National Emission Standards for Hazardous Air Pollutants: Off-Site Waste and Recovery Operations

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Part 63

[EPA-HQ-OAR-2012-0360; FRL-9911-93-0A]

RIN 2060-AR47

National Emission Standards for Hazardous Air Pollutants: Off-Site Waste and Recovery Operations

AGENCY:

Environmental Protection Agency.

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing amendments to the national emission standards for hazardous air pollutants (NESHAP) for off-site waste and recovery operations (OSWRO) to address the results of the residual risk and technology review (RTR) conducted under the Clean Air Act (CAA). In light of our residual risk and technology review, we are proposing to amend the requirements for leak detection and repair and the requirements for certain tanks. In addition, the EPA is proposing amendments to revise regulatory provisions pertaining to emissions during periods of startup, shutdown and malfunction; add requirements for electronic reporting of performance test results; revise the routine maintenance provisions; clarify provisions pertaining to open-ended valves and lines; add monitoring requirements for pressure relief devices; clarify provisions for some performance test methods and procedures; and make several minor clarifications and corrections.

DATES:

Comments.

Comments must be received on or before August 18, 2014. A copy of comments on the information collection provisions should be submitted to the Office of Management and Budget (OMB) on or before August 1, 2014.

Public Hearing.

We do not plan to conduct a public hearing unless requested. If requested, we will hold a public hearing on July 17, 2014. To request a hearing, please contact the person listed in the following

FOR FURTHER INFORMATION CONTACT

section by July 14, 2014.

ADDRESSES:

Comments.

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2012-0360, by one of the following methods:

•

Federal eRulemaking Portal: http://www.regulations.gov.

Follow the online instructions for submitting comments.

•

Email: A-and-R-docket@epa.gov.

Include Docket ID No. EPA-HQ-OAR-2012-0360 in the subject line of the message.

•

Fax:

(202) 566-9744, Attention Docket ID No. EPA-HQ-OAR-2012-0360.

•

Mail:

Environmental Protection Agency, EPA Docket Center (EPA/DC), Mail Code 28221T, Attention Docket ID No. EPA-HQ-OAR-2012-0360, 1200 Pennsylvania Avenue NW., Washington, DC 20460. Please include a total of two copies. In addition, please mail a copy of your comments on the information collection provisions to the Office of Information and Regulatory Affairs, Office of Management and Budget (OMB), Attn: Desk Officer for EPA, 725 17th Street NW., Washington, DC 20503.

•

Hand/Courier Delivery:

EPA Docket Center, Room 3334, EPA WJC West Building, 1301 Constitution Avenue NW., Washington, DC 20004, Attention Docket ID No. EPA-HQ-OAR-2012-0360. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for deliveries of boxed information.

Instructions.

Direct your comments to Docket ID No. EPA-HQ-OAR-2012-0360. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at

http://www.regulations.gov

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

http://www.regulations.gov

or email. The

http://www.regulations.gov

Web site is an “anonymous access” system, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through

http://www.regulations.gov

, your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should 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.

Docket.

The EPA has established a docket for this proposed rule under Docket ID No. EPA-HQ-OAR-2012-0360. 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, WJC West Building, Room 3334, 1301 Constitution Ave., NW., Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742.

Public Hearing.

If requested, we will hold a public hearing concerning this proposed rule on July 17, 2014 in the Research Triangle Park, North Carolina area. The EPA will provide further information about the hearing at the following Web site,

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

if a hearing is requested. Persons interested in presenting oral testimony at the hearing should contact Ms. Virginia Hunt, Sector Policies and Programs Division (E143-01), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, telephone number (919) 541-0832, by July 17, 2014. If no one requests to speak at the public hearing by July 14, 2014, then a public hearing will not be held, and a notification of such will be posted on

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

FOR FURTHER INFORMATION CONTACT:

For questions about this proposed action, contact Ms. Paula Hirtz, Sector Policies and Programs Division (E143-01), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711; telephone number: (919) 541-2618; fax number: (919) 541-0246; and email address:

hirtz.paula@epa.gov.

For specific information regarding the risk modeling methodology, contact Ms. Darcie Smith, Health and Environmental Impacts Division (C504-06), Office of Air Quality Planning and

Standards, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711; telephone number (919) 541-2076; fax number: (919) 541-0840; and email address:

smith.darcie@epa.gov.

For information about the applicability of the National Emission Standards for Hazardous Air Pollutants (NESHAP) to a particular entity, contact Ms. Marcia Mia, EPA Office of Enforcement and Compliance Assurance, telephone number (202) 564-7042; email address:

mia.marcia@epa.gov.

SUPPLEMENTARY INFORMATION:

Preamble Acronyms and Abbreviations

We use multiple acronyms and terms in this preamble. While this list may not be exhaustive, to ease the reading of this preamble and for reference purposes, the EPA defines the following terms and acronyms here:

AEGL—acute exposure guideline levels

AERMOD—air dispersion model used by the HEM-3 model

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

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 Mdel, Version 1.1.0

HF—hydrogen fluoride

HI—hazard index

HON—Hazardous Organic NESHAP

HQ—hazard quotient

ICR—Information Collection Request

IRIS—Integrated Risk Information System

km—kilometer

kPa—kilopascal

LDAR—leak detection and repair

LOAEL—lowest-observed-adverse-effect level

MACT—maximum achievable control technology

m

3

—cubic meter

mg/kg-day—milligrams per kilogram per day

mg/m

3

—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

NESHAP—National Emissions Standards for Hazardous Air Pollutants

NOAA—National Oceanic and Atmospheric Organization

NOAEL—no-observed-adverse-effect level

NRC—National Research Council

NTTAA—National Technology Transfer and Advancement Act

OAQPS—Office of Air Quality Planning and Standards

OMB—Office of Management and Budget

OSWRO—off-site waste and recovery operations

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

PEL—probable effect levels

POM—polycyclic organic matter

ppm—parts per million

PRD— pressure relief device

PTE—permanent total enclosure

RCO—recuperative thermal oxidizer

RCRA—Resource Conservation and Recovery Act

REL—reference exposure level

RFA—Regulatory Flexibility Act

RfC—reference concentration

RfD—reference dose

RIA—Regulatory Impact Analysis

RTR—residual risk and technology review

SAB—Science Advisory Board

SBA—Small Business Administration

SCC—source classification code

S/L/Ts—State, local and tribal air pollution control agencies

SOP—standard operating procedures

SSM—startup, shutdown and malfunction

TEQ—toxicity equivalence factor

TOC—total organic compound

TOSHI—target organ-specific hazard index

tpy—tons per year

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

TSDF—Solid Waste Treatment, Storage and Disposal Facility

TTN—Technology Transfer Network

UF—uncertainty factor

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?

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

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

II. Background

A. What is the statutory authority for this action?

B. What is this source category and how does the current NESHAP regulate its HAP emissions?

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

III. Analytical Procedures

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

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

C. How did we perform the technology review?

IV. Analytical Results and Proposed Decisions

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

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

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

D. What other actions are we proposing?

E. What compliance dates are we proposing?

V. Summary of Cost, Environmental, and Economic Impacts

A. What are the affected sources?

B. What are the air quality impacts?

C. What are the cost impacts?

D. What are the economic impacts?

E. What are the benefits?

VI. Request for Comments

VII. Submitting Data Corrections

VIII. Statutory and Executive Order Reviews

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

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

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

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

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

I. National Technology Transfer and Advancement Act

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

A red-line version of the regulatory language that incorporates the proposed changes in this action is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2012-0360).

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 to provide a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources. The Off-site Waste and Recovery Operations source category was initially titled the “Solid Waste Treatment, Storage, and Disposal Facilities (TSDF)” source category, which included commercial facilities that treat, store or dispose of any solid waste received from off-site, as well as commercial facilities that recycle, recover and re-refine wastes received from off-site.

1

On October 13,

1994 (59 FR 51913), the EPA explained that the source category was intended to represent those off-site waste and recovery operations that are not specifically listed as a separate distinct NESHAP source category such as hazardous waste incineration or municipal solid waste landfills and changed the title of the Solid Waste TSDF source category to “Off-Site Waste and Recovery Operations” to avoid confusion, to better distinguish this source category from other source categories, and to emphasize that this source category addresses only activities that manage wastes received from off-site.

1

See Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990 (57 FR 31576, July 16, 1992); U.S. EPA.

Documentation for Developing the Initial Source Category List

(EPA-450/3-91-030; July 1992).

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

Source category

NESHAP

Examples of regulated entities

Off-Site Waste and Recovery Operations

Off-Site Waste and Recovery Operations

Businesses or government agencies that operate any of the following: Hazardous waste TSDF; Resource Conservation and Recovery Act (RCRA) exempt hazardous wastewater treatment facilities; nonhazardous wastewater treatment facilities other than publicly-owned treatment works; used solvent recovery plants; RCRA exempt hazardous waste recycling operations; used oil re-refineries.

This table is not intended to be exhaustive, but rather is meant to provide a guide for readers regarding entities likely to be affected by this action. If you have any questions regarding the applicability of this action to a particular entity, consult either the air permitting authority for the entity or your EPA regional representative, as listed in 40 CFR 63.13 (General Provisions).

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

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

. Following publication in the

Federal Register

, the EPA will post the

Federal Register

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

http://www.epa.gov/ttn/atw/offwaste/oswropg.html

. Information on the overall RTR program is available at the following Web site:

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

.

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

Submitting CBI.

Do not submit information containing CBI to the EPA through

http://www.regulations.gov

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI for inclusion in the public docket. If you submit a CD-ROM or disk that does not contain CBI, mark the outside of the disk or CD-ROM clearly that it does not contain CBI. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver information identified as CBI only to the following address: Roberto Morales, 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-2012-0360.

II. Background

A. What is the statutory authority for this action?

Section 112 of the CAA establishes a two-stage regulatory process to address emissions of hazardous air pollutants (HAPs) from stationary sources. In the first stage, after the EPA has identified categories of sources emitting one or more of the HAP listed in CAA section 112(b), CAA section 112(d) requires us to promulgate technology-based NESHAP for those sources. “Major sources” are those that emit or have the potential to emit 10 tons per year (tpy) or more of a single HAP or 25 tpy or more of any combination of HAPs. For major sources, the technology-based NESHAP must reflect the maximum degree of emission reductions of HAPs 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 required to review these technology-based standards and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less frequently than every eight years. CAA section 112(d)(6). In conducting this review, the EPA is not required to recalculate the MACT floor. Natural Resources Defense Council (

NRDC

) v.

EPA,

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

Association of Battery Recyclers, Inc.

v.

EPA,

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

The second stage in standard-setting focuses on reducing any remaining (i.e., “residual”) risk according to CAA section 112(f). Section 112(f)(1) required EPA to 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. Section 112(f)(2) then provides that if Congress does not act on any recommendation in the Report, EPA must analyze and address residual risk for each category or subcategory of sources within 8 years after promulgation of such standards pursuant to 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 subsection 112(f)(2) incorporates the approach established in the Benzene NESHAP.

See NRDC

v.

EPA,

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

Federal Register

.”);

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

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

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

1. Step 1—Determination of Acceptability

The agency in the Benzene NESHAP concluded that “the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information” and that the “judgment on acceptability cannot be reduced to any single factor.” Benzene NESHAP at 38046. The determination of what represents an “acceptable” risk is based on a judgment of “what risks are acceptable in the world in which we live” (

Risk Report

at 178, quoting

NRDC

v.

EPA,

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

In the Benzene NESHAP, we stated that “EPA will generally presume that if the risk to [the maximum exposed] individual is no higher than approximately one in 10 thousand, that risk level is considered acceptable.” 54 FR at 38045, September 14, 1989. We discussed the maximum individual lifetime cancer risk (or maximum individual risk (MIR)) as being “the estimated risk that a person living near a plant would have if he or she were exposed to the maximum pollutant concentrations for 70 years.”

Id.

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

Id.

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

Id.

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

Id.

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

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

Id.

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

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

estimation uncertainties associated with the risk measures, weight of the scientific evidence for human health effects, other quantified or unquantified health effects, effects due to co-location of facilities, and co-emission of pollutants.

Id.

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

As noted earlier, in

NRDC

v.

EPA,

the court held that 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 at 38046, September 14, 1989.

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

NRDC

v.

EPA,

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

2

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

2

“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 current NESHAP regulate its HAP emissions?

The NESHAP for OSWRO was proposed on October 13, 1994 (59 FR 51913), promulgated on July 1, 1996 (61 FR 34140), and codified at 40 CFR part 63, subpart DD. The final rule was amended on July 20, 1999 (64 FR 38950). In general, the rule applies to waste management units and recovery operations that are: (1) Located at major sources of HAP emissions; and (2) used to manage, convey or handle used oil, used solvent or waste received from other facilities and that contain at least one of 97 organic HAP specified in the rule.

3

The HAP emission sources at facilities subject to the OSWRO NESHAP are tanks, containers, surface impoundments, oil-water separators, organic-water separators, process vents and transfer systems used to manage off-site material and equipment leaks. The MACT standards regulate these emissions sources through emission limits, equipment standards and work practices.

3

The OSWRO MACT rule defines “waste,” “used oil” and “used solvent” in 40 CFR 63.681 Definitions.

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

Under the authority of CAA section 114, we sent questionnaires to nine companies that own and operate OSWRO facilities. In the CAA section 114 questionnaires, we asked for information about process equipment, control devices, work practices, associated emission reductions, point and fugitive emissions, and other aspects of facility operations. We visited three facilities, and reviewed permit data from 18 state and local agencies. In addition, we reviewed several EPA databases to identify facilities that may be part of the source category. We also reviewed data in the EPA's National Emissions Inventory (NEI) to identify emission sources and quantities of emissions and the Toxics Release Inventory (TRI) to verify emissions estimates.

The data gathered through these activities are described further in the memorandum

Development of the RTR Emissions Dataset for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this proposed rule.

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

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category.

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

4

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

4

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 38 OSWRO facilities were used to create an RTR emissions dataset (i.e., risk model input file). This RTR emissions dataset is based on a combination of data gathered through the CAA section 114 questionnaire and the 2005 NEI. 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. Other databases, including the TRI and Envirofacts, were consulted to verify emissions estimates and to identify facilities that are part of the OSWRO source category. As part of our quality assurance review, we reviewed the emissions data and release characteristics data in the RTR emissions dataset to ensure the data were accurate. We also checked the coordinates of each emission source in the dataset using tools such as Google Earth and ArcView to ensure the emission point locations were correct.

While data for 38 OSWRO facilities were included in the RTR emissions dataset, available data indicate there are 52 currently operating major source facilities that are subject to the OSWRO MACT standards. The remaining 14 facilities were not included in the modeling file because the information available to the EPA, including the NEI, did not attribute any amount of HAP emissions to off-site waste and recovery operations at these facilities. It was also not possible to discern from the emission point identifiers or characteristics in the inventory which emissions could be attributed to the OSWRO source category. We note that available permit information indicates that five of these 14 facilities are only subject to off-site waste HAP content determination requirements and are not subject to the emissions standards and other requirements of the OSWRO NESHAP due to the low amount of HAP in the off-site waste accepted by these facilities. Also, available permit data indicates that two additional facilities are not subject to the emissions standards and other requirements of the OSWRO NESHAP because they comply instead with 40 CFR part 61, subpart FF, as allowed by the OSWRO NESHAP. For these seven facilities, we would not expect any emission points to be labeled as OSWRO emission points in the NEI because those emission points are not subject to any OSWRO MACT emissions standards. We also did not collect data from these facilities through our CAA section 114 questionnaire. As noted in section VI of this preamble, we are requesting site-specific emissions data that would enable us to better characterize the maximum risks from the OSWRO source category. A list of the 52 facilities and additional information about the development of the RTR emissions dataset is provided in the technical document:

Development of the RTR Emissions Dataset for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

2. How did we estimate MACT-allowable emissions?

The available emissions data in the RTR emissions dataset include estimates of the mass of HAP emitted during the specified annual time period. In some cases, these “actual” emission levels are lower than the emission levels required to comply with the MACT standards. The emissions level allowed to be emitted by the MACT standards is referred to as the “MACT-allowable” emissions level. We discussed the use of both MACT-allowable and actual emissions in the final Coke Oven Batteries residual risk rule (70 FR 19998-19999, April 15, 2005) and in the proposed and final Hazardous Organic NESHAP residual risk rules (71 FR 34428, June 14, 2006, and 71 FR 76609, December 21, 2006, respectively). In those previous actions, we noted that assessing the risks at the MACT-allowable level is inherently reasonable since these risks reflect the maximum level facilities could emit and still comply with national emission standards. We also explained that it is reasonable to consider actual emissions, where such data are available, in both steps of the risk analysis, in accordance with the Benzene NESHAP approach. (54 FR 38044, September 14, 1989.)

We used the emissions data gathered from the 2005 NEI and responses to the CAA section 114 questionnaire to estimate the MACT-allowable emissions levels. We estimate that the actual emissions level is representative of the MACT-allowable level for all emissions sources except tanks and process vents. Based on responses to the CAA section 114 questionnaire, we estimate that MACT-allowable emissions from tanks and process vents could be up to five times the actual emissions. For some facilities, we cannot assign HAP emissions to a specific type of emission source (e.g., a process vent) due to a lack of specificity in the emission point identifiers in the NEI. For facilities where we could identify specific emission source types, we applied a factor of 5 to the actual emissions attributable to tanks and process vents. A factor of 1 was applied to the actual emissions for other emissions sources (e.g., equipment leaks). For facilities where we could not identify specific emission source types, we developed and applied a factor of 2.5 to all the OSWRO emissions. The 2.5 factor is

based on the factor of 5 for tanks and process vents and information from the responses to the CAA section 114 questionnaire indicating that tank and process vent emissions comprise approximately half of the total OSWRO emissions.

For more detail about this estimate of the MACT-allowable emissions, see the memorandum,

MACT-Allowable Emissions for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

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

5

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

5

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.

6

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

7

internal point locations and populations provides the basis of human exposure calculations (U.S. Census, 2010). In addition, for each census block, the census library includes the elevation and controlling hill height, which are also used in dispersion calculations. A third library of pollutant unit risk factors and other health benchmarks is used to estimate health risks. These risk factors and health benchmarks are the latest values recommended by the EPA for HAP and other toxic air pollutants. These values are available at:

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

and are discussed in more detail later in this section.

6

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).

7

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

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

3

)) by its unit risk estimate (URE). The URE is an upper bound estimate of an individual's probability of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the pollutant per cubic meter of air. For residual risk assessments, we generally use URE values from the EPA's Integrated Risk Information System (IRIS). For carcinogenic pollutants without EPA IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) URE values, where available. In cases where new, scientifically credible dose response values have been developed in a manner consistent with the EPA guidelines and have undergone a peer review process similar to that used by the EPA, we may use such dose-response values in place of, or in addition to, other values, if appropriate.

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

8

) 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.

8

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 Science Advisory Board (SAB) in their 2002 peer review of EPA's National Air Toxics Assessment (NATA) entitled,

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

available at:

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

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

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

), defined as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.” Alternatively, in cases where an RfC from the EPA's IRIS database is not available, or where the EPA determines that using a value other than the RfC is appropriate, the chronic reference level can be a value from the following prioritized sources: (1) The Agency for Toxic Substances and Disease Registry Minimum Risk Level (

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

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

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

), which is defined as “the concentration level (that is expressed in units of micrograms per

cubic meter (μg/m3) for inhalation exposure and in a dose expressed in units of milligram per kilogram-day (mg/kg-day) for oral exposures), at or below which no adverse health effects are anticipated for a specified exposure duration”; or (3) as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with the EPA guidelines and has undergone a peer review process similar to that used by the EPA, in place of or in concert with other values.

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

As described in the

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

an acute REL value (

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

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

Id.

at page 2. Acute REL values are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. Acute REL values are designed to protect the most sensitive individuals in the population through the inclusion of margins of safety. Because margins of safety are incorporated to address data gaps and uncertainties, exceeding the REL does not automatically indicate an adverse health impact.

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

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

(

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

),

9

“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.

9

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 non-regulatory 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/m3 (milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic non-sensory 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 non-disabling odor, taste, and sensory irritation or certain asymptomatic, non-sensory effects.”

Id.

Similarly, the document defines AEGL-2 values as “the airborne concentration (expressed as parts per million or milligrams per cubic meter) of a substance above which it is predicted that the general population, including susceptible individuals, could experience irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape.”

Id.

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

ERPGS Procedures and Responsibilities

(

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

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

10

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.

10

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.

11

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, there was no such information available and the default factor of 10 was used in the acute screening process.

11

See

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

or docket to access the source of these data.

As part of our acute risk assessment process, for cases where acute HQ values from the screening step were less than or equal to 1 (even under the conservative assumptions of the screening analysis), acute impacts were deemed negligible and no further analysis was performed. In cases where an acute HQ from the screening step was greater than 1, additional site-specific data were considered to develop a more refined estimate of the potential for acute impacts of concern. For this source category, there were no offsite acute values greater than 1, and no refined estimates were developed. 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,

12

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

13

for HAP have been developed, we consider additional acute values (i.e., occupational and international values) to provide a more complete risk characterization.

12

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.

13

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

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

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

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

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

).

For the OSWRO source category, we identified emissions of polycyclic organic matter (POM) (analyzed as benzo(a)pyrene toxicity equivalence factor (TEQ)), polychlorinated biphenyls, hexachlorobenzene, chlordane, lindane (gamma hch), methoxyclor, toxaphene, heptachlor, and trifluralin. Because one or more of these PB-HAP are emitted by at least one facility in the OSWRO 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 thresholds 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 thresholds are: Lead, cadmium, chlorinated dibenzodioxins and furans, mercury compounds, and polycyclic organic matter (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 threshold values 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 I TRIM-screen or Tier I screen.

For the purpose of developing emissions rates for our Tier I 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 hazard quotient would be 1. If the emissions rate of any PB-HAP included in the Tier I screen exceeds the Tier I screening emissions rate for any facility, we conduct a second screen, which we call the Tier II TRIM-screen or Tier II screen. In the Tier II screen, the location of each facility that exceeded the Tier I emission rate is used to refine the assumptions associated with the environmental scenario while maintaining the exposure scenario assumptions. We then adjust the risk-based Tier I screening level for each PB-HAP for each facility based on an understanding of how exposure concentrations estimated for the

screening scenario change with meteorology and environmental assumptions. PB-HAP emissions that do not exceed these new Tier II screening levels are considered to pose no unacceptable risks. When facilities exceed the Tier II screening levels, it does not mean that multipathway impacts are significant, only that we cannot rule out that possibility based on the results of the screen. These facilities may be further evaluated for multipathway risks using the TRIM.FaTE model.

For further information on the multipathway analysis approach, see the

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

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

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

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

a. Adverse Environmental Effect

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

b. Environmental HAP

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

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

In addition to accounting for almost all of the mass of PB-HAP emitted, we note that the TRIM.Fate model that we use to evaluate 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 National Ambient Air Quality Standard (NAAQS) for lead.

14

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

14

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.” 73 FR 66964, November 12, 2008.

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.

• 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 (e.g., a no-observed-adverse-effect level (NOAEL)) through scientific study. For PB-HAP, we identified, where possible, ecological benchmarks at the following effect levels:

Probable effect levels (PEL):

Level above which adverse effects are expected to occur frequently.

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

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

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

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

We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, the EPA sources that are used at a programmatic level (e.g., Office of Water, Superfund Program) were used, if available. If not, the EPA benchmarks used in regional programs (e.g., Superfund) were used. If benchmarks were not available at a programmatic or regional level, we used benchmarks developed by other federal agencies (e.g., National Oceanic and Atmospheric Organization (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 OSWRO source category emitted any of the seven environmental HAP. For the OSWRO source category, we identified emissions of POM, HCl and HF.

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 threshold emission rate that corresponded to the relevant exposure benchmark concentration value for each assessment endpoint. To assess emissions from a facility, the reported emission rate for each PB-HAP was compared to the screening threshold emission rate for that PB-HAP for each assessment endpoint. If emissions from a facility do not exceed the Tier I threshold, the facility “passes” the screen, and therefore, is not evaluated further under the screening approach. If emissions from a facility exceed the Tier I threshold, we evaluate the facility further in Tier II.

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

g. Acid Gas Methodology

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

are in the ecological risk screening methodology for PB-HAPs.

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

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

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

7. How did we conduct facility-wide assessments?

To put the source category risks in context, we typically examine the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, we examine the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emission sources at the facility for which we have data. The emissions data for estimating these “facility-wide” risks were obtained from the 2005 NEI (available at

http://www.epa.gov/ttn/atw/nata2005

). 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

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category

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.

8. How did we consider uncertainties in risk assessment?

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

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category,

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 estimated ambient pollutant concentrations, the user chooses certain options to apply. For RTR assessments, we select some model options that have the potential to overestimate ambient air concentrations (e.g., not including plume depletion or pollutant transformation). We select other model options that have the potential to underestimate ambient impacts (e.g., not including building downwash). Other options that we select have the potential to either under- or overestimate ambient levels (e.g., meteorology and receptor locations). On balance, considering the directional nature of the uncertainties commonly present in ambient concentrations estimated by dispersion models, the approach we apply in the RTR assessments should yield unbiased estimates of ambient HAP concentrations.

c. Uncertainties in Inhalation Exposure

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

15

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

15

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

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

The assessment evaluates the cancer inhalation risks associated with

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

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

16

16

U.S. EPA.

National-Scale Air Toxics Assessment for 1996.

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

In addition to the uncertainties highlighted above, there are several factors specific to the acute exposure assessment that should be highlighted. The accuracy of an acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, meteorology and human activity patterns. In this assessment, we assume that individuals remain for 1 hour at the point of maximum ambient concentration as determined by the co-occurrence of peak emissions and worst-case meteorological conditions. These assumptions would tend to be worst-case actual exposures as it is unlikely that a person would be located at the point of maximum exposure 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 2005 Cancer Guidelines,

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

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

Cancer URE values used in our risk assessments are those that have been developed to generally provide an upper bound estimate of risk. That is, they represent a “plausible upper limit to the true value of a quantity” (although this is usually not a true statistical confidence limit).

17

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

18

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

17

IRIS glossary (

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

).

18

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

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

19

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

19

According to the NRC report,

Science and Judgment in Risk Assessment

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

Risk Assessment in the Federal Government: Managing the Process,

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

An Examination of EPA Risk Assessment Principles and Practices,

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

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

.

While collectively termed “UF,” these factors account for a number of different quantitative considerations when using observed animal (usually rodent) or human toxicity data in the development of the RfC. The UF are intended to account for: (1) Variation in susceptibility among the members of the human population (i.e., inter-individual variability); (2) uncertainty in extrapolating from experimental animal data to humans (i.e., interspecies

differences); (3) uncertainty in extrapolating from data obtained in a study with less-than-lifetime exposure (i.e., extrapolating from sub-chronic to chronic exposure); (4) uncertainty in extrapolating the observed data to obtain an estimate of the exposure associated with no adverse effects; and (5) uncertainty when the database is incomplete or there are problems with the applicability of available studies.

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

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

Although every effort is made to identify appropriate human health effect dose-response assessment values for all pollutants emitted by the sources in this risk assessment, some HAP emitted by 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 not speciated (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 two-tiered screening analysis that relies on the outputs from models that estimate environmental pollutant concentrations and human exposures for four PB-HAP. Two important types of uncertainty associated with the use of these models in RTR risk assessments and inherent to any assessment that relies on environmental modeling are model uncertainty and input uncertainty.

20

20

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

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

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

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

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

Despite the uncertainties, when individual pollutants or facilities do screen out, we are confident that the potential for adverse multipathway impacts on human health is very low. On the other hand, when individual pollutants or facilities do not screen out, it does not mean that multipathway impacts are significant, only that we cannot rule out that possibility and that a refined multipathway analysis for the

site might be necessary to obtain a more accurate risk characterization for the source category.

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

f. Uncertainties in the Environmental Risk Screening Assessment

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

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

21

21

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

variability

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

uncertainty

in being able to accurately estimate the true result.

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

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

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

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

Uncertainty also exists in the ecological benchmarks for the environmental risk screening analysis. We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. In general, EPA benchmarks used at a programmatic level (e.g., Office of Water, Superfund Program) were used if available. If not, we used EPA benchmarks used in regional programs (e.g., Superfund 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.6 of this preamble:

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

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

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

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

The EPA evaluated the following seven HAP in the environmental risk screening assessment: cadmium, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), lead compounds, HCl and HF. These seven HAP represent pollutants that can cause adverse impacts for plants and animals either through direct exposure to HAP in the air or through exposure to HAP that is deposited from the air onto soils and surface waters. These seven HAP also represent those HAP for which we can conduct a meaningful environmental risk screening assessment. For other HAP not included in our screening assessment, 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 I and II environmental screening methods is provided in Appendix 5 of the document “Technical Support Document for TRIM-Based Multipathway Tiered Screening Methodology for RTR: Summary of Approach and Evaluation.” Also, see the

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category,

available in the docket for this action.

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

As discussed in section II.A of this preamble, in evaluating and developing standards under section 112(f)(2), we apply a two-step process to address residual risk. In the first step, the EPA determines whether risks are acceptable. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR)

22

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 tighter emission standards if necessary to provide an ample margin of safety.

22

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

In past residual risk actions, the EPA considered a number of human health risk metrics associated with emissions from the categories under review, including the MIR, the number of persons in various risk ranges, cancer incidence, the maximum non-cancer HI and the maximum acute non-cancer hazard.

See, e.g.,

72 FR 25138, May 3, 2007; 71 FR 42724, July 27, 2006. The EPA considered this health information for both actual and MACT-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.”

23

23

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

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

) are outlined in a memo in this proposed rule docket from David Guinnup entitled,

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

In response to the SAB recommendations, the EPA is incorporating cumulative risk analyses into its RTR risk assessments, including those reflected in 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 hazard indices from all non-carcinogens affecting the same target organ system.

Although we are interested in placing source category and facility-wide HAP risks in the context of total HAP risks from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Because of the contribution to total HAP risk from emission sources other than those that we have studied in depth during this RTR review (i.e., those sources located at facilities within the source category), 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.

• Any significant changes in the cost (including cost effectiveness) of applying controls (including controls the EPA considered during the development of the original MACT standards).

We reviewed a variety of data sources in our investigation of potential practices, processes or controls to consider. Among the sources we reviewed were the NESHAP for various industries that were promulgated since the MACT standards 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 OSWRO 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

This section of the preamble provides the results of our RTR for the OSWRO source category and our proposed decisions concerning changes to the OSWRO NESHAP.

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

1. Inhalation Risk Assessment Results

Table 2 of this preamble provides a summary of the results of the inhalation risk assessment for the source category.

Table 2—Off-Site Waste and Recovery Operations Inhalation Risk Assessment Results

Maximum individual

cancer risk

(in 1 million)

a

Actual

emissions

level

MACT-

allowable

emissions

level

c

Estimated population

at increased

risk levels of cancer

Estimated

annual cancer

incidence

(cases per year)

Maximum

chronic non-cancer

TOSHI

b

Actual

emissions

level

MACT-

allowable

emissions

level

Maximum

screening

acute

non-cancer HQ

d

9

20

≥ 1-in-1 million: 210,000

≥ 10-in-1 million: 0

0.02

0.6

1

HQ

REL

= 1 (glycol ethers)

a

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

b

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

c

The development of allowable emission estimates can be found in the memo entitled MACT-Allowable Emissions for the Off-Site Waste and Recovery Operations Source Category, which is available in the docket for this action.

d

The maximum off-site acute value of 1 for actuals is driven by emissions of glycol ethers. See Section III.A.E for an explanation of acute dose-response values. Acute assessments are not performed with MACT-allowable emissions.

The inhalation risk modeling performed to estimate risks based on actual and MACT-allowable emissions relied primarily on data from the CAA section 114 questionnaire responses and the NEI. The results of the chronic inhalation cancer risk assessment indicate that, based on estimates of current actual emissions, the maximum lifetime individual cancer risk posed by the OSWRO source category is 9-in-1 million, with emissions of benzidine and 2,4-toluene diamine accounting for the majority of the risk. The total estimated cancer incidence from the OSWRO source category based on the actual emissions levels is 0.02 excess cancer cases per year, or one case every 50 years, with emissions of benzidine and 2,4-toluene diamine contributing to the majority of the incidence. In addition, we note that approximately 210,000 people are estimated to have cancer risks greater than or equal to 1-in-1 million as a result of actual emissions from this source category. When considering MACT-allowable emissions, the maximum individual lifetime cancer risk is estimated to be up to 20-in-1 million, driven by emissions of benzidine and 2,4-toluene diamine. Due to the way MACT-allowable risks were calculated, estimates of population exposure and cancer incidence are not available, but would be greater than those estimates presented based on actual emissions. However, since the MIR based on MACT-allowable emissions is 20-in-1 million, there are no people exposed to cancer risks greater than 100-in-1 million.

The maximum modeled chronic non-cancer TOSHI value for the OSWRO source category based on actual emissions was estimated to be 0.6, with emissions of chlorine contributing to the majority of the TOSHI. There are no people estimated to have exposure to TOSHI levels greater than 1 as a result of actual emissions from this source category. When considering MACT-allowable emissions, the maximum chronic non-cancer TOSHI value was estimated to be up to 1, driven by emissions of chlorine. There are no people estimated to have exposure to TOSHI levels greater than 1 as a result of emissions at the MACT-allowable levels from this source category.

Our screening analysis for worst-case acute impacts based on actual emissions indicates that an HQ value of 1 is not exceeded for any pollutants at any facility, indicating that the HAP emissions are believed to be without appreciable risk of acute health effects. In characterizing the potential for acute non-cancer risks of concern, it is important to remember the upward bias of these exposure estimates (e.g., worst-case meteorology coinciding with a person located at the point of maximum concentration during the hour) and to consider the results along with the conservative estimates used to develop peak hourly emissions as described earlier. Refer to Appendix 6 of the

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category

in the docket for this action for the detailed acute risk results.

2. Multipathway Risk Screening Results

Multiple facilities reported emissions of PB-HAP, including 2-acetylaminofluorene (a POM compound), heptachlor, and trifluralin. Only one facility reported emissions of a PB-HAP that has an available RTR multipathway screening value: 2-acetylaminofluorene, a polycylic organic matter (POM) compound that was analyzed as benzo(a)pyrene TEQ. Reported emissions of the POM 2-acetylaminofluorene are below the multipathway screening level for this compound, indicating low potential for multipathway risks as a result of emissions of this PB-HAP. The remaining PB-HAP do not currently have RTR multipathway screening values, and they were not evaluated for potential non-inhalation risks. These HAP, however, are not emitted in appreciable quantities from OSWRO facilities. (For more information on PB-HAP emitted from this source category, please see the

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category

document available in the docket for this action.)

3. Environmental Risk Screening Results

As described in section III.A.5, we conducted an environmental risk screening assessment for the OSWRO source category. Emissions of three environmental HAP were reported by OSWRO facilities: POM, hydrogen chloride and hydrogen fluoride. For POM, none of the individual modeled concentrations for any facility in the source category exceeded any of the ecological benchmarks (either the LOAEL or NOAEL). For the acid gases HCl and HF, the average modeled concentration of these chemicals around each facility (i.e., the average concentration of all off-facility-site data points in the modeling domain) did not exceed any ecological benchmarks. In addition, each individual modeled concentration of hydrogen chloride and hydrogen fluoride (i.e., each off-facility-site data point in the modeling domain) was below the ecological benchmarks for all facilities.

4. Facility-wide Inhalation Risk Assessment Results

Table 3 displays the results of the facility-wide risk assessment. This assessment is based on actual emission levels. For detailed facility-specific results, see Appendix 5 of the

Draft Residual Risk Assessment for the Off-Site Waste and Recovery Operations Source Category

in the docket for this proposed rule.

Table 3—Off-Site Waste and Recovery Operations Facility-Wide Risk Assessment Results

Number of facilities analyzed

38

Cancer Risk:

Estimated maximum facility-wide individual cancer risk (in 1 million)

200

Number of facilities with estimated facility-wide individual cancer risk of 100-in-1 million or more

1

Number of facilities at which the OSWRO source category contributes 50 percent or more to the facility-wide individual cancer risks of 100-in-1 million or more

0

Number of facilities with estimated facility-wide individual cancer risk of 1-in-1 million or more

17

Number of facilities at which the OSWRO source category contributes 50 percent or more to the facility-wide individual cancer risk of 1-in-1 million or more

7

Chronic Non-cancer Risk:

Maximum facility-wide chronic non-cancer TOSHI

4

Number of facilities with facility-wide maximum non-cancer TOSHI greater than 1

2

Number of facilities at which the OSWRO source category contributes 50 percent or more to the facility-wide maximum non-cancer TOSHI of 1 or more

0

The facility-wide MIR and TOSHI are based on actual emissions from all emissions sources at the identified OSWRO facilities. The results indicate that 17 facilities have a facility-wide cancer MIR greater than or equal to 1-in-1 million and one facility has a facility-wide cancer MIR greater than or equal to 100-in-1 million. The maximum facility-wide MIR is 200-in-1 million due to emissions of beryllium compounds from the cement manufacturing processes at the facility site, with emission points from the OSWRO production source category contributing less than 1 percent of the maximum facility-wide risk. The results indicate that two facilities have a facility-wide non-cancer TOSHI greater than or equal to 1. The maximum facility-wide TOSHI is 4, and this TOSHI occurs at two facilities. At one of these facilities, the TOSHI is driven mainly by emissions of beryllium compounds from the same cement manufacturing processes mentioned above. The TOSHI at the other facility is driven mainly by emissions of chlorine from industrial inorganic chemical manufacturing processes and synthetic organic chemical manufacturing processes at the facility site. In each instance, the OSWRO production source category contributes less than 1 percent to the facility-wide TOSHI. The focus of this analysis is the OSWRO source category and its low relative contribution to facility-wide risk. The maximum facility-wide MIR and TOSHI values presented here are the result of a screening analysis for the other source categories located at common facility sites. The screening analysis requires further refinement and takes place during the RTR review for those source categories. We anticipate reductions of HAP from the cement manufacturing processes due to the implementation of the recently promulgated MACT standard, with a compliance date of September 9, 2015, and the upcoming RTR review, with a consent decree deadline of June 15, 2017 for proposal and June 15, 2018 for promulgation. We may consider options for achieving further reduction of HAP from the inorganic chemical and synthetic organic chemical manufacturing processes in future reviews for those source categories.

5. What demographic groups might benefit from this regulation?

To determine whether or not to conduct a demographics analysis, which is an assessment of risks to individual demographic groups, we look at a combination of factors including the MIR, non-cancer TOSHI, population around the facilities in the source category, and other relevant factors. Actual emissions from the OSWRO source category result in no individuals being exposed to cancer risk greater than 9-in-1 million or a non-cancer TOSHI greater than 1. In addition, we estimate the cancer incidence for the source category to be 0.02 cases per year. Therefore, we did not conduct an assessment of risks to individual demographic groups for this proposed rule. However, we did conduct a proximity analysis, which identifies any overrepresentation of minority, low income or indigenous populations near facilities in the source category. The results of this analysis are presented in the section of this preamble entitled “Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations.”

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

1. Risk Acceptability

As discussed in sections II.A and III.B of this preamble, we weigh all health risk factors in our risk acceptability determination, including the cancer MIR; the number of persons in various cancer and non-cancer risk ranges; cancer incidence; the maximum non-cancer TOSHI; the maximum acute non-cancer HQ; the extent of non-cancer risks; the potential for adverse environmental effects; the distribution of cancer and non-cancer risks in the exposed population; and risk estimation uncertainties (54 FR 38044, September 14, 1989).

For the OSWRO source category, the risk analysis we performed indicates that the cancer risks to the individual most exposed could be up to 9-in-1 million due to actual emissions and up to 20-in-1 million due to MACT-allowable emissions. These risks are considerably less than 100-in-1 million, which is the presumptive upper limit of acceptable risk. The risk analysis also shows relatively low cancer incidence (0.02 cases per year), as well as no appreciable risk of deleterious chronic or acute non-cancer health effects. In addition, the risk assessment indicates no significant potential multipathway health effects.

While our analysis of facility-wide risks shows one facility with a maximum facility-wide cancer risk of 100-in-1 million or greater and two facilities with a maximum chronic non-cancer TOSHI greater than 1, it also shows that OSWRO operations did not drive these risks. In fact, OSWRO operations contribute less than 1 percent to the cancer MIR and less than 1 percent to the non-cancer TOSHI).

Considering all of the health risk information and factors discussed above, including the uncertainties discussed in section III.A.8 of this preamble, we propose that the risks from the OSWRO source category are acceptable.

2. Ample Margin of Safety Analyses and Proposed Controls

Although we are proposing that the risks from the OSWRO source category are acceptable, risk estimates for 210,000 individuals in the exposed population are above 1-in-1 million based on actual emissions. We recognize that our risk analysis indicates that the cancer risks to the individual most exposed are well within EPA's acceptable range (i.e., up to 9-in-1 million due to actual emissions and up to 20-in-1 million due to MACT-allowable emissions). However, as stated in the Benzene NESHAP, in protecting public health with an ample margin of safety, “EPA strives to provide maximum feasible protection against risks to health from HAP,” considering available health information, the incremental risk reduction associated with more stringent standards, technological feasibility, and other factors, such as costs and economic impacts of controls. 54 FR at 38044-38045. Consequently, in this analysis, we investigated available emissions control options that might reduce the risk associated with emissions from the source category. We considered this information along with all of the health risks and other health information considered in determining risk acceptability. As explained below, we are proposing additional control requirements for equipment leaks and certain tanks because considering costs and other factors, we have determined that these additional controls are capable of further reducing risks to the individual most exposed, and thus, they provide an ample margin of safety.

For the OSWRO source category, we did not identify any options that would reduce HAP emissions from containers, surface impoundments, oil-water separators, organic-water separators or transfer systems beyond what is currently required in the rule. For process vents, tanks and equipment leaks, we identified additional control options, which are described below.

For 19 of the 38 facilities included in the OSWRO risk analysis, the available data (see discussion of emissions data in section III.A of this preamble) did not,

in general, attribute OSWRO emissions to specific emission sources. For example, the NEI data for many of these facilities grouped emissions under source classification codes (SCC) for non-specific processes, such as 39999999—Miscellaneous Industrial Processes. For these facilities, we lack information as to which processes and emission point types are contributing to the risk estimates developed in the risk assessment. In contrast, CAA section 114 response data for the other 19 facilities were available, and the emissions data for these facilities were attributed to specific emission point types. However, the maximum cancer MIR and noncancer TOSHI values for the OSWRO source category are attributed to a facility for which only NEI data are available and for which we lack information regarding the processes and emission point types that contribute to these maximum risk values. Because we were unable to precisely determine the magnitude of HAP emissions from specific process types and how those emissions relate to the risk estimates, we conservatively assumed that the type of equipment under investigation was responsible for the maximum risks. For example, in our assessment of process vents, we assumed the maximum risks for the OSWRO source category were due to process vents, and then we evaluated how further controls might reduce this risk. While these assumptions may introduce some uncertainty regarding the risk reductions that would be achieved for each equipment type, we are presenting our analysis using the best information available. As noted in section VI of this preamble, we are requesting commenters to provide any site-specific emissions or other data that would enable us to better characterize the maximum risks and the risk reductions from the proposed control options for the OSWRO source category.

In the ample margin of safety analysis, factors related to the appropriate level of control are considered, including the costs and economic impacts of the controls. For the OSWRO source category, the control options identified to reduce risks are the same as those identified in the technology review. As such, we relied on the control cost estimates and estimates of control cost effectiveness derived from the technology review analyses in our ample margin of safety determination. We believe that our ample margin of safety analysis is reasonable. However, we note that if we had data to more precisely assign HAP emissions to particular emission sources in the risk modeling file and if that data were to lead us to conclude that the MACT standards reflect an ample margin of safety, we are still proposing these same control options under the technology review because they are technologically applicable and cost effective for this source category based on our experience with similar emission sources emitting similar HAP at other chemical type facilities. We request comments on the proposed controls discussed below to provide an ample margin of safety for this source category.

For process vents, as discussed in section IV.C of this preamble, we identified an emissions control option of requiring compliance with a 98 percent reduction rather than a 95 percent reduction in HAP emissions. To assess the maximum potential for risk reduction that could result from this process vent control option, we assumed that the maximum risks for the OSWRO source category are due to emissions from a process vent with emissions controlled at 95 percent. In this scenario, we estimate the HAP reduction resulting from compliance with a 98 percent reduction would be 10 tpy from the current emissions level, with a cost effectiveness of $350,000/ton HAP reduction. We estimate this option would reduce the MIR at the MACT-allowable emissions level for the source category from 20-in-1 million to 8-in-1 million and reduce the maximum chronic non-cancer TOSHI from 1 to 0.4. Considering all of the health risks and other health information considered in our determination of risk acceptability, the potential for reductions in HAP emissions and risk, the uncertainty associated with the estimated potential risk reductions and the costs associated with this option, we are proposing that no additional HAP emissions controls for OSWRO process vents are necessary to provide an ample margin of safety to protect public health.

For tanks, as discussed in section IV.C of this preamble, we identified two emissions control options. Option 1 requires Level 2 control of emissions for additional tanks containing liquids with lower vapor pressures. Option 2 requires compliance with a 98 percent reduction rather than a 95 percent reduction in HAP emissions from tanks. As discussed above for process vents, to assess the maximum potential for risk reduction that could result from these two tank control options, we have assumed that the maximum risks for the OSWRO source category are due to emissions from tanks. For Option 1, we have assumed that the maximum risks are due to tanks that are not currently subject to Level 2 controls, which require a 95 percent reduction in emissions. In this scenario, we estimate the HAP reduction resulting from compliance with the control of additional tanks would be 73 tpy from the current emissions level, with a cost effectiveness of $300/ton HAP reduction. We estimate this option would reduce the MIR at the MACT-allowable emissions level for the source category from 20-in-1 million to 1-in-1 million and reduce the maximum chronic non-cancer TOSHI from 1 to 0.05. Under Option 2, we estimate the HAP reduction incremental to Option 1 would be approximately 22 tpy, with a cost effectiveness of $13,000/ton HAP reduction and a cost effectiveness incremental to Option 1 of $56,000/ton HAP reduction. We estimate this option would reduce the MIR at the MACT-allowable emissions level incremental to Option 1 for the source category from 1-in-1 million to 0.4-in-1 million and reduce the maximum chronic non-cancer TOSHI from 0.05 to 0.02. Considering all of the health risks and other health information considered in our determination of risk acceptability, the potential risk reductions and the costs associated with Option 1, we are proposing to require this additional level of control to provide an ample margin of safety. Considering all of the health risks and other health information considered in our determination of risk acceptability, the potential for reductions in risk, the uncertainty associated with the estimated potential risk reductions and the costs associated with Option 2, we are proposing that the additional HAP emissions controls for OSWRO tanks under Option 2 are not necessary to provide an ample margin of safety to protect public health. In addition, as discussed further in preamble section IV.C, we are also proposing the Option 1 additional control level as a result of the technology review.

For equipment leaks, as discussed in section IV.C of this preamble, we identified two emission control options: Option 1 requires compliance with 40 CFR part 63, subpart H, rather than 40 CFR part 61, subpart V, without the connector leak detection and repair (LDAR) requirements of subpart H; Option 2 requires the same as Option 1 but includes the connector LDAR requirement of subpart H. As discussed above for tanks, to assess the maximum potential for risk reduction that could result from these equipment leaks control options, we assumed that the maximum risks for the OSWRO source category are due to emissions from equipment leaks. We also assumed that

since emissions from equipment leaks are estimated to be the same at actual and MACT-allowable emission levels, the risks due to equipment leaks at the MACT-allowable level are the same as risks due to equipment leaks at actual emissions levels. We additionally assumed, based on our analysis of estimated baseline equipment leak emissions,

24

that half of the equipment leak emissions causing the maximum risks are from non-connector components (i.e. pumps and valves), and the other half are from connectors. Given these assumptions, under Option 1, we estimate the HAP reduction resulting from compliance with subpart H without the subpart H connector monitoring requirements would be 69 tpy from the baseline actual emissions level, with a cost effectiveness of $1,000/ton HAP reduction. We estimate this option would reduce the MIR at the MACT-allowable emissions level for the equipment leaks at the source category from 9-in-1 million to 7-in-1 million and reduce the maximum chronic non-cancer TOSHI from 0.6 to 0.5. Under Option 2, we estimate the incremental HAP reduction resulting from compliance with subpart H including the subpart H connector monitoring requirements would be 70 tpy more than Option 1, with an overall cost effectiveness of $4,000/ton HAP reduction and a cost effectiveness incremental to Option 1 of $7,000/ton HAP reduction. We estimate this option would reduce the MIR at the MACT-allowable emissions level incremental to Option 1 for the equipment leaks at the source category from 7-in-1 million to 5-in-1 million and reduce the maximum chronic non-cancer TOSHI from 0.5 to 0.3. We note, as discussed in preamble section IV.C, we are proposing the additional control level of Option 2 as a result of the technology review. Considering the health risks and other health information evaluated in our determination of risk acceptability, that some risk reduction occurs with Option 2, and the costs associated with Option 2 are reasonable, we are proposing to require this additional level of control to provide an ample margin of safety.

24

See

Technology Review and Cost Impacts for the Proposed Amendments to the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

In accordance with the approach established in the Benzene NESHAP, the EPA weighed all health risk measures and information considered in the risk acceptability determination, along with the costs of emissions controls, technological feasibility, uncertainties and other relevant factors in making our ample margin of safety determination. Considering the health risk information, the potential risk reductions and the reasonable cost effectiveness of certain control options identified for tanks and equipment leaks, we propose that the standards for the OSWRO source category be revised to include the proposed control Option 1 for tanks and the proposed control Option 2 for equipment leaks to provide an ample margin of safety to protect public health.

3. Adverse Environmental Effects

We conducted an environmental risk screening assessment for the OSWRO source category for POM, HCl and HF. For POM, none of the individual modeled Tier I concentrations for any facility in the source category exceeded any of the ecological benchmarks (either the LOAEL or NOAEL). For HF and HCl, the average modeled concentration around each facility (i.e., the average concentration of all off-site data points in the modeling domain) did not exceed any ecological benchmark. Based on these results, we are proposing that it is not necessary to set a more stringent standard to prevent such an adverse environmental effect, taking into consideration costs, energy, safety, and other relevant factors.

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

As described in section III.C of this preamble, our technology review focused on identifying developments in practices, processes and control technologies for the emission sources in the OSWRO production source category. To identify such developments since the MACT standards were developed, we consulted the EPA's RACT/BACT/LAER Clearinghouse, reviewed subsequent regulatory development efforts and reviewed data from the 2013 CAA Section 114 survey of OSWRO facilities. For the OSWRO source category, we did not identify any developments in practices, processes or control technologies for containers, surface impoundments, oil-water separators, organic-water separators or transfer systems beyond what is currently required in the rule. For process vents, tanks and equipment leaks, we identified additional control options, and the following sections summarize the results of our technology review for these emissions sources.

To perform the technology review, we needed information that was not included in the RTR emissions dataset used for modeling OSWRO risks. Therefore, to evaluate the costs and cost-effectiveness of various control options, we used a model plant approach. The model plant approach we used resulted in different baseline emission estimates than those included in the risk modeling dataset. More information concerning our technology review and model plant approach can be found in the memorandum titled,

Technology Review and Cost Impacts for the Proposed Amendments to the Off-Site Waste and Recovery Operations Source Category,

which is available in the docket for this action.

1. Tanks

For tanks at existing affected sources, we identified two potential developments in practices and control techniques. The current OSWRO MACT requirements at 40 CFR 63.685(b)(1) for tanks at an existing affected source depend on the capacity of the tank and the vapor pressure of the material being stored. “Level 2” control is required for: (1) Tanks with capacities greater than or equal to 75 cubic meters (m

3

), but less than 151 m

3

and a vapor pressure of 27.6 kilopascals (kPa) or greater and (2) tanks with capacities greater than or equal to 151 m

3

and a vapor pressure of 5.2 kPa or greater. “Level 2” control essentially requires one of five options: (1) A fixed roof tank equipped with an internal floating roof; (2) a fixed roof tank equipped with an external floating roof; (3) a tank with a vapor-tight cover and vented through a closed-vent system to a control device that has an efficiency of 95 percent or more; (4) a pressure tank; or (5) a tank inside a permanent total enclosure (PTE) that is vented through a closed-vent system to an enclosed combustion control device. Tanks of any capacity (effectively those less than 75 m

3

) with a vapor pressure of 76.6 kPa or greater are required to use one of the options listed above for Level 2 control, except that fixed roof tanks with either an internal or an external floating roof cannot be used. For tanks with capacities and vapor pressures less than those stated above, “Level 1” control is required. “Level 1” control generally requires a fixed roof with closure devices.

We evaluated two control options that would change the tank requirements if adopted. Option 1 would lower the vapor pressure threshold above which Level 2 controls would be required for some tanks. Option 2 would revise the vapor pressure threshold as in Option 1 and increase the required control efficiency from the current 95 percent to a 98 percent emissions reduction for all tanks required to use Level 2 controls. Through the review of air toxics MACT standards developed subsequent to the

OSWRO MACT standards, we noted that several other MACT standards refer to the Hazardous Organic NESHAP (HON) for their storage tank requirements. We evaluated revising the applicability of the OSWRO existing source requirements to use the same thresholds for Level 2 control as the thresholds for control required by the HON. As shown in Table 4, Option 1 would require Level 2 emissions control for tanks with capacities greater than or equal to 75 m

3

, but less than 151 m

3

, if the vapor pressure of the stored material is 13 kPa or greater, instead of 27.6 kPa or greater as required by the current MACT standard. No other tank size or vapor thresholds would be changed with Option 1. For tanks at new affected sources, the current OSWRO applicability thresholds are consistent with those required for the chemical industry under other NESHAP, including the HON, so no revised applicability requirements were evaluated for tanks located at new sources.

Because available data for the source category indicate most OSWRO tanks currently have fixed-roofs with emissions routed through a closed vent system to a control device, under Option 2 we considered the impacts of requiring a higher control efficiency than currently required by the OSWRO MACT standard. While carbon adsorption and other control devices are assumed to have a control efficiency of 95 percent, other technologies are capable of achieving greater emissions control, such as thermal incinerators. Several of these devices have been demonstrated to achieve a control efficiency of 98 percent or greater. Under Option 2, we considered the impacts of requiring a 98 percent emissions reduction for tanks meeting the lowered vapor pressure threshold under Option 1, and all other tanks required to use Level 2 emission controls, assuming a recuperative thermal oxidizer (RCO) would be used to attain this increased level of control.

Table 5 presents the emission reductions and costs of the two options considered for tanks at existing affected sources in the OSWRO source category under the technology review. For Option 1, data collected through our CAA section 114 questionnaire indicate that only some facilities have tanks in the size and vapor pressure range considered for this option, and based on these data we estimate that approximately three OSWRO facilities have tanks that would require additional control under Option 1. As seen in Table 5, for Option 1, we estimate the capital costs to be approximately $76,000, and the total annualized costs are estimated to be approximately $21,000. The estimated HAP emissions reduction is approximately 73 tpy, and the cost effectiveness is approximately $300/ton. For Option 2, data collected through our CAA section 114 questionnaire indicate that only some facilities have tanks that currently require Level 2 emissions controls or that would require Level 2 control with the revised vapor pressure threshold of Option 1, and based on this data we estimate that approximately 10 OSWRO facilities have tanks that would require additional control under Option 2. We estimate the capital costs to be approximately $2.8 million, and the total annualized costs are estimated to be approximately $1.3 million. The estimated HAP emissions reduction incremental to Option 1 is approximately 22 tpy, and the incremental cost effectiveness between Option 1 and Option 2 is approximately $56,000/ton.

Table 4—Requirements of Tank Options 1 and 2 for Existing OSWRO Affected Sources

Options 1 and 2 applicability thresholds

If size (m

3

) is

And vapor pressure (kPa) is

Then control level for options 1 and 2

Option 1 Requirements

Option 2 Requirements

<75

<76.6

1

Fixed roof.

≥76.6

a

2

95% control

b

98% control.

b

75 ≤ capacity < 151

<13.1

1

Fixed roof.

≥13.1

2

95% control

c

98% control.

c

151 ≤ capacity

<5.2

1

Fixed roof.

≥5.2

2

95% control

c

98% control.

c

a

Except that fixed roof tanks equipped with an internal floating roof and tanks equipped with an external floating roof shall not be used.

b

Control efficiency would apply to tanks vented through a closed vent system to a control device and tanks inside a PTE that are vented to a combustion control device; use of a pressure tank would still be an available control option.

c

Control efficiency would apply to tanks vented through a closed vent system to a control device and tanks inside a PTE that are vented to a combustion control device; use of an internal or external floating roof or a pressure tank would still be available control options.

Table 5—Nationwide Emissions Reductions and Costs of Control Options for Tanks at OSWRO Facilities

Regulatory options

HAP emissions reduction (tpy)

Capital cost ($)

Annual cost

($/yr)

Cost

effectiveness

($/ton HAP

removed)

Incremental cost effectiveness

($/ton HAP

removed)

Option 1

72.8

76,000

21,000

300

Option 2

95.0

2,800,000

1,300,000

13,000

56,000

Based on our analysis, the costs of Option 1 are reasonable, given the level of HAP emissions reduction that would be achieved with this control option. The costs of Option 2 do not appear reasonable, given the level of HAP emissions reduction it would achieve. Therefore, as a result of the technology review, we are proposing to revise the

OSWRO MACT standards in accordance with Option 1, i.e., to require Level 2 controls for tanks at existing affected sources with capacities greater than or equal to 75 m

3

, but less than 151 m

3

, and a vapor pressure of 13.1 kPa or greater. We solicit comment on our assessment and conclusions regarding all aspects of both options. As noted in section IV.B.2, we are concurrently proposing to revise the OSWRO MACT standards for existing affected sources to require Level 2 controls for these tanks under sect

This text is long and has been trimmed here. Open the source document for the complete record.