United States Office of Air Quality EPA 453/R-02-001

Environmental Planning and Standards February 2002

Protection Agency Research Triangle Park, 27711

 

Air 

Guidelines for MACT

Determinations under

Section 112(j) Requirements
[This page intentionally left blank]
ABSTRACT

Section 112(j) of the Clean Air Act as amended in 1990

requires owners or operators of major sources to apply for a

Title V permit should the Environmental Protection Agency fail to

promulgate emission standards for an applicable source category

within 18 months after the date specified in the regulatory

schedule established through Section 112(e) of the Act. The

Title V permit that is issued must require the owner or operator

to meet a maximum achievable control technology (MACT) emission

limitation for all hazardous air pollutant (HAP) emissions within

the source category. Regulations to implement Section 112(j) are

codified in 40 CFR Part 63, Subpart B. This document provides

guidance for complying with these regulations by identifying and

evaluating control technology options to determine the MACT

emission limitation. In this document, the term "control

technology" is defined broadly to be consistent with section

112(d)(2) of the Clean Air Act to include measures, processes,

methods, systems or techniques which reduce the volume of, or

eliminate emissions of, HAP through process changes, substitution

of materials or other modifications; enclose systems or processes

to eliminate emissions; collect, capture or treat HAP when

released from a process, stack, storage or fugitive emissions
point; are design, equipment, work practice, or operational

standards; or a combination of the above.
i

Table of Contents

Introduction ....................... iv

Chapter 1.0 An Overview of the MACT Determination Process for

Section 112(j) ................ 1-1

1.1 Overview of Statutory Requirements ... 1-1

1.2 Overview of the Section 112(j) Regulatory

Requirements .............. 1-4

1.3 Affected Source and New Affected Source

Review ................ 1-11

Chapter 2.0 The MACT Determination ............ 2-1

2.1 Criteria for the MACT Determination ... 2-1

2.2 Compliance Provisions .......... 2-3

2.3 Approaches to the MACT Determination . . 2-5

2.4 Available Information .......... 2-8

2.5 General Permits ............. 2-9

Chapter 3.0 The MACT Analysis .............. 3-1

3.1 Overview of the MACT Analysis Process . . 3-2

3.2 A Detailed Look at the MACT Analysis . . 3-7

3.3 Determining the MACT Emission Unit and

"Affected Source" ........... 3-12

3.4 Similar Emission Units ........ 3-18

3.5 Subcategorization ........... 3-20

Chapter 4.0 The MACT Floor Finding ............ 4-1

4.1 Calculation of the MACT Floor ...... 4-2

4.2 Method 1- Computing the MACT Floor Using

Existing State and Local Regulations . . 4-7

4.3 Method 2 - Computing the MACT Floor Using

Control Efficiency Ratings ....... 4-8

4.4 Method 3 - Computing the MACT Floor Using

Emission Reduction Ratios ........ 4-9

4.5 Technology Approach . . . . . . . . . . . 4-12

4.6 Other Methods to Compute the MACT Floor .4-13

Chapter 5.0 The MACT Emission Limitation and Permit Conditions

....................... 5-1

5.1 MACT Emission Limitation ........ 5-1

5.2 Alternative Ways to Comply ....... 5-5

5.3 Applicable Monitoring, Reporting,

Recordkeeping, and Compliance ...... 5-6
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Chapter 6.0 Costs, Non-Air Quality Health and Environmental

Impacts and Energy Impacts .......... 6-1

6.1 Cost Impacts .............. 6-3

6.2 Environmental Impacts .......... 6-6

6.3 Energy Impacts ............. 6-8

Chapter 7.0 Sources of Information ............ 7-1

Appendix A Examples of MACT Analyses .......... A-1

Appendix B Federal Register Notice on Determining an Average

Emission Limitation for Existing Sources, June 6,

1994 (59 FR 29196) .............. B-1

Appendix C Example Notice of MACT Approval ....... C-1

Appendix D Federal Register Notice on Final Amendments to

Regulations Governing Equivalent Emission

Limitations by Permit ............ D-1
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LIST OF FIGURES

Figure 1 Sources in Existence and Subject to 112(j) at Deadline

for Source Category ............... 1-9

Figure 2 Source Becomes Subject to 112(j) After the 112(j)

Deadline but Before Issuance of Permit ..... 1-10

Figure 3 The MACT Analysis ................. 3-4
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Introduction

The purpose of this manual is to provide State and local

agencies with guidance for establishing the case-by-case maximum

achievable control technology (MACT) determinations required by

Section 112(j) of the Clean Air Act in the event that EPA should

miss the deadline for promulgating a Section 112(d) standard by

more than 18 months. As with any guidance, this document does

not impose legally binding requirements for either the permitting

authority or an owner or operator. For a complete understanding

of the regulatory requirements, readers should refer to the

General Provisions for National Emission Standards for Hazardous

Air Pollutants for Source Categories (40 CFR Part 63, Subpart A)

and sections 63.50 through 63.56 implementing the Section 112(j)

requirements (40 CFR Part 63, Subpart B).

This manual is divided into seven chapters and four

appendices. Chapter 1 of this manual provides an overview of the

statutory and regulatory requirements and discusses the

procedures for applying for a Notice of MACT Approval. Chapter 2

outlines the criteria a permitting authority should use when

evaluating applications as well as possible approaches permitting

authorities may use for determining the appropriate level of

control for each source. Chapter 3 describes a process for

selecting control technology that meets the criteria discussed in
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Chapter 2. Chapter 4 provides a detailed discussion on

determining the minimum level of control that can be MACT for the

source (the MACT floor). Chapter 5 briefly discusses some

calculation procedures for the equivalent (MACT) emission

limitation. Chapter 6 describes the analysis that may be

required to assess the costs of achieving the emission reduction,

and any non-air quality health and environmental impacts and

energy requirements associated with use of different control

options. Chapter 7 discusses sources that may assist in the

collection of available information.

Appendix A illustrates examples for defining a MACT-affected

emission unit, and selecting a control technology to meet MACT. 

Appendix B contains the June 6, 1994 Federal Register clarifying

EPA's use of the word "average" to determine how an average

emission limitation should be computed for existing sources. 

Appendix C provides a suggested format for the Notice of MACT

Approval, which the permitting authority may issue consistent

with the requirements in 40 CFR 63.54 of Subpart B. Finally,

Appendix D contains the Federal Register notice on the final

amendments to Regulations Governing Equivalent Emission

Limitations by Permit. 

While the examples and methodologies in this guidance

attempt to illustrate ways the EPA may determine the emission

limitation for the purposes of a national Section 112(d) emission
vi

standard, they may not represent the only methodology or they may

not be the best methodology for establishing a MACT emission

limitation. The methods used to establish an emission standard

or case-by-case MACT emission limitation will be highly dependent

upon the amount and type of information available, the complexity

of the source, and the number of feasible control options. In

some instances, a permitting authority's control technology

determination procedures may yield the appropriate level of

control without specifically following this guidance or making a

MACT floor finding. The EPA is less concerned with the actual

methodologies used, and more concerned that the outcome requires

sources to comply with an emission limitation based on MACT.

Also, throughout this manual, the reader will find that the

roles and responsibilities in the case-by-case MACT determination

have been delineated between the permitting authority and the

permit applicant. This delineation of roles and responsibilities

is intended to indicate a lead role, but is not intended to

establish any sole responsibilities. Permitting authorities and

applicants should recognize that establishing the appropriate

level of control is an iterative process that will require ongoing communication and exchange of information between the

permitting authority and the applicant.

In summary, the EPA encourages State and local agencies to

cooperatively use this guidance, methods used by the EPA in
vii

developing Section 112(d) MACT standards, and various State

control technology determination procedures to establish timely,

accurate, and consistent MACT emission limitations.
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Chapter 1.0

An Overview of the 

MACT Determination Process

for Section 112(j)

1.1 Overview of Statutory Requirements

Beginning after the effective date of an approved permit

program, Section 112(j) of the Clean Air Act as amended in 1990

(the Act) requires an owner or operator of a major source to

submit either a new Title V permit application or revise an

existing permit if such major source incorporates a source

category for which the promulgation deadline for a relevant

Section 112(d) or 112(h) standard has been missed by 18 months. 

The promulgation deadline for each source category was

established through the regulatory schedule in accordance with

Section 112(e) of the Act. A final regulatory schedule was

published on December 3, 1993 in the Federal Register (58 FR

63941). To obtain the most current list of categories of sources

to be regulated under Section 112 of the Act, or to obtain the

most recent regulation promulgation schedule established pursuant

to Section 112(e) of the Act, contact the Office of the Director,

Emission Standards Division, Office of Air Quality Planning and

Standards, U.S. Environmental Protection Agency (C504-03),

Research Triangle Park, North Carolina 27711.

Section 112(j) also requires States or local agencies with

approved permit programs to issue permits or revise existing
1-2

permits for all of these major sources. These permits must

contain either an equivalent emission limitation or an alternate

emission limitation for the control of hazardous air pollutants

(HAP) from the equipment within the source category. An

equivalent emission limitation, also referred to as a MACT

emission limitation, will be determined on a case-by-case basis

by the permitting authority for each source category that becomes

subject to the provisions of Section 112(j). The MACT emission

limitation will be "equivalent" to the emission limitation that

the source category would have been subject to if a relevant

standard had been promulgated under Section 112(d) (or

Section 112(h)). 

In accordance with Section 112(d), the MACT emission

limitation will require a maximum degree of reduction of HAP

emissions, taking into consideration the costs of achieving such

emission reductions and any non-air quality health and

environmental impacts and energy requirements. For new sources,

the MACT emission limitation will be no less stringent than the

emission control that is achieved in practice by the best

controlled similar source. For existing sources the MACT

emission limitation will be no less stringent than:

1. The average emission limitation achieved by the best

performing 12 percent of the existing sources (for which the

Administrator has emissions information), excluding those

sources that have, within 18 months before the emission

standard is proposed or within 30 months before such

standard is promulgated, whichever is later, first achieved
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a level of emission rate or emission reduction which

complies, or would comply if the source is not subject to

such standard, with the lowest achievable emission rate (as

defined by Section 171 (of the Act)) applicable to the

source category and prevailing at the time, in the category

or subcategory for categories and subcategories with 30 or

more sources; or,

2. The average emission limitation achieved by the best

performing 5 sources (for which the Administrator has or

could reasonably obtain emissions information) in the

category or subcategory for categories or subcategories with

fewer than 30 sources. (Sections 112(d)(3)(A) and (B) of

the Act.)

These minimum requirements for the MACT emission limitation for

new and existing sources are termed the "maximum achievable

control technology (MACT) floor".

An alternate emission limitation is a voluntary emission

limitation that an owner or operator of a major source has agreed

to achieve through the early reductions program (see 57 FR 61970;

December 29, 1992). (This regulation is codified in Subpart D,

40 CFR 63.70.) The alternate emission limitation can be written

into the permit in lieu of an equivalent emission limitation only

if the source has achieved the required reduction in HAP

emissions before the missed promulgation deadline for the

relevant Section 112(d) (or 112(h)) standard.

Section 112(j) also requires the EPA to establish

requirements for owners or operators and reviewing agencies to

carry out the intent of Section 112(j). These regulatory

requirements are contained in Chapter 40, Part 63, Subpart B of

the Code of Federal Regulations.
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1.2 Overview of the Section 112(j) Regulatory Requirements

The owner or operator of a major source is required to apply

for a Title V permit or permit revision, when the statutory

deadline for a relevant Section 112(d) emission standard is

missed by 18 months. The content of applications, details of the

application approval process, timing of submittals, reviews, and

permit issuance are in sections 63.52 and 63.53 of the

Section 112(j) rule.

The application for a case-by-case MACT determination is a

two-part process. Part 1 of the application requests very basic

information about the affected source; the substantive

information required by the permitting authority to make its MACT

determination is tied to submittal of the Part 2 application. 

The application content for a MACT determination is contained in

section 63.53. Information available as of the date on which the

first Part 2 MACT application is filed for a source in the

relevant source category or subcategory in the State or

jurisdiction will be considered by the permitting authority in

making its case-by-case MACT determination. The definition of

"available information" in section 63.51 specifies the type of

information and sources of information available to the affected

source owner or operator for use in completing the application or

to the permitting authority in determining the terms and

conditions of case-by-case MACT.
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The cutoff date for what information may be considered by

the permitting authority is in the context of the development of

control technologies that could be considered in the MACT floor

determination. The definition does not preclude the permitting

authority from considering information that was brought to its

attention after the cutoff date through public comment or other

means, so long as the information (e.g., control technology) had

been developed prior to the cutoff date. 

The following is a synopsis of the approval process under

several scenarios for existing sources, affected sources, and new

affected sources as described in section 63.52 of the rule. This

synopsis includes situations where an affected source is subject

to Section 112(g) requirements and later becomes subject to

Section 112(j) and area sources become major affected sources

subject to Section 112(j). This synopsis is provided for

information purposes only. To the extent the reader identifies

any potential conflicts or errors compared to the actual rule

language, the language in Subpart B governs.

Sources in existence at the Section 112(j) deadline:

(1) The owner or operator can reasonably determine the

affected source is subject to the Section 112(j) rule and submits

the Part 1 application as described under Section 63.53(a) of the

rule by the Section 112(j) deadline.
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(2) If an owner or operator submits a Part 1 application in

error, the State is responsible for notifying them that they are

not subject to Section 112(j). (That is, the source is not in a

category or subcategory subject to Section 112(j)). 

(3) The owner or operator of the affected source who does

not submit a Part 1 application is notified by the State that

he/she is subject to the Section 112(j) rule and submits the Part

1 MACT application within 30 days of the notification. Owners or

operators who can reasonably determine they are subject and do

not submit an application may be subject to enforcement action.

(4) The affected source has a Title V permit or application

that addresses Section 112(g) emission limitation requirements:

- affected source has a Section 112(g) MACT

determination and submits Part 1 MACT application

per timing in (1) or (3) above;

- affected source has an application and completes

the Title V permit process under Section 112(g). 

Within 30 days of issuance of the Title V permit

containing the Section 112(g) MACT determination,

affected source submits the Part 1 MACT

application.

Sources that become subject after the Section 112(j) deadline and

do not have a Title V permit addressing the Section 112(j)

requirements:
1-7

(1) Installation at a major source or installation that

results in the source becoming a major source, but Section 112(g)

is not triggered. The owner or operator submits the Part 1 MACT

application within 30 days of startup.

(2) The owner or operator has a Title V permit or

application satisfying the requirements of Section 112(g). The

owner or operator submits the Part 1 MACT application within

30 days of issuance of the Title V permit that addresses the

emission limitation requirements of Section 112(g).

(3) Area source becomes major as a result of change in

potential to emit (PTE). Source submits a Part 1 MACT

application for a Title V permit or an application for a Title V

permit revision within 30 days after such source becomes a major

source.

(4) Area source becomes major as a result of a lesser

quantity emission rate established by the Administrator. Source

submits a Part 1 MACT application for a Title V permit or Title V

permit revision within 6 months after such source becomes a major

source.

Sources that become subject after the Section 112(j) deadline and

have a Title V permit addressing the requirements of Section

112(j):

(1) If the "event" is covered by the permit, then the

affected source owner or operator complies with the permit;
1-8

(2) If the "event" is not covered by the permit, then the

existing source submits a Part 1 MACT application for a revision

to the permit within 30 days of beginning construction.

Requests for applicability determinations and for Notice of MACT

Approval:

(1) If a source owner or operator is unsure whether any of

the above scenarios apply, then he/she may submit a Part 1 MACT

application to ask the State for an applicability determination.

(2) Owners or operators of new affected sources can obtain

preconstruction review through an application for a Notice of

MACT approval under section 63.54 of the rule.

Figures 1 and 2 illustrate the obligations and associated

timing requirements of sources subject to Section 112(j)

requirements.
1-9
1-10
1-11

1.3 Affected Source and New Affected Source Review

In some instances an owner/operator may be required to

obtain preconstruction review or provide notice of intent to

change a source subject to Section 112(j). If an owner or

operator is not required to obtain or revise a Title V permit

before construction of the new affected source (and has not

elected to do so), but the new affected source is covered by any

preconstruction or pre-operation review requirements established

pursuant to Section 112(g) of the Act, then the preconstruction

review requirements under Section 112(g) would fulfill the

requirements of Section 112(j). If the new affected source is

not covered by Section 112(g), the permitting authority, in its

discretion, may issue a Notice of MACT Approval, or the

equivalent, consistent with the requirements in 40 CFR 63.54 of

Subpart B before construction or operation of the new affected

source. Appendix C provides a suggested format for the Notice of

MACT Approval. If a Section 112(j) case-by-case MACT

determination has been made for such a source, it will include a

determination of existing source MACT and new source MACT as well

as the applicability of new source MACT. Such a case-by-case

determination is the basis for preconstruction review. This

process would require owners and operators of major sources to

undergo preconstruction review before constructing a new affected

source or reconstructing an affected source, if construction is
1-12

to commence after the Section 112(j) deadline. Details of the

requirements for the approval process for affected sources and

new affected sources are described in Section 63.52 of Subpart B;

preconstruction review procedures for new affected sources are

described in Section 63.54. Regardless of the review process,

the MACT determination must be consistent with the principles

established in Section 63.55.
2-1

Chapter 2.0

The MACT Determination

2.1 Criteria for the MACT Determination

The process of determining an equivalent (MACT) emission

limitation is called a MACT determination. For MACT

determinations under Section 112(j), the MACT emission limitation

should be comparable to the emission limitation(s) or

requirements that would likely be imposed if a Section 112(d) or

Section 112(h) emission standard had been promulgated for that

source category. The Clean Air Act sets forth specific criteria

for setting a hazardous air pollutant emission standard under

Section 112(d) and Section 112(h). These criteria should also be

used when establishing the MACT emission limitation under

Section 112(j).

Permit conditions created through Section 112(j) of the Act

should establish limitations that:

1) Are no less stringent than the MACT floor when a MACT

floor can be determined; and,

2) Achieve a maximum degree of HAP emission reduction with

consideration to the cost of achieving such emission

reductions, and the non-air-quality health and

environmental impacts, and energy requirements; and,
2-2

3) Limit the quantity, rate, or concentration of HAP

emissions on a continuous basis; or,

4) Designate specific design, equipment, work practice,

operational standard, or a combination thereof, that

achieves a maximum degree of emission reduction, when

it is not practicable (economically or technologically)

to prescribe a specific numerical emission limitation.

The MACT emission limitation could be expressed as a

numerical emission limitation on the total quantity of HAP

emissions from the source in tons per year (tpy), a production

ratio (e.g., 10 lbs of HAP/100 lbs of polymer), or as a

concentration limit (e.g., 10 ppm HAP). The MACT emission

limitation could also be a performance standard based on the

expected efficiency of MACT in reducing HAP emissions. For

example, a source may be required to reduce emissions by 90

percent from a 1990 baseline or to achieve a specified reduction

from uncontrolled emission rates. The MACT emission limitation

can also be based on a design, equipment, work practice,

operational standard, or any combination of these. In some

cases, the EPA found that it is appropriate to require a source

to use a high efficiency spray gun in the coating process; to

conduct a leak detection and repair program for various items of

equipment; or to install a floating roof with primary and
2-3

secondary seals on a storage tank in lieu of establishing a

numerical emission limitation.

If an individual hazardous air pollutant is of particular

concern, a MACT limitation may also be placed on that pollutant

based on the expected level of reduction with MACT in place. 

Reviewing agencies should consider whether it is appropriate to

impose such a limitation on a specific hazardous air pollutant. 

In addition to specifying the MACT emission limitation, the 

permit should establish the terms and conditions that are

necessary to make the emission limitation federally enforceable

as a legal and practical matter. This involves establishing

appropriate operational and/or monitoring parameters to ensure

compliance with the MACT emission limitation. The following

section discusses compliance provisions in greater detail.

2.2 Compliance Provisions

Each Title V permit and Notice of MACT Approval must contain

sufficient testing, monitoring, reporting, and recordkeeping

requirements to assure compliance with the MACT emission

limitation.

When the permit or Notice of MACT Approval requires an addon control, operating parameters and assumptions that can be used

to determine the efficiency of the device or its emission rate

should be specified. For example, a source may have a MACT
2-4

emission limitation that requires a control device to be

installed and operated at a 95-percent emission reduction

efficiency. An operational limit on the range of temperatures

that the device can be operated under could be sufficient to

ensure compliance, if operating the control device within this

temperature range ensures that the device achieves a 95-percent

destruction efficiency.

If establishing operating parameters for control equipment

is infeasible in a particular situation, a short term emission

limit (e.g., lbs/hr) would be sufficient provided that such

limits reflect the operation of the control equipment, and

additional requirements are imposed to install, maintain, and

operate a continuous emission monitoring system (CEMS) or other

periodic monitoring that yields sufficiently reliable data to

determine the source's compliance with the MACT emission

limitation.

If parameter monitoring of the process is infeasible due to

the wide variety of operating conditions, emission limits coupled

with a requirement to calculate daily emissions may be required. 

For instance, a source could be required to keep the records of

the daily emission calculation, including daily quantities and

the HAP content of each coating used.

For limitations to be enforceable as a practical matter, the

limitations should extend over the shortest practicable time
2-5

period, generally not to exceed one month. If it is not

practicable to place a monthly limit on the source, a longer time

can be used with a rolling average period. However, the limit

should not exceed an annual limit rolled on a monthly basis.

In addition to conveying practical enforceability of a MACT

emission limitation, the Title V permit or Notice of MACT

Approval should require testing or monitoring that yields data

that are representative of the source's operations and can be

used to certify the source's compliance with the terms and

conditions of the Title V permit or Notice of MACT Approval. 

Testing or monitoring must be performed in a manner to ensure

that the limitations are achieved at all times, except during

startup, shutdown, or malfunction. Such testing or monitoring

requirements may be in the form of continuous emission monitoring

systems, continuous opacity monitoring systems, or periodic

monitoring. If periodic testing is required, the specific EPAapproved method or equivalent method that is to be used should be

specified in the permit or notice.

2.3 Approaches to the MACT Determination

When the Administrator fails to promulgate a standard by the

promulgation deadline, the EPA intends to make all nonconfidential information collected during the development of a

source category standard available to the public. If the
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Administrator has conducted a MACT floor finding, this analysis

will be made available as well. Information will be conveyed

either through a Federal Register notice, a background

information document, the Technology Transfer Network (TTN), or

other available mechanism.

A permitting authority could use several different

approaches for the MACT determination process. For example, a

permitting authority could wait until all applications for

permits are received to determine the equivalent emission

limitations that would apply to all of the sources within its

jurisdiction. Or, a permitting authority or a group of

permitting authorities could conduct a "MACT analysis" based on

available information before the first Part 2 MACT application is

filed for a source in the relevant source category or subcategory

in the State or jurisdiction.

The first approach requires less upfront coordination on the

part of the permitting authority and is likely to be used when

the EPA fails to collect sufficient information on the source

category or subcategory during the standards development process. 

Once the permit applications are received, information from each

application can be compiled to determine the appropriate

emissions control level. When this approach is used, the EPA

strongly encourages different permitting authorities to share

information received through the permit application process.
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After the appropriate level of control is determined using the

permit application information, permit applicants may need to

submit additional information to demonstrate how the required

emission reductions will be met so that permit terms and

conditions can be developed.

The second approach is most likely to be used when there is

a substantial amount of information already available for a

source category or subcategory, or when the EPA has already

proposed standards for that source category or subcategory. 

Based on this available information, the permitting authority (or

coalition of permitting authorities) could conduct a MACT

analysis (See Chapter 3) to determine the appropriate level of

control for each source. This control level could be made

federally enforceable for all sources in the category through the

use of general permits, or each applicant could undergo a

separate review in the Title V permitting process. Section 2.5

discusses the concept of general permits in greater detail.

Regardless of the approach taken to issue or revise Title V

permits under Section 112(j), permitting authorities are reminded

that the equivalent emission limitation is to be determined on a

case-by-case basis for each source category or subcategory for

which a Section 112(j) MACT determination is required. This

determination should be viewed as a "source category-by-source

category" determination and terms and conditions in each permit
2-8

issued should yield an essentially equivalent degree of emission

reductions for all affected sources in the category or

subcategory.

2.4 Available Information

Section 112(j) states that permits issued pursuant to

Section 112(j) shall contain an equivalent emission limitation. 

This emission limitation is to be "equivalent" to that which the

source would have been subject had an applicable Section 112(d)

or Section 112(h) emission standard been promulgated. In order

to establish an emission limitation that would be equivalent, the

permitting authority must determine the equivalent emission

limitation with consideration of the MACT floor using available 

information as defined in 40 CFR 63.51.

It is not necessary for the MACT floor to be determined

based on emissions information from every existing source in the

source category or subcategory if such information is not

available. The permitting authority, however, should check with

EPA Regional Offices and EPA Headquarters for any available

information that could be used in determining the MACT floor. 

Once a permitting authority has obtained available information,

the MACT floor can be determined using this information if it is

representative of the source category or subcategory. For

example, suppose there are 100 sources in a source category or
2-9

subcategory. Control technology X and Y are generally considered

to achieve the greatest amount of emission reductions among

existing sources. Thirty sources in the category use these

technologies. The MACT floor could be determined based on these

technologies, even if information was not available on the other

seventy sources.

2.5 General Permits

A general permit is a type of Title V permit. A single

general permit could be issued by a permitting authority to cover

a number of sources. The specific requirements for a general

permit are contained in 40 CFR Part 70.6(d). 

The general permit can be written to set forth requirements

for an entire source category or subcategory, or portion of the

source category or subcategory. The facilities that are covered

by the general permit, should be homogenous in terms of

operations, processes, and emissions. In addition, the

facilities should have essentially similar operations or

processes and emit pollutants with similar characteristics. The

facilities should be subject to the same or substantially similar

requirements governing operations, emissions monitoring,

reporting, or recordkeeping.

Because the case-by-case determination under Section 112(j)

is a source category-by-source category determination of an
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equivalent emission limitation, the permitting authority could

use the general permit as a mechanism to issue Title V permits to

the entire source category or subcategory, or specific components

within the source category or subcategory. By using this

mechanism, a permitting authority would not be required to issue

individual permits to sources covered by the general permit. 

Also, once the general permit has been issued and after

opportunity for public participation, EPA review and affected

State review, the permitting authority may grant or deny a

source's request to be covered by a general permit without

further outside review.

Major sources that do not require a specific Title V permit

for any other reason, could be covered by the general permit

indefinitely. For a major source that already has a Title V

permit, the owner or operator can apply for coverage under the

general permit, and then incorporate the general permit

requirements into the source specific permit through an

administrative amendment at permit renewal.

General permits would not be an appropriate mechanism to

issue permit conditions if the terms and conditions necessary to

establish federal enforceability as a legal and practical matter

might vary from source to source within the category. For

instance, if a MACT emission limitation restricted emissions from

multiple emission points within the source category or
2-11

subcategory and the number of emission points varied from major

source to major source, a general permit may not be appropriate.
3-1

Chapter 3.0

The MACT Analysis

For most source categories, the process by which the

permitting authority will determine the appropriate level of

control involves a number of different determinations. First,

the emission points at the major source that are related to the

activities and equipment in a source category or subcategory must

be identified. There may be a number of emitting activities and

equipment at a single major source. In some cases, not all of

these emissions are from a single source category or subcategory. 

Only the emission points in the source category or subcategory

undergoing the Section 112(j) MACT determination are subject to

control through an equivalent emission limitation. 

The collection of equipment and/or activities in the source

category or subcategory at the source subject to Section 112(j)

is the affected source as defined in 40 CFR 63.2. An affected

source may have only one emission unit comprised of all of the

emission points; or, it may have several emission units each

comprised of some portions of the total number of emission points

in the source category or subcategory. In this context the term

"emission unit" is equipment or a grouping of equipment for which

a floor determination and MACT will be determined. Note that

this term has no regulatory or statutory meaning under Section
3-2

112(j). It is used here for convenience. Existing source MACT

and new source MACT and their respective applicability must be

determined for the affected source and new affected source

consistent with 40 CFR 63.2, 40 CFR 63.5, and 40 CFR 63.52. The

process of establishing the scope of the source category or

subcategory, the affected source and new affected source, and the

appropriate levels of control by the permitting authority

requires ongoing communication and exchange of information

between the permitting authority and applicants. This

interaction between the permitting authority and applicants is

essential in making these determinations.

The process by which these determinations are made is termed

the MACT analysis. The following sections of this chapter

describe a MACT analysis process that EPA has developed to meet

the requirements of 40 CFR Part 63, Subpart B.

3.1 Overview of the MACT Analysis Process

The MACT analysis by the permitting authority uses available

information to make a MACT floor finding. There are several

possible situations that may arise in the course of conducting a

MACT analysis. First, the MACT floor could be determined based

on emission reductions currently being achieved by other

controlled sources. A second possible outcome is that the MACT

floor cannot be determined due to the nature of the pollutants
3-3

emitted from the source, or because of the lack of available

data. A third possibility is that the MACT floor could equal "no

control" if the group of sources on which the MACT floor

determination is based are not currently controlling HAP

emissions. In the latter two cases, the EPA believes that a more

detailed analysis is required in order to determine the

appropriate level of control. 

Because of the variety of situations that could arise, the

MACT analysis has been divided into three tiers. Figure 3

diagrams the steps for Tier I, Tier II and Tier III of the

analysis. A MACT floor finding by the permitting authority is

made during Tier I. During Tier II, the permitting authority, in

consultation with the applicant, evaluates all commercially 
3-4
3-5

available and demonstrated controls that are reasonably

applicable to such source. Tier III uses the information

developed in Tier I or Tier II to establish a MACT emission

limitation. 

This process is presented here as suggested guidance in

determining MACT. Permitting authorities are free to use the

process with which they are most familiar to determine MACT.

If a MACT floor is determined, it is only necessary to complete

Tier I and Tier III of the MACT analysis. This analysis compares

the costs, non-air quality health and environmental impacts and

energy requirements associated with using control technologies

that obtain a level of HAP emission reductions that are equal to

or greater than the MACT floor. A key assumption is that the

Tier I analysis yields sufficient information to conduct the Tier

III MACT analysis. If additional information is needed, the

permitting authority and the source would develop that

information as part of the Tier III analysis. 

If, under Tier I, the MACT floor cannot be determined or is

equal to "no control," Tier II of the analysis should be

completed before moving on to Tier III.

The purpose of Tier II is to identify all commercially

available and demonstrated control technologies that are

reasonably applicable to such source. Available control

technologies include but are not limited to: reducing the volume
3-6

of, or eliminating emissions of pollutants through process

changes, substitution of materials or other techniques; enclosing

systems or processes to eliminate emissions; collecting,

capturing, or treating pollutants when released from a process,

stack, storage, or fugitive emission point; using design,

equipment, work practices, or operational standards (including

requirements for operator training or certification); or, a

combination of any of these methods. The permitting authority in

consultation with the applicant is responsible for developing a

list of technologies that are reasonably applicable to the

source.

Once a list of control technologies that are reasonably

applicable to the source is developed, each control technology

should be evaluated to consider the costs, non-air quality health

and environmental impacts, and energy requirements associated

with using each control technology.

In Tier III, the control technology(s) achieving the maximum

degree of HAP emission reductions taking into consideration the

costs of achieving such emission reductions and the non-air

quality health and environmental impacts and energy requirements

should be selected as MACT. Once MACT has been selected, a MACT

emission limitation(s) should be established by the permitting

authority based on the degree of emission reductions that can be

achieved through the application of the maximum achievable
3-7

control technology (MACT). A design, equipment, work practice or

operational standard, or combination thereof, may be designated

as the MACT emission limitation, if it is not practicable, in the

judgement of the permitting authority, to prescribe or enforce a

numerical MACT emission limitation.

If an owner or operator wishes to comply with the MACT

emission limitation using a control strategy other than the

control strategy selected as MACT, then the Title V permit

application should be submitted or revised to demonstrate that

this alternative strategy achieves the required level of emission

reductions.

3.2 A Detailed Look at the MACT Analysis

Tier I - Making a MACT floor finding

Step 1 -- Identify the MACT-affected emission unit(s)

In accordance with the provisions established in 40 CFR

63.53, the owner or operator is required to identify all HAP

emission points within the affected source. These emission

points will be grouped into emission units (MACT emission units)

that will be subject to a MACT determination by the permitting

authority.

When a relevant emission standard has been proposed, the

scope of the affected source and the emission units should be

consistent with the scope of the affected source and the emission
3-8

units for which MACT was determined in the proposed emission

standard, unless an alternative can be adequately supported. 

When no relevant emission standard has been proposed, the MACT

emission unit will be determined on a case-by-case basis. 

Section 3.3 of this chapter discusses principles for determining

the MACT emission unit on a case-by-case basis.

The collection of emission points (and hence the collection

of emission units) at the source subject to Section 112(j) that

are in the source category or subcategory subject to this subpart

is the affected source as defined in 40 CFR 63.2. 

Step 2 -- Make a MACT floor finding

Using the available information provided by the EPA, other

permitting authorities, and/or the permit applications, a level

of HAP emission control that is equal to the MACT floor for each

type of emission unit undergoing review should be calculated by

the permitting authority according to 40 CFR 63.55. 

Chapter 4 discusses three ways to establish a MACT floor:

using (1) State and local regulations, (2) control efficiencies,

and (3) emission reduction ratios. Use of any of these

methodologies to determine the floor depends on the format of

available information. It is possible that a hybrid of these

approaches may be necessary, or none of the methods may be

appropriate given the format of the available information. These

methods are provided in this guidance document to demonstrate the
3-9

types of methodologies that would be appropriate for establishing

a MACT floor.

If the MACT floor cannot be determined or if it is equal to

"no control", the permitting authority should proceed to Tier II

of the analysis.

Tier II - Considering all control technologies

Step 1 -- List all available/reasonable applicable control

technologies

Using available information, the permitting authority in

consultation with source owners/operators should develop a list

of commercially available control technologies that have been

successfully demonstrated in practice for similar emission units

and that are reasonably applicable to sources in the category or

subcategory. Similar emission units are discussed in more detail

in Section 3.4 of this chapter. 

Step 2 -- Eliminate technically infeasible control technologies

All control technologies that could not be applied to the

MACT emission unit because of technical infeasibility should be

eliminated from the list. A technology is generally considered

technically infeasible if there are structural, design, physical

or operational constraints that prevent the application of the

control technology to the emission unit. A technology may also

be eliminated if the permitting authority deems it unreasonable. 

A technology is considered unreasonable if the operational
3-10

reliability and performance have not been demonstrated by

approved methods under conditions representative of those

applicable to the source for which MACT is being determined.

Step 3 -- Determine efficiency of applicable control technologies

The permitting authority should conduct a detailed analysis

of all of the available reasonably applicable control

technologies. The efficiency of each control technology in

reducing overall HAP emissions should be determined. Generally,

MACT has been selected based on an overall reduction of all HAP

emissions. However, a permitting authority may also select MACT

based on the degree of emission reductions achieved for one or

more specific HAPs when the risk to human health and the

environment warrants establishing MACT emission limitations

specifically for these HAPs. It should also be noted that the

application of more than one control technology may be necessary

in order to address multiple types of HAP emissions.

Tier III - Identifying MACT

Step 1 -- Identify the maximum emission reduction control

technology

When a MACT floor finding is made, the permitting authority

will need to use available information to identify the control

technology(s) that reduce HAP emissions from the MACT emission

units to the maximum extent considering the factors in Section

112(d)(2) of the Act and to a level that is at least equal to or
3-11

greater than the MACT floor. Consideration can be given to

transfer and innovative technologies used to control emissions

from other emission units that use technologies that can be

applied to the MACT emission unit.

As in Tier II, the permitting authority should conduct an

analysis to eliminate any technically infeasible control

technologies and to determine the efficiency of applicable

control technologies.

While the Clean Air Act establishes that MACT shall be no

less stringent than the MACT floor, in establishing MACT, the

Administrator must take into consideration “the cost of achieving

such emission reduction, and any non-air quality health and

environmental impacts and energy requirements” [section

112(d)(2)]. In some cases, the EPA has developed MACT standards

that are more stringent than the MACT floor when the following

criteria are met: 

(1) The economic impact and incremental cost-effectiveness

are not unreasonable;

(2) The standard would control emissions of high risk or

highly toxic pollutants, e.g., chromium; or

(3) The standard resulted from a negotiated rulemaking,

e.g., the wood furniture NESHAP or the HON equipment

leaks standard.

Step 2 -- Conduct an impacts analysis
3-12

The control technology that achieves the maximum degree of

HAP emission reductions with consideration to costs, non-air

quality health and environmental impacts, and energy requirements

is MACT. The Act does not provide direction on the significance

of one consideration to another. The EPA believes that it is

inappropriate to provide specific guidance for determining the

amount of consideration that should be given to any one factor. 

Such decisions will need to be made based on the information

available at the time of the MACT determination. See Chapter 6

of this guidance document for a more detailed discussion on the

analysis of the costs, non-air quality health and environmental

impacts, and energy requirements.

Step 3 -- Establish the MACT emission limitation

The MACT emission limitation established by the permitting

authority is based on the degree of emission reduction that can

be obtained by the affected source if MACT is applied and is

properly operated and maintained. See Chapter 5 for a detailed

discussion on the MACT emission limitation and permit conditions.

3.3 Determining the MACT Emission Unit and "Affected Source"

In some cases available information is adequate to support a

MACT floor determination for the grouping of equipment and

activities comprising the affected source. However, in some

cases the EPA has found it necessary to evaluate smaller
3-13

groupings of equipment and activities for the purpose of the MACT

floor and MACT determination. This smaller grouping is referred

to herein as a MACT emission unit.

There are four basic principles to follow when designating

the MACT emission unit. The principles can be summarized as

follows: 1) When a relevant Section 112(d) or Section 112(h)

standard has been proposed, the permitting authority should refer

to the relevant standard to determine the MACT emission unit; or,

(2) The EPA's Office of Air Quality Planning and Standards should

be consulted to determine if a suggested method for grouping

affected emission points is available; or, (3) When a specific

piece of equipment is designated as a source category or

subcategory on the source category or subcategory list, the MACT

emission unit is that piece of equipment or apparatus; or,

(4) Emission points should be combined into a single MACT

emission unit when the combination of points leads to a much more

cost-effective method of control, and achieves a greater degree

of emission reductions when compared to point-by-point

compliance.

The best indicator of how a source category or subcategory

may be regulated by a future promulgated relevant standard may be

found in the proposed standard. For this reason, the EPA

believes that permitting authorities should first consider the

guidelines in the proposed standard to determine the MACT
3-14

emission unit for a Section 112(j) MACT determination. In

addition, although there may be no proposed standard for the

source category or subcategory, information on the source

category or subcategory may have been collected which allows the

EPA to recommend a specific method for determining the emission

unit for a Section 112(j) MACT determination. Therefore, the EPA

should be consulted before attempts are made to define the MACT

emission unit on a case-by-case basis.

When a source category or subcategory is associated with a

piece of equipment or apparatus specifically listed on the source

category or subcategory list, that piece of equipment or

apparatus is the MACT emission unit. The source category or

subcategory list contains sources that are defined at various

levels of complexity: from an integrated manufacturing or

process operation to an individual piece of equipment. In

developing the source category or subcategory list, the EPA

determined that some individual pieces of equipment may be colocated with other HAP-emitting equipment that, independently or

collectively, have the potential to emit major amounts of HAPs. 

For example, under the fuel combustion industrial grouping,

stationary internal combustion engines are listed as a source

category or subcategory. When a source category or subcategory

is designated by a single type of apparatus, the EPA believes

that the intent is for emission limitations and requirements to
3-15

be placed on that specific piece of equipment. As such, if a

Section 112(j) determination is conducted for any one of these

source categories or subcategories, the specific piece of

equipment or apparatus should be designated as the MACT emission

unit.

A single emission point such as a storage tank could be

considered the MACT emission unit. By contrast, emission points

from a distillation column, a condenser and distillate receiver

could be consolidated into one emission unit. Larger groupings

of emission points may be appropriate when a single control

technology can be used to control the aggregation or when a

pollution prevention or waste reduction strategy is considered. 

For instance, the entire wastewater treatment operation within

the source category or subcategory could be considered one

emission unit. Collectively, a single steam-stripper could be

used at the beginning of the operation to remove HAPs from the

wastewater and prevent downstream emissions from occurring. 

Another example is illustrated with a surface coating operation. 

Rather than individually controlling the emissions from a spray

booth, flash-off area, and bake oven, switching to a water-based

paint could reduce emissions from all of these emission points. 

Another reason to combine affected emission points into a

single emission unit is that many major sources are already

subject to regulation under 40 CFR Part 60. In promulgating
3-16

these standards, "affected facility" definitions were developed

to designate the apparatus to which a standard applies. It may

make sense to use these same boundaries to designate the "MACT

emission unit" subject to a MACT determination. It should be

noted that a particular piece of apparatus or equipment should

not be excluded from a MACT determination because of an

applicability "cut-off" established under a Part 60 regulation.

Emission points could be consolidated into an emission unit

that is as large as the source category or subcategory boundary

for several reasons. First, the information that is available to

calculate the MACT floor may only apply to the source category or

subcategory as a whole, not individual points within the

category. Also, the operations of some source categories are

quite variable. Either the nature of the process requires a

large latitude of flexibility in establishing the emission unit

that should be controlled, or the types of facilities within the

category are so diverse that it only makes sense to compare the

existing sources on a source category or subcategory wide level. 

In these instances, a source category or subcategory wide MACT

emission unit could allow some emission points to be undercontrolled while others are controlled to a level that would

exceed the level of control that would be placed on that

individual point through the application of MACT.
3-17

Permitting authorities are cautioned that, consistent with

the EPA's emissions averaging decisions, as prescribed in 40 CFR

63.150, it would be generally inappropriate to include emission

points associated with equipment leak emissions together with

other types of emission points in a MACT emission unit until the

EPA determines that emissions can be appropriately estimated for

this purpose.

There are some situations that would make the combination of

emission points unreasonable. For example, the combination

should not be done in order to generate an emission unit that is

so unique that it precludes comparing the emission unit to other

sources in the source category or subcategory. In other cases,

the EPA has established thresholds for types of emission points

within a MACT emission unit, which define whether such points are

required to be further controlled in order to meet MACT. For

example, as illustrated by Group 2 sources (40 CFR Part 63,

Subpart G), the MACT floor for smaller or more dilute sources may

be no control, and nothing more stringent than the floor may be

justified.

Determining the MACT emission unit on a case-by-case basis

is a complex undertaking. While this document includes this step

as a separate component of the Tier I approach, in actual

practice the identification of methods to control specific groups

of emission units and the identification of control technology
3-18

options will be integrated processes. Some aggregations of

emission points may be inappropriate because the information

available to calculate the MACT floor would dictate combining

emission points into certain emission units, or because controls

applied to the unit would not achieve a MACT level of control

when compared to point-by-point compliance or some other

combination of emission units. Appendix A provides an example of

ways in which available control technologies would affect the

aggregation of emission points into an emission unit.

3.4 Similar Emission Units

The permitting authority should evaluate control

technologies used by similar emission units in other source

categories during Tier II. Whether control technologies from

other source categories should be considered in the MACT analysis

depends on whether the emission unit is "similar". At least two

questions should be answered to determine if an emission unit is

similar: 1) Do the two emission units have similar emission

types, and 2) Can the emission units be controlled with the same

type of control technology. If the two emission units do have

similar emission types and are controllable to approximately the

same extent with the same control technologies, then the two

emission units can be considered similar for the purposes of a

case-by-case MACT determination under Section 112(j).
3-19

For example, suppose Section 112(j) applies to the captan

production source category or subcategory (a source listed on the

source category or subcategory list), and a major source produces

captan with equipment using product accumulation vessels (tanks)

and additional pipes, pumps, flanges and valves to direct the

product to the tanks. During Tier I of the MACT analysis, it is

determined that there are no regulations controlling HAP

emissions from pumps, etc. within this source category or

subcategory. There is also not enough emission information

available on other emission units within the source category or

subcategory to calculate a MACT floor. During Tier II of the

analysis, it is discovered that the Synthetic Organic Chemical

Manufacturing Industry (SOCMI) source category or subcategory is

currently subject to regulations controlling equipment leaks. 

Because the pipes, pumps, and flanges all have equipment leak

emissions and can be controlled to the same extent by a leak

detection and repair program, such equipment in the SOCMI source

category or subcategory would be considered similar emission

units. The regulations for SOCMI equipment leaks should be

considered for the control of the MACT emission unit during

Tier II of the analysis. When determining the existing source

level of control, identification of a similar emission unit does

not mean that the controls will automatically be applied to the

MACT emission unit. Costs, non-air quality health and
3-20

environmental impacts, and energy requirements should be used to

assess the technologies ability to meet MACT criteria.

Also during Tier I of the analysis, it may be determined

that the best controlled tank within this source category or

subcategory does not have state-of-the-art controls. Yet, tanks

from outside the source category or subcategory storing similar

organic liquids use state-of-the-art controls vented to an

emission control device. The controls used on these tanks would

be considered in establishing MACT.

After identifying MACT, the permitting authority proceeds to

establish the MACT emission limitation, monitoring, and

recordkeeping as outlined previously.

3.5 Subcategorization

When the source category list was developed, sources with

some common features were grouped together to form a "category". 

During the standard-setting process, the EPA has found it

appropriate to combine several categories or to further divide a

category into subcategories. The EPA chose to establish broad

source categories at the time the source category list was

developed because there was too little information to anticipate

specific groupings of similar sources that are appropriate for

defining MACT floors for the purpose of establishing emission

standards.
3-21

The broad nature of some source category descriptions may

pose some difficulty in establishing an appropriate MACT emission

limitation for a MACT emission unit on a case-by-case basis. 

Subcategorization within a source category for the purposes of a

case-by-case MACT determination should be considered when there

is enough evidence to clearly demonstrate that there are air

pollution control engineering differences. Criteria to consider

include process operations (including differences between batch

and continuous operations), emissions characteristics, control

device applicability and costs, safety, and opportunities for

pollution prevention. When separate subcategories are

established, the MACT floor and MACT are then determined

separately for each such subcategory.
4-1

Chapter 4.0

The MACT Floor Finding

During Tier I of the MACT analysis, the permitting authority

will make a MACT floor finding if there is enough information to

determine an emission control level that is at least equal to the

MACT floor. If a MACT floor cannot be determined due to the

nature of the pollutant or process, or there is not enough

emissions information to compute a MACT floor, then the analysis

in Tier II would be completed. Similarly, if the MACT floor

equals "no control," the permitting authority should proceed to

the Tier II analysis.

The Act specifically directs EPA to consider the "average

emission limitation" achieved in practice to establish the MACT

floor for existing sources. Section 4.1 of this chapter

discusses calculation procedures for determining an "average

emission limitation". 

Using the calculation procedures discussed in Section 4.1,

this chapter explains four approaches for determining a MACT

floor. If the emissions information is available, the first

three methods should be considered before the permitting

authority concludes that a MACT floor cannot be determined. The

three emissions-based methods include using: (1) existing State

and local air toxic control regulations; (2) control efficiency

ratings; or (3) emission reduction ratios.
4-2

A fourth method, the technology approach, can be used when

insufficient emissions data are available to determine an average

emissions limitation.

The first method compares air pollution regulations in

different States. The second method is applicable when the

control technologies under consideration can be assigned an

efficiency rating for HAP emission reductions. This is most

likely to occur with add-on control devices. The third method

can be used for add-on control devices, work practices,

recycling, reuse or pollution prevention strategies. Depending

on the format of available information, a hybrid of the three

approaches may be necessary. The fourth method involves

determining which technology is being used by the best performing

sources in the category as defined in sections 112(d)(3)(A) and

(B) and then determining the emissions limit that the technology

is capable of achieving in practice on a continuous basis. Later

in this chapter each of these methods is discussed in greater

detail.

4.1 Calculation of the MACT Floor

Section 112(d) of the Act instructs the EPA to set emission

standards for new sources based on the emissions control achieved

in practice by the best controlled similar source and to set

emission standards for existing sources based on an average
4-3

emission limitation achieved by the best performing 12 percent of

existing sources or best performing five sources in the source

category or subcategory for categories with fewer than

30 sources. For new sources, the direction provided by the Act

is relatively clear. For existing sources, further clarification

is required by the EPA to determine how an average emission

limitation should be computed.

The word "average" can have several different meanings,

including arithmetic mean, median, and mode. As stated

previously, the EPA published a Federal Register notice

describing these methods of determining the average as well as

other common sense considerations at 59 FR 29196 et.seq., June 6,

1994. A copy of this notice is contained in Appendix B of this

document.

The following examples illustrate the average as represented

by the mean, median, and mode.

Example 1

The following emission limitations are representative of the

best performing 12 percent of existing sources:

% reduction

95 Average emission limitation 

95 defined by the mean =

93

93 644/7 = 92% 

92

88
4-4

88

 Total 644 

Number of sources in the best performing 12% = 7

In this case the MACT floor would be 92%.

Under some circumstances the arithmetic mean results in a

number that may not correspond to the application of a specific

control technology. If there is a large discrepancy between the

amount of emission reductions that can be achieved by available

control options, other factors should be considered to determine

the MACT floor. This is illustrated with the following example:

Example 2

An arithmetic mean is computed for the best performing

12 percent of storage tanks. There are 10 sources among the

best performing 12 percent of storage tanks. Two tanks are

controlled at 99 percent, and the remaining 8 tanks are not

controlled. The emissions limitations considered in the

floor calculation are:

% reduction

99

99 average emission limitation = 

 0

 0 19.8% reduction

 0

 0

 0

 0

 0

 0
4-5

 Total 198

Number of sources in top 12% = 10 

In this example, no technology corresponds to 19.8-percent

control, and it might be inappropriate to elevate the MACT floor

to 99-percent control.

If there is a large discrepancy between the amount of

emission reductions that can be achieved by available control

options, the median should be used in lieu of the arithmetic mean

to determine the average emission limitation equal to the MACT

floor. A median is the value that falls in the middle of a set

of numbers when those numbers are arranged in an increasing order

of magnitude; in other words, there will be an equal number of

values above and below the median. If the middle falls between

two values, the median is equal to the arithmetic mean of those

two numbers. This situation will occur when there is an even

number of values in the set of numbers. In this example, the

median would be 0-percent reduction, and this could be selected

as the MACT floor. 

 However, if there is a large discrepancy between the control

technologies used to establish a median such that no technology

could realistically obtain a reduction close to the median, the

mode should be used to calculate the MACT floor. A mode is the

most frequent occurrence among a set of data. In Example 1,
4-6

there are two modes, 95-percent and 88-percent emission

reductions. In Example 2, the mode would be equal to 0-percent

emission reduction. When there is more than one mode in the data

set, the MACT floor should be based on the least degree of

emission control. However, the existence of more than one mode

may be an indicator that the MACT should be established at a

level of control more stringent than the MACT floor.

The mode may also be used as a method to compute an average

emission limitation if the emissions data for a source category

or subcategory are not numerically based. This situation could

occur if sources were regulated by several different equipment or

work practice standards. Unless a specific level of emission

reduction can be associated with each different standard or

unless the standards can be ranked in some order of increasing

level of control, an arithmetic mean and median cannot be

calculated. A mode could be used if one of the control options

is used more frequently by the best performing 12 percent of

existing sources. For example:

Example 3

There are 44 tanks in the source category or subcategory. 

Five sources are among the best performing 12 percent of

existing sources. These five tanks are subject to the

following regulations in the source category or subcategory:
4-7

3 of the 5 must be covered and vented to a carbon

canister;

2 of the 5 must use a fixed roof.

The mode would be to cover and vent the tank to a carbon

canister.

4.2 Method 1 - Computing the MACT Floor Using Existing State and

Local Regulations

The steps for computing a MACT floor using this method are

as follows:

Step A: Conduct a geographical survey.

Determine the total number of existing similar emission

units in the source category or subcategory, and conduct a survey

to determine the geographical location of these similar emission

units. Group the emission units according to the State or

locality in which they are located.

Step B: Review State or local air pollution regulations.

Review the different State or local air pollution control

regulations that are applicable to the emission unit in each

State or locality where an emission unit is located.

Step C: Rank the State or local air pollution regulations.

For the State and local regulations identified in Step B, 

rank the regulations in order of stringency. The regulations
4-8

that require the greatest level of control should be listed

first.

Step D: Rank emission units.

Determine the total number of emission units and the number

of emission units complying with each stringency level. Based on

the level of regulation stringency, rank the emission units in

order from most stringent to least stringent.

Step E: Make a MACT floor finding.

Based on the distribution of sources in the various States

and the stringency of the respective State requirements, it may

be possible to construct a database that would support a MACT

floor determination as described in Section 4.1. Note that a

determination must also be made that sources in the States

actually achieve the required control levels.

4.3 Method 2 - Computing the MACT Floor Using Control Efficiency

Ratings

To use this method to calculate the MACT floor, the

permitting authority will evaluate emission units that use add-on

control devices or other methods whose HAP control efficiencies

have been clearly demonstrated in practice. The MACT floor and

MACT emission limitation can be computed as follows:

Step A: Determine HAP emission reduction efficiency for each

control device.
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For each emission unit in the source category or

subcategory, the ability of each control technology to reduce HAP

emissions should be determined as a percentage of reduction

efficiency. Acceptable methods for determining the efficiency

rating are:

(1) Federal and State enforceable permits limits on

operation of the control technology, where compliance

has been demonstrated;

(2) Actual reported efficiencies.

 In addition vendor data of demonstrated performance achieved

in similar service may be used in conjunction with good

engineering judgement.

Step B: Calculate the MACT floor using the methodology in

Section 4.1.

4.4 Method 3 - Computing the MACT Floor Using Emissions

Reduction Ratios

The emission reduction ratio is a fraction of uncontrolled

emissions to controlled emissions. The MACT floor is computed

using the emission reduction ratios. To compute the emission

reduction ratio for each emission unit, the permitting authority

must review emissions data or other information to determine

uncontrolled and controlled emissions levels for these units. 

The step-by-step process is detailed below.
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Step A: Compute an uncontrolled emission level for each emission

unit.

The uncontrolled emission level for an emission unit is the

maximum amount of HAP that could be emitted from the emission

unit using current design specifications at full capacity

utilization in the absence of controls.

Step B: Compute a controlled emission level for each emission

unit.

The controlled emission level is the maximum amount of HAP

that could be emitted from the emission unit under the source's

current design specification and at full capacity utilization

taking into consideration the application of federally

enforceable controls. Ideally, a controlled emission level

should be computed for all emission units, even when a single

uncontrolled emission level is used. However, if only general

information is known about the types of control technologies that

are being used in practice, a controlled emission level could be

estimated for each control scenario. Then a controlled emission

level for each emission unit would be assigned based on the types

of controls that major sources use. Readers should review

Chapter 5 for more information on controlled emission levels.

Step C: Compute the emission reduction ratio for each emission

unit.
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The emission reduction ratio for each emission unit can be

computed using the following formula:

Uncontrolled Emission Limit - Controlled Emission Limit

Uncontrolled Emission Limit 

Step D: Determine the MACT floor using the methodology in

Section 4.1.
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4.5 Technology Approach

The technology approach is used when insufficient emissions

data are available to determine an average emission limitation. 

Under this approach, EPA determines which technology is being

used by the average of the best performing 12 percent of sources

in the category, and then determines the average emission limit

that this technology is capable of achieving in practice on a

continuous basis. Available emissions data are used to assign a

performance value for each emission control identified (percent

removal, outlet grain loading, etc.). The MACT floor calculation

is performed based on these performance values. Typically, a

median is used rather than the arithmetic average since an

arithmetic average generally would not correspond to any given

control. The following example illustrates this approach.

A source category emitting metal HAP is comprised of 500

sources. A survey of the sources finds that 300 facilities use

cyclones to control HAP emissions, 150 facilities use wet

scrubbers, and 50 facilities use fabric filters. Based on

available emissions data, it is determined that cyclones are 25-

percent efficient at removing HAP emissions, wet scrubbers are

75-percent efficient, and fabric filters are 99-percent

efficient. The best controlled 12-percent of sources would

include 10 sources with wet scrubbers and 50 sources with fabric

filters. The median corresponds to fabric filters. Therefore,
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fabric filters would be identified as the MACT floor technology,

and an emission limitation would be set based on the available

performance data for fabric filters.

4.6 Other Methods to Compute the MACT Floor

As future MACT standards are proposed or promulgated for

different source categories, more methods for determining the

MACT floor could be developed. The reader is referred to the

June 6, 1994 (59 FR 29196 et.seq.) in Appendix B and other

Federal Register notices to locate any other methods for

calculating the MACT floor that have been approved by the EPA and

used in developing a MACT standard under Section 112(d) or 112(h)

of the Act.
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Chapter 5.0

The MACT Emission Limitation and Permit Conditions

5.1 MACT Emission Limitation

The MACT emission limitation established by the permitting

authority is based on the level of emission reductions that can

be obtained by the affected source when MACT is applied and

properly operated and maintained. The MACT emission limitation

should be based on an overall reduction of all HAP emissions. 

The MACT emission limitation may need to account for differing

kinds of equipment within the affected source and may include

emission averaging provisions to allow such equipment to achieve

MACT in the most cost-effective manner possible. The permitting

authority may establish a MACT emission limitation for an

individual HAP when the risk to human health and the environment

warrants such an emission limitation. If it is not practicable

to establish a specific numerical or efficiency limitation, then

a specific design, process, or control technology should be

designated as the MACT emission limitation. For example, a

floating roof with a primary and secondary seal on a storage

vessel or an equipment leak detection and repair practice could

be determined as MACT.

Determining the expected emission reductions from an add-on

control may require some engineering judgement. In some
5-2

instances, the add-on control may achieve different levels of

reduction efficiency even when it is applied to the same type of

emission unit. Lower efficiency ratings may be due to different

operational parameters or poor maintenance practices. The MACT

emission limitation should be based on the level of control that

the technology is likely to obtain for all emission units

operating under good operational and maintenance practices.

Chapter 4 of this manual describes possible methodologies

for calculating a MACT floor. It is likely that the regulatory

format of the MACT emission limitation will be similar to the

format of the MACT floor. For instance, if the MACT floor is

computed to be a limit of 0.30 lbs/ton of feed, the regulatory

format of the MACT emission limitation is also likely to be

expressed as lbs/ton of feed. The following sections provide

guidance on calculating the MACT emission limitation for a source

category or subcategory. These sections also discuss how a

permitting authority can determine what amount of control an

individual source needs to achieve the required reductions.

When control efficiencies are used to establish a MACT

floor, the MACT emission limitation could be expressed as this

efficiency. In other words, all sources could be required to

reduce emissions by some percent (i.e., 90-percent reduction). 

Additional terms and conditions would be necessary to make this

practically enforceable, but such an emission limitation may be
5-3

appropriate when all emission units are operated relatively

homogeneously within the source category or subcategory. For

other source categories it may be appropriate to convert this

efficiency rating into another format. This can be accomplished

by multiplying the efficiency of MACT by the uncontrolled

emission level of the emission unit as follows: 

 MACT 

Emission = Uncontrolled Emission Level * MACT efficiency 

 Limit 

The uncontrolled emission level for an emission unit is the

maximum amount of HAP that could be emitted from the emission

unit using current design specifications at full capacity

utilization in the absence of controls. It could be computed

using a variety of different formats, i.e. tons/yr, lbs/hr,

lbs/ton, etc. The following sources of information may be

acceptable:

(1) Engineering calculation using material balance or

emission factors;

(2) Actual emission data from similar emission units;

(3) Average annual hourly emission rate multiplied by hours

of operation; 

(4) Emission limits and test data from EPA documents,

including background information documents;
5-4

(5) State emission inventory questionnaires for comparable

sources;

(6) Federal or State enforceable permit limits; or,

(7) For equipment leaks use, "Protocols for Equipment Leak

Emission Estimates," EPA-453/R-93-026.

The selection of the uncontrolled emission level will likely

require some engineering judgement on the part of the permitting

authority. Typical throughputs, flow rates, concentrations, etc.

should be used to estimate a uncontrolled emission level that can

be applied to the source category or subcategory. 

The definition of a control technology includes the use of

pollution prevention and source reduction strategies. The

permitting authority should take into consideration the use of

such control measures when computing the uncontrolled emission

level for an emission unit. For example, some MACT emission

units in the source category or subcategory may use a high VOC

solvent as a process input to the emission unit. Other units may

use a lower VOC solvent as a process input to the same type of

emission unit. No distinction in the type of process inputs have

been made in designating the emission unit. The MACT for this

emission unit is identified as control technology X. If this

control technology was determined to have a control efficiency

rating of 90 percent, then the current design specifications for

each emission unit in the category would require all sources to
5-5

reduce emissions by 90 percent. However, this would not account

for the different baseline emissions from different emission

units in the source category or subcategory. By calculating the

uncontrolled emission level for all emission units in the

category based on the high VOC process input, emission units with

inherently lower potentials to emit can take credit for the

emission reduction in the controlled emissions calculation and

the calculation of additional required control.

5.2 Alternative Ways to Comply

Once the permitting authority determines the MACT emission

limitation, the applicant will determine a control strategy that

allows the affected source to meet MACT. In many cases, this

will be through the application of the MACT technologies. 

However, in some cases, the emission unit at the major source may

already be controlled to some extent with an existing control

technology. The owner or operator could demonstrate that using

additional control strategies in combination with existing

controls will allow the emission unit to achieve the required

emission reductions. For instance, an emission unit may

currently be controlled with a baghouse. The MACT emission

limitation for the emission unit may be based on use of an

electrostatic precipitator. The emission unit may be able to
5-6

meet the MACT emission limitation by installing a series of

baghouses in lieu of the electrostatic precipitator.

Owners or operators are reminded that the application of a

case-by-case MACT to an affected source does not exempt that

owner or operator from complying with any future emission

standards affecting that affected source. The applicability and

impact of subsequently promulgated MACT standards is addressed in

40 CFR 63.56. Owners or operators may wish to consider these

factors when selecting a control technology to meet the MACT

emission limitation.

5.3 Applicable Monitoring, Reporting and Recordkeeping, and

Compliance

The permitting authority should identify monitoring

parameters in consultation with the applicant to assure

compliance with the MACT emission limitation. However, the

permitting authority is ultimately responsible for these

monitoring parameters, as well as reporting and recordkeeping

requirements at permit issuance. Section 2.2 of Chapter 2

discusses compliance provisions in greater detail.
6-1

Chapter 6.0

Costs, Non-Air Health 

and Environmental Impacts,

 and Energy Impacts

Section 112(d) of the Act specifies that if control

technology alternatives are being considered to establish an

emission standard that would result in emission limitations more

stringent than the emission "floors," they must be evaluated by

considering costs, non-air quality health and environmental

impacts, and energy requirements associated with the expected

emission reductions.

The costs, non-air quality health and environmental impacts,

and energy requirements discussed below are illustrative only and

are not intended as an exclusive list of considerations for MACT

determinations. Some of these factors may not be appropriate in

all cases, while in other instances, factors which are not

included here may be relevant to the MACT determination. The

discussion does not address the evaluation of each factor nor the

weighing of any factor relative to another. Such determinations

should be made on a case-by-case basis by the owner/operator and

permitting authority. For the purpose of this guidance, terms

such as "emission control system" or "MACT system" refer to

design, equipment, or operating standards and inherently less

polluting processes, as well as add-on control equipment.
6-2

In general, the impact analyses for MACT determinations

should address the direct impacts of alternative control systems. 

Indirect energy or environmental impacts are usually difficult to

assess, but may be considered when such impacts are found to be

significant and quantifiable. Indirect energy impacts include

such impacts as energy to produce raw materials for construction

of control equipment, increased use of imported oil, or increased

fuel use in the utility grid. Indirect environmental impacts

include such considerations as pollution at an off-site

manufacturing facility that produces materials needed to

construct or operate a proposed control system. Indirect impacts

generally will not be considered in the MACT analysis since the

complexity of consumption and production patterns in the economy

makes those impacts difficult to quantify. For example, since

manufacturers purchase capital equipment and supplies from many

suppliers, who in turn purchase goods from other suppliers,

accurate assessment of indirect impacts may not be possible. Raw

materials may be needed to operate control equipment, and

suppliers of these resources may change over time. Similarly, it

is usually not possible to determine specific power stations and

fuel sources that would be used to satisfy demand over the

lifetime of a control device.

In most cases, duplicative analyses are not required in

preparing the MACT impact analyses. Any studies previously
6-3

performed for Environmental Impact Statements, air permits, water

pollution permits, or other programs may be used when

appropriate. The permitting authority also may consider any

special economic or physical constraints that might limit the

application of certain control techniques to an existing emission

unit, such as retro-fitting costs that would not be borne by a

new unit, or the remaining useful life of the emission unit. The

result may be that the level of control required for an existing

emissions unit may not be as stringent as that which would be

required if the same unit were being newly constructed at an

existing plant or at a "greenfield" facility. However, in no

event shall the level of control yield an emission limit less

stringent than the MACT floor when information is available to

compute the MACT floor.

6.1 Cost Impacts

Cost impacts are the costs associated with installing,

operating, and maintaining alternative emission control systems

(add-on emission control devices or process changes.) Normally,

the submittal of very detailed and comprehensive cost data is not

necessary. Presentation of the quantified costs of various

emission control systems (referred to as control costs,) coupled

with quantities of HAP emission reductions associated with each

of the emissions control systems, is usually sufficient.
6-4

Once the control technology alternatives and emission

performance levels have been identified, total capital investment

and total annual cost should be developed. Total capital

investment (purchased equipment plus installation) and total

annual costs of each emission control system should be presented

separately. Total annual costs are comprised of operation and

maintenance costs ("direct annual costs",) administrative charges

("indirect annual costs"), plus overhead, taxes, insurance, and

capital recovery costs minus recovery credits (credit for product

recovery and by-product sales generated from the use of control

systems and other emission reduction credits.) These costs

should be reported in equal end-of-year payments over the time of

the equipment. Total annual costs should be reported on an

overall basis, as well as an incremental basis. The various

emission control systems should be presented or arrayed in terms

of increasing total annual cost. The incremental annual cost of

a particular emission control system is the difference in its

cost and the cost of the next less stringent control.

A method for determining the acceptability of control costs

is the comparison of the cost effectiveness of alternative

control systems. Average cost effectiveness is the ratio of

total annual costs (calculated using the above guidelines) to the

total amount (tons or Mg) of HAP removed. Incremental cost

effectiveness is calculated using the same procedure as outlined
6-5

for calculating incremental annual cost. Generally, costeffectiveness values falling within the range of previously

acceptable MACT decisions are considered acceptable. Therefore,

consistency with the relative cost, or cost effectiveness, of a

past MACT determination for a similar source is an indication

that such a cost is reasonable for the MACT determination in

question.

For most MACT determinations, a cost analysis focusing on

incremental cost effectiveness of various MACT alternatives is

sufficient. The analysis should include and distinguish the

various components used to calculate the incremental cost

effectiveness of the control alternatives (i.e., lifetime of the

equipment, total annual costs, tons of total HAP removed, etc.).

If there is reason to believe that the control costs place a

significant burden on the entity being controlled, then the cost

analysis should include financial or economic data that provide

an indication of the affordability of a control relative to the

source. For example, if the per unit cost is a significant

portion of the unit price of a product or if the economic status

of the industry is declining, then the cost analysis should

present the relevant economic or financial data. Financial or

economic data should include parameters such as after-tax income

or total liabilities. 
6-6

6.2 Environmental Impacts

The environmental impacts concentrate on collateral

environmental impacts due to control of emissions of the

pollutant in question, such as solid or hazardous waste

generation, discharges of polluted water from a control device,

visibility impacts (e.g., visible steam plume), or emissions of

other air pollutants. The permitting authority should identify

any environmental impacts associated with a control alternative

that has the potential to affect the selection or rejection of

that control alternative. Some control technologies may have

potentially significant secondary environmental impacts. 

Scrubber effluent, for example, may affect water quality and land

use, and, similarly, technologies using cooling towers may affect

visibility. Other examples of secondary environmental impacts

could include hazardous waste discharges, such as spent catalysts

or contaminated carbon. Generally, these types of environmental

concerns become important when sensitive site-specific receptors

exist or when the incremental emissions reduction potential of

one control option is only marginally greater than the next most

effective option.

The procedure for conducting an analysis of environmental

impacts should be made based on a consideration of site-specific

circumstances. In general, the analysis of environmental impacts

starts with the identification and quantification of the solid,
6-7

liquid, and gaseous discharges from the control device or devices

under review. Initially, a qualitative or semi-quantitative

screening can be performed to narrow the analysis to discharges

with potential for causing adverse environmental effects. Next,

the mass and composition of any such discharges should be

assessed and quantified to the extent possible, based on readily

available information. As previously mentioned, the analysis

need only address those control alternatives with any

environmental impacts that have the potential to affect the

selection or rejection of a control alternative. Pertinent

information about the public or environmental consequences of

releasing these materials should also be assembled. Thus, the

relative environmental impacts (both positive and negative) of

the various alternatives can be compared with each other. 

Also the generation or reduction of toxic and hazardous

emissions other than those for which the MACT determination is

being made and compounds not regulated under the Clean Air Act

are considered part of the environmental impacts analysis. A

permitting authority should take into account the ability of a

given control alternative for regulated pollutants to affect

emissions of pollutants not subject to regulation under the Clean

Air Act in making MACT decisions. Consequently, the ability of a

given control alternative to control toxic or hazardous air
6-8

contaminants other than those for which the MACT determination is

being made, should be considered in the MACT analysis.

6.3 Energy Impacts

Energy impacts should address energy use in terms of

penalties or benefits associated with a control system and the

direct effects of such energy use on the facility. A source may,

for example, benefit from the combustion of a concentrated gas

stream rich in volatile organic compounds; on the other hand,

extra fuel or electricity is frequently required to power a

control device or incinerate a dilute gas stream. If such

benefits or penalties exist, they should be quantified to the 

extent possible.

In quantifying energy impacts, the direct energy impacts of

the control alternative in units of energy consumption at the

source (e.g., Btu, Kwh, barrels of oil, tons of coal) should be

estimated. The energy requirements of the control options could

be shown in terms of total and/or incremental energy costs per

ton of pollutant removed. In many cases, because energy

penalties or benefits can usually be quantified in terms of

additional cost or income to the source, the energy impacts

analysis can be converted into dollar costs and, where

appropriate, be factored into the cost analysis.
6-9

Indirect energy impacts (such as energy to produce raw

materials for construction of control equipment) are usually not

considered. However, if the reviewing agency determines, either

independently or based on a showing by the applicant, that an

indirect energy impact is unusual or significant, the indirect

impact may be considered. The energy impact should still,

however, relate to the application of the control alternative and

not to a concern over energy impacts associated with the project

in general.

The energy impact analysis may also address the concern over

the use of locally scarce fuels. The designation of a scarce

fuel may vary from region to region, but in general a scarce fuel

is one which is in short supply locally and can be better used

for alternative purposes, or one which may not be reasonably

available to the source either at the present time or in the near

future.
7-1

Chapter 7.0

Sources of Information

There are currently several programs under development to

house and disseminate toxics information. Some of these programs

are designed for specific, narrow purposes, while others are

employed in a broader range of uses. Most data collection

programs are designed to be compatible with the Aerometric

Information Retrieval System (AIRS)/AIRS Facility Subsystem

(AFS).

The purpose of this chapter is to present various sources of

toxics information which may be of assistance to States and

industry in making MACT floor determinations. These sources of

toxic information are available in a database format. The EPA

believes the requirements of Section 112(j) can be less

burdensome to both industry and States by employing a database

system to document similar-category sources and provide a

bibliography of information to make a sound MACT floor

determination. The MACT floor determinations and MACT must be

based on data demonstrating performance levels actually achieved

in practice by sources. Performance claims, expectations, design

plans, etc. should be substantiated by methods representative of

those that sources will have to comply with.
7-2

Another significant resource to aid permitting authorities

in developing case-by-case MACT will be proposed regulations for

the subject source categories, or closely related regulations in

similar industries. Proposed regulations will contain what EPA

believes MACT is at the time of proposal. Although permitting

authorities are not required to adopt proposed MACT, and the

proposed rule should not be considered a default MACT, it can

still serve as a suggestion for what the latest thinking is and

would be the result of analysis of the largest body of

information.

In addition to the following sources of information, the EPA

home page on the World Wide Web includes a wealth of information,

including some of the data bases described below. The reader may

wish to consult the following websites for additional

information:

1. EPA: http://www.epa.gov/epahome/index.html

2. Office of Air and Radiation:

http://www.epa.gov/oar/oarhome.html

3. Office of Air Quality Planning and Standards:

http://www.epa.gov/oar/oaqps

4. Air Toxics Website: http://www.epa.gov/ttn/atw/

AEROMETRIC INFORMATION RETRIEVAL SYSTEM (AIRS) TOXICS PROGRAM
7-3

The AIRS is designed to accommodate the expansion of

emissions data. The AIRS/AFS is a National Data System currently

residing on the National Computer Center (NCC). The stationary

source component of this system replaced the old National

Emission Data System (NEDS) as the data repository for point

source data (e.g., electric utilities, industrial plants and

commercial enterprises). The AIRS/AFS system is expected to

eventually provide the capabilities needed to house information

from the Title V operating permits program.

Many States input their data directly into the AIRS and

perform calculations and retrievals. When a converter (an

interface between AIRS and the State system) is used, the data

can be input directly to the State system and to the appropriate

fields in AIRS in a single step. Data can also be retrieved from

AIRS directly, or into the State format using a converter.

Because many data sources are fed into AIRS/AFS, some of

this data may be useful for case-by-case MACT determinations and

MACT standards. This advantage is expected to become more

visible as the search for the 12-percent floor for a source

category or subcategory becomes a common occurrence.

INFORMATION COLLECTION REQUESTS (ICR) DATA

For the national MACT standards program, the EPA is

currently involved in data collection activities for many of the
7-4

source categories on the list. These data collection activities

are designed to help answer, for a given category, a number of

important questions:

-- What are the sources of emissions for the category?

-- Which HAPs are emitted and at what rates?

-- What alternatives are available to reduce those

emissions?

-- What costs would be imposed for the control

alternatives, and what economic impacts would the

alternatives have on the business climate for the

industry?

-- Which alternatives meet or exceed the "MACT floor" (for

new sources, the "best controlled similar source;" for

existing sources, the level achievable by the "average

of the best performing 12 percent" of sources in the

category)?

-- Given the alternatives available, which alternative

represents the "maximum degree of reduction

achievable," taking into account costs, benefits, and

the constraints imposed by the "MACT floor?"

RACT/BACT/LAER CLEARINGHOUSE (RBLC)

The RBLC maintains a database consisting of 3,600 (and

growing) Reasonably Available Control Technology (RACT), Best

Available Control Technology (BACT), and Lowest Achievable

Emission Rate (LAER) determinations made by State and local

agencies for specific sources, as required by the Act. The RACT

determinations address emission requirements for existing sources

located in nonattainment areas. The BACT and LAER address

emission requirements for major new or modified sources located
7-5

in attainment and nonattainment areas, respectively. Database

parameters include: facility information; process description;

pollutant information (including emission limit); pollution

prevention and/or control technology method; compliance

verification information; and cost information (if it exists). 

The Act requires agencies to submit LAER determinations to the

RBLC. The RACT and BACT determinations are submitted on a

voluntary basis.

The RBLC also maintains a regulation database that

summarizes Federal new source performance standards (NSPS),

national emission standards for hazardous air pollutants

(NESHAP), and maximum achievable control technology (MACT)

standards. The regulation database parameters are similar to

those in the RACT/BACT/LAER database, but also include Federal

Register and regulation background documentation information.

The RBLC can be accessed through the Office of Air Quality

Planning and Standards (OAQPS) Technology Transfer Network (TTN)

electronic bulletin board system. For more information, access

the RBLC on the TTN or contact the EPA Information Transfer Group

at (919) 541-5547.
7-6

GREAT WATERS PROGRAM

In order to provide information needed for decision making,

the Great Waters program is evaluating HAPs emission data,

especially for the Great Lakes region. (Section 112(c)(6)

requires national emission inventories for alkylated lead;

polycyclic organic matter; hexachlorobenzene; mercury; PCBs;

2,3,7,8-tetrachlorodibenzofurans; and 2,3,7,8-tetrachlorodibenzop-dioxin.) Periodic reports to Congress are required to provide

information on: relative pollutant loading contributed to

aquatic ecosystems from the atmosphere; adverse effects of that

loading on human health and the environment; whether the

atmospheric deposition causes or contributes to violations of

water quality standards or criteria; and sources of the

atmospherically deposited pollutants. The goal of the program is

to determine if additional regulation is warranted, and if so,

what it should entail. For additional information on the Great

Waters Program, or for referral to related emission inventory

efforts, call the EPA Visibility and Ecosystem Protection Group

at 919-541-5531.

AIR TOXIC EMISSION FACTORS

Emission factors are used in lieu of emission estimates

based upon source testing, and they can be used to estimate the

emissions of a particular HAP per unit process rate (i.e., pounds
7-7

of nickel emitted for each ton of nickel ore processed). These

emission factors can be based on controlled and uncontrolled

processes, and can, therefore, be used to help determine which

control measures are best suited to a particular process. The

EPA has developed screening methods for the development of air

toxics emission factors, and applies the screening methods to

test results as they become available for use.

The toxic emission factors available through the Factor

Information Retrieval System (FIRE) and the EPA document,

Compilation of Air Pollution Emission Factors (AP-42) are rated A

(most reliable, based on several tests meeting high confidence

criteria) through E (least reliable, having limited available

information). Toxic emission factors are being developed for

about 170 the 189 HAPs on the Section 112(b) list, representing

many (but not all) processes in Section 112 source categories.

About 40 of the HAPs in FIRE have been targeted as

"critical" pollutants because they are found in a wide variety of

industries, and/or are especially toxic. Many of the emission

factors for this critical group have a rating of A or B, enabling

users to arrive at the most accurate emissions estimates

presently possible. For more information on FIRE, contact 

INFOCHIEF at 919-541-5285.

STATE AIR OFFICE DATABASES
7-8

Emission Standards Division (ESD) staff have worked with

STAPPA/ALAPCO to better characterize the toxics information

available in database form and hard copy within the State air

offices.

Most States have compiled pollutant information in some form

in response to State Implementation Plan (SIP) requirements. 

Many States also have toxics information collection systems, as

well as State requirements for toxics programs. Most States find

that although internally their system is widely used (intra-State

system), to down load or upload data on an inter-State basis is

nearly impossible (with the primary exception to this being

States within a transport region, and then usually under limited

circumstances). 

TRADE JOURNALS AND VENDOR INFORMATION

Caution should be taken when employing information in trade

journals and from vendors, especially in noting the method of

emissions estimation, number of tests that were used in

developing estimates, and the conditions under which tests were

conducted. Other factors that may affect the emissions estimates

should also be identified, and the effects of their differences

quantified as accurately as possible. Because results applicable

to only one or a small group of facilities cannot be completely

accurate for other facilities, this source of information is not
7-9

regarded as highly accurate, but may provide some useful

information on control alternatives.

Other sources of information that may be consulted in making

MACT floor determinations are listed below. This list is not

inclusive, but may provide useful information.

Air Pollution Training Institute (APTI). December 1983. 

Overview of PSD Regulations. EPA 450/2-82-008.

Air Pollution Training Institute (APTI). June 1983. Air

Pollution Control Systems for Selected Industries. 

EPA 450/2-82-006.

Environmental Protection Agency (EPA). May 1992. Facility

Pollution Prevention Guide. EPA 600/R-92/088.

Environmental Protection Agency (EPA). February 1992. 

Documentation for Developing the Initial Source category or

subcategory List. EPA 450/3-91-030.

Environmental Protection Agency (EPA). June 1991. 

Hazardous Waste TSDF - Background Information for Proposed

RCRA Air Emission Standards. EPA 450/3-89-023 (a) and (c).

Environmental Protection Agency (EPA). October, 1990. New

Source Review Workshop Manual. EPA, Research Triangle Park,

NC (Draft Document).

Environmental Protection Agency (EPA), January 1990. OAQPS

Control Cost Manual. EPA 450/3-90-006.

Environmental Protection Agency (EPA). June 1991. Control

Technologies for Hazardous Air Pollutants. 

EPA 625/6-91/014.
7-10

Air & Waste Management Association. 1992. Air Pollution

Engineering Manual. Van Norstrand Reinhold.
A-1

Appendix A

Examples of MACT Analyses

The following detailed examples presented in this manual are

for illustrative purposes only. Numbers and values presented in

this Appendix do not necessarily reflect any known cases and are

not meant to establish any official EPA position regarding MACT

determinations for a particular MACT-affected source. These

examples are hypothetical and are designed to highlight many of

the subtle aspects of the MACT determination process. In many

cases, the scenarios and available control technologies have been

grossly oversimplified to streamline the presentation of the

examples.

The following examples are presented in this Appendix:

Example 1 - Determining the MACT Emission Unit

Example 2 - Using Control Efficiency Ratings to Determine

 the MACT Floor

Example 3 - When the MACT Floor is Determined Using Emission

 Reduction Ratios

Example 4 - When the MACT Floor is Equal to "No Control"
A-2

Example 1

Determining the MACT Emission Unit

This example illustrates possible grouping mechanisms and

rationale for developing one or more MACT emission units at a

given facility subject to a MACT determination under

Section 112(j).

Description of Source

In this example, a metal furniture manufacturer produces

military-specification office furniture for use in military

barracks. The plant currently operates 2,080 hr/yr and produces

12,000 units of furniture annually. The facility is considered a

major source of HAP emissions.

Existing unit operations include:

1) Wood Processing

Raw wood and formica are glued together to form a laminate. 

The glue is applied using an automatic application system. 

Several laminates are then positioned in a press for glue curing. 

Next, the boards undergo various woodworking operations

including, cutting, drilling, and routing. Boards are either

transferred to assembly or directly packaged and shipped. 

Tetrachloroethylene is a component of the glue. Glue stations

are vented to emission stacks on the ceiling. The stacks are

currently uncontrolled. 
A-3

The glue is stored in 50 gallon drums. Glue is transferred

to the application equipment through a pumping mechanism. 

Estimated yearly emissions of HAP from this operation is

0.50 tpy.

2) Metal Processing

Metal stock is cleaned by immersion in a toluene dip tank. 

A toluene, grease, and dirt sludge is produced, which is pumped

from the bottom of the tank for disposal. After cleaning, the

metal undergoes various metalworking operations including

cutting, punching, folding, and welding. Pieces are partially

assembled, then transferred to one of two paint coating

operations. The dip tank is currently controlled with a

condensing unit and a freeboard ratio of 0.75. Yearly controlled

emissions are estimated at 19 tons/yr. Uncontrolled emissions

are estimated at 55 tpy.

3) Cleaning Operations

The spray coating operations begin with a five-stage

cleaning process. The first stage is an alkaline-wash tank. 

Next, parts are sprayed with an iron phosphate solution. The

fourth stage is a rinse tank. Finally, parts are sprayed with a

rust preventive. After cleaning, the parts are conveyed to a

dry-off oven and then to the paint coating line. No HAP

emissions occur during this part of the operation.

4) Painting Operations
A-4

There are currently four spray booths in the paint coating

operation and one coating dip-tank. Large metal parts are coated

using the spray booths. A one-color coating is applied at a

coating depth of 1 ml. Two of the booths are equipped with

continuously recirculating water curtains to entrap paint

overspray. Entrapped paint solids and wastewater are dumped to a

holding tank periodically. Air filters are used in the two

remaining spray booths. The air filters are periodically

replaced. The used filters are placed in storage drums for later

disposal.

All spray booths are equipped with hand-held spray guns. 

Transfer efficiency is estimated at 45 percent for both types of

booths. The paint is a high solvent paint containing xylene and

toluene with an estimated 35-percent solids content and

65-percent solvent content. The spray guns are periodically

sparged and rinsed with acetone to prevent clogging. The acetone

paint mixture is sent to storage tanks for later disposal. 

Emissions from the booths are currently vented to the roof with

no control device.

After painting, parts are conveyed through a flash-off area

to one of two dry-off ovens and then to assembly. Small metal

parts are dip-painted in the coating dip-tank, allowed to air

dry, and then transferred to the assembly area.
A-5

Total annual HAP emissions from this area are estimated at

55 tpy. Each spray booth contributes 8 tpy and each drying oven

4 tpy. Estimated emissions from the coating dip-tank are 15 tpy. 

No emission estimates are available for the flash-off area.

From this description, the following emission points are

identified as potentially "affected emission points" by the

Section 112(j) MACT determination process:

! Glue storage drums

! Glue stations (stack emissions)

--Application equipment

--Curing presses

! Toluene dip tank*

! Toluene storage tanks*

! Toluene/sludge waste storage tanks*

! Spray booths (stack emissions)

-- Feed and waste lines

-- Application equipment

! Coating dip-tank

! Flash-off area (large parts)

! Drying area (small parts)

! Paint storage tanks

! Solvent storage vessels

! Paint sludge storage tanks

! Drying ovens (stack emissions)

! Air filter storage drums

* These units would be eliminated from any MACT emission

unit because the emission points would be part of the

degreasing source category or subcategory, not the

miscellaneous metal parts surface coating source category or

subcategory.

Possible MACT emission unit scenarios:

Scenario #1: Five MACT emission units:

! Wood processing 

! Spray coating operations
A-6

! Storage tanks

! Storage drums

! Equipment leaks

This scenario could make sense if a MACT floor could be

identified or control technologies could be applied to the

emission units. In wood processing, the emissions are vented to

a stack on the roof. These emissions could be controlled with a

variety of add-on control devices. The source could also

consider switching to a glue that has a lower concentration of a

HAP or does not contain any HAPs.

In the spray operations, the source could switch to a lowsolvent paint or water-based paint. This control option would

need to be weighed against controlling the individual emission

points. Other control options to consider would be an add-on

control device to control the stack emissions from the spray

booth and oven, increasing the transfer efficiency of the spray

application equipment, and controlling the drying, flash-off

areas, and the coating dip-tank with separate control

technologies.

Controlling the storage tanks as one emission unit may allow

flexibility in meeting MACT. Some tanks could remain under

controlled while others could be over-controlled. This option

would need to be weighed against the cost effectiveness and

emission reductions of applying controls to all of the storage
A-7

tanks. The storage drums could be placed in a contained area and

the emissions vented to one control device.

Equipment leaks are not suitable for combination with other

emission units because they are only controllable using work

practice and other unquantifiable emissions reductions

procedures.

Scenario #2: Four MACT-affected emission units:

! Stack emissions (spray booths, glue stations, drying

ovens)

! Storage tanks and drums

! Coating dip-tank

! Equipment leaks

In this scenario, the stack emissions from the spray booths,

glue stations and drying oven could all be vented to a single

control device. This option would need to be weighed against the

emission reductions that could be obtained by applying pollution

prevention strategies to the individual operations. If the

storage tanks and drums are stored in a common location, such

that the emissions from the area could be vented to a control

device, this emission point aggregation could make sense. The

emission reduction would need to be weighed against controlling

the emission points separately. If greater emission reductions

could be obtained by controlling these points separately, this

aggregation of points may not be acceptable.

Scenario #3: Seven MACT emission units:

! Each storage tank

! Each spray booth
A-8

! Stack emissions from glue stations and drying ovens

! Equipment leaks

! Each storage tank 

! Each storage drum

! Coating dip-tank

If detailed data are available for each of these individual

emissions units, then one approach would be to compile that data

and develop a MACT floor data base for each type of emission

unit. This scenario would generally be acceptable unless a

pollution prevention method could be applied to one of the

processes that could obtain a greater degree of emission

reductions then point-by-point compliance.

Scenario #4: All emission points.

This scenario would generally be unacceptable because, as

described in Scenario #1, equipment leak emissions should not be

included in a source category- or subcategory-wide emission unit.

Scenario #5: Two MACT emission units:

! Equipment leaks

! Remaining emission points

This aggregation of emission units could be acceptable if

emissions information were available on HAP emissions or control

technologies from the source category or subcategory as a whole,

or if the nature of the industry demanded a large degree of

flexibility in the application of MACT.
A-9

Example 2

Using Control Efficiency Ratings

to Determine the MACT Floor

Description of Source

In this example, a MACT determination is to be conducted on

a quenching process at a coke-by product plant. Hazardous

emissions can be released when the hot coke in the quench car is

sprayed with water to decrease the coke's temperature. Phenol

and naphthalene emissions can occur in the gaseous state. Other

pollutants can sorb to particulate matter and be collectively

released. The permitting authority will need to conduct a MACT

analysis to determine the MACT emission limitation based on the

emission reduction that can be achieved by MACT. The permitting

authority will begin with the Tier I analysis.

Step 1: Identify the MACT emission unit(s)

MACT unit: quenching tower and coke car # of existing

sources: 36

The equipment used in this production process includes the

quenching tower, coke car, water delivery system, and water

storage system. The permitting authority decides that emission

points from the quenching tower and coke car should be considered

one MACT emission unit, and the water delivery system and water
A-10

storage system as another MACT emission unit. The example will

be continued for only the quench tower/coke car emission unit.

Step 2: Make a MACT Floor Finding

Technology # of plants using

Emission

control

efficiency, %

1) Use clean water

to quench coke

with baffles at

the top of the

quench tower

10 not

quantifiable

2) Use covered

quenched car. 

Cool outside of

car. Water does

not impact coke. 

Place car on

cooling rack

after quenching

for additional

heat dissipation

1 almost 100%

3) Wet scrubber,

connected to

fixed duct system

10 80-90%

4) Wet scrubber,

mobile unit

attached to coke

quench car

14 80-90%

5) Dry quenching

with inert gases.

Heat transported

to waste-heat

boiler

1 99-100%

The permitting authority decides to use the control

efficiency ratings to determine the MACT floor. There are a
A-11

total of 36 existing sources. The MACT floor would be equivalent

to the arithmetic mean of the control efficiency ratings for the

best five sources. If a specific control efficiency rating is

not available for the best performing five sources, a median or

mode could be used to calculate the MACT floor. Using the

information provided, the median of the best performing

12 percent of sources would be equal to 80-90 percent or control

technology 3 or 4. The mode would be technology number 4.

Step 3: Identify MACT 

Technologies 2, 3, 4, or 5 could be chosen as MACT. 

Technology 1 could also be considered because its control

efficiency is not quantifiable. If technology 1 is to be

considered further, a more detailed analysis would be required to

prove that the technology could obtain an equal or greater amount

of emission reductions. In this case, the efficiency of

technology 1 will vary by the concentration of hazardous

constituents. Using clean water could result in a less toxic

release when the concentration of toxins in the hot coke are

less, but increased emissions could result with increased

concentrations. The other proposed technologies would operate at

a relatively constant efficiency rate, regardless of the

pollutant concentration. Therefore, technology 1 would be

considered inferior to the other technologies and should be

eliminated as a potential candidate.
A-12

The permitting authority should identify MACT based on the

control technology that achieves a maximum degree of emission

reduction with consideration of the costs, non-air quality health

and environmental impacts and energy requirements associated with

use of each control technology. After identifying MACT, the

permitting authority would proceed to Tier III of the analysis.
A-13

Example 3

When the MACT floor is Determined 

Using Emission Reduction Ratios

Description of Source

 A surface coating operation treats a product with its

existing equipment consisting of a dip-tank priming stage

followed by a two-step spray application and bake-on enamel

finish coat. The product is a specialized electronics component

(resistor) with strict resistance property specifications that

restrict the types of coatings that may be employed. 

Step 1: Identify the MACT emission unit(s)

MACT emission units:

! Dip-tank

! Feed and waste lines in prime coating operation

! Spray coat booth, spray coat application equipment

! Drying oven

! Storage tank in prime coating operation

! Storage tank in finish coating line

! Paint supply system

There are two process units within this source category or

subcategory: the prime coating line and the finish coating line. 

Equipment within the prime coating line that have affected

emission points are a dip-tank, storage containers, feed line to

supply new coating into the dip-tank, and a waste line to drain

the dip-tank. Because the feed line and waste lines have

equipment leak emissions, these emission points should be
*

 The permitting authority should consider whether the process

constraints resulting from production specification or other requirements (see

Step 3) warrant subcategorization within the category for the purpose of MACT

determinations. For the purpose of this example, it is assumed that there

will be no subcategorization.

A-14

combined to form a MACT emission unit. The permitting authority

will consider the dip-tank and each storage container a separate

affected emission unit. Therefore, the three MACT emission units

in this process unit are the dip-tank, the storage container, and

the feed and waste lines. 

The finish coating line consists of two spray booths, spray

application equipment, paint supply system, a storage container,

and a drying oven. The permitting authority decides to combine

affected emission points to form the following MACT emission

units: the spray application equipment and spray booths; the

paint supply system, the storage container, and the drying oven. 

For simplicity of this example, the MACT analysis will be

continued for only the spray application equipment and spray

booths.

Step 2: Make a MACT floor finding

Parts A and B: Compute the Uncontrolled Emissions and 

Controlled Emissions

Table 1 presents an overview analysis of emissions

information for similar emission units within the source category

or subcategory.*

Table 1.
A-15

TECHNOLOGY # OF SOURCES

USING

1) Water-based coat 2

2) Low-VOC solvent/high solids 

coat

4

3) Electrostatic spray application

to enhance transfer efficiency

7

4) Low-VOC solvent/high solids 

coating with electrostatic spray

application

8

5) Powder coat paint with

electrostatic spray application

1

6) High-VOC solvent coating 7

Total: 29

Table 2 presents the detailed analysis of emission

information in this example.

Table 2.

SOURCE TECHNOLOGY

#

UNCONTROLLED

EMISSIONS

(TONS/YR)

CONTROLLED

EMISSIONS

(TONS/YR)

EMISSION

REDUCTION

RATIO

1 6 10 10 0

2 3 26 14 .46

3 2 48 22 .54

4 3 86 56 .35

5 3 98 55 .44

6 6 26 22 .15

7 6 35 34 .03

8 3 78 55 .29
A-16

9 2 69 25 .64

10 2 15 11 .27

11 6 11 11 0

12 6 12 12 0

13 6 23 22 .04

14 3 85 52 .39

15 2 141 89 .39

16 3 25 20 .20

17 4 159 100 .37

18 5 126 11 .91

19 4 35 14 .6

20 3 25 16 .36

21 4 68 22 .70

22 4 46 10 .78

23 1 95 10 .89

24 6 96 16 .83

25 4 64 25 .61

26 4 98 31 .68

27 4 168 45 .73

28 4 196 63 .68

1 255 26 .90

Table 3 presents the top 5 ranked sources.

Table 3.

SOURCE TECHNOLOGY

#

UNCONTROLLED

EMISSIONS

(TONS/YR)

CONTROLLED

EMISSIONS

(TONS/YR)

EMISSION

REDUCTION

RATIO

18 5 126 11 .91

29 1 255 26 .90

23 1 95 10 .89

24 6 96 16 .83

22 4 46 10 .88
A-17

Average of

Top 5 618 73 .88

Part C: Compute the Emission Reduction Ratio for the MACT

Emission Unit

One option is to calculate the MACT floor based on the

average of the emission reduction ratio achieved by the top 5

existing emission units. The top 5 sources are used for this

calculation because there are less than 30 sources in the source

category. In this case, the MACT floor would be equal to the

arithmetic mean of the emission reductions obtained by the top 5

sources in the source category or subcategory, or an 88 percent

emission reduction ratio [1 - (sum of controlled emissions ÷ sum

of uncontrolled emissions)] or the emission reductions that can

be achieved when control technologies 1, 4, or 5 are used at the

top-ranked sources.

Part D: Determine a MACT emission limitation (MEL)

Calculate an uncontrolled emission rate (UCEL) for the MACT

emission unit based on the normal operation of the emission unit. 

Emission reductions obtained through a pollution prevention

strategy would not be included in the UCEL calculation. The

permitting authority calculates the UCEL for this emission unit

to be 125 tons/yr total HAPs. Based on this UCEL, The MEL for

this emission unit would be 

MEL = 125 tons/yr * (1 - 0.88)
A-18

 = 15 tons/yr

The permitting authority would advise the permit applicant

of the MEL and allow the applicant to determine how this level of

emission reductions will be achieved.

Step 3: Select a control technology to meet the MACT Emission

Limitation

In this example, the nature of the product requires a

specific type of coating, and the applicant is unable to use any

of the reviewed technologies to meet the MEL. The owner and

operator will analyze other control technologies that are applied

to control similar emission points. In this example, the similar

emission points have operational losses. Review of control

technologies to control operational losses identifies add-on

control devices such as a carbon absorber, a thermal or catalytic

incinerator, or a condenser. The owner or operator should

conduct a cost, non-air quality health and environmental impacts

and energy requirements analysis on the available control

technologies.

The major source already has a catalytic incinerator on

site. The emissions from the spray application equipment and

spray booth could be channeled to the incinerator. This would

require the installation of a venting system including a pump

mechanism. It would also require an increased volumetric flow
A-19

rate to the incinerator and increase auxiliary fuel requirements. 

The incinerator had been operating at a 90-percent efficiency. 

With an increased volumetric flow rate, the efficiency is

projected to drop to 87-percent efficiency. The owner and

operator must obtain an additional 1-percent emission reductions. 

Possible control technologies include increasing the operating

temperature of the incinerator, or adding electrostatic

application to the spray process to enhance transfer efficiency. 

Limiting the hours of operation at the MACT emission unit could

be considered if the reduced production were part of an overall

source reduction program.

Use of the specialized coating in this operation will

increase the concentration of hazardous pollutants in the water

used for the water curtain. The proposed control technology does

not affect the concentration of pollutants in the wastewater. 

This could be considered a negative environmental impact and may

be reason to consider another control technology to meet the MACT

emission limitation. In this instance, the owner or operator

will not violate the NPDES permit, so the control technology will

not be eliminated from consideration.

The owner or operator uses this step to demonstrate that

despite the increase in volumetric flow rate and the auxiliary

fuel requirement, a significant increase in CO2 emissions does
A-20

not occur. The owner or operator concludes that the impacts

associated with use of this technology are reasonable.

After reviewing the technologies the owner or operator

selects the incinerator with a limit on the hours of operation. 

The owner or operator proposes to start a training program for

spray booth operators to decrease the error and product rejection

rate. By doing this, the owner or operator can reduce the hours

of operation and still meet customer demands for the product. 

This option is chosen over the other two because increasing the

incinerator's operating temperature would require additional

auxiliary fuel input, and enhancing the transfer efficiency with

electrostatic application would be cost prohibitive. The owner

or operator would document that use of the selected control

technologies can reduce emissions to the required level.
A-21

Example 4

When the MACT floor is Equal to "No Control"

Description of Source

A commercial treatment storage and disposal facility

receives off-site wastes from various pesticide manufacturers. A

solvent/aqueous/pesticide mixed waste is passed through a

distillation column where the organic solvents are vaporized and

then condensed into a distillate receiver. The solvent is

transferred using tank cars to a tank farm that is located at

another portion of the plant. The low-grade solvent is then sold

to industrial users. The pesticide-laden wastewater is then

passed through a series of carbon adsorbers where the majority of

pesticide is removed from the water. The water is then

discharged to a Publically Owned Treatment Works (POTW). The

carbon adsorbers are periodically steam stripped to regenerate

the carbon.

Tier I - Step 1: Identify the MACT emission unit(s)

MACT emission units:

! Each storage tank

! Distillation column, condenser, and distillate

receiver

! Three carbon absorbers

! Pumps, feed lines and transfer lines

! Loading racks

The two process units that contain emission points affected

by this modification are the recycling process and the tank farm. 
A-22

The equipment and apparatus associated with the affected emission

points are pumps, feed lines, a distillation column, a condenser,

a distillate receiving tank, three carbon absorber and transfer

lines, and a loading rack. The permitting authority will

consider the three carbon absorbers and the associated emission

points as one emission unit because a single control technology

could be practically designed to cover all three affected

emission points. The permitting authority will also group the

distillation column, distillate receiver and condenser into one

MACT emission unit. The feed lines, pumps, and transfer lines

would have equipment leak emission losses and would be another

affected emission unit. The permitting authority decides to

consider the emission points and equipment for the loading rack

and tanks as separate MACT emission units. If all the tanks were

structurally similar in design one determination could be made

that would be applicable to all the tanks.

Step 2: Make a MACT floor finding

For simplicity of this example, the MACT analysis will only

be continued for a tank emission unit. All the storage tanks

will be structurally similar, so only one MACT determination will

be required. The permitting authority reviews existing data

bases and determines that less than 12 percent of tanks in the

source category or subcategory are controlled. Therefore the
A-23

MACT floor is equal to "no control". This is not automatically

an acceptable "control" measure, therefore Tier II of the MACT

analysis must be completed. In Tier II of the analysis control

technologies for similar emission points from outside the source

category or subcategory will also be considered.

Tier II - Step 1: List all available control technologies

The following technologies have been identified as possible

control technologies that can be applied to a storage tank to

control working and breathing emission losses:

Technology

Emission control

efficiency, %

1) Fixed-roof 93

2) Fixed-roof plus internal floating roof 96

3) Pressure tank 96

4) Fixed-roof vented to a carbon canister 98

5) Fixed-roof vented to a combustion device 99

6) Fixed-roof vented to a carbon absorber 100

Step 2: Eliminate technically infeasible control technologies

All of the available control technologies are technically

feasible.

Step 3: Conduct a non-air quality health, environmental,

economic and energy impacts analysis

The following series of tables illustrate a non-air quality

health, environmental, cost and energy impacts analysis for each

control option.
A-24

Table 1 presents information describing the secondary air

impacts and other resource demands of the various control

technologies that are technically feasible.

Table 2 presents the control options along with their costs

and emission reductions. The average cost effectiveness of each

control option is also presented. The average cost effectiveness

is the ratio of the total annual cost to the total amount of HAP

removed compared to the baseline. Note that the control options

are presented in terms of increasing emission reductions (i.e., 
A-25

Table 1.

CONTROL OPTION

SECONDARY AIR

IMPACTS RESOURCE DEMANDS

1) Fixed roof None None

2) Fixed roof +

 internal roof

None None

3) Pressure tank None None

4) Cover and 

 vented to 

 carbon canister

Emissions if 

carbon regenerated

Disposal of 

container, solvents

for regeneration

5) Cover and vent

 to combustion 

 device

Increased CO, NOx,

SOx, and

particulate

emissions

Fuel source, 

disposal of ash

6) Cover and vent

 to carbon

 absorber

Emissions when 

carbon regenerated

Disposal of spent

carbon, solvents

for regeneration

Table 2.

CONTROL

OPTION

CONTROL

EFFICIENCY

ANNUAL COST

($) 

EMISSION

REDUCTION

(Mg/Yr)

AVERAGE

COST

EFFECTIVENESS

($/Mg)a

1 93 85,000 72 1,181

2 96 113,000 88 1,284

3 96 232,000 88 2,636

4 98 110,000 92 1,196

5 99 136,000 103 1,320

6 100 189,000 117 1,615

a Average cost effectiveness is the annual cost of each control

 option divided by the annual emission reduction of that option

 (e.g., $85,000/yr ÷ 72 Mg/yr = $1,181/Mg).
A-26

control option 1 has the smallest emission reduction, control

option 2 has the second smallest emission reduction, etc.)

Using Table 2, several control options can be eliminated

from further consideration. Control option 3 should be

eliminated because control option 2 achieves the same amount of

HAP reductions, but at a lower cost. Control option 2 should be

eliminated because control option 4 achieves a greater degree of

emission reduction for lower cost. The elimination of control

options 2 and 3 reduces the number of technically feasible and

economically efficient options to four control technologies.

Table 3 presents the incremental cost effectiveness of the

remaining options. The incremental cost effectiveness of control

option 1 is the same as its average cost effectiveness, because

control option 1 is the first incremental option from the

baseline. The incremental cost effectiveness of control option 4

is the ratio of the difference in cost between options 1 and 4 to

the difference in HAP emission reductions between the two ratios.
**"Decisions" based on the cost-effectiveness values provided in this example

are for illustrative purposes only. In real life situations, cost

effectiveness would be evaluated on a case-by-case basis, and the results of

one case would not determine absolute bounds on the circumstances under which

one would select a level of emission reduction beyond the floor.

A-27

Table 3.

CONTROL

OPTION

ANNUAL COST

($)

EMISSION

REDUCTION

(Mg/Yr)

AVERAGE

COST

EFFECTIVENESS

($/Mg)a

INCREMENTAL

COST

EFFECTIVENESS ($/Mg)b

1 85,000 72 1,181 1,181

4 110,000 92 1,196 1,250

5 136,000 103 1,320 2,364

6 189,000 117 1,615 3,786

a Average cost effectiveness calculated as described in Table 2.

b Incremental cost effectiveness is the difference in the annual

 cost between two options divided by the difference in emission

 reductions between the same options (e.g., ($110,000/yr -

 $85,000/yr) ÷ (92 Mg/yr - 72 Mg/yr) = $1,250/Mg).

Tier III - Step 1: Identify MACT

Examination of the cost effectiveness of the remaining

control options can lead to the elimination of other control

options.** Control option 6 is eliminated because the

incremental cost is deemed too high. The incremental cost of

control option 5 is deemed acceptable, but, upon closer

examination, the secondary air and energy impacts make this
A-28

option undesirable. The incremental cost of both options 1 and 4

are deemed acceptable; however, control option 1 is eliminated

because other considerations (secondary air impacts, etc) do not

preclude the selection of control option 4 which achieves a

greater degree of emission reductions.
B-1

Appendix B

Federal Register Notice on Determining an Average Emission

Limitation for Existing Sources, June 6, 1994 (59 FR 29196).
B-2

[Federal Register: June 6, 1994] 

 

ENVIRONMENTAL PROTECTION

AGENCY 

40 CFR Part 63 

[AD-FRL-4892-5] 

National Emission Standards for

Hazardous Air Pollutants for Source

Category: Organic Hazardous Air

Pollutants From the Synthetic Organic

Chemical Manufacturing Industry and

Other Processes Subject to the Negotiated

Regulation for Equipment Leaks;

Determination of MACT ``Floor'' 

AGENCY: Environmental Protection

Agency (EPA). 

ACTION: Final rule. 

-------------------------------------------------

SUMMARY: On December 31, 1992, the

EPA proposed standards to regulate the

emissions of certain organic hazardous air

pollutants from synthetic organic chemical

manufacturing industry (SOCMI) production

processes and seven other processes which

are part of major sources under section 112

of the Clean Air Act as amended in 1990

(the Act). This rulemaking is commonly

called the Hazardous Organic NESHAP or

the HON. In the final action regarding the

December 31, 1992 proposal, which was

signed on February 28, 1994, and published

in the Federal Register on April 22, 1994,

EPA deferred taking final action regarding

provisions applicable to medium storage

vessels due to the need to resolve an issue of

statutory interpretation of section

112(d)(3)(A) of the Act. On March 9, 1994,

EPA reopened the comment period to request

additional comment on the appropriate

interpretation of this statutory provision and

the effect of that interpretation on the

appropriate control requirements for medium

storage vessels at facilities subject to the

HON. 

This action announces EPA's final

decision regarding the interpretation of

Clean Air Act section 112(d)(3)(A) for

purposes of the HON and the final decision

regarding control provisions applicable to

medium storage vessels in SOCMI facilities

subject to the HON. The decision announced

in this action regarding the interpretation of

Clean Air Act section 112(d)(3)(A) for

purposes of the HON will be presumptively

followed in subsequent MACT rulemakings,

but it will not be binding. Although EPA

believes that Congress intended one

interpretation--referred to as the ``Higher

Floor Interpretation''--in Clean Air Act

section 112(d)(3)(A), EPA also believes that

the Agency retains discretion in important

respects in setting Floors for MACT

standards. EPA intends to exercise its

discretion, within the statutory framework, to

promulgate MACT standards that best serve

the public interest.

 

EFFECTIVE DATE: June 6, 1994. 

See Supplementary Information section

concerning judicial review. 

ADDRESSES: Dockets. The following

dockets contain supporting information used

in developing the proposed provisions.

Docket Number A-90-19 contains general

information used to characterize emissions

and control costs for the industry and Docket

A-90-21 contains information on storage

vessels. These dockets are available for

public inspection and copying between 8

a.m. and 4 p.m., Monday through Friday, at

the EPA's Air and Radiation Docket and

Information Center, Waterside Mall, room

M1500, 401 M Street SW., Washington, DC

20460. A reasonable fee may be charged for

copying. 

FOR FURTHER INFORMATION

CONTACT: On technical issues, Dr. Janet S.

Meyer, Standards Development Branch,

Emission Standards Division (MD- 13), U.S.

Environmental Protection Agency, Office of

Air Quality Planning and Standards,

Research Triangle Park, North Carolina

27711, telephone number (919) 541-5254.

For further information on the legal issue

addressed in this notice, contact Michael S.

Winer, Assistant General Counsel, Air and

Radiation Division (2344), Office of General

Counsel, Environmental Protection Agency,

401 M Street SW., Washington, DC 20460,

telephone number (202) 260-7606. 

SUPPLEMENTARY INFORMATION: 

Judicial Review 

Under section 307(b)(1) of the Clean Air

Act (CAA), judicial review of the actions

taken by this document is available only on

the filing of a petition for review in the U.S.

Court of Appeals for the District of

Columbia Circuit within 60 days of today's

publication of this rule. Under section

307(b)(2) of the CAA, the requirements that

are subject to today's document may not be

challenged later in civil or criminal

proceedings brought by EPA to enforce these

requirements. 

Public Comment: Approximately 55

comment letters were received in response to

the March 9, 1994 (59 FR 11018) reopening

of the comment period. The majority of these

letters were from industries or industrial

trade associations, arguing in favor of the

less stringent ``Lower Floor Interpretation.''

Environmental groups, State or local

governments and labor unions argued almost

uniformly in favor of the more stringent

``Higher Floor Interpretation.'' The EPA

considered all public comments in framing

the final policy for MACT floor

determination and in selection of the

requirements for medium storage vessels.

The major issues raised by the comments are

addressed in this preamble. The EPA's

responses to all the comments can be found

in docket A-90-19, Subcategory VI-B.

 

I. Summary of Decision on MACT Floor

Determination 

This section describes EPA's decision

with respect to the interpretation of Clean

Air Act section 112(d)(3)(A) for purposes of

this rulemaking. As set forth in more detail

below, EPA believes that one of the

interpretations of section

112(d)(3)(A)--referred to as the ``Higher

Floor Interpretation''--is the better and more

natural reading of the statutory language. 

A. Background 

Section 112(d)(3) of the Clean Air Act

provides that Emissions standards

promulgated under this subsection for

existing sources * * * shall not be less

stringent * * * than-- 

(A) The average emission limitation

achieved by the best performing 12 percent

of existing sources * * * 42 U.S.C. section

7412(d)(3). Existing sources for which the

Administrator lacks emissions information

and those that have recently achieved LAER

are excluded from consideration. Id. (For

categories or subcategories with fewer than

30 sources, standards may not be less

stringent than ``the average emission

limitation achieved by the best performing 5

sources.'' CAA section 112(d)(3)(B)). The

minimum level of stringency defined by this

language has come to be known as the

MACT Floor. 

In the March 9, 1994 Federal Register,

EPA published a notice soliciting comment

on ``the appropriate interpretation of'' section

112(d)(3)(A). Two interpretations of section

112(d)(3)(A) were discussed. Under the first,

referred to as the ``Higher Floor

Interpretation,'' EPA would look at emission

limitations achieved by each of the best

performing 12 percent of existing sources,

and average those limitations. ``Average''

would be interpreted to mean a measure of

central tendency such as the arithmetic mean

or median. (The arithmetic mean of a set of

measurements is the sum of the

measurements divided by the number of
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measurements in the set. The median is the

value in a set of measurements below and

above which there are an equal number of

values, when the measurements are arranged

in order of magnitude). 

Under the second, ``Lower Floor

Interpretation,'' EPA would look at the

average emission limits achieved by each of

the best performing 12 percent of existing

sources, and take the lowest. This second

interpretation groups the words ``average

emission limitation'' into a single phrase, and

asks what ``average emission limitation''

(accounting for variability over time, or

between different pollutants being emitted

from a facility) is ``achieved by'' all members

of the best performing 12 percent. 

B. EPA's Interpretation of Section

112(d)(3)(A) 

The EPA believes that the ``Higher

Floor Interpretation'' is a better reading of

Clean Air Act section 112(d)(3)(A) than the

``Lower Floor Interpretation.'' This

conclusion is based on a review of the

statute, legislative history and comments

received in response to EPA's March 9

notice. 1. The Statutory Language Section

112(d)(3)(A) requires that standards be no

less stringent than ``* * * the average

emission limitation achieved by the best

performing 12 percent of existing sources * *

*''. The EPA believes that the most natural

and straightforward reading of this language

would have EPA first determine the emission

limitations achieved by sources within the

best performing 12 percent, and then average

those limitations. This is the method

described above as the ``Higher Floor

Interpretation.'' 

The EPA believes that if Congress had

intended the Lower Floor Interpretation,

language other than that actually used in

section 112(d)(3)(A) would have been far

more natural. For example, Congress could

easily have expressed the Lower Floor

Interpretation by requiring standards to be no

less stringent than ``the emission limitation

achieved by all sources within the best

performing 12 percent.'' Similarly, Congress

could have required standards to be no less

stringent than ``the average emission

limitation achieved by the worst performing

member of the best performing 12 percent,''

or ``the emission limitation (averaged over

time to take account of variability in the

effectiveness of control) achieved by all

sources within the best performing 12

percent.'' Any of such phrases would have

been a more natural way to convey the Lower

Floor Interpretation than the language

Congress chose. However, the actual

language of section 112(d)(3)(A) provides,

in straightforward fashion, that standards

may be no less stringent than the ``average

emission limitation achieved by the best

performing 12 percent * * *''. To glean the

Lower Floor Interpretation from this

language is a strain; words and concepts not

set forth in the statute must be added or

inferred.

The language of section 112(d)(3)(B)

makes this point even clearer. That section

requires that standards for existing sources in

categories or subcategories with fewer than

30 sources be no less stringent than, “The

average emission limitation achieved by the

best performing 5 sources * * *” 42 U.S.C.

7412(d)(3)(B). 

If an interpretation parallel to the Lower

Floor Interpretation were intended, it would

have been more natural for this provision to

read ``the emission limitation achieved by

the 5th best performing source.'' 

2. The Legislative History 

The legislative history lends strong

support to the view that, in passing section

112(d)(3)(A), Congress intended the Higher

Floor Interpretation. 

On the House side, the language that

would eventually become section

112(d)(3)(A) was offered as a compromise

amendment by Rep. Dingell on the House

Floor on May 23, 1990. (The language of the

amendment was identical to section

112(d)(3)(A) as ultimately enacted into law;

only the numbers were different). Rep.

Dingell yielded time to Rep. Collins ``for

purposes of explaining the amendment.''

Legislative History of 1990 CAA

Amendments at 2896. In doing so, Rep.

Collins noted that she had originally

supported slightly more stringent numbers

than those included in the amendment, and

that under her original proposal 

The average of emissions from

the 10 percent cleanest sources would be

the MACT standard. In cases where

there are less than 30 sources in a

category or subcategory, the average of

the 3 cleanest sources would determine

the standard. 

Id. She went on to explain that under the

compromise amendment introduced by Rep.

Dingell 

MACT for existing stationary

sources would be the average of the best

15 [percent] of technologies within each

category or subcategory. For categories

or subcategories where there are less

than 30 sources, the standard is based on

the average emissions from the best

performing 5 sources. 

Legislative History of 1990 CAA

Amendments at 2897. 

Rep. Collins' formulations are consistent

with the Higher Floor Interpretation, not the

Lower. The ``average of the 3 cleanest

sources'' cannot mean, as the Lower Floor

Interpretation would require, the level of

control achieved by all three of the ``cleanest

sources.'' Nor can the ``average of the best 15

[percent] of technologies'' mean a technology

as good as that used by all sources within the

top 15 percent. 

Another discussion of section 112(d)(3)

is similar. On October 27, 1990, Sen.

Durenberger (a principal supporter of the

Clean Air Act Amendments) explained the

provision on the Senate floor. His

explanation was as follows: 

The standard may not be less

stringent than the average of the

emission levels achieved by the best

performing 12 percent of the existing

sources within the category* * * The

Administrator is to exclude from the

calculation of the average of top 12

percent any source which met the

following conditions* * * 

Legislative History of 1990 CAA

Amendments at 870 (Cong. Rec. S16929--

Oct. 27, 1990). The second sentence of Sen.

Durenberger's statement, in particular, is

inconsistent with the Lower Floor

Interpretation. Sen. Durenberger makes clear

that the ``average'' called for in the statute is

of the ``top 12 percent,'' not the emission

limitations achieved over time at each

individual source. 

No legislative history was found that

supports the Lower Floor Interpretation. The

EPA believes that the legislative history

indicates that individual

legislators--including those central to the

drafting of section 112(d)(3)--understood the

word ``average'' to mean that once the

emission limitations achieved by the best

performers in a category had been

determined, those results should be averaged.

This is the method of the Higher Floor

Interpretation, not the Lower. 

3. Issues Raised in Public Comment 

a. Arguments Concerning the Statutory

Language. 

(i) Plain Meaning of the Statute. Several

commenters argued that the meaning of the

statute was plain on its face and that

Congress clearly intended the Higher Floor

Interpretation. These commenters argued that

when section 112(d)(3)(A) is read as a whole

in its most natural way, the Congressional

intent in favor of the Higher Floor
B-4

Interpretation is clear. They argued that if

Congress had intended the Lower Floor

Interpretation, it would have used different

language in the statute. 

The EPA agrees with these comments.

As set forth in greater detail above, EPA

believes the plain statutory language strongly

favors the Higher Floor Interpretation. 

(ii) Congress' Failure to Use the Words

``of the''. Several commenters argued that if

Congress had meant the Higher Floor

Interpretation, it would have added the words

``of the'' to the statute, so that section

112(d)(3)(A) would read ``the average of the

emission limitations achieved by the best

performing 12 percent.'' These commenters

saw the absence of the words ``of the'' in the

statute as evidence that Congress intended

the Lower Floor Interpretation. 

The EPA agrees that the statute would

be more clear if Congress had used the words

``of the,'' but disagrees with the conclusion

drawn by these commenters for two reasons.

First, standard English usage often permits

dropping the prepositions ``of the'' without

changing the meaning of a phrase. (For

example, ``the biggest mountain in North

America'' has the same meaning as ``the

biggest of the mountains in North America.''

``Best singer in the band'' has the same

meaning as ``best of the singers in the

band.'') The same cannot be said, however,

for the various phrases and concepts that

must be read into section 112(d)(3)(A) in

order to arrive at the Lower Floor

Interpretation. Phrases like ``the worst

performing member of...'' or ``averaged over

time...'' simply are not dropped as part of

standard English. Their absence from section

112(d)(3)(A)--unlike the absence of the

words ``of the''--must be considered

significant in interpreting the provision. 

Second, although the words ``of the'' do not

appear in section 112(d)(3)(A), they were

used by key legislators in summarizing that

section prior to passage of the 1990 Clean

Air Act Amendments. As noted above, when

Sen. Durenberger (a principal supporter of

the Clean Air Act Amendments) spoke on

the Senate floor on October 27, 1990, he

explained section 112(d)(3)(A) as follows: 

The standard may not be less

stringent than the average of the

emission levels achieved by the best

performing 12 percent of the existing

sources within the category* * * 

Legislative History of 1990 CAA

Amendments at 870 (Cong. Rec. S16929--

Oct. 27, 1990) (emphasis added). As also

noted above, when Rep. Collins introduced

the provision in the House, she described it

as follows: 

The average of emissions from

the 10 percent cleanest sources would be

the MACT standard. In cases where

there are less than 30 sources in a

category or subcategory, the average of

the 3 cleanest sources would determine

the standard. 

Legislative History of 1990 CAA

Amendments at 2896 (emphasis added)

(describing a provision with identical

language but different numbers than the one

ultimately enacted into law). 

In EPA's view, the fact that Congress

did not use the words ``of the'' in section

112(d)(3)(A) is fully consistent with standard

English. However, the fact that key

legislators did use these words in describing

the provision to their colleagues, in

combination with the failure of those

legislators to use the phrases on which the

Lower Floor Interpretation depends, provides

a strong indication that Congress intended

the Higher Floor Interpretation in enacting

section 112(d)(3)(A). 

(iii) Purpose of the Word ``Average''.

Several commenters argued that the word

``average'' in section 112(d)(3)(A) should be

read to require averaging not of emissions

from different sources within the top 12

percent, but instead of emissions from

individual sources at different times, or from

different emission points, or made up of

different HAP. The EPA does not agree that

the word ``average'' in section 112(d)(3)(A)

can reasonably be read to serve this purpose.

First, such a reading is difficult, if not

impossible, to reconcile with the provision of

section 112(d)(3) establishing a ``floor'' for

new sources. Under those provisions, new

source standards may not be less stringent

than 

The emission control that is

achieved in practice by the best

controlled similar source. 

42 U.S.C. 7412(d)(3). Notably, Congress did

not use the word ``average'' in this provision.

If the word ``average'' in section

112(d)(3)(A) was intended to refer to

averages across time, or between emission

points, or among different HAP, then

Congress must have intended that such

averaging would take place for existing

source standards, but not for new source

standards. There is no reason to believe

Congress intended this implausible result. 

There is a much more likely explanation:

That to the extent Congress contemplated

that averaging across time, or between

emission points, or among HAP would play a

role in either existing or new source MACT

standards, it considered the terms ``emission

limitation'' and ``emission control'' fully

adequate to reflect that fact. In EPA's air

program, emission limitations have routinely

been expressed in terms of averages across

time, for example, without any special

statutory direction or authority. There is no

reason to believe that Congress would have

thought that special instructions were needed

to ensure that EPA continued this practice,

and even less reason to believe Congress

would have thought special instructions were

needed with respect to existing source

standards, but not new source standards. 

Furthermore, the legislative history of

section 112 casts doubt on the interpretation

of the word ``average'' offered by these

commenters. When Congress

comprehensively revised section 112 in the

Clean Air Act Amendments of 1990, it based

the revisions in substantial part on the Clean

Water Act's effluent guidelines program.

(See, e.g., Remarks of Sen. Durenberger,

Cong. Rec. S516 (January 30, 1990) (``* * *

this approach to regulation of toxic air

pollutants is not without precedent. A

program very similar to the one I have just

described has already been implemented

under the Clean Water Act'').) Under that

program, certain limits (known as ``BPT

limits'') have long been based on the

``average of the best'' performance at existing

facilities. (See generally Remarks of Sen.

Muskie, Legislative History of Federal Water

Pollution Control Act of 1972 at 169-70

(``The Administrator should establish the

range of `best practicable' levels based upon

the average of the best existing performance

by plants of various sizes, ages and unit

processes.'')) In determining ``average of the

best'' under the Clean Water Act, EPA has

historically identified the best performers in

an industrial category, and then averaged

their performances. This methodology is

consistent with the Higher Floor

Interpretation and not the Lower. 

(iv) Proximity of the Word ``Average'' to

the Words ``Emission Limitation''. Several

commenters argued that the proximity of the

word ``average'' to the words ``emission

limitation'' suggests that ``average'' modifies

``emission limitation,'' and not the entire

phrase following those words. The EPA does

not agree with this argument. In English,

adjectives often modify not only the noun

immediately following, but an entire phrase.

In the phrase ``the biggest mountain in North

America climbed by members of the

Washington, D.C. Climbing Club,'' for

example, the adjective ``biggest'' modifies

the entire remainder of the phrase. There is

no reason to conclude that the word

``average'' in section 112(d)(3)(A) plays a

different role. 

(v) Use of the Words ``Achieved By''.

Several commenters argued that the use of

the words ``achieved by'' in the statute
B-5

indicates that all sources within the top 12

percent must be achieving the emission

limitations used to set the MACT Floor. 

The EPA does not agree with this

argument. The EPA believes the argument

depends both on inferring the presence of the

word ``all'' in section 112(d)(3)(A), and (as

discussed above) on ignoring, or incorrectly

construing, the meaning of the word

``average.'' Section 112(d)(3)(A) simply does

not say ``the emission limitation achieved by

all sources within the best performing 12

percent* * *''. Congress' use of the words

``achieved by'' cannot reasonably be

stretched to accomplish such a rewriting of

the statute. 

 b. Arguments Concerning Structure of

the Statute. Several commenters argued that

elements of the statute's structure support the

Lower Floor Interpretation. For example,

some commenters argued that the Lower

Floor Interpretation best reflects EPA's

authority to consider cost and other factors in

setting standards more stringent than MACT

Floor. Other commenters argued that the

Lower Floor Interpretation best reflects the

distinction between existing source MACT

and new source MACT. 

The EPA does not agree with these

arguments. In fact, the Higher Floor

Interpretation fully preserves both of these

structural elements of the statute. With the

Higher Floor Interpretation, just as with the

Lower, EPA still has authority to establish

existing source standards more stringent than

the Floor based on enumerated criteria. With

the Higher Floor Interpretation, just as with

the Lower, there is still a distinction between

the Floor for existing sources and the level of

control required for new sources. (Under

section 112(d)(3), standards for new sources

must be at least as stringent as ``the emission

control that is achieved in practice by the

best controlled similar source''). The fact that

there may be ``less distance'' to travel above

the Floor with the Higher Floor Interpretation

does not establish an inconsistency between

that interpretation and other parts of the

statute, nor does it mean that the

interpretation is flawed in any way. 

Furthermore, structural arguments tend

to favor the Higher Floor Interpretation more

strongly than the Lower. Section 112 was

passed in its current form to ensure quick

and dramatic reductions in air toxics

emissions. Congress was frustrated with the

slow pace of toxics control prior to 1990,

and many members in part blamed EPA for

weak controls. See, e.g., H. Comm. Rep.

101-490 at 150-54, 322-23; S. Rpt. 101-228

at 128-33. The structure and purpose of

section 112 as a whole indicates that section

112(d)(3)(A) was intended to establish a

stringent minimum level of control for

hazardous air pollutants. 

c. Additional Arguments. Several

commenters argued that the Higher Floor

Interpretation would require EPA to set

MACT Floors that failed to correspond to

real-world control technologies. 

The EPA does not agree with this

argument. The EPA believes that the

argument depends upon a flawed premise:

That the word ``average'' can only mean

``arithmetic mean.'' In fact, there are a

number of conventional methods for

determining the average of a data set,

including the median. Congress did not

mandate a particular method of determining

``average'' or central tendency in section

112(d)(3)(A), and the choice of

methodology--whether median, mean, or

some other measure--can often change the

results markedly. For example, if the five

facilities that make up the top 12 percent of a

source category are achieving reductions

equal to 99 percent, 98 percent, 95 percent,

94 percent and 93 percent, EPA need not set

the MACT Floor equal to the arithmetic

mean of these values, which is 95.8 percent.

Using the Higher Floor Interpretation, EPA

could set the MACT Floor equal the median

of these values, which is 95 percent. 

This discussion responds to the most

significant comments on legal issues

received in response to the March 9, 1994

Federal Register document. Other comments

on legal issues are addressed in item number

VI-B-61 in docket A-90-19. 

C. Conclusion 

The EPA believes that Congress spoke

with clarity in section 112(d)(3)(A) of the

Clean Air Act. That provision--requiring

standards to be no less stringent than ``the

average emission limitation achieved by the

best performing 12 percent of existing

sources''--lends little support for an

interpretation under which standards might

be set at the emission limitation achieved by

the worst performing member of the best

performing 12 percent of existing sources.

The legislative history offers no support for

such an interpretation, and indeed points

strongly in the opposite direction. The EPA

believes that the Higher Floor Interpretation

represents the best reading of the statutory

language. 

II. Discretion in Setting Floors for MACT

Standards 

In today's notice, EPA announces its

conclusion that Congress intended the

Higher Floor Interpretation. The effect of this

decision, however, is not to identify any

particular number (e.g. the 94th percentile)

as the Floor for all MACT standards. EPA

retains discretion in important respects in

setting Floors for MACT standards, and

intends to exercise its discretion, within the

statutory framework, to promulgate MACT

standards that best serve the public interest. 

EPA believes the Agency retains

substantial discretion, within the statutory

framework, to set MACT Floors at

appropriate levels. For example, because

Congress did not define the term ``average''

in section 112(d)(3), or in the legislative

history, it implicitly delegated the authority

to EPA to do so. The choice of

methodology-- whether mean, median, mode,

or some other measure--can often change the

results. (The mean of a set of measurements

is the sum of the measurements divided by

the number of measurements in the set. The

median is the value in a set of measurements

below and above which there are an equal

number of values, when the measurements

are arranged in order of magnitude. The

mode is the value that occurs most often in a

set of measurements). As some commenters

noted, the ``average of the best performing

12%'' corresponds to the 94th percentile

when the word ``average'' is construed to be

the ``median.'' If, however, ``average'' is

construed to be the ``arithmetic mean'' or

``mode,'' a different result may obtain. EPA

construes the word ``average'' in section

112(d)(3) to authorize the Agency to use any

reasonable method, in a particular factual

context, of determining the central tendency

of a data set. In addition, EPA has discretion

to use its best engineering judgment in

collecting and analyzing the data, and in

assessing the data's comprehensiveness,

accuracy and variability, in order to

determine which sources achieve the best

emission reductions. EPA also has discretion

in determining how to analyze the data, and

thus in determining the appropriate

``average'' in each category or subcategory. 

There are other important ways that EPA

retains discretion in setting MACT floors.

For example, Congress authorized EPA to

subcategorize source categories based on

classes, types and sizes of sources, which

will result in different Floors for different

subcategories. CAA section 112(d)(1). Using

this authority, EPA can tailor standards to

certain characteristics of particular emission

units and sources. EPA retains flexibility, for

example, to conclude that the production

processes used at particular sources in the

relevant category are sufficiently different

from processes used at other sources in the

same category to justify the creation of a new

subcategory. 

These examples are not meant to be

exhaustive. EPA has only begun the process

of setting MACT standards. As EPA gains

experience in setting MACT Floors, other

issues may arise that will require EPA to

exercise its discretion in determining, for
B-6

each case, what represents the average

emission limitation achieved by the best

performing 12% of existing sources (or the

best performing five sources, in categories or

subcategories with fewer than 30 sources). 

III. Precedential Impact of Today's

Determination 

In its March 9, 1994 document, EPA

stated that ``the MACT floor decision * * *

in this rulemaking will have broad

precedential effect, and will be

presumptively followed in subsequent

MACT rulemakings.'' 59 FR 11018. Several

commenters objected this statement, arguing

that the issue of how best to interpret section

112(d)(3)(A) should have been addressed in

a separate, generally applicable rulemaking. 

The EPA wishes to emphasize that,

although today's decision concerning the

interpretation of Clean Air Act section

112(d)(3) for purposes of the HON will be

precedential for future rulemakings, it will

not be binding. Specifically, EPA will fully

consider all comments on individual MACT

standards, including those regarding the

proper interpretation of the language in sec.

112(d)(3)(A), received on or before the close

of the comment periods for those standards. 

IV. Application of MACT Floor Decision to

Medium Storage Vessels at Facilities Subject

to the HON 

As described in the March 9, 1994

Federal Register reopening the comment

period, EPA requested comment on whether

the control requirements for medium storage

vessels previously proposed by EPA would

be appropriate in the event those proposed

controls were to be determined to be more

stringent than the floor. Only four

commenters addressed the question of the

appropriate controls requirement for medium

storage vessels and provided rationale for

their opinions. Of these commenters, only

one submitted information which purported

to represent control information for SOCMI

storage vessels. This information was

reviewed and found to not provide any

information on control performance and to

represent storage vessels associated with

non-SOCMI processes (i.e., other source

categories) as well as SOCMI processes.

Therefore, the submitted information could

not be used to revise the database. The EPA

review of this information is contained in

item VI-B-62 in docket A-90-19. This

section of the preamble, therefore, only

presents the basis for the final decision on

control requirements for medium sized

storage vessels. 

For medium vessels, about 8 percent of

the vessels are controlled with either a

90-percent efficient control device or an IFR

or EFR with a continuous seal. All of the

controlled medium-sized vessels contained

liquids with vapor pressures of 13.1 kPa (1.9

psia). Because the arithmetic mean

characteristics of the top 12 percent of the

medium vessels would not represent the

performance of any known technology, the

EPA used the median as the average for

these vessels. Thus, for medium-sized

storage vessels, the floor determined by the

average characteristics of the top 12 percent

of the sources would require control of

vessels storing liquids with vapor pressures

of 13.1 kPa (1.9 psia) by either a 90-percent

efficient control device or an IFR or EFR

with a continuous seal. 

In selection of the control provisions for

medium-sized storage vessels, EPA

considered the regulatory alternatives that

were presented in the April 22, 1994 Federal

Register document. These alternatives

reflected a combination of: (1) The floor

control for medium-sized storage vessels,

which at the time of proposal, were equipped

with the floor controls and (2) the proposed

control provisions for medium-sized storage

vessels which were equipped with no control

or less efficient controls than the

performance of the revised floor component

for the source-wide floor. The EPA did not

develop a regulatory alternative

corresponding to application of the revised

floor control level to all storage vessels. Such

an alternative would have essentially the

same control costs as the proposed control

provisions, but would result in a lower

emission reduction. Because the floor control

would represent a less economically efficient

option and would add to the complexity of

the rule, this option was not formally

evaluated. 

For medium storage vessels at existing

sources, control at the regulatory alternative

used to represent the floor control was

estimated to cost $2.4 million/yr and to result

in an emission reduction of 370 Mg/yr (110

tons/yr). The regulatory option for control

level beyond the floor component is

estimated to further reduce emissions by less

than 100 Mg/yr (110 tons/yr) at an additional

cost of $4 million/yr, or $48,000/Mg for

each additional Mg of emission reduction.

Due to the relatively high incremental costs

and low emission reductions of this

alternative, the EPA believes that the control

level for the medium storage vessels

component of the source- wide floor

represented the maximum reduction

achievable considering cost and other

impacts. 

IV. Administrative Requirements 

A. Docket 

The docket is an organized and complete

file of all the information submitted to or

otherwise considered by EPA in the

development of this rulemaking. The

principal purposes of the docket are: (1) To

allow interested parties to identify and locate

documents so that they can effectively

participate in the rulemaking process and (2)

to serve as the record in case of judicial

review (except for interagency review

materials) (Section 307(d)(7)(A)). 

B. Paperwork Reduction Act 

The information collection requirements

of these provisions in this rule have been

submitted for approval to the OMB under the

Paperwork Reduction Act, 44 U.S.C. 3501 et

seq. An Information Collection Request

document has been prepared by the EPA

(ICR No. 1414.02), and a copy may be

obtained from Sandy Farmer, Information

Policy Branch, EPA, 401 M Street, SW.,

(2136), Washington, DC 20460, or by

calling (202) 260- 2740. These requirements

are not effective until OMB approves them

and a technical amendment to that effect is

published in the Federal Register. 

The reporting and recordkeeping burden

of the information collection requirements of

the provisions for medium sized storage

vessels are included in the estimate of the

overall reporting burden, which is presented

in ICR No. 1414.02. The information

collection requirements for the entire rule has

an estimated annual reporting burden

averaging 1,400 hours per response, and an

estimated annual recordkeeping burden

averaging 5,400 hours per respondent. These

estimates include time for reviewing

instructions, searching existing data sources,

gathering and maintaining the data needed,

and completing and reviewing the collection

of information. 

Send comments regarding the burden

estimate or any other aspect of this collection

of information, including suggestions for

reducing this burden, to Chief, Information

Policy Branch, EPA, 401 M Street, SW.,

(Mail code 2136); Washington, DC 20460;

and to the Office of Information and

Regulatory Affairs, Office of Management

and Budget, Washington, DC 20503, marked

``Attention: Desk Officer for EPA.'' 

C. Executive Order 12866 

This final action regarding provisions

applicable to medium sized storage vessels in

facilities subject to the HON has been

reviewed in accordance with Executive

Order 12866. Under the terms of the Order,

the Administrator has assessed the potential

costs and benefits of the regulatory action.

The methods for and results of these cost and
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benefit analyses are described in the HON's

Regulatory Impact Analysis (RIA). The RIA

was included in the HON docket at proposal,

and thus it was made available for public

comment. 

Executive Order 12866 also requires

that the record for ``significant'' rules include

an assessment of the potentially effective and

reasonably feasible alternatives to the

planned action. The potentially effective and

reasonably feasible alternatives to the control

requirements in the HON were also analyzed

as part of the rule development process. The

methods for and results of these analyses are

described in the HON's Background

Information Document (BID). The BID was

included in the HON docket at proposal, and

thus it was also available for public

comment. In addition, many of the

alternative requirements considered by the

Administrator were described in the

preamble for the HON proposal. 

The potential costs associated with

selection of the final provisions are primarily

the result of statutory requirements. All

elements of the cost that are not directly

attributable to statutory requirements were

deemed appropriate because the

Administrator determined that they were

necessary for administering this program

effectively and efficiently. In assessing the

potential costs and benefits--both

quantitative and qualitative--of this rule, the

Administrator has determined that the

benefits justify the costs. 

The Administrator has also determined

that this regulatory action does not unduly

interfere with State, local and tribal

governments in the exercise of their

governmental functions. 

D. Regulatory Flexibility Act Compliance 

The Regulatory Flexibility Act (5 U.S.C.

601 et seq.) requires the EPA to consider

potential impacts of Federal regulations on

small business entities. If a preliminary

analysis indicates that a proposed regulation

would have a significant economic impact

on 20 percent or more of small entities, then

a regulatory flexibility analysis must be

prepared. 

Regulatory impacts are considered

significant if any of the following criteria are

met: (1) Compliance increases annual

production costs by more than 5 percent,

assuming costs are passed on to consumers;

(2) compliance costs as a percentage of sales

for small entities are at least 10 percent more

than compliance costs as a percentage of

sales for large entities; (3) capital costs of

compliance represent a ``significant'' portion

of capital available to small entities,

considering internal cash flow plus external

financial capabilities; or (4) regulatory

requirements are likely to result in closures

of small entities. 

The potential costs of the requirements

for medium sized storage vessels were

considered as part of the economic impact

analysis for the entire regulation. The

assessment of the economic impacts of the

overall regulation were presented in the April

22, 1994 Federal Register (59 FR 19449).

Therefore, the addition of the final

provisions to the standard does not alter the

conclusion that the standard is not expected

to have a significant economic impact on a

substantial number of small firms. 

Pursuant to the provisions of 5 U.S.C.

605(b), I hereby certify that this attached rule

will not have an economic impact on small

entities because no additional costs will be

incurred. 

List of Subjects in 40 CFR Part 63 

Environmental protection, Air pollution

control, Hazardous substances, Reporting

and recordkeeping requirements. 

Dated: May 27, 1994. 

Carol M. Browner, 

Administrator. 

For the reasons set out in the preamble,

part 63, title 40, chapter I, of the Code of

Federal Regulations is amended as follows: 

PART 63--[AMENDED] 

1. The authority citation for part 63

continues to read as follows: 

Authority: Sections 101, 112, 114, 116,

and 301 of the Clean Air Act (42 U.S.C.

7401, et seq., as amended by Pub. L.

101-549, 104 Stat. 2399). 

Subpart G--National Emission Standards for

Organic Hazardous Air Pollutants from

Synthetic Organic Chemical Manufacturing

Industry Process Vents, Storage Vessels,

Transfer Operations, and Wastewater 

2. Table 5 of the appendix to subpart G

is revised to read as follows:

 

Table 5.--Group 1 Storage Vessels at

Existing Sources

Vessel capacity

(cubic meters)

Vapor Pressure1

(kilopascals)

75 # capacity < 151

151 # capacity

$ 13.1

$ 5.2

1Maximum true vapor pressure of total

organic HAP at storage temperature.

[FR Doc. 94-13666 Filed 6-3-94; 8:45 am] 

BILLING CODE 6560-50-P
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Appendix C

EXAMPLE NOTICE OF MACT APPROVAL

Notice of MACT Approval

CFR 40, Part 63, Subpart B

Maximum Achievable Control Technology Emission Limitation

 for 

Constructed and Reconstructed Sources 

under Section 112(j)

This notice establishes practicable, enforceable maximum

achievable control technology emission limitation(s) and

requirements for Name of major source for the MACT-affected

emission unit(s) located at location of all MACT-affected

emission units. The emission limitations and requirements set

forth in this document are enforceable on effective date of

notice.

A. Major Source Information

1. Mailing address of owner or operator:

2. Mailing address for location of major source:

3. Source category or subcategory for major source:

4. MACT-affected emission unit(s): List all emission unit(s)

subject to this Notice of MACT Approval along with the

source identification number if applicable.

5. Type of construction or reconstruction: Describe the action

taken by the owner or operator of the major source that

qualifies as the construction of a new affected source or

reconstruction of an affected source under the requirements

of 40 CFR Part 63, Subpart B, sections 63.50-63.56

6. Anticipated commencement date for construction or

reconstruction:

7. Anticipated start-up date of construction or reconstruction:

8. List of the hazardous air pollutants emitted by MACTaffected emission unit(s): List all hazardous air

pollutants that are or will be emitted from the affected
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emission unit(s). Any pollutant not listed in this section

cannot be emitted by the emission unit without an amendment

to the Notice of MACT Approval.

B. MACT Emission Limitation

1. The above stated owner or operator shall not exceed the

following emission limitation(s) for the above stated MACTaffected emission unit(s). Write in emission standard or

MACT emission limitation for overall hazardous air pollutant

emissions from each affected emission unit. If the

permitting authority determines that an individual pollutant

emission limitation is appropriate, it should also be listed

in this section.

2. The above stated owner or operator shall install and operate

the following control technology(s), specific design,

equipment, work practice, operational standard, or

combination thereof to meet the emission standard or MACT

emission limitation listed in paragraph 1 of this section. 

List all control technologies to be installed by the owner

or operator and which emission units to which the control

technologies apply.

3. The above stated owner or operator shall adhere to the

following production or operational parameters for the

technologies listed in paragraph 2 of this section. State

all production or operational parameters. For example:

The owner or operator may, subject to [name of agency]

approval, by-pass the emission control device for a

limited period of time for purposes such as maintenance

of the control device.

The owner or operator shall operate and maintain the

control equipment such that it has a 95% hazardous air

pollutant destruction efficiency.

The owner or operator shall not operate the MACTaffected emission unit for greater than 6 hours in any

24-hour period of time.

C. Monitoring Requirements

For each MACT emission limitation and operational requirement

established in Section B (MACT emission limitation) the above
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stated owner or operator shall comply with the following

monitoring requirements. State all monitoring requirements. 

For example:

After installing the control equipment required to comply

with Section B.1 visually inspect the internal floating

roof, the primary seal, and the secondary seal, before

filling the storage vessel

The owner or operator shall calibrate, maintain and operate

a continuous monitoring system for the measurement of

opacity of emissions discharged from the control device

required in Section B.2 according to the following

procedures: etc.

D. Reporting and Recordkeeping Requirements

List all reporting and recordkeeping requirements in this

section. For example:

The owner or operator shall maintain at the source for a

period of at least 5 years records of the visual

inspections, maintenance and repairs performed on each

secondary hood system as required in Section B.2.

E. Other Requirements

1. The above stated owner or operator shall comply with the

General Provisions set forth in Subpart A of 40 CFR Part 63,

as specified in 40 CFR 63.1(a) and as specified herein by

the permitting authority. 

2. In addition to the requirements stated in paragraph 1 of

this section, the owner or operator will be subject to the

following additional requirements. If there are any

specific requirements that the reviewing agency would like

to clarify or add, those requirements should also be stated

in this paragraph. This paragraph could also include

requirements for emergency provisions and start-up and shutdown procedures.

F. Compliance Certifications

The above stated owner or operator shall certify compliance

with the terms and conditions of this notice according to the

following procedures: This section should include a
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description of the terms and conditions that the owner or

operator will use to certify compliance, as well as the format

and frequency of the certification.
D-1

Appendix D

Federal Register Notice on Final Amendments to Regulations

Governing Equivalent Emission Limitations by Permit.

Also see: http://www.epa.gov/ttn/atw/112j/112jaypg.html
TECHNICAL REPORT DATA

(Please read Instructions on reverse before completing)

1. REPORT NO.

 EPA-453/R-02-001

2. 3. RECIPIENT' S ACCESSION NO.

4. TITLE AND SUBTITLE

Guidelines for MACT Determinations under Section 112(j)

Requirements

5. REPORT DATE

 February 2002

6. PERFORMING ORGANIZATION CODE

7. AUTHOR(S) 8. PERFORMING ORGANIZATION REPORT NO.

9. PERFORMING ORGANIZATION NAME AND ADDRESS

 Emission Standards Division (C504-03)

 Office of Air Quality Planning and Standards

 U.S. Environmental Protection Agency

 Research Triangle Park, NC 27711

10. PROGRAM ELEMENT NO.

11. CONTRACT/GRANT NO.

 68-D1-0118 

12. SPONSORING AGENCY NAME AND ADDRESS

 Office of Air Quality Planning and Standards

 U.S. Environmental Protection Agency

 Research Triangle Park, NC 27711

13. TYPE OF REPORT AND PERIOD COVERED

 Final

14. SPONSORING AGENCY CODE

 EPA/200/04

15. SUPPLEMENTARY NOTES

16. ABSTRACT

The section 112(j) rule, 40 CFR 63 subpart B, requires that permitting authorities develop case-by-case

maximum achievable control technology (MACT) for major sources in source categories for which

standards are not promulgated within 18 months after the date established under section 112(e). This

document provides guidance to those permitting authorities on how to develop case-by-case MACT. 

17. KEY WORDS AND DOCUMENT ANALYSIS

a. DESCRIPTORS b. IDENTIFIERS/OPEN ENDED TERMS c. COSATI Field/Group

 Hazardous Air Pollutants

 General Provisions

 Section 112(j) 

Air Pollution Control

18. DISTRIBUTION STATEMENT

 Release Unlimited

19. SECURITY CLASS (Report)

 Unclassified

21. NO. OF PAGES

120

20. SECURITY CLASS (Page)

 Unclassified

22. PRICE

 EPA Form 2220-1 (Rev. 4-77) PREVIOUS EDITION IS OBSOLETE