# New Source Performance Standards for the Synthetic Organic Chemical Manufacturing Industry and National Emission Standards for Hazardous Air Pollutants for the Synthetic Organic Chemical Manufacturing Industry and Group I & II Polymers and Resins Industry > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2023-07188 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** April 25, 2023 - **Citation:** 88 FR 25080 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Parts 60 and 63 [EPA-HQ-OAR-2022-0730; FRL-9327-01-OAR] RIN 2060-AV71 New Source Performance Standards for the Synthetic Organic Chemical Manufacturing Industry and National Emission Standards for Hazardous Air Pollutants for the Synthetic Organic Chemical Manufacturing Industry and Group I & II Polymers and Resins Industry AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing amendments to the New Source Performance Standards (NSPS) that apply to the Synthetic Organic Chemical Manufacturing Industry (SOCMI) and to the National Emission Standards for Hazardous Air Pollutants (NESHAP) that apply to the SOCMI (more commonly referred to as the Hazardous Organic NESHAP or HON) and Group I and II Polymers and Resins Industries (P&R I and P&R II). The EPA is proposing decisions resulting from the Agency's technology review of the HON, P&R I, and P&R II, and its eight-year review of the NSPS that apply to the SOCMI. The EPA is also proposing amendments to the NSPS for equipment leaks of volatile organic compounds (VOC) in SOCMI based on its reconsideration of certain issues raised in an administrative petition for reconsideration. Furthermore, the EPA is proposing to strengthen the emission standards for ethylene oxide (EtO) emissions and chloroprene emissions after considering the results of a risk assessment for the HON and Neoprene Production processes subject to P&R I. Lastly, the EPA is proposing to remove exemptions from standards for periods of startup, shutdown, and malfunction (SSM), to add work practice standards for such periods where appropriate, and to add provisions for electronic reporting. We estimate that the proposed amendments to the NESHAP would reduce hazardous air pollutants (HAP) emissions (excluding EtO and chloroprene) from the SOCMI, P&R I, and P&R II sources by approximately 1,123 tons per year (tpy), reduce EtO emissions from HON processes by approximately 58 tpy, and reduce chloroprene emissions from Neoprene Production processes in P&R I by approximately 14 tpy. We also estimate that these proposed amendments to the NESHAP will reduce excess emissions of HAP from flares in the SOCMI and P&R I source categories by an additional 4,858 tpy. Lastly, we estimate that the proposed amendments to the NSPS would reduce VOC emissions from the SOCMI source category by approximately 1,609 tpy. DATES: Comments. Comments must be received on or before June 26, 2023. Under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of consideration if the Office of Management and Budget (OMB) receives a copy of your comments on or before May 25, 2023. Public hearing: The EPA will hold a virtual public hearing on May 16, 2023. See SUPPLEMENTARY INFORMATION for information on the public hearing. ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-OAR-2022-0730, by any of the following methods: • Federal eRulemaking Portal: https://www.regulations.gov/ (our preferred method). Follow the online instructions for submitting comments. • Email: a-and-r-docket@epa.gov. Include Docket ID No. EPA-HQ-OAR-2022-0730 in the subject line of the message. • Fax: (202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-2022-0730. • Mail: U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2022-0730, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460. • Hand/Courier Delivery: EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-Friday (except Federal Holidays). Instructions: All submissions received must include the Docket ID No. for this rulemaking. Comments received may be posted without change to https://www.regulations.gov/, including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the SUPPLEMENTARY INFORMATION section of this document. FOR FURTHER INFORMATION CONTACT: Mr. Andrew Bouchard, 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) 541-4036; and email address: bouchard.andrew@epa.gov. SUPPLEMENTARY INFORMATION: Participation in virtual public hearing. The public hearing will be held via virtual platform on May 16, 2023. The hearing will convene at 11:00 a.m. Eastern Time (ET) and will conclude at 7:00 p.m. ET. The EPA may close a session 15 minutes after the last pre-registered speaker has testified if there are not additional speakers. The EPA will announce further details on the virtual public hearing website at https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, and https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and-non-nylon-polyamides-national-emission. If the EPA receives a high volume of registrations for the public hearing, we may continue the public hearing on May 17, 2023. The EPA will begin pre-registering speakers for the hearing no later than 1 business day following the publication of this document in the Federal Register . The EPA will accept registrations on an individual basis. To register to speak at the virtual hearing, please use the online registration form available at any of the following websites: https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, or https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and-non-nylon-polyamides-national-emission; or contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov. The last day to pre-register to speak at the hearing will be May 10, 2023. Prior to the hearing, the EPA will post a general agenda that will list pre-registered speakers in approximate order at: https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, and https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and- non-nylon-polyamides-national-emission. 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 hearings to run either ahead of schedule or behind schedule. Each commenter will have 4 minutes to provide oral testimony. The EPA encourages commenters to submit a copy of their oral testimony as written comments to the rulemaking docket. 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 testimony and supporting information presented at the public hearing. Please note that any updates made to any aspect of the hearing will be posted online at https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, and https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and-non-nylon-polyamides-national-emission. While the EPA expects the hearing to go forward as set forth above, please monitor these websites or contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov to determine if there are any updates. The EPA does not intend to publish a document in the Federal Register announcing updates. If you require the services of a translator or a special accommodation such as audio description, please pre-register for the hearing with the public hearing team and describe your needs by May 2, 2023. The EPA may not be able to arrange accommodations without advanced notice. Docket. The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2022-0730. All documents in the docket are listed in https://www.regulations.gov/. Although listed, some information is not publicly available, e.g., Confidential Business Information (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. With the exception of such material, publicly available docket materials are available electronically in https://www.regulations.gov/ or in hard copy at the EPA Docket Center, Room 3334, WJC West Building, 1301 Constitution Avenue NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742. Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-2022-0730. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at https://www.regulations.gov/, including any personal information provided, unless the comment includes information claimed to be CBI or other information whose disclosure is restricted by statute. Do not submit electronically to https://www.regulations.gov/ any information that you consider to be CBI or other information whose disclosure is restricted by statue. This type of information should be submitted as discussed below. The EPA may publish any comment received to its public docket. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission ( i.e., on the Web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit https://www.epa.gov/dockets/commenting-epa-dockets. The https://www.regulations.gov/ website allows you to submit your comment anonymously, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through https://www.regulations.gov/, your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any digital storage media you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should not include special characters or any form of encryption and be free of any defects or viruses. For additional information about the EPA's public docket, visit the EPA Docket Center homepage at https://www.epa.gov/dockets. Submitting CBI. Do not submit information containing CBI to the EPA through https://www.regulations.gov/. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on any digital storage media that you mail to the EPA, note the docket ID, mark the outside of the digital storage media as CBI, and identify electronically within the digital storage media the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI directly to the public docket through the procedures outlined in Instructions above. If you submit any digital storage media that does not contain CBI, mark the outside of the digital storage media clearly that it does not contain CBI and note the docket ID. 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. Our preferred method to receive CBI is for it to be transmitted electronically using email attachments, File Transfer Protocol, or other online file sharing services ( e.g., Dropbox, OneDrive, Google Drive). Electronic submissions must be transmitted directly to the Office of Air Quality Planning and Standards (OAQPS) CBI Office at the email address oaqpscbi@epa.gov and, as described above, should include clear CBI markings and note the docket ID. If assistance is needed with submitting large electronic files that exceed the file size limit for email attachments, and if you do not have your own file sharing service, please email oaqpscbi@epa.gov to request a file transfer link. If sending CBI information through the postal service, please send it to the following address: OAQPS Document Control Officer (C404-02), OAQPS, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2022-0730. The mailed CBI material should be double wrapped and clearly marked. Any CBI markings should not show through the outer envelope. Preamble acronyms and abbreviations. Throughout this preamble the use of “we,” “us,” or “our” is intended to refer to the EPA. 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: ACS American Community Survey ADAF age-dependent adjustment factor AEGL acute exposure guideline levels AERMOD American Meteorological Society/EPA Regulatory Model dispersion modeling system AIHA American Industrial Hygiene Association AMEL alternative means of emission limitation APCD air pollution control device ATSDR Agency for Toxic Substances and Disease Registry 1-BP 1-bromopropane BAAQMD Bay Area Air Quality Management District BACT Best Available Control Technology BLR basic liquid epoxy resins BPT benefit per-ton BSER best system of emissions reduction BTU British thermal units CAA Clean Air Act CBI Confidential Business Information CDX Central Data Exchange CEDRI Compliance and Emissions Data Reporting Interface CFR Code of Federal Regulations CMAS Chemical Manufacturing Area Sources CMPU chemical manufacturing process unit CO carbon monoxide CO 2 carbon dioxide EAV equivalent annual value ECHO Enforcement and Compliance History Online EFR external floating roof EIS Emission Information System EJ environmental justice EMACT Ethylene Production MACT EPA Environmental Protection Agency EPPU elastomer product process unit ERPG emergency response planning guidelines ERT Electronic Reporting Tool EtO Ethylene Oxide FID flame ionization detector GACT generally available control technologies HAP hazardous air pollutant(s) HCl hydrochloric acid HEM Human Exposure Model HF hydrofluoric acid HON Hazardous Organic NESHAP HQ hazard quotient HQ REL hazard quotient reference exposure level HRVOC highly reactive volatile organic compound ICR information collection request IFR internal floating roof IRIS Integrated Risk Information System ISA Integrated Science Assessment ISO International Standards Organization km kilometer kPa kilopascals LAER Lowest Achievable Emission Rate lb/hr pound per hour LDAR leak detection and repair LDSN leak detection sensor network LEL lower explosive limit MACT maximum achievable control technology MPGF multi-point ground flare MIR maximum individual lifetime [cancer] risk MON Miscellaneous Organic Chemical Manufacturing NESHAP MTVP maximum true vapor pressure NAAQS National Ambient Air Quality Standard NAICS North American Industry Classification System NEI National Emissions Inventory NESHAP national emission standards for hazardous air pollutants NHVcz net heating value in the combustion zone gas NHVdil net heating value dilution parameter NHVvg net heating value in the vent gas NOAEL No Observed Adverse Effects Level NO X nitrogen oxides N 2 O nitrous oxide NRDC Natural Resources Defense Council NSPS new source performance standards NTTAA National Technology Transfer and Advancement Act OAQPS Office of Air Quality Planning and Standards OAR Office of Air and Radiation OECA Office of Enforcement and Compliance Assurance's OEL open-ended valves or lines OGI optical gas imaging OLD Organic Liquids Distribution OMB Office of Management and Budget OSHA Occupational Safety and Health Administration P&R I Group I Polymers and Resins NESHAP P&R II Group II Polymers and Resins NESHAP PDF portable document format PM2.5 particulate matter 2.5 POM polycyclic organic matter ppm parts per million ppmv parts per million by volume ppmw parts per million by weight PRA Paperwork Reduction Act psig pounds per square inch gauge PRD pressure relief devices PV present value RACT Reasonably Available Control Technology RDL representative detection limit REL Reference Exposure Level RFA Regulatory Flexibility Act RfC reference concentration RIA Regulatory Impact Analysis RTR Risk and Technology Reviews SCAQMD South Coast Air Quality Management District scmm standard cubic meter per minute scf standard cubic foot SOCMI Synthetic Organic Chemical Manufacturing Industry SO 2 sulfur dioxide SSM startup, shutdown, and malfunction TAC Texas Administrative Code TCEQ Texas Commission on Environmental Quality TOC total organic carbon TOSHI target organ-specific hazard index tpy tons per year TRE total resource effectiveness TRIM Total Risk Integrated Methodology UF uncertainty factor UMRA Unfunded Mandates Reform Act UPL upper prediction limit URE unit risk estimate U.S.C. United States Code USGS U.S. Geological Survey VOC volatile organic compound(s) WSR wet strength resins 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? II. Background A. What is the statutory authority for this action? B. What are the source categories and how do the current standards regulate emissions? C. What data collection activities were conducted to support this action? D. What other relevant background information and data are available? E. How do we consider risk in our decision-making? F. How do we estimate post-MACT risk posed by the source category? G. How does the EPA perform the NESHAP technology review and NSPS review? III. Proposed Rule Summary and Rationale A. What are the results of the risk assessment and analyses? B. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effect? C. What are the results and proposed decisions based on our CAA section 112(d)(6) technology review and CAA section 111(b)(1)(B) NSPS reviews, and what are the rationale for those decisions? D. What actions related to CAA section 112(d)(2) and (3) are we taking in addition to those identified in the CAA sections 112(f)(2) and (d)(6) risk and technology reviews and CAA section 111(b)(1)(B) NSPS reviews? E. What other actions are we proposing, and what is the rationale for those actions? F. What compliance dates are we proposing, and what is the rationale for the proposed compliance dates? IV. 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? F. What analysis of environmental justice did we conduct? G. What analysis of children's environmental health did we conduct? V. Request for Comments VI. 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 (PRA) C. Regulatory Flexibility Act (RFA) D. Unfunded Mandates Reform Act (UMRA) 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 (NTTAA) and 1 CFR Part 51 J. Executive Order 12898: Federal Actions To Address Environmental Justice in Minority Populations and Low-Income Populations I. General Information A. Executive Summary 1. Purpose of the Regulatory Action The source categories that are the subject of this proposal are the SOCMI and various polymers and resins source categories. The SOCMI source category includes chemical manufacturing processes producing commodity chemicals while the polymers and resins source categories covered in this action include elastomers production processes and resin production processes that use epichlorohydrin feedstocks (see sections I.B and II.B of this preamble for detailed information about these source categories). The EPA has previously promulgated maximum achievable control technology (MACT) standards for certain processes in the SOCMI source category in the HON rulemaking at 40 CFR part 63, subparts F, G, and H. In 1994, the EPA finalized MACT standards in subparts F, G, and H for SOCMI processes (59 FR 19454), 1 and conducted a residual risk and technology review for these NESHAP in 2006 (71 FR 76603). In 1995, the EPA finalized MACT standards in P&R II (40 CFR part 63, subpart W) for epoxy resin and non-nylon polyamide resin manufacturing processes (60 FR 12670) and completed a residual risk and technology review for these standards in 2008 (73 FR 76220). In 1996, the EPA finalized MACT standards in P&R I (40 CFR part 63, subpart U) for elastomer manufacturing processes in the SOCMI source category (61 FR 46906) and completed residual risk and technology reviews for these standards in 2008 and 2011 (73 FR 76220 and 76 FR 22566). 1 Around the same time, the EPA set MACT standards for equipment leaks from certain non-SOCMI processes at chemical plants regulated under 40 CFR part 63, subpart I (59 FR 19587). The EPA has also promulgated NSPS for certain processes in the SOCMI source category. In 1983, the EPA finalized NSPS (40 CFR part 60, subpart VV) for equipment leaks of VOC in SOCMI (48 FR 48328). In 1990, the EPA finalized NSPS (40 CFR part 60, subparts III and NNN) for VOC from air oxidation unit processes and distillation operations (55 FR 26912 and 55 FR 26931). In 1993, the EPA finalized NSPS (40 CFR part 60, subpart RRR) for VOC from reactor processes (58 FR 45948). In 2007, the EPA promulgated NSPS (40 CFR part 60, subpart VVa) for VOC from certain equipment leaks (72 FR 64883), which reflects the EPA's review and revision of the standards in 40 CFR part 60, subpart VV. The statutory authority for this action is sections 111, 112, 301(a)(1), and 307(d)(7)(B) of the Clean Air Act (CAA). Section 111(b)(1)(B) of the CAA requires the EPA to promulgate standards of performance for new sources in any category of stationary sources that the Administrator has listed pursuant to 111(b)(1)(A). Section 111(a)(1) of the CAA provides that these performance standards are to “reflect[ ] the degree of emission limitation achievable through the application of the best system of emission reduction which (taking into account the cost of achieving such reduction and any non-air quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.” We refer to this level of control as the best system of emission reduction or “BSER.” Section 111(b)(1)(B) of the CAA requires the EPA to “at least every 8 years, review and, if appropriate, revise” the NSPS. For NESHAP, CAA section 112(d)(2) requires the EPA to establish MACT standards for listed categories of major sources of HAP. Section 112(d)(6) of the CAA requires the EPA to review standards promulgated under CAA section 112, and revise them “as necessary (taking into account developments in practices, processes, and control technologies),” no less often than every 8 years following promulgation of those standards. This is referred to as a “technology review” and is required for all standards established under CAA section 112. Section 112(f) of the CAA requires the EPA to assess the risk to public health remaining after the implementation of MACT emission standards promulgated under CAA section 112(d)(2). If the standards for a source category do not provide “an ample margin of safety to protect public health,” the EPA must promulgate health-based standards for that source category to further reduce risk from HAP emissions. Section 301(a)(1) of the CAA authorizes the Administrator to prescribe such regulations as are necessary to carry out his functions under the CAA. Section 307(d)(7)(B) of the CAA requires the reconsideration of a rule only if the person raising an objection to the rule can demonstrate that it was impracticable to raise such objection during the period for public comment or if the grounds for the objection arose after the comment period (but within the time specified for judicial review), and if the objection is of central relevance to the outcome of the rule. The proposed new NSPS for SOCMI equipment leaks, air oxidation unit processes, distillation operations, and reactor processes ( i.e., NSPS subparts VVb, IIIa, NNNa, and RRRa, respectively) are based on the Agency's review of the current NSPS (subparts VVa, III, NNN, and RRR) pursuant to CAA section 111(b)(1)(B), which requires that the EPA review the NSPS every eight years and, if appropriate, revise. In addition, the EPA is proposing amendments to the NSPS for equipment leaks of VOC in SOCMI based on its reconsideration of certain aspects of subparts VV and VVa that were raised in an administrative petition and of which the Agency has granted reconsideration pursuant to section 307(d)(7)(B) of the CAA. These proposed amendments are primarily included in the new NSPS subpart VVb; the EPA is not proposing to make these changes in subparts VV and VVa because, in light of the time that has passed since the promulgation of these two subparts, the EPA finds it inappropriate to now change the obligations of sources subject to these subparts after all these years. The proposed amendments to the HON (NESHAP subparts F, G, H, and I), P&R I (NESHAP subpart U), and P&R II (NESHAP subpart W) are based on the Agency's review of the current NESHAP (subparts F, G, H, I, U, and W) pursuant to CAA section 112(d). Also, due to the development of the EPA's Integrated Risk Information System (IRIS) inhalation unit risk estimate (URE) for chloroprene in 2010, the EPA conducted a CAA section 112(f) risk review for the SOCMI source category and Neoprene Production source category. In the first step of the CAA section 112(f)(2) determination of risk acceptability for this rulemaking, the use of the 2010 chloroprene risk value resulted in the EPA identifying unacceptable residual cancer risk caused by chloroprene emissions from affected sources producing neoprene subject to P&R I. 2 Consequently, the proposed amendments to P&R I address the EPA review of additional control technologies, beyond those analyzed in the technology review conducted for P&R I, for one affected source producing neoprene and contributing to unacceptable risk. Additionally, in 2016, the EPA updated the IRIS inhalation URE for EtO. In the first step of the CAA section 112(f)(2) determination of risk acceptability for this rulemaking, the use of the updated 2016 EtO risk value resulted in the EPA identifying unacceptable residual cancer risk driven by EtO emissions from HON processes. Consequently, the proposed amendments to the HON also address the EPA review of additional control technologies, beyond those analyzed in the technology review conducted for the HON, focusing on emissions sources emitting EtO that contribute to unacceptable risk. 2 As discussed further in section III.B of this preamble, chloroprene emissions from HON processes do not on their own present unacceptable cancer risk. 2. Summary of the Major Provisions of the Regulatory Action in Question The most significant amendments that we are proposing are described briefly below. However, all of our proposed amendments, including amendments to remove exemptions for periods of SSM, are discussed in detail with rationale in section III of this preamble. a. HON We are proposing amendments to the HON for heat exchange systems, process vents, storage vessels, transfer racks, wastewater, and equipment leaks. i. NESHAP Subpart F As detailed in section II.B.1.a of this preamble, NESHAP subpart F contains provisions to determine which chemical manufacturing processes at a facility are subject to the HON, monitoring requirements for HAP ( i.e., HAP listed in Table 4 of NESHAP subpart F) that may leak into cooling water from heat exchange systems, and requirements for maintenance wastewater. For NESHAP subpart F, we are proposing: • Compliance dates for all of the proposed HON requirements (see proposed 40 CFR 63.100(k)(10) through (12); and section III.F of this preamble). • to move all of the definitions from NESHAP subparts G and H ( i.e., 40 CFR 63.111 and 40 CFR 63.161, respectively) into the definition section of NESHAP subpart F (see proposed 40 CFR 63.101; and section III.E.5.a of this preamble). • a new definition for “in ethylene oxide service” (for equipment leaks, heat exchange systems, process vents, storage vessels, and wastewater) (see proposed 40 CFR 63.101; and section III.B.2.a of this preamble). • new operating and monitoring requirements for flares; and a requirement that owners and operators can send no more than 20 tons of EtO to all of their flares combined in any consecutive 12-month period (see proposed 40 CFR 63.108; and section III.B.2.a.vi of this preamble). • sampling and analysis procedures for owners and operators to demonstrate that process equipment does, or does not, meet the proposed definition of being “in ethylene oxide service” (see proposed 40 CFR 63.109; and section III.B.2.a.vii of this preamble). For heat exchange systems, we are proposing: • To require owners or operators to use the Modified El Paso Method and repair leaks of total strippable hydrocarbon concentration (as methane) in the stripping gas of 6.2 parts per million by volume (ppmv) or greater (see proposed 40 CFR 63.104(g) through (j); and section III.C.1 of this preamble). • to require owners or operators to conduct more frequent leak monitoring (weekly instead of quarterly) for heat exchange systems in EtO service and repair leaks within 15 days from the sampling date (in lieu of the current 45-day repair requirement after receiving results of monitoring indicating a leak in the HON), and delay of repair would not be allowed (see proposed 40 CFR 63.104(g)(6) and (h)(6); and section III.B.2.a.iii of this preamble). • that the current leak monitoring requirements for heat exchange systems at 40 CFR 63.104(b) may be used in limited instances in lieu of using the Modified El Paso Method for heat exchange systems cooling process fluids that will remain in the cooling water if a leak occurs (see proposed 40 CFR 63.104(l); and section III.C.1 of this preamble). ii. NESHAP Subpart G As detailed in section II.B.1.b of this preamble, NESHAP subpart G contains requirements for process vents, storage vessels, transfer racks, wastewater streams, and closed vent systems. For process vents, we are proposing: • To remove the 50 ppmv and 0.005 standard cubic meter per minute (scmm) Group 1 process vent thresholds from the Group 1 process vent definition, and instead require owners and operators of process vents that emit greater than or equal to 1.0 pound per hour (lb/hr) of total organic HAP to reduce emissions of organic HAP using a flare meeting the proposed operating and monitoring requirements for flares in NESHAP subpart F; or reduce emissions of total organic HAP or total organic compounds (TOC) by 98 percent by weight or to an exit concentration of 20 ppmv, whichever is less stringent (see proposed 40 CFR 63.101 and 40 CFR 63.113(a)(1) and (2); and section III.C.3.a of this preamble). • to remove the total resource effectiveness (TRE) concept in its entirety (see proposed 40 CFR 63.113(a)(4); and section III.C.3.a of this preamble). • to add an emission standard of 0.054 nanograms per dry standard cubic meter (ng/dscm) at 3 percent oxygen (toxic equivalency basis) for dioxins and furans from chlorinated process vents (see proposed 40 CFR 63.113(a)(5); and section III.D.5. of this preamble). • that owners and operators reduce emissions of EtO from process vents in EtO service by either: (1) Venting emissions through a closed-vent system to a control device that reduces EtO by greater than or equal to 99.9 percent by weight, to a concentration less than 1 ppmv for each process vent, or to less than 5 lb/yr for all combined process vents; or (2) venting emissions through a closed-vent system to a flare meeting the proposed operating and monitoring requirements for flares in NESHAP subpart F (see proposed 40 CFR 63.113(j), 40 CFR 63.108, and 40 CFR 63.124; and section III.B.2.a.i of this preamble). 3 3 We are also proposing to remove the option to allow use of a design evaluation in lieu of performance testing to demonstrate compliance for controlling various emission sources in ethylene oxide service. In addition, owners or operators that choose to control emissions with a non-flare control device would be required to conduct an initial performance test on each control device in ethylene oxide service to verify performance at the required level of control, and would also be required to conduct periodic performance testing on non-flare control devices in ethylene oxide service every 5 years (see proposed 40 CFR 63.124). • a work practice standard for maintenance vents requiring that, prior to opening process equipment to the atmosphere, the equipment must either: (1) Be drained and purged to a closed system so that the hydrocarbon content is less than or equal to 10 percent of the lower explosive limit (LEL); (2) be opened and vented to the atmosphere only if the 10-percent LEL cannot be demonstrated and the pressure is less than or equal to 5 pounds per square inch gauge (psig), provided there is no active purging of the equipment to the atmosphere until the LEL criterion is met; (3) be opened when there is less than 50 lbs of VOC that may be emitted to the atmosphere; or (4) for installing or removing an equipment blind, depressurize the equipment to 2 psig or less and maintain pressure of the equipment where purge gas enters the equipment at or below 2 psig during the blind flange installation, provided none of the other proposed work practice standards can be met (see proposed 40 CFR 63.113(k); and section III.D.4.a of this preamble). • that owners and operators of process vents in EtO service would not be allowed to use the proposed maintenance vent work practice standards; instead, owners and operators would be prohibited from releasing more than 1.0 ton of EtO from all maintenance vents combined in any consecutive 12-month period (see proposed 40 CFR 63.113(k)(4); and section III.B.2.a.v of this preamble). For storage vessels, we are proposing: • That owners and operators reduce emissions of EtO from storage vessels in EtO service by either: (1) Venting emissions through a closed-vent system to a control device that reduces EtO by greater than or equal to 99.9 percent by weight or to a concentration less than 1 ppmv for each storage vessel vent; or (2) venting emissions through a closed-vent system to a flare meeting the proposed operating and monitoring requirements for flares in NESHAP subpart F (see proposed 40 CFR 63.119(a)(5), 40 CFR 63.108, and 40 CFR 63.124; and section III.B.2.a.i of this preamble). 4 4 See footnote 3. • a work practice standard to allow storage vessels to be vented to the atmosphere once a storage vessel degassing concentration threshold is met ( i.e., less than 10 percent of the LEL) and all standing liquid has been removed from the vessel to the extent practicable (see proposed 40 CFR 63.119(a)(6); and section III.D.4.b of this preamble). • to define pressure vessel and remove the exemption for “pressure vessels designed to operate in excess of 204.9 kilopascals and without emissions to the atmosphere” from the definition of storage vessel (see proposed 40 CFR 63.101); and require initial and annual performance testing using EPA Method 21 of 40 CFR part 60, appendix A-7 to demonstrate no detectable emissions ( i.e., would be required to meet a leak definition of 500 parts per million (ppm) at each point on the pressure vessel where total organic HAP could potentially be emitted) (see proposed 40 CFR 63.119(a)(7); and section III.D.6 of this preamble). • to require all openings in an internal floating roof (IFR) (except those for automatic bleeder vents (vacuum breaker vents), rim space vents, leg sleeves, and deck drains) be equipped with a deck cover; and the deck cover would be required to be equipped with a gasket between the cover and the deck (see proposed 40 CFR 63.119(b)(5)(ix); and section III.C.2 of this preamble). • controls for guidepoles for all storage vessels equipped with an IFR (see proposed 40 CFR 63.119(b)(5)(x), (xi), and (xii); and section III.C.2 of this preamble). • a work practice standard that would apply during periods of planned routine maintenance of a control device, fuel gas system, or process equipment that is normally used for compliance with the storage vessel emissions control requirements; owners and operators would not be permitted to fill the storage vessel during these periods (such that the vessel would emit HAP to the atmosphere for a limited amount of time due to breathing losses only while working losses are controlled) (see proposed 40 CFR 63.119(e)(7); and section III.D.4.c of this preamble). • to revise the Group 1 storage capacity criterion (for storage vessels at existing sources) from between 75 cubic meters (m 3 ) and 151 m 3 to between 38 m 3 and 151 m 3 (see proposed Table 5 to subpart G; and section III.C.2 of this preamble). • to revise the Group 1 stored-liquid maximum true vapor pressure (MTVP) of total organic HAP threshold (for storage vessels at existing sources) from greater than or equal to 13.1 kilopascals (kPa) to greater than or equal to 6.9 kPa (see proposed Table 5 to subpart G; and section III.C.2 of this preamble). For transfer racks, we are proposing: • To remove the exemption for transfer operations that load “at an operating pressure greater than 204.9 kilopascals” from the definition of transfer operation (see proposed 40 CFR 63.101; and section III.D.8 of this preamble). For wastewater streams, we are proposing: • To revise the Group 1 wastewater stream threshold to include wastewater streams in EtO service ( i.e., wastewater streams with total annual average concentration of EtO greater than or equal to 1 ppm by weight at any flow rate) (see proposed 40 CFR 63.132(c)(1)(iii) and (d)(1)(ii); and section III.B.2.a.iv of this preamble). • to prohibit owners and operators from injecting wastewater into or disposing of water through any heat exchange system in a chemical manufacturing process unit (CMPU) meeting the conditions of 40 CFR 63.100(b)(1) through (3) if the water contains any amount of EtO, has been in contact with any process stream containing EtO, or the water is considered wastewater as defined in 40 CFR 63.101 (see proposed 40 CFR 63.104(k); and section III.B.2.a.iv of this preamble). For closed vent systems, we are proposing: • That owners and operators may not bypass an air pollution control device (APCD) at any time (see proposed 40 CFR 63.114(d)(3), 40 CFR 63.127(d)(3), and 40 CFR 63.148(f)(4)), that a bypass is a violation, and that owners and operators must estimate and report the quantity of organic HAP released (see proposed 40 CFR 63.118(a)(5), 40 CFR 63.130(a)(2)(iv), 40 CFR 63.130(b)(3), 40 CFR 63.130(d)(7), and 40 CFR 63.148(i)(3)(iii) and (j)(4); and section III.D.3 of this preamble). iii. NESHAP Subparts H and I As detailed in sections II.B.1.c and II.B.1.d of this preamble, NESHAP subparts H and I contain requirements for equipment leaks. Also, due to space limitations in the HON, we are proposing fenceline monitoring ( i.e., monitoring along the perimeter of the facility's property line) in NESHAP subpart H for all emission sources. For equipment leaks and fenceline monitoring, we are proposing: • That all connectors in EtO service would be required to be monitored monthly at a leak definition of 100 ppm with no skip period, and delay of repair would not be allowed (see proposed 40 CFR 63.174(a)(3), (b)(3)(vi), and (g)(3), and 40 CFR 63.171(f); and section III.B.2.a.ii of this preamble). • that all gas/vapor and light liquid valves in EtO service would be required to be monitored monthly at a leak definition of 100 ppm with no skip period, and delay of repairs would not be allowed (see proposed 40 CFR 63.168(b)(2)(iv) and (d)(5), and 40 CFR 63.171(f); and section III.B.2.a.ii of this preamble). • that all light liquid pumps in EtO service would be required to be monitored monthly at a leak definition of 500 ppm, and delay of repairs would not be allowed (see proposed 40 CFR 63.163(a)(1)(iii), (b)(2)(iv), (c)(4), and (e)(7), and 40 CFR 63.171(f); and section III.B.2.a.ii of this preamble). • a work practice standard for pressure relief devices (PRDs) that vent to the atmosphere that would require owners and operators to implement at least three prevention measures, perform root cause analysis and corrective action in the event that a PRD does release emissions directly to the atmosphere, and monitor PRDs using a system that is capable of identifying and recording the time and duration of each pressure release and of notifying operators that a pressure release has occurred (see proposed 40 CFR 63.165(e); and section III.D.2 of this preamble). • that all surge control vessels and bottoms receivers would be required to meet the requirements we are proposing for process vents (see proposed 40 CFR 63.170(b); and section III.D.7 of this preamble). • that owners and operators may not bypass an APCD at any time (see proposed 40 CFR 63.114(d)(3), 40 CFR 63.127(d)(3), and 40 CFR 63.148(f)(4)), that a bypass is a violation, and that owners and operators must estimate and report the quantity of organic HAP released (see proposed 40 CFR 63.118(a)(5), 40 CFR 63.130(a)(2)(iv), 40 CFR 63.130(b)(3), 40 CFR 63.130(d)(7), and 40 CFR 63.148(i)(3)(iii) and (j)(4); and section III.D.3 of this preamble). • to add a fenceline monitoring standard that requires owners and operators to monitor for any of 6 specific HAP they emit ( i.e., benzene, 1,3-butadiene, ethylene dichloride, vinyl chloride, EtO, and chloroprene) and conduct root cause analysis and corrective action upon exceeding the annual average concentration action level set forth for each HAP (see proposed 40 CFR 63.184; and section III.C.7 of this preamble). b. P&R I As detailed in section II.B.2 of this preamble, P&R I (40 CFR part 63, subpart U) generally follows and refers to the requirements of the HON, with additional requirements for batch process vents. We are proposing amendments to P&R I for heat exchange systems, process vents, storage vessels, wastewater, and equipment leaks. For NESHAP subpart U, we are proposing: • Compliance dates for all of the proposed P&R I requirements (see proposed 40 CFR 63.481(n) and (o); and section III.F of this preamble). • new operating and monitoring requirements for flares (see proposed 40 CFR 63.508; and section III.D.1 of this preamble). • removing provisions to assert an affirmative defense to civil penalties (see proposed 40 CFR 63.480(j)(4); and section III.E.2 of this preamble). • to reference the same fenceline monitoring requirements that we are proposing in Subpart H for HON sources. • sampling and analysis procedures for owners and operators of affected sources producing neoprene to demonstrate that process equipment does, or does not, meet the proposed definition of being “in chloroprene service” (see proposed 40 CFR 63.509; and section III.B.2.b.iv of this preamble). • A facility-wide chloroprene emissions cap of 3.8 tpy in any consecutive 12-month period for all neoprene production emission sources (see proposed 40 CFR 63.483(a)(10); and section III.B.2.b.v of this preamble). For heat exchange systems, we are proposing: • To add the same requirements (except for EtO standards) listed in section I.A.2.a.i of this preamble that we are proposing for heat exchange systems subject to the HON to also apply to heat exchange systems subject to P&R I (see proposed 40 CFR 63.502(n)(7); and section III.C.1 of this preamble). For continuous front-end process vents, we are proposing: • That owners and operators reduce emissions of chloroprene from continuous front-end process vents in chloroprene service at affected sources producing neoprene by venting emissions through a closed-vent system to a non-flare control device that reduces chloroprene by greater than or equal to 99.9 percent by weight, to a concentration less than 1 ppmv for each process vent, or to less than 5 lb/yr for all combined process vents (see proposed 40 CFR 63.485(y), and 40 CFR 63.510; and sections III.B.2.b.i of this preamble). 5 5 We are also proposing to remove the option to allow use of a design evaluation in lieu of performance testing to demonstrate compliance for controlling various emission sources in chloroprene service. In addition, owners or operators would be required to conduct an initial performance test on each non-flare control device in chloroprene service to verify performance at the required level of control, and would also be required to conduct periodic performance testing on non-flare control devices in chloroprene service every 5 years (see proposed 40 CFR 63.510). • to add the same requirements (except for EtO standards) listed in section I.A.2.a.ii of this preamble that we are proposing for process vents subject to the HON to also apply to continuous front-end process vents subject to P&R I (see proposed 40 CFR 63.482, 40 CFR 63.485(l)(6), (o)(6), (p)(5), and (x), 40 CFR 63.113(a)(1) and (2), 40 CFR 63.113(a)(4), 40 CFR 63.113(k), 40 CFR 63.114(a)(5)(v); and section III.C.3 of this preamble). • that continuous front-end process vents in chloroprene service would not be allowed to use the proposed maintenance vent work practice standards; instead, owners and operators would be prohibited from releasing more than 1.0 ton of chloroprene from all maintenance vents combined in any consecutive 12-month period (see proposed 40 CFR 63.485(z); and section III.B.2.b.iii of this preamble). • to add an emission standard of 0.054 ng/dscm at 3 percent oxygen (toxic equivalency basis) for dioxins and furans from chlorinated continuous front-end process vents (see proposed 40 CFR 63.485(x); and section III.D.5. of this preamble). For batch front-end process vents, we are proposing: • To remove the annual organic HAP emissions mass flow rate, cutoff flow rate, and annual average batch vent flow rate Group 1 process vent thresholds from the Group 1 batch front-end process vent definition (these thresholds are currently determined on an individual batch process vent basis). Instead, owners and operators of batch front-end process vents that release total annual organic HAP emissions greater than or equal to 4,536 kilograms per year (kg/yr) (10,000 pounds per year (lb/yr)) from all batch front-end process vents combined would be required to reduce emissions of organic HAP from these process vents using a flare meeting the proposed operating and monitoring requirements for flares; or reduce emissions of organic HAP or total organic carbon (TOC) by 90 percent by weight (or to an exit concentration of 20 ppmv if considered an “aggregate batch vent stream” as defined by the rule) (see proposed 40 CFR 63.482, 40 CFR 63.487I(1)(iv), 40 CFR 63.488(d)(2), (e)(4), (f)(2), and (g)(3); and section III.C.3 of this preamble). • to add the same chloroprene standards that we are proposing for continuous front-end process for batch front-end process vents at affected sources producing neoprene (see proposed 40 CFR 63.487(j); and section III.B.2.b.i of this preamble). • to add the same work practice standards that we are proposing for maintenance vents as described for HON to P&R I (see proposed 40 CFR 63.487(i); and section III.D.4.a of this preamble). • that batch front-end process vents in chloroprene service would not be allowed to use the proposed maintenance vent work practice standards; instead, owners and operators would be prohibited from releasing more than 1.0 tons of chloroprene from all maintenance vents combined in any consecutive 12-month period (see proposed 40 CFR 63.487(i)(4); and section III.B.2.b.v of this preamble). • to add an emission standard of 0.054 ng/dscm at 3 percent oxygen (toxic equivalency basis) for dioxins and furans from chlorinated batch front-end process vents (see proposed 40 CFR 63.487(a)(3) and (b)(3); and section III.D.5. of this preamble). For storage vessels, we are proposing: • That owners and operators reduce emissions of chloroprene from storage vessels in chloroprene service at affected sources producing neoprene by venting emissions through a closed-vent system to a non-flare control device that reduces chloroprene by greater than or equal to 99.9 percent by weight or to a concentration less than 1 ppmv for each storage vessel vent (see proposed 40 CFR 63.484(u) and 40 CFR 63.510; and section III.B.2.b.i of this preamble). 6 6 See footnote 5. • to add the same requirements (except for EtO standards) listed in section I.A.2.a.ii of this preamble that we are proposing for storage vessels subject to the HON except the proposed requirements would apply to storage vessels subject to P&R I (see proposed 40 CFR 63.484(t); and section III.C.2 of this preamble). For wastewater streams, we are proposing: • To revise the Group 1 wastewater stream threshold to include wastewater streams in chloroprene service at affected sources producing neoprene ( i.e., wastewater streams with total annual average concentration of chloroprene greater than or equal to 10 parts per million by weight (ppmw) at any flow rate) (see proposed 40 CFR 63.501(a)(10)(iv); and section III.B.2.b.ii of this preamble). • to prohibit owners and operators from injecting wastewater into or disposing of water through any heat exchange system in an elastomer product process unit (EPPU) if the water contains any amount of chloroprene, has been in contact with any process stream containing chloroprene, or the water is considered wastewater as defined in 40 CFR 63.482 (see proposed 40 CFR 63.502(n)(8); and section III.B.2.b.ii of this preamble). For equipment leaks and fenceline monitoring, we are proposing: • To add the same requirements (except for EtO standards) listed in section I.A.2.a.iii of this preamble that we are proposing for equipment leaks subject to the HON except the proposed requirements would apply to equipment leaks subject to P&R I (see proposed 40 CFR 63.502(a)(1) through (a)(6); and sections III.D.2 and III.D.3 of this preamble). • to cross-reference P&R I facilities to the same fenceline monitoring standard in the HON (see proposed 40 CFR 63.184) that requires owners and operators to monitor for any of 6 specific HAP they emit ( i.e., benzene, 1,3-butadiene, ethylene dichloride, vinyl chloride, EtO, and chloroprene) and conduct root cause analysis and corrective action upon exceeding the annual average concentration action level set forth for each HAP (see section III.C.7 of this preamble). c. P&R II The most significant amendments that we are proposing for P&R II (40 CFR part 63, subpart W) are to add requirements for heat exchange systems (see proposed 40 CFR 63.523(d) and 40 CFR 63.524(c); and section III.D.9 of this preamble) and require owners and operators of wet strength resins (WSR) sources to comply with both the equipment leak standards in the HON and the HAP emissions limitation for process vents, storage tanks, and wastewater systems (see proposed 40 CFR 63.524(a)(3) and (b)(3); and section III.D.10 of this preamble). We are also proposing to add the same dioxin and furan emission standard of 0.054 ng/dscm at 3 percent oxygen (toxic equivalency basis) for chlorinated process vents as in the HON and P&R I (see proposed 40 CFR 63.523(e) (for process vents associated with each existing, new, or reconstructed affected basic liquid epoxy resins (BLR) source), 40 CFR 63.524(a)(3) (for process vents associated with each existing affected WSR source), and 40 CFR 63.524(b)(3) (for process vents associated with each new or reconstructed affected WSR source)). d. NSPS Subparts III, NNN, and RRR We are proposing to amend the applicability of NSPS subparts III, NNN, and RRR so that they would only apply to sources constructed, reconstructed, or modified on or before April 25, 2023. Affected facilities that are constructed, reconstructed, or modified after April 25, 2023 would be subject to the new proposed NSPS subparts IIIa, NNNa, and RRRa (see section A.2.e of this preamble). e. NSPS Subparts IIIa, NNNa, and RRRa Rather than comply with a TRE concept which is currently used in NSPS subparts III, NNN, and RRR, we are proposing in new NSPS subparts IIIa, NNNa, and RRRa to require owners and operators to reduce emissions of total organic carbon (TOC) (minus methane and ethane) from all vent streams of an affected facility ( i.e., SOCMI air oxidation unit processes, distillation operations, and reactor processes for which construction, reconstruction, or modification occurs after April 25, 2023) by 98 percent by weight or to a concentration of 20 ppmv on a dry basis corrected to 3 percent oxygen, whichever is less stringent, or combust the emissions in a flare meeting the same operating and monitoring requirements for flares that we are proposing for flares subject to the HON. We are also proposing to eliminate the relief valve discharge exemption from the definition of “vent stream” such that any relief valve discharge to the atmosphere of a vent stream is a violation of the emissions standard. In addition, we are proposing the same work practice standards for maintenance vents that we are proposing for HON process vents, and the same monitoring requirements that we are proposing for HON process vents for adsorbers that cannot be regenerated and regenerative adsorbers that are regenerated offsite (see section III.C.3.b of this preamble). f. NSPS Subpart VVa We are proposing to amend the applicability of the existing NSPS subpart VVa so that it would apply to only sources constructed, reconstructed, or modified after November 6, 2006, and on or before April 25, 2023. Affected facilities that are constructed, reconstructed, or modified after April 25, 2023 would be subject to the new proposed NSPS subpart VVb. g. NSPS Subpart VVb We are proposing in a new NSPS subpart VVb the same requirements in NSPS subpart VVa plus requiring that all gas/vapor and light liquid valves be monitored quarterly at a leak definition of 100 ppm and all connectors be monitored once every 12 months at a leak definition of 500 ppm (see section III.C.6.b of this preamble). For each of these two additional requirements, we are also proposing skip periods for good performance. 3. Costs and Benefits Pursuant to E.O. 12866, the EPA prepared an analysis of the potential costs and benefits associated with this action. This analysis titled Regulatory Impact Analysis, (referred to as the RIA in this document) is available in the docket, and is also briefly summarized in section VI of this preamble. B. Does this action apply to me? The source categories that are the subject of this proposal include the SOCMI source category (and whose facilities, sources and processes we often refer to as “HON facilities,” “HON sources,” and “HON processes” for purposes of the NESHAP) and several Polymers and Resins Production source categories covered in P&R I and P&R II (see section II.B of this preamble for detailed information about the source categories). 7 The North American Industry Classification System (NAICS) code for SOCMI facilities begins with 325, for P&R I is 325212, and for P&R II is 325211. The list of NAICS codes is not intended to be exhaustive, but rather provides a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources and/or affected facilities. Federal, state, local, and tribal government entities would not be affected by this proposed action. 7 P&R I includes nine listed elastomer production source categories ( i.e., Butyl Rubber Production, Epichlorohydrin Elastomers Production, Ethylene-Propylene Elastomers Production, Hypalon TM Production, Neoprene Production, Nitrile Butadiene Rubber Production, Polybutadiene Rubber Production, Polysulfide Rubber Production, and Styrene-Butadiene Rubber and Latex Production). P&R II includes two listed source categories that use epichlorohydrin feedstock (Epoxy Resins Production and Non-Nylon Polyamides Production). 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 Documentation for Developing the Initial Source Category List, Final Report (see EPA-450/3-91-030, July 1992), the SOCMI source category is any facility engaged in “manufacturing processes that produce one or more of the chemicals [listed] that either: (1) Use an organic HAP as a reactant or (2) produce an organic HAP as a product, co-product, by-product, or isolated intermediate.” 8 In the development of NESHAP for this source category, the EPA considered emission sources associated with: equipment leaks (including leaks from heat exchange systems), process vents, transfer racks, storage vessels, and wastewater collection and treatment systems. The elastomer production source categories in P&R I and resins produced with epichlorohydrin feedstock in P&R II have many similar emission sources with SOCMI sources and are discussed further in section II.B of this preamble. 8 The original list of chemicals is located in Appendix A (beginning on page A-71) of EPA-450/3-91-030 dated July 1992. Alternatively, the most recent list of chemicals is documented in the HON applicability rule text at 40 CFR 63.100(b)(1) and (2). The original list of organic HAPs for the SOCMI source category is located in Table 3.1 of Section 3.0 of EPA-450/3-91-030. The EPA Priority List (40 CFR 60.16, 44 FR 49222, August 21, 1979) included “Synthetic Organic Chemical Manufacturing” 9 as a source category for which standards of performance were to be promulgated under CAA section 111. In the development of NSPS for this source category, the EPA considered emission sources associated with unit processes, storage and handling equipment, fugitive emission sources, and secondary sources. 9 For readability, we also refer to this as the SOCMI source category for purposes of the NSPS. 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 action is available on the internet. Following signature by the EPA Administrator, the EPA will post a copy of this proposed action at https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, and https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and-non-nylon-polyamides-national-emission. Following publication in the Federal Register , the EPA will post the Federal Register version of the proposal and key technical documents at these same websites. A memorandum showing the edits that would be necessary to incorporate the changes to: 40 CFR part 60, subparts VV, VVa, III, NNN, RRR; 40 CFR part 63, subparts F, G, H and I (HON), U (P&R I), and W (P&R II); and 40 CFR part 60, new subparts VVb, IIIa, NNNa, and RRRa proposed in this action are available in the docket (Docket ID No. EPA-HQ-OAR-2022-0730). Following signature by the EPA Administrator, the EPA also will post a copy of these documents to https://www.epa.gov/stationary-sources-air-pollution/synthetic-organic-chemical-manufacturing-industry-organic-national, https://www.epa.gov/stationary-sources-air-pollution/group-i-polymers-and-resins-national-emission-standards-hazardous, and https://www.epa.gov/stationary-sources-air-pollution/epoxy-resins-production-and-non-nylon-polyamides-national-emission. II. Background A. What is the statutory authority for this action? 1. NESHAP The statutory authority for this action related to NESHAP is provided by sections 112 and 301 of the CAA, as amended (42 U.S.C. 7401 et seq. ). Section 112 of the CAA establishes a two-stage regulatory process to develop standards for emissions of HAP from stationary sources. Generally, the first stage involves establishing technology-based standards and the second stage involves evaluating those standards that are based on MACT to determine whether additional standards are needed to address any remaining risk associated with HAP emissions. This second stage is commonly referred to as the “residual risk review.” In addition to the residual risk review, the CAA also requires the EPA to review standards set under CAA section 112 every 8 years and revise the standards as necessary taking into account any “developments in practices, processes, and control technologies.” This review is commonly referred to as the “technology review.” When the two reviews are combined into a single rulemaking, it is commonly referred to as the “risk and technology review.” The discussion that follows identifies the most relevant statutory sections and briefly explains the contours of the methodology used to implement these statutory requirements. A more comprehensive discussion appears in the document titled CAA Section 112 Risk and Technology Reviews: Statutory Authority and Methodology, in the docket for this rulemaking. In the first stage of the CAA section 112 standard setting process, the EPA promulgates technology-based standards under CAA section 112(d) for categories of sources identified as emitting one or more of the HAP listed in CAA section 112(b). Sources of HAP emissions are either major sources or area sources, and CAA section 112 establishes different requirements for major source standards and area source standards. “Major sources” are those that emit or have the potential to emit 10 tpy or more of a single HAP or 25 tpy or more of any combination of HAP. All other sources are “area sources.” For major sources, CAA section 112(d)(2) provides that the technology-based NESHAP must reflect the maximum degree of emission reductions of HAP achievable (after considering cost, energy requirements, and non-air quality health and environmental impacts). These standards are commonly referred to as MACT standards. CAA section 112(d)(3) also establishes a minimum control level for MACT standards, known as the MACT “floor.” In certain instances, as provided in CAA section 112(h), the EPA may set work practice standards in lieu of numerical emission standards. The EPA must also consider control options that are more stringent than the floor. Standards more stringent than the floor are commonly referred to as beyond-the-floor standards. For area sources, CAA section 112(d)(5) gives the EPA discretion to set standards based on generally available control technologies or management practices (GACT standards) in lieu of MACT standards. The second stage in standard-setting focuses on identifying and addressing any remaining ( i.e., “residual”) risk pursuant to CAA section 112(f). For source categories subject to MACT standards, section 112(f)(2) of the CAA requires the EPA to determine whether promulgation of additional standards is needed to provide an ample margin of safety to protect public health or to prevent an adverse environmental effect. Section 112(d)(5) of the CAA provides that this residual risk review is not required for categories of area sources subject to GACT standards. Section 112(f)(2)(B) of the CAA further expressly preserves the EPA's use of the two-step approach for developing standards to address any residual risk and the Agency's interpretation of “ample margin of safety” developed in the National Emissions Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA notified Congress in the Residual Risk Report that the Agency intended to use the 1989 Benzene NESHAP approach in making CAA section 112(f) residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently adopted this approach in its residual risk determinations and the United States Court of Appeals for the District of Columbia Circuit upheld the EPA's interpretation that CAA section 112(f)(2) incorporates the approach established in the 1989 Benzene NESHAP. See Natural Resources Defense Council (NRDC) v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008). The approach incorporated into the CAA and used by the EPA to evaluate residual risk and to develop standards under CAA section 112(f)(2) is a two-step approach. In the first step, the EPA determines whether risks are acceptable. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR) 10 of approximately 1 in 10 thousand.” (54 FR 38045). If risks are unacceptable, the EPA must determine the emissions standards necessary to reduce risk to an acceptable level without considering costs. In the second step of the approach, the EPA considers whether the emissions standards provide an ample margin of safety to protect public health “in consideration of all health information, including the number of persons at risk levels higher than approximately 1 in 1 million, as well as other relevant factors, including costs and economic impacts, technological feasibility, and other factors relevant to each particular decision.” Id. The EPA must promulgate emission standards necessary to provide an ample margin of safety to protect public health or determine that the standards being reviewed provide an ample margin of safety without any revisions. After conducting the ample margin of safety analysis, we consider whether a more stringent standard is necessary to prevent, taking into consideration costs, energy, safety, and other relevant factors, an adverse environmental effect. 10 Although defined as “maximum individual risk,” MIR refers only to cancer risk. MIR, one metric for assessing cancer risk, is the estimated risk if an individual were exposed to the maximum level of a pollutant for a lifetime. CAA section 112(d)(6) requires the EPA to review standards promulgated under CAA section 112 and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less often than every 8 years. In conducting this review, which we call the “technology review,” the EPA is not required to recalculate the MACT floors that were established in earlier rulemakings. NRDC v. EPA, 529 F.3d at 1084; Association of Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C. Cir. 2013). The EPA may consider cost in deciding whether to revise the standards pursuant to CAA section 112(d)(6). The EPA is required to address regulatory gaps, such as missing MACT standards for listed air toxics known to be emitted from major source categories, and any new MACT standards must be established under CAA sections 112(d)(2) and (3), or, in specific circumstances, CAA sections 112(d)(4) or (h). Louisiana Environmental Action Network (LEAN) v. EPA, 955 F.3d 1088 (D.C. Cir. 2020). The EPA conducted a residual risk and technology review for the HON in 2006, concluding that there was no need to revise the HON under the provisions of either CAA section 112(f) or 112(d)(6). As part of the residual risk review, the EPA conducted a risk assessment, and based on the results of the risk assessment, determined that the then current level of control called for by the existing MACT standards both reduced HAP emissions to levels that presented an acceptable level of risk and provided an ample margin of safety to protect public health (see 71 FR 76603, December 21, 2006 for additional details). In 2008, the EPA conducted a residual risk and technology review for four of the P&R I source categories (including the Polysulfide Rubber Production, Ethylene-Propylene Elastomers Production, Butyl Rubber Production, and Neoprene Production source categories) and all P&R II source categories (Epoxy Resins Production and Non-Nylon Polyamides Production source categories). In 2011, the EPA completed the residual risk and technology review for the remaining five P&R I source categories (Epichlorohydrin Elastomers Production, Hypalon TM Production, Polybutadiene Rubber Production, Styrene-Butadiene Rubber and Latex Production, and Nitrile Butadiene Rubber Production); and the EPA concluded in these actions that there was no need to revise standards for any of the nine P&R I source categories and two P&R II source categories under the provisions of either CAA section 112(f) or 112(d)(6) (see 73 FR 76220, December 16, 2008 and 77 FR 22566, April 21, 2011 for additional details). This action constitutes another CAA section 112(d)(6) technology review for the HON, P&R I, and P&R II. This action also constitutes an updated CAA section 112(f) risk review based on new information for the HON and for affected sources producing neoprene subject to P&R I. We note that although there is no statutory CAA obligation under CAA section 112(f) for the EPA to conduct a second residual risk review of the HON or standards for affected sources producing neoprene subject to P&R I, the EPA retains discretion to revisit its residual risk reviews where the Agency deems that is warranted. See, e.g., Fed. Commc'ns Comm'n v. Fox Television Stations, Inc., 556 U.S. 502, 515 (2009); Motor Vehicle Mfrs. Ass'n v. State Farm Mut. Auto. Ins. Co., 463 U.S. 29, 42 (1983); Ethylene Oxide Emissions Standards for Sterilization Facilities; Final Decision, 71 FR 17712, 17715 col. 1 (April 7, 2006) (in residual risk review for EtO, EPA asserting its “authority to revisit (and revise, if necessary) any rulemaking if there is sufficient evidence that changes within the affected industry or significant improvements to science suggests the public is exposed to significant increases in risk as compared to the risk assessment prepared for the rulemaking ( e.g., CAA section 301).”). Here, the specific changes to health information related to certain pollutants emitted by these unique categories led us to determine that it is appropriate, in this case, to conduct these second residual risk reviews under section 112(f). In particular, the EPA is concerned about the cancer risks posed from the SOCMI ( i.e., HON) source category due to the EPA's 2016 updated IRIS inhalation URE for EtO, which shows EtO to be significantly more toxic than previously known. 11 The EPA's 2006 risk and technology review (RTR) could not have had the benefit of this updated URE at the time it was conducted, but if it had would have necessarily resulted in different conclusions about risk acceptability and the HON's provision of an ample margin of safety to protect public health. Similarly, for chloroprene, when the EPA conducted the first residual risk assessment for the SOCMI and Neoprene Production source categories, there was no inhalation URE for chloroprene and, therefore, no cancer risk was attributed to chloroprene emissions in either of those risk reviews. The EPA's 2006 and 2008 RTRs could not have had the benefit of this new URE at the time they were conducted, but if they had would have necessarily resulted in different conclusions about risk acceptability and P&R I's provision of an ample margin of safety to protect public health. The development of the EPA's IRIS inhalation URE for chloroprene was concluded in 2010, which allows us to assess cancer risks posed by chloroprene for the first time. Thus, we are conducting this analysis in this action. In order to ensure our standards provide an ample margin of safety to protect public health following the new IRIS inhalation UREs for EtO and chloroprene, we are exercising our discretion and conducting risk assessments in this action for HON sources and for affected sources producing neoprene subject to P&R I. Finally, we note that on September 15, 2021, the EPA partially granted a citizen administrative petition requesting that the EPA conduct a second residual risk review under CAA section 112(f)(2) for the HON, stating our intent to conduct a human health risk assessment concurrently with the section 112(d)(6) review. 12 Likewise, on March 4, 2022, the EPA partially granted another citizen administrative petition requesting that the EPA also conduct a second residual risk review under CAA section 112(f) for P&R I, stating that we intend to conduct a human health risk assessment concurrently with the section 112(d)(6) review. 13 This proposed rulemaking is partly undertaken to take action in response to those citizen administrative petitions. In sum, even though we do not have a mandatory duty to conduct repeated residual risk reviews under CAA section 112(f)(2), we have the authority to revisit any rulemaking if there is sufficient evidence that changes within the affected industry or significant new scientific information suggesting the public is exposed to significant increases in risk as compared to the previous risk assessments prepared for earlier rulemakings. 11 U.S. EPA. Evaluation of the Inhalation Carcinogenicity of Ethylene Oxide (CASRN 75-21-8) In Support of Summary Information on the Integrated Risk Information System (IRIS). December 2016. EPA/635/R-16/350Fa. Available at: https://cfpub.epa.gov/ncea/iris/iris_documents/documents/toxreviews/1025tr.pdf. See also, 87 FR 77985 (Dec. 21, 2022), “Reconsideration of the 2020 National Emission Standards for Hazardous Air Pollutants: Miscellaneous Organic Chemical Manufacturing Residual Risk and Technology Review,” Final action; reconsideration of the final rule. 12 See letter dated September 15, 2021, from Joseph Goffman to Kathleen Riley, Emma Cheuse, and Adam Kron which is available in the docket for this rulemaking. 13 See letter dated March 4, 2022, from Joseph Goffman to Emma Cheuse, Deena Tumeh, Michelle Mabson, Maryum Jordan, and Dorian Spence which is available in the docket for this rulemaking. 2. NSPS The EPA's authority for this proposed rule related to NSPS is CAA section 111, which governs the establishment of standards of performance for stationary sources. Section 111(b)(1)(A) of the CAA requires the EPA Administrator to list categories of stationary sources that in the Administrator's judgment cause or contribute significantly to air pollution that may reasonably be anticipated to endanger public health or welfare. The EPA must then issue performance standards for new (and modified or reconstructed) sources in each source category pursuant to CAA section 111(b)(1)(B). These standards are referred to as new source performance standards, or NSPS. The EPA has the authority to define the scope of the source categories, determine the pollutants for which standards should be developed, set the emission level of the standards, and distinguish among classes, types, and sizes within categories in establishing the standards. CAA section 111(b)(1)(B) requires the EPA to “at least every 8 years review and, if appropriate, revise” NSPS. However, the Administrator need not review any such standard if the “Administrator determines that such review is not appropriate in light of readily available information on the efficacy” of the standard. When conducting a review of an existing performance standard, the EPA has the discretion and authority to add emission limits for pollutants or emission sources not currently regulated for that source category. In setting or revising a performance standard, CAA section 111(a)(1) provides that performance standards are to reflect “the degree of emission limitation achievable through the application of the BSER which (taking into account the cost of achieving such reduction and any non-air quality health and environmental impact and energy requirements) the Administrator determines has been adequately demonstrated.” The term “standard of performance” in CAA section 111(a)(1) makes clear that the EPA is to determine both the BSER for the regulated sources in the source category and the degree of emission limitation achievable through application of the BSER. The EPA must then, under CAA section 111(b)(1)(B), promulgate standards of performance for new sources that reflect that level of stringency. CAA section 111(h)(1) authorizes the Administrator to promulgate “a design, equipment, work practice, or operational standard, or combination thereof” if in his or her judgment, “it is not feasible to prescribe or enforce a standard of performance.” CAA section 111(h)(2) provides the circumstances under which prescribing or enforcing a standard of performance is “not feasible,” such as, when the pollutant cannot be emitted through a conveyance designed to emit or capture the pollutant, or when there is no practicable measurement methodology for the particular class of sources. CAA section 111(b)(5) precludes the EPA from prescribing a particular technological system that must be used to comply with a standard of performance. Rather, sources can select any measure or combination of measures that will achieve the standard. Pursuant to the definition of new source in CAA section 111(a)(2), standards of performance apply to facilities that begin construction, reconstruction, or modification after the date of publication of the proposed standards in the Federal Register . Under CAA section 111(a)(4), “modification” means any physical change in, or change in the method of operation of, a stationary source which increases the amount of any air pollutant emitted by such source or which results in the emission of any air pollutant not previously emitted. Changes to an existing facility that do not result in an increase in emissions are not considered modifications. Under the provisions in 40 CFR 60.15, reconstruction means the replacement of components of an existing facility such that: (1) The fixed capital cost of the new components exceeds 50 percent of the fixed capital cost that would be required to construct a comparable entirely new facility; and (2) it is technologically and economically feasible to meet the applicable standards. Pursuant to CAA section 111(b)(1)(B), the standards of performance or revisions thereof shall become effective upon promulgation. In the development of NSPS for the SOCMI source category, the EPA considered emission sources associated with unit processes, storage and handling equipment, fugitive emission sources, and secondary sources. In 1983, the EPA promulgated NSPS for VOC from equipment leaks in SOCMI (40 CFR part 60, subpart VV). In 1990, the EPA promulgated NSPS (40 CFR part 60, subparts III and NNN) for VOC from air oxidation unit processes and distillation operations in the SOCMI (55 FR 26912 and 55 FR 26931). In 1993, the EPA promulgated NSPS (40 CFR part 60, subpart RRR) for VOC from reactor processes in the SOCMI (58 FR 45948). In 2007, based on its review of NSPS subpart VV, the EPA promulgated certain amendments to NSPS subpart VV and new NSPS (40 CFR part 60, subpart VVa) for VOC from certain equipment leaks in the SOCMI (72 FR 64883). This proposed action presents the required CAA 111(b)(1)(B) review of the NSPS for the air oxidation unit processes (subpart III), distillation operations (subpart NNN), reactor processes (subpart RRR), and equipment leaks (subpart VVa). 3. Petition for Reconsideration In addition to the proposed action under section 111(b)(1)(B) described above, this action includes proposed amendments to the NSPS for VOC from equipment leaks in SOCMI based on its reconsideration of certain aspects of NSPS subparts VV and VVa that were raised in an administrative petition and of which the Agency has granted reconsideration pursuant to section 307(d)(7)(B) of the CAA. In January 2008, the EPA received one petition for reconsideration of the NSPS for VOC from equipment leaks in SOCMI (40 CFR part 60, subparts VV and VVa) and the NSPS for equipment leaks in petroleum refineries (40 CFR part 60, subparts GGG and GGGa) pursuant to CAA section 307(d)(7)(B) from the following petitioners: American Chemistry Council, American Petroleum Institute, and National Petrochemical and Refiners Association (now the American Fuel and Petrochemical Manufacturers). A copy of the petition and subsequent EPA correspondence granting reconsideration is provided in the docket for this rulemaking (see Docket No. EPA-HQ-OAR-2022-0730). The petitioners primarily requested the EPA reconsider four provisions in those rules: (1) The clarification of the definition of process unit in subparts VV, VVa, GGG, and GGGa; (2) the assignment of shared storage vessels to specific process units in subparts VV, VVa, GGG, and GGGa; (3) the monitoring of connectors in subpart VVa; and (4) the definition of capital expenditure in subpart VVa. 14 The rationale for this request is provided in the petition. The petitioners also requested that the EPA stay the effectiveness of these provisions of the rule pending resolution of their petition for reconsideration. On March 4, 2008, the EPA sent a letter to the petitioners informing them that the EPA was granting their request for reconsideration on issues (2) through (4) above. The letter also indicated that the EPA was not taking action on the first issue related to the definition of process unit. Finally, the letter indicated that the EPA was granting a 90-day stay of the provisions of the rules under reconsideration (see CAA section 307(d)(7)(B)), as well as the clarification of the definition of process unit, because of its reliance upon the new provision on the allocation of shared storage vessels. On June 2, 2008, the EPA published three actions in the Federal Register relative to extending the 90-day stay. Specifically, the EPA published a direct final rule (73 FR 31372) and a parallel proposal (73 FR 31416) in the Federal Register to extend the stay until we take final action on the issues of which EPA granted reconsideration. Under the direct final rule, the stay would take effect 30 days after the close of the comment period on the proposed stay if no adverse comments were received. The third notice published that same day was an interim final rule extending the 90-day stay at the time for an additional 60 days so that the stay would not expire before the direct final rule could take effect (73 FR 31376). The EPA did not receive adverse comments on the proposed stay and, as a result, the stay became effective August 1, 2008. 14 Note that this action does not respond to the reconsideration of NSPS subparts GGG and GGGa, as the EPA is not reviewing those subparts in this action. In the June 2, 2008, actions, the EPA indicated that it would be publishing a Federal Register notice in response to the petition; therefore, the purpose of today's notice is to formally respond to the issues raised in the petition with respect to NSPS subparts VV and VVa. This proposed action presents the EPA's proposed revisions to the NSPS for VOC from equipment leaks in SOCMI based on the EPA's reconsideration of issues (2) through (4) in the petition. We are also proposing amendments that address the stay on issue (1) in the petition. See section III.E.4 of this preamble for details about these proposed amendments. B. What are the source categories and how do the current standards regulate emissions? The source categories that are the subject of this proposal are the SOCMI source category subject to the HON and 11 Polymers and Resins Production source categories subject to P&R I and P&R II. The NESHAP and NSPS included in this action that regulate emission sources from the SOCMI and Polymers and Resins Production source categories are described below. 1. HON The sources affected by the current HON include heat exchange systems and maintenance wastewater located at SOCMI facilities that are regulated under NESHAP subpart F; process vents, storage vessels, transfer racks, and wastewater streams located at SOCMI facilities that are regulated under NESHAP subpart G; equipment leaks associated with SOCMI processes regulated under NESHAP subpart H; and equipment leaks from certain non-SOCMI processes at chemical plants regulated under NESHAP subpart I. As previously mentioned, these four NESHAP are more commonly referred together as the HON. In general, the HON applies to CMPUs that: (1) Produce one of the listed SOCMI chemicals, 15 and (2) either use as a reactant or produce a listed organic HAP in the process. A CMPU means the equipment assembled and connected by pipes or ducts to process raw materials and to manufacture an intended product. A CMPU consists of more than one unit operation. A CMPU includes air oxidation reactors and their associated product separators and recovery devices; reactors and their associated product separators and recovery devices; distillation units and their associated distillate receivers and recovery devices; associated unit operations; associated recovery devices; and any feed, intermediate and product storage vessels, product transfer racks, and connected ducts and piping. A CMPU includes pumps, compressors, agitators, PRDs, sampling connection systems, open-ended valves or lines (OEL), valves, connectors, instrumentation systems, and control devices or systems. A CMPU is identified by its primary product. 15 See Table 1 to NESHAP subpart F. a. NESHAP Subpart F NESHAP subpart F contains provisions to determine which chemical manufacturing processes at a SOCMI facility are subject to the HON. Table 1 of NESHAP subpart F contains a list of SOCMI chemicals, and Table 2 of NESHAP subpart F contains a list of organic HAP regulated by the HON. In general, if a process both: (1) Produces one of the listed SOCMI chemicals and (2) either uses as a reactant or produces a listed organic HAP in the process, then that SOCMI process is subject to the HON. Details on how to determine which emission sources ( i.e., heat exchange systems, process vents, storage vessels, transfer racks, wastewater, and equipment leaks) are part of a chemical manufacturing process are also contained in NESHAP subpart F. NESHAP subpart F also contains monitoring requirements for HAP ( i.e., HAP listed in Table 4 of NESHAP subpart F) that may leak into cooling water from heat exchange systems. Additionally, NESHAP subpart F requires sources to prepare a description of procedures for managing maintenance wastewater as part of a SSM plan. b. NESHAP Subpart G NESHAP subpart G contains the standards for process vents, transfer racks, storage vessels, and wastewater at SOCMI facilities; it also includes emissions averaging provisions. NESHAP subpart G provides an equation representing a site-specific allowable overall emission limit for the combination of all emission sources subject to the HON at a SOCMI facility. Existing sources must demonstrate compliance using one of two approaches: the point-by-point compliance approach or the emissions averaging approach. New sources are not allowed to use emissions averaging, but rather must demonstrate compliance using the point-by-point approach. Under the point-by-point approach, the owner or operator would apply control to each Group 1 emission source. A Group 1 emission source is a point which meets the control applicability criteria, and the owner or operator must reduce emissions to specified levels; whereas a Group 2 emission source is one that does not meet the criteria and no additional emission reduction is required. Under the emissions averaging approach, an owner or operator may elect to control different groups of emission sources to different levels than specified the point-by-point approach, as long as the overall emissions do not exceed the overall allowable emission level. For example, an owner or operator can choose not to control a Group 1 emission source (or to control the emission source with a less effective control technique) if the owner or operator over-controls another emission source. For the point-by-point approach, NESHAP subpart G contains the following standards: • Group 1 process vents must reduce emissions of organic HAP using a flare meeting 40 CFR 63.11(b); reduce emissions of total organic HAP or TOC by 98 percent by weight or to an exit concentration of 20 ppmv, whichever is less stringent; or achieve and maintain a TRE index value 16 greater than 1.0. 17 16 See section III.C.3.a of this preamble for a description of the TRE index value and how the concept is currently used in the HON. 17 Halogenated vent streams (as defined in NESHAP subpart G) from Group 1 process vents may not be vented to a flare and must reduce the overall emissions of hydrogen halides and halogens by 99 percent (or 95 percent for control devices installed prior to December 31, 1992) or reduce the outlet mass emission rate of total hydrogen halides and halogens to less than 0.45 kg/hr. • Group 1 transfer racks must reduce emissions of total organic HAP by 98 percent by weight or to an exit concentration of 20 ppmv, whichever is less stringent; or reduce emissions of organic HAP using a flare meeting 40 CFR 63.11(b), using a vapor balancing system, or by routing emissions to a fuel gas system or to a process. • Group 1 storage vessels must reduce emissions of organic HAP using a fixed roof tank equipped with an IFR; using an external floating roof (EFR); using an EFR tank converted to a fixed roof tank equipped with an IFR; by routing emissions to a fuel gas system or to a process; or reduce emissions of organic HAP by 95 percent by weight using a closed vent system ( i.e., vapor collection system) and control device, or combination of control devices (or reduce emissions of organic HAP by 90 percent by weight using a closed vent system and control device if the control device was installed before December 31, 1992). • Group 1 process wastewater streams and equipment managing such streams at both new and existing sources must meet control requirements for: (1) Waste management units including wastewater tanks, surface impoundments, containers, individual drain systems, and oil-water separators; (2) treatment processes including the design steam stripper, biological treatment units, or other treatment devices; and (3) closed vent systems and control devices such as flares, catalytic incinerators, etc. Existing sources are not required to meet control requirements if Group 1 process wastewater streams are included in a 1 megagram per year source-wide exemption allowed by NESHAP subpart G. • In general, Group 2 emission sources are not required to apply any additional emission controls (provided they remain below Group 1 thresholds); however, they are subject to certain monitoring, reporting, and recordkeeping requirements to ensure that they were correctly determined to be Group 2 and that they remain Group 2. c. NESHAP Subpart H NESHAP subpart H contains the standard for equipment leaks at SOCMI facilities, including leak detection and repair (LDAR) provisions and other control requirements. Equipment regulated includes pumps, compressors, agitators, PRDs, sampling connection systems, OEL, valves, connectors, surge control vessels, bottoms receivers, and instrumentation systems in organic HAP service. A piece of equipment is in organic HAP service if it contains or contacts a fluid that is at least 5 percent by weight organic HAP. Depending on the type of equipment, the standards require either periodic monitoring for and repair of leaks, the use of specified equipment to minimize leaks, or specified work practices. Monitoring for leaks must be conducted using EPA Method 21 in appendix A-7 to 40 CFR part 60 or other approved equivalent monitoring techniques. d. NESHAP Subpart I NESHAP subpart I provides the applicability criteria for certain non-SOCMI processes subject to the negotiated regulation for equipment leaks. Regulated equipment is the same as that for NESHAP subpart H. 2. P&R I P&R I generally follows and refers to the requirements of the HON, with additional requirements for batch process vents. Generally, P&R I applies to EPPUs and associated equipment. Similar to a CMPU in the HON, an EPPU means a collection of equipment assembled and connected by hard-piping or duct work used to process raw materials and manufacture elastomer product. The EPPU includes unit operations, recovery operations, process vents, storage vessels, and equipment that are covered by equipment leak standards and produce one of the elastomer types listed as an elastomer product, including: butyl rubber, epichlorohydrin elastomer, ethylene propylene rubber, halobutyl rubber, Hypalon TM , neoprene, nitrile butadiene latex, nitrile butadiene rubber, polybutadiene rubber/styrene butadiene rubber by solution, polysulfide rubber, styrene butadiene latex, and styrene butadiene rubber by emulsion. An EPPU consists of more than one unit operation. An EPPU includes, as “equipment,” pumps, compressors, agitators, PRDs, sampling connection systems, OEL, valves, connectors, surge control vessels, bottoms receivers, instrumentation systems, and control devices or systems. The emissions sources affected by P&R I include heat exchange systems and maintenance wastewater at P&R I facilities regulated under NESHAP subpart F; storage vessels, transfer racks, and wastewater streams at P&R I facilities regulated under NESHAP subpart G; and equipment leaks at P&R I facilities regulated under NESHAP subpart H. Process vents are also regulated emission sources but, unlike the HON, these emissions sources are subdivided into front and back-end process vents in P&R I. The front-end are unit operations prior to and including the stripping operations. These are further subdivided into continuous front-end process vents regulated under NESHAP subpart G and batch front-end process vents that are regulated according to the requirements within P&R I. Back-end unit operations include filtering, coagulation, blending, concentration, drying, separating, and other finishing operations, as well as latex and crumb storage. The requirements for back-end process vents are not subcategorized into batch or continuous and are also found within P&R I. 3. P&R II P&R II regulates HAP emissions from two source categories, Epoxy Resins Production (also referred to as basic liquid epoxy resins or BLR) and Non-Nylon Polyamides Production (also referred to as wet strength resins or WSR). P&R II takes a different regulatory and format approach from P&R I but still refers to HON provisions for a portion of the standards. BLR are resins made by reacting epichlorohydrin and bisphenol A to form diglycidyl ether of bisphenol-A. WSR are polyamide/epichlorohydrin condensates which are used to increase the tensile strength of paper products. The emission sources affected by P&R II are all HAP emission points within a facility related to the production of BLR or WSR. These emission points include process vents, storage tanks, wastewater systems, and equipment leaks. Equipment includes connectors, pumps, compressors, agitators, PRDs, sampling connection systems, OEL, and instrumentation system in organic HAP service. Equipment leaks are regulated under the HON ( i.e., NESHAP subpart H). Process vents, storage tanks, and wastewater systems combined are regulated according to a production-based emission rate ( e.g., pounds HAP per million pounds BLR or WSR produced). For existing sources, the rate shall not exceed 130 pounds per 1 million pounds of BLR produced and 10 pounds per 1 million pounds of WSR produced. For new sources, BLR requires all uncontrolled emissions to achieve 98 percent reduction or limits the total emissions to 5,000 pounds of HAP per year. New WSR sources are limited to 7 pounds of HAP per 1 million pounds of WSR produced. 4. NSPS Subpart VVa NSPS subpart VVa contains VOC standards for leaks from equipment within a process unit for which construction, reconstruction, or modification commenced after November 7, 2006. Under NSPS subpart VVa, equipment means each pump, compressor, PRD, sampling connection system, OEL, valve, and flange or other connector in VOC service and any devices or systems required by the NSPS. Process units consist of components assembled to produce, as intermediate or final products, one or more of the chemicals listed in 40 CFR 60.489. A process unit can operate independently if supplied with sufficient feed or raw materials and sufficient storage facilities for the product. The standards in NSPS subpart VVa include LDAR provisions and other control requirements. A piece of equipment is in VOC service if it contains or contacts a fluid that is at least 10 percent by weight VOC. Depending on the type of equipment, the standards require either periodic monitoring for and repair of leaks, the use of specified equipment to minimize leaks, or specified work practices. Monitoring for leaks must be conducted using EPA Method 21 in appendix A-7 to 40 CFR part 60 or other approved equivalent monitoring techniques. 5. NSPS Subpart III NSPS subpart III regulates VOC emissions from SOCMI air oxidation reactors for which construction, reconstruction, or modification commenced after October 21, 1983. For the purpose of NSPS subpart III, air oxidation reactors are devices or process vessels in which one or more organic reactants are combined with air, or a combination of air and oxygen, to produce one or more organic compounds. The affected facility is designated as a single air oxidation reactor with its own individual recovery system (if any) or the combination of two or more air oxidation reactors and the common recovery system they share that produces one or more of the chemicals listed in 40 CFR 60.617 as a product, co-product, by-product, or intermediate. Owners and operators of an affected facility must reduce emissions of TOC (minus methane and ethane) by 98 percent by weight or to a concentration of 20 ppmv on a dry basis corrected to 3 percent oxygen, whichever is less stringent; combust the emissions in a flare meeting 40 CFR 60.18(b); or maintain a TRE index value 18 greater than 1.0 without use of VOC emission control devices. 18 See section III.C.3.b of this preamble for a description of the TRE index value and how the concept is currently used in NSPS Subpart III. 6. NSPS Subpart NNN NSPS subpart NNN regulates VOC emissions from SOCMI distillation operations for which construction, reconstruction, or modification commenced after December 30, 1983. For the purpose of NSPS subpart NNN, distillation operations are operations separating one or more feed stream(s) into two or more exit stream(s), each exit stream having component concentrations different from those in the feed stream(s); and the separation is achieved by the redistribution of the components between the liquid and vapor-phase as they approach equilibrium within a distillation unit. The affected facility is designated as a single distillation column with its own individual recovery system (if any) or the combination of two or more distillation columns and the common recovery system they share that is part of a process unit that produces any of the chemicals listed in 40 CFR 60.667 as a product, co-product, by-product, or intermediate. Owners and operators of an affected facility must reduce emissions of TOC (minus methane and ethane) by 98 percent by weight or to a concentration of 20 ppmv on a dry basis corrected to 3 percent oxygen, whichever is less stringent; combust the emissions in a flare meeting 40 CFR 60.18(b); or maintain a TRE index value 19 greater than 1.0 without use of VOC emission control devices. 19 See section III.C.3.b of this preamble for a description of the TRE index value and how the concept is currently used in NSPS Subpart NNN. 7. NSPS Subpart RRR NSPS subpart RRR regulates VOC emissions from SOCMI reactor processes for which construction, reconstruction, or modification commenced after June 29, 1990. For the purpose of NSPS subpart RRR, reactor processes are unit operations in which one or more chemicals, or reactants other than air, are combined or decomposed in such a way that their molecular structures are altered and one or more new organic compounds are formed. The affected facility is designated as a single reactor process with its own individual recovery system (if any) or the combination of two or more reactor processes and the common recovery system they share that is part of a process unit that produces any of the chemicals listed in 40 CFR 60.707 as a product, co-product, by-product, or intermediate. Owners and operators of an affected facility must reduce emissions of TOC (minus methane and ethane) by 98 percent by weight or to a concentration of 20 ppmv on a dry basis corrected to 3 percent oxygen, whichever is less stringent; combust the emissions in a flare meeting 40 CFR 60.18(b); or maintain a TRE index value 20 greater than 1.0 without use of VOC emission control devices. 20 See section III.C.3.b of this preamble for a description of the TRE index value and how the concept is currently used in NSPS Subpart RRR. C. What data collection activities were conducted to support this action? The EPA used several data sources to determine the facilities that are subject to the NESHAP and NSPS discussed in section II.B of this preamble. We identified facilities in the 2017 National Emissions Inventory (NEI) and the Toxics Release Inventory system having a primary facility NAICS code beginning with 325, Chemical Manufacturing. We also used information from the 2006 HON RTR, the 2008 and 2011 P&R RTRs, other internal chemical sector facility lists from the EPA's recent petrochemical sector RTR rulemakings ( e.g., Miscellaneous Organic Chemical Manufacturing NESHAP (MON), Organic Liquids Distribution (Non-Gasoline) NESHAP (OLD), Ethylene Production MACT standards (EMACT), and Petroleum Refinery MACT 1 standards (the Petroleum Refinery Sector rule)), and the Office of Enforcement and Compliance Assurance's (OECA) Enforcement and Compliance History Online (ECHO) tool ( https://echo.epa.gov ). To inform our reviews of our emission standards, we reviewed the EPA's Reasonably Available Control Technology (RACT)/Best Available Control Technology (BACT)/Lowest Achievable Emission Rate (LAER) Clearinghouse and regulatory development efforts for similar sources published after the rules that are subject to this proposal were developed. The EPA also reviewed air permits to determine facilities subject to the HON, and P&R I and P&R II. We also met with industry representatives from the American Chemistry Council, American Fuel & Petrochemical Manufacturers, and Vinyl Institute to collect data and discuss industry practices. In June 2021 and January 2022, the EPA issued requests, pursuant to CAA section 114, to collect information from HON facilities (one being also subject to P&R I and several being also subject to NSPS subparts III, NNN, and/or RRR) owned and operated by nine entities ( i.e., corporations). Many of the entities chosen have facilities that produce, use, and emit EtO or chloroprene, which are pollutants with considerable concern for cancer risk for the SOCMI and Neoprene Production source categories. This effort focused on gathering comprehensive information about process equipment, control technologies, point and fugitive emissions, and other aspects of facility operations. Companies submitted responses (and follow-up responses) to the EPA between March 2022 and December 2022 (for the January 2022 request). Additionally, as part of the January 2022 CAA section 114 requests, the EPA requested stack testing for certain emission sources ( e.g., pollutants for vent streams associated with each EtO production line). Also, the EPA required, as part of the January 2022 CAA section 114 request, that facilities conduct fugitive emission testing ( i.e., fenceline monitoring) for benzene, 1,3-butadiene, chloroprene, EtO, ethylene dichloride, or vinyl chloride. The results of the January 2022 requests were submitted to the EPA during the summer and fall of 2022. For the one facility that received a CAA section 114 request in June 2021, the EPA has received responses (and follow-up responses) from them in the fall and winter of 2021, and also began receiving fenceline monitoring data for chloroprene and 1,3-butadiene in January 2022 (and is continuing to receive this data). 21 The EPA has used the collected information to fill data gaps, establish the baseline emissions and control levels for purposes of the regulatory reviews, identify the most effective control measures, and estimate the public health and environmental and cost impacts associated with the regulatory options considered and reflected in this proposed action. The information not claimed as CBI by respondents is available in the document titled Data Received From Information Collection Request for Chemical Manufacturers, in the docket for this action, Docket ID No. EPA-HQ-OAR-2022-0730. A list of facilities located in the United States that are part of the SOCMI source category with processes subject to the HON, P&R I, P&R II, and/or the SOCMI NSPS (40 CFR part 60, subparts VVa, III, NNN, and RRR), is available in the document titled Lists of Facilities Subject to the HON, Group I and Group II Polymers and Resins NESHAPs, and NSPS subparts VV, VVa, III, NNN, and RRR, in the docket for this action, Docket ID No. EPA-HQ-OAR-2022-0730. 21 As fenceline monitoring data continues to be gathered for this facility, it is being posted on the following web page: https://www.epa.gov/la/denka-air-monitoring-data-summaries. D. What other relevant background information and data are available? As mentioned above, today's action includes proposed amendments to the current flare requirements in the SOCMI NSPS for air oxidation reactors, distillation columns, and reactor processes, and NESHAP for the HON and P&R I. In proposing these amendments, we relied on certain technical reports and memoranda that the EPA developed for flares used as APCDs in the Petroleum Refinery Sector residual risk and technology review and NSPS rulemaking (80 FR 75178, December 1, 2015). The Petroleum Refinery sector docket is at Docket ID No. EPA-HQ-OAR-2010-0682. For completeness of the rulemaking record for today's action and for ease of reference in finding these items in the publicly available petroleum refinery sector rulemaking docket, we are including the most relevant flare related technical support documents in the docket for this proposed action (Docket ID No. EPA-HQ-OAR-2022-0730) and including a list of all documents used to inform the 2015 flare provisions in the Petroleum Refinery Sector residual risk and technology review and NSPS rulemaking in the document titled Control Option Impacts for Flares Located in the SOCMI Source Category that Control Emissions from Processes Subject to HON and for Flares that Control Emissions from Processes Subject to Group I and Group II Polymers and Resins NESHAPs, which is available in the docket for this rulemaking. We are also relying on data gathered to support the RTRs for the EMACT standards, MON, and OLD NESHAP, as well as memoranda documenting the technology reviews for those processes. Many of the emission sources for ethylene production facilities, MON facilities, and OLD facilities are similar to HON, P&R I, and P&R II facilities, and several of the control options analyzed for the HON, and P&R I and P&R II, were also analyzed for the RTRs for the EMACT standards, MON, and OLD NESHAP. The memoranda and background technical information can be found in the Ethylene Production RTR rulemaking docket, Docket ID No. EPA-HQ-OAR-2017-0357; the MON RTR rulemaking docket, Docket ID No. EPA-HQ-OAR-2018-0746; and the OLD RTR rulemaking docket, Docket ID No. EPA-HQ-OAR-2018-0074. Additional information related to the promulgation and subsequent amendments of the NSPS subparts VVa, III, NNN, and RRR, the HON, and P&R I and P&R II is available in Docket ID Nos. A-80-25, A-81-22, A-83-29, A-90-19, EPA-HQ-OAR-2002-0026, EPA-HQ-OAR-2002-0281, EPA-HQ-OAR-2002-0284, EPA-HQ-OAR-2002-0475, EPA-HQ-OAR-2006-0699, EPA-HQ-OAR-2007-0211, and EPA-HQ-OAR-2010-0600. Lastly, the EPA acknowledges that there is also some unique ambient community monitoring data available for chloroprene concentrations near the Neoprene Production facility that was developed since 2016 separately from this rulemaking process. 22 This unique ambient community monitoring data includes data gathered by the EPA and the Louisiana Department of Environmental Quality and consists of short-term, 24-hour cannister sampling data gathered over various days throughout a four-year period both before and after the Neoprene Production facility installed controls to reduce emissions of chloroprene. The data generally indicate that concentrations in the community have decreased over time, but the current levels corroborate the need for further reductions. 22 https://www.epa.gov/la/denka-air-monitoring-data-summaries. Consistent with our usual practice in developing proposed rules under CAA section 112(f)(2), the EPA has conducted its risk assessment based on modeling of current allowable and/or actual emissions and projected future emissions. The EPA has not relied on the unique ambient community monitoring data for the Neoprene Production facility: (1) In assessing the remaining risk from chloroprene emissions from the SOCMI or Neoprene Production source categories after compliance with existing emission standards or (2) in projecting future risks that would remain after compliance with the proposed standards here. Consequently, the unique ambient community monitoring data is not part of our rulemaking record. The EPA relies on modeling, which is not dependent on the availability (or lack thereof) of monitoring data, to perform our risk assessments when developing residual risk analyses under CAA section 112(f)(2). Modeling provides the EPA with the ability and flexibility to estimate risks for all populations living near the sources across an impacted industrial source category, and to estimate various risk metrics, such as the MIR, cancer incidence, and number of people above specific risk thresholds. Modeling also allows the EPA to assess the risks that will remain after the implementation of proposed controls. With these caveats in mind, the EPA seeks comment on the relevance (if any) of the unique ambient community monitoring data to the EPA's rulemaking. E. How do we consider risk in our decision-making? As discussed in section II.A.1 of this preamble and in the 1989 Benzene NESHAP, in evaluating and developing standards under CAA section 112(f)(2), our longstanding and consistent policy is that we apply a two-step approach to determine whether or not risks are acceptable and to determine if the standards provide an ample margin of safety to protect public health. As explained in the 1989 Benzene NESHAP, “the first step judgment on acceptability cannot be reduced to any single factor” and, thus, “[t]he Administrator believes that the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information.” (54 FR 38046). 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 1989 Benzene NESHAP approach provides flexibility regarding factors the EPA may consider in making determinations and how the EPA may weigh those factors for each source category. The EPA conducts a risk assessment that provides estimates of the MIR posed by emissions of HAP that are carcinogens from each source in the source category, the hazard index (HI) for chronic exposures to HAP with the potential to cause noncancer health effects, and the hazard quotient (HQ) for acute exposures to HAP with the potential to cause noncancer health effects. 23 The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The scope of the EPA's risk analysis is consistent with the explanation in EPA's response to comments on our policy under the 1989 Benzene NESHAP: 23 The MIR is defined as the cancer risk associated with a lifetime of exposure at the highest concentration of HAP where people are likely to live. The HQ is the ratio of the potential HAP exposure concentration to the noncancer dose-response value; the HI is the sum of HQs for HAP that affect the same target organ or organ system. The policy chosen by the Administrator permits consideration of multiple measures of health risk. Not only can the MIR figure be considered, but also incidence, the presence of non-cancer health effects, and the uncertainties of the risk estimates. In this way, the effect on the most exposed individuals can be reviewed as well as the impact on the general public. These factors can then be weighed in each individual case. This approach complies with the Vinyl Chloride mandate that the Administrator ascertain an acceptable level of risk to the public by employing his expertise to assess available data. It also complies with the Congressional intent behind the CAA, which did not exclude the use of any particular measure of public health risk from the EPA's consideration with respect to CAA section 112 regulations, and thereby implicitly permits consideration of any and all measures of health risk which the Administrator, in his judgment, believes are appropriate to determining what will “protect the public health”. (54 FR 38057). Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risk. The 1989 Benzene NESHAP explained that “an MIR of approximately one in 10 thousand should ordinarily be the upper end of the range of acceptability. As risks increase above this benchmark, they become presumptively less acceptable under CAA section 112, and would be weighed with the other health risk measures and information in making an overall judgment on acceptability. Or, the Agency may find, in a particular case, that a risk that includes an MIR less than the presumptively acceptable level is unacceptable in the light of other health risk factors.” Id. at 38045. In other words, risks that include an MIR above 100-in-1 million may be determined to be acceptable, and risks with an MIR below that level may be determined to be unacceptable, depending on all of the available health information. Similarly, with regard to the ample margin of safety analysis, the EPA stated in the 1989 Benzene NESHAP that: “EPA believes the relative weight of the many factors that can be considered in selecting an ample margin of safety can only be determined for each specific source category. This occurs mainly because technological and economic factors (along with the health-related factors) vary from source category to source category.” Id. at 38061. We also consider the uncertainties associated with the various risk analyses, as discussed earlier in this preamble, in our determinations of acceptability and ample margin of safety. The EPA notes that it has not considered certain health information to date in making residual risk determinations. At this time, we do not attempt to quantify the HAP risk that may be associated with emissions from other facilities that do not include the source category under review, mobile source emissions, natural source emissions, persistent environmental pollution, or atmospheric transformation in the vicinity of the sources in the category. The EPA understands the potential importance of considering an individual's total exposure to HAP in addition to considering exposure to HAP emissions from the source category and facility. We recognize that such consideration may be particularly important when assessing noncancer risk, where pollutant-specific exposure health reference levels ( e.g., reference concentrations (RfCs)) are based on the assumption that thresholds exist for adverse health effects. For example, the EPA recognizes that, although exposures attributable to emissions from a source category or facility alone may not indicate the potential for increased risk of adverse noncancer health effects in a population, the exposures resulting from emissions from the facility in combination with emissions from all of the other sources ( e.g., other facilities) to which an individual is exposed may be sufficient to result in an increased risk of adverse noncancer health effects. In May 2010, the Science Advisory Board (SAB) advised the EPA “that RTR assessments will be most useful to decision makers and communities if results are presented in the broader context of aggregate and cumulative risks, including background concentrations and contributions from [Text truncated at 120,000 characters. The full text is on the page linked above.] --- Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A2023-07188. Public record. Not legal advice.