 

exposures in the assessment, and assumes that outdoor concentrations are equivalent to indoor 

exposures. The commenter notes that for particulate types 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 commenter concludes that risks projected for POM 

emissions are overestimated by 25 to 30 percent. 

Response: As noted in the previous response, while consideration of time-activity patterns (i.e., indoor 

versus outdoor exposures) may minimally effect our risk estimates, we do not anticipate that the 

maximum individual risk would significantly change such as to alter our risk-based decision. 

Comment: In response to the 2011 proposal, one commenter (0166) stated that the EPA’s risk 

assessment is not sufficiently protective of public health 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 used industry-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 demonstrated that the data used 

in the proposed rulemaking are an appropriate substitute for actual emission test data. 
18 

The commenter recommended collecting actual emissions data, as it could identify any additional 

pollutants of which the EPA is not aware. The commenter 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 would not provide information on any HAPs of which the 

EPA is not already aware. The commenter was also concerned that relying only on the NEI and 

estimated data is unlikely to provide even estimates of the actual HAP emissions coming from a facility 

that has installed control devices and has never measured the amount or types of HAPs coming from 

those control devices. The commenter stated that not collecting 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 explanation of why its inventory is 

representative or why its rule is sufficiently protective in view of these data concerns. The commenter 

further asserted that it also has not adequately explained its decision not to collect or use actual emission 

test data from all emission points in this rulemaking. The commenter asserts that the EPA’s choice of 

data must be rational, supported by a reasoned explanation, and consistent with the statutory requirement 

to provide an “ample margin” to protect public health. The commenter suggests that to strengthen and 

finalize its rule proposal, the EPA must set a stronger 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 for the 2011 proposal was based on limited data and other information 

we received in April 2013 through an Information Collection Request (ICR) from 11 of the 15 facilities 

in the source category at that time. These ICR data were then used along with the 2005 NATA inventory 

data to develop the emissions dataset for this source category for the 2011 proposal, which included our 

best estimates of actual emissions of HAP for the facilities at that time. However, after considering comments received in 2012 (such as the comment described 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 additional 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 gather 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 POM 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 PAH, speciated HAP metals (including mercury, 

nickel, arsenic, chromium, cadmium, lead, manganese, etc.), speciated PCBs and speciated 

polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans 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 information available with regard to estimating actual emissions of HAP from 

this source category. With regard to allowable emissions, the emissions estimates used for assessment of 

risk associated with allowable emissions provides a conservative approach to the risk estimation. 

Furthermore, the public comment period for the 2011 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 provided multiple opportunities for third party review of: 

data the EPA’s risk assessment included; an evaluation of facilities contained in the source category; the 

emissions units expected to be included for the processes in the source category; coordinates and stack 

parameters; and the HAP compounds and emissions levels typically seen. Therefore, 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 from this source category for conducting the RTR. 

Comment: One commenter (0166) asks that the EPA consider the control efficiency for the control 

devices when analyzing risk in the case of the control 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 operation of the reduction process and in the event of failure it would be 

impossible to continue producing aluminum and emitting 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 would be far less than one hundred fold. Fabric filters, 

used as part of the control system are designed with 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 requirements 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 malfunction or a violation of the standard. As we discuss in more detail 

in another response below, we disagree with the commenter that emissions that exceed standards and are 

violations, whether or not they are caused by malfunction events, should be considered as part of the risk 

analysis. The purpose of the risk review is to evaluate whether the emission limits – the “standards 

promulgated pursuant to subsection (d)” not the 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 assessment starts with a significant amount of uncertainty and the EPA’s 

modeling has underestimated or completely 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 device, without providing a basis; and (2) without explanation the EPA 

decided to equally divide emissions from potlines between the control device outlet stacks, and to divide 

roof vent emissions equally. The commenter proposes 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 analysis uses assumptions and estimates that have an unclear basis. 

Response: Control devices are in use at all facilities to limit emissions from potrooms, anode bake 

furnaces and paste plants. As explained in a response above, we have a substantial 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 constitutes the best information the EPA has concerning the 

emissions and risk from this source category for conducting the RTR. Nevertheless, 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 facilities potroom vent lengths are identical; in some 

cases the lengths vary slightly. All estimated emissions from each facility are accounted for within that 

facility, even if the precise allocation of estimated emissions cannot be confirmed. Notwithstanding 

these technical difficulties, as stated above, 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 from this source category for conducting the RTR and we do not believe that the emissions 

proportioning method employed introduced significant error to the estimated risk results. 

3.2.3 Gap Filling 

Comment: One commenter (0166) states that under section 112(f)(2) the EPA must assess health risk 

for all emission points in order to ensure emissions are reduced to a safe level and to provide an “ample 

margin of safety to protect public health.” The commenter asserts that the promulgation of any section 

112(d) standard for a source category is what triggers the EPA’s obligation to conduct a complete section 

112(f)(2) rulemaking for the entire source category (or subcategory), and all HAP emissions and 

emission points, including but not limited to any emission points that the section 112(d) standard 

previously covered. The commenter quotes, “A [section 112] program which deliberately and 

consistently under-regulates in the 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 continues 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 adverse health and environmental 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 standard to aim to eliminate those 

effects and provide an ample margin of safety. 
21 

The commenter asks that the EPA assess whether the other HAPs listed (i.e., chromium, cadmium, 

arsenic, biphenyl, chlorine, ethyl benzene, hydrochloric acid, lead, manganese, 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 facility 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 currently 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 reference information that it is using. 

The commenter observes that failing to assess and reduce the health risk for all HAPs emitted from the 

source category is unlawful under section 112(f)(2), which requires a full assessment 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 source category and for which we are able to estimate emissions of, including 

several HAP metals (e.g., nickel, arsenic, beryllium, lead, 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 emissions data for several of these HAP (chromium, 

cadmium, arsenic, lead, manganese, and nickel) and 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 reference 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 includes MACT emissions standards for POM from all known 

emissions sources (potlines, paste plants, pitch storage tanks and anode bake furnaces). Naphthalene is a 

POM. Therefore, from a regulatory perspective, the 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 that the 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 facility and cover all emissions from all facilities 

before finalizing action on this source category. Another facility mentioned by the commenter is the 
22 

Columbia Falls facility in Montana, which is located on the Flathead River just a few miles from Glacier 

National Park. The commenter notes that the Columbia Falls facility was 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 regulation 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, this facility was idle, but still had a permit. Therefore, for the 

supplemental proposal, since the plant was not operating, we did not assess actual emissions. However, 

we estimated allowable emissions and included these emissions in the primary aluminum risk 

assessment for allowable emissions in the 2014 supplemental proposal. However, after publication of the 

2014 supplemental proposal, we learned that the negotiations 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 Flathead Beacon, available in the docket). Therefore, 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 that the EPA proposes to set standards 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 currently uncontrolled emission points for which the EPA 

proposes to set standards and asserts that these 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 proposal to find risk unacceptable from the 

Soderberg subcategory of primary aluminum reduction plants based on the risk the EPA has found. 

Commenter (0373) cited the reasons that it agrees with the unacceptable risk finding. 

Response: We acknowledge the commenter’s support for the finding of our residual risk review for 

Soderberg plants for the 2014 supplemental proposal. However, as we explain in the preamble, since 

this facility is now permanently shut down, we determined 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 that by ignoring risk from malfunctions, other violations and 

higher emissions during startup periods, the EPA’s proposal fails to consider 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 analysis 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 may indeed occur during a malfunction and other types 

of violations, even with the MACT standard in place. 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 from a given facility under the existing MACT, but that 

analysis is incomplete because facilities may violate 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 the malfunction exemption and enforcement actions in the past and other 

information it has regarding the history or likelihood of malfunctions or other violations. 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 risk accordingly for acute, cancer and non-cancer risk when emissions 

spike above the allowable level under the existing standard. 

Response: We disagree with the commenter that emissions that exceed standards and are violations, 

whether or not they are caused by malfunction events, should be considered as part of the risk analysis. 

The purpose of the risk review is to evaluate whether the emission limits – the “standards promulgated 

pursuant to subsection (d)” not the 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. 

To the extent that a source is violating the underlying 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 under section 112(d) would not be 

any more likely to be able to avoid such violations 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 they 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 not contribute significantly to cancer or chronic non-cancer risks for 

the source category in this rulemaking because malfunction events are inherently short-term and 

infrequent relative to annual operations and emissions. 

The EPA further disagrees that it should create an emissions factor that would account for the potential 

for malfunctions and violations of the standard. The EPA has no information on which to base such a 

factor. With respect to the suggestion 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 questionable (e.g., they are not obtained via the EPA’s reference test methods) 

and we believe that these emission estimates are not suitable for use in a risk assessment. The EPA 

believes that increases in emissions over a short time 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 which 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 states 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 reference 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 uncertainty 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 that the 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 that its health risk assessment 

is an underestimation. 

The commenter points to section 112(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, reference concentrations, 

or potency values. The commenter asserts that the EPA should prevent the delay in this process from 

undermining its residual risk analysis for this and other source categories. 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 and lack of reference values for some pollutants, 

and the fact that it is still updating the toxicity information for other pollutants, the EPA must set a 

regulatory deadline no later than 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 such values that have undergone adequate 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 documented 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 toxicity values for all HAP utilizing all credible and 

relevant toxicity information. The need to update assessments 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 always 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 vast majority 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 estimates for those HAP which dominate the risks from 

any one source category. In the course of each residual risk assessment, should we encounter HAP 

without dose-response values which carry the potential to create significant risks, we shall clearly point 

those out as uncertainties and target them for future IRIS assessments. Moreover, as additional doseresponse values become available, the EPA will incorporate 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 available cancer, chronic noncancer, and/or acute dose-response 

value. 

Comment: One commenter (0166) argues that even if a chronic, non-cancer health risk number below 

the EPA’s safety HQ threshold of 1 might be acceptable 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 exposed to this source category. The commenter states that the EPA may 

not permit a single source covered by this rulemaking 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 there 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 concentrations (RfCs) are not absolute thresholds, 

but estimates of chronic inhalation exposures 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 approach and TOSHI values of 1 or less are generally considered to carry no 

appreciable risk of adverse health effects. We generally draw no bright lines of acceptability regarding 
26 

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 source category in 

question when deciding exactly what level of cancer and noncancer 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 all potential health impacts - 

chronic and acute, cancer and noncancer, and multipathway - along with their uncertainties, when 

determining the acceptable level of source category risk. The Benzene NESHAP decision framework 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, and the 

accuracy and uncertainty of each piece of information must be considered in a weight-of-evidence 

approach for each decision. This relevant body of information is growing fast (and will likely continue 

to grow faster and faster), necessitating a flexible 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 nonetheless 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 the 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 additional 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 Soderberg potlines under section 112(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 conservative assumptions 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. Rather, the results of the screening multipathway assessment only 

indicate that we cannot rule out the 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, assigning each group the URE of the most potent compound 

in the group. The commenter notes that this approach tends to overestimate risk. 

Response: The commenter is incorrect. The emissions inventory for this source category contained 

individual POM and those pollutants were not assigned to a group. For each POM, a chemical-specific 

URE was applied in conducting 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 that 
27 

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 given 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 consider that the human body has natural defense 

mechanisms against health effects associated with POM exposure and note that, the commenter provided 

no evidence as to the extent of these defenses. Regardless, 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 any) 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 allowable emissions. The commenter disagreed with the 

EPA’s reliance on the 1989 Benzene Rule’s presumption that a 100-in-1 million lifetime cancer risk is 

acceptable today, as this fails to account for evolving science and societal standards. The commenter 

states that this analysis is arbitrary and capricious for the following reasons: 

 The CAA requires an up-to-date contemporary assessment, section 112(f)(2) directs the EPA to 

assess and address risk remaining to public health and the environment 8 years after the MACT 

standard is in place, an inherent direction to take account of new circumstances; 

 There is significant new information on the factors 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, studies 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 provided as attachments to the commenter’s letter); 

 The EPA’s commitment to environmental justice must inform its consideration of what level of 

risk is “acceptable” as required 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 health 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 Congress 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 risk is “acceptable.” Rather, we consider this health 

metric in conjunction with a variety of health factors and their associated uncertainties to determine 

whether the risk is acceptable. Where we conclude that the risk is not acceptable, 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 the endpoint. Once we determine that controls 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 conjunction with the costs of controls, technical feasibility, and other 

relevant factors, to determine whether additional controls 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 source category in question when deciding exactly what 

level of cancer and noncancer risk should be considered 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 impacts – 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 framework 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, and the accuracy and uncertainty of each piece of 

information must be considered in a weight-of-evidence approach for 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 complexity and uncertainty in the simplest and 

most transparent way possible. While this challenge is formidable, it is nonetheless 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. 

Moreover, the commenter does not support its contention 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 statutorily codified framework for 

determining risk acceptability. Also, for purposes of this rulemaking, we performed a demographic 

analysis to inform our risk-based decision process and that analysis is available in the docket. 

Comment: One commenter (0166) states that the EPA should reduce the threshold of what cancer risk is 

presumed to be acceptable, and find the estimated cancer risk in the proposed rule to be unacceptable. 

The commenter observes that although the HON decision found that the EPA was not required to 

achieve a lifetime cancer risk of 1-in-1 million, that decision recognizes that the EPA has full authority 

to protect public health by reducing risk to a lower level, and the decision 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 consider the 1-in-1 million MIR level as a bright line 

mandated level of protection for establishing residual risk standards. In determining the ample margin of 

safety (i.e., setting the level of the standard), health risk is one factor that we must consider, along with 

other factors such as cost and technological feasibility. 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 all RTR reviews, as part of the second step ample 

margin of safety analysis, we considered additional controls and process improvements that might 

further reduce risks in a cost-effective, technically feasible manner. For the 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 calculates the acute health risk of exposures 

using a combination of worst case factors, which exaggerates 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 acute 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 patterns. The EPA conservatively assumes that 

individuals remain for 1 hour at the point of maximum ambient concentration (as determined by the cooccurrence of peak emissions and worst-case meteorological conditions) and these assumptions would 

tend to result in worst-case estimates of actual exposures as it is unlikely that a person would be located 

at the point of maximum exposure during the time when peak emissions and worst-case meteorological 

conditions occur simultaneously. 

Comment: In response to the 2011 proposal, one commenter (0162) disagrees with the EPA’s use of 

hourly emission rates estimated from long term emission averages and then used for short term acute 

health concerns. The commenter disagrees with the EPA’s use of a safety factor applied to the estimated 

hourly maximum for short term acute health concerns. The commenter notes that the EPA proposed a 

factor of 5, instead of a default factor of 10, for aluminum 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 which operate in cycles that are not in phase with 

each other. The commenter observes that the EPA conducted a statistical analysis of available data and 

established a factor of 4.5 times the mean for estimating maximum hourly concentrations. The 

commenter states that the EPA uses a conservative factor of 5 times the average hourly emissions rate, 

rather 4.5, in the acute screening assessment. The commenter agrees that the factor of five is more 

realistic than the default value the EPA commonly uses of 10, but states that the 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 emissions data, we develop 

estimates of maximum hourly emissions rates by multiplying the estimated average actual annual hourly 

emissions rates by a default factor to cover routinely variable emissions or by a source category specific 

factor developed based on source category specific information. We choose the factor based on process 

knowledge and engineering judgment reflecting, where appropriate, circumstances of the particular 

source category. The default factor reflects the findings 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 the potlines are relatively consistent over time with 

minimal fluctuation. 

The EPA estimated that the maximum allowable emissions for potlines are about 1.5 times higher than 

the average long-term actual emissions for these sources. Therefore, the EPA also assumes that hourly 

emissions rates from potlines could occasionally increase by a factor of up to 1.5 times the average 

hourly emissions. The EPA believes this is a valid multiplier to estimate maximum acute emissions from 

potlines. Paste production and anode baking processes may 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 use 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 attachment to the comment letter) stating that startup 

emissions have caused a serious concern 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 safety 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 not address higher startup emissions at all under section 112(f)(2). 

The commenter argues that this is a significant oversight that the EPA should correct, and it must finalize 

a more protective standard accordingly. 

Response: We believe startup events do not contribute significantly to chronic cancer or noncancer risks 

for the source category. Startup events for this source category are inherently short-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 EPA should at least use a factor of ten to 

calculate and assess the worst case scenario of what acute health risk the existing MACT would allow, 

as it has done for other rulemakings. The commenter proposes that even a factor of ten, however, is not 

necessarily high enough to assess the 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 expected to be less variable than typical industrial 

sources because they are composed of contributions from numerous individual pots which are operated 

continuously and are not synchronized with regard to anode changes, crust breaking and other events 

that may affect emissions. Based on a substantial data set, as well as the process characteristics, the EPA 

concluded that primary aluminum source category emissions were generally 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 would indicate that the EPA should change the acute multipliers used to 

estimate acute peak emissions for this source category. 

Comment: One commenter (0166) questions why the EPA has failed to justify not requiring the 

reduction of acute health risk below 1 after finding a level of acute risk that is 10 times the EPA’s safety 

threshold. The commenter disagrees with the EPA’s determination that the acute health risk could be safe 

or acceptable, based on concerns that the EPA did not consider 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 health risk; is not accounting for health risk due to 

malfunctions; and did not consider the Columbia Falls Aluminum Company facility because it was not 

operational. The commenter asserts that the EPA’s risk 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 worst-case screening scenario. It assumes worstcase meteorology, peak emissions for all emission points occurring concurrently, and an individual being 
32 

located at the site of maximum concentration for an hour. The screen provides us information that for 

those facilities where the hazard quotients are less than 1, we do not expect acute effects, and for those 

situations where the hazard quotients are greater than 1, the potential for acute effects exists. For those 

situations where the acute hazard quotients are greater than 1 based on our screening assessment, the 

fact that it is a screening-level assessment is taken into consideration in the decision. The finding of 

unacceptable risks is not based on any one risk metric (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 context of all the available 

health evidence and risk analyses, including the results of the chronic, non-cancer and cancer risk 

analyses. Using this holistic approach, the EPA considers 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 Guidelines (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 industrial 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 Concentration Processes,” where the EPA stated that the 

primary purpose of the AEGL program is to develop guidelines for once-in-a-lifetime short-term 

exposures to airborne concentrations of acutely toxic chemicals. Commenters (0165 and 0369) observes 

that they are not meant to evaluate the acute impacts from routine emissions that occur over the life of a 

facility. Further, commenter (0165 and 0369) asserts that, unlike the reference concentrations (RfCs) for 

chronic exposures, the AEGLs and ERPGs do not include adequate safety and uncertainty factors and 

cannot be relied upon to protect the public from the adverse effects of exposure to toxic air pollutants. 

The commenter concludes that use of AEGLs or ERPGs in residual risk assessments is not appropriate 

and does not ensure that public health 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 health risks associated with estimated acute exposures to HAP, and in 

response to a key recommendation from the SAB’s peer 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/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-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 Arrays8

 for HAP have been developed, 

we consider additional acute values (i.e., occupational and international values) to provide a more 

complete risk characterization. As discussed in the preamble to the proposed rule (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 uses 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 health risk in relation to the acute health values 

that are available. Importantly, when interpreting the results, we are careful to identify the benchmark 

being used and the health implications associated with any specific benchmark being exceeded. 

d. Chronic Non-Cancer 

Comment: One commenter (0166) states that failing to look at the potential for spikes in emissions over 

a person’s lifetime may underestimate the amount of chronic risk based on pollutants that persist in the 

environment, including POM, which is one of the primary 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 emissions that exceed standards and are violations, 

whether or not they are caused by malfunction events, should be considered as part of the risk analysis. 

The purpose of the risk review is to evaluate whether the emission limits – the “standards promulgated 

pursuant to subsection (d)” not the 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. 

To the extent that a source is violating the underlying 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 under section 112(d) would not be 

any more likely to be able to avoid such violations 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 they are caused by malfunctions if an emissions event 

poses a significant health or environmental risk. 

Primary aluminum potlines are typically operated in continuous mode. Some batch processing of anode 

baking and paste production occurs, however the bake furnaces and paste 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 based on performance tests which are conducted during 

maximum periods of production. Furthermore, we believe SSM events do not contribute significantly to 

 

8 U.S. EPA. (2009) Chapter 2.9 Chemical Specific Reference Values for Formaldehyde 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 category in this rulemaking because SSM events are 

inherently short-term and infrequent relative to annual operations and emissions. 

Comment: One commenter (0166) disagrees with the EPA’s acceptability determination for chronic 

non-cancer health risk. The commenter urges the EPA to not assume that 1 is an acceptable level of 

chronic non-cancer risk from a single major air toxics source category. The commenter states that by 

finding that a non-cancer TOSHI of 1 or below is not a human health concern, the EPA has arbitrarily 

ignored its staff’s past scientific assessment of this issue, in the 2002 internal memo Residual Risk 

Program: Selection of Hazard Index Limits, 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 commenter 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 communities exposed to multiple sources and types of toxic air pollution. 

The commenter also notes that the EPA has not evaluated other nearby sources of HAPs (beyond this 

source category) (except in its facility-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 concedes that the TOSHI itself “may have been 

underestimated,” in a statement, confusing to the commenter, that only says that “impacts on organs or 

systems that occur above the critical dose have not been included in the TOSHI calculations.” The 

commenter observes that this is a dramatic way of underestimating risk, in that if the EPA takes out 

impacts that are occurring above the critical dose, the EPA is ignoring 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 that TOSHI value greater than 0.2 should be 

considered unacceptable. Pollutant-specific reference concentrations (RfCs) are not absolute thresholds, 

but estimates of chronic inhalation exposures 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 approach, and TOSHI values of 1 or less are generally considered to carry no 

appreciable risk of adverse health effects. Therefore, there is no need to compound this protection by 

suggesting that a source category maximum TOSHI value 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 memo (from 2002) which was never adopted as agency 

policy (and never reviewed by the public or by any peer review body) and consequently 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 regarding the source category in question when deciding 

exactly what level of cancer and noncancer 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 all potential health impacts - chronic and acute, cancer and noncancer, 

and multipathway - along with their uncertainties, when determining the acceptable level of source 
35 

category risk. The Benzene NESHAP decision framework 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, and the accuracy and uncertainty of each piece of 

information must be considered in a weight-of-evidence approach for 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 complexity and uncertainty in the simplest and 

most transparent way possible. While this challenge is formidable, it is nonetheless 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. 

With respect to TOSHI values potentially underestimating risk, and the confusion over the statement that 

“impacts on organs or systems that occur above the critical 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 in section 2.7.2: 

All TOSHI calculations presented here were based exclusively on effects occurring at the 

“critical dose” (i.e., the lowest dose that produces adverse health effects). Although HQs 

associated with some pollutants have been aggregated 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 TOSHI values from multiple HAP that have the same 

target organ identified as the basis for the quantitative reference concentration (e.g., RfC) for that HAP. 

This means that if a HAP has a reference concentration based on kidney effects, it will be included in 

TOSHI calculations with other HAP whose reference concentration is based on kidney effects. Thus, the 

above statement is meant to acknowledge that it is possible that a HAP whose reference 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 reference concentration for kidney effects would not 

be the same as if a reference concentration had been developed for respiratory effects). Importantly 

however, the TOSHI should not be interpreted as a probability of adverse effects, or as strict delineation 

of “safe” and “unsafe” levels. Rather, the TOSHI is another measure of the potential for adverse health 

outcomes associated with pollutant exposure, and needs to be interpreted carefully 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 analysis, stating that the EPA should also include 

in the preamble discussion that the small annual POM emissions for the entire source category (91 tpy) 

is minuscule compared to other sources. The commenter states that the EPA should note in the preamble 
36 

that the contribution of primary aluminum facilities to this universe of multipathway POM exposures is 

too insignificant to merit further review and the potential 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 proximity of a source to a receptor 

also affects the associated impacts. 

Comment: One commenter (0166) states that the EPA’s choice to restrict multipathway risk screening to 

only contaminants that are identified in the 2003 Risk Assessment Guidance as being both persistent and 

bioaccumulative in the environment is not supported 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 pollutants 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 zero for these pollutants, and asserts that doing so 

when science shows otherwise is arbitrary and capricious. The commenter states that to not assess 

multipathway risk from exposure to these HAPs via 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 values 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 all of the available information on persistence and 

bioaccumulation (see http://www2.epa.gov/fera/air-toxics-risk-assessment-reference-library-volumes-1-

3), specifically Volume 1 Appendix D). (The Air Toxics Risk Assessment Reference Library provides 

information on the fundamental principles of risk-based assessment for air toxics and how to apply those 

principles in different settings (e.g., facility-specific) as well as strategies for reducing 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 the SAB and found to be acceptable, 

and therefore we consider it to be reasonable for use in the RTR program. Based on these sources and 

the limited available information on the persistence and bioaccumulation of other HAP, we do not 

believe that the potential for multipathway risk from other HAP rises to the level of the PB-HAP 

currently on the list. However, in the future we may add more pollutants 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 health 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. The commenter also notes that intermittent or short 

spikes of PB-HAPs can represent a significant health 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 that the EPA’s existing standard allows, or for risk 
37 

due to violations from that standard, violates the section 112(f)(2) requirement 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 emissions that facilities are 

permitted to emit. As discussed in the preamble, the uncertainties associated with the multipathway 

screen combined with the uncertainties associated with the allowable emissions estimates, would make a 

multipathway risk assessment based on allowable emissions highly uncertain. Such an assessment would 

be too uncertain to support a regulatory 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 that the residual risk assessment underestimates risk to the 

developing child and fetus. The commenter observes that biological differences in the developing child 

and fetus can result in increased cancer and non-cancer 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 assessment 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 the 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 most 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 available literature, and importantly, these are the values used in our risk 

assessments.9

We acknowledge that population subgroups, including children, may have a potential for risk that is 

greater than the general population due to greater relative exposure and/or greater susceptibility to the 

toxicant. The assessments we undertake to estimate risk account for this potential vulnerability. With 

respect to exposure, the risk assessments 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 continuously, 24 hours per day for a full lifetime, 

including childhood. With regard to children’s potentially greater susceptibility to non-cancer toxicants, 

the assessments rely on the EPA (or comparable) hazard identification and dose-response values which 

have been developed to be protective for all subgroups of the general population, including children. 

 

9 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. Available online at 

http://www.epa.gov/raf/publications/pdfs/rfd-final.pdf 
38 

For example, a review10 of the chronic reference value process concluded that the EPA’s reference 

concentration (RfC) derivation processes adequately considered potential susceptibility of different 

subgroups with specific consideration of children, such that the resultant RfC values pertain to the full 

human population “including sensitive subgroups,” a phrase which is inclusive of childhood. With 

respect to cancer, the EPA uses the age-dependent adjustment 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-stage specific risk estimates or potencies 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 MOA. With regard to other carcinogenic pollutants 

for which early-life susceptibility data are lacking, it is the Agency’s long-standing science policy 

position that use of the linear low-dose extrapolation approach (without further adjustment) provides 

adequate public health conservatism in the absence of chemical-specific 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 plausible 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 values 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 commenter, is not needed in the RfC/RfD methodology 

because the currently available factors are considered sufficient to account for uncertainties in the 

database from which the reference values are derived. After considering these and other factors, we 

continue to consider the risks based on existing emissions from this source category to provide an ample 

margin of safety (consistent with the Benzene NESHAP framework). 

Comment: One commenter (0166) suggests that the EPA should adopt the Office of Environmental 

Health Hazard Assessment (OEHHA) of the California Environmental Protection Agency childprotective scientific approach on cancer and other pollutants, and use at least an additional 10-fold 

uncertainty factor to protect children in addition to the uncertainty factors 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 age-dependent adjustment 

factors for all carcinogens emitted by this source, including naphthalene, PAHs and arsenic; should 

account for prenatal susceptibility to POM; and use the OEHHA factors for prenatal susceptibility and 

exposures. The commenter recommends using a 10X adjustment 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/cancerguidelines/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 risks from POM, PAHs and arsenic. 

The commenter observes that Congress recognized this science in toxics legislation in 1996 (i.e., in the 

Food Quality Protection Act (FQPA) for pesticide chemical residue) wherein Congress 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 expressly 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.gov/raf/publications/pdfs/rfd-final.pdf). With respect to cancer, the 

EPA uses the age-dependent adjustment factor, but limits the use of those factors only to carcinogenic 

pollutants that are known to act via mutagenic mode of action, in contrast to the OEHHA approach 

which uses them across the board for all carcinogens regardless of mode of action. The EPA believes the 

OEHHA approach is unwarranted and overly conservative, and provides a lengthy rationale for its 

approach in the 2005 Supplemental Guidance, as referred 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 it is appropriate to use 

the CalEPA child-specific reference doses, and further notes that there are currently no such values for 

HAP inhalation, so their current utility would be limited to PB-HAP which may be associated with nonnegligible ingestion exposures. That is, before using these child-specific 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-reviewed values. Our approach, which uses conservative 

tools and assumptions, ensures that our decisions are appropriately health protective and 

environmentally protective. The approach for selecting appropriate health benchmark values, in general, 

places greater weight on the EPA derived health benchmarks 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 scrutinize values that emerge as drivers of risk 

assessment results and the Agency has incorporated 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 currently relies on the ATSDR Minimal Risk Level 
40 

(MRL) for manganese, published in 201213 rather than the IRIS Reference Concentration (RfC) 

published in 199314. 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 pharmacokinetic 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 process15 concluded that the 

EPA’s reference concentration (RfC) derivation processes adequately considered potential susceptibility 

of different subgroups with specific consideration of children, such that the resultant RfC values pertain 

to the full human population “including sensitive subgroups,” a phrase which is inclusive of childhood. 

With respect to cancer, the EPA uses the age-dependent adjustment factor approach referred to by the 

commenter, but limits the use of those factors only to carcinogenic pollutants that are known to act via 

mutagenic mode of action, in contrast to the OEHHA approach, which uses them across the board for all 

carcinogens regardless of mode of action (MOA). In lieu 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 early-life exposures to chemicals which cause cancer 

through a mutagenic MOA. With regard to other carcinogenic pollutants for which early-life susceptibility data are lacking, it is the Agency’s long-standing science policy position that use of the linear lowdose extrapolation approach (without further adjustment) provides adequate public health conservatism 

in the absence of chemical-specific data indicating differential 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 that the EPA does not have authority to consider demographics 

in conducting residual risk assessments. The commenter notes that the EPA evaluated HAP-related risks 

across different social, demographic, and economic groups within the populations living near the 

facilities of this source category in order to examine the potential for 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 health” cannot reasonably be interpreted to include 

consideration of environmental justice in the section 112(f) context, and that the term “public health” 

refers to all people, not particular demographic segments. The commenter states that the EPA’s 

established approach to assessing potential impacts on public health under the NAAQS program is 

 

13 Agency for Toxic Substances & Disease Registry Toxicological Profile for Manganese (2012) available at 

http://www.atsdr.cdc.gov/toxprofiles/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 consideration 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 rather 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 unreasonable and, as such, would 

not be a supportable interpretation 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) part of their mission by identifying and addressing, as 

appropriate, disproportionately high and adverse human health or environmental effects of their 

programs, policies, and activities on minority populations and low-income populations in the United 

States. Consistent with EO 12898 and the Presidential 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 minority, 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 population groups may be experiencing disproportionate impacts. In 

addition, the EPA notes that there are many factors, in addition to health-based sensitivities, that may 

influence whether a population experiences 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 process 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 regardless of racial or socioeconomic status. However, in 

determining whether to require additional 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 measures and factors in both 

the decision regarding risk acceptability 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 surrounding the facilities within the source category 

addressed by this rule making, we ultimately concluded 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 the demographic makeup of the populations exposed to the source 

category, as noted by the commenter, the EPA did not base its decision on these analyses. 
42 

The EPA disagrees that the term “public health” cannot include consideration of EJ. The EPA defines EJ 

to mean fair treatment and meaningful involvement of all people, and this definition represents a 

commitment to ensuring that the EPA works to improve conditions affecting the public health of all 

Americans so that everyone has access to clean water, clean air, and healthy communities. 

Comment: One commenter (0166) notes that 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 EPA does not assess the disproportionate impact of 

chronic non-cancer and acute health risk, but its demographic analysis suggests 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 person 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 follow the recommendations of the EPA’s own interim 

guidance and presented in the Environmental Justice 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 acceptable for particular 

individuals or communities to have this type of disproportionate impact. 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 disproportionately 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 level have a high level of 

risk. In the demographics analysis, the EPA noted that 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 percentage of Native Americans. With respect 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 the 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 individual representing the MIR is Native American, the 
43 

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 that it should be used in our demographic analyses 

because EJSEAT is currently a draft tool in development, 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 and the Action Development Process. 

In addition to proximity and exposure to environmental 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 disproportionate 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 pathways, ability to participate in the decision making 

process, or physical infrastructure were identified 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 did not describe which tribal communities are 

affected, where they are located, or which sources in the source category 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 demographics analysis, the purpose of the 

demographics analysis was to generally identify demographic groups that may be impacted by the 

proposed rule. For this purpose, the EPA believes that a source-category wide demographics analysis is a 

reasonable approach. Note that the emissions dataset provided in the docket for this proposed rule did 

include the addresses of the primary 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 statement of the health risks and benefits from 

the EPA’s final action, and in future rule proposals. The commenter states that although it provides the 

MIR and chronic and risk numbers, these are not easily understandable by the general public. The 

commenter asks for expanded discussion of health disorders or other adverse effects, stating that without 

a full discussion of health impacts and risks, it is difficult for the public 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 EPA 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 harm to public health the EPA is 
44 

determining are “acceptable” and “unacceptable.” This is needed to inform the EPA’s and the public’s 

consideration of what level of risk is acceptable or unacceptable, and 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 public. As future risk assessment documents and rulemakings are 

written, we will consider the comments provided and continue 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 sources, the EPA must also analyze those who are the 

most exposed, within 5 km of primary aluminum plants, regardless of projected risk, consistent with the 

approach used for the Hard and Decorative Chromium 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 located in urban or higher density population areas. Commenters (0165 and 

0369) observes that the EPA’s socioeconomic analysis for this rule did not evaluate 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 the EPA only evaluated the risk to the 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-income 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 adjacent to the facility. Commenters (0165 and 0369) 

recommends that the EPA conduct the demographic analysis on individuals projected 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 groups 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 reasonable approach. Also, selecting 50 km is a reasonable approach given that 

we modeled cancer and chronic, noncancer risk out to 50 km. It is also possible, especially around 

facilities with larger stacks, that those with a cancer 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 cancer 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 rulemaking 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, because 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 specific guidance on how to interpret and apply the outcome of these 

types of analyses in the rulemaking process. With respect to the 2010 census data, these data were not 
45 

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 that the EPA released the Plan EJ 2014 to direct ways the 

agency intends to address environmental justice impacts, and it includes the development of scientific 

tools on cumulative impacts. The commenter suggests that the EPA use this and other similar 

rulemakings to inform the implementation of Plan EJ 2014. 

Response: The EPA appreciates the commenter’s recommendation to use this and other similar 

rulemakings to inform the implementation of Plan EJ 2014. The EPA is collecting feedback across 

offices and is examining various rulemakings to assist in the creation of scientific tools on cumulative 

impacts. 

d. Cumulative Risk 

Comment: One commenter (0166) maintains that for cancer, chronic and acute health risks, the EPA has 

not appropriately assessed cumulative risk. The commenter provides extensive 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 the 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 indices 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 individual cancer risks for the source 

category were aggregated for all carcinogens. In assessing 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 non-cancer impacts to understand the risk contribution 

of the sources within the primary aluminum source category. 

Comment: One commenter (0166) asserts that the EPA has failed to assess the cumulative impact of 

exposure by not including past background exposure as part of the health risk assessment. The 

commenter states that section 112(f) includes recognition of background 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 risks into its residual risk analysis as section 

112(f)(2) requires, including a full assessment 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 the cumulative noncancer hazard indices from all 

emitted non-carcinogens affecting the same target organ system for both the source category emissions 

and the facility-wide emissions. While the incorporation 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 challenging, they are neither mandated nor barred from our analysis. 
46 

In developing the decision framework in the Benzene NESHAP currently used for making residual risk 

decisions, the EPA rejected approaches that would have mandated consideration of background levels of 

pollution in assessing the acceptability of risk, concluding 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 section 112(f) analysis. This assessment 

excludes background contributions because the available 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) expresses concern that the EPA has not combined risks from 

multiple HAP and pathways, thus not assessing cumulative impacts and health risk appropriately. The 

commenter notes that the EPA should assess the synergistic, carcinogenic (and other) effects of different 

pollutants; create a combined acute risk number that would represent the total 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 combines 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 cumulative health risk is 

unlawful, arbitrary, and capricious, and it undermines the EPA’s acceptability determination. 

Response: We disagree with the commenter that the EPA should create a combined acute risk number 

that would represent the total acute risk for all pollutants 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 occurring 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 basis rather than using a TOSHI approach. 

Comment: One commenter (0166) suggests that in order to appropriately conduct the risk assessment, 

the multipathway risks should be combined with the inhalation risks before proceeding 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 level 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 full risk to the most-exposed person from the combined impact of both 

inhalation and other routes of exposure. 

Response: We have combined risk assessment results to the extent that it is appropriate to do so. We 

consider the effect of mixtures of carcinogens and use a target organ-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 rule 
47 

were screening-level assessments (Tier 1 and Tier 2 screens). (We note that we conducted a more 

refined multipathway analysis for one Soderberg facility, as described in the risk assessment documents, 

which are available in the docket. However, that one Soderberg facility is now permanently shut down. 

In fact, all Soderberg facilities are now shut down. So, those results are now less relevant.) 

The screening assessments used highly conservative assumptions 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 lead smelters), it was for two refined assessments 

conducted for an operating facility, and still serves as a conservative 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 that cumulative impacts analysis 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. sections 7475 and 7503 (requiring a localized, cumulative 

assessment of whether or not a new or modified source’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 combine current baseline emissions, exposures, and 

health impacts in addition to those of the specific source 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 individual sources within it); facility-wide risk from collocated sources outside of 

this category; and all other sources of toxic air pollution 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 unacceptable and that, thus, the current acceptability 

determination is incomplete, and therefore arbitrary 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 carcinogens emitted by a facility. Similarly, the use of 

the TOSHI for chronic non-cancer effects 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 aluminum reduction facilities (i.e., those 

facilities with potlines and anode bake furnaces) are collocated with secondary aluminum production 

facilities. As a result, the facility-wide analysis that was conducted as part of the risk assessment for the 

secondary aluminum source category provides a facility-wide analysis for most of the primary 

aluminum production facilities. The facility-wide risk assessment and results are also described in the 

risk assessment document for the primary aluminum source category, which is available in the docket 
48 

for this action. As mentioned in a response above, the facility-wide risks (i.e., facility-wide results 

including those associated with primary aluminum operations) did not change the conclusions reached in 

this rulemaking. With respect to “all other sources of toxic air pollution in the area,” the commenter did 

not provide any information as to what other sources 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 still 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 sources, providing even more evidence as to why the EPA should reduce 

risks from the primary and secondary aluminum source categories, as discussed in the 2012 Comments 

and reincorporated here by reference. 

Response: We also disagree with the commenter’s assertion that additional quantitative assessment of 

risks from sources outside the source category is required under the statute. The statute requires the EPA 

to provide the quantitative risk information 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 for primary aluminum facilities did take into account 

emissions from collocated secondary aluminum facilities. 

e. Margin of Safety 

Comment: One commenter (0166) asserts that the EPA’s ample margin of safety determination does not 

consider the full range of control options available and arbitrarily relies on unsupported assumptions for 

the options it does consider. The commenter states that the EPA’s cost-based determination 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 NESHAP, 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 measures it does evaluate is arbitrary and capricious. 

Response: 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 

concentration 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. 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 required in this final rule include all of the controls that 

are technically and economically feasible to reduce risks due to HAP emissions from this source 

category. These requirements will protect the public health with an ample margin of safety. 
49 

Comment: One commenter (0166) states that the EPA fails to set a residual risk standard that provides 

the requisite “ample margin of safety to protect public health” pursuant to CAA 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 assess 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 finds 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-based metric. 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 not subjugate health interests and objectives to cost. The commenter 

observes that the EPA fails to consider what the “margin” of safety is for the rule it has proposed, or 

what margin would provide “ample” protection, as the EPA’s proposal would still 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 “ample margin of safety” under its proposed rule. The 

commenter asserts that the EPA has not considered the uncertainty that has likely led it to underestimate 

health risk; the combination of cancer, non-cancer chronic, acute, and 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 safety.” The commenter states that the EPA includes no 

discussion or analysis regarding what the maximum feasible protection would be, or how many people 

could be protected from a greater level of risk and whether they are the greatest number. The commenter 

objects to setting the standard without finding or explaining how the proposal provides more than bare 

minimum protection for public health, and claims that this action would render the phrase “ample 

margin of safety to protect public health” superfluous and violate section 112(f)(2). 

The commenter states that the EPA may not lawfully consider cost in deciding what is the “ample 

margin of safety to protect public health,” rather there is only an authorization to consider cost in 

determining whether additional standards are needed to prevent environmental harm. The commenter 

states that although the D.C. Circuit previously allowed the agency to consider cost in the HON 

decision, that case was wrongly decided and the EPA should not rely on it as justification 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 modifies the environmental effect prong of the EPA’s 

duty. The commenter further notes that the statement in section 112(f)(2)(B) is not a clear statement 

authorizing the consideration of cost and it does not enshrine the EPA’s prior Benzene rule analysis 

forever in all instances. The commenter further asserts that the purpose of citing the Benzene Rule was 

not to enshrine that rule or its statutory interpretations for all time, but rather to prevent back-sliding by 

the Agency after the 1990 Amendments. The commenter concludes that the statute 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 (AMOS). Under the AMOS analysis, we evaluated the 

cost and feasibility of available control technologies and other measures (including developments in 

practices, processes and control technologies assessed under the section 112(d)(6) technology review) 

that could be applied in this source category to further reduce the risks (or potential risks) due to 
50 

emissions of HAP identified in our risk assessment, along with all of the health risks and other health 

information considered in the risk acceptability determination described above. We believe it is 

appropriate to consider costs, feasibility 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, because at that time one Soderberg facility was still 

operating and another Soderberg facility was idle and the Soderberg facilities 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 Notice, 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 efficient and higher emitting nature of the Soderberg 

technology compared to prebake technology. 

With regard to the 2014 supplemental proposal (79 FR 72914, December 8, 2014), after gathering 

additional data and conducting additional risk analyses, we provided a revised ample margin of safety 

analysis and explained our decisions based on the ample margin of safety analysis. The ample margin of 

safety analysis in the supplemental proposal was largely focused on possible options to reduce emissions 

from prebake facilities (see pages 72947-72948 of the December 8, 2014 FR Notice). 

For example, under the ample margin of safety analysis (AMOS) in the 2014 supplemental proposal, we 

evaluated possible options to reduce HAP metal and POM emissions from the prebake potline roof 

vents. The main option we evaluated was based on requiring most prebake facilities to install wet roof 

scrubbers to reduce secondary HAP metals emissions from their potline roof vents. Under this option we 

estimated that post-control cancer MIR would be 40-in-1 million for prebake facilities (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 concentration leading to an acute HQ greater than 5, and that about 

3,600 people could be exposed to a concentration 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 expect that this would happen for very few hours of 

the 8,760 hours that are in a year. For HF, the maximum off-site HQ would be reduced from 3 to 2 and 

is at a location where we would not expect 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 per 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 PM2.5 reductions with CE of $185,000 per ton PM2.5. 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 several facilities would be at risk of closure under this option. The option would also be associated with potentially adverse environmental effects (more wastewater discharge), and increased energy usage (with attendant carbon pollution), although these are not the most 

significant factors in the EPA’s proposed decision. Therefore, given all the factors described above, we 

did not propose this option in 2014. In the final rule, we arrived at the same conclusions and therefore 
51 

did not promulgate tighter standards for prebake facilities based on the AMOS. However, as described 

in the final rule preamble, we did promulgate standards for As, Ni, and POM for Soderberg potlines 

based on the AMOS analysis. 

In accordance with the approach established 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, technological feasibility, uncertainties and other relevant 

factors in our ample margin of safety determination. Considering the health risk information and the 

costs of the options identified, 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 that 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 acceptable for the most-exposed 

person must be less for each source category to which 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 commensurate fraction of the threshold. The commenter further suggests a 

case-by-case determination of whether stronger emission limits are needed. 

The commenter asserts that the EPA has 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 section 112(f)(2), the EPA is required to decide whether to set a 

standard for a given source category if the cancer risk from that specific source category is 1-in-1 

million or more. The commenter observes that if the risk associated with a source category’s emissions 

are between 1-in-1 million and the presumptive limit on acceptability (currently 100-in-1 million) and 

that source category is contributing risk along with numerous other source 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 similar contribution-based 

approach in the Clean Air Act’s prevention of significant deterioration program, where a source’s 

contribution or increment of new pollution is analyzed to see whether it would cause too much 

deterioration of air quality based on national ambient air quality standards. 

Response: We disagree with the commenter that the EPA 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 quantitative risk information necessary to inform RTR 

regulatory decisions, the EPA conducts a comprehensive assessment of the risks 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 risks, as appropriate. In some cases, we have additional information 

about HAP emissions that are outside the scope of the particular rulemaking but within the boundaries of 

the subject facilities. In other cases, we may have ambient HAP monitoring data that can be considered 
52 

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 cases, however, when we consider additional information 

about risks, we also consider its attendant uncertainties, and information which carries significant 

uncertainties generally carries much less weight in the overall regulatory decision. 

All of the quantitative risk assessment information about HAP emissions from the source category under 

consideration is also considered in the manner prescribed by the decision framework set forth by the 

CAA for residual risk decision-making (i.e., the Benzene NESHAP decision framework), and this means 

that the general guidelines of risk acceptability have been developed in a way that they already take into 

account the impossibility of accurately 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 source 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 health assessment. The commenter expresses concern 

that the EPA’s proposed rule preamble contains no proposed determination regarding 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 “prevent an adverse environmental effect.” The commenter 

notes that only in the multipathway risk assessment is there any discussion 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 commenter 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) argues 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 environmental HAP from the Primary Aluminum Production 

source category: cadmium, PAHs, dioxins, methyl mercury and hydrogen fluoride. In our Tier 1 

analysis, emissions of dioxins and methyl mercury did not exceed the threshold emission rates for any of 

the ecological benchmarks for any facility 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 facility 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 fluoride, the average modeled concentration around each 

facility (i.e., the average concentration of all off-site data points in the 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 Primary Aluminum Production Source Category in 
53 

Support of the September 2015 Risk and Technology Review Final Rule which can be found in the 

docket. 

Comment: One commenter (0166) recommended that the 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 concerns included PAH concentrations in the environment, the use of 

control technologies, and fluoride emission spikes during startup. 

Response: With respect to assessing ecological risk from startup, we note that the commenter did not 

provide any such data. We did analyze ambient total fluoride concentration data for Glacier National 

Park provided by the NPS for the period in 2002 during which the potlines were restarted (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 concentrations measured 

in 2001 or 2004. The CFAC/Glacier National Park reports 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 Alcoa 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, respectively, during this time). The emissions on a mass 

basis do not appear to be strongly related to the production. Between 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 increase in TF emissions on a mass basis 

during startup. Line 2 emitted slightly more HF than the lines operating at steady state and slightly less 

particulate matter (and presumably slightly less particulate F) than the lines operating at steady state. 

As mentioned previously, we conducted a screening-level evaluation of the potential adverse 

environmental risks that included hydrogen fluoride and PAHs. In our Tier 1 analysis, we did find that 

emissions of PAHs exceeded some ecological benchmarks for one facility, therefore, a Tier 2 analysis 

was performed. In the Tier 2 analysis, we found that emissions of PAHs exceeded the NOAEL sediment 

benchmark for one lake by 2 times, but did not exceed the threshold effect level. For hydrogen fluoride, 

the average modeled concentration around each facility (i.e., the average concentration of all off-site 
54 

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 emissions from primary aluminum production facilities. 

Additional details on the environmental risk screen methodology and results are located in the Residual 

Risk Assessment for the Primary 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 health risk numbers, stating that 

these numbers are above the threshold and that the EPA’s reference doses apply to rodents, but are not 

necessarily sufficient for protecting more sensitive wildlife or other environmental receptors. The 

commenter notes that the SAB has stated “[t]he assumption that ecological receptors will be protected if 

human health is protected is incorrect.” The commenter observes that risks include inhalation risk for 

wildlife and persistent or bioaccumulative chemicals in the environment. The commenter asks that the 

EPA perform an appropriate ecological assessment. 

Response: The EPA has developed a screening 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 mercury 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 protected if human health is protected.” In the environmental risk screen, we 

evaluate four exposure media: terrestrial soils, surface water bodies, fish consumed by wildlife, and air. 

Within these four exposure media, we evaluate a total of nine Generic Ecological Assessment Endpoints 

(GEAEs) that reflect the overall “health” of aquatic and terrestrial ecosystems and any important biota 

or community types that could be exposed in those ecosystems. For each HAP and GEAE we screen for 

adverse environmental effects using ecological benchmarks. Ecological benchmarks represent a level of 

exposure to a chemical in the environmental that has been linked to a particular environmental effect 

level (e.g., a no-effect level or a threshold effect level) through scientific study. Additional details on the 

environmental risk screen methodology, the ecological benchmarks used, and the screening results are 

located in the Residual Risk Assessment for the Primary 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 considered 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 required 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 statement 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 likelihood 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 assessment of actual emissions, but they believe the risk 

screening for gaseous HF should include an assessment of allowable emissions on plant life and indicate 

which specific fluoride standard is being applied (i.e., 24-hour or 30-day average). 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 effects on grazing wildlife and grazing domestic animals are 

not expected to occur. 

Commenter (0165) notes that fluorosis in grazing ruminants has been shown to occur with continuing 

low level fluoride ingestion and is the direct result of livestock grazing (ingestion) on fluoride 

contaminated forage. The commenter cites concerns 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 surrounding the identified facilities and the potential 

for animal grazing should be a concern. The commenter expresses concern that the RTR fails to 

recognize this welfare effect and the important exposure pathway of ingestion needs to be accounted for 

in addition to direct inhalation exposure for all mammals 

Response: The commenter is correct that we did not base 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 emissions estimates would make an 

ecological risk assessment based on allowable emissions too uncertain for use in making a regulatory 

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. 

In our environmental risk screening analysis we determined that for hydrogen fluoride, the average 

modeled concentration around each facility (i.e., the average concentration 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, only 0.2% of the modeled area exceeded the ecological benchmarks. The 

facility with the highest average concentration of HF over the modeling domain had a concentration of 

0.0472 ug/m3. This concentration is approximately 10 times lower than the ecological benchmark or 

12% of the benchmark value. 

For HF, the environmental risk screen evaluates the potential phytotoxicity and 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 facility to the ecological benchmark for HF. The 
56 

Environment Canada benchmark that was used for HF (0.4 ug HF/m3

) represents a lowest observed effect level (LOEL), which is defined as: 

"”The level above which there are demonstrated effects on human health and/or the 

environment. It is scientifically based and defines 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 investigations into the effects of HF 

on plants that represented 32 separate effects results. The data set included 18 effects results from 

studies using plants of horticultural importance, 10 from studies using agricultural species, and 4 from 

studies of effects on forest (conifer) species. We agree with the commenter, that high concentrations of 

HF in the air have been linked to fluorosis in livestock. However, the HF concentrations at which 

fluorosis in livestock occur are higher 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 conservative by design. The commenter further notes 

that AERMOD is designed as a point, area or volume source model and does not specifically address 

line sources of emissions, such as aluminum potlines, 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 large or long buildings. As an example the commenter 

provides data (see table titled Over Predictions Using Modeling, below) comparing AERMOD 

predictions with two years of ambient SO2 measurement data for one US aluminum smelter, showing 

that the model over-predicts short-term SO2 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 99th 

Percentile 1-hr 

SO2 ug/m3

AERMOD 

Predicted* 99th

Percentile 1-hr 

SO2 ug/m3

Over Prediction 

Plant No. 1 Station PS2 2009 99.56 3112 3126% 

 Station PS2 2010 47.16 3472 7362% 

* Modeling performed with actual SO2 emissions for 2009 or 2010. 
57 

Response: The EPA disagrees that the AERMOD model overestimates concentrations for sources like 

potroom roof monitors, and that the BLP model needs to be used to correctly model such sources. An 

analysis performed by the EPA to compare the modeled estimates from AERMOD and the BLP model 

for a typical Primary Aluminum facility indicated that the maximum modeled concentrations were only 

twenty percent different.18 The EPA concluded that this difference 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 comparisons between modeled and measured short-term 

concentrations of SO2, we note that in this assessment we are primarily modeling annual HAP 

concentrations and therefore a comparison between modeled 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 individual exposures and risks throughout the RTR program. 

With respect acute health risks, which do take into account 1-hour maximum HAP concentrations, the 

data provided with respect to SO2 are again of questionable utility. Other than stating that AERMOD 

was run with “regulatory default assumptions to primary control device stacks,” the commenter provides 

little additional detail about the analysis, thus making it difficult to assess (e.g., the commenter did not 

state the name of the facility used in 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 SO2. 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 that a flaw in the risk assessment is that the risk assessment 

does not include short or long term population mobility. The commenter expresses concern that the EPA 

assumes full-exposures of 70 years outdoors and full-time at the census blocks modeled in HEM3, and 

that omission of a mobility/activity analysis is estimated 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 long 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 and 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 consider the actual level of risk for 

the “individual most exposed to emissions” as required by section 112(f). Commenter 0166 notes that 

the EPA adjusted receptor points in the HEM-AERMOD 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-

0175 
58 

residents living on the fence line. Commenter 0166 concludes that failing to assess risk at the fence line 

would be unlawful, arbitrary, and capricious 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 assumptions 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 exposures at the census block centroid as surrogates for the 

exposure concentrations for all people living in that block. Instead, Commenters (0165 and 0369) 

recommend that the EPA use the truly maximum individual risk, irrespective of its location in the census 

block, in its section 112(f)(2) risk assessments. 

Response: As we have noted in the development of previous residual risk regulations in a national-scale 

assessment of lifetime inhalation exposures and health risks from facilities in a source category, it is 

appropriate to identify exposure locations where it may be reasonably expected that an individual will 

spend a majority of his or her lifetime. Further, in determining chronic risks, it is appropriate to use 

census block information on where people actually reside, 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 approximately 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 location of maximum exposure, and the entire population 

of that census block is assumed to experience the maximum individual 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 (although there is no systematic bias 

for average levels). Given the relatively small dimensions of census blocks in densely-populated areas, 

there is little uncertainty introduced by using the census block centroids. There is more uncertainty when 

census blocks are larger, although there is still no systematic bias. Thus, the EPA concludes that the most 

appropriate locations at which to estimate chronic exposures and risks are the census block centroids 

because (1) census blocks are the finest resolution available in the national census data, (2) facility fence 

lines do not typically represent locations where chronic exposures are likely (i.e., people do not typically 

live at the fence line of facilities), and (3) as described above, there is no systematic bias with respect to 

using census block centroids as an exposure surrogate for all individuals residing in that block. 

Assessing risk at the geographic centroid of each census block containing at least one person has been 

the EPA’s approach for estimating chronic maximum individual exposures and risks throughout the RTR 

program. In addition, in its peer review of the methodologies used to estimate risks as part of the RTR 

rulemaking efforts, the EPA’s SAB endorsed this approach. 

In addition, the commenter is correct that the EPA does not consider in its model that homes and 

businesses may locate closer to facilities over time (i.e., population growth over time). While this could 

result in an underestimation of risk, there are also modeling assumptions that could lead to an 

overestimation of risk. Thus, we do not believe that there is a significant bias in the risk results in any 
59 

one direction. Notably, uncertainties are described in section 4.1 of the Residual Risk Assessment for the 

Primary Aluminum Production Source Category in Support of the 2014 Supplemental Proposal. In part, 

this section states: 

If anything, the population exposure estimates are biased high by not accounting for short- or long-term 

population mobility, and by neglecting processes like deposition, plume depletion, and atmospheric 

degradation. Additionally, estimates of the maximum individual risk (MIR) contain uncertainty, because 

they are derived at census block centroid locations rather than actual residences. This uncertainty is 

known to create potential underestimates and overestimates of the 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 possibility of a source closure occurring 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 downward bias in both the MIR and population risk estimates. 

Comment: Commenter (0369) appreciated the development of the Summary Data Facility, Maximum 

Achievable Control Technology, Hazardous Air Pollutants and Emissions Data Access database to 

evaluate the emissions inventory from each primary 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 Pollutants and Emissions Data Access database.

3.3 Startup, Shutdown and Malfunction 

3.3.1 General 

Comment: One commenter (0162) agrees that work practices 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 deleting the phrase “but in no case 

more than 24 hours from the time the crust was broken” from this provision. The commenter believes 

that the proposed restriction to reseal pot crust within “no more than 24 hours from the time the crust 

was broken” would be counter-productive or even infeasible 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 the pot within 24 hours will introduce excess alumina into 

the bath, further destabilizing the pot, and (2) startup of side-worked pots requires 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 increasing the risk of 

pot instability. The commenter suggests a revised provision to read as follows: “(iii) Reseal 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 commenter recommends revising 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 such a “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 practice standards during 

startup periods and agrees with the commenter’s suggested revisions and has changed these sections in 

the final rule. In addition, a provision has been added to the final rule requiring that the written operating 

plan include a specified pot temperature that will trigger corrective action. 

Comment: One commenter (0162) notes that the proposed definition for anode bake furnace startup 

does not capture the full range of startups 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 situations, 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 temperatures 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 temperature 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 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 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 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 concludes at the start of the 

second anode bake cycle if the furnace was at ambient temperature upon startup. The re-start 
61 

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 revised the final definition to capture the full 

range of startups typical for an anode bake furnace. 

Comment: One commenter (0162) asks that the EPA clarify 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 “Records 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 ambient 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 time 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 read “A requirement to develop 

an anode bake furnace startup schedule.” The EPA has clarified section 63.847(l)(2) and (4) as suggested 

by the commenter. 

Comment: One commenter (0166) asserts that the EPA’s proposed 6-month startup practices for 

potlines is unlawful, by creating new provisions that would perpetuate the problem of the SSM 

exemption. The commenter agrees with the proposed removal 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 requirement 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 the 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 the statements, “it is economically and technically 

infeasible to measure emissions during 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 that the primary capture and control 

system is operating at all times during startup, the commenter asserts, emission testing from the control 

device is also feasible. The commenter notes that technology is available to perform continuous 

emission monitoring for HF and asserts that, therefore, under section 112(h), the EPA cannot avoid 

setting a numerical standard that applies during startup. 
62 

The commenter notes that in an attached document, the National Park Service expresses serious concern 

about fluoride level spikes during startups at primary aluminum plants. The commenter asserts that the 

EPA should not create a startup exemption loophole that would allow high levels of emissions to 

continue to occur during startup periods, without any numerical limitation. 

Response: The commenter has misinterpreted the 180 day period following startup as an exemption. 

This refers to the deadline for conducting initial performance tests or performance tests following a 

restart. Prior to any startup, the operator is required to start the control device and operate 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 typically 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. During startup, this sample is not representative as 

it is largely representative of the status of the pots that are located close to the sampling equipment. 

Further since emissions rates are normalized by production rates, during periods when production is 

zero, calculated production based emission rates are not meaningful. It may be feasible to determine 

emission rates from the primary control system during 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 the 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 during 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 monitoring for HF, the fluoride emission standard is expressed in terms 

of total fluoride (TF), which includes both HF and particulate fluoride. Reliable continuous emission 

monitors may not be available for measurement of TF. 

Comment: One commenter (0166) states that 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. The commenter suggests that the EPA consider example 

violation and malfunctions that have occurred in the past, based on Enforcement and Compliance 

History Online (ECHO) reports 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 allows citizens to commence a civil action against any 

person alleged to be in violation of “an emission standard or limitation under this chapter.” In exercising 

its authority under section 112 to establish emission standards at a level that meets the stringency 

requirements of section 112, the EPA necessarily defines 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 relief is available. All other violations of the emission standard are 

subject to injunctive relief and penalties. 
63 

Comment: One commenter (0166) recommends further actions in the case of an exceedance or 

malfunction as follows: 

 The EPA must require automatic shut off of the malfunctioning equipment or process for the time 

needed to take corrective action, whenever an exceedance or malfunction occurs. 

 The EPA must assign responsibility and liability to the 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 measures 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 equipment 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 require its Regional office to communicate this 

determination to all interested members of the public, including local community representatives. 

 If a facility has more than 4 exceedances or malfunctions during the same quarter, then the EPA 

must require automatic shut down 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 mechanism in the standards that ensure that a 

citizen complaint of air pollution incidents or health concerns receive 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 off the affected sources within this source category 

in the event of a malfunction and automatic shut off of malfunctioning equipment may not ensure that 

emissions are minimized. Owners or operators must, at all times, operate and maintain any affected 

source, including associated air pollution control equipment, in a manner consistent with safety and 

good air pollution control practices 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 the 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 that reduces the incentive to comply and may make malfunction-based 
64 

violations more likely. While the commenter agrees with the EPA’s proposal to remove the malfunction 

exemption from the MACT standard, the commenter asserts that the EPA also proposes 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 facilities 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 standards under the CAA using 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 thus Congress flatly barred the EPA from limiting when 

civil penalties can be assessed, and that in this proposal the EPA acts outside 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 participation and the ability to win an effective, 

deterrent remedy in CAA enforcement actions. 

The commenter states that the CAA grants the EPA minimal discretion that only applies to 

administrative penalties which may be imposed under section 113(d) and that there is no similar 

authority to compromise, modify or limit civil penalties 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 “appropriate” under CAA section 304(a), and the EPA should not ask a court to 

ignore its legal duty. The commenter notes that it is improper for the EPA 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 protect themselves from pollution and in direct conflict with congressional 

intent. The commenter expresses concern that the affirmative 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 in order 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 measures – an outcome Congress 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 violators 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 penalties 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 when the congressionally 

mandated (see 42 U.S.C. section 7413(e)) factors are met. The commenter believes that the proposed 
65 

exemption would also be barred under Chevron step two or found to be arbitrary 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 specifically 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 further hold that the EPA’s interpretation of the 

Act in a manner to maximize its own discretion is unreasonable because the clear intent of Congress in 

enacting the 1990 Amendments was to the contrary.”); see also Gen. Instrument Corp. v. F.C.C., 213 

F.3d 724, 732 (D.C. Cir. 2000) (explaining that “an arbitrary 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 that 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 affirmative defense undercut Congress’s 

intent that citizen suit enforcement should avoid re-delving into “technological or other considerations.” 

The commenter proposes that both result from the technical 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 defense 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 deterrent 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 likely to claim that any violation of the standard is 

due to a malfunction in order to evade the requirements. The commenter observes that allowing polluters 

to evade financial penalties through this type of measure is likely to lead to polluters simply ignoring or 

factoring potential standard violations into their cost of doing business. The commenter states that the 

EPA has provided no evidence that an affirmative defense for malfunctions would serve the purpose of 

section 112 (that is, to protect people from toxic air pollution). 

Comment: One commenter (0166) asserts that, assuming that the EPA had authority to promulgate any 

type of affirmative defense to penalties for malfunctions, the EPA should also promulgate the following 

provisions: 

 The commenter suggests that the EPA apply a specific 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 facility 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 has 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 that with the removal of the “Affirmative 

Defense” provisions (DC Circuit Court ruling in NRDC v. EPA, 749 F. 3d1055 2014) that there will be a 

regulatory expectation that emission limits must be complied with during malfunction periods. 

Commenters stated that the Agency’s proposed approach of only offering case-by-case enforcement 

discretion in the event malfunction events occur does not provide an adequate regulatory framework for 

managing them. Commenters stated that malfunctions are by definition sudden, unavoidable events and 

an approach of treating these events as violations of emission limits 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 framework that could allow biased 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 the final rule and/or its accompanying preamble contain clear and 

unambiguous language indicating that there is not an expectation that the final emission limits be 

complied with during periods of malfunction. Commenter (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 malfunction 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 action 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 emission 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 an affirmative defense to civil penalties for excess 

emissions associated with malfunction events, provided the malfunction meets certain criteria and the 

operator complies with reporting requirements. 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 Standards in light of that change does not comply 

with the CAA. Commenter (0374) stated that the affirmative defense was something that the EPA 

considered necessary when the EPA initially proposed revised emission standards for primary 
67 

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 explain at all why the remainder of the proposed standards does not need 

to be revised in light of that elimination. Commenter (0374) stated that the EPA 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 publish a new or supplemental statement of basis and 

purpose for the proposed rule that explains and allows for public comment on the appropriateness of 

the entire proposed primary aluminum emission standards 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 more regulatory clarity.” 79 FR 72950. Commenter (0374) stated that 

this statement does not excuse the EPA’s failure to reconsider entirely its statement of basis and purpose 

for the Proposed Rule with the affirmative defense 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 during malfunctions, but that do not reflect what is 

achievable with available technology during malfunctions. See proposed 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 MACT standards be based on what is achievable with 

available technology; otherwise, the EPA would have had no statutory authority to promulgate the 

affirmative defense. 

Commenter (0374) stated that the EPA staff almost inevitably had to have considered the effect of the 

affirmative defense on compliance obligations when they were deriving the Proposed Standards. 

Commenter (0374) stated that in the Response to Comments document 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 these flagged ‘malfunctions’ occur too often. We revised 

the analysis of the CO CEMS data to 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 amended final Boiler MACT frequent 

periods of malfunction cannot qualify for the Affirmative Defense provisions in the amended final rule 

and these data will need to be included in the rolling 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 with unavoidable equipment failures would qualify for the affirmative 

defense dictated whether the EPA would factor those emissions into setting the standard, or would rely 

instead on the affirmative defense to address those emissions. 

Commenter (0374) stated that having taken the affirmative defense into account when deciding what 

emission standards to include in the Proposed Rule, the EPA cannot now eliminate the affirmative 

defense from the proposal without reassessing the appropriateness of those emission standards and 

how they will affect primary aluminum plants if the standards are no longer mitigated by the 
68 

affirmative defense. Commenter (0374) stated that the EPA must then publish its analysis and seek 

public comment on it before promulgating a final rule that makes emission limitations based on data 

from normal operations applicable even during malfunctions but deletes any affirmative defense for 

malfunctions. 

Commenter (0374) stated that the EPA cannot simply eliminate the affirmative defense for malfunctions 

without considering its effect on the reasonableness of the emission standards. 

Comment: Commenter (0374) stated that the EPA is required, before eliminating SSM provisions in the 

original MACT standards for Primary Aluminum Production, to demonstrate that the resulting standards 

will be consistent with CAA section 112 and congressional 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 essentially just restates the 

EPA’s inadequate statement in the Proposed Rule addressing the EPA’s purported authority to 

promulgate technology- based standards under section 112 without taking the inevitability of 

malfunctions of the technology into account. 

Commenter (0374) stated that the court decision that the EPA cites as the reason for eliminating the 

affirmative defense provisions of the current standards said nothing about (a) whether the EPA must 

consider the effect of malfunctions when it sets emission standards that apply at all times (except during 

some startup and shutdown periods); or (b) whether it is appropriate for the emission standards 

themselves to contain an alternative emission standard that applies during malfunction events that meet 

certain criteria. Commenter (0374) stated 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 the authority to determine an appropriate 

penalty for a violation to the court. See 749 F.3d at 1063-64. Commenter (0374) stated 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 occurred, rather than being part of how a violation is determined, the 

affirmative defense intruded into the sole discretion of the district courts. Commenter (0374) stated that 

thus, while the court decision is grounds for the EPA eliminating the affirmative defense as it was 

written in the Proposed Rule, it in no way authorizes the EPA to remove the affirmative defense from 

the emission standards for primary aluminum plants without substituting 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 existing sources, and to limit emissions only “where 

achievable.” Commenter (0374) stated that section 112(d)(3) requires the standards at minimum to 

reflect actual achievements in the field by best performers. Commenter (0374) stated that for new 

sources, section 112(d)(3) sets this “floor” for what is “achievable” 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 reflect 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 decisions on actual performance. Commenter (0374) stated that when 

the EPA ignores emissions that even best- performing sources experience during malfunctions, the 

EPA breaches its duty to set standards on the basis of real-world performance. Commenter (0374) 

stated that it fails to take into account how sources actually operate and 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 violate a standard supposed to be based on what it “achieve[s] in 

practice”); see also 76 FR 15628 (rejecting a comment as “inappropriate” because it “would result in 

emission limits that even the best performing sources would be expected to exceed”). Commenter 

(0374) stated that the EPA's position — that the statute requires it to set section 112-compliant 

emission standards that apply at all times, but that the EPA can meet this mandate by setting emission 

standards based on what is achieved and achievable only part of the time — simply makes no sense. 

Commenter (0374) stated that every court that has addressed the issue, both under the CAA section 111 

requirement that new source performance standards be based on the best demonstrated control 

technology and under the similar technology-based requirements of CAA section 112(d) and (h), has 

indicated that the EPA must take the effect of malfunctions 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 Recycling 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 the effect of malfunctions on what standards are achievable with 

available technology. See 79 FR 72950. Commenter (0374) stated that the statute directs the EPA to 

set standards based on what the available technology can do or, in the case of MACT floor standards, 

based on what the best performers are actually doing. Commenter (0374) stated that nothing in the 

statutory language or legislative history indicates that Congress intended the EPA to establish MACT 

standards that apply at all times, but that even best performers cannot meet during unavoidable 

malfunctions, and then have penalties potentially mitigated in an enforcement action. 

Commenter (0374) stated that the courts agree with this analysis, stating repeatedly that relying on 

enforcement discretion is no substitute for setting technology-based standards that reflect the 

performance of that technology during all reasonably anticipated conditions (such 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 discretion approach does not satisfy the purpose of 

CAA section 112 — reducing HAP emissions. Commenter (0374) stated that a post-hoc case-by-case 
70 

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 the affirmative defense), the starting point for the 

approach in the supplemental notice is the post-emission presumption 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 tools for accounting for malfunctions in the 

standards once the affirmative defense 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 emission standards and that doing so would result in 

standards that are too lenient. See 79 FR 72,949. Commenter (0374) stated that 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 set 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 rulemakings to set alternative emission 

standards that apply during startup and shutdown periods. Commenter (0374) stated that the EPA may 

well have sufficient data on emissions from primary aluminum plants and/or on the performance of 

processes and control equipment to set alternative emission standards that apply during malfunctions, at 

least during certain types of malfunctions whose effect on emissions may be predicted. Commenter 

(0374) stated that nothing in the EPA’s mandate to set emission standards that are achievable with 

available technology and, in the case of MACT floor standards, are actually achieved in practice by best 

performers allows the EPA to decline to even assess 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 level that would assure those limitations would not be exceeded 

even during malfunction events, as the EPA describes in its straw-man argument in the supplemental 

notice (see 79 FR 72949). Commenter (0374) stated that establishing alternative emission standards for 

malfunction events, whether numerical limitations or work practice standards, would (based on how the 

EPA defines “malfunctions”) by definition not allow excess emissions that could be avoided with proper 

design, operation, and maintenance of the facility. Commenter (0374) stated that it is not advocating an 

approach to standard setting that “could lead 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 defines “malfunction” in 40 CFR §63.2 not to include 

negligent operation, much less deliberate malfeasance, the EPA’s suggestion that accounting for 

malfunctions in standard-setting would excuse excess emissions associated 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 sections 
71 

112(h) and 302(k) to substitute a design, equipment, work practice, or operational standard for a 

numerical emission limitation. Commenter (0374) stated that the use of such “work practices” will in 

most cases be more practicable and more comprehensive 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 designed or operated to avoid malfunctions, it is eminently reasonable to 

address malfunctions through requirements that the source take all reasonably available measures to 

reduce the frequency, magnitude, and duration of the 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 that the 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 shown 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 standards in lieu of numerical emission limitations for numerous source 

categories that apply during startup or shutdown. Commenter (0374) stated that the EPA also often has 

recognized that conditions during startup 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 have specified that malfunctions 

are not representative conditions for 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 plants that apply even during malfunctions but that 

contain no affirmative defense or other provision addressing 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 associated 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 alternative standards. 

Comment: Commenter (0374) urged the EPA to withdraw its proposal, as reflected in the supplemental 

notice, to remove the affirmative defense provision of the Proposed Rule without evaluating the 

reasonableness of the Proposed Standards in light of 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 emissions during malfunction events, rather than setting 

standards that do not comply with CAA section 112 because they do not reflect the effect of process or 

equipment malfunctions on what emissions the identified technology can achieve at all times. 

Comment: Commenter (0373) supported the EPA’s removal 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 Comments 
72 

Response: In the 2012 proposed rule, the EPA proposed to include an affirmative defense to civil 

penalties for violations caused by malfunctions in an effort to create a system that incorporates some 

flexibility, recognizing that there is a tension, inherent in many types of air regulation, to ensure 

adequate compliance while simultaneously recognizing that 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 discretion 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. Costle, 590 F.2d 1011, 1057-58 (D.C. Cir. 1978) (holding 

that an informal case-by-case enforcement discretion approach 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 judicial or administrative proceeding that it had met the 

requirements of the affirmative defense in the regulation, civil penalties would not be assessed. After the 

2012 proposal, the United States Court of Appeals for the District of Columbia Circuit vacated an 

affirmative defense in one of the EPA’s section 112 regulations. NRDC v. EPA, 749 F.3d 1055 (D.C. 

Cir., 2014) (vacating affirmative defense provisions in section 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 exclusively 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 civil suit is a job for the courts, not EPA.”).19 In light of 

NRDC, the EPA in the 2014 supplemental proposal withdrew the proposed affirmative defense and is 

not including a regulatory affirmative defense provision in the final rule. As explained 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 enforcement action, the court has the discretion to consider any defense 

raised and determine whether penalties are appropriate. Cf. NRDC, 749 F. 3d at 1064 (arguments that 

violation were caused by unavoidable technology 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 defense and the EPA’s decision not to include the affirmative defense in the final rule, we are not responding 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 whether 

penalties 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 establish an affirmative defense to penalties that is 

available in administrative enforcement actions, the EPA is not including such an affirmative defense in the final rule. As 

explained above, such an affirmative defense is not necessary, and in the 2014 supplemental proposal we withdrew the proposed affirmative defense. Moreover, assessment of penalties for violations caused by malfunctions in administrative proceedings and judicial proceedings should be consistent. Cf. CAA section 113(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 proposed 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 that to satisfy section 112(d)(6) the EPA must recalculate the 

MACT floor and perform a beyond-the-floor analysis to determine what emissions reductions are being 

“achieved” and are now “achievable” under sections 112(d)(2) and (3), and assess emission reduction 

“developments” in current industry “practices, processes, and technologies” under section 112(d)(6) to 

ensure that it does not miss “achievable” emission reductions. The commenter asserts that the EPA did 

not perform these actions and did not recalculate the MACT floor to address greater emission reductions 

now achievable. The commenter believes that the EPA interpreted the term “developments” 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 must recalculate 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 standards promulgated under section 112(d)(2) & (3). Nothing in section 

112(d)(6) expressly or implicitly requires that the EPA recalculate the MACT floor as part of the section 

112(d)(6) review. This position has been upheld by the D.C. Circuit, repeatedly. NRDC v. EPA, 529 F.3d 

1077, 1084 (D.C. Cir. 2008). Notwithstanding this clear holding, the commenter 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, processes and control technologies for the 

primary aluminum reduction source category and evaluated costs of potentially more stringent standards 

reflecting any such developments. The EPA believes this review and the revisions finalized in this 

rulemaking satisfy the EPA’s obligations under CAA 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, including POM from prebake potlines, COS from potlines 

and POM from existing storage tanks. However, the 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 been 
74 

“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 unregulated emissions has been increased to the extent 

possible. New data were collected for PM, HAP metals, POM, D/F, PCB, and speciated organics. 

MACT floors, emission limits, and the RTR analysis were 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 MACT technical memoranda, which are 

available in the docket) adequately demonstrates what has been and is achievable. 

Comment: One commenter (0163) states that the EPA is not authorized by CAA sections 112(d)(2) or 

(d)(3) to fill “gaps” in existing MACT standards. The commenter asserts that the EPA does not have 

unfettered discretion to revisit a prior MACT determination once that determination has been issued. 

Rather, the commenter states, the EPA may revise a prior 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] because “for EPA to avoid a literal interpretation at 

Chevron step one, it must show either that, as a matter of historical fact, Congress did not mean what it 

appears to have said, or that, as a matter of logic and statutory structure, it almost surely could not have 

meant it,” Engine Mfrs. Ass’n v. EPA, 88 F.3d 1075, 1089 (D.C. Cir. 1996), showings the EPA has failed 

to make. 

The commenter notes that in the proposal, the EPA explains that “pursuant to CAA sections 112(d)(2) 

and 112(d)(3)” it is proposing MACT standards for POM emissions not specifically currently regulated 

by the NESHAP for primary aluminum reduction plants. 76 FR at 76267. The commenter points to this 

statement to show that the EPA is not invoking section 112(d)(6) as the authority for the new proposed 

standards, as the preamble provides no analysis of “developments in practices, processes, and control 

technologies” to justify the proposed standards, 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 invoking 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) provides the only authority for the Agency to later 

review and possibly revise the determination, which forecloses the Agency’s ability to directly invoke 

sections 112(d)(2) and (3) for a given source category 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 improper MACT determinations, including amendments to 

improperly promulgated floor determinations, using its authority under section 112(d)(2) and (3). (The 

lack of a remand on these issues here is a distinction without a difference.) The 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-compliance data, is permissible when originallyestablished floor was improperly established, and permissibility of the EPA’s action does not turn on 
75 

whether the prior standard was remanded or vacated). The D.C. Circuit’s December 9, 2011 decision in 

Portland Cement Ass’n v. EPA, 665 F. 3d 177, 189) confirms 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 initially, it is not amending a MACT standard but 

adopting one for the first time. That is the case here for POM from prebake potlines and COS and PM 

from all potlines. In the case of primary aluminum 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 identified 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 the 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 sources not only deploy the appropriate 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 monitoring parameters during 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 operating during the performance tests. A source’s emission levels with a 

particular process configuration and control device may not be “largely within their control” beyond the 

necessity to maintain the equipment and monitor parameters to ensure a continuing level of control. 

Given that there is inherent variability associated with EPA Reference Test Methods, if the MACT floor 

level of control were established with no allowance for 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 performance test that established the 

MACT floor. 

The EPA must exercise its judgment, based on an evaluation of the relevant factors and available data, to 

determine the level of emissions control that has been achieved by the best performing sources under 

variable conditions. It is recognized in the case law that the EPA may consider variability in estimating 

the degree of emissions reduction achieved by best-performing 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 performance achieved by best-performing sources and 

may set the floor at a level that a best-performing 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 that (citing dicta in a D.C. Circuit decision) industry groups 

have argued that the EPA must set weak standards to accommodate sources’ worst reasonably 

foreseeable performance. The commenter argues that those dicta have no precedential value, and do not 
76 

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 achieves in practice, that source may emit far higher 

levels if it is not run properly. The commenter states that the high emissions that occur when a source is 

poorly operated must be treated as exceedances or violations 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 should 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 frustrates its intent. The commenter argues that, rather, 

floors must be set at the average emission level achieved by the best performers when they are operating 

properly – i.e., in the way that identified them as the best performers. The commenter states that using 

an “upper prediction limit” to set standards reflecting the worst performance these sources could have in 

a purely statistical sense does not yield an accurate picture of the best sources’ actual performance, and it 

is especially arbitrary in the absence of any explanation of why the EPA thinks that the relevant best 

sources’ performance would ever be so bad, other than the fact that it is statistically possible. 

Response: The MACT floor limits were developed by incorporating variability, as has been done in 

other MACT standards. In determining the MACT floor 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 existing 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 designed to estimate a MACT floor level based on the average of the best 

performing sources using the expected distribution of future compliance tests. We used the UPL because 

for a future observation, the UPL will, with a specified degree of confidence, contain the next (or some 

other pre-specified) randomly selected observation from a population. 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 sampling 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 the previous comment above. 

Comment: One commenter (0166) states that the EPA must set a standard to limit all HAP emissions, 

including naphthalene and the HAPs listed 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 the 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 a 
77 

reasonable surrogate for HF, and disagrees 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 aluminum reduction plants and are measured during 

performance tests (as methylene chloride extractable material - MCEM). 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 transformation between these forms. As an alternative 

to attempting to account for inaccuracy in measurement 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) and (3) emission limits established to achieve good 

control of TF will also achieve good control of HF (good capture of particulate is associated with good 

capture of HF - in the primary control system good control of HF is achieved through 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 evidence 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 modeling shows that the level 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 under section 112(d)(6) this 

information should lead the EPA to revise the existing 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 aluminum reduction plants. The revised potline POM 

emissions limits being promulgated reflect a recognition 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, which is available in the docket, the MACT floor 

emissions limits promulgated today for HAP emissions (e.g., POM and PM) from prebake potlines, 

anode bake furnaces and paste production plants reflect the achieved level of “actual” HAP emissions of 

the best performing sources. The POM limit promulgated today for Soderberg facilities, under section 

112(f) of the CAA, is three times lower than the limit in the 1997 NESHAP. Based on our analyses, this 

limit is lower than the level “achieved” by those sources and reflects the assumption that if any 
78 

Soderberg potline ever reopened in the U.S., it would need to install roof top wet scrubbers to comply 

with the revised POM limit for Soderberg 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 rule 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 believed 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 Falls. In spite of this information, the EPA is promulgating POM, As 

and Ni emission limits for existing VSS2 potlines to ensure 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) and (3), the EPA is additionally promulgating MACT limits for emissions 

of POM from new and existing prebake potlines and existing pitch storage 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 proposal. 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 that the section 112(d)(6) text plainly requires that the EPA 

review and revise as necessary the existing section 112(d)(2) MACT standards, and it also explicitly 

requires that the EPA take account of new technological or industrial developments. The commenter 

argues that to give meaning to the phrase “as necessary” as it is used in section 112(d)(6), it must be read 

in the context of the rest of section 112(d). The commenter observes that section 112(d)(2) by its plain 

language applies to “emission standards promulgated under 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 essential thrust of section 112(d)(2) is to require 

technology-based standards that reflect the maximum achievable degree of emission reduction. 

The commenter continues that all national emission standards for hazardous air pollutants must satisfy 

the requirements of sections 112(d)(2) and (3), both when set initially 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 112(d)(6), rather, the substantive 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 interpretation. 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 technology-in other words, to start from scratch. We do not think the 

words ’review, and revise as necessary’ can be construed reasonably as imposing any such obligation.”). 

We thus disagree with the assertion that the HON Court’s ruling that CAA section 112(d)(6) does not 
79 

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 EPA to consider costs and risks in 

conducting CAA section 112(d)(6) reviews, as the issue was rendered moot by the litigants’ failure to 

preserve it. As noted above, the commenter’s argument has been twice more rejected by the D.C. 

Circuit. 

Comment: One commenter (0166) asserts that a revision of the existing standard is necessary under 

section 112(d)(6) if the prior standard was not established in a manner that complies with the 

requirements of the CAA. The commenter states that since the adoption of the primary aluminum 

reduction plants MACT, the D.C. Circuit has specifically 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 evaluation of control technology performance rather than 

plant performance; (3) adopting “no control” MACT limits where active pollution controls were not in 

use in a subcategory; (4) employing regulatory limits where actual performance data are available; (5) 

rejecting MACT floor technologies and limits based on cost or feasibility; and (6) rejecting the use of a 

surrogate where not supported. (The commenter provides citations of court cases.) Further, the 

commenter notes, the EPA has recognized 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 distinguishable from the facts in NRDC v. EPA, 529 

F.3d 1077, 1084 (D.C. Cir. 2008), in which the court explained that recalculating the floors was not 

necessary because “petitioners have not identified any post-1994 technological innovations that EPA has 

overlooked.” In the case of the proposed rule here, the commenter asserts, there have been developments 

in practices, processes, and 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 showing that greater emission reductions have been 

“actually achieved.” The commenter states that based on the information the EPA has in the record, it is 

“necessary” for the EPA to strengthen the existing MACT floor and to appropriately set a beyond-thefloor standard to ensure that the MACT standards for primary aluminum reduction plants comply with 

sections 112(d)(2), (3) and (6). The commenter observes that if the EPA were not required at the very 

least to address and update the standard when significant improvements are made in practice, consistent 

with the overall purpose and requirements of sections 112(d)(2) and (3), it would be unclear what the 

standard of review actually is for an action taken under section 112(d)(6). The commenter claims that 

the court’s job is to determine whether the Administrator 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 decide whether, just as section 112(d)(6) requires the 

EPA to satisfy section 112(d)(2), the Administrator has made a decision consistent with section 

112(d)(3), which gives definition to section 112(d)(2). 

The commenter states that the EPA interprets the term “developments” too narrowly, and that the EPA 

needs to consider an increase in acceptance and utilization of a technology or process within a category 

as a “development” warranting consideration during a review. The commenter asserts that the EPA is 
80 

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 justification 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 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 EPA to consider costs and risks in 

conduction CAA section 112(d)(6) reviews, as the issue 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 the obligation to recalculate MACT floors. Further, 

the commenter has not identified any applicable technological innovations that the EPA has overlooked. 

Comment: One commenter (0166) states that the EPA’s eight-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, processes, and technologies that are achieving HAP 

emission levels well below the existing and proposed standards and that the EPA look to jurisdictions 

with the most stringent standards for HAP emissions to gather data from facilities and information about 

control systems that are attaining the highest control efficiencies. The 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 commenter notes that the EPA has not provided a review 

of other air permits to see whether any other facilities are also meeting 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 condensers and activated 

carbon adsorbers would reduce emissions, yet the EPA failed to consider requiring emission 

reductions based on the use of these devices, which 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 possible 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., the availability of suitable low sulfur 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 the standards for new potlines promulgated in the final rule. 

Comment: One commenter (0166) asserts that the EPA’s section 112(f) analysis 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 options 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 the EPA’s consideration in this rulemaking (attached 

to comment letter - see Nat’l Park Service Comments 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 regarding regional haze plan”). 

Response: The letter from the National Parks Service to Stuart Clark referred to scrubbing technologies 

to control SO2 emissions. The commenter provided no data regarding the efficiency of this process to 

control of HAP. Further, wet scrubbers were considered as beyond-the-floor control options for 

secondary emissions from potlines and determined not to be cost effective (see 76 FR at 76274). 

Comment: Commenter (0373) supported the EPA’s recognition of the need to propose and finalize 

standards for HAPs and emissions points that are currently 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 prebake 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 arbitrary and capricious for the EPA not to 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 inappropriately 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 existing 
82 

potline subcategory) that different configurations generate inherently different emissions profiles, 

but does not apply this methodology to the new 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 propose. 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 CWPB1 category (1.1 lbs POM/ton Al). Commenters 

stated that the proposed new source performance standard ensures that no single new facility could 

ever be constructed absent costly add-on emission control systems (i.e. wet roof scrubbers) that the 

EPA has already found in the supplemental rule analysis to not be cost-effective. Commenters stated 

that this essentially guarantees that no new primary 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 protective 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. Commenters 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 the commenters believe is the most likely to be 

constructed in the US if such new construction were 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, that 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 the Primary Aluminum Production Source Category” 

(EPA-HQ-OAR-2011-0797) for more detail. 

Based on data provided by industry, Alumax - Mt. Holly (CWPB1) is the best performing source for PM 

based on the average emissions of three test runs. However, 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 discretion 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 data and 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, four CWPB1 facilities are 

already in compliance with the new source standard. As such, the EPA believes that newly constructed 

sources can meet these limits. 

3.4.2 POM Requirements 
83 

Comment: One commenter (0162) asks that the EPA re-evaluate the proposed POM emission limits for 

the SWPB and CWPB1 subcategories. The commenter expresses concern that the underlying technical 

assumptions used by the EPA to predict current POM emissions for existing prebake potlines, and to 

develop the proposed POM emission limits for existing 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 emissions 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 data or technical basis 

to demonstrate that the ratio of POM emissions to TF emissions is the same for different potlines or pot 

types (e.g. CWPB1 and SWPB), or to expect this ratio to be a constant. The commenter observes that the 

primary source of POM emitted from a potroom is the consumption of anode material while fluoride 

emissions can come from numerous sources, some tied to production and others tied to pot design and 

operating practices. The commenter concludes that the 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 data were received for prebake potlines and as a result, new MACT 

floors and emission limits were established for prebake potlines. As such, the comment above no longer 

applies to the current data set.

Comment: One commenter (0162) states that Equation 3 in the proposed rule is based on an assumption 

that the ratio of concentration of POM to TF in secondary roof emissions is that same as the ratio of 

concentration of POM to TF at the primary control device exit (Cpp1/CpF1). The commenter observes 

that the POM to TF concentration ratio changes substantially across the control device, and when 

performance of the TF control device is optimized, the ratio Cpp1/CpF1 (and, therefore, 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 data were received for prebake potlines. Based on this new data, the 

EPA is finalizing POM emission standards for prebake potlines and requiring annual and semi-annual 

POM testing for the primary and secondary potline emission sources, respectively. Equation 3 has been 

revised to remove the provisions regarding the ratio of TF to POM. 

Comment: One commenter (0162) states that actual data on POM emissions 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 preliminary POM tests completed on the only existing SWPB 

facility (i.e., the Intalco Aluminum Corporation facility in Ferndale, WA) demonstrate that the proposed 

POM emission limit for this category is not achievable, with measured emissions from limited testing of 
84 

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 some 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 opposed 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 notes that POM contribution from secondary emissions could not be 

measured as this facility uses Method 14A cassettes for secondary emissions sampling.) The commenter 

plans to provide further comment to the EPA on achievability of the proposed prebake POM emission 

limits when sufficient test data become available. 

The commenter expresses concern that POM standards may not be achievable for each of the prebake 

subcategories because the commenter is not aware of cost-effective measures 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 the 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 data were received for prebake potlines and as a result, new MACT 

floors and emission limits were established for prebake 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. facility 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 emissions). Additional performance test data 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 data were received for prebake potlines and as a result, new MACT 

floors and emission limits were established for prebake 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) provides a viable alternative for aluminum production facilities that have 

installed Method 14A cassette sampling systems to determine total fluoride emissions. 
85 

The commenter observes that at least 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. The 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 commenter states that the installation of Method 14 

sampling manifolds at these existing 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 proposed 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 cassette-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 Method 14A cassette method. Commenters stated that 

facilities with Method 14 downcomers installed need to be able to use their Method 14 downcomers 

for the collection of PM, POM and metal HAP samples. Commenters stated that any facility that uses a 

Method 14 downcomer to sample is not able to use the manifold for Method 315 sampling and would 

therefore also be required to install Method 14A cassettes to be able to sample for Method 315. 

Commenters stated that they believe that it was not the intent of the proposed regulatory language to 

require both systems. Commenters 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 the intent of the supplemental proposal was to 

allow the use of the Method 14 (manifold/downcomer) or Method 14A (cassette method) to demonstrate 

POM compliance. We have modified the final text to clarify that both methods are allowed. 

Comment: One commenter (0165) agrees with the EPA’s proposal to address emissions of POM from 

Soderberg potlines and from other previously unregulated 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 additional 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 increasing the flow rate through the dry alumina 

scrubber; and 
86 

 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 not 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. Further, the design and operation of the 

dry alumina scrubber is integral to the operation of the associated 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 control 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 devices 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 the 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 revise 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 more broadly to include anode 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 accordance with the commenter’s suggestion in the 

final amendments. 

Comment: One commenter (0162) agrees with the EPA’s decision to reject beyond-the-floor options for 

COS based on the substantial potential cost impacts. The commenter has significant 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 clarification of the facility site-wide COS limit for facilities 

that have both new and existing potlines. The commenter explains that all anodes made at an aluminum 

production facility are produced in a single paste plant and anode bake furnace, and it would typically 
87 

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 requests that the final rule allow calculation of a 

production-weighted average COS limit for facilities that 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: 

	ா಴ೀೄୀ

ቀଷ.ଽ	௟௕	஼ைௌ

்஺௉ ቁ	ൈ	൫௓ಶೣ೔ೞ೟೔೙೒൯	ା	ቀଷ.ଵ	௟௕	஼ைௌ

்஺௉ ቁ	ൈ	ሺ௓ಿ೐ೢሻ

௓ಶೣ೔ೞ೟೔೙೒	ା	௓ಿ೐ೢ

Where: ECOS = The facility-wide production weighted COS 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; 

ZExisting = The tons of aluminum produced at the facility in existing potlines during the calendar 

month; 

ଷ.ଵ	௟௕	஼ைௌ

்஺௉ = The proposed COS emission limit for new potlines; and 

ZNew = The tons of aluminum produced at the facility in new potlines during the calendar 

month. 

Response: The proposed amendments to the primary aluminum NESHAP include MACT floor level 

standards for COS emissions from potlines. The proposed 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 that permits emissions averaging between existing sources and new 

sources, which is not permitted. The EPA believes that the 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) either in a separate dedicated paste plant 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 emissions of COS from 

previously unregulated emission points. 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 that the 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 reflects the fact that only 

anode material actually consumed in the potline has the potential to release COS emissions. 

Response: The EPA acknowledges the commenter’s support for the revision to the revised parameter 
88 

“Y” in §63.847(j). 

3.4.4 PM Requirements 

a. Anode Bake Furnace 

Comment: 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 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 anode bake furnaces (ABFs), respectively. 

Commenter (0371) stated that the PM emissions data 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 EPA 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 are 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 incorporated and both the new and existing PM standards for 

anode bake furnaces have been re-calculated. The EPA 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 for 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 further simplify compliance demonstration. 

Response: In this final action, the EPA is setting existing and new source standards for COS, POM, and 

PM. For the purpose of compliance with these final standards, the EPA is amending the final rule to 

specify what constitutes a new source. Based on these new source dates, all currently constructed anode 

bake furnaces will be considered existing sources for compliance with the PM standards established in 

this rule making. As such, the EPA does not believe that an alternative 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 the definition of Pb in equation 3 

utilized for the calculation of paste plant PM emissions. Commenters stated that the proposed 

definition of Pb is “quantity of green anode material placed in the anode bake furnace, mg/hr 

(ton/hr)”. Commenters stated that this is an inappropriate value to use in calculating the denominator 

of Equation 3 as there is not a correlation 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 material placed in the anode 

bake furnace. 
89 

Commenters stated that operation of the paste plant necessarily involves some amount of green 

anodes produced that are scrapped as unusable prior to baking, placed in inventory for future baking, 

etc. Commenters stated that the scenario may exist 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 Pb value would be zero and 

thus result in an indivisible equation. 

Commenter (0372) requested that the definition of Pb 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 from the paste production plant”. Commenter (0375) 

stated that this change will require adding a definition 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 that which is produced from the paste 

production plant. We do not believe that it is necessary to prescribe a specific method for determining 

the rate of green anode produced during a testing event. It is the responsibility of the facility conducting 

the test event to accurately determine and report Pb. 

3.4.5 UPL Methodology 

Comment: Commenter (0373) stated that when setting standards, the EPA must follow the Act’s 

requirements to assure that such standards are at least as stringent as the emission limitation achieved by 

the best-performing sources, under § 7412(d)(3), and that the EPA assures the maximum achievable 

degree of emission reduction, as required by § 7412(d)(2). Commenter (0373) stated that instead of 

following the Act’s requirements, the EPA has proposed 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. Circuit 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 unlawful, arbitrary, and capricious. 
90 

Commenter (0373) stated that the D.C. Circuit in 2013 addressed the agency’s upper prediction 

approach in the context of another air toxics rule that the EPA had issued for sewage sludge 

incinerators under the virtually identical floor language of Clean Air Act § 7429(a)(2). Commenter 

(0373) stated that the Court found that the EPA seemed to have interpreted “‘average emissions 

limitation achieved by the best performing 12 percent’ . . . [to] refer to the future average of a 3-run 

test that EPA predicts a source in the best-performing 12 percent will fall below with 99 percent 

confidence.” Commenter (0373) stated that the court 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, one sentence in the Federal Register is not 

enough of a basis to uphold the EPA’s new approach to incorporating variability against 

arbitrary and capricious review. Accordingly, on remand, we expect the EPA to clarify how 

the upper prediction limit represents the “average 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 EPA predicted a “higher MACT floor 

for an incinerator with raw test data ranging from 0.31 to 2.26 than for a group of incinerators 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 underlying principles or reasons why its formulas would 

produce an accurate result, particularly when the ‘facts found’ – the MACT floor datasets – demonstrate 

flaws in the formula.” 

Commenter (0373) stated that in this rulemaking, the EPA may not evade the requirement to follow the 

plain text of § 7412(d)(3) to set standards based on the “average emission limitation achieved.” 

Commenter (0373) stated that Clean Air Act § 7412(d)(3) requires that floors reflect the “average” 

emission level “achieved in practice” by the best-performing 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 failed to provide the necessary factual support to use 

the approach it chooses even if it could be considered to meet the statutory test. 

Commenter (0373) stated that although § 7412(d)(3) unambiguously requires floors to reflect the 

“average” emission level actually “achieved” by the best-performing 12 percent of units, the EPA 

proposes to use a floor in this rule based on the upper prediction limit, not based on the “average 

emission limitation” achieved. Commenter (0373) stated that as the EPA itself 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 it is the level that a 

source or sources “would be expected to meet a specified percent of the time that the source is 

operating” based on the EPA’s calculation of hypothetically higher emissions at some (unmeasured) 

times. Commenter (0373) stated that it is neither the required “average” nor even any measure of what 

units have actually “achieved.” 

Commenter (0373) stated that the EPA’s claim that it has discretion to set standards using a UPL is 
91 

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 not exist, nor ignore the use 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 just because it uses an “average of the short- term 

emissions test data” at some step of its calculation, does not make the UPL an accurate reflection of the 

“average emission limitation” actually achieved. Commenter (0373) stated 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 not reflect 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 limitation achieved’” by the relevant 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 EPA 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 emission limitation” that they have achieved. 

Commenter (0373) highlighted several 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 selects a confidence level for calculating the UPL to reasonably 

assure that the limit calculated can be met at all 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 would be predicted to meet during 99 out of 100 

performance tests. Commenter (0373) stated that the use of this confidence level reflects the 

failure of the UPL to calculate the average of the best performing 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) stated that it is not based on actual performance, but on 

hypothetically much higher emission levels that the EPA has made up and that are unsupported 

by the data before the EPA in the record. Commenter (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 UPL as a method for accounting for variability is 

just as likely to create a weaker standard due to sources operating improperly as it is to account 

for any other causes of variability. Commenter (0373) stated that the EPA does not explain how 
92 

this use will avoid that problem, and thus its use is unlawful and arbitrary. Commenter (0373) 

stated that the EPA may not lawfully account for malfunctions in setting standards, and thus it 

may not use a method for accounting for variability that builds in potential malfunction-caused 

higher emissions as a potential driver of the floor. Commenter (0373) stated that the record 

demonstrates that the floors the EPA is proposing, 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 standards or otherwise allow sources to get away 

with emission exceedances resulting from malfunctions, which is counter to the Act. 

 Commenter (0373) stated that the proposed floors 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 emissions limitations achieved. 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 these floors reflects the “average 

emission limitation” achieved – and many are over 2 times higher. Commenter (0373) stated 

that the EPA’s approach turns the statute on its head. Commenter (0373) stated that the EPA 

may not call something an average when it is two 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 performing 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 “for which 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) stated 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 range 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 use emissions information it has (or could reasonably obtain). 

Commenter (0373) stated that recognizing that the EPA may do some calculations and 

modeling to evaluate the data it has, it cannot justify distorting the emission data as far as 

its UPL approach does: to make the emission inventory look dramatically 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 provide no valid justification for discounting the 

actual test and emission data that it has. Commenter (0373) stated that these are the “facts 

found” that the EPA may not lawfully or rationally distort or ignore. 
93 

Commenter (0373) stated that the EPA has failed to justify its use of its proposed mathematical 

calculations based on the science, record, or the clear text 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 terms and concepts that cannot be reconciled with the UPL approach, 

which adds uncertainty and unreliability, and falls far from the achieved average. Commenter (0373) 

stated that by using a floor higher than the average emissions actually achieved by the best performing 

units, the EPA fails to meet the Act’s requirements and fails to propose the legally required, necessary, 

and appropriate protection for communities living near Primary Aluminum Reduction Plants. 

Commenter (0373) stated that by using the UPL, the EPA is increasing the limit above the average of 

what data in the record show is actually achieved. Commenter (0373) stated that as a result, the emission 

limits the EPA proposes to set are higher and weaker than the statute directs and 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 “achieved” beyond its meaning. Commenter (0373) stated that if the EPA 

believes test data it is using 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) stated that in essence, the EPA 

makes up new math to try to reach the result it prefers 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 higher emission limits that increase the amount of 

pollution allowed to go into the air and harm the health of neighboring communities. Commenter 

(0373) stated that this proposal also runs directly contrary to the text and Congressional intent of the § 

7412(d)(2)-(3) and (d)(6) provisions, which were designed to ensure minimum levels of protection for 

communities from hazardous air pollution, based on pollution control achievements, 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 sources 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 explained in more detail below. For a single best 

controlled emission source that serves as the basis for a new source MACT floor, the 99 percent UPL 

is the emissions level that the source would be predicted to be below during 99 out of 100 performance 

tests, including emissions tests conducted in the past, present, and future, based on the short term stack 

test data available for that source. It is important to note that the UPL does not represent the worst 

emissions performance of the best performing units at any time, but rather the average level expected 

to have been achieved over time, as the first element 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 dataset (in the case of MACT standards, the dataset 

representing the performance of the best performers as specified in the CAA) over a long-term period 

based on its previous, measured performance history as reflected in short-term 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 explanation from the Agency. The UPL memorandum provides 

the explanation of what the UPL represents sought 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 limitation achieved by the best performing 12 percent” 

must be equal to the mean of the available data, as suggested by the commenter, and in past decisions 

the court has upheld that it is appropriate for the EPA to account for variability when establishing 

numeric MACT standards. See Mossville Environmental Action Now v. EPA, 370 F.3d 1232, 1241-42 

(D.C. Cir. 2004). 

We also refer the commenter to the “Approach for 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 the rulemaking docket. This memorandum provides a detailed 

discussion of the EPA’s authority to consider variability, especially given that MACT and other 

technology-based standards are necessarily derived from short term emissions test data and such data are 

not representative of the range of operating conditions that the best-performing 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 long 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 variability 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 address 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) floor requirements. Commenter (0373) 

stated that the EPA’s cursory statement 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 pollutant(s) must invariably be present in the surrogate; (2) the control 

technology used to control the surrogate must indiscriminately capture both the surrogate and the target 

pollutant(s); and (3) control of the surrogate must be “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) stated that the EPA has not shown that it has met the 

surrogacy test and thus has not shown that controlling 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 some 
95 

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 otherwise 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) stated that the EPA has not shown and cannot show 

that the UPL has any relationship at all 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 filters and scrubbers) achieve broad spectrum 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 standards for Iron and Steel Foundries (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 control PM.’ Foundry metal HAP emissions, particularly 

those associated with melting processes, include PM emissions in the exhaust stream. Thus, the use of 

control devices (e.g., fabric filters and wet scrubbers) to reduce metal HAP emissions to comply with 

the Foundry MACT will also result in the control of PM. 

The commenter’s argument that the EPA is legally 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 MACT floors. This argument has been rejected, as 

noted above. Best performing sources do not perform day-in, day-out at one constant 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 metals 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 HAP metals are present as a component 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 commenter states that the proposed method (i.e., ASTM 

Method D-3177-02) is not the predominant method used for 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 sulfur analysis. The commenter requests that the rule 

either incorporate ASTM Method D6376-06 as an alternative method for coke sulfur analysis, or include 

it as the required method in lieu of ASTM Method D-3177-02. 

Response: The final rule has been revised to allow for the use of either ASTM D4239-14 or ASTM 

D6376-10 method. 
96 

Comment: One commenter (0162) asks that the EPA revise the proposed rule 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 would reduce the overall cost of POM compliance testing by a factor of 

two or three, and may help resolve the secondary POM sampling issue 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 Method 14A already have a Method 14 manifold in one 

of their potlines to allow sampling 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 represent 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 emissions from a representative new 

prebake potline to represent emissions of all new 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. 

Comment: One commenter (0166) states that the EPA must require periodic monitoring that will 

demonstrate to the EPA, states and the public whether or not the facilities are in compliance. The 

commenter suggests that the EPA require performance tests every year instead of every 5 years. 

Response: We have finalized new performance test requirements for all numerical MACT standards. 

Primary emissions from all potlines for all MACT standards 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 standards will be required to test annually. 

Comment: One commenter (0166) states that the EPA must require continuous monitoring of emissions 

from this source category. The commenter recommends that the EPA should require the use of CEMS 

technology for HF, particularly due to the issue with alleged high startup emissions, and should require 

immediate reporting on the Internet of all monitoring reports. 

Response: HF CEMS are not in common use, and it is not 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 malfunctions or any other emission exceedances. The commenter states 

that the proposed malfunction reporting is not adequate and proposes telephone reporting by the facility 

no later than 24 hours after the malfunction or exceedance. The commenter further proposes that when a 

facility provides the EPA with telephone notification of a malfunction or emission exceedance under the 

regulations, this notice be made publicly available 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 provide this information to the Regional Office within 24 hours of 
97 

receiving notification, and direct the Regional Office to notify the local community on the Internet, by 

direct communication, and through all available means, by the next day. 

The commenter further states that the EPA must promulgate the requirement that when such notification 

is made, the facility must also provide for community notification of the malfunction or emission 

standard exceedance within 24 hours, through an appropriate public forum that is 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 local municipality and local school district, a press release to the local 

newspaper, radio and TV news station that contains any information community members may need to 

try to protect themselves and their families from the additional air pollution. 

The commenter also recommends that the EPA should also require a written report to be submitted 

within 7 days, and use the same distribution method as outlined above, including publication on ECHO, 

the EPA’s Regional Office websites, and sending this to active local community members who are 

interested (such as through setting up an email list, a local listserv, Twitter, and other media). In the 

written report, the commenter states, the EPA should require the facility to include: (1) the nature of the 

event; (2) the duration of the event; (3) estimate of emissions released 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 established 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 114. Further, the General Provisions specify that 

submittal of a report to a State that has been delegated 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 provides no justification and 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 needed, 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 use cost as a basis for creating a loophole in the 

standard. The commenter further argues that the EPA cannot justify the use of emissions averaging under 

section 112(d), because that provision requires the EPA to set and ensure compliance with emission 

standards that meet the requirements of sections 112(d)(2) and (3). 

Response: The final rule includes an emissions averaging 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 importantly, will achieve no less 

emissions reductions than unit by unit implementation of the MACT requirements. 

In general, the EPA has concluded that it is permissible to establish within a NESHAP a unified 
98 

compliance regimen that permits averaging across affected units subject to the standard under certain 

conditions. Averaging across affected units is permitted 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 mechanism than it would be if each 

individual affected unit complied separately with the applicable standard. Under this rigorous test, the 

practical outcome of averaging is equivalent in every respect to compliance 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 emissions 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 included 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 limits 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 that decreasing the frequency to three times each semiannual 

period would not provide a practical means of demonstrating continuous compliance with the emission 

standards for total fluorides (TF), polycyclic organic matter (POM), and particulate matter (PM) from 

roof vents. Commenter (0370) stated that a reduced testing frequency may allow unidentified problems 

to persist for significant periods of time before discovery and result in substantial exceedances of the 

standards. Commenter (0370) stated that within the past 4 years in Kentucky, exceedances of 40 CFR 

63, Subpart LL standards revealed at the current testing frequency resulted in identification and quick 

correction of substantial issues causing the excess emissions. Commenter (0370) stated that the issues 

included sick pots, fan failures, storage 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 States. As such, the commenter’s statement regarding 

decreased testing frequency for POM and PM from roof vents is without basis and requires no further 

response. 

Based on the consistency of previous test results and considering the potline work practices included in 

the final rule, the EPA believes that a reduced testing frequency for TF is appropriate and would be 

adequate in determining compliance with the secondary TF emission limits. Commenter (0370) pointed 

out that decreasing the testing frequency would not provide a practical means of demonstrating 
99 

compliance. The commenter stated that the current testing frequency aided in the identification and 

quick correction of substantial issues causing excess 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 implemented to correct the issues. 

 Whether or not the issues leading to the exceedance 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 these issues. Based on the TF data 

received as part of the information request, it appears that the majority of facilities that we have data for 

are sampling monthly because they exceed the thresholds 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 position that a reduced testing frequency for TF from roof vents is 

appropriate. The EPA is promulgating the final secondary TF potline testing at three times each semiannual period. 

Comment: Commenter (0372) raised several issues related to §63.848(a) and (b). Commenter (0372) 

stated that they believe the appropriate testing frequency to include in the final rule for secondary 

potline TF is semi-annual. Commenter (0372) stated that the sampling frequencies for secondary POM 

and PM emissions should be set annually to align 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 that particularly 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 indicates 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 implementation of many of the work practices proposed in §63.854 have 

the effect of minimizing secondary PM emissions, which based on member company experience are not 

as variable as secondary 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 the EPA under the 2013 ICR request 

was between 2.5 and 4 hours to complete a run (minimum volume of 3 dscm per run). Commenters 

stated the duration of a test run has a direct impact on the accuracy 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 runs 
100 

that were used to establish the emission limits. Commenters 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 conditions and operations to ensure that that a sufficient amount of sample is collected. 

Commenters stated that since the regulatory authority has to approve the test plan, there is no added 

benefit for specifying a test run duration in the regulation. Commenters 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 duration 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 control system, and semiannual 

performance tests on the secondary TF emissions, and annual performance tests on the 

secondary PM emissions....The owner or operator 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 owner or operator must compute 

and record the semiannual average from at least three runs per year for secondary emissions and 

at least three runs per year for the primary control systems to determine compliance with the 

applicable emission limit. The owner 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-specific 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 three runs from the roof 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 determine 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 annual testing) and the words “per 

year” need to be deleted. 

Commenter (0371) requested that secondary 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 testing (primary and secondary) be required once per 

year so that all testing can be conducted simultaneously for each pollutant at the required sources. 

Response: Commenters have not provided sufficient emissions data for secondary POM and PM from 
101 

prebake potlines to support their position that annual testing would be adequate to demonstrate 

compliance with the standard. The EPA retains its original position that semi-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 plan. However, the proposed language makes allowance for 

reduced sample duration, subject to approval of the regulatory authority and the EPA does not believe 

the suggested modification is necessary. 

The EPA will amend §63.848(b) to remove the per year reference related to the semi-annual average as 

follows: “The owner or operator must compute and record the average from at least three runs per semiannual period for secondary emissions and at least three 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) stated that the POM results obtained for the CWPB1 and CWPB3 

subcategories were similar to those initially estimated. Commenter (0375) stated that the one CWPB2 

facility is currently shut down and there is only one SWPB facility. Commenter (0375) stated that the 

EPA should consider separate POM testing frequencies based on potline subcategories that takes into 

consideration the approximate order of magnitude difference in POM emissions from different potline 

subcategories. 

Commenter (0375) stated that alternatively, the EPA should consider a reduced testing option that 

would allow facilities to change the secondary emissions testing frequency 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 testing of the secondary emissions. 

Response: As stated previously, commenters have not provided sufficient emissions data for POM 

from prebake potlines to justify consideration of separate POM testing frequencies for the individual 

sub-categories. The EPA retains its original position requiring semi-annual testing of POM for 

secondary roof vent emissions and annual testing of POM from the prebake potline primary emission 

control device. 

The EPA does not have sufficient data to establish 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 current rule under §63.847(c) allows for the use of results from 

performance tests conducted 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. Commenters 
102 

stated that this provision was available in 1999 for the performance testing done to determine initial 

compliance with TF and POM emission limits. Commenters stated that the EPA should provide 

facilities with this same flexibility to schedule and conduct performance tests in advance of the initial 

compliance date to determine initial compliance with POM emission limits for prebake potlines and 

existing pitch storage tank controls (where applicable), and PM emission limits for potlines, anode 

bake furnaces, and paste production plants. 

Commenters stated that the EPA’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 down at the time compliance 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 anode bake cycle (but no later than 

the 180 day from the startup of the anode bake furnace).” Commenters stated that the current 

proposed rule deletes the performance test date for anode bake furnaces and instead requires the initial 

anode bake furnace performance test to be conducted “[d]uring 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 that the initial annual performance test on a new anode 

bake furnace is conducted after the furnace achieves normal operation. Commenters stated that, as 

noted in the final preamble to these amendments, furnace 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 typically performed with baked or 

partially-baked anodes. Commenters stated that conditions during this period will likely produce POM 

emissions that are lower than normal at the control device inlet, and clearly do not represent normal 

operation. Commenters stated that similar conditions exist during the startup of an existing anode bake 

furnace that was shut down for more than one year. Commenters 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 applicable MACT emission limits. 

Commenters stated that the proposed rule establishes additional performance testing requirements 

for new or reconstructed and existing paste production plants and, as an option, for existing pitch 

storage tanks. Commenters stated that the proposed rule appears to inadvertently have removed 

the initial performance test date provision for a new or reconstructed potline. 

Commenters suggested revisions to §63.847(c).

Response: The EPA agrees with the commenters that performance 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 test provisions were inadvertently removed in some 

cases and left out in other cases. Section 63.847(c) is being amended 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 proposed electronic test reporting 

requirement does not apply to potline performance testing. The commenter disagrees with the EPA’s 
103 

proposed requirement to submit performance test reports 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 procedure required for potlines in the NESHAP for primary aluminum 

reduction plants. The commenter explains that monthly fluoride compliance 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 designed to report compliance from tests conducted in a 

single test campaign, does not have the capability to combine results from monthly tests with results 

from a prior annual test, and does not have the capability to accept and calculate secondary roof 

emissions from Methods 14 and 14A. In addition, the commenter notes that the 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 use in-house staff for secondary potline emission test 

reporting and reporting of monthly fluoride test results is currently 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 supplant these other periodic NESHAP and title V SIP 

reports and only adds a new monthly burden to facility personnel, the 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 furnace 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 test 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 the EPA through the use of the ERT and the Compliance 

and Emissions Data Reporting Interface (CEDRI) in CDX under §63.850(b)(1) and additionally 

proposes to add a requirement under §63.850(b)(2) to submit results of performance tests directly to the 

Regional Administrator when performance test data are obtained using test methods that are not 

supported by the ERT at the time of the test. Commenters stated that based on a recent review of the 

ERT Web site, all the test methods specified in proposed §63.849(a) are supported by the ERT with the 

exception of Methods 14 and 14A. 

Commenters stated that this is problematic because it would require that performance test results that 

require summation (of primary control system emissions and secondary roof vent emissions) to calculate 

compliance with an applicable emission limit be submitted via two different means (electronic and 

hardcopy) across different entities within Federal and State agencies. Commenters stated that emissions 

testing of the potline primary control system does not involve Method 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 currently would not have to 

be submitted via ERT. Commenters stated that this will present recordkeeping and compliance 

evaluation challenges for regulatory agencies as well as the facilities. 

Commenter (0372) stated that a less confusing and more efficient approach is to allow the hardcopy 

submittal of both existing non-ERT supported test methods as well as existing ERT supported test 
104 

methods when the sum of both the 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 through 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 and 14A performance tests to the Administrator. For 

data that requires summation of results from both ERT and non-ERT supported test methods in order to 

demonstrate compliance with an emission limit, the owner operator will only be required to submit hard 

copy results of the performance tests to the Administrator. This has been clarified in the final 

amendments. 

Comment: One commenter (0166) supports the EPA’s proposal for electronic reporting. The commenter 

notes that as the public has a right to all collected reports under the CAA, it is important that the EPA 

ensure immediate disclosure of these reports to the public on the Internet within 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 for the proposed electronic reporting. The 

electronic reports will be submitted to the EPA via the 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) related several concerns regarding the proposed work 

practice standards under §63.854(a). 

Commenters stated that when the proposed requirements §63.854(a)(1) and (2) are read literally, it 

would mean that any electrical trips or other unexpected brief operational interruptions/maintenance 

would be considered violations of the work practice standards when the regulation already contains 

parametric limits (63.848(f)) along with excursion/exceedance reporting, 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 establishes the appropriate work practices for the potline 

primary control system and that proposed §63.854(a)(1) and (2) are not needed and should be removed. 

Commenters stated that additionally placing these requirements in the work practices section creates a 

‘double jeopardy’ situation wherein the same excursion/exceedance would be enforceable against two 

different parts of the regulation. 

Commenters stated that §63.854(a)(4)(i) requires that unstable pots be identified. 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 that an ‘unstable’ pot may not give off any more or less emissions 
105 

than a stable pot and therefore the commenter does not support its continued inclusion in the work 

practices section. Commenters stated that in the absence of a clear definition of what constitutes an 

‘unstable pot’ and how this relates to increased emissions, 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 the time that is ‘as soon as practicable’. 

Commenters stated that reducing pot temperature to as low as practicable reduces the solubility of the 

alumina in the bath, puts alumina sludge on the bottom, makes the pot more unstable, and causes higher 

fluoride emissions. Commenters stated that premature attempts to reseal the pot crust by raking alumina 

and bath into open cracks and holes can put additional sludge on the bottom of the pot and that this will 

lead to further instability and increased emissions. Commenters stated that the requirements of (4)(ii) 

and (4)(iii) should be removed. 

Commenters stated that they agree that hooding of the pots is important to capturing emissions. 

Commenters stated that different pot activities require a different number of hoods to be removed. 

Commenters stated that the NSPS preamble addresses specific hooding expectations that are more 

comprehensive than what the EPA has proposed. Commenters suggested removing the work practices 

proposed in §63.854(a) completely and replacing them with applicable potline work practices as 

contained in the 1980 NSPS Preamble (45 FR 44202). Commenters provided brief description of why 

the standards are a better alternative. Commenters recommend that §63.854(a) is revised. 

Response: The EPA has reviewed the commenter’s position regarding the proposed work practices and 

the suggested work practices. The EPA agrees with the 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 the 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 inclusion of work practice requirements for the startup of 

anode bake furnaces and paste production plants under §63.847(l) and (m), respectively, in the proposed 

supplemental rule. Commenters (0372 and 0375) stated concern about the 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 immediate” are unclear and not defined. 

Commenters stated that the best course of action to minimize emissions may not be the immediate 

shutdown of the anode bake furnace or paste production. 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-set and re-start may result in fewer emissions than an immediate 

shutdown of the anode bake furnace (which could involve venting the furnace to prevent an explosion) 

or the paste production plant (which could involve dumping the initial mixer contents of hot green mix). 

Commenters stated that the proposed requirement for immediate shutdown of the source could actually 

result in actions that are in conflict with the 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 plant when its associated control device goes off line should be left to 

the operator and that the written startup plans should include a requirement to operate the source and its 

emissions control device in a manner that is consistent with safety 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 conflict with the general compliance requirements and in some cases lead 

to higher emissions. We agree that the operators should employ the appropriate corrective actions for off 

line emission control systems, based on site specific conditions. The EPA has finalized text clarifying 

that operators have discretion in implementing the best corrective action in accordance with the general 

compliance requirements. 

3.7 Changes to General Provisions Monitoring Requirements 

Comment: One commenter (0162) states that 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 commenter 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 Appendix A to the applicability of several monitoring 

requirements under the General Provisions, including provisions related to continuous parametric 

monitoring systems (CPMS) and continuous monitoring systems (CMS). The commenter notes that the 

Agency proposes changing some of these requirements 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 allow public review and comment of 

these significant changes. The commenter cited the Quality Control Program required under section 

63.8(d), currently not applicable under 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 the monitoring requirements included in this final 

rule were made to conform to the amendments to the General Provisions. The final rule has been revised 

to correct an error in the proposal changing the applicability of 63.8(d). This provision does not apply to 

this subpart. In addition, the General Provisions table has been updated to reflect the reserved 

paragraphs are not applicable to this subpart. 

Comment: Commenters (0372 and 0375)) stated that the section §63.7 of the general provisions 

establishes the performance testing requirements for the NESHAP regulations. Commenters stated that 

the proposed Appendix A to subpart LL lists both the applicable and non-applicable requirements of the 

general provisions to subpart LL and 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 stated 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 have added clarifying text to the final rule. 
107 

Comment: Commenters (0372 and 0375) stated that the rule-specific provisions contained in Appendix 

A of the current subpart LL rule were not correctly incorporated into Appendix A of the proposed rule 

and that some additional requirements 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 §63.841 of current subpart LL is not 

incorporated in §63.2 of proposed Appendix A. 

 The rule-specific provisions of §63.850(a)(9) regarding a notification of re-start of a previously 

shutdown existing source are not addressed in the comments of proposed §63.9(b). 

 Rule- specific provisions regarding notification of performance test, notification of VE/opacity 

test, and addition CMS notifications are not correctly incorporated 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 reporting 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) provides 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 adding “(a)(3)” to the list. The commenter’s 

recommended revised text would read “...any emission limits in paragraphs (a)(1), (a)(2) and 

(a)(3).” 

Response: Table 2 of the proposed rule included errors. Table 2 has been revised in the final 

amendments to reflect the EPA’s intention to maintain the discount factor for 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 accordance with the commenter’s suggestion to read “...any 

emission limits in paragraphs (a)(1), (a)(2) and (a)(3).” 
108 

Comment: Commenter (0370) requested that through the process of updating the testing frequency for 

roof vents that the EPA further define 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 testing 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 total 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 because any increase would meet the definition. The 

current definition will be retained.

Comment: Commenter (0372) stated that the Tables 1, 2 and 3 provided for Potline PM, TF, and 

POM averaging require revision to account for the fact that the supplemental rule requires testing 

frequencies that do not match up with the testing frequencies found 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 consistency 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 sampling frequency. We have revised the headings of 

Tables 1, 2, and 3 to reflect the final sampling frequencies. 

Comment: Commenter (0375) stated that 63.847(d) (1) has missing references 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 section, the owner or operator shall compute and record the average 

of at least three runs semiannually for secondary emissions and at least three runs each year 

for the primary control system to determine compliance with the applicable emission limit. 

Compliance is demonstrated when the emission rates of TF, POM and PM is are equal to or 

less than the applicable TF, POM and PM emission limits in §63.843, §63.844, or §63.846. 

Response: The EPA agrees with the Commenter regarding missing references to POM and PM in 

63.847(d)(1). The final text has been revised to include reference to POM and PM.

Comment: Commenter (0375) stated that the 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 reconstructed source potlines under §63.844(e). 

Response: The rule citation for the COS limit in the 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 and 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 support 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 that the delineation 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 helpful when any facility, previously subject to the 

limits of a CWPB3 potline, changes processes, feed materials, or customer base such that the facility no 

longer produces "very high purity aluminum." Commenter (0370) stated that this definition is necessary 

for the permitting agency to appropriately classify sources and establish the appropriate emission 

limitations. 

Response: The EPA agrees with the commenter that a definition 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.) incorporates by reference the comments 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 the comments submitted to this docket by the 

Commenter (0374) concerning removal 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.