National Emission Standards for Hazardous Air Pollutants: Publicly Owned Treatment Works

Federal RegisterDec 27, 2016

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2016-0490; FRL-9956-87-OAR]

RIN 2060-AS85

National Emission Standards for Hazardous Air Pollutants: Publicly Owned Treatment Works

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 Publicly Owned Treatment Works (POTW) to address the results of the residual risk and technology review (RTR) conducted under the Clean Air Act (CAA). As a result of our review, we are proposing to include pretreatment requirements to limit emissions from collection systems and the POTW treatment plant; requirements for existing, new, or reconstructed industrial (Group 1) POTW to comply with both the requirements in this rule and those in the applicable NESHAP for which they act as control; and hazardous air pollutants (HAP) emission limits for existing, non-industrial (Group 2) POTW. In addition, the EPA is proposing to revise the applicability criteria, revise the names and definitions of the industrial (Group 1) and non-industrial (Group 2) subcategories, revise regulatory provisions pertaining to emissions during periods of startup, shutdown, and malfunction, add requirements for electronic reporting, and make other miscellaneous edits and technical corrections.

DATES:

Comments.

Comments must be received on or before February 27, 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 26, 2017.

Public Hearing.

A public hearing will be held on January 11, 2017, if requested by January 3, 2017.

ADDRESSES:

Comments.

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2016-0490, at

http://www.regulations.gov

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

http://www.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

http://www2.epa.gov/dockets/commenting-epa-dockets

FOR FURTHER INFORMATION CONTACT:

For questions about this proposed action, contact Karen Marsh, Sector Policies and Programs Division (E143-05), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-1065; fax number: (919) 541-3470; and email address:

marsh.karen@epa.gov

. For specific information regarding the risk modeling methodology, contact Michael Stewart, Health and Environmental Impacts Division (C539-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-7524; fax number: (919) 541-0237; and email address:

stewart.michael@epa.gov

. For information about the applicability of the NESHAP to a particular entity, contact Patrick Yellin, 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: (202) 564-2970; fax number: (202) 564-0050; and email address:

yellin.patrick@epa.gov

SUPPLEMENTARY INFORMATION:

Docket.

The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2016-0490. 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-2016-0490. 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

http://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 Washington, DC campus located at 1201 Constitution Avenue NW., Washington, DC. The hearing, if requested, will begin at 9:00 a.m. (local time) and will conclude at 4:00 p.m. (local time) on January 11, 2017. 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 9, 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/publicly-owned-treatment-works-potw-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/publicly-owned-treatment-works-potw-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

BACT Best available control technology

CAA Clean Air Act

CalEPA California EPA

CBI Confidential Business Information

CDX Central Data Exchange

CEDRI Compliance and Emissions Data Reporting Interface

CFR Code of Federal Regulations

CWA Clean Water Act

ECHO Enforcement and Compliance History Online

EJ Environmental justice

EPA Environmental Protection Agency

ERPG Emergency Response Planning Guidelines

ERT Electronic Reporting Tool

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

LAER Lowest achievable emission rate

LOAEL Lowest-observed-adverse-effect level

MACT Maximum achievable control technology

MGD Million gallons per day

mg/kg-day Milligrams per kilogram per day

mg/m

Milligrams per cubic meter

MIR Maximum individual risk

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NAS National Academy of Sciences

NATA National Air Toxics Assessment

NEI National Emissions Inventory

NESHAP National emissions standards for hazardous air pollutants

NOAA National Oceanic and Atmospheric Administration

NOAEL No-observed-adverse-effect levels

NRC National Research Council

NSR New source review

NTTAA National Technology Transfer and Advancement Act

OAQPS Office of Air Quality Planning and Standards

OMB Office of Management and Budget

PAH polycyclic aromatic hydrocarbons

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

PEL Probable effect level

POM Polycyclic organic matter

POTW Publicly owned treatment works

ppm Parts per million

PRA Paperwork Reduction Act

RACT Reasonably available control technology

REL Reference exposure level

RFA Regulatory Flexibility Act

RfC Reference concentration

RfD Reference dose

RTR Residual risk and technology review

SAB Science Advisory Board

SOP Standard operating procedure

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

UF Uncertainty factor

μg/m

microgram per cubic meter

UMRA Unfunded Mandates Reform Act

URE Unit risk estimate

VCS Voluntary consensus standards

Organization of this Document.

The information in this preamble is organized as follows:

I. General Information

A. Does this action apply to me?

Table 1 of this preamble lists the NESHAP and 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 governments would be affected as discussed below. By definition, a POTW is owned by a municipality, state, intermunicipal or interstate agency, or any department, agency, or instrumentality of the federal government (See 40 CFR 63.1595 of subpart VVV). If a POTW has a design capacity to treat at least 5 million gallons per day (MGD) of wastewater, receives wastewater from industrial users, and is either a major source of HAP emissions or treats wastewater to comply with requirements of another NESHAP, then the POTW is affected by these standards. (Note, these applicability criteria represent proposed revisions to the current criteria and are discussed further in section IV.D.1 of this document.) 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 POTW source category includes emissions from wastewaters that are treated at a POTW. These wastewaters are generated by industrial, commercial, and domestic sources, although only industrial and commercial dischargers might consistently discharge HAP in quantities high enough to potentially result in an exceedance of the major source emission threshold at the POTW. Emissions from these wastewaters can

occur within the collection system (sewers) as well as during treatment at the POTW. Control options include, but are not limited to, reduction of HAP at the industrial discharger before wastewater enters the collection systems, add-on emission controls on the collection system and at the POTW, and/or treatment process modifications/substitutions.

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

Source category

NESHAP

NAICS code

Sewage Treatment Facilities

Subpart VVV

221320

North American Industry Classification System.

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

In addition to being available in the docket, an electronic copy of this action is available on the Internet. A redline version of the regulatory language that incorporates the proposed changes in this action is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2016-0490). 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/publicly-owned-treatment-works-potw-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 residual risk and technology review (RTR) program is available at

http://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 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-2016-0490.

II. Background

A. What is the statutory authority for this action?

Section 112 of the CAA establishes a two-stage regulatory process to address emissions of HAP from stationary sources. In the first stage, after the EPA has identified categories of sources emitting one or more of the HAP listed in CAA section 112(b), CAA section 112(d) requires us to promulgate technology-based NESHAP for those sources. “Major sources” are those that emit or have the potential to emit 10 tons per year (tpy) or more of a single HAP or 25 tpy or more of any combination of 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)

EPA,

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

Association of Battery Recyclers, Inc.

EPA,

716 F.3d 667 (D.C. Cir. 2013).

The second stage in standard-setting focuses on reducing any remaining (

i.e.,

“residual”) risk according to CAA section 112(f). CAA section 112(f)(1) requires 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

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 54 FR 38046, September 14, 1989. The determination of what represents an “acceptable” risk is based on a judgment of “what risks are acceptable in the world in which we live” (

Risk Report

at 178, quoting

NRDC

EPA,

824 F. 2d 1146, 1165 (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 km exposure radius around facilities, the science policy assumptions and estimation uncertainties associated with the risk measures, weight of the scientific evidence for human health effects, other quantified or unquantified health effects, effects due to co-location of facilities, and co-emission of pollutants.

Id.

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

As noted earlier, in

NRDC

EPA,

the court held that 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

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,

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

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

The CAA does not specifically define the terms “individual most exposed,” “acceptable level,” and “ample margin of safety.” In the Benzene NESHAP, 54 FR at 38044-38045, 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 2002 NESHAP regulate its HAP emissions?

1. Definition of the POTW Source Category and the Affected Source

The NESHAP for the POTW source category (henceforth referred to as the “POTW NESHAP”) was promulgated on October 26, 1999 (64 FR 57572) and codified at 40 CFR part 63, subpart VVV. The POTW NESHAP was amended on October 21, 2002 (67 FR 64742). As amended in 2002, the POTW NESHAP applies to new and existing POTW treatment plants that are located at a POTW that is a major source of HAP emissions and that is required to develop and implement a pretreatment program as defined by 40 CFR 403.8 under the Clean Water Act. Emissions from a POTW originate from wastewaters that are treated at a POTW. These wastewaters are generated by industrial, commercial, and domestic sources, although only industrial and commercial dischargers might consistently discharge HAP in quantities high enough to potentially result in an exceedance of the major source emission threshold at the POTW. Emissions from these wastewaters can occur within the collection system (sewers) as well as during treatment at the POTW treatment plant. Control options include, but are not limited to, reduction of HAP at the source before they enter the collection system, add-on emission controls on the collection system and at the POTW, and/or treatment process modifications/substitutions.

The POTW NESHAP (40 CFR 63.1595) defines “POTW” as “a treatment works, as that term is defined by section 112(e)(5) of the Clean Air Act, which is owned by a municipality (as defined by section 502(4) of the Clean Water Act),

a state, an intermunicipal or interstate agency, or any department, agency, or instrumentality of the federal government. This definition includes any intercepting sewers, outfall sewers, sewage collection systems, pumping, power, and other equipment. The wastewater treated by these facilities is generated by industrial, commercial, and domestic sources. As used in this regulation, the term POTW refers to both any publicly owned treatment works which is owned by a state, municipality, or intermunicipal or interstate agency and therefore eligible to receive grant assistance under the Subchapter II of the Clean Water Act, and any federally owned treatment works as that term is described in section 3023 of the Solid Waste Disposal Act.” The “affected source” regulated by the 2002 POTW NESHAP is defined in 40 CFR 63.1595 of the POTW NESHAP as the “group of all equipment that comprise the POTW treatment plant.” The “POTW treatment plant” is defined as the “portion of the POTW which is designed to provide treatment (including recycling and reclamation) of municipal sewage and industrial waste.” The 2002 POTW NESHAP excludes collection systems, including sewers, pump stations, and other conveyance equipment located outside the POTW treatment plant from the definition of affected source.

CAA section 112(e)(5) adopts the definition of “treatment works” from Clean Water Act (CWA) section 212(2), 33 U.S.C. 1292(2).

2. Applicability of the 2002 NESHAP: Industrial (Group 1) and Non-Industrial (Group 2) Subcategories

The 2002 POTW NESHAP set air pollution control requirements or emission limits on existing, new, and reconstructed POTW. Briefly, a POTW

is subject to the POTW NESHAP if: (1) The POTW is required to establish and implement a pretreatment program per the requirements in 40 CFR 403.8 under the CWA. Pretreatment programs are required for POTW with a design capacity of greater than 5 MGD and that receive wastewater from an “industrial user” that contains pollutants which pass through or interfere with the operation of the POTW. Pollutants that pass through are those that remain in the wastewater and are not removed during treatment operations at the POTW; and (2) either of the following:

• The POTW accepts waste streams regulated by another NESHAP and provides treatment and controls as an agent for the industrial facility. The industrial facility complies with its NESHAP requirements specific to that wastewater stream by using the treatment and controls located at the POTW; or

• The POTW is a major source of HAP emissions.

Accordingly, POTW that are area sources are not subject to the requirements in the 2002 rule unless they receive wastewater that is subject to control under another NESHAP.

Today we estimate that six facilities are subject to the POTW NESHAP. A complete list of facilities subject to the POTW NESHAP is available in the POTW RTR database, which is available for review in the docket for this proposed rulemaking. The EPA recognizes that there are approximately 16,000 POTW in the U.S.; however, most of these are small municipalities that do not treat wastewater from industrial users, and therefore, would not be subject to this regulation. Additionally, POTW that do treat wastewater from industrial users are generally required to develop and implement a pretreatment program that limits the concentration of pollutants in wastewaters received at the POTW, thus reducing the potential emissions of HAP so that they are below major source thresholds. The EPA requests comment specifically identifying other POTW that are subject to the POTW NESHAP.

In the 2002 NESHAP, the source category is subcategorized based on the way in which the POTW is providing treatment for wastewaters received from an industrial source. The 2002 POTW NESHAP defines (40 CFR 63.1595) an “industrial POTW” as “a POTW that accepts a waste stream regulated by another NESHAP and provides treatment and controls as an agent for the industrial discharger. The industrial discharger complies with its NESHAP by using the treatment and controls located at the POTW. For example, an industry discharges its benzene-containing waste stream to the POTW for treatment to comply with 40 CFR part 61, subpart FF—National Emission Standard for Benzene Waste Operations. This definition does not include POTW treating waste streams not specifically regulated under another NESHAP.” In other words, if a POTW is used as the control method by which an industrial source meets the wastewater requirements in their source category NESHAP, then the POTW is considered an “industrial POTW treatment plant.” An “industrial POTW treatment plant” is affected by the 2002 POTW NESHAP regardless of the HAP emissions (

i.e.,

does not have to be a major source).

In contrast, under the 2002 NESHAP, a “non-industrial POTW” is defined (40 CFR 63.1595) as “a POTW that does not meet the definition of an industrial POTW as defined above.” If a POTW treats wastewater from industrial users, but does not treat industrial wastewaters subject to control requirements in another NESHAP, then the POTW is a “non-industrial POTW treatment plant.” See section IV.D.2 of this preamble for a discussion on proposed changes to these subcategories, including proposed changes to the names for these subcategories (

i.e.,

Group 1 and Group 2).

3. HAP Emission Points

The amount and type of HAP emitted from a POTW is dependent on the composition of the wastewater streams discharged to a POTW by industrial users. Because HAP are not typically used in large quantities by domestic dischargers, we do not expect domestic dischargers to consistently or frequently contribute HAP constituents to the wastewater and any domestic discharges of HAP are trivial in comparison to industrial dischargers. An industrial user is defined in the 2002 regulation to include both industrial and commercial facilities that discharge wastewaters to the POTW. The primary HAP emitted from the POTW that were identified as subject to the 2002 NESHAP include acetaldehyde, acetonitrile, chloroform, ethylene glycol, formaldehyde, methanol, methylene chloride, tetrachloroethylene, toluene, and xylenes. HAP present in wastewater entering POTW can biodegrade, adhere to sewage sludge, volatilize to the air, or pass through (remain in the wastewater discharge) to receiving waters. Within the POTW source category, wastewater treatment units are the most likely source for HAP emissions, but wastewater collection systems, including sewers and other transport systems, may also have significant emissions in cases where the systems transport industrial wastewater. In addition to the wastewater treatment processes at a POTW, other sources of HAP emissions, such as sewage sludge incinerators, may be collocated at the same site. Sewage sludge incineration is regulated under section 129 of the CAA and is not a part of the POTW source category regulated under the POTW NESHAP as discussed in this preamble. However, HAP emissions from any collocated sources must be included when determining whether a source is a major source of HAP.

4. Regulation of HAP Emissions in the 2002 POTW NESHAP

The POTW NESHAP specifies requirements for both subcategories. Under the POTW NESHAP, an existing, industrial (Group 1) POTW must meet the requirements of the industrial source's NESHAP. For example, a POTW that accepts and treats wastewater for a pulp and paper facility in order to meet the wastewater requirements in 40 CFR part 63, subpart S is subject to the specific requirements found in subpart S, instead of requirements found in 40 CFR part 63, subpart VVV. A new or reconstructed, industrial (Group 1) POTW must meet the requirements of the industrial source's NESHAP or the requirements for new or reconstructed, non-industrial (Group 2) POTW, whichever is more stringent.

There are no control requirements in the 2002 NESHAP for existing, non-industrial (Group 2) POTW. However, new or reconstructed, non-industrial (Group 2) POTW must equip each treatment unit up to, but not including, the secondary influent pumping station, with a cover. The affected emission points at new or reconstructed non-industrial (Group 2) POTW include, but are not limited to, influent waste stream conveyance channels, bar screens, grit chambers, grinders, pump stations, aerated feeder channels, primary clarifiers, primary effluent channels, and primary screening stations. In addition, all covered units, except the primary clarifiers, must have the air in the headspace ducted to a control device in accordance with 40 CFR 63.693, the standards for closed-vent systems and control devices found in subpart DD of this part. As an alternative to these requirements, a new or reconstructed, non-industrial (Group 2) POTW can demonstrate, for all units up to the secondary influent pumping station or the secondary treatment units, that the HAP fraction emitted does not exceed 0.014. This is demonstrated by dividing the sum of all HAP emissions

from the primary treatment units by the sum of all HAP mass loadings (

i.e.,

the concentration of all HAP in the influent wastewater) on an annual rolling average. The POTW is allowed to use any combination of pretreatment, wastewater treatment plant modifications, and control devices to achieve this performance standard.

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

In October 2015, the EPA issued an information collection request (ICR), pursuant to CAA section 114, to nine POTW (covering a total of 18 facilities) that were known to, or thought to potentially, own and operate a POTW subject to the POTW NESHAP. EPA requested information on the treatment units that are subject to requirements in the POTW NESHAP (primary treatment units), as well as information on pretreatment programs, collection sewers, and secondary treatment units. EPA also requested information on control devices and location coordinates (latitude and longitude) of the individual treatment units (if fugitive sources) and emission points (if point sources). The ICR requested information on any HAP-containing chemicals used as part of the wastewater treatment process, point and fugitive HAP emissions, practices used to control HAP emissions, and other aspects of facility operations. The respondents to the ICR provided information on a total of five facilities subject to the POTW NESHAP and 12 synthetic area

or area source facilities not subject to the POTW NESHAP. Only the POTW subject to the NESHAP were included in the risk modeling analysis. One facility did not provide a response and it is unknown if this POTW is subject to the POTW NESHAP. We received emissions data directly from each POTW subject to the POTW NESHAP that responded to the survey in the form of ToxChem+ or WATER9 modeling results. Following the initial response, one POTW that was previously thought to be subject to the POTW NESHAP submitted correspondence from their state, which defines the POTW as an area source of HAP emissions, therefore, not subject to the POTW NESHAP.

Thus, we identified a total of four POTW subject to the POTW NESHAP through the 2015 ICR.

A synthetic area facility installs controls in order to reduce HAP emissions below major source thresholds prior to the initial compliance date of the NESHAP.

See

Letter from State of Missouri regarding Bissell Point,

2016. While the agency no longer considers this POTW to be a major source or subject to the POTW NESHAP, the POTW is still included in discussions in supporting materials and risk modeling.

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

The 2011 National Emissions Inventory (NEI version 2) provided supplemental information for this RTR. The NEI is a database that contains information about sources that emit criteria air pollutants, their precursors, and HAP. The database includes estimates of annual air pollutant emissions from point, nonpoint, and mobile sources in the 50 states, the District of Columbia, Puerto Rico, and the Virgin Islands. The EPA collects this information and releases an updated version of the NEI database every 3 years. The NEI includes information necessary for conducting risk modeling, including annual HAP emissions estimates from individual emission points at facilities and the related emissions release parameters.

For each emission record needed for the model input file for the risk assessment (hereafter referred to as the “RTR emissions dataset”) that was not available from the 2015 ICR responses, the EPA used available data in the 2011 NEI as the first alternative.

The 2011 NEI was used to identify an additional two POTW that are subject to the POTW NESHAP that had not received the ICR. For the six sources found subject to the POTW NESHAP (the four POTW identified in the ICR responses and the two POTW identified from the NEI), the 2011 NEI provided emissions estimates for co-located emission points that are not part of the POTW source category. These data include emissions from boilers, engines, and sewage sludge incinerators that are located at the POTW, but are not in the POTW source category. These data were incorporated into the RTR emissions dataset to determine the whole facility risk.

See Inputs to the Publicly Owned Treatment Works March 2016 Residual Risk Modeling,

June 2016, located in docket number EPA-HQ-OAR-2016-0490.

The EPA's Enforcement Compliance History Online (ECHO) database was also used as a tool to identify which POTW were potentially subject to the POTW NESHAP and provided a list of sources to consider for the 2015 ICR. ECHO provides integrated compliance and enforcement information for approximately 800,000 regulated facilities nationwide. Using the search feature in ECHO, the EPA identified twenty POTW that could potentially be subject to the POTW NESHAP. The EPA then searched state Web sites for operating permits for these 20 POTW to determine whether the permits stated the POTW was subject to the rule. The four POTW identified as subject to the POTW NESHAP through the ICR were identified in the list of potential sources found in the ECHO database and subsequent permit search.

The EPA searched for Reasonably Available Control Technology (RACT), Best Available Control Technology (BACT), and Lowest Achievable Emission Rate (LAER) determinations in the RACT/BACT/LAER Clearinghouse. This is a database that contains case-specific information of air pollution technologies that have been required to reduce the emissions of air pollutants from stationary sources. Under the EPA's New Source Review (NSR) program, if a facility is planning new construction or a modification that will increase the air emissions by a large amount, an NSR permit must be obtained. This central database promotes the sharing of information among permitting agencies and aids in case-by-case determinations for NSR permits. We examined information contained in the RACT/BACT/LAER Clearinghouse to determine what technologies are currently used at POTW to reduce air emissions.

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 seven sections that follow this paragraph describe how we estimated emissions and conducted the risk assessment. The docket for this rulemaking contains the following document which provides more information on the risk assessment inputs and models:

Residual Risk Assessment for the Publicly Owned Treatment Works Source Category in Support of the December 2016 Risk and Technology Review Proposed Rule (hereafter “Residual Risk Report”).

The

methods used to assess risks (as described in the seven primary steps below) are consistent with the methods that were 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.

The methods used here are also consistent with the key recommendations contained in that report.

U.S. EPA SAB.

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

May 2010.

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

Data for seven POTW were used to create the RTR emissions dataset, as described in section II.C of this preamble. As stated in section II.C of this preamble, we evaluated the risk associated with emissions from seven POTW, even though one POTW was later determined to be an area source of HAP emissions. The emissions sources included in the RTR emissions dataset include the following types of emission sources currently regulated by the POTW NESHAP: Primary treatment units including, lift stations, bar screens, grit chambers, grinders, Parshall flumes, denitrification, primary clarifiers, primary settling basins, and primary effluent channels. The RTR emissions dataset also includes the following types of emission sources not currently regulated by the POTW NESHAP: Secondary treatment units, including secondary clarifiers, aeration tanks, trickling filters, UNOX systems, and open lagoons; tertiary treatment units, including chlorine sumps, splitter boxes, and chlorine contact tanks; and gravity thickeners for sludge handling. For both emissions sources that are and those that are not currently regulated by the POTW NESHAP, the dataset includes both fugitive emissions and stack emissions. This RTR emissions dataset is based primarily on data gathered through the 2015 ICR and supplemented with data from 2011 NEI, 2011 NATA, and ECHO, as described in sections II.C and II.D of this preamble. These data sources provided all of the emissions data in the RTR emissions dataset and nearly all of the facility-specific data needed to conduct the risk modeling analysis. However, there were limited instances where default values were used to fill gaps in the facility-specific data used in the risk modeling analysis. For example, default values were used for stack and fugitive release parameters. Use of defaults are discussed in detail in the memorandum,

Inputs to the Publicly Owned Treatment Works March 2016 Residual Risk Modeling,

June 2016 (Modeling Inputs Memo), available in the docket for this action.

The RTR emissions dataset was refined following an extensive quality assurance check of source locations, emission release characteristics, and annual emission estimates. We checked the coordinates of each emission source in the dataset using ArcGIS to ensure the emission point locations were correct. For further information on the EPA's quality assurance review, see the Modeling Inputs Memo available in the docket for this action.

A list of the six POTW and additional information used to develop the RTR emissions dataset are available in the POTW RTR database itself, and additional documentation on the development of this database is provided in the Modeling Inputs Memo, both of which are 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.)

We used the RTR emissions dataset to estimate MACT-allowable emissions levels. POTW were asked to provide their design capacity and their average treatment capacity as part of the 2015 ICR. In discussions with the POTW that responded, EPA noted that most POTW operate below their design capacity. To be conservative, the EPA estimated that the reported emissions were for operations at half capacity. Therefore, the EPA chose to use a single multiplier of 2.0 to scale the actual annual emissions to allowable annual emissions. The docket for this rulemaking contains information on the development of estimated MACT-allowable emissions in the Modeling Inputs Memo.

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 kilometers (km) of the modeled sources,

and (3) estimating individual and population-level inhalation risks using the exposure estimates and quantitative dose-response information.

This metric comes from the Benzene NESHAP.

See

54 FR 38046.

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

To perform the dispersion modeling and to develop the preliminary risk estimates, HEM-3 draws on three data libraries. The first is a library of meteorological data, which is used for dispersion calculations. This library includes 1 year (2011) 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

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.

U.S. EPA. Revision to the

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

(70 FR 68218, November 9, 2005).

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

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

)) 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)

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.

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://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%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 (ATSDR) 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/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0

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

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

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.

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, 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.

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/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary

) 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). The National Advisory Committee (NAC) for the Development of Acute Exposure Guideline Levels for Hazardous Substances, usually referred to as the AEGL Committee or the NAC/AEGL committee, developed AEGL values for at least 273 of the 329 chemicals on the AEGL priority chemical list. The last meeting of the NAC/AEGL Committee was in April 2010, and its charter expired in October 2011. The NAC/AEGL Committee ended in October 2011, but the AEGL program continues to operate at the EPA and works with the National Academies to publish final AEGLs, (

https://www.epa.gov/aegl

As described in

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

(

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

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

Id.

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

Id.

at 2.

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

(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 Emergency Response Planning (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.”

Id.

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

Id.

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

Id.

at 1.

ERP Committee Procedures and Responsibilities.

November 1, 2006. American Industrial Hygiene Association.

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

Acute REL values for 1-hour exposure durations are typically lower than their corresponding AEGL-1 and ERPG-1 values. Even though their definitions are slightly different, AEGL-1 values are often the same as the corresponding ERPG-1 values, and AEGL-2 values are often equal to ERPG-2 values. Maximum HQ values from our acute screening risk assessments typically result when basing them on the acute REL value for a particular pollutant. In cases where our maximum acute HQ value exceeds 1, we also report the HQ value based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1 value).

To develop screening estimates of acute exposures in the absence of hourly

emissions data, generally we first develop estimates of maximum hourly emissions rates by multiplying the average actual annual hourly emissions rates by a default factor to cover routinely variable emissions. We choose the factor to use partially based on process knowledge and engineering judgment. The factor chosen also reflects a Texas study of short-term emissions variability, which showed that most peak emission events in a heavily-industrialized four-county area (Harris, Galveston, Chambers, and Brazoria Counties, Texas) were less than twice the annual average hourly emissions rate. The highest peak emissions event was 74 times the annual average hourly emissions rate, and the 99th percentile ratio of peak hourly emissions rate to the annual average hourly emissions rate was 9.

Considering this analysis, to account for more than 99 percent of the peak hourly emissions, we apply a conservative screening multiplication factor of 10 to the average annual hourly emissions rate in our acute exposure screening assessments as our default approach. However, we use a factor other than 10 if we have information that indicates that a different factor is appropriate for a particular source category. For this source category, the default factor of 10 was used.

Allen, et al., 2004. Variable Industrial VOC Emissions and their impact on ozone formation in the Houston Galveston Area. Texas Environmental Research Consortium.

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

and_their_Impact_on_Ozone_Formation_in_the_Houston_Galveston_Area.

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. Ideally, we would prefer to have continuous measurements over time to see how the emissions vary by each hour over an entire year. Having a frequency distribution of hourly emissions rates over a year would allow us to perform a probabilistic analysis to estimate potential threshold exceedances and their frequency of occurrence. Such an evaluation could include a more complete statistical treatment of the key parameters and elements adopted in this screening analysis. Recognizing that this level of data is rarely available, we instead rely on the multiplier approach. To better characterize the potential health risks associated with estimated acute exposures to HAP, and in response to a key recommendation from the SAB's peer review of the EPA's RTR risk assessment methodologies,

we generally examine a wider range of available acute health metrics (

e.g.,

RELs, AEGLs) than we do for our chronic risk assessments. This is in response to the SAB's acknowledgement that there are generally more data gaps and inconsistencies in acute reference values than there are in chronic reference values. In some cases, when Reference Value Arrays

for HAP have been developed, we consider additional acute values (

i.e.,

occupational and international values) to provide a more complete risk characterization.

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

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

U.S. EPA. 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 multipathway exposure and risk screening?

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

i.e.,

ingestion). We first determined whether any sources in the source 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 POTW source category, we identified emissions of a single polycyclic organic matter (POM) species, specifically 2-methylnaphthalene. Because one or more of these PB-HAP are emitted by at least one facility in the POTW source category, we proceeded to the next step of the evaluation. In this step, we determined whether the facility-specific emissions rates of the emitted PB-HAP were large enough to create the potential for significant non-inhalation human health risks under reasonable worst-case conditions. To facilitate this step, we developed emissions rate screening levels for several PB-HAP using a hypothetical upper-end screening exposure scenario developed for use in conjunction with the EPA's Total Risk Integrated Methodology.Fate, Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with emissions rate screening levels are: Lead, cadmium, chlorinated dibenzodioxins and furans, mercury compounds, and POM. We conducted a sensitivity analysis on the screening scenario to ensure that its key design parameters would represent the upper end of the range of possible values, such that it would represent a conservative, but not impossible scenario. The facility-specific emissions rates of these PB-HAP were compared to the emission rate screening levels for these PB-HAP to assess the potential for significant human health risks via non-inhalation pathways. We call this application of the TRIM.FaTE model the Tier 1 TRIM-screen or Tier 1 screen.

For the purpose of developing emissions rates for our Tier 1 TRIM-screen, we derived emission levels for these PB-HAP (other than lead compounds) at which the maximum excess lifetime cancer risk would be 1-in-1 million (

i.e.,

for polychlorinated dibenzodioxins and furans and POM) or, for HAP that cause non-cancer health effects (

i.e.,

cadmium compounds and mercury compounds), the maximum HQ would be 1. If the emissions rate of any PB-HAP included in the Tier 1 screen exceeds the Tier 1 screening emissions rate for any facility, we conduct a second screen, which we call the Tier 2 TRIM-screen or Tier 2 screen.

In the Tier 2 screen, the location of each facility that exceeded the Tier 1 emission rate is used to refine the assumptions associated with the environmental scenario while maintaining the exposure scenario assumptions. A key assumption that is part of the Tier 1 screen is that a lake is located near the facility; we confirm the existence of lakes near the facility as part of the Tier 2 screen. We then adjust the risk-based Tier 1 screening level for each PB-HAP for each facility based on an understanding of how exposure concentrations estimated for the screening scenario change with meteorology and environmental assumptions. PB-HAP emissions that do not exceed these new Tier 2 screening levels are considered to pose no unacceptable risks. If the PB-HAP emissions for a facility exceed the Tier 2 screening emissions rate and data are available, we may decide to conduct a more refined Tier 3 multipathway

assessment. There are several analyses that can be included in a Tier 3 screen depending upon the extent of refinement warranted, including validating that the lake is fishable and considering plume-rise to estimate emissions lost above the mixing layer. If the Tier 3 screen is exceeded, the EPA may further refine the assessment. Notably, for the POTW source category, emissions of POM did not exceed the Tier 1 screening level. Therefore, the Tier 2 and 3 screening scenarios were not necessary.

For further information on the multipathway analysis approach, see the

Residual Risk Report,

which is available in the docket for this action.

5. 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, 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 EPA NEI).

In addition to accounting for almost all of the mass of PB-HAP emitted, we note that the TRIM.FaTE model that we use to evaluate multipathway risk allows us to estimate concentrations of cadmium compounds, dioxins/furans, POM, and mercury in soil, sediment, and water. For lead 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 NAAQS for lead.

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

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

Due to their well-documented potential to cause direct damage to terrestrial plants, we include two acid gases, HCl, and HF in the environmental screening analysis. According to the 2005 NEI, HCl and HF account for about 99 percent (on a mass basis) of the total acid gas HAP emitted by stationary sources in 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 multipathway 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. Ecological Assessment Endpoints and Benchmarks for PB-HAP

An important consideration in the development of the EPA's screening methodology is the selection of ecological assessment endpoints and benchmarks. Ecological assessment endpoints are defined by the ecological entity (

e.g.,

aquatic communities, including fish and plankton) and its attributes (

e.g.,

frequency of mortality). Ecological assessment endpoints can be established for organisms, populations, communities or assemblages, and ecosystems.

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

• Local terrestrial communities (

i.e.,

soil invertebrates, plants) and populations of small birds and mammals that consume soil invertebrates exposed to PB-HAP in the surface soil;

• Local benthic (

i.e.,

bottom sediment dwelling insects, amphipods, isopods, and crayfish) communities exposed to PB-HAP in sediment in nearby water bodies; and

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

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

• Piscivorous (

i.e.,

fish-eating) wildlife consuming PB-HAP-contaminated fish from nearby water bodies.

For cadmium compounds, dioxins/furans, POM, and mercury, we identified the available ecological benchmarks for each assessment endpoint. An ecological benchmark represents a concentration of HAP (

e.g.,

0.77 ug of HAP per liter of water) that has been linked to a particular environmental effect level through scientific study. For PB-HAP we identified, where possible, ecological benchmarks at the following effect levels:

•

Probable effect levels (PEL):

Level above which adverse effects are expected to occur frequently;

•

Lowest-observed-adverse-effect level (LOAEL):

The lowest exposure level tested at which there are biologically significant increases in frequency or severity of adverse effects; and

•

No-observed-adverse-effect levels (NOAEL):

The highest exposure level tested at which there are no biologically significant increases in the frequency or severity of adverse effect.

We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, the EPA sources that are used at a programmatic level (

e.g.,

Office of Water, Superfund Program) were used in the analysis, if available. If not, the EPA benchmarks used in regional programs (

e.g.,

Superfund) were used. If benchmarks were not available at a programmatic or regional level, we used benchmarks developed by other federal agencies (

e.g.,

National Oceanic and Atmospheric Administration (NOAA)) or state agencies.

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

d. Ecological Assessment Endpoints and Benchmarks for Acid Gases

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

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

The selection of ecological benchmarks for the effects of acid gases on plants followed the same approach as for PB-HAP (

i.e.,

we examine all of the available chronic benchmarks). For HCl, the EPA identified chronic benchmark concentrations. We note that the benchmark for chronic HCl exposure to plants is greater than the reference concentration for chronic inhalation exposure for human health. This means that where the EPA includes regulatory requirements to prevent an exceedance of the reference concentration for human health, additional analyses for adverse environmental effects of HCl would not be necessary.

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

e. Screening Methodology

For the environmental risk screening analysis, the EPA first determined whether any facilities in the POTW source category emitted any of the seven environmental HAP. For the POTW source category, we identified emissions of a single POM species, specifically 2-methylnaphthalene.

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

f. PB-HAP Methodology

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

To facilitate this step, TRIM.FaTE was run for each PB-HAP under hypothetical environmental conditions designed to provide conservatively high HAP concentrations. The model was set to maximize runoff from terrestrial parcels into the modeled lake, which in turn, maximized the chemical concentrations in the water, the sediments, and the fish. The resulting media concentrations were then used to back-calculate a screening level emission rate that corresponded to the relevant exposure benchmark concentration value for each assessment endpoint. To assess emissions from a facility, the reported emission rate for each PB-HAP was compared to the screening level emission rate for that PB-HAP for each assessment endpoint. If emissions from a facility do not exceed the Tier 1 screening level, the facility “passes” the screen, and, therefore, is not evaluated further under the screening approach. If emissions from a facility exceed the Tier 1 screening level, we evaluate the facility further in Tier 2.

In Tier 2 of the environmental screening analysis, the emission rate screening levels are adjusted to account for local meteorology and the actual location of lakes in the vicinity of facilities that did not pass the Tier 1 screen. The modeling domain for each facility in the Tier 2 analysis consists of 8 octants. Each octant contains 5 modeled soil concentrations at various distances from the facility (5 soil concentrations × 8 octants = total of 40 soil concentrations per facility) and one lake with modeled concentrations for water, sediment, and fish tissue. In the Tier 2 environmental risk screening analysis, the 40 soil concentration points are averaged to obtain an average soil concentration for each facility for each PB-HAP. For the water, sediment, and fish tissue concentrations, the highest value for each facility for each pollutant is used. If emission concentrations from a facility do not exceed the Tier 2 screening level, the facility passes the screen, and typically is not evaluated further. If emissions from a facility exceed the Tier 2 screening level, the facility does not pass the screen and, therefore, may have the potential to cause adverse environmental effects. Such facilities are evaluated further to investigate factors such as the magnitude and characteristics of the area of exceedance. Notably, for the POTW source category, emissions of POM did not exceed the Tier 1 ecological screening level. Therefore, the Tier 2 screen was not necessary.

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

Residual Risk Report,

which is available in the docket for this action.

6. 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 from all other emission sources at the facility for which we have data. Using the most current available NEI data at the time of the analysis, the EPA developed “facility-wide” emissions estimates. For this category, the latest available version of the NEI was the 2011 NEI Version 2. It is important to note that the NEI

facility-wide inventory may not always reflect the level of detail or be representative of the same temporal period that is found in the source category specific inventory. Further information on the NEI, which is developed from state/local/tribal submitted data, can be found on the EPA's Web site at:

https://www.epa.gov/air-emissions-inventories/national-emissions-inventory

We analyzed risks due to the inhalation of HAP that are emitted facility-wide for the populations residing within 50 km of each facility, consistent with the methods used for the source category analysis described above. For these facility-wide risk analyses, the modeled source category risks were compared to the facility-wide risks to determine the portion of facility-wide risks that could be attributed to the source category addressed in this proposal. We specifically examined the facility that was associated with the highest estimate of risk and determined the percentage of that risk attributable to the source category of interest. The

Residual Risk Report,

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

7. 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 Report,

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.

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

e.g.,

1-in-10 thousand or 1-in-1 million).

Short-term mobility is movement from one 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.

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 Report,

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).

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

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

e.g.,

priority-setting or expected benefits analysis).

IRIS glossary (

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

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,

e.g.,

factors of 10 or 3, used in the absence of compound-specific data; where data are available, UF may also be developed using compound-specific information. When data are limited, more assumptions are needed and more UF are used. Thus, there may be a greater tendency to overestimate risk in the sense that further study might support development of reference values that are higher (

i.e.,

less potent) because fewer default assumptions are needed. However, for some pollutants, it is possible that risks may be underestimated.

According to the NRC report,

Science and Judgment in Risk Assessment

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

Risk Assessment in the Federal Government: Managing the Process,

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

See

EPA,

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.

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

For a group of compounds that are unspeciated (

e.g.,

glycol ethers), we conservatively use the most protective reference value of an individual compound in that group to estimate risk. Similarly, for an individual compound in a group (

e.g.,

ethylene glycol diethyl ether) that does not have a specified reference value, we also apply the most protective reference value from the other compounds in the group to estimate risk.

e. Uncertainties in the Multipathway Assessment

For each source category, we generally rely on site-specific levels of PB-HAP emissions to determine whether a refined assessment of the impacts from multipathway exposures is necessary. This determination is based on the results of a three-tiered screening analysis that relies on the outputs from models that estimate environmental pollutant concentrations and human exposures for four PB-HAP. Two important types of uncertainty associated with the use of these models in RTR risk assessments and inherent to any assessment that relies on environmental modeling are model uncertainty and input uncertainty.

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

variability

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

uncertainty

in being able to accurately estimate the true result.

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

Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier 1 of the multipathway screen, we configured the models to avoid underestimating exposure and risk. This was accomplished by selecting upper-end values from nationally-representative datasets for the more influential parameters in the environmental model, including selection and spatial configuration of the area of interest, lake location and size, meteorology, surface water and soil characteristics, and structure of the aquatic food web. We also assume an ingestion exposure scenario and values for human exposure factors that represent reasonable maximum exposures.

In Tier 2 of the multipathway assessment, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values, and we identify the actual location of lakes near the facility rather than the default lake location that we apply in Tier 1. By refining the screening approach in Tier 2 to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screen. The assumptions and the associated uncertainties regarding the selected ingestion exposure scenario are the same for Tier 1 and Tier 2.

For both Tiers 1 and 2 of the multipathway assessment, our approach to addressing model input uncertainty is generally cautious. We choose model inputs from the upper end of the range of possible values for the influential parameters used in the models, and we assume that the exposed individual exhibits ingestion behavior that would lead to a high total exposure. This approach reduces the likelihood of not identifying high risks for adverse impacts.

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

For further information on uncertainties and the Tier 1 and 2 screening methods, refer to the risk document, Appendix 2,

Technical Support Document for TRIM-Based Multipathway Tiered Screening Methodology for RTR: Summary and Evaluation.

f. Uncertainties in the Environmental Risk Screening Assessment

For each source category, we generally rely on site-specific levels of environmental HAP emissions to perform an environmental screening assessment. The environmental screening assessment is based on the outputs from models that estimate environmental HAP concentrations. The same models, specifically the

TRIM.FaTE multipathway model and the AERMOD air dispersion model, are used to estimate environmental HAP concentrations for both the human multipathway screening analysis and for the environmental screening analysis. Therefore, both screening assessments have similar modeling uncertainties.

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

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

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

Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier 1 of the environmental screen for PB-HAP, we configured the models to avoid underestimating exposure and risk to reduce the likelihood that the results indicate the risks are lower than they actually are. This was accomplished by selecting upper-end values from nationally-representative datasets for the more influential parameters in the environmental model, including selection and spatial configuration of the area of interest, the location and size of any bodies of water, meteorology, surface water and soil characteristics, and structure of the aquatic food web. In Tier 1, we used the maximum facility-specific emissions for the PB-HAP (other than lead compounds, which were evaluated by comparison to the secondary lead NAAQS) that were included in the environmental screening assessment and each of the media when comparing to ecological benchmarks. This is consistent with the conservative design of Tier 1 of the screen. In Tier 2 of the environmental screening analysis for PB-HAP, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values, and we identify the locations of water bodies near the facility location. By refining the screening approach in Tier 2 to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screen. To better represent widespread impacts, the modeled soil concentrations are averaged in Tier 2 to obtain one average soil concentration value for each facility and for each PB-HAP. For PB-HAP concentrations in water, sediment, and fish tissue, the highest value for each facility for each pollutant is used.

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

For both Tiers 1 and 2 of the environmental screening assessment, our approach to addressing model input uncertainty is generally cautious. We choose model inputs from the upper end of the range of possible values for the influential parameters used in the models, and we assume that the exposed individual exhibits ingestion behavior that would lead to a high total exposure. This approach reduces the likelihood of not identifying potential risks for adverse environmental impacts.

Uncertainty also exists in the ecological benchmarks for the environmental risk screening analysis. We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, EPA benchmarks used at a programmatic level (

e.g.,

Office of Water, Superfund Program) were used if available. If not, we used EPA benchmarks used in regional programs (

e.g.,

Superfund Program). If benchmarks were not available at a programmatic or regional level, we used benchmarks developed by other agencies (

e.g.,

NOAA) or by state agencies.

In all cases (except for lead compounds, which were evaluated through a comparison to the NAAQS), we searched for benchmarks at the following three effect levels, as described in section III.A.5 of this preamble:

1. A no-effect level (

i.e.,

NOAEL).

2. Threshold-effect level (

i.e.,

LOAEL).

3. Probable effect level (

i.e.,

PEL).

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

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

Further information on uncertainties and the Tier 1 and 2 environmental screening methods is provided in Appendix 5 of the document,

Technical Support Document for TRIM-Based Multipathway Tiered Screening Methodology for RTR: Summary of Approach and Evaluation.

Also,

see

the

Residual Risk Report,

available in the docket for this action.

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

As discussed in section II.A of this preamble, in evaluating and developing standards under 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)

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.

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.”

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 POTW 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?

1. Inhalation Risk Assessment Results

Table 2 of this preamble provides an overall summary of the results of the inhalation risk assessment.

Table 2—POTW Inhalation Risk Assessment Results

Maximum individual cancer risk

(1-in-1 million)

Estimated population at increased risk levels of cancer

Estimated

annual cancer

incidence

(cases per

year)

Maximum chronic

non-cancer

TOSHI

Maximum screening acute

non-cancer

Actual Emissions

0.8

≥ 1-in-1 million: 0

0.0006

0.007

REL

= 2 (formaldehyde).

≥ 10-in-1 million: 0

≥ 100-in-1 million: 0

Allowable Emissions

≥ 1-in-1 million: 240

0.001

0.01

≥ 10-in-1 million: 0

≥ 100-in-1 million: 0

Estimated maximum individual excess lifetime cancer risk due to HAP emissions from the source category.

Maximum TOSHI. The target organ with the highest TOSHI for POTW source category for both actual and allowable emissions is the respiratory system.

See

section III.A.3 of this preamble for explanation of acute dose-response values. Acute assessments are not performed on allowable emissions.

The development of allowable emission estimates can be found in the memorandum titled

Inputs to the Publicly Owned Treatment Works March 2016 Residual Risk Modeling,

June 2016 (Modeling Inputs Memo), which is available in the docket.

The results of the chronic baseline inhalation cancer risk assessment indicate that, based on estimates of current actual emissions, the MIR posed for the POTW source category is 0.8-in-1 million, with emissions of formaldehyde from the primary clarifier accounting for the majority of the risk. The total estimated cancer incidence from POTW based on actual emission levels is 0.0006 excess cancer cases per year or one case every 1,667 years, with emissions of formaldehyde and acrylonitrile contributing 50 percent and 21 percent, respectively, to the cancer incidence.

When considering MACT-allowable emissions, the MIR is estimated to be up to 2-in-1 million, driven by emissions of formaldehyde from the primary clarifier. The cancer incidence is estimated to be 0.001 excess cancer cases per year, or one excess case in every 1,000 years. Approximately 240 people are estimated to have cancer risks greater than or equal to 1-in-1 million considering allowable emissions from the POTW source category.

The maximum modeled chronic non-cancer HI (TOSHI) for the source category based on actual emissions is estimated to be 0.007, driven by formaldehyde emissions from the primary clarifier. When considering MACT-allowable emissions, the maximum chronic non-cancer TOSHI is estimated to be 0.01, driven by formaldehyde emissions.

2. Acute Risk Results

Our screening analysis for worst-case acute impacts based on actual emissions indicates the potential for one pollutant, formaldehyde, from one facility, to have an HQ above 1, based on the formaldehyde REL. Six out of seven POTW treatment plants had an estimated worst-case HQ less than or equal to 1 for all HAP.

To better characterize the potential health risks associated with the estimated worst-case acute exposure to HAP from the POTW source category, and in response to a key recommendation from the SAB's peer review of the EPA's CAA section 112(f) RTR risk assessment methodologies, we examine a wider range of available acute health metrics than we do for our chronic risk assessments. This is because there generally are greater uncertainties associated with the use of acute reference values.

By definition, the acute CalEPA REL represents a health-protective level of exposure, with no risk anticipated below those levels, even for repeated exposures; however, the health risk from higher-level exposures is unknown. Therefore, when a CalEPA REL is exceeded and an AEGL-1 or ERPG-1 level (

i.e.,

levels at which mild effects are anticipated in the general public for a single exposure) is available, we have used them as a second comparative measure. For the purpose of characterizing public health risks in RTR assessments, we typically have not compared estimated maximum off-site 1-hour exposure levels to occupational levels. This is because occupational ceiling values are not generally considered protective for the general public since they are designed to protect the worker population (presumed healthy adults) against short-duration (less than 15-minutes) exposures. As a result, for most chemicals, the 15-minute occupational ceiling values are higher than a 1-hour AEGL-1 and/or ERPG-1, making comparisons to them irrelevant unless the AEGL-1 or ERPG-1 levels are also exceeded.

The worst-case maximum estimated 1-hour exposure to formaldehyde outside the POTW treatment plant fenceline exceeds the 1-hour REL by about a factor of 2 (HQ

REL

=2) but is substantially less than the AEGL-1 and ERPG-1 values for formaldehyde (HQ

AEGL-1

= 0.2 and HQ

ERPG-1

= 0.2). All other HAP in this analysis have worst-case acute HQs of 1 or less, indicating little to no potential for acute health risk.

In characterizing the potential for acute non-cancer impacts of concern, it is important to remember the upward bias of these exposure estimates. First, peak 1-hour emissions were conservatively assumed to be 10 times the annual emission rate. It was then assumed that emissions from all emission points at a given POTW peaked concurrently, and at the same time worst-case hourly meteorology was occurring. Finally, it was assumed that a person would be located at the point of maximum concentration for at least an hour. When these factors are taken together, there is likely little potential for acute health risk from POTW emissions.

3. Multipathway Risk Screening Results

PB-HAP emissions of 2-methylnaphthalene (

i.e.,

the only PB-HAP emitted from the POTW source category) did not exceed the worst-case Tier I screening emission rate. No other PB-HAP are emitted by any source in the source category.

4. Environmental Risk Screening Results

As described in section III.A of this preamble, we conducted a screening-level evaluation of the potential for adverse environmental effects associated with emissions of 2-methylnaphthalene.

In the Tier 1 screening analysis for 2-methylnaphthalene, the modeled Tier 1 concentrations of this PB-HAP did not exceed any ecological benchmarks for any POTW in the source category.

5. Facility-Wide Risk Results

The facility-wide chronic MIR and TOSHI were estimated based on emissions from all sources at the identified facilities (both MACT and non-MACT sources). The results of the facility-wide assessment of cancer risks indicate that three facilities with POTW operations have a facility-wide cancer MIR greater than or equal to 1-in-1 million. The maximum facility-wide cancer MIR is 10-in-1 million, primarily driven by formaldehyde. The maximum facility-wide TOSHI for the source category is estimated to be 0.09, primarily driven by emissions of formaldehyde.

6. What demographic groups might benefit from this regulation?

To examine the potential for any environmental justice (EJ) concerns that might be associated with the source category, we performed a demographic analysis of the population close to the facilities. In this analysis, we evaluated the distribution of HAP-related cancer and non-cancer risks from the POTW source category 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 POTW Facilities,

available in the docket for this action.

The results of the demographic analysis are summarized in Table 3 of this preamble. These results, for various demographic groups, are based on the estimated risks from actual emissions levels for the population living within 50 km of the facilities.

Table 3—POTW Demographic Risk Analysis Results

Nationwide

Population with cancer risk at or above 1-in-1 million due to POTW

Population with chronic hazard index above 1 due to POTW

Total Population

312,861,265

Race by Percent

White

All Other Races

Race by Percent

White

African American

Native American

1.1

Other and Multiracial

Ethnicity by Percent

Hispanic

Non-Hispanic

Income by Percent

Below Poverty Level

Above Poverty Level

+86

Education by Percent

Over 25 and without High School Diploma

Over 25 and with a High School Diploma

The results of the POTW source category demographic analysis indicate that emissions from the source category expose no person to a cancer risk at or above 1-in-1 million or to a chronic non-cancer TOSHI greater than 1. The demographics of the population living within 50 km of POTW can be found in Table 2 of the document:

Risk and Technology Review—Analysis of Socio-Economic Factors for Populations Living Near Publicly Owned Treatment Works.

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

1. Risk Acceptability

As noted in section II.A.1 of this preamble, the EPA sets standards under CAA section 112(f)(2) using “a two-step standard-setting approach, with an analytical first step to determine an `acceptable risk' that considers all health information, including risk estimation uncertainty, and includes a presumptive limit on MIR of approximately 1 in 10 thousand.” 54 FR 38045, September 14, 1989.

In determining whether risks are acceptable for the POTW source category, the EPA considered all available health information including any uncertainty in risk estimates. Also, as noted in section IV.A of this preamble, the Agency estimated risk from both actual and allowable emissions. While there are uncertainties associated with both the actual and allowable emissions, we consider the allowable emissions to be an upper bound, based on the conservative methods we used to calculate allowable emissions.

The estimated inhalation cancer risk based on actual emissions is less than 1-in-1 million. Additionally, the estimated inhalation cancer risk based on allowable emissions is 10-in-1 million. Both of these results are considerably less than the presumptive limit of acceptability (

i.e.,

100-in-1 million). The maximum chronic inhalation non-cancer hazard indices for both the actual and allowable emissions are less than 1, indicating that chronic exposures are without appreciable risk of non-cancer health effects.

The multipathway screening analysis indicates that PB-HAP emissions did not exceed the screening emission rates for any PB-HAP evaluated.

The screening assessment of worst-case acute inhalation exposures resulting from actual emissions indicates that the worst-case maximum estimated 1-hour exposure to formaldehyde outside the facility fence line exceeds the 1-hour REL by a factor of 2 (HQ

REL

= 2). It is important to note that this highest offsite HQ value assumes an hourly emissions multiplier of 10 times the annual emissions rate, while also assuming that a person will be present at the location of highest exposure for at least 1 hour when emissions from all emission points are at their peak. We further assume these peak emissions are occurring at same time worst-case meteorology is occurring. Finally, it is important to note that this conservatively estimated 1-hour formaldehyde concentration is well below the AEGL-1 and ERPG-1 for formaldehyde. Taken together, we believe there is little potential for acute health risk from formaldehyde. All other HAP in this analysis have worst-case acute HQ values outside facility fencelines of 1 or less indicating little potential risk of acute health effects.

Considering all of the health risk information and factors discussed above, including the uncertainties discussed in section III.A.7 of this preamble, the EPA proposes that additional standards are not necessary to bring risk to an acceptable level because cancer risks are well below the presumptive limit of acceptability, and

other health risk information indicates there is minimal likelihood of adverse non-cancer (including chronic, acute, and multipathway) health effects due to HAP emissions from this source category.

2. Ample Margin of Safety Analysis

In the ample margin of safety analysis, we evaluate available control technologies and other measures (including those evaluated under the technology review, as well as the risk reductions achieved by such potential additional measures, to determine whether additional standards are required to reduce risks further. In conducting the ample margin of safety analysis we consider the costs and economic impacts and technological feasibility of additional standards.

We are proposing that the 2002 POTW NESHAP requirements provide an ample margin of safety to protect public health. As explained in section IV.A of this preamble, we estimate that the MIR in the exposed population is less than 1-in-1 million at the actual emission levels. Additionally, the chronic non-cancer TOSHI is less than 1 and there is negligible potential for acute risk. Thus, EPA proposes that standards in the 2002 POTW NESHAP achieve the goal of providing the maximum feasible protection against risks to health from HAP.

Moreover, as noted in our discussion of the technology review in section IV.C of this preamble, no additional measures were identified for reducing HAP emissions from the POTW source category. Therefore, we propose that the 2002 standards provide an ample margin of safety to protect public health.

Although we are proposing to find that the 2002 standards provide an ample margin of safety to protect public health, we are proposing additional standards under CAA section 112(d)(6) that address HAP emissions from collection systems and all treatment units located at the POTW treatment plant. This is described more fully in Section IV.C.1 below. We are proposing that POTW develop and implement pretreatment programs to reduce organic HAP emissions from collection systems as wastewater is conveyed from an industrial user to the POTW treatment plant. All of the POTW identified as subject to the POTW NESHAP already have pretreatment programs in place; therefore, no additional emission reductions are expected. However, requiring control of emissions from collection systems by implementing pretreatment programs will allow POTW to limit potential future increases in emissions since the POTW will set limits on pollutants discharged to collection systems from industrial users. As noted above, we are proposing that the MACT standards, prior to the implementation of these proposed standards for collection systems, provide an ample margin of safety to protect public health. Therefore, we are proposing that, after the implementation of these standards for collection systems, the rule will continue to provide an ample margin of safety to protect public health. Consequently, it will not be necessary to conduct another residual risk review under CAA section 112(f) for this source category 8 years following promulgation of the new standards for collection systems, merely due to the addition of these MACT requirements. While our decisions on risk acceptability and ample margin of safety are supported even in the absence of these standards for collection systems, if we finalize the proposed requirements for these emission sources they will further strengthen our conclusions that risk is acceptable and the standards provide an ample margin of safety to protect public health.

Although we did not identify any new technologies to reduce risk for this source category, we are specifically requesting comment on whether there are additional control measures that may be able to reduce risks from the source category. We request any information on potential emission reductions of such measures, as well as the cost and health impacts of such reductions to the extent they are known.

3. Adverse Environmental Effects

Based on the results of our environmental risk screening assessment, we conclude that there is not an adverse environmental effect as a result of HAP emissions from the POTW source category. 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?

As described in section III.C of this preamble, our technology review focused on identifying developments in the practices, processes, and control technologies for the POTW source category. The EPA reviewed various information sources regarding POTW emission sources that are currently regulated by the POTW NESHAP, which include, but are not limited to, influent waste stream conveyance channels, bar screens, grit chambers, grinders, pump stations, aerated feeder channels, primary clarifiers, primary effluent channels, and primary screening stations.

As discussed further in sections II.C and D of this preamble, we conducted a search of the RBLC Clearinghouse, other regulatory actions (MACT standards, area source standards, and residual risk standards) subsequent to promulgation of the 2002 POTW NESHAP, literature related to research conducted for emission reductions from POTW emission sources, and state permits. Further, we reviewed the responses to the 2015 ICR to determine the technologies and practices reported by POTW.

We reviewed these data sources for information on add-on control technologies, other treatment units, work practices, procedures, and process changes or pollution prevention alternatives that were not considered during the development of the POTW NESHAP. We also looked for information on improvements in add-on control technology, other treatment units, work practices, procedures, and process changes or pollution prevention alternatives that have occurred since development of the POTW NEHSAP. Regarding work practices or pollution prevention alternatives, we examined data provided by the POTW in the 2015 ICR for the POTW NESHAP related to the pretreatment programs they implement.

As found during the development of the POTW NESHAP, there are generally two different control options that may be used at POTW: pretreatment programs and add-on controls (

i.e.,

covers or covers vented to a control device). The following sections summarize our technology review with respect to these work practices and controls as they can be used at industrial (Group 1) POTW and non-industrial (Group 2) POTW. (See section IV.D.2 of this preamble for a discussion of the proposed terminology change from “industrial” and “non-industrial” POTW to “Group 1” and “Group 2” POTW.)

1. Pretreatment Requirements

The applicability of the 2002 POTW NESHAP to a particular POTW depends in part on whether the POTW has or is required to develop a pretreatment program. However, we are proposing to remove having a pretreatment program as a condition for the applicability of the NESHAP and make it a requirement of the NESHAP.

See

section IV.D.1 of this preamble for a discussion of these changes. This section describes the

inclusion of pretreatment requirements as a requirement of the rule.

In the 2015 ICR for the POTW NESHAP, the EPA requested data related to any pretreatment programs the POTW had developed and implemented. All 17 of the POTW that responded to the ICR included information about their specific pretreatment programs, and all six of the sources subject to the POTW NESHAP have pretreatment requirements established for all industrial wastewaters they receive. The pretreatment requirements established by the POTW are based on the National Pretreatment Program, which was developed under the CWA to prevent pollutants from being introduced into a POTW that could interfere with the operation of the POTW, or could be passed through the treatment process and impact the use or disposal of sludge or be discharged to surface waters (40 CFR 403.5).

Under the Pretreatment Program, POTW subject to the requirement to develop a pretreatment program must identify their industrial users and control, through permits, orders, or other means, the contribution of pollutants to the POTW in order to ensure compliance with all national pretreatment standards and requirements. The industrial discharger must comply with the general requirements and specific prohibitions of EPA's regulations at 40 CFR part 403.5, categorical pretreatment standards spelled out for industrial categories at 40 CFR Subchapter N—Effluent Guidelines and Standards, and specific local limits that must be developed in defined circumstances. The specific prohibitions address characteristics of the wastewater streams and include specifications such as flashpoint, pH, solids size (to avoid obstructions), flowrates, and temperature of the wastewater. The specific prohibitions also prohibit “Pollutants which result in the presence of toxic gases, vapors, or fumes within t

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