# National Emission Standards for Hazardous Air Pollutants: Nutritional Yeast Manufacturing Risk and Technology Review > Briefs, arguments, decisions, and more. URL: https://www.frixlaw.com/law-library/documents/fr%3A2016-30645 ## Record - **Collection:** Federal Register - **Document type:** Proposed Rule - **Published:** December 28, 2016 - **Citation:** 81 FR 95810 ## Text ENVIRONMENTAL PROTECTION AGENCY 40 CFR Part 63 [EPA-HQ-OAR-2015-0730; FRL-9956-21-OAR] RIN 2060-AS93 National Emission Standards for Hazardous Air Pollutants: Nutritional Yeast Manufacturing Risk and Technology Review AGENCY: Environmental Protection Agency (EPA). ACTION: Proposed rule. SUMMARY: The Environmental Protection Agency (EPA) is proposing amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP) for the Manufacturing of Nutritional Yeast source category. The proposed amendments address the results of the residual risk and technology reviews (RTRs) conducted as required under the Clean Air Act (CAA) as well as other actions deemed appropriate during the review of these standards. The proposed amendments include revising the form of the fermenter volatile organic compounds (VOC) emission limits, changing the testing and monitoring requirements, and updating the reporting and recordkeeping requirements. DATES: Comments. Comments must be received on or before February 13, 2017. 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, 2017. Public Hearing. A public hearing will be held, if requested by January 3, 2017. ADDRESSES: Comments. Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2015-0730, at http://www.regulations.gov . Follow the online instructions for submitting comments. Once submitted, comments cannot be edited or removed from Regulations.gov . The EPA may publish any comment received to its public docket. Do not submit electronically any information you consider to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. 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 . FOR FURTHER INFORMATION CONTACT: For questions about this proposed action, contact Allison Costa, Sector Policies and Programs Division (Mail Code E140), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-1322; fax number: (919) 541-3470; and email address: costa.allison@epa.gov . For specific information regarding the risk modeling methodology, contact Chris Sarsony, Health and Environmental Impacts Division (Mail Code C539-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-4843; fax number: (919) 541-0840; and email address: sarsony.chris@epa.gov . For information about the applicability of the NESHAP to a particular entity, contact Scott Throwe, Office of Enforcement and Compliance Assurance, U.S. Environmental Protection Agency, EPA WJC South Building (Mail Code 2227A), 1200 Pennsylvania Avenue NW., Washington, DC 20460; telephone number: (919) 564-7013; fax number: (202) 564-0050; and email address: throwe.scott@epa.gov . SUPPLEMENTARY INFORMATION: Docket. The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2015-0730. All documents in the docket are listed in the Regulations.gov index. Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the Internet and will be publicly available only in hard copy. Publicly available docket materials are available either electronically in Regulations.gov or in hard copy at the EPA Docket Center, Room 3334, EPA WJC West Building, 1301 Constitution Avenue NW., Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742. Instructions. Direct your comments to Docket ID No. EPA-HQ-OAR-2015-0730. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at http://www.regulations.gov , including any personal information provided, unless the comment includes information claimed to be CBI or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through http://www.regulations.gov or email. The http://www.regulations.gov Web site is an “anonymous access” system, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through http://www.regulations.gov , your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should 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 . Public Hearing. A public hearing will be held, if requested by January 3, 2017, to accept oral comments on this proposed action. If a hearing is requested, it will be held at the EPA's North Carolina campus located at 109 T.W. Alexander Drive, Research Triangle Park, NC 27711. The hearing, if requested, will begin at 9:00 a.m. (local time) and will conclude at 8:00 p.m. (local time). To request a hearing, to register to speak at a hearing, or to inquire if a hearing will be held, please contact Aimee St. Clair at (919) 541-1063 or by email at StClair.Aimee@epa.gov . The last day to pre-register to speak at a hearing, if one is held, will be January 10, 2017. Additionally, requests to speak will be taken the day of the hearing at the hearing registration desk, although preferences on speaking times may not be able to be fulfilled. Please note that registration requests received before the hearing will be confirmed by the EPA via email. The EPA will make every effort to accommodate all speakers who arrive and register. Because the hearing will be held at a U.S. governmental facility, individuals planning to attend the hearing should be prepared to show valid picture identification to the security staff in order to gain access to the meeting room. Please note that the REAL ID Act, passed by Congress in 2005, established new requirements for entering federal facilities. If your driver's license is issued by Alaska, American Samoa, Arizona, Kentucky, Louisiana, Maine, Massachusetts, Minnesota, Montana, New York, Oklahoma or the state of Washington, you must present an additional form of identification to enter the federal building. Acceptable alternative forms of identification include: federal employee badges, passports, enhanced driver's licenses and military identification cards. In addition, you will need to obtain a property pass for any personal belongings you bring with you. Upon leaving the building, you will be required to return this property pass to the security desk. No large signs will be allowed in the building, cameras may only be used outside of the building and demonstrations will not be allowed on federal property for security reasons. Please note that any updates made to any aspect of the hearing, including whether or not a hearing will be held, will be posted online at https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards . We ask that you contact Aimee St. Clair at (919) 541-1063 or by email at StClair.Aimee@epa.gov or monitor our Web site to determine if a hearing will be held. The EPA does not intend to publish a notice in the Federal Register announcing any such updates. Please go to https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards for more information on the public hearing. Preamble Acronyms and Abbreviations. We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here: AEGL Acute exposure guideline levels AERMOD Air dispersion model used by the HEM-3 model ATSDR Agency for Toxic Substances and Disease Registry CAA Clean Air Act CalEPA California EPA CBI Confidential Business Information CDX Central Data Exchange CEDRI Compliance and Emissions Data Reporting Interface CEMS Continuous emission monitoring system CFR Code of Federal Regulations EGU Electric generation unit EPA Environmental Protection Agency ERPG Emergency Response Planning Guidelines FR Federal Register HAP Hazardous air pollutants HCl Hydrochloric acid HEM-3 Human Exposure Model, Version 1.1.0 HF Hydrogen fluoride HI Hazard index HQ Hazard quotient ICR Information Collection Request IRIS Integrated Risk Information System km Kilometer MACT Maximum achievable control technology MATS Mercury Air Toxics Standard mg/kg-day Milligrams per kilogram per day mg/m 3 Milligrams per cubic meter MIR Maximum individual risk MON Miscellaneous organic chemical manufacturing NESHAP NAAQS National Ambient Air Quality Standards NAICS North American Industry Classification System NAS National Academy of Sciences NATA National Air Toxics Assessment NEI National Emissions Inventory NESHAP National emissions standards for hazardous air pollutants NO X Nitrogen oxides NRC National Research Council QA/QC Quality assurance/quality control OAQPS Office of Air Quality Planning and Standards OMB Office of Management and Budget PB-HAP Hazardous air pollutants known to be persistent and bio-accumulative in the environment POM Polycyclic organic matter ppmv Parts per million by volume PRA Paperwork Reduction Act PS Performance Specification RBLC RACT/BACT/LAER Clearinghouse REL Reference exposure level RFA Regulatory Flexibility Act RfC Reference concentration RfD Reference dose RTO Regenerative thermal oxidizer RTR Residual risk and technology review SAB Science Advisory Board SBA Small Business Administration SOP Standing Operating Procedures SSM Startup, shutdown, and malfunction TOSHI Target organ-specific hazard index tpy Tons per year TRIM.FaTE Total Risk Integrated Methodology. Fate, Transport, and Ecological Exposure model TTN Technology Transfer Network UF Uncertainty factor µg/m 3 Microgram per cubic meter UMRA Unfunded Mandates Reform Act URE Unit risk estimate VOC Volatile organic compounds 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? C. What should I consider as I prepare my comments for the EPA? II. Background A. What is the statutory authority for this action? B. What is this source category and how does the current NESHAP regulate its HAP emissions? C. What data collection activities were conducted to support this action? D. What other relevant background information and data are available? III. Analytical Procedures A. How did we estimate post-MACT risks posed by the source category? B. How did we consider the risk results in making decisions for this proposal? C. How did we perform the technology review? IV. Analytical Results and Proposed Decisions A. What are the results of the risk assessment and analyses? B. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effects? C. What are the results and proposed decisions based on our technology review? D. What other actions are we proposing? E. 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? 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 13563: Improving Regulation and Regulatory Review B. Paperwork Reduction Act (PRA) C. Regulatory Flexibility Act (RFA) D. Unfunded Mandates Reform Act (UMRA) E. Executive Order 13132: Federalism F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments G. Executive Order 13045: Protection of Children from Environmental Health Risks and Safety Risks H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use I. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR part 51 J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations I. General Information A. Does this action apply to me? Table 1 of this preamble lists the NESHAP and the associated regulated industrial source category that is the subject of this proposal. Table 1 is not intended to be exhaustive, but rather provides a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources. Federal, state, local, and tribal government entities would not be affected by this proposed action. As defined in the Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990 ( see 57 FR 31576, July 16, 1992), the Manufacturing of Nutritional Yeast source category includes any facility engaged in the manufacture of baker's yeast by fermentation (both active dry yeast and compressed yeast). The category includes, but is not limited to, the following manufacturing process units: fermentation vessels and the drying and packaging system. The original source category was named Baker's Yeast Manufacturing, but it was revised to Manufacturing of Nutritional Yeast to provide clarity on the scope (63 FR 55812, October 19, 1998). Table 1—NESHAP and Industrial Source Categories Affected By This Proposed Action NESHAP and source category NAICS code 1 Manufacturing of Nutritional Yeast 311999 1 North American Industry Classification System (NAICS). B. Where can I get a copy of this document and other related information? In addition to being available in the docket, an electronic copy of this action is available on the Internet. Following signature by the EPA Administrator, the EPA will post a copy of this proposed action at https://www.epa.gov/stationary-sources-air-pollution/manufacturing-nutritional-yeast-national-emission-standards . Following publication in the Federal Register , the EPA will post the Federal Register version of the proposal and key technical documents at this same Web site. Information on the overall RTR program is available at https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html . C. What should I consider as I prepare my comments for the EPA? Submitting CBI. Do not submit information containing CBI to the EPA through http://www.regulations.gov or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI for inclusion in the public docket. If you submit a CD-ROM or disk that does not contain CBI, mark the outside of the disk or CD-ROM clearly that it does not contain CBI. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver information identified as CBI only to the following address: OAQPS Document Control Officer (C404-02), OAQPS, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2015-0730. II. Background A. What is the statutory authority for this action? Section 112 of the CAA establishes a two-stage regulatory process to address emissions of hazardous air pollutants (HAP) from stationary sources. In the first stage, after the EPA has identified categories of sources emitting one or more of the HAP listed in CAA section 112(b), CAA section 112(d) requires us to promulgate technology-based NESHAP for those sources. “Major sources” are those that emit or have the potential to emit 10 tons per year (tpy) or more of a single HAP or 25 tpy or more of any combination of HAP. For major sources, 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) and are commonly referred to as maximum achievable control technology (MACT) standards. MACT standards must reflect the maximum degree of emissions reduction achievable through the application of measures, processes, methods, systems or techniques, including, but not limited to, measures that: (1) Reduce the volume of or eliminate pollutants through process changes, substitution of materials, or other modifications; (2) enclose systems or processes to eliminate emissions; (3) capture or treat pollutants when released from a process, stack, storage, or fugitive emissions point; (4) are design, equipment, work practice, or operational standards (including requirements for operator training or certification); or (5) are a combination of the above. CAA section 112(d)(2)(A)-(E). The MACT standards may take the form of design, equipment, work practice, or operational standards where the EPA first determines either that: (1) A pollutant cannot be emitted through a conveyance designed and constructed to emit or capture the pollutant, or that any requirement for, or use of, such a conveyance would be inconsistent with law; or (2) the application of measurement methodology to a particular class of sources is not practicable due to technological and economic limitations. CAA section 112(h)(1)-(2). The MACT “floor” is the minimum control level allowed for MACT standards promulgated under CAA section 112(d)(3) and may not be based on cost considerations. For new sources, the MACT floor cannot be less stringent than the emissions control that is achieved in practice by the best-controlled similar source. The MACT floor for existing sources can be less stringent than floors for new sources, but not less stringent than the average emissions limitation achieved by the best-performing 12 percent of existing sources in the category or subcategory (or the best-performing five sources for categories or subcategories with fewer than 30 sources). In developing MACT standards, the EPA must also consider control options that are more stringent than the floor. We may establish standards more stringent than the floor based on considerations of the cost of achieving the emission reductions, any non-air quality health and environmental impacts, and energy requirements. The EPA is then required to review these technology-based standards and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less frequently than every 8 years. CAA section 112(d)(6). In conducting this review, the EPA is not required to recalculate the MACT floor. Natural Resources Defense Council ( NRDC) v. EPA, 529 F.3d 1077, 1084 (D.C. Cir. 2008). Association of Battery Recyclers, Inc. v. EPA, 716 F.3d 667 (D.C. Cir. 2013). The second stage in standard-setting focuses on reducing any remaining ( i.e., “residual”) risk according to CAA section 112(f). CAA section 112(f)(1) required that the EPA prepare a report to Congress discussing (among other things) methods of calculating the risks posed (or potentially posed) by sources after implementation of the MACT standards, the public health significance of those risks, and the EPA's recommendations as to legislation regarding such remaining risk. The EPA prepared and submitted the “Residual Risk Report to Congress,” EPA-453/R-99-001 (“Risk Report”) in March 1999. CAA section 112(f)(2) then provides that if Congress does not act on any recommendation in the Risk Report, the EPA must analyze and address residual risk for each category or subcategory of sources 8 years after promulgation of such standards pursuant to CAA section 112(d). Section 112(f)(2) of the CAA requires the EPA to determine for source categories subject to MACT standards whether the emission standards provide an ample margin of safety to protect public health. Section 112(f)(2)(B) of the CAA expressly preserves the EPA's use of the two-step process for developing standards to address any residual risk and the Agency's interpretation of “ample margin of safety” developed in the National Emissions Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants (Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA notified Congress in the Risk Report that the Agency intended to use the Benzene NESHAP approach in making CAA section 112(f) residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently adopted this approach in its residual risk determinations and in a challenge to the risk review for the Synthetic Organic Chemical Manufacturing source category, the United States Court of Appeals for the District of Columbia Circuit upheld as reasonable the EPA's interpretation that CAA section 112(f)(2) incorporates the approach established in the Benzene NESHAP. See NRDC v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008)(“[S]ubsection 112(f)(2)(B) expressly incorporates the EPA's interpretation of the Clean Air Act from the Benzene standard, complete with a citation to the Federal Register .”); see also, A Legislative History of the Clean Air Act Amendments of 1990, vol. 1, p. 877 (Senate debate on Conference Report). The first step in the process of evaluating residual risk is the determination of acceptable risk. If risks are unacceptable, the EPA cannot consider cost in identifying the emissions standards necessary to bring risks to an acceptable level. The second step is the determination of whether standards must be further revised in order to provide an ample margin of safety to protect public health. The ample margin of safety is the level at which the standards must be set, unless an even more stringent standard is necessary to prevent, taking into consideration costs, energy, safety, and other relevant factors, an adverse environmental effect. 1. Step 1—Determination of Acceptability The Agency in the Benzene NESHAP concluded that “the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information” and that the “judgment on acceptability cannot be reduced to any single factor.” Benzene NESHAP at 38046. The determination of what represents an “acceptable” risk is based on a judgment of “what risks are acceptable in the world in which we live” (Risk Report at 178, quoting NRDC v. EPA, 824 F.2d 1146, 1165 (D.C. Cir. 1987) (en banc) (“Vinyl Chloride”), recognizing that our world is not risk-free. In the Benzene NESHAP, we stated that “EPA will generally presume that if the risk to [the maximum exposed] individual is no higher than approximately one in 10 thousand, that risk level is considered acceptable.” 54 FR at 38045, September 14, 1989. We discussed the maximum individual lifetime cancer risk (or maximum individual risk (MIR)) as being “the estimated risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years.” Id. We explained that this measure of risk “is an estimate of the upper bound of risk based on conservative assumptions, such as continuous exposure for 24 hours per day for 70 years.” Id. We acknowledged that maximum individual lifetime cancer risk “does not necessarily reflect the true risk, but displays a conservative risk level which is an upper-bound that is unlikely to be exceeded.” Id. Understanding that there are both benefits and limitations to using the MIR as a metric for determining acceptability, we acknowledged in the Benzene NESHAP that “consideration of maximum individual risk * * * must take into account the strengths and weaknesses of this measure of risk.” Id. Consequently, the presumptive risk level of 100-in-1 million (1-in-10 thousand) provides a benchmark for judging the acceptability of maximum individual lifetime cancer risk, but does not constitute a rigid line for making that determination. Further, in the Benzene NESHAP, we noted that: “[p]articular attention will also be accorded to the weight of evidence presented in the risk assessment of potential carcinogenicity or other health effects of a pollutant. While the same numerical risk may be estimated for an exposure to a pollutant judged to be a known human carcinogen, and to a pollutant considered a possible human carcinogen based on limited animal test data, the same weight cannot be accorded to both estimates. In considering the potential public health effects of the two pollutants, the Agency's judgment on acceptability, including the MIR, will be influenced by the greater weight of evidence for the known human carcinogen.” Id. at 38046. The Agency also explained in the Benzene NESHAP that: “[i]n establishing a presumption for MIR, rather than a rigid line for acceptability, the Agency intends to weigh it with a series of other health measures and factors. These include the overall incidence of cancer or other serious health effects within the exposed population, the numbers of persons exposed within each individual lifetime risk range and associated incidence within, typically, a 50 kilometers (km) exposure radius around facilities, the science policy assumptions and estimation uncertainties associated with the risk measures, weight of the scientific evidence for human health effects, other quantified or unquantified health effects, effects due to co-location of facilities, and co-emission of pollutants.” Id. at 38045. In some cases, these health measures and factors taken together may provide a more realistic description of the magnitude of risk in the exposed population than that provided by maximum individual lifetime cancer risk alone. As noted earlier, in NRDC v. EPA, the Court held that CAA section 112(f)(2) “incorporates the EPA's interpretation of the Clean Air Act from the Benzene Standard.” The Court further held that Congress' incorporation of the Benzene standard applies equally to carcinogens and non-carcinogens. 529 F.3d at 1081-82. Accordingly, we also consider non-cancer risk metrics in our determination of risk acceptability and ample margin of safety. 2. Step 2—Determination of Ample Margin of Safety CAA section 112(f)(2) requires the EPA to determine, for source categories subject to MACT standards, whether those standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, “the second step of the inquiry, determining an `ample margin of safety,' again includes consideration of all of the health factors, and whether to reduce the risks even further. . . . Beyond that information, additional factors relating to the appropriate level of control will also be considered, including costs and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors. Considering all of these factors, the agency will establish the standard at a level that provides an ample margin of safety to protect the public health, as required by section 112.” 54 FR 38046, September 14, 1989. According to CAA section 112(f)(2)(A), if the MACT standards for HAP “classified as a known, probable, or possible human carcinogen do not reduce lifetime excess cancer risks to the individual most exposed to emissions from a source in the category or subcategory to less than one in one million,” the EPA must promulgate residual risk standards for the source category (or subcategory), as necessary to provide an ample margin of safety to protect public health. In doing so, the EPA may adopt standards equal to existing MACT standards if the EPA determines that the existing standards ( i.e., the MACT standards) are sufficiently protective. NRDC v. EPA, 529 F.3d 1077, 1083 (D.C. Cir. 2008) (“If EPA determines that the existing technology-based standards provide an 'ample margin of safety,' then the Agency is free to readopt those standards during the residual risk rulemaking.”) The EPA must also adopt more stringent standards, if necessary, to prevent an adverse environmental effect, 1 but must consider cost, energy, safety, and other relevant factors in doing so. 1 “Adverse environmental effect” is defined as any significant and widespread adverse effect, which may be reasonably anticipated to wildlife, aquatic life, or natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental qualities over broad areas. CAA section 112(a)(7). The CAA does not specifically define the terms “individual most exposed,” “acceptable level,” and “ample margin of safety.” In the Benzene NESHAP, 54 FR 38044, September 14, 1989, we stated as an overall objective: In protecting public health with an ample margin of safety under section 112, EPA strives to provide maximum feasible protection against risks to health from hazardous air pollutants by (1) protecting the greatest number of persons possible to an individual lifetime risk level no higher than approximately 1-in-1 million and (2) limiting to no higher than approximately 1-in-10 thousand [ i.e., 100-in-1 million] the estimated risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years. The Agency further stated that “[t]he EPA also considers incidence (the number of persons estimated to suffer cancer or other serious health effects as a result of exposure to a pollutant) to be an important measure of the health risk to the exposed population. Incidence measures the extent of health risks to the exposed population as a whole, by providing an estimate of the occurrence of cancer or other serious health effects in the exposed population.” Id. at 38045. In the ample margin of safety decision process, the Agency again considers all of the health risks and other health information considered in the first step, including the incremental risk reduction associated with standards more stringent than the MACT standard or a more stringent standard that the EPA has determined is necessary to ensure risk is acceptable. In the ample margin of safety analysis, the Agency considers additional factors, including costs and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors. Considering all of these factors, the Agency will establish the standard at a level that provides an ample margin of safety to protect the public health, as required by CAA section 112(f). 54 FR 38046, September 14, 1989. B. What is this source category and how does the current NESHAP regulate its HAP emissions? In the original 1992 list of sources under CAA section 112(c)(1), the EPA defined the Baker's Yeast Manufacturing source category as including any facility engaged in the manufacture of baker's yeast by fermentation (both active dry yeast and compressed yeast) (57 FR 31576). The EPA explained that the category included, but was not limited to, the following manufacturing process units: Fermentation vessels and the drying and packaging system. The original source category was renamed to Manufacturing of Nutritional Yeast in 1998 to clarify that the source category covered the manufacturing of yeast, not its use in facilities such as breweries or bakeries. Both “baker's yeast” and “nutritional yeast” are common names for Saccharomyces cerevisiae, which is a specific species of yeast that is used to produce many common food and beverage products and whose manufacturing process typically emits HAP. The 40 CFR part 63, subpart CCCC NESHAP, which was finalized in 2001, defines a manufacturer of nutritional yeast as a facility that makes yeast for the purpose of becoming an ingredient in dough for bread or any other yeast-raised baked product, or for becoming a nutritional food additive intended for consumption by humans (66 FR 27876). Facilities that manufacture nutritional yeast intended for consumption by animals, such as an additive for livestock feed, are not included in the description of sources covered by this subpart in 40 CFR 63.2131. In addition, the NESHAP clarifies that fermenters are not subject to emission limits during the production of specialty yeast ( e.g., yeast for use in wine, champagne, whiskey, or beer) in 40 CFR 63.2132. We are not proposing to amend the source category definition in this action and are, therefore, not seeking comment on the source category definition at this time. Only facilities that are located at or are part of a major source of HAP emissions are subject to the Manufacturing of Nutritional Yeast NESHAP; area sources of HAP are not subject to the rule. The HAP emitted by nutritional yeast manufacturing facilities is acetaldehyde, a probable carcinogen. In 2016, there are four nutritional yeast manufacturing facilities that are subject to the NESHAP. The affected sources at nutritional yeast manufacturing facilities are the collection of equipment used to manufacture Saccharomyces cerevisiae yeast, including fermenters. The sizes of the fermenters vary; generally smaller fermenters are used for earlier fermentation stages and larger fermenters are used for later fermentation stages. The initial, smaller fermenters, where the sugar source is added only at the start of the batch ( e.g., laboratory and pure culture fermenters), are not subject to emission limits. The 40 CFR part 63, subpart CCCC emission limits apply to the final three stages of the fermentation process where the sugar source is added intermittently throughout the process, which are often referred to as stock (third-to-last stage), first generation (second-to-last stage), and trade (last stage) fermentation. Currently, the fermenters are subject to batch average VOC emission limits that differ for each fermentation stage, and which must be met for 98 percent of all batches in each fermentation stage on a rolling 12-month basis. VOC is used as a surrogate for the HAP of interest, acetaldehyde. The batch average VOC limits are 300 parts per million by volume (ppmv) for stock fermenters (third-to-last stage), 200 ppmv for first generation fermenters (second-to-last stage), and 100 ppmv for trade fermenters (last stage). In the current NESHAP, facilities can continuously monitor either the VOC concentration in the fermenter exhaust or the brew ethanol concentration in the fermenter liquid to determine compliance with the emission limits. If a facility monitors brew ethanol concentration, it must conduct an annual performance test to determine the correlation between the brew ethanol concentration in the fermenter liquid and the VOC concentration in the fermenter exhaust gas. C. What data collection activities were conducted to support this action? The EPA visited three nutritional yeast manufacturing facilities during the development of the NESHAP. Those facilities were the American Yeast and AB Mauri Fleischmann's Yeast facilities in Memphis, Tennessee, which we visited in December 2015, and the Red Star Yeast facility in Cedar Rapids, Iowa, which we visited in June 2016. We also held a conference call with the Minn-Dak Wahpeton facility, located in Wahpeton, North Dakota, in May 2016. The EPA discussed the specific yeast fermentation processes employed by each facility, including a discussion of the number and design of their fermenters and associated emission points, the process controls and monitors used, unregulated emission sources, and other aspects of facility operations. The site visits and conference call are documented in separate memoranda: “Site Visit Report—American Yeast Corporation, Memphis Plant,” “Site Visit Report—AB Mauri Fleischmann's Yeast, Memphis Plant,” “Site Visit Report—Red Star Yeast, Cedar Rapids, IA,” and “Notes from May 6, 2016 Conference Call Between the EPA and Minn-Dak Wahpeton,” which are available in the docket for this action. D. What other relevant background information and data are available? The EPA used information from the National Emissions Inventory (NEI) and the RACT/BACT/LAER Clearinghouse (RBLC) to support this proposed rulemaking. We used the NEI emissions and supporting data to develop the modeling file for the risk review. The EPA utilized the RBLC to identify additional control technologies for the technology review. See sections III.A, III.C, and IV.C of this preamble for further details on the use of these sources of information. III. Analytical Procedures In this section, we describe the analyses performed to support the proposed decisions for the RTR and other issues addressed in this proposal. A. How did we estimate post-MACT risks posed by the source category? The EPA conducted a risk assessment that provides estimates of the MIR posed by the HAP emissions from each source in the source category, the hazard index (HI) for chronic exposures to HAP with the potential to cause non-cancer health effects, and the hazard quotient (HQ) for acute exposures to HAP with the potential to cause non-cancer health effects. The assessment also provides estimates of the distribution of cancer risks within the exposed populations, cancer incidence, and an evaluation of the potential for adverse environmental effects. The eight 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 Manufacturing of Nutritional Yeast Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule.” The methods used to assess risks (as described in the eight primary steps below) are consistent with those peer-reviewed by a panel of the EPA's Science Advisory Board (SAB) in 2009 and described in their peer review report issued in 2010; 2 they are also consistent with the key recommendations contained in that report. 2 U.S. EPA SAB. Risk and Technology Review (RTR) Risk Assessment Methodologies: For Review by the EPA's Science Advisory Board with Case Studies—MACT I Petroleum Refining Sources and Portland Cement Manufacturing, May 2010. 1. How did we estimate actual emissions and identify the emissions release characteristics? Fermenters are the primary emission source at nutritional yeast facilities. Each fermenter emission source has a stack through which the emissions are vented. The HAP emitted is acetaldehyde, which is a by-product of the fermentation process. We used acetaldehyde emissions data from the 2011 NEI and state emission reports ( i.e., Iowa Emissions Inventory Questionnaire reports) as the basis of the actual emission estimates for each facility. The stack parameters used for each fermenter were obtained from the 2011 NEI, title V permits, or were provided to the Agency during site visits. We used default parameters if site-specific information was not available. Additional details on the data and methods used to develop actual emissions for the risk modeling are provided in the memorandum, “Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Manufacturing of Nutritional Yeast Source Category,” which is available in the docket for this action. 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 the specified annual time period. In some cases, these “actual” emission levels are lower than the emission levels required to comply with the current MACT standards. The emissions level allowed to be emitted by the MACT standards is referred to as the “MACT-allowable” emissions level. We discussed the use of both MACT-allowable and actual emissions in the final Coke Oven Batteries RTR (70 FR 19998-19999, April 15, 2005) and in the proposed and final Hazardous Organic NESHAP RTRs (71 FR 34428, June 14, 2006, and 71 FR 76609, December 21, 2006, respectively). In those actions, we noted that assessing the risks at the MACT-allowable level is inherently reasonable since these risks reflect the maximum level facilities could emit and still comply with national emission standards. We also explained that it is reasonable to consider actual emissions, where such data are available, in both steps of the risk analysis, in accordance with the Benzene NESHAP approach. (54 FR 38044, September 14, 1989.) For nutritional yeast manufacturing facilities, we used the actual emissions as the basis for the MACT-allowable emissions in the risk assessment. We set allowable emissions equal to actual emissions based on information gathered during the site visits that the facilities are operating near maximum capacity and close to the level of emissions allowed under the NESHAP. It is difficult to calculate a precise allowable emissions level for this industry because the emission limits are based on the average emissions concentration during each batch and the absolute number of batches produced at a facility fluctuates each year based on market demand for yeast. Furthermore, facilities are also unlikely to emit significantly higher levels of HAP due to a business incentive to minimize acetaldehyde emissions and continuous monitoring requirements in the rule. Acetaldehyde is a by-product of sub-optimal yeast production. Increasing concentrations of acetaldehyde indicate decreases relative to the potential amount and/or quality of yeast that can be produced within a fermentation batch, resulting in a loss of profit for the yeast manufacturer. Therefore, companies have a business incentive to reduce HAP emissions as much as possible. Additionally, continuous monitoring ensures that the facilities receive real-time information about emissions throughout the yeast manufacturing process. These monitoring systems have enabled facilities to set up control systems that automatically adjust process parameters in real-time to reduce emissions if they reach a specified level. As stated above, MACT-allowable emissions are used to develop estimates of risk when actual emissions are lower than those required to meet current emission standards. Due to the difficulties that limit the calculation of allowable emissions ( e.g., the current NESHAP standard requirements) and the low likelihood of facilities emitting significantly higher levels of HAP than current amounts, actual emissions provide the most accurate estimate of emissions that will be emitted from nutritional yeast manufacturing facilities. Therefore, we determined that the use of actual emissions as the basis of the MACT-allowable emissions in this risk assessment is the most appropriate option for this subpart. 3. How did we conduct dispersion modeling, determine inhalation exposures, and estimate individual and population inhalation risks? Both long-term and short-term inhalation exposure concentrations and health risks from the source category addressed in this proposal were estimated using the Human Exposure Model (Community and Sector HEM-3 version 1.1.0). The HEM-3 performs three primary risk assessment activities: (1) Conducting dispersion modeling to estimate the concentrations of HAP in ambient air, (2) estimating long-term and short-term inhalation exposures to individuals residing within 50 km of the modeled sources, 3 and (3) estimating individual and population-level inhalation risks using the exposure estimates and quantitative dose-response information. 3 This metric comes from the Benzene NESHAP. See 54 FR 38046. The air dispersion model used by the HEM-3 model (AERMOD) is one of the EPA's preferred models for assessing pollutant concentrations from industrial facilities. 4 To perform the dispersion modeling and to develop the preliminary risk estimates, HEM-3 draws on three data libraries. The first is a library of meteorological data, which is used for dispersion calculations. This library includes 1 year (2014) of hourly surface and upper air observations for more than 800 meteorological stations, selected to provide coverage of the United States and Puerto Rico. A second library of United States Census Bureau census block 5 internal point locations and populations provides the basis of human exposure calculations (U.S. Census, 2010). In addition, for each census block, the census library includes the elevation and controlling hill height, which are also used in dispersion calculations. A third library of pollutant unit risk factors and other health benchmarks is used to estimate health risks. These risk factors and health benchmarks are the latest values recommended by the EPA for HAP and other toxic air pollutants. These values are available at https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants and are discussed in more detail later in this section. 4 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). 5 A census block is the smallest geographic area for which census statistics are tabulated. In developing the risk assessment for chronic exposures, we used the estimated annual average ambient air concentrations of each HAP emitted by each source for which we have emissions data in the source category. The air concentrations at each nearby census block centroid were used as a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. We calculated the MIR for each facility as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, and 52 weeks per year for a 70-year period) exposure to the maximum concentration at the centroid of inhabited census blocks. Individual cancer risks were calculated by multiplying the estimated lifetime exposure to the ambient concentration of each of the HAP (in micrograms per cubic meter (μg/m 3 )) by its unit risk estimate (URE). The URE is an upper bound estimate of an individual's probability of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the pollutant per cubic meter of air. For residual risk assessments, we generally use URE values from the EPA's Integrated Risk Information System (IRIS). For carcinogenic pollutants without IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) URE values, where available. In cases where new, scientifically credible dose response values have been developed in a manner consistent with the EPA guidelines and have undergone a peer review process similar to that used by the EPA, we may use such dose-response values in place of, or in addition to, other values, if appropriate. The EPA estimated incremental individual lifetime cancer risks associated with emissions from the facilities in the source category as the sum of the risks for each of the carcinogenic HAP (including those classified as carcinogenic to humans, likely to be carcinogenic to humans, and suggestive evidence of carcinogenic potential) 6 emitted by the modeled sources. Cancer incidence and the distribution of individual cancer risks for the population within 50 km of the sources were also estimated for the source category as part of this assessment by summing individual risks. A distance of 50 km is consistent with both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044, September 14, 1989) and the limitations of Gaussian dispersion models, including AERMOD. 6 These classifications also coincide with the terms “known carcinogen, probable carcinogen, and possible carcinogen,” respectively, which are the terms advocated in the EPA's previous “Guidelines for Carcinogen Risk Assessment,” published in 1986 (51 FR 33992, September 24, 1986). Summing the risks of these individual compounds to obtain the cumulative cancer risks is an approach that was recommended by the EPA's SAB in their 2002 peer review of the EPA's National Air Toxics Assessment (NATA) titled, “NATA—Evaluating the National-scale Air Toxics Assessment 1996 Data—an SAB Advisory,” available at http://yosemite.epa.gov/sab/sabproduct.nsf/214C6E915BB04E14852570CA007A682C/$File/ecadv02001.pdf . To assess the risk of non-cancer health effects from chronic exposures, we summed the HQ for each of the HAP that affects a common target organ system to obtain the HI for that target organ system (or target organ-specific HI, TOSHI). The HQ is the estimated exposure divided by the chronic reference value, which is a value selected from one of several sources. First, the chronic reference level can be the EPA reference concentration (RfC) ( https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=Risk %20Assessment%20Glossary ), defined as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.” Alternatively, in cases where an RfC from the EPA's IRIS database is not available or where the EPA determines that using a value other than the RfC is appropriate, the chronic reference level can be a value from the following prioritized sources: (1) The Agency for Toxic Substances and Disease Registry Minimum Risk Level ( http://www.atsdr.cdc.gov/mrls/index.asp ), which is defined as “an estimate of daily human exposure to a hazardous substance that is likely to be without an appreciable risk of adverse non-cancer health effects (other than cancer) over a specified duration of exposure”; (2) the CalEPA Chronic Reference Exposure Level (REL) ( http://oehha.ca.gov/media/downloads/crnr/2015guidancemanual.pdf ), which is defined as “the concentration level (that is expressed in units of micrograms per cubic meter (μg/m 3 ) for inhalation exposure and in a dose expressed in units of milligram per kilogram-day (mg/kg-day) for oral exposures), at or below which no adverse health effects are anticipated for a specified exposure duration”; or (3), as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with the EPA guidelines and has undergone a peer review process similar to that used by the EPA, in place of or in concert with other values. As mentioned above, in order to characterize non-cancer chronic effects, and in response to key recommendations from the SAB, the EPA selects dose-response values that reflect the best available science for all HAP included in RTR risk assessments. 7 More specifically, for a given HAP, the EPA examines the availability of inhalation reference values from the sources included in our tiered approach ( e.g., IRIS first, Agency for Toxic Substances and Disease Registry (ATSDR) second, CalEPA third) and determines which inhalation reference value represents the best available science. Thus, as new inhalation reference values become available, the EPA will typically evaluate them and determine whether they should be given preference over those currently being used in RTR risk assessments. 7 The SAB peer review of RTR Risk Assessment Methodologies is available at http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf . The EPA also evaluated screening estimates of acute exposures and risks for each of the HAP (for which appropriate acute dose-response values are available) at the point of highest potential off-site exposure for each facility. To do this, the EPA estimated the risks when both the peak hourly emissions rate and worst-case dispersion conditions occur. We also assume that a person is located at the point of highest impact during that same time. In accordance with our mandate in section 112 of the CAA, we use the point of highest off-site exposure to assess the potential risk to the maximally exposed individual. The acute HQ is the estimated acute exposure divided by the acute dose-response value. In each case, the EPA calculated acute HQ values using best available, short-term dose-response values. These acute dose-response values, which are described below, include the acute REL, acute exposure guideline levels (AEGL) and emergency response planning guidelines (ERPG) for 1-hour exposure durations. As discussed below, we used conservative assumptions for emissions rates, meteorology, and exposure location. As described in the CalEPA's “Air Toxics Hot Spots Program Risk Assessment Guidelines, Part I, The Determination of Acute Reference Exposure Levels for Airborne Toxicants,” an acute REL value ( http://oehha.ca.gov/media/downloads/crnr/acuterel.pdf ) is defined as “the concentration level at or below which no adverse health effects are anticipated for a specified exposure duration.” Id. at page 2. Acute REL values are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. Acute REL values are designed to protect the most sensitive individuals in the population through the inclusion of margins of safety. Because margins of safety are incorporated to address data gaps and uncertainties, exceeding the REL does not automatically indicate an adverse health impact. AEGL values were derived in response to recommendations from the National Research Council (NRC). As described in “Standing Operating Procedures (SOP) of the National Advisory Committee on Acute Exposure Guideline Levels for Hazardous Substances” ( https://www.epa.gov/sites/production/files/2015-09/documents/sop_final_standing_operating_procedures_2001.pdf ), 8 “the NRC's previous name for acute exposure levels—community emergency exposure levels was replaced by the term AEGL to reflect the broad application of these values to planning, response, and prevention in the community, the workplace, transportation, the military, and the remediation of Superfund sites.” Id. at 2. This document also states that AEGL values “represent threshold exposure limits for the general public and are applicable to emergency exposures ranging from 10 minutes to eight hours.” Id. at 2. 8 National Academy of Sciences (NAS), 2001. Standing Operating Procedures for Developing Acute Exposure Levels for Hazardous Chemicals, page 2. The document lays out the purpose and objectives of AEGL by stating that “the primary purpose of the AEGL program and the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances is to develop guideline levels for once-in-a-lifetime, short-term exposures to airborne concentrations of acutely toxic, high-priority chemicals.” Id. at 21. In detailing the intended application of AEGL values, the document states that “[i]t is anticipated that the AEGL values will be used for regulatory and nonregulatory purposes by U.S. Federal and state agencies and possibly the international community in conjunction with chemical emergency response, planning, and prevention programs. More specifically, the AEGL values will be used for conducting various risk assessments to aid in the development of emergency preparedness and prevention plans, as well as real-time emergency response actions, for accidental chemical releases at fixed facilities and from transport carriers.” Id. at 31. The AEGL-1 value is then specifically defined as “the airborne concentration (expressed as ppm (parts per million) or mg/m 3 (milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.” Id. at 3. The document also notes that, “Airborne concentrations below AEGL-1 represent exposure levels that can produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects.” Id. Similarly, the document defines AEGL-2 values as “the airborne concentration (expressed as parts per million or milligrams per cubic meter) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.” Id. ERPG values are derived for use in emergency response, as described in the American Industrial Hygiene Association's ERP Committee document titled, “ERPGS Procedures and Responsibilities” ( https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf ), which states that, “Emergency Response Planning Guidelines were developed for emergency planning and are intended as health based guideline concentrations for single exposures to chemicals.” 9 Id. at 1. The ERPG-1 value is defined as “the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to 1 hour without experiencing other than mild transient adverse health effects or without perceiving a clearly defined, objectionable odor.” Id. at 2. Similarly, the ERPG-2 value is defined as “the maximum airborne concentration below which it is believed that nearly all individuals could be exposed for up to one hour without experiencing or developing irreversible or other serious health effects or symptoms which could impair an individual's ability to take protective action.” Id. at 1. 9 ERP Committee Procedures and Responsibilities. March 2014. American Industrial Hygiene Association. As can be seen from the definitions above, the AEGL and ERPG values include the similarly-defined severity levels 1 and 2. For many chemicals, a severity level 1 value AEGL or ERPG has not been developed because the types of effects for these chemicals are not consistent with the AEGL-1/ERPG-1 definitions; in these instances, we compare higher severity level AEGL-2 or ERPG-2 values to our modeled exposure levels to screen for potential acute concerns. When AEGL-1/ERPG-1 values are available, they are used in our acute risk assessments. Acute REL values for 1-hour exposure durations are typically lower than their corresponding AEGL-1 and ERPG-1 values. Even though their definitions are slightly different, AEGL-1 values are often the same as the corresponding ERPG-1 values, and AEGL-2 values are often equal to ERPG-2 values. Maximum HQ values from our acute screening risk assessments typically result when basing them on the acute REL value for a particular pollutant. In cases where our maximum acute HQ value exceeds 1, we also report the HQ value based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1 value). To develop screening estimates of acute exposures in the absence of hourly emissions data, generally we first develop estimates of maximum hourly emissions rates by multiplying the average actual annual hourly emissions rates by a default factor to cover routinely variable emissions. We choose the factor to use partially based on process knowledge and engineering judgment. The factor chosen also reflects a Texas study of short-term emissions variability, which showed that most peak emission events in a heavily-industrialized four-county area (Harris, Galveston, Chambers, and Brazoria Counties, Texas) were less than twice the annual average hourly emissions rate. The highest peak emissions event was 74 times the annual average hourly emissions rate, and the 99th percentile ratio of peak hourly emissions rate to the annual average hourly emissions rate was 9. 10 Considering this analysis, to account for more than 99 percent of the peak hourly emissions, we apply a conservative screening multiplication factor of 10 to the average annual hourly emissions rate in our acute exposure screening assessments as our default approach. However, we use a factor other than 10 if we have information that indicates that a different factor is appropriate for a particular source category. 10 Allen, et al., Variable Industrial VOC Emissions and their impact on ozone formation in the Houston Galveston Area. Texas Environmental Research Consortium, 2004, and available online at: https://www.researchgate.net/publication/237593060_Variable_Industrial_VOC_Emissions and_their_Impact_on_Ozone_Formation_in_the_Houston_Galveston_Area For this source category, we used an acute multiplication factor of 1.2 for all emission sources from nutritional yeast manufacturing facilities. The factor equals the average peak-to-mean ratio developed using 5 years of batch-averaged fermenter VOC concentration data from the facility with the highest emissions in the 2011 NEI. While the current rule requires continuous monitoring of emissions, facilities are required to report whether the percentage of batches that meet emission limits based on the average concentration of VOC emitted from each batch meets the current compliance requirements; not the continuous levels of emissions at the facility. Using the data above, we developed a multiplier to estimate potential acute emissions from each facility in this source category. A further discussion of why this factor was chosen can be found in the memorandum, “Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Manufacturing of Nutritional Yeast Source Category,” available in the docket for this rulemaking. As part of our acute risk assessment process, for cases where acute HQ values from the screening step were less than or equal to 1 (even under the conservative assumptions of the screening analysis), acute impacts were deemed negligible and no further analysis was performed for these HAP. In cases where an acute HQ from the screening step was greater than 1, additional site-specific data were considered to develop a more refined estimate of the potential for acute impacts of concern. For this source category, all acute HQ screening values were less than 1. Therefore, we did not employ additional data refinements. Ideally, we would prefer to have continuous measurements over time to see how the emissions vary by each hour over an entire year. Having a frequency distribution of hourly emissions rates over a year would allow us to perform a probabilistic analysis to estimate potential threshold exceedances and their frequency of occurrence. Such an evaluation could include a more complete statistical treatment of the key parameters and elements adopted in this screening analysis. Recognizing that this level of data is rarely available, we instead rely on the multiplier approach. To better characterize the potential health risks associated with estimated acute exposures to HAP, and in response to a key recommendation from the SAB's peer review of the EPA's RTR risk assessment methodologies, 11 we generally examine a wider range of available acute health metrics ( e.g., RELs, AEGLs) than we do for our chronic risk assessments. This is in response to the SAB's acknowledgement that there are generally more data gaps and inconsistencies in acute reference values than there are in chronic reference values. In some cases, when Reference Value Arrays 12 for HAP have been developed, we consider additional acute values ( i.e., occupational and international values) to provide a more complete risk characterization. 11 The SAB peer review of RTR Risk Assessment Methodologies is available at http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf . 12 U.S. EPA. Chapter 2.9, Chemical Specific Reference Values for Formaldehyde in Graphical Arrays of Chemical-Specific Health Effect Reference Values for Inhalation Exposures (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/061, 2009, and available online at http://cfpub.epa.gov/ncea/cfm/recordisplay.cfm?deid=211003 . 4. How did we conduct the multi-pathway exposure and risk screening? The EPA conducted a screening analysis examining the potential for significant human health risks due to exposures via routes other than inhalation ( i.e., ingestion). We first determined whether any sources in the source category emitted any HAP known to be persistent and bioaccumulative in the environment (PB-HAP). The PB-HAP compounds or compound classes are identified for the screening from the EPA's Air Toxics Risk Assessment Library (available at http://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library ). For the Manufacturing of Nutritional Yeast source category, we did not identify emissions of any PB-HAP. Because we did not identify PB-HAP emissions, no further evaluation of multi-pathway risk was conducted for this source category. 5. How did we assess risks considering emissions control options? The proposed rule amendments include changes to the form of the current emission limits, additional testing requirements, changes to the current monitoring requirements, and updates to the reporting and recordkeeping requirements. The proposed amendments to the emission limits may lead to a slight decrease in the overall emissions from the facilities, but we are unable to quantify this reduction. Facilities will continue to employ current process controls to comply with the emission limits ( i.e., they are not required to install additional control technologies); however, the facilities may need to make minor adjustments to the level of process controls to comply with the new limits. The proposed amendments to testing and monitoring requirements will increase the reliability of the emissions data that is monitored by each facility to ensure that the current emission limits are being met consistently. Therefore, risks considering the proposed amendments are estimated to be the same as actual risks under the current MACT standard. 6. How did we conduct the environmental risk screening assessment? a. Adverse Environmental Effect The EPA conducts a screening assessment to examine the potential for adverse environmental effects as required under section 112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines “adverse environmental effect” as “any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.” b. Environmental HAP The EPA focuses on seven HAP, which we refer to as “environmental HAP,” in its screening analysis: Five PB-HAP and two acid gases. The five PB-HAP are cadmium, dioxins/furans, polycyclic organic matter (POM), mercury (both inorganic mercury and methyl mercury), and lead compounds. The two acid gases are hydrogen chloride (HCl) and hydrogen fluoride (HF). The rationale for including these seven HAP in the environmental risk screening analysis is presented below. HAP that persist and bioaccumulate are of particular environmental concern because they accumulate in the soil, sediment, and water. The PB-HAP are taken up, through sediment, soil, water, and/or ingestion of other organisms, by plants or animals ( e.g., small fish) at the bottom of the food chain. As larger and larger predators consume these organisms, concentrations of the PB-HAP in the animal tissues increases as does the potential for adverse effects. The five PB-HAP we evaluate as part of our screening analysis account for 99.8 percent of all PB-HAP emissions nationally from stationary sources (on a mass basis from the 2005 NEI. In addition to accounting for almost all of the mass of PB-HAP emitted, we note that the TRIM.FaTE model that we use to evaluate multi-pathway risk allows us to estimate concentrations of cadmium compounds, dioxins/furans, POM, and mercury in soil, sediment and water. For lead compounds, we currently do not have the ability to calculate these concentrations using the TRIM.FaTE model. Therefore, to evaluate the potential for adverse environmental effects from lead compounds, we compare the estimated HEM-modeled exposures from the source category emissions of lead with the level of the secondary National Ambient Air Quality Standards (NAAQS) for lead. 13 We consider values below the level of the secondary lead NAAQS to be unlikely to cause adverse environmental effects. 13 The secondary lead NAAQS is a reasonable measure of determining whether there is an adverse environmental effect since it was established considering “effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being.” Due to their well-documented potential to cause direct damage to terrestrial plants, we include two acid gases, HCl, and HF in the environmental screening analysis. According to the 2005 NEI, HCl, and HF account for about 99 percent (on a mass basis) of the total acid gas HAP emitted by stationary sources in the U.S. In addition to the potential to cause direct damage to plants, high concentrations of HF in the air have been linked to fluorosis in livestock. Air concentrations of these HAP are already calculated as part of the human multi-pathway exposure and risk screening analysis using the HEM3-AERMOD air dispersion model, and we are able to use the air dispersion modeling results to estimate the potential for an adverse environmental effect. The EPA acknowledges that other HAP beyond the seven HAP discussed above may have the potential to cause adverse environmental effects. Therefore, the EPA may include other relevant HAP in its environmental risk screening in the future, as modeling science and resources allow. The EPA invites comment on the extent to which other HAP emitted by the source category may cause adverse environmental effects. Such information should include references to peer-reviewed ecological effects benchmarks that are of sufficient quality for making regulatory decisions, as well as information on the presence of organisms located near facilities within the source category that such benchmarks indicate could be adversely affected. c. Screening Methodology For the environmental risk screening analysis, the EPA first determined whether any facilities in the Manufacturing of Nutritional Yeast source category emitted any of the seven environmental HAP. For this source category, we did not identify emissions of any of the seven environmental HAP included in the screen. Because we did not identify environmental HAP emissions, we did not conduct a further evaluation of environmental risk. 7. How did we conduct facility-wide assessments? To put the source category risks in context, we typically examine the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, we examine the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emission sources at the facility for which we have data. The current NESHAP does not set emission limits for equipment other than fermenters at the affected sources. There is a potential for temporary wastewater storage tanks ( e.g., pH adjustment tanks) and dryers to emit small amounts of acetaldehyde at nutritional yeast facilities covered by this subpart. The NEI does not include emissions from wastewater storage tanks at any of the four facilities subject to this rule. Only one of the four facilities has dryers; the NEI did report estimated emissions from these dryers, which were included in the risk assessment for this source category. We did not perform a separate facility-wide risk assessment for facilities that manufacture nutritional yeast. One facility (American Yeast) reported 43 pounds of additional HAP emissions, composed largely of hexane and formaldehyde, from equipment sources not covered by 40 CFR part 63, subpart CCCC ( e.g., boilers, equipment covered by other NESHAP). 14 However, because these emissions were so low and from pollutants with low risk factors, we concluded that a facility-wide risk assessment would yield the same or only very slightly different results as the source category assessment. 14 Because these emissions originate from sources outside the manufacturing of nutritional yeast source category, they were also excluded from the source category risk analysis. 8. How did we consider uncertainties in risk assessment? In the Benzene NESHAP, we concluded that risk estimation uncertainty should be considered in our decision-making under the ample margin of safety framework. Uncertainty and the potential for bias are inherent in all risk assessments, including those performed for this proposal. Although uncertainty exists, we believe that our approach, which used conservative tools and assumptions, ensures that our decisions are health protective and environmentally protective. A brief discussion of the uncertainties in the RTR emissions dataset, dispersion modeling, inhalation exposure estimates, and dose-response relationships follows below. A more thorough discussion of these uncertainties is included in the “Residual Risk Assessment for the Manufacturing of Nutritional Yeast Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule,” which is available in the docket for this action. 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. c. Uncertainties in Inhalation Exposure The EPA did not include the effects of human mobility on exposures in the assessment. Specifically, short-term mobility and long-term mobility between census blocks in the modeling domain were not considered. 15 The approach of not considering short or long-term population mobility does not bias the estimate of the theoretical MIR (by definition), nor does it affect the estimate of cancer incidence because the total population number remains the same. It does, however, affect the shape of the distribution of individual risks across the affected population, shifting it toward higher estimated individual risks at the upper end and reducing the number of people estimated to be at lower risks, thereby increasing the estimated number of people at specific high risk levels ( e.g., 1-in-10 thousand or 1-in-1 million). 15 Short-term mobility is movement from one micro-environment to another over the course of hours or days. Long-term mobility is movement from one residence to another over the course of a lifetime. In addition, the assessment predicted the chronic exposures at the centroid of each populated census block as surrogates for the exposure concentrations for all people living in that block. Using the census block centroid to predict chronic exposures tends to over-predict exposures for people in the census block who live farther from the facility and under-predict exposures for people in the census block who live closer to the facility. Thus, using the census block centroid to predict chronic exposures may lead to a potential understatement or overstatement of the true maximum impact, but is an unbiased estimate of average risk and incidence. We reduce this uncertainty by analyzing large census blocks near facilities using aerial imagery and adjusting the location of the block centroid to better represent the population in the block, as well as adding additional receptor locations where the block population is not well represented by a single location. The assessment evaluates the cancer inhalation risks associated with pollutant exposures over a 70-year period, which is the assumed lifetime of an individual. In reality, both the length of time that modeled emission sources at facilities actually operate ( i.e., more or less than 70 years) and the domestic growth or decline of the modeled industry ( i.e., the increase or decrease in the number or size of domestic facilities) will influence the future risks posed by a given source or source category. Depending on the characteristics of the industry, these factors will, in most cases, result in an overestimate both in individual risk levels and in the total estimated number of cancer cases. However, in the unlikely scenario where a facility maintains, or even increases, its emissions levels over a period of more than 70 years, residents live beyond 70 years at the same location, and the residents spend most of their days at that location, then the cancer inhalation risks could potentially be underestimated. However, annual cancer incidence estimates from exposures to emissions from these sources would not be affected by the length of time an emissions source operates. The exposure estimates used in these analyses assume chronic exposures to ambient (outdoor) levels of pollutants. Because most people spend the majority of their time indoors, actual exposures may not be as high, depending on the characteristics of the pollutants modeled. For many of the HAP, indoor levels are roughly equivalent to ambient levels, but for very reactive pollutants or larger particles, indoor levels are typically lower. This factor has the potential to result in an overestimate of 25 to 30 percent of exposures. 16 16 U.S. EPA. National-Scale Air Toxics Assessment for 1996. (EPA 453/R-01-003; January 2001; page 85.) In addition to the uncertainties highlighted above, there are several factors specific to the acute exposure assessment that the EPA conducts as part of the risk review under section 112 of the CAA that should be highlighted. The accuracy of an acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, meteorology, and the presence of humans at the location of the maximum concentration. In the acute screening assessment that we conduct under the RTR program, we assume that peak emissions from the source category and worst-case meteorological conditions co-occur, thus, resulting in maximum ambient concentrations. These two events are unlikely to occur at the same time, making these assumptions conservative. We then include the additional assumption that a person is located at this point during this same time period. For this source category, these assumptions would tend to be worst-case actual exposures as it is unlikely that a person would be located at the point of maximum exposure during the time when peak emissions and worst-case meteorological conditions occur simultaneously. d. Uncertainties in Dose-Response Relationships There are uncertainties inherent in the development of the dose-response values used in our risk assessments for cancer effects from chronic exposures and non-cancer effects from both chronic and acute exposures. Some uncertainties may be considered quantitatively, and others generally are expressed in qualitative terms. We note as a preface to this discussion a point on dose-response uncertainty that is brought out in the EPA's 2005 Cancer Guidelines; namely, that “the primary goal of EPA actions is protection of human health; accordingly, as an Agency policy, risk assessment procedures, including default options that are used in the absence of scientific data to the contrary, should be health protective” (EPA's 2005 Cancer Guidelines, pages 1-7). This is the approach followed here as summarized in the next several paragraphs. A complete detailed discussion of uncertainties and variability in dose-response relationships is given in the “Residual Risk Assessment for the Manufacturing of Nutritional Yeast Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule,” which is available in the docket for this action. Cancer URE values used in our risk assessments are those that have been developed to generally provide an upper bound estimate of risk. That is, they represent a “plausible upper limit to the true value of a quantity” (although this is usually not a true statistical confidence limit). 17 In some circumstances, the true risk could be as low as zero; however, in other circumstances the risk could be greater. 18 When developing an upper bound estimate of risk and to provide risk values that do not underestimate risk, health-protective default approaches are generally used. To err on the side of ensuring adequate health protection, the EPA typically uses the upper bound estimates rather than lower bound or central tendency estimates in our risk assessments, an approach that may have limitations for other uses ( e.g., priority-setting or expected benefits analysis). 17 IRIS glossary ( https://ofmpub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&glossaryName=IRIS%20Glossary ). 18 An exception to this is the URE for benzene, which is considered to cover a range of values, each end of which is considered to be equally plausible, and which is based on maximum likelihood estimates. Chronic non-cancer RfC and reference dose (RfD) values represent chronic exposure levels that are intended to be health-protective levels. Specifically, these values provide an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure (RfC) or a daily oral exposure (RfD) to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime. To derive values that are intended to be “without appreciable risk,” the methodology relies upon an uncertainty factor (UF) approach (U.S. EPA, 1993 and 1994), which considers uncertainty, variability, and gaps in the available data. The UF are applied to derive reference values that are intended to protect against appreciable risk of deleterious effects. The UF are commonly default values, 19 e.g., factors of 10 or 3, used in the absence of compound-specific data; where data are available, UF may also be developed using compound-specific information. When data are limited, more assumptions are needed and more UF are used. Thus, there may be a greater tendency to overestimate risk in the sense that further study might support development of reference values that are higher ( i.e., less potent) because fewer default assumptions are needed. However, for some pollutants, it is possible that risks may be underestimated. 19 According to the NRC report, “Science and Judgment in Risk Assessment” (NRC, 1994) “[Default] options are generic approaches, based on general scientific knowledge and policy judgment, that are applied to various elements of the risk assessment process when the correct scientific model is unknown or uncertain.” The 1983 NRC report, “Risk Assessment in the Federal Government: Managing the Process,” defined default option as “the option chosen on the basis of risk assessment policy that appears to be the best choice in the absence of data to the contrary” (NRC, 1983a, p. 63). Therefore, default options are not rules that bind the Agency; rather, the Agency may depart from them in evaluating the risks posed by a specific substance when it believes this to be appropriate. In keeping with the EPA's goal of protecting public health and the environment, default assumptions are used to ensure that risk to chemicals is not underestimated (although defaults are not intended to overtly overestimate risk). See EPA, “An Examination of EPA Risk Assessment Principles and Practices,” EPA/100/B-04/001, 2004, available at https://nctc.fws.gov/resources/course-resources/pesticides/Risk%20Assessment/Risk%20Assessment%20Principles%20and%20Practices.pdf . While collectively termed “UF,” these factors account for a number of different quantitative considerations when using observed animal (usually rodent) or human toxicity data in the development of the RfC. The UF are intended to account for: (1) Variation in susceptibility among the members of the human population ( i.e., inter-individual variability); (2) uncertainty in extrapolating from experimental animal data to humans ( i.e., interspecies differences); (3) uncertainty in extrapolating from data obtained in a study with less-than-lifetime exposure ( i.e., extrapolating from sub-chronic to chronic exposure); (4) uncertainty in extrapolating the observed data to obtain an estimate of the exposure associated with no adverse effects; and (5) uncertainty when the database is incomplete or there are problems with the applicability of available studies. Many of the UF used to account for variability and uncertainty in the development of acute reference values are quite similar to those developed for chronic durations, but they more often use individual UF values that may be less than 10. The UF are applied based on chemical-specific or health effect-specific information ( e.g., simple irritation effects do not vary appreciably between human individuals, hence a value of 3 is typically used), or based on the purpose for the reference value ( see the following paragraph). The UF applied in acute reference value derivation include: (1) Heterogeneity among humans; (2) uncertainty in extrapolating from animals to humans; (3) uncertainty in lowest observed adverse effect (exposure) level to no observed adverse effect (exposure) level adjustments; and (4) uncertainty in accounting for an incomplete database on toxic effects of potential concern. Additional adjustments are often applied to account for uncertainty in extrapolation from observations at one exposure duration ( e.g., 4 hours) to derive an acute reference value at another exposure duration ( e.g., 1 hour). Not all acute reference values are developed for the same purpose, and care must be taken when interpreting the results of an acute assessment of human health effects relative to the reference value or values being exceeded. Where relevant to the estimated exposures, the lack of short-term dose-response values at different levels of severity should be factored into the risk characterization as potential uncertainties. For a group of compounds that are unspeciated ( e.g., glycol ethers), we conservatively use the most protective reference value of an individual compound in that group to estimate risk. Similarly, for an individual compound in a group ( e.g., ethylene glycol diethyl ether) that does not have a specified reference value, we also apply the most protective reference value from the other compounds in the group to estimate risk. B. How did we consider the risk results in making decisions for this proposal? As discussed in section II.A of this preamble, in evaluating and developing standards under CAA section 112(f)(2), we apply a two-step process to address residual risk. In the first step, the EPA determines whether risks are acceptable. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR) 20 of approximately [1-in-10 thousand] [ i.e., 100-in-1 million].” 54 FR 38045, September 14, 1989. If risks are unacceptable, the EPA must determine the emissions standards necessary to bring risks to an acceptable level without considering costs. In the second step of the process, the EPA considers whether the emissions standards provide an ample margin of safety “in consideration of all health information, including the number of persons at risk levels higher than approximately 1-in-1 million, as well as other relevant factors, including costs and economic impacts, technological feasibility, and other factors relevant to each particular decision.” Id. The EPA must promulgate emission standards necessary to provide an ample margin of safety. 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. 20 Although defined as “maximum individual risk,” MIR refers only to cancer risk. MIR, one metric for assessing cancer risk, is the estimated risk were an individual exposed to the maximum level of a pollutant for a lifetime. In past residual risk actions, the EPA considered a number of human health risk metrics associated with emissions from the categories under review, including the MIR, the number of persons in various risk ranges, cancer incidence, the maximum non-cancer HI and the maximum acute non-cancer hazard. See, e.g., 72 FR 25138, May 3, 2007; and 71 FR 42724, July 27, 2006. The EPA considered this health information for both actual and allowable emissions. See, e.g., 75 FR 65068, October 21, 2010; 75 FR 80220, December 21, 2010; 76 FR 29032, May 19, 2011. The EPA also discussed risk estimation uncertainties and considered the uncertainties in the determination of acceptable risk and ample margin of safety in these past actions. The EPA considered this same type of information in support of this action. The Agency is considering these various measures of health information to inform our determinations of risk acceptability and ample margin of safety under CAA section 112(f). As explained in the Benzene NESHAP, “the first step judgment on acceptability cannot be reduced to any single factor” and, thus, “[t]he Administrator believes that the acceptability of risk under [previous] section 112 is best judged on the basis of a broad set of health risk measures and information.” 54 FR 38046, September 14, 1989. Similarly, with regard to the ample margin of safety determination, “the Agency again considers all of the health risk and other health information considered in the first step. Beyond that information, additional factors relating to the appropriate level of control will also be considered, including cost and economic impacts of controls, technological feasibility, uncertainties, and any other relevant factors.” Id. The Benzene NESHAP approach provides flexibility regarding factors the EPA may consider in making determinations and how the EPA may weigh those factors for each source category. In responding to comment on our policy under the Benzene NESHAP, the EPA explained that: “[t]he policy chosen by the Administrator permits consideration of multiple measures of health risk. Not only can the MIR figure be considered, but also incidence, the presence of non-cancer health effects, and the uncertainties of the risk estimates. In this way, the effect on the most exposed individuals can be reviewed as well as the impact on the general public. These factors can then be weighed in each individual case. This approach complies with the Vinyl Chloride mandate that the Administrator ascertain an acceptable level of risk to the public by employing [her] expertise to assess available data. It also complies with the Congressional intent behind the CAA, which did not exclude the use of any particular measure of public health risk from the EPA's consideration with respect to CAA section 112 regulations, and thereby implicitly permits consideration of any and all measures of health risk which the Administrator, in [her] judgment, believes are appropriate to determining what will `protect the public health'.” See 54 FR at 38057, September 14, 1989. Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risks. The Benzene NESHAP explained that “an MIR of approximately one in 10 thousand should ordinarily be the upper end of the range of acceptability. As risks increase above this benchmark, they become presumptively less acceptable under CAA section 112, and would be weighed with the other health risk measures and information in making an overall judgment on acceptability. Or, the Agency may find, in a particular case, that a risk that includes MIR less than the presumptively acceptable level is unacceptable in the light of other health risk factors.” Id. at 38045. Similarly, with regard to the ample margin of safety analysis, the EPA stated in the Benzene NESHAP that: “EPA believes the relative weight of the many factors that can be considered in selecting an ample margin of safety can only be determined for each specific source category. This occurs mainly because technological and economic factors (along with the health-related factors) vary from source category to source category.” Id. at 38061. We also consider the uncertainties associated with the various risk analyses, as discussed earlier in this preamble, in our determinations of acceptability and ample margin of safety. The EPA notes that it has not considered certain health information to date in making residual risk determinations. At this time, we do not attempt to quantify those HAP risks that may be associated with emissions from other facilities that do not include the source categories in question, mobile source emissions, natural source emissions, persistent environmental pollution, or atmospheric transformation in the vicinity of the sources in these categories. The Agency understands the potential importance of considering an individual's total exposure to HAP in addition to considering exposure to HAP emissions from the source category and facility. We recognize that such consideration may be particularly important when assessing non-cancer risks, where pollutant-specific exposure health reference levels ( e.g., RfCs) are based on the assumption that thresholds exist for adverse health effects. For example, the Agency recognizes that, although exposures attributable to emissions from a source category or facility alone may not indicate the potential for increased risk of adverse non-cancer health effects in a population, the exposures resulting from emissions from the facility in combination with emissions from all of the other sources ( e.g., other facilities) to which an individual is exposed may be sufficient to result in increased risk of adverse non-cancer health effects. In May 2010, the SAB advised the EPA “that RTR assessments will be most useful to decision makers and communities if results are presented in the broader context of aggregate and cumulative risks, including background concentrations and contributions from other sources in the area.” 21 21 The EPA's responses to this and all other key recommendations of the SAB's advisory on RTR risk assessment methodologies (which is available at: http://yosemite.epa.gov/sab/sabproduct.nsf/4AB3966E263D943A8525771F00668381/$File/EPA-SAB-10-007-unsigned.pdf ) are outlined in a memorandum to this rulemaking docket from David Guinnup titled, “EPA's Actions in Response to the Key Recommendations of the SAB Review of RTR Risk Assessment Methodologies.” In response to the SAB recommendations, the EPA is incorporating cumulative risk analyses into its RTR risk assessments, including those reflected in this proposal. The Agency is: (1) Conducting facility-wide assessments, which include source category emission points, as well as other emission points within the facilities; (2) considering sources in the same category whose emissions result in exposures to the same individuals; and (3) for some persistent and bioaccumlative pollutants, analyzing the ingestion route of exposure. In addition, the RTR risk assessments have always considered aggregate cancer risk from all carcinogens and aggregate non-cancer HI from all non-carcinogens affecting the same target organ system. Although we are interested in placing source category and facility-wide HAP risks in the context of total HAP risks from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Because of the contribution to total HAP risk from emission sources other than those that we have studied in depth during this RTR review, such estimates of total HAP risks would have significantly greater associated uncertainties than the source category or facility-wide estimates. Such aggregate or cumulative assessments would compound those uncertainties, making the assessments too unreliable. C. How did we perform the technology review? Our technology review focused on the identification and evaluation of developments in practices, processes, and control technologies that have occurred since the MACT standards were promulgated. Where we identified such developments, in order to inform our decision of whether it is “necessary” to revise the emissions standards, we analyzed the technical feasibility of applying these developments and the estimated costs, energy implications, non-air environmental impacts, as well as considering the emission reductions. We also considered the appropriateness of applying controls to new sources versus retrofitting existing sources. Based on our analyses of the available data and information, we identified potential developments in practices, processes, and control technologies. For this exercise, we considered any of the following to be a “development”: • Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standards; • Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standards) that could result in additional emissions reduction; • Any work practice or operational procedure that was not identified or considered during development of the original MACT standards; • Any process change or pollution prevention alternative that could be broadly applied to the industry and that was not identified or considered during development of the original MACT standards; and • Any significant changes in the cost (including cost effectiveness) of applying controls (including controls the EPA considered during the development of the original MACT standards). In addition to reviewing the practices, processes, and control technologies that were considered at the time we originally developed (or last updated) the NESHAP, we reviewed a variety of data sources in our investigation of potential practices, processes, or controls to consider. Among the sources we reviewed were the NESHAP for various industries that were promulgated since the MACT standards being reviewed in this action. We reviewed the regulatory requirements and/or technical analyses associated with these regulatory actions to identify any practices, processes, and control technologies considered in these efforts that could be applied to emission sources in the Manufacturing of Nutritional Yeast source category, as well as the costs, non-air impacts, and energy implications associated with the use of these technologies. Additionally, we requested information from facilities regarding developments in practices, processes, or control technology. Finally, we reviewed information from other sources, such as state and/or local permitting agency databases and industry-supported databases. IV. Analytical Results and Proposed Decisions A. What are the results of the risk assessment and analyses? As described above, for the Manufacturing of Nutritional Yeast source category, we conducted an inhalation risk assessment for all HAP emitted. We present results of the risk assessment briefly below and in more detail in the document: “Residual Risk Assessment for the Manufacturing of Nutritional Yeast Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule,” which is available in the docket for this action. 1. Inhalation Risk Assessment Results Table 2 of this preamble provides a summary of the results of the inhalation risk assessment for the source category. As discussed in section III.A.2 of this preamble, we set MACT-allowable HAP emission levels at nutritional yeast manufacturing facilities equal to actual emissions. For more detail about the MACT-allowable emission levels, see the memorandum, ``Emissions Data and Acute Risk Factor Used in Residual Risk Modeling: Manufacturing of Nutritional Yeast Source Category,” which is available in the docket for this action. Table 2—Nutritional Yeast Manufacturing Inhalation Risk Assessment Results Number of facilities 1 Maximum individual cancer risk (in 1 million) 2 Based on actual emissions level 2 Based on allowable emissions level Estimated population at increased risk of cancer ≥ 1-in-1 Million Based on actual emissions level 2 Based on allowable emissions level Estimated annual cancer incidence (cases per year) Based on actual emissions level 2 Based on allowable emissions level Maximum chronic non-cancer TOSHI 3 Based on actual emissions level 2 Based on allowable emissions level Maximum screening acute non-cancer HQ 4 Based on actual emissions level 2 Based on allowable emissions level 4 2 2 750 750 0.0009 0.0009 0.08 0.08 HQ REL = 0.2 HQ REL = 0.2. 1 Number of facilities evaluated in the risk analysis. 2 Maximum individual excess lifetime cancer risk due to HAP emissions from the source category. 3 Maximum TOSHI. The target organ with the highest TOSHI for the Manufacturing of Nutritional Yeast source category is the respiratory system. 4 The maximum estimated acute exposure concentration was divided by available short-term threshold values to develop an array of HQ values. HQ values shown use the lowest available acute threshold value, which in most cases is the REL. When HQ values exceed 1, we also show HQ values using the next lowest available acute dose-response value. See section III.A.3 of this preamble for explanation of acute dose-response values. The results of the inhalation risk modeling using actual emissions data, as shown in Table 2 of this preamble, indicate that the maximum lifetime individual cancer risk could be up to 2-in-1 million, the maximum chronic non-cancer TOSHI value could be up to 0.08, and the maximum off-facility site acute HQ value could be up to 0.2. The total estimated national cancer incidence from these facilities based on actual emission levels is 0.0009 excess cancer cases per year or 1 case in every 1,100 years. 2. Acute Risk Results Table 2 of this preamble shows the acute risk results for the Manufacturing of Nutritional Yeast source category. The screening analysis for acute impacts was based on an industry specific multiplier of 1.2, to estimate the peak emission rates from the average rates. For more detailed acute risk results, refer to the draft document: “Residual Risk Assessment for the Manufacturing of Nutritional Yeast Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule,” which is available in the docket for this action. 3. Multi-Pathway Risk Screening Results There are no PB-HAP emitted by facilities in this source category. Therefore, we do not expect any human health multi-pathway risks as a result of emissions from this source category. 4. Environmental Risk Screening Results The emissions data for the Manufacturing of Nutritional Yeast source category indicate that sources within this source category do not emit any of the seven pollutants that we identified as “environmental HAP,” as discussed earlier in this preamble. Additionally, the processes and materials used in the source category typically do not emit any of the seven environmental HAP. Also, we are unaware of any adverse environmental effect caused by emissions of HAP that are emitted by this source category (acetaldehyde). Therefore, we do not expect an adverse environmental effect as a result of HAP emissions from this source category. 5. Facility-Wide Risk Results As explained in section III.A.7 of this preamble, we did not perform a separate facility-wide risk assessment because we expect facility-wide risks to be equal to the risks we assessed for this source category. 6. What demographic groups might benefit from this regulation? To examine the potential for any environmental justice issues that might be associated with the source category, we performed a demographic analysis, which is an assessment of risks to individual demographic groups within the population near the four nutritional yeast manufacturing facilities that are subject to the NESHAP. In this analysis, we evaluated the distribution of HAP-related cancer risks and non-cancer hazards from the nutritional yeast manufacturing facilities across different social, demographic, and economic groups within the populations living near facilities identified as having the highest risks. The methodology and the results of the demographic analyses are included in a technical report, “Risk and Technology Review—Analysis of Socio-Economic Factors for Populations Living Near Nutritional Yeast Manufacturing Facilities,” available in the docket for this action. The analysis indicates that the minority population living within 50 km (1,700,000 people, of whom 41 percent are minority) and within 5 km (131,567 people, of whom 68 percent are minority) of the four nutritional yeast manufacturing facilities is greater than the minority population found nationwide (28 percent). The specific demographics of the population within 5 and 50 km of the facilities indicate potential disparities in risks in certain demographic groups, including the “African American,” “Below the Poverty Level,” and “Over 25 and without high school diploma” groups. When examining the risk levels of those exposed to emissions from the four nutritional yeast manufacturing facilities, we find approximately 750 persons are exposed to a cancer risk greater than or equal to 1-in-1 million, and the highest cancer risk for these individuals is less than 2-in-1 million. Of these 750 persons, 100 percent of them are defined as minority. When examining the noncancer risks surrounding these facilities, no one is predicted to have a chronic non-cancer TOSHI greater than 1. B. What are our proposed decisions regarding risk acceptability, ample margin of safety, and adverse environmental effects? 1. Risk Acceptability As noted in section III.B of this preamble, we weigh all health risk factors in our risk acceptability determination, including the cancer MIR, the number of persons in various cancer and non-cancer risk ranges, cancer incidence, the maximum non-cancer TOSHI, the maximum acute non-cancer HQ, the extent of non-cancer risks, the potential for adverse environmental effects, the distribution of cancer and non-cancer risks in the exposed population, and risk estimation uncertainties (54 FR 38044, September 14, 1989). For the Manufacturing of Nutritional Yeast source category, the risk analysis indicates that the cancer risks to the individual most exposed could be up to 2-in-1 million due to actual emissions and up to 2-in-1 million based on allowable emissions. As explained in section III.A.2 of this preamble, we determined that actual emissions provide an accurate representation of maximum emissions from the source category and used the actual emissions in both steps of the risk assessment ( i.e., determination of risk based on actual and MACT-allowable emissions). These risks are considerably less than 100-in-1 million, which is the presumptive upper limit of acceptable risk. The risk analysis also shows very low cancer incidence (0.0009 cases per year), as well as no potential for adverse chronic or multi-pathway health effects. In addition, the risk assessment indicates no significant potential for multi-pathway health effects or adverse environmental effects. The acute non-cancer risks based on actual and allowable emissions are all below an HQ of 1. Therefore, we find there is little potential concern of acute non-cancer health impacts from actual and allowable emissions. Considering all of the health risk information and factors discussed above, including the uncertainties discussed in section III.A.8 of this preamble, we propose to find that the risks from the Manufacturing of Nutritional Yeast source category are acceptable. 2. Ample Margin of Safety Analysis Although we are proposing that the risks from the Manufacturing of Nutritional Yeast source category are acceptable, risk estimates for approximately 750 individuals in the exposed population are above 1-in-1 million at the actual and MACT-allowable emissions levels. Consequently, we further considered whether the MACT standards for the Manufacturing of Nutritional Yeast source category provide an ample margin of safety to protect public health. In this ample margin of safety analysis, we investigated available emissions control options that might reduce the risk from the source category. We considered this information along with all of the health risks and other health information considered in our determination of risk acceptability. As discussed in section IV.C of this preamble, during the technology review for this source category, we evaluated two control technologies for reducing acetaldehyde emissions from fermenters at nutritional yeast facilities: Thermal oxidizers and wet (packed bed) scrubbers. Thermal oxidizers have the potential to reduce total acetaldehyde emissions from this source category by 11 tpy to 36 tpy, for a total of 90 tpy for the industry, but would also lead to increases in energy use and emissions of approximately 89 tpy of nitrogen oxides (NO X ) from these facilities. The cost effectiveness for thermal oxidizers varied per facility, with an average cost of $56,000 per ton of acetaldehyde reduced. The average cost effectiveness for packed bed scrubbers was $74,000 per ton of acetaldehyde per facility. The use of packed bed scrubbers would also lead to additional environmental impacts, such as increased energy and water usage, as well as the need to use and dispose of solvents. These cost-effectiveness values are significantly higher than values that we have historically deemed to be cost effective for organic HAP in other NESHAP. Due to the additional environmental impacts that would be imposed and the low level of current risk, along with the substantial costs associated with these options, we are proposing that additional emissions controls for this source category are not necessary to provide an ample margin of safety. 3. Environmental Effects We did not identify emissions of any of the seven environmental HAP included in our environmental risk screening, and are unaware of any adverse environmental effects caused by HAP emitted by this source category (acetaldehyde). Therefore, we do not expect there to be an adverse environmental effect as a result of HAP emissions from this source category and we are proposing that it is not necessary to set a more stringent standard to prevent, taking into consideration costs, energy, safety, and other relevant factors, an adverse environmental effect. C. What are the results and proposed decisions based on our technology review? In order to fulfill our obligations under CAA section 112(d)(6), we conducted a technology review to identify developments in practices, processes, and control technologies that may advise revisions to the current NESHAP standards applicable to the Manufacturing of Nutritional Yeast source category ( i.e., 40 CFR part 63, subpart CCCC). In conducting our technology review, we utilized the RBLC database, reviewed title V permits for each nutritional yeast facility, and reviewed regulatory actions related to emissions controls at similar sources that could be applicable to nutritional yeast manufacturing facilities. After reviewing information from the sources above, we identified two control technologies for further evaluation that are technically feasible for use at nutritional yeast facilities: thermal oxidizers and wet scrubbers. 22 These control technologies were identified both in the RBLC database and in a review of the miscellaneous organic chemical manufacturing NESHAP (MON). The RBLC database contains multiple sources with similar production processes as nutritional yeast manufacturing facilities that employ thermal oxidizers or wet scrubbers, e.g., fermenters at ethanol facilities. We also identified the MON in particular as being a potentially useful analog for manufacturing of nutritional yeast because the MON regulates emissions from ethanol fermenters (the same sources identified in the RBLC) that are located at facilities that are major sources of HAP emissions. Our review of this rule revealed that facilities use thermal oxidizers as a control technology to comply with the process vent emission limits in the MON. 22 Additional information about this determination is documented in the memorandum, “Technology Review for the Manufacturing of Nutritional Yeast Source Category,” which is available in the docket for this action. After identifying control technologies that are technically feasible for reducing acetaldehyde emissions from nutritional yeast fermenters, we then evaluated the costs and emissions reductions associated with installing regenerative thermal oxidizers (RTOs) and packed bed scrubbers at each of the four nutritional yeast facilities. The total capital investment to install RTOs ranged from $2 million to $6.9 million per facility for a total of approximately $14.9 million for the industry. Annual costs for each facility were approximately $0.8 million to $2.2 million, for a total of $5.2 million per year for the industry. Applying a control efficiency of 98 percent, acetaldehyde emissions for each facility would be reduced by approximately 11 tpy to 36 tpy, for a total of 90 tpy for the industry. To install RTOs at each facility, the resulting cost effectiveness ranged from $32,000 to $90,000 per ton of acetaldehyde reduced. Furthermore, use of RTOs would result in increased energy use and NO X emissions of approximately 89 tpy from nutritional yeast manufacturing facilities. Additional information about the assumptions and methodologies used in these calculations is documented in the memorandum, “Technology Review for the Manufacturing of Nutritional Yeast Source Category,” which is available in the docket for this action. The total capital investment to install packed bed scrubbers on fermenters ranged from $3 million to $11.6 million per facility for a total of about $24.5 million for the industry. Annual costs for each facility were approximately $0.8 million to $2.5 million, for a total of $5.8 million per year for the industry. Applying a control efficiency of 85 percent, acetaldehyde emissions for each facility would be reduced by approximately 9.4 tpy to 31 tpy, for a total of 78 tpy for the industry. To install packed bed scrubbers at each facility, the resulting cost effectiveness ranged from $43,000 to $110,000 per ton of acetaldehyde reduced. Furthermore, the use of packed bed scrubbers would lead to increased energy usage and other environmental impacts, such as the usage and disposal of water and caustic solutions ( e.g., sodium hydroxide). These cost-effectiveness values are significantly higher than values that we have historically deemed to be cost effective for organic HAP in other NESHAP. Additional information about the assumptions and methodologies used in these calculation is documented in the memorandum, “Technology Review for the Manufacturing of Nutritional Yeast Source Category,” which is available in the docket for this action. [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%3A2016-30645. Public record. Not legal advice.