# Review of National Emission Standards for Hazardous Air Pollutants for Polyether Polyols Production Industry > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2024-29466 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** December 27, 2024 - **Citation:** 89 FR 105986 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 63 [EPA-HQ-OAR-2023-0282; FRL-10854-01-OAR] RIN 2060-AW01 Review of National Emission Standards for Hazardous Air Pollutants for Polyether Polyols Production Industry AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The U.S. Environmental Protection Agency (EPA) is proposing amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) under the Clean Air Act (CAA) that apply to the Polyether Polyols (PEPO) Production industry (referred to as the PEPO NESHAP in this document). The EPA is proposing decisions resulting from the Agency's technology review of the PEPO NESHAP and decisions 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 after considering the results of a risk assessment for the PEPO NESHAP. The EPA is also proposing to require performance testing once every 5 years, to add work practice standards for certain activities where alternatives are appropriate, and to add provisions for electronic reporting. We estimate that the proposed amendments to the PEPO NESHAP, excluding the EtO emission standards, would reduce hazardous air pollutant (HAP) emissions from PEPO sources by approximately 157 tons per year (tpy). Additionally, the proposed EtO emission standards are expected to reduce EtO emissions by approximately 14 tpy. We also estimate that these proposed amendments to the NESHAP will reduce excess emissions of HAP from flares in the PEPO Production source category by an additional 75 tpy. DATES: Comments. Comments must be received on or before February 25, 2025. 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 January 27, 2025. Public hearing. If anyone contacts us requesting a public hearing on or before January 3, 2025, we will hold a virtual public hearing. See SUPPLEMENTARY INFORMATION for information on requesting and registering for a public hearing. ADDRESSES: You may send comments, identified by Docket ID No. EPA-HQ-OAR-2023-0282, 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-2023-0282 in the subject line of the message. • Fax: 202-566-9744. Attention Docket ID No. EPA-HQ-OAR-2023-0282. • Mail: U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2023-0282, 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: For questions about this proposed action, contact U.S. EPA, Attn: Ms. Johanna Klein, Mail Drop: E143-01, 109 T.W. Alexander Drive, P.O. Box 12055, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-2283; and email address: klein.johanna@epa.gov. For specific information regarding the risk modeling methodology, contact U.S. EPA, Attn: Ms. Dianna Francisco, Mail Drop: C539-02, 109 T.W. Alexander Drive, P.O. Box 12055, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-3182; and email address: francisco.dianna@epa.gov. SUPPLEMENTARY INFORMATION: Participation in virtual public hearing. To request a virtual public hearing, contact the public hearing team at (888) 372-8699 or by email at SPPDpublichearing@epa.gov. If requested, the hearing will be held via virtual platform. The EPA will announce the date of the hearing and further details on the virtual public hearing at https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous. The hearing will convene at 11:00 a.m. Eastern Time (ET) and will conclude at 4:00 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 begin pre-registering speakers for the hearing no later than 1 business day after a request has been received. To register to speak at the virtual hearing, please use the online registration form available at https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous 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 January 13, 2025. Prior to the hearing, the EPA will post a general agenda that will list pre-registered speakers at: https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous. 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/polyether-polyols-production-national-emission-standards-hazardous. 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 January 7, 2025. The EPA may not be able to arrange accommodations without advance notice. Docket. The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2023-0282. 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 Regulations.gov . Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-2023-0282. 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 (FTP), 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: U.S. EPA, Attn: OAQPS Document Control Officer, Mail Drop: C404-02, 109 T.W. Alexander Drive, P.O. Box 12055, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2023-0282. 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: ACC American Chemistry Council 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 ANSI American National Standards Institute APCD air pollution control device ASME American Society of Mechanical Engineers ATSDR Agency for Toxic Substances and Disease Registry 1-BP 1-bromopropane BACT best available control technology 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 DNA deoxyribonucleic acid EAV equivalent annualized value ECHO Enforcement and Compliance History Online ECO extended cookout EFR external floating roof EIA Economic Impact Analysis EJ environmental justice EMACT Ethylene Production MACT EPA Environmental Protection Agency ERPG emergency response planning guidelines ERT Electronic Reporting Tool EtO ethylene oxide FID flame ionization detector FTIR Fourier transform infrared spectrometry 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 HRVOC highly reactive volatile organic compound ICR information collection request IFR internal floating roof IRIS Integrated Risk Information System ISA Integrated Science Assessment km kilometer kPa kilopascals LAER lowest achievable emission rate lb/hr pounds per hour LDAR leak detection and repair LEAN Louisiana Environmental Action Network LEL lower explosive limit MACT maximum achievable control technology 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 NO X nitrogen oxides 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 OLD Organic Liquids Distribution OMB Office of Management and Budget P&R I Group I Polymers and Resins NESHAP PDF portable document format PEPO polyether polyol PMPU polyether polyol manufacturing process unit POM polycyclic organic matter ppmv parts per million by volume ppmw parts per million by weight PRA Paperwork Reduction Act psia pounds per square inch absolute 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 RTR Risk and Technology Review SAB Science Advisory Board SCAQMD South Coast Air Quality Management District scmm standard cubic meters per minute scf standard cubic foot SOCMI Synthetic Organic Chemical Manufacturing Industry SO 2 sulfur dioxide SSM startup, shutdown, and malfunction TCEQ Texas Commission on Environmental Quality THF tetrahydrofuran TOC total organic compound 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 URE unit risk estimate U.S. United States U.S.C. United States Code USGS U.S. Geological Survey VCS voluntary consensus standards VOC volatile organic compound(s) μg/m3 micrograms per cubic meter Organization of this document. The information in this preamble is organized as follows: I. General Information A. Does this action apply to me? B. Where can I get a copy of this document and other related information? II. Background A. What is the statutory authority for this action? B. What is the source category and how do the current standards regulate its HAP emissions? C. What data collection activities were conducted to support this action? D. What other relevant background information and data are available? E. What outreach was conducted? III. Analytical Procedures and Decision-Making A. How do we consider risk in our decision-making? B. How do we estimate post-MACT risk posed by the source category? C. How do we perform the technology review? D. How do we determine a MACT floor and consider beyond-the-floor? IV. Analytical Results and Proposed Decisions A. What are the results of the risk assessment and analyses? B. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effect? C. What are the results and proposed decisions based on our technology review? D. What actions are we taking pursuant to CAA sections 112(d)(2) and (3) and 112(h)? E. What other actions are we proposing? F. What compliance dates are we proposing? V. 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? VI. Request for Comments VII. Submitting Data Corrections VIII. Statutory and Executive Order Reviews A. Executive Order 12866: Regulatory Planning and Review and Executive Order 14094: Modernizing 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 and Executive Order 14096: Revitalizing Our Nation's Commitment to Environmental Justice for All I. General Information A. Does this action apply to me? This action applies to the PEPO Production source category (and whose facilities, sources, and processes we often refer to as “PEPO” for purposes of the NESHAP). The PEPO NESHAP is codified at 40 CFR part 63, subpart PPP. The North American Industry Classification System (NAICS) code for PEPO facilities is 325199, although this is not intended to be exhaustive but rather to provide a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources. Federal, State, local, and Tribal government entities would not be affected by this proposed action. As defined in the Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990 (see 57 FR 31576, July 16, 1992) and Documentation for Developing the Initial Source Category List, Final Report (see EPA-450/3-91-030, July 1992), the PEPO Production source category is any facility which “manufactures these polymers by starting with cyclic ethers ( e.g., oxides, epoxides) and initiating polymerization by adding ethylene oxide, butylene oxide, propylene oxide or other chemicals which would result in the potential emission of HAPs. The reaction is base-catalyzed, with potassium hydroxide being the most commonly used catalyst. The physical properties of the polyols are influenced primarily by the functionality of the initiator molecules and by the type and quantity of alkylene oxide and hydroxyl groups present in the polyol.” 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, storage vessels, and wastewater collection and treatment systems. B. Where can I get a copy of this document and other related information? In addition to being available in the docket, an electronic copy of this action is available on the internet. In accordance with 5 U.S.C. 553(b)(4), a brief summary of this rulemaking may be found at https://www.regulations.gov, Docket ID No. EPA-HQ-OAR-2023-0282. 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/polyether-polyols-production-national-emission-standards-hazardous. Following publication in the Federal Register , the EPA will post the Federal Register version of the proposal and key technical documents at this same website. A memorandum showing the edits that would be necessary to incorporate the changes to the PEPO NESHAP (40 CFR part 63, subpart PPP) proposed in this action is available in the docket (Docket ID No. EPA-HQ-OAR-2023-0282). Following signature by the EPA Administrator, the EPA also will post a copy of this document to https://www.epa.gov/stationary-sources-air-pollution/polyether-polyols-production-national-emission-standards-hazardous. II. Background A. What is the statutory authority for this action? 1. NESHAP The statutory authority for this action is provided by sections 112 and 301 of the CAA, as amended (42 U.S.C. 7401 et seq. ). Section 112 of the CAA establishes a two-stage regulatory process to develop standards for emissions of HAP from stationary sources. Generally, the first stage involves establishing technology-based standards and the second stage involves evaluating those standards that are based on maximum achievable control technology (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, or 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 listed under section 112(c) and 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,” that the EPA must establish without consideration of costs. Under CAA section 112(d)(2), the EPA must also consider control options that are more stringent than the floor, taking into consideration costs, non-air quality health and environmental impacts, and energy requirements. Standards more stringent than the floor are commonly referred to as “beyond-the-floor” or “BTF” standards. In certain instances, as provided in CAA section 112(h), the EPA may set work practice standards in lieu of numerical emission 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 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 affirmed that CAA section 112(f)(2) incorporates the approach established in the 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) 1 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. 1 Although defined as “maximum individual risk,” MIR refers only to cancer risk. MIR, one metric for assessing cancer risk, is the estimated risk if an individual were exposed to the maximum level of a pollutant for a lifetime. CAA section 112(d)(6) separately requires the EPA to review standards promulgated under CAA section 112 and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less often than every 8 years. In conducting this review, which we call the “technology review,” the EPA is not required to recalculate the MACT floors that were established during earlier rulemakings. NRDC v. EPA, 529 F.3d at 1084 (D.C. Cir. 2008); 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 the source category. Louisiana Environmental Action Network (LEAN) v. EPA, 955 F.3d 1088 (D.C. Cir. 2020). The EPA conducted a residual risk and technology review (RTR) for the PEPO NESHAP in 2014, concluding that there was no need to revise the PEPO NESHAP under the provisions of either CAA sections 112(f) or (d)(6). However, the EPA did address emissions during periods of startup, shutdown, and malfunction (SSM), including from pressure relief devices (PRDs) in organic HAP service that release to the atmosphere, and also required electronic reporting of performance test results (see 79 FR 17340, March 27, 2014). As part of the 2014 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. This action constitutes another CAA section 112(d)(6) technology review for the PEPO NESHAP. This action also constitutes an updated CAA section 112(f) risk review based on new information for the PEPO NESHAP. As noted above, CAA section 112(f)(2)(A) requires the EPA to promulgate standards that “provide an ample margin of safety to protect public health” and prevent “an adverse environmental effect.” While CAA section 112(f) does not require the EPA to periodically revisit a residual risk review, neither does it preclude the EPA from exercising its inherent authority to revisit a previous regulatory decision where new scientific, technical, or other relevant information indicates such action is warranted. Moreover, the Act does include a gap-filling provision that reinforces the authority for the EPA to do so. CAA section 301(a)(1) provides authority to the Administrator “to prescribe such regulations as are necessary to carry out his functions” under the CAA. Such authority extends to the EPA's discretion to revisit its section 112(f) residual risk review where the Agency deems warranted. See NRDC v. EPA, 22 F.3d 1125, 1148 (D.C. Cir. 1994) (“[Section 301] is sufficiently broad to allow the promulgation of rules that are necessary and reasonable to effect the purposes of the Act.”). 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 PEPO NESHAP, the EPA retains discretion to revisit its residual risk reviews where the Agency deems that it 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 the 2006 residual risk review of the EtO emissions standards for sterilization facilities, the EPA asserted 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 a certain pollutant emitted by the PEPO Production source category led us to determine that it is appropriate, in this case, to conduct this second residual risk review under CAA section 112(f). In particular, the EPA is concerned about the cancer risks posed from the PEPO Production source category based on the EPA's 2016 updated Integrated Risk Information System (IRIS) inhalation unit risk estimate (URE) for EtO, which shows EtO to be significantly more toxic than previously known. 2 The EPA's 2014 RTR could not have had the benefit of this updated URE at the time it was conducted, but if it had the RTR would have necessarily resulted in different conclusions about risk acceptability and the PEPO NESHAP's provision of an ample margin of safety to protect public health. To ensure our standards provide an ample margin of safety to protect public health following the new IRIS inhalation URE for EtO, we are exercising our discretion and conducting a risk assessment in this action for PEPO Production sources. In sum, even though we do not have a mandatory duty to conduct repeated residual risk reviews under CAA sections 112(f)(2) and 301(a)(1), we have the authority to revisit any rulemaking if there is sufficient evidence of changes within the affected industry or significant new scientific information suggesting the public is exposed to higher risks than previously understood. Our conducting a discretionary second residual risk review for the PEPO Production source category to account for the new IRIS inhalation URE for EtO is consistent with recent similar actions regarding other source categories. See 89 FR 24090, April 5, 2024, and 89 FR 42932, May 16, 2024. 2 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. 2. Petition for Reconsideration In addition to the proposed action under sections 112 and 301 of the CAA described above, this action includes proposed amendments to the PEPO NESHAP based on the EPA's reconsideration of certain aspects of the NESHAP that were raised in an administrative petition submitted pursuant to section 307(d)(7)(B) of the CAA. In May 2014, the EPA received one petition for reconsideration of the PEPO NESHAP (40 CFR part 63, subpart PPP), Pesticide Active Ingredient Production NESHAP (40 CFR part 63, subpart MMM), and Group IV Polymers and Resins NESHAP (40 CFR part 63, subpart JJJ) pursuant to CAA section 307(d)(7)(B) from the Louisiana Environmental Action Network, Ohio Valley Environmental Coalition, and Sierra Club. 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-2023-0282). For the PEPO NESHAP, the petitioners requested that the EPA: (1) remove the affirmative defense provisions from the rules in light of the court opinion in Natural Resources Defence Council v. EPA (D.C. Cir. April 18, 2014); (2) provide adequate opportunity to comment on the requirements associated with emissions from PRDs (including associated compliance dates, the EPA's decision to not specifically require electronic indicators and alarms to monitor PRD releases to the atmosphere, and the standard's applicability to PRDs in organic HAP service versus PRDs in total HAP service); (3) redo the risk assessment using updated emission factors; (4) set additional monitoring requirements for flares to reduce flaring emissions; (5) set fenceline monitoring requirements; (6) reconsider its decision not to set standards that account for developments in leak detection and repair (LDAR); and (7) use existing regulatory authority to strengthen chemical facility safety and prevent accidents in accordance with the U.S. Chemical Safety and Hazard Investigation Board and Executive Order 13650. On August 26, 2014, the EPA sent a letter to the petitioners informing them that the EPA was granting their request for reconsideration at least on issues (1) and (2) above. A copy of the August 26, 2014, letter is provided in the docket for this rulemaking (see Docket No. EPA-HQ-OAR-2023-0282). In the letter, the EPA also indicated that it would be initiating a notice and comment rulemaking on the issues for which we granted reconsideration; therefore, one purpose of this action is to formally respond to the issues raised in the petition with respect to the PEPO NESHAP. 3 3 Although the issues identified in this paragraph (in addition to one other issue related to alternative compliance demonstration methods for periods of startup and shutdown) were also raised for 40 CFR part 63, subparts JJJ and MMM; this action does not respond to the reconsideration of these NESHAP, as the EPA is not reviewing these subparts in this action. In a separate rulemaking (see 89 FR 52425, June 24, 2024), the EPA is addressing issue (1), the affirmative defense against civil penalties for violations occurring during malfunctions. That separate rulemaking removes affirmative defense provisions from both NSPS and NESHAP rules, including the PEPO NESHAP. Therefore, this proposed action does not address removal of the affirmative defense provisions. This action presents the EPA's proposed revisions to the PEPO NESHAP based on the EPA's reconsideration of issue (2) in the petition (see section IV.E.1 of this preamble for details about these proposed amendments). Coincidentally, we also believe this action addresses issues (3), (4), (5), and (6) in our normal course of review of the PEPO NESHAP in accordance with sections 112 and 301 of the CAA. See sections IV.A and IV.B of this preamble for our proposed decisions relvant to issue (3), section IV.D.1 of this preamble for our proposed decisions relevant to issue (4), section IV.C.6 of this preamble for our proposed decisions relevant to issue (5), and sections IV.B.2.b and IV.C.5 of this preamble for our proposed decisions relevant to issue (6). With regard to issue (7), the EPA's authority to address catastrophic releases under the NESHAP program was viewed as limited under the pre-1990 CAA. Congress added CAA section 112(r) to address this gap. In light of the extensive history and efforts of the agency on inherently safer technology specifically and catastrophic accidents generally under the section 112(r) program, and in light of the statutory structure of section 112, we view the request to enact such provisions in this rulemaking to be outside the scope of section 112(f)(2) and section 112(d)(6). We note that the EPA's regulations on catastrophic releases appear in 40 CFR part 68. Prompted by Executive Order 13650, “Improving Chemical Facility Safety and Security,” the Risk Management Program regulations were amended on January 13, 2017, to include new provisions on safer technology and alternatives analysis and other prevention program elements; most recently, the regulations were amended on March 11, 2024, to further enhance the accident prevention and emergency preparedness requirements (89 FR 17622). B. What is the source category and how do the current standards regulate its HAP emissions? The source category that is the subject of this proposal is the PEPO Production source category subject to the PEPO NESHAP. The EPA promulgated the PEPO NESHAP on June 1, 1999 (64 FR 29420), and codified the NESHAP at 40 CFR part 63, subpart PPP. As promulgated in 1999, and further amended on July 1, 2004 (69 FR 39862) and March 27, 2014 (59 FR 17340), the PEPO NESHAP regulates HAP emissions from polyether polyol manufacturing process units (PMPUs) that produce PEPO as its primary product. 4 5 A PMPU consists of purification systems, reactors and their associated product separators and recovery devices, distillation units and their associated distillate receivers and recovery devices, other associated unit operations, storage vessels, surge control vessels, bottoms receivers, product transfer racks, connected ducts and piping, combustion, recovery, or recapture devices or systems. A PMPU also includes pumps, compressors, agitators, PRDs, sampling connection systems, open-ended valves or lines, valves, connectors, and instrumentation systems. 4 PEPO are compounds formed through the polymerization of EtO or propylene oxide or other cyclic ethers with compounds having one or more reactive hydrogens ( i.e., a hydrogen atom bonded to nitrogen, oxygen, phosphorus, sulfur, etc. ) to form polyethers ( i.e., compounds with two or more ether bonds). This definition of PEPO excludes cellulose ethers (such as methyl cellulose, carboxymethyl cellulose, hydroxyethyl cellulose, hydroxy ethyl cellulose, and hydroxypropyl methyl cellulose) and materials regulated under the HON, such as glycols and glycol ethers. 5 A PMPU also includes flexible operation process units when an owner or operator cannot determine that a PEPO is not the primary product, and a PEPO is produced or anticipated to be produced during time spans described in 40 CFR 63.1420(e)(2). PEPO are used to make a variety of other products including lubricants, adhesives, sealants, cosmetics, pharmaceuticals, soaps, and a feedstock for polyurethanes production. Urethane grade PEPO ( i.e., those that are free of water) are used as raw material in the production of polyurethanes, including slabstock and molded flexible foams, rigid foams and other polyurethanes, including microcellular products, surface coatings, elastomers, fibers, adhesives, and sealants. PEPO can be produced by either polymerization of epoxides ( i.e., a three-membered cyclic ether, such as EtO or propylene oxide) or tetrahydrofuran (THF). The former process is usually conducted as a batch process, while production of polyols using THF is generally a continuous process. EtO and propylene oxide are both HAP, but THF is not. For the MACT regulation, the EPA created two subcategories of PEPO based on the use of either epoxides or THF in polymerization. The HAP emission sources at PEPO facilities include process vents, storage vessels, equipment leaks, and wastewater. Additionally, some facilities have cooling towers or other heat exchangers which could become HAP emission sources if process fluids leak into the heat exchange water. In the production of PEPO, HAP are used primarily as reactants or extraction solvents. HAP emitted from PEPO facilities include EtO, propylene oxide, toluene, methanol, and glycol ethers. The MACT standards for PEPO production include emission limits for process vents; a combination of equipment standards and work practices for storage vessels, wastewater, and equipment leaks; and work practice standards for cooling towers. As of March 1, 2024, the EPA identified 25 PEPO facilities in operation that are subject to the PEPO NESHAP. The list of facilities located in the United States that are part of the PEPO Production source category with processes subject to the PEPO NESHAP is presented in the document titled List of Facilities Subject to the PEPO NESHAP, which is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2023-0282). 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 PEPO NESHAP 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 2014 PEPO NESHAP RTR, other facility lists from the EPA's recent chemical sector rulemakings ( e.g., HON), and the Office of Enforcement and Compliance Assurance's Enforcement and Compliance History Online (ECHO) tool ( https://echo.epa.gov ). To inform our reviews of the Agency's 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 PEPO NESHAP was developed. The EPA also reviewed air emissions permits issued by State regulatory agencies to determine facilities subject to the PEPO NESHAP. Additionally, we met with industry representatives from the American Chemistry Council (ACC) to collect data and discuss industry practices. In January 2022, the EPA issued requests, pursuant to CAA section 114, to collect information from synthetic organic chemical manufacturing industry (SOCMI) facilities subject to the hazardous organic NESHAP (HON) at 40 CFR part 63, subparts F, G, and H (nine facilities being also subject to the PEPO NESHAP) owned and operated by eight entities ( i.e., corporations). Many of the entities chosen for the CAA section 114 request own or operate facilities that produce, use, and emit EtO, which is a pollutant with considerable concern for cancer risk for the PEPO Production source category. This CAA section 114 request focused on gathering comprehensive information about process equipment, control technologies, point and fugitive emissions, and other aspects of facility operations. Additionally, 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 any of six specific HAP they emit: benzene; 1,3-butadiene; chloroprene; EtO; ethylene dichloride; and vinyl chloride. Companies submitted responses (and follow-up responses) and testing results to the EPA during the summer and fall of 2022. The EPA 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-2023-0282. D. What other relevant background information and data are available? As mentioned above, this action includes proposed amendments to the current flare requirements in the PEPO NESHAP. In proposing these amendments, we relied on certain technical reports and memoranda that the EPA developed for flares used as air pollution control devices (APCDs) in the Petroleum Refinery Sector RTR and new source performance standards (NSPS) rulemaking (80 FR 75178, December 1, 2015). The Petroleum Refinery Sector rulemaking docket is at Docket ID No. EPA-HQ-OAR-2010-0682. For completeness of the rulemaking record for this 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-2023-0282) and including a list of all documents used to inform the 2015 flare provisions in the Petroleum Refinery Sector RTR and NSPS rulemaking in the document titled Control Option Impacts for Flares in the PEPO Production Source Category that Control Emissions from Processes Subject to the PEPO NESHAP, which is available in the docket for this rulemaking. We are also relying on data gathered to support the rulemakings for the EMACT standards, HON, and MON, as well as memoranda documenting the technology reviews for those processes. Many of the emission sources for ethylene production facilities, HON facilities, and MON facilities are similar to PEPO facilities, so the EPA analyzed several control options for the PEPO NESHAP that the Agency also analyzed for the rulemakings for the EMACT standards, HON, and MON. 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 HON rulemaking docket (Docket ID No. EPA-HQ-OAR-2022-0730), and the MON RTR rulemaking docket (Docket ID No. EPA-HQ-OAR-2018-0746). Additional information related to the promulgation and subsequent amendments of the PEPO NESHAP is available in Docket ID Nos. A-96-38, EPA-HQ-OAR-2004-0467, and EPA-HQ-OAR-2011-0435. E. What outreach was conducted? We conducted pre-proposal outreach by sharing an overview of the industry and planned rulemaking to the EPA's national environmental justice (EJ) engagement call on August 20, 2024, and the EPA's monthly call with the National Tribal Air Association on August 31, 2023, and August 29, 2024. We also met with members of the ACC on August 13, 2024. The EPA also previously engaged in outreach activities with communities we expected to be impacted by chemical plants emitting EtO in 2021. 6 6 https://www.epa.gov/hazardous-air-pollutants-ethylene-oxide/inspector-general-follow-ethylene-oxide-0. III. Analytical Procedures and Decision-Making A. How do we consider risk in our decision-making? As discussed in section II.A of this preamble and in the Benzene NESHAP, in evaluating and developing standards under CAA section 112(f)(2), we apply a two-step approach to determine whether or not risks are acceptable and to determine if the standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, “the first step judgment on acceptability cannot be reduced to any single factor” and, thus, “[t]he Administrator believes that the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information.” (54 FR 38046). Similarly, with regard to the ample margin of safety determination, “the Agency again considers all of the health risk and other health information considered in the first step. Beyond that information, additional factors relating to the appropriate level of control will also be considered, including cost and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors.” Id. The Benzene NESHAP approach provides flexibility regarding factors the EPA may consider in making determinations and how the EPA may weigh those factors for each source category. The EPA conducts a risk assessment that provides estimates of the MIR posed by 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. 7 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 the EPA's response to comments on our policy under the 1989 Benzene NESHAP: 7 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 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 (1-in-10 thousand) 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 other sources in the area.” 8 8 Recommendations of the SAB Risk and Technology Review Methods Panel are provided in their report, which is available at: https://www.epa.gov/sites/default/files/2021-02/documents/epa-sab-10-007-unsigned.pdf. In response to the SAB recommendations, the EPA incorporates cumulative risk analyses into its RTR risk assessments. The Agency: (1) conducts facility-wide assessments, which include source category emission points, as well as other emission points within the facilities; (2) combines exposures from multiple sources in the same category that could affect the same individuals; and (3) for some persistent and bioaccumulative pollutants, analyzes the ingestion route of exposure. In addition, the RTR risk assessments consider aggregate cancer risk from all carcinogens and aggregated noncancer HQs for all noncarcinogens affecting the same target organ or target organ system. Although we are interested in placing source category and facility-wide HAP risk in the context of total HAP risk from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Estimates of total HAP risk from emission sources other than those that we have studied in depth during this RTR review would have significantly greater associated uncertainties than the source category or facility-wide estimates. While we evaluated the risk from HAP emitted by all stationary point sources near facilities within this source category in the community-based risk assessment, that assessment is intended to provide additional context to the public and was not used for decision-making in this proposed rule. B. How do we estimate post-MACT risk posed by the source category? In this section, we provide a complete description of the types of analyses that we generally perform during the risk assessment process. In some cases, we do not perform a specific analysis because it is not relevant. For example, in the absence of emissions of HAP known to be persistent and bioaccumulative in the environment (PB-HAP), we would not perform a multipathway exposure assessment. Where we do not perform an analysis, we state that we do not and provide the reason. While we present all of our risk assessment methods, we only present risk assessment results for the analyses actually conducted (see section IV.A of this preamble). The EPA conducts a risk assessment that provides estimates of the MIR for cancer posed by the HAP emissions from each source in the source category, the HI for chronic exposures to HAP with the potential to cause noncancer health effects, and the HQ for acute exposures to HAP with the potential to cause noncancer health effects. The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The nine sections that follow this paragraph describe how we estimated emissions and conducted the risk assessment. The docket for this rulemaking contains the following document which provides more information on the risk assessment inputs and models: Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule. The methods used to assess risk (as described in the nine primary steps below) are consistent with those described by the EPA in the document reviewed by a panel of the EPA's SAB in 2009; 9 and described in the SAB review report issued in 2010. They are also consistent with the key recommendations contained in that report. 9 U.S. EPA. Risk and Technology Review (RTR) Risk Assessment Methodologies: For Review by the EPA's Science Advisory Board with Case Studies—MACT I Petroleum Refining Sources and Portland Cement Manufacturing, June 2009. EPA-452/R-09-006. https://www3.epa.gov/airtoxics/rrisk/rtrpg.html. 1. How did we estimate actual emissions and identify the emissions release characteristics? As previously discussed, we updated the risk assessment in this action for the PEPO Production source category because the source category has sources that emit EtO. The EPA developed the list of 25 facilities for the PEPO Production source category as described in section II.B of this preamble. We developed the emissions modeling input files using the EPA's 2017 NEI. However, in a few instances where facility-specific data were not available or not reflective of current controls in the 2017 NEI, we obtained data from a more recent dataset ( e.g., review of emissions inventory data from our CAA section 114 request, more recent inventories submitted to States, or 2018 NEI). The EPA also used the NEI data to develop the other parameters needed to perform the risk modeling analysis including the emissions release characteristics, such as stack heights, stack diameters, volumetric flow rates, temperatures, and emission release point locations. For further details on the assumptions and methodologies used to estimate actual emissions, see appendix 1 of the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. 2. How did we estimate MACT-allowable emissions? The available emissions data in the RTR emissions dataset include estimates of the mass of HAP emitted during a specified annual time period. These “actual” emission levels are often lower than the emission levels allowed under the requirements of the current MACT standards. The emissions allowed under the MACT standards are referred to as the “MACT-allowable” emissions. We discussed the consideration of both MACT-allowable and actual emissions in the 2005 final RTR for Coke Oven Batteries (70 FR 19992, 19998-99, April 15, 2005) and in the 2006 proposed and final RTR for the HON (71 FR 34421, 34428, June 14, 2006, and 71 FR 76603, 76609, December 21, 2006, respectively). In those actions, we noted that assessing the risk at the MACT-allowable level is inherently reasonable since that risk reflects the maximum level facilities could emit and still comply with national emission standards. We also explained that it is reasonable to consider actual emissions, where such data are available, in both steps of the risk analysis, in accordance with the Benzene NESHAP approach. (54 FR 38044.) For this analysis, we have determined that the actual emissions data are reasonable estimates of the MACT-allowable emissions levels for the PEPO Production source category, as we are not generally aware of any situations in which a facility is conducting additional work practices or operating a control device such that it achieves a far greater emission reduction than required by the NESHAP. However, in cases where we encountered a permit emissions limit that appeared to be higher than the reported emissions, we recorded that in the allowable emissions column of the modeling file to assess the risk of allowable emissions. For further details on the assumptions and methodologies used to estimate MACT-allowable emissions, see appendix 1 of the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. 3. How do we conduct dispersion modeling, determine inhalation exposures, and estimate individual and population inhalation risk? Both long-term and short-term inhalation exposure concentrations and health risk from the source category addressed in this proposal were estimated using the Human Exposure Model (HEM-4). 10 The HEM-4 performs three primary risk assessment activities: (1) conducting dispersion modeling to estimate the concentrations of HAP in ambient air, (2) estimating long-term and short-term inhalation exposures to individuals residing within 50 kilometers (km) of the modeled sources, and (3) estimating individual and population-level inhalation risk using the exposure estimates and quantitative dose-response information. 10 For more information about HEM-4, go to https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem. a. Dispersion Modeling The air dispersion model AERMOD (American Meteorological Society/EPA Regulatory Model dispersion modeling system), used by the HEM-4, is one of the EPA's preferred models for assessing air pollutant concentrations from industrial facilities. 11 To perform the dispersion modeling and to develop the preliminary risk estimates, HEM-4 draws on three data libraries. The first is a library of meteorological data, which is used for dispersion calculations. This library includes 1 year (2019) of hourly surface and upper air observations from over 800 meteorological stations, selected to provide coverage of the United States and Puerto Rico. A second library of United States Census Bureau census block 12 internal point locations and populations provides the basis of human exposure calculations (U.S. Census, 2020). In addition, for each census block, the census library includes the elevation and controlling hill height, which are also used in dispersion calculations. A third library of pollutant-specific dose-response values is used to estimate health risk. These are discussed below. 11 U.S. EPA. Revision to the Guideline on Air Quality Models: Adoption of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions (70 FR 68218, November 9, 2005). 12 A census block is the smallest geographic area for which census statistics are tabulated. b. Risk From Chronic Exposure to HAP In developing the risk assessment for chronic exposures, we use the estimated annual average ambient air concentrations of each HAP emitted by each source in the source category. The HAP air concentrations at each nearby census block centroid located within 50 km of the facility are a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. A distance of 50 km is consistent with both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044) and the limitations of Gaussian dispersion models, including AERMOD. For each facility, we calculate the MIR as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, 52 weeks per year, 70 years) exposure to the maximum annual average concentration at the centroid of each inhabited census block. We calculate individual cancer risk by multiplying the estimated lifetime exposure to the ambient concentration of each HAP (in micrograms per cubic meter (μg/m 3 )) by its URE. The URE is an upper-bound estimate of an individual's incremental risk of contracting cancer over a lifetime of exposure to a concentration of 1 μg/m 3 of air. For residual risk assessments, we generally use UREs from the EPA's IRIS. For carcinogenic pollutants without IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) UREs, where available. In cases where new, scientifically credible dose-response values have been developed in a manner consistent with EPA guidelines and have undergone a peer review process similar to that used by the EPA, we may use such dose-response values in place of, or in addition to, other values, if appropriate. The pollutant-specific dose-response values used to estimate health risk are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants. To estimate individual lifetime cancer risks associated with exposure to HAP emissions from each facility in the source category, we sum the risks for each of the carcinogenic HAP 13 emitted by the modeled facility. We estimate cancer risk at every census block within 50 km of every facility in the source category. The MIR is the highest individual lifetime cancer risk estimated for any of those census blocks. In addition to calculating the MIR, we estimate the distribution of individual cancer risks for the source category by summing the number of individuals within 50 km of the sources whose estimated risk falls within a specified risk range. We also estimate annual cancer incidence by multiplying the estimated lifetime cancer risk at each census block by the number of people residing in that block, summing results for all of the census blocks, and then dividing this result by a 70-year lifetime. 13 The EPA's 2005 Guidelines for Carcinogen Risk Assessment classifies carcinogens as: “carcinogenic to humans,” “likely to be carcinogenic to humans,” and “suggestive evidence of carcinogenic potential.” These classifications also coincide with the terms “known carcinogen,” “probable carcinogen,” and “possible carcinogen,” respectively, which are the terms advocated in the EPA's Guidelines for Carcinogen Risk Assessment, published in 1986 (51 FR 33992, September 24, 1986). In August 2000, the document, Supplemental Guidance for Conducting Health Risk Assessment of Chemical Mixtures (EPA/630/R-00/002), was published as a supplement to the 1986 document. Copies of both documents can be obtained from https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944. Summing the risk of these individual compounds to obtain the cumulative cancer risk is an approach that was recommended by the EPA's SAB in their 2002 peer review of the EPA's National Air Toxics Assessment (NATA) titled NATA—Evaluating the National-scale Air Toxics Assessment 1996 Data—an SAB Advisory, available at https://yosemite.epa.gov/sab/sabproduct.nsf/214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf. To assess the risk of noncancer health effects from chronic exposure to HAP, we calculate either an HQ or a target organ-specific hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is emitted. Where more than one noncancer HAP is emitted, we sum the HQ for each of the HAP that affects a common target organ or target organ system to obtain a TOSHI. The HQ is the estimated exposure divided by the chronic noncancer dose-response value, which is a value selected from one of several sources. The preferred chronic noncancer dose-response value is the EPA RfC, defined as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime” ( https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary ). In cases where an RfC from the EPA's IRIS is not available or where the EPA determines that using a value other than the RfC is appropriate, the chronic noncancer dose-response value can be a value from the following prioritized sources, which define their dose-response values similarly to the EPA: (1) the Agency for Toxic Substances and Disease Registry (ATSDR) Minimal Risk Level ( https://www.atsdr.cdc.gov/mrls/index.asp ); (2) the CalEPA Chronic Reference Exposure Level (REL) ( https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0 ); or (3) as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with the EPA guidelines and has undergone a peer review process similar to that used by the EPA. The pollutant-specific dose-response values used to estimate health risks are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants. c. Risk From Acute Exposure to HAP That May Cause Health Effects Other Than Cancer For each HAP for which appropriate acute inhalation dose-response values are available, the EPA also assesses the potential health risks due to acute exposure. For these assessments, the EPA makes health protective assumptions about emission rates, meteorology, and exposure location. As part of our efforts to continually improve our methodologies to evaluate the risks that HAP emitted from categories of industrial sources pose to human health and the environment, 14 we revised our treatment of meteorological data to use reasonable worst-case air dispersion conditions in our acute risk screening assessments instead of worst-case air dispersion conditions. This revised treatment of meteorological data and the supporting rationale are described in more detail in the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule and in appendix 5 of the report Technical Support Document for Acute Risk Screening Assessment, which are available in the docket for this rulemaking. This revised approach has been used in this proposed rule and in all other RTR rulemakings proposed on or after June 3, 2019. 14 See, e.g., U.S. EPA. Screening Methodologies to Support Risk and Technology Reviews (RTR): A Case Study Analysis (Draft Report, May 2017. ( https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html ). To assess the potential acute risk to the maximally exposed individual, we use the peak hourly emission rate for each emission point, 15 reasonable worst-case air dispersion conditions ( i.e., 99th percentile), and the point of highest off-site exposure. Specifically, we assume that peak emissions from the source category and reasonable worst-case air dispersion conditions co-occur and that a person is present at the point of maximum exposure. 15 In the absence of hourly emission data, we develop estimates of maximum hourly emission rates by multiplying the average actual annual emissions rates by a factor (either a category-specific factor or a default factor of 10) to account for variability. This is documented in Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, and in appendix 5 of the report: Technical Support Document for Acute Risk Screening Assessment. Both of these documents are available in the docket for this rulemaking. To characterize the potential health risks associated with estimated acute inhalation exposures to a HAP, we generally use multiple acute dose-response values, including acute RELs, acute exposure guideline levels (AEGLs), and emergency response planning guidelines (ERPG) for 1-hour exposure durations, if available, to calculate acute HQs. The acute HQ is calculated by dividing the estimated acute exposure concentration by the acute dose-response value. For each HAP for which acute dose-response values are available, the EPA calculates acute HQs. An acute REL is defined as “the concentration level at or below which no adverse health effects are anticipated for a specified exposure duration.” 16 Acute RELs are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. They are designed to protect the most sensitive individuals in the population through the inclusion of margins of safety. Because margins of safety are incorporated to address data gaps and uncertainties, exceeding the REL does not automatically indicate an adverse health impact. AEGLs represent threshold exposure limits for the general public and are applicable to emergency exposures ranging from 10 minutes to 8 hours. 17 They are guideline levels for “once-in-a-lifetime, short-term exposures to airborne concentrations of acutely toxic, high-priority chemicals.” Id. at 21. The AEGL-1 is specifically defined as “the airborne concentration (expressed as ppm (parts per million) or mg/m3 (milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.” The document also notes that “Airborne concentrations below AEGL-1 represent exposure levels that can produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects.” Id. AEGL-2 are defined as “the airborne concentration (expressed as parts per million or milligrams per cubic meter) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.” Id. 16 CalEPA issues acute RELs as part of its Air Toxics Hot Spots Program, and the 1-hour and 8-hour values are documented in Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The Determination of Acute Reference Exposure Levels for Airborne Toxicants, which is available at https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary. 17 National Academy of Sciences, 2001. Standing Operating Procedures for Developing Acute Exposure Levels for Hazardous Chemicals, page 2. Available at https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf. Note that the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances ended in October 2011, but the AEGL program continues to operate at the EPA and works with the National Academies to publish final AEGLs ( https://www.epa.gov/aegl ). ERPGs are developed, by the American Industrial Hygiene Association (AIHA), for emergency planning and are intended to be health-based guideline concentrations for single exposures to chemicals. The ERPG-1 is the maximum airborne concentration, established by AIHA, below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or without perceiving a clearly defined, objectionable odor. Similarly, the ERPG-2 is the maximum airborne concentration, established by AIHA, below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action. An acute REL for 1-hour exposure durations is typically lower than its corresponding AEGL-1 and ERPG-1. Even though their definitions are slightly different, AEGL-1s are often the same as the corresponding ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from our acute inhalation screening risk assessment typically result when we use the acute REL for a HAP. In cases where the maximum acute HQ exceeds 1, we also report the HQ based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1). For the PEPO Production source category, we did not use a default acute emissions multiplier of 10, but rather we used process level-specific acute emissions multipliers, generally ranging from a factor of 2 to 10 as was done in past chemical and petrochemical residual risk reviews such as for the 2015 Petroleum Refinery Sector rule, 2024 HON rulemaking, 2020 MON RTR, and 2020 EMACT standards RTR, where similar emission sources and standards exist. These refinements are discussed more fully in appendix 1 of the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. In our acute inhalation screening risk assessment, acute impacts are deemed negligible for HAP for which acute HQs are less than or equal to 1, and no further analysis is performed for these HAP. In cases where an acute HQ from the screening step is greater than 1, we assess the site-specific data to ensure that the acute HQ is at an off-site location. For the PEPO Production source category, the data refinements employed consisted of reviewing satellite imagery of the locations of the maximum acute HQ values to determine if the maximum was off facility property. For any maximum value that was determined to be on facility property, the next highest value that was off facility property was used. These refinements are discussed more fully in the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. 4. How do we conduct the multipathway exposure and risk screening assessment? The EPA conducts a tiered screening assessment examining the potential for significant human health risks due to exposures via routes other than inhalation ( e.g., ingestion). We first determine whether any sources in the source category emit any HAP known to be persistent and bioaccumulative in the environment, as identified in the EPA's Air Toxics Risk Assessment Library (see Volume 1, appendix D, at https://www.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library). For the PEPO Production source category, we identified PB-HAP emissions of arsenic compounds, cadmium compounds, polycyclic organic matter (POM), and mercury, so we proceeded to the next step of the evaluation. Except for lead, the human health risk screening assessment for PB-HAP consists of three progressive tiers. In a Tier 1 screening assessment, we determine whether the magnitude of the facility-specific emissions of PB-HAP warrants further evaluation to characterize human health risk through ingestion exposure. To facilitate this step, we evaluate emissions against previously developed screening threshold emission rates for several PB-HAP that are based on a hypothetical upper-end screening exposure scenario developed for use in conjunction with the EPA's Total Risk Integrated Methodology—Fate, Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with screening threshold emission rates are arsenic compounds, cadmium compounds, chlorinated dibenzodioxins and furans, mercury compounds, and POM. Based on the EPA estimates of toxicity and bioaccumulation potential, these pollutants represent a health protective list for inclusion in multipathway risk assessments for RTR rules. (See Volume 1, Appendix D at https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf. ) In this assessment, we compare the facility-specific emission rates of these PB-HAP to the screening threshold emission rates for each PB-HAP to assess the potential for significant human health risks via the ingestion pathway. We call this application of the TRIM.FaTE model the Tier 1 screening assessment. The ratio of a facility's actual emission rate to the Tier 1 screening threshold emission rate is a “screening value.” We derive the Tier 1 screening threshold emission rates for these PB-HAP (other than lead compounds) to correspond to a maximum excess lifetime cancer risk of 1-in-1 million ( i.e., for arsenic compounds, polychlorinated dibenzodioxins and furans, and POM) or, for HAP that cause noncancer health effects ( i.e., cadmium compounds and mercury compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP or combination of carcinogenic PB-HAP in the Tier 1 screening assessment exceeds the Tier 1 screening threshold emission rate for any facility ( i.e., the screening value is greater than 1), we conduct a second screening assessment, which we call the Tier 2 screening assessment. The Tier 2 screening assessment separates the Tier 1 combined fisher and farmer exposure scenario into fisher, farmer, and gardener scenarios that retain upper-bound ingestion rates. In the Tier 2 screening assessment, the location of each facility that exceeds a Tier 1 screening threshold emission rate is used to refine the assumptions associated with the Tier 1 fisher and farmer exposure scenarios at that facility. A key assumption in the Tier 1 screening assessment is that a lake and/or farm is located near the facility. As part of the Tier 2 screening assessment, we use a U.S. Geological Survey (USGS) database to identify actual waterbodies within 50 km of each facility and assume the fisher only consumes fish from lakes within that 50-km zone. We also examine the differences between local meteorology near the facility and the meteorology used in the Tier 1 screening assessment. We then adjust the previously-developed Tier 1 screening threshold emission rates for each PB-HAP for each facility based on an understanding of how exposure concentrations estimated for the screening scenario change with the use of local meteorology and the USGS lakes database. In the Tier 2 farmer scenario, we maintain an assumption that the farm is located within 0.5 km of the facility and that the farmer consumes meat, eggs, dairy, vegetables, and fruit produced near the facility. We may further refine the Tier 2 screening analysis by assessing a gardener scenario to characterize a range of exposures, with the gardener scenario being more plausible in RTR evaluations. Under the gardener scenario, we assume the gardener consumes home-produced eggs, vegetables, and fruit products at the same ingestion rate as the farmer. The Tier 2 screen continues to rely on the high-end food intake assumptions that were applied in Tier 1 for local fish (adult female angler at 99th percentile fish consumption 18 ) and locally grown or raised foods (90th percentile consumption of locally grown or raised foods for the farmer and gardener scenarios 19 ). If PB-HAP emission rates do not result in a Tier 2 screening value greater than 1, we consider those PB-HAP emissions to pose risks below a level of concern. If the PB-HAP emission rates for a facility exceed the Tier 2 screening threshold emission rates, we may conduct a Tier 3 screening assessment. 18 Burger, J. 2002. Daily consumption of wild fish and game: Exposures of high end recreationists. International Journal of Environmental Health Research, 12:343-354. 19 U.S. EPA. Exposure Factors Handbook 2011 Edition (Final). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/052F, 2011. There are several analyses that can be included in a Tier 3 screening assessment, depending upon the extent of refinement warranted, including validating that the lakes are fishable, locating residential/garden locations for urban and/or rural settings, considering plume-rise to estimate emissions lost above the mixing layer, and considering hourly effects of meteorology and plume-rise on chemical fate and transport (a time-series analysis). If necessary, the EPA may further refine the screening assessment through a site-specific assessment. In evaluating the potential multipathway risk from emissions of lead compounds, rather than developing a screening threshold emission rate, we compare maximum estimated chronic inhalation exposure concentrations to the level of the current National Ambient Air Quality Standard (NAAQS) for lead. 20 Values below the level of the primary (health-based) lead NAAQS are considered to have a low potential for multipathway risk. 20 In doing so, the EPA notes that the legal standard for a primary NAAQS—that a standard is requisite to protect public health and provide an adequate margin of safety (CAA section 109(b))—differs from the CAA section 112(f) standard (requiring, among other things, that the standard provide an “ample margin of safety to protect public health”). However, the primary lead NAAQS is a reasonable measure of determining risk acceptability ( i.e., the first step of the 1989 Benzene NESHAP analysis) since it is designed to protect the most susceptible group in the human population—children, including children living near major lead emitting sources. 73 FR 67002/3; 73 FR 67000/3; 73 FR 67005/1. In addition, applying the level of the primary lead NAAQS at the risk acceptability step is conservative, since that primary lead NAAQS reflects an adequate margin of safety. For further information on the multipathway assessment approach, see the document titled Residual Risk Assessment for the Polyether Polyols ( PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. 5. How do we assess risks considering emissions control options? In addition to assessing baseline inhalation risks and screening for potential multipathway risks, we also estimate risks considering the potential emission reductions that would be achieved by the control options under consideration. In these cases, the expected emission reductions are applied to the specific HAP and emission points in the RTR emissions dataset to develop corresponding estimates of risk and incremental risk reductions. 6. How do we conduct the environmental risk screening assessment? a. Adverse Environmental Effect, Environmental HAP, and Ecological Benchmarks The EPA conducts a screening assessment to examine the potential for an adverse environmental effect as required under section 112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines “adverse environmental effect” as “any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.” The EPA focuses on eight HAP, which are referred to as “environmental HAP,” in its screening assessment: six PB-HAP and two acid gases. The PB-HAP included in the screening assessment are arsenic compounds, cadmium compounds, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), and lead compounds. The acid gases included in the screening assessment are hydrochloric acid (HCl) and hydrofluoric acid (HF). HAP that persist and bioaccumulate are of particular environmental concern because they accumulate in the soil, sediment, and water. The acid gases, HCl and HF, are included due to their well-documented potential to cause direct damage to terrestrial plants. In the environmental risk screening assessment, we evaluate the following four exposure media: terrestrial soils, surface water bodies (includes water-column and benthic sediments), fish consumed by wildlife, and air. Within these four exposure media, we evaluate nine ecological assessment endpoints, which are defined by the ecological entity and its attributes. For PB-HAP (other than lead), both community-level and population-level endpoints are included. For acid gases, the ecological assessment evaluated is terrestrial plant communities. An ecological benchmark represents a concentration of HAP that has been linked to a particular environmental effect level. For each environmental HAP, we identified the available ecological benchmarks for each assessment endpoint. We identified, where possible, ecological benchmarks at the following effect levels: probable effect levels, lowest-observed-adverse-effect level, and no-observed-adverse-effect level. In cases where multiple effect levels were available for a particular PB-HAP and assessment endpoint, we use all of the available effect levels to help us to determine whether ecological risks exist and, if so, whether the risks could be considered significant and widespread. For further information on how the environmental risk screening assessment was conducted, including a discussion of the risk metrics used, how the environmental HAP were identified, and how the ecological benchmarks were selected, see appendix 9 of the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. b. Environmental Risk Screening Methodology For the environmental risk screening assessment, the EPA first determined whether any facilities in the PEPO Production source category emitted any of the environmental HAP. For the PEPO Production source category, we identified emissions of arsenic compounds, cadmium compounds, POM, and mercury. 21 Because one or more of the environmental HAP evaluated are emitted by at least one facility in the PEPO Production source category, we proceeded to the second step of the evaluation. 21 We note that in many instances, we did not have sufficient information to parse out emissions from PEPO processes from facility-wide emissions inventories; thus, to avoid underestimating emissions from PEPO sources, we modeled most or all of certain facilities' emissions records as if they all are from the PEPO Production source category. c. PB-HAP Methodology The environmental screening assessment includes six PB-HAP, arsenic compounds, cadmium compounds, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), and lead compounds. With the exception of lead, the environmental risk screening assessment for PB-HAP consists of three tiers. The first tier of the environmental risk screening assessment uses the same health-protective conceptual model that is used for the Tier 1 human health screening assessment. TRIM.FaTE model simulations were used to back-calculate Tier 1 screening threshold emission rates. The screening threshold emission rates represent the emission rate in tons of pollutant per year that results in media concentrations at the facility that equal the relevant ecological benchmark. To assess emissions from each facility in the category, the reported emission rate for each PB-HAP was compared to the Tier 1 screening threshold emission rate for that PB-HAP for each assessment endpoint and effect level. If emissions from a facility do not exceed the Tier 1 screening threshold emission rate, the facility “passes” the screening assessment, and, therefore, is not evaluated further under the screening approach. If emissions from a facility exceed the Tier 1 screening threshold emission rate, we evaluate the facility further in Tier 2. In Tier 2 of the environmental screening assessment, the screening threshold emission rates are adjusted to account for local meteorology and the actual location of lakes in the vicinity of facilities that did not pass the Tier 1 screening assessment. For soils, we evaluate the average soil concentration for all soil parcels within a 7.5-km radius for each facility and PB-HAP. For the water, sediment, and fish tissue concentrations, the highest value for each facility for each pollutant. If emissions from a facility do not exceed the Tier 2 screening threshold emission rate, the facility “passes” the screening assessment and typically is not evaluated further. If emissions from a facility exceed the Tier 2 screening threshold emission rate, we evaluate the facility further in Tier 3. As in the multipathway human health risk assessment, in Tier 3 of the environmental screening assessment, we examine the suitability of the lakes around the facilities to support life and remove those that are not suitable ( e.g., lakes that have been filled in or are industrial ponds), adjust emissions for plume rise, and conduct hour-by-hour time-series assessments. If these Tier 3 adjustments to the screening threshold emission rates still indicate the potential for an adverse environmental effect ( i.e., facility emission rate exceeds the screening threshold emission rate), we may elect to conduct a more refined assessment using more site-specific information. If, after additional refinement, the facility emission rate still exceeds the screening threshold emission rate, the facility may have the potential to cause an adverse environmental effect. To evaluate the potential for an adverse environmental effect from lead, we compared the average modeled air concentrations (from HEM-4) of lead around each facility in the source category to the level of the secondary NAAQS for lead. The secondary lead NAAQS is a reasonable means of evaluating environmental risk because it is set to provide substantial protection against adverse welfare effects which can include “effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being.” d. Acid Gas Environmental Risk Methodology The environmental screening assessment for acid gases evaluates the potential phytotoxicity and reduced productivity of plants due to chronic exposure to HF and HCl. The environmental risk screening methodology for acid gases is a single-tier screening assessment that compares modeled ambient air concentrations (from AERMOD) to the ecological benchmarks for each acid gas. To identify a potential adverse environmental effect (as defined in section 112(a)(7) of the CAA) from emissions of HF and HCl, we evaluate the following metrics: the size of the modeled area around each facility that exceeds the ecological benchmark for each acid gas, in acres and square km; the percentage of the modeled area around each facility that exceeds the ecological benchmark for each acid gas; and the area-weighted average screening value around each facility (calculated by dividing the area-weighted average concentration over the 50-km modeling domain by the ecological benchmark for each acid gas). For further information on the environmental screening assessment approach, see appendix 9 of the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. 7. How do we conduct facility-wide assessments? To put the source category risks in context, we typically examine the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, we examine the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emission sources at the facility for which we have data. For the PEPO Production source category, we conducted the facility-wide assessment using a dataset compiled from the 2017 NEI and other emissions information discussed in section II.C of this preamble. Once a quality assured source category dataset was available, it was placed back with the remaining records from the NEI for that facility (which in most instances was 2017 NEI data). The facility-wide file was then used to analyze risks due to the inhalation of HAP that are emitted “facility-wide” for the populations residing within 50 km of each facility, consistent with the methods used for the source category analysis described above. For these facility-wide risk analyses, the modeled source category risks were compared to the facility-wide risks to determine the portion of the facility-wide risks that could be attributed to the source category addressed in this proposal. We also specifically examined the facility that was associated with the highest estimate of risk and determined the percentage of that risk attributable to the source category of interest. The document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, available through the docket for this rulemaking, provides the methodology and results of the facility-wide analyses, including all facility-wide risks and the percentage of source category contribution to facility-wide risks. 8. How do we conduct community-based risk assessments? In addition to the source category and facility-wide risk assessments, we also assessed the combined inhalation cancer risk from all local stationary sources of HAP for which we have emissions data. Specifically, we combined the modeled impacts from the facility-wide assessment (which includes category and non-category sources) with other nearby stationary point source model results. Section II.C of this preamble discusses the facility-wide emissions used in this assessment. For the other nearby point sources, we used AERMOD model results with emissions based primarily on the 2020 NEI. After combining these model results, we assessed cancer risks due to the inhalation of all HAP emitted by point sources for the populations residing within 10 km (~6.2 miles) of PEPO facilities. In the community-based risk assessment, we compared the modeled source category and facility-wide cancer risks to the cancer risks from other nearby point sources to determine the portion of the risks that could be attributed to the source category addressed in this proposal. The document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking, provides the methodology and results of the community-based risks analyses. 9. How do we consider uncertainties in risk assessment? Uncertainty and the potential for bias are inherent in all risk assessments, including those performed for this proposal. Although uncertainty exists, we believe that our approach, which used health protective tools and assumptions, ensures that our decisions are health and environmentally protective. A brief discussion of the uncertainties in the RTR emissions dataset, dispersion modeling, inhalation exposure estimates, and dose-response relationships follows below. Also included are those uncertainties specific to our acute screening assessments, multipathway screening assessments, and our environmental risk screening assessments. A more thorough discussion of these uncertainties is included in the document titled Residual Risk Assessment for the Polyether Polyols (PEPO) Production Source Category in Support of the 2024 Risk and Technology Review Proposed Rule, which is available in the docket for this rulemaking. If a multipathway site-specific assessment was performed for this source category, a full discussion of the uncertainties associated with that assessment can be found in appendix 11 of that document, Site-Specific Human Health Multipathway Residual Risk Assessment Report. a. Uncertainties in the RTR Emissions Dataset Although the development of the RTR emissions dataset involved quality assurance/quality control processes, the accuracy of emissions values will vary depending on the source of the data, the degree to which data are incomplete or missing, the degree to which assumptions made to complete the datasets are accurate, errors in emission estimates, and other factors. The emission estimates considered in this analysis generally are annual totals for certain years, and they do not reflect short-term fluctuations during the course of a year or variations from year to year. The estimates of peak hourly emission rates for the acute effects screening assessment were based on an emission adjustment factor applied to the average annual hourly emission rates, which are intended to account for emission fluctuations due to normal facility operations. b. Uncertainties in Dispersion Modeling We recognize there is uncertainty in ambient concentration estimates associated with any model, including the EPA's recommended regulatory dispersion model, AERMOD. In using a model to estimate ambient pollutant concentrations, the user chooses certain options to apply. For RTR assessments, we select some model options that have the potential to overestimate ambient air concentrations ( e.g., not including plume depletion or pollutant transformation). We select other model options that have the potential to underestimate ambient impacts ( e.g., not including building downwash). Other options that we select have the potential to either under- or overestimate ambient levels ( e.g., meteorology and receptor locations). On balance, considering the directional nature of the uncertainties commonly present in ambient concentrations estimated by dispersion models, the approach we apply in the RTR assessments should yield unbiased estimates of ambient HAP concentrations. We also note that the selection of meteorology dataset location could have an impact on the risk estimates. As we continue to update and expand our library of meteorological station data used in our risk assessments, we expect to reduce this variability. c. Uncertainties in Inhalation Exposure Assessment Although every effort is made to identify all of the relevant facilities and emission points, as well as to develop accurate estimates of the annual emission rates for all relevant HAP, the uncertainties in our emissions inventory likely dominate the uncertainties in the exposure assessment. Some uncertainties in our exposure assessment include human mobility, using the centroid of each census block, assuming lifetime exposure, and assuming only outdoor exposures. For most of these factors, there is neither an under nor overestimate when looking at the maximum individual risk or the incidence, but the shape of the distribution of risks may be affected. With respect to outdoor exposures, actual exposures may not be as high if people spend time indoors, especially for very reactive pollutants or larger particles. For all factors, we reduce uncertainty when possible. For example, with respect to census-block centroids, we analyze large blocks using aerial imagery and adjust locations of the block centroids to better represent the population in the blocks. We also add additional receptor locations where the population of a block is not well represented by a single location. d. Uncertainties in Dose-Response Relationships There are uncertainties inherent in the development of the dose-response values used in our risk assessments for cancer effects from chronic exposures and noncancer effects from both chronic and acute exposures. Some uncertainties are generally expressed quantitatively, and others are generally expressed in qualitative terms. We note, as a preface to this discussion, a point on dose-response uncertainty that is stated in the EPA's 2005 Guidelines for Carcinogen Risk Assessment; namely, that “the primary goal of EPA actions is protection of human health; accordingly, as an Agency policy, risk assessment procedures, including default options that are used in the absence of scientific data to the contrary, should be health protective” (the EPA's 2005 Guidelines for Carcinogen Risk Assessment, page 1-7). This is the approach followed here as summarized in the next paragraphs. Cancer UREs used in our risk assessments are those that have been developed to generally provide an upper bound estimate of risk. 22 That is, they represent a “plausible upper limit to the true value of a quantity” (although this is usually not a true statistical confidence limit). In some circumstances, the true risk could be as low as zero; however, in other circumstances the risk could be greater. 23 Chronic noncancer RfC and reference dose values represent chronic exposure levels that are intended to be health-protective levels. To derive dose-response values that are intended to be “without appreciable risk,” the methodology relies upon an uncertainty factor (UF) approach, 24 which considers uncertainty, variability, and gaps in the available data. The UFs are applied to derive dose-response values that are intended to protect against appreciable risk of deleterious effects. 22 IRIS glossary ( https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary ). 23 An exception to this is the URE for benzene, which is considered to cover a range of values, each end of which is considered to be equally plausible, and which is based on maximum likelihood estimates. 24 See A Review of the Reference Dose and Reference Concentration Processes, U.S. EPA, December 2002, and Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry, U.S. EPA, 1994. Many of the UFs used to account for variability and uncertainty in the development of acute dose-response values are quite similar to those developed for chronic durations. Additional adjustments are often applied to account for uncertainty in extrapolation from observations at one exposure duration ( e.g., 4 hours) to derive an acute dose-response value at another exposure duration ( e.g., 1 hour). Not all acute dose-response values are developed for the same purpose, and care must be taken when interpreting the results of an acute assessment of human health effects relative to the dose-response value or values being exceeded. Where relevant to the estimated exposures, the lack of acute dose-response values at different levels of severity should be factored into the risk characterization as potential uncertainties. Uncertainty also exists in the selection of ecological benchmarks for the environmental risk screening assessment. We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. We searched for benchmarks for three effect levels ( i.e., no-effects level, threshold-effect level, and probable-effect level), but not all combinations of ecological assessment/environmental HAP had benchmarks for all three effect levels. Where multiple effect levels were available for a particular HAP and assessment endpoint, we used all of the available effect levels to help us determine whether risk exists and whether the risk could be considered significant and widespread. Although we make every effort to identify appropriate human health effect dose-response values for all pollutants emitted by the sources in this risk assessment, some HAP emitted by the source category are lacking dose-response assessments. Accordingly, these pollutants cannot be included in the quantitative risk assessment, which could result in quantitative estimates understating HAP risk. To help to alleviate this potential underestimate, where we conclude similarity with a HAP for which a dose-response value is available, we use that value as a surrogate for the assessment of the HAP for which no value is available. To the extent use of surrogates indicates appreciable risk, we may identify a need to increase priority for an IRIS assessment for that substance. We additionally note that, generally speaking, HAP of greatest concern due to environmental exposures and hazard are those for which dose-response assessments have been performed, reducing the likelihood of understating risk. Further, HAP not included in the quantitative assessment are assessed qualitatively and considered in the risk characterization that informs the risk management decisions, including consideration of HAP reductions achieved by various control options. For a group of compounds that are unspeciated ( e.g., groups of compounds that we do not know the exact composition of like glycol ethers), we conservatively use the most protective dose-response value of an individual compound in that group to estimate risk. Similarly, for an individual compound in a group ( e.g., ethylene glycol diethyl ether) that does not have a specified dose-response value, we also apply the most protective dose-response value from the other compounds in the group to estimate risk. e. Uncertainties in Acute Inhalation Screening Assessments In addition to the uncertainties highlighted above, there are several factors specific to the acute exposure assessment that the EPA conducts as part of the risk review under section 112 of the CAA. The accuracy of an acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, meteorology, and the presence of a person. In the acute screening assessment that we conduct under the RTR program, we assume that peak emissions from the source category and reasonable worst-case air dispersion conditions ( i.e., 99th percentile) co-occur. We then include the additional assumption that a person is located at this point at the same time. Together, these assumptions represent a reasonable worst-case actual exposure scenario. In most cases, it is unlikely that a person would be located at the point of maximum exposure during the time when peak emissions and reasonable worst-case air dispersion conditions occur simultaneously. f. Uncertainties in the Multipathway and Environmental Risk Screening Assessments For each source category, we generally rely on site-specific levels of PB-HAP or environmental HAP emissions to determine whether a refined assessment of the impacts from multipathway exposures is necessary or whether it is necessary to perform an environmental screening assessment. This determination is based on the results of a three-tiered screening assessment that relies on the outputs from models—TRIM.FaTE and AERMOD—that estimate environmental pollutant concentrations and human exposures for five PB-HAP (dioxins, POM, mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For lead, we use AERMOD to determine ambient air concentrations, which are then compared to the secondary NAAQS standard for lead. Two important types of uncertainty associated with the use of these models in RTR risk assessments and inherent to any assessment that relies on environmental modeling are model uncertainty and input uncertainty. 25 25 In the context of this discussion, the term “uncertainty” as it pertains to exposure and risk encompasses both variability in the range of expected inputs and screening results due to existing spatial, temporal, and other factors, as well as uncertainty in being able to accurately estimate the true result. Model uncertainty concerns whether the model adequately represents the actual processes ( e.g., movement and accumulation) that might occur in the environment. For example, does the model adequately describe the movement of a pollutant through the soil? This type of uncertainty is difficult to quantify. However, based on feedback received from previous EPA SAB reviews and other reviews, we are confident that the models used in the screening assessments are appropriate and state-of-the-art for the multipathway and environmental screening risk assessments conducted in support of RTRs. Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier 1 of the multipathway and environmental screening assessments, we configured the models to avoid underestimating exposure and risk. This was accomplished by selecting upper-end values from nationally representative datasets for the more influential parameters in the environmental model, including selection and spatial configuration of the area of interest, lake location and size, meteorology, surface water, soil characteristics, and structure of the aquatic food web. We also assume an ingestion exposure scenario and values for human exposure factors that represent reasonable maximum exposures. In Tier 2 of the multipathway and environmental screening assessments, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values, and we identify the actual location of lakes near the facility rather than the default lake location that we apply in Tier 1. By refining the screening approach in Tier 2 to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screening assessment. In Tier 3 of the screening assessments, we refine the model inputs again to account for hour-by-hour plume-rise and the height of the mixing layer. We can also use those hour-by-hour meteorological data in a TRIM.FaTE run using the screening configuration corresponding to the lake location. These refinements produce a more accurate estimate of chemical concentrations in the media of interest, thereby reducing the uncertainty with those estimates. The assumptions and the associated uncertainties regarding the selected ingestion exposure scenario are the same for all three tiers. For the environmental screening assessment for acid gases, we employ a single-tiered approach. We use the modeled air concentrations and compare those with ecological benchmarks. For all tiers of the multipathway and environmental screening assessments, our approach to addressing model input uncertainty is generally cautious. We choose model inputs from the upper end of the range of possible values for the influential parameters used in the models, and we assume that the exposed individual exhibits ingestion behavior that would lead to a high total exposure. This approach reduces the likelihood of not identifying high risks for adverse impacts. Despite the uncertainties, when individual pollutants or facilities do not exceed screening threshold emission rates ( i.e., screen out), we are confident that the potential for adverse multipathway impacts on human health is very low. On the other hand, when individual pollutants or facilities do exceed screening threshold emission rates, it does not mean that impacts are significant, only that we cannot rule out that possibility and that a refined assessment for the site might be necessary to obtain a more accurate risk characterization for the source category. The EPA evaluates the following HAP in the multipathway and/or environmental risk screening assessments, where applicable: arsenic, cadmium, dioxins/furans, lead, mercury (both inorganic and methyl mercury), POM, HCl, and HF. These HAP represent pollutants that can cause adverse impacts either through direct exposure to HAP in the air or through exposure to HAP that are deposited from the air onto soils and surface waters and then throug [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%3A2024-29466. Public record. Not legal advice.