National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units-Reconsideration of Supplemental Finding and Residual Risk and Technology Review

Federal RegisterFeb 7, 2019

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2018-0794; FRL-9988-93-OAR]

RIN 2060-AT99

National Emission Standards for Hazardous Air Pollutants: Coal- and Oil-Fired Electric Utility Steam Generating Units—Reconsideration of Supplemental Finding and Residual Risk and Technology Review

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing a revision to its response to the U.S. Supreme Court decision in

Michigan

EPA

which held that the EPA erred by not considering cost in its determination that regulation under section 112 of the Clean Air Act (CAA) of hazardous air pollutant (HAP) emissions from coal- and oil-fired electric utility steam generating units (EGUs) is appropriate and necessary. After considering the cost of compliance relative to the HAP benefits of regulation, the EPA proposes to find that it is not “appropriate and necessary” to regulate HAP emissions from coal- and oil-fired EGUs, thereby reversing the Agency's prior conclusion under CAA section 112(n)(1)(A) and correcting flaws in the Agency's prior response to

Michigan

EPA.

We further propose that finalizing this new response to

Michigan

EPA

will not remove the Coal- and Oil-Fired EGU source category from the CAA section 112(c) list of sources that must be regulated under CAA section 112(d) and will not affect the existing CAA section 112(d) emissions standards that regulate HAP emissions from coal- and oil-fired EGUs. We are soliciting comment, however, on whether the EPA has the authority or obligation to delist EGUs from CAA section 112(c) and rescind (or to rescind without delisting) the National Emission Standards for Hazardous Air Pollutants (NESHAP) for Coal- and Oil-Fired EGUs, commonly known as the Mercury and Air Toxics Standards (MATS). The EPA is also proposing the results of the residual risk and technology review (RTR) of the NESHAP that the Agency is required to conduct in accordance with CAA section 112. The results of the residual risk analysis indicate that residual risks due to emissions of air toxics from this source category are acceptable and that the current standards provide an ample margin of safety to protect public health. No new developments in HAP emission controls to achieve further cost-effective emissions reductions were identified under the technology review. Therefore, based on the results of these analyses and reviews, we are proposing that no revisions to MATS are warranted. Finally, the EPA is also taking comment on establishing a subcategory for emissions of acid gas HAP from existing EGUs firing eastern bituminous coal refuse.

DATES:

Comments.

Comments must be received on or before April 8, 2019. Under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of consideration if the Office of Management and Budget (OMB) receives a copy of your comments on or before March 25, 2019.

Public Hearing.

The EPA is planning to hold at least one public hearing in response to this proposed action. Information about the hearing, including location, date, and time, along with instructions on how to register to speak at the hearing, will be published in a second

Federal Register

document.

ADDRESSES:

Comments.

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2018-0794, at

https://www.regulations.gov.

Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from

Regulations.gov

. See

SUPPLEMENTARY INFORMATION

for detail about how the EPA treats submitted comments.

Regulations.gov

is our preferred method of receiving comments. However, the following other submission methods are also accepted:

•

Email: a-and-r-docket@epa.gov.

Include Docket ID No. EPA-HQ-OAR-2018-0794 in the subject line of the message.

•

Fax:

(202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-2018-0794.

•

Mail:

To ship or send mail via the United States Postal Service, use the following address: U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2018-0794, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.

•

Hand/Courier Delivery:

Use the following Docket Center address if you are using express mail, commercial delivery, hand delivery, or courier: EPA Docket Center, EPA WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. Delivery verification signatures will be available only during regular business hours.

FOR FURTHER INFORMATION CONTACT:

For questions about this proposed action, contact Mary Johnson, Sector Policies and Programs Division (D243-01), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-5025; fax number: (919) 541-4991; and email address:

johnson.mary@epa.gov

or Nick Hutson, Sector Policies and Programs Division (D243-01), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-2968; fax number: (919) 541-4991; and email address:

hutson.nick@epa.gov.

For specific information regarding the risk modeling methodology, contact Mark Morris, Health and Environmental Impacts Division (C539-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-5416; and email address:

morris.mark@epa.gov.

For information about the applicability of the NESHAP to a particular entity, contact Sara Ayres, Office of Enforcement and Compliance Assurance, U.S. Environmental Protection Agency, U.S. EPA Region 5 (E-19J), 77 West Jackson Boulevard, Chicago, Illinois 60604; telephone number: (312) 353-6266; and email address:

ayres.sara@epa.gov.

SUPPLEMENTARY INFORMATION:

Docket.

The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2018-0794. All documents in the docket are listed in

Regulations.gov

. Although listed, some information is not publicly available,

e.g.,

CBI (Confidential Business Information) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly available only in hard copy. Publicly available docket materials are available either electronically in

Regulations.gov

or in hard copy at the EPA Docket Center, Room 3334, EPA WJC West Building, 1301 Constitution Avenue NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742.

Instructions.

Direct your comments to Docket ID No. EPA-HQ-OAR-2018-0794. The EPA's policy is that all

comments received will be included in the public docket without change and may be made available online at

https://www.regulations.gov,

including any personal information provided, unless the comment includes information claimed to be CBI or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through

https://www.regulations.gov

or email. This type of information should be submitted by mail as discussed below.

The EPA may publish any comment received to its public docket. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (

i.e.,

on the Web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit

https://www.epa.gov/dockets/commenting-epa-dockets.

The

https://www.regulations.gov

website allows you to submit your comment anonymously, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through

https://www.regulations.gov,

your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any digital storage media you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should not include special characters or any form of encryption and be free of any defects or viruses. For additional information about the EPA's public docket, visit the EPA Docket Center homepage at

https://www.epa.gov/dockets.

The EPA is soliciting comment on numerous aspects of the proposed rule. The EPA has indexed each comment solicitation with an alpha-numeric identifier (

e.g.,

“C-1,” “C-2,” ”C-3”) to provide a consistent framework for effective and efficient provision of comments. Accordingly, the EPA asks that commenters include the corresponding identifier when providing comments relevant to that comment solicitation. The EPA asks that commenters include the identifier in either a heading, or within the text of each comment (

e.g.,

“In response to solicitation of comment C-1, . . .”) to make clear which comment solicitation is being addressed. The EPA emphasizes that the Agency is not limiting comment to these identified areas and encourages provision of any other comments relevant to this proposal.

Submitting CBI.

Do not submit information containing CBI to the EPA through

https://www.regulations.gov

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on any digital storage media that you mail to the EPA, mark the outside of the digital storage media as CBI and then identify electronically within the digital storage media the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI directly to the public docket through the procedures outlined in

Instructions

above. If you submit any digital storage media that does not contain CBI, mark the outside of the digital storage media clearly that it does not contain CBI. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver information identified as CBI only to the following address: OAQPS Document Control Officer (C404-02), OAQPS, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2018-0794.

Preamble Acronyms and Abbreviations.

We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here:

AEGL acute exposure guideline level

AERMOD air dispersion model used by the HEM-3 model

ATSDR Agency for Toxic Substances and Disease Registry

CAA Clean Air Act

CalEPA California EPA

CAMR Clean Air Mercury Rule

CBI Confidential Business Information

CEMS continuous emissions monitoring systems

CFR Code of Federal Regulations

CPMS continuous parameter monitoring system

ECMPS Emissions Collection and Monitoring Plan System

EGU electric utility steam generating unit

EIA Energy Information Administration

EPA Environmental Protection Agency

EPRI Electric Power Research Institute

ERPG Emergency Response Planning Guideline

fPM filterable particulate matter

HAP hazardous air pollutant(s)

HCl hydrochloric acid

HEM-3 Human Exposure Model, Version 1.1.0

HF hydrogen fluoride

Hg mercury

HI hazard index

HQ hazard quotient

ICR information collection request

IGCC integrated gasification combined cycle

IRIS Integrated Risk Information System

km kilometer

lb/GWh pounds per gigawatt-hour

lb/MMBtu pounds per million British thermal units

lb/MWh pounds per megawatt-hour

lb/TBtu pounds per trillion British thermal units

MACT maximum achievable control technology

MATS Mercury and Air Toxics Standards

mg/m

milligrams per cubic meter

MIR maximum individual risk

MMBtu million British thermal units

MMBtu/hr million British thermal units per hour

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NEEDS National Electric Energy Data System

NEI National Emissions Inventory

NESHAP national emission standards for hazardous air pollutants

nitrogen oxides

NTTAA National Technology Transfer and Advancement Act

OAQPS Office of Air Quality Planning and Standards

OMB Office of Management and Budget

PB-HAP hazardous air pollutants known to be persistent and bio-accumulative in the environment

PDF Portable Document Format

PM particulate matter

2.5

fine particulate matter

POM polycyclic organic matter

PRA Paperwork Reduction Act

RDL representative detection level

REL reference exposure level

RFA Regulatory Flexibility Act

RfC reference concentration

RfD reference dose

RIA regulatory impact analysis

RTR residual risk and technology review

SAB Science Advisory Board

sulfur dioxide

TOSHI target organ-specific hazard index

tpy tons per year

TRIM.FaTE Total Risk Integrated Methodology.Fate, Transport, and Ecological Exposure model

UARG Utility Air Regulatory Group

UF uncertainty factor

µg/m

microgram per cubic meter

UMRA Unfunded Mandates Reform Act

URE unit risk estimate

USGS United States Geological Survey

Organization of this Document.

The information in this preamble is organized as follows:

I. General Information

A. Does this action apply to me?

B. Where can I get a copy of this document and other related information?

II. Appropriate and Necessary Finding

A. Overview

B. Background

C. The EPA's Proposed Finding Under CAA Section 112(n)(1)(A)

D. Effects of This Proposed Replacement of the Supplemental Finding

III. Criteria for Delisting a Source Category Under CAA Section 112(c)(9)

IV. Background on the RTR Action

A. What is the statutory authority for this action?

B. What is this source category and how does the current NESHAP regulate its HAP emissions?

C. What data collection activities were conducted to support this action?

D. What other relevant background information and data are available?

V. RTR Analytical Procedures and Decision-Making

A. How do we consider risk in our decision-making?

B. How do we perform the technology review?

C. How do we estimate post-MACT risk posed by the source category?

VI. RTR Analytical Results and Proposed Decisions

A. What are the results of the risk assessment and analyses?

B. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effect?

C. What are the results and proposed decisions based on our technology review?

VII. Consideration of Separate Subcategory and Acid Gas Standard for Existing EGUs That Fire Eastern Bituminous Coal Refuse

A. Background

B. Basis for Consideration of a Subcategory

C. Potential Subcategory Emission Standards

VIII. Summary of Cost, Environmental, and Economic Impacts

IX. Request for Comments

X. Submitting Data Corrections

XI. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Executive Order 13771: Reducing Regulation and Controlling Regulatory Costs

C. Paperwork Reduction Act (PRA)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

G. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments

H. Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks

I. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

J. National Technology Transfer and Advancement Act (NTTAA)

K. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations

I. General Information

A. Does this action apply to me?

Table 1 of this preamble lists the NESHAP and associated regulated industrial source categories that are the subject of this proposal. Table 1 is not intended to be exhaustive, but rather provides a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources. Federal, state, local, and tribal government entities that own and/or operate EGUs subject to 40 CFR part 63, subpart UUUUU would be affected by this proposed action. The Coal- and Oil-Fired EGU source category was added to the list of categories of major and area sources of HAP published under section 112(c) of the CAA on December 20, 2000 (65 FR 79825). CAA section 112(a)(8) defines an electric utility steam generating unit as:

Any fossil fuel fired combustion unit of more than 25 megawatts that serves a generator that produces electricity for sale. A unit that cogenerates steam and electricity and supplies more than one-third of its potential electric output capacity and more than 25 megawatts electrical output to any utility power distribution system for sale

is also considered an EGU.

Table 1—NESHAP and Industrial Source Categories Affected by This Proposed Action

Source category

NESHAP

NAICS code

Coal- and Oil-Fired EGUs

40 CFR part 63, subpart UUUUU

221112, 221122, 921150

North American Industry Classification System.

B. Where can I get a copy of this document and other related information?

In addition to being available in the docket, an electronic copy of this action is available on the internet. Following signature by the EPA Administrator, the EPA will post a copy of this proposed action at

https://www.epa.gov/mats/regulatory-actions-final-mercury-and-air-toxics-standards-mats-power-plants.

Following publication in the

Federal Register

, the EPA will post the

Federal Register

version of the proposal and key technical documents at this same website. Information on the overall RTR program is available at

https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.

II. Appropriate and Necessary Finding

A. Overview

The EPA proposes this revised action in response to the U.S. Supreme Court decision in

Michigan

EPA,

135 S.Ct. 2699 (2015), which held that the EPA erred by not considering cost in its determination that regulation of HAP emissions from coal- and oil-fired EGUs is appropriate and necessary under CAA section 112. In this action, after considering the cost of compliance relative to the HAP benefits of regulation, the EPA proposes to find that it is not “appropriate and necessary” to regulate HAP emissions from coal- and oil-fired EGUs, thereby reversing the Agency's conclusion under CAA section 112(n)(1)(A), first made in 2000 and later affirmed in 2012 and 2016. This proposed response corrects flaws in the EPA's prior 2016 response to

Michigan

(82 FR 24420) and, if finalized, would supplant that 2016 action. We also propose that finalizing this action will not remove the Coal- and Oil-Fired EGU source category from the CAA section 112(c)(1) list, nor will finalizing this action affect the existing CAA section 112(d) emissions standards promulgated in 2012 that regulate HAP emissions from coal- and oil-fired EGUs, although this action requests comment on that proposed conclusion and whether the EPA has the authority or obligation to

delist the source category and rescind the standards, or to rescind the standards without delisting (Comment C-1).

B. Background

In the 1990 Amendments to the CAA, Congress substantially modified CAA section 112, the provision of the CAA addressing HAP. That provision includes CAA section 112(b)(1), which sets forth a list of 187 identified HAP, and CAA sections 112(b)(2) and (3), which give the EPA the authority to add or remove pollutants from the list. CAA section 112(a)(1) and (2) also specify the two types of sources to be addressed: Major sources and area sources. A major source is any stationary source or group of stationary sources at a single location and under common control that emits or has the potential to emit, considering controls, 10 tons per year (tpy) or more of any HAP or 25 tpy or more of any combination of HAP. CAA section 112(a)(1). Any stationary source of HAP that is not a major source is an area source. CAA section 112(a)(2). All major source categories, besides EGUs, were required to be included on a published list of sources subject to regulation under CAA section 112,

see

CAA sections 112(a)(1) and (c)(1), and area sources “which the Administrator finds presents a threat of adverse effects to human health or the environment (by such sources individually or in the aggregate) warranting regulation under this section” were also required to be added to the list,

see

CAA section 112(c)(3). The EPA was to promulgate emission standards under CAA section 112(d) for those source categories on the list.

This general CAA section 112(c) process of listing and regulation does not apply to EGUs. Instead, Congress enacted a special provision, CAA section 112(n)(1)(A), which established a separate process by which the EPA was to determine whether to regulate emissions of HAP from EGUs under CAA section 112. CAA section 112(n)(1)(A) directs the EPA to conduct a study to evaluate the hazards to public health that are reasonably anticipated to occur as a result of the HAP emissions from EGUs, after the imposition of other CAA provisions. The provision directs that the EPA shall regulate EGUs under CAA section 112 if the Administrator determines, after considering the results of the study, that such regulation is “appropriate and necessary.” CAA section 112(n)(1)(A), therefore, sets a unique process by which the Administrator is to determine whether to establish CAA section 112(d) standards for EGUs. Moreover, the statute includes a separate definition of “EGU” which does not distinguish between major and area sources. CAA section 112(a)(8).

On December 20, 2000, the EPA determined, pursuant to CAA section 112(n)(1)(A), that it was appropriate and necessary to regulate coal- and oil-fired EGUs under CAA section 112(d) and added such units to the CAA section 112(c) List of Categories of Major and Area Sources. 65 FR 79825 (2000 Finding). The EPA reversed that finding in 2005, concluding that it was neither appropriate nor necessary to regulate EGUs under CAA section 112(n)(1)(A), and stating that the effect of its reversal of the appropriate and necessary finding was removal of coal- and oil-fired EGUs from the CAA section 112(c)(1) source category list. 70 FR 15994 (March 29, 2005) (2005 Delisting Rule). The EPA concurrently issued the Clean Air Mercury Rule (CAMR), which regulated mercury (Hg) from new and existing coal-fired EGUs under CAA sections 111(b) and (d). The United States Court of Appeals for the District of Columbia (DC) Circuit (the Court) vacated the EPA's 2005 Delisting Rule in

New Jersey

EPA,

517 F.3d 574 (D.C. Cir. 2008). The Court ruled that the fact that the EPA had reversed its prior appropriate and necessary finding did not mean that the Agency could remove the Coal- and Oil-Fired EGU source category from the CAA section 112(c)(1) list without going through the generally applicable CAA section 112(c)(9) delisting procedures.

Id.

Instead, the Court held that the Agency could only remove EGUs from the CAA section 112(c)(1) list after finding that the statutory criteria for delisting set forth in CAA section 112(c)(9) had been met.

Id.

In addition, the Court also vacated CAMR in light of the EPA's concession that it had no authority to regulate Hg from EGUs under CAA section 111 so long as EGUs remained on the CAA section 112(c)(1) source category list. 517 F.3d 574 (D.C. Cir. 2008). (The Court did not address the merits of CAMR under CAA section 111; its vacatur was based solely on its holding that the delisting from CAA section 112 was improper.)

On May 3, 2011, the EPA proposed to reaffirm the 2000 appropriate and necessary finding and proposed NESHAP for coal- and oil-fired EGUs, known as MATS. 76 FR 24976. The final MATS rule was subsequently issued on February 16, 2012. 77 FR 9304. Industry, states, environmental organizations, and public health organizations challenged many aspects of both the re-affirmed appropriate and necessary finding and the final MATS rule in the D.C. Circuit. The Court denied all challenges.

White Stallion Energy Center

EPA,

748 F.3d 1222 (D.C. Cir. 2014). Some industry and state petitioners sought further review of the final MATS rule, and the U.S. Supreme Court granted

certiorari

to determine whether the EPA erred when it concluded that it could properly make the appropriate and necessary finding under CAA section 112(n)(1)(A) without consideration of cost. On June 29, 2015, the Supreme Court ruled that the EPA “strayed far beyond [the] bounds” of reasonable interpretation when it determined cost was irrelevant to the appropriate and necessary finding.

Michigan

EPA,

135 S Ct. 2699, 2707 (2015). Specifically, the Supreme Court held that cost was “an important aspect of the problem” and that the Agency was required to consider the cost of regulation before deciding whether it was appropriate and necessary to impose that regulation on EGUs under CAA section 112.

Id.

On remand from the Supreme Court, the D.C. Circuit left MATS in effect while the Agency addressed the

Michigan

decision. Order,

White Stallion Energy Center

EPA,

No. 12-1100 (D.C. Cir. Dec. 15, 2015) (ECF No. 1588459).

On April 25, 2016, after public notice and comment,

the EPA finalized a supplemental finding (2016 Supplemental Finding) concluding that its consideration of cost did not change its previous determination that regulation of HAP emissions from coal- and oil-fired EGUs is appropriate and necessary. 82 FR 24420. In the 2016 Supplemental Finding, the EPA considered costs under two alternative approaches. Under the first approach, the EPA evaluated compliance costs in comparison to the industry's historical annual revenues and annual capital expenditures, and examined impacts of the rule on retail electricity prices. The EPA concluded that because these costs were within the range of historical variability, the cost of MATS was reasonable. The EPA also found that the power sector could continue to perform its primary function—the generation, transmission, and distribution of reliable electricity at reasonable cost—after imposition of the MATS rule. Based on the conclusion that the costs of the rule were “reasonable” and considering the benefits of reducing HAP that had been identified in earlier agency determinations, the Agency affirmed the appropriate and necessary finding under CAA section 112(n)(1)(A).

80 FR 75025 (December 1, 2015).

In the 2016 Supplemental Finding, the EPA also presented a second, alternative and independent, approach

to considering cost. This approach considered the results of the formal cost-benefit analysis that the Agency had previously performed for the regulatory impact analysis (RIA) for the final MATS rule.

That RIA cost-benefit analysis accounted for the monetized and non-monetized benefits of MATS, including HAP-related benefits that could not be quantified or monetized, as well as the monetized co-benefits of reducing pollutants other than HAP. The RIA analysis found that its projection of these aggregated benefits ($37 to $90 billion each year) exceeded the costs of compliance ($9.6 billion) by three to nine times. The EPA, therefore, concluded that the RIA's cost-benefit analysis also supported its affirmation of the prior appropriate and necessary finding under CAA section 112(n)(1)(A). 82 FR 24420.

U.S. EPA. 2011.

Regulatory Impact Analysis for the Final Mercury and Air Toxics Standards.

EPA-452/R-11-011. Available at

https://www3.epa.gov/ttn/ecas/docs/ria/utilities_ria_final-mats_2011-12.pdf.

Docket ID No. EPA-HQ-OAR-2009-0234-20131.

A number of state and industry groups petitioned for review of the 2016 Supplemental Finding in the D.C. Circuit.

Murray Energy Corp.

EPA,

No. 16-1127 (D.C. Cir. filed April 25, 2016). In April 2017, given its interest in reviewing the 2016 action, the EPA moved the Court to continue oral argument and hold the case in abeyance in order to give the new Administration an opportunity to undertake that review. The Court granted the EPA's request for a continuance on April 27, 2017. Order,

Murray Energy Corp.

EPA,

No. 16-1127 (D.C. Cir. April 27, 2017) (ECF No. 1672987).

C. The EPA's Proposed Finding Under CAA Section 112(n)(1)(A)

In this action, the EPA proposes to conclude that the 2016 Supplemental Finding was flawed and that, after considering the cost of compliance relative to the HAP benefits of MATS, it is not appropriate and necessary to regulate coal- and oil-fired EGUs under section 112 of the CAA. CAA section 112(n)(1)(A) requires the EPA to determine that both the appropriate

and

the necessary prongs are met. Therefore, if the EPA finds that either prong is not satisfied, it cannot make an affirmative appropriate and necessary finding.

Cf.

70 FR 16000. The EPA's reexamination of its determination in this proposal focuses on the first prong of that analysis: Whether regulation is “appropriate,” after consideration of the costs and benefits of such regulation. The EPA has reexamined the cost analyses presented in the 2016 Supplemental Finding and proposes to determine that neither of the Finding's approaches to considering cost satisfies the Agency's obligation under CAA section 112(n)(1)(A) as interpreted by the Supreme Court in

Michigan.

Instead, we use a different consideration of cost for purposes of the appropriate and necessary finding, one that we believe aligns with the purpose of CAA section 112(n)(1)(A) as set forth in

Michigan.

We propose to directly compare the cost of compliance with MATS with the benefits specifically associated with reducing emissions of HAP as the primary inquiry in this finding, in order to satisfy our duty to consider cost in the context of CAA section 112(n)(1)(A).

Agencies have inherent authority to reconsider past decisions and to revise, replace, or repeal a decision to the extent permitted by law and supported by a reasoned explanation.

FCC

Fox Television Stations, Inc.,

556 U.S. 502, 515 (2009);

Motor Vehicle Mfrs. Ass'n

State Farm Mutual Auto. Ins. Co.,

463 U.S. 29, 42 (1983) (“

State Farm”

). The EPA's interpretations of the statutes it administers are not “carved in stone,” but must be evaluated “on a continuing basis,” for example, “in response to . . . a change in administrations.”

Nat'l Cable & Telecomms. Ass'n

Brand X internet Servs.,

545 U.S. 967, 981 (2005) (internal quotation marks and citations omitted). An agency's reasoning can include a change in policy on the basis that “the agency

believes

it to be better,” even if a court might disagree.

White Stallion,

748 F.3d at 1235;

see also Nat'l Ass'n of Home Builders

EPA,

682 F.3d 1032, 1038 & 1043 (D.C. Cir. 2012) (a revised rulemaking based “on a reevaluation of which policy would be better in light of the facts” is “well within an agency's discretion,” and “ `[a] change in administration brought about by the people casting their votes is a perfectly reasonable basis for an executive agency's reappraisal of the costs and benefits of its programs and regulations' ”) (quoting

State Farm,

463 U.S. at 59 (Rehnquist, J., concurring in part and dissenting in part)). The CAA complements the EPA's inherent authority to reconsider prior rulemakings by providing the Agency with broad authority to prescribe regulations as necessary to carry out the Administrator's authorized functions under the statute. 42 U.S.C. 7601(a). This broad discretion can be limited by Congress, however. In

New Jersey

EPA,

the D.C. Circuit held that a reversal of the appropriate and necessary finding would not have the effect of removing Coal- and Oil-Fired EGUs from the CAA section 112(c)(1) source category list because Congress “unambiguously limit[ed] EPA's discretion” by fashioning a statutorily mandated avenue for removing source categories from the list in CAA section 112(c)(9). 517 F.3d 574, 582-83. (D.C. Cir. 2008).

The EPA also proposes that, because a negative appropriate and necessary finding cannot by itself remove a source category from the CAA section 112(c) list,

see New Jersey,

517 F.3d at 582, finalizing this finding will neither remove the Coal- and Oil-Fired EGU source category from the CAA section 112(c) list, nor will it alter or eliminate the CAA section 112(d) emissions standards imposed by MATS. The EPA solicits public comment on all aspects of this proposal, and retains the discretion, as always, to make changes in response to those comments prior to finalizing this rule or to decide not to finalize some or all aspects of this proposal after considering public comments.

1. The 2016 Supplemental Finding Was an Improper Response to

Michigan

EPA

a. The “Cost Reasonableness” Approach Does Not Satisfy the Agency's Obligation Under CAA Section 112(n)(1)(A)

We propose to find that the Agency's 2016 Supplemental Finding erred in its consideration of cost. Specifically, we find that what was described in the 2016 Supplemental Finding as the preferred approach, or “cost reasonableness test,” does not meet the statute's requirements to fully consider costs, and was an unreasonable interpretation of CAA section 112(n)(1)(A)'s mandate, as informed by the Supreme Court's opinion in

Michigan.

In its 2016 Supplemental Finding, the EPA developed a “cost reasonableness test” based on D.C. Circuit opinions that had evaluated the Agency's consideration of cost in the context of setting new source performance standards under section 111 of the CAA.

See Legal Memorandum Accompanying the Proposed Supplemental Finding that it is Appropriate and Necessary to Regulate Hazardous Air Pollutants from Coal- and Oil-Fired Electric Utility Steam Generating Units (EGUs)

(2015 Legal Memorandum). Because those opinions interpreted CAA section 111 to only prohibit the Agency from adopting standards for new sources whose cost would be “exorbitant,”

Lignite Energy Council

EPA,

198 F.3d 930, 933 (D.C. Cir. 1999), “excessive,” or “unreasonable,”

Sierra Club

Costle,

657 F.2d 298, 383 (D.C. Cir. 1981), we concluded that we could consider cost for CAA section 112(n)(1)(A) by determining whether cost of compliance was “reasonable”—in other words, whether the cost of regulation could be absorbed by the power sector without negatively affecting the industry's ability to continue performing its primary function. That “cost reasonableness test” compared compliance costs of MATS relative to historical annual revenues and annual capital expenditures, and evaluated the impacts of the rule on retail electricity prices. Because we found that the costs of compliance with the rule across the entire utility sector were within historical variability and would not shut down the sector as a whole, the EPA

concluded that the cost of compliance with MATS was reasonable.

The Agency claimed that use of the “cost reasonableness test” for its CAA section 112(n)(1)(A) appropriate and necessary finding was supported by the “overall statutory objectives of section 112,” and stated that “cost was but one factor among many” that the EPA must consider.

See

Legal Memorandum at 20. We also interpreted CAA section 112(n)(1)(A) and

Michigan

not to require the EPA to assume that a consideration of cost should predominate or take primary significance to the subordination of other considerations, because of CAA section 112's overall concern with the nature of HAP emissions and populations that might be particularly sensitive to harms associated with those emissions.

Id.

In this notice, we are proposing to find that the EPA did not comply with its statutory duty to consider cost as part of the appropriate and necessary finding in the 2016 Supplemental Finding. The 2016 Supplemental Finding repeatedly emphasized that the

Michigan

Court did not hold that the CAA “unambiguously required” the EPA to perform a formal cost-benefit analysis to satisfy CAA 112(n)(1)(A). 135 S. Ct. at 2711. But, as discussed below, the 2016 Supplemental Finding, among other flaws, ignored observations about the importance of the cost consideration to the appropriate and necessary finding, as provided by the Court in

Michigan.

Contrary to the 2015 Legal Memorandum's suggestion that cost should not “trump” or “predominate” other considerations, the Supreme Court observed that “[a]gencies have long treated cost as a

centrally relevant factor

when deciding whether to regulate.”

Id.

at 2707 (emphasis added). The Supreme Court rejected arguments that the general goals of CAA section 112 make cost irrelevant to a CAA section 112(n)(1)(A) appropriate and necessary finding. As such, the EPA must meaningfully consider cost when making this threshold finding. In addition, the Supreme Court emphasized that CAA section 112(n)(1)(A) reflects Congress's intent that the EPA treat EGUs

differently

from other sources.

Id.

at 2710. The attempt made in the 2016 Supplemental Finding to “harmonize” CAA section 112(n)(1)(A) with the remainder of CAA section 112 is, therefore, not consistent with Congress's intent and the Supreme Court's decision in

Michigan

EPA.

The 2016 Supplemental Finding's reliance on case law pertaining to CAA section 111(b) new source rules was similarly misguided. The methodologies that courts have approved for considering costs of control technologies for new sources that have not yet been constructed are not particularly informative in the context of EPA's deciding whether it is appropriate to impose control requirements on sources that are already operating. Costs of control technologies for new sources are borne as each source is added to the fleet of existing sources and are not imposed on the entire fleet of existing sources within a period of a few years, as is required under CAA section 112. Moreover, the case law cited by the 2015 Legal Memorandum is distinguishable even without regard to the fact that different statutory provisions (CAA section 111 versus 112) are at issue. For example, in

Lignite Council,

the D.C. Circuit found that the “new standards will only modestly increase the cost of producing electricity in newly constructed boilers.”

Lignite Energy Council

United States EPA,

198 F.3d at 933. Even in its flawed conclusion that the cost of MATS was “reasonable,” the EPA did not go so far as to say that the costs of that rule were in any way “modest.”

The primary, fatal flaw of the 2016 Supplemental Finding's “preferred approach” was its disregard for the

Michigan

Court's suggestion that, under CAA section 112(n)(1)(A), the Agency must meaningfully consider cost within the context of a regulation's benefits. The decision contemplated that a proper consideration of cost would be relative to benefits. For example, the Court questioned whether a regulation could be considered “rational” where there was a gross imbalance between costs and benefits and stated that “[n]o regulation is “appropriate” if it does more harm than good.”

Id.

The Court also made numerous references to a direct comparison of the costs of MATS with benefits from reducing emissions of HAP. For instance, the Court pointed out that “[t]he costs [of MATS] to power plants were thus between 1,600 and 2,400 times as great as the quantifiable benefits from reduced emissions of hazardous air pollutants.”

Id.

at 2706. Although the decision established no bright-line rules, it suggested that CAA section 112(n)(1)(A)'s requisite consideration of cost would not be met if the cost analysis did not “ensure cost-effectiveness” or “prevent the imposition of costs far in excess of benefits.”

Id.

at 2710.

For these reasons, the 2016 Supplemental Finding's “test” of whether an industry can bear the cost of regulation does not demonstrate that the cost of MATS was “reasonable” under the particular statutory context. More importantly, the metrics “tested” by the Agency in the 2016 Supplemental Finding are irrelevant to the determination of whether it is “appropriate and necessary” to impose that regulation. Each cost metric the Agency examined compared the cost of MATS to other costs borne by the industry, but never in its “preferred approach” did the Agency make the statutorily mandated assessment of whether the benefits garnered by the rule were worth it—

i.e.,

a direct comparison of costs and benefits. Because the “cost reasonableness test” failed to consider cost in a meaningful way relative to benefits, we, therefore, conclude that approach did not adequately address the Supreme Court's instruction that a reasonable regulation requires an agency to fully consider “the advantages

and

the disadvantages” of a decision.

See Michigan,

135 S. Ct. at 2707 (emphasis in original). Instead, we propose to reconsider cost using a more direct comparison of benefits and costs to address the Supreme Court's remand of the appropriate and necessary determination, as described below. As noted below, final action on this proposal would replace the 2016 Supplemental Finding.

b. The Cost-Benefit Approach in the 2016 Supplemental Finding's Alternative Approach Improperly Considered Co-benefits From Non-HAP Emissions Reductions

In the 2016 Supplemental Finding's alternative approach, the EPA improperly made an independent finding under CAA section 112(n)(1)(A) that was based on a formal benefit-cost analysis, which evaluates whether a regulation will increase economic efficiency, to find that it was appropriate and necessary to regulate EGUs under CAA section 112.

See

81 FR 24425.

The formal benefit-cost analysis relied on information reported in the RIA performed for the MATS rule. The quantified benefits accounted for in the formal benefit-cost analysis in the 2016 Supplemental Finding's alternative approach included both HAP and non-HAP air quality benefits. In this action, we propose to find that the EPA's equal reliance on the particulate matter (PM) air quality co-benefits projected to occur as a result of the reductions in HAP was flawed as the focus of CAA section

112(n)(1)(A) is HAP emissions reductions.

We use the term “formal benefit-cost analysis” to refer to an economic analysis that attempts to quantify all significant consequences of an action in monetary terms in order to determine whether an action increases economic efficiency. Assuming that all consequences can be monetized, actions with positive net benefits (

i.e.,

benefits exceed costs) improve economic efficiency.

The EPA developed an RIA for the 2012 final MATS rule pursuant to Executive Orders 12866 and 13563 and other applicable statutes (

e.g.,

the Regulatory Flexibility Act and the Unfunded Mandates Reform Act), as informed by OMB guidance

and the EPA's Economic Guidelines.

The analyses the EPA conducted generated an estimate of the quantifiable benefits of HAP reductions under the rule of $4 to $6 million annually.

The EPA also analyzed the PM air quality co-benefits of MATS and attributed these benefits to the rule. The RIA included in its analysis a consideration of the co-benefit reductions in the emissions of pollutants other than the HAP regulated by MATS, such as nitrogen oxides (NO

) and sulfur dioxide (SO

), which contribute to the formation of fine particulate matter (PM

2.5

). Reductions of these NO

and SO

emissions result from installing control technologies and implementing the compliance strategies necessary to reduce the HAP emissions directly regulated by MATS. The EPA projected that the co-benefits associated with reducing these non-HAP pollutants would be substantial. Indeed, these projected co-benefits comprised the overwhelming majority (approximately 99.9 percent) of the monetized benefits of MATS reflected in the EPA's RIA ($36 billion to $89 billion). By comparison, compliance costs of the final MATS rule were projected to be $9.6 billion in 2015, and $8.6 billion and $7.4 billion in 2020 and 2030, respectively.

These compliance costs are an estimate of the increased expenditures in capital, fuel, and other inputs by the entire power sector to comply with the EPA's requirements, while continuing to provide a given level of electricity demand. In the 2016 Supplemental Finding's alternative approach, to satisfy the required consideration of cost when determining whether it is appropriate and necessary to regulate under CAA section 112(n)(1)(A), the EPA compared these monetized costs to the monetized benefits, along with unquantified and unmonetized effects, to conclude that MATS would increase economic efficiency and, therefore, reaffirmed its earlier finding that it was appropriate and necessary to regulate EGUs.

U.S. OMB. 2003.

Circular A-4 Guidance to Federal Agencies on Preparation of Regulatory Analysis.

Available at

https://www.whitehouse.gov/sites/whitehouse.gov/files/omb/circulars/A4/a-4.pdf.

U.S. EPA. 2014.

Guidelines for Preparing Economic Analyses.

EPA-240-R-10-001. National Center for Environmental Economics, Office of Policy. Washington, DC. December. Available at

https://www.epa.gov/environmental-economics/guidelines-preparing-economic-analyses.

Docket ID No. EPA-HQ-OAR-2009-0234-20503.

Like the MATS RIA, all benefits and costs in this and subsequent sections are reported in 2007 dollars.

See

Table 3-5 of the RIA:

https://www3.epa.gov/ttn/ecas/docs/ria/utilities_ria_final-mats_2011-12.pdf.

The EPA's justification for its equal reliance on the co-benefits of non-HAP emissions when setting the MATS standards in its CAA section 112(n)(1)(A) determination was flawed. The Agency erred in concluding that the statutory text of CAA section 112(n)(1)(A) and the legislative history of CAA section 112 more generally “expressly support[ed]” the position that it was reasonable to consider co-benefits, and give equal weight to those co-benefits, in a CAA section 112(n)(1)(A) appropriate and necessary finding. 81 FR 24439. The 2016 Supplemental Finding pointed to CAA section 112(n)(1)(A)'s directive to “perform a study of the hazards to public health reasonably anticipated to occur as a result of emissions by electric utility steam generating units of [HAP] after imposition of the requirements of [the CAA],” and noted that the requirement to consider co-benefit reduction of HAP resulting from other CAA programs highlighted Congress' understanding that programs targeted at reducing non-HAP pollutants can and do result in the reduction of HAP emissions.

Id.

The finding also noted that the Senate Report on CAA section 112(d)(2) recognized that maximum achievable control technology (MACT) standards would have the collateral benefit of controlling criteria pollutants.

Id.

However, these statements acknowledging that reductions in HAP can have the collateral benefit of reducing non-HAP emissions and vice versa, provides no support for the proposition that any such co-benefits should be the Agency's primary consideration when making a finding under CAA section 112(n)(1)(A). Indeed, it would be highly illogical for the Agency to make a determination that regulation under CAA section 112, which is expressly designed to deal with HAP, is justified principally on the basis of the criteria pollutant impacts of these regulations. That is, if the HAP-related benefits are not at least moderately commensurate with the cost of HAP controls, then no amount of co-benefits can offset this imbalance for purposes of a determination that it is appropriate to regulate under CAA section 112(n)(1)(A).

Cf. Michigan,

135 S. Ct. at 2707 (“One would not say that it is even rational, never mind “appropriate,” to impose billions of dollars in economic costs in return for a few dollars in health or environmental benefits.”).

The 2016 Supplemental Finding's benefit-cost approach also erred in implying that the results of an economic efficiency test, as informed by the benefit-cost analysis presented in the MATS RIA, should govern the cost consideration assessment in CAA section 112(n)(1)(A). A formal benefit-cost analysis does not dictate how cost should be considered under CAA section 112(n)(1)(A), particularly where, as noted above, the statutory provision indicates Congress' particular concern about risks associated with HAP and the benefits that would accrue from reducing those risks. Although an analysis of all benefits and costs in accordance with generally recognized benefit-cost analysis practices is appropriate for informing the public about the potential effects of any regulatory action, as well as for complying with the requirements of Executive Order 12866, this does not mean that equal consideration of all benefits and costs, including co-benefits, is appropriate for the specific statutory appropriate and necessary finding called for under CAA section 112(n)(1)(A). Rather this finding is necessarily governed by the particular statutory language and context of this provision, as discussed below.

In sum, the Agency did not provide any meaningful support for its conclusion that the statutory text and legislative history support placing consideration of co-benefits in a CAA section 112(n)(1)(A) determination on equal footing with the consideration of HAP-specific benefits and, as explained below, the statutory text strongly supports the use of a different approach.

2. It Is Not Appropriate and Necessary To Regulate EGUs Under CAA Section 112

In this action, the EPA proposes to conclude that it is not appropriate and necessary to regulate HAP from EGUs under CAA section 112 because the costs of such regulation grossly outweigh the HAP benefits. The EPA is taking comment on its proposal that direct comparison of the rule's costs and benefits is a reasonable approach, if not the only permissible approach, to considering costs in response to

Michigan,

and, further, that such a comparison performed under CAA section 112(n)(1)(A) should focus primarily on benefits associated with reduction of HAP (Comment C-2). A proper consideration of costs based on this approach demonstrates that the

total cost of compliance with MATS ($7.4 to $9.6 billion annually) dwarfs the monetized HAP benefits of the rule ($4 to $6 million annually). As discussed further below, while there are unquantified HAP benefits and significant monetized PM co-benefits associated with MATS, the Administrator has concluded that the identification of these benefits is not sufficient, in light of the gross imbalance of monetized costs and HAP benefits, to support a finding that it is appropriate and necessary to regulate EGUs under CAA section 112.

The statutory text of CAA section 112(n)(1)(A) and the

Michigan

decision both support focusing the “appropriate and necessary” determination on HAP-specific benefits and costs. The study referenced in CAA section 112(n)(1)(A) specifically focuses on the hazards to public health that will reasonably occur as a result of HAP emissions, not harmful emissions in general. According to this section, “The Administrator shall regulate electric utility steam generating units under this section, if the Administrator finds such regulation is appropriate and necessary after considering the results of the study required by this subparagraph.” The text, on its face, thus, suggests that Congress wanted the Administrator's appropriate and necessary determination to be focused on the health hazards related to HAP emissions and the potential benefits of avoiding those hazards by reducing HAP emissions. As noted in section II.C.1.b. of this preamble, while the provision acknowledges the existence of the phenomenon of co-benefits by referencing the potential for ancillary reductions of HAP emissions by way of CAA provisions targeted at other pollutants, acknowledgement of that fact does not address whether ancillary reductions of criteria pollutants should be part of the Administrator's determination under CAA section 112(n)(1)(A), which is undeniably focused on hazards resulting from HAP-specific emissions. Indeed, the direction to consider whether it is appropriate and necessary to regulate HAP after criteria pollutants have been addressed by the CAA's other requirements is, if anything, support for the conclusion that it is

not

proper to place much weight on the co-benefits of further criteria pollutant reductions as part of the CAA section 112(n)(1)(A) determination. Directing the EPA to study HAP effects under CAA section 112

after

other provisions of the CAA had been implemented suggests that Congress envisioned that the judgement about whether additional regulation was appropriate and necessary should be predicated primarily on an assessment of HAP emissions from this source category. Similarly, the general recognition of the existence of collateral benefits or controlling criteria pollutants in CAA section 112's legislative history

does not shed any light on whether such benefits should be given equal consideration in a CAA section 112(n)(1)(A) determination. This is particularly so where that legislative history is unconnected to CAA section 112(n)(1)(A), a special provision written by Congress to address the unique circumstances facing EGUs. In fact, it would not be reasonable to rely on such legislative history in light of the Supreme Court's conclusion that the Agency erred attempting to “harmonize” CAA section 112(n)(1)(A) with the remainder of CAA section 112. As the Court noted, “[t]his line of reasoning overlooks the whole point of having a separate provision about power plants: Treating power plants different from other stationary sources.”

Michigan,

135 S. Ct. at 2710.

See

Legal Memorandum at 25 n.28 (citing

A Legislative History of the Clean Air Act Amendments of 1990,

Vol. 5, at 8512 (CAA Amendments of 1989, at 172,

Report of the Committee on Environment and Public Works,

S.1630)).

Finally, we note that this action proposes to primarily consider the costs of MATS in comparison with the HAP benefits of the hazardous pollution reductions from MATS. In keeping with CAA section 112(n)(1)(A) and the overall structure of the CAA, we think it is appropriate not to give equal weight to non-HAP co-benefits in this comparison. Congress established a rigorous system for setting standards of acceptable levels of criteria air pollutants and wrote a comprehensive framework directing the implementation of those standards in order to address the health and environmental impacts associated with those pollutants.

See, e.g.,

42 U.S.C. 7409; 7410; 7501; 7502; 7505a; 7506; 7506a; 7507; 7509; 7509a; 7511; 7511a; 7511b; 7511c; 7511d; 7511e; 7511f; 7512; 7512a; 7513; 7513a; 7513b; 7514; and 7515. As noted above, the vast majority of estimated monetized benefits resulting from MATS are associated with reductions in PM

2.5

precursor emissions, principally NO

and SO

. Both NO

and SO

are criteria pollutants and precursors to criteria pollutants that are already addressed by the cavalcade of statutory provisions governing levels of these pollutants, including the National Ambient Air Quality Standards (NAAQS) provisions that require the EPA to set standards for criteria pollutants requisite to protect public health with an adequate margin of safety, and by state, regional, and national rulemakings establishing control measures to meet those levels. To the extent that additional reductions of these criteria pollutants are necessary to protect public health, regulation explicitly targeted at these pollutants is best reserved for the NAAQS program, under which Congress provided the EPA ample authority to regulate.

The total cost of compliance with MATS ($7.4 to $9.6 billion annually)

vastly outweighs the monetized HAP benefits of the rule ($4 to $6 million annually).

Even with the substantial monetized PM co-benefits and the significant unquantified HAP benefits associated with MATS, the gross disparity between monetized costs and HAP benefits, which we believe to be the primary focus of the Administrator's determination in CAA section 112(n)(1)(A), is too large to support an affirmative appropriate and necessary finding. As explained in the MATS RIA, the only health benefit attributed to reducing Hg emissions that the EPA could quantify and monetize was IQ loss in children born to a subset of recreational fishers who consume fish during pregnancy.

The EPA also identified benefits associated with regulation of HAP from EGUs that could not be quantified. These effects include impacts of Hg on human health (including neurologic, cardiovascular, genotoxic, and immunotoxic effects), a variety of adverse health effects associated with exposure to certain non-Hg HAP (including cancer, and chronic and acute health disorders that implicate multiple organ systems such as the lungs and kidneys), and effects on wildlife and ecosystems.

13 14

See

Table 3-5 on page 3-14 and Table 3-16 on page 3-31 of the MATS RIA.

See

Table ES-4 on page ES-6 of the MATS RIA.

U.S. EPA, 2011.

Revised Technical Support Document: National-Scale Assessment of Mercury Risk to Populations with High Consumption of Self-Caught Freshwater Fish In Support of the Appropriate and Necessary Finding for Coal- and Oil-Fired Electric Generating Units.

Office of Air Quality Planning and Standards. November. EPA-452/R-11-009. Docket ID No. EPA-HQ-OAR-2009-0234-19913.

See

Chapters 4 and 5 of the MATS RIA.

In addition, the MATS RIA attributed unquantified health benefits to reductions in emissions of nitrogen dioxide (NO

) and SO

. However, as discussed above, these unquantified criteria pollutant co-benefits are no longer relevant given the different approach to considering such co-benefits that the EPA is now proposing to take.

See

Chapter 5 of the MATS RIA.

The EPA acknowledges the importance of these benefits and the limitations on the Agency's ability to monetize HAP-specific benefits. The

EPA agrees that such benefits are relevant to any comparison of the benefits and costs of a regulation. Because unquantified benefits are, by definition, not considered in monetary terms, the Administrator must evaluate the evidence of unquantified benefits and determine the extent to which they alter any conclusions based on the comparison of monetized costs and benefits. The MATS RIA accounts for all the monetized

and

unquantified benefits of the rule, and the EPA's proposed approach to the cost-benefit analysis in the RIA does not discount the existence or importance of the unquantified benefits of reducing HAP emissions.

Instead, after fully acknowledging the existence and importance of such benefits, the EPA proposes to conclude that substantial and important unquantified benefits of MATS are not sufficient to overcome the significant difference between the monetized benefits and costs of this rule. As noted, the unquantified HAP-related benefits of MATS involve only a limited set of mercury and other HAP-related morbidity effects in humans and ecosystems. The EPA has provided an updated comparison of costs and target pollutant benefits in a memorandum to the rulemaking docket.

Table 1 of the memorandum estimates that the net target HAP benefits of the rule (HAP benefits—costs) are negative. As noted elsewhere in the notice, the actual costs and benefits of the MATS rule may differ from the EPA's analysis. However, as explained in the memorandum, given that the CAA section 112(n)(1)(A) finding is a threshold analysis that Congress intended the Agency would complete prior to regulation, the EPA believes it is reasonable for purposes of this reconsideration to rely on the estimates projected prior to the rule's taking effect,

i.e.,

the estimates of costs and benefits calculated in the 2011 RIA. In addition, even assuming that actual costs and benefits differed from projections made in 2011, given the large difference between target HAP benefits and estimated costs, the outcome of the Agency's proposed finding here would likely stay the same.

Id.

The Agency is not in this proposed replacement to the 2016 Supplemental Finding reopening the prior findings and risk assessments made over the last two decades. The EPA also explained in the MATS RIA that there are significant obstacles to successfully quantifying and monetizing the public health benefits from reducing HAP emissions. These obstacles include gaps in toxicological data, uncertainties in extrapolating results from high-dose animal experiments to estimate human effects at lower doses, limited monitoring data, difficulties in tracking diseases such as cancer that have long latency periods, and insufficient economic research to support the valuation of the health impacts often associated with exposure to individual HAP.

Compliance Cost, HAP Benefits, and Ancillary Co-Pollutant Benefits for “National Emission Standards for Hazardous Air Pollutants: Coal-and Oil-Fired Electric Utility Steam Generating Units—Reconsideration of Supplemental Finding and Residual Risk and Technology Review.”

For all of these reasons, and paying particular heed to the statutory text and purpose of CAA section 112(n)(1)(A) as well as the Supreme Court's direction in

Michigan,

we propose to find that it is not appropriate and necessary to regulate coal- and oil-fired EGUs under section 112 of the CAA.

D. Effects of This Proposed Replacement of the Supplemental Finding

1. Effects of This Proposed Replacement

Final action on this proposed replacement of the 2016 Supplemental Finding will reverse the Agency's conclusion under CAA section 112(n)(1)(A), first made in 2000 and later affirmed in 2012 and 2016, that it is appropriate and necessary to regulate HAP from EGUs. We propose to conclude that finalizing this replacement will not remove the Coal- and Oil-Fired EGU source category from the CAA section 112(c)(1) list, nor will finalizing this revision otherwise affect the existing CAA section 112(d) emissions standards promulgated in 2012. Under D.C. Circuit case law, the EPA's determination that a source category was listed in error does not by itself remove a source category from the CAA section 112(c)(1) list—even EGUs, notwithstanding their special treatment under CAA section 112(n).

New Jersey

EPA,

517 F.3d 574 (D.C. Cir. 2008). Instead, in order to remove a source category from the CAA section 112(c)(1) list, the EPA must determine that the CAA section 112(c)(9) statutory criteria for delisting have been met.

Id.

The EPA requests comment on its interpretation of

New Jersey

in the context of this proposed finding (Comment C-3).

In 2005, the EPA reversed the December 2000 Finding and concluded that it was neither appropriate nor necessary to regulate coal- and oil-fired EGUs under CAA section 112 and delisted such units from the CAA section 112(c) source category list. 70 FR 15994. In that rule we stated, “EPA reasonably interprets section 112(n)(1)(A) as providing it authority to remove coal- and oil-fired units from the section 112(c) list at any time that it makes a negative appropriate and necessary finding under the section.” 70 FR 16032 (2005 Delisting Rule). In the 2005 Delisting Rule, the EPA “identified errors in the prior [2000] finding and determined that the finding lacked foundation.”

Id.

at 16033. Because we found that the 2000 Finding had been in error at the time of listing, we concluded that coal- and oil-fired EGUs “should never have been listed under section 112(c) and therefore the criteria of section 112(c)(9) do not apply” in removing the source category from the list.

Id.

In addition, we pointed out that the inclusion of EGUs on the 112(c)(1) list was not a “final agency action.”

Id.

Therefore, we stated that we had “inherent authority under the CAA to revise [the listing] at any time based on either identified errors in the December 2000 finding or on new information that bears upon that finding.”

Id.

The D.C. Circuit rejected the EPA's interpretations and vacated the 2005 Delisting Rule, holding that the CAA unambiguously requires the delisting criteria in CAA section 112(c)(9) to have been met before “any” source category can be removed from the CAA section 112(c)(1) list.

New Jersey,

517 F.3d at 582. It specified that, under the CAA's plain text and under step one of

Chevron,

“the

only

way the EPA could remove EGUs from the section 112(c)(1) list” was to satisfy those criteria.

Id.

(emphasis added). The Court expressly rejected the EPA's argument that, “[l]ogically, if EPA makes a determination under section 112(n)(1)(A) that power plants should not be regulated at all under section 112 . . . [then] this determination

ipso facto

must result in removal of power plants from the section 112(c) list.”

Id.

(quoting the EPA's brief). Instead, the Court maintained that CAA section 112(n)(1) governed only how the Administrator determines whether to list EGUs, and that any and all attempts to remove categories from the list were under the exclusive purview of CAA section 112(c)(9).

See id.

The Court further held that the existence of CAA section 112(c)(9) limited the normal discretion an Agency would typically have to reverse its position and undo the administrative determination to list EGUs as a source category.

See Id.

at 582-83.

In this action, we propose to reverse the conclusions presented in the 2016 Supplemental Finding and to find that, after consideration of the cost of compliance with the CAA section 112(d) standards, it is not appropriate and necessary to regulate HAP emissions from EGUs under CAA section 112. Consistent with

New Jersey,

the EPA is proposing to find that this reversal of the CAA section 112(n)(1)(A) determination, if finalized, would not have the effect of removing EGUs from the CAA section 112(c)(1) source category list. Because EGUs would remain on the CAA section 112(c)(1)

source category list, the CAA section 112(d) standards for that category, as promulgated in the MATS rule, would be unaffected by final action on this proposal.

2. Alternative Interpretations of Effects of This Proposed Replacement: Requests for Comment

The EPA also solicits comment on two alternative interpretations of the impact of reversing the 2016 Supplemental Finding. Specifically, the Agency solicits comment under two separate theories on whether, contrary to the interpretation discussed above, the EPA would have authority to rescind the MATS rule and delist EGUs from CAA section 112 if, acting on remand following the Supreme Court's opinion in

Michigan,

it were to finalize its proposed conclusion that it is not appropriate and necessary to regulate HAP from coal- and oil-fired EGUs (Comment C-4). The Agency also solicits comment on whether, in light of the fact that the CAA section 112(n)(1)(A) finding is a threshold determination to setting the CAA section 112(d) standards, we would be obligated to rescind the rule if we were to finalize our proposed finding that it is not appropriate and necessary to regulate HAP from these sources, even if such a finding did not remove EGUs from the list of covered sources under CAA section 112(c) (Comment C-5).

In particular, we solicit comment on whether the EPA could reasonably conclude that the D.C. Circuit's holding in

New Jersey

EPA

does not limit the Agency's authority to rescind the MATS rule, under two alternative interpretations (Comment C-6). Under the first alternative interpretation, we seek comment on whether

New Jersey

is distinguishable because the facts here are sufficiently different from those considered by the Court reviewing the 2005 Delisting Rule at issue (Comment C-7). In that case, the original 2000 Finding and CAA section 112(c)(1) listing were in place, but because the EPA had not yet promulgated CAA section 112(d) standards, the finding itself was not yet reviewable. CAA section 112(e)(4);

see also UARG

EPA,

No. 01-1074, 2001 U.S. App. LEXIS 18436, 2001 WL 936363 (D.C. Cir. July 26, 2001). Here, the 2012 Finding was challenged and reviewed by the Supreme Court in

Michigan

EPA,

which found that the EPA's determination that it was appropriate and necessary to regulate HAP from EGUs was flawed. Because the Supreme Court found that determination to be flawed, the EPA necessarily retains the discretion to reach a different conclusion from that reached in 2012 when we promulgated MATS. This proposed reversal of the 2016 Supplemental Finding is a continuation of the Agency's response to the Supreme Court's remand, and

New Jersey

does not limit the effect of an action made in response to a Supreme Court decision finding the original action flawed, nor does it limit the Agency's ability to revise its response to a Supreme Court decision. Therefore, the EPA would have authority to rescind MATS and remove EGUs from the list of source categories regulation under CAA section 112 after finalizing this reversal of the 2016 Supplemental Finding.

Under the second alternative interpretation, the EPA seeks comment on whether, were the proposed reversal to be finalized, EGUs would remain on the CAA section 112(c) list of sources, but the EPA would have the authority to rescind the standards regulating those source's emissions under CAA section 112(d) in light of the fact that CAA section 112(n)(1)(A) plainly establishes that the Administrator must find regulation under CAA section 112 is appropriate and necessary as a prerequisite to undertaking such regulation (Comment C-8).

New Jersey

EPA

held that the EPA may not remove a source category from the CAA section 112(c) list without demonstrating that the delisting analysis under CAA section 112(c)(9) has been satisfied, but the decision did not address the question whether, in the absence of a valid appropriate and necessary finding, the EPA must regulate EGUs for HAP.

Finally, although the alternative interpretations described immediately above both suggest the EPA would have the discretionary authority to rescind MATS (either with or without delisting), the EPA solicits comment on whether, under either alternative interpretation, the Agency would instead be

obligated

to rescind MATS once it finalized a reversal of the 2016 Supplemental Finding (Comment C-9).

We solicit comment on all aspects of these alternative interpretations of the impacts of replacing the 2016 Supplemental Finding and these potential alternate readings of the Court's decision in

New Jersey

(Comment C-10).

III. Criteria for Delisting a Source Category Under CAA Section 112(c)(9)

As noted above,

New Jersey

held that the EPA cannot remove a source category from the CAA section 112(c) source category list without addressing the delisting criteria in CAA section 112(c)(9). CAA section 112(c)(9)(B) provides that “[t]he Administrator may delete any source category” from the CAA section 112(c) source category list if the Agency determines that: (1) For HAP that may cause cancer in humans, “no source in the category (or group of sources in the case of area sources) emits such hazardous air pollutants in quantities which may cause a lifetime risk of cancer greater than one in one million to the individual in the population who is most exposed to emissions of such pollutants from the source (or group of sources in the case of area sources)”; and (2) for HAP that may result in human health effects other than cancer or adverse environmental effects, “a determination that emissions from no source in the category or subcategory concerned (or group of sources in the case of area sources) exceed a level which is adequate to protect public health with an ample margin of safety and no adverse environmental effect will result from emissions from any source.”

In this action, the EPA is neither conducting a delisting analysis under CAA section 112(c)(9) for the Coal- and Oil-Fired EGU source category, nor soliciting comment on whether such an analysis should be conducted, or on what any such analysis would demonstrate. Any such comments would be outside the scope of this action.

The Agency notes that the proposed results of its risk review indicate that with the MATS rule in place, the estimated inhalation cancer risk to the individual most exposed to actual emissions from the source category is 9-in-1 million. As noted above, the EPA is not proposing a delisting analysis and any such analysis would likely differ from the analysis done for the CAA section 112(f)(2) risk review in important aspects.

In addition, on two previous occasions, the EPA has examined the statutory delisting criteria with respect to EGUs and found that the criteria were not met. We summarize without adding to those findings below.

In 2011, in response to the EPA's request for comments on the proposed MATS rule, the Utility Air Regulatory Group (UARG) submitted a petition pursuant to CAA section 112(c)(9) requesting that coal-fired EGUs be removed from the CAA section 112(c) List of Categories of Major and Area Sources.

In its petition, UARG

asserted that: (1) No coal-fired EGU or group of coal-fired EGUs emit HAP in amounts that will cause a lifetime cancer risk greater than 1-in-1 million; and (2) no coal-fired EGU or group of coal-fired EGUs emit non-carcinogenic HAP in amounts that will exceed a level which is adequate to protect public health with an ample margin of safety or cause adverse environmental effects. The EPA denied this petition on several grounds.

First, the EPA rejected UARG's request on the basis that, under D.C. Circuit precedent, the Agency is not permitted to delist a portion of a source category that poses cancer risks.

Second, the EPA found that UARG's data and analyses identified a maximum individual cancer risk of 4-in-1 million, which exceeds the statutory threshold in CAA section 112(c)(9)(B)(i) of 1-in-1 million. Additionally, the EPA found that UARG's analysis did not fully characterize noncancer human health effects for the source category and further, that UARG failed to show that “no adverse environmental effects will result from emissions from any source” pursuant to CAA section 112(c)(9)(B)(ii). For all these reasons, the EPA denied UARG's petition to delist coal-fired EGUs from the CAA section 112(c) source category list. UARG challenged the EPA's denial of its delisting petition as arbitrary and capricious, and the D.C. Circuit dismissed UARG's challenge on the basis that the EPA had adequately demonstrated that the CAA section 112(c)(9) delisting criteria were not met by UARG's analysis.

White Stallion,

748 F.3d at 1248.

Petition of the Utility Air Regulatory Group for the De-Listing of Coal-Fired Electric Utility Steam Generating Units as a Source Category Subject to Section 112 of the Clean Air Act.

Docket ID No. EPA-HQ-OAR-2009-0234-17777.

77 FR 9365 (February 16, 2012).

UARG petitioned the Agency to delist coal-fired EGUs, which represent only a portion of the listed source category. The EPA believed it was not permitted to delist a portion of a source category, where that source category poses cancer risks.

NRDC

U.S. EPA,

489 F.3d 1364 (D.C. Cir. 2007). Specifically, in

NRDC,

the D.C. Circuit held that the Agency's attempt to delist a “low-risk” subcategory was “contrary to the plain language of the statute,” and that the statute only authorized the Agency to remove source categories pursuant to CAA section 112(c)(9).

Id.

at 1373 (“Because EPA's interpretation of Section 112(c)(9) as allowing it to exempt the risk-based subcategory is contrary to the plain language of the statute, the EPA's interpretation fails at

Chevron

step one.”).

The EPA also independently conducted an analysis which also confirmed that the Coal- and Oil-Fired EGU source category cannot be delisted pursuant to CAA section 112(c)(9).

The EPA analyzed non-Hg inhalation risks from 16 EGU facility case studies, including both coal- and oil-fired EGUs. Of the 16 facilities analyzed, six had cancer risks greater than 1-in-1 million, exceeding the delisting criteria in CAA section 112(c)(9)(B)(i). Because EGUs failed to meet the first delisting requirement, the Agency did not need to determine whether the second delisting requirement was satisfied.

U.S. EPA, 2011.

Supplement to the Non-Hg Case Study Chronic Inhalation Risk Assessment in Support of the Appropriate and Necessary Finding for Coal- and Oil-Fired Electric Generating Units.

November. EPA-452/R-11-013. Docket ID No. EPA-HQ-OAR-2009-0234-19912.

IV. Background on the RTR Action

A. What is the statutory authority for this action?

The statutory authority for this action is provided by sections 112 and 301 of the CAA, as amended (42 U.S.C. 7401

et seq.

). Section 112 of the CAA establishes a two-stage regulatory process to develop standards for emissions of HAP from stationary sources. Generally, the first stage involves establishing technology-based standards and the second stage involves evaluating those standards that are based on MACT to determine whether additional standards are needed to address any remaining risk associated with HAP emissions. This second stage is commonly referred to as the “residual risk review.” In addition to the residual risk review, the CAA also requires the EPA to review standards set under CAA section 112 every 8 years to determine if there are “developments in practices, processes, or control technologies” that may be appropriate to incorporate into the standards. This review is commonly referred to as the “technology review.” When the two reviews are combined into a single rulemaking, it is commonly referred to as the “risk and technology review.” The discussion that follows identifies the most relevant statutory sections and briefly explains the contours of the methodology used to implement these statutory requirements. A more comprehensive discussion appears in the document titled

CAA Section 112 Risk and Technology Reviews: Statutory Authority and Methodology

in the docket for this rulemaking.

In the first stage of the CAA section 112 standard setting process, the EPA promulgates technology-based standards under CAA section 112(d) for categories of sources identified as emitting one or more of the HAP listed in CAA section 112(b). Sources of HAP emissions are either major sources or area sources, and CAA section 112 establishes different requirements for major source standards and area source standards. “Major sources” are those that emit or have the potential to emit 10 tpy or more of a single HAP or 25 tpy or more of any combination of HAP. All other sources are “area sources.” For major sources, CAA section 112(d)(2) provides that the technology-based NESHAP must reflect the maximum degree of emission reductions of HAP achievable (after considering cost, energy requirements, and non-air quality health and environmental impacts). These standards are commonly referred to as MACT standards. CAA section 112(d)(3) also establishes a minimum control level for MACT standards, known as the MACT “floor.” The EPA must also consider control options that are more stringent than the floor. Standards more stringent than the floor are commonly referred to as beyond-the-floor standards. In certain instances, as provided in CAA section 112(h), the EPA may set work practice standards where it is not feasible to prescribe or enforce a numerical emission standard. For area sources, CAA section 112(d)(5) gives the EPA discretion to set standards based on generally available control technologies or management practices (GACT standards) in lieu of MACT standards.

The second stage in standard-setting focuses on identifying and addressing any remaining (

i.e.,

“residual”) risk according to CAA section 112(f). For source categories subject to MACT standards, section 112(f)(2) of the CAA requires the EPA to determine whether promulgation of additional standards is needed to provide an ample margin of safety to protect public health or to prevent an adverse environmental effect. Section 112(d)(5) of the CAA provides that this residual risk review is not required for categories of area sources subject to GACT standards. Section 112(f)(2)(B) of the CAA further expressly preserves the EPA's use of the two-step approach for developing standards to address any residual risk and the Agency's interpretation of “ample margin of safety” developed in the

National Emissions Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants

(Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA notified Congress in the Risk Report that the Agency intended to use the Benzene NESHAP approach in making CAA section 112(f) residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently adopted this approach in its residual risk determinations and the Court upheld the EPA's interpretation that CAA section 112(f)(2) incorporates the approach established in the Benzene

NESHAP.

See NRDC

EPA,

529 F.3d 1077, 1083 (D.C. Cir. 2008).

The approach incorporated into the CAA and used by the EPA to evaluate residual risk and to develop standards under CAA section 112(f)(2) is a two-step approach. In the first step, the EPA determines whether risks are acceptable. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR)

of approximately 1 in 10 thousand.” 54 FR 38045, September 14, 1989. If risks are unacceptable, the EPA must determine the emissions standards necessary to reduce risk to an acceptable level without considering costs. In the second step of the approach, the EPA considers whether the emissions standards provide an ample margin of safety to protect public health “in consideration of all health information, including the number of persons at risk levels higher than approximately 1 in 1 million, as well as other relevant factors, including costs and economic impacts, technological feasibility, and other factors relevant to each particular decision.”

Id.

The EPA must promulgate emission standards necessary to provide an ample margin of safety to protect public health. After conducting the ample margin of safety analysis, we consider whether a more stringent standard is necessary to prevent, taking into consideration costs, energy, safety, and other relevant factors, an adverse environmental effect.

Although defined as “maximum individual risk,” MIR refers only to cancer risk. MIR, one metric for assessing cancer risk, is the estimated risk if an individual were exposed to the maximum level of a pollutant for a lifetime.

CAA section 112(d)(6) separately requires the EPA to review standards promulgated under CAA section 112 and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less often than every 8 years. In conducting this review, which we call the “technology review,” the EPA is not required to recalculate the MACT floor.

Natural Resources Defense Council (NRDC)

EPA,

529 F.3d 1077, 1084 (D.C. Cir. 2008).

Association of Battery Recyclers, Inc.

EPA,

716 F.3d 667 (D.C. Cir. 2013). The EPA may consider cost in deciding whether to revise the standards pursuant to CAA section 112(d)(6).

B. What is this source category and how does the current NESHAP regulate its HAP emissions?

The NESHAP for the Coal- and Oil-Fired EGU source category (commonly referred to as MATS) were initially promulgated on February 16, 2012 (77 FR 9304), under title 40 part 63, subpart UUUUU. The MATS rule was amended on April 19, 2012 (77 FR 23399), to correct typographical errors and certain preamble text that was inconsistent with regulatory text; on April 24, 2013 (78 FR 24073), to update certain emission limits and monitoring and testing requirements applicable to new sources; on November 19, 2014 (79 FR 68777), to revise definitions for startup and shutdown and to finalize work practice standards and certain monitoring and testing requirements applicable during periods of startup and shutdown; and on April 6, 2016 (81 FR 20172), to correct conflicts between preamble and regulatory text and to clarify regulatory text. In addition, the electronic reporting requirements of the rule were amended on March 24, 2015 (80 FR 15510), to allow for the electronic submission of Portable Document Format (PDF) versions of certain reports until April 16, 2017, while the EPA's Emissions Collection and Monitoring Plan System (ECMPS) is revised to accept all reporting that is required by the rule, and on April 6, 2017 (82 FR 16736), and on July 2, 2018 (83 FR 30879), to extend the interim submission of PDF versions of reports through June 30, 2018, and July 1, 2020, respectively.

The MATS rule applies to coal- and oil-fired EGUs located at both major and area sources of HAP emissions. The sources subject to the MATS rule include each individual or group of coal- or oil-fired EGUs. An existing affected source is the collection of coal- or oil-fired EGUs in a subcategory within a single contiguous area and under common control. A new affected source is each coal- or oil-fired EGU for which construction or reconstruction began after May 3, 2011. As previously stated in section I of this preamble, an electric utility steam generating unit is a fossil fuel-fired combustion unit of more than 25 megawatts (MW) that serves a generator that produces electricity for sale. A unit that cogenerates steam and electricity and supplies more than one-third of its potential electric output capacity and more than 25 MW electric output to any utility power distribution system for sale is also considered an electric utility steam generating unit. The MATS rule defines additional terms for determining rule applicability, including, but not limited to, definitions for “Coal-fired electric utility steam generating unit,” “Oil-fired electric utility steam generating unit,” and “Fossil fuel-fired.” Certain types of electric generating units are not subject to 40 CFR part 63, subpart UUUUU: Any unit designated as a major source stationary combustion turbine subject to subpart YYYY of part 63 and any unit designated as an area source stationary combustion turbine, other than an integrated gasification combined cycle (IGCC) unit; any EGU that is not a coal- or oil-fired EGU and that meets the definition of a natural gas-fired EGU in 40 CFR 63.10042; any EGU greater than 25 MW that has the capability of combusting either coal or oil, but does not meet the definition of a coal- or oil-fired EGU because it did not fire sufficient coal or oil to satisfy the average annual heat input requirement set forth in the definitions for coal-fired and oil-fired EGUs in 40 CFR 63.10042; and any electric steam generating unit combusting solid waste (

i.e.,

a solid waste incineration unit) subject to standards established under sections 129 and 111 of the CAA.

For coal-fired EGUs, the rule established standards to limit emissions of Hg, acid gas HAP, non-Hg HAP metals (

e.g.,

nickel, lead, chromium), and organic HAP (

e.g.,

formaldehyde, dioxin/furan). Standards for hydrochloric acid (HCl) serve as a surrogate for the acid gas HAP, with an alternate standard for SO

that may be used as a surrogate for acid gas HAP for those coal-fired EGUs with flue gas desulfurization (FGD) systems and SO

continuous emissions monitoring systems (CEMS) installed and operational. Standards for filterable particulate matter (fPM) serve as a surrogate for the non-Hg HAP metals, with standards for total non-Hg HAP metals and individual non-Hg HAP metals provided as alternative equivalent standards. Work practice standards limit formation and emission of the organic HAP.

For oil-fired EGUs, the rule establishes standards to limit emissions of HCl and hydrogen fluoride (HF), total HAP metals (

e.g.,

Hg, nickel, lead), and organic HAP (

e.g.,

formaldehyde, dioxin/furan). Standards for fPM serve as a surrogate for total HAP metals, with standards for total HAP metals and individual HAP metals provided as alternative equivalent standards. Work practice standards limit formation and emission of the organic HAP.

The MATS rule includes standards for existing and new EGUs for seven subcategories: Two for coal-fired EGUs, one for IGCC EGUs, one for solid oil-derived fuel-fired EGUs, and three for liquid oil-fired EGUs. EGUs in six of the subcategories are subject to numeric emission limits for the pollutants

described above except for organic HAP. Organic HAP are regulated by a work practice standard that requires periodic combustion process tune-ups. EGUs in the subcategory of limited-use liquid oil-fired EGUs with an annual capacity factor of less than 8 percent of its maximum or nameplate heat input are also subject to a work practice standard consisting of periodic combustion process tune-ups, but are not subject to any numeric emission limits. Emission limits for existing EGUs and new or reconstructed EGUs are summarized in Table 2 and Table 3, respectively.

Table 2—Emission Limits for Existing Affected EGUs

Subcategory

Pollutant

Emission limit

1. Coal-fired unit not low rank virgin coal

a. fPM

3.0E-2 lb/MMBtu or 3.0E-1 lb/MWh.

Total non-Hg HAP metals

5.0E-5 lb/MMBtu or 5.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-1 lb/TBtu or 8.0E-3 lb/GWh.

Arsenic, As

1.1 lb/TBtu or 2.0E-2 lb/GWh.

Beryllium, Be

2.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

Cadmium, Cd

3.0E-1 lb/TBtu or 3.0E-3 lb/GWh.

Chromium, Cr

2.8 lb/TBtu or 3.0E-2 lb/GWh.

Cobalt, Co

8.0E-1 lb/TBtu or 8.0E-3 lb/GWh.

Lead, Pb

1.2 lb/TBtu or 2.0E-2 lb/GWh.

Manganese, Mn

4.0 lb/TBtu or 5.0E-2 lb/GWh.

Nickel, Ni

3.5 lb/TBtu or 4.0E-2 lb/GWh.

Selenium, Se

5.0 lb/TBtu or 6.0E-2 lb/GWh.

b. HCl

2.0E-3 lb/MMBtu or 2.0E-2 lb/MWh.

2.0E-1 lb/MMBtu or 1.5 lb/MWh.

c. Hg

1.2 lb/TBtu or 1.3E-2 lb/GWh.

2. Coal-fired unit low rank virgin coal

a. fPM

3.0E-2 lb/MMBtu or 3.0E-1 lb/MWh.

Total non-Hg HAP metals

5.0E-5 lb/MMBtu or 5.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-1 lb/TBtu or 8.0E-3 lb/GWh.

Arsenic, As

1.1 lb/TBtu or 2.0E-2 lb/GWh.

Beryllium, Be

2.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

Cadmium, Cd

3.0E-1 lb/TBtu or 3.0E-3 lb/GWh.

Chromium, Cr

2.8 lb/TBtu or 3.0E-2 lb/GWh.

Cobalt, Co

8.0E-1 lb/TBtu or 8.0E-3 lb/GWh.

Lead, Pb

1.2 lb/TBtu or 2.0E-2 lb/GWh.

Manganese, Mn

4.0 lb/TBtu or 5.0E-2 lb/GWh.

Nickel, Ni

3.5 lb/TBtu or 4.0E-2 lb/GWh.

Selenium, Se

5.0 lb/TBtu or 6.0E-2 lb/GWh.

b. HCl

2.0E-3 lb/MMBtu or 2.0E-2 lb/MWh.

2.0E-1 lb/MMBtu or 1.5 lb/MWh.

c. Hg

4.0 lb/TBtu or 4.0E-2 lb/GWh.

3. IGCC unit

a. fPM

4.0E-2 lb/MMBtu or 4.0E-1 lb/MWh.

Total non-Hg HAP metals

6.0E-5 lb/MMBtu or 5.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

1.4 lb/TBtu or 2.0E-2 lb/GWh.

Arsenic, As

1.5 lb/TBtu or 2.0E-2 lb/GWh.

Beryllium, Be

1.0E-1 lb/TBtu or 1.0E-3 lb/GWh.

Cadmium, Cd

1.5E-1 lb/TBtu or 2.0E-3 lb/GWh.

Chromium, Cr

2.9 lb/TBtu or 3.0E-2 lb/GWh.

Cobalt, Co

1.2 lb/TBtu or 2.0E-2 lb/GWh.

Lead, Pb

1.9E+2 lb/MMBtu or 1.8 lb/MWh.

Manganese, Mn

2.5 lb/TBtu or 3.0E-2 lb/GWh.

Nickel, Ni

6.5 lb/TBtu or 7.0E-2 lb/GWh.

Selenium, Se

2.2E+1 lb/TBtu or 3.0E-1 lb/GWh.

b. HCl

5.0E-4 lb/MMBtu or 5.0E-3 lb/MWh.

c. Hg

2.5 lb/TBtu or 3.0E-2 lb/GWh.

4. Liquid oil-fired unit—continental (excluding limited-use liquid oil-fired subcategory units)

a. fPM

3.0E-2 lb/MMBtu or 3.0E-1 lb/MWh.

Total HAP metals

8.0E-4 lb/MMBtu or 8.0E-3 lb/MWh.

Individual HAP metals:

Antimony, Sb

1.3E+1 lb/TBtu or 2.0E-1 lb/GWh.

Arsenic, As

2.8 lb/TBtu or 3.0E-2 lb/GWh.

Beryllium, Be

2.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

Cadmium, Cd

3.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

Chromium, Cr

5.5 lb/TBtu or 6.0E-2 lb/GWh.

Cobalt, Co

2.1E+1 lb/TBtu or 3.0E-1 lb/GWh.

Lead, Pb

8.1 lb/TBtu or 8.0E-2 lb/GWh.

Manganese, Mn

2.2E+1 lb/TBtu or 3.0E-1 lb/GWh.

Nickel, Ni

1.1E+2 lb/TBtu or 1.1 lb/GWh.

Selenium, Se

3.3 lb/TBtu or 4.0E-2 lb/GWh.

2.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

b. HCl

2.0E-3 lb/MMBtu or 1.0E-2 lb/MWh.

c. HF

4.0E-4 lb/MMBtu or 4.0E-3 lb/MWh.

5. Liquid oil-fired unit—non-continental (excluding limited-use liquid oil-fired subcategory units)

a. fPM

3.0E-2 lb/MMBtu or 3.0E-1 lb/MWh.

Total HAP metals

6.0E-4 lb/MMBtu or 7.0E-3 lb/MWh.

Individual HAP metals:

Antimony, Sb

2.2 lb/TBtu or 2.0E-2 lb/GWh.

Arsenic, As

4.3 lb/TBtu or 8.0E-2 lb/GWh.

Beryllium, Be

6.0E-1 lb/TBtu or 3.0E-3 lb/GWh.

Cadmium, Cd

3.0E-1 lb/TBtu or 3.0E-3 lb/GWh.

Chromium, Cr

3.1E+1 lb/TBtu or 3.0E-1 lb/GWh.

Cobalt, Co

1.1E+2 lb/TBtu or 1.4 lb/GWh.

Lead, Pb

4.9 lb/TBtu or 8.0E-2 lb/GWh.

Manganese, Mn

2.0E+1 lb/TBtu or 3.0E-1 lb/GWh.

Nickel, Ni

4.7E+2 lb/TBtu or 4.1 lb/GWh.

Selenium, Se

9.8 lb/TBtu or 2.0E-1 lb/GWh.

4.0E-2 lb/TBtu or 4.0E-4 lb/GWh.

b. HCl

2.0E-4 lb/MMBtu or 2.0E-3 lb/MWh.

c. HF

6.0E-5 lb/MMBtu or 5.0E-4 lb/MWh.

6. Solid oil-derived fuel-fired unit

a. fPM

8.0E-3 lb/MMBtu or 9.0E-2 lb/MWh.

Total non-Hg HAP metals

4.0E-5 lb/MMBtu or 6.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-1 lb/TBtu or 7.0E-3 lb/GWh.

Arsenic, As

3.0E-1 lb/TBtu or 5.0E-3 lb/GWh.

Beryllium, Be

6.0E-2 lb/TBtu or 5.0E-4 lb/GWh.

Cadmium, Cd

3.0E-1 lb/TBtu or 4.0E-3 lb/GWh.

Chromium, Cr

8.0E-1 lb/TBtu or 2.0E-2 lb/GWh.

Cobalt, Co

1.1 lb/TBtu or 2.0E-2 lb/GWh.

Lead, Pb

8.0E-1 lb/TBtu or 2.0E-2 lb/GWh.

Manganese, Mn

2.3 lb/TBtu or 4.0E-2 lb/GWh.

Nickel, Ni

9.0 lb/TBtu or 2.0E-1 lb/GWh.

Selenium, Se

1.2 lb/Tbtu 2.0E-2 lb/GWh.

b. HCl

5.0E-3 lb/MMBtu or 8.0E-2 lb/MWh.

3.0E-1 lb/MMBtu or 2.0 lb/MWh.

c. Hg

2.0E-1 lb/TBtu or 2.0E-3 lb/GWh.

Units of emission limits:

lb/MMBtu = pounds pollutant per million British thermal units fuel input;

lb/TBtu = pounds pollutant per trillion British thermal units fuel input;

lb/MWh = pounds pollutant per megawatt-hour electric output (gross); and

lb/GWh = pounds pollutant per gigawatt-hour electric output (gross).

Alternate SO

limit may be used if the EGU has some form of FGD system and SO

CEMS installed.

Table 3—Emission Limits for New or Reconstructed Affected EGUs

Subcategory

Pollutant

Emission limit

1. Coal-fired unit not low rank virgin coal

a. fPM

9.0E-2 lb/MWh.

Total non-Hg HAP metals

6.0E-2 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-3 lb/GWh.

Arsenic, As

3.0E-3 lb/GWh.

Beryllium, Be

6.0E-4 lb/GWh.

Cadmium, Cd

4.0E-4 lb/GWh.

Chromium, Cr

7.0E-3 lb/GWh.

Cobalt, Co

2.0E-3 lb/GWh.

Lead, Pb

2.0E-2 lb/GWh.

Manganese, Mn

4.0E-3 lb/GWh.

Nickel, Ni

4.0E-2 lb/GWh.

Selenium, Se

5.0E-2 lb/GWh.

b. HCl

1.0E-2 lb/MWh.

1.0 lb/MWh.

c. Hg

3.0E-3 lb/GWh.

2. Coal-fired units low rank virgin coal

a. fPM

9.0E-2 lb/MWh.

Total non-Hg HAP metals

6.0E-2 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-3 lb/GWh.

Arsenic, As

3.0E-3 lb/GWh.

Beryllium, Be

6.0E-4 lb/GWh.

Cadmium, Cd

4.0E-4 lb/GWh.

Chromium, Cr

7.0E-3 lb/GWh.

Cobalt, Co

2.0E-3 lb/GWh.

Lead, Pb

2.0E-2 lb/GWh.

Manganese, Mn

4.0E-3 lb/GWh.

Nickel, Ni

4.0E-2 lb/GWh.

Selenium, Se

5.0E-2 lb/GWh.

b. HCl

1.0E-2 lb/MWh.

1.0 lb/MWh.

c. Hg

4.0E-2 lb/GWh.

3. IGCC unit

a. fPM

7.0E-2 lb/MWh.

9.0E-2 lb/MWh.

Total non-Hg HAP metals

4.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

2.0E-2 lb/GWh.

Arsenic, As

2.0E-2 lb/GWh.

Beryllium, Be

1.0E-3 lb/GWh.

Cadmium, Cd

2.0E-3 lb/GWh.

Chromium, Cr

4.0E-2 lb/GWh.

Cobalt, Co

4.0E-3 lb/GWh.

Lead, Pb

9.0E-3 lb/GWh.

Manganese, Mn

2.0E-2 lb/GWh.

Nickel, Ni

7.0E-2 lb/GWh.

Selenium, Se

3.0E-1 lb/GWh.

b. HCl

2.0E-3 lb/MWh.

4.0E-1 lb/MWh.

c. Hg

3.0E-3 lb/GWh.

4. Liquid oil-fired unit—continental (excluding limited-use liquid oil-fired subcategory units)

a. fPM

3.0E-1 lb/MWh.

Total HAP metals

2.0E-4 lb/MWh.

Individual HAP metals:

Antimony, Sb

1.0E-2 lb/GWh.

Arsenic, As

3.0E-3 lb/GWh.

Beryllium, Be

5.0E-4 lb/GWh.

Cadmium, Cd

2.0E-4 lb/GWh.

Chromium, Cr

2.0E-2 lb/GWh.

Cobalt, Co

3.0E-2 lb/GWh.

Lead, Pb

8.0E-3 lb/GWh.

Manganese, Mn

2.0E-2 lb/GWh.

Nickel, Ni

9.0E-2 lb/GWh.

Selenium, Se

2.0E-2 lb/GWh.

1.0E-4 lb/GWh.

b. HCl

4.0E-4 lb/MWh.

c. HF

4.0E-4 lb/MWh.

5. Liquid oil-fired unit—non-continental (excluding limited-use liquid oil-fired subcategory units)

a. fPM

2.0E-1 lb/MWh.

Total HAP metals

7.0E-3 lb/MWh.

Individual HAP metals:

Antimony, Sb

8.0E-3 lb/GWh.

Arsenic, As

6.0E-2 lb/GWh.

Beryllium, Be

2.0E-3 lb/GWh.

Cadmium, Cd

2.0E-3 lb/GWh.

Chromium, Cr

2.0E-2 lb/GWh.

Cobalt, Co

3.0E-1 lb/GWh.

Lead, Pb

3.0E-2 lb/GWh.

Manganese, Mn

1.0E-1 lb/GWh.

Nickel, Ni

4.1 lb/GWh.

Selenium, Se

2.0E-2 lb/GWh.

4.0E-4 lb/GWh.

b. HCl

2.0E-3 lb/MWh.

c. HF

5.0E-4 lb/MWh.

6. Solid oil-derived fuel-fired unit

a. fPM

3.0E-2 lb/MWh.

Total non-Hg HAP metals

6.0E-1 lb/GWh.

Individual HAP metals:

Antimony, Sb

8.0E-3 lb/GWh.

Arsenic, As

3.0E-3 lb/GWh.

Beryllium, Be

6.0E-4 lb/GWh.

Cadmium, Cd

7.0E-4 lb/GWh.

Chromium, Cr

6.0E-3 lb/GWh.

Cobalt, Co

2.0E-3 lb/GWh.

Lead, Pb

2.0E-2 lb/GWh.

Manganese, Mn

7.0E-3 lb/GWh.

Nickel, Ni

4.0E-2 lb/GWh.

Selenium, Se

6.0E-3 lb/GWh.

b. HCl

4.0E-4 lb/MWh.

1.0 lb/MWh.

c. Hg

2.0E-3 lb/GWh.

Units of emission limits:

lb/MWh = pounds pollutant per megawatt-hour electric output (gross); and

lb/GWh = pounds pollutant per gigawatt-hour electric output (gross).

Alternate SO

limit may be used if the EGU has some form of FGD system (or, in the case of IGCC EGUs, some other acid gas removal system either upstream or downstream of the combined cycle block) and SO

CEMS installed.

Duct burners on syngas; gross output.

Duct burners on natural gas; gross output.

C. What data collection activities were conducted to support this action?

The EPA did not issue a new information collection request (ICR) to affected coal- and oil-fired EGUs to obtain the data used to support this action, but did use some information from the 2010 ICR which collected data during development of the MATS rule. The data and data sources used to conduct the residual risk assessment and technology review for the Coal- and Oil-Fired EGU source category are described below in section IV.D of this preamble.

D. What other relevant background information and data are available?

The EPA used multiple sources of information to support this proposed action. A comprehensive list of facilities and EGUs that are subject to the MATS rule was compiled primarily using publicly available information reported to the EPA and information contained in the Agency's National Electric Energy Data System (NEEDS) database.

Affected sources are required to use the 40 CFR part 75-based ECMPS

for reporting emissions and related data either directly for EGUs that use Hg, HCl, HF, or SO

CEMS or Hg sorbent traps for compliance purposes or indirectly as PDF files for EGUs that use performance test results, PM continuous parameter monitoring system (CPMS) data, or PM CEMS for compliance purposes. Directly submitted data are maintained in ECMPS; indirectly submitted data are maintained in WebFIRE.

The NEEDS database contains generation unit information used in the Agency's power sector modeling. Other sources used to refine the facility list included an EPA technical support document that contained a list of potentially affected EGUs in U.S. territories,

the U.S. Department of Energy's Energy Information Administration's (EIA's) list of existing generators that reported for 2016 under Form EIA-860,

and the list of coal-fired EGUs included in a June 2018 Electric Power Research Institute (EPRI) technical report that summarizes EPRI's evaluation of HAP emissions and their associated inhalation health risks from coal-fired power plants after implementation of MATS.

As of early 2018, we estimate

that there are 713 existing coal- and oil-fired EGUs located at 323 facilities that are subject to 40 CFR part 63, subpart UUUUU.

See https://www.epa.gov/airmarkets/power-sector-modeling-platform-v515.

See https://ampd.epa.gov/ampd/.

See https://cfpub.epa.gov/webfire; https://www.epa.gov/electronic-reporting-air-emissions/webfire.

U.S. EPA, October 2014.

Technical Support Document for Calculating Carbon Pollution Goals for Existing Power Plants in Territories and Areas of Indian Country.

Available at

https://archive.epa.gov/epa/sites/production/files/2014-10/documents/20141028tsd-supplemental-proposal.pdf.

See https://www.eia.gov/electricity/data/eia860/.

EPRI. June 8, 2018.

Hazardous Air Pollutants (HAPs) Emission Estimates and Inhalation Human Health Risk Assessment for U.S. Coal-Fired Electric Generating Units: 2017 Base Year Post-MATS Evaluation.

Available at

https://www.epri.com/#/pages/product/3002013577/?lang=en. Note:

There is a companion June 22, 2018 EPRI technical report,

Multi-Pathway Human Health Risk Assessment for Coal-Fired Power Plants,

that describes EPRI's

multi-pathway human health assessment of HAP emissions from five coal-fired electric facilities based on 2017 configurations (available at

https://www.epri.com/#/pages/product/3002013523/?lang=en

In developing the RTR emissions dataset for the risk review, the primary sources used to estimate annual HAP emissions were the emissions data as reported to the ECMPS and WebFIRE databases by facilities with affected EGUs. Emissions release point parameters and locations for each EGU were primarily based on information reported to the ECMPS and generator-level specific information about existing generators and their associated environmental equipment that is collected by the EIA under Form EIA-860. The EPA sources of information that were used to supplement the ECMPS, WebFIRE, and EIA data include emissions information collected through the 2010 ICR during development of the MATS rule and the 2014 National Emissions Inventory (NEI) database. The NEI is a database that contains information about sources that emit criteria air pollutants, their precursors, and HAP. The database includes estimates of annual air pollutant emissions from point, nonpoint, and mobile sources in the 50 states, the District of Columbia, Puerto Rico, and the Virgin Islands. The EPA collects this information and releases an updated version of the NEI database every 3 years. The NEI includes information necessary for conducting risk modeling, including annual HAP emissions estimates from individual emission points at facilities and the related emissions release parameters. The June 2018 EPRI technical report was also used as a source of supplemental information.

In conducting the technology review, the EPA examined information submitted to the EPA's ECMPS as well as information that supports previous 40 CFR part 63, subpart UUUUU actions to identify technologies currently being used by affected EGUs and determine if there have been developments in practices, processes, or control technologies. In addition to the ECMPS data, we reviewed regulatory actions for similar combustion sources and conducted a review of literature published by industry organizations, technical journals, and government organizations.

V. RTR Analytical Procedures and Decision-Making

In this section, we describe the analyses performed to support the proposed decisions for the RTR and other issues addressed in this proposal.

A. How do we consider risk in our decision-making?

As discussed in section IV.A of this preamble and in the Benzene NESHAP, in evaluating and developing standards under CAA section 112(f)(2), we apply a two-step approach to determine whether or not risks are acceptable and to determine if the standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, “the first step judgment on acceptability cannot be reduced to any single factor” and, thus, “[t]he Administrator believes that the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information.” 54 FR 38046, September 14, 1989. Similarly, with regard to the ample margin of safety determination, “the Agency again considers all of the health risk and other health information considered in the first step. Beyond that information, additional factors relating to the appropriate level of control will also be considered, including cost and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors.”

Id.

The Benzene NESHAP approach provides flexibility regarding factors the EPA may consider in making determinations and how the EPA may weigh those factors for each source category. The EPA conducts a risk assessment that provides estimates of the MIR posed by the HAP emissions from each source in the source category, the hazard index (HI) for chronic exposures to HAP with the potential to cause noncancer health effects, and the hazard quotient (HQ) for acute exposures to HAP with the potential to cause noncancer health effects.

The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The scope of the EPA's risk analysis is consistent with the EPA's response to comments on our policy under the Benzene NESHAP where the EPA explained that:

The MIR is defined as the cancer risk associated with a lifetime of exposure at the highest concentration of HAP where people are likely to live. The HQ is the ratio of the potential exposure to the HAP to the level at or below which no adverse chronic noncancer effects are expected; the HI is the sum of HQs for HAP that affect the same target organ or organ system.

[t]he policy chosen by the Administrator permits consideration of multiple measures of health risk. Not only can the MIR figure be considered, but also incidence, the presence of non-cancer health effects, and the uncertainties of the risk estimates. In this way, the effect on the most exposed individuals can be reviewed as well as the impact on the general public. These factors can then be weighed in each individual case. This approach complies with the

Vinyl Chloride

mandate that the Administrator ascertain an acceptable level of risk to the public by employing his expertise to assess available data. It also complies with the Congressional intent behind the CAA, which did not exclude the use of any particular measure of public health risk from the the EPA's consideration with respect to CAA section 112 regulations, and thereby implicitly permits consideration of any and all measures of health risk which the Administrator, in his judgment, believes are appropriate to determining what will `protect the public health'.

See

54 FR 38057, September 14, 1989. Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risk. The Benzene NESHAP explained that “an MIR of approximately one in 10 thousand should ordinarily be the upper end of the range of acceptability. As risks increase above this benchmark, they become presumptively less acceptable under CAA section 112, and would be weighed with the other health risk measures and information in making an overall judgment on acceptability. Or, the Agency may find, in a particular case, that a risk that includes an MIR less than the presumptively acceptable level is unacceptable in the light of other health risk factors.”

Id.

at 38045. Similarly, with regard to the ample margin of safety analysis, the EPA stated in the Benzene NESHAP that: “EPA believes the relative weight of the many factors that can be considered in selecting an ample margin of safety can only be determined for each specific source category. This occurs mainly because technological and economic factors (along with the health-related factors) vary from source category to source category.”

Id.

at 38061. We also consider the uncertainties associated with the various risk analyses, as discussed earlier in this preamble, in our determinations of acceptability and ample margin of safety.

The EPA notes that it has not considered certain health information to date in making residual risk determinations. At this time, we do not attempt to quantify the HAP risk that may be associated with emissions from other facilities that do not include the

source category under review, mobile source emissions, natural source emissions, persistent environmental pollution, or atmospheric transformation in the vicinity of the sources in the category.

The EPA understands the potential importance of considering an individual's total exposure to HAP in addition to considering exposure to HAP emissions from the source category and facility. We recognize that such consideration may be particularly important when assessing noncancer risk, where pollutant-specific exposure health reference levels (

e.g.,

reference concentrations (RfCs)) are based on the assumption that thresholds exist for adverse health effects. For example, the EPA recognizes that, although exposures attributable to emissions from a source category or facility alone may not indicate the potential for increased risk of adverse noncancer health effects in a population, the exposures resulting from emissions from the facility in combination with emissions from all of the other sources (

e.g.,

other facilities) to which an individual is exposed may be sufficient to result in an increased risk of adverse noncancer health effects. In May 2010, the Science Advisory Board (SAB) advised the EPA “that RTR assessments will be most useful to decision makers and communities if results are presented in the broader context of aggregate and cumulative risks, including background concentrations and contributions from other sources in the area.”

Recommendations of the SAB RTR Panel are provided in their report, which is available at

https://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf.

In response to the SAB recommendations, the EPA incorporates cumulative risk analyses into its RTR risk assessments, including those reflected in this proposal. The Agency (1) conducts facility-wide assessments, which include source category emission points, as well as other emission points within the facilities; (2) combines exposures from multiple sources in the same category that could affect the same individuals; and (3) for some persistent and bioaccumulative pollutants, analyzes the ingestion route of exposure. In addition, the RTR risk assessments consider aggregate cancer risk from all carcinogens and aggregated noncancer HQs for all noncarcinogens affecting the same target organ or target organ system.

Although we are interested in placing source category and facility-wide HAP risk in the context of total HAP risk from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Estimates of total HAP risk from emission sources other than those that we have studied in depth during this RTR review would have significantly greater associated uncertainties than the source category or facility-wide estimates. Such aggregate or cumulative assessments would compound those uncertainties, making the assessments too unreliable.

B. How do we perform the technology review?

Our technology review focuses on the identification and evaluation of developments in practices, processes, and control technologies that have occurred since the MACT standards were promulgated. Where we identify such developments, we analyze their technical feasibility, estimated costs, energy implications, and non-air environmental impacts. We also consider the emission reductions associated with applying each development. This analysis informs our decision of whether it is “necessary” to revise the emissions standards. In addition, we consider the appropriateness of applying controls to new sources versus retrofitting existing sources. For this exercise, we consider any of the following to be a “development”:

• Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standards;

• Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standards) that could result in additional emissions reduction;

• Any work practice or operational procedure that was not identified or considered during development of the original MACT standards;

• Any process change or pollution prevention alternative that could be broadly applied to the industry and that was not identified or considered during development of the original MACT standards; and

• Any significant changes in the cost (including cost effectiveness) of applying controls (including controls the EPA considered during the development of the original MACT standards).

In addition to reviewing the practices, processes, and control technologies that were considered at the time we originally developed (or last updated) the NESHAP, we review a variety of data sources in our investigation of potential practices, processes, or controls to consider.

See

sections IV.C and IV. D of this preamble for information on the specific data sources that were reviewed as part of the technology review.

C. How do we estimate post-MACT risk posed by the source category?

In this section, we provide a complete description of the types of analyses that we generally perform during the risk assessment process. In some cases, we do not perform a specific analysis because it is not relevant. For example, in the absence of emissions of HAP known to be persistent and bioaccumulative in the environment (PB-HAP), we would not perform a multipathway exposure assessment. Where we do not perform an analysis, we state that we do not and provide the reason. While we present all of our risk assessment methods, we only present risk assessment results for the analyses actually conducted (

see

section VI.B of this preamble).

The EPA conducts a risk assessment that provides estimates of the MIR for cancer posed by the HAP emissions from each source in the source category, the HI for chronic exposures to HAP with the potential to cause noncancer health effects, and the HQ for acute exposures to HAP with the potential to cause noncancer health effects. The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The seven sections that follow this paragraph describe how we estimated emissions and conducted the risk assessment. The docket for this rulemaking contains the following document which provides more information on the risk assessment inputs and models:

Residual Risk Assessment for the Coal- and Oil-Fired EGU Source Category in Support of the 2019 Risk and Technology Review Proposed Rule

(risk document). The methods used to assess risk (as described in the seven primary steps below) are consistent with those described by the EPA in the document reviewed by a panel of the EPA's SAB in 2009;

and described in the SAB review report issued in 2010. They are also consistent with the key recommendations contained in that report.

U.S. EPA. June 2009.

Risk and Technology Review (RTR) Risk Assessment Methodologies: For Review by the EPA's Science Advisory Board with Case Studies—MACT I Petroleum Refining Sources and Portland Cement Manufacturing

(EPA-452/R-09-006). Available at

https://www3.epa.gov/airtoxics/rrisk/rtrpg.html.

1. How did we estimate actual emissions and identify the emissions release characteristics?

Data for existing EGUs were used to create the RTR emissions dataset for the risk review as described in section IV.D of this preamble. The RTR emissions dataset includes information for 608 emission release points (

i.e.,

stacks). Because in some cases multiple EGUs are routed to a single stack or a single EGU is routed to two stacks, the number of stacks is not the same as the number of EGUs. The MATS rule regulates emissions of HAP in four pollutant categories: Hg, non-Hg metals, acid gases, and organics. As described in section IV.B of this preamble, EGUs in six subcategories are subject to numeric emission limits for specific HAP, or surrogates for those HAP, in the three pollutant categories of Hg, non-Hg metals, and acid gases. EGUs are not required to meet numeric emission limits for organic HAP or to test and report organic HAP emissions. During the 2010 ICR effort of the original MATS rulemaking process, most of the organic HAP emissions data for EGUs were at or below the detection levels of the prescribed test methods, even when long duration test runs (

i.e.,

approximately 8 hours) were required. In developing the RTR emissions dataset, the EPA reviewed the available organic HAP test results from the 2010 ICR. For each organic HAP tested, if 40 percent or more of the available test data were above test method detection limits, emissions estimates for that HAP were included in the modeling file. Emissions of the following HAP in each of the four pollutant categories were estimated for each emission release point and included in the RTR emissions dataset:

• Hg: elemental gaseous Hg, gaseous divalent Hg, particulate divalent Hg;

• Non-Hg metals: antimony, arsenic, beryllium, cadmium, hexavalent chromium, trivalent chromium, cobalt, lead, manganese, nickel, selenium;

• Acid gases: HCl, HF; and

• Organics: formaldehyde, naphthalene, 2-methylnaphthalene, phenanthrene, two dioxin congeners, three furan congeners, and seven polychlorinated biphenyls congeners.

As explained in section IV.D of this preamble, emissions estimates for the RTR emissions dataset were based primarily on data submitted via the EPA's ECMPS by facilities with affected EGUs. Calendar year 2017 data were used where available because all affected EGUs subject to numeric emission limits would be required to submit compliance data by then. Where calendar year 2017 data were not available, the most recent data available were used. CEMS emissions data for Hg, HCl, and SO

reported to the EPA's ECMPS were available as 2017 actual annual values (

i.e.,

pounds per year or tpy).

Some emissions data for Hg, non-Hg HAP metals, HCl, and fPM was submitted to the EPA's ECMPS, but maintained in the WebFIRE database. For those sources, the EPA extracted data associated with operations in summer 2017, when EGUs would be expected to operate more frequently given increased demand for electricity, and used those summertime emissions to estimate annual emissions of the pollutants of interest. Specifically, test averages from third quarter performance stack tests (

i.e.,

conducted between July and September 2017) for any pollutant and 30-day rolling average values as of June 30, 2017, for PM CEMS and PM CPMS were extracted and then converted from pounds of pollutant per million British thermal units or trillion British thermal units (lb/MMBtu or lb/TBtu) or pounds of pollutant per megawatt-hour or gigawatt-hour (lb/MWh or lb/GWh) to actual annual emissions using 2017 total heat input (MMBtu) or total gross load (MWh) values, as appropriate. When ECMPS-submitted data for HAP in the RTR emissions dataset were not available, actual annual emissions estimates were based on data from the 2014 NEI and the June 2018 EPRI technical report. Some annual emissions estimates were also generated using the ratio of non-Hg metals to fPM and acid gases to SO

from the 2010 ICR in conjunction with more recent fPM or SO

emissions data. Emissions data from the 2010 ICR were used to develop emission factors for the non-Hg metals and acid gases included in the RTR emissions dataset and to develop ratios based on each of those emission factors divided by average fPM or SO

values, respectively. Emissions data for EGUs no longer operating were excluded in the calculation of emission factors or average fPM or SO

values. In addition, we included in each emission factor and ratio calculation only the 2010 ICR data for EGUs where data for both the non-Hg metal HAP (

e.g.,

antimony) and fPM, or the acid gas HAP (

e.g.,

HCl) and SO

, were available. Emission factors and emission factor-based ratios were developed for the various combinations of fuel types and emissions control device types. Actual annual HAP-specific emissions for each stack were then estimated by multiplying each emission factor-based ratio by the most recent fPM or SO

annual emissions value (

e.g.,

2017 ECMPS or WebFIRE data or 2014 NEI data). Because EGUs in the subcategory of limited-use liquid oil-fired EGUs are not subject to any numeric emission limits, actual annual HAP-specific emissions were estimated using 2014 NEI data or emission factor-based ratios along with 2014 NEI data for PM and SO

. Development of the emission factors and emission factor-based ratios is explained in the memorandum,

Emission Factor Development for RTR Risk Modeling Dataset for Coal- and Oil-fired EGUs,

which is available in the docket for this action.

The majority of the total (

i.e.,

non-speciated) Hg actual annual emissions estimates were based on data maintained in the EPA's ECMPS for CEMS data or sorbent traps or in WebFIRE for performance stack tests along with 2017 total heat input or total gross load values, as appropriate. Where such data were not available, total Hg actual annual emissions were estimated using the 2014 NEI or the June 2018 EPRI technical report. For a small number of oil-fired EGUs, EPA-developed emission factors and emission factor-based ratios were used to estimate total Hg actual annual emissions. Hg emissions were modeled as three different species: elemental gaseous Hg, gaseous divalent Hg, and particulate divalent Hg. The EPA utilized Hg speciation factors—percentages based on fuel type and installed emissions control equipment—that were updated versions of those that had been used in the development of the MATS rule.

Total Hg emissions were then multiplied by the factors to develop the speciated Hg actual annual emissions estimates.

See

Attachment E of the

Risk Modeling Dataset Memo

for the list of Hg speciation factors utilized in compiling the RTR emissions dataset for the risk review, available in the docket for this action.

See

Appendix G of the Technical Support Document for the Proposed Rule Emissions Inventories (available in the rulemaking docket at EPA-HQ-OAR-2009-0234-19908) for Hg speciation factors used in the development of MATS.

For the several EGUs that submitted individual non-Hg HAP metals data to the EPA, actual annual emissions were estimated using the stack test values maintained in WebFIRE and 2017 total heat input or total gross load values, as appropriate. The majority of the non-Hg HAP metals actual annual emissions estimates were based on emission factor-based ratios for non-Hg HAP metals and fPM annual emissions values. Chromium emissions were modeled as hexavalent chromium (Cr(VI)) and trivalent chromium (Cr(III)). Actual annual emissions of Cr(VI) and Cr(III) were estimated by multiplying total chromium emissions by the

speciation factors for coal or oil, as appropriate.

Actual annual emissions estimates for HCl for EGUs that submitted data to the EPA's ECMPS were based on those ECMPS CEMS data or WebFIRE performance stack test data and 2017 total heat input or total gross load values, as appropriate. Where acid gas HAP data were not available in the WebFIRE database, but SO

data were available in the ECMPS for requirements other than those in the MATS rule (

e.g.,

the acid rain rule), emission factor-based ratios for the acid gas HAP (

i.e.,

HCl and HF) and SO

annual emissions values were used to estimate actual annual HCl and HF emissions. In some instances, actual annual HCl and HF emissions were estimated based on emission factor-based ratios and 2014 NEI data for SO

. In a small number of other instances, actual annual HCl and HF emissions were estimated using the June 2018 EPRI technical report.

As previously explained, EGUs are not required to meet numeric emission limits for organic HAP or to test and report organic HAP emissions. Actual annual emissions for the 16 organic HAP included in the RTR emissions dataset are based on EPA-developed representative detection level (RDL) equivalent emissions values (lb/MMBtu) based on fuel type. RDL equivalent emissions values for 15 of the organic HAP are based on the averages of better-performing unit method detection levels across many source categories. Because we did not have an RDL analysis across source categories for formaldehyde, detection levels from the 2010 ICR data were used to develop the RDL equivalent emissions value for formaldehyde. Actual annual emissions of the 16 organic HAP were estimated by multiplying the RDL equivalent emissions values by 2017 total heat input. Development of the RDL equivalent emissions values is explained in the memorandum,

Development of Representative Detection Levels of Certain Organic HAP Expressed as Pounds per Million British Thermal Units of Fuel Input for RTR Risk Modeling Dataset for Coal- and Oil-fired EGUs,

which is available in the docket for this action.

Stack parameter values and locations for each emissions release point included in the RTR emissions dataset were primarily based on information reported to the ECMPS and generator-level specific information about existing generators and their associated environmental equipment that is collected under Form EIA-860. Specifically, the ECMPS was the primary source for stack height, diameter, and latitude/longitude coordinates, and the EIA-860 database was the primary source for stack temperature, velocity, and flow rate. Other sources of information that were used to fill gaps in the site-specific emissions release point data included the 2014 NEI, parameters from similar stacks at a specific facility, and default parameter values based on MACT source category 2014 NEI information.

The RTR emissions dataset was refined as necessary following a quality assurance check of source locations, emissions release characteristics, and annual emissions estimates. Latitude and longitude coordinates were checked using Google Earth® to ensure that stack locations were correct. Stack parameters were checked to ensure that they were within acceptable quality assurance range check boundaries. Emissions estimates were reviewed for completeness and accuracy. Additional details on the data and methods used to develop “actual” emissions estimates for the RTR emissions dataset are provided in the memorandum,

Development of the RTR Risk Modeling Dataset for the Coal- and Oil-Fired EGU Source Category

(

Risk Modeling Dataset Memo

), included as Appendix 1 of the risk document, which is available in the docket for this action.

A comparison of the actual annual HAP emissions in 2017 to the annual HAP emissions prior to promulgation of the MATS rule shows a 96-percent reduction in total HAP emissions from coal- and oil-fired EGUs. The actual emissions from coal- and oil-fired EGUs for 2017 and estimated emissions from 2010 are shown in Table 4. Estimates of pre-MATS emissions of organic HAP were not available. As discussed previously in this section, the 2017 emissions of organic HAP are based on RDL equivalent emissions values; the actual 2017 emissions are likely lower than the estimate of 3 tpy.

Table 4—HAP Emissions From Coal- and Oil-Fired EGUs Pre- and Post-MATS

Pollutant

2010

Emissions

(tons)

2017

Emissions

(tons)

Reduction

(%)

Acid Gases

125,708

4,831

Non-Hg Metals

1,170

221

Organic HAP

Total

126,907

5,059

Note:

The compliance date for the vast majority of affected EGUs was on or before April 16, 2016.

* Not available.

2. How did we estimate MACT-allowable

emissions?

Memorandum: Emissions Overview: Hazardous Air Pollutants in Support of the Final Mercury and Air Toxics Standard.

EPA-454/R-11-014. November 2011; Docket ID No. EPA-HQ-OAR-2009-0234-19914.

The available emissions data in the RTR emissions dataset include estimates of the mass of HAP emitted during a specified annual time period. These “actual” emission levels are often lower than the emission levels allowed under the requirements of the current MACT standards. The emissions allowed under the MACT standards are referred to as the “MACT-allowable” emissions. We discussed the consideration of both MACT-allowable and actual emissions in the final Coke Oven Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed and final Hazardous Organic NESHAP RTR (71 FR 34428, June 14, 2006, and 71 FR 76609, December 21, 2006, respectively). In those actions, we noted that assessing the risk at the MACT-allowable level is inherently reasonable since that risk reflects the maximum level facilities could emit and still comply with national emission standards. We also explained that it is reasonable to consider actual emissions, where such data are available, in both steps of the risk analysis, in accordance with the Benzene NESHAP approach. (54 FR 38044, September 14, 1989.)

MACT-allowable annual emissions of Hg, non-Hg HAP metals, and acid gas HAP were estimated using numeric emission limits for existing sources in the MATS rule along with 2017 total heat input. For Hg, allowable annual emissions of total Hg were estimated by multiplying subcategory-specific Hg emission limits by 2017 total heat input. Allowable annual emissions of elemental gaseous Hg, gaseous divalent Hg, and particulate divalent Hg were estimated by multiplying annual emissions of total Hg by EPA-developed Hg speciation factors which are based on fuel type and emissions control device type.

With regard to non-Hg HAP metals, performance stack test data in almost all instances was for fPM, a surrogate for non-Hg HAP metals, and, as such, allowable annual emissions were estimated using the MATS rule's fPM emission limits. Specifically, allowable annual emissions of the non-Hg HAP metals were estimated by multiplying subcategory-based fPM emission limits by 2017 total heat input and by the emission factor-based ratios for non-Hg HAP metals that were calculated by the EPA. Allowable annual emissions of chromium as Cr(VI) and Cr(III) were estimated by multiplying the total chromium allowable emissions estimates by the chromium speciation factors for coal or oil, as appropriate.

For acid gas HAP, allowable annual emissions of HCl and HF from oil-fired EGUs were estimated by multiplying subcategory-specific HCl and HF emission limits by 2017 total heat input. With regard to acid gas HAP for coal-fired EGUs, some coal-fired sources submitted data for HCl, a surrogate for acid gas HAP, whereas other sources submitted data for SO

, a surrogate for acid gas HAP for certain coal-fired EGUs. Allowable annual emissions of HCl and HF from coal-fired EGUs were estimated two different ways—one based on the MATS rule's HCl emission limits and HF actual emissions adjusted using an HCl emissions ratio and the other based on the MATS rule's SO

emission limits and emission factor-based ratios—and the more conservative estimate was used. In the first approach, allowable annual emissions of HCl were estimated by multiplying subcategory-specific HCl emission limits by 2017 total heat input, and allowable annual emissions of HF were estimated by multiplying actual annual emissions of HF by a ratio of HCl allowable annual emissions to HCl actual annual emissions. In the second approach, allowable annual emissions of HCl and HF were estimated by multiplying subcategory-based SO

emission limits by 2017 total heat input and by the emission factor-based ratios for HCl and HF that were calculated by the EPA.

Because there are no numeric emission limits for organic HAP, allowable annual emissions for the 16 organic HAP were assumed equal to the actual annual emissions estimates for the 16 organic HAP. The

Risk Modeling Dataset Memo,

available in the docket for this action, contains additional information on the development of estimated MACT-allowable emissions.

3. How do we conduct dispersion modeling, determine inhalation exposures, and estimate individual and population inhalation risk?

Both long-term and short-term inhalation exposure concentrations and health risk from the source category addressed in this proposal were estimated using the Human Exposure Model (HEM-3).

The HEM-3 performs three primary risk assessment activities: (1) Conducting dispersion modeling to estimate the concentrations of HAP in ambient air, (2) estimating long-term and short-term inhalation exposures to individuals residing within 50 kilometers (km) of the modeled sources, and (3) estimating individual and population-level inhalation risk using the exposure estimates and quantitative dose-response information.

For more information about HEM-3, go to

https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem.

a. Dispersion Modeling

The air dispersion model AERMOD, used by the HEM-3 model, is one of the EPA's preferred models for assessing air pollutant concentrations from industrial facilities.

To perform the dispersion modeling and to develop the preliminary risk estimates, HEM-3 draws on three data libraries. The first is a library of meteorological data, which is used for dispersion calculations. This library includes 1 year (2016) of hourly surface and upper air observations from 824 meteorological stations, selected to provide coverage of the United States and Puerto Rico. A second library of United States Census Bureau census block

internal point locations and populations provides the basis of human exposure calculations (U.S. Census, 2010). In addition, for each census block, the census library includes the elevation and controlling hill height, which are also used in dispersion calculations. A third library of pollutant-specific dose-response values is used to estimate health risk. These are discussed below.

U.S. EPA. Revision to the

Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions

(70 FR 68218, November 9, 2005).

A census block is the smallest geographic area for which census statistics are tabulated.

b. Risk From Chronic Exposure to HAP

In developing the risk assessment for chronic exposures, we use the estimated annual average ambient air concentrations of each HAP emitted by each source in the source category. The HAP air concentrations at each nearby census block centroid located within 50 km of the facility are a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. A distance of 50 km is consistent with both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044, September 14, 1989) and the limitations of Gaussian dispersion models, including AERMOD.

For each facility, we calculate the MIR as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, 52 weeks per year, 70 years) exposure to the maximum concentration at the centroid of each inhabited census block. We calculate individual cancer risk by multiplying the estimated lifetime exposure to the ambient concentration of each HAP (in micrograms per cubic meter (μg/m

)) by its unit risk estimate (URE). The URE is an upper-bound estimate of an individual's incremental risk of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the pollutant per cubic meter of air. For residual risk assessments, we generally use UREs from the EPA's Integrated Risk Information System (IRIS). For carcinogenic pollutants without IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) UREs, where available. In cases where new, scientifically credible dose-response values have been developed in a manner consistent with EPA guidelines and have undergone a peer review process similar to that used by the EPA, we may use such dose-response values in place of, or in addition to, other values, if appropriate. The pollutant-specific dose-response values used to estimate health risk are available at

https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.

To estimate individual lifetime cancer risks associated with exposure to HAP emissions from each facility in the source category, we sum the risks for

each of the carcinogenic HAP

emitted by the modeled facility. We estimate cancer risk at every census block within 50 km of every facility in the source category. The MIR is the highest individual lifetime cancer risk estimated for any of those census blocks. In addition to calculating the MIR, we estimate the distribution of individual cancer risks for the source category by summing the number of individuals within 50 km of the sources whose estimated risk falls within a specified risk range. We also estimate annual cancer incidence by multiplying the estimated lifetime cancer risk at each census block by the number of people residing in that block, summing results for all of the census blocks, and then dividing this result by a 70-year lifetime.

The EPA's 2005

Guidelines for Carcinogen Risk Assessment

classifies carcinogens as: “carcinogenic to humans,” “likely to be carcinogenic to humans,” and “suggestive evidence of carcinogenic potential.” These classifications also coincide with the terms “known carcinogen, probable carcinogen, and possible carcinogen,” respectively, which are the terms advocated in the EPA's

Guidelines for Carcinogen Risk Assessment,

published in 1986 (51 FR 33992, September 24, 1986). In August 2000, the document,

Supplemental Guidance for Conducting Health Risk Assessment of Chemical Mixtures

(EPA/630/R-00/002), was published as a supplement to the 1986 document. Copies of both documents can be obtained from

https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944.

Summing the risk of these individual compounds to obtain the cumulative cancer risk is an approach that was recommended by the EPA's SAB in their 2002 peer review of the EPA's National Air Toxics Assessment (NATA) titled

NATA—Evaluating the National-scale Air Toxics Assessment 1996 Data—an SAB Advisory,

available at

https://yosemite.epa.gov/sab/sabproduct.nsf/214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf.

To assess the risk of noncancer health effects from chronic exposure to HAP, we calculate either an HQ or a target organ-specific hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is emitted. Where more than one noncancer HAP is emitted, we sum the HQ for each of the HAP that affects a common target organ or target organ system to obtain a TOSHI. The HQ is the estimated exposure divided by the chronic noncancer dose-response value, which is a value selected from one of several sources. The preferred chronic noncancer dose-response value is the EPA RfC, defined as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime” (

https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary

). In cases where an RfC from the EPA's IRIS is not available or where the EPA determines that using a value other than the RfC is appropriate, the chronic noncancer dose-response value can be a value from the following prioritized sources, which define their dose-response values similarly to the EPA: (1) The Agency for Toxic Substances and Disease Registry (ATSDR) Minimum Risk Level (

https://www.atsdr.cdc.gov/mrls/index.asp

); (2) the CalEPA Chronic Reference Exposure Level (REL) (

https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0

); or (3), as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with EPA guidelines and has undergone a peer review process similar to that used by the EPA. The pollutant-specific dose-response values used to estimate health risks are available at

https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.

c. Risk From Acute Exposure to HAP That May Cause Health Effects Other Than Cancer

For each HAP for which appropriate acute inhalation dose-response values are available, the EPA also assesses the potential health risks due to acute exposure. For these assessments, the EPA makes conservative assumptions about emission rates, meteorology, and exposure location. We use the peak hourly emission rate,

worst-case dispersion conditions, and, in accordance with our mandate under section 112 of the CAA, the point of highest off-site exposure to assess the potential risk to the maximally exposed individual.

In the absence of hourly emission data, we develop estimates of maximum hourly emission rates by multiplying the average actual annual emissions rates by a factor (either a category-specific factor or a default factor of 10) to account for variability. This is documented in

Residual Risk Assessment for Coal- and Oil-Fired EGU Source Category in Support of the 2019 Risk and Technology Review Proposed Rule

and in Appendix 5 of the report:

Analysis of Data on Short-term Emission Rates Relative to Long-term Emission Rates.

Both are available in the docket for this rulemaking.

To characterize the potential health risks associated with estimated acute inhalation exposures to a HAP, we generally use multiple acute dose-response values, including acute RELs, acute exposure guideline levels (AEGLs), and emergency response planning guidelines (ERPG) for 1-hour exposure durations, if available, to calculate acute HQs. The acute HQ is calculated by dividing the estimated acute exposure by the acute dose-response value. For each HAP for which acute dose-response values are available, the EPA calculates acute HQs.

An acute REL is defined as “the concentration level at or below which no adverse health effects are anticipated for a specified exposure duration.”

Acute RELs are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. They are designed to protect the most sensitive individuals, including children and the elderly, in the population through the inclusion of margins of safety. Because margins of safety are incorporated to address data gaps and uncertainties, exceeding the REL does not automatically indicate an adverse health impact. AEGLs represent threshold exposure limits for the general public and are applicable to emergency exposures ranging from 10 minutes to 8 hours.

They are guideline levels for “once-in-a-lifetime, short-term exposures to airborne concentrations of acutely toxic, high-priority chemicals.”

Id.

at 21. The AEGL-1 is specifically defined as “the airborne concentration (expressed as ppm (parts per million) or mg/m

(milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.” The document also notes that “Airborne concentrations below AEGL-1 represent exposure levels that can produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects.”

Id.

AEGL-2 are defined as “the airborne

concentration (expressed as parts per million or milligrams per cubic meter) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.”

Id.

CalEPA issues acute RELs as part of its Air Toxics Hot Spots Program, and the 1-hour and 8-hour values are documented in

Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The Determination of Acute Reference Exposure Levels for Airborne Toxicants,

which is available at

https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary.

National Academy of Sciences, 2001.

Standing Operating Procedures for Developing Acute Exposure Levels for Hazardous Chemicals,

page 2. Available at

https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.

pdf. Note that the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances ended in October 2011, but the AEGL program continues to operate at the EPA and works with the National Academies to publish final AEGLs, (

https://www.epa.gov/aegl

ERPGs are “developed for emergency planning and are intended as health-based guideline concentrations for single exposures to chemicals.”

Id.

at 1. The ERPG-1 is defined as “the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or without perceiving a clearly defined, objectionable odor.”

Id.

at 2. Similarly, the ERPG-2 is defined as “the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action.”

Id.

at 1.

ERPGS Procedures and Responsibilities.

March 2014. American Industrial Hygiene Association. Available at

https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf.

An acute REL for 1-hour exposure durations is typically lower than its corresponding AEGL-1 and ERPG-1. Even though their definitions are slightly different, AEGL-1s are often the same as the corresponding ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from our acute inhalation screening risk assessment typically result when we use the acute REL for a HAP. In cases where the maximum acute HQ exceeds 1, we also report the HQ based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1).

For the Coal- and Oil-Fired EGU source category, facility-level acute factors (

i.e.,

multipliers) developed by the EPA were used to estimate acute emissions and the potential health risks due to acute exposure. First, 2017 total heat input (MMBtu) and boiler maximum rated heat input (MMBtu/hr) data were used to calculate an acute factor for EGUs where both values were available. Next, facility-level acute factors were calculated using a heat input-weighted average based on 2017 heat input for each EGU located within a facility fenceline. The facility-level acute factor was used for each stack at the facility. For units at facilities that did not have a facility-level factor (

e.g.,

2017 total heat input and boiler maximum rated heat input were not available), a default facility-level value of 6 was used. The default facility-level value of 6 was developed by taking the average of the calculated facility-level factors. If the calculated facility-level acute factor was greater than 10 (

e.g.,

in cases where the EGU had a low 2017 heat input relative to the maximum rated heat input), the RTR program default acute emission adjustment factor of 10 was used. The default emission adjustment factor of 10 reflects a Texas study of short-term emissions variability, which showed that most peak emission events in a heavily-industrialized four-county area (Harris, Galveston, Chambers, and Brazoria Counties, Texas) were less than twice the annual average hourly emissions rate. The highest peak emissions event was 74 times the annual average hourly emissions rate and the 99th percentile ratio of peak hourly emissions rate to the annual average hourly emissions rate was 9.

Considering this analysis, to account for more than 99 percent of the peak hourly emissions, a conservative screening multiplication factor of 10 is applied to the average annual hourly emissions rate in the EPA's acute exposure screening assessments as the default approach. In this analysis, we inadvertently used allowable emissions (rather than actual emissions, which is our standard practice) in conjunction with the facility level acute factors in our screening assessment of acute risk. Because the results showed acute risks below a level of concern even with acute emissions being overstated due to the use of allowable emissions, we did not correct the analysis and consider it to clearly support the conclusion that acute risks are below a level of concern as shown in Table 5 of this preamble. A further discussion of the development of facility-level acute factors and emissions used to estimate acute exposure for the risk modeling can be found in the

Risk Modeling Dataset Memo,

available in the docket for this rulemaking.

Allen,

et al.,

2004.

Variable Industrial VOC Emissions and their impact on ozone formation in the Houston Galveston Area.

Texas Environmental Research Consortium. Available at

https://www.researchgate.net/publication/237593060_Variable_Industrial_VOC_Emissions_and_their_Impact_on_Ozone_Formation_in_the_Houston_Galveston_Area.

In our acute inhalation screening risk assessment, acute impacts are deemed negligible for HAP for which acute HQs are less than or equal to 1 (even under the conservative assumptions of the screening assessment), and no further analysis is performed for these HAP. In cases where an acute HQ from the screening step is greater than 1, we consider additional site-specific data to develop a more refined estimate of the potential for acute exposures of concern.

4. How do we conduct the multipathway exposure and risk screening assessment?

The EPA conducts a tiered screening assessment examining the potential for significant human health risks due to exposures via routes other than inhalation (

i.e.,

ingestion). We first determine whether any sources in the source category emit any PB-HAP, as identified in the EPA's Air Toxics Risk Assessment Library (

See

Volume 1, Appendix D, at

https://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library.

For the Coal- and Oil-Fired EGU source category, we identified PB-HAP emissions of lead compounds, arsenic compounds, Hg compounds, cadmium compounds, polycyclic organic matter (POM), and dioxins, so we proceeded to the next step of the evaluation. In this step, we determine whether the facility-specific emission rates of the emitted PB-HAP are large enough to create the potential for significant human health risk through ingestion exposure under reasonable worst-case conditions. To facilitate this step, we use previously developed screening threshold emission rates for several PB-HAP that are based on a hypothetical upper-end screening exposure scenario developed for use in conjunction with the EPA's Total Risk Integrated Methodology.Fate, Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with screening threshold emission rates are arsenic compounds, cadmium compounds, chlorinated dibenzodioxins and furans, Hg compounds, and POM. Based on EPA estimates of toxicity and bioaccumulation potential, the pollutants above represent a conservative list for inclusion in multipathway risk assessments for RTR rules. (

See

Volume 1, Appendix D at

https://www.epa.gov/sites/production/files/201308/documents/volume_1_reflibrary.pdf

). In this assessment, we compare the facility-specific emission rates of these PB-HAP to the screening threshold emission rates for each PB-HAP to assess the potential for significant human health risks via the ingestion pathway. We call this application of the TRIM.FaTE model the Tier 1 screening assessment. The ratio of a facility's actual emission rate to the Tier 1 screening threshold emission rate is a “screening value.”

We derive the Tier 1 screening threshold emission rates for these PB-HAP (other than lead compounds) to correspond to a maximum excess lifetime cancer risk of 1-in-1 million (

i.e.,

for arsenic compounds, polychlorinated dibenzodioxins and furans and POM) or, for HAP that cause noncancer health effects (

i.e.,

cadmium compounds and Hg compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP or combination of carcinogenic PB-HAP in the Tier 1 screening assessment exceeds the Tier 1 screening threshold emission rate for any facility (

i.e.,

the screening value is greater than 1), we conduct a second screening assessment, which we call the Tier 2 screening assessment.

In the Tier 2 screening assessment, the location of each facility that exceeds a Tier 1 screening threshold emission rate is used to refine the assumptions associated with the Tier 1 fisher and farmer exposure scenarios at that facility. A key assumption in the Tier 1 screening assessment is that a lake and/or farm is located near the facility. As part

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