National Emission Standards for Hazardous Air Pollutants: Generic Maximum Achievable Control Technology Standards; and Manufacture of Amino/Phenolic Resins

Federal RegisterJan 9, 2014

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2012-0133; FRL-9903-68-OAR]

RIN 2060-AR49

National Emission Standards for Hazardous Air Pollutants: Generic Maximum Achievable Control Technology Standards; and Manufacture of Amino/Phenolic Resins

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The EPA is proposing amendments, with regard to regulations applicable to three industrial source categories, to two national emission standards for hazardous air pollutants (NESHAP): NESHAP for Source Categories: Generic Maximum Achievable Control Technology Standards; and NESHAP: Manufacture of Amino/Phenolic Resins. The three source categories addressed in this action are Acrylic and Modacrylic Fibers Production, Polycarbonate Production and Amino/Phenolic Resins Production. For all three of these source categories, the EPA is proposing decisions concerning the residual risk and technology reviews. The EPA is also proposing amendments to correct and clarify regulatory provisions related to emissions during periods of startup, shutdown and malfunction; add provisions for affirmative defense; add requirements for electronic reporting of performance test results; clarify provisions pertaining to open-ended valves and lines; add monitoring requirements for pressure relief devices; and add standards for previously unregulated hazardous air pollutant (HAP) emissions sources for certain emission points. We estimate that these proposed amendments will reduce HAP emissions from these three source categories by a combined 22 tons per year.

DATES:

Comments.

Comments must be received on or before March 10, 2014. A copy of comments on the information collection provisions should be submitted to the Office of Management and Budget (OMB) on or before February 10, 2014.

Public Hearing.

If anyone contacts the EPA requesting a public hearing by January 24, 2014, we will hold a public hearing on February 10, 2014. If a hearing is requested, the last day to pre-register in advance to speak at the hearing will be February 3, 2014. Additionally, requests to speak will be taken the day of the hearing at the hearing registration desk, although preferences on speaking times may not be able to be fulfilled. If you require the service of a translator or special accommodations such as audio description, please let us know at the time of registration. If no one contacts the EPA requesting a public hearing to be held concerning this proposed rule by January 24, 2014, a public hearing will not take place. For further information on the hearing, see section I.E of this preamble.

ADDRESSES:

Comments.

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2012-0133, by one of the following methods:

•

http://www.regulations.gov:

Follow the online instructions for submitting comments.

•

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

Attention Docket ID No. EPA-HQ-OAR-2012-0133.

•

Fax:

(202) 566-9744, Attention Docket ID No. EPA-HQ-OAR-2012-0133.

•

Mail:

U.S. Postal Service, send comments to: EPA Docket Center, EPA West (Air Docket), Attention Docket ID No. EPA-HQ-OAR-2012-0133, U.S. Environmental Protection Agency, Mailcode: 2822T, 1200 Pennsylvania Ave. NW., Washington, DC 20460. Please include a total of two copies. In addition, please mail a copy of your comments on the information collection provisions to the Office of Information and Regulatory Affairs, Office of Management and Budget (OMB), Attn: Desk Officer for EPA, 725 17th Street NW., Washington, DC 20503.

•

Hand Delivery:

U.S. Environmental Protection Agency, EPA West (Air Docket), Room 3334, 1301 Constitution Ave. NW., Washington, DC 20004, Attention Docket ID No. EPA-HQ-OAR-2012-0133. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions.

Direct your comments to Docket ID No. EPA-HQ-OAR-2012-0133. 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

http://www.regulations.gov,

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

http://www.regulations.gov

or email. The

http://www.regulations.gov

Web site is an “anonymous access” system, 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

http://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 disk or CD-ROM 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 avoid the use of 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:

http://www.epa.gov/dockets.

Docket.

The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2012-0133. All documents in the docket are listed in the

regulations.gov

index. Although listed in the index, some information is not publicly available, e.g., CBI 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, EPA West, Room 3334, 1301 Constitution Ave. 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.

Public Hearing.

If a public hearing is requested by January 24, 2014, it will be held on February 10, 2014, at the EPA's Research Triangle Park Campus, 109 T.W. Alexander Drive, Research Triangle Park, North Carolina 27711. The hearing will convene at 10:00 a.m. (Eastern Standard Time) and end at 5:00 p.m. (Eastern Standard Time). A lunch break will be held from 12:00 p.m. (Eastern Standard Time) until 1:00 p.m. (Eastern Standard Time). Please contact Ms. Virginia Hunt at (919) 541-0832 or at

hunt.virginia@epa.gov

to request a

hearing, to determine if a hearing will be held and to register to speak at the hearing, if one is held.

FOR FURTHER INFORMATION CONTACT:

For questions about this proposed action, contact Mr. Nick Parsons, Sector Policies and Programs Division (E143-01), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-5372; fax number: (919) 541-0246; and email address:

parsons.nick@epa.gov.

For specific information regarding the risk modeling methodology, contact Mr. 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; fax number: (919) 541-0840; email address:

morris.mark@epa.gov.

For information about the applicability of these three NESHAP to a particular entity, contact Ms. Tavara Culpepper, Office of Enforcement and Compliance Assurance (OECA), telephone number: (202) 564-0902; email address:

culpepper.tavara@epa.gov.

SUPPLEMENTARY INFORMATION:

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:

ACGIH American Conference of Governmental Industrial Hygienists

ADAF age-dependent adjustment factors

AEGL acute exposure guideline levels

AERMOD air dispersion model used by the HEM-3 model

AMF Acrylic and Modacrylic Fibers

APR Amino/Phenolic Resins

BACT best available control technology

CAA Clean Air Act

CalEPA California EPA

CBI Confidential Business Information

CDX Central Data Exchange

CEDRI Compliance and Emissions Data Reporting Interface

CFR Code of Federal Regulations

EJ environmental justice

EPA Environmental Protection Agency

ERPG Emergency Response Planning Guidelines

ERT Electronic Reporting Tool

Federal Register

GACT generally achievable control technology

HAP hazardous air pollutants

HCl hydrochloric acid

HEM-3 Human Exposure Model, Version 1.1.0

HI hazard index

HON National Emission Standards for Organic Hazardous Air Pollutants From the Synthetic Organic Chemical Manufacturing Industry

HQ hazard quotient

ICR Information Collection Request

IRIS Integrated Risk Information System

km kilometer

LAER lowest achievable emission rate

LDAR leak detection and repair

MACT maximum achievable control technology

MACT Code Code within the NEI used to identify processes included in a source category

mg/m

milligrams per cubic meter

MIR maximum individual risk

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NAS National Academy of Sciences

NATA National Air Toxics Assessment

NEI National Emissions Inventory

NESHAP National Emissions Standards for Hazardous Air Pollutants

NIOSH National Institutes for Occupational Safety and Health

NRC National Research Council

NTTAA National Technology Transfer and Advancement Act

OAQPS Office of Air Quality Planning and Standards

OECA Office of Enforcement and Compliance Assurance

OMB Office of Management and Budget

PAH polycyclic aromatic hydrocarbons

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

PC Polycarbonate

POM polycyclic organic matter

ppm parts per million

PRD pressure relief device

RACT reasonably available control technology

RBLC RACT/BACT/LAER Clearinghouse

REL reference exposure level

RFA Regulatory Flexibility Act

RfC reference concentration

RfD reference dose

RTO regenerative thermal oxidizer

RTR residual risk and technology review

SAB Science Advisory Board

SBA Small Business Administration

SOCMI Synthetic Organic Chemical Manufacturing Industry

SOP standard operating procedures

SSM startup, shutdown and malfunction

TEQ toxic equivalency quotient

TLV threshold limit value

TOSHI target organ-specific hazard index

tpy tons per year

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

TTN Technology Transfer Network

UF uncertainty factor

μg/m

microgram per cubic meter

UMRA Unfunded Mandates Reform Act

URE unit risk estimate

VCS voluntary consensus standards

VOC volatile organic compounds

Organization of this Document.

The information in this preamble is organized as follows:

I. General Information

A. Executive Summary

B. Does this action apply to me?

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

D. What should I consider as I prepare my comments for the EPA?

E. Public Hearing

II. Background

A. What is the statutory authority for this action?

B. What are the source categories and how did the MACT standards regulate their HAP emissions?

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

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

III. Analytical Procedures

A. How did we estimate post-MACT risks posed by the source categories?

B. How did we consider the risk results in making decisions for this proposal?

C. How did we perform the technology review?

IV. Analytical Results and Proposed Decisions for the AMF Source Category

A. What actions are we taking pursuant to CAA sections 112(d)(2) and 112(d)(3)?

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

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

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

V. Analytical Results and Proposed Decisions for the APR Source Category

A. What actions are we taking pursuant to CAA sections 112(d)(2) and 112(d)(3)?

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

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

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

VI. Analytical Results and Proposed Decisions for the PC Source Category

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 effects?

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

VII. What other actions are we proposing?

A. Startup, Shutdown and Malfunction

B. Electronic Reporting

C. Open-Ended Valves and Lines

D. Flare Performance

VIII. What compliance dates are we proposing?

IX. Summary of Cost, Environmental and Economic Impacts

A. What are the affected sources?

B. What are the air quality impacts?

C. What are the cost impacts?

D. What are the economic impacts?

E. What are the benefits?

X. Request for Comments

XI. Submitting Data Corrections

XII. Statutory and Executive Order Reviews

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

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

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

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

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

I. National Technology Transfer and Advancement Act

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

A red-line version of the regulatory language that incorporates the proposed changes in this action is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2012-0133).

I. General Information

A. Executive Summary

1. Purpose of the Regulatory Action

Section 112(d)(1) of the CAA requires the EPA to establish NESHAP for source categories and subcategories of both major sources and area sources of HAP that are listed for regulation under CAA section 112(c). For major sources of HAP, under CAA sections 112(d)(2) and (3), the EPA is required to set standards that reflect the emissions performance achieved by the maximum achievable control technology (MACT) and by other measures used at sources in the subject source category. For area sources, under CAA section 112(d)(5) the EPA is allowed to instead adopt standards reflecting generally achievable control technology (GACT). Section 112(d)(6) of the CAA requires the EPA to review these NESHAP regulations for each covered source category and to revise them as necessary (taking into account developments in practices, processes and control technologies) no less frequently than every 8 years. Section 112(f)(2) of the CAA requires the EPA to assess, within 8 years of promulgation of the original NESHAP for major sources and area sources subject to MACT, the remaining risks due to emissions of HAP from these source categories and determine whether the emissions standards provide an ample margin of safety to protect public health. Section 112(f)(5) provides that the EPA is not required to conduct this latter review for area sources subject to GACT. We refer to these reviews collectively as residual risk and technology reviews (RTRs).

This action presents the results of, and proposed decisions based on, the EPA's reviews of the following three source categories: Acrylic and Modacrylic Fibers Production (AMF), Amino/Phenolic Resins Production (APR) and Polycarbonate Production (PC). As detailed below, the EPA is proposing amendments, based on the relevant RTR, to regulations applicable to each of these three source categories. In addition, we are also proposing amendments to the relevant regulations to address the following: Emissions during periods of startup, shutdown and malfunction; standards for previously unregulated HAP emissions sources; revisions to require monitoring of pressure relief devices in organic HAP service that release to the atmosphere; clarification of provisions pertaining to open-ended valves and lines; and revisions to require electronic reporting of performance test results.

2. Summary of the Major Provisions of the Regulatory Action in Question

With regard to the AMF source category, the EPA has determined that no amendments are needed for this source category based on the risk review under CAA section 112(f). However, based on the technology review under CAA section 112(d)(6), the EPA is proposing to eliminate the less stringent of two currently available options for complying with leak detection and repair program requirements—while retaining the more stringent compliance requirement. In addition, under CAA sections 112(d)(2) and (3), the EPA is proposing requirements to address certain emission points that were not previously regulated.

With regard to the APR source category, the EPA has determined that no amendments are needed for this source category based on the risk and technology reviews under CAA sections 112(d)(6) and 112(f). However, under CAA sections 112(d)(2) and (3), the EPA is proposing requirements to address certain emission points that were not previously regulated.

With regard to the PC source category, the EPA has determined that no amendments are needed for this source category based on the risk review under CAA section 112(f). However, based on the technology review under CAA section 112(d)(6), the EPA is proposing to eliminate the less stringent of two currently available options for complying with leak detection and repair program requirements—while retaining the more stringent compliance requirement.

The EPA is also proposing revisions to all three source categories in four areas. First, the EPA is proposing to revise the standards so that they apply at all times, including during periods of startup, shutdown and malfunction (SSM). Second, the EPA is proposing to require electronic reporting of performance test results. Third, the EPA is clarifying the provisions regarding open-ended lines by adding a definition for what constitutes a “sealed” open-ended line. Finally, the EPA is proposing to require monitoring of pressure relief devices (PRDs) in organic HAP service that release to the atmosphere, and that a pressure release from such a PRD is a violation.

3. Costs and Emissions Reductions

Table 1 below summarizes the estimated costs and potential emissions reductions for this action. See section IX of this preamble for further discussion of the costs and impacts.

Table 1—Summary of the Costs and Emissions Reductions for the Proposed Acrylic and Modacrylic Fibers Production, Amino/Phenolic Resins Production and Polycarbonate Production NESHAP Amendments

Source category

Number

affected

plants

Capital costs ($)

Annualized costs

($/yr)

Emissions

reductions

(tpy)

Acrylic and Modacrylic Fibers Production

$38,000

$6,000

0.2

Amino/Phenolic Resins Production

1,500,000

400,000

20.1

Polycarbonate Production

67,000

9,400

2.1

B. Does this action apply to me?

Table 2 of this preamble lists the NESHAP and associated regulated industrial source categories that are the subject of this proposal. Table 2 is not intended to be exhaustive, but rather to provide a guide for readers regarding entities that this proposed action is likely to affect. The proposed standards, once finalized, will be directly applicable to the affected sources. Federal, state, local and tribal government entities would not be affected by this proposed action. As defined in the “Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990” (see 57 FR 31576, July 16, 1992), the “Acrylic and Modacrylic Fibers Production” source category includes any facility engaged in manufacturing fibers in which the fiber-forming substance is any long-chain, synthetic polymer composed of at least 85 percent, by weight, acrylonitrile units. As defined in the “Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990” (see 57 FR 31576, July 16, 1992) and subsequently amended (see 65 FR 3276, January 20, 2000), the “Amino/Phenolic Resins Production” source category includes any facility engaged in manufacturing amino resins or phenolic resins. As defined in the “Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990” (see 57 FR 31576, July 16, 1992), the “Polycarbonate Production” source category includes any facility which manufactures a special class of polyester formed from the dihydroxy compound and any carbonate diester or by ester interchange.

Table 2—NESHAP and Industrial Source Categories Affected by This Proposed Action

NESHAP and source category

NAICS Code

Generic Maximum Achievable Control Technology Standards

Acrylic and Modacrylic Fibers Production

325220

(325222)

Polycarbonate Production

325211

(325211)

Amino/Phenolic Resins Production

325211

(325211)

North American Industry Classification System 2012 (2007 in parenthesis).

C. 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 proposal is available on the Internet through the EPA's Technology Transfer Network (TTN) Web site, a forum for information and technology exchange in various areas of air pollution control. Following signature by the EPA Administrator, the EPA will post a copy of this proposed action on the TTN's policy and guidance page for newly proposed or promulgated rules at:

http://www.epa.gov/ttn/oarpg/t3pfpr.html

. The TTN provides information and technology exchange in various areas of air pollution control. Following publication in the

Federal Register

, the EPA will post the

Federal Register

version of the proposal and key technical documents on the project Web sites:

http://www.epa.gov/ttn/atw/gmact/gmactpg.html

and

http://www.epa.gov/ttn/atw/amino/aminopg.html

. Information on the overall residual risk and technology review program is available at the following Web site:

http://www.epa.gov/ttn/atw/rrisk/rtrpg.html

D. What should I consider as I prepare my comments for the EPA?

Submitting CBI.

Do not submit information containing CBI to the EPA through

http://www.regulations.gov

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM 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 for inclusion in the public docket. If you submit a CD-ROM or disk that does not contain CBI, mark the outside of the disk or CD-ROM 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: Nick Parsons, c/o OAQPS Document Control Officer (C404-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Attn: Docket ID No. EPA-HQ-OAR-2012-0133.

E. Public Hearing

If a hearing is held, it will provide interested parties the opportunity to present data, views or arguments concerning the proposed action. The EPA will make every effort to accommodate all speakers who arrive and register. Because this hearing, if held, will be at a U.S. governmental facility, individuals planning to attend the hearing should be prepared to show valid picture identification to the security staff in order to gain access to the meeting room. In addition, you will need to obtain a property pass for any personal belongings you bring with you. Upon leaving the building, you will be required to return this property pass to the security desk. No large signs will be allowed in the building, cameras may only be used outside of the building and demonstrations will not be allowed on federal property for security reasons. The EPA may ask clarifying questions during the oral presentations but will not respond to the presentations at that time. Written statements and supporting information submitted during the comment period will be considered with the same weight as oral comments and supporting information presented at the public hearing. If a hearing is held on February 10, 2014, written comments on the proposed rule must be postmarked by March 10, 2014. Commenters should notify Ms. Virginia Hunt if they will need specific equipment, or if there are other special needs related to providing comments at the hearing. The EPA will provide equipment for commenters to show overhead slides or make computerized slide presentations if we receive special requests in advance. Oral testimony will be limited to 5 minutes for each

commenter. The EPA encourages commenters to provide the EPA with a copy of their oral testimony electronically (via email or CD) or in hard copy form. Verbatim transcripts of the hearings and written statements will be included in the docket for the rulemaking. The EPA will make every effort to follow the schedule as closely as possible on the day of the hearing; however, please plan for the hearing to run either ahead of schedule or behind schedule. Information regarding the hearing (including information as to whether or not one will be held) will be available at:

http://www.epa.gov/ttn/oarpg/t3main.html

. Again, all requests for a public hearing to be held must be received by January 24, 2014.

II. Background

A. What is the statutory authority for this action?

Section 112 of the CAA establishes a two-stage regulatory process to address emissions of HAP from stationary sources. In the first stage, after the EPA has identified categories of sources emitting one or more of the HAP listed in CAA section 112(b), CAA section 112(d) requires us to promulgate technology-based NESHAP for those sources. “Major sources” are those that emit or have the potential to emit 10 tons per year (tpy) or more of a single HAP or 25 tpy or more of any combination of HAPs. For major sources, the technology-based NESHAP must reflect the maximum degree of emissions reductions of HAPs achievable (after considering cost, energy requirements and non-air quality health and environmental impacts) and are commonly referred to as MACT standards.

MACT standards must require the maximum degree of emissions reduction achievable through the application of measures, processes, methods, systems or techniques, including, but not limited to, measures that: (1) Reduce the volume of or eliminate pollutants through process changes, substitution of materials or other modifications; (2) enclose systems or processes to eliminate emissions; (3) capture or treat pollutants when released from a process, stack, storage or fugitive emission point; (4) are design, equipment, work practice or operational standards (including requirements for operator training or certification); or (5) are a combination of the above. CAA section 112(d)(2)(A)-(E). The MACT standards may take the form of design, equipment, work practice or operational standards where the EPA first determines that either: (1) a pollutant cannot be emitted through a conveyance designed and constructed to emit or capture the pollutants or that any requirement for, or use of, such a conveyance would be inconsistent with law; or (2) the application of measurement methodology to a particular class of sources is not practicable due to technological and economic limitations. CAA section 112(h)(1)-(2).

The MACT “floor” is the minimum control level allowed for MACT standards promulgated under CAA section 112(d)(3) and may not be based on cost considerations. For new sources, the MACT floor cannot be less stringent than the emissions control that is achieved in practice by the best-controlled similar source. The MACT floor for existing sources can be less stringent than floors for new sources but not less stringent than the average emissions limitation achieved by the best-performing 12 percent of existing sources in the category or subcategory (or the best-performing five sources for categories or subcategories with fewer than 30 sources). In developing MACT standards, the EPA must also consider control options that are more stringent than the floor. We may establish standards more stringent than the floor based on considerations of the cost of achieving the emissions reductions, any non-air quality health and environmental impacts and energy requirements.

The EPA is then required to review these technology-based standards and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less frequently than every eight years. CAA section 112(d)(6). In conducting this 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 second stage in standard-setting focuses on reducing any remaining (i.e., “residual”) risk according to CAA section 112(f). This provision requires, first, that the EPA prepare a Report to Congress discussing (among other things) methods of calculating the risks posed (or potentially posed) by sources after implementation of the MACT standards, the public health significance of those risks and the EPA's recommendations as to legislation regarding such remaining risk. The EPA prepared and submitted the

Residual Risk Report to Congress,

EPA-453/R-99-001 (

Risk Report

) in March 1999. Congress did not act in response, thereby triggering the EPA's obligation under CAA section 112(f)(2) to analyze and address residual risk.

Section 112(f)(2) of the CAA requires the EPA to determine for source categories subject to MACT standards whether the emission standards provide an ample margin of safety to protect public health. Section 112(f)(2)(B) of the CAA expressly preserves the EPA's use of the two-step process 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 in a challenge to the risk review for the Synthetic Organic Chemical Manufacturing source category, the United States Court of Appeals for the District of Columbia Circuit upheld as reasonable the EPA's interpretation that subsection 112(f)(2) incorporates the approach established in the Benzene NESHAP.

See NRDC

EPA,

529 F.3d 1077, 1083 (D.C. Cir. 2008)(“[S]ubsection 112(f)(2)(B) expressly incorporates the EPA's interpretation of the Clean Air Act from the Benzene standard, complete with a citation to the

Federal Register

.”);

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

vol. 1, p. 877 (Senate debate on Conference Report).

The first step in the process of evaluating residual risk is the determination of acceptable risk. If risks are unacceptable, the EPA cannot consider cost in identifying the emissions standards necessary to bring risks to an acceptable level. The second step is the determination of whether standards must be further revised in order to provide an ample margin of safety to protect public health. The ample margin of safety is the level at which the standards must be set, unless an even more stringent standard is necessary to prevent, taking into consideration costs, energy, safety and other relevant factors, an adverse environmental effect.

1. Step 1-Determination of Acceptability

The agency in the Benzene NESHAP concluded that “the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information” and that the “judgment on acceptability cannot be reduced to any single factor.”

Id.

at 38046. The determination of what represents an “acceptable” risk is based on a judgment of “what risks are acceptable in the world in which we live” (

Risk Report

at 178, quoting

NRDC

EPA,

824 F. 2d 1146, 1165 (DC Cir. 1987) (en banc) (“Vinyl Chloride”), recognizing that our world is not risk-free.

In the Benzene NESHAP, we stated that “EPA will generally presume that if the risk to [the maximum exposed] individual is no higher than approximately one in 10 thousand, that risk level is considered acceptable.” 54 FR 38045. We discussed the maximum individual lifetime cancer risk (or maximum individual risk (MIR)) as being “the estimated risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years.”

Id.

We explained that this measure of risk “is an estimate of the upper bound of risk based on conservative assumptions, such as continuous exposure for 24 hours per day for 70 years.”

Id.

We acknowledged that maximum individual lifetime cancer risk “does not necessarily reflect the true risk, but displays a conservative risk level which is an upper-bound that is unlikely to be exceeded.”

Id.

Understanding that there are both benefits and limitations to using the MIR as a metric for determining acceptability, we acknowledged in the Benzene NESHAP that “consideration of maximum individual risk * * * must take into account the strengths and weaknesses of this measure of risk.”

Id.

Consequently, the presumptive risk level of 100-in-1 million (1-in-10 thousand) provides a benchmark for judging the acceptability of maximum individual lifetime cancer risk, but does not constitute a rigid line for making that determination. Further, in the Benzene NESHAP, we noted that:

[p]articular attention will also be accorded to the weight of evidence presented in the risk assessment of potential carcinogenicity or other health effects of a pollutant. While the same numerical risk may be estimated for an exposure to a pollutant judged to be a known human carcinogen, and to a pollutant considered a possible human carcinogen based on limited animal test data, the same weight cannot be accorded to both estimates. In considering the potential public health effects of the two pollutants, the Agency's judgment on acceptability, including the MIR, will be influenced by the greater weight of evidence for the known human carcinogen.

Id.

at 38046. The agency also explained in the Benzene NESHAP that:

[i]n establishing a presumption for MIR, rather than a rigid line for acceptability, the Agency intends to weigh it with a series of other health measures and factors. These include the overall incidence of cancer or other serious health effects within the exposed population, the numbers of persons exposed within each individual lifetime risk range and associated incidence within, typically, a 50 km exposure radius around facilities, the science policy assumptions and estimation uncertainties associated with the risk measures, weight of the scientific evidence for human health effects, other quantified or unquantified health effects, effects due to co-location of facilities, and co-emission of pollutants.

Id.

at 38045. In some cases, these health measures and factors taken together may provide a more realistic description of the magnitude of risk in the exposed population than that provided by maximum individual lifetime cancer risk alone.

As noted earlier, in

NRDC

EPA,

the court held that section 112(f)(2) “incorporates the EPA's interpretation of the Clean Air Act from the Benzene Standard.” The court further held that Congress' incorporation of the Benzene approach applies equally to carcinogens and non-carcinogens. 529 F.3d at 1081-82. Accordingly, we also consider non-cancer risk metrics in our determination of risk acceptability and ample margin of safety.

2. Step 2—Determination of Ample Margin of Safety

CAA section 112(f)(2) requires the EPA to determine, for source categories subject to MACT standards, whether those standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, “the second step of the inquiry, determining an `ample margin of safety,' again includes consideration of all of the health factors, and whether to reduce the risks even further . . . . Beyond that information, additional factors relating to the appropriate level of control will also be considered, including costs and economic impacts of controls, technological feasibility, uncertainties and any other relevant factors. Considering all of these factors, the agency will establish the standard at a level that provides an ample margin of safety to protect the public health, as required by section 112.” 54 FR 38046.

According to CAA section 112(f)(2)(A), if the MACT standards for HAP “classified as a known, probable, or possible human carcinogen do not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in the category or subcategory to less than one in one million,” the EPA must promulgate residual risk standards for the source category (or subcategory), as necessary to provide an ample margin of safety to protect public health. In doing so, the EPA may adopt standards equal to existing MACT standards if the EPA determines that the existing standards (i.e. the MACT standards) are sufficiently protective.

NRDC

EPA,

529 F.3d 1077, 1083 (DC Cir. 2008) (“If EPA determines that the existing technology-based standards provide an 'ample margin of safety,' then the Agency is free to readopt those standards during the residual risk rulemaking.”) The EPA must also adopt more stringent standards, if necessary, to prevent an adverse environmental effect,

but must consider cost, energy, safety and other relevant factors in doing so.

“Adverse environmental effect” is defined as any significant and widespread adverse effect, which may be reasonably anticipated to wildlife, aquatic life or natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental qualities over broad areas. CAA section 112(a)(7).

The CAA does not specifically define the terms “individual most exposed,” “acceptable level” and “ample margin of safety.” In the Benzene NESHAP, 54 FR 38044-38045, we stated as an overall objective:

In protecting public health with an ample margin of safety under section 112, EPA strives to provide maximum feasible protection against risks to health from hazardous air pollutants by (1) protecting the greatest number of persons possible to an individual lifetime risk level no higher than approximately 1-in-1 million and (2) limiting to no higher than approximately 1-in-10 thousand [i.e., 100-in-1 million] the estimated risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years.

The agency further stated that “[t]he EPA also considers incidence (the number of persons estimated to suffer cancer or other serious health effects as a result of exposure to a pollutant) to be an important measure of the health risk to the exposed population. Incidence measures the extent of health risks to the exposed population as a whole, by providing an estimate of the occurrence of cancer or other serious health effects in the exposed population.”

Id.

at 38045.

In the ample margin of safety decision process, the agency again considers all of the health risks and other health

information considered in the first step, including the incremental risk reduction associated with standards more stringent than the MACT standard or a more stringent standard that EPA has determined is necessary to ensure risk is acceptable. In the ample margin of safety analysis, the agency considers additional factors, including costs and economic impacts of controls, technological feasibility, uncertainties and any other relevant factors. Considering all of these factors, the agency will establish the standard at a level that provides an ample margin of safety to protect the public health, as required by CAA section 112(f). 54 FR 38046.

B. What are the source categories and how did the MACT standards regulate their HAP emissions?

1. Acrylic and Modacrylic Fibers Production Source Category

The NESHAP for Acrylic and Modacrylic Fibers Production (“AMF MACT standards”), with the exception of wastewater processes, were promulgated on June 29, 1999 (64 FR 34854), and codified at 40 CFR part 63, subpart YY. The provisions for wastewater were promulgated separately on November 22, 1999 (64 FR 63695), and also codified at 40 CFR part 63, subpart YY. The AMF MACT standards were established in a consolidated rulemaking for certain small source categories consisting of five or fewer major sources. The standards for these source categories were developed under the EPA's Generic MACT program.

Acrylic and modacrylic fibers are manufactured fibers in which the fiber-forming substance is a long-chain synthetic polymer containing acrylonitrile units. The fiber-forming substance in acrylic fibers is composed of at least 85 percent acrylonitrile units by weight, whereas modacrylic fibers are less than 85 but at least 35 percent acrylonitrile units by weight. These acrylic and modacrylic fibers have been used in textiles (including apparel, carpet, awnings, tents, sandbags and auto upholstery) and in industrial applications like concrete reinforcements and industrial filters. These fibers are also used as carbon fiber precursors. Carbon fibers developed from acrylic fibers have high tensile strength and are used in aerospace applications, such as aircraft airframes and engine structures, as well as other applications where light weight and high strength are needed, including racing car bodies, golf club shafts, bicycle frames, fishing rods, automobile springs, sailboat masts and many other items.

The production of AMF involves a polymerization reaction process using either a solution or suspension process in either a batch or continuous mode. The resulting polymer (called “spin dope”) is spun into fibers using either wet or dry spinning techniques. The spun fibers are then treated to remove excess solvent and to improve fiber characteristics through processes such as washing, stretching, crimping and drying.

Sources of HAP emissions from the production of AMF include: (1) Storage vessels used to store acrylonitrile monomer and co-monomers; (2) process vents on reactors, vessels and storage vessels used for acrylic polymerization, monomer recovery, fiber spinning and solvent recovery operations; (3) fugitive emissions from AMF spinning lines; (4) wastewater treatment systems; and (5) equipment leaks. In the production of AMF, HAP are used primarily as raw materials or reaction inhibitors in the polymerization reaction process. The AMF MACT standards include emission limits for existing and new fiber spinning lines using spin dope from a suspension polymerization process, new sources using a solution polymerization process and for process vents at all facilities. The AMF MACT standards include a combination of equipment standards and work practices for equipment leaks and wastewater, and a combination of equipment standards and emission limits for storage vessels.

To meet the requirements of the AMF MACT standards, the emissions from storage vessels are typically controlled either by floating roofs or fixed roofs that route emissions through a closed vent system to a combustion or recovery device. Emissions from wastewater are generally controlled by equipment modifications (e.g., covers on surface impoundments, containers and drain systems) and pretreatment to remove HAP and biodegradation or pretreatment and discharge to a publicly owned treatment works for biodegradation. Emissions from equipment leaks are typically reduced by leak detection and repair (LDAR) work practice programs. Controls for process vents include combustion or recovery devices, and controls for fiber spinning lines include enclosure of the spinning and washing areas with venting to a combustion or recovery device.

We identified one major source currently operating that is subject to the AMF MACT standards. Acrylonitrile accounts for the majority of the HAP emissions from the AMF processes at this facility (approximately 32 tpy and over 99 percent of the total HAP emissions by mass). The only other HAP reported by this facility is hydroquinone (approximately 3 lbs/yr). As we have stated previously, other organic HAP, where present, would only be associated with those pollutant streams containing acrylonitrile, and where sources control acrylonitrile emissions, comparable levels of control will be achieved for other organic HAP emitted from AMF facilities. See NESHAP: Generic Maximum Achievable Control Technology (Generic MACT); Final Rule, Process Wastewater Provisions; Proposed Rule, 64 FR 34854, 34858 (June 29, 1999). The same is true here—hydroquinone is emitted only from equipment leaks, and equipment leaks are already subject to control through the LDAR program in the rule.

We estimate that the actual emissions levels for all emission sources are representative of the MACT-allowable levels (i.e., the maximum emission levels allowed if in compliance with the MACT standards), as we are not aware of any situations in which the facility is conducting additional work practices or operating a control device such that it achieves a greater emission reduction than required. For more detail about this estimate of the ratio of actual-to-MACT-allowable emissions and the estimation of the MACT-allowable emission levels (and associated risks and impacts), see the memorandum,

MACT Allowable Emissions and Risks for the Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production Source Categories,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

2. Amino/Phenolic Resins Production

The NESHAP for the Manufacture of Amino/Phenolic Resins (“APR MACT standards”; also referred to as Group III Polymers and Resins) were promulgated on January 20, 2000 (65 FR 3275), and codified at 40 CFR part 63, subpart OOO. The APR MACT standards apply to major sources and regulate HAP emissions resulting from the manufacture of amino resins or phenolic resins. These two products can broadly be classified as formaldehyde-based thermosetting resins. An amino resin is a resin produced through the reaction of formaldehyde, or a formaldehyde-containing solution, with one or more compounds that contain an amino group; these compounds include melamine, urea and urea derivatives. A phenolic resin is a resin that is a condensation product of formaldehyde and phenol, or a formaldehyde substitute and/or a phenol substitute.

Substitutes for formaldehyde include acetaldehyde or furfuraldehyde. Substitutes for phenol include other phenolic-starting compounds such as cresols, xylenols, p-tert-butylphenol, p-phenylphenol and nonylphenol. Formaldehyde, phenol, acetaldehyde and cresols are HAP, but the other reactants are not. Amino/phenolic resins are used in the manufacture of plywood, particle board, adhesives, wood furniture and plastic parts.

Generally, the production of APR entails four processes: (1) Raw material (i.e., solvent and catalyst) storage and refining; (2) polymer formation in a reactor; (3) material recovery; and (4) finishing (e.g., cooling, filtering, drying or pulverizing).

Sources of HAP emissions from the production of APR include reactor batch process vents, non-reactor batch process vents, continuous process vents, equipment leaks, wastewater, storage vessels and heat exchangers. In the production of APR, HAP are used primarily as reactants or extraction solvents. The APR MACT standards include a combination of equipment standards and emission limits for the various emission sources.

To meet the requirements of the APR MACT standards, the typical control techniques used to reduce emissions include LDAR programs for heat exchangers and other equipment. Boilers, combustion and recovery devices may be used to control emissions from batch process vents.

We identified 18 currently-operating facilities subject to the APR MACT standards. Methanol, formaldehyde and phenol account for the majority of the HAP emissions from the APR production processes at these facilities (approximately 357 tpy and 96 percent of the total HAP emissions by mass). A variety of other chemicals are used in the production of APR, and these facilities also reported emissions of 23 other HAP. Emissions of three persistent bioaccumulative HAP (PB-HAP) are reported in the data set for this source category, including lead compounds, cadmium compounds, and polycyclic organic matter (POM) (which includes polyaromatic hydrocarbons (PAH)).

We estimate that the actual emissions levels for all sources are representative of the MACT-allowable levels (i.e., the maximum emission levels allowed if in compliance with the MACT standards), as we are not aware of any situations in which facilities are conducting additional work practices or operating a control device such that it achieves a greater emission reduction than required, except batch process vents. As it is possible that the capture systems and control devices used at some facilities achieve greater emission reductions than what is required by the NESHAP for batch process vents, the MACT-allowable level for organic HAP emissions from reactor batch process vents could be up to 3.4 times the actual emissions and the MACT-allowable level for organic HAP emissions from non-reactor batch process vents could be up to 1.6 times the actual emissions for some facilities in this source category. For more detail about this estimate of the ratio of actual-to-MACT-allowable emissions and the estimation of MACT-allowable emission levels (and associated risks and impacts), see the memorandum,

MACT Allowable Emissions and Risks for the Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production Source Categories,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

3. Polycarbonate Production Source Category

The NESHAP for Polycarbonate Production (“PC MACT standards”), with the exception of wastewater processes, were promulgated on June 29, 1999 (64 FR 34854), and codified at 40 CFR part 63, subpart YY. The provisions for wastewater were promulgated separately on November 22, 1999 (64 FR 63695), and also codified at 40 CFR part 63, subpart YY. Along with the AMF and other source categories, the PC source category standards were established in a consolidated rulemaking for certain small source categories consisting of five or fewer major sources. The standards for these source categories were developed under the EPA's Generic MACT program.

Polycarbonates are thermoplastic polymers that can be either transparent or opaque, are heat resistant and are scratch and impact resistant. These properties make PC useful in a variety of applications, including as a dielectric in capacitors, car headlights, water bottles, sports helmets, compact discs and DVDs, eyewear lenses, medical devices, toys and other products.

The production of PC involves a polymerization reaction process using either a solution or suspension process in either a batch or continuous mode. All production of PC in the United States is currently based on the polymerization reaction of bisphenols with phosgene in the presence of catalysts, solvents (mainly methylene chloride) and other additives. After the reaction, the resulting polymer is purified and sent to a recovery process to remove remaining methylene chloride. The resin is dried and stored in silos.

All phosgene used as a feedstock for the production of PC is produced onsite to reduce potential hazards associated with transporting and storing this material. The phosgene is fed directly from dedicated phosgene production equipment to PC polymerization process equipment. Consequently, phosgene production is integrated with the production of PC; the production of PC cannot occur without the other process operating. Since dedicated phosgene production units are integral to the PC production process, the EPA considers such phosgene production units to be part of the PC source category (63 FR 55178, October 18, 1998).

Sources of HAP emissions from the production of PC include storage vessels used to store methylene chloride and other organic solvents; process vents on polymerization, polymer solution purification and solvent recovery equipment; wastewater treatment systems; and equipment leaks. In the production of PC, HAP are used as monomers, co-monomers and solvents in the polymerization reaction. The PC MACT standards include emission limits for continuous process vents. The PC MACT standards include a combination of equipment standards and work practices for equipment leaks and wastewater and a combination of equipment standards and emission limits for storage vessels.

To meet the requirements of the PC MACT standards, the typical control devices used to reduce emissions from storage vessels are fixed roofs with emissions routed through a closed vent system to a combustion or recovery device. Emissions from wastewater are generally controlled by equipment modifications (e.g., covers on surface impoundments, containers and drain systems) and treatment to remove the HAP, including steam stripping followed by recovery or combustion of the stripped HAP. Emissions from equipment leaks are typically reduced by leak detection and repair work practice programs. Controls for continuous and batch process vents include combustion or recovery devices.

We identified four currently-operating facilities subject to the PC MACT standards. Methylene chloride, ethyl chloride and triethylamine account for the majority of the HAP emissions from the PC production processes at these facilities (approximately 330 tpy and over 99 percent of the total HAP emissions by mass). Phosgene and chlorobenzene emissions were also reported from the PC production processes at these facilities.

We estimate that the actual emissions levels for all sources are representative of the MACT-allowable levels (i.e., the maximum emission levels allowed if in compliance with the MACT standards), as we are not aware of any situations in which facilities are conducting additional work practices or operating a control device such that it achieves a greater emission reduction than required, except storage vessels. As it is possible that the capture systems and control devices used at some facilities achieve greater HAP emission reductions than what is required by the NESHAP for some storage vessels, depending on the vessel capacity and vapor pressure of the stored material, the MACT-allowable level of HAP emissions could be up to 2.5 times the actual emissions for storage vessels in this source category. For more detail about this estimate of the ratio of actual to MACT-allowable emissions and the estimation of the MACT-allowable emission levels (and associated risks and impacts), see the memorandum,

MACT Allowable Emissions and Risks for the Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production Source Categories,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

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

To perform the risk assessments for these source categories, we developed data sets for the APR and PC source categories based on information in the 2005 National Emissions Inventory (NEI) (available at

http://www.epa.gov/ttnchie1/net/2005inventory.html

). 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. We reviewed the NEI data and made adjustments where necessary to ensure the proper facilities were included and to ensure the proper processes were allocated to each source category. We also reviewed the emissions and other data to identify data anomalies that could affect risk estimates, such as whether a pollutant was expected to be emitted from facilities in a source category or whether an emission point was located within a facility's fenceline. The NEI data were also reviewed by industry trade groups, including the American Chemistry Council and the Society of Chemical Manufacturers and Affiliates, as well as several state air agencies. Where the EPA received new information from the industry and air agency review, including updated emissions data and process information, facility closure information and information that some facilities were not subject to the APR or PC MACT standards, we revised the NEI data where we concluded the comments supported such adjustment. We used this reviewed and revised data set to conduct the risk assessment and other analyses for each source category. Due to the conservative nature of our emissions estimates, as described in the emissions data memo cited below, we believe that the data set provides a conservative estimate for use in assessing the risk from these source categories. Further details on the changes made to the 2005 NEI data can be found in the memorandum,

Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

To perform the risk assessment for the AMF source category, we developed a data set based on information submitted to the EPA for this purpose by the one operating facility in the source category. On February 23, 2012, the EPA visited this facility, Cytec Carbon Fibers, LLC, located in Piedmont, South Carolina. The purpose of this visit was to better understand the acrylic fiber production processes, the controls in place to reduce HAP emissions and the characteristics of the emission points at this facility. As part of this visit, the EPA requested that facility personnel examine the 2008 NEI HAP inventory data that the EPA had for the facility. The EPA provided this data to the facility prior to the site visit to give the facility the opportunity to correct or update the data. After review of the data, the facility submitted updated information, and the updated data formed the basis for the data set used for modeling.

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

To conduct the technology review, we reviewed information developed since these rules were originally promulgated in 1999 and 2000. Since those rules have been promulgated, the EPA has developed other air toxics regulations for a number of other source categories that emit organic HAP from the same type of emission sources that are present in the three source categories included in this technology review. In these other air toxic regulatory actions, we consistently evaluated any new practices, processes and control techniques. For this technology review, we took into account the regulatory requirements and/or technical analyses associated with these other regulatory actions to identify any practices, processes and control techniques considered in these efforts that could possibly be applied to the source categories addressed in this action.

We also downloaded from the reasonably available control technology (RACT)/best available control technology (BACT)/lowest achievable emission rate (LAER) Clearinghouse for processes in the AMF, APR and PC source categories with permits dating back to the promulgation dates of each MACT regulation. Finally, we conducted an online search of all relevant publications, journals, permits and other documents to identify any new practices, processes or control technologies for HAP emissions sources since the dates of promulgation of the standards.

To evaluate unregulated emission points at facilities regulated by the APR MACT standards, we relied on existing data submitted to the EPA during development of the existing APR MACT standards. To evaluate unregulated emission points for the AMF MACT standards, we relied primarily on data submitted to the EPA by the one operating facility in the source category, along with information gathered during the EPA's visit to the facility.

III. Analytical Procedures

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 did we estimate post-MACT risks posed by the source categories?

The EPA conducted risk assessments that provided estimates of the MIR posed by the HAP emissions from each source in each source category, the hazard index (HI) for chronic exposures to HAP with the potential to cause non-cancer health effects, and the hazard quotient (HQ) for acute exposures to HAP with the potential to cause non-cancer health effects. The assessments also provided estimates of the distribution of cancer risks within the exposed populations, cancer incidence and an evaluation of the potential for adverse environmental effects for each source category. The risk assessment consisted of eight primary steps, as discussed below. The docket for this rulemaking contains the following documents which provide more

information on the risk assessment inputs and models:

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category.

The methods used to assess risks (as described in the eight primary steps below) are consistent with those peer-reviewed by a panel of the EPA's Science Advisory Board (SAB) in 2009 and described in their peer review report issued in 2010

; they are also consistent with the key recommendations contained in that report.

U.S. EPA SAB.

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,

May 2010.

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

As discussed in section II.C of this preamble, we created the preliminary data sets for the APR and PC source categories using data in the 2005 NEI, supplemented by data collected from industry, industry trade associations and state air agencies (when available). For the AMF source category, we used data collected from the one facility subject to the AMF MACT standards.

2. How did we estimate MACT-allowable emissions?

The available emissions data in the MACT dataset include estimates of the mass of HAP emitted during the specified annual time period. In some cases, these “actual” emission levels are lower than the emission levels required to comply with the MACT standards. The emissions level allowed to be emitted by the MACT standards is referred to as the “MACT-allowable” emissions level. We discussed the use of both MACT-allowable and actual emissions in the final Coke Oven Batteries residual risk rule (70 FR 19998-19999, April 15, 2005) and in the proposed and final Hazardous Organic NESHAP residual risk rules (71 FR 34428, June 14, 2006, and 71 FR 76609, December 21, 2006, respectively). In those previous actions, we noted that assessing the risks at the MACT-allowable level is inherently reasonable since these risks reflect 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.)

As described above, the actual emissions data were compiled based on the NEI and information gathered from facilities through industrial trade associations and state air agencies for the APR and PC source categories and through the one facility subject to the AMF MACT standards. To estimate emissions at the MACT-allowable level, we developed a ratio of MACT-allowable to actual emissions for each emissions source type in each source category, based on the level of control required by the MACT standards compared to the level of reported actual emissions and available information on the level of control achieved by the emissions controls in use. For example, if there was information to suggest several facilities in a source category were controlling storage tank emissions by 98 percent while the MACT standards required only 92-percent control, we would estimate that MACT-allowable emissions from these emission points could be as much as four times higher (8-percent allowable emissions compared with 2 percent actually emitted), and the ratio of MACT-allowable to actual would be 4:1 for this emission point type at the facilities in this source category. After developing these ratios for each emission point type in each source category, we next applied these ratios on a facility-by-facility basis to the maximum chronic risk values from the inhalation risk assessment to obtain facility-specific maximum risk values based on MACT-allowable emissions. Further explanation of this evaluation is provided in the technical document,

MACT Allowable Emissions and Risks for the Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production Source Categories,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

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

Both long-term and short-term inhalation exposure concentrations and health risks from the source categories addressed in this proposal were estimated using the Human Exposure Model (Community and Sector HEM-3 version 1.1.0). 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 risks using the exposure estimates and quantitative dose-response information.

This metric comes from the Benzene NESHAP. See 54 FR 38046.

The air dispersion model used by the HEM-3 model (AERMOD) is one of the EPA's preferred models for assessing 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 of hourly surface and upper air observations for 189 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 unit risk factors and other health benchmarks is used to estimate health risks. These risk factors and health benchmarks are the latest values recommended by the EPA for HAP and other toxic air pollutants. These values are available at

http://www.epa.gov/ttn/atw/toxsource/summary.html

and are discussed in more detail later in this section.

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 generally the smallest geographic area for which census statistics are tabulated.

In developing the risk assessment for chronic exposures, we used the estimated annual average ambient air concentration of each HAP emitted by each source for which we have emissions data in the source category. The air concentrations at each nearby census block centroid were used as a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. We calculated the MIR for each facility as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week and 52 weeks per year for a 70-year period) exposure to the maximum concentration at the centroid of inhabited census blocks. Individual cancer risks were calculated by multiplying the estimated lifetime

exposure to the ambient concentration of each of the 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 probability 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 URE values from the EPA's Integrated Risk Information System (IRIS). For carcinogenic pollutants without EPA IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) URE values, where available. In cases where new, scientifically credible dose response values have been developed in a manner consistent with the 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.

With regard to formaldehyde (one of the primary HAP emitted by facilities in the APR source category), the EPA determined in 2004 that the Chemical Industry Institute of Toxicology (CIIT) cancer dose-response value for formaldehyde (5.5 × 10

−9

per mg/m

) was based on better science than the IRIS cancer dose-response value (1.3 × 10

−5

per mg/m

). Thus, we switched at that time from using the IRIS value to the CIIT value in risk assessments supporting regulatory actions. Based on subsequent published research, however, the EPA changed its determination regarding the CIIT model and, in 2010, the EPA returned to using the 1991 IRIS value. The EPA has been working on revising the formaldehyde IRIS assessment, and the National Academy of Sciences (NAS) completed its review of the EPA's draft in April of 2011.

The EPA is reviewing the public comments and the NAS independent scientific peer review. The EPA will follow the NAS Report recommendations and will present results obtained by implementing the biologically-based dose-response (BBDR) model for formaldehyde. The EPA will compare these estimates with those currently presented in the External Review draft of the assessment and will discuss their strengths and weaknesses. As recommended by the NAS committee, appropriate sensitivity and uncertainty analyses will be an integral component of implementing the BBDR model. The draft IRIS assessment will be revised in response to the NAS peer review, and public comments and the final assessment will be posted on the IRIS database. In the interim, we will present findings using the 1991 IRIS value as a primary estimate, and may also consider other information as the science evolves. As noted above and described in the risk assessment, the IRIS URE for formaldehyde is 1.3 × 10

−5

mg/m

, whereas, the CIIT URE for formaldehyde is 5.5 × 10

−9

mg/m

http://www.nap.edu/catalog.php?record_id=13142

We note here that several carcinogens have a mutagenic mode of action.

Of these compounds, POM is emitted by facilities in the APR source category. For these compounds, the age-dependent adjustment factors (ADAF) described in the EPA's

Supplemental Guidance for Assessing Susceptibility from Early-Life Exposure to Carcinogens

were applied. This adjustment has the effect of increasing the estimated lifetime risks for these pollutants by a factor of 1.6.

In addition, the EPA expresses carcinogenic potency for compounds in the POM group in terms of benzo[a]pyrene equivalence, based on evidence that carcinogenic POM have the same mutagenic mechanism of action as does benzo[a]pyrene. For this reason, the EPA's Science Policy Council

recommends applying the

Supplemental Guidance

to all carcinogenic polycyclic aromatic hydrocarbons for which risk estimates are based on relative potency. Accordingly, we have applied the ADAF to benzo[a]pyrene equivalent portion of all POM mixtures.

U.S. EPA, 2006. Performing risk assessments that include carcinogens described in the

Supplemental Guidance

as having a mutagenic mode of action.

Science Policy Council Cancer Guidelines Implementation Workgroup Communication II:

Memorandum from W.H. Farland dated June 14, 2006.

http://epa.gov/osa/spc/pdfs/CGIWGCommunication_II.pdf

U.S. EPA, 2005. Supplemental Guidance for Assessing Early-Life Exposure to Carcinogens. EPA/630/R-03/003F.

http://www.epa.gov/ttn/atw/childrens_supplement_final.pdf

Only one of these mutagenic compounds, benzo[a]pyrene, is emitted by any of the sources covered by this proposal.

U.S. EPA, 2005. Science Policy Council Cancer Guidelines Implementation Workgroup Communication I: Memorandum from W.H. Farland dated October 4, 2005, to Science Policy Council.

http://www.epa.gov/osa/spc/pdfs/canguid1.pdf

The EPA estimated incremental individual lifetime cancer risks associated with emissions from the facilities in the source categories as the sum of the risks for each of the carcinogenic HAP (including those classified as carcinogenic to humans, likely to be carcinogenic to humans and suggestive evidence of carcinogenic potential

) emitted by the modeled sources. Cancer incidence and the distribution of individual cancer risks for the population within 50 km of any source were also estimated for the source categories as part of these assessments by summing individual risks. A distance of 50 km is consistent with both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044) and the limitations of Gaussian dispersion models, including AERMOD.

These classifications also coincide with the terms “known carcinogen, probable carcinogen, and possible carcinogen,” respectively, which are the terms advocated in the EPA's previous

Guidelines for Carcinogen Risk Assessment,

published in 1986 (51 FR 33992, September 24, 1986). Summing the risks of these individual compounds to obtain the cumulative cancer risks 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) entitled,

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

available at:

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

To assess the risk of non-cancer health effects from chronic exposures, we summed the HQ for each of the HAP that affects a common target organ system to obtain the HI for that target organ system (or target organ-specific HI, TOSHI). The HQ is the estimated exposure divided by the chronic reference level, which is a value selected from one of several sources. First, the chronic reference level can be the EPA reference concentration (RfC) (

http://www.epa.gov/riskassessment/glossary.htm

), 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.” Alternatively, in cases where an RfC from the EPA's IRIS database is not available or where the EPA determines that using a value other than the RfC is appropriate, the chronic reference level can be a value from the following prioritized sources: (1) The Agency for Toxic Substances and Disease Registry Minimum Risk Level (

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

), which is defined as “an estimate of daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse non-cancer health effects (other than cancer) over a specified duration of exposure”; (2) the CalEPA Chronic Reference Exposure Level (REL) (

http://www.oehha.ca.gov/air/hot_spots/pdf/HRAguidefinal.pdf

), which is defined as “the concentration level (that is expressed in units of micrograms per cubic meter (μg/m

) for inhalation exposure and in a dose expressed in units of milligram per kilogram-day (mg/kg-day) for oral exposures), at or

below which no adverse health effects are anticipated for a specified exposure duration”; or (3), as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with the EPA guidelines and has undergone a peer review process similar to that used by the EPA, in place of or in concert with other values.

The EPA also evaluated screening estimates of acute exposures and risks for each of the HAP at the point of highest off-site exposure for each facility (i.e., not just the census block centroids), assuming that a person is located at this spot at a time when both the peak (hourly) emission rates and worst-case dispersion conditions occur. The acute HQ is the estimated acute exposure divided by the acute dose-response value. In each case, the EPA calculated acute HQ values using best available, short-term dose-response values. These acute dose-response values, which are described below, include the acute REL, acute exposure guideline levels (AEGL) and emergency response planning guidelines (ERPG) for 1-hour exposure durations. As discussed below, we used conservative assumptions for emission rates, meteorology and exposure location for our acute analysis.

As described in the

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

an acute REL value (

http://www.oehha.ca.gov/air/pdf/acuterel.pdf

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

Id.

at page 2. Acute REL values are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. Acute REL values are designed to protect the most sensitive individuals 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 value does not automatically indicate an adverse health impact.

AEGL values were derived in response to recommendations from the National Research Council (NRC). As described in

Standing Operating Procedures (SOP) of the National Advisory Committee on Acute Exposure Guideline Levels for Hazardous Substances

(

http://www.epa.gov/opptintr/aegl/pubs/sop.pdf

“the NRC's previous name for acute exposure levels—community emergency exposure levels—was replaced by the term AEGL to reflect the broad application of these values to planning, response and prevention in the community, the workplace, transportation, the military and the remediation of Superfund sites.”

Id.

at 2. This document also states that AEGL values “represent threshold exposure limits for the general public and are applicable to emergency exposures ranging from 10 minutes to eight hours.”

Id.

at 2.

NAS, 2001.

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

page 2.

The document lays out the purpose and objectives of AEGL by stating that “the primary purpose of the AEGL program and the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances is to develop guideline levels for once-in-a-lifetime, short-term exposures to airborne concentrations of acutely toxic, high-priority chemicals.”

Id.

at 21. In detailing the intended application of AEGL values, the document states that “[i]t is anticipated that the AEGL values will be used for regulatory and nonregulatory purposes by U.S. Federal and state agencies, and possibly the international community in conjunction with chemical emergency response, planning and prevention programs. More specifically, the AEGL values will be used for conducting various risk assessments to aid in the development of emergency preparedness and prevention plans, as well as real-time emergency response actions, for accidental chemical releases at fixed facilities and from transport carriers.”

Id.

at 31.

The AEGL-1 value is then 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.”

Id.

at 3. 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.

Similarly, the document defines AEGL-2 values 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.

ERPG values are derived for use in emergency response, as described in the American Industrial Hygiene Association's ERP Committee document entitled,

ERPGS Procedures and Responsibilities

(

http://sp4m.aiha.org/insideaiha/GuidelineDevelopment/ERPG/Documents/ERP-SOPs2006.pdf

), which states that, “Emergency Response Planning Guidelines were developed for emergency planning and are intended as health based guideline concentrations for single exposures to chemicals.”

Id.

at 1. The ERPG-1 value 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 value 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.

ERP Committee Procedures and Responsibilities.

November 1 2006. American Industrial Hygiene Association.

As can be seen from the definitions above, the AEGL and ERPG values include the similarly-defined severity levels 1 and 2. For many chemicals, a severity level 1 value AEGL or ERPG has not been developed because the types of effects for these chemicals are not consistent with the AEGL-1/ERPG-1 definitions; in these instances, we compare higher severity level AEGL-2 or ERPG-2 values to our modeled exposure levels to screen for potential acute concerns. When AEGL-1/ERPG-1 values are available, they are used in our acute risk assessments.

Acute REL values for 1-hour exposure durations are typically lower than their corresponding AEGL-1 and ERPG-1 values. Even though their definitions are slightly different, AEGL-1 values are often the same as the corresponding ERPG-1 values, and AEGL-2 values are often equal to ERPG-2 values. Maximum HQ values from our acute screening risk assessments typically result when basing them on the acute

REL value for a particular pollutant. In cases where our maximum acute HQ value exceeds 1, we also report the HQ value based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1 value).

To develop screening estimates of acute exposures in the absence of hourly emissions data, generally we first develop estimates of maximum hourly emissions rates by multiplying the average actual annual hourly emissions rates by a default factor to cover routinely variable emissions. We choose the factor to use partially based on process knowledge and engineering judgment. The factor chosen also 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, we apply a conservative screening multiplication factor of 10 to the average annual hourly emissions rate in our acute exposure screening assessments as our default approach. However, we use a factor other than 10 if we have information that indicates that a different factor is appropriate for a particular source category. For these source categories, a factor of 10 was applied to all emissions, with one exception. A factor of two was applied for emissions from equipment leaks for all three source categories. A further discussion of why these factors were chosen can be found in the memorandum,

Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Acrylic and Modacrylic Fibers, Amino/Phenolic Resins, and Polycarbonate Production,

available in the docket for this action (EPA-HQ-OAR-2012-0133).

See

http://www.tceq.state.tx.us/compliance/field_ops/eer/index.html

or docket to access the source of these data.

As part of our acute risk assessment process, for cases where acute HQ values from the screening step were less than or equal to 1 (even under the conservative assumptions of the screening analysis), acute impacts were deemed negligible and no further analysis was performed. In cases where an acute HQ from the screening step was greater than 1, additional site-specific data were considered to develop a more refined estimate of the potential for acute impacts of concern. For these source categories, the data refinements employed consisted of using a peak-to-mean hourly emissions ratio based on source category-specific knowledge or data (rather than the default factor of 10) and using the site-specific facility layout to distinguish facility property from an area where the public could be exposed. These refinements are discussed more fully in the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

which are available in the docket for this action. Ideally, we would prefer to have continuous measurements over time to see how the emissions vary by each hour over an entire year. Having a frequency distribution of hourly emissions rates over a year would allow us to perform a probabilistic analysis to estimate potential threshold exceedances and their frequency of occurrence. Such an evaluation could include a more complete statistical treatment of the key parameters and elements adopted in this screening analysis. Recognizing that this level of data is rarely available, we instead rely on the multiplier approach.

To better characterize the potential health risks associated with estimated acute exposures to HAP, and in response to a key recommendation from the SAB's peer review of the EPA's RTR risk assessment methodologies,

we generally examine a wider range of available acute health metrics (e.g., RELs, AEGLs) than we do for our chronic risk assessments. This is in response to the SAB's acknowledgement that there are generally more data gaps and inconsistencies in acute reference values than there are in chronic reference values. In some cases, when Reference Value Arrays

for HAP have been developed, we consider additional acute values (i.e., occupational and international values) to provide a more complete risk characterization. As a result, for most chemicals, the 15-minute occupational ceiling values are set at levels higher than a one-hour AEGL-1, making comparisons to them irrelevant unless the AEGL-1 or ERPG-1 levels are exceeded (U.S. EPA 2009). Such is not the case when comparing the available acute inhalation health effect reference values for formaldehyde (U.S. EPA 2009). See section V.B.2 of this preamble for additional information on the acute dose-response values for formaldehyde.

The SAB peer review of RTR Risk Assessment Methodologies is available at:

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

U.S. EPA. (2009) Chapter 2.9 Chemical Specific Reference Values for Formaldehyde in Graphical Arrays of Chemical-Specific Health Effect Reference Values for Inhalation Exposures (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/061, and available online at

http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003

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

The EPA conducted a screening analysis examining the potential for significant human health risks due to exposures via routes other than inhalation (i.e., ingestion). We first determined whether any sources in the source categories emitted any hazardous air pollutants known to be persistent and bioaccumulative in the environment (PB-HAP). The PB-HAP compounds or compound classes are identified for the screening from the EPA's Air Toxics Risk Assessment Library (available at

http://www.epa.gov/ttn/fera/risk_atra_vol1.html

For the AMF and PC source categories, we did not identify emissions of any PB-HAP. Because we did not identify PB-HAP emissions, no further evaluation of multipathway risk was conducted for these source categories.

For the APR source category, we identified emissions of lead compounds (1 facility), cadmium compounds (2 facilities) and POM (analyzed as benzo(a)pyrene toxic equivalency quotient (TEQ)) (2 facilities). Because one or more of these PB-HAP are emitted by at least one facility in the APR source category, we proceeded to the second step of the evaluation. In this step, we determined whether the facility-specific emissions rates of each of the emitted PB-HAP were large enough to create the potential for significant non-inhalation human health risks under reasonable worst-case conditions. To facilitate this step, we developed emissions rate thresholds for each PB-HAP using 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. We conducted a sensitivity analysis on the screening scenario to ensure that its key design parameters would represent the upper end of the

range of possible values, such that it would represent a conservative but not impossible scenario. The facility-specific emissions rates of each of the PB-HAP were compared to the emission rate threshold values for each of the PB-HAP identified to assess the potential for significant human health risks via non-inhalation pathways. We call this application of the TRIM.FaTE model the Tier I TRIM-Screen.

For the purpose of developing emissions rates for our Tier I TRIM-Screen, we derived emission levels for each PB-HAP (other than lead) at which the maximum excess lifetime cancer risk would be 1-in-1 million or, for HAP that cause non-cancer health effects, the maximum hazard quotient would be 1. If the emissions rate of any PB-HAP exceeds the Tier I screening emissions rate for any facility, we conduct a Tier II multipathway screen. In the Tier II screen, the location of each facility that exceeds the Tier I emission rate is used to refine the assumptions associated with the environmental scenario while maintaining the exposure scenario assumptions. We then adjust the risk-based Tier I screening level for each PB-HAP for each facility based on an understanding of how exposure concentrations estimated for the screening scenario change with meteorology and environmental assumptions. PB-HAP emissions that do not exceed these new Tier II screening levels are considered to pose no unacceptable risks. When facilities exceed the Tier II screening levels, it does not mean that multipathway impacts are significant, only that we cannot rule out that possibility based on the results of the screen. These facilities may be further evaluated for multipathway risks using the TRIM.FaTE model.

In evaluating the potential multi-pathway risk from emissions of lead compounds, rather than developing a screening emissions rate for them, we compared maximum estimated chronic inhalation exposures with the level of the current National Ambient Air Quality Standard (NAAQS) for lead. Values below the level of the primary (health-based) lead NAAQS were considered to have a low potential for multi-pathway risk.

For further information on the multipathway analysis approach, see the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

which are available in the docket for this action.

5. How did we assess risks considering emissions control options?

In addition to assessing baseline inhalation risks and screening for potential multipathway risks, we also estimated risks considering the potential emissions reductions that would be achieved by the control options under consideration. In these cases, the expected emissions reductions were applied to the specific HAP and emissions points in the source category dataset to develop corresponding estimates of risk and incremental risk reductions.

6. How did we conduct the environmental risk screening assessment?

a. Adverse Environmental Effect

The EPA has developed a screening approach to examine the potential for adverse environmental effects as required under section 112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines “adverse environmental effect” as “any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.”

b. Environmental HAP

The EPA focuses on seven HAP, which we refer to as “environmental HAP,” in its screening analysis: five persistent bioaccumulative HAP (PB-HAP) and two acid gases. The five PB-HAP are cadmium, dioxins/furans, polycyclic organic matter (POM), mercury (both inorganic mercury and methyl mercury) and lead. The two acid gases are hydrogen chloride (HCl) and hydrogen fluoride (HF). The rationale for including these seven HAP in the environmental risk screening analysis is presented below.

HAP that persist and bioaccumulate are of particular environmental concern because they accumulate in the soil, sediment and water. The PB-HAP are taken up, through sediment, soil, water, and/or ingestion of other organisms, by plants or animals (e.g., small fish) at the bottom of the food chain. As larger and larger predators consume these organisms, concentrations of the PB-HAP in the animal tissues increases as does the potential for adverse effects. The five PB-HAP we evaluate as part of our screening analysis account for 99.8 percent of all PB-HAP emissions (on a mass basis from the 2005 NEI).

In addition to accounting for almost all of the mass of PB-HAP emitted, we note that the TRIM.Fate model that we use to evaluate multipathway risk allows us to estimate concentrations of cadmium compounds, dioxins/furans, POM and mercury in soil, sediment and water. For lead, we currently do not have the ability to calculate these concentrations using the TRIM.Fate model. Therefore, to evaluate the potential for adverse environmental effects from lead, we compare the HEM modeled inhalation exposures from the source category emissions of lead with the level of the secondary National Ambient Air Quality Standard (NAAQS) for lead.

We consider values below the level of the secondary lead NAAQS to be unlikely to cause adverse environmental effects.

The secondary lead NAAQS is a reasonable measure of determining whether there is an adverse environmental effect since it was established considering “effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being.”

Due to their well-documented potential to cause direct damage to terrestrial plants, we include two acid gases, HCl and HF, in the environmental screening analysis. According to the 2005 NEI, HCl and HF account for about 99 percent (on a mass basis) of the total acid gas HAP emitted by stationary sources. In addition to the potential to cause direct damage to plants, high concentrations of HF in the air have been linked to fluorosis in livestock. Air concentrations of these HAP are already calculated as part of the human multipathway exposure and risk screening analysis using the HEM3-AERMOD air dispersion model, and we are able to use the air dispersion modeling to estimate the potential for an adverse environmental effect.

The EPA acknowledges that other HAP beyond the seven HAP discussed above may have the potential to cause adverse environmental effects. Therefore, the EPA may include other relevant HAP in its environmental risk screening in the future, as modeling science and resources allow. The EPA invites comment on the extent to which other HAP emitted by the source category may cause adverse environmental effects. Such information should include references to peer-reviewed ecological effects benchmarks that are of sufficient quality for making regulatory decisions, as well as information on the presence of

organisms located near facilities within the source category that such benchmarks indicate could be adversely affected.

c. Ecological Assessment Endpoints and Benchmarks for PB-HAP

An important consideration in the development of the EPA's screening methodology is the selection of ecological assessment endpoints and benchmarks. Ecological assessment endpoints are defined by the ecological entity (e.g., aquatic communities including fish and plankton) and its attributes (e.g., frequency of mortality). Ecological assessment endpoints can be established for organisms, populations, communities or assemblages, and ecosystems.

For PB-HAP except for lead, we evaluated the following community-level ecological assessment endpoints to screen for organisms directly exposed to HAP in soils, sediment and water:

• Local terrestrial communities (i.e., soil invertebrates, plants) and populations of small birds and mammals that consume soil invertebrates exposed to PB-HAP in the surface soil.

• Local benthic (i.e., bottom sediment dwelling insects, amphipods, isopods and crayfish) communities exposed to PB-HAP in sediment in nearby water bodies.

• Local aquatic (water-column) communities (including fish and plankton) exposed to PB-HAP in nearby surface waters.

For PB-HAP, we also evaluated the following population-level ecological assessment endpoint to screen for indirect HAP exposures of top consumers via the bioaccumulation of HAP in food chains:

• Piscivorous (i.e., fish-eating) wildlife consuming PB-HAP-contaminated fish from nearby water bodies.

For cadmium compounds, dioxins/furans, POM and mercury, we identified the available ecological benchmarks for each assessment endpoint. An ecological benchmark represents a concentration of HAP (e.g., 0.77 ug of HAP per liter of water) that has been linked to a particular environmental effect level (e.g., a no-observed-adverse-effect level (NOAEL)) through scientific study. For PB-HAP we identified, where possible, ecological benchmarks at the following effect levels:

Probable effect levels (PEL): Level above which adverse effects are expected to occur frequently.

Lowest-observed-adverse-effect level (LOAEL): The lowest exposure level tested at which there are biologically significant increases in frequency or severity of adverse effects.

No-observed-adverse-effect levels (NOAEL): The highest exposure level tested at which there are no biologically significant increases in the frequency or severity of adverse effect.

We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, the EPA sources that are used at a programmatic level (e.g., Office of Water, Superfund Program) were used, if available. If not, the EPA benchmarks used in regional programs (e.g., Superfund) were used. If benchmarks were not available at a programmatic or regional level, we used benchmarks developed by other federal agencies (e.g., NOAA) or state agencies.

Benchmarks for all effect levels are not available for all PB-HAP and assessment endpoints. In cases where multiple effect levels were available for a particular PB-HAP and assessment endpoint, we use all of the available effect levels to help us to determine whether ecological risks exist and, if so, whether the risks could be considered significant and widespread.

d. Ecological Assessment Endpoints and Benchmarks for Acid Gases

The environmental screening analysis also evaluated potential damage and reduced productivity of plants due to direct exposure to acid gases in the air. For acid gases, we evaluated the following ecological assessment endpoint:

• Local terrestrial plant communities with foliage exposed to acidic gaseous HAP in the air.

The selection of ecological benchmarks for the effects of acid gases on plants followed the same approach as for PB-HAP (i.e., we examine all of the available benchmarks). For HCl, the EPA identified chronic benchmark concentrations. We note that the benchmark for chronic HCl exposure to plants is greater than the reference concentration for chronic inhalation exposure for human health. This means that where EPA includes regulatory requirements to prevent an exceedance of the reference concentration for human health, additional analyses for adverse environmental effects of HCL would not be necessary.

For HF, EPA identified chronic benchmark concentrations for plants and evaluated chronic exposures to plants in the screening analysis. High concentrations of HF in the air have also been linked to fluorosis in livestock. However, the HF concentrations at which fluorosis in livestock occur are higher than those at which plant damage begins. Therefore, the benchmarks for plants are protective of both plants and livestock.

e. Screening Methodology

For the environmental risk screening analysis, EPA first determined whether any facilities in the AMF, APR and PC source categories emitted any of the seven environmental HAP. For the AMF and PC source categories, we did not identify emissions of any of the seven environmental HAP included in the screen. Because we did not identify environmental HAP emissions, no further evaluation of environmental risk was conducted for those source categories. For the APR source category, we identified emissions of lead compounds (1 facility), cadmium compounds (2 facilities) and POM (analyzed as benzo(a)pyrene TEQ) (2 facilities).

Because one or more of the seven environmental HAP evaluated are emitted by at least one facility in the APR source category, we proceeded to the second step of the evaluation.

f. PB-HAP Methodology

For cadmium, mercury, POM and dioxins/furans, the environmental screening analysis consists of two tiers, and lead is analyzed differently as discussed earlier. In the first tier, we determined whether the maximum facility-specific emission rates of each of the emitted environmental HAP were large enough to create the potential for adverse environmental effects under reasonable worst-case environmental conditions. These are the same environmental conditions used in the human multipathway exposure and risk screening analysis.

To facilitate this step, TRIM.FaTE was run for each PB-HAP under hypothetical environmental conditions designed to provide conservatively high HAP concentrations. The model was set to maximize runoff from terrestrial parcels into the modeled lake, which in turn, maximized the chemical concentrations in the water, the sediments, and the fish. The resulting media concentrations were then used to back-calculate a screening threshold emission rate that corresponded to the relevant exposure benchmark concentration value for each assessment endpoint. To assess emissions from a facility, the reported emission rate for each PB-HAP was compared to the screening threshold emission rate for that PB-HAP for each assessment endpoint. If emissions from a facility do not exceed the Tier I threshold, the

facility “passes” the screen, and therefore, is not evaluated further under the screening approach. If emissions from a facility exceed the Tier I threshold, we evaluate the facility further in Tier II.

In Tier II of the environmental screening analysis, the screening emission thresholds are adjusted to account for local meteorology and the actual location of lakes in the vicinity of facilities that did not pass the Tier I screen. The modeling domain for each facility in the Tier II analysis consists of eight octants. Each octant contains 5 modeled soil concentrations at various distances from the facility (5 soil concentrations × 8 octants = total of 40 soil concentrations per facility) and 1 lake with modeled concentrations for water, sediment and fish tissue. In the Tier II environmental risk screening analysis, the 40 soil concentration points are averaged to obtain an average soil concentration for each facility for each PB-HAP. For the water, sediment and fish tissue concentrations, the highest value for each facility for each pollutant is used. If emission concentrations from a facility do not exceed the Tier II threshold, the facility passes the screen, and typically is not evaluated further. If emissions from a facility exceed the Tier II threshold, the facility does not pass the screen and, therefore, may have the potential to cause adverse environmental effects. Such facilities are evaluated further to investigate factors such as the magnitude and characteristics of the area of exceedance.

g. Acid Gas Methodology

The environmental screening analysis evaluates the potential phytotoxicity and reduced productivity of plants due to chronic exposure to acid gases. The environmental risk screening methodology for acid gases is a single-tier screen that compares the average off-site ambient air concentration over the modeling domain to ecological benchmarks for each of the acid gases. Because air concentrations are compared directly to the ecological benchmarks, emission-based thresholds are not calculated for acid gases as they are in the ecological risk screening methodology for PB-HAPs.

For purposes of ecological risk screening, EPA identifies a potential for adverse environmental effects to plant communities from exposure to acid gases when the average concentration of the HAP around a facility exceeds the LOAEL ecological benchmark. In such cases, we further investigate factors such as the magnitude and characteristics of the area of exceedance (e.g., land use of exceedance area, size of exceedance area) to determine if there is an adverse environmental effect.

For further information on the environmental screening analysis approach, see the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

which are available in the docket for this action.

7. How did we conduct facility-wide assessments?

To put the source category risks in context, we typically examine the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, we examine the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emissions sources at the facility for which we have data. The emissions data for generating these “facility-wide” risks were obtained from the 2005 NEI for the APR and PC source categories, and from the 2008 NEI for the AMF source category. We analyzed risks due to the inhalation of HAP that are emitted “facility-wide” for the populations residing within 50 km of each facility, consistent with the methods used for the source category analysis described above. For these facility-wide risk analyses, the modeled source category risks were compared to the facility-wide risks to determine the portion of facility-wide risks that could be attributed to each of the three source categories addressed in this proposal. The

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

available through the docket for this action, provide the methodology and results of the facility-wide analyses, including all facility-wide risks and the percentage of source category contribution to facility-wide risks.

8. How did we consider uncertainties in risk assessment?

In the Benzene NESHAP, we concluded that risk estimation uncertainty should be considered in our decision-making under the ample margin of safety framework. Uncertainty and the potential for bias are inherent in all risk assessments, including those performed for this proposal. Although uncertainty exists, we believe that our approach, which used conservative tools and assumptions, ensures that our decisions are health protective and environmentally protective. A brief discussion of the uncertainties in the emissions datasets, dispersion modeling, inhalation exposure estimates and dose-response relationships follows below. A more thorough discussion of these uncertainties is included in the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

which are available in the docket for this action (EPA-HQ-OAR-2012-0133).

a. Uncertainties in the Emissions Datasets

Although the development of the RTR datasets involved quality assurance/quality control processes, the accuracy of emissions values will vary depending on the source of the data, the degree to which data are incomplete or missing, the degree to which assumptions made to complete the datasets are accurate, errors in emissions estimates and other factors. The emission estimates considered in this analysis generally are annual totals for certain years, and they do not reflect short-term fluctuations during the course of a year or variations from year to year. The estimates of peak hourly emissions rates for the acute effects screening assessment were based on an emission adjustment factor applied to the average annual hourly emissions rates, which are intended to account for emission fluctuations due to normal facility operations.

b. Uncertainties in Dispersion Modeling

We recognize there is uncertainty in ambient concentration estimates associated with any model, including the EPA's recommended regulatory dispersion model, AERMOD. In using a model to estimate ambient pollutant concentrations, the user chooses certain options to apply. For RTR assessments, we select some model options that have the potential to overestimate ambient air concentrations (e.g., not including plume depletion or pollutant transformation). We select other model options that have the potential to underestimate ambient impacts (e.g., not including building downwash). Other options that we select have the potential to either under- or overestimate ambient levels (e.g., meteorology and receptor

locations). On balance, considering the directional nature of the uncertainties commonly present in ambient concentrations estimated by dispersion models, the approach we apply in the RTR assessments should yield unbiased estimates of ambient HAP concentrations.

c. Uncertainties in Inhalation Exposure

The EPA did not include the effects of human mobility on exposures in the assessment. Specifically, short-term mobility and long-term mobility between census blocks in the modeling domain were not considered.

The approach of not considering short or long-term population mobility does not bias the estimate of the theoretical MIR (by definition), nor does it affect the estimate of cancer incidence because the total population number remains the same. It does, however, affect the shape of the distribution of individual risks across the affected population, shifting it toward higher estimated individual risks at the upper end and reducing the number of people estimated to be at lower risks, thereby increasing the estimated number of people at specific high risk levels (e.g., 1-in-10 thousand or 1-in-1 million).

Short-term mobility is movement from one microenvironment to another over the course of hours or days. Long-term mobility is movement from one residence to another over the course of a lifetime.

In addition, the assessment predicted the chronic exposures at the centroid of each populated census block as surrogates for the exposure concentrations for all people living in that block. Using the census block centroid to predict chronic exposures tends to over-predict exposures for people in the census block who live farther from the facility and under-predict exposures for people in the census block who live closer to the facility. Thus, using the census block centroid to predict chronic exposures may lead to a potential understatement or overstatement of the true maximum impact, but is an unbiased estimate of average risk and incidence. We reduce this uncertainty by analyzing large census blocks near facilities using aerial imagery and adjusting the location of the block centroid to better represent the population in the block, as well as adding additional receptors where the block population is not well represented by a single location.

The assessment evaluates the cancer inhalation risks associated with pollutant exposures over a 70-year period, which is the assumed lifetime of an individual. In reality, both the length of time that modeled emissions sources at facilities actually operate (i.e., more or less than 70 years) and the domestic growth or decline of the modeled industry (i.e., the increase or decrease in the number or size of domestic facilities) will influence the future risks posed by a given source or source category. Depending on the characteristics of the industry, these factors will, in most cases, result in an overestimate both in individual risk levels and in the total estimated number of cancer cases. However, in the unlikely scenario where a facility maintains, or even increases, its emissions levels over a period of more than 70 years, residents live beyond 70 years at the same location, and the residents spend most of their days at that location, then the cancer inhalation risks could potentially be underestimated. However, annual cancer incidence estimates from exposures to emissions from these sources would not be affected by the length of time an emissions source operates.

The exposure estimates used in these analyses assume chronic exposures to ambient (outdoor) levels of pollutants. Because most people spend the majority of their time indoors, actual exposures may not be as high, depending on the characteristics of the pollutants modeled. For many of the HAP, indoor levels are roughly equivalent to ambient levels, but for very reactive pollutants or larger particles, indoor levels are typically lower. This factor has the potential to result in an overstatement of 25 to 30 percent of exposures.

U.S. EPA.

National-Scale Air Toxics Assessment for 1996.

(EPA 453/R-01-003; January 2001; page 85.)

In addition to the uncertainties highlighted above, there are several factors specific to the acute exposure assessment that should be highlighted. The accuracy of an acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, meteorology and human activity patterns. In this assessment, we assume that individuals remain for 1 hour at the point of maximum ambient concentration as determined by the co-occurrence of peak emissions and worst-case meteorological conditions. These assumptions would tend to be worst-case actual exposures as it is unlikely that a person would be located at the point of maximum exposure during the time of worst-case impact.

d. Uncertainties in Dose-Response Relationships

There are uncertainties inherent in the development of the dose-response values used in our risk assessments for cancer effects from chronic exposures and non-cancer effects from both chronic and acute exposures. Some uncertainties may be considered quantitatively, and others generally are expressed in qualitative terms. We note as a preface to this discussion a point on dose-response uncertainty that is brought out in the EPA's

2005 Cancer Guidelines;

namely, that “the primary goal of EPA actions is protection of human health; accordingly, as an Agency policy, risk assessment procedures, including default options that are used in the absence of scientific data to the contrary, should be health protective” (

EPA 2005 Cancer Guidelines,

pages 1-7). This is the approach followed here as summarized in the next several paragraphs. A complete detailed discussion of uncertainties and variability in dose-response relationships is given in the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

which are available in the docket for this action.

Cancer URE values used in our risk assessments are those that have been developed to generally provide an upper bound estimate of risk. That is, they

represent a “plausible upper limit to the true value of a quantity” (although this is usually not a true statistical confidence limit).

In some circumstances, the true risk could be as low as zero; however, in other circumstances the risk could be greater.

When developing an upper bound estimate of risk and to provide risk values that do not underestimate risk, health-protective default approaches are generally used. To err on the side of ensuring adequate health protection, the EPA typically uses the upper bound estimates rather than lower bound or central tendency estimates in our risk assessments, an approach that may have limitations for other uses (e.g., priority-setting or expected benefits analysis).

IRIS glossary (

http://www.epa.gov/NCEA/iris/help_gloss.htm

An exception to this is the URE for benzene, which is considered to cover a range of values, each end of which is considered to be equally plausible, and which is based on maximum likelihood estimates.

Chronic non-cancer RfC and reference dose (RfD) values represent chronic exposure levels that are intended to be health-protective levels. Specifically, these values provide an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure (RfC) or a daily oral exposure (RfD) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. To derive values that are intended to be “without appreciable risk,” the methodology relies upon an uncertainty factor (UF) approach (U.S. EPA, 1993, 1994) which considers uncertainty, variability and gaps in the available data. The UF are applied to derive reference values that are intended to protect against appreciable risk of deleterious effects. The UF are commonly default values,

e.g., factors of 10 or 3, used in the absence of compound-specific data; where data are available, UF may also be developed using compound-specific information. When data are limited, more assumptions are needed and more UF are used. Thus, there may be a greater tendency to overestimate risk in the sense that further study might support development of reference values that are higher (i.e., less potent) because fewer default assumptions are needed. However, for some pollutants, it is possible that risks may be underestimated.

According to the NRC report,

Science and Judgment in Risk Assessment

(NRC, 1994) “[Default] options are generic approaches, based on general scientific knowledge and policy judgment, that are applied to various elements of the risk assessment process when the correct scientific model is unknown or uncertain.” The 1983 NRC report,

Risk Assessment in the Federal Government: Managing the Process,

defined default option as “the option chosen on the basis of risk assessment policy that appears to be the best choice in the absence of data to the contrary” (NRC, 1983a, p. 63). Therefore, default options are not rules that bind the agency; rather, the agency may depart from them in evaluating the risks posed by a specific substance when it believes this to be appropriate. In keeping with the EPA's goal of protecting public health and the environment, default assumptions are used to ensure that risk to chemicals is not underestimated (although defaults are not intended to overtly overestimate risk). See EPA 2004,

An examination of EPA Risk Assessment Principles and Practices,

EPA/100/B-04/001 available at:

http://www.epa.gov/osa/pdfs/ratf-final.pdf

While collectively termed “UF,” these factors account for a number of different quantitative considerations when using observed animal (usually rodent) or human toxicity data in the development of the RfC. The UF are intended to account for: (1) Variation in susceptibility among the members of the human population (i.e., inter-individual variability); (2) uncertainty in extrapolating from experimental animal data to humans (i.e., interspecies differences); (3) uncertainty in extrapolating from data obtained in a study with less-than-lifetime exposure (i.e., extrapolating from sub-chronic to chronic exposure); (4) uncertainty in extrapolating the observed data to obtain an estimate of the exposure associated with no adverse effects; and (5) uncertainty when the database is incomplete or there are problems with the applicability of available studies.

Many of the UF used to account for variability and uncertainty in the development of acute reference values are quite similar to those developed for chronic durations, but they more often use individual UF values that may be less than 10. The UF are applied based on chemical-specific or health effect-specific information (e.g., simple irritation effects do not vary appreciably between human individuals, hence a value of 3 is typically used), or based on the purpose for the reference value (see the following paragraph). The UF applied in acute reference value derivation include: (1) Heterogeneity among humans; (2) uncertainty in extrapolating from animals to humans; (3) uncertainty in lowest observed adverse effect (exposure) level to no observed adverse effect (exposure) level adjustments; and (4) uncertainty in accounting for an incomplete database on toxic effects of potential concern. Additional adjustments are often applied to account for uncertainty in extrapolation from observations at one exposure duration (e.g., 4 hours) to derive an acute reference value at another exposure duration (e.g., 1 hour).

Not all acute reference values are developed for the same purpose and care must be taken when interpreting the results of an acute assessment of human health effects relative to the reference value or values being exceeded. Where relevant to the estimated exposures, the lack of short-term dose-response values at different levels of severity should be factored into the risk characterization as potential uncertainties.

Although every effort is made to identify appropriate human health effect dose-response assessment values for all pollutants emitted by the sources in this risk assessment, some HAP emitted by these source categories are lacking dose-response assessments. Accordingly, these pollutants cannot be included in the quantitative risk assessment, which could result in quantitative estimates understating HAP risk. To help to alleviate this potential underestimate, where we conclude similarity with a HAP for which a dose-response assessment value is available, we use that value as a surrogate for the assessment of the HAP for which no value is available. To the extent use of surrogates indicates appreciable risk, we may identify a need to increase priority for new IRIS assessment of that substance. We additionally note that, generally speaking, HAP of greatest concern due to environmental exposures and hazard are those for which dose-response assessments have been performed, reducing the likelihood of understating risk. Further, HAP not included in the quantitative assessment are assessed qualitatively and considered in the risk characterization that informs the risk management decisions, including with regard to consideration of HAP reductions achieved by various control options.

For a group of compounds that are unspeciated (e.g., glycol ethers), we conservatively use the most protective reference value of an individual compound in that group to estimate risk. Similarly, for an individual compound in a group (e.g., ethylene glycol diethyl ether) that does not have a specified reference value, we also apply the most protective reference value from the other compounds in the group to estimate risk.

e. Uncertainties in the Multipathway Screening Assessment

For each source category, we generally rely on site-specific levels of PB-HAP emissions to determine whether a refined assessment of the impacts from multipathway exposures is necessary. This determination is based on the results of a two-tiered

screening analysis that relies on the outputs from models that estimate environmental pollutant concentrations and human exposures for four PB-HAP. Two important types of uncertainty associated with the use of these models in RTR risk assessments and inherent to any assessment that relies on environmental modeling are model uncertainty and input uncertainty.

In the context of this discussion, the term “uncertainty” as it pertains to exposure and risk encompasses both variability in the range of expected inputs and screening results due to existing spatial, temporal, and other factors, as well as uncertainty in being able to accurately estimate the true result.

Model uncertainty concerns whether the selected models are appropriate for the assessment being conducted and whether they adequately represent the actual processes that might occur for that situation. An example of model uncertainty is the question of whether the model adequately describes the movement of a pollutant through the soil. This type of uncertainty is difficult to quantify. However, based on feedback received from previous EPA Science Advisory Board reviews and other reviews, we are confident that the models used in the screen are appropriate and state-of-the-art for the multipathway risk assessments conducted in support of RTR.

Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier I of the multipathway screen, we configured the models to avoid underestimating exposure and risk. This was accomplished by selecting upper-end values from nationally-representative data sets for the more influential parameters in the environmental model, including selection and spatial configuration of the area of interest, lake location and size, meteorology, surface water and soil characteristics and structure of the aquatic food web. We also assume an ingestion exposure scenario and values for human exposure factors that represent reasonable maximum exposures.

In Tier II of the multipathway assessment, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values and we identify the actual location of lakes near the facility rather than the default lake location that we apply in Tier I. By refining the screening approach in Tier II to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screen. The assumptions and the associated uncertainties regarding the selected ingestion exposure scenario are the same for Tier I and Tier II.

For both Tiers I and II of the multipathway assessment, our approach to addressing model input uncertainty is generally cautious. We choose model inputs from the upper end of the range of possible values for the influential parameters used in the models, and we assume that the exposed individual exhibits ingestion behavior that would lead to a high total exposure. This approach reduces the likelihood of not identifying high risks for adverse impacts.

Despite the uncertainties, when individual pollutants or facilities do screen out, we are confident that the potential for adverse multipathway impacts on human health is very low. On the other hand, when individual pollutants or facilities do not screen out, it does not mean that multipathway impacts are significant, only that we cannot rule out that possibility and that a refined multipathway analysis for the site might be necessary to obtain a more accurate risk characterization for the source category.

For further information on uncertainties and the Tier I and II screening methods, refer to the risk document Appendix 4, “Technical Support Document for TRIM-Based Multipathway Tiered Screening Methodology for RTR.”

f. Uncertainties in the Environmental Risk Screening Assessment

For each source category, we generally rely on site-specific levels of environmental HAP emissions to perform an environmental screening assessment. The environmental screening assessment is based on the outputs from models that estimate environmental HAP concentrations. The same models, specifically the TRIM.FaTE multipathway model and the AERMOD air dispersion model, are used to estimate environmental HAP concentrations for both the human multipathway screening analysis and for the environmental screening analysis. Therefore, both screening assessments have similar modeling uncertainties.

Two important types of uncertainty associated with the use of these models in RTR environmental screening assessments—and inherent to any assessment that relies on environmental modeling—are model uncertainty and input uncertainty.

In the context of this discussion, the term “uncertainty,” as it pertains to exposure and risk assessment, encompasses both

variability

in the range of expected inputs and screening results due to existing spatial, temporal, and other factors, as well as

uncertainty

in being able to accurately estimate the true result.

Model uncertainty concerns whether the selected models are appropriate for the assessment being conducted and whether they adequately represent the movement and accumulation of environmental HAP emissions in the environment. For example, does the model adequately describe the movement of a pollutant through the soil? This type of uncertainty is difficult to quantify. However, based on feedback received from previous EPA Science Advisory Board reviews and other reviews, we are confident that the models used in the screen are appropriate and state-of-the-art for the environmental risk assessments conducted in support of our RTR analyses.

Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier I of the environmental screen for PB-HAP, we configured the models to avoid underestimating exposure and risk to reduce the likelihood that the results indicate the risks are lower than they actually are. This was accomplished by selecting upper-end values from nationally-representative data sets for the more influential parameters in the environmental model, including selection and spatial configuration of the area of interest, the location and size of any bodies of water, meteorology, surface water and soil characteristics and structure of the aquatic food web. In Tier I, we used the maximum facility-specific emissions for the PB-HAP (other than lead, which was evaluated by comparison to the secondary lead NAAQS) that were included in the environmental screening assessment and each of the media when comparing to ecological benchmarks. This is consistent with the conservative design of Tier I of the screen. In Tier II of the environmental screening analysis for PB-HAP, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values, and we identify the locations of water bodies near the facility location. By refining the screening approach in Tier II to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screen. To better represent widespread impacts, the modeled soil concentrations are averaged in Tier II to

obtain one average soil concentration value for each facility and for each PB-HAP. For PB-HAP concentrations in water, sediment and fish tissue, the highest value for each facility for each pollutant is used.

For the environmental screening assessment for acid gases, we employ a single-tiered approach. We use the modeled air concentrations and compare those with ecological benchmarks.

For both Tiers I and II of the environmental screening assessment, our approach to addressing model input uncertainty is generally cautious. We choose model inputs from the upper end of the range of possible values for the influential parameters used in the models, and we assume that the exposed individual exhibits ingestion behavior that would lead to a high total exposure. This approach reduces the likelihood of not identifying potential risks for adverse environmental impacts.

Uncertainty also exists in the ecological benchmarks for the environmental risk screening analysis. We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, EPA benchmarks used at a programmatic level (e.g., Office of Water, Superfund Program) were used if available. If not, we used EPA benchmarks used in regional programs (e.g., Superfund). If benchmarks were not available at a programmatic or regional level, we used benchmarks developed by other agencies (e.g., NOAA) or by state agencies.

In all cases (except for lead, which was evaluated through a comparison to the NAAQS), we searched for benchmarks at the following three effect levels, as described in Section III.A.6 of this preamble:

1. A no-effect level (i.e., NOAEL).

2. Threshold-effect level (i.e., LOAEL).

3. Probable effect level (i.e., PEL).

For some ecological assessment endpoint/environmental HAP combinations, we could identify benchmarks for all three effect levels, but for most, we could not. In one case, where different agencies derived significantly different numbers to represent a threshold for effect, we included both. In several cases, only a single benchmark was available. In cases where multiple effect levels were available for a particular PB-HAP and assessment endpoint, we used all of the available effect levels to help us to determine whether risk exists and if the risks could be considered significant and widespread.

The EPA evaluated the following seven HAP in the environmental risk screening assessment: Cadmium, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), lead compounds, HCl and HF. These seven HAP represent pollutants that can cause adverse impacts for plants and animals either through direct exposure to HAP in the air or through exposure to HAP that is deposited from the air onto soils and surface waters. These seven HAP also represent those HAP for which we can conduct a meaningful environmental risk screening assessment. For other HAP not included in our screening assessment, we may not have appropriate multipathway models that allow us to predict the concentration of that pollutant. The EPA acknowledges that other HAP beyond the seven HAP that we are evaluating may have the potential to cause adverse environmental effects and, therefore, the EPA may evaluate other relevant HAP in the future, as modeling science and resources allow.

Further information on uncertainties and the Tier I and II environmental screening methods is provided in Appendix 5 of the document “Technical Support Document for TRIM-Based Multipathway Tiered Screening Methodology for RTR: Summary of Approach and Evaluation.” Also, see the

Draft Residual Risk Assessment for the Acrylic and Modacrylic Fibers Production Source Category, Draft Residual Risk Assessment for the Amino/Phenolic Resins Production Source Category,

and

Draft Residual Risk Assessment for the Polycarbonate Production Source Category,

available in the docket for this action.

B. How did we consider the risk results in making decisions for this proposal?

As discussed in section II.A of this preamble, in evaluating and developing standards under section 112(f)(2), we apply a two-step process to address residual risk. 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 level on maximum individual lifetime [cancer] risk (MIR)

of approximately [1-in-10 thousand] [i.e., 100-in-1 million].” 54 FR 38045. If risks are unacceptable, the EPA must determine the emissions standards necessary to bring risks to an acceptable level without considering costs. In the second step of the process, the EPA considers whether the emissions standards provide an ample margin of safety “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 tighter emission standards if necessary to provide an ample margin of safety.

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

In past residual risk actions, the EPA considered a number of human health risk metrics associated with emissions from the categories under review, including the MIR, the number of persons in various risk ranges, cancer incidence, the maximum non-cancer HI and the maximum acute non-cancer hazard. See, e.g., 72 FR 25138, May 3, 2007; 71 FR 42724, July 27, 2006. The EPA considered this health information for both actual and allowable emissions. See, e.g., 75 FR 65068, October 21, 2010; 75 FR 80220, December 21, 2010; 76 FR 29032, May 19, 2011. The EPA also discussed risk estimation uncertainties and considered the uncertainties in the determination of acceptable risk and ample margin of safety in these past actions. The EPA considered this same type of information in support of this

Federal Register

proposed rule.

The agency is considering these various measures of health information to inform our determinations of risk acceptability and ample margin of safety under CAA section 112(f). 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 [previous] section 112 is best judged on the basis of a broad set of health risk measures and information.” 54 FR 38046. 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. In responding to comment on our policy under the Benzene NESHAP, the EPA explained that:

“[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 [her] 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 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 [her] judgment, believes are appropriate to determining what will `protect the public health'.”

54 FR 38057. Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risks. 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 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 those HAP risks that may be associated with emissions from other facilities that do not include the source categories in question, mobile source emissions, natural source emissions, persistent environmental pollution or atmospheric transformation in the vicinity of the sources in these categories.

The agency 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 non-cancer risks, where pollutant-specific exposure health reference levels (e.g., RfCs) are based on the assumption that thresholds exist for adverse health effects. For example, the agency recognizes that, although exposures attributable to emissions from a source category or facility alone may not indicate the potential for increased risk of adverse non-cancer 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 increased risk of adverse non-cancer health effects. In May 2010, the 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.”

EPA's responses to this and all other key recommendations of the SAB's advisory on RTR risk assessment methodologies (which is available at:

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

) are outlined in a memo to this rulemaking docket from David Guinnup entitled,

EPA's Actions in Response to the Key Recommendations of the SAB Review of RTR Risk Assessment Methodologies.

In response to the SAB recommendations, the EPA is incorporating cumulative risk analyses into its RTR risk assessments, including those reflected in today's proposal. The agency is: (1) Conducting facility-wide assessments, which include source category emission points as well as other emission points within the facilities; (2) considering overlapping sources in the same category; and (3) for some persistent and bioaccumulative pollutants, analyzing the ingestion route of exposure. In addition, the RTR risk assessments have always considered aggregate cancer risk from all carcinogens and aggregate non-cancer hazard indices from all non-carcinogens affecting the same target organ system.

Although we are interested in placing source category and facility-wide HAP risks in the context of

total

HAP risks from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Because of the contribution to total HAP risk from emissions sources other than those that we have studied in depth during this RTR review, such estimates of total HAP risks 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.

C. How did we perform the technology review?

Our technology review focused on the identification and evaluation of developments in practices, processes and control technologies that have occurred since the MACT standards were promulgated. Where we identified such developments, in order to inform our decision of whether it is “necessary” to revise the emissions standards, we analyzed the technical feasibility of applying these developments, and the estimated costs, energy implications, non-air environmental impacts, as well as considering the emissions reductions. We also considered the appropriateness of applying controls to new sources versus retrofitting existing sources.

Based on our analyses of the available data and information, we identified potential developments in practices, processes and control technologies. For this exercise, we considered 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.

• 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).

We reviewed a variety of data sources in our investigation of potential practices, processes or controls to consider. Among the sources we

reviewed were the NESHAP for various industries that were promulgated since the MACT standards being reviewed in this action. We reviewed the regulatory requirements and/or technical analyses associated with these regulatory actions to identify any practices, processes and control technologies considered in these efforts that could be applied to emissions sources in the AMF, APR and PC source categories, as well as the costs, non-air impacts and energy implications associated with the use of these technologies.

We also consulted the EPA's RACT/BACT/LAER Clearinghouse (RBLC), which is a central database of air pollution control technology information that was established by the EPA to promote the sharing of information among permitting agencies and to aid in identifying future possible control technology options that might apply broadly to numerous sources within a category or apply only on a source-by-source basis.

Finally, we reviewed information from other sources, such as state and/or local permitting agency databases and industry-supported databases.

IV. Analytical Results and Proposed Decisions for the AMF Source Category

A. What actions are we taking pursuant to CAA sections 112(d)(2) and 112(d)(3)?

We identified the absence of an emissions limit for a potentially significant emission source within the provisions of the AMF MACT standards. Specifically, there are no emissions standards or other requirements for spinning lines that use a spin dope produced from a solution polymerization process at existing facilities.

As this process is a significant source of emissions for the one facility in the source category, we are proposing to set standards for this process under CAA section 112(d)(2) and (3) in this action.

Note that these uncontrolled emissions were included in the risk assessment for the AMF source category.

Since there is only one facility in the source category, the current emissions level of the spinning line at this affected source at this facility represents the MACT floor. As part of our beyond-the-floor analysis, we considered control options for the spinning line more stringent than the MACT floor. We identified two beyond-the-floor options: (1) A scrubber operating at 85 percent control efficiency; and (2) a regenerative thermal oxidizer operating at 95 percent control efficiency. Based on the emission stream flow rate and emissions information provided by the one facility in this source category, the capital costs of the scrubber option are estimated to be approximately $2.6 million, and the total annualized costs are estimated to be approximately $622,000. The capital costs of the thermal oxidizer option are estimated to be approximately $3.4 million and the total annualized costs are estimated to be approximately $1.5 million.

The estimated HAP emissions reduction from the scrubber option is approximately 27 tpy. The cost effectiveness for the scrubber option is approximately $23,000/ton. The estimated HAP emissions reduction from the thermal oxidizer option is approximately 30 tpy. The cost effectiveness for the thermal oxidizer option is approximately $50,000/ton. The incremental cost effectiveness between the 85 percent control option and the 95 percent control option is approximately $280,000/ton of HAP emission reduction. Table 3 summarizes the cost and emission reduction impacts of the proposed options.

For further details on the assumptions and methodologies used in this analysis, see the technical memorandum titled

MACT Floor and Beyond-the-Floor Analyses for Unregulated Emission Sources in the Acrylic and Modacrylic Fibers and Amino and Phenolic Resins Production Source Categories,

available in the docket for this action.

As discussed in section IV.C below, neither of these options are needed in order to support the EPA's finding under CAA section 112(f) that the AMF MACT standards already protect public health with an ample margin of safety. While we do not factor quantified risk reductions into CAA section 112(d)(2) beyond-the-floor analyses, for informational purposes we note that the scrubber option would reduce the MIR for the source category from 20 to 3 and reduce the maximum chronic non-cancer TOSHI from 0.1 to 0.02. The thermal oxidizer option would reduce the MIR for the source category from 20 to 1 and reduce the maximum chronic non-cancer TOSHI from 0.1 to 0.01.

Table 3—AMF Solution Polymerization Spinning Line Options Impacts

Regulatory alternatives

HAP emissions

reduction

(tpy)

Capital cost

($ million)

Annual cost

($ million/yr)

Cost

effectiveness

($/ton

HAP removed)

Incremental

cost

effectiveness

($/ton

HAP removed)

1 Baseline (MACT floor)

2 Scrubber (Beyond-the-floor)

2.6

0.6

23,000

3 Thermal Oxidizer (Beyond-the-floor)

3.4

1.5

50,000

280,000

We believe that the costs of these beyond-the-floor options are not reasonable, given the level of HAP emission reduction they would achieve. Therefore, we are proposing an emission standard that reflects the MACT floor. We determined the MACT floor using the emissions and production data provided by the facility and calculated production-based emission rates for several years of production. Taking into account expected

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