National Emission Standards for Hazardous Air Pollutants: Municipal Solid Waste Landfills Residual Risk and Technology Review

Federal RegisterJul 29, 2019

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ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 60 and 63

[EPA-HQ-OAR-2002-0047; FRL-9996-22-OAR]

RIN 2060-AU18

National Emission Standards for Hazardous Air Pollutants: Municipal Solid Waste Landfills Residual Risk and Technology Review

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The U.S Environmental Protection Agency (EPA) is proposing amendments to the National Emission Standards for Hazardous Air Pollutants (NESHAP): Municipal Solid Waste (MSW) Landfills source category. The EPA is proposing decisions concerning the residual risk and technology review (RTR). The EPA is also proposing amendments to correct and clarify regulatory provisions related to emissions during periods of startup, shutdown, and malfunction (SSM); revise wellhead operational standards and corrective action to improve effectiveness and provide compliance flexibility; reorganize rule text to incorporate provisions from the new source performance standards (NSPS) within this subpart; and add requirements for electronic reporting of performance test results. The EPA is also proposing minor changes to the MSW Landfills NSPS and Emission Guidelines and Compliance Times for MSW Landfills. Specifically, the EPA is proposing to add provisions to the most recent MSW Landfills NSPS and Emission Guidelines (EG) that would allow affected sources to demonstrate compliance with landfill gas control, operating, monitoring, recordkeeping, and reporting requirements of the most recent NSPS and EG by following the corresponding requirements in the MSW Landfills NESHAP.

DATES:

Comments.

Comments must be received on or before September 12, 2019. Under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of consideration if the Office of Management and Budget (OMB) receives a copy of your comments on or before August 28, 2019.

Public hearing.

If anyone contacts us requesting a public hearing on or before August 5, 2019, we will hold a hearing. Additional information about the hearing, if requested, will be published in a subsequent

Federal Register

document and posted at

https://www.epa.gov/stationary-sources-air-pollution/municipal-solid-waste-landfills-national-emission-standards.

See

SUPPLEMENTARY INFORMATION

for information on requesting and registering for a public hearing.

ADDRESSES:

You may send comments, identified by Docket ID No. EPA-HQ-OAR-2002-0047, by any of the following methods:

•

Federal eRulemaking Portal:

https://www.regulations.gov/

(our preferred method). Follow the online instructions for submitting comments.

•

Email:

a-and-r-docket@epa.gov.

Include Docket ID No. EPA-HQ-OAR-2002-0047 in the subject line of the message.

•

Fax:

(202) 566-9744. Attention Docket ID No. EPA-HQ-OAR-2002-0047.

•

Mail:

U.S. Environmental Protection Agency, EPA Docket Center, Docket ID No. EPA-HQ-OAR-2002-0047, Mail Code 28221T, 1200 Pennsylvania Avenue NW, Washington, DC 20460.

•

Hand/Courier Delivery:

EPA Docket Center, WJC West Building, Room 3334, 1301 Constitution Avenue NW, Washington, DC 20004. The Docket Center's hours of operation are 8:30 a.m.-4:30 p.m., Monday-Friday (except Federal holidays).

Instructions:

All submissions received must include the Docket ID No. for this rulemaking. Comments received may be posted without change to

https://www.regulations.gov/,

including any personal information provided. For detailed instructions on sending comments and additional information on the rulemaking process, see the

SUPPLEMENTARY INFORMATION

section of this document.

FOR FURTHER INFORMATION CONTACT:

For questions about this proposed action, contact Andrew Sheppard, Natural Resources Group, Sector Policies and Programs Division (E143-03), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-4161; fax number: (919) 541-0516; and email address:

Sheppard.Andrew@epa.gov.

For specific information regarding the risk modeling methodology, contact Jim Hirtz, Health and Environmental Impacts Division (C539-02), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-0881; fax number: (919) 541-0840; and email address:

Hirtz.James@epa.gov.

For questions about monitoring and testing requirements, contact Muntasir Ali, Sector Policies and Programs Division (D243-05), Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number: (919) 541-0833; fax number: (919) 541-4991; and email address:

Ali.Muntasir@epa.gov.

For information about the applicability of the NESHAP to a particular entity, contact Maria Malave, Office of Enforcement and Compliance Assurance, U.S. Environmental Protection Agency, WJC South Building (Mail Code 2227A), 1200 Pennsylvania Avenue NW, Washington, DC 20460; telephone number: (202) 564-7027; and email address:

Malave.Maria@epa.gov.

SUPPLEMENTARY INFORMATION:

Public hearing.

Please contact Virginia Hunt at (919) 541-0832 or by email at

hunt.virginia@epa.gov

to request a public hearing, to register to speak at the public hearing, or to inquire as to whether a public hearing will be held.

Docket.

The EPA has established a docket for this rulemaking under Docket ID No. EPA-HQ-OAR-2002-0047. All documents in the docket are listed in

Regulations.gov

. Although listed, some information is not publicly available,

e.g.,

Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, is not placed on the internet and will be publicly available only in hard copy. Publicly available docket materials are available either electronically in

Regulations.gov

or in hard copy at the EPA Docket Center, Room 3334, WJC West Building, 1301 Constitution Avenue NW, Washington, DC. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The telephone number for the Public Reading Room is (202) 566-1744, and the telephone number for the EPA Docket Center is (202) 566-1742.

Instructions.

Direct your comments to Docket ID No. EPA-HQ-OAR-2002-0047. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at

https://www.regulations.gov/,

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

protected through

https://www.regulations.gov/

or email. This type of information should be submitted by mail as discussed below.

The EPA may publish any comment received to its public docket. Multimedia submissions (audio, video, etc.) must be accompanied by a written comment. The written comment is considered the official comment and should include discussion of all points you wish to make. The EPA will generally not consider comments or comment contents located outside of the primary submission (

i.e.,

on the Web, cloud, or other file sharing system). For additional submission methods, the full EPA public comment policy, information about CBI or multimedia submissions, and general guidance on making effective comments, please visit

https://www.epa.gov/dockets/commenting-epa-dockets.

The

https://www.regulations.gov/

website allows you to submit your comment anonymously, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through

https://www.regulations.gov/,

your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any digital storage media you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should not include special characters or any form of encryption and be free of any defects or viruses. For additional information about the EPA's public docket, visit the EPA Docket Center homepage at

https://www.epa.gov/dockets.

Submitting CBI.

Do not submit information containing CBI to the EPA through

https://www.regulations.gov/

or email. Clearly mark the part or all of the information that you claim to be CBI. For CBI information on any digital storage media that you mail to the EPA, mark the outside of the digital storage media as CBI and then identify electronically within the digital storage media the specific information that is claimed as CBI. In addition to one complete version of the comments that includes information claimed as CBI, you must submit a copy of the comments that does not contain the information claimed as CBI directly to the public docket through the procedures outlined in

Instructions

above. If you submit any digital storage media that does not contain CBI, mark the outside of the digital storage media clearly that it does not contain CBI. Information not marked as CBI will be included in the public docket and the EPA's electronic public docket without prior notice. Information marked as CBI will not be disclosed except in accordance with procedures set forth in 40 Code of Federal Regulations (CFR) part 2. Send or deliver information identified as CBI only to the following address: OAQPS Document Control Officer (C404-02), OAQPS, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711, Attention Docket ID No. EPA-HQ-OAR-2002-0047.

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:

ADI Applicability Determination Index

AEGL acute exposure guideline level

AERMOD air dispersion model used by the HEM-3 model

ATSDR Agency for Toxic Substances and Disease Registry

BACT best available control technology

CAA Clean Air Act

CalEPA California EPA

CBI Confidential Business Information

CDX Central Data Exchange

CEDRT Compliance and Emissions Data Reporting Interface

CFR Code of Federal Regulations

CHIEF Clearinghouse for Inventories and Emissions Factors

CO carbon monoxide

DASEC discrete area source eddy covariance

DFW Dallas Fort Worth

EC eddy covariance

EG emission guidelines

EL expansion lag

EPA Environmental Protection Agency

ERPG Emergency Response Planning Guideline

ERT Electronic Reporting Tool

GCCS gas collection and control system

GHGRP Greenhouse Gas Reporting Program

HAP hazardous air pollutant(s)

HCl hydrochloric acid

HEM-3 Human Exposure Model, Version 1.1.0

HF hydrogen fluoride

HI hazard index

HOV higher operating value

HQ hazard quotient

IBR incorporation by reference

IRIS Integrated Risk Information System

km kilometer

LAER lowest achievable emissions rate

LFG landfill gas

LMOP Landfill Methane Outreach Program

MACT maximum achievable control technology

mg/kg-day milligrams per kilogram per day

mg/m

milligrams per cubic meter

Mg/yr megagrams per year

MIR maximum individual risk

MSW municipal solid waste

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NATA National Air Toxics Assessment

HEM-3 Human Exposure Model

NESHAP national emission standards for hazardous air pollutants

NMOC non-methane organic compounds

NRC National Research Council

NSPS new source performance standards

NTTAA National Technology Transfer and Advancement Act

OAQPS Office of Air Quality Planning and Standards

OECA Office of Enforcement and Compliance Assurance

OMB Office of Management and Budget

OTM Other Test Method

PAH polycyclic aromatic hydrocarbons

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

PM particulate matter

POM polycyclic organic matter

ppm parts per million

ppmv parts per million by volume

PRA Paperwork Reduction Act

RACT reasonably available control technology

RCRA Resource Conservation and Recovery Act

REL reference exposure level

RFA Regulatory Flexibility Act

RfC reference concentration

RfD reference dose

RTR residual risk and technology review

SAB Science Advisory Board

SBA Small Business Administration

SCC Source Classification Code

SOE subsurface oxidation event

SSM startup, shutdown, and malfunction

SWANA Solid Waste Association of North America

TC tracer correlation

TOSHI target organ-specific hazard index

tpy tons per year

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

UF uncertainty factor

µg/m

micrograms per cubic meter

UMRA Unfunded Mandates Reform Act

URE unit risk estimate

USGS U.S. Geological Survey

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?

II. Background

A. What is the statutory authority for this action?

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

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

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

III. Analytical Procedures and Decision-Making

A. How do we consider risk in our decision-making?

B. How do we perform the technology review?

C. How do we estimate post-MACT risk posed by the source category?

IV. Analytical Results and Proposed Decisions

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

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

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

D. What 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

A. Methane Emissions Measurement Methodologies

B. Areas With Declining Gas Flow

VII. Submitting Data Corrections

VIII. Incorporation by Reference

IX. Statutory and Executive Order Reviews

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

B. Executive Order 13771: Reducing Regulations and Controlling Regulatory Costs

C. Paperwork Reduction Act (PRA)

D. Regulatory Flexibility Act (RFA)

E. Unfunded Mandates Reform Act (UMRA)

F. Executive Order 13132: Federalism

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

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

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

J. National Technology Transfer and Advancement Act (NTTAA) and 1 CFR Part 51

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

I. General Information

A. Does this action apply to me?

Table 1 of this preamble lists the NESHAP (40 CFR part 63, subpart AAAA) and associated regulated industrial source categories that are the subject of this proposal. Table 1 is not intended to be exhaustive, but rather provides a guide for readers regarding the entities that this proposed action is likely to affect. The proposed standards, once promulgated, will be directly applicable to the affected sources. Federal, state, local, and tribal government entities could be affected by this proposed action because these entities are often the owners or operators of MSW landfills. As defined in the

Initial List of Categories of Sources Under Section 112(c)(1) of the Clean Air Act Amendments of 1990

(see 57 FR 31576, July 16, 1992) and

Documentation for Developing the Initial Source Category List, Final Report

(see EPA-450/3-91-030, July 1992), the MSW Landfills source category is any facility that is an entire disposal facility in a contiguous geographical space where household waste is placed in or on land. An MSW landfill may also receive commercial waste, sludges, and industrial waste. An MSW landfill may also receive other types of Resource Conservation and Recovery Act (RCRA) Subtitle D wastes (see 40 CFR 257.2) such as commercial solid waste, nonhazardous sludge, conditionally exempt small quantity generator waste, and industrial solid waste portions of an MSW landfill may be separated by access roads. An MSW landfill may be publicly or privately owned.

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

Source category

NESHAP

NAICS code

Industry: Air and water resource and solid waste management

MSW Landfills

924110

Industry: Refuse systems—solid waste landfills

562212

State, local, and tribal government agencies

562212, 924110

North American Industry Classification System.

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

In addition to being available in the docket, an electronic copy of this action is available on the internet. Following signature by the EPA Administrator, the EPA will post a copy of this proposed action at

https://www.epa.gov/stationary-sources-air-pollution/municipal-solid-waste-landfills-national-emission-standards.

Following publication in the

Federal Register

, the EPA will post the

Federal Register

version of the proposal and key technical documents at this same website. Information on the overall RTR program is available at

https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html.

A redline version of the regulatory language that incorporates the proposed changes in this action is available in the docket for this action (Docket ID No. EPA-HQ-OAR-2002-0047).

II. Background

A. What is the statutory authority for this action?

The statutory authority for revisions to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) is provided by sections 112 and 301 of the Clean Air Act (CAA), as amended (42 U.S.C. 7401

et seq.

). Section 112 of the CAA establishes a two-stage regulatory process to develop standards for emissions of hazardous air pollutants (HAP) from stationary sources. Generally, the first stage involves establishing technology-based standards and the second stage involves evaluating those standards that are based on maximum achievable control technology (MACT) to determine whether additional standards are needed to address any remaining risk associated with HAP emissions. This second stage is commonly referred to as the “residual risk review.” In addition to the residual risk review, the CAA also requires the EPA to review standards set under CAA section 112 every 8 years to determine if there are “developments in practices, processes, and control technologies” that may be appropriate to incorporate into the standards. CAA section 112(d)(6). This review is commonly referred to as the “technology review.” When the two reviews are combined into a single rulemaking, it is commonly referred to as the “risk and technology review.” The discussion that follows identifies the most relevant statutory sections and briefly explains the contours of the methodology used to implement these

statutory requirements. A more comprehensive discussion appears in the document titled

CAA Section 112 Risk and Technology Reviews: Statutory Authority and Methodology,

in the docket for this rulemaking.

In the first stage of the CAA section 112 standard setting process, the EPA promulgates technology-based standards under CAA section 112(d) for categories of sources identified as emitting one or more of the HAP listed in CAA section 112(b). Sources of HAP emissions are either major sources or area sources, and CAA section 112 establishes different requirements for major source standards and area source standards. “Major sources” are those that emit or have the potential to emit 10 tons per year (tpy) or more of a single HAP or 25 tpy or more of any combination of HAP. All other sources are “area sources.” For major sources, CAA section 112(d)(2) provides that the technology-based NESHAP must reflect the maximum degree of emission reductions of HAP achievable (after considering cost, energy requirements, and non-air quality health and environmental impacts). These standards are commonly referred to as MACT standards. CAA section 112(d)(3) also establishes a minimum control level for MACT standards, known as the MACT “floor.” The EPA must also consider control options that are more stringent than the floor. Standards more stringent than the floor are commonly referred to as beyond-the-floor standards. In certain instances, as provided in CAA section 112(h), the EPA may set work practice standards where it is not feasible to prescribe or enforce a numerical emission standard. For area sources, CAA section 112(d)(5) gives the EPA discretion to set standards based on generally available control technologies or management practices (GACT standards) in lieu of MACT standards.

The second stage in standard-setting focuses on identifying and addressing any remaining (

i.e.,

“residual”) risk according to CAA section 112(f). For source categories subject to MACT standards, section 112(f)(2) of the CAA requires the EPA to determine whether promulgation of additional standards is needed to provide an ample margin of safety to protect public health or to prevent an adverse environmental effect. Section 112(d)(5) of the CAA provides that this residual risk review is not required for categories of area sources subject to GACT standards. Section 112(f)(2)(B) of the CAA further expressly preserves the EPA's use of the two-step approach for developing standards to address any residual risk and the Agency's interpretation of “ample margin of safety” developed in the

National Emissions Standards for Hazardous Air Pollutants: Benzene Emissions from Maleic Anhydride Plants, Ethylbenzene/Styrene Plants, Benzene Storage Vessels, Benzene Equipment Leaks, and Coke By-Product Recovery Plants

(Benzene NESHAP) (54 FR 38044, September 14, 1989). The EPA notified Congress in the Risk Report that the Agency intended to use the Benzene NESHAP approach in making CAA section 112(f) residual risk determinations (EPA-453/R-99-001, p. ES-11). The EPA subsequently adopted this approach in its residual risk determinations and the United States Court of Appeals for the District of Columbia Circuit (the Court) upheld the EPA's interpretation that CAA section 112(f)(2) incorporates the approach established in the Benzene NESHAP. See

National Resources Defense Council (NRDC)

EPA,

529 F.3d 1077, 1082-1083 (D.C. Cir. 2008).

The approach incorporated into the CAA and used by the EPA to evaluate residual risk and to develop standards under CAA section 112(f)(2) is a two-step approach. In the first step, the EPA determines whether risks are acceptable. This determination “considers all health information, including risk estimation uncertainty, and includes a presumptive limit on maximum individual lifetime [cancer] risk (MIR)

of approximately 1 in 10 thousand.” 54 FR 38045, September 14, 1989. If risks are unacceptable, the EPA must determine the emissions standards necessary to reduce risk to an acceptable level without considering costs. In the second step of the approach, the EPA considers whether the emissions standards provide an ample margin of safety to protect public health “in consideration of all health information, including the number of persons at risk levels higher than approximately 1 in 1 million, as well as other relevant factors, including costs and economic impacts, technological feasibility, and other factors relevant to each particular decision.”

Id.

The EPA must promulgate emission standards necessary to provide an ample margin of safety to protect public health. After conducting the ample margin of safety analysis, we consider whether a more stringent standard is necessary to prevent, taking into consideration costs, energy, safety, and other relevant factors, an adverse environmental effect.

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

CAA section 112(d)(6) separately requires the EPA to review standards promulgated under CAA section 112 and revise them “as necessary (taking into account developments in practices, processes, and control technologies)” no less often than every 8 years. In conducting this review, which we call the “technology review,” the EPA is not required to recalculate the MACT floor.

Natural Resources Defense Council (NRDC)

EPA,

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

Association of Battery Recyclers, Inc.

EPA,

716 F.3d 667, 673-674 (D.C. Cir. 2013). The EPA may consider cost in deciding whether to revise the standards pursuant to CAA section 112(d)(6).

The EPA is proposing amendments to the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpaft Cf) under the authority of CAA sections 111(b) and 111(d). In 1991, under authority of section 111(b)(1)(A) of the CAA, the EPA added the source category MSW Landfills to the priority list in 40 CFR 60.16 because, in the judgment of the Administrator, the source category contributes significantly to air pollution which may reasonably be anticipated to endanger public health and welfare (56 FR 24468, May 30, 1991). In that same action (56 FR 24468), the EPA proposed NSPS for new MSW landfills under section 111(b) of the CAA and proposed EG for existing MSW landfills under section 111(d) of the CAA.

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

The NESHAP for the MSW Landfills source category, the National Emission Standards for Hazardous Air Pollutants: Municipal Solid Waste Landfills (herein after referred to as the “MSW Landfills NESHAP”), was promulgated on January 16, 2003 (68 FR 2227), and is codified at 40 CFR part 63, subpart AAAA. As promulgated in 2003 and further amended on April 20, 2006 (71 FR 20462), the MSW Landfills NESHAP regulates HAP emissions from MSW landfills that are either major and area sources.

The MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) applies to MSW landfills that have accepted waste since November 8, 1987, or have additional capacity for waste deposition and are major sources, are collocated with major sources, or are area source landfills with a design capacity equal to or greater than 2.5 million megagrams (Mg) and 2.5 million cubic meters (m

) and have estimated uncontrolled emissions equal to or greater than 50 Mg/yr non-methane organic compounds (NMOC). The MSW

Landfills NESHAP (40 CFR part 63, subpart AAAA) also applies to MSW landfills that have accepted waste since November 8, 1987, and include a bioreactor and are major sources, are collocated with major sources, or are area source landfills with a design capacity equal to or greater than 2.5 million Mg and 2.5 million m

that were not permanently closed as of January 16, 2003.

The majority of emissions of HAP at MSW landfills come from the continuous biodegradation of the MSW in the landfill and the formation of landfill gas emissions. Landfill gas emissions contain methane, carbon dioxide, and more than 100 different NMOC. The HAP emitted by MSW landfills include, but are not limited to, vinyl chloride, ethyl benzene, toluene, and benzene (61 FR 9906, March 12, 1996). The owner or operator of a landfill may control the gas by routing it to a non-enclosed flare, an enclosed combustion device, or a treatment system that processes the collected gas for subsequent sale or beneficial use.

The MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) regulates HAP emissions by requiring MSW landfills that exceed the size and emission thresholds to install and operate a landfill gas collection and control system (GCCS), as enumerated in the original NSPS for MSW landfills (40 CFR part 60, subpart WWW), the Federal Plan (40 CFR part 62, subpart GGG), or an EPA-approved state plan or tribal plan that implements the EG (40 CFR part 60, subpart Cc). The MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) achieves emission reductions through a well-designed and well-operated landfill gas (LFG) collection and control system with a control device capable of reducing NMOC by 98 percent by weight. NMOC is a surrogate for LFG. The GCCS must be installed within 30 months after an MSW landfill that exceeds the design capacity threshold (2.5 million Mg and 2.5 million m

) reaches or exceeds an NMOC level of 50 Mg/yr. The landfill must expand the system to collect gas from each area, cell, or group of cells in the landfill in which the initial solid waste has been placed for a period of 5 years or more if active; or 2 years or more if closed or at final grade. The collection and control system may be capped or removed when the landfill is closed, the system has operated 15 years, and NMOC emissions are below 50 Mg/yr.

In addition, the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) requires timely control of bioreactors. A bioreactor is an MSW landfill or portion of the landfill where any liquid other than leachate is added to the waste mass to reach a minimum average moisture content of at least 40 percent by weight to accelerate or enhance the biodegradation of the waste. New bioreactors must install the GCCS in the bioreactor prior to initiating liquids addition, regardless of whether the landfill emissions rate equals or exceeds the estimated uncontrolled emissions rate; existing bioreactors must install the GCCS before initiating liquids addition and must begin operating the GCCS within 180 days after initiating liquids addition or within 180 days after achieving a moisture content of 40 percent by weight, whichever is later.

Based on modeled emission estimates in the 2016 NSPS/EG datasets, and supplementary searching of the Greenhouse Gas Reporting Program (GHGRP) data, located in 40 CFR part 98, subpart HH, the EPA Landfill Methane Outreach Program (LMOP) Landfill and LFG Energy Project Database, and selected permits, as of 2014, there were between 664 and 709 MSW landfills subject to the collection and control requirements of the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA). The exact list of facilities subject to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) is unknown because many landfills collect site-specific data for NMOC concentrations using the Tier 2 provisions allowed under the regulation to compute the NMOC annual emission rates. A list of facilities that were expected to be subject to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) based on modeled emissions and a default NMOC concentration of 595 parts per million by volume (ppmv) is available in the RTR dataset.

It is estimated that these landfills emit between 2,242 and 4,586 Mg/yr of HAP, after considering current control requirements. Most of these emissions are fugitive emissions.

MSW Landfills NESHAP RTR Draft Emissions Modeling File.

May 2018. Available at:

https://www.epa.gov/stationary-sources-air-pollution/municipal-solid-waste-landfills-national-emission-standards.

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

The EPA did not gather a substantial amount of new data for this RTR proposal because data were recently gathered and compiled to support the 2016 NSPS/EG rulemaking (see 81 FR 59332 and 81 FR 59276, August 29, 2016). These regulations are codified at 40 CFR part 60, subpart XXX (NSPS) and 40 CFR part 60, subpart Cf (EG) and are hereinafter referred to as the “MSW Landfills NSPS” and “MSW landfills EG.” However, the EPA did focus additional data collection efforts in three main areas.

First, the EPA analyzed locations of the landfills, flares, and any engines, turbines or other destruction devices for the approximately 700 affected facilities by utilizing Google Maps©. Because the database for the MSW Landfills NSPS (40 CFR part 60, subpart XXX) contained only a single coordinate for each facility, every landfill was visually inspected on Google Maps© to ensure the correct location for each emission point. Additionally, some coordinates in the MSW Landfills NSPS (40 CFR part 60, subpart XXX) were for an office or headquarters away from the actual landfill location, so state records or permits were gathered to assist narrowing down the true location of these sources.

Second, the EPA visited four landfills in September 2018. These landfills were the Waste Management Dallas Fort-Worth (DFW) Landfill in Lewisville, Texas; the 121 Regional Disposal Facility and renewable natural gas production plant in Melissa, Texas; the City of Grand Prairie Landfill in Grand Prairie, Texas; and the Hunter Ferrell Landfill in Irving, Texas. The EPA discussed materials handling, materials/waste screening and separation, basic overview of waste acceptance history and general size, the use of liquids addition or leachate recirculation at the landfill, and design and operation of landfill GCCS components, including energy recovery devices and monitoring procedures to ensure a well-operated and well-controlled LFG GCCS. At the DFW Landfill, the EPA observed a quarterly surface emission monitoring event. The site visits are documented in separate reports that are available in the docket for this action: Site Visit Report—DFW Landfill, Lewisville, Texas; Site Visit Report—121 Landfill, Melissa, Texas; Site Visit Report—City of Grand Prairie Landfill, Grand Prairie, Texas; and Site Visit Report—Hunter Ferrell Landfill, Irving, Texas.

Third, emission factors were calculated for conventional landfills using data that were initially used for the 2008 Compilation of Air Pollutant Emission Factors (AP-42) draft emission factors for this source category in addition to data submitted in response of this draft.

Although thesse data are not “new,” these data came after the

original promulgation of the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA). These emission factors were applied to estimated landfill gas flow rates to estimate the HAP emissions from landfills for the risk analysis. Further detail on the emission factor devleopment can be found in the document,

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the 2019 Risk and Technology Review Proposed Rule, located

in EPA-HQ-OAR-2002-0047.

U.S. EPA. AP42, Fifth Edition, Volume I Chapter 2.4:

Municipal Solid Waste Landfills Draft Section.

October 2008. Available at:

https://www3.epa.gov/ttn/chief/ap42/ch02/index.html.

Finally, we are coordinating with the EPA Office of Land and Emergency Management on relevant data received on the Advanced Notice of Proposed Rulemaking (ANPRM), Revisions to the Criteria for Municipal Solid Waste Landfills To Address Advances in Liquids Management (83 FR 66210; December 26, 2018). Specifically, this notice describes the NESHAP definition for bioreactor landfill units, but indicates the EPA is contemplating future revisions that could define a bioreactor landfill as including other factors such as whether liquids are added intentionally for any purpose other than cleaning, maintenance, and wetting of daily cover; the average amount of annual precipitation in an area; whether leachate is recirculated; and the magnitude of the first-order biodegradation constant (k), or unintentially (

i.e.,

from extreme weather events). Relatedly, the ANPRM distinguishes between bioreactor landfill units to which liquids are purposefully added and “wet landfill units,” which are MSW landfills operating at high levels of moisture content. Readers are directed to that docket (EPA-HQ-OAR-2002-0047) to review the data and information solicited and received in response to the ANPRM, which will inform the EPA in making determinations concerning what actions, if any, to take when undertaking future revisions to MSW landfill related provisions.

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

The EPA used data and information from the 2016 NSPS/EG MSW Landfill rulemaking databases, the GHGRP (40 CFR part 98, subpart HH), and the EPA LMOP Landfill and LFG Energy Project Database to support this proposed rulemaking. We used these data to develop the modeling file for the risk review. The EPA used these same sources as well as additional information regarding the timing of GCCS installations and expansions and the types of LFG control devices installed at landfills from selected permits, state regulations, Federal regulations affecting landfills other than the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA), consent decrees for MSW landfills, and Reasonably Available Control Technology/Best Available Control Technology/Lowest Achievable Emission Rate (RACT/BACT/LAER) Clearinghouse, and literature sources, to identify additional control technologies for the technology review. The EPA also reviewed the Applicability Determination Index (ADI),

consent decrees, and data available from EPA Regions related to requests for corrective action and higher operating values for wellheads. See sections IV.A, IV.B, IV.C, and IV.E of this preamble for further detail on the use of these sources of information.

U.S. EPA. ADI.

https://cfpub.epa.gov/adi/.

III. Analytical Procedures and Decision-Making

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 do we consider risk in our decision-making?

As discussed in section II.A of this preamble and in the Benzene NESHAP, in evaluating and developing standards under CAA section 112(f)(2), we apply a two-step approach to determine whether or not risks are acceptable and to determine if the standards provide an ample margin of safety to protect public health. As explained in the Benzene NESHAP, “the first step judgment on acceptability cannot be reduced to any single factor” and, thus, “[t]he Administrator believes that the acceptability of risk under section 112 is best judged on the basis of a broad set of health risk measures and information.” 54 FR 38046, 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. The EPA conducts 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 noncancer health effects, and the hazard quotient (HQ) for acute exposures to HAP with the potential to cause noncancer health effects.

The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The scope of the EPA's risk analysis is consistent with the EPA's response to comments on our policy under the Benzene NESHAP where the EPA explained:

The MIR is defined as the cancer risk associated with a lifetime of exposure at the highest concentration of HAP where people are likely to live. The HQ is the ratio of the potential HAP exposure concentration to the noncancer dose-response value; the HI is the sum of HQs for HAP that affect the same target organ or organ system.

[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 noncancer health effects, and the uncertainties of the risk estimates. In this way, the effect on the most exposed individuals can be reviewed as well as the impact on the general public. These factors can then be weighed in each individual case. This approach complies with the

Vinyl Chloride

mandate that the Administrator ascertain an acceptable level of risk to the public by employing his expertise to assess available data. It also complies with the Congressional intent behind the CAA, which did not exclude the use of any particular measure of public health risk from the EPA's consideration with respect to CAA section 112 regulations, and thereby implicitly permits consideration of any and all measures of health risk which the Administrator, in his judgment, believes are appropriate to determining what will `protect the public health'.

See 54 FR 38044, 38057, September 14, 1989. Thus, the level of the MIR is only one factor to be weighed in determining acceptability of risk. The Benzene NESHAP explained that a “MIR of approximately 1 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 [a]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 the HAP risk that may be associated with emissions from other facilities that do not include the source category under review, mobile source emissions, natural source emissions, persistent environmental pollution, or atmospheric transformation in the vicinity of the sources in the category.

The EPA understands the potential importance of considering an individual's total exposure to HAP in addition to considering exposure to HAP emissions from the source category and facility. We recognize that such consideration may be particularly important when assessing noncancer risk, where pollutant-specific exposure health reference levels (

e.g.,

reference concentrations (RfCs)) are based on the assumption that thresholds exist for adverse health effects. For example, the EPA recognizes that, although exposures attributable to emissions from a source category or facility alone may not indicate the potential for increased risk of adverse noncancer health effects in a population, the exposures resulting from emissions from the facility in combination with emissions from all of the other sources (

e.g.,

other facilities) to which an individual is exposed may be sufficient to result in an increased risk of adverse noncancer health effects. In May 2010, the Science Advisory Board (SAB) advised the EPA “that RTR assessments will be most useful to decision makers and communities if results are presented in the broader context of aggregate and cumulative risks, including background concentrations and contributions from other sources in the area.”

Recommendations of the SAB Risk and Technology Review (RTR) Panel are provided in their report, which is available at:

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

In response to the SAB recommendations, the EPA incorporates cumulative risk analyses into its RTR risk assessments, including those reflected in this proposal. The Agency: (1) Conducts facility-wide assessments, which include source category emission points, as well as other emission points within the facilities; (2) combines exposures from multiple sources in the same category that could affect the same individuals; and (3) for some persistent and bioaccumulative pollutants, analyzes the ingestion route of exposure. In addition, the RTR risk assessments consider aggregate cancer risk from all carcinogens and aggregated noncancer HQs for all noncarcinogens affecting the same target organ or target organ system.

Although we are interested in placing source category and facility-wide HAP risk in the context of total HAP risk from all sources combined in the vicinity of each source, we are concerned about the uncertainties of doing so. Estimates of total HAP risk from emission sources other than those that we have studied in depth during this RTR review would have significantly greater associated uncertainties than the source category or facility-wide estimates. Such aggregate or cumulative assessments would compound those uncertainties, making the assessments too unreliable.

B. How do we perform the technology review?

Our technology review focuses on the identification and evaluation of developments in practices, processes, and control technologies that have occurred since the MACT standards were promulgated. Where we identify such developments, we analyze their technical feasibility, estimated costs, energy implications, and non-air environmental impacts. We also consider the emission reductions associated with applying each development. This analysis informs our decision of whether it is “necessary” to revise the emissions standards. In addition, we consider the appropriateness of applying controls to new sources versus retrofitting existing sources. For this exercise, we consider any of the following to be a “development”:

• Any add-on control technology or other equipment that was not identified and considered during development of the original MACT standards;

• Any improvements in add-on control technology or other equipment (that were identified and considered during development of the original MACT standards) that could result in additional emissions reduction;

• Any work practice or operational procedure that was not identified or considered during development of the original MACT standards;

• Any process change or pollution prevention alternative that could be broadly applied to the industry and that was not identified or considered during development of the original MACT standards; and

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

In addition to reviewing the practices, processes, and control technologies that were considered at the time we originally developed the NESHAP, we review a variety of data sources in our investigation of potential practices, processes, or controls to consider. See sections II.C and II.D of this preamble for information on the specific data sources that were reviewed as part of the technology review.

C. How do we estimate post-MACT risk posed by the source category?

In this section, we provide a complete description of the types of analyses that we generally perform during the risk assessment process. In some cases, we do not perform a specific analysis because it is not relevant. For example, in the absence of emissions of HAP known to be persistent and bioaccumulative in the environment (PB-HAP), we would not perform a multipathway exposure assessment. Where we do not perform an analysis, we state that we do not and provide the reason. While we present all of our risk assessment methods, we only present risk assessment results for the analyses actually conducted (see section IV.B of this preamble).

The EPA conducts a risk assessment that provides estimates of the MIR for cancer posed by the HAP emissions from each source in the source category, the HI for chronic exposures to HAP with the potential to cause noncancer health effects, and the HQ for acute exposures to HAP with the potential to cause noncancer health effects. The assessment also provides estimates of the distribution of cancer risk within the exposed populations, cancer incidence, and an evaluation of the potential for an adverse environmental effect. The eight sections that follow this paragraph describe how we estimated emissions and conducted the risk assessment. The docket for this rulemaking contains the following document which provides more information on the risk assessment inputs and models:

Residual Risk Assessment for the MSW Landfills Source Category in Support of the 2019

Risk and Technology Review Proposed Rule.

The methods used to assess risk (as described in the eight primary steps below) are consistent with those described by the EPA in the document reviewed by a panel of the EPA's SAB in 2009;

and described in the SAB review report issued in 2010. They are also consistent with the key recommendations contained in that report.

U.S. EPA.

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

June 2009. EPA-452/R-09-006.

https://www3.epa.gov/airtoxics/rrisk/rtrpg.html.

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

The initial list of facilities was based on the 2016 NSPS/EG database by selecting landfills that had an annual NMOC emission rate of 50 Mg/yr or greater in 2014. This faciliy list was then examined one-by-one using Google Earth to verify the boundaries of the landfill itself, as well as stack locations for any flare or control devices. Total flow rate of landfill gas was estimated utilizing the same method as the 2016 NSPS/EG, described below.

The EPA created a Microsoft® Access database of landfills for the 2016 NSPS and EG rules. Additional detail about the database can be found in the docketed memorandum,

Summary of Updated Landfill Dataset Used in the Cost and Emission Reduction Analysis of Landfills Regulations, 2016.

Within the database, we programmed a series of calculations in the database (hereinafter referred to as the “model”) to estimate LFG flow rates using a first-order decay equation and the associated cost and emission reduction impacts for each landfill expected to control emissions by the NSPS and EG regulations in a particular year. The model estimated flow rates using default parameters from AP-42

for NMOC, methane generation potential (L

), and the methane generation rate (k). A detailed discussion of the methodology, modeling parameters, and equations used to estimate the LFG flow rate are available in the docketed memorandum,

Revised Methodology for Estimating Cost and Emission Impacts of MSW Landfill Regulations,

2016.

U.S. EPA, AP-42, Fifth Edition,

Compilation of Air Pollutant Emission Factors, Volume 1: Stationary Point and Area Sources.

1995.

http://www.epa.gov/ttnchie1/ap42/.

Total collected landfill gas was estimated using available information including the calculated LFG flow rate described above. Total collected landfill gas was estimated by using the maximum value of landfill gas reported as collected in GHGRP for 2014, LMOP reported collected gas where GHGRP collection in 2014 was not provided, LMOP reported flow rate to projects or 85 percent of the 2016 NSPS and EG database's total flow rate. In cases where the total collected landfill gas estimation exceeded the modeled total flow rate of landfill gas, total landfill gas flow rate was back-calculated using GHGRP's estimated gas collection efficiency (or 85 percent when not available). Fugitive landfill emissions were calculated by subtracting the total collected landfill gas estimation from the total landfill gas flow rate, whether it was modeled or back-calculated. Landfill gas flow to engines was used for instances that LMOP had reported landfill gas flow to projects. We assumed that all LMOP projects were engines with 98-percent destruction efficiency for this modeling effort. We also assumed any additional collected landfill gas estimation beyond what LMOP listed as flow to a project went to a flare with 86-percent destruction efficiency. Stack parameters were not available for the source category, therefore, default parameters were developed using RTR default values developed by the EPA based on Source Classification Code (SCC) and assigned accordingly. Once we calculated all landfill gas emissions and estimated the amount of landfill gas flow to engines and flares, we applied emission factors to estimate HAP emissions from these sources.

To estimate HAP using a factor applied to landfill gas collection or generation estimates, we determined the appropriate basis of the factor. Although the 1998 Final AP-42 is commonly used to calculate emissions in inventories, the 1998 Final AP-42 is outdated and has very few HAP emission factors. The 1998 Final AP-42 has factors for 47 different compounds, 23 of which are HAP. In 2008, the EPA drafted AP-42 emission factors for this source category. The 2008 proposed factors were based on 47 test reports containing speciated organic and reduced sulfur compound data that could be corrected for air infiltration. This draft had emission factors for 173 compounds. In response to this draft, the EPA received public comments and additional data on the proposed AP-42 emission factor updates. This included 446 new test reports, of which 242 were unique complete test reports. 116 unique landfills were represented in the new data. Overall, including the original data and additional data submissions, test reports were available for landfills in 37 different states. This complete dataset (the data used to calculate the 2008 Draft AP-42 plus the new test reports) was used to calculate HAP emission factors for use in the RTR for the MSW Landfills NESHAP.

These data were analyzed for errors and the concentrations were corrected for air infiltration, in the same fashion the 2008 data were quality controlled. These two datasets were combined with the 2008 dataset. All non-detect data were removed. Then to remove outliers, data points that were two standard deviations above or below the mean of each HAP were removed. Each HAP's data were then averaged to develop the emission factor. The docket for this rulemaking contains the following document, which provides more information on the emission factor development as well as the emission estimation calculations:

Residual Risk Modeling File Documentation for the Municipal Solid Waste Landfills Source Category.

2. How did we estimate MACT-allowable emissions?

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

Because the requirements under the NESHAP are for all landfills that exceed the NMOC threshold to install a gas collection and control system, allowable emissions were equal to the calculated actual emissions, therefore, the allowable multiplier is 1. Because the landfill owner or operator is required to operate the GCCS at all times, there is

no differentiation between actual and allowable emissions.

3. How do we conduct dispersion modeling, determine inhalation exposures, and estimate individual and population inhalation risk?

Both long-term and short-term inhalation exposure concentrations and health risk from the source category addressed in this proposal were estimated using the Human Exposure Model (HEM-3).

The HEM-3 performs three primary risk assessment activities: (1) Conducting dispersion modeling to estimate the concentrations of HAP in ambient air, (2) estimating long-term and short-term inhalation exposures to individuals residing within 50 kilometers (km) of the modeled sources, and (3) estimating individual and population-level inhalation risk using the exposure estimates and quantitative dose-response information.

For more information about HEM-3, go to

https://www.epa.gov/fera/risk-assessment-and-modeling-human-exposure-model-hem.

a. Dispersion Modeling

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

To perform the dispersion modeling and to develop the preliminary risk estimates, HEM-3 draws on three data libraries. The first is a library of meteorological data, which is used for dispersion calculations. This library includes 1 year (2016) of hourly surface and upper air observations from 824 meteorological stations, selected to provide coverage of the United States and Puerto Rico. A second library of United States Census Bureau census block

internal point locations and populations provides the basis of human exposure calculations (U.S. Census, 2010). In addition, for each census block, the census library includes the elevation and controlling hill height, which are also used in dispersion calculations. A third library of pollutant-specific dose-response values is used to estimate health risk. These are discussed below.

U.S. EPA. Revision to the Guideline on Air Quality Models:

Adoption of a Preferred General Purpose (Flat and Complex Terrain) Dispersion Model and Other Revisions

(70 FR 68218, November 9, 2005).

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

b. Risk From Chronic Exposure to HAP

In developing the risk assessment for chronic exposures, we use the estimated annual average ambient air concentrations of each HAP emitted by each source in the source category. The HAP air concentrations at each nearby census block centroid located within 50 km of the facility are a surrogate for the chronic inhalation exposure concentration for all the people who reside in that census block. A distance of 50 km is consistent with both the analysis supporting the 1989 Benzene NESHAP (54 FR 38044, September 14, 1989) and the limitations of Gaussian dispersion models, including AERMOD.

For each facility, we calculate the MIR as the cancer risk associated with a continuous lifetime (24 hours per day, 7 days per week, 52 weeks per year, 70 years) exposure to the maximum concentration at the centroid of each inhabited census block. We calculate individual cancer risk by multiplying the estimated lifetime exposure to the ambient concentration of each HAP (in micrograms per cubic meter (μg/m

)) by its unit risk estimate (URE). The URE is an upper-bound estimate of an individual's incremental risk of contracting cancer over a lifetime of exposure to a concentration of 1 microgram of the pollutant per cubic meter of air. For residual risk assessments, we generally use UREs from the EPA's Integrated Risk Information System (IRIS). For carcinogenic pollutants without IRIS values, we look to other reputable sources of cancer dose-response values, often using California EPA (CalEPA) UREs, 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 pollutant-specific dose-response values used to estimate health risk are available at

https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.

To estimate individual lifetime cancer risks associated with exposure to HAP emissions from each facility in the source category, we sum the risks for each of the carcinogenic HAP

emitted by the modeled facility. We estimate cancer risk at every census block within 50 km of every facility in the source category. The MIR is the highest individual lifetime cancer risk estimated for any of those census blocks. In addition to calculating the MIR, we estimate the distribution of individual cancer risks for the source category by summing the number of individuals within 50 km of the sources whose estimated risk falls within a specified risk range. We also estimate annual cancer incidence by multiplying the estimated lifetime cancer risk at each census block by the number of people residing in that block, summing results for all of the census blocks, and then dividing this result by a 70-year lifetime.

The EPA's 2005

Guidelines for Carcinogen Risk Assessment

classifies carcinogens as: “carcinogenic to humans,” “likely to be carcinogenic to humans,” and “suggestive evidence of carcinogenic potential.” These classifications also coincide with the terms “known carcinogen, probable carcinogen, and possible carcinogen,” respectively, which are the terms advocated in the EPA's

Guidelines for Carcinogen Risk Assessment,

published in 1986 (51 FR 33992, September 24, 1986). In August 2000, the document,

Supplemental Guidance for Conducting Health Risk Assessment of Chemical Mixtures

(EPA/630/R-00/002), was published as a supplement to the 1986 document. Copies of both documents can be obtained from

https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=20533&CFID=70315376&CFTOKEN=71597944.

Summing the risk of these individual compounds to obtain the cumulative cancer risk is an approach that was recommended by the EPA's SAB in their 2002 peer review of the EPA's National Air Toxics Assessment (NATA) titled

NATA—Evaluating the National-scale Air Toxics Assessment 1996 Data

—an SAB Advisory, available at

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

To assess the risk of noncancer health effects from chronic exposure to HAP, we calculate either an HQ or a target organ-specific hazard index (TOSHI). We calculate an HQ when a single noncancer HAP is emitted. Where more than one noncancer HAP is emitted, we sum the HQ for each of the HAP that affects a common target organ or target organ system to obtain a TOSHI. The HQ is the estimated exposure divided by the chronic noncancer dose-response value, which is a value selected from one of several sources. The preferred chronic noncancer dose-response value is the EPA RfC, defined as “an estimate (with uncertainty spanning perhaps an order of magnitude) of a continuous inhalation exposure to the human population (including sensitive subgroups) that is likely to be without an appreciable risk of deleterious effects during a lifetime.”

(https://iaspub.epa.gov/sor_internet/registry/termreg/searchandretrieve/glossariesandkeywordlists/search.do?details=&vocabName=IRIS%20Glossary).

In cases where an RfC from the EPA's IRIS is not available or where the EPA determines that using a value other than the RfC is appropriate, the chronic noncancer dose-response value can be a value from the following prioritized sources, which define their dose-response values similarly to the EPA: (1) The Agency for Toxic

Substances and Disease Registry (ATSDR) Minimum Risk Level

(https://www.atsdr.cdc.gov/mrls/index.asp);

(2) the CalEPA Chronic Reference Exposure Level (REL)

(https://oehha.ca.gov/air/crnr/notice-adoption-air-toxics-hot-spots-program-guidance-manual-preparation-health-risk-0);

or (3), as noted above, a scientifically credible dose-response value that has been developed in a manner consistent with the EPA guidelines and has undergone a peer review process similar to that used by the EPA. The pollutant-specific dose-response values used to estimate health risks are available at

https://www.epa.gov/fera/dose-response-assessment-assessing-health-risks-associated-exposure-hazardous-air-pollutants.

c. Risk From Acute Exposure to HAP That May Cause Health Effects Other Than Cancer

For each HAP for which appropriate acute inhalation dose-response values are available, the EPA also assesses the potential health risks due to acute exposure. For these assessments, the EPA makes conservative assumptions about emission rates, meteorology, and exposure location. In this proposed rulemaking, as part of our efforts to continually improve our methodologies to evaluate the risks that HAP emitted from categories of industrial sources pose to human health and the environment,

we are revising our treatment of meteorological data to use reasonable worst-case air dispersion conditions in our acute risk screening assessments instead of worst-case air dispersion conditions. This revised treatment of meteorological data and the supporting rationale are described in more detail in

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the 2019 Risk and Technology Review Proposed Rule

and in Appendix 5 of the report:

Technical Support Document for Acute Risk Screening Assessment.

We will be applying this revision in RTR rulemakings proposed on or after June 3, 2019.

See,

e.g.,

U.S. EPA.

Screening Methodologies to Support Risk and Technology Reviews (RTR): A Case Study Analysis

(Draft Report, May 2017.

https://www3.epa.gov/ttn/atw/rrisk/rtrpg.html

To assess the potential acute risk to the maximally exposed individual, we use the peak hourly emission rate for each emission point,

reasonable worst-case dispersion conditions (

i.e.,

99th percentile), and the point of highest off-site exposure. Specifically, we assume that peak emissions from the source category and reasonable worst-case air dispersion conditions co-occur and that a person is present at the point of maximum exposure.

In the absence of hourly emission data, we develop estimates of maximum hourly emission rates by multiplying the average actual annual emissions rates by a factor (either a category-specific factor or a default factor of 10) to account for variability. This is documented in

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the 2019 Risk and Technology Review Proposed Rule

and in Appendix 5 of the report:

Technical Support Document for Acute Risk Screening Assessment.

Both are available in the docket for this rulemaking.

To characterize the potential health risks associated with estimated acute inhalation exposures to a HAP, we generally use multiple acute dose-response values, including acute RELs, acute exposure guideline levels (AEGLs), and emergency response planning guidelines (ERPG) for 1-hour exposure durations, if available, to calculate acute HQs. The acute HQ is calculated by dividing the estimated acute exposure concentration by the acute dose-response value. For each HAP for which acute dose-response values are available, the EPA calculates acute HQs.

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

Acute RELs are based on the most sensitive, relevant, adverse health effect reported in the peer-reviewed medical and toxicological literature. They are designed to protect the most sensitive individuals in the population through the inclusion of margins of safety. Because margins of safety are incorporated to address data gaps and uncertainties, exceeding the REL does not automatically indicate an adverse health impact. AEGLs represent threshold exposure limits for the general public and are applicable to emergency exposures ranging from 10 minutes to 8 hours.

They are guideline levels for “once-in-a-lifetime, short-term exposures to airborne concentrations of acutely toxic, high-priority chemicals.”

Id.

at 21. The AEGL-1 is specifically defined as “the airborne concentration (expressed as ppm (parts per million) or mg/m

(milligrams per cubic meter)) of a substance above which it is predicted that the general population, including susceptible individuals, could experience notable discomfort, irritation, or certain asymptomatic nonsensory effects. However, the effects are not disabling and are transient and reversible upon cessation of exposure.” The document also notes that “Airborne concentrations below AEGL-1 represent exposure levels that can produce mild and progressively increasing but transient and nondisabling odor, taste, and sensory irritation or certain asymptomatic, nonsensory effects.”

Id.

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

Id.

CalEPA issues acute RELs as part of its Air Toxics Hot Spots Program, and the 1-hour and 8-hour values are documented in

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

which is available at

https://oehha.ca.gov/air/general-info/oehha-acute-8-hour-and-chronic-reference-exposure-level-rel-summary.

National Academy of Sciences, 2001.

Standing Operating Procedures for Developing Acute Exposure Levels for Hazardous Chemicals,

page 2. Available at

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

Note that the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances ended in October 2011, but the AEGL program continues to operate at the EPA and works with the National Academies to publish final AEGLs,

(https://www.epa.gov/aegl).

ERPGs are “developed for emergency planning and are intended as health-based guideline concentrations for single exposures to chemicals.”

Id.

at 1. The ERPG-1 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 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.

ERPGS Procedures and Responsibilities. March 2014. American Industrial Hygiene Association. Available at:

https://www.aiha.org/get-involved/AIHAGuidelineFoundation/EmergencyResponsePlanningGuidelines/Documents/ERPG%20Committee%20Standard%20Operating%20Procedures%20%20-%20March%202014%20Revision%20%28Updated%2010-2-2014%29.pdf.

An acute REL for 1-hour exposure durations is typically lower than its corresponding AEGL-1 and ERPG-1. Even though their definitions are slightly different, AEGL-1s are often the same as the corresponding ERPG-1s, and AEGL-2s are often equal to ERPG-2s. The maximum HQs from our acute inhalation screening risk assessment typically result when we use the acute REL for a HAP. In cases where the maximum acute HQ exceeds 1, we also report the HQ based on the next highest acute dose-response value (usually the AEGL-1 and/or the ERPG-1).

For this source category, we used the default multiplication factor of 10. While we don't anticipate large variations in acute hourly emissions, we took a conservative approach to determine if the default multiplication factor would result in high risk. Upon modeling the emissions using the acute multiplication factor of 10, we determined that the noncancer risk was still below a HQ of 1. Due to the low risk results, further research to justify a lower multiplication factor was not necessary.

In our acute inhalation screening risk assessment, acute impacts are deemed negligible for HAP for which acute HQs are less than or equal to 1, and no further analysis is performed for these HAP. In cases where an acute HQ from the screening step is greater than 1, we assess site-specific data to ensure that the acute HQ is at an off-site location. For this source category, we did not have to perform any refined acute assessments.

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

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

i.e.,

ingestion). We first determine whether any sources in the source category emit any PB-HAP, as identified in the EPA's Air Toxics Risk Assessment Library (see Volume 1, Appendix D, at

https://www2.epa.gov/fera/risk-assessment-and-modeling-air-toxics-risk-assessment-reference-library.

)

For the MSW Landfills source category, we identified PB-HAP emissions of mercury, so we proceeded to the next step of the evaluation. In this step, we determine whether the facility-specific emission rates of the emitted PB-HAP are large enough to create the potential for significant human health risk through ingestion exposure under reasonable worst-case conditions. To facilitate this step, we use previously developed screening threshold emission rates for several PB-HAP that are based on a hypothetical upper-end screening exposure scenario developed for use in conjunction with the EPA's Total Risk Integrated Methodology.Fate, Transport, and Ecological Exposure (TRIM.FaTE) model. The PB-HAP with screening threshold emission rates are arsenic compounds, cadmium compounds, chlorinated dibenzodioxins and furans, mercury compounds, and polycyclic organic matter (POM). Based on the EPA estimates of toxicity and bioaccumulation potential, the pollutants above represent a conservative list for inclusion in multipathway risk assessments for RTR rules. (See Volume 1, Appendix D at

https://www.epa.gov/sites/production/files/2013-08/documents/volume_1_reflibrary.pdf.

) In this assessment, we compare the facility-specific emission rates of these PB-HAP to the screening threshold emission rates for each PB-HAP to assess the potential for significant human health risks via the ingestion pathway. We call this application of the TRIM.FaTE model the Tier 1 screening assessment. The ratio of a facility's actual emission rate to the Tier 1 screening threshold emission rate is a “screening value.”

We derive the Tier 1 screening threshold emission rates for these PB-HAP (other than lead compounds) to correspond to a maximum excess lifetime cancer risk of 1-in-1 million (

i.e.,

for arsenic compounds, polychlorinated dibenzodioxins and furans and POM) or, for HAP that cause noncancer health effects (

i.e.,

cadmium compounds and mercury compounds), a maximum HQ of 1. If the emission rate of any one PB-HAP or combination of carcinogenic PB-HAP in the Tier 1 screening assessment exceeds the Tier 1 screening threshold emission rate for any facility (

i.e.,

the screening value is greater than 1), we conduct a second screening assessment, which we call the Tier 2 screening assessment.

In the Tier 2 screening assessment, the location of each facility that exceeds a Tier 1 screening threshold emission rate is used to refine the assumptions associated with the Tier 1 fisher and farmer exposure scenarios at that facility. A key assumption in the Tier 1 screening assessment is that a lake and/or farm is located near the facility. As part of the Tier 2 screening assessment, we use a U.S. Geological Survey (USGS) database to identify actual waterbodies within 50 km of each facility. We also examine the differences between local meteorology near the facility and the meteorology used in the Tier 1 screening assessment. We then adjust the previously-developed Tier 1 screening threshold emission rates for each PB-HAP for each facility based on an understanding of how exposure concentrations estimated for the screening scenario change with the use of local meteorology and USGS waterbody data. If the PB-HAP emission rates for a facility exceed the Tier 2 screening threshold emission rates and data are available, we may conduct a Tier 3 screening assessment. If PB-HAP emission rates do not exceed a Tier 2 screening value of 1, we consider those PB-HAP emissions to pose risks below a level of concern.

There are several analyses that can be included in a Tier 3 screening assessment, depending upon the extent of refinement warranted, including validating that the lakes are fishable, considering plume-rise to estimate emissions lost above the mixing layer, and considering hourly effects of meteorology and plume rise on chemical fate and transport. If the Tier 3 screening assessment indicates that risks above levels of concern cannot be ruled out, the EPA may further refine the screening assessment through a site-specific assessment.

For further information on the multipathway assessment approach, see the

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the Risk and Technology Review 2019 Proposed Rule,

which is available in the docket for this action.

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

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

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

a. Adverse Environmental Effect, Environmental HAP, and Ecological Benchmarks

The EPA conducts a screening assessment to examine the potential for an adverse environmental effect as required under section 112(f)(2)(A) of the CAA. Section 112(a)(7) of the CAA defines “adverse environmental effect”

as “any significant and widespread adverse effect, which may reasonably be anticipated, to wildlife, aquatic life, or other natural resources, including adverse impacts on populations of endangered or threatened species or significant degradation of environmental quality over broad areas.”

The EPA focuses on eight HAP, which are referred to as “environmental HAP,” in its screening assessment: Six PB-HAP and two acid gases. The PB-HAP included in the screening assessment are arsenic compounds, cadmium compounds, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), and lead compounds. The acid gases included in the screening assessment are hydrochloric acid (HCl) and hydrogen fluoride (HF).

HAP that persist and bioaccumulate are of particular environmental concern because they accumulate in the soil, sediment, and water. The acid gases, HCl and HF, are included due to their well-documented potential to cause direct damage to terrestrial plants. In the environmental risk screening assessment, we evaluate the following four exposure media: Terrestrial soils, surface water bodies (includes water-column and benthic sediments), fish consumed by wildlife, and air. Within these four exposure media, we evaluate nine ecological assessment endpoints, which are defined by the ecological entity and its attributes. For PB-HAP (other than lead), both community-level and population-level endpoints are included. For acid gases, the ecological assessment evaluated is terrestrial plant communities.

An ecological benchmark represents a concentration of HAP that has been linked to a particular environmental effect level. For each environmental HAP, we identified the available ecological benchmarks for each assessment endpoint. We identified, where possible, ecological benchmarks at the following effect levels: Probable effect levels, lowest-observed-adverse-effect level, and no-observed-adverse-effect level. In cases where multiple effect levels were available for a particular PB-HAP and assessment endpoint, we use all of the available effect levels to help us to determine whether ecological risks exist and, if so, whether the risks could be considered significant and widespread.

For further information on how the environmental risk screening assessment was conducted, including a discussion of the risk metrics used, how the environmental HAP were identified, and how the ecological benchmarks were selected, see Appendix 9 of the

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the Risk and Technology Review 2019 Proposed Rule,

which is available in the docket for this action.

b. Environmental Risk Screening Methodology

For the environmental risk screening assessment, the EPA first determined whether any facilities in the MSW Landfills source category emitted any of the environmental HAP. For the MSW Landfills source category, we identified emissions of mercury. Because mercury is listed as an environmental HAP and is emitted by at least one facility in the source category, we proceeded to the second step of the evaluation.

c. PB-HAP Methodology

The environmental screening assessment includes six PB-HAP, arsenic compounds, cadmium compounds, dioxins/furans, POM, mercury (both inorganic mercury and methyl mercury), and lead compounds. With the exception of lead, the environmental risk screening assessment for PB-HAP consists of three tiers. The first tier of the environmental risk screening assessment uses the same health-protective conceptual model that is used for the Tier 1 human health screening assessment. TRIM.FaTE model simulations were used to back-calculate Tier 1 screening threshold emission rates. The screening threshold emission rates represent the emission rate in tons of pollutant per year that results in media concentrations at the facility that equal the relevant ecological benchmark. To assess emissions from each facility in the category, the reported emission rate for each PB-HAP was compared to the Tier 1 screening threshold emission rate for that PB-HAP for each assessment endpoint and effect level. If emissions from a facility do not exceed the Tier 1 screening threshold emission rate, the facility “passes” the screening assessment and, therefore, is not evaluated further under the screening approach. If emissions from a facility exceed the Tier 1 screening threshold emission rate, we evaluate the facility further in Tier 2.

In Tier 2 of the environmental screening assessment, the screening threshold emission rates are adjusted to account for local meteorology and the actual location of lakes in the vicinity of facilities that did not pass the Tier 1 screening assessment. For soils, we evaluate the average soil concentration for all soil parcels within a 7.5-km radius for each facility and PB-HAP. For the water, sediment, and fish tissue concentrations, the highest value for each facility for each pollutant is used. If emission concentrations from a facility do not exceed the Tier 2 screening threshold emission rate, the facility “passes” the screening assessment and typically is not evaluated further. If emissions from a facility exceed the Tier 2 screening threshold emission rate, we evaluate the facility further in Tier 3.

As in the multipathway human health risk assessment, in Tier 3 of the environmental screening assessment, we examine the suitability of the lakes around the facilities to support life and remove those that are not suitable (

e.g.,

lakes that have been filled in or are industrial ponds), adjust emissions for plume-rise, and conduct hour-by-hour time-series assessments. If these Tier 3 adjustments to the screening threshold emission rates still indicate the potential for an adverse environmental effect (

i.e.,

facility emission rate exceeds the screening threshold emission rate), we may elect to conduct a more refined assessment using more site-specific information. If, after additional refinement, the facility emission rate still exceeds the screening threshold emission rate, the facility may have the potential to cause an adverse environmental effect.

To evaluate the potential for an adverse environmental effect from lead, we compared the average modeled air concentrations (from HEM-3) of lead around each facility in the source category to the level of the secondary National Ambient Air Quality Standards (NAAQS) for lead. The secondary lead NAAQS is a reasonable means of evaluating environmental risk, because it is set to provide substantial protection against adverse welfare effects which can include “effects on soils, water, crops, vegetation, man-made materials, animals, wildlife, weather, visibility and climate, damage to and deterioration of property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being.”

d. Acid Gas Environmental Risk Methodology

The environmental screening assessment for acid gases evaluates the potential phytotoxicity and reduced productivity of plants due to chronic exposure to HF and HCl. The environmental risk screening methodology for acid gases is a single-tier screening assessment that compares modeled ambient air concentrations (from AERMOD) to the ecological benchmarks for each acid gas. To identify a potential adverse

environmental effect (as defined in Section 112(a)(7) of the CAA) from emissions of HF and HCl, we evaluate the following metrics: The size of the modeled area around each facility that exceeds the ecological benchmark for each acid gas, in acres and km

; the percentage of the modeled area around each facility that exceeds the ecological benchmark for each acid gas; and the area-weighted average screening value around each facility (calculated by dividing the area-weighted average concentration over the 50-km modeling domain by the ecological benchmark for each acid gas). For further information on the environmental screening assessment approach, see Appendix 9 of the

Residual Risk Assessment for the Municipal Solid Waste Landfills Source Category in Support of the Risk and Technology Review 2019 Proposed Rule,

which is available in the docket for this action.

7. How do we conduct facility-wide assessments?

To put the source category risks in context, we typically examine the risks from the entire “facility,” where the facility includes all HAP-emitting operations within a contiguous area and under common control. In other words, we examine the HAP emissions not only from the source category emission points of interest, but also emissions of HAP from all other emission sources at the facility for which we have data. For this source category, we conducted the facility-wide assessment using the same dataset that was compiled for actual emissions. The modeled emissions were based upon EPA-derived emission factors for the source category. The facility-wide file was then used to analyze risks due to the inhalation of HAP that are emitted “facility-wide” for the populations residing within 50 km of each facility, consistent with the methods used for the source category analysis described above. For these facility-wide risk analyses, the modeled source category risks were the same as the facility-wide risks. The

Residual Risk Assessment for the MSW Landfills Source Category in Support of the Risk and Technology Review 2019 Proposed Rule,

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

8. How do we consider uncertainties in risk assessment?

Uncertainty and the potential for bias are inherent in all risk assessments, including those performed for this proposal. Although uncertainty exists, we believe that our approach, which used conservative tools and assumptions, ensures that our decisions are health and environmentally protective. A brief discussion of the uncertainties in the RTR emissions dataset, dispersion modeling, inhalation exposure estimates, and dose-response relationships follows below. Also included are those uncertainties specific to our acute screening assessments, multipathway screening assessments, and our environmental risk screening assessments. A more thorough discussion of these uncertainties is included in the

Residual Risk Assessment for the MSW Landfills Source Category in Support of the Risk and Technology Review 2019 Proposed Rule,

which is available in the docket for this action. If a multipathway site-specific assessment was performed for this source category, a full discussion of the uncertainties associated with that assessment can be found in Appendix 11 of that document,

Site-Specific Human Health Multipathway Residual Risk Assessment Report.

a. Uncertainties in the RTR Emissions Dataset

Although the development of the RTR emissions dataset involved quality assurance/quality control processes, the accuracy of emissions values will vary depending on the source of the data, the degree to which data are incomplete or missing, the degree to which assumptions made to complete the datasets are accurate, errors in emission estimates, and other factors. The emission estimates considered in this analysis generally are annual totals for certain years, and they do not reflect short-term fluctuations during the course of a year or variations from year to year. The estimates of peak hourly emission rates for the acute effects screening assessment were based on an emission adjustment factor applied to the average annual hourly emission rates, which are intended to account for emission fluctuations due to normal facility operations.

b. Uncertainties in Dispersion Modeling

We recognize there is uncertainty in ambient concentration estimates associated with any model, including the EPA's recommended regulatory dispersion model, AERMOD. In using a model to estimate ambient pollutant concentrations, the user chooses certain options to apply. For RTR assessments, we select some model options that have the potential to overestimate ambient air concentrations (

e.g.,

not including plume depletion or pollutant transformation). We select other model options that have the potential to underestimate ambient impacts (

e.g.,

not including building downwash). Other options that we select have the potential to either under- or overestimate ambient levels (

e.g.,

meteorology and receptor locations). On balance, considering the directional nature of the uncertainties commonly present in ambient concentrations estimated by dispersion models, the approach we apply in the RTR assessments should yield unbiased estimates of ambient HAP concentrations. We also note that the selection of meteorology dataset location could have an impact on the risk estimates. As we continue to update and expand our library of meteorological station data used in our risk assessments, we expect to reduce this variability.

c. Uncertainties in Inhalation Exposure Assessment

Although every effort is made to identify all of the relevant facilities and emission points, as well as to develop accurate estimates of the annual emission rates for all relevant HAP, the uncertainties in our emission inventory likely dominate the uncertainties in the exposure assessment. Some uncertainties in our exposure assessment include human mobility, using the centroid of each census block, assuming lifetime exposure, and assuming only outdoor exposures. For most of these factors, there is neither an under nor overestimate when looking at the maximum individual risk or the incidence, but the shape of the distribution of risks may be affected. With respect to outdoor exposures, actual exposures may not be as high if people spend time indoors, especially for very reactive pollutants or larger particles. For all factors, we reduce uncertainty when possible. For example, with respect to census-block centroids, we analyze large blocks using aerial imagery and adjust locations of the block centroids to better represent the population in the blocks. We also add additional receptor locations where the population of a block is not well represented by a single location.

d. Uncertainties in Dose-Response Relationships

There are uncertainties inherent in the development of the dose-response values used in our risk assessments for cancer effects from chronic exposures and noncancer effects from both chronic and acute exposures. Some uncertainties are generally expressed quantitatively, and others are generally expressed in qualitative terms. We note, as a preface to this discussion, a point on dose-response uncertainty that is

stated in the EPA's

2005 Guidelines for Carcinogen Risk Assessment;

namely, that “the primary goal of EPA actions is protection of human health; accordingly, as an Agency policy, risk assessment procedures, including default options that are used in the absence of scientific data to the contrary, should be health protective” (the EPA's

2005 Guidelines for Carcinogen Risk Assessment,

page 1-7). This is the approach followed here as summarized in the next paragraphs.

Cancer UREs used in our risk assessments are those that have been developed to generally provide an upper bound estimate of risk.

That is, they represent a “plausible upper limit to the true value of a quantity” (although this is usually not a true statistical confidence limit). In some circumstances, the true risk could be as low as zero; however, in other circumstances the risk could be greater.

Chronic noncancer RfC and reference dose (RfD) values represent chronic exposure levels that are intended to be health-protective levels. To derive dose-response values that are intended to be “without appreciable risk,” the methodology relies upon an uncertainty factor (UF) approach,

which considers uncertainty, variability, and gaps in the available data. The UFs are applied to derive dose-response values that are intended to protect against appreciable risk of deleterious effects.

IRIS glossary

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

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

See

A Review of the Reference Dose and Reference Concentration Processes, U.S. EPA, December 2002 (

https://www.epa.gov/sites/production/files/2014-12/documents/rfd-final.pdf

), and Methods for Derivation of Inhalation Reference Concentrations and Application of Inhalation Dosimetry, U.S. EPA, 1994 (

https://cfpub.epa.gov/ncea/risk/recordisplay.cfm?deid=71993

Many of the UFs used to account for variability and uncertainty in the development of acute dose-response values are quite similar to those developed for chronic durations. Additional adjustments are often applied to account for uncertainty in extrapolation from observations at one exposure duration (

e.g.,

4 hours) to derive an acute dose-response value at another exposure duration (

e.g.,

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

Uncertainty also exists in the selection of ecological benchmarks for the environmental risk screening assessment. We established a hierarchy of preferred benchmark sources to allow selection of benchmarks for each environmental HAP at each ecological assessment endpoint. We searched for benchmarks for three effect levels (

i.e.,

no-effects level, threshold-effect level, and probable effect level), but not all combinations of ecological assessment/environmental HAP had benchmarks for all three effect levels. Where multiple effect levels were available for a particular HAP and assessment endpoint, we used all of the available effect levels to help us determine whether risk exists and whether the risk could be considered significant and widespread.

For a group of compounds that are unspeciated (

e.g.,

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

e.g.,

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

e. Uncertainties in Acute Inhalation Screening Assessments

In addition to the uncertainties highlighted above, there are several factors specific to the acute exposure assessment that the EPA conducts as part of the risk review under section 112 of the CAA. The accuracy of an acute inhalation exposure assessment depends on the simultaneous occurrence of independent factors that may vary greatly, such as hourly emissions rates, meteorology, and the presence of a person. In the acute screening assessment that we conduct under the RTR program, we assume that peak emissions from the source category and reasonable worst-case air dispersion conditions (

i.e.,

99th percentile) co-occur. We then include the additional assumption that a person is located at this point at the same time. Together, these assumptions represent a reasonable worst-case actual exposure scenario. In most cases, it is unlikely that a person would be located at the point of maximum exposure during the time when peak emissions and reasonable worst-case air dispersion conditions occur simultaneously.

f. Uncertainties in the Multipathway and Environmental Risk Screening Assessments

For each source category, we generally rely on site-specific levels of PB-HAP or environmental HAP emissions to determine whether a refined assessment of the impacts from multipathway exposures is necessary or whether it is necessary to perform an environmental screening assessment. This determination is based on the results of a three-tiered screening assessment that relies on the outputs from models—TRIM.FaTE and AERMOD—that estimate environmental pollutant concentrations and human exposures for five PB-HAP (dioxins, POM, mercury, cadmium, and arsenic) and two acid gases (HF and HCl). For lead, we use AERMOD to determine ambient air concentrations, which are then compared to the secondary NAAQS standard for lead. Two important types of uncertainty associated with the use of these models in RTR risk assessments and inherent to any assessment that relies on environmental modeling are model uncertainty and input uncertainty.

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

variability

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

uncertainty

in being able to accurately estimate the true result.

Model uncertainty concerns whether the model adequately represents the actual processes (

e.g.,

movement and accumulation) that might occur in the environment. For example, does the model adequately describe the movement of a pollutant through the soil? This type of uncertainty is difficult to quantify. However, based on feedback received from previous EPA SAB reviews and other reviews, we are confident that the models used in the screening assessments are appropriate and state-of-the-art for the multipathway and environmental screening risk assessments conducted in support of RTR.

Input uncertainty is concerned with how accurately the models have been configured and parameterized for the assessment at hand. For Tier 1 of the multipathway and environmental screening assessments, we configured the models to avoid underestimating exposure and risk. This was accomplished by selecting upper-end values from nationally representative datasets for the more influential parameters in the environmental model,

including selection and spatial configuration of the area of interest, lake location and size, meteorology, surface water, soil characteristics, and structure of the aquatic food web. We also assume an ingestion exposure scenario and values for human exposure factors that represent reasonable maximum exposures.

In Tier 2 of the multipathway and environmental screening assessments, we refine the model inputs to account for meteorological patterns in the vicinity of the facility versus using upper-end national values, and we identify the actual location of lakes near the facility rather than the default lake location that we apply in Tier 1. By refining the screening approach in Tier 2 to account for local geographical and meteorological data, we decrease the likelihood that concentrations in environmental media are overestimated, thereby increasing the usefulness of the screening assessment. In Tier 3 of the screening assessments, we refine the model inputs again to account for hour-by-hour plume rise and the height of the mixing layer. We can also use those hour-by-hour meteorological data in a TRIM.FaTE run using the screening configuration corresponding to the lake location. These refinements produce a more accurate estimate of chemical concentrations in the media of interest, thereby reducing the uncertainty with those estimates. The assumptions and the associated uncertainties regarding the selected ingestion exposure scenario are the same for all three tiers.

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

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

Despite the uncertainties, when individual pollutants or facilities do not exceed screening threshold emission rates (

i.e.,

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

The EPA evaluates the following HAP in the multipathway and/or environmental risk screening assessments, where applicable: Arsenic, cadmium, dioxins/furans, lead, mercury (both inorganic and methyl mercury), POM, HCl, and HF. These HAP represent pollutants that can cause adverse impacts either through direct exposure to HAP in the air or through exposure to HAP that are deposited from the air onto soils and surface waters and then through the environment into the food web. These HAP represent those HAP for which we can conduct a meaningful multipathway or environmental screening risk assessment. For other HAP not included in our screening assessments, 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 these that we are evaluating may have the potential to cause adverse effects and, therefore, the EPA may evaluate other relevant HAP in the future, as modeling science and resources allow.

IV. Analytical Results and Proposed Decisions

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

1. Inhalation Risk Assessment Results

The inhalation risk modeling performed to estimate risks based on actual, allowable, and whole facility emissions relied primarily on emissions factors derived by the EPA.

The results of the chronic baseline inhalation cancer risk assessment indicate that, based on estimates of current actual, allowable, and whole facility emissions under 40 CFR part 63, subpart AAAA, the MIR posed by the source category could be as high as 10-in-1 million. The total estimated cancer incidence based on actual emission levels is 0.04 excess cancer cases per year, or 1 case every 25 years. The total estimated cancer incidence based on allowable emission levels is 0.05 excess cancer cases per year, or 1 case every 20 years. Fugitive air emissions of benzene-based pollutants contributed approximately 50 percent to the cancer incidence. The population exposed to cancer risks greater than or equal to 1-in-1 million based upon actual emissions is 18,300 (see Table 2 of this preamble).

Table 2—Inhalation Risk Assessment Summary for Municipal Solid Waste Landfills Source Category

[40 CFR part 63, subpart AAAA]

Cancer MIR

(in 1 million)

Based on actual emissions

Based on allowable emissions

Based upon actual emissions

Cancer

incidence

(cases per

year)

Population with risk

of 1-in-1

million or

Population

with risk of

10-in-1

million or

Max chronic noncancer HI

(actuals and

allowables)

Source Category

10 (p-dichlorobenzene, ethyl benzene, benzene)

0.04

18,300

HI < 1

Whole facility emissions are equal to actual emissions and have the same risk.

2. Acute Risk Results

Our screening analysis for worst-case acute impacts based on actual emissions indicates that no pollutants exceed an acute HQ value of 1 based upon the REL. The acute hourly multiplier utilized a default factor of 10 for all emission processes.

3. Multipathway Risk Screening Results

The multipathway risk screening assessment resulted in a maximum Tier 2 noncancer screening value of less than 1 for mercury. Mercury was the only PB-HAP emitted by the source category. Based on these results, we are confident that the noncancer risks due to multipathway exposures have an HI less than 1.

4. Environmental Risk Screening Results

The ecological risk screening assessment indicated all modeled points were below the Tier 1 screening threshold based on actual emissions of mercury emitted by the source category.

5. Facility-Wide Risk Results

An assessment of whole-facility risks was performed as described above in Table 2 of this preamble. Whole-facility modeled emissions were the same as actuals for this source category. Refer to Section B1 of the Inhalation Risk Assessment Results for a discussion of the health risks.

6. What demographic groups might benefit from this regulation?

Results of the demographic analysis indicate that, for six of the 11 demographic groups; (African American, Other and Multiracial, Hispanic, below the poverty level, and those individuals over 25 without a highschool diploma) that are living within 5 km of facilities in the source category exceed the corresponding national percentage for the same demographic groups. When examining the risk levels of those exposed to emissions from MSW landfill facilities, we find 18,200 people are exposed to a cancer risk at or above 1-in-1 million and no individuals or groups exposed to a chronic noncancer TOSHI greater than 1.

There may be small differences between the Environment Justice (EJ) Tool's total population within 50 km and HEM-3's total domain population, because some of the 2010 Census blocks modeled by HEM-3 (which have a non-zero population) match to American Community Survey 2014 Census block groups that have a population of zero.

The methodology and the results of the demographic analysis are presented in a technical report,

Risk and Technology Review—Analysis of Demographic Factors for Populations Living Near MSW Landfills,

available in the docket for this action.

To examine the potential for any environmental justice issues that might be associated with the source category, we performed a demographic analysis, which is an assessment of risk to individual demographic groups of the populations living within 5 km and within 50 km of the facilities. In the analysis, we evaluated the distribution of HAP-related cancer and noncancer risk from the MSW Landfills source category across different demographic groups within the populations living near facilities.

Demographic groups included in the analysis are: White, African American, Native American, other races and multiracial, Hispanic or Latino, children 17 years of age and under, adults 18 to 64 years of age, adults 65 years of age and over, adults without a high school diploma, people living below the poverty level, people living two times the poverty level, and linguistically isolated people.

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

Table 3—MSW Landfills Demographic Risk Analysis Results

Municipal Solid Waste landfills Source Category: Demographic Assessment Results—50 km Study Area Radius

Population

with cancer

risk greater

than or equal

to 1-in-1

million

Population

with HI

greater

than 1

Nationwide

Source Category

Total Population

317,746,049

18,217

White and minority by percent

White

Minority

Minority by percent

African American

Native American

0.8

0.1

Hispanic or Latino (includes white and nonwhite)

Other and Multiracial

Income by percent

Below Poverty Level

Above Poverty Level

Education by percent

Over 25 and without a High School Diploma

Over 25 and with a High School Diploma

Linguistically isolated by percent

Linguistically Isolated

The percentages of the at-risk population in each demographic group (except for White, Native American, and Non-Hispanic) are lower than their respective nationwide percentages.

The methodology and the results of the demographic analysis are presented in a technical report,

Risk and

Technology Review—Analysis of Demographic Factors for Populations Living Near Municipal Solid Waste Landfills Source Category Operations,

available in the docket for this action.

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

1. Risk Acceptability

As noted in section III of this preamble, the EPA sets standards under CAA section 112(f)(2) using “a two-step standard-setting approach, with an analytical first step to determine an ‘acceptable risk’ that considers all health information, including risk estimation uncertainty, and includes a presumptive limit on MIR of approximately 1-in-10 thousand” (54 FR 38045, September 14, 1989). In this proposal, the EPA estimated risks based on actual and allowable emissions from MSW landfills, and we considered these in determining acceptability.

For the MSW Landfills source category, the risk analysis indicates that the cancer risk to the individual most exposed is below 10-in-1 million from both actual and allowable emissions. This risk is considerably less than 100-in-1 million, which is the presumptive upper limit of acceptable risk. The risk analysis also estimates a cancer incidence of 0.04 excess cancer cases per year, or 1 case every 20 years, as well as a maximum chronic noncancer TOSHI value below 1 (0.1). In addition, the risk assessment indicates no significant potential for multipathway health effects.

The results of the acute screening analysis also estimate a maximum acute noncancer HQ value of less than 1 based on the acute REL. By definition, the acute REL represents a health-protective level of exposure, with effects not anticipated below those levels, even for repeated exposures.

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

2. Ample Margin of Safety Analysis

As directed by CAA section 112(f)(2), we conducted an analysis to determine whether the current emissions standards provide an ample margin of safety to protect public health. Under the ample margin of safety analysis, we evaluated the cost and feasibility of available control technologies and other measures (including the controls, measures, and costs reviewed under the technology review) that could be applied to this source category to further reduce the risks (or potential risks) due to emissions of HAP identified in the risk assessment. In this analysis, we considered the results of the technology review, risk assessment, and other aspects of our MACT rule review to determine whether there are any cost-effective controls or other measures that would reduce emissions further.

The risks from this source category were deemed acceptable with a maximum upper-bound chronic excess cancer risk of 10-in-1 million from 1 facility and 168 facilities with an excess cancer risk greater than or equal to 1-in-1 million but less than 10-in-1 million. Our risk analysis indicated the risks from this source category are low for both cancer and noncancer health effects, and, therefore, any risk reductions to control fugitive landfill emissions would result in minimal health benefits. Fugitive landfill emissions result in 84 percent of the cancer incidence for this source category. Based upon results of the risk analysis and our evaluation of the technical feasibility and cost of the option(s) to reduce landfill fugitive emissions, we are proposing that the current MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) provides an ample margin of safety to protect the public health.

3. Adverse Environmental Effect

For the MSW Landfills source category, we did not identify emissions of any environmental HAP. Because we did not identify environmental HAP emissions, we expect no adverse environmental effects.

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

To fulfill the obligations under CAA section 112(d)(6), we conducted a technology review to identify developments in practices, processes, and control technologies that may warrant revisions to the current MSW Landfills NESHAP (40 CFR part 63, subpart AAAA). In conducting our technology review, we researched data reported to the U.S. EPA GHGRP (40 CFR part 98, subpart HH), the U.S. EPA LMOP Landfill and LFG Energy Database, state regulations, Federal regulations other than the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA), permits, the RACT/BACT/LAER Clearinghouse, enforcement consent decrees, and literature sources.

Our research identified three types of developments that could lead to additional control of HAP from MSW landfills. The three potential developments are practices to reduce HAP formation within a landfill, to collect more landfill gas for control or treatment, and to achieve a greater level of HAP destruction in the collected landfill gas. After analyzing these options, we determined that changes to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) are not warranted at this time, because each option is either not technically feasible or the cost is not justified for the level of emission reduction achievable.

1. Reduce HAP Formation

To reduce HAP formation in a landfill requires a program to divert or restrict certain types of wastes from disposal in an MSW landfill. Restricting certain wastes would reduce emissions because the quantity of HAP emitted is a function of the amount of waste disposed and the composition of the waste. For example, household wastes could contain numerous components that emit HAP,

e.g.,

paints, solvents, paint thinners, used motor oil, insecticides, pesticides, and household cleaning products. Diverting these materials from MSW landfills will reduce both the volume and HAP concentration of landfill gas emitted. Many states already have programs to prohibit landfill disposal of such products and other materials, such as electronic devices, tires, plastics, batteries, and yard waste.

We have determined that mandating programs for landfill operators to ban or recycle wastes is not technically feasible. Although some successful programs exist for waste diversion, recycling, and alternative disposal, these programs are not typically operated by landfill owners or operators, but often involve rules that affect generators, haulers, and third party processors. A landfill owner or operator could require waste separation by banning certain materials from entering the landfill. However, it would not be feasible for the landfill owner or operator to enforce such bans, because policing the content of every truck passing the gate of a landfill is economically unreasonable and technically impracticable.

2. Collect More Landfill Gas

More gas could be collected by requiring the GCCS to be installed earlier, requiring the GCCS to be expanded more frequently than currently required by the NESHAP, or requiring the GCCS to remain in place longer than currently required. The current MSW Landfills NESHAP (40

CFR part 63, subpart AAAA) requires that landfills with a design capacity of 2.5 million Mg and 2.5 million m

and an NMOC emission rate exceeding 50 Mg/yr must install controls. The GCCS must be installed within 30 months of the initial NMOC report that exceeds the 50 Mg/yr emission threshold and then expanded every 5 years in active fill areas, or every 2 years in closed areas.

Earlier gas collection is technically feasible. Earlier gas collection could be accomplished by lowering the NMOC emission rate below 50 Mg/yr either alone or in conjunction with the design capacity to below 2.5 million Mg and 2.5 million m

. Earlier gas collection could also be accomplished by shortenting the initial 30-month lag time for installing a GCCS or reducing the amount of time required before the GCCS is expanded. Although earlier gas collection, or more frequent expansion of a GCCS expansion, could require some technical design changes (

e.g.,

horizontal gas collection system), this equipment is commercially available and in use at many landfills today. Horizontal collection trenches can be installed during the filling of the landfill so that gas collection can commence earlier than with the more typically used vertical gas wells, although sufficient waste must be placed on top of the trenches before vacuum can be applied to the trench, in order to minimize air intrustion. Passive flares have been demonstrated to operate more effectively than active flares when the quantity of gas generation is low or the quality of the gas decreases to lower methane content, or if the landfill gas is contained by impermeable liners on the bottom, sides, and top of the landfill. Our evaluation of available data from the GHGRP and LMOP indicate that 1,199 landfills have installed a GCCS in 2014, compared to between 625 and 700 landfills that are estimated to have installed controls, based on modeling under the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA). These data demonstrate that earlier gas collection is technically feasible. Additionally, the 2016 MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf) both employ an NMOC emission rate of 34 Mg/yr, but it is not known how many landfills are controlling pursuant to these new 2016 regulations. Moreover, states, including California, Minnesota, Wisconsin, and Pennsylvania, use different regulatory metrics to require gas collection earlier than required by the NESHAP.

Another means of increasing the collection efficiency of GCCSs is to install cover material earlier. Studies have shown increased collection efficiencies, depending on the type of cover. However, the effectiveness of early final cover installation depends on site-specific circumstances such as the filling sequence and cell design of the landfill. We identified no state regulations, permit conditions, or other research that prescribed conditions under which regulating the timing of final cover installation is a technically and economically feasible strategy for improving gas collection.

We also considered whether a biocover provides more HAP control than a traditional clay cover. A biocover is a layer of media containing methanotrophic bacteria that digest and oxidize organic matter. Although these bacteria can be found in soil, other materials can be used as cover material or added to clay covers to enhance the environmental conditions for bacteria growth, which increases the oxidation. Most biocover research and most installations have been directed at methane emission reductions. However, a few studies have indicated that biocovers can microbially degrade volatile organic compounds as well, including some of the HAP contained in landfill gas. Although a number of landfills have reported using a biocover on at least a portion of the surface, the long-term HAP reduction performance of oxidative covers has not yet been adequately demonstrated in a full-scale industrial setting at a landfill.

Biocovers and earlier installation of final covers were not deemed technically feasible, and, therefore, the cost and reductions for these control practices were not further analyzed. Because earlier GCCS installation was technically feasible, we evaluated the cost for three options for enhanced gas collection, which are as follows:

• Reduce the NMOC emission threshold for initial installation of GCCS from 50 Mg/yr to 34 Mg/yr for all landfills that are open in 2015. For landfills that closed in 2014 or earlier, these remained at the baseline level of 50 Mg/yr NMOC.

• Retain the baseline NMOC emission threshold (50 Mg/yr NMOC) but reduce the expansion lag (EL) time from an average of 4 to 3 years for landfills that closed after 2014. The “expansion lag time” is the amount of time allotted for the landfill to expand the GCCS into new areas of the landfill. The rule currently allows 5 years for active areas and 2 years for areas that are closed or at final grade, but the EPA understands most landfills are choosing the 5-year option and, therefore, the average lag time of 4 years was modeled. A modeled EL of 3 years could represent a reduction from 5 years to 3 years in active areas.

• Retain the baseline NMOC emission threshold (50 Mg/yr NMOC) but reduce the EL time from an average of 4 to 2 years for landfills that closed after 2014. A modeled EL of 2 years could represent a requirement for all landfills to expand their system within two years.

For each scenario, we estimated the incremental net annualized costs of each regulatory option in 2023 relative to a baseline of the current NESHAP requirements. The costs incorporate the annualized capital costs to install the GCCS, operation and maintenance costs for the GCCS, and costs for monthly wellhead monitoring and continuous combustor monitoring. The costs have been offset by the revenue anticipated from electricity sales for any landfills that would likely operate cost-effective energy recover projects. Table 4 of this preamble shows the incremental cost effectiveness of 14 different HAP compounds if requiring earlier gas collection as well as the incremental HAP cost effectivness of total HAP, inclusive of 47 different HAP. Of these 14 HAP, toluene, ethyl benzene, dichloromethane, hexane, and xylenes are five of the most prevalent (HAP) in LFG, while the remaining nine HAP, although less prevalent, are driving our estimates of health risks. The LFG emissions vary each year because the emissions profile follows a first-order decay equation pattern over time, as a landfill accepts additional waste. Additionally, the number of landfills controlling in any given year and the site-specific collection efficiency of the controlling landfills varies given the GCCS installation and expansion lag times. The EPA selected the year 2023 to quantify the impacts because it is 3 years after the final MSW Landfill NESHAP amendments are expected to be finalized, which is the maximum time allowable under the General Provisions of part 63.

Table 4—Cost Effectiveness of Earlier Gas Collection

Compound

Cost effectiveness ($100,000 per Mg HAP), year 2023

Reduce from

50 Mg/yr to

34 Mg/yr

Reduce EL

from 4 to

2 years

Reduce EL

from 4 to

3 years

Toluene

6.75

5.38

6.36

Hexane

11.48

9.15

10.82

Xylenes (Mixture of o, m, and p Isomers)

14.28

11.38

13.46

Ethyl Benzene

37.10

29.55

34.96

Methylene Chloride

37.84

30.14

35.66

1,4-Dichlorobenzene

119

94.56

112

Benzene

122

97.36

115

Trichloroethylene

160

128

151

Vinyl Chloride

215

171

202

Ethylene Dichloride

785

625

739

1,1,2-Trichloroethane

1,022

814

963

Naphthalene

1,183

943

1,115

1,3-Butadiene

1,695

1,350

1,597

Ethylene Dibromide

10,534

8,392

9,927

Total HAP

2.07

1.64

1.94

Total HAP includes 47 of the 48 HAP based on the

Updated MSW Landfill Emission Factors for RTR Risk Modeling

in 2018. No reductions were estimated for mercury as a result of earlier gas collection. Factors are available at:

https://www.epa.gov/stationary-sources-air-pollution/updated-msw-landfill-emission-factors-rtr-risk-modeling.

Considering the high costs per ton of HAP reduced, we did not consider these control options to be cost effective for further reducing HAP emissions from MSW landfills. With respect to the non-air environmental impacts, the options for earlier gas collection may result in additional LFG becoming available for LFG energy production. Considering these costs, we concluded that requiring additional collection of landfill gas is not warranted pursuant to CAA section 112(d)(6).

3. Increased HAP Destruction

The NESHAP currently provides three options for controlling HAP from the collected landfill gas:

• An open flare that meets specified design and operating requirements;

• A control device that reduces NMOC by 98 weight-percent or 20 ppmv NMOC as hexane adjusted to 3-percent oxygen; or

• A treatment system that processes the collected gas for subsequent sale or use.

Another means of reducing HAP is to require increased destruction of HAP in the collected gas. Our technology review identified three potential methods: enclosed flares, thermal oxidation, and increased use of certain energy recovery technologies for beneficial use of landfill gas.

Enclosed flares.

An open flare meeting the NESHAP design and operating requirements can achieve approximately 98-percent organic HAP reduction from landfill gas. Note that in this proposed action, flares must be designed and operated in accordance with 40 CFR 63.11, which is equivalent to 40 CFR 60.18 as referenced by the MSW Landfills NSPS (40 CFR part 60, subparts WWW and XXX). About 17 percent of landfills report using an enclosed flare. The achievable destruction efficiency varies between 99.5 and 99.9 percent depending on local regulations for emissions of other pollutants (oxides of nitrogen and carbon monoxide (CO)) and how the flare is operated.

The HAP-specific destruction efficiencies were not reported.

LFG Technologies Brochure. http://lfgtech.com/wp-content/uploads/docs/low-emissions-brochure.pdf.

John Zink.

https://www.johnzinkhamworthy.com/products-applications/landfill-biogas/.

While the technical feasibility of an enclosed flare for landfills is widely demonstrated, an enclosed flare is more expensive and, for landfill gas, is more complex to operate. As a result, the capital and operating cost of an enclosed flare is estimated at about 1.5 to 2 times greater. Open flares provide greater operational flexibility for handling large variations in flow rate and British thermal units (Btu) content, managing certain trace gas constituents, and serving as a backup for landfills with energy recovery projects. We estimate that to require landfills to replace all open flares with enclosed flares would reduce emissions by between 630 to 800 Mg/yr NMOC in 2023. There is a significant range in these estimates depending on the destruction efficiency. Also, because many landfills already employ at least one enclosed flare or energy recovery project, it is unknown how many conversions would actually occur. Table 5 shows the cost for converting to enclosed flares. The costs are estimated for the same 14 HAP, which represent the five most prevalent HAP and the nine HAP driving health risk and takes into consideration the variations in flare peformance and flare cost. The table also shows incremental HAP cost effectivness of total HAP, inclusive of 47 different HAP. With respect to the non-air environmental impacts, the options for requiring conversion to enclosed flares could negatively impact the number of LFG energy projects, because open flares tend to serve as back-up destruction devices at landfills with energy projects in place. Additionally, enclosed flares may require supplemental pilot fuels to operate. We conclude that the requirement to use enclosed flares is not cost effective.

Table 5—Cost Effectiveness of Enclosed Flares

Compound

Cost effectiveness

($100,000 per

Mg HAP),

year 2023

Conversion of open

flares to

enclosed flares

Toluene

$5-14

Hexane

9-23

Xylenes (Mixture of o, m, and p Isomers)

11-29

Ethyl Benzene

30-75

Methylene Chloride

30-77

1,4-Dichlorobenzene

95-240

Benzene

98-250

Trichloroethylene

130-330

Vinyl Chloride

170-440

Ethylene Dichloride

630-1,590

1,1,2-Trichloroethane

820-2,070

Naphthalene

950-2,400

1,3-Butadiene

1,360-3,440

Ethylene Dibromide

8,430-21,400

Total HAP

1.65-4.17

The minimum cost effectiveness range represents a cost factor increase of 1.5 compared to an open flare and an assumed HAP destruction efficiency of 99.9 percent. The maximum of the cost effectiveness range represents a cost factor increase of 2 compared to an open flare and an assumed HAP destruction efficiency of 99.5 percent.

Total HAP includes 47 of the 48 HAP based on the

Updated MSW Landfill Emission Factors for RTR Risk Modeling

in 2018. No reductions were estimated for mercury as a result of earlier gas collection. Factors are available at:

https://www.epa.gov/stationary-sources-air-pollution/updated-msw-landfill-emission-factors-rtr-risk-modeling.

Thermal oxidizers.

The technical feasibility of installing thermal oxidizers appears to be limited to landfills that employ an energy project with gas purification equipment or other gas treatment equipment that involves a tail gas. Flares are better equipped than thermal oxidizers to manage the large fluctuations in flow rates that can occur at landfills where the primary control device is not associated with an energy recovery project. Our technical review concludes that thermal oxidizers have not been commercially demonstrated to be technologically feasible as an alternative for the destruction of landfill gas at all landfills.

Energy recovery devices.

Some types of energy recovery projects can achieve destructions higher than the 98-percent reduction or 20 ppmv NMOC as required by the NESHAP. About 47 percent of landfills that have GCCS installed use some form of energy recovery system. Energy recovery systems that are capable of additional HAP control are gas turbines (including microturbines) to combust landfill gas to produce electricity and gas purification systems to produce renewable natural gas for pipeline injection or direct sale.

The technical feasibility of the landfill gas cleaning that is required to implement any energy recovery project must be assessed by in-depth engineering analysis of the site-specific conditions at each individual landfill. The economic feasibility depends on the available flow rate for the extracted landfill gas over the expected lifetime of the project; landfill gas quality; and physical and market access to either the electrical grid, a natural gas pipeline, end-users with a consistent energy demand, or an alternative fueling station (

i.e.,

compressed natural gas or liquid natural gas) with an adequate market to consume the landfill gas-derived vehicle fuel. Research has not identified specific objective criteria for stipulating when a specific energy recovery system is economically feasible for landfill gas. Accordingly, we conclude that requiring specific energy recovery devices for landfill gas is not technologically feasible or cost effective given that it is highly dependent on engineering analyses of site-specific conditions.

We request comment on the technologies and practices considered for this technology review as well as the basis for estimating the cost effectivness of those technologies at MSW landfills.

D. What other actions are we proposing?

In addition to the proposed decisions resulting from the RTR described above, we are proposing revisions to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) that promote consistency between MSW landfills regulations under CAA sections 111 and 112. We are also proposing changes to the wellhead temperature operating standards, and associated monitoring, corrective action, and reporting and recordkeeping requirements for temperature. We are proposing to adjust provisions for GCCS removal to provide additional flexibility for landfill owners and operators. In addition, we are proposing updates to SSM requirements and electronic reporting requirements.

1. Overall Rule Reorganization

We are proposing to streamline the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) by incorporating the landfill gas control, operational standards, monitoring, recordkeeping, and reporting rule requirements (

i.e.,

the major compliance provisions) from the NSPS program directly into the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA), thus, minimizting cross referencing to another subpart. While the original MSW Landfills NESHAP references the 1996 MSW Landfills NSPS (40 CFR part 60, subpart WWW), updated requirements from the 2016 MSW Landfills NSPS (40 CFR part 60, subpart XXX) are incorporated where appropriate. These include sections for GCCS installation and removal (40 CFR 63.1957), GCCS operational standards (40 CFR 63.1958), NMOC calculation procedures (40 CFR 63.1959), compliance provisions (40 CFR 63.1960), monitoring (40 CFR 63.1961), specifications for active collection systems (40 CFR 63.1962), reporting (40

CFR 63.1981), and recordkeeping (40 CFR 63.1983). These changes modernized and streamlined the original NSPS. An MSW landfill would have up to 18 months after publication of the final rule to comply with these reorganized provisions. Before this time, landfills would comply with the provisions in the MSW Landfills NSPS (40 CFR part 60, subpart WWW), which continue to be cross referenced in the short term. Incorporating these provisions consolidates requirements between the MSW Landfills NSPS (40 CFR part 60, subparts WWW and XXX) and the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) and is expected to reduce confusion because many landfills are subject to an NSPS and the NESHAP.

To help distinguish the applicability of the two MSW Landfills NSPS, the EPA proposes to revise the title of 40 CFR part 60, subpart WWW, to identify the subpart's applicability dates. Specifically, the revised title for 40 CFR part 60, subpart WWW would read, “Standards of Performance for Municipal Solid Waste Landfills that Commenced Construction, Reconstruction, or Modification on or after May 30, 1991, but before July 18, 2014.” The EPA is making a similar change to 40 CFR part 60, subpart WWW at 40 CFR 60.750(a) to say that the provisions of 40 CFR part 60, subpart WWW apply to each MSW landfill that commenced construction, reconstruction, or modification on or after May 30, 1991, but before July 18, 2014.

To enhance consistency between the regulations and streamline compliance, we are also proposing minor edits to the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and the EG (40 CFR part 60, subpaft Cf) that would allow MSW landfills affected by the MSW Landfills NSPS and EG to demonstrate compliance with the “major compliance provisions” of the MSW Landfills NESHAP (GCCS operational standards at 40 CFR 63.1958, compliance provisions at 40 CFR 63.1960, and monitoring at 40 CFR 63.1961) in lieu of NSPS and EG.

With the incorporation of the major compliance provisions from the MSW Landfills NSPS (40 CFR part 60, subpart XXX), we are, thus, incorporating corresponding revisions from the MSW Landfills NSPS (40 CFR part 60, subpart XXX) that were finalized in 2016, including removing the requirement to monitor and take corrective action for oxygen and nitrogen monitoring at the wellhead, refining the procedures for taking corrective action (40 CFR 63.1960), and adding flexibility for when to cap, remove, or decommission the GCCS (40 CFR 63.1957(b)). Revisions for consistency with the MSW Landfills NSPS (40 CFR part 60, subpart XXX) also include other conforming changes that were finalized in 2016, such as allowing the use of portable gas composition analyzers to monitor the oxygen level at a wellhead (40 CFR 63.1961(a)), the requirement to report more precise locational data for each surface emissions exceedance (40 CFR 63.1961(f)), changes to the procedure for submitting a design plan (40 CFR 63.1981(d)), and changes to definitions (40 CFR 63.1990). These are described below and in the preamble to the final MSW Landfills NSPS (81 FR 59332, August 29, 2016).

To further enhance consistency between the MSW landfills regulations, we are adopting in the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) the same requirements for SSM that the MSW Landfills NSPS (40 CFR part 60, subpart XXX) adopted (40 CFR 63.1930(b)). Consistent with other CAA regulations, we are proposing additional revisions to the SSM provisions of the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) in order to ensure that they are consistent with the decision in

Sierra Club

EPA,

551 F. 3d 1019 (D.C. Cir. 2008), in which the Court vacated provisions that exempted sources from the requirement to comply with applicable CAA section 112 emission standards during periods of SSM. We are also adding electronic reporting (40 CFR 63.1981(l)).

We request comment on this re-organization of the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) structure to create a more uniform set of standards for all affected landfills. The EPA specifically requests comments from landfill owners and operators, as well as state regulatory agencies, on whether reorganization of the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) and amendments to NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf) clarifies compliance for sources affected by both the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) and the NSPS (40 CFR part 60, subpart XXX) or EG (40 CFR part 60, subpart Cf).

2. Operational Standards for Gas Collection Systems

To ensure proper operation of the gas collection system, the current MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) requires wellhead monitoring of the collected landfill gas and establishes standards at the wellhead for negative pressure, temperature, and concentration of either nitrogen or oxygen, as described in the MSW Landfills NSPS (40 CFR part 60, subpart WWW). If an operational limit is exceeded, then corrective action is required to return the measured parameter to the required level. Consistent with the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf), we are proposing to eliminate the operational standard and the corresponding corrective action for nitrogen and oxygen concentration, because we concluded that nitrogen and oxygen concentration by itself is not an effective indicator of proper landfill gas system operation. This conclusion is explained in the preamble to the 2016 NSPS (81 FR 59332, August 29, 2016). In addition, we propose to further amend the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) by increasing the operational standard for temperature at wellheads from 131 degrees Fahrenheit (°F) to 145 °F (40 CFR 63.1958(c)). The MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) maintains the existing operational standards for negative pressure (40 CFR 63.1958(b)). The proposed changes to eliminate the nitrogen and oxygen operating standard and increase the wellhead temperature operating standard would reduce the burden on regulated entities and delegated state, local, and tribal agencies addressing inquiries related to operating standards in several ways. First, this proposed change removes the requirement to take corrective action for nitrogen and oxygen limits. Second, this change would reduce the number of requests and burden associated with submitting and reviewing the requests for higher operating values for oxygen and nitrogen. Third, the proposed increase in temperature operating limit is expected to reduce the number of requests for higher operating values. Similarly, the higher temperature standard is expected to reduce the frequency of corrective action for exceeding the temperature limit. In addition to reducing the burden associated with these wellhead operating standards, these changes are expected to promote greater flexibility and autonomy to landfill owners and operators with regards to wellhead operations. For example, landfill owners or operators may employ cover practices or GCCS best management practices that are suitable for their sites and GCCS designs, thereby allowing them to collect more LFG and reduce emissions without the risk of exceeding a wellhead operating parameter.

The purpose of the wellhead monitoring is to prevent fires and avoid conditions that inhibit anaerobic decomposition of the waste. In revising the NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf), the EPA received substantial comments that operation at a specific fixed level of nitrogen and oxygen concentration does not achieve the intended objectives and can become a barrier that prevents proactive landfill gas collection practices, such as connecting the gas collection system to the leachate collection system or installing early gas collectors (81 FR 59346 and 81 FR 59292, August 29, 2016). Although landfill owners or operators are not required to maintain specific nitrogen and oxygen operating limits, we propose to retain the requirement to monitor nitrogen and oxygen and maintain records at the wellhead because this parameter is an important factor for the landfill operator to evaluate along with other factors to determine how well the landfill is being operated to effectively capture landfill gas, promote efficient anaerobic decomposition, and prevent fires (40 CFR 63.1961(a)). The landfill owner or operator must make these records available to the Administrator (EPA Administrator or administrator of a state air pollution control agency or his or her designee) upon request (40 CFR 63.1983(i)).

Regarding temperature, the EPA did not increase the operating standard in the 2016 MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (81 FR 59276, August 29, 2016). Although several commenters supported removing the temperature parameters, other commenters were concerned with fire risks if the parameter was removed. At the time, the EPA consulted with EPA Regions about approaches taken in consent decrees and other enforcement actions involving elevated temperature values. Since the 2016 revisions to the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf), the EPA has reviewed several consent decrees in additional detail.

26 27 28

These consent decrees have temperature operating limits ranging between 131 °F to 185 °F. With higher temperatures come several addditional monitoring requirements. In addition, higher operating value guidance from Ohio EPA indicated that Ohio EPA generally will concur with requests for operating limits up to 150 °F, as long as additional data are made available.

The EPA has also reviewed data on requests for higher temperature operating values in EPA Region 5. Based on these data, 64 percent of all higher operating value (HOV) requests were at 145 °F or less and 95 percent of requests were below 150 °F.

Additionally, a Solid Waste Assosciation of North America (SWANA) manual of practice for LFG GCCS indicates that polyvinyl chloride piping begins to fail at 145 °F and fails at 165 °F, temperatures above 140 °F could indicate aerobic conditions, and landfill gas temperature over 135 °F indicates a possible subsurface oxidation event (SOE). Optimal range for mesophilic bacteria is 77-104 °F, and for thermophilic bacteria is 131-149 °F (see page 9-8).

United States

Forward, Inc.,

Consent Decree, Case No. 2:11-cv-00590 EFB (E.D.Cal. May 2, 2012).

United States of America

County of Maui,

Consent Decree, Case No. 1:12-cv-00571-LEK-RLP (D.Haw. December 27, 2012).

Waimanalo:

United States of America

Waste Management of Hawaii, Inc., and City and County of Honolulu,

Consent Decree, Case No. 1:13 cv-00095 (D.Haw. April 18, 2013).

Ohio EPA.

Guidance Document for Higher Operating Value Demonstrations. http://web.epa.state.oh.us/eBusinessCenter/Agency/DAPC/HOV%20Demonstration.doc.

See docketed memorandum,

Analysis of HOV Requests for Wellhead Temperature.

SWANA/National Renewable Energy Laboratory (NREL).

Landfill Gas Operation and Maintenance Manual of Practice.

1997. NREL/SR-430-23070.

Based on the review of these additional data, the EPA is proposing to increase the temperature operating standard 14 °F, from 131 °F to 145 °F (40 CFR 63.1958(c)). We propose to require the landfill owner or operator to report any temperature readings that exceed 145 °F in semi-annual reports and maintain records of all temperature monitoring at the wellhead because this parameter is an important factor for the landfill operator to evaluate along with other factors to determine how well the landfill is being operated to effectively capture landfill gas, promote efficient anaerobic decomposition, and prevent fires. The landfill owner or operator must make these records available to the Administrator (EPA Administrator or administrator of a state air pollution control agency or his or her designee) upon request (40 CFR 63.1983(i)).

We request comment on the removal of oxygen and nitrogen wellhead operating standards and increased temperature operating standard.

3. Enhanced Monitoring and Reporting for Elevated Wellhead Temperature

Given previous concerns with fire risks from elevated temperatures, and the fact that parameters other than temperature can be indicators of SOE, and based on review of the aforementioned consent decrees and guidance materials, the EPA is also proposing enhanced wellhead monitoring and visual inspections for SOE (40 CFR 63.1961(a)), and in some cases more frequent reporting, for any landfill with wellhead temperature exceeding 145 °F. These requirements would apply to all wells with an exceedance, unless a higher operating value has been approved, in which case the stipulations of the approved HOV applies (40 CFR 63.1961(a)). The EPA is proposing to require weekly observations for SOE, as well as weekly monitoring of CO, oxygen, and methane. Temperature readings will also be required weekly at the wellhead and at downwell increments for every 10 vertical feet in the well (40 CFR 63.1961(a)).

The EPA is proposing to require an independent laboratory analysis of each CO measurement, using EPA Method 10 (40 CFR 63.1961(a)(5)(vi)(A)). The EPA is proposing to monitor methane with a methane meter using EPA Method 3C or EPA Method 18 or a portable gas composition analyzer provided that the analyzer is calibrated and the analyzer meets all quality assurance and quality control requirements for EPA Method 3C or EPA Method 18 (40 CFR 63.1961(a)(5)). The EPA is proposing downwell temperature measurements with either a removable thermotet or temporary or permanat thermocouples installed in the well. All of these data will be required to be submitted in the semi-annual report and maintained as records (40 CFR 63.1981(h)). Each report will also include a trend analysis of the weekly monitoring results over time, for each well. Enhanced monitoring will begin for 7 days and continue until the measured wellhead operating temperature is 145 °F or less, or the higher operating value is approved, whichever comes first.

For landfills that have any temperature reading of 170 °F or above at either the wellhead or on any of the downwell measurements, and a CO reading of 1,500 ppmv or above, a 24-hour electronic report will be required to notify the delegated agency about the well.

We request comment on the enhanced monitoring and reporting requirements for elevated temperatures.

4. Corrective Action

Under the current MSW Landfills NESHAP (40 CFR part 63, subpart AAAA), if a landfill exceeds a wellhead operating parameter, the landfill owner or operator must initiate corrective action within 5 days of the measurement as described in the MSW Landfills NSPS (40 CFR part 60, subpart

WWW). If the exceedance cannot be corrected within 15 days, the landfill owner or operator must prepare to expand the GCCS within 120 days or obtain approval by the EPA or the delegated state agency for an alternative operating limit. Commenters on the revised NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf) that were proposed in 2015 stated that exceedances of elevated nitrogen and oxygen concentration are often not solved by expanding the gas collection system, especially in older areas of the landfill. Commenters also stated that wellhead corrective action often requires site-specific and highly technical solutions other than expanding a collection system. The commenters also stated that despite the 1998 amendments to the MSW Landfills NSPS (63 FR 32748, June 16, 1998), which clarified procedures for landfill owners or operators to submit an alternative timeline for correcting exceedances, there is inconsistency in how delegated state and local agencies are inconsistently interpreting when a landfill must expand the GCCS (see additional discussion at 81 FR 59332, August 29, 2016) or when landfills must submit requests for alternative timelines to correct exceedances. Commenters also expressed concern that many requests for alternative timelines are not approved in a timely manner. Since the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) references the regulatory language for corrective action in the MSW Landfills NSPS (40 CFR part 60, subpart WWW), these same concerns with implementation of corrective action affect landfills subject to the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA).

For those reasons, we are proposing to eliminate the requirements for corrective action for nitrogen and oxygen as we have eliminated the operating standard for nitrogen and oxygen, as previously discussed. We are also proposing changes to the corrective action procedures to address positive pressure and elevated temperature to provide flexibility to owners or operators in determining the appropriate remedy, as well as the timeline for implementing the remedy (40 CFR 63.19620(a)). The proposed changes to the timeline and the process for correcting for positive pressure would make the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) requirements the same as the current requirements of the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf). Because the MSW Landfills NESHAP (40 CFR part 63, subpart AAAA) is also proposing changes to the temperature wellhead operating standard, the requirements for corrective action procedures being proposed are tied to the exceedance of the 145 °F (instead of 131 °F) standard, otherwise the proposed changes are consistent with the current requirements of the MSW Landfills NSPS (40 CFR part 60, subpart XXX) and EG (40 CFR part 60, subpart Cf). Under these proposed provisions, corrective action must be initiated within 5 days of the measured exceedance (40 CFR 63.1960(a)). If the exceedance cannot be corrected within 15 days, then the owner or operator must conduct a root cause analysis and correct the exceedance as soon as practicable, but within no later than 60 days of the measured exceedance. If corrective actions cannot be implemented within 60 days, then the owner or operator must prepare a corrective action analysis and an implementation schedule to complete the corrective actions within 120 days. The root cause analysis and the corrective action analysis for restoring flow does not have to be submitted or approved but must be kept on site as a record. If the exceedance cannot be corrected within 120 days, then within 75 days of the exceedance the owner or operator must submit the root cause analysis, corrective action analysis, and the corresponding implementation timeline to the Administrator for approval.

For the corrective action required to address positive pressure or elevated temperature, the owner or operator must keep a record of the root cause analysis conducted, including a description of the recommended corrective actions; the date for corrective actions already completed following the positive pressure reading or wellhead temperature measurement above 145 °F; and for actions not already completed within 60 days of the initial positive pressure reading or wellhead temperature measurement above 145 °F, a schedule for implementation, including proposed commencement and completion dates. For corrective actions taking longer than 60 days to correct the exceedance, the owner or operator would also include in the annual report the root cause analysis, recommended corrective actions, date corrective actions were completed, and schedule for implementing corrective actions. The owner or operator must also notify the Administrator within 75 days. For corrective actions that take longer than 120 days to correct the exceedance, the owner or operator would include, in a separate notification submitted to the Administrator for approval as soon as practicable, but no later than 75 days after the initial positive pressure reading or wellhead temperature measurement above 145 °F, the root cause analysis, recommended corrective actions, date corrective actions taken to date were completed, and proposed schedule for implementing corrective actions (40 CFR 63.1960(a)).

For any wells that have any temperature reading of 170 °F or above at either the wellhead or on any of the downwell measurements, and a CO reading of 1,500 ppmv or above, a shortened period of corrective action, not to exceed 15 days, is being proposed (40 CFR 63.1960(a)). High temperatures in combination with high levels of CO are considered a positive indication of an active underground landfill fire. As such, timely corrective action of such operating conditions is required to minimize fire risk.

We request comment on the revisions to the corrective action process.

5. Criteria for Removing GCCS

Consistent with the MSW Landfills NSPS and EG (81 FR 59357), the EPA is proposing to ad

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