# Prevention of Significant Deterioration (PSD)

for P articulate Matter Less Than

2.5 Micrometers (PM 2.5 

# )

— Increments, Significant Impact Levels (SILs) and Significant Monitoring Concentration (SMC)

Response to Comments(This page intentionally left blank

. )

# Prevention of Signi ficant Deterioration (PSD)

for Particulate Matter Less Than

2.5 Micrometers (PM 2.5 

# )

— Increments, Significant Impact Levels (SILs) and Significant Monitoring Concentration (SMC)

Response to Comments

New Source Review Group Air Quality Policy Divi sion Office of Air Quality Policy and Standards U. S. Environmental Protection Agency Research Triangle Park, NC 27711

August 2010(This page intentionally left blank.)i 

## Table of Contents

Acronyms and Abbrev iations

................................ ................................ ................................ ........ iii

Units of Measure

................................ ................................ ................................ ............................ iv

1 Introduction

................................ ................................ ................................ ............................... 1

1.1 Background

................................ ................................ ................................ ........................ 1

1.2 The Commenters

................................ ................................ ................................ ................ 1

1.3 Organization of This Document

................................ ................................ ........................ 1

2 Com ments on PM 2.5 Increments

................................ ................................ ............................... 6

2.1 Comments on the Legal Basis for PM 2.5 Increments

................................ ......................... 7

2.1.1 Comments Supporting and Opposing Sectio ns 166(a) and 166(f) of the Act as the

Basis for PM 2.5 Increments

................................ ................................ ..................... 8

2.1.2 Comments on EPA’s Interpretation of the Requirements under the Section 166(a) Contingent Safe Harbor Approach

– Sectio ns 166(a)

- (d) of the Act

.................... 15

2.1.3 Comments on EPA’s Interpretation of the Requirements under the Section 166(f) Equivalent Substitution Approach

................................ ................................ ........ 18

2.2 Comments on Option 1 for PM 2.5 Increments

– Contingent Safe Harbor Approach for

Annual and Short

- Term Increments

................................ ................................ ................ 21

2.2.1 Comments Supporting and Opposing Finalizing Op tion 1 at the Proposed Levels

................................ ................................ ................................ ............................... 21

2.2.2 Comments on the Proposed Framework for PSD Regulations for PM 2.5 and on EPA’s Evaluation of the Statutory Factors for Increments

................................ ... 24

2.3 Comments on Option 2 for PM 2.5 Increments

– Equivalent Substitution Approach for

Annual Increments

................................ ................................ ................................ ........... 38

2.3.1 General Comments on Option 2

................................ ................................ ........... 39

2.3.2 Comments on Option 2A

................................ ................................ ...................... 42

2.3.3 Comments on Option 2B

................................ ................................ ...................... 43

2.4 Oth er Comments on Increments

................................ ................................ ...................... 44

2.4.1 Comments on Baseline Areas

................................ ................................ ............... 44

2.4.2 Comments on Baseline Dates for the PSD Increments for PM 2 .5

......................... 47

2.4.3 Miscellaneous Comments on Increments for PM

................................ ................. 51

3 Comments on the PM 10 Increments

................................ ................................ ........................ 53

4 Comments on Significant Impact Levels (SILs) for PM 2.5

................................ ..................... 59

4.1 Comments on the Legal Basis for SILs

................................ ................................ ........... 59

4.2 General Comments on SILs for PM 2.5

................................ ................................ ............. 60

4.3 Comments on the Relationship of SILs to AQRVs

................................ ......................... 64

4.4 Comments on the Propo sed Levels for SILs

................................ ................................ ... 65

4.4.1 General Comments on Proposed SIL Levels

................................ ........................ 65

4.4.2 Comments on Proposed Levels for Class I SILs

................................ .................. 69

4.4.3 Comments on Proposed Levels for Class II and III SILs

................................ ..... 74

4.5 Other Comments on SILs

................................ ................................ ................................ 83

4.5.1 Comments on SILs for Other Pollutants

................................ ............................... 83

4.5.2 Miscellaneous Comments on SILs

................................ ................................ ........ 84ii

5 Comments on the Significant Monitoring Concentration (SMC) for PM 2.5

........................... 87

5.1 General Comments on an SMC for PM 2.5

................................ ................................ ....... 87

5.2 Comments on the Lega l Basis for the SMC

................................ ................................ .... 89

5.3 Comments on the Proposed Level of the SMC for PM 2.5

................................ ................ 93

5.4 Other Comments on SMCs

................................ ................................ .............................. 97

6 Comments on Transition Issues

................................ ................................ .............................. 99

6.1 Comments on the Effective Date for PM 2.5 Increments

................................ ................... 99

6.2 Comments on the Implementation Date for PM 2.5 Increments

................................ ...... 102

6.2.1 Comments on the Schedule for Submitting SIP Revisions

................................ . 102

6.2.2 Comments on Coordinating Implementation of PM 2.5 Increments in the State and Federal Programs

................................ ................................ ................................ 105

6.2.3 Other Comments on Implementation

................................ ................................ .. 107

6.3 Comments on Timing for the Revocation of the PM 10 Increments

............................... 108

6.4 Comments on a Transition Period for Permit Applicants

................................ .............. 108

6.5 Comments on Whether SILs and SMCs Should Be Mandatory Program Elements

..... 109

7 Comments on Statutory and Executive Order Reviews

................................ ........................ 111

7.1 Comments on Review under the Unfunded Mandates Reform Act

.............................. 111

7.2 Comments on Review under Executive Order 13211: Actions that Significantly Aff ect Energy Supply, Distribution, and Use

................................ ................................ ........... 112

8 Other Comments on the Proposed Rulemaking

................................ ................................ .... 113

8.1 Comments on Secondary PM 2.5

................................ ................................ ..................... 113

8.1.1 Comments on Inclusion of Secondary PM 2.5 in PSD Modeling Analyses

......... 113

8.1.2 Comments on Models for Secondary PM 2.5

................................ ........................ 115

8.2 Comments on Inclusion of the Condensable Fraction of PM 2.5 in PSD Modeling Analyses

................................ ................................ ................................ ......................... 116

8.3 General Comments on the Proposed R ulemaking

................................ ......................... 121iii 

## Acronyms and Abbreviations

Act Clean Air Act (42 U.S.C. 7401

- 7671q)

AQRV Air Quality Related Value

BACT Best Achievable Control Technology

CAA Clean Air Act (42 U.S.C. 7401

- 7671q)

CAIR Clean Air I nterstate Rule

CFR Code of Federal Regulations

EGU Electric g enerating u nit

EPA U.S. Environmental Protection Agency

FLM Federal Land Manager

FR Federal Register

LAER Lowest Achievable Emission Rate

LDC Lowest d etectable c oncentration

MDL M inimu m detection limit

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NEI National Emissions Inventory

NESCAUM Northeast States for Coordinated Air Use Management

NO Nitric oxide

NO 2 Nitrogen dioxide

NO

x Nitrogen oxides

NSR New Source Review

PM Particulate matter

PM 10 Particulate matter with aerodynamic diameter less than or equal to a nominal

10 μm

PM 10

- 2.5 Particulate matter with aerodynamic diameter less than or equal to a nominal

10 μm but greater than a nominal 2.5 μm

PM 2.5 Particulate matter with aerodynamic dia meter less than or equal to a nominal

2.5 μm

PSD Prevention of Significant Deterioration

SIL Significant impact level

SIP State Implementation Planiv 

## Acronyms and Abbreviations

SMC Significant monitoring concentration

SO 2 Sulfur dioxide

SO

x Sulfur oxides

TSP Total suspended par ticulate matter

U.S.C. United States Code



## Units of Measure

MW Megawatt

μm Micrometer (one

- millionth of a meter)

μg/m 3 Microgram per cubic meter

km Kilometer1



## 1 Introduction

1.1 Background

On September 21, 2007, the U.S. Environmental Protectio n Agency ( EPA or ―we‖ ) proposed to amend the requirements for particulate matter (PM) with aerodynamic diameter less than or equal to a nominal 2.5 micrometers ( μm ) ( PM 2.5 ) under the Prevention of Significant Deterioration (PSD) program by adding maximum a llowable increases in ambient pollutant concentrations (―increments‖) and two screening tools, known as the Significant Impact Levels (SILs) and a Significant Monitoring Concentration (SMC) for PM 2.5

. 1 The SILs for PM 2.5 we re also proposed to be added to two other New Source Review (NSR) rules that regulate the construction and modification of major stationary sources locating in attainment and unclassifiable areas, where the source’s emissions may cause or contribute to a violation of the

national ambient air quality standards (NAAQS). 2 The EPA also proposed to revoke the annual

increments for PM with aerodynamic diameter less than or equal to a nominal 10 μm ( PM 10 ) in

the PSD rules

.



### 1.2 The Commenters

The public comment period was originally scheduled to e nd on November 20, 2007, but was extended to January 21, 2008 as the result of two timely requests for an extension. W e received a total of 3 5 sets of comment s on the proposed rulemaking (not counting duplicates and requests for extension of the comment p eriod)

. The se commenters can be classified by general type as follows: 9 s tate/local regulatory agencies and regulatory agency associations, 21 industry

and industry association commenters, 1 environmental group commenter

, 1 f ederal agency

, 2 t ribal comme nters, and 1 private citizen . The commenters are listed in Table 1, which appears

at the end of this s ection

.



### 1.3 Organization of This Document

After this introductory s ection, this document is divided into s even additional s ections as

follows:

 Comments o n PM 2.5 Increments

 Comments on PM 10 Increments

 Comments on Significant Impact Levels (SILs) for PM 2.5

 Comments on the Significant Monitoring Concentration (SMC) for PM 2.5

 Comments on Transition Issues

 Comments on Statutory and Executive Order Reviews

 Oth er Comments on the Proposed Rulemaking

1 The rulemaking was proposed in the Federal Register , Volume 72, pages 54112 through 54156 (72 FR 54112). The PSD rules that were proposed for revision are in the Code of Federal Regulations , Title 40, Part 51, section 51.166, and Part 52, sectio n 52.21 (40 CFR 51.166 and 52.21).

2 These additional NSR rules are 40 CFR 51.165 (b) and 40 CFR part 51, A ppendix S.2 Table 1. List of Commenters

Document Id a b

EPA

- HQ

- OAR

2006

- 0605

- XXXX Title Type of Commenter Notes

0007 Comment and attachment submitted by Julie C. Becker, Assistant General Counsel, Alliance

of Automobile Man ufacturers Industry Ass'n Request for

extension

0008 Comment and attachment submitted by Ted Steichen, Senior Regulatory Analyst, American

Petroleum Institute (API) Industry Ass'n Request for

extension

0011 Comment and attachment submitted by Josep h S. Casper, Vice President, Environmental,

Health & Safety, The Brick Industry Association (BIA) Industry Ass'n

0012 Comment submitted by B. Sachau Private Citizen

0013 Comment and attachment submitted by Leon Brasowski, Senior Environmental Mana ger,

Covanta Energy Corporation Industry

0014 Comment submitted by Marion Loomis, Executive Director, Wyoming Mining Association

(WMA) Industry Ass'n

0015 Comment and attachment submitted by Glenn Shankle, Executive Director, Texas

Commission on En vironmental Quality (TCEQ) S/L Agency

0016 Comment and attachment submitted by Howard L. Gilberg, Guida, Slavich & Flores, P.C. on

behalf of Monarch Ceramic Tile, Inc. and American Marazzi Tile, Inc. Industry

0017 Comment submitted by Glenn Shankle , Executive Director, Texas Commission on

Environmental Quality (TCEQ) S/L Agency Duplicate of

0015

0018 Comment and attachment submitted by Arthur N. Marin, Executive Director, Northeast

States for Coordinated Air Use Management (NE SCAUM) S/L Agency Ass’n

0019 Comment and attachment submitted by David J. Shaw, Director, Division of Air Resources,

New York State Department of Environmental Conservation (NYSDEC) S/L Agency

0020 Comment submitted by Peter Manousos, FirstEnergy C orp. (FE) Industry

0021 Comment and attachment submitted by John Paul, Co

- Chair, Bill O'Sullivan, Co

- Chair, et al.,

National Association of Clean Air Agencies (NAC A A) S/L Agency Ass’n

0022 Comment and attachment submitted by David A. Finley, Admin istrator, Air Quality Division,

Wyoming Department of Environmental Quality (WDEQ) S/L Agency3 Table 1. List of Commenters

Document Id a b

EPA

- HQ

- OAR

2006

- 0605

- XXXX Title Type of Commenter Notes

0023 Comment submitted by John W. Fainter, Jr., Chief Executive Officer (CEO) and President,

Association of Electric Companies of Texas (AECT) Industry Ass' n

0024 Comment and attachment submitted by Craig Wysong, Environmental Health and Safety

(EHS) Supervisor, CARBO Ceramics Inc. Industry Support

0046

0025 Comment and attachment submitted by William Skrabak, Chief, Department of

Transportation and En vironmental Services, Division of Environmental Quality, City of

Alexandria S/L Agency

0026 Comment and attachment submitted by Pamela F. Faggert, Vice President and Chief

Environmental Officer, Dominion Resources Services, Inc. Industry

0027 Comm ent submitted by Russell A. Wozniak, Environmental Health & Safety (EH&S)

Operations Regulatory Management, The Dow Chemical Company Industry

0028 Comment and attachment submitted by John A. Paul, Administrator, Regional Air Pollution

Control Agency ( RAPCA) S/L Agency Concur with

0021

0029 Comment and attachment submitted by Andrea Bear Field, Hunton & Williams LLP on behalf

of Utility Air Regulatory Group (UARG) Industry Ass’n

0030 Comment and attachment submitted by Smith Aldridge, Inc. on beh alf of Craig Wysong, EHS

Supervisor, Carbo Ceramics, Inc. Industry Duplicate of

0024

0031 Comment and attachment submitted by Britt D. Banks, Executive Vice President, Newmont

Mining Corporation and Newmont USA Limited (collectively re ferred to as "Newmont") Industry Support

0034

0032 Comment and attachment submitted by Ted Steichen, Advisor, American Petroleum Institute

(API) Industry Ass'n

0033 Comment submitted by Ali Mirzakhalili, P.E., Administrator, State of Delaware Depa rtment of

Natural Resources and Environmental Control (DNREC) S/L Agency

0034 Comment and attachment submitted by Harold P. Quinn, Jr., Executive Vice President and

General Counsel, National Mining Association (NMA) Industry Ass'n

0035 Comment and attachment submitted by Leslie Sue Ritts, Counsel, National Environmental

Development Association's Clean Air Project (NEDA/CAP) Industry Ass'n4 Table 1. List of Commenters

Document Id a b

EPA

- HQ

- OAR

2006

- 0605

- XXXX Title Type of Commenter Notes

0036 Comment and attachment submitted by David A. Buff, Principal Engineer, Golder Associates

Inc. (Golder) on behalf of Florida Sugar Industry (FSI) Industry Ass’n

0037 Comment and attachment submitted by Terry Behrman, Manager, Alliance of Automobile

Manufacturers Industry Ass'n

0038 Comment and attachment submitted by Frank W. Rambo, Baker Botts, LLP on behalf of

Class of '85 Regulatory Response Group Industry Ass'n

0039 Comment and attachment submitted by C.V. Mathai, President, WEST Associates (Western

Energy Supply and Transmission Associates, or “WEST”) Industry Ass'n

0040 Comment and atta chment submitted by David S. Baron, et al, Counsel, Earthjustice, on

behalf of Environmental Defense and Sierra Club Environmental Group

0041 Comment submitted by Brandy Toft, Air Quality Specialist, Leech Lake Band of Ojibwe Trib e

0042 Comment and attachment submitted by William C. Scott, Modrall, Sperling, Roehl, Harris

and Sisk, PA., on behalf of BHP Navajo Coal Company Industry

0043 Comment and attachment submitted by Barry H. Christensen, Manager Air Quality,

Occidental Chemical Corporati on (OCC) Industry

0044 Comment submitted by John Bunyak, Chief, Policy, Planning and Permit Review Branch, Air

Resources Division, National Park Service (NPS), U. S. Department of the Interior (DOI) Federal Agency

0045 Comment submitted by Barry H . Christensen, Manager Air Quality, Occidental Chemical

Corporation (OCC) Industry Duplicate of

0043

0046 Comment and attachment submitted by Lee R. Lemke, Executive Vice President, Georgia

Mining Association (GMA) Industry Ass'n

0047 Comment submitted by David A. Finley, Administrator, Air Quality Division, Wyoming

Department of Environmental Quality (WDEQ) S/L Agency Duplicate of

0022

0048 Comment submitted by John Bunyak, Chief, Policy, Planning and Permit R eview Branch,

National Park Service (NPS), Air Resources Division, United States Department of the

Interior Federal Agency Duplicate of

00445 Table 1. List of Commenters

Document Id a b

EPA

- HQ

- OAR

2006

- 0605

- XXXX Title Type of Commenter Notes

0049 Comment submitted by Karen R. Diver, Chairwoman, Fond du Lac Band of Lake Superior

Chippewa (t he Band) Trib e

0050 Comment submitted by John A. Paul, Administrator, Regional Air Pollution Control Agency

(RAPCA) S/L Agency Duplicate of

0028

0051 Comment submitted by Maya Rao, P.E., DEE, Chief, Air Divi sion, Mississippi Department of

Environmental Quality (MDEQ), State of Mississippi S/L Agency

0052 Comment submitted by Ali Mirzakhalili, P.E., Administrator, Division of Air & Waste

Management, Delaware Department of Natural Resources & Environmental C ontrol (DNREC) S/L Agency Duplicate of

00 33

0053 Comment submitted by John W. Fainter , Jr., CEO and President, Association of Electric

Companies of Texas (AECT) Industry Ass'n Duplicate of

002 3

a Document ID identifies comments found in Docket No. EPA

- H Q

- OAR

- 2006

- 0605 by document number.

b Documents submitted to the docket together appear in the docket as multiple documents with the same 4

- digit "root number" followed by a unique extension. For example, comments received via email are generally assi gned two numbers. First, the email message itself is assigned the root number (e.g., 0015). Second, the attache d comment document is assigned an extended number based on the root number (e.g., 0015.1). Additional attachments, if any, would follow the sa me pattern (e.g., 0015.2, 0015.3, etc.). For the purposes of this table and the summary text , we listed all related
documents under the root number.6 (This page intentionally left blank.)7



## 2 Comments on PM 2.5 

## Increments

2.1 Comments on the Legal Basis for PM 2.5 

### Increments

Comment:

One industry c ommenter (0016) assert s that EPA failed to expressly state and support its legal authority for the PM 2.5 increments, offering two possible sources of authority ( ―c ontingent

s afe h arbor ,‖ ―equivalent substitution,‖ or possibly a combination of the two) but never stating its legal position with clarity. The commenter agree s with EPA’s assessment that the PM 2.5 increments should and must fulfill the legal requirements of the Clean Air Act (CAA or the Act) ( citing 72 FR 54121

, c olumn 3) , and added that it is t he government’s burden of proof to establish its legal authority for action . The commenter state s that it would be arbitrary and capricious to promulgate these regulations for which EPA has no stated legal authority.

The commenter stat e s that EPA discus sed in the proposal preamble its belief that the NSR permitting process is sufficient to satisfy the requirements of section 165 of the Act ( citing

72 FR 54125, column 1, and 54140

- 54141 ) . The commenter expresse s concern that EPA’s sole

focus is on major PSD sources , and that EPA failed to consider the impact of NSR permitting for

non

- major (PSD) sources or their consumption of a portion of the allowable increment . The

commenter believes that this is arbitrary and capricious.

Response:

We acknowledge that the proposal described two possible legal authorities for the two different options for establishing increments, but we disagree that these discussions did not clearly present the alternative legal bases that EPA was considering for taking action in this

rule. We also disagree with the comment that our presentation of two sets of legal authority for developing the PM 2.5 increments was arbitrary and capricious. W e clearly described our legal authority for developing the 24

- hour and annual PM 2.5 incre ments under section 166(a) of the Act, which is the basis on which we decided to finalize the rule. First, we expressly stated that Option 1 was based on the statutory authority of section 166(a) of the Act. See 72 FR 54123 (Under the first option, “we w ould use the authority of section 166(a) of the Act to develop new increments for PM 2.5 ”). Second, we provided a discussion of this authority both in general ( see 72 FR 54118

– 54119 and 54120

– 54123), and how it would be applied to establish increments for PM

2.5 ( see 72 FR 54119

– 54 120 and 54123

– 54 136).

In addition, w e described how section 166(f) of the Act might provide alternative authority for establishing increments for PM 2.5 (see, e.g., 72 FR 54120

- 54121), but will not

repeat that informat ion in detail here because we did not base the increments in th e final rule on section 166(f) authority

. Commen ts, and our responses to those comments, regarding support for or opposition to the two legal authorities presented in the proposal

, and on our interpretation of the requirements for PM 2.5 increments under each

, are present ed in the following sub sections

contained in this section 2.1

.8

With regard to the commenter‟s concern that EPA focuses only on “major (PSD) sources” to satisfy the requirement s of section 165 of the Act, we respond that section 165 clearly applies to major stationary sources and major modifications. The section begins by saying, “No major em i tting facility...may be constructed...unless....” Section 165 of the Act is

one component o

f the statutory requirements for Prevention of Significant Deterioration of Air Quality, which provides for a preconstruction review and permitting program for major emitting facilities (major stationary sources). We do not deny that emissions from minor sources also contribute to the PSD increments and air quality levels associated with the NAAQS, but such sources are not the concern of the specific statutory program prerequisites for obtaining a PSD construction permit. The commenter has not provided an y basis for a conclusion that section 165 of the Act also pertains to permitting minor sources of air pollution.



### 2.1.1 Comments Supporting and Opposing Sections 166(a) and 166(f) of
the Act as the Basis for PM 2.5 

### Increments



### 2.1.1.1 Comments on Statutory Considerations

Comments Supporting Section 166(a) and/or Opposing Section 166(f):

Two tribal commenters (0041, 0049) and o ne e nvironmental group commenter (0040) expressly support our proposed reliance on section 166(a) authority to promulgate PM 2.5 increments. Anothe r e ight commenters support proposed Option 1

, which relies on authority

under section 166(a) of the Act for developing the PM 2.5 increments , but do not explicitly express support for the use of section 166(a) authority. The latter comments are summarized in

Section 2.2.1 of this document

.

T he t wo supportive tribal commenters (0041, 0049) support utilizing section 166(a) of the Act for developing and setting the PM 2.5 increments because they believe that the advantages of this approach better suit the tri bal and environmental perspectives.

Th e supportive e nvironmental group commenter (0040) argue s that adoption of the rules

under s ection 166(a) of the Act is the only legally available option. The commenter assert s that

s ection 166(a) plainly appl ies to PM 2.5 , because PM 2.5 is a pollutant for which NAAQS were promulgated after August 7, 1977 . The commenter indicate s that EPA’s rulemaking duty under section 166 is not confined to ―new pollutants,‖ but is triggered by post

- 1977 NAAQS promulgations, regardl ess of whether for new or previously regulated pollutants. The commenter
add s that limitation of the section 166(a) rulemaking duty to new pollutan ts would conflict with

s ection s 166(c) and (d), which require post

- 1977 PSD rules to (among other things) pr ovide specific measures at least as effective as the statutory increments in s ection 163, and to fulfill the goals and purposes of the PSD program and the Act. The commenter contend s that where EPA strengthens the NAAQS f or a pollutant after 1977, the A ge ncy must adopt stronger increments to maintain the same percentage of the NAAQS as the statutory increments, and to ensure that the other requirements of s ections 166(c) and (d) are met. The commenter note s that in proposing

increments for PM 10 in 1989, E PA read section 166(a) as not being limited to wholly new criteria pollutants (54 FR 41218, 41220, October 5, 1989).9

This e nvironmental group commenter also argue s that EPA does not ha ve the authority to adopt PM 2.5 increments pursuant to s ection 166(f). The commenter explain s that by its terms

,

s ection 166(f) is limited to authorizing the adoption of PM 10 increments as a substitute for the
statutory PM increments based on total suspended PM (TSP) and does not provide for

substitution of PM 2.5 increments for TSP or PM 10 increments. The commenter believes that there is no ambiguity in the statute that would allow EPA to infer otherwise.

One industry association commenter ( 0029) believes that EPA’s analysis of the approach based on section 166(a) of the Act ( i.e., Option 1) is correct and indicate s support for this approach. However, this commenter believes that EPA also is authorized to use the equivalent

substitution approach for developing PM 2.5 increments based on section 166(f) (i.e.

, Option s 2 A

and 2B )

.

Comments Supporting Section 166(f) and/or Opposing Section 166(a):

Ten commenters ( 0018, 0019, 0021, 0025, 0028, 0031, 0033 , 0034, 0039, 0042 ) support section 166(f) of the Act as the basis for PM 2.5 increments

. T hese commenters either explicit ly
express support and provide reasons for th eir support of section 166(f) or indicate their

oppos ition to the use of s ection 166(a) of the Act as the basis for PM 2.5 increments

. Four of the commenters (0019, 0033, 0034, 0042) assert that section 166(f) p rovides the only legitimate

basis for PM 2.5 increments under the Act, and three of these (0019, 0033, 0034) specifically

include the 24

- hour PM 2.5 increments in this assertion. Another four of the commenters (0018, 0021, 0031, 0039) believe section 166(f) provides a better basis than does section 166(a) , and two of the commenters (0025, 0028) simply recommend that EPA use the section 166(f) approach

.

One state / l ocal a genc y commenter (0019) who believes that the section 166(f) approach is the only legitim ate approach under the Act agree s with EPA’s proposed interpretation that Congress intended to authorize EPA to update PM increments when another indicator is defined

, and that s ection 166(f) allows EPA to do so as long as these increments are of equal str ingency to the prior increments

.

An industry association commenter (0034) similarly concur s with EPA’s position in the proposal that it is permissible for the Agency to construe s ection 166(f) as a continuing grant of authority for the Administrator to update the increments for PM whenever a new form of PM is adopted as the indicator for the NAAQS. Th is commenter believes that s ection 166(f) contains principles for updating PM increments, which are summarized in Section 2.1.3 of this document.

Anot her state / l ocal a gency commenter (0033) does not share EPA’s concern that because

the 24

- hour PM 10 NAAQS has not been revoked, section 166(f) is inappropriate to use. The

commenter believe s that s ection 166(f) was included in the 1990 CAA Amendments becau se Congress knew that EPA was struggling with methods for replacing the then

- existing TSP

increments with PM 10 increments. The commenter explain s that s ection 166(f) was written to

facilitate th e move to PM 10 and that it is broad enough to cover further e xtension to cover the

PM 2.5 fraction of particulate.10

An industry commenter (0042) concludes that s ection 166(f)

– not section 166(a)

– of the

A ct provide s EPA authority to promulgate increment s for PM 2.5 , not ing that Congress added

s ection 166(f) to the A ct to define EPA’s authority to issue a PM increment and to establish the framework for EPA’s development of such an increment. The commenter believes that the

annual PM 2.5 increment should be substituted for the annual PM 10 increment , but indicates that

EPA should first properly calculate the PM 2.5 increment to satisfy the equal stringency requirement of s ection 166(f). The commenter’s comments on the methodology for calculating

the increments are summarized in Section 2.3 of this document.

A state/lo cal agency association commenter ( 0021) asserts that section 166(f) is a better statutory fit for PM 2.5 increments

, and state s that because EPA retained the 24

- hour PM 10 NAAQS in its PM NAAQS revision, and has specifically included regulation of PM 2.5 in t hat standard, this section provides a more appropriate statutory basis for PM 2.5 increments. The

commenter add s that EPA has continued the PM 10 24

- hour standard and included the fine PM 2.5 fraction within it; by logical extension, section 166(f), which ad dresses PM 10 increments, can and should provide the statutory basis for PM 2.5 increments.

Another industry association commenter ( 0039) also believes that EPA may rely on the
statutory authority of s ection 166(f ) when adopting PM 2.5 increments. The comm enter note s that

, from a physical standpoint, PM 10 is merely a fraction (subset) of total PM, and PM 2.5 is merely a fraction of PM 10

. The commenter argued that it is reasonable to conclude that Congress

intended to authorize EPA to continue updating the p articular matter increments contained in

s ection 163 if EPA promulgated a NAAQS for another indicator for particular matter. The commenter believes that this statutory grant of authority extends naturally to developing another

indicator of the same PM air quality standard

– that is, merely a smaller fraction of the same ambient PM pollutant in the atmosphere

– not a new or en tirely different air pollutant.

On e state/local agency commenter (0019) f i nd s unpersuasive EPA’s argument that it is
not ―substitut ing‖ increments (as section 166(f) requires for PM 10 ) but rather adding PM 2.5 increments to the existing PM 10 increments, and that only section 166(a) allows such an approach ( citing 72 FR 54121). The commenter indicates that if EPA had defined a coarse

f raction to the partic ulate standards, then that fraction, together with the PM 2.5 standards

, would

form the set of sub stituted new standards for the existing PM 10 standards, and, thus, the

increments. The commenter assert s that EPA’s argument that there is lack of language in

s ection 166(f) for adding other PM indicators while retaining the existing PM 10 indicator s misrep resents the pur pose of what Congress intended when it added s ection 166(f), and also

conveys an unrea sonable expectation of finding such language in a 1990 revision to the A ct for future prediction of how exactly the PM indicators would progress since that time. The

commenter add s that the term ― substitution ‖ need not mean replacement in total, but rather, replace ment of portions de termined not to serve the originally intended purpose, and th is is what

the PM 2.5 increments, in addition to the PM 10 increments, will achieve.

Two state/local agency commenters (0019, 0033) contend that s ection 166(a) cannot be

used as the basis for PM 2.5 increments because section 166(a) can only be used for a new pollutant and PM 2.5 is not a new pollutant. One of the commenter s (0019) argues that nothing in

s ection 166(a) of the Act can be interpreted to allow it to be used as the basis of increments when11

EPA revises an existing NAAQS. The commenter explain s that

, o n its face, s ection 166(a) can only be interpreted to apply to pollutants other than PM and sulfur dioxide ( SO 2 ) since increments for these pollutants were enacted by Congress in s ection 1 63 of the A ct . The

commenter add s that it can be argued that Congress intended to have s ection 166(a) apply to the four other pollutants specifically listed there. The commenter disagree s with EPA’s argument

that it can treat PM 2.5 as a new pollutant und er s ection 166(a) of the Act since it has been

demonstrated that sub

- PM 2.5 particles have distinctly different health and welfare effects than the other forms of PM (i.e.

, coarse or PM 10 ). The commenter indicates that just as EPA replaced the

TSP standard s by PM 10 as a better indicator of health effects, ongoing research has lead to

establishment of the PM 2.5 standards as a better indicator of certain health effects

, and it is the natural outcome of such research that has enabled EPA to separate the effect of total particulates

into two fractions with distinct effects. The commenter add s that g iven that the definition of particulates includes a vast conglomeration of solids and liquids, the finding of differing effects should not come as a surprise. The c ommenter explain s that as is the case of different pollutants having similar effects and are, nonetheless, treated as separate pollutants, the same concept should apply to a range or fraction of particulates found to have different effects in establishing it as another indicator and not a different pollutant

.

One i ndustry association commenter ( 0034) also believes that s ection 166(a) of the Act does not provide EPA with authority to promulgate its proposed PM 2.5 increments. The

commenter believes that th e legal and Congressional history regarding the establishment of PM

increments show that Congress added section 166(f) to the Act based on the conviction that without it, EPA had no authority to revise the PM increments for PM 10 ( citing and quoting from

S. Rep. No. 228, 101 st Cong., 2 nd Sess. 75 (1990), reprinted in 1990 U.S.C.C.A.N. 3385, 3461)

. The commenter conclude s that EPA did not have authority in 1987 under s ection 166(a) to adopt

PM 10 increments, and does not have authority today under s ection 166 (a) to adopt PM 2.5 increments.

Response:

We read section 166(a) of the Act to authorize EPA to promulgate pollutant

- specific PSD regulations meeting the requirements of sections 166(c) and 166(d) of the Act for any pollutant for which EPA promulgates a NAAQS after 1977. Most of the pollutants identified in

section 166(a) ( nitrogen oxides ( NO

x ) , photochemical oxidants, carbon monoxide) are pollutants for which EPA had established NAAQS in 1977 when Congress adopted section 166 of the Act.

There was no n eed for Congress to list the other criteria pollutants, SO 2 and PM , in

section 166(a) because Congress had already established increments for these pollutants in section 163 of the Act. In addition to requiring regulations for the enumerated pollutants,

C ongress clearly intended to authorize EPA to establish additional pollutant

- specific PSD regulations, potentially containing increments, for any additional pollutants for which EPA promulgated a NAAQS under section 109 of the Act. Furthermore, because sec tion 166(a) refers to pollutants for which EPA promulgates NAAQS after 1977, and does not use the phrase “additional pollutants,” or “new pollutants” or some other phrasing that limits the scope of the provision, EPA concludes that section 166(a) provides authority for EPA to promulgate new increments after revising an existing NAAQS (including NAAQS first promulgated before 1977), when we find that such action is appropriate.12

Moreover, any new increments developed pursuant to section 166(a) have no eff ect on existing increments, as there is no indication therein that an existing increment should be revoked or replaced when additional increments are promulgated. This was the situation following the promulgation of new NAAQ S for PM in 1987 when EPA repla ced the old NAAQS

based on TSP with new ones based on PM 10

. Had Congress not added new section 166(f) in 1990, increments for PM 10 could have been developed pursuant to section 166(a) of the Act, but such increments would have had no effect on the origina l statutory increments for PM (based on TSP). Consequently, seeing no basis for retaining the original increments, Congress added section 166(f) which explicitly authorizes EPA to “substitute” PM 10 increments for the statutory
TSP increments defined by Co ngress

.

A ccordingly , we believe that PM 2.5 should be considered a “ new ” pollutant for regulatory purposes. This position is supported by the fact that we have retained the PM 10 indicator for the 24

- hour NAAQS and the PM 2.5 and PM

10 24

- hour NAAQS are re gulated separately

– t hey co

- exist, they are classified independently for attainment purposes, they are enforced separately, etc. We acknowledge that we considered section 166(f) as a possible option for adopting the annual PM 2.5 increment as a justificat ion for eliminating the existing annual

PM 10 increments. We recognized that the annual PM 10 increments could not simply be eliminated in response to revocation of the annual PM 10 NAAQS; they are replacement (equivalent substitute) increments for the statu tory TSP increments.

Again, when EPA established the PM 10 increments in 1993, we were replacing the existing statutory increments for TSP in light of the fact that we had eliminated the TSP NAAQS (24

- hour and annual). The “replacement” approach was ne cessitated by the fact that the TSP increments were set by statute (and remain in the statute) and, therefore, could not simply be removed. Instead, using the explicit authority under section 166(f) of the Act, we could adopt

substitute increments of equi valent stringency that would exist in lieu of the statutory TSP

increments. Without this statutory authorization, EPA would have been required to retain the existing (statutory) TSP increments, while at the same time considering the need for new

increment s based on the PM 10 indicator. Moreover, reliance on section 166(f) has implications for the baseline dates and baseline areas that we believe would be problematic for implementation of the new PM 2.5 increments. We have concluded that section 166(a) prov ides the clearest reading of the Act, as well as the most straightforward approach for developing increments for a pollutant or pollutant indicator for which there are no statutory increments.

Our position also relies, to some extent, on the fact that a re a number of practical issues

related to the implementation of the new PM 2.5 increments, including issues related to the “major source baseline date” and “trigger date” for the PM 2.5 increment system, and highlight the complexities involved with having t o establish and maintain two sets of emissions inventories for the 24

- hour and annual PM 2.5 increments. The s ection 166(a) approach clearly provides the basis for creating new baseline dates for the PM 2.5 increments. The relevant comments and our

respons es to these issues are presented in later section s of this document

.13



### 2.1.1.2 Comments on Alternatives to Increments

Comment:

T wo state/local agency commenter s (0019 , 0025 ) and one state /local agency association

commenter (0018) indicate their preference for the section 166(f) approach because it would require numerical increments for PM 2.5 , whereas the section 166(a) approach would allow states to develop alternatives to PM 2.5 increments. For o ne of the state/local agency commenter s (0019) , the primary concern with the section 166(a) approach is that the proposal allows states to substitute other measures in the place of uniform national increments for PM 2.5

. The state /local

agency association commenter (0018) similarly notes that not following the section 166( f) provisions would potentially open the door to alternatives to numerical increments that at this time are undefined and have the potential to decrease national consistency and rigor in the PSD

program.

Response:

U nlike the section 166(f) approach, th e section 166(a) approach , specifically at

section 16 6 ( d

) of the Act

, allows for the possibility of states to adopt alternatives to increments to prevent the significant deterioration of air quality

. W e acknowledge the potential problems (e.g., lack of un iformity) that could be created if some states with approved State Implementation Plan (SIP) provisions for PSD (referred to as “ SIP

- approved states ”) elect to develop alternatives to

PM 2.5 increments and receive approval from EPA for th o se alternative mea sures

. Notwithstanding th at concern

, consistent with our proposal and our decision to finalize PM 2.5 increments under section 166(a) authority ( for the reasons discussed in the Federal Register notice of this final action, this response to comments

, and e lsewhere in the record for this rulemaking ), we have also decided to provide states with the authority to adopt alternatives to increments for PM 2.5 (where an adequate demonstration can be provided), just as they now can for nitrogen dioxide (

NO 2 ) . See Se ction 2.1.2 of this document for more on the topic of

alternatives to increments.



### 2.1.1.3 Comments on Considerations Related to Surface Mining

Comment:

One industry commenter ’s (0031) primary concern is with how EPA addresses issues related to coarse, crustal fugitive dust emissions from western surface mining operations in developing measures to prevent significant deterioration from PM emissions. The commenter provides extensive comments on the history of the PM NAAQS and increments and associated litigation

. The commenter asserts that fugitive coarse PM (―fugitive dust‖) at ambient levels is of little public health or welfare concern , quoting experts in the field. The commenter contends

that the 1987 24

- hour PM 10 NAAQS was actually set based on the health effects of fine PM , and

that the increments for PM 10 set in 1993 using the ―equivalent substitution‖ approach under

section 166(f) of the Act did not take into account th e difference in effects that result from sources of fine PM and course PM (such as sur face mines)

. The commenter points out that the mining industry has had an ongoing problem with meeting the resulting PM 10 increments, and14

the commenter regards PM 10 as a confounded indicator for coarse PM because it consists of an

indeterminate mixture of fine and coarse PM.

Based on this background, the commenter (0031) believes that section 166(f) provides the most logical avenue for EPA’s revision of the PM increments precisely because it would result in the replacement of the annual and 24

- hour PM 10 increments

. The commenter contends that this would resolve the issue of how to address multiple forms of PM NAAQS in the PSD program, the confounded PM 10 indicator used in the existing PM 10 increments, and the mining industry’s continued inability to meet the PM 10 increments (which, the commenter asserts, are essentially premised on concerns with fine PM). In addition, the commenter argues that PM 2.5 increments alone would fulfill the requirements of section 166(c) of the Act, and that the Act

does not re quire that each NAAQS have a matching increment.

While the commenter (0031) believes that section 166(f) of the Act is the preferred avenue for adoption of PM 2.5 24

- hour increments , the commenter also stated that if EPA decides to adopt PM 2.5 increments pursuant to section 166(a) of the Act, section 166(a) is also the required avenue for adoption of new PM coarse increments. The commenter contends that

because the 2006 24

- hour PM coarse NAAQS is, indeed, a new standard (for the first time, EPA

is directl y regulating coarse PM with a NAAQS), EPA must consider whether the existing PM 10 increments should be revised in light of the new PM 10 NAAQS. Given the emphasis in the new NAAQS on concerns in urban areas and the focus on those areas for enforcement, and the confounding of PM 10 with PM 2.5 as found by the court in American Trucking Ass‟n. v. EPA , 175 F3d 1027 (D.C Cir. 1999), the commenter believes that the relationship of the new PM coarse standard to the statutory TSP increments may well have a different outcome than the 1993 PM 10 increments that were adopted in reference to the 1987 PM 10 NAAQS.

Response:

For the reasons already discussed above, we have decided to finalize PM 2.5 increments

under section 166(a) authority. We note that the alleged diffi culties experienced by the surface mining industry with the existing PM 10 increments will not be affected (relieved or exacerbated) by this action, and we do not believe that the considerations related to surface mining should drive this decision in light of the factors discussed previously

.

In th e final rule, EPA is not setting or amending any increments for PM 10 or otherwise taking action with respect to PM 10 increments. The pre

- existing annual and 24

- hour increments for PM

10 are being retained

. (Th is is discussed further in Section 3 of this document .) Similarly, EPA is not taking any action with respect to coarse PM in this rule. For these reasons, the commenter‟s arguments on what authority must be used to set increments for PM 10 and/or

coarse P M, and that EPA has some obligation to take action with respect to course PM, are not on point for this rule. Thus, no substantive response to this comment is needed. Nevertheless, as mentioned earlier, it is clear that Congress provided explicit authori ty under section 166(f) of the Act to address increments for PM 10 , because it intended for such increments to be substitute increments for the original statutory increments for PM , which were measured by the TSP indicator for PM

. Thus, the PM

10 increments legally supersede the original statutory increments for TSP . Had the PM 10 increments been developed under section 166(a), which prior to the 199015

Act Amendments was the only authority available for developing new increments, then the original statutory P

M increments would have remained in effect in addition to the PM 10 increments.



### 2.1.2 Comments on EPA’s Interpretation of the Requirements under the Section 166(a) Contingent Safe Harbor Approach

– Section s 166(a)

- (d) of the Act

Comment s on the Goals and Purpose s of S ections 101 and 160 of the Act :

One e nvironmental group (0040) claim s that in describing the contingent safe harbor approach, EPA incorrectly assert ed that PSD rules satisfying the goals and purposes of

s ection 160 of the Act will necessarily satis fy all of those in s ection 101 ( citing 72 FR 54122)

. The commenter notes that a lthough there is some overlap between the two s ections, they are not

identical. As an example, the commenter points out that section 101 expressly states that a primary goal o f the Act is to promote pollution prevention , but that goal is not stated in

section 160.

Response:

We disagree with the commenter and continue to believe that measures that satisfy the specific goals and purposes of section 160 also satisfy the more general purposes and goals identified in section 101 of the Act. As we stated in the 2005 NO 2 increment rulemaking, the overall goals and purposes of the Act listed in sections 101(b) and 101(c) are general goals regarding protecting and enhancing the nat ion‟s air resources and controlling and preventing pollution. Because these broad goals are given more specific meaning in section 160, EPA does not believe it is necessary to consider them in detail when evaluating whether PSD regulations satisfy the cri teria in section 166(c). 70 FR 59587 FN 3, October 12, 2005.

Regarding pollution prevention specifically, we believe that this general goal is encompassed in, and given more specific meaning by, sections 160(1), 160(2), and 160(4) of the

Act. These sec tions spell out the specific purposes under the PSD program for the general section 101 goals of controlling and preventing pollution. We believe that any requirement to limit or reduce emissions serves to promote pollution prevention, which is often the most cost effective means of lowering pollutant emissions.

Comment s on Balancing of Factors Applicable under Section 166(c) :

One e nvironmental group (0040) state s that EPA ― incorrectly and repeatedly assert s ‖ that

s ections 101(b)(1) and 160(3) of the Ac t pronounce goals of promoting economic growth or maximizing opportunities for economic growth ( citing 72 FR 54122) . The commenter note s that

these phrases appear nowhere in either s ection . I nstead, the commenter believes that both

s ections state only th at any growth that does occur must be consistent with protection of air quality.16

The commenter (0040) believes that EPA further err s by asserting that its PSD rules should allow some level of economic growth in Class I areas ( citing 72 FR 54123) . T he

c ommenter state s t hat this assertion is not only contrary to the statutory purposes, but to the plain language of the Act as well. As examples, the commenter offer s that where statutory increments

are consumed or where emissions will cause or contribute to a violation of the NAAQS, the Act plainly does not allow for some level of additional growth

– at least not via raising or exceeding

the increment. The commenter conclud e s that EPA’s notion that the need to satisfy the other requirements of s ection 166 a nd the other goals and purposes in s ections 101 and 160 can never preclude additional emissions from economic growth unlawfully elevates such growth ov er all other statutory factors.

Response:

The language in section 160( 3 ) of the Act provides that one of the purposes of the PSD program is “to insure that economic growth will occur in a manner consistent with the preservation of existing clean air resources.” The commenter suggests that this language can only be read as if the statutory phrase “economic growth” actually said “ any economic growth that does occur” such that section 160(3) says “to insure that any economic growth that does occur will occur in a manner consistent with the preservation of existing clean air resources.”
We disagree . T

he phra sing used by Congress is “to insure that economic growth will occur



### ... .” Thus, we believe the plain language of the statute supports EPA‟s reading that section 160(3) requires a balancing of the goals of (1) economic growth and (2) preservation of existing clean air resources. At a minimum, if the language were to be considered ambiguous enough to allow the commenter‟s reading, then the Agency‟s interpretation is also a reasonable reading of the statutory language.

We do not agree with the commenter‟s int erpretation of our position concerning economic growth. It is not our intention to say that the other goals and purposes in sections 101

and 160 can never preclude additional emissions from economic growth. In recognizing the need to balance the differen t goals set forth under sections 101 and 160, economic growth needs to be given fair treatment as a specific goal of the PSD program under the Act. That is not to say, however, that it must preclude consideration of other specific goals set forth by the A ct. We acknowledge that under certain circumstances, such as when a source‟s emissions exceed the maximum allowable increment, or would have an adverse effect on an air quality related value ( AQRV ) in a Class I area, then economic growth cannot be allowed to occur unless some remedial action can be taken to insure that such other goals of the Act are met.

Comments on States’ Authority to Adopt Alternatives to Increments:

One state /local agency (0015) and one f ederal agency (0044 ) expresse s support for our proposal that state s may develop alternatives to increments, provided that the alternative approach otherwise meets the requirements of sections 166(c) and (d) of the Act. The federal

agency (0044) suggest s that EPA add specific language to that effe ct to 40 CFR 51.166 to make that intention clear in the regulations. An industry commenter (0031) also support s the use of alternatives to increments, argu ing that g iven the differences in the states and the issue s confronting those states , such flexibili ty is key to making the PSD program work. This17

commenter further argue s that the flexibility to adopt alternative measures recognizes Congress’ grant of significant discretion to states in implementing the PSD program, and continues the

federal

- state part nership that is a key underpinning of the Clean Air Act.

Two state / local agency commenters ( 0019, 0033)

, two state/local agency association commenters ( 0018, 0021) , and one environmental group (0040) oppose revising 40 CFR 51.166(c)(2) to allow alternati ves to PM 2.5 increments

. These commenters generally warn against sacrificing the national consistency of uniform PM 2.5 increments.

For two of the c ommenters ( 0018 and 0019 ) , the potential for states not to use the

uniform national increments for PM 2.5 w as a prim ary reason for opposing section 166(a) as the

basis for PM 2.5 increments. One of these commenters (0019) add s that alternative increments

would undermine desired national consistency, and EPA has failed to identif y any CAA programs which wou ld be nefit from this approach.

One of the state/local agency association commenters ( 0021) disagree s with the legal interpretation that would remove nation uniformity from PM 2.5 increments

. The commenter (0021) assert s that a nationally inconsistent regulato ry ap p roach to PM 2.5 in attainment areas could result in a patchwork of state PSD regulations

– and the exact kinds of economic repercussions that Congress wished to avoid. The commenter explain s that some states might

sacrifice clean air for industrial development

, and more industrialized states could see the erosion

of their industrial base as sources move to attainment areas. The commenter add s that varying

increment

- equivalent measures could also result in an uneven playing field for industry and

co uld exacerbate difficulties between states experiencing transport problems.

Similarly, o ne of the state / local agency commenters ( 0033) object s to this approach

because it w ould likely lead to a ― mish

- mash ‖ of state approaches . The commenter believes tha t
this would defeat the intention of Congress that there be uniformity in PSD rules to avoid

economic dissimilarities from state to state which could allow interstate competition for industry based upon which state offers the best (least expensive) environ mental compliance regulations.‖

The e nvironmental group (0040) agree s that the Act allows for other approaches, but believes that such approaches must be in addition to the national increments. Specifically, this

commenter state s that although EPA can provide for states to adopt approaches in addition to

increments in order to fulfi ll the statutory purposes, the A gency must make clear that states cannot adopt approaches that are less protective tha n the national increments. The commenter
believes that the rules will not meet th is requirement if they allow states to adopt alternative approaches that are less protective of air quality values, parks, and natural areas than EPA itself has determined are warranted by the statute. T hus, t he commenter argue s that to the extent that EPA is suggesting that it can allow states to adopt PSD programs that do not include the minimum federal increments, that position is contrary to the statute.

Response:

As in the 2005 NO 2 increment rulemaking, we have decided to codify the basic principle

that states can seek to use alternative measures in their plans other than increments

, without defining any specific type of alternative program that would be approved or otherwise creating18

standards beyond the requirements of se ctions 166(c) and 166(d). Instead, in the event that a state proposes a specific alternative approach for EPA to approve as part of a SIP, we plan to

make determinations on a case

- by

- case basis. In making those determinations, we will address the specifi c alternative measures as states propose them to the Agency in light of the requirements of sections 166(c) and 166(d), including whether the alternative program is “at least as effective as the increments established in section 163,” as required in sectio n 166(d).

While we acknowledge the potential problems identified by the commenters associated with allowing states to adopt alternative approaches to the numerical increments that we are establishing, we also note that section 166( d ) of the Act provides that the measures to fulfill the goals of section 166 “may contain” increments, emission density requirements

, “or other measures,” which we conclude is properly read to give states latitude to submit a plan that does

not include ma

x imum allowable increase s (increments) for pollutants for which new or revised NAAQS are promulgated. Thus, EPA is authorized to provide that states may consider

alternatives to the increments established in th e final rule for PM 2.5 increments, SILs

, and SMC

. That said, the sta tutory authority is not a blank check for states to do as they please, but enables states to consider options that may provide a meaningful way for them to manage their air

resources within the framework allowed by the statutory PSD requirements

.

In EPA‟ s proposed rule notice, we discussed this issue and proposed to revise the existing 40 CFR 51.166(c)(2) to allow states to adopt alternatives to any increments that we

would codify pursuant to section 166(a) of the Act (72 FR 54123) . Consistent with our

d iscussion of this issue, we are confirming our interpretation that the authority to adopt alternative measures covers any pollutant subject to section 166(a), and revising 40 CFR 51.166(c)(2) to make it inclusive to all applicable pollutants rather than ju st NO 2

.



### 2.1.3 Comments on EPA’s Interpretation of the Requirements under the Section 166(f) Equivalent Substitution Approach

Comment:

One environmental group (0040)

, who believes that EPA does not have the authority to adopt PM 2.5 increments pursuant to secti on 166(f)

, state s that, even if EPA could adopt PM 2.5 increments pursuant to section 166(f), the proposal to use the 1993 ―equivalent to statutory increments‖ approach is not consistent with the statute. The commenter explain s that under that approach, EP A would reject the percentage

- of

- NA AQS approach used under section 166(a) based on the argument that Congress could have easily revised the increments in section 163 of the Act instead of providing EPA discretion to establish increments following the stand ard provided in section 166(f) (citing 72 FR 54123 )

. The commenter argu e s that the fact that Congress did not revise the increments does not show that Congress meant for the PM 2.5 increments to be any less protective (in terms of percentage of the NAAQS) than increments adopted under s ection 166(a). Instead, t he commenter believes that by specifying an equal

stringency

- in

- effect test in section 166(f), rather than just stating minimum increments, Congress gave EPA authority to establish increments or othe r measures that would ensure greater protection than a strict percentage

- of

- the

- NAAQS approach, where the latter would not in fact provide the same level of environmental protection as the TSP increments. The commenter19

state s that EPA offers no rational e xplanation, and none exists, why Congress would want to provide a less protective benchmark for PM 10 increments than for increments for other pollu tants such as nitrogen dioxide.

The same commenter claim s that EPA is also wrong in asserting that the ―equ al stringency in effect‖ language allows the agency to completely ignore the welfare and visibility effects of any new PM 2.5 increments. The commenter sta te s that such an approach impermissibly ignores the statutory purposes set out in s ection 160 of the Act

. According to the commenter

, what ever discretion EPA may have in construing the ― equal stringency in effect ‖ language, it cannot adopt a construction that wholly ignores the statutory purposes. The commenter state s that contrary to the A gency’s asser tions, the purpose of increments is not merely to allow the same the level of degradation in each area of the same classification, but to protect public health and welfare, preserve and enhance air quality in natural areas, and achieve the other purposes i n

s ection 160 of the Act

.

Response:

U nder the final rule we did not rely upon the authority of section 166(f) of the Act to promulgate the new increments for PM 2.5 . Irrespective of this, we wish to make one point concerning the comment that our propose d increments based on the equal stringency approach called for under section 166(f) were flawed by the fact that the resulting increments could not be considered fully protective of public health, welfare and visibility effects : Neither the original

stat utory increments for PM nor the substitute PM 10 increments are intended to be by themselves fully protective of public health and welfare

, a s well as visibility effects. A specific PSD provision at section 165(a)(3)(B) i n the Act require s sources to demon strate compliance with the health and welfare based NAAQS, even when a portion of the increment remains available. In addition, another specific provision of the statutory PSD program provide s for the protection of AQRVs even when the entire Class I incre ment is not consumed (section 165(a)(5)(d)).

Comment:

An i ndustry a ssociation commenter (0034)

, who believes that s ection 166(f) provides the exclusive authority for EPA to adopt PM 2.5 increments

, asserts that s ection 166(f) contains principles for updating PM increments, which are summarized as follows:

 The EPA is authorized but not required to promulgate a new PSD increment for PM when it changes the indic ator through the NAAQS process.

 The Administrator may substitute a new PM increment for the pre

- existing increment , but cannot maintain the pre

- existing increment and the new increment at the same time.

 Replacement of PM increments must have the same stringency in effect as the one they replace, which differs from the percentage

- of

- the

- NAAQS ap proach used by Congress to define the original PM increments.

 The PSD program must have one effec tive PM increment at all times. The existing increments must remain in place until the replacement increments are in place.20

One state /local agenc y commenter (0019)

, who believes that section 166(f) is the only legitimate basis for PM 2.5 increments

, nevertheless does not disagree with the specific numerical increments proposed by EPA under Option 1 (which were developed under section 166(a) authority ) since th e method relies upon the same percent age

- of

- the

- NAAQS approach used in the

A ct to establish the SO 2 and TSP increments

. The commenter believes that EPA is free to define

the PM 2.5 increments under section 166(f) using either the percentage

- of

- the

- NAAQS ap proach or the ―equivalent substitution‖ approach it used when it set the PM 10 increments in 1993

, asserting that the percentage

- of

- the

- NAAQS approach meets the equal

- stringency requirement of section 166(f) of the Act. The commenter notes that EPA’s final rulemaking for PM 10 increments in 1993 stated that both methods were permissible. The commenter adds that the two

methods yield very similar values for the PM 2.5 increments with only slight differences.

Response:

W here EPA determines that a new PM NAA QS is covered by section 166(a) of the Act, we interpret the Act to require EPA to promulgate regulations to prevent significant deterioration of air quality as a result of emissions of the new PM indicator, which may or may

not include increments.

As di scussed previously, we agree with the commenter that section 166(f) authorizes EPA

to substitute a PM 10 increment for the previously existing TSP increment, but does not allow us to maintain both the new and previously existing increments. We also agree t hat the PSD program must have at least one effective PM increment at all times (as long as a PM NAAQS is in existence)

, but we do not believe that the PSD program is limited to increments for only one

PM indicator at a time

. As explained in Section 2.2.1 of this document, we have developed PM 2.5 increments under section 166(a) authority in part because we believe that the PSD program should include increments for both PM 10 and PM

2.5

. We do not believe that having only one set of PM increments for the 24

- h our averaging period would necessarily provide adequate protection for both the 24

- hour PM 10 NAAQS and 24

- hour PM 2.5 NAAQS

. For example , we continue to believe that the combination of the PM 2.5 increments and the retention of the 24

- hour

PM 10 increments w ill help address non

- visibility welfare impacts attributable to deposition of particles of any size.

We agree conceptually with the commenter who indicated that the percentage

- of

- the

NAAQS approach may be used to develop PM increments under section 166( f) of the Act, and we disagree with the commenter who asserted that such an approach is unacceptable. Although we elected to use the “equivalent substitution” to finalize the PM 10 increments under section 166(f) in 1993 and proposed to use that approach f or PM 2.5 increments if we finalized them under section 166(f), we did not in 1993, and we do not now, interpret section 166(f) to preclude the use of the percentage

- of

- the

- NAAQS approach.

Any use of the percentage

- of

- NAAQS approach, however, would need t o ensure that the resulting increments are of equal stringency in effect to the PM 10 (and TSP) increments that they would replace under the procedures set forth in section 166(f) of the Act. This “equivalency” condition is an important consideration as pa rt of the unique purpose of section 166(f) to21

develop “equivalent” increments that effectively replace the original TSP increments defined by Congress under the 1977 Clean Air Act. “Equivalence” under section 166(f) of the Act would

also seem to necessita te retaining the baseline areas and baseline dates that exist for the PM 10 increments (and previous TSP increments) , a concept that was opposed by most commenters, including this one.



### 2.2 Comments on Option 1 for PM 2.5 

### Increments

– Contingent Safe Harbor App roach for Annual and Short

- Term Increments

2.2.1 Comments Supporting and Opposing Finalizing Option 1 at the Proposed Levels

Proposed Option 1 is termed the ―contingent safe harbor approach‖ and is based on the authority of section 166(a) of the Act. See Envi ronmental Defense Fund v EPA , 898 F.2d 183,

188

- 189 (D.C. Cir. 1990); Environmental Defense v. EPA , 489 F.3d 1320, 1325

- 33 (D.C. Cir. 2007). This approach involves first deriving the increment values based on the percentage of the NAAQS used by Congress t o derive the original PM increments in terms of TSP

, and then evaluating whether alternative increments or additional measures are necessary to meet the criteria of section 166(c) of the Act. Under Option 1, we proposed to adopt the safe harbor

increments for PM 2.5

.

Comments Favoring Option 1:

Seven commenters ( 0015

, 0020, 0023, 0026, 0027

, 0029

, 0046 ) support Option 1 for

PM 2.5 increments , either explicitly or implicitly supporting our method of calculating the safe

harbor increments and their use as t he final PM 2.5 increments. These commenters do not take a position on the use of section 166(a) of the Act as the legal authority for the increments

. Two additional tribal commenters (0041, 0049) express support for section 166(a) as the basis for the

in crements without explicitly mentioning Option 1.

In support, a state / local agency (0015) point s out that the increments under proposed Option 1 are consistent with the approach followed to develop the annual NO 2 increment s

. Similarly, an i ndustry commen ter (0026) note s that the same Option 1 approach was up held for

NO 2 by the U

. S

. Court of Appeals in June 2007

.

In addition, o ne i ndustry commenter (0016) offer s conditional support for Option 1

, indic at ing that issues regarding EPA’s legal authority to create increments must be addressed for this approach to have value. (See th is comment and our response in Section 2.1 of this document.) If it is established that EPA has sufficiently stated and, in fact, has legal authority for the proposed regulation of PM 2.5 in the general manners proposed, the commenter would support Option 1 for the establishment of PSD increments (and SILs and SMCs).

One environmental group commenter (0040) agree s with the safe harbor increment approach under Option 1, but dis agree s with our analysis of the adequacy of the safe harbor increments, as discussed in Section 2.2.2 of this document

.22

Comments Opposing Option 1 :

An industry association commenter (0036) state s that the Option 1 approach for determining the PM 2.5 incr ements under Option 1 i s not scientifically supported. The commenter believes that basing the PM 2.5 increments on the same percentages of the NAAQS that were used

to set PM 10 increments based on the TSP NAAQS ignores the relationship between PM 10 and

PM 2. 5 emissions, which may be much different than the relationship between TSP and PM 10 emissions. Because the ratio of PM 2.5 to PM 10 emissions is 0.8, it appears that using the percentages proposed by EPA would indirectly restrict PM 10 /TSP emissions and air quality impacts to proportionally lower levels than the PM 10 increments in order to avoid exceeding the

PM 2.5 increments. The commenter concede s that using the 0.8 factor to set PM 2.5 increments may seem too high, but asserted that using the Safe Harbor a pproach would set increments for

PM 2.5 that are too low.

Another industry association commenter (0014) contends that the PM 2.5 increments

should be twice the propos ed levels because scientific studies do not support the need for such low levels for prote ction of health and welfare. The commenter believes that increments at the proposed levels would jeopardize the goal of providing opportunities for economic growth. The
commenter expresse s concern over EPA’s use of epidemiologic studies and questioned th e ability of such studies to provide a reliable evaluation of health risks. The commenter claim s that epidemiologic studies are capable of finding association between a substance or exposure and a health effect but rarely capable of determining if there i s causation, while toxicological studies using randomized trials are specifically designed to determine causation. The commenter

add s that other factors providing evidence for causation include dose

- response relation ships, consistency, and repeatability of studies, which the commenter sa ys are not present in the studies cited by EPA. The commenter specifically refer s to two studies, acknowledged by EPA to show

no evidence of a dose

- response relationship gradient between PM 2.5 and specific health related

effects. Because the PM 2.5 NAAQS is low relative to the PM 10 NAAQS, the commenter as s erts that it is not appropriate to use the same percentages of the NAAQS for establishing increments

as were used for TSP and PM 10

. The commenter indicates that higher l evels would still provide adequate protection of public health with an adequate margin of safety.

Response:

We agree with the commenters who support Option 1. A fter determining that

section 166(a) of the Act is the appropriate basis for PM 2.5 increment

, as previously discussed in

Section 2.1.1 of this document, we evaluated the Option 1 safe harbor increments based on a percentage of the NAAQS approach to determine whether they are sufficient to meet the requirements of section 166(c) of the Act. Based on our evaluation of the effects of PM 2.5 and a balancing of the criteria in section 166(c) of the Act (and the incorporated goals and purposes of the Act contained in section 101 and the statutory PSD program in section 160 of the Act), we concluded that the safe harbor increments for PM 2.5 (which satisfy section 166(d) of the Act) are sufficient to fulfill the criteria in section 166(c) when combined with the other measures in the PSD program that we apply to PM 2.5

.23

We agree with these comme nters about the appropriateness of using Option 1 to develop the new increments for PM 2.5

. A s discussed in Section 2.1

, we believe that in the proposal we explained our preliminary interpretation of the legal authority available for developing the PM 2.5 increments u nder either Option 1

, Option 2A or 2B

. While we solicited comments on the possibility of using the substitution approach for the 24

- hour PM 2.5 increment, we have

concluded

, among other things, that there is no strong justification for using the substituti on approach over the approach provided via section 166(a) to replace the existing 24

- hour PM 10 increments since we are not revoking the 24

- hour PM 10 NAAQS. Howe ver, we believe that the section 166(a) approach is the most direct and supportable approach fo r developing all the

PM 2.5 increments. W

e have not reached any final conclusion as to whether the Option 2 equivalent substitution approach under section 166(f) of the Act is permissible under the Act

.

The opposing commenter is incorrect in claiming th at we based the PM 2.5 increments on the same percentage of the NAAQS that were used to set the PM 10 increments. We adopted the

PM 10 increments using the “equivalent substitution” approach set forth under section 166(f) of the Act. Under that approach, ra ther than calculating the PM 10 increments as specific percentages of the PM 10 NAAQS (using the same percentages that Congress used for setting the statutory increments for PM and SO 2 ), EPA determined the levels of the PM 10 increments that could represent a n equivalent amount of increment consumed, as if the TSP increments were still in effect. See 58 FR 31622, June 3, 1993, at 31626

- 31627. Nevertheless, the commenter is correct that, in cases where the ratio of PM 2.5 to PM

10 emissions is 0.8 for an indi vidual source, the source may have to reduce its PM 10 emissions more than would otherwise be necessary to

meet the PM

10 increments in order to control its PM 2.5 emissions sufficiently to meet the safe

harbor PM

2.5 increments. 3 This is because the safe har bor PM 2.5 increments are less than

80 percent of the PM 10 increments. For example, the Class II 24

- hour PM 2.5 safe harbor increment (9 μg/m 3 ) is only 30 percent of the corresponding PM 10 increment (30 μg/m 3 ).

The underlying reason that the safe harbor P M 2.5 increments are so much l ower than the

PM 10 increments is that the PM 2.5 NAAQS are considerabl y lower than the PM 10 NAAQS. 4 This is the result of the evolution in our knowledge about the health and welfare effects of PM, in particular the effects of t he fine PM represented by PM 2.5 . We believe that it is fitting for PM 2.5 increments to reflect our greater knowledge about PM 2.5 effects (as embodied in the NAAQS), rather than to simply maintain the control level required by the PM 10 increments as sugges ted by the commenter. If this results in PM 2.5 increments that are more limiting than PM 10 increments, we believe that this outcome is appropriate in light of our statutory requirement to prevent significant deterioration of air quality as it relates to P M 2.5

.

We disagree with the second opposing commenter‟s recommendation that the increments should be twice the proposed (and final) levels. The scientific studies to which the commenter referred pertain to studies that EPA used to determine the health

- ba sed NAAQS for PM 2.5 , and we do not believe it is relevant to this rule to respond to comments related to the setting of the NAAQS. The NAAQS are designed to protect public health and welfare; increments then are

3 Note that the PM 10 increment may still be more limiting in areas where much of that increment has already been consumed.

4 The 24

- hour PM 2.5 NAAQS (35 μg/m 3 ) is about 23 percent of the 24

- hour PM 10 NAAQS (150 μg/m 3 ).24

intended to insure that air quality in clea n areas is not allowed to deteriorate significantly, and the PSD regulations insure that any such deterioration does not lead to air pollution levels that exceed the levels defined by the NAAQS.

As discussed previously, we have decided to finaliz e this rulemaking using the contingent safe harbor approach under section 166(a) of the Act. Using this approach, we calculated the

“ contingent safe harbor” increments as percentages of the NAAQS equal to the percentages that Congress used to establish the orig inal statutory increments for PM and SO 2 . These values represent the level of effectiveness necessary to satisfy section 166(d) of the Act, and could be tightened if necessary based on further analysis to determine if additional measures are

necessary to fulfill the requirements of section 166(c) of the Act. Thus, under this approach and on this record, we do not conclude that it is appropriate to finalize increments at levels any less stringent than the contingent safe harbor increments, as the commenter recommends.



### 2.2.2 Comments on the Proposed Framework for PSD Regulations for PM 2.5 

### and on EPA’s Evaluation of the Statutory Factors for Increments

One environmental group (0040), while believing that the contingent safe harbor approach (Option 1) based on sec tion 166(a) authority is the only option that is consistent with the Clean Air Act (see Section 2.1.1 ), nevertheless asserted that EPA’s proposed application of that approach to PM 2.5 is flawed. This commenter’s extensive comments are summarized in the

su bsections below, along with the comments of a few other commenters who addressed these

issues.



### 2.2.2.1 Comments on Stimulating Improved Control Technology

One of the requirements of section 166(c) of the Act

, which apply to increments developed under section 166 (a)

, is to provide ― a framework for stimulating improved control technology. ‖

Comment:

Th e environmental group commenter (0040) state s that, although increments may encourage the use of existing control technologies, EPA has not cited any evidence tha t increments actually stimulate the development of improved technologies. Moreover, the

commenter assert s that even if increments provide the incentive asserted by EPA, any encouragement of improved control technology is wholly incidental and hardly amoun ts to a ―framework‖ whose purpose is to stimulate such technology.

Response:

We have concluded that the total program, encompassing increments and the requirement to install best available control technology ( BACT ) controls , does provide an appropriate framework to stimulate BACT in such a way that it is not simply “wholly incidental,” as the commenter claims. The fact that economic growth in an area must occur within a defined amount of allowable air quality deterioration should logically lead to the25

a pplication of improved pollution control technology as the amount of deterioration increases, and should not be regarded as an incidental consequence. As we stated at proposal, Congress envisioned that the increments they originally established would serv e as an incentive: “the incremental ceiling should serve as an incentive to technology, as a potential source may wish to push the frontiers of technology in a particular case to obtain greater productive capacity with the limits of the increments.” S. Re p. 95

- 127 at 18, 30 (3 LH at 1392, 1404). We, too, believe that as the available increment in an area becomes smaller, and as states try to preserve some of the remaining increments for future growth, it will be necessary to require sources to install

mor e stringent controls in that area. Such levels of control ultimately must be considered in subsequent BACT evaluations in other PSD areas throughout the country. T he increasing stringency of control technologies over time, as observed in EPA‟s BACT/Lowes t Achievable Emission Rate (LAER) Clearinghouse, supports that the PSD program has already stimulated development of improved control technology , though this does not conclusively demonstrate that

because there are undoubtedly a number of factors that coul d cause such trends. Nevertheless, even the need to require a more stringent BACT determination in only a few PSD areas (due to dwindling increment availability) necessitates consideration of that level of control for all other PSD sources wherever they m ay decide to locate. In any event, while the commenter generally question ed the effectiveness of the increments as an incentive for tightening BACT, they provided no evidence that more stringent BACT is not related to the increment system established as a n integral part of the PSD program.



### 2.2.2.2 Comments on Protecting National Parks and Other Special Areas

Another requirement of section 166(c) of the Act is to provide ―protection of air quality values, and fulfill the goals and purposes‖ in sections 101 and 1 60 of the Act. Section 160(2) sets forth the purpose ―to preserve, protect, and enhance the air quality in national parks, national wilderness areas, national monuments, national seashores, and other areas of special national or regional natural, recreati on, scenic, or historic value.‖

Comment :

The environmental group commenter (0040) stated that EPA has not complied with section 166(c) of the Act because the Agency has not made a finding or demonstrated that the

PM 2.5 PSD rules will (as required by sec tion 160(2) of the Act) preserve, protect, and enhance the air quality in parks and special areas. The commenter states that EPA concedes that parks

and natural areas throughout the nation are already suffering from air quality degradation, visibility imp airment, and significant ecological damage due to fine particle pollution ( citing 72

FR 54 129 (PM 2.5 contribution to visibility impairment in Class I areas); EPA, Air Quality Criteria for Particulate Matter, Vol. 1, Ch. 4 (2004) )

. The commenter contends t hat the proposed Option 1 increments and related baselines and trigger dates will allow fine particle

- related pollution to worsen in parks and natural areas whose air quality is already degraded , and questions how the proposal c an be found to ―preserve, pr otect, and enhance‖ air quality in parks

and natural areas. The commenter believes that EPA has not made such a finding or demonstration, but instead offered only vague assertions that the proposed increments would ―satisfy‖ the statutory factors and that they, along with other programs, would ―help‖ to fulfill the statutory purposes. The commenter went on to argue that EPA sought to excuse its failure to26

show fulfillment of the statutory purposes by asserting that it cannot develop a uniform, quantitativ e, dose

- response relationship between fine particle levels and certain ecosystem impacts (citing 72 FR 54134), but that, even if true, such a claim does not excuse the agency from satisfying its statutory duty under section 166(c).

Response:

We conclude that the proposal demonstrated that the contingent safe harbor increments, in combination with the other aspects of the regulatory framework, fulfill the statutory requirements despite the scientific uncertainties. We reiterate d that finding in the final rulemaking . The fact that we did not, at proposal, explicitly state this as a finding does not

diminish the demonstration made at that time and reiterated in th e final rulemaking

. The analysis presented at proposal, as well as the comments and responses in the balance of this

section

, illustrate that the proposed and final Option 1 increments fulfill the requirement to

“ preserve, protect, and enhance” air quality in parks and other special areas. We explained in a previous response that provisions of th e statutory PSD requirements separate from the requirements for increments are intended to provide protections not necessarily provided by the

increments.

Comments on “Critical Loads”

Comment:

The environmental group commenter (0040) believes that the relationship between PM 2.5 and adverse effects can be quantified to a greater extent than stated by EPA. Regarding acid rain and other adverse ecological impacts, the commenter asserted that critical loads can be established as a way of quantifying and li miting the PM 2.5 contribution to degradation, and noted that critical loads are now used by authorities in Europe, have been endorsed by leading North American scientists, and have been used by federal land management agencies. To comply with section 166( c), the commenter believes that EPA must establish a mechanism to supplement the nationally uniform increments with additional measures, including a requirement to establish

area

- specific critical loads or equally protective limits, where necessary to prot ect and enhance air quality in specific parks and natural areas.

Response:

With regard to the critical load concept, we agree conceptually with the commenter that critical loads could be used to supplement the existing increments, especially as a means of protecting the known sensitive ecosystems within Class I areas. While we disagree that the critical loads concept can be used as an effective replacement to increments for limiting air quality degradation, we believe that the concept offers considerabl e promise in helping to protect sensitive receptors in specific Class I areas. However, we do not believe that it would be appropriate at this time to establish a requirement for area

- specific critical loads under the PSD program. In our 2005 PSD rule fo r NO 2 increments, we indicated that states could propose using information on critical loads as part of their approach for managing air quality in their

individual SIP

- approved PSD programs, but sufficient information was not yet available for EPA27

to incor porate the use of critical loads into the national PSD program. See 70 FR 59582, October 12, 2005 at page 59613.

The concept of critical loads is useful for estimating how much pollution a particular ecosystem can experience on a prolonged basis without showing adverse effects. In addition to addressing the opportunity for using critical loads under its NO 2 i ncrement r ule, EPA has addressed the concept of critical loads in the last review of the PM NAAQS and currently in the secondary NO

x

/ sulfur oxides ( SO

x ) NAAQS review. 5 To date in the United States, critical loads have had their primary application in the area of atmospheric deposition of sulfur (S) and nitrogen (N). In the last review of the PM NAAQS, EPA found that ambient PM was contributing to t he total load of pollutants entering the U.S. ecosystem annually. However, the review also concluded that there was “insufficient data for the vast majority of U.S. ecosystems that differentiate the PM contribution to total N [nitrate] or S [sulfate] depo sition to allow for practical application of this approach as a basis for developing national standards to protect sensitive U.S. ecosystems from adverse effects related to PM deposition.” The 2005 Staff Paper for the PM NAAQS, in reaching this conclusion , addressed various important factors, including (1) the lack of a long

- term, historic database of annual speciated PM deposition rates to establish relationships between PM deposition and ecosystem responses; (2) uncertainty in predicting the amount of PM deposited to sensitive receptors from measured concentrations of PM in the ambient air; and (3) the unique nature of each ecosystems and the current inability to extrapolate with confidence any effect from one ecosystem to another. The 2005 Staff Paper

r ecommended that EPA give serious attention to the critical load concept and recommended the collection of data from a “greater variety of ecosystems over longer time scales to determine how ecosystems respond to different loading rates over time.” Staff P aper at page 7

- 19.

The review of the secondary NAAQS for NO

x and SO

x , which is currently underway, is evaluating ecological effects due to the deposition of NO

x and SO

x . The two main targeted effects are acidification and nutrient enrichment in both aq uatic and terrestrial ecosystems. This

review i s attempting to use critical loads to evaluate the impact of current depositional loads and alternative loads in several case study areas. However, as mentioned earlier, the estimation of ecosystem critical loads expressed in terms of PM requires long

- term ecosystem

- level data on speciated PM deposition rates for which an adequate database is currently lacking for most sites

in the United States.

Comments on Deterioration of Air Quality

Comment:

Th e e nvir onmental group commenter (0040) states that EPA provided no review of the

PM 2.5 incre ments added to baseline concentrations to assess how well the proposed increments

will prevent significant deterioration of air quality relative to the NAAQS. The commen ter
obtained 2006 PM 2.5 monitoring data for all U.S. monitor locations reported on EPA’s AirData

5 In the 2005 OAQPS Staff Paper reviewing the NAAQS for PM, EPA cited the following accepted definition of “critical load”: “quantitative estimate of an exposure to one or more pollutants below which significant harmful effects on specified sensitive elements of the environment do not occur according to present knowledge.” See page 6

- 45.28

website and evaluated the 98th percentile value of the 24

- hour average PM 2.5 concentrations and the annual average PM 2.5 concen trations and added the EPA’s pr oposed PM 2.5 increments to those values. The commenter evaluated the most stringent of EPA’s options: 2 μg/m 3 (24

- hour average) and 1 μg/m 3 (annual average) for Class I areas, and 9 μg/m 3 (24

- hour average) and 4 μg/m 3 (annual average) for Class II areas ( i.e., Option s 1 and 2A).‖

The commenter ’s evaluation results to the 24

- hour increments and NAAQS are as follows :

• EPA’s AirData website identified 1,174 PM 2.5 ambient air monitoring sites operating in

2006.

• Fourteen percent of 98th percentile values alre ady exceeded the 24

- hour PM 2.5 NAAQS of 35 μg/m 3

.

• For the remaining monitors, adding the proposed Class II PM 2.5 increment of 9 μg/m 3 to the 2006 98th percentile 24

- hr average resulted in exceedances of the 24

- hour NAAQS at

55 percent of those locations.

Th us, th e commenter concluded that for 55 percent of the locations with PM 2.5 monitors that were not already exceeding the PM 2.5 NAAQS, 24

- hour average PM 2.5 concentrations would be allowed under EPA’s proposed PM 2.5 increments to degrade up to the level of the NAAQS, assuming that the PM 2.5 baseline date was triggered in 2006 for all of these areas.

Using the same assumptions , the commenter’s analysis also showed that for 84 percent of locations not already exceeding the NAAQS, the 24

- hour PM 2.5 concen trations would be allowed to increase to a level of 30 μg/m 3 or more. The commenter believes that allowing such levels would not be protective of public health, given that we stated at proposal that we had previously

found that PM 2.5 concentrations less t han a range of 30

- 35 μg/m 3 (24

- hour average) were protective of public health (citing 72 FR 54128). The commenter claim s that th is analysis shows that for the majority of areas, the proposed 24

- hour average PM 2.5 increments would not prevent

PM 2.5 conce ntrations from increasing up to the level of the NAAQS and also would not be protective of public health.

The environmental group commenter’s analysis showed similar results for the proposed

annual PM 2.5 increments. Based on the same methodology, t he commenter asserted that PM 2.5 concentrations would be allowed to increase up to the level of the annual NAAQS in 55 percent of the locations that are currently in attainment, and that 87 percent of these sites would be

allowed PM 2.5 concentrations of 12 μg/m 3 or higher. Again, the commenter believes that allowing annual concentrations at or above 12 μg/m 3 would not be protective of public health,

based on our statement at proposal that we had previously found that PM 2.5 concentrations less than a range o f 12

- 15 μg/m 3 (annual average) were protective of public health (citing 72 FR 54128).

Response:

We do not believe that increments must be set at levels that ensure that the full amount of increment will be available in all locations. The statutory pr ovisions in the PSD program have always been clear that a source must demonstrate that it will comply with both the NAAQS and29

increments for any pollutant. Consistent with Congressional intent, the PSD program does not allow a source to violate the NAAQS just because its emissions will not cause the increments to be exceeded. If the increments were to be developed in such a way that all areas, taking into account current ambient air quality status, would be able to use the full amount of increment,

then t he increment levels would have to be unnecessarily stringent in areas that are substantially cleaner than levels allowed by the NAAQS.

Congress recognized that all areas of the country might not be able to use the full amount of increment when they pro vided provisions within the Act requiring that both the NAAQS and increments must continue to be met at all times. In areas where the full amount of increment is not available due to levels of pollution approaching the NAAQS, emissions reductions may be

r equired to allow for economic growth to occur within the limits allowed by the increments. Hence, we do not believe it is reasonable to unduly restrict economic growth in cleaner areas by setting more restrictive increments to help maintain air quality le vels below the NAAQS in areas which are currently only marginally attainment.

In addition, we disagree with the commenter‟s assertion that the increments will not protect public health. In setting the PM 2.5 NAAQS at 35 μg/m 3 (24

- hour) and 15 μg/m 3 (annual), EPA concluded that these levels protect public health with an adequate margin of safety. Regardless of the level at which the increments are set, no source is permitted to cause the NAAQS to be exceeded. That is, the upper bound on the permissible concentration of PM 2.5 is determined by the increment or the NAAQS, whichever is more restrictive in each particular case. Thus, the entire framework of the PM 2.5 regulations, including the safe harbor increme nts, is protective of public health. In asserting otherwise, the commenter has misconstrued our statements in this regard.

In the proposal preamble‟s section on the health effects of PM 2.5 (72 FR 54127

– 54128), we discussed the fact that we considere d setting the 24

- hour NAAQS in the range of 30 to 35 μg/m 3 and the annual NAAQS in the range of 12 to 15 μg/m 3 . However, we concluded in setting the NAAQS that 35 μg/m 3 (24

- hour) and 15 μg/m 3 (annual) are protective of public health with an adequate margi n of safety. We did not say, nor do we believe, that PM 2.5 concentrations must be below 30 μg/m 3 (24

- hour average) or 12 μg/m 3 (annual average) to protect public health.

Comments on Visibility

Comment:

The environmental group commenter (0040) believes that there is a quantifiable relationship between visibility impairment and PM 2.5 levels, citing the proposal discussion (72 FR 54135)

, as well as the most recent Criteria Document and Staff Paper for PM 2.5 . The commenter point s out that at proposal ( cit ing 72 FR 54135), EPA observed that the proposed

Class II short

- term safe har bor increment of 9 μg/m 3 , if combined with the estimated daily background levels in most areas (i.e., 10 μg/m 3 ), would be below the minimum values recommended in the 2005 Staff Paper for the secondary short

- term standard for PM 2.5 (which was 20 μg/m 3 ). Ra ther than supporting the adequacy of 9 μg/m 3 as an increment level to protect visibility, the commenter believes that this shows that the safe harbor increment is inadequate30

because consumption of an increment of 9 μg/m 3 combined with background levels alo ne would cause an area to reach within 1 μg/m 3 of the staff

- recommended value of 20 μg/m 3 . The

commenter add s that most areas would have PM 2.5 pollution from motor vehicles and stationary sources in concentrations substantially greater than background lev els, easily placing these areas above 20 μg/m 3 (citing the 2005 Staff Paper at 2

- 77).

The environmental group commenter (0040) also assert s that the safe harbor PM 2.5 increments will not be sufficient to protect visibility in parks and other natural area s. According

to the commenter , we stated at proposal that a 24

- hour average PM 2.5 concentration of 20 μg/m 3
correlates to a visual range of approximately 25 to 35 kilometers (citing 72 FR 54129 ) . The

commenter contends that this visual range distance fal ls far short of what the National Park Service considers to be good visibility for national parks, adding that the National Park Service has stated that visibility used to be 90 miles (145 km) on average in eastern parks, and 140 miles (225 km) on average in western parks. 6 The commenter stated that the safe harbor increments would allow parks and other natural areas to experience PM 2.5 pollution that is correlated with a

25

– 35 km visual range.

A federal agency commenter (0044) state s that the proposed 24

- hour Class I increment ( 2 μg/m 3 ) would no t be protective of AQRVs, pa rt icularly v isibility. This commenter note s that the National Park Service uses a 5 percent change in light extinction from estimated natural
conditions as the threshold for ―adverse impacts‖ to Class I visibility. The commenter indicate s that depending on the constituents of the ambient PM 2.5 and the humidity, a concentration of

2 μg/m 3 in a typical Class I area would result in a change in light extinction ranging from 13 to 80 perce nt in the Western United States and from 8 to 50 percent in the Eastern United States (depending on the makeup of the PM and the humidity) and, therefore, would likely constitute

― adverse impacts ‖ to Class I visibility. While acknowledging that the federa l land manager ( FLM ) may still determine that the visibility in the Class I area is adversely affected by an

increase in concentration that is less than the increment, this commenter pointed out that we

stated at proposal that ―generally speaking an increm ent should not be so large that it routinely results in substantially more pollution in Class I areas than is generally acceptable under the AQRV approach‖ (citing 72 FR 54135). The commenter concluded that the proposed 24

- hour

PM 2.5 increment does not me et this test and recommended that EPA set a lower PM 2.5 24

- hour

increment.

Response:

The visibility impairment issue is more complex than suggested by the commenter s . In addition to predicting what the maximum ambient change in air quality is for a p articular area, a visibility impairment assessment considers such things as the frequency, magnitude, and duration of visibility impacts in order to conclude that an adverse impact will occur.

In addition, the environmental group commenter misconstrued the illustration we included in the NPRM. We noted that the lowest level we considered as a secondary PM 2.5

6 The commenter cited http://www.nps.gov/shen/naturescience/visibility_and_haze.htm for historic visibility in national parks.31

NAAQS was 20 μg/m 3 , which was considered to address visibility issues in urban areas. We also noted that in most areas, the estimated 98 th percentile of daily background concentrations is less than 10 μg/m 3 . In adding the Class II safe harbor increment (9 μg/m 3 ) to the 98 th percentile of background levels, we were simply showing that even in the worst case, the combination of the safe harbor increment and background PM 2.5 would not exceed the most stringent level we considered for the secondary NAAQS . T he commenter presented this rough, worst

- case calculation as if it represented the typical situation that would result from the safe harbor increments. In addition, the commenter‟s statements do not apply to parks and special areas that are classified as Class I areas because the safe harbor increments for such areas are much

lower.

Th e federal agency commenter appears to have identified a worst

- case scenario in terms of increment concentrations, and although we agree with the visibility impacts related to those concentrations discussed in the comment, we do not believe the proposed increment level compromises the protection of visibility or other AQRVs. Although the “AQRV test” uses

5 percent light extinction as a screening threshold, the determination of adverse impact is made

on a case

- by

- case basis taking into account the geographic extent, intensity, duration, frequency, and time of visibility impairment and how these factors correlate with visitation to the Class I area. The suggestion that the 5 p ercent threshold is routinely exceeded by PSD sources or that

an absolute worst

- case scenario is occurring to the geographic extent, intensity, duration, and frequency that would warrant an adverse impact determination is unsupported, especially

considerin g the relatively few adverse impact determinations that have been made in the past. It is, however, important to note that the AQRV analysis is independent of the PSD increment analysis; whether or not the increment is projected to be exceeded does not de termine the need for an AQRV analysis. The determination that a facility does or does not cause an adverse impact on a Class I area is not solely contingent upon the PSD increment, so we do not believe that lowering the proposed increment is necessarily m ore protective of the AQRV.

With respect to these two commenters‟ concerns about visibility protection, we continue to believe that the increments cannot be expected to be the sole means of protecting various welfare concerns. At proposal , we stated tha t “visibility protection in Class I areas is more adequately provided by the AQRV process.” Congress defined AQRVs to specifically include visibility and left it for the FLMs to define other special attributes of Class I areas that warranted special prote ction. (See additional discussion of AQRV review below.) We also noted that Congress has established several visibility programs that target emissions reductions to achieve desired visibility benefits. See 72 FR 54135. Collectively, these protective pr ograms, along with the totality of the PSD program, offer an effective means of addressing unique local problems that cannot be addressed solely by uniform national increments.

Comment:

The environmental group commenter (0040) sta te s that we cited the r egional haze program as a justification for adopting less protective PSD rules (referring to 72 FR 54135), but the commenter point s out that the haze program applies only to Class I areas and does not apply at all to the majority of the nation, which is Cl ass II. The commenter further note s that we stated at proposal that ―some State and local governments have also developed programs to improve32

visual air quality in specific urban areas‖ (citing 72 FR 54135), and point s out that we gave no specific informa tion on such programs, nor any information about the visibility protection that they provide beyond that provided by the proposed increments. The commenter requests that we identify the specific state and local programs, and that we specify how much visib ility protection such programs are providing.

Response:

The commenter is correct that the regional haze program directly addresses only Class I areas. These are the areas that Congress defined as deserving of the most protection under PSD, including th e visibility protection provisions in subpart 2 of title I, part C of the Act, which is the statutory basis for the regional haze program. While Class I areas are the target for the regional haze program, we believe that many areas of the nation will rece ive collateral visibility benefits from this program. As emissions of the pollutants that cause regional haze are reduced, many areas in the paths of transport will benefit. In addition, as discussed previously, PSD applicants must prepare an analysis of “other impacts,” including visibility impacts, in areas

other than Class I areas.

Regarding state and local visibility programs, the 2005 Staff Paper EPA described several existing programs designed to improve visual air quality in urban areas. These programs were located in Denver, CO; Phoenix, AZ; and Lake Tahoe, CA. Also, the states of California and Vermont have each established standards to protect visibility. See the 2005 Staff Paper, pages 6

- 17 through 6

- 23. “Review of the National Ambient Ai r Quality Standards for Particulate Matter: Policy Assessment of Scientific and Technical Information. OAQPS Staff Paper ” EPA

- 452/R

- 05

- 005a, December 2005.

Comment:

The environmental group commenter (0040) cited the proposal (72 FR 54135) where we

said that the use of ―distinct PM increments for visibility protection is not the most effective means of addressing the visibility problem.‖ The commenter believes that this claim is based on false premises, including the idea that other programs effectively protect visibility nationwide, and the idea that the only option is a ―distinct‖ PM increment for visibility protection. As to the latter, the commenter stated that EPA can strengthen the safe harbor increment to ensure visibility protection and need not adopt a separate ―visibility‖ increment. In addition, the commenter asserted that EPA has ignored the statutory mandate that the PSD rules fulfill the statutory goals and purposes, and that we cannot shirk that statutory duty merely because we

claim some other type of action would be ―more effective.‖

Response:

We continue to believe that Class I area visibility protection under the PSD program is appropriately addressed via the AQRV process , which is discussed in greater detail below

. Briefly state d

, Congress explicitly included “visibility” as an AQRV for which FLMs would have an affirmative responsibility to protect in Class I areas under their jurisdictions. Where the FLM successfully demonstrates that there would be an adverse impact on the AQR V (e.g.,33

visibility), a state cannot issue a PSD permit, even when the source‟s emissions do not violate the

PM 2.5 increments. In addition, we continue to believe that the “other impacts analysis” (including analysis of visibility ) in non

- Class I areas is the appropriate means of addressing visibility protection in these areas, as envisioned by Congress when it enacted the PSD provisions of the Act.

As a result, we do not believe it is necessary to create a distinct increment (e.g., with a different aver

aging period) or to lower the contingent safe harbor increments to protect visibility in urban, non

- urban, or Class I areas across the United States. We reach this conclusion in proper consideration of the other, more direct approaches being used to addre ss visibility problems in the United States. The primary such approach, the regional haze program, is within the PSD framework for PM 2.5 . Note that part C of title I of the Act, “Prevention of Significant Deterioration of Air Quality,” includes subpart 2 , which is the statutory basis for the regional haze program. Regarding our consideration of other state and local visibility protection measures that are outside the PSD framework, we do not believe it is reasonable to disregard

these area

- specific measu res that focus on the preferences of individual communities where a uniform national increment for visibility protection generally cannot.

In addition, as explained earlier, it should be recognized that increments cannot by

themselves be relied on to pro tect against visibility impairment problems because increments define a maximum allowable increase of pollution above a baseline concentration which, in itself, could be at or near concentrations that represent poor visibility conditions. Congress explici tly included special provisions to protect AQRVs in the Act; b y utilizing the AQRV process, FLMs are provided with a mechanism for directly relating to air quality levels associated with any existing or potential visibility problem. The AQRVs afford a lev el of protection that can be used even when a source‟s emissions would fall within an acceptable range for increment consumption (that is, the source‟s emissions increase would not consume the remaining increment).

Comments on Extending AQRV Review to PM 2.5

Comment:

Two state/local agency commenters ( 0015, 0022) support our proposals to develop PM 2.5 increments for Class I areas and to apply the requirement to eva luate impacts on AQRVs in

Class I areas to PM 2.5 review. However, th e environmental group commenter (0040) indicate s that this review by FLMs does not and cannot assure the prevention of all significant PM 2.5 - related deterioration because it applies only to the construction or modification of very large stationary sources (e.g., factories and power plants) affecting Class I areas. This commenter point s out that Class I areas do not include Bureau of Land Management wilderness and wilderness study areas (encompassing more than 15 million acres), 341 of the nation’s 390 national park units (only 49 national parks are Class I), and many U.S. Forest Service lands (including a number of wilderness areas). The commenter add s that FLM review does not help

to fulfill section 160(2)’s goal of preserving and protecting air quality in ―other areas of spe cial national or regional natural, recreational, scenic, or historic value,‖ such as state and local parks, wildlife refuges, recreation areas, lakes, and historic areas, none of which are Class I areas. In34

addition, the commenter note s that FLM review do es not apply to emissions increases from

sources of PM 2.5 and precursor pollution other than major stationary sources, such as motor

vehicles and non

- major industrial sources (which are sources that emit substantial amounts of

PM 2.5 and precursors). Alaba ma Power v. Costle , 636 F.2d 323, 362 (D.C. Cir. 1979) (expressly recognizing that ―[s]ignificant deterioration may occur due to increased emissions from unregulated minor sources.‖).

The environmental group commenter (0040) also assert s that FLM review is of limited reach even where it does apply. Under the current PSD regulations, a state must consider an FLM’s objections and must justify its decision in writing when it disagrees with those objections, but the state can still issue a PSD permit over th ose objections unless emissions are predicted to cause an exceedance of the applicable increment. The commenter believes that, given these limitations, EPA cannot plausibly claim that the existing provision for FLM review ensures the preservation, protect ion, and enhancement of air quality for parks and natural areas throughout the nation as required by section 160(2) of the Act.

Response:

In our rulemakings addressing PSD for NO

x , EPA extended the AQRV review procedures set forth in 40 CFR 51.166(p) an d 52.21(p) to cover NO 2 . These AQRV review procedures were established based on section 165(d) of the Act, and they were originally applied only in the context of the statutory increments for PM and SO 2 . However, because they also address many of the fac tors applicable under section 166(c) of the Act, EPA also applied them to NO

x through regulation. In this final rule, we are amending the existing PSD regulations to extend, as proposed, the AQRV review procedures to include PM 2.5 by explicitly including PM 2.5 in the regulatory text that now simply references “particulate matter.” See revised 40 CFR 51.166(p)(4) and 52.21(p)(5).

Section 165(d) creates a regulatory structure in which the FLM and reviewing authority must review the impacts of a proposed n ew or modified source‟s emissions on AQRVs. The Act assigns to the FLM an “affirmative responsibility” to protect the AQRVs in Class I areas

. This is in notable contrast to the reviewing authority‟s responsibility for protecting the increments

– includin g Class I increments. The FLM may object to or concur in the issuance of a PSD permit based on the impact, or lack thereof, that new emissions may have on any affected AQRV that the FLM has identified and for which information is available to the general public. If the proposed source‟s emissions are shown not to cause or contribute to a violation of a Class I increment, the FLM may still prevent issuance of the permit by demonstrating to the satisfaction of the reviewing authority that the source or modi fication will have an adverse impact on AQRVs. Section 165(d)(2)(C). On the other hand, if the proposed source is shown to cause or contribute to a violation of a Class I increment, the reviewing authority (state or EPA) shall not issue the permit unless the owner or operator demonstrates to the satisfaction of the FLM that there will be no adverse impact on AQRVs. 7 Thus, the showing of compliance with the increment

7 Even if such a waiver of the Class I increment is allowed upon a finding of no adverse impact, the source must comply with such emissions li mitations as may be necessary to ensure that alternative increments specified in the rules for SO 2 or PM are not exceeded. The alternative increments are generally at the level of the Class II increments, with the lone exception being a more restrictive 3

- hour increment for SO 2 . Section 165(d)(2)(C)(iv).35

determines whether the FLM or the permit applicant has the burden of satisfactorily

demon strating whether or not the proposed source‟s emissions would have an adverse impact on AQRVs. 8 In any event, the FLM plays an important and material role by raising these issues for consideration by the reviewing authority, which in the majority of cases will be the state.

Extending the AQRV review procedures of the PSD regulations to PM 2.5 helps to provide protection with respect to potential adverse effects from PM 2.5 for parks and special areas (which are generally the Class I areas subject to this r eview) not afforded by the increment system alone. W

e believe the factors applicable under section 166(c) of the Act can be fulfilled when the review of AQRVs is applied in conjunction with increments and other aspects of our PSD regulations. In those ca ses where the increment is not violated and the reviewing authority agrees that a proposed project will adversely affect AQRVs, the parks and other special areas will be protected by denying issuance of the permit or by requiring the applicant to modify th e project to alleviate the adverse impact.

We read the legislative history to show that Congress intended the AQRV review provisions of section 165(d) to provide a special layer of protection, beyond that provided by

increments. The Senate committee r eport stated the following: “A second test of protection is provided in specified federal land areas (Class I areas), such as national parks and wilderness areas; these areas are also subjected to a review process based on the effect of pollution on the

a rea‟s air quality related values.” S. Rep. 95

- 127, at 17, 4 LH at 1401. As we stated in the NO 2 increment rule, we believe the term “air quality values” should be given the same meaning as “air quality related values.” Legislative history indicates that the term “air quality value” was used interchangeably with the term “air quality related value” (AQRV) regarding Class I lands. 9

The commenter is correct that the FLM (or AQRV) review applies only to Class I areas, and not to other “special” areas such as the numerous state and local parks and some other areas that could be seen as being covered by the protective purposes of section 160(2) of the Act. This level of coverage by FLM review to protect AQRVs was established by Congress when it

enacted the P SD program, including the purposes set out in section 160(2). Thus, we conclude that Congress believed that the special areas not designated as Class I areas were properly addressed by the other elements of the PSD program. One such element that we belie ve is

The EPA made this provision applicable to the PSD provisions for NO

x at the level of the NO 2 Class II increment (53 FR 3704; 53 FR 40656) and substituted the PM 10 Class II increments for the statutory al ternative PM increments, which were based on TSP (58 FR 31622). This final rule expands this provision to include the PM 2.5 Class II increments as well. See 40 CFR 51.166(p)(4) and 52.21(p)(5).

8 In response to concerns that Class I increment would hinde r growth in areas surrounding the Class I area, Congress established Class I increments as a means of determining where the burden of proof should lie for a demonstration of adverse effects on AQRVs. See Senate Debate, June 8, 1977 (3 LH at 725).

9 See S. Rep. 95

- 127, at 12, reprinted at 3 LH at 1386, 1410 (describing the goal of protecting “air quality

values” in “Federal lands

– such as national parks and wilderness areas and international parks,” and in the next paragraph and subsequent text using the t erm “air quality related values” to describe the same goal); id. at 35, 36 (“The bill charges the Federal land manager and the supervisor with a positive role to protect air quality values associated with the land areas under the jurisdiction of the [FLM]” and then describing the statutory term as “air quality related values”). H.R. Report 95

- 564 at 532 (describing duty of Administrator to consider “air quality values” of the tribal and s tate lands in resolving an appeal of a tribal or s tate redesignation, which is described in the final bill as “air quality related values”).36

especially helpful for satisfying the requirements of section 166(c) in Class II and Class III areas, including the types of areas described by the commenter, is the requirement for sources to conduct an “additional impacts analysis,” which includes an analysis of the impacts on visibility, soils, and vegetation of the proposed source and associated growth, regardless of the classification of the area impacted by the source. [See 40 CFR 51.166(o) and 52.21(o).] While the additional impacts analysis typically is not as intensive a review as the AQRV analysis required in Class I areas, it contributes to satisfying the factors applicable under section 166(c) of the Act in all areas, including Class II and Class III areas. Note also that states have the option under the Act of designating additional areas as Class I areas and providing for AQRV review for these state Class I areas if they believe that there are areas within their borders that merit such protection.

The commenter is not correct in sayin g that the review to protect AQRVs does not apply to emissions increases from sources other than major stationary sources. While it is generally true that a major stationary source may trigger the analysis as part of the required PSD review for new major stationary sources and major modifications where such source‟s emissions increase may affect a Class I area, the review itself generally include s the impacts on an AQRV of other emissions in the area, including emissions from non

- major sources. In additio n, states may adopt requirements in their state implementation plans to require certain minor sources seeking a permit to undergo an AQRV analysis if they choose to do so.

We agree with the commenter that the AQRV review has certain limitations in that a state can, under some circumstances, issue a PSD permit over the objection of the FLM. Here again, Congress enabled this outcome when it provided that a permit would not be issued when the FLM demonstrates “to the satisfaction of the State” that the so urce will have an adverse impact on AQRVs in a Class I area. Section 165(d)(2)(C)(ii). We read this provision to reflect Congress‟s judgment on the appropriate balance between state and FLM discretion in the reach of AQRV review. That said, when a revie wing authority declines to follow a determination of adverse impact by the FLM, the reviewing authority is expected to provide a rational basis for doing so, and a reviewing authority‟s rejection of an FLM‟s finding may not be arbitrary and capricious. As stated by EPA‟s Environmental Appeals Board in In the Matter of: Hadson

Power 14

– Buena Vista , 4 E.A.D. 258, 1992 WL 345661 (October 5, 1992) (in Section II.A):

States do not have unfettered discretion to reject an FLM's adverse impact

determination. If a state determines that an FLM has not satisfactorily demonstrated an adverse impact on AQRVs from the proposed facility, the state must provide a “rational basis” for such a conclusion, “given the FLMS' affirmative responsibility and expertise regardin g the Class I areas within their jurisdiction.” 50 FR 28549, July 12, 1985. Arbitrary and capricious rejections of adverse impact determinations are not sustainable. ( C itations omitted

. )

In sum, the commenter correctly enumerated some of the limitat ions of the AQRV review under the Act. However, such review is only one element of the full PSD program, which must be evaluated against the statutory requirements in their entirety. We continue to believe, as previously stated, that under the regulatory structure that includes increments , FLM review for AQRV impacts is an additional measure that helps satisfy the factors in sections 166(c) and37

160(2) of the Act [ which require EPA‟s pollutant

- specific PSD regulations to protect (1) air quality values, and (2) parks and other special areas, respectively ] in balance with the other statutory factors. We add that the AQRV review requirements of the existing regulations mirror these requirements in the Act, which reflect Congress‟ judgment of how AQRV review s hould properly be used to promote the purposes of the program as set out in section 160 of the Act.

Comments on the Enhancement Goal

Comment:

The environmental group commenter (0040) stated that the proposed PSD rules fail to

ensure fulfillment of the ―enhancement goal‖ set out in the Act. The commenter noted that section 101(a) states as the Act’s first purpose: ―to protect and enhance the quality of the Nation’s air resources,‖ while section 160(2) states that the purpose of the PSD program is to ―pr eserve, protect, and enhance ‖ air quality in parks and other special areas. The commenter asserted that the proposed rule did not address these enhancement requirements or explain how the proposed increments would fulfill those requirements.

Response :

Th is same issue was raised in the 2005 PSD rule affirming the NO

x increments. At that time we expressed our belief that the goal to enhance air quality in national parks and

wilderness areas is implemented through the regional haze program while the PSD p rogram focuses on preserving and protecting air quality in these areas. 70 FR 59582, October 12, 2005, at page 59589. However, when a PSD increment violat ion is identified , we agree that EPA may require a state to revise its SIP to correct a violation. See 40 CFR 51.166(a)(3). Otherwise, we do not interpret these PSD provisions to authorize us to direct states in their SIPs to achieve reductions in emissions from existing sources for PSD purposes.

We recognized at that time, and continue to believe, that the growth management goals of PSD may also be fulfilled when the states adopt controls on existing sources that would reduce emissions and allow growth from new sources and major modifications to existing sources without causing significant deterior ation. Under the increment approach, we have interpreted the PSD rules to allow states to require reductions from existing sources in order to expand the allowable increments and, thereby, allow for more growth under the PSD program. However,

we have nev er required states to do so because, in the absence of an increment violation, we do not believe section 166 and other provisions in part C of title I of the Act give us the legal authority to mandate such reductions for PSD purposes.



### 2.2.2.3 Comments on Promoting Pollution Prevention

Comment:

T he environmental group commenter (0040) states that the proposal contains no

discussion of how the rules will fulfill the pollution prevention purpose set out in section 101 of the Act, as required under section 166(c) o f the Act . The commenter contends that a lthough the38

proposed increments will limit some pollution increases, there is no provision in the proposal that requires or promotes pollution prevention.

Response:

As discussed in Section 2.1.2 of this document, w e believe that measures that satisfy the specific goals and purposes of section 160 of the Act also satisfy the more general purposes and goals identified in section 101 of the Act. As we stated in the 2005 NO 2 increment rulemaking, the overall goals an d purposes of the Act listed in sections 101(b) and 101(c) are general goals regarding protecting and enhancing the nation‟s air resources and controlling and preventing pollution. Because these broad goals are given more specific meaning in section 160, EPA does not believe it is necessary to consider them in detail when evaluating whether PSD regulations satisfy the criteria in section 166(c). 70 FR 59587 FN 3, October 12, 2005.

Regarding pollution prevention specifically, we believe that this general goal is encompassed in, and given more specific meaning by, sections 160(1), 160(2), and 160(4) of the Act. These sections spell out the specific purposes under the PSD program for the general section 101 goals of controlling and preventing pollution. W e believe that any requirement to limit or reduce emissions serves to promote pollution prevention, which is often the most cost effective means of lowering pollutant emissions.

In addition to citing the purposes set out in section 160, section 166(c) in cludes the criterion that pollutant

- specific PSD regulations should provide a framework for stimulating improved control technology. W e believe that this criterion is fulfilled by the system of increments for PM 2.5 and by the requirement for PSD permittee s to apply BACT to minimize

PM 2.5 emissions. In stimulating improved control technology generally, these elements of the PSD program also promote pollution prevention. As noted above , pollution prevention is often the most cost effective means of control , particularly for new sources and new process lines at existing sources. In addition, because BACT is a case

- by

- case determination that considers cost and collateral environmental impacts, pollution prevention, where technically feasible, often fairs wel l in BACT analyses because it is typically free from the negative environmental impacts that result from the use of add

- on air pollution control devices.



### 2.3 Comments on Option 2 for PM 2.5 

### Increments

– Equivalent Substitution Approach for Annual Increments

P roposed Option 2 is termed the ―equivalent substitution approach‖ and is based on the authority of section 166(f) of the Act. Under section 166(f), increments for a new PM indicator completely replace the increments for the previous PM indicator, and the new increments are to be ―of equal stringency in effect‖ as the old PM increments that they replace. We proposed two different methods for determining annual PM 2.5 increments to replace the existing annual PM 10 increments, Option 2A and 2B. We did not pr opose to use this approach to replace the 24

- hour

PM 10 increments because the 24

- hour NAAQS for PM 10 remains in place, although the annual NAAQS for PM 10 has been revoked.39

We received some comments that addressed Option 2 in general, which are addressed below in Section 2.3.1. Comments specific to Options 2A and 2B are addressed in

Sections 2.3.2 and 2.3.3, respectively.



### 2.3.1 General Comments on Option 2

Comment:

One industry association commenter (0032) states that the ―equivalence approach‖ is

rational and should be adopted, without stating a preference for Option 2A or 2B. Another industry association commenter (0034) and two industry commenters (0031, 0042) also support the Option 2 equivalent substitution approach under section 166(f) of the Act, but have issues with the methodology that EPA used to derive the increments proposed under Options 2A and

2B ( as discussed further below ) . While preferring the Option 1 approach under section 166(a) of the Act, another industry association commenter (0029) b elieves that EPA is authorized to use the Option 2 equivalent substitution approach but also has issues with EPA’s methodology ( as discussed further below )

.

One state/local a gency commenter (0051) does not believe that using the Option 2

e quivalent subst itution approach to determine the increment would be appropriate since it has not yet been determined if any precursors will be regulated in regards to PM 2.5

. The commenter adds

that since measurements of PM 10 have not considered precursors or the formati on of secondary

PM 10 , it seems comparing PM 2.5 to PM 10 inventories would likely be inaccurate.

Response:

For the reasons discussed in the previous sections of this document, we have decided to finalize Option 1 for the entire suite of PM 2.5 increments

, based on authority under section 166(a) of the Act. Thus, while EPA acknowledges that there are a number of issues (as described by some of the comments provided in this section) with aspects of the methodology used to develop Option 2, those issues do no t need to be resolved in this action, and EPA does not need to respond to these comments in detail at this time."

Comment:

Six commenters do not agree with the methodology used to develop the proposed increments under Option 2.

Although favoring Option 2’s equivalent substitution approach under section 166(f) of the Act, o ne industry association commenter (0034) and one industry commenter (0042) believe

that the equivalent substitution methodology EPA employ ed under Option 2A and 2B of the

propose d rule is inconsistent with prior EPA methodology used to derive the PM 10 increments

under section 166(f). The commenters argue that the ratios us ed under both Option 2A and 2B are not well supported and do not provide source

- specific scrutiny to demonstr ate that the new

increment s are of equal stringency to the PM 10 increment s they are designed to replace. The

commenters note that for the PM 10 increments, EPA compared the TSP impact to the PM 1040

impact for each 249 separate sources in the NSR data base an d determined each such source’s

PM 10 impact by multiplying its TSP impact times the PM 10 /TSP emissions ratio for that source. The commenters point out that for Option 2A, EPA determined a single PM 2.5 /PM 10 emission

ratio for all utilities and industrial point sources combined and multiplied that number time the

value of the PM 10 increment. The commenters contend that this gross approximation approach fails to satisfy the requirements of section 166(f).

The commenters (0034, 0042) also claim that the methodology used under Option 2B was deficient. One commenter (0034) asks whether multiplying the PM 10 increment times the

ratio of the PM 2.5 NAAQS to the PM 10 NAAQS can accurately represent the ―equivalent effect‖

in terms of PM 10 and PM 2.5 increment con sumption for the population of PSD sources. The

other commenter (0042) recommends that EPA revise the proposed rule to comply with requirement to provide for equal stringency in compliance with the requirements of

section 166(f).

One industry associat ion commenter (0037) states that EPA should not apply NAAQS

based ratio s because these do not translate back to the emissions point level when comparing

PM 10 and PM 2.5 . The commenter believes that this is an invalid method because EPA has not

shown that t here is a correlation between the NAAQS and direct PM 2.5 since there is no account

ing for precursors

, and EPA does not have a quantifiable sense of the portion of PM 2.5 that is condensable for various industries. The commenter express es concern that if E PA were to proceed with a NAAQS ratio approach, it would clearly result in a very small PM 2.5 increment and this would not take into account the expected condensable fraction.

The same commenter indicates that based on a review of the regulatory history of the

establishment of increments for Class I

- III areas, the record is very clear that the original increments were established at levels which were designed to accommodate moderate, well

controlled develop ment. 39 FR 42510 (Dec ember 5, 1974) (―The Ad ministrator continues to feel that a Class II increment should be compatible with moderate, well

- controlled development

in a nationwide context...‖); see also 45 FR 52676 (Aug ust 7, 1980). The commenter question s whether EPA’s proposal to use the NAAQS rati os to set the increments ( and SILs ) will accommodate moderate, well

- controlled development

, or if this approach will actually inhibit additional growth. The commenter suggest s that the EPA should provide a demonstration assuring that this proposal will no t conflict with the prior regulatory history and intent of Congress and will allow for sufficient growth consistent with air quality needs.

Another i ndustry association commenter (0036) sta te s that EPA inappropriately rejected

the 80 percent ratio of PM 2 .5 to PM 10 emissions in setting the PM 2.5 increments . The commenter

argue s that ignoring this basic scientific fact and us ing lower percentages to set the PM 2.5 increments results in effectively lowering the PM 10 increments, because the PM 2.5 increments will, in effect, be much more stringent than the PM 10 increments and, consequently, will require

sources to reduce total PM emissions and PM 10 emissions further to comply with PM 2.5 increments.

Another industry commenter (0031) who favors Option 2’s e quivalent substitution approach under section 166(f) of the Act contends that EPA’s methodology in adopting the 199341

PM 10 increments was flawed, and so is the analogous methodology used to derive the PM 2.5 increments. The commenter believes that the metho ds used by EPA all rely on a fundamental assumption that there is a fixed relationship between TSP and PM 10 and between PM 10 and

PM 2.5 , both in terms of mass percent and in terms of health and welfare impact.

One industry association commenter ( 0029) que stion s EPA ’s approach to determining the ―stringency ratio‖ of 0.3 u se d under Option 2 to convert the PM 10 increments into PM 2.5 increments, which was derived for the annual averaging period by computing the ratio of the

annual PM 2.5 NAAQS to the annual PM 10 NAAQS . The commenter believes this is an inappropriate ―apples to oranges‖ comparison, and that a more appropriate approach would be to

us e a multiplier based on the ratio of the PM 10 increment to the PM 10 NAAQS for each averaging period. The commente r provide s an example for the PM 2.5 Class II 24

- hour increment , which he would derive by (a) dividing the PM 10 Class II 24

- hour increment (30 μg/m 3 ) by the PM 10 24

- hour ambient standard (150 μg/m 3 ); (b) multiplying that by the PM 2.5 24

- hour ambient

standar d (35 μg/m 3 ); and then (c) rounding that product to the nearest whole number: 7 μg/m 3

.

Response:

For the reasons discussed in other sec tions of this document, we have decided to finalize Option 1, based on authority under section 166(a) of the Ac t. W e have not reached any final conclusion as to whether the Option 2 equivalent substitution approach under section 166(f) of the Act is permissible under the Act, but we acknowledge problems associated with the specific methodologies we relied on to propose equivalent increments. For example, we agree with commenters that the emissions ratio approach does adequately account for precursor emissions. The percentage of NAAQS approach used in Option 1 did not suffer from this problem associated with the precurs or source contribution because the calculated values do not distinguish between direct and secondarily formed PM 2.5 ; that is, the calculated values represent total ambient concentrations of PM 2.5 regardless of their origin. This further supports our

decis ion to select Option 1.

Regarding the last comment on our use under Option 2 of the ratio of the PM 2.5 NAAQS

to the PM

10 NAAQS, we note that our methodology under Option 2B and the commenter‟s example methodology are computationally identical. While we did not propose under Option 2 to use section 166(f) authority to substitute PM 2.5 increments for PM 10 increments for the

24

- hour averaging period, had we done so, our input values and results under Option 2B would

have been identical to the commenter ‟s ex ample. Specifically , the commenter‟s methodology is as follows:

O ur Op tion 2B methodology is as follows:42

When looked at closely, one can see that these two expressions are identical except for the order of the multiplicands in the numerator and, t herefore, yield identical results.



### 2.3.2 Comments on Option 2A

Comment:

One commenter explicitly expresses support for Option 2A, and another explicitly expresses opposition to that option. As discussed above, other commenters support and oppose Option 2 ge nerally without specifying Option 2A or 2B, and some of these raise issues with the methodology that we used to develop both the Option 2A and 2B increments.

One state / local agency (0033) support s EPA’s proposed Option 2A. The commenter

believes that Op tion 2A meshe s well with the intent of achieving equal stringency as stated in

section 166(f), but only if the annual and 24

- hour increments are determined in the same manner.

One industry association commenter (0039) opposes Option 2A. Th e commenter a sserts
that deriving the PM 2.5 increments using a multiplier determined from the ratio of PM 2.5 emissions to PM 10 emissions ( which yields PM 2.5 increments that are up to 87 percent of the

PM 2.5 NAAQS ) results in increments that are too high . Accordingly

, the commenter believes

that EPA should not perpetuate this calculation method as part of Option 2A. The commenter

note s that while EPA correct ed this overstated PM 2.5 increment in Option 2A by multiplying the

PM 2.5 /PM 10 emissions ratio by the ratio of the PM 2.5 NAAQS to the PM 10 NAAQS, this method in Option 2A is not well founded.

Response:

For the reasons discussed in other sections of this document, we have decided to finalize Option 1, based on authority under section 166(a) of the Act. W hile we sol icited comments on the possibility of using the substitution approach for the 24

- hour PM 2.5 increment, we did so because we found no strong justification for using the substitution approach to replace the existing 24

- hour PM 10 increments since we were not revoking the 24

- hour PM 10 NAAQS. In the final rule, we have concluded that the section 166(a) approach is the most direct and supportable approach for developing all the PM 2.5 increments.

W e agree that deriving the PM 2.5 increments based solely on th e 0.8 multiplier derived from the ratio of PM 2.5 emissions to PM 10 emissions would have resulted in increments that were inappropriately high. As one commenter noted, i t was for this reason that we proposed in Option 2A also to use a multiplier based on t he ratio of the PM 2.5 and PM

10 NAAQS. Nevertheless, we agree that the use of the emissions ratio component does not adequately account for the precursor emissions that significantly affect PM 2.5 air quality.43



### 2.3.3 Comments on Option 2B

Comment:

One state/ local agency association commenter (0021), one i ndustry commenter (0043)

, and o ne i ndustry a ssociation commenter (0039) explicitly express support for Option 2B. One industry association commenter (0037) opposes the methodology we used to develop the Opti on 2B increments. As discussed above, other commenters support and oppose Option 2 generally without specifying Option 2A or 2B, and some of these raise issues with the methodology that we used to develop both the Option 2A and 2B increments.

Th e suppor tive i ndustry commenter (0043) opines that the arguments for one option versus another are not compelling, and notes that the various proposed increment options are similar in magnitude. The commenter recommends Option 2B because this option appear s to
ha ve the lowest economic impact.

Th e supportive i ndustry a ssociation commenter (0039) strongly recommends that EPA adopt Option 2B. The commenter believes that the new PM 2.5 increments should remain as consistent with Congress’ original PM increments as f easible. The commenter contends that Option 2B is the appropriate method of adopting PM 2.5 increments consistent with Congress’ intent for the following reasons:

 W hen Congress enacted the CAA s ection 163 PM increments, it established each

increment as a percentage of the PM NAAQS.

 Option 2B does not use the ― flawed ‖ ratio of PM 2.5 / PM 10 emissions used in Option 2A. (See this commenter’s comments in Section 2.3.2 above.)

 T he use of the NAAQS ratio is generally consistent with Congress’ original statutory determination of PM increments as a percentage of the PM NAAQS.

Response :

For the reasons discussed in other sections of this document, we have decided to promulgate PM

2.5 increments using Option 1, based on authority under section 166(a) of the Act. Although we have not reached any final conclusion as to whether the Option 2 equivalent substitution approach under section 166(f) is permissible under the Act , we believe that the NAAQS ratio approach could part of a reasonable way to develop equivalent i ncrements

. .

The industry association commenter did not provide an explanation of why Option 2B would have the lowest economic impact. Th at alleged outcome is questionable in light of the fac t
that , as proposed, O

ption 2B would involve annual and 24

- hour PM 2.5 increments that w ere based on two separate statutory authorities and would requir e two separate implementation approaches . F

or example, the 24

- hour increments (based on section 166(a) authority) would use new baseline dates, while the annual increm ents (based on section 166(f) authority) would use existing baseline dates and areas that ha d been established previously for PM 10 or TSP. This would likely involve the maintenance of two separate source/emissions inventories, and the44

inventory for the an nual increments would have to be converted from PM 10 emissions to PM 2.5 emissions

.



### 2.4 Other Comments on Increments

2.4.1 Comments on Baseline Areas

Comment:

A state/local agency association commenter ( 0021 ) notes that with regard to identifying air quality co ntrol regions, states currently have the authority to permit major sources and track increments in accord with 40 CFR 52.21(b)(15)(i), which defines ―baseline areas‖ as areas classified as attainment or unclassifiable in which a proposed major stationary s ource or modification has a 1 μg/m 3 impact. The commenter indicate s that states have considerable latitude, within this regulatory boundary, to identify geographic areas for the purpose of managing and implementing their PSD programs. The commenter add s that some states have made adjustments in their original identification of air quality control regions, redefining section 107 areas into reasonably

- sized, geographically related areas that enhance their ability to manage the complex increment program. Th e commenter believes that such redefinition is within the intent of the Act and regulations and can rightfully be undertaken by states with regard to PM 2.5 increments.

One state agency commenter (0019 ) believes that states should be required to use the

b aseline areas previously established for their PSD program, unless the process for redefining these areas strictly follow procedures in the PSD regulations and EPA policy. The commenter indicates that this will minimize any inconsistent applications of th e regulations for PM 2.5 . The commenter notes that in establishing the PSD increments and baseline dates for the NO 2 increment, EPA did not allow the establish ment of new baseline areas.

Response:

We agree with the first commenter‟s interpretation tha t states have flexibility to redefine section 107 area designations in order to redefine the boundaries of baseline areas once they have been established for a pollutant. The commenter‟s position seems to be taken in conjunction with their support for sec tion 166(f) of the Act as the appropriate legal path for implementing new PM 2.5 increments. While we did not use section 166(f) as the legal path for developing and implementing of the new increments, we believe that the same flexibility is

available to s tates under the section 166(a) approach which we believe is the most legally defensible approach for promulgating the PM 2.5 increments. While a PSD source establishes the

baseline area in all intrastate attainment and unclassifiable areas in which it woul d have a significant impact

– not just the area in which it would locate

– longstanding EPA guidance provides that states may request the redefinition of a baseline area by seeking the redefinition of the attainment or unclassifiable area boundaries affect ing the baseline area. Principles set out

in 45 FR 52676, August 8, 1980 at 52716 are available to assist states in the proper manner for redefining existing baseline area s . Generally, as long as the redefined area (that is, a redefined boundary for an a ttainment or unclassifiable area) continues to include all locations where the45

source‟s impact is significant for PM 2.5 on an annual basis, we believe that states may request the desired adjustments.

We are unclear as to what the second commenter mean s when saying that states should be “required to use the baseline areas previously established for their PSD program....” Baseline areas are established independently for each pollutant for which increments have been established in accordance with the def inition of “baseline area” under 40 CFR 51.166(b)(15) and 52.21(b)(15), and they are established consistent with the area designation boundaries that the state established for the particular pollutant. We have not made any changes to the definition of “ba seline area” in these provisions to alter the way in which the baseline area concept is applied for purposes of PM 2.5 . The only change we have made to the definition of “baseline area” at 40 CFR 51.166(b)(15) and 52.21(b)(15) adds the significant impact level (annual average) for PM 2.5 to determine what attainment or unclassifiable areas need to be included in the baseline area established by a PSD source (see below) . Accordingly, baseline areas for PM

2.5 would be defined consistent with area designation s for PM 2.5 , and such areas may be altered if the state properly redefines the applicable attainment and unclassifiable areas as described in the response provided above.

Comment:

One i ndustry a ssociation commenter (0032) indicates that EPA did not inc lude proposed regulatory language to establish new baseline areas to accompany the new baseline dates for the

24

- hour PM 2.5 increments. The commenter states that b aseline areas are addressed in the definitions at 40 CFR 52.21(b)(15) but EPA proposes no am endment to this provision, making it

unclear how a minor source baseline date could be established when the area for PM 2.5 is not

established. The commenter contends that EPA needs to establish the baseline areas so that sources can clearly understand the geographic boundaries of the baseline area when the baseline date for that area is triggered.

Response:

We disagree with this comment claiming that new regulatory language is needed as part of the definition of “baseline area” (40 CFR 52.21(b)(15) and 51.166(b)(15 ) ) to allow the establishment of new baseline areas for the PM 2.5 increments. We believe the existing definition of “baseline area” is applicable to any pollutant for which area designations of “attainment” or “unclassifiable” have been made. We published the area designations for PM 2.5 in the Federal Register at 74 FR 58688, November 13, 2009. The existing definition of “baseline area” is adequate to enable the establishment of new baseline areas for the PM 2.5 increments for any

PSD source e mitting PM 2.5 emissions that submits a complete PSD application and ther e by establishes the “minor source baseline date” for PM 2.5 . The definition of “baseline area ” refers to air quality impacts “for the pollutant for which the baseline date is establish ed.” Under 40

CFR 52.21(b)(14)(ii i ) and 51.166(b)(14)(iii)

, a baseline date “is established for each pollutant for which increments...have been established.”46

Comment:

One environmental group commenter (0400) state s that EPA must revise its existing

def inition of ―baseline area‖ with respect to the PM 2.5 increment. The commenter note s that if a proposed PSD source’s impact would be less than 1 μg/m 3 (annual average) in a PM 2.5 attainment area adjacent or near to the area in which the source proposes to locate, the minor

source baseline date for PM 2.5 would not be triggered in that area. The commenter indicate s that a comparison of the 1 μg/m 3 (annual average) significant level to the NAAQS for PM 10 , SO 2 , NO 2 , and PM 2.5 shows that this significant level could allow greater deterioration of air quality

for PM 2.5 pollution than is currently allowed for PM 10 , SO 2 , and NO 2 pollution. The commenter point s out that a 1 μg/m 3 (annual average) significant level reflects 1

- 2 percent of the annual NAAQS for PM 10 , SO 2 , and NO 2 . In contrast, the commenter note s that this significant level
represents 6.7 percent of the annual PM 2.5 NAAQS of 15 μg/m 3 , as well as the entire amount of what EPA propos ed for the annual Class I PM 2.5 increment and 25 percent of what EPA

pr oposed for the annual Class II PM 2.5 increment.

The commenter (0040) argue s that allowing for such a lax significant level to define

where the PM 2.5 minor source baseline date is triggered will allow for PM 2.5 pollution growth to be considered part of baseline concentration rather than consuming the available PM 2.5 increment in many locations. The commenter also point s out that, in a departure from its past practice with respect to PM 10 , SO 2 , and NO 2 (for which EPA often designated one attainment area encompassing an entire state, except the areas designated nonattainment), EPA has designated

PM 2.5 attainment areas by counties. 70 FR 944, January 5, 2005. The commenter add s that these much smaller attainment area designations greatly increase the like lihood that the PM 2.5 minor source baseline date will not be triggered for many areas, especially if EPA adopts new baseline

areas and baseline dates for PM 2.5 . The commenter further add s that this is very likely for Class I areas, because PSD sources do not usually propose to locate in Class I areas, and thus the PM 2.5 minor source baseline date will only be trigged for most Class I areas based on a proposed PSD source having a ―significant‖ impact on PM 2.5 concentrations in that area. The commenter

asse rt s that the use of this significant level for PM 2.5 will not ensure the prevention of significant deterioration of air quality or fulfill the statutory purposes as mandated by section 166 of the Act. The commenter argue s that such a high significance lev el will illegally and arbitrarily allow worsening of air quality in parks and natural areas in many parts of the nation, and recommended

that the PM 2.5 significant level should be no higher than an annual average of 0.15

– 0.30 μg/m 3

(i.e., no more than 1

- 2 percent of the annual PM 2.5 NAAQS) to be consistent with the approach used for the definition of ―significant‖ for PM 10 , SO 2 , and NO 2

.

Response:

W e agree with the comment er‟s concern about the use of a 1 μg/m 3 impact level to

determine whether a parti cular attainment or unclassifiable area should be included in a

baseline area established by a PSD application for PM 2.5 , and, as explained below, we have revised the definition of “baseline area” to address this concern. As explained in the preamble for the 1980 PSD regulations, EPA selected an impact of 1 μg/m 3 , annual average, for the definition of “baseline area” because that value was considered the significant impact level for47

both SO 2 and PM when the definition was originally established. 10 There wa s no mandate at that time that a 1 μg/m 3 impact be used to determine the baseline area for increments for other pollutants; however, the use of a 1 μg/m 3 impact in the definition of “baseline area” was not changed when EPA developed increments for NO 2 in 1 988 because EPA also defined “significant” for NO 2 using the same annual average concentration of 1 μg/m 3

. We ha ve determined, however, that “significant” for PM 2.5 ambient impacts should be considered to occur at a lower concentration than 1 μg/m 3

. In f inalizing the rule , we decided that the significant impact level (SIL) for PM 2.5 should be 0.3 μg/m 3 , annual average. (See Section 5 of this document for more on SILs.) Consequently, although no change to the definition of “baseline area” was proposed in this rule, we believe it is necessary and appropriate to define in this final rule a level of significance of 0.3 μg/m 3 , annual average, for establishing a new baseline area for purposes of PM 2.5 increments. See revised 40 CFR 51.166 (b)(15)(i) and

52.21 (b)(15)(i).

Had we established the SIL at 1 μg/m 3 , annual average, as proposed under Option 1 for

SILs , then the definition of “baseline area” would not need to be revised. However, the revised definition in this final rule is consistent with our deci sion to establish a SIL of 0.3 μg/m 3 , annual average, for PM

2.5 . We consider this revision to the definition of “baseline area” to be a logical outgrowth of our decision to establish a SIL for PM 2.5 and the comment concerning the effect of

that action on the definition of “baseline area.” Thus, we believe that our failure to initial ly

propos e such a change to the definition of “baseline area,” based on the possibility of selecting Option 3 for defining the SIL for PM 2.5 , does not warrant a reproposal.



### 2.4.2 Com ments on Baseline Dates for the PSD Increments for PM 2.5

Three dates comprise the ―baseline date‖ concept for the PSD increments

– ―trigger date‖ and ―major source baseline date‖ (both of which are fixed dates), and ―minor source baseline date‖ ( which is set based on the submittal date of the first PSD application submitted for a source

located within an area or with emissions that have a significant impact in an area ). In the proposal, EPA proposed two options for defining the trigger date and major sou rce baseline date

for the new PM 2.5 increments. Under Option 1 , based on the provisions of section 166(a) of the

Act

, we proposed that the se fixed baseline dates be defined as the effective date of the final rule

, thereby creating new baseline dates for P M 2.5 for both the annual and 24

- hour averaging periods

. . Under Options 2A and 2B, we proposed to retain the existing baseline dates being used for

TSP/PM 10 for the annual PM 2.5 NAAQS based on the provisions of section 166(f) , while following Option 1 for defining new fixed baseline dates for the 24

- hour PM 2.5 increments. We also requested comment under Options 2A and 2B on the a lternative of new baseline dates for

both the annual and 24

- hour PM 2.5 increments . In addition, we requested comment on the issu e of the multiple emissions inventories that would be required if we finalized different baseline

dates for the annual and 24

- hour PM 2.5 increments as propose d under Options 2A and 2B

.

10 “A source will be considered to impact an area if it has an impact of 1 μ g/m 3 or more of SO 2 or PM on an annual basis. This figure has been selected because it corresponds to levels of significance used in previous Agency determinations for SO 2 and PM.” 45 FR 52676, August 7, 1980 at 52716.48

Comment:

Eleven commenters, including four state/local agency comm enters (0015, 0019, 0022, 0033), two state/local agency association commenters (0018, 0021), two industry commenters (0026, 0031), and three industry association commenters (0023, 0029, 0036), support the

establishment of new baseline dates for PM 2.5 for b oth the 24

- hour and annual averaging periods rather than retaining the existing baseline dates that were previously established for TSP / PM 10 , even in cases where they support section 166(f) of the Act as the basis for the PM 2.5 increments

. One industry as sociation commenter (0032) supports retaining the TSP baseline dates for both

the 24

- hour and annual PM 2.5 increments.

The commenters that support new baseline dates for PM 2.5 generally contend that retaining existing baseline dates would create problems . For example, one state/local agency (0015) indicates that for early minor source baseline dates (circa the mid

- late 1970’s), establishing the PM 2.5 emissions inventory would be extremely difficult, cumbersome

, and necessarily inaccurate and unreliable b ecause historic emissions inventories did not speciate

PM 2.5 emissions. Similarly, a state/local agency association commenter (0018) and a state/local
agency commenter (0019) contend that any attempt to calculate the PM 2.5 component of previously establis hed PM 10 increment consumption would be an insurmountable task due to lack of appropriate data, especially in cumulative impact analysis cases

, and another state/local agency association commenter (0022) indicates that resurrecting PM 2.5 inventories based on the

PM 10 baseline dates would be insurmountable.

A nother state/local agency association commenter (0021) supports new baseline dates for

PM 2.5 because the commenter believes this will assist in insuring the accuracy of increment consumption calculatio ns for the fine and coarse particle fractions. The commenter indicates that, as a practical matter, it would be virtually impossible for states to calculate the PM 2.5 component of previously consumed PM 10 increments because data on the fine and coarse

fra ctions of source emissions are largely unavailable.

One industry association commenter (0023) believes that making the PM 2.5 increments effective retroactively would cause unreasonable burdens on both permittees and permitting agencies, and would not p rovide any real benefits. One industry commenter (0026) and one industry association commenter (0029) opine that prospective application of PM 2.5 increments is sensible and more consistent with the PSD program, because it will give more time for developme nt of PM 2.5 emissions inventories rather than forcing affected permit applicants to try

to recreate PM 2.5 inventories for some earlier baseline date. Another industry commenter (0031) believes that EPA made a significant change in 1997 when it identified coarse and fine PM as separate pollutants, and that given the significant strides in the understanding of PM since the original adoption of the PM NAAQS in 1977, it no longer makes sense to draft new PM

increments onto an outdated baseline date/baseline co ncentration system.

As further support for new baseline dates, two commenters (0018, 0019) point out that

the establishment of new dates for PM 2.5 would not abandon past cases of increment consumption for PM 10 because the 24

- hour PM 10 increments will sti ll be in effect

. Another of

the commenters (0036) supporting new baseline dates add s that because EPA’s proposed49

increments are very low, facilities may find themselves immediately out of compliance with the

PM 2.5 increments upon promulgation of the rule, based on a January 1975 or 1977 baseline date.

Four of the commenters (0015, 0026, 0029, 0036) that support new baseline dates for

PM 2.5 explicitly raise issues with the Option 2 proposal to have new baseline dates for the

24

- hour averaging period whil e retaining the existing baseline dates for the annual averaging period. One of the se commenters (0015) believes this would unnecessarily complicate the review process without providing a significant environmental benefit. Another of the

commenter s (0029 ) contends that a system with different baseline dates would create an unrealistic burden on both permit applicants and permit reviewers, and suggests that EPA should modify the Option 2 approach to avoid relying on the retroactive application of the annua l PM 10 major source baseline date. Without expressing a preference for the use of new or existing baseline dates, a nother industry commenter (0043) states that EPA should establish a way to select just one baseline date in order to avoid the need for faci lities to maintain emission

inventories for both the 24

- h ou r and annual increment reviews.

Three of the commenters (0015, 0036, 0038) that support new baseline dates for PM 2.5 suggest that EPA should define the major source baseline and trigger date as t he effective date of the rule as proposed under Option 1. (Note that under proposed Option 1, the effective date of the rule was to have been the date 1 year after promulgation of the final rule.) However, another of the supportive commenters (0019) reco mmend s that EPA establish the trigger date as of the date when it officially established the nonattainment and attainment areas for PM 2.5 , that is, April 5, 2005. The commenter explain s that this approach is consistent with the PSD regulations

from the ir inception and partially mitigates EPA’s delays in implementing the PSD program for

PM 2.5

.

One industry association commenter ( 0032) supports the ― equivalence approach ‖ (presumably referring to Option 2 ) for developing the PM 2.5 increments, and recommends that

EPA not use new baseline dates for the 24

- hour increments as proposed. The commenter urges

EPA to retain the TSP baseline dates for both the 24

- hour and annual PM 2.5 increments, stating

that recent reductions in PM 2.5 will not oversubscribe the incr ement because states will retain authority in their SIPs to assure attainment and maintenance of the NAAQS.

Re sponse:

Having considered all the comments, we believe that the most reasonable approach for addressing the relevant dates associated with the PM 2.5 increments is to start anew with the baseline date concept. As already mentioned, th e commenters have identified difficulties that would occur if the PM 2.5 emissions inventory for increment analyses had to be created for an earlier period of time

, and the existence of these difficulties supports the approach under Option 1 to establish new dates for implementing the PM 2.5 increments . Also, these new baseline dates for PM

2.5 increments will no t undo the current protection provided by the existing in crements for PM because we are not revoking the 24

- hour or annual PM 10 increments under th e new rule. Accordingly, th e final rule establishes independent PM 2.5 increments using a “trigger date” and “major source baseline date” that are separate from the dates defined for the PM 10 increments. Consequently, new minor source baseline dates and the corresponding baseline areas will be50

used for the annual and 24

- hour PM 2.5 increments

, and will be established when a source submits a complete PSD permit applica tion any time on or after the new trigger date for PM 2.5

. (See also the discussion about changes to the definition of “baseline area” above in S ection

2.4.1 of this document .)

The “major source baseline date” for PM 2.5 is being set as the date of pub lication of th e final rule in the Federal Register. The setting of this date differs from previous major source baseline dates which were set as the date of publication of the proposed rule, but is similar to the major source baseline date set for the oth er increments in that the date precedes the effective date for implementing the increments, and thereby requires that certain major source emissions increases that occur before the trigger date retroactively count toward the amount of increment

consumed.

The “trigger date” is being set as the date 1 year after publication of th e final rule in the Federal Register. We are using this approach to define the date on which the PM 2.5 increments become effective as the date 1 year from the date of publication, consistent with the 1

- year delay required under section 166(b) of the Act. This date for the trigger date separates the effective date of the PM

2.5 increments from the effective date of th e final rule in general (which is 60 days after publication in the Federal Register) , but also ensures that the “minor source baseline date” for PM

2.5 for any particular PM 2.5 attainment or unclassifiable area cannot be established until after the increments become effective in th e final rule. The implementation of thes e dates as part of the new PM 2.5 increment system is discussed in greater detail in S ection 6 of th is

document

.

We recognize that some commenters may still have a concern about our decision to set the major source baseline date as the date of publicati on of th e final rule in light of the fact that

the PM

2.5 NAAQS have been in place since 1997; however, we believe that the selection of possible earlier dates would require states to retroactively establish PM 2.5 emissions inventories for increment analyse s during a period when sources were generally not required to conduct

PM 2.5 air quality analyses. Hence, given the lack of information, and considering the technical difficulties in doing so, we do not believe that it would be appropriate to require state s and sources to retroactively account for PM 2.5 increment consumption by setting the major source

baseline date at an earlier date than the date we have selected.

Comment:

Four of the commenters (0018, 0019, 0021, 0033) that support new baseline dates for

PM 2.5 do so despite explicitly supporting section 166(f) authority and/or Option 2 as the basis for

PM 2.5 increments. These commenters believe that EPA has ample authority under section 166(f)

to define new baseline dates for PM 2.5

.

Response:

As d iscussed above, we are finalizing the PM 2.5 increments under the authority of

section 166(a) of the Act and establishing new baseline dates for PM 2.5 for both the 24

- hour and annual averaging periods. Thus, the issue of the permissibility of establishing new baseline dates under section 166(f) authority does not need to be addressed here. Nevertheless, as we51

pointed out i n the 2007 NPRM, section 166(f) does not explicitly address how EPA should handle baseline dates for a substituted increment. We propos ed to retain the existing baseline dates for TSP/PM 10 for the annual averaging period under Option 2, consistent with the approach we took when we replaced the statutory PM increments with PM 10 increments pursuant to section 166(f). However , we also point ed out at proposal that given PM 2.5 emissions trends, our judgment is that establishing new baseline dates for PM 2.5 may be more effective at preventing significant deterioration because the baseline concentrations will reflect emissions

reductions , and we took comment on whether this would provide sufficient justification for establishing new baseline dates under the section 166(f) substitution approach

. See 72 FR

54138.

Because we have not used section 166(f) authority in the current rulemaking, we n eed not make a final determination at this time on whether new baseline dates are permissible under that section of the statute. Accordingly, we do not adopt or rule out any interpretation of

section 166(f) in this regard at this time.



### 2.4.3 Miscellaneous Comme nts on Increments for PM

Comment:

One industry commenter (0016) suggest s that EPA develop geographic area

- specific increments (and SILs and SMCs ) that take local conditions into account. The commenter pointed out that PM 2.5 levels in PSD areas proximat e to international borders may be elevated by sources outside the legal and practical control of the United States and state authorities. The

commenter also note s that PM 2.5 levels may be elevated by natural conditions, such as drought, fires, geologic fo rmations (sandy or fine

- grained surface features)

, high winds, etc., leading to excessively dusty ambient conditions over which the local area has no control. The commenter

indicate s that local area baselines must reflect these PM emissions, though they a re not reflected in the local area’s emissions inventory. The commenter urge s EPA not to penalize such PSD areas by imposing uniform national PSD increments (or SILs or SMCs) where the conditions of concern are not capable of control.

Response:

The fin al rule establishes an area classification system with prescribed, uniform PM 2.5 increments for C lass I, II and III areas . We have not defined different increments for different areas of the country , although states can propose to use more stringent incre ments or propose alternative measures within their individual jurisdictions where they deem it appropriate to do

so

. With regard to the commenter‟s concern about e missions from natural conditions ( such as those described by the commenter ) we do not believ e that such emissions would consume

increment because of their natural and temporary nature. In addition, if a state wishes to disregard new emissions from sources outside the United States, the state‟s PSD program may provide that such emissions do not c onsume increment ( see 40 CFR 51.166(f)(1)(iv)).52

Comment:

One federal agency (0044) points out a typographical error in the proposed regulatory language at 72 FR 54147 for Option 1 for the 24

- hour Class I PM 2.5 increment in 40 CFR 51.166(c). The comment er (0044) note s that this number should have be en 2 μg/m 3 to be consistent with the remainder of the proposal.

Response:

The commenter is correct in pointing out that the proposed Option 1 value for the

24

- hour Class I increment was intended to be 2 μg/ m 3 as discussed in the preamble and reflected in the regulatory language proposed in 40 CFR 52.21(c). The correct value appears in the final regulatory language

.

Comment:

One industry commenter (0031) believes that PM 2.5 increments must take into accou nt the evidence that significant levels of coarse PM can intrude into PM 2.5 measurements. In this argument, the commenter discusses the bimodal nature of PM, indicating that ―fine particles‖ as evaluated for regulation are formed primarily by combustion o r chemical reaction of gases and typically have a diameter smaller than 1 μm, while ―coarse particles‖ are formed by the mechanical breakdown of mineral, crustal material and organic debris and typically have a diameter greater than 3 μm. These types of p articles have distinct health effects, with the effects of fine particles being of concern. The commenter notes that the PM 2.5 indicator was adopted as a means to regulate fine PM, and argues that with a 2.5 μm threshold, the PM 2.5 indicator also inapprop riately includes some coarse particles of crustal origin. The commenter contends that coarse particle intrusion into PM 2.5 is a significant issue, particularly in arid western area s where a high proportion of PM 2.5 can be coarse PM. The commenter believe s that it is a basic distortion to adopt a PM 2.5 NAAQS based on fine PM and then to measure compliance based on coarse PM, and that increments derived from the PM 2.5 NAAQS are similarly flawed. Based on this argument, the commenter asserts that PM 2.5 incr ements or other measures to prevent significant deterioration must address and account for coarse intrusion into PM 2.5 measurements.

Response:

This commenter is critical of the Agency‟s selection of an indicator for particulate matter that includes part iculate matter of a size that the commenter feels should not be included. The EPA made the decision concerning the PM 2.5 indicator in defining the NAAQS under a separate rulemaking . The final rule to adopt PM 2.5 increments, SILs

, and the SMC for PM 2.5 is not the appropriate rule to address the commenter‟s concerns about the appropriate indicator for PM

. Thus, we provide no formal response to th e comment herein.53



## 3 Comments on the PM 10 

## Increments

Under our preferred option (Option 1) for developing PM 2 .5 increments, we proposed to rely on the authority under section 166(a) of the Act to establish annual and 24

- hour increments. In addition, we proposed to revoke the annual PM 10 increments based on the same technical

evidence that led us to revoke the an nual PM 10 NAAQS, and retain the existing 24

- hour PM 10 increments. Alternatively, under O ptions 2A and 2B, we proposed to again use the 24

- hour increment values derived under Option 1 to promulgate 24

- hour PM 2.5 increments, but to develop

annual PM 2.5 incr ements to replace the existing annual PM 10 increments using the equivalent substitution approach under the authority of section 166(f) of the Act. In addition, under

O ptions 2A and 2B we sought comment on whether we should rely on section 166(f) of the Ac t to develop 24

- hour PM 2.5 increments to replace the existing 24

- hour PM 10 increments, even though the primary and secondary 24

- hour PM 10 NAAQS had not been revoked.

Comments Supporting Revocation of PM 10 Increments:

Six commenters , including two stat e/local agency commenters (0015, 0022 )

, three industry commenters ( 0031, 0034, 0043)

, and one industry association commenter (0042), support EPA’s proposal to revoke the annual PM 10 increments. In addition, five of these

commenters (0015, 0031, 0034, 0042 , 0043) recommend that EPA revoke the 24

- hour PM 10 increments as well.

One state/local agency commenter (0022) agrees with the proposal to adopt the 24

- hour

and annual PM 2.5 increments and revoke the annual PM 10 increments. The commenter indicates

that counting and tracking increment is confusing enough without adding the confusion of potentially overlapping PM standards. According to the commenter

, the cleanest approach is to establish a single new PM 2.5 increment and work from there

– EPA can develop a coarse fraction increment, once EPA establishes co a rse PM NAAQS. The commenter add s that the removal of

the PM 10 annual increment is supported by the removal of the health

- based standard for annual

PM 10

.

Another state/local agency commenter (0015) als o supports proposed Option 1 for developing the annual and 24

- hour PM 2.5 increments and revoking the annual PM 10 increments.

However , the commenter does not agree that the EPA should retain the 24

- hour PM 10 increments

since the PM 10 emissions include PM 2. 5 emissions. The commenter believes that t he

combination of the current 24

- hour PM 10 increments and the proposed 24

- hour PM 2.5 increments will be unnecessarily conservative . The commenter contends that t he proposal does not adequately discuss the potenti al for double

- counting of 24

- hour PM 2.5 emissions within a

24

- hour PM 10 increment analysis.

An industry association commenter (0034) and an industry commenter (0042) agree that EPA’s regulations should not contain an annual increment for PM 10 since an an nual PM 10 NAAQS no longer exists. In addition, the commenters believe that section 166(f) provides the only authority under the Act to establish increments for PM, and that under section 166(f) any update to the PM increment s must be achieved only by a su bstitution of the new increment for54

the old increment. Thus, the commenters believe that EPA is without authority to retain the

PM 10 annual increment if it adopts a PM 2.5 annual increment.

The se commenters (0034, 0042) also argue that EPA’s rationale for retaining the 24

- hour

PM 10 increments is flawed. As noted above, these commenters believe that EPA must address PM increments under section 166(f) of the Act, and they believe that section 166(f) allows increments for only one indicator for PM at a ti me. Thus, the commenters assert that EPA does not have the authority to retain the 24

- hour PM 10 increments if it adopts the 24

- hour PM 2.5 increments. In addition, t he commenters poi nt out that in previous actions, EPA has stated that a

dual

- increment sys tem would be unnecessarily burdensome and cumbersome ( variously citing

52 FR 24685 and 24701 , July 1, 1987; 54 FR 41220 , October 5, 1989; and 58 FR 31

, 6 2 4,

June 3, 1993 ).

The industry association commenter (0034) also states that EPA seems to be lieve t hat

because it has retained the 24

- hour PM NAAQS for PM 10 , it must retain the 24

- hour PM

increment for PM 10 . The commenter argue s that there is no statutory provision that requires such

a one

- to

- one correlation of NAAQS and increment when the NAAQS is exp ressed by more than

one indicator. The commenter refer s to two examples as support for th at comment : (1) EPA’s 1984 proposal to replace the primary PM NAAQS expressed as TSP with a primary PM 10 NAAQS while retaining the secondary PM NAAQS and PM increment s expressed as TSP; and (2) the fact that the PM 2.5 NAAQS have been in place for over 10 years with no PM 2.5 increments, and PM 10 increments have been used as a surrogate for PM 2.5

.

In addition, the industry association commenter (0034) contends that s ec tion 166(f) ensures that a single increment system protects public health and welfare by requiring that ―substituted maximum allowable increases [of the new increments] shall be of equal stringency in effect as those specified in the [increment] provisions for which they are substituted.‖ The

commenter claim s that the elimination of the 24

- hour PM 10 increment would not result in a diminution of public health or welfare because the new 24

- hour PM 2.5 increment must provide the same level of protection.

An other i ndustry commenter (0031) argues against reten tion of either the annual or

24

- hour PM 10 increment, and support s replacing both with annual and 24

- hour PM 2.5 increments. The commenter argues that the existing PM 10 increments were developed based on t he 1987

PM 10 NAAQS which have been found by the courts to ―confounded‖ because the coarse PM regulated under that standard depend s ‖quite arbitrarily‖ on the existing levels of PM fine in an

area. This commenter recommends that EPA use section 166(f) of t he Act to replace both the

annual and 24

- hour PM 10 NAAQS with annual and 24

- hour PM 2.5 NAAQS or with alternative measures. Alternatively, the commenter indicates that, should EPA decide to establish new

PM 2.5 increments based on section 166(a) of the Act, then EPA must also establish PM 10 increments under section 166(a) because (according to the commenter’s analysis) PM 10 is also a new pollutant. In this case, the commenter believes that EPA has the freedom under

section 166(a) to evaluate alternatives to increments for PM 10 , which could include a finding that

the PM 2.5 increments adopted pursuant to section 166(a) adequately address coarse PM emissions for PSD purposes. Regardless of the statutory basis, the commenter believes that EPA could

more appropr iately address the goals of the PSD program for coarse PM by separating PSD55

protection from the level of the NAAQS, which the commenter believes is excessively conservative as applied to coarse, crustal PM of a rural type. Thus, the commenter recommends

t hat EPA consider alternative measures designed to better address the goals of the PSD program, which include protection of economic development, such as western surface mines.

Th e other i ndustry commenter (0043) recommends that EPA revoke the 24

- hour PM 1 0 standard as we did the annual PM 10 standard. From the context of the comment, w e presume that by recommending that both PM 10 standards be revoked, the commenter also recommends that

both the annual and 24

- hour increments should be revoked as well.

Comm ents Opposing Revocation of Annual PM 10 Increments:

Five state / local agenc y commenters (0018, 0019, 0025, 0028, 0033) , one state/local agency association commenter (0021), and one environmental group commenter (0040) oppose the revo cation the annual PM 10 increments . The commenters generally believe it is premature to

revoke the annual PM 10 increments and/or that these increments continue to play protective role.

T hree of the state / local agency commenters (0018, 0019, 0025 ) oppose revoking the

annual PM 10 increments until EPA makes a determination on a NAAQS for PM

- coarse and establishes equivalent increments for PM

- coarse. Two of the state / local agency commenter s (0018 , 0019 ) believe that it is prudent to maintain the PM 10 increments until EPA makes a

determin ation on the health and environmental effects of the coarse fraction of PM. The se com

menter indicate that PM 2.5 and PM 10 increments can play complement ary roles to avoid any discontin uities or unwanted degradation concerns.

One of the state / local agency commenters (0019) elaborates that the basis for dismissing

the annual PM 10 NAAQS by the substitution of fine particle NAAQS to address certain health and welfare effects does not provide a basis for dismissing a PSD increment which is meant to stop significant degradation of air quality. The commenter note s that as refinements are made to estimation of fine particle emissions or in instances where these are deemed not to be a major component of particulate emissions, the PM 10 annual increment could prevent long term deterioration of air quality associated with the coarse component.

This state / local agency commenter (0019) also states that EPA propose d to replace the

PM 10 annual increment with the corresponding PM 2.5 increment under the s ect ion 166(f) options 2A and 2B, but d id not provide a substantive basis for this action. The commenter does not see the tension noted by EPA between s ections 166(a) and (f) with respect to reaching a holistic

solution if EPA views PM 2.5 as a new indicator o f PM, as the commenter believe s it can. The commenter (0019) explain s that under this approach, if EPA determines that coarse particle levels are necessary to protect the public from certain exposures not addressed by PM 2.5 , then it will be appropriate fo r EPA to define compl e mentary increments for coarse particulates as

another indicator of PM. The commenter also asserts that the 24

- hour increments for PM 2.5 must be based on section 166(f) authority, but believes that the PM 2.5 increment need not replace the

PM 10 increment for this averaging period.56

Similarly, a state/local agency association commenter ( 0021) believes that EPA can and

should continue both the 24

- hour and annual average PM 10 PSD increment program until NAAQS for PM with aerodynamic dia meter less than or equal to a nominal 10 μm but greater

than a nominal 2.5 μm ( PM 10

- 2.5 ) are promulgated, and that EPA has the discretion to accomplish

this under section 166(f)

. T he commenter asserts that , at a minimum, EPA should continue the

24

- hour PM 10 increments in conjunction with the continuation of the 24

- hour PM 10 NAAQS.

Two of the state / local agency commenter s (0028, 0033) request that EPA keep the PM 10 PSD increments in place until the full PM 2.5 program is adopted and in place. One of thes e

commenter s (0033) believes that there are too many uncertainties regarding PM 2.5 to revoke the

annual PM 10 increments . The commenter notes that the PM 2.5 program has been dragging for years, analytical methods are not formulated, the NSR part of the imp lementation rule has not issued, condensables are not yet included, and the impact of precursors has not been definitively explored. The commenter contends that under these conditions, nothing concerning PM 10 should be revoked until the reasons for doing so are clearly understood and the overall impact on ensuring clean air and the public health and welfare have been fully explored. The commenter
suggest s that PM 10 increments and NAAQS should remain in effect until these issues have been

resolved to the s atisfaction of the Administrator. This commenter believes that Options 2A and 2B must be based entirely on section 166(f) of the Act, but that the presence of increments for

both PM 10 and PM 2.5 is supportable under this section because they complement eac h other. The commenter indicates that the problem will be resolved when sufficient data are available to

revoke the PM 10 NAAQS and increments and/or PM 10 is replaced by PM 10

- 2.5

.

The e nvironmental group commenter (0040) claim s that EPA has no authority to repeal an existing PM 10 increment without at the same time restoring the corresponding TSP increment.

The commenter note s that Congress established the TSP increments by statute and gave EPA no authority to revoke them, but instead gave EPA only limite d authority to substitute PM 10 increments for TSP increments under the conditions specified in s ection 166(f). The commenter

asserts that EPA cannot revoke the annual PM 10 increments, either by ―replacing‖ them with

PM 2.5 increments or otherwise, unless E PA at the same time restores the annual TSP increment s

. The commenter also contends that retention of the annual PM 10 increment s is entirely compatible with the statutory purposes, notwithstanding EPA’s revocation of the annual PM 10 NAAQS. The

commenter notes that the courts have observed that the unique congressional objectives of the PSD program may necessitate the imposition of increment metrics that differ from the related NAAQS (citing Environmental Defense Fund v. EPA , 898 F.2d 183, 190 (D.C. Cir. 1 990).

The e nvironmental group commenter (0040) giv e s the following examples/evidence that

retention of the annual PM 10 increments is important to achieving the goals of the Act’s PSD provisions :

 While EPA attributes the visibility impairing impacts of PM pollution primarily to

elevated short

- term fine particle concentrations, EPA recognizes that PM 10 plays a significant role in the other welfare related impacts of PM pollution (citing 72 FR 54136 )

.

 The EPA also states that the most significant PM

- rela ted ecosystem

- level effects result from long term cumulative deposition . . . that exceeds the natural buffering or storage57

capacity of the ecosystem and/or affects the nutrient status of the ecosystem (citing 72 FR

54131 )

.

Response:

As explained elsew here in this document and the preamble to the final rule, we are not using a section 166(f) legal path to promulgate PM 2.5 increments to replace the existing PM 10 increments, and we are not taking final action on our proposal to otherwise revoke the PM 10 i ncrements. We agree that section 166(f) of the Act is a “substitution” approach, as mentioned by some commenters supporting the us e of that approach as the legal path to substitute the new

PM 2.5 increments for the existing PM 10 increments . H

owever, as we stated in our 2007 NPRM, we expressed some concern about using section 166(f) to substitute PM 2.5 increments for PM 10 increments. In fact, as described above, some commenters challenged our authority under section 166(f) to replace the PM 10 increments wi th new PM 2.5 increments. We have not reached any final conclusion as to whether the Option 2 equivalent substitution approach under

section 166(f) is permissible under the Act.

In th e final rule, EPA is promulgating new PM 2.5 increments under the authority of section 166(a) of the Act, but is not amending in any way the existing increments for PM 10 . We continue to believe, as we indicated in the 2007 NPRM, that the combination of the new PM 2.5 increments and the existing 24

- hour PM 10 increment wil l address non

- visibility welfare impact s attributable to deposition (primarily sulfate and nitrate particles larger than PM 2.5 ).

The obvious effect of not taking final action with respect to the PM 10 annual increments is to leave those increments in p lace and unchanged. See section V.H of the preamble to the final

rule

. Similarly, EPA is not taking any action with respect to coarse PM in this rule as recommended by a commenter. For these reasons, the commenter‟s arguments on what authority must be u sed to set increments for PM 10 and/or coarse PM, and that EPA has some obligation to take action with respect to coarse PM, are not on point for this rule. Thus, no substantive response to this comment is needed.

We disagree with the comment that the removal of the PM 10 annual increment is supported by the removal of the health

- based standard for annual PM 10

. Based on legal arguments contained in some of the comments and our own legal analysis of the PM 10 increments, we have concluded that there is a strong legal basis for not revoking the annual

increments at this time , even though we have revoked the annual PM 10 NAAQS

. T

he PM 10 increments were promulgated on June 3, 1993 (58 FR 31622) as replacement increments for the then existing statutory increme nts for PM measured as TSP. The fact that EPA promulgated the

PM 10 increments as “equivalent” replacements for the TSP increments under the authority of section 166(f) of the Act is important in that EPA does not have authority to simply remove the

TSP in crements that were explicitly defined within the PSD program requirements in the Act. Accordingly, w e believe that the annual TSP increments would be restored by default should we

decide to revoke the annual PM 10 increments as proposed. H owever, e ven if the original annual TSP increments were not restored, there is no basis for automatically revoking the annual PM 10 increments simply because we have revoked the annual PM 10 NAAQ , because annual increments

are not contingent up on the existence of annual NAA QS. Th is is clear from the court‟s decision58

in the earlier NO 2 increment litigation stating that increments for a particular pollutant do not necessarily need to match the averaging periods that have been established for NAAQS for the same pollutant. Env ironmental Defense Fund, Inc. v. EPA , 898 F.2d 183, 189

- 190 (D.C. Cir. 1990) (“... the „goals and purposes‟ of the PSD program, set forth in § 160, are not identical to the criteria on which the ambient standards are based.”)

The commenter‟s concerns about the alleged excessive conservativeness of the PM 10 NAAQS is not relevant to this final rule establishing increments, SILs

, and SMC for PM 2.5 under the PSD program. Therefore, we are not responding to that particular concern in this document.59



## 4 Comments o n Significant Impact Levels (SILs) for PM 2.5



### 4.1 Comments on the Legal Basis for SILs

Comment:

One environmental group (0040) presented extensive legal and policy arguments against

SILs. The legal arguments are summarized in this section, while the policy arguments are
discussed below in S ection 4

. 2 of this document. In brief, the main points of the commenter’s legal concerns are as follows:

 The EPA has no authority to promulgate SILs. Congress codified increments in section 163 of the Act, directing tha t SIPs contain measures assuring that the

increments shall not be exceeded (emphasis added in the comments). A primary method for assuring that increments are not exceeded is the requirement that PSD
sources must demonstrate that their emissions ―will not cause or contribute‖ to a violation. The Act plainly provides that no major source may be constructed unless it meets this requirement, and may not contribute to an exceedance ―for any pollutant in any area.‖ Congress did provide exemptions where they w ere intended, but did not provide for exemption based on SILs or anything similar. Thus, SILs are plainly incompatible with the statutory language . The EPA cannot justify SILs as being just a shortcut to determining compliance with increments and NAAQS b ecause there is no data or analysis in EPA’s proposal showing any necessary or rational connection

– the SILs are arbitrary numbers based on ratios that have no demonstrated or rational relationship to compliance with increments and NAAQS.

 The de minimis d octrine does not apply to increment analyses and preconstruction monitoring requirements. This doctrine does not apply where Congress has expressly directed that the letter of the law applies in all circumstances [ Shays v. FEC , 414 F.3d 76 (D.C.Cir. 2005) ], as it has in this case. There is no room for de minimis exceptions in the statute. In any case, the de minimis doctrine is inapplicable because it applies only where the regulation will yield a gain that is demonstrably trivial or zero. The

EPA has o ffered no evidence that sources with impacts below the proposed SILs will

never cause or contribute to violations of increments or NAAQS, or that the gain from regulating such sources will in fact be trivial.

, The proposed SIL values are hardly trivial, am ounting to a quarter to a half of proposed increments in some cases. Moreover, the idea that a single national number can define ―trivial‖ is flawed, given that even very small impact can be of great significance in an area that is close to an

increment o r NAAQS.

Response:

As EPA explained in the preamble to the proposed rule, the legal basis for SILs is grounded on the de minimis principles described by the court in Alabama Power Co. v. Costle

, 636 F.2d, 323, 360 (D.C. Cir. 1980 ) ( “Categorical exemptio ns may also be permissible as an exercise of agency power, inherent in most statutory schemes, to overlook circumstances that in60

context may fairly be considered de minimis.”). See 72 FR 54112, 54139 (Sept ember 21, 2007). Further, as the Alabama Power co urt explained, the proper use of a de minimis exemption is not a departure from the statute, but is instead “a tool to be used in implementing the legislative

directive.” 636 F.2d at 360. The Alabama Power court concluded that “most regulatory

statutes, including the Clean Air Act, permit [de minimis] showings in appropriate cases. 636 F.2d at 360. The court went on to say that, “unless Congress has been extraordinarily rigid, there is likely a basis for an implication of de minimis authority to provide exemption when the burdens of regulation yield a gain of trivial or no value.” 636 F.2d at 360

- 361. Although this comment identifies several statutory provisions that the comment e r contends are inconsistent with a de minimis exemption based on SILs, the comment e r does not provide any basis for concluding that these provisions are the kind of “extraordinary rigid” provision that forecloses the use of a de minimis exemption. Thus, where the SIL values set by a rule identify a level of impact such that “th e burdens of regulation” (in this case certain requirements under CAA

section 165) will “yield a gain of trivial or no value,” the establishment of SILs is a permissible de minimis exemption.

Further, the comment cites Shays v. FEC , 414 F.3d 76 (D.C. Cir . 2005) as support for the conclusion that the de minimis doctrine does not apply here. The Shays case, however, does not support the contention that Congress in the CAA foreclosed the use of the de minimis exemption. The Shays case simply confirms the l imits of the de minimis doctrine from the

Alabama Power decision: that the de minim i s doctrine does not apply where the statute is “extraordinarily rigid” or where “the regulatory function does provide benefits, in the sense of furthering the regulatory ob jectives.” 414 F.3d at 114.

As explained above, the SIL is expressly used as a screening tool to determine whether a source‟s impact is considered to be significant enough to cause or contribute to a violation of an increment or NAAQS. Accordingly, a r elatively small contribution (an air quality impact below the SIL) to an existing modeled violation will generally not be considered to contribute to the violation, recognizing that the violation results from existing facilities causing more substantive

im pacts that result in the air quality levels exceeding the NAAQS or increments

.



### 4.2 General Comments on SILs for PM 2.5

EPA received overwhelming support for the development of SILs to serve as a screening tool for implementing the air quality impact requireme nts under PSD. Nevertheless, commenters varied in their support of a specific option for defining the PM 2.5 SILs. This section summarizes both the supporting and opposing comments that we received.

Comments Supporting SILs:

Two state/local agency com menter s ( 0015, 0025) and f our industry and industry association commenters (0013, 0035, 0038, 0043) express general support for EPA’s proposal to codify PM 2.5 SILs. One of the state/local agency commenter s (0025) recommend s that EPA finalize SILs as exped itiously as possible to facilitate their use for both determining the significance of a source on its surroundings (in attainment and nonattainment areas) and determining when and if a cumulative impacts review is necessary.61

One i ndustry commenter (0013 ) support s EPA’s efforts to address the final elements that aid implementation of the PSD program for PM 2.5 , which includes SILs (and i ncrements and

SMC ). An i ndustry a ssociation commenter (0038) strongly support s the establishment of PM 2.5 SILs (and incr ements and SMCs) that properly balance the economic and environmental goals of the PSD program

.

Another industry association commenter (0035) support s the use of SILs (and SMCs) in screening models to estimate the impact of proposed projects in order to avoid costly air quality impact analyses for projects that are unlikely to have consequential impacts on air quality. Similarly, an industry commenter (0043) agree s that SILs can serve as an effective screening tool

to establish de minimis impact levels s o that more time

- consuming

, extensive analys e s are not required for situations with only minimal potential impact.

Comments Opposing SILs:

One environmental group commenter (0040) opposes SILs on legal and policy grounds. The policy grounds are summari zed in this section, while the legal grounds are discussed above

in Section 4.1 of this document. In brief, the main points of the commenter’s policy concerns are

as follow s:

 A revie w of the implementation of the proposed SILs for other PSD pollutants sh ows that impacts that are not de minimis are often exempted. The Class I SIL for NO 2 is virtually never exceeded, with the result that almost all PSD sources have been permitted with no review of whether the facility will cause or contribute to an NO 2 inc rement violation in a Class I area. Compliance with the NO 2 increments has become a significant issue in recent years, in large part because of a boom in NO

x emissions associated with oil and gas development, much of which is from minor

sources. Under th e SILs for NO 2 , virtually no new PSD source locating in an area affected by such minor sources would be required to evaluate whether its additional

NO

x emissions would actually be contributing to NO 2 increment violations. The commenter presented examples of cases where these concerns are alleged to have been born out. The commenter added that experience shows similar issues with PM 10 and SO 2 SILs. Finally, the commenter gave examples of some facilities impacting

areas known to be in violation of incremen ts that have been permitted based on modeling showing that their contributions will be at levels less than the proposed

SILs.

 The EPA must assure that SILs are truly de minimis and must also include limitations on the use of SILs as necessary to prevent si gnificant deterioration of air quality. The specific numbers proposed for PM 2.5 SILs cannot rationally be characterized as trivial or insignificant. Moreover, the proposed rule would exempt a source meeting SILs from conducting an increment analysis even if there is an existing or projected

increment violation in the area

– no situation where an a NAAQS or increment is being violated can lawfully or rationally be considered de minimis relative to the requirement in section 165(a)(3)(A) of the Act that PSD sources cannot be allowed to cause or contribute to a violation of any increment or NAAQS62

Response:

We believe that the PM 2.5 SILs will provide a useful screening tool that provides an effective means of implementing the requirements for an air quality impact analysis for PSD. The SILs in general help to streamline the PSD process for determining which PSD sources must conduct a comprehensive cumulative air quality impact for PM 2.5 under the PSD rules

. Alternatively, sources whose impacts are considere d de minimis are allowed to avoid the expenditure of completing a comprehensive cumulative analysis that will have only minimal effects on the environment. (Our legal rationale for the SILs is provided in the next section.) When a proposed source‟s impac t by itself is not considered to be “significant,” EPA has long maintained that any further effort on the part of the applicant to complete a cumulative source impact analysis involving other source impacts would only yield information of trivial or no

val ue with respect to the required air quality impact assessment for the proposed source or modification.

We believe that we have the discretion to use the de minimis concept to help determine
whether an emissions increase will “cause or contribute to” a vi olation of a NAAQS or increment. Consequently, we believe that it is reasonable to allow new or modified sources that contribute only minimally (SILs represent relatively small percentages of the corresponding NAAQS and increments) to a modeled violation of a NAAQS or increment to receive their construction permits in light of the fact that the modeled violation can be attributed to emissions from other existing sources whose operation generally plays a more dominant role in the air quality exceeding the N

AAQS or increment. Accordingly, states that consider de minimis impacts not to cause or contribute to a violation must still substantiate and then address any violations of a NAAQS or an increment, if appropriate. For example, a state might choose to use their SIP planning process to address the violations by requiring the a reduction of emissions from existing sources, where more meaningful remedies, producing more substantial air quality improvements, are available from such existing sources . Further reducing the emissions from an already well

- controlled source (such as the proposed PSD source) with relatively small air quality impacts would naturally yield only minimal air quality improvements (as illustrated by the level associated with the SIL) and would not produce the levels of air quality improvement that could come from the control of older, existing sources.

In short , it is not our intent that the SILs be used as a means of allowing known adverse air quality situations to be ignored just bec ause they are small . If, for example, the cumulative effect of a number of de minimis impacts in an area can be shown to cause air quality problems that are not being addressed simply because no source‟s impact is “significant” then the permitting authori ty must address the air quality problems, whether by us ing lower de minimis levels or temporarily cease using the de minimis concept altogether where it is known to allow the adverse conditions to worsen without remedy , or taking some other step to address the problems

.63

Comment:

The same environmental group commenter (0040) provides that EPA’s a doption of any SILs must include detailed requirements as to how a source must evaluate its impact to compare to the SILs. The EPA must adopt rules setting cri teria for this analysis under section 165(e)(3). These criteria must ensure a conservative analysis, such as modeling direct and precursor emissions, modeling worst case potential emissions for each averaging time, comparing maximum modeled impact against the SILs, following the Guideline on Air Quality Models, and following EPA requirements for acceptable receptor spacing, among other things.

Response:

We agree with the commenter‟s recommendation that we provide information for comparing a source‟s imp act against the SILs. We do not, however, believe that this information needs to be in the form of “detailed requirements,” which presumably would be contained in the PSD rules. Instead, we believe that procedures in the form of guidance are appropriate for assisting permit applicants and permitting authorities. To this end, we have already provided guidance for comparing the impacts of a proposed project‟s PM 2.5 emissions against the SIL for purposes of complying with the NAAQS. This guidance specifica lly takes into account the form of both the annual and 24

- hour PM 2.5 standards and recognizes that the application of the SILs should follow a conservative approach for estimating a source‟s modeled ambient impacts. See

EPA memorandum titled “ Modeling Pro cedures for Demonstratin g Compliance with PM 2 5 NAAQS

. ” (March 23, 2010.) We also plan to address our recommended approach for using the

PM 2.5 SILs for purposes of meeting the new PM 2.5 increments in forthcoming guidance.

Comment:

One industry assoc iation commenter (0029) states that SILs must be consistent with the twin goals and purposes of the PSD program: preventing significant deterioration while allowing reasonable economic growth. The commenter explain s that EPA must consider the

administrati ve burdens associated with setting SILs at very low levels, which would require PSD permit applicants to undertake onerous and time

- consuming cumulative impact assess ments for

propose d sources that are w e ll controlled, have trivial impacts, and are locate d up to 300 km from any Class I areas. The commenter argue s that i mposing such an administrative burden upon the reviewing authority and the permit applicant is neither reasonable nor legally justified when it is triggered by a trivial predicted impact on the PSD increments for a Class I area, especially when other PSD program elements

– e.g., the AQRV

- evaluation provisions of s ection 165(d) of the Act

– will fully protect Class I areas.

Response :

This comment contains a number of misconceptions about how SILs are set. First, SILs are not set based on the need to balance the goal of preventing significant deterioration in air quality SILs and the goal of allowing reasonable economic growth. Second, SILs are not set at a level to ensure that permit ap plicants will avoid the “administrative burdens” of meeting the statutory requirements for getting a PSD permit. Third, the fact that a proposed source is well

-64

controlled or located a far distance from where it causes impacts does not enter into the

calcu lus. Instead, as EPA explained in the preamble to the proposed rule, the legal basis for SILs is grounded on the de minimis principles described by the court in Alabama Power Co. v.

Costle , 636 F.2d, 323, 360 (D.C. Cir. 1980). See 72 FR 54139. Thus, the proper value to select for a SIL is a value that “implements the legislative design” by avoiding “trifling matters,” “pointless expenditures of effort,” and “trivial items.” 636 F.2d at 360 (“The ability ... to exempt de minimis situations from a statutory command is not an ability to depart from a statute, but rather a tool to be used in implementing the legislative design.”).



### 4.3 Comments on the Relationship of SILs to AQRVs

Comment:

One industry association commenter (0038) and one federal agency comme nter (0044) support position set out by EPA in the 2007 NPRM that PM 2.5 SILs for Class I areas are not
in t en d ed to serve as thresholds for determining the need for an AQRV analysis or whether an adverse impact on an AQRV will occur . The federal agency com menter (0044) indicates that the

2007 NPRM makes clear that the fact that a source’ s predicted impact is less than the Class I SIL would neither relieve the source from having to complete an AQRV impact analysis, nor automatically allow the reviewing autho ri ty to reject the FLM ’ s demons tr ation of adverse AQRV impacts ( citing 72 FR 54139) , and adds that th is an important cla ri fication given the separate Class I increment and AQRV impact tests of the PSD regulations.

The generally supportive industry associ ation commenter (0038) and one state/local agency commenter (0015) believe that SILs should be used as an appropriate de minimis

threshold when a n FLM has not identified a specific AQRV related to the pollutant under

evaluation . The state/local agency com menter (0015) believes that SILs also should be used as a

de minimis threshold when an FLM has not obtained ambient air monitoring to confirm that predicted concentrations from air dispersion models are representative of actual AQRV impacts

in a Class I ar ea. Th is commenter added that without this flexibility, applicants would be required to conduct complex and extensive Class I air dispersion modeling with no clear objective

, and regulatory agencies would have to review the modeling with limited informati on to determine if the emissions could cause an ― adverse ‖ impact or to determine if potentially

cost ly controls should be required.

Response:

We agree with the commenters who support the position on the relationship between SILs and AQRVs that EPA set o ut in the 2007 NPRM

. 72 FR at 54139 (September 21, 2007). We reiterate that this remains our position

With regard to the comments recommending the use of SILs for AQRVs, we believe that by following these commenters‟ recommendation, a source would be required to complete an air quality analysis for a Class I area when the source‟s emissions would exceed the Class I SIL

– even though the FLM has not identified a specific AQRV that may experience adverse effects. It is difficult to see what kind of ana lysis would be conducted in the absence of any known AQRV65

that could be adversely affected by a pollutant emitted by the proposed source. We believe that the need for a Class I analysis, other than the required analysis of the NAAQS and Class I

increments (for both of which the SILs were intended to be used), should be based solely on the potential for adverse effects on an AQRV that the FLM identifies as being sensitive to the pollutant under consideration. When the FLM does not identify an AQRV for whic h an adverse effect could occur, sources should not be required to perform a Class I analysis, other than the analysis of the NAAQS and Class I increments, regardless of the relation between the source

emissions and the Class I SIL

.



### 4.4 Comments on the Propose d Levels for SILs

4.4.1 General Comments on Proposed SIL Levels

Comment:

One industry commenter (0016) suggest s that EPA develop geographic area

- specific SILs (and increments and SMC) that take local conditions into account. The commenter pointed out

that PM 2.5 levels in PSD areas proximate to international borders may be elevated by sources outside the legal and practical control of the United States and state authorities. The commenter

also noted that PM 2.5 levels may be elevated by natural conditions, suc h as drought, fires, geologic formations (sandy or fine

- grained surface features) high winds, etc., leading to excessively dusty ambient conditions over which the local area has no control. The commenter

indicated that local area baselines must reflect th ese PM emissions, though they are not reflected in the local area’s emissions inventory. The commenter urged EPA not to penalize such PSD areas by imposing uniform national SILs (and increments and SMC) where the conditions of concern are not capable of c ontrol.

Response :

We do not believe it is necessary or appropriate to establish geographic area

- specific SILs to identify a significant impact. Regardless of the existing air quality and what sources of a pollutant may contribute to such levels, we bel ieve that it is reasonable to identify a source‟s “significant” impact consistently from one area to another. The SILs define a projected ambient impact that a stationary source of PM 2.5 would cause relative to the applicable PM 2.5 NAAQS or

increments. T

his value is not directly affected by the total amounts of PM 2.5 that may exist in an area or by what the source of such PM 2.5 concentration may be. We believe that the use of area

specific SILs is best left up to the discretion of the individual state/lo cal air pollution control agencies that are charged with managing the air quality in a particular area. Thus, i ndividual states may adopt significance levels that differ from the EPA

- defined levels as long as the level selected is at least as stringent as the EPA definition. Moreover, states are not required to

consider an y impact as being insignificant, and may alternatively choose to require proposed

sources with minimal impacts to complet e a comprehensive analysis under the PSD requirements.66

Comment:

One i ndustry commenter (0046) generally oppose s all the proposed SILs , contending that

a ll the proposed SILs are extremely low

. The commenter also note s that EPA has propos ed the

same concentrations for Class II and III SILs for all three options

. The commenter claim s that the proposed SILs imply a level of monitoring and modeling sophistication that is currently absent in our regulatory scheme and suggest s that EPA rethink the level of the proposed SILs and select concentrations less likely to be withi n the level of error inherent in current monitoring and modeling methods.

Response:

We disagree with th is commenter‟ s view that all the proposed SILs are too low. For all of the reasons that we have provided on the record of this rulemaking, the SILs m ust be set sufficiently low so as to be de minimis.

We also disagree that the SILs should be consistent with current monitoring capabilities for PM

2.5 . The SIL represents a screening tool that is used in comparison with modeled prediction

– not monito red concentrations

– of PM 2.5

. Ambient air quality m onitoring accuracy is not a relevant concern in predicting concentrations of a pollutant that a source will cause if its construction and operation are allowed to occur. While the values that we selecte d are lower than the values under Option 1, we believe that they represent values that are in line percentage

wise with the other pollutants in comparison to the respective NAAQS. We provide further discussion of our reasons for selecting the Option 3 val ues in section VI.B.2.a and VI.B.2.b of the preamble to the final rulemaking

.

Comment:

One industry association commenter (0014) argue s that the proposed SILs (and increments) should be twice the proposed levels. The commenter (0014) claim s that scient ific studies do not support the need for this low a level for protection of public health and welfare

, and that EPA is jeopardizing the goal of providing opportunities for economic growth, especially given that EPA has provided no guidance on how modeling will be done and what factors will be

used. The commenter contends that EPA has relied t oo much on epidemiological studies (which cannot establish causation) and not enough on laboratory

- based toxicological studies specifically designed to determine causa tion.

Response:

The commenter‟s inference that the SIL should be set at a level that provides protection of health and welfare is unfounded, as is the commenter‟s linking of the SIL and opportunities for economic growth. It is the express purpose of th e NAAQS to define levels of air quality consistent with the protection of health and welfare. The SILs, on the other hand, are intended as a screening tool to determine the level of air quality analysis required for any proposed new or modified source und er the PSD preconstruction review process. As explained elsewhere, EPA has discretion to allow the exemption of de minimis impacts from the burdens associated with67

completing a comprehensive, cumulative air quality analysis. Such de minimis impacts are n ot based on scientific findings related to the health and welfare effects of a particular pollutant.

The SIL is used largely as a screening tool to determine the level of air quality analysis that a proposed source or modification must undertake to satis fy the requirements for an air quality impact analysis. We do not believe that being used in this capacity is a factor in determining whether source will decide whether it will construct or modify its facility. The SIL‟s ability to affect opportunities f or economic growth may become a factor if the source , based on the use of the SIL, is found to contribute to a modeled violation of a NAAQS or increment. The SIL is thereby used to determine whether the source‟s contribution is significant enough to be

co nsidered to “cause or contribute to” such modeled violation. We believe we have set the levels of the SILs for PM 2.5 relative to the PM 2.5 NAAQS to where they are comparable to the SILs for other pollutants relative to their corresponding NAAQS.

Comment :

One industry association commenter (0029) submitted comments discussing all the proposed options for setting SILs without endorsing a ny option. The commenter believes that

propos ed Option 1 for Class II and III SILs is consistent with the Act, but con tends that the

Class I SILs proposed under Option 1 are without legal or practical support. (The comment er ’ s arguments opposing the Option 1 Class I SILs are summarized below in Section 4.2.2 of this document.)

The commenter agrees that EPA is authori zed under the Act to use approaches like those underlying Options 2 and 3. However, the commenter requests that if EPA chooses to adopt Option 2, which uses the 0.8 multiplier (based on the overall ratio of PM 2.5 emissions to PM 10 emissions), EPA make cle ar that this ratio should not be used for other regulatory purposes. Despite agreeing that an approach like that underlying Option 3 is acceptable under the Act, t he

commenter contends that EPA’s use the 0.3 ―stringency factor‖ based on the ratio of the P M 2.5 NAAQS to the PM 10 NAAQS is not appropriate for the same reasons discussed above in

Section 2.3.1 in relation to increments

.

Response:

For the final rule, we decided to finalize Option 3 for the PM 2.5 SILs for the reasons discussed further in the se ctions that follow. We agree with the commenter that the SILs promulgated in this rule are consistent with the Act

. With respect to the commenter‟s support of some of the other proposed SILs, we will not address those comments here, as those options were not selected for the final rule.

Regarding the use of the 0.8 multiplier for other regulatory purposes, see our response to this issue in Section 8.3 of this document. Regarding the comment on the “stringency factor”

derived based on the ratio of the P M 2.5 NAAQS to the PM 10 NAAQS

, see our response to the commenter‟s similar assertion related to increments in Section 2.3.1 of this document. The commenter did not provide specifics in this comment about SILs as he did in the comment on increments, but we believe that the same computational principles apply.68

Comment:

An environmental group commenter (0040) claims that the proposal illegally and arbitrarily ignores PM 2.5 precursors. The commenter points out that the proposed text of the rule

would allow a source to show compliance with a SIL by analyzing only the impact of direct

PM 2.5 emissions. T he commenter asserts that t his approach is illegal and irrational given that EPA itself has found that precursors can and do contribute significantly to ambien t PM 2.5 concentrations.

Response:

The commenter is correct that in the 2007 NPRM we proposed to add SILs for PM 2.5 to the PSD regulations at 40 CFR 51.166 and 52.21 by add ing a new paragraph to the regulations explaining that the requirements for a sou rce impact analysis for PM 2.5 would be considered to be satisfied, without further air quality modeling, if it were to be shown that the increase in

direct PM

2.5 emissions from the source or modification will cause air quality impacts less than the prescri bed SILs for PM 2.5 . The reasoning at the time was that state

- of

- the

- art modeling would not be available to adequately account for secondary PM 2.5 impacts resulting from emissions of precursors of PM 2.5 , e.g., SO 2 and NO

x . Nevertheless, the existing PSD r ules currently define potential precursors of PM 2.5 . Based on the proposed language, the required compliance demonstration for the PM 2.5 NAAQS and the PM 2.5 increments (when promulgated) would be limited by regulation to an analysis of direct PM 2.5 emissi ons, and would not include consideration of emissions of PM 2.5 precursors for comparing the modeled source impacts to the prescribed SILs for PM 2.5

.

The technical tools needed to complete a comprehensive analysis of all emissions that

contribute to ambie nt concentrations of PM 2.5 are only in the developmental stage; nevertheless, we believe that it would be inappropriate to restrict the regulatory language in such a way that future regulatory amendments would be required to enable the inclusion of precurs or impacts in

the PM

2.5 analysis as the necessary technical tools become available. When EPA develops the necessary techniques for estimating the impacts of precursor emissions on ambient PM 2.5 concentrations, we intend to consider those impacts in determ ining whether a source will have a significant impact using the SIL values in the final rule , which we could not do if the regulatory language precluded th at fro m being done . We acknowledge the concerns that have been expressed by some commenters about th e shortcomings of not considering the impacts of PM 2.5 precursors under the PM 2.5 air quality analyses. Accordingly, we believe that the new provision for applying the SILs for PM 2.5 to the required analyses for the NAAQS and increments should not be self

- limiting by specifying the use of only direct PM 2.5 emissions. Instead, the new provision contained in th e final rule provides that the test will be based on whether “the emissions increase ... would cause ... air quality impacts less than [the PM 2.5 SILs].” See new 40 CFR 51.166(k)(2) and 52.21(k)(2). We believe that it would be more effective to rely on interim policy and guidance as appropriate to help determine the best methods available to make the required assessment of source impacts on ambient PM 2.5 resulting from any emissions.69



### 4.4.2 Comments on Proposed Levels for Class I SILs

In this section, we present all the comments supporting and opposing the proposed options for Class I SILs and advocating other levels for the Class I SILs , and then provid e a single response to all the comments

.

Comments Supporting Option 1 Level for Class I SILs:

One state / local agency commenter (0015) and two tribal commenters (0041, 0049)
support SIL Option 1 for all areas, including Class I areas . The state / local ag ency commenter (0015) indicates that the use of a percentage of the NAAQS is consistent with Option 1 for

increments

. [ We note that the commenter is incorrect; the Option 1 approach for the C lass I increments relies on the use of 4 percent of the Class I increments

– not the NAAQS .] The tribal commenters believe that the advantages of Option 1 better suit the tribal and environmental perspectives.

In addition, o ne industry commenter (0016) offers conditional support for Option 1

, indicating that i f it i s established that EPA has sufficiently stated and, in fact, has legal authority for the proposed regulation of PM 2.5 in the general manners proposed, the commenter would support Option 1 for the establishment of SILs (and increments and SMCs).

One fed eral agency commenter (0044) that serves as the FLM for some Class I areas supports proposed Option 1 level for the annual SIL for Class I areas and either the Option 1 or Option 3 level for the 24

- hour SIL for Class I areas. The commenter reports on a mo del ing study

of four different coal

- fired power plant scenarios using the EPA approved long

- range transport CALPUFF model with the associated three dimensional CALMET metrological data for each particular scenario to assess the effectiveness of the differe nt proposed PM 2.5 Class I SILs. The commenter explains that the analysis consisted of four different analyses representing different geographic and climatic areas of the country where the National Park Service is seeing large

scale electrical energy devel opment from new coal

- fired power plants, summarized as follows:

1. A large 1,500 MW coal

- fired power plant in the desert southwest Four Corners area

. 2. A moderate sized 500 MW coal

- fired plant in central Wyoming

. 3. A medium 800 MW coal

- fired power plant located in the northern Great Lakes area

. 4. A medium 800 MW coal

- fired power plant located in the central Mid

- Atlantic States

area

.

Based on the analysis, t he commenter argue s that the 24

- hr proposed SILs of 0.07 μg/m 3
(Option 3) and 0.08 μg/m 3 (Option 1) are more appropriately protective of the proposed Class I

PM 2.5 increment and impacts to visibility than the Option 2 proposed level of 0.24 μg/m 3 (see

this commenter ’ s objections to the Option 2 level below).

F or consistency with the SO 2 , NO 2 , and PM 10 SILs t hat EPA proposed in 1996, the same commenter recommend s that EPA set the PM 2.5 SILs at 4 percent of the respective Class I

increments. The commenter note s that if EPA lowers the proposed Class I PM 2.5 24

- hour70

increment as the commenter recommend s (see Sec tion 2.2.2.2 on visibility)

, 4 percent of the lower level would be less than the values currently proposed by EPA.

Comments Opposing Option 1 Levels for Class I SILs:

Two industry commenter s (0020, 0026) and two industry association commenters ( 0023,

00 29) express opposition to Option 1 levels for Class I SILs.

One of the industry association commenters (0029) contends that establishing the Class I SILs by multiplying the proposed PM 2.5 increment by 4 percent is without legal or practical
support. T he commenter add s that if these SILs for Class I areas w ere codif ied, emissions from

even the most well

- controlled coal

- fired electric generating station, located as far away as

300 km from a Class I area, could well exceed the threshold levels , triggering an extensive, time

consuming

, and expensive cumulative air quality analyses of the projected PM 2.5 emission s from the proposed source and from sources located within a 300 km radius, possibly including sources located in multiple states

, which would be ev en more burdensome when applied to a new pollutant like PM 2.5 for which no historic data exist. The commenter stated that such an undertaking makes no sense when it is triggered by projected emissions impacts so trivial as to be barely measurable

, and whe n other PSD program elements serve to address concerns associated with the protec tion of AQRVs in Class I areas.

One of the industry commenter s (0020) similarly argue s that there is no legal or reasonable justification for promulgating a level based on t he historical use (1996 NSR reform proposal) of 4 percent of PM 2.5 increments in setting PSD applicability levels when it is not needed to ensure protection of Class I area s

.

The other industry commenter ( 0026 ) questions EPA’s divergence from the metho d used to derive the Class II and III SILs under Option 1, which was based on the SILs for PM 10

. The commenter argues that Option 1 produces Class I SILs that are very stringent and will likely require extensive and costly cumulative air quality impact an alyses even when predicted impacts

would be minimal.

Comments Supporting Option 2 Levels for Class I SILs:

One state/local agency commenter (0033) , three industry commenters (0026, 0027, 0043), and one industry association commenter (0039) support the O ption 2 levels for Class I SILs. The state/local agency commenter (0033) believe s it is appropriate to achieve some degree of consistency by using Option 2 for both SILs and the SMC. One of the i ndustry commenter s (0027) favors the Option 2 for Class I S ILs because they are sufficiently low to protect Class I

areas. Another of the industry commenter s (0043) believes that the Option 2 values established by converting the PM 10 SIL values to PM 2.5 seem to properly balance the protection of Class II

and Cla ss I areas.

The industry association commenter (0039) supports Option 2 for Class I, II, and III SILs

and expresse s concerns over the already extensive timeline required for new or modified sources

to obtain PSD permits. The commenter believes that i f E PA set s the SIL s unnecessarily low,71

many more projects than necessary would be required to conduct air quality i ncrement

a ssessment s, which would take at least an additional year to perform. The commenter urge s EPA to adopt SILs that will only require a f ull i ncrement a ssessment where the SIL would accurately predict an exceedance of a PM 2.5 increment for the project. The commenter agree s with EPA ’s state ment in the 2007 NPRM that Option 2 SILs would serve as an appropriate de

minimis SIL value and repres ent insignificant impact on ambient air quality (72 FR 54140)

. Additional detail regarding this commenter’s arguments, and our responses to them, are presented below in Section 4.4.3 of this document addressing the Class II and III SILs.

One industry co mmenter (0026) that is supportive of the Class I SILs proposed under Option 2 express ed concern regarding the use of the uniform 0.8 PM 2.5 /PM 10 ratio EPA has applied under this approach. The commenter states that if EPA uses this approach, it should

clari fy that the 0.8 ratio should not be used broadly for other regulatory purposes because the

conversion ratio of PM 10 to PM 2.5 will differ for individual sources and from one area to another. (See our response to this issue in Section 8.3 of this document.)

Comments Opposing Option 2 Levels for Class I SILs:

One federal agency commenter (0044) that serves as the FLM for some Class I areas

oppose s Option 2 for Class I areas. The commenter (0044) reports on the results of a modeling analysis conducted for four different geographic and climatic areas of the country where the

N ational P ark S ervice is seeing large

- scale electrical energy development from new coal

- fired

power plants (see description above). B ased on the results, the commenter state s that the

p roposed Option 2 24

- hr PM 2.5 SIL of 0.24 μg/m 3 would not be protective of the proposed

Class I PM 2.5 incremen t since it is approximately one

- eighth of the proposed increment and is not

exceeded in some scenarios as close as 20 km from a new coal

- fired powe r plant. The commenter (0044) not e s that the proposed 0.24 μg/m 3 SIL would preclude a cumulative Class I increment analysis of the new source with other existing PSD source(s) located farther than

20 km from the new source, but still close enough to a Cla ss I area to affect its ambient PM 2 .5 concentration and visibility impacts.

One state/local agency commenter (0015) , o ne industry commenter (0020) , and o ne i ndustry association commenter (0036) oppose Option 2 for SILs because it uses the 0.8 multipli er derived from the ratio of PM 2.5 to PM 10 emissions for point sources in the 2001 extrapolation of the final 1999 National Emissions Inventory ( NEI ) . The state/local agency

commenter (0015) indicates that EPA has not demonstrated that this ratio reasonab ly represents

PM 2.5 emissions from all source types , and explain s that that an increment analysis should include emissions from minor point sources, area sources, and mobile sources, The commenter

believes that the proposal d id not adequately explain how a ratio derived from utilities and industrial point source emissions would be representative or appropriate.

Th e i ndustry association commenter (0036) question s the use of the 1999 NEI for PM 2.5 that is based on the ratio of direct PM 2.5 to direct PM 10 emissions. The commenter (0036)

believes that the inventory is outdated and incomplete , noting that the state of knowledge regarding both direct and indirect PM 2.5 emissions has advanced significantly since 1999. The72

commenter suggest s that an u p dated in ventory that incorporates both direct and indirect PM 2.5 emissions should be used for this purpose

.

Another state/local agency commenter (0019) disagrees with EPA ’s state ment in the 2007 NPRM that the SIL Option 2 app roach is very similar to Option 2A fo r the increments

. The commenter points out that in increment Option 2A, EPA use d the emission ratio approach only for the annual PM 2.5 increment and use d this emission ratio in concert with the ratio of the corresponding PM 2.5 - to

- PM 10 NAAQS to derive the increments. The commenter indicates that if

EPA had used both of these factors, Option 2 would have resulted in Class I SILs of 0.05 and 0.07 μg/m 3 for the annual and 24

- hour cases, respectively, which are very close to the Option 1

Class I SILs.

Comment s Supporting Option 3 Levels for Class I SILs :

Two state/local agency commenter s (0019

, 00 25) and two state/local agency association

commenter s (0018 , 0021 ) support Option 3 for Class I SILs (or for all Classes)

. One of the state/local agency commente r s (0019) states that the Option 3 SILs are the SILs which can properly be interpreted to be truly de minimis

. The other state/local agency commenter (0025)

believe s that Option 3 is the most health

- protective method by which to derive SILs.

One e nviro nmental group (0040) state s that all the proposed options for SILs are irrational and illegal (see Sections 4.1 and 4.2 above) , but Option 3 SILs are the least objectionable since they are the lowest, and therefore allow the least circumvention of the Act.

One federal agency commenter (0044) that serves as the FLM for some Class I areas supports proposed Option 1 level for the annual SIL for Class I areas and either the Option 1 or Option 3 level for the 24

- hour SIL for Class I areas.

Comments Opposing Option 3 Levels for Class I SILs:

One industry commenter (0043) and two industry association commenter s (0037 , 0038 ) believe that the Option 3 Class I SILs are unreasonably low. The industry commenter (0043)

argue s that the values appear to be unrealis tically low and, if selected, would point to the need for EPA to conduct an economic impact analysis.

One industry association commenter (0037) states that EPA should not simply apply NAAQS

- based ratios because these do not translate back to the emissio ns point level when comparing PM 10 and PM 2.5 . The commenter believes that this is an invalid method of proceeding because EPA has not shown that there is a correlation between the NAAQS and

direct PM 2.5 since there is no account ing for precursors and EPA does not have a quantifiable sense of the portion of PM 2.5 that is condensable for various industries.

The commenter question s whether EPA ’ s proposal of using the NAAQS ratios to set the

SILs (and increments) will accommodate moderate, well

- controlled development , as intended by Congress when it set the original increments, or if this approach will inhibit additional growth. The commenter suggest s that EPA should provide a demonstration assuring that this proposal73

will not conflict with the prior regu latory history and intent of Congress and will allow for sufficient growth consistent with air quality needs. The commenter gave citations related to the congressional intent regarding increments ( 39 FR 42510

, Dec ember 5, 1974 ; 45 FR 52676

, (Aug ust 7, 198 0).

Comments Suggesting Other Levels for Class I SILs:

Two industry commenter s ( 0020, 0026) suggest that EPA revise the Option 1 SILs for

Class I areas by us ing the PM 10 Class I increments (4.0 μg/m 3 annual and 8.0 μg/m 3 24

- hours) as

the starting point , which would result in Class I SILS of 0 .16 μg/m 3 ( annual ) and 0 .32 μg/m 3

( 24

- hour ). One industry association commenter ( 0023) also recommends that SILs for Class I

areas should be raised to 0 .16 μg/m 3 (annual) and 0 .32 μg/m 3 (24

- hour) without specifying the methodology for deriving these levels. The commenters believe that Class I SILs at these levels

would meet EPA goals of prevent ing significant deterioration while ensuring economic growth.

One industry association commenter (0029) offer s the follow ing alternatives for determining Class I SILs under Option 1:

 Use the currently accepted Class I SILs for PM 10 , 0.2 μg/m 3 (annual) and 0.3 μg/m 3

(24

- hour). These values were interpreted by EPA as complying with the goals and purposes of the PSD program wh en they were proposed in 1996 (61 FR 38338, July 23, 1996). This approach also would be consistent with how the Class II and III SILs were determined under Option 1.

 Start with the PM 10 increments that already exist, 4.0 μg/m 3 (annual) and 8.0 μg/m 3 (24

- h our). These values could be used for SILs, or multiplied by a suitable multiplier. If a

4

- percent multiplier were used, the Class I SILs would be 0.16 μg/m 3 (annual) and

0.32 μg/m 3 (24

- hour). This level would accomplish the goals and purposes of the PSD program and would reasonably limit the scope of the complex

– and environmentally

unwarranted

– air quality analyses that would be required under the proposed Option 1

level

 If starting with the proposed PM 2.5 increments, use a reasonable multiplier. J us t because 4 percent may have been a reasonable multiplier to use in establishing a significant emission rate threshold does not mean that the multiplier should be used for a completely different regulatory purpose.

Response:

We chose the Class I SILs ba sed on Option 3 because we believe that this option yields the most appropriate combination of SILs for all area classifications. While the Class I SILs under Option 3 represent levels that are somewhat different than 4 percent of the respective

PM 2.5 inc rements for Class I areas (6 percent for the annual SIL and 3.5 percent for the 24

- hour SIL) , they are sufficiently close (as derived from a ratio of the PM 2.5 NAAQS to the PM 10 NAAQS) so as to provide reasonable thresholds for defining de minimis for purp oses of conducting a Class I increment analysis. We had proposed the use of 4 percent of the existing Class I increments to develop SILs for pollutants in a 1996 NPR M for a PSD rulemaking; however, that particular component of the proposal was never final ized. See 61 FR 3825074

beginning at page 38291. We will further discuss our rationale for selecting the suite of SILs under Option 3 in the discussion which follows for the Class II and III SILs.

With regard to the comment alleg ing trivial impacts from sources located up to 300 km from any Class I areas, we note that it is not supported by any technical documentation provided by the commenter. However, while we have not substantiated the reported results

, a modeling analysis carried out and reported by a federal agency commenter (0044) did predict that certain

new coal

- fired power plants locating within 125 km from a Class I area could trigger the Class I

24

- hour SIL for PM 2.5 as defined under either Option 1 or 3. That commenter further noted that

unde r some scenarios a moderate to large coal

- fired power plant could trigger those SILs values at distances of 300 km or greater. Distance is an important factor in determining the impact that a source‟s emissions may have on a Class I area, but many other f actors play an important role, including stack height and other release parameters, topographic influences along the plume trajectory, and prevailing wind and other meteorological patterns across the modeling domain. Therefore, a source located a relative ly great distance away from a particular Class I area should not simply be ignored because of its distance.

Regarding the comment that the Option 3 Class I SILs are unrealistically low and, if selected, would point to the need for EPA to conduct an econ omic impact analysis, we wish to point out that EPA is required to complete and submit for Office of Management and Budget approval an Information Collection Request (ICR), which accounts for the burdens placed on state and local agencies and the permit ap plicants to meet the PSD program requirements. The ICR includes an estimate of the burdens associated with completing a pollutant

- specific air quality analysis for each permit applicant. In estimating such burden, we do not take into

account the various screening tools, including SILs. Thus, whether or not a source is actually exempted from having to complete a comprehensive cumulative impact analysis for a particular pollutant is not considered. Hence, the use of a SIL, regardless of its actual level, only serves to lower the burden on an applicant that is estimated as part of the ICR.



### 4.4.3 Comments on Proposed Levels for Class II and III SILs

Comments Supporting Option 1 Levels for Class II and III SILs

Comment:

One industry commenter (0026) supports Option I for Class II and III SILs , while another

i ndustry commenter (0027) supports Option I for Class II SILs. Two tribal commenters (0041, 0049) support Option 1 for the SILs for all areas. The se commenters believe that the advantages of this option better suit the tribal and environmental perspectives.

One industry commenter (0016) provides conditional support for the Option I SILs (and increments) . The commenter indicates that other issues raised by the commenter (related to legal authority, prec ursors, lack of accurate stack tests, and the superiority of regional SILs (and increments) over national levels) must be addressed for this approach to have value.75

One industry association commenter (00 29 ) indicates that the approach used in Option 1

fo r Class II and III SILs is consistent with the requirements of the Act, although the commenter does not explicitly express support for Option 1.

Response:

While these commenters support Option 1 for selecting the PM 2.5 SILs levels, they do not provide a ny substantive basis for their support. As we indicate in our responses to the following commenters, we believe that the SILs defined under Option 1 for Class II and III areas are too large to reasonably represent de minimis levels for PM 2.5 impacts.

Com ment:

One state / local agency commenter ( 0015 ) agree s with EPA’s SIL Option 1. The commenter (0015) states that the use of a percentage of the NAAQS is consistent with i ncrement Option 1.

Response:

The commenter is incorrect in stating that the SILs under Option 1 are based on a percentage of the NAAQS. The Class I SILs were based on a percentage (4 percent ) of the respective Class I increments, while the Class II and III SILs under Option 1 are the same SILs values used for other criteria pollutan ts, including PM 10 , currently contained in 40 CFR 51.165(b).

Comment:

One industry association commenter (0038) believes that the daily and annual SILs proposed under Option 1 would be sufficiently stringent and fully consistent with the de minimis ju stification for SILs. The commenter add s that when conducting an air quality impact analysis to determine compliance with the SIL, most applicants assume all coarse PM 10 to be PM 2.5 . The

commenter claim s that this is a conservative assumption, which over estimates the amount of fine particles being emitted and renders the effective SIL thresholds for PM 2.5 lower than those written into the regulations. The commenter believes that meeting a modeled 5.0 μg/m 3 limit in

the 24

- hour air quality analysis would likely equate to an actual impact of 4.0 μg/m 3 or less.

The commenter contends that this conservative skewing of the PM 2.5 SIL analysis is compounded in the case of the daily SIL because the 24

- hour SIL analysis typically uses the worst case meteorolog ical data, assumes the highest emitting fuel for the source (even if that fuel is used only as back up fuel), and assumes maximum operating conditions. The commenter add s that the daily SIL modeling includes a conservative emission rate (us ually based on the
manufacturer’ s guarantee) and, where applicable, an additional conservative estimate of PM contributions after selective catalytic reduction and oxidation catalyst control technologies. The
commenter encourage s EPA to set the 24

- hour SIL to 5.0 μg/m 3 because of these built

- in

conservatisms.76

The same commenter further asserts that setting the 24

- hour PM 2.5 SIL at the 5.0 μg/m 3

l evel would match the PM 10 daily SIL , while establishing a daily PM 2.5 SIL that differs from the daily PM 1 0 SIL would introduc e unnecessary regulatory burden for even the cleanest fossil

- fuel burning electric generating units. The commenter explain s that new, low emitting units are constrained by Good Engineer ing Practice stack height requirements and do not have a long

range, downwind impact ; thus, such units generally do not have to undertake the cumulative impact analysis for predicted PM 10 impact. The commenter notes that these units could be forced to conduct that analysis if EPA were to set the PM 2.5 daily SIL lower than the PM 10 daily

SIL.

Finally, t he commenter concludes that this new burden would yield little environmental benefit because unless the other sources in the cumulative impact analysis align with the wind direction and are in the immediate vicinity of the source project, the in

- depth, complex analysis will ultimately demonstrate that the new source will have virtually no impact. The commenter

claim s that having to perform a 24

- hour cumulative analysis would be a needless exercise, and broad, national appli cation of a PM 2.5 SIL that differs from the PM 1 0 daily SIL could unnecessarily delay or even derail the in stallation of even the cleanest

- burning electric generating units ( EGUs )

.

Response:

We are particularly concerned about the c lass II and III SILs values being too high to use for PM

2.5 purposes. In our final determination for selecting the SILs, we concluded that the option 1 SILs for class II and III areas represented too large a portion of the PM 2.5 NAAQS to be considered de minimis. Most of the commenters supporting this option failed to provide substantive reasons for selecting those particular values.

We disagree with the comment suggestin g that the development of the SILs for PM 2.5 , or any other pollutant, should be influenced by the poss ibility that some sources currently may use “conservative techniques” (such as assuming that all coarse PM is PM 2.5 ) for estimating a source‟s emissions rate. Conservative techniques, such as the ones described by the commenter, may be needed on an interi m basis until technical issues associated with the calculation of PM 2.5 emissions for a particular source are resolved , and can always be used as a screening methodology when appropriate . However, over time more accurate techniques will be available

and s hould be relied upon whenever an alternative approach yields results that overestimate the source‟s impact.

The commenter recommends that EPA set the PM 2.5 SIL at same level as the PM 10 SIL (i.e., based on Option 1), because of the various conservative assumptions factored into the modeling analysis . We recognize the conservative nature of the screening analysis and believe that a screening technique by its very nature should have a conservative tendency. W e established the SIL for PM 2.5 on the basis of what we believe to be a de minimis source impact on air quality relative to the 24

- hour PM 2.5 NAAQS and increments. Moreover , the 24

- hour PM 2.5 NAAQS is considerably lower than the 24

- hour PM 10 NAAQS

, but t he commenter does not account for th is fact. Thus, the commenter‟s recommendation that the two 24

- hour SILs should be the same does not result in an equitable representation of the relative impact that each SIL77

has on the corresponding NAAQS. That is, while the 24

- hour PM 10 SIL represents about 3

pe rcent of the 24

- hour PM 10 NAAQS, the 24

- hour PM 2.5 SIL would represent about 14 percent of

the 24

- hour PM

2.5 NAAQS. Moreover, that value would represent about 55 percent of the

24

- hour PM

2.5 increment ( C lass II) contained in this final rule. We do not be lieve that such a result would provide an acceptable showing of de minimis consistent with other SIL values for criteria pollutants.

Comments Opposing Option 1 Levels for Class I I and III SILs:

One state/local agency commenter (0051) states that Optio n 1 ( and Option 2 ) result in unacceptably high SILs values

, allow ing impact levels as much as 50 percent of the proposed

increments for Class II areas. The commenter note s that her state ’s air monitoring network shows that many areas are within 1 to 3 μg/ m 3 of the annual PM 2.5 NAAQS of 15 μg/m 3 and within 3 to 5 μg/m3 of the 24

- hour PM 2.5 NAAQS of 35 μg/m 3 , while Option 1 would allow for impacts of up to 1 μg/m 3 and 5 μg/m 3 on an annual and 24

- hour basis, respectively. The commenter (0051) asserts that to allow sources to construct or modify with the potential to have air quality impacts that would threaten the NAAQS

, yet not require them to perform an extensive air quality analysis

, appears to undermine the state ’ s effort and ability to maintain attainmen t
status for PM 2.5 through regulation of stationary sources.

A nother state / l ocal agency commenter (0019) indicates that EPA provides no rationale for continuing the use of the current PM 10 SILs under Option 1 , except their historical use. In addition, t he commenter points out that under Option 1 EPA proposed to use 4 percent of the

PM 2.5 increments for the Class I SILs , but d id not propose to use this approach to define the

Class II and III SILs. The commenter notes that had EPA done so, the resultant P M 2.5 Class II SILs would be 0.6 and 1.4 μg/m 3 for the annual and 24

- hour averages, respectively.

Response:

As explained above, we agree that the SILs proposed under Option 1 for the Class II and

III areas represent ambient concentrations of PM 2.5 that a re unreasonably high for defining de minimis impact levels relative to the existing PM 2.5 NAAQS and for the increments selected in the final rule.

Comments Supporting Option 2 Levels for Class I I and III SILs:

Three commenters ( 00 33 , 0039, 0043) suppo rt Option 2 for the Class II and III SILs (and the Class I SILs). One supportive state/local agency commenter (0033) believes it is appropriate to achieve some degree of consistency by using Option 2 for both SILs and the SMC. One supportive industry com menter (0043) believe s that the Option 2 values established by converting the PM 10 increment values to PM 2.5 seems to properly balance the protection of

Class II and Class I areas.

One supportive industry association commenter (0039) points out that t he SIL is a screening tool that estimates whether a source may cause or contribute to a violation of a PSD

increment or the NAAQS. The commenter indicates that t ypically, if the ambient impact from78

the proposed source would exceed the SIL, states and EPA re quire the project applicant to

conduct 1 year’s worth of ambient air quality modeling to assess such future impacts from the project. The commenter expresse s concerns over the already extensive timeline required for new or modified source projects to obta in PSD permits. The commenter believes that i f EPA set s the

SIL s unnecessarily low, many more projects than necessary would be required to conduct air quality i ncrement a ssessment s, which would take at least an additional year to perform. Accordingly, t h e commenter urge s EPA to adopt SILs that will only require a full i ncrement

a ssessment where the SIL would accurately predict an exceedance of a PM 2.5 increment for the project.

The same commenter believes that the simplest, most straightforward approa ch would be

for EPA to build on the SILs proposed for PM 10 in the 1996 NSR Reform proposal and by further adapting those SILs by the emissions ratio of PM 2.5 to PM 10

. The commenter agree s with

EPA ’s state ment in the 2007 NPRM that Option 2 SILs would serv e as an appropriate de minimis SIL value and represent insignificant impact on ambient air quality (72 FR 54140)

.

Response:

We find no relevance in being consistent in the methods used for selecting the screening

tools

– SILs and SMC

– for PM 2.5 as re commended by one of the comment ers

. The SILs represent ambient impacts, determined by modeling, that are counted against the respective NAAQS and increments. The SMC, as discussed later in this document, represents an ambient

concentration that can be re liably measured by an ambient monitoring device. Thus, “significant” is considered in a completely different context for those two types of screening

tools.

We disagree with the comments that support Option 2 as the most appropriate option for

the Class II and III SILs. In particular, t he comment suggesting that a lower SIL level will adversely affect the time required to obtain a permit is somewhat confusing. The commenter is correct in saying that the SILs are used to determine whether a proposed sou rce would cause or contribute to a violation of either a NAAQS or PSD increment; however, the remainder of the comment then focuses only on impacts associated with the PSD increments. It is important to understand that applicants that model ambient concen trations above the SIL must complete a comprehensive cumulative air quality analysis for both the NAAQS and the increments, where applicable. The commenter then indicates that the applicant must submit 1 year‟s worth of

ambient air quality modeling to ass ess such future impacts from the project. Typically, applicants must submit a modeling analysis including modeled impacts over a 5

- year period based on 5 years of National Weather Service meteorological data. The commenter may be confusing th is with the fact that 1 year of ambient air quality monitoring data may need to be collected as part of the analysis. The monitoring data is used primarily for the NAAQS analysis

– not the increment analysis

. The analysis for increment consumption tends to be based only on modeling projections.

The same comment er‟s recommend ation that EPA adopt SILs (based on Option 2) that will only require a full i ncrement a ssessment where the SIL would accurately predict an exceedance of a PM 2.5 increment for the project is al so confusing

. For one thing, the commenter79

only addresses the use of th e SIL for purposes of analyzing the PM 2.5 increments, and not the NAAQS. Secondly, it is not clear what is meant by “the SIL would accurately predict an exceedance of a PM 2.5 incremen t for the project .” We explained in the proposal that the SIL would be compared against the ambient concentration that would result from a proposed
source‟s emissions increase to determine whether that ambient impact was “significant.” As such, the SIL d oes not predict violations of increments, unless the source‟s estimated ambient impact is in itself greater than the applicable incremen t

. Nor is it clear why a predicted increment violation should be the trigger for a comprehensive, cumulative air qualit y impact analysis. In general, t he permitting authority should be aware of, and the public should be given an opportunity to comment on, the amount of increment that is available in an area because this may determine the amount of subsequent development t hat can occur in the area

. The PSD regulations provide that the public be apprised of the amount of increment being consumed as part of the public notification process for each PSD permit.

Finally, we do not believe the comment recommend ing that the S ILs be based on adapting the PM 10 SILs using a ratio of PM 2.5 to PM

10 emissions adequately account s for the levels of the PM

2.5 NAAQS upon which de minimis impact is being defined. In addition, as pointed out by various commenters , that ratio does not acc ount for precursor impacts on

ambient PM

2.5 concentrations, which are included in the provision containing the PM 2.5 SILs in the final rule. Thus, we believe that scaling the existing PM 10 SILs using a PM 2.5 - to

- PM

10 NAAQS ratio represents a more reasonabl e approach for defining the Class II and III SILs for

PM 2.5

.

Comments Opposing Option 2 Levels for Class I I and III SILs:

One state/local agency commenter (0051) believe s that Option 2 (and Option 1) result in unacceptably high SILs values

, allow ing im pact levels as much as 50 percent of the proposed

increments for Class II areas. As discussed above in quantitative terms for Class I, the
commenter’s state is quite close to the PM 2.5 NAAQS in many area, and adoption of the Option 2

SILs would allow sour ces to construct or modify with the potential to have air quality impacts that would threaten the NAAQS

, yet not require them to perform an extensive air quality analysis

. The commenter believes that this appears to undermine the state ’ s effort and abilit y to
maintain attainment status for PM 2.5 through regulation of stationary sources.

One state/local agency commenter (0015) , o ne industry commenter (0020) , and o ne i ndustry association commenter (0036) oppose Option 2 for SILs because it uses the 0.8

mul tiplier derived from the ratio of PM 2.5 to PM 10 emissions for point sources in the 2001 extrapolation of the final 1999 NEI. The state/local agency commenter (0015) indicates that EPA has not demonstrated that this ratio reasonably represents PM 2.5 emissi ons from all source
types , and explain s that that an increment analysis should include emissions from minor point sources, area sources, and mobile sources

. The commenter believes that the proposal d id not adequately explain how a ratio derived from utili ties and industrial point source emissions would be representative or appropriate.

Th e i ndustry association commenter (0036) question s the use of the 1999 NEI for PM 2.5 that is based on the ratio of direct PM 2.5 to direct PM 10 emissions. The commenter ( 0036)80

believes that the inventory is outdated and incomplete , noting that the state of knowledge regarding both direct and indirect PM 2.5 emissions has advanced significantly since 1999. The
commenter suggest s that an u p dated inventory that incorporates b oth direct and indirect PM 2.5 emissions should be used for this purpose

.

Another state/local agency commenter (0019) disagrees with EPA ’s state ment in the 2007 NPRM that the SIL Option 2 app roach is very similar to Option 2A for the increments

. The comm enter points out that in increment Option 2A, EPA use d the emission ratio approach only for the annual PM 2.5 increment and use d this emission ratio in concert with the ratio of the corresponding PM 2.5 - to

- PM 10 NAAQS to derive the increments. The commenter indicates that if

EPA had used both of these factors, the SILs for Option 2 would have resulted in Class II annual

and 24

- hour SILs of 0.24 and 1.4 μg/m 3 , respectively, which are much lower than the values proposed for Option 1 and very similar to those o f Option 3.

Response:

We agree with these commenters ‟ concern about the Option 1 and 2 SILs for C lass I and II areas being too high. We acknowledge as well that the use of the 0.8 ratio for PM 2.5 - to

- PM

10 emissions does not adequately represent the impa cts on ambient PM 2.5 concentrations caused by

PM 2.5 precursor emissions. W e also concluded that basing the SILs levels on an emissions ratio does not adequately consider the stringency of the PM 2.5 NAAQS in comparison to the PM 10 NAAQS. Since the SIL is intended to be a measure of the impact of source‟s emissions relative to the NAAQS (and increments), we believe the level of the NAAQS must be an essential consideration for formulating the SIL level.

Comments Supporting Option 3 Levels for Class I I and III SILs:

Two state/local agency commenters (0019, 0025) and two state/local agency association

commenters (0018 , 0021 ) support Option 3 SILs for Class II and III areas (or all areas)

.

One of the supportive state/local agency commenter s (0019) argue s t hat the Option 3

SILs can properly be interpreted to be truly de minimis and not es that the Class II SILs established under Option 3 are at 2 and 3.4 percent of the corresponding PM 2.5 NAAQS, which is

well in line with the 4 percent criterion used previous ly by EPA and the s tates to establish other

de minimis values. The commenter add s that these percentages are in line with Class II SILs for all other pollutant s (PM 10 , SO 2 , and NO 2 ) established by EPA and used by the s tates, which range

from 1 percent (an nual NO 2 ) to 3.3 percent (24

- hour PM 10 ) of the corresponding NAAQS. The

commenter also note s that O ptions 1 and 2 would establish SILs at about 25 and 50 percent of

the proposed PM 2.5 Class II increments for the annual and 24

- hour cases, respectively. Th e

commenter asserts that these can hardly be defined as de minimis values.

The other supportive state/local agency commenter (0025) believe s that Option 3 is the

most health

- protective method by which to derive SILs.81

One e nvironmental group (0040) st ates that all the proposed options are irrational and illegal (see Sections 4.1 and 4.2 above) , but Option 3 SILs are the least objectionable since they are the lowest, and therefore allow the least circumvention of the Act.

Response:

We agree with thes e commenters who support O ption 3

, without necessarily agreeing

with all the statements that the commenters make in conjunction with their support for that option

. First, w e d id not select the SILs under Option 3 under the premise that such SILs are

more protect ive of health. The NAAQS are established to protect against adverse health effects and are defined to provide a margin of safety. The SILs are a screening tool to determine, based
on a source‟s ambien t impact relative to the NAAQS, the extent to w hich a source must complete an air quality analysis to satisfactorily demonstrate compliance with the NAAQS and increments

. T he use of the SIL should not enable exceedances of the NAAQS to go unaddressed. T o the

extent that a particular SIL value enables a proposed source that completes a comprehensive, cumulative air quality impact analysis that shows violations of the NAAQS to be constructed

without itself being considered to cause or contribute to such modeled violation, the state must

still substantia te and address , as appropriate, any potential violation and ultimately demonstrate attainment with the NAAQS as part of the applicable implementation plan

.

Secondly, we clearly do not agree with the comment that the SILs are “irrational and illegal.” We address the legality of the SILs in section 4.2 of this document.

Comments Opposing Option 3 Levels for Class II and III SILs

Comment:

One industry commenter (0043) argues that the Option 3 values appear to be unrealistically low and, if selected, wou ld point to the need for EPA to conduct an economic impact analysis.

As summarized above in relation to Class I increments, o ne industry association commenter (0037) states that EPA should not simply apply NAAQS

- based ratios because these

do not transla te back to the emissions point level when comparing PM 10 and PM 2.5 . The

commenter believes that this is an invalid method of proceeding because EPA has not shown that there is a correlation between the NAAQS and direct PM 2.5 since there is no account ing for precursors and EPA does not have a quantifiable sense of the portion of PM 2.5 that is condensable

for various industries. The commenter express es concern that if EPA were to proceed with a NAAQS ratio approach, it would result in very low PM 2.5 increm ent s, and this would not take into account the expected condensable fraction.

The same commenter question s whether EPA ’ s proposal of using the NAAQS ratios to

set the SILs (and increments) will accommodate moderate, well

- controlled development , as intend ed by Congress when it set the original increments, or if this approach will inhibit additional growth. The commenter suggest s that EPA should provide a demonstration assuring that this proposal will not conflict with the prior regulatory history and inte nt of Congress and82

will allow for sufficient growth consistent with air quality needs. The commenter gave citations related to the congressional intent regarding increments ( 39 FR 42510

, Dec ember 5, 1974 ; 45 FR

52676

, (Aug ust 7, 1980).

Response:

See ou r response concerning the alleged need for an economic impact analysis in

S ection 4.4.2 of this document

.

By using the NAAQS ratio to set the levels of the SILs , we believe we are establishing comparable SILs for both PM 10 and PM

2.5 . That is, the SILs r epresent similar impacts relative to the NAAQS with which they are associated. Because the NAAQS consider all ambient concentrations of PM 2.5 , they include ambient concentrations resulting from both direct PM 2.5 (which includes the condensable fraction) a nd the secondary (precursor) component. Similarly,

a s set forth in the final rule, the PM 2.5 SILs values represent ambient concentrations of PM 2.5 that include the effects of both direct PM 2.5 emissions and indirect (PM 2.5 precursor) emissions.

We dis agree with these two commenters‟ conclusion that the SILs levels have an adverse effect on economic development, as the SILs are generally not directly indicative of economic growth. The SILs are a screening tool for determining whether individual PSD app licants must complete a comprehensive cumulative analysis of source impacts to satisfy the air quality impact analysis requirement. As such, the SILs do not prohibit source construction but merely establish the level of analysis required to satisfy the pr econstruction requirements associated with the permit review process. Even when the SIL is used to determine that a proposed source‟s emissions would cause or contribute to a modeled violation of a NAAQS or increment, the source has opportunities to mitig ate its impact so as not to have its permit denied.

Comment:

One industry association commenter (0038) believes that the Option 3 SILs would be unreasonably low

, especially in the case of the daily SIL a s shown by the burden such a

threshold could have on EGUs burning clean fossil fuels (e.g., natural gas and ultra

- low sulfur distillate). The commenter claim s that based on preliminary, internal modeling and analysis, the 1.2 μg/m 3 daily SIL proposed under Option 3 would exacerbate the problem of modeli ng demonstra tions in urban areas when the source must demonstrate impacts below the PM 2.5 SILs for both ground level and elevated receptors. The commenter explain s that rules for modeling

demonstrations for stable nonatt a inment pollutants (e.g., PM 1 0 and presumably PM 2.5 ) require that a net benefits analysis be performed at all ambient receptors, and because elevated receptors generally experience higher concentrations since these locations are closer to the centerline of the plume, the net benefit is mor e difficult to demonstrate at elevated receptors due to the higher impacts predicted at these receptors

.

Response:

The commenter seems to recommend that we develop different SILs for use at different receptor elevations, or at least consider a higher SI L that accounts for potentially higher83

ambient air impacts at elevated receptors. We do not believe that it is necessary or appropriate to make such a distinction. The ceiling imposed by any NAAQS makes no distinction based on receptor elevation and the SILs are intended to define a threshold for significant impacts on the NAAQS (as well as the increments). We do not find a compelling argument here to lead us to consider a SIL that accounts for receptor elevation.

Comment:

One industry commenter (00 20) express es concern over the use of 0 .8 PM 2.5 /PM 10 emissions ratio in SIL Options 2 and 3 because the ratio is not technically accurate

. Similarly,

o ne state/local agency commenter (0015) sta te s that SIL O ptions 2 and 3 used a ratio of PM 2.5 to

PM 10 emi ssions for point sources in the 2001 extrapolation of the final 1999 NEI.

Response:

The se commenter

s stated that SIL Options 2 and 3 use the PM 2.5 /PM 10 emissions ratio

, but this is not correct with regard to the approach used for Option 3.



### 4.5 Other Comment

s on SILs

4.5.1 Comments on SILs for Other Pollutants

T wo state / l ocal agency commenters (0019, 0022), one state / l ocal agency association commenter (0018) , and one federal agency commenter (0044) request that EPA finalize SILs for all pollutants (including PM 2. 5 ). The state / l ocal agency association commenter (0018) note s that SILs have been established as a PSD program screening tool to determine when cumulative reviews are necessary , but permitting authorities have also widely used SILs to determine the signif icance of the impact from a source in an attainment area on its surroundings, both within

and outside nonattainment areas. One of the state/local agency commenter s (0022) encourage s EPA to codify the Class I SIL s for NO

x , SO 2 , and PM 10 proposed in 1996 be cause permitting agencies rely on the 1996 proposed levels as well as the promulgated Class II SILs in PSD permitting actions.

Th e f ederal agency (0044) recommend s that EPA promulgate the 1996 proposed SILs for pollutants other than PM 2.5 at this time fo r the reasons that EPA state d in the preamble of the proposed PM 2.5 increment ( citing 72 FR 54138

- 54139). The commenter explains that although the 1996 SILs are only proposed, those levels are commonly used by state s, permit applic an ts,
and FLMs to determ ine the need for a cumulative increment analysis. The commenter note s that promulgating PM 2.5 SILs provides EPA a great opportunity to close the regulatory loop by promulgating SILs for the other pollutants as well. The commenter support s the use of SlLs

because otherwise, a cumulative increment analysis would be required of every source, regardless of impact.

The other state /local a gency commenter (0019) also suggests that the current action offers the opportunity for EPA to incorporate the Class I and Class II SILs for other pollutants in to the PSD regulations. The commenter note s that many states have been using the Class I SILs in the84

1996 NSR Reform proposal since that time. The commenter add s that the SILs for sources in

Class II attainment areas which are used to judge the contribution of these sources to nearby nonattainment areas pursuant to 40 CFR 51.165(b) have also traditionally been used by EPA and

s tates to determine the significance of the impact from a source in an attainment area on its surroundings, not just for impacts on nearby nonattainment areas. The commenter points out that

s tates and their organizations (e.g.

, NESCAUM and Western States Air Resources Council ( WESTAR ) ) have previously asked EPA to finalize these SILs in the NSR p rograms to facilitate regulatory applications.

The same commenter recommends that EPA extend the applicability of the SILs in

40 CFR 51.165(b)(2), which currently apply only for sources in attainment areas that impact nonattainment areas, to sources in nonattainment areas as well. The commenter note s that these SILs have traditionally been used by states not only for the purposes of addressing sources in attainment areas impacting on nonattainment areas, but also for determining the contribution to

stan dards violations by sources in nonattainment areas. The commenter note s that this requirement is clearly mandated by s ection 110(a)(2)(D) of the A ct which prohibits any source

within a s tate from significantly contributing to nonattainment or to projected NAAQS

violations. Thus, the commenter urges EPA to clarify this requirement in the nonattainment major NSR provisions of the federal regulations and in the approval of s tate SIPs.

Response:

We have amended 40 CFR 51.165(b)(2) to define PM 2.5 SILs as a screening tool to

determine whether a major stationary so urce or major modification locating in an attainment

area causes or contributes to a NAAQS violation at any location (including nonattainment areas). See 40 CFR 51. 16 5 (b)(2) in the final rule. I t should be noted that a proposed major source or modification of a pollutant for which an area is designated nonattainment is not excluded from satisfying the relevant nonattainment NSR requirements based on a de minimis air quality impact in the nonattai nment area ; that source must obtain offsets because of the fact that it proposes to locate in the nonattainment area.

The EPA is not taking any action in the final rule for PM 2.5 increments, SILs

, and SMC to codify the Class I SILs for various pollutants that we proposed in 1996. The EPA will consider taking such action in a subsequent rulemaking.



### 4.5.2 Miscellaneous Comments on SILs

Comment on Repowering or Replacement Projects:

One industry association commenter (0038) explain s that repowering and replace ment projects can result in the substitution of cleaner, more efficient electric generating unit s operating in the place of older units

, yet the repowered or replac ement unit may have direct PM emissions that exceed the PM SIL, particularly at receptors pr oximate to the source (especially if the Option 3 SILs are adopted). The commenter add s that such units also have lower emissions of

PM 2.5 precursors (S O 2 and NO

x ) compared to the replaced unit, and so would help lower PM 2.5 levels in downwind nonattainme nt areas. The commenter state s that EPA should recognize the85

net positive PM 2.5 impact resulting from the reduction of emissions of PM precursors in the modeling demonstration for repowering or replacement projects by crediting them for their overall impa ct , perhaps through the use of a standard conversion rate across the board that would provide some credit. The commenter also suggest s that another method worth considering would

be to use the average PM 2.5 receptor reduction throughout the nonattainment area attributable to

the SO 2 and NO

x reductions.

Response:

In t his final rulemaking for PM 2.5 increments, SILs

, and SM C, we are not tak ing any action to address the commenter‟s recommendations to allow PM 2.5 netting credit for reductions in precursor (S O 2 , NO

x ) emissions. We are currently unable to quantify the “net positive PM 2.5 impacts ” resulting from reductions in precursor reductions. As we make progress in terms of estimating (modeling) precursor impacts on PM 2.5 , we will give additional consider ation to the issue of precursor netting credits.

Comment on the Form of the SILs:

One industry association commenter (0038) note s that the p roposal d id not indicate how the proposed PM 2.5 SILs are to be interpreted. The commenter contends that the form of the SIL (and

, therefore, the predicted impact value to be compared with the SIL) should be consistent

with the form of the PM 2.5 NAAQS , which require that compliance with the 24

- hour and annual standards be determined using 3

- year averaging. Specifica lly, the commenter points out that t he annual standard is calculated based upon the 3

- year average of annual mean PM 2.5 concentrations, and the 24

- hour standard is based on the 3

- year average of the 98th percentile (or high

- 8th

- high) of 24

- hour concentrati ons.

The same commenter claim s that in employing a 3

- year test, the form of this NAAQS differs significantly from that of the PM 1 0 NAAQS and other criteria pollutant s for which SILs have been long

- established. The commenter note s that SILs have histo rically been applied in modeling through comparison of the highest predicted impact at any receptor during any individual year of the analysis with the appropriate SIL, and usually 5 consecutive years of meteorological data are employed in the analysis. T he commenter believes that this is a reasonable approach because, in the cumulative, multi

- source modeling analysis, the contribution of the new or modified source to a potential exceedance of the NAAQS could, theoretically, be as much as that highest valu e.

The same commenter explain s that when a 3

- year averaging is employed to determine compliance as in this case, it is not possible for a source to contribute its single year maximum predicted 24

- hour impact to an exceedance of the 24

- hour PM 2.5 NAAQS ; r ather, t he most that a new or modified source could theoretically contribute would be its highest 3

- year average of maximum predicted 24

- h our average impacts. The commenter add s that the use of a single year

maximum 24

- hour predicted impact for comparison with the SIL is therefore overly conservative and unnecessary to assure that sources which cannot significantly contribute are eliminated from cumulative analysis. Accordingly, t he commenter suggests that the use of a rolling 3

- year average of the three predicted single year 24

- hour highest concentrations at any receptor is more86

appropriate and is still conservative in that highest concentrations are used rather than the high

8th

- high.

For comparison with the annual PM 2.5 SIL, t he commenter suggest s t he use of a typical

5

- year meteorological database and determin ation of the predicted annual PM 2.5 impact concentration at each receptor for each year. The commenter explain s that once these values were determined, the facility would then generate three P M 2.5 3

- year average impacts at each
receptor (i.e., for Years 1

- 3, Years 2

- 4, and Years 3

- 5). The commenter indicates that the overall

maximum 3

- year average value (at any receptor) would be selected for comparison with the SIL,

rather than the single

- yea r maximum.

The commenter suggests that the methodology for comparison of the 24

- hour PM 2.5 predicted impacts to the 24

- hour SIL would be similar and use the same basic procedure, but averaging maximum 24

- hour impact predictions at each receptor across 3 years rather than annual impact predictions. T he commenter expresses the opinion that despite the standard being based upon the 3 year average of the 98th

- percentile 24

- hour impacts for each year, the 98th percentile values cannot be used ; instead, the 3

- year average of maximum concentrations must be used because the facility could contribute up to that amount to a potential exceedance.

Response:

We agree that the use of the SIL for PM 2.5 should take into account the form of the NAAQS. Accordingly, i n a March 23, 2010 EPA memorandum titled “Modeling Procedures for Demonstrating Compliance with PM 2.5 NAAQS,” 11 we provided guidance for using the SILs in conjunction with the 24

- hour and annual PM 2.5 NAAQS, which takes into account the statistical form of the NAAQS

, consistent with the rationale presented by the commenter that the form of the SIL should reflect the potential contribution that the source could have to a potential

exceedance . We note, however, that the recommended method for using modeling data does not rely on 3

- year rolling averages but generally relies on a 5

- year average calculation based on

5 years of National Weather Service data. Thus, for the annual NAAQS, we recommend that the highest average of the modeled annual averages across 5 years for National Weather Service (NWS) meteorological data or the highest modeled annual average of 1 year of site

- specific data be compared to the annual SIL for PM 2.5 . For the 24

- hour NAAQS, we recommend that the highest average of the maximum 24

- hou r averages across 5 years for NWS data or the highest

modeled 24

- hour average for 1 year of site

- specific meteorological data should be compared to

the 24

- hour SIL for PM 2.5

. In the March 23 guidance memo, we note that by using the average of the highest values across the years modeled, we preserve one aspect of the form of the PM 2.5 NAAQS, and using the average of the first highest 24

- hour averages rather than the 98 th
percentile (8 th highest) values from the distribution is consistent with the screening

- level nature of the analysis. We also note that, following promulgation of the PM 2.5 increments in the final rule, we intend to provide guidance for interpreting the SILs for their use with the 24

- hour and

annual PM

2.5 increments as well.

11 This EPA memorandum is available on EPA‟s website containing NSR/PSD guidance: http://www.epa.gov/region07/air/nsr/nsrmemos/pm25memo.pdf

.87



## 5 Comments on t he Significant Monitoring Concentration (SMC) for PM 2.5



### 5.1 General Comments on an SMC for PM 2.5

Three commenters (0013, 0035, 0038) express general support for EPA’s proposal to codify a PM 2.5 S MC without indicating a preferred SMC level

. Another commenter (0051) appears to support the SMC concept, but cautions that necessary actions should be completed prior to promulgating the SMC for PM 2.5 . In addition, other commenters indirectly indicate their support of the SMC concept by providing comments on their preferred option for setting the SMC level. These comments on the level of the SMC are presented in S ection 5.3 of this

document.

One commenter (0040) opposes the concept of SMC for PM 2.5 under the PSD program claiming that the Act does not authorize EP A to exempt sources from the PSD ambient monitoring requirements.

Comments Supporting an SMC:

One industry commenter (0013) support s EPA’s efforts to complete the rulemaking process required to address the final elements that aid implementation of the PSD program for

PM 2.5 , which includes an S MC (and i ncrements and S ILs).

One industry association commenter (0035) support s the use of S MCs (and SILs) as screening models to estimate the impact of proposed new and major modifications of major

sources bec ause they will greatly assist companies and regulators in managing resources for air quality impact analyses that truly have the potential to result in environmental impacts. The

commenter indicates that the use of the SMC (and SILs) in screening models w ill avoid costly analyses for projects that are unlikely to have consequential impacts on air quality.

One industry association commenter (0038) strongly support s the establishment of PM 2.5 S MC s (and increments and S IL s) that properly balance the economi c and environmental goals of the PSD program

.

Although appearing to support the concept of an SMC (and increments and SILs), o ne

state /local agency commenter (0051) expresse s general concerns over the proposed regulations aimed at establishing the SMC value (and increment and SIL values) without first promulgating regulations or developing tools that (1) define PM 2.5 and any precursors, (2) establish approved test methods or emission factors for determining PM 2.5 from various common sources, and (3)

pro vide an approved air dispersion model for determining PM 2.5 air quality impacts from a

source

.88

Comments Opposing an SMC:

One environmental group (0040) opposes EPA’s proposed development of an SMC for

PM 2.5 , believing that such screening tools are contr ary to the requirements of the Act. The commenter’s extensive legal arguments are presented in S ection 5 .2 of this document.

Response:

We agree with the commenters who support promulgation of an SMC for PM 2.5

. Accordingly, the final rule includes an S MC for PM

2.5 in revised 40 CFR 51.166(i)(5)(i)( c ) and 52.21(i)(5)(i)( c ).

With regard to the comment that the SMC for PM 2.5 should be delayed pending action concerning definitions for PM 2.5 and its precursors, approved test methods or emissions factors,

a nd approved air dispersion modeling, we acknowledge the importance of each of those components of the overall PM 2.5 implementation program , and note that these issues are now being addressed

. The E PA has in fact taken action on each of the commenter‟s con cerns as follows:

 In the May 16, 2008 final rule for PM 2.5 NSR implementation, EPA identified precursors of PM 2.5 that must be regulated (73 FR 28321) under the PSD permit program

.

 For a number of years, EPA has been post ing guidance on its website for measuring emissions of PM

2.5 , including the condensable fraction. The equipment, supplies

, and procedures provided by this guidance have been improved over time by stakeholders who

have submitted constructive comments. We believe th is posted guidance ha s provided a reasonable means to quantify emissions that are suitable for use in developing emissions

inventories ; for developing information that is useful in developing appropriate achievable emissions levels for sources ; and for assessing the performanc e of a source‟s particulate matter control s . Currently, e xisting published test methods for measuring

direct PM

2.5 emissions, as well as the condensable fraction, are being reviewed following formal notice and comment

, and we expect them to be promulgated within the same timeframe as this final rule.

 The EPA issued guidance on PM 2.5 modeling and the recommended procedures for carrying out a PM 2.5 source impact analysis ( March 23, 2010 EPA memorandum signed by Stephen D. Page, Director, Office of Air Qua lity Planning and Standards, titled “Modeling Procedures for Demonstrating Compliance with PM 2.5 NAAQS

)

.

We respond to the comments concerning legal opposition to the SMC for PM 2.5 in the following section.89



### 5.2 Comments on the Legal Basis for the SMC

Comme nt:

One environmental commenter (0040) asserts that the proposal to establish SMCs for

PM 2.5 is illegal and arbitrary for the same reasons that the commenter gave for SILs (see

Section 4.1 of this document) . The commenter add s that in s ection 165(e)(2) of the Act Congress mandate s a full year of continuous air quality monitoring for each major source subject to the PSD program. The commenter indicates that there are no exceptions, other than the limited provision allowing for less than a year’s worth of monitoring based on a determination ―that a complete and adequate analysis for such purposes may be accomplished in a shorter period.‖ The commenter argue s that the allowance for a ―shorter period‖ hardly amounts to authority to waive monitoring entirely , which is what the SMC proposal would do.

The same commenter claim s that there is no data or analysis in the proposal showing any necessary or rational connection between compliance with SMCs and compliance with increments and NAAQS , or to the need for monitoring . The commenter add s that the SMC levels are arbitrary numbers based on application of an arbitrary multiplication factor to

detection levels. The commenter contends that under the proposed rule, a source showing impacts below the SMCs will be totally exempt from the monitoring requirement even if the source will cause or contribute to an increment or NAAQS violation , which has occurred under prior EPA guidance to allow such an unlawful and arbitrary result s

.

The same commenter claim s that EP A’s attempt to invoke the de minimis theory to justify SMCs fails for the same reasons as discussed with respect to SILs in Section 4 .1 of this

document . The commenter add s that the statute is explicit that monitoring is always required, leaving no room f

or de minimis exceptions. In addition, t he commenter contends that Congress ’

intent to foreclose EPA from inventing de minimis exceptions is shown by the fact that Congress

did specify a narrow test for allowing less than a full years’ monitoring, and by the fact that Congress itself defined the universe of sources too insignificant to justify regulation by applying the permit program only to major sources.

The same commenter add s that the de minimis theory is particularly inapplicable to monitoring req uirements, which are by their nature meant to provide information to accurately determine the nature and degree of a source’s impact on air quality. The commenter claim s it is illegal and irrational for EPA to assert that monitoring will yield trivial or no benefit due to the supposed insignificance of a source’s air quality impact, when Congress required such monitoring precisely ― for the purpose of deter mining whether emissions from such facility will

exceed the maximum allowable increases or the maximu m allowable concentration permitted‖

under the Act (citing section 165 (e)(2) of the Act )

. The comment er sta te s that EPA apparently believes it can allow substitution of modeling for the Act’s monitoring requirement, but the

statute forecloses such substit ution. Based on a comparison of sections 165(e)(2) and 165(e)(3)(D), the commenter believes that Congress plainly knew the difference between monitoring and modeling, and did not allow EPA to substitute the latter for the former.90

The same commenter not e s that the continuous air quality monitoring data is typically used to determine background concentration for the NAAQS analysis conducted by a PSD permit applicant (citing EPA’s NSR Workshop Manual at C.27, C.34, C.46 ; as well as 40 CFR

p art 51, Appendix W, s ection 8.2.1.b ) . The commenter argue s that without preconstruction monitoring data on existing PM 2.5 concentrations, the results of the permit applicant’s NAAQS analysis will lack credible support. The commenter note s that EPA’s proposed regulations would exempt a PSD permit applicant from preconstruction monitoring without any determination that existing, current, quality

- assured monitoring data exist and that such data accurately represents background concentrations in the vicinity of the proposed source and would prevent an adequate or credible assessment of whether a proposed new or modified source would cause or contribute to a NAAQS violation. The commenter claim s that for many areas, the NAAQS will be a more restrictive limitation on deteriora tion of air quality than the PM 2.5 increments proposed by EPA, and EPA cannot allow any exemption from collecting the air quality data necessary to accurately define background concentrations of PM 2.5

.

The same commenter opines that even if use of the d e minimis doctrine was not precluded by the statute, it would be inapplicable in this case . The commenter explain s that the

de minimis doctrine applies only where regulation will yield a gain that is demonstrably trivial or

zero. The commenter sta te s tha t EPA has offered no evidence that sources with impacts below the proposed SMC levels will never cause or contribute to violations of increments or NAAQS, or that the gain from requiring monitoring by such sources will

, in fact, always be trivial. In

addi tion, the commenter believes that , objectively, the specific SMC numbers proposed by EPA are hardly trivial. The commenter points out that proposed Option 1 would set the 24

- hour SMC

at 10 μg/m 3 , which is higher than the proposed 24

- hour Class II incremen ts ; t hus Option 1 proposes to waive monitoring for sources that are projected to violate the increments. The

commenter contends that this is an unlawful and arbitrary result. The commenter also notes that the proposed Option 2 and 3 SMCs (24

- hour) are bo th higher than the proposed 24

- hour Class I increments, and would allow projected consumption of significant portions of the proposed

Class II incre ments without any monitoring : the O ption 2 SMC is 89 percent of the Class II

increment level while the O ptio n 3 SMC is 26 percent of that level. The c ommenter believes that it is absurd to claim that a source projected to consume such a large portion of the allowable increment is too trivial to warrant monitoring. The commenter add s that the notion that EPA ca n develop a single national number that defines ― trivial ‖ impact for all attainment areas is fundamentally flawed, given that even a very small impact can be of great significance in an area that is very close to exceeding an increment or a NAAQS.

The same commenter argue s that the proposed rule is further flawed because it fails to specify how a source is to demonstrate compliance with a n SMC. The commenter believes that

EPA intends that such compliance will be shown through some sort of modeling, but contends

that the statute does not allow EPA to wholly supplant with modeling the monitoring mandated by s ection 165(e)(2). The commenter add s that even if modeling were allowed to supplant monitoring, EPA would need to adopt rationally justified criteri a for determining when to allow such substitution, and would have to do so by rule (citing section 165(e)(3)(D) ) . The commenter

state s that such criteria would need to include requirements to ensure a conservative analysis, such as modeling PM 2.5 primary and prec ursor emissions, modeling worst

- case potential emissions for the averaging time in question, comparing maximum modeled impact against the91

SMC, following the Guideline on Air Quality Models to ensure sufficient and representative meteorological data , use of EPA

- approved models (and EPA

- approved model settings), and following EPA requirements for acceptable receptor placement and spacing.

The same commenter believe s that even assuming that the A ct did allow for exempting a source from preconstructi on monitoring, the proposed SMCs are arbitrary because the specific numbers proposed cannot rationally be characterized as trivial or insignificant. The commenter

add s that the proposal is also arbitrary because it allows a waiver of monitoring even in th e absence of a demonstration that current, quality assured monitoring data reflective of background concentrations in the area of the proposed source is available for use in the NAAQS modeling, or, if no such data is available, a requirement that all other sources of PM 2.5 or precursors to

PM 2.5 (including area and mobile sources) are included in the air quality modeling done in lieu of monitoring.

Finally, the commenter argue s that EPA has no authority to allow the use of SMCs ( or SILs ) to obviate the st atutorily required protection of AQRV s, or to obviate or impair FLM review of and objection to permits under section 165 of the Act

.

Response:

As with the SMCs adopted by EPA in 1980, the SMC that we have selected for PM 2.5 is supported by the de minimi s doctrine set forth in the Alabama Power opinion , contrary to the assertion of the commenter

. As previously discussed in Section 4.1 of this document in response to this commenter‟s legal objections to SILs, t he Alabama Power court concluded that “most

r egulatory statutes, including the Clean Air Act, permit [de minimis] showings in appropriate cases. 636 F.2d at 360. The court went on to say that, “unless Congress has been extraordinarily rigid, there is likely a basis for an implication of de minimis authority to provide exemption when the burdens of regulation yield a gain of trivial or no value.” 636 F.2d at 360

- 361. Although the comment e r contends that the monitoring requirements of section 166(e)(2) are inconsistent with a de minimis exemption ba sed on an S MC , the comment e r does not provide any basis for concluding that these provisions are the kind of “extraordinary rigid” provision that forecloses the use of a de minimis exemption. Thus, where the S MC values set by a rule identify a level of im

pact such that “the burdens of regulation” (in this case certain requirements

under CAA section 165) will “yield a gain of trivial or no value,” the establishment of an S MC is a permissible de minimis exemption.

Like the other pollutants for which EPA h as promulgated SMCs, EPA believes there is little to be gained from requiring the collection of preconstruction monitoring data for PM 2.5 concentrations that are at levels so low that they cannot be accurately measured. As indicated in the preamble to the final rule , we selected a final value for the PM 2.5 SMC based on the principle underlying Option 1 (i.e., derived from the lowest detectable concentration (LDC) as modified based on the appropriate uncertainty correction factor). However, the promulgated value is lower than the value proposed under O ption 1 , which the commenter considered to be too high, because we adjusted the correction factor being applied to the LDC

. The updated analysis of the correction factor is contained in a March 12, 2009 inter nal EPA memorandum that we have placed in the docket for this rulemaking , which describes “compelling data from 9 years of more92

advanced ambient monitoring technology and associated quality assurance measurements of

PM 2.5 ....” See further discussion of this analysis in the response to comments in S ection 5.3 of

this document.

Because the final SMC is based on the capabilities of the ambient monitors and associated quality assurance procedures to measure PM 2.5 , there is little benefit to be gained from pr e construction monitoring of ambient concentrations that are below the SMC

. In this situation, the source would be trying to measure concentrations that are in the range where

measurement uncertainties exist , and the results of the monitoring could not be used for any quantitative purposes because they would not provide the desired confidence of accuracy and precision . Thus, the time and expense of a year of preconstruction monitoring essentially would

be wasted.

A similar situation would exist where a source ‟s emissions will result in ambient impacts that are less than the final SMC. Any difference in the ambient concentration due to such a

source would be too small to be measured accurately, so any attempt to quantify the impact of

the source based on preconstruction and post

- construction monitoring in the area would be

inconclusive. In addition, increment analyses typically are based solely on modeling of the emission increases and decreases at sources that affect the increment, without the use of

mo nitoring data. Thus, preconstruction monitoring data generally are not useful for increment analyses for any sources, including sources with impacts below the SMC.

However, as pointed out by the commenter, preconstruction monitoring can be useful in

det ermining the background concentration for purposes of a NAAQS analysis. Accordingly, where representative ambient concentration data are not available from other sources and the ambient air quality is at levels near the PM 2.5 NAAQS, we do not encourage th e continued use of

the SMC to exempt sources from collecting preconstruction monitoring data . We believe that the PSD regulations provide discretion to individual reviewing a uthorities to determine when it is appropriate to require the collection of ambie nt data as part of a complete application regardless of whether or not the SMC is being exceeded. Specifically, the PSD regulations provide that the reviewing authority may exempt a source from the preconstruction monitoring

data requirements based on the SMC, but neither require such an exemption nor require that the exemption be established without exceptions or limitations

.

We do not agree with the commenter that the final SMC for PM 2.5 is too large to be considered trivial based on comparisons with t he PM 2.5 increments. The SMC is based on the measurement capability of ambient monitors and associated quality assurance procedures

, which are unrelated to the level at which increments are set. In addition, as noted above, increment analyses typically a re modeling exercises, and ambient monitoring results do not enter into these analyses

. Thus, the level of the increments is not material to the level of the

SMC that we are setting in this final rule

.

We also do not agree with the commenter that settin g a single national SMC is

“ fundamentally flawed .” The final SMC is based on the ambient concentration of PM 2.5 that can be accurately measured, which is the same everywhere. In locations where other considerations

enter into the determination of whether preconstruction monitoring data should be required

, as93

discussed previously the reviewing authority retains discretion under the PSD regulations to require the collection of monitoring data regardless of whether the source‟s projected ambient impact is ab ove or below the SMC , and should do so when warranted

.

The commenter also expresses concern about our alleged failure to demonstrate how a source is to show compliance with the SMC for PM 2.5

. The SMCs for regulated NSR pollutants have been defined in th e PSD regulations since 1980; in order to compare a proposed source‟s impact against the applicable SMC we have previously indicated that the source should use the highest modeled concentration for the applicable averaging time or the existing air pollutio n concentration in the area of concern. See EPA‟s New Source Review Workshop Manual (Draft, October 1990) at page C.16. The SMC values are linked to direct measurements or predictions of an air pollutant concentration and are not affected by the form of the individual standards upon which compliance is based. Nevertheless, we will continue to review our current guidance and provide clarifications as deemed appropriate.



### 5.3 Comments on the Proposed Level of the SMC for PM 2.5

While the SMC level proposed und er Option 1, based in part on the sensitivity of existing

ambient monitors for PM 2.5 , received the most support, the other two options received some support as well. Some commenters that opposed O ption 1 did not indicate a strong preference

between O ption s 2 and 3.

Comments on Option 1:

A total of 10 commenters express support for the SMC level proposed under Option 1. The reasons for support given by these commenters are summarized below.

Four of those commenters prefer Option 1 because it is the on ly option that considers factors associated with actual sampling of ambient PM 2.5 concentrations. Two industry

commenter s (0026 , 0027 ) state that the option is reasonable because it reflects pollutant levels at

which low level concen trations or small inc remental changes in pollutant concentrations can be reasonably determined

, which is the same methodology originally used to set the SMC for TSP.

Two industry association commenter s ( 0032, 0037) prefer Option 1 because it is the only option

that relates to monitoring measurement sensitivity.

One state / local agency commenter (0015) prefer s Option 1 . The commenter notes that

EPA has retain ed the 24

- hour PM 10 NAAQS, and the development of the PM 2.5 SMC under this option is consistent with past SMC developmen t for PM 10

.

One industry commenter (0020) expresse s a preference for Option 1 by default. The commenter explain s that the other options cannot be supported for reasons explained below in the comments pertaining to O ptions 2 and 3. Another industry asso ciation commenter (0029)

also support s Option 1 and believes 10 μg/m 3 is a reasonable value. However, t h is commenter also believes that EPA is authorized under the Act to choose Option 2. One i ndustry association

commenter (0046) provide s general support for Option s 1 and 2 because there is little difference

between them.94

One supportive industry association commenter (0039) recommend s that the SMC values be set at a level that would avoid unnecessary collection of pre

- application monitoring data , and

b elieves tha t the proposed Option 1 SMC is sufficiently conservative for this purpose

. The
commenter argue s that if the SMC were set correctly, modeled exceedances of the SMC would

better demonstrate an actual need for collection of a year of pre

- applicat ion monitoring data.

The commenter add s that collecting such data, if found to not be needed, unduly delays successful permitting of much needed power plant projects in the West.

Finally, o ne industry commenter (0016) indicates support for Option 1 for the SMC, yet proposes that EPA develop area

- specific SMCs (and i ncrement s and SILs) that take local

conditions into account.

Two commenters oppose the level proposed under Option 1 because of its relation to the level of the proposed Class II increment. Specifically, a state / local agency commenter (0019)

and a state / local agency association commenter (0018) oppose the proposed Option 1 SMC (10 μg/m 3 ) because it exceeds any of the corresponding proposed Class II 24

- hour increments for

PM 2.5 (9 μg/m 3 )

.

Co mments on Option 2:

One state/local agency commenter (0019) and o ne state/local agency association

commenter (0018) express support for either Option 2 or Option 3. However, the commenters express concern that the justification for choosing either Optio n 2 or 3 would need to be clearly explained.

One state / l ocal a gency commenter (0033) believe s it is appropriate to achieve some degree of consistency by using Option 2 for both SILs and SMCs.

One i ndustry association commenter (0046) provide s general s upport for Option s 1 and 2

because there is little difference between them.

One state / l ocal a gency commenter (00 15 ) and t wo industry commenters (0020, 0026) who support Option 1 also explicitly oppose Option 2. These commenter s express concern with

the factor of 0.8 ( based on the NEI ratio of total PM 2.5 emissions to PM 10 emissions ) that was

used to derive the Option 2 SMC . The state / l ocal a gency commenter (00 15 ) and one of the industry commenters (0020) believe that the ratio is technically inaccurate

. The two industry commenters (0020, 0026) are concerned that use of this factor could set a n inappropriate precedent for other, source

- specific other regulatory processes.

Comments on Option 3:

One s tate/local a gency commenter (0025) support s EPA’s pr oposed Option 3 because this option is the most stringent.

As noted above, one state/local agency commenter (0019) and o ne state/local agency

association commenter (0018) express support for either Option 2 or Option 3. However, the95

commenters express c oncern that the justification for choosing either Option 2 or 3 would need to be clearly explained.

One environmental group commenter (0040)

, although believ ing that all of the SMC options are unlawful and irrational , indicates that the Option 3 SMC is t he least objectionable

because it is the lowest and therefore allow s the least amount of circumvention of the Act’s requirements.

Five commenters oppose the use of Option 3 to set levels for the SMC for PM 2.5 , expressing their reasons as follows:

 One in dustry commenter (0046) believes that the Option 3 SMC is too low.

 Two industry commenters (0020, 0026) and one industry association commenter (0029) believe that the Option 3 SMC is too close to the LDC for PM 2.5 to be us ed effectively.

Two of these com menters (0026 , 0029) add that the determination as to whether or not a source needs to monitor emissions should be based on a value that can be expected to be measured accurately, and an SMC level set so close to the LDC does not provide this

assurance.

 On e industry association commenter (0038) sta tes that the final PM 2.5 SMC should complement the adopted SILs and notes that the SMC under Option 3 is smaller than the proposed 24

- hour Class II SILs under Options 1 and 2. The commenter explains that

under th is scenario, a PSD applicant could potentially trigger preconstruction monitoring but not be required to conduct a cumulative modeling analysis , which the commenter believes would be inappropriate

. T o avoid requiring preconstruction monitoring where

no cu mulative impact analysis is required, the commenter believes that EPA should not adopt Option 3 for the SMC

.

Other Comments on the SMC Level:

One industry commenter (0029) (who supports Option 1) indicates that EPA also is authorized to use its Option 2 approach . However

, t h is commenter cautions that EPA should

make it clear that the PM 2.5 /PM 10 emissions ratio used in this option is intended to be used only for the setting of the nationwide threshold values being addressed in this rulemaking and is not

intended to be used for other regulatory purposes.

One environmental group (0040) , while believ ing that all the proposed SMCs are unlawful and irrational

, indicates that a less objectionable (though still impermissible) option

would be to set a n SMC bas ed on the LDC of 2.0 μg/m 3 (24

- hour average).

Response:

In developing the three proposed options for an SMC, EPA sought to use methods that

would attempt to identify levels representing a de minimis or insignificant impact on PM 2.5 ambient air quality t hat makes the requirement to collect additional continuous air monitoring

data extraneous. We agree with the commenters who conclude that Option 1 is the most supportable option for defining the SMC for PM 2.5 . The ability to accurately measure ambient96

PM 2.5 concentrations is not related to a ratio of PM 2.5 to PM

10 either directly in terms of emissions or as expressed by the respective NAAQS, which were used to define the SMC for

PM 2.5 under Options 2 and 3, respectively. We selected the Option 1 approach because it relies on the concept of a minimum detect ion limit (MDL) to argue that there is little to be gained by trying to monitor ambient concentrations lower than the concentration that available monitoring techniques and quality assurance procedures c an reliably measure. Our original concern w ith Option 1 w as that, while it l inked the SMC directly to the concept of the MDL (in order to identify de minimis monitoring circumstances), the value originally derived from that approach

in the 2007 NPRM was h igh in relationship to the concentrations of PM 2.5 defined by the existing NAAQS and increments for PM 2.5

.

In considering the use of Option 1 for developing the SMC in the final rules, however, we recognized during the administrative process after publ ication of the proposed rule that it was

necessary to re

- examine the assumptions that we relied upon in 1980 to develop the numerical values for the original SMCs so that we could most accurately reflect current monitoring techniques and quality assurance procedures for PM 2.5 . Our re

- examination for the final rule

use d the most current information concerning the physical capabilities of the PM 2.5 Federal Reference Method Samplers, and addresses uncertainties introduced to the measurement of

PM 2.5 due to va riability in the mechanical performance of the PM 2.5 samplers and the micro

gravimetric analytical balances that weigh filter samples.

The minimum detection limit (MDL) of 2 μg/m 3 , originally used in 1980 for the SMC for PM and promulgated for PM 2.5 in 1997 ( see 40 CFR part 50, Appendix L, section 3.1), has been reaffirmed by 9 years of field blank data collected by EPA through the PM 2.5 Performance Evaluation Program. However, we found that new data exist to “indicate a conservative estimate of the ag gregate uncertainty factor is no greater tha n „2‟ at the concentration equal to the MDL of 2 μg/m 3 .” 12 Accordingly, the lowering of the uncertainty factor from “five” to “two” under Option 1 yields an SMC of 4 μg/m 3 PM 2.5 , 24

- hour average, rather than the proposed concentration of 10 μg/m 3

.

We conclude that the modified level of 4 μg/m 3 PM 2.5 , 24

- hour average, for the SMC under Option 1, based upon a more current understanding of monitoring precision for PM, especially fine PM, addresses commenter suppo rt for the use of a method that is consistent with the way other SMCs were developed and most directly reflects monitoring technology and quality assurance measurement capabilit ies for the pollutant of concern, while at the same time responding to the conc ern of other commenters that a value in the lower range of proposed SMC values is most reasonable considering the levels of the NAAQS and increments for PM 2.5

.

12 This information is contained in a March 12, 2009 internal EPA memorandum from Dennis Crumpler to Raj Rao, titled “PSD Monitoring De Minimis Concentration for PM 2.5 ,” which has been placed in the docket for this rulemaking.97



### 5.4 Other Comments on SMCs

Comment:

One i ndustry commenter (0027) states that if ambient air mon itoring is required as part of a PSD permit review (i.e., the source exceeds the SMC) EPA should, either in rulemaking or associated guidance

, enable the permit applicant to use and rely on ambient air measurements

from established PM 2.5 ambient air qualit y monitors that are operated by EPA, state agencies, or established air quality research organizations. The commenter states that the PSD permitting program should encourage the use of existing data and data networks, and should only require

the installat ion of a new ambient air monitoring system on a limited case

- by

- case basis. The commenter explain s that in many cases, existing PM 2.5 ambient air monitors should be sufficient to establish baseline or pre

- proj ect ambient air concentrations.

Response:

T he PSD regulations do not require that the ambient monitoring requirements be satisfied with data collected specifically by the PSD applicant. Rather, the PSD regulations require PSD applications to “contain an analysis of ambient air quality” and that “t he continuous air monitoring data that is required shall have been gathered over a period of one year.” (See, e.g., 40 CFR 51.166(m)(1)(i) and (m)(1)(iv), respectively.) Accordingly, EPA‟s longstanding policy is to allow PSD applicants to rely upon exist ing representative data , where available, to satisfy the preconstruction monitoring requirements. We continue to believe that, to the extent that existing data is representative of air quality in the area that the proposed sources would affect, such exist ing monitoring data may be used in the PSD application lieu of requiring applicants to establish separate ambient monitoring networks to collect new air quality data.

Comment:

One industry commenter (0016) suggests that EPA develop geographic area

- speci fic

SMC s (and increments and SILs) that take local conditions into account. The commenter points

out that PM 2.5 levels in PSD areas proximate to international borders may be elevated by sources outside the legal and practical control of the United States and state authorities. The commenter

also notes that PM 2.5 levels may be elevated by natural conditions, such as drought, fires, geologic formations (sandy or fine

- grained surface features) high winds, etc., leading to excessively dusty ambient condition s over which the local area has no control. The commenter indicates that local area baselines must reflect these PM emissions, though they are not reflected in the local area’s emissions inventory. The commenter urges EPA not to penalize such PSD

areas b y imposing a uniform national SMC (or increments or SILs) where the conditions of concern are not capable of control.

Response:

We do not agree with the commenter‟s recommendation for area

- specific SMC levels for

PM 2.5

. The air quality analysis for det ermining compliance with the annual and 24

- hour PM 2.5 NAAQS must consider the existing air quality in the area of concern, regardless of its origin. We98

do not allow certain emissions to be excluded from measures of actual air quality, except in specific c ases of “exceptional events” that may occur during a period when the ambient concentrations are showing levels exceeding the NAAQS. We do not find any basis for setting different SMCs for PM 2.5 based on geographic location “where the conditions of concern are not capable of control.”99



## 6 Comments on Transition Issues

6.1 Comments on the Effective Date for PM 2.5 

### Increments

We proposed that if we promulgated PM 2.5 increments under section 166(a) of the Act (Option 1), the effective date of the final rules would b e 1 year after the date of promulgation consistent with the timeline of section 166(b) of the Act. However, we also took comment on whether we could make the increment regulations effective 60 days after promulgation under Option 1, noting that Congress i ntended increments and other measures to become effective within 3 years after promulgation of a NAAQS and that there has a been an extended delay of over 10 years since we established the PM 2.5 NAAQS. Further, we pointed out that the 1 year delay embodie d in section 166(b) of the Act was intended to give Congress time to intervene if it did not agree with EPA’s rules. Since section 166(b) was added to the Act, the Congressional Review Act (CRA) has been enacted, which provides an expedited mechanism for Congress to block any final rule within 60 days of promulgation. Thus, we requested comment on whether, given the procedures under the CRA, a 60

- day delay in the effective date of the final PM 2.5 increment rules could satisfy the Congressional intent of s ection 166(b).

In addition, we proposed that if we promulgated PM 2.5 increments under section 166(f) of the Act (Option 2), the effective date of the final rules would be 60 days after promulgation consistent with the CRA timeline. We do not interpre t section 166(b) as applying to increments promulgated under section 166(f).

Although in the proposal preamble we discussed the effective date of the final rule in the context of the section of the Act under which we promulgate the PM 2.5 increments, many commenters expressed preferences on this timing either regardless of which of the two options we select or without reference to the options. As a result, the comments on the effective date of

the final rule for PM 2.5 increments are organized around the p referred effective date rather than the options discussed in the preamble. However, where commenters included comments on the proposed options, these are noted as well.

In addition, it should be noted that at proposal we equated the effective date of th e final

rule with the effective date of the PM 2.5 increments (either 60 days or 1 year after promulgation). However, in the final rule we have decoupled the effective date of the increments from the effective date of the final rule, which will be 60 days after promulgation in the Federal Register

.

Comments Supporting an Effective Date 1 Year after Promulgation and/or Opposing

60 Days:

A total of nine commenters support a 1

- year delay in the effective date for the PM 2.5 increments, for the following rea sons:

Two state/local agency commenters ( 0015, 0022) support delaying the effective date by

1 year rather than 60 days because states need time to establish a process and revise rules. One

of these commenters (0015) specifically recommends that we foll ow section 166(a) of the Act under Option 1 and does not concur with the proposal to make increments effective within100

60 days of promulgation under Option 1 or with Option 2. The same commenter notes that the

PM 2.5 NAAQS still have not been implemented in the NSR program, and indicate s that state s will need time to establish a process and revise rules that include PM 2.5 NAAQS, PM 2.5 and PM 10 increments, SILs, SMCs, and significant related PSD issues, such as coordination with the

FLMs.

Eight i ndustry and industry association commenters support EPA’s proposal to make the

final rule for PM 2.5 increment s effective 1 year after promulgation. Three of these commenters (0023, 0026, 0029) indicate that this time is necessary to develop the needed PM 2.5 inventor ies. Two of these (0023, 0029) add that accurate inventories of PM 2.5 emissions data that are necessary for implementation of the PM 2.5 PSD program.

Three of the industry association commenters ( 0032, 0035 , 0037 ) urge EPA to allow state programs suffici ent time to adopt increments, particularly if condensable particulate is included in the increment and its analysis. T he commenter s sta te that the federal rule should not be

effective for at least 1 year . (They also state that states should have 3 years for the associated SIP revisions.) These commenters add that this time would provide time for sources that have permits in the pipeline or are just about to submit an application to be able to complete the permitting process without undue delay. One of t he commenters (0035) specifically voices support for Option 1 for the effective date of the final rule (1 year) and Option 2 B for the period granted for SIP revisions (3 years ). Another of the commenters (0032) supports Option 1 if the

increments are base d on filterable PM 2.5 only

, and proposes a modified Option 2 if condensables are included that would postpone the effective date for the federal program for 3 years and allow

a 3

- year period for SIP submittal in states with approved PSD programs. The latt er two

commenter s explain that this additional time may give the Agency time to promulgate changes to improve test methods for sources of condensable particulate.

Another of the industry association commenters ( 0038) note s that, at the time of the

propos al, the NSR portion of the Clean Air Fine Particle Implementation Rule ha d not yet been promulgated

, and that state s will need time to incorporate that rule as well as the requirements of

the p roposal into their SIPs. The commenter add s that making the PM 2.5 increments effective

before state s and sources have had a reasonable opportunity to begin, let alone complete, the SIP process for the two related rulemakings would unnecessarily complicate an already

- complex regulatory process.

One of the industry commenter s (0043) states simply that the proposed 60

- day timeline was unreasonably short.

Comments Supporting an Effective Date 60 Days after Promulgation and/or Opposing

1 Year:

Two commenters, one state/local agency commenter (0019) and one state/l ocal agency association commenter ( 0018), support EPA’s proposal to implement the PM 2.5 PSD program as soon as possible

, and encourage d EPA to apply the 60

- day period for the effective date under whatever option is finalized. The state/local agency (0019) urges EPA to take measures to expedite the implementation of the PM 2.5 final rule and suggested the Agency choose the shortest101

of the proposed effective dates which are allowed under any of the applicable regulations. The

commenter (0019) stat e s that one of the detrimental effects of EPA’s preferred approach of developing PM 2.5 increments under section 166(a) of the Act (Option 1) could be to delay the regulatory effective date of applicability by 1 year, versus the 60 days time frame required under

the s ection 166(f) approach. The commenter (0019) indicates that in light of the excessive delay in the implementation of the PM 2.5 PSD program since the NAAQS were promulgated, the

60

- day effective date should also appl y under EPA’s preferred option.

Comme nts Supporting Other Effective Dates:

Two industry commenters (0016, 0020) and one industry association commenter (0036) suggest different approaches to setting the effective date of the final rule for PM 2.5 increments. One of these industry commenters (0020) states that the rule should take effect only when

sufficient PM 2.5 emissions data become available to derive the 24

- hour baseline, and no earlier than 1 year after promulgation to allow time for all to address inventory issues.

Another of the comm enters (0016) argues that the proposed effective dates relative to permitting are unrealistic, arbitrary

, and capricious. The commenter note s that the foundation of the proposed PM 2.5 program is emissions inventory data

, and stated that many PSD areas of the United States have no data, others have an insufficient amount , and all the data are of questionable accuracy due to testing concerns

. The commenter recommend s that the proposed

deadlines be rewritten, couched in terms of the dates by which accurate P M 2.5 emissions inventory data can be realistically be developed using an EPA

- approved stack test methodology, integrated

, and made available for use by the PSD

- regulated community in convenient format.

The same commenter adds that the regulations and pre amble of the final regulations

should state that the obligation to develop the necessary baseline PM 2.5 data rest, for verification, quality assurance

, and cost reasons, solely on EPA and state governments throughout the
country. The commenter believes t hat to impose such data development on the regulated community and , in particular, on the first of the PSD permit applicants in a PSD area is unreasonable, and would raise the cost for that applicant to prohibitive levels. The commenter

believes that fina lizing the rules before there are adequate and accurate emissions inventory data will grind PSD permitting to a halt until there is an accurate EPA

- approved stack test method for

PM 2.5

. The commenter states that this is inconsistent with one of the goals of the PSD program

as set forth in section 160 of the Act

– to insure economic growth will occur in a manner that is consistent with the preservation of existing clean air resources. The commenter also states that the proposed effective dates fail to take into account the lack of emissions data, the time necessary to integrate PM 2.5 emissions data by and between adjoining PM 2.5 areas in the same and different states, and the potential for selection of alternative increment approaches by states.

The indus try association commenter ( 0036), while agree ing with EPA’s approach to establish the effective date of the rule as expeditiously as possible for Options 1 and 2 , also states

that EPA must recognize that, to address the air quality impacts of PM 2.5 emissio ns, adequate air dispersion models must be made available for the modeling community. The commenter note s that there are no adequate air dispersion models to address the direct and indirect PM 2.5 emissions for near

- field applications. The commenter asser ts that there needs to be appropriate102

modeling guidance provided by EPA and sufficient time to evaluate this guidance to ensure consistent application of air dispersion modeling to assess PM 2.5 impacts, prior to requiring the

PM 2.5 increments be demonstrat ed through modeling analysis.

Response:

In light of our decision to promulgate PM 2.5 increments under the authority of

section 166(a) of the Act (proposed Option 1), we faced the issue of to how to most effectively implement the long

- awaited PM 2.5 incr ements, recognizing that section 166(b) provides for a

1

- year implementation delay. We have concluded that it is most appropriate to follow the plain language of section 166(b), which calls for a 1

- year effective date for implementing new

increments devel oped under section 166(a) of the Act. We agree with the commenters who suggested that a shortened implementation delay was desirable because of the substantial delay in the promulgation of measures to prevent significant air quality deterioration with res pect to

PM 2.5 . Nevertheless, we believe it would be inappropriate in this action to disregard the statutory language which plainly calls for a 1

- year delay. Accordingly, we are setting the effective date of the PM 2.5 increments a s the date 1 year after t he date of publication of this final

rule. See new 40 CFR 51.166(b)(14)(i)( c ) and (ii)( c ), and new 40 CFR 52.21(b)(14)(i)( c ) and (ii)( c ). It should be noted that the same trigger date applies to both the f ederal PSD rule at

40 CFR 52 .21 and the state (SI P

- approved) programs consistent with the 40 CFR part 51 PSD regulations.

At the same time, we are establishing a different effective date for the other provisions, i.e., the SILs and SMC for PM 2.5 , in this final rule by establishing the effective date of the final

rule as the date 60 days after publication of th e final rule in the Federal Register . This will enable the implementation of these key elements of this rule under the federal PSD program as soon as possible.



### 6.2 Comments on the Implementation Date for PM 2.5 

### Increments

6.2.1 Comments on the Schedule for Submitting SIP Revisions

We proposed that if we promulgated PM 2.5 increments under section 166(a) of the Act (Option 1), we would require states to submit revised implementation plans within 21 mon ths of promulgation of the final rule according to timeline specified in section 166(b) of the Act, regardless of whether we made the effective date of the rule 1 year or 60 days after promulgation (see Section 6 .1 above). Similarly, we proposed under Opt ion 1 that we would approve or disapprove the SIP revisions within 4 additional months, that is, by 25 months after promulgation.

In contrast, we proposed that if we promulgated PM 2.5 increments under section 166(f) of the Act (Option 2 A or 2B ), we wou ld follow the existing regulatory provisions of 40 CFR

51. 166(a)(6) and require states to submit revised implementation plans within 3 years of promulgation. However, we also requested comment on whether we should require a shorter

timeline for SIP submis sion, such as the 21 months required under Option 1.103

Although in the proposal preamble we discussed the timeline for implementation of state programs in the context of the section of the Act under which we promulgate the PM 2.5 increments, many commenters expressed preferences on this timing without regard to the options that they supported. As a result, the comments on the implementation timeline for state programs are organized around the preferred schedule rather than the options discussed in the

pream ble. However, where commenters included comments on the proposed options, these are

noted as well.

Comments Supporting 21 Months:

One i ndustry commenter (0026) indica te s that her company was receptive to EPA’s suggestion to apply the statutory minimum of 21 months for requiring SIP revision submittals and 4 additional months for EPA approval. The commenter (0026) agree s that allowing state s up to a full 3 years to adopt and submit PM 2.5 implementation plan revisions w ould delay implantation of a PM 2.5 PSD process. An industry association commenter ( 0037) indicates that if

condensable PM is not included in the PM 2.5 increment rules, a period shorter than 3 years, such as the 21 months proposed in Option 1, makes sense. However, this commenter favors 3 years if condensables are included under the rule (see below).

Comments Supporting 3 Years:

A total of four commenters support the 3

- year SIP submittal period, consistent with the proposed use of section 166(f) of the Act for developing the PM 2.5 increm ents, for the following

reasons:

 T hree industry association commenters ( 0032, 0035, 0037) urge EPA to allow state programs sufficient time to adopt increments, particularly if condensable particulate is included in the increment and its analysis. The com menters recommend that state s be

allowed 3 years for the associated SIP revisions. (They also state that the federal rule

should not be effective for at least 1 year.) These commenters add that this amount of

time would enable sources that have permits i n the pipeline or are just about to submit an application to be able to complete the permitting process without undue delay. One of the commenters (0035) specifically voice s support for Option 2 B for the period granted for SIP revisions (3 years) and Opti on 1 for the effective date of the final rule (1 year). Another of the commenters (0032) supports the Option 1 implementation time line if the

increments are based on filterable PM 2.5 only, and proposes a modified Option 2 if

condensables are included tha t would allow a 3

- year period for SIP submittal in states with approved PSD programs and postpone the effective date for the federal program for 3 years. The latter two commenter s also explain that this recommended amount of time may give the Agency time to promulgate changes to improve tes t methods for sources of condensable particulate.

 One state/local agency commenter (0033) believes that Option 2, consistent with the use

of section 166(f) as the basis for the increment determination, is sensible and provides sufficient time for the effort required to implement the rule. The commenter indicates

that the PM 2.5 program is a good and sorely needed program, and it is important to be104

sure that it is properly structured. Thus, EPA should resist a last minu te rush to get it up and running.

Comments Supporting Other Dates for Submitting SIP Revisions:

One state / l ocal a gency commenter (0019) urge s EPA to establish a time shorter than

21 months for requiring states to submit revised PSD rules for SIP approva l. The commenter believes that any further delays in the implementation of the PM 2.5 increments or the NSR rule are contrary to the intent of Act for the PM 2.5 NAAQS established in 1997.

Response:

In this final rule, we are establishing the final PM 2.5 increments as minimum program elements for all state PSD programs. Accordingly, states must submit for EPA‟s approval revised SIPs that incorporate the final PM 2.5 increments or alternative measures that can be demonstrated to EPA‟s satisfaction to provi de an equivalent level of protection as the PM 2.5 increments. In accordance with section 166(b) of the Act, we are requiring states to submit revised implementation plans to EPA for approval within 21 months of promulgation, that is, by

the date 21 months after the date of publication of the final rule in the Federal Register.

Section 166(b) also specifies that we must approve or disapprove these revisions within 25 months of promulgation (4 months from the statutory deadline for SIP submittal). We regar d these statutory deadlines as maximum allowed timeframes for action. Moreover, we do not believe that the Act restricts our ability to approve SIP revisions requested by a state at any time before these deadlines. In this final rule, we are amending the regulatory provisions at 40 CFR 51.166(a)(6)(i) to articulate the deadline set forth by the statute for the SIP submittals involving

the PM

2.5 increments pursuant to section 166(a) of the Act.

As described earlier, the trigger date and major source base line date are fixed dates applicable to the PSD program nationwide. This means that the same trigger date and major source baseline date apply to the federal PSD rule under 40 CFR 52.21 as well as to all SIP

related PSD rules developed consistent with the requirements under 40 CFR 51.166. Only a few states continue to rely on the federal PSD permit program (40 CFR 52.21) for issuing PSD permits; most states now have their own PSD programs under an EPA

- approved SIP. The

1

- year delay in the trigger date wi ll mean that sources applying for PSD permits under the federal PSD rules must address the PM 2.5 increments beginning on or after the date 1 year after the date of publication of the final rule in the Federal Register, depending on the date the first compl ete PSD application for a source of PM 2.5 is submitted (the minor source baseline date for

PM 2.5 ).

Sources applying for PSD permits under a state PSD program generally will not be required to address the PM 2.5 increments until the effective date of the applicable state rule in

which the PM

2.5 increments are contained, which will be some time after the trigger date and major source baseline date for the PM 2.5 increments. In either case, the date of submittal of the first complete application for a PSD p ermit after the effective date of the applicable PSD rule will establish the “minor source baseline date” in an attainment or unclassifiable area. As

described in section IV.D of the preamble , the “minor source baseline date” is not a fixed date,105

but inst ead applies independently to each baseline area based on the submittal date of a complete application for a PSD permit , and marks the date after which actual emissions changes from all sources affect the available increment.

The EPA does not expect that states will revise their SIPs and submit them to EPA for approval prior to the effective date of the PM 2.5 increments in this final rule, which is the date 1 year after the date of publication of this final rule in the Federal Register. Therefore, there i s likely to be a period of time after the date of publication of this final rule in the Federal Register when state laws will not require PSD applicants otherwise subject to PSD for PM 2.5 to complete an increment analysis for the PM 2.5 increments, even tho ugh the PM 2.5 increments, major source baseline date, and trigger date have been established as a result of this final rule. Similarly, it is not clear whether states will have the authority to consider such applicants as having triggered

the minor source baseline date during this interim period before their revised PSD rules containing the new PM 2.5 increments and relevant baseline dates become effective.

The EPA does not intend to prescribe the implementation timeline for state programs; rather, each state will need to determine how increment consumption and the setting of the minor source baseline date for PM 2.5 will occur under its own PSD program. Nevertheless, regardless of when a state begins to require PM 2.5 increment analyses and how it choose s to set the PM 2.5 minor source baseline date, the emissions from sources subject to PSD for PM 2.5 on which

construction commenced after the date of publication of the final rule in the Federal Register (the major source baseline date) will consume PM 2.5 i ncrement and must be included in increment analyses occurring after the minor source baseline date is established for an area under the state‟s revised PSD program.



### 6.2.2 Comments on Coordinating Implementation of PM 2.5 

### Increments in the State and Federal Prog rams

Under Option 1, we proposed to begin implementing PM 2.5 increments in the federal

p art 52 PSD program on the effective date of the final rules, that is, either 1 year or 60 days after promulgation. We also requested comment on the option of delayin g implementation of the

federal p art 52 PSD program until 25 months after promulgation to coordinate it with the outside date by which EPA would be required to approve SIP revisions under the Option 1 timeline. Under Option 2, we proposed to begin impleme nting PM 2.5 increments in the federal p art 52 PSD program on the effective date of the final rules, that is, 60 days after promulgation. We did not propose to consider coordinating implementation with the timeline under Option 2, which could take up to 4 years (3 years for SIP submissions and 1 year for EPA approval).

Comment:

Two commenters support an effort to coordinate the timing for implementation of new PSD requirements.

 One industry commenter (0043) recommends that state s with their own PSD prog rams and states implementing the federal program should have approximately the same implementation schedule.106

 One industry commenter (0026) urge s the Agency to adopt a national implementation date in order to provide consistency across the state s. The c ommenter (0026) urge s the Agency to hol d off implementation of state programs administrated under P art 52 PSD regulations in order to provide a uniform and consistent national approach.

Response:

As explained in section 6.1 of this document, w e have c oncluded that it is most appropriate to follow the plain language of section 166(b) of the Act

, which calls for a 1

- year effective date for implementing new increments developed under section 166(a) of the Act. We

agree that there is some merit to coordin ating the implementation commencement date of both the federal PSD program and individual state PSD programs. However, one problem is that it would be difficult to predict exactly when individual state programs will be approved. We have decided to begin implementing the revised federal PSD program as set out previously in our introductory discussion of this issue in section VIII.A of the preamble to the final rule . That is, the revised regulations at 40 CFR 52.21 will become effective 60 days after the p ublication of th e final rule in the Federal Register. This will allow EPA or the delegated state agency to begin using the SILs and SMC for PM 2.5 on that date, as described in section VIII.C of th e preamble to the final rule

. However, the date establishe d in the regulations for the trigger date will ensure

that the PM

2.5 increments do not become effective for 1 year, consistent with section 166(b) of the Act, and that the minor source baseline date cannot be established until the PM 2.5 increments

become e ffective

. With the 1

- year delay in implementing the new increments, which primarily affects the implementation of the federal PSD program for PM 2.5 , there will be less of a gap in implementing the new requirements in the federal program as compared with t he state programs than if the increments were to become effective immediately in the federal PSD program. T he “trigger date” and “major source baseline date” for PM 2.5 increments will be the same fixed dates for both the federal program and all state PSD programs.

In accordance with section 166(b) of the Act, we are requiring states to submit revised implementation plans to EPA for approval within 21 months of the date of publication of the final rule in the Federal Register . Section 166(b) of the Ac t also specifies that we must approve or disapprove these revisions within 25 months of publication ( that is, 4 months from the statutory deadline for SIP submittal). We regard these statutory deadlines as maximum allowed timeframes for action. Moreover, we do not believe that the Act restricts our ability to approve SIP revisions requested by a state at any time before these deadlines. In this final rule, we are amending the regulatory provisions at 40 CFR 51.166(a)(6)(i) to articulate the deadline set forth by the statute for the SIP submittals involving the PM 2.5 increments pursuant to section 166(a) of

the Act.

EPA does not expect that states will revise their SIPs and submit them to EPA for approval prior to the effective date of the PM 2.5 incremen ts in this final rule, which is the date one year after the date of publication of this final rule in the Federal Register. Therefore, there is likely to be a period of time when state laws will not require PSD applicants otherwise subject to PSD for PM

2. 5 to complete an increment analysis for the PM 2.5 increments, even though the

PM 2.5 increments, major source baseline date, and trigger date have been established as a result107

of this final rule. Similarly, it is not clear whether states will have the auth ority to consider such applicants as having triggered the minor source baseline date during the interim period between the national trigger date for the PM 2.5 increments and the date their revised PSD rules containing the new PM 2.5 increments and relevant baseline dates become effective.

The EPA does not intend to prescribe the implementation timeline for state programs; rather, each state will need to determine how increment consumption and the setting of the minor source baseline date for PM 2.5 will o ccur under its own PSD program. Nevertheless, regardless of when a state begins to require PM 2.5 increment analyses and how it chooses to set the PM 2.5 minor source baseline date, the emissions from sources subject to PSD for PM 2.5 on which

construction c ommenced after the date this final rule is published in the Federal Register (the major source baseline date) will consume PM 2.5 increment and must be included in increment analyses occurring after the minor source baseline date is established for an area under the state‟s revised PSD program.



### 6.2.3 Other Comments on Implementation

Comment:

One state / l ocal a gency commenter (0019) states that EPA should impose a requirement similar to the one it imposed under the PM 2.5 nonattainment provisions on April 5, 200 5, where EPA used applicable EPA regulations (Appendix S of 40 CFR p art 51) in the transition period

between the effective date of the rule and the state SIP submissions. The commenter note s that

for state s with appropriate regulations, EPA urged the use of existing PM 10 nonattainment provisions to address PM 2.5 nonattainment requirements. The commenter suggests that EPA should use similar approaches and time frames for the implementation of the PM 2.5 PSD requirements. The commenter believe s that any fur ther delays in the implementation of the

PM 2.5 increments or the NSR rule are contrary to the intent of A ct per the 1997 PM 2.5 NAAQS.

One state/local agency association commenter ( 0018) similarly encourages EPA to impose mandatory requirements that would provide for EPA PM 2.5 PSD regulations to serve as a backstop during the transition period between the effective date of EPA regulations and completion of the state SIP submissions and adoption process.

Response:

As one commenter notes, EPA currently do es not have a rule comparable to the Emissions Offset Interpretative Rule (40 CFR part 51, Appendix S) to provide an interim means for states to implement the PSD requirements in advance of an approved PSD program for PM 2.5 in their SIPs. The EPA‟s “backs top” rule is contained in 40 CFR part 52, where EPA has established a federal PSD program to be implemented in states with SIPs that lack an adequate state PSD program. However, that program cannot be used as an interim implementation measure, by either EPA or a state agency, for SIP

- approved programs that are in the process of being revised to address new PSD requirements. The EPA first would have to make a finding that the state rule is deficient in order to impose those part 52 PSD program requirement s on a state that currently has a SIP

- approved PSD program. The EPA is giving consideration to a108

part 51 PSD program similar to the existing Interpretative Rule in Appendix S and may take some action in the future. In this rule, however, no final decisio n has been made and no action is being taken.



### 6.3 Comments on Timing for the Revocation of the PM 10 

### Increment s

Comment:

One state/l ocal a gency (0015) support s the proposal to revoke the PM 10 annual increment in conjunction with the commencement of the PM 2 .5 increment sy stem under the p art 51 and

p art 52 PSD regulations. A second state/l ocal a gency (0022) similarly agrees with the proposal

to revoke the PM 10 annual increment from any SIP on or after the date EPA approves the SIP for

PM 2.5 increments. (The second commenter is silent regarding the federal p art 52 PSD program.)

One state/l ocal a gency (0033) does not support specification of a fixed PM 10 increment revocation date at this time. The commenter (0033) explain s that this date depends upon too

ma ny other factors whose time impact is unknown.

One i ndustry commenter (0016) states that if it is necessary to delay withdrawal of the

PM 10 PSD increment (and SILs and SMC ) to allow for the orderly development, integration, and public availability of PM 2 .5 emissions inventory data, the commenter would support such a delay

. [This commenter argues that the proposed effective dates for the final rules for PM 2.5 increments are unrealistic, arbitrary

, and capricious , given that the foundation of the PM 2.5 PSD program is emissions inventory data and that many areas have insufficient and inaccurate data (see

Section 6 .1 of this document).]

Response:

As discussed in Sections 2 and 3 of this document, the PM 2.5 increments in the final rule are based on propose d Option 1, the “contingent safe harbor” approach under section 166(a) of the Act, and we are taking no final action on our proposal to revoke the annual PM 10 increments

at this time. We also explained our position that the PM 10 increments cannot be revok ed because they are statutory increments set forth as numerical limitations in the Act itself. Thus, the potential timing of such a revocation is no longer at issue, and no further response to these

comments is warranted at this time

.



### 6.4 Comments on a Transi tion Period for Permit Applicants

Comment:

Two state / l ocal agency commenters ( 0015 , 0022 ) support the proposal to give state s the discretion to continue the existing PM 10 increment program or to begin implementing the new

PM 2.5 increment programs during the transition period. One of t he se commenter s (0015) states
that it is unclear how the implementation of the new PM 2.5 increment program would be federally enforceable during the transition period.109

One i ndustry commenter (0026) urges that we retain t he exemption for permit applications submitted before the implementation date of the new increment regulations from having to transition to the new program that EPA has allowed in past programs. The commenter

asserts that where a permit application has al ready been submitted and deemed complete, the applicants must be allowed to continue the permit process under existing regulations, and urge d EPA to explicitly clarify this in the final rule.

Another i ndustry commenter (0043) states that it is reasonable to allow states a choice between using PM 10 or PM 2.5 incre ments during a transition period involving SIP approval, where applicable. This commenter also indicates that transition periods with a mixture of both

PM 10 and PM 2.5 requirements should be avoid ed, even if PM 2.5 implementation must be delayed

be several months

.

Response:

During the time since the proposal of this rule in 2007, we have reconsidered the need for the proposed transition period in the federal PSD program to effectively implement t he PM 2.5 increments. In light of the importance of preventing significant deterioration of PM 2.5 air quality and the amount of time that has passed since the initial promulgation of the PM 2.5 NAAQS, we do not believe that further delay is warranted. We e xpect that most permits issued after the effective date of the increments in th e final rule, i.e., 1 year from publication of the final rule in the Federal Register, will be from sources that submitted their PSD applications after the major

source baseline date for PM 2.5 , which is defined as the date of publication of this final rule, so that they will be increment

- consuming sources. Therefore, when these sources apply for their PSD permits, they will have had significant advance notice of when the new inc rements will become effective, i.e., 1 year from the date of publication of this final rule. The review and permitting of permit applications submitted prior to the publication date of this final rule should generally be completed prior to the effective d ate of PM

2.5 increments and thus effectively have a transition period of 1 year to complete processing.



### 6.5 Comments on Whether SILs and SMCs Should Be Mandatory Program Elements

Comment:

One state/local agency (0033) believe s SILs and SMCs should not be a required element

of the SIP.

Another state/local agency ( 0015 ) believes that EPA has the authority to include SILs and SMCs as minimum program elements per the opinion set forth in Alabama Power v. Costle

. The

commenter add s that the EPA Environment al A ppeals Board has affirmed EPA’s interpretation of the Act to allow EPA to evaluate the significance of a source’s impact when determ ining
whether it would ―cause or contribute‖ to a NAAQS or increment violation under s ection 165(a)(3) of the Act.‖ In Re: Prairie State Generating Company , PSD Appeal No. 05

- 05, slip op. at 139

- 144 (Aug. 24, 2006).110

Three industry association commenters ( 0032, 0035 , 0037 ) state that SILs and SMCs should be mandatory elements of the PSD program. One of these commenters (0032 ) believes

that the SILs and SMC provide an important way for sources to show that there is not an adverse impact without conducting expensive modeling. Another of the commenters (0035) believes that modeling PM 2.5 (or any other pollutant) without using s creening models with SILs and SMCs is

so unreasonable that EPA must require that state s adopt the SILs and SMCs to meet the Purpose

clause of the A ct

, which requir es a balancing of environmental and economic considerations.

The commenter also argues that s ectio n 116 of the Act, which allows state s to be ―more stringent‖ absent state law that provides otherwise, does not authorize state s to be irresponsible in the use of their air quality resources.

Another of the industry association commenters ( 0037) st ates that the increment, SILs

, and SMC need to be adopted as a single regulatory approach because the SILs and SMC define when additional work is needed to ensure that PSD requirements, such as maintaining adequate

increment are met. The commenter stresse s the importance of sources having the ability to use screening models to show they will not have a significant impact and that modeling is futile where the impact is below the measurement sensitivity of the monitor. The commenter claim s that there is sim ply no reason for sources to be placed in the position of conducting expensive modeling that can delay a project when it is unnecessary from an air quality perspective.

Response:

In the 2007 NPRM, we explained our position that SILs and SMCs are not min imum required elements of an approvable SIP. While these de minimis values are widely considered to be useful components for implementing the PSD program, they are not absolutely necessary for the states to implement their PSD programs. That is, states c an satisfy the statutory requirements for a PSD program by requiring each PSD applicant to submit air quality monitoring data and to conduct a comprehensive air quality impacts analysis for PM 2.5 without using de minimis thresholds to exempt certain source s from such requirements. Because the de

minimis values for PM 2.5 (and other pollutants) are not mandatory elements, we proposed not to establish specific deadlines for submitting revisions to incorporate the specific values for PM 2.5 into SIPs.

We ag ree that the SILs and SMCs used as de minimis thresholds for the various pollutants are useful tools that enable permitting authorities and PSD applicants to screen out “insignificant” activities; however, the fact remains that these values are not require d by the Act as part of an approvable SIP program. We believe that most states are likely to adopt the SILs and SMCs because of the useful purpose they serve regardless of our position that the values are not mandatory. Alternately, states may develop mo re stringent values if they desire to do so. In any case, states are not under any SIP

- related deadline for revising their PSD programs to add these screening tools.111



## 7 Comments on Statutory and Executive Order Reviews

7.1 Comments on Review under the Unfunde d Mandates Reform Act

Comment:

T wo i ndustry commenter s (0024, 0043 ) and two industry association commenters ( 0014, 0046) express concern that EPA has dramatically underestimated the impact of these regulations on the regulated community. The commenters believe that the cost impact could exceed the threshold of $100 million in any 1 year that triggers additional review under the Unfunded

Mandates Reform Act.

Two of these commenters ( 0024 , 0046 ) focus on the costs of source testing for PM 2.5

. One (002 4) states that, although the proposed rule adds a relatively small number of new requirements to the existing permit requirements

, EPA is simultaneously requiring (through the implied need for source knowledge) sources to test for PM 2.5 emissions when ther e exists no qualified method for testing stationary sources. The commenter (0024) believes that when such a method is finalized that it will be neither simple nor cheap

, and that such testing will cost many 10’s of thousands of dollars with no demo nstrabl e benefit to air quality. The second of these commenters (0046) also expresses the opinion that source testing alone could exceed the threshold, and encouraged EPA to revisit the cost impacts of the proposed rule and consider regulatory alternatives.

Th e other two commenter s ( 0014, 0043) express more general concerns about the cost impacts of the proposed rule. One of these commenters (0043) states that the cost burden on each facility will be significant and that the overall impact on industry will be significantly greater than $100 million , with the proposed options with lower values requir ing incrementally

more analysis and more permit effort, subjecting more sources to BACT control, and requiring

more modeling and more ambient air monitoring. The se cond of these commenters (0014)

asserts that gathering 1 year of baseline PM 2.5 data and doing the modeling for PM 2.5 for any facility could easily cost $20,000 to $30,000 or even more

, and pointed out that if 5

, 000 facilities do PSD permitting the cost wo uld be over the $100 million threshold. T his commenter (0014) urges EPA to do a cost

- benefit analysis.

Response:

We believe that the commenters‟ claims that we have dramatically underestimated the impact of this final rule on the regulated community ar e incorrect . Clearly, there is a cost associated with the testing of individual sources to generate needed information on PM 2.5 emissions. Similarly, there are costs associated with the modeling and air monitoring that will

need to be done to meet the re quirements for ambient impacts. Nevertheless, the need for such data does not stem solely from this rule, but from the series of EPA regulations that have been issued to meet the requirements associated with implementing the PM 2.5 NAAQS. This includes

th e requirements associated with the 2007 Clean Air Fine Particle Implementation Rule, the

2008 PM

2.5 NSR Implementation Rule, as well as the forthcoming PM Test Methods Rule. Thus,112

we believe that it is inappropriate to link to this particular rule the bur dens described by the commenters (source testing for PM 2.5 emissions, subjecting sources to BACT control and requiring more modeling and ambient air monitoring). Moreover , with the promulgation of the new SILs and SMC for PM 2.5 in this final rule, sources will have important screening tools that can be used to help to reduce the costs associated with implementing the various PSD/NSR requirements for PM 2.5 . Thus, there will be fewer situations where modeling and monitoring

must be done than would be the ca se in the absence of these tools.



### 7.2 Comments on Review under Executive Order 13211: Actions that Significantly Affect Energy Supply, Distribution, and Use

Comment:

One i ndustry association commenter ( 0014) disagree s with EPA’s argument that this

action will cause no significant energy impact s, asserting that until modeling factors are determined and modeling actually done

, EPA has no idea what the impacts will be. The

commenter state s that it is very possible that increment under these very low levels c ould easily already be consumed or be so close to it that no more coal development or power plant development could occur , for example in the Powder River Basin

. The commenter concluded

that the impacts could be very significant and that EPA should be req uired to address this.

Response:

Although the commenter suggests that the new PM 2.5 increments could have significant energy impacts with regard to coal development or power plant development , no specific information was provided to convince us that suc h significant impacts will actually occur. In order for an energy project to be prevented under the PSD program, the project‟s emissions must be shown to cause or contribute to a violation of a NAAQS or PSD increment. Even where modeling shows that a PM 2 .5 violation may occur, it must further be shown that the project‟s proposed emissions will cause or contribute to the modeled violations. The required analysis

involves a case

- by

- case determination that is difficult to make in the abstract because of the importance of knowing the specific location, source design, and meteorological conditions that interact as part of the source impact analysis that must be completed for permit approval.

In addition, the commenter appears to imply that the PM 2.5 incremen t may already have been consumed by other sources in the areas where energy projects seek to locate. However, under the final rule, new baseline dates will be established for PM 2.5 , and no PM

2.5 increment has been consumed in any area.113



## 8 Other Comments on the Proposed Rulemaking

8.1 Comments on Secondary PM 2.5



### 8.1.1 Comments on Inclusion of Secondary PM 2.5 

### in PSD Modeling Analyses

Comment:

Several commenters express concern over the lack of mention of secondary PM 2.5 formation in the proposal and indicate that th e final rule should address whether secondary PM 2.5 is to be included in modeling analyses for PM 2.5 . The commenters suggest a range of courses for the handling of secondary PM 2.5 as summarized below.

In identical comments, two t ribal commenters (0041, 0049) state that secondary particles, derived from the oxidation of primary gases such as sulfur and NO

x , should be taken into account for all analysis and modeling in Class I and Class II areas. The t ribal commenters note that EPA has acknowledged that t he secondary pollutants contribute a large portion of total

PM 2.5 . The commenters add that secondary sulfate and nitrate aerosols are strong light

scatterers, which is important for Regional Haze analysis and the analysis of permits that could

affect Clas s I areas. The commenters also note that the inclusion of secondary particulates is important for Class II areas where sources are clustered , such as in northeast Minnesota, and the accumulation of these pollutants could create issues for the health and w elfare of the environment and the people.

Two state/local agency association commenters ( 0018, 0021) state that the presumed

norm in a Class II PM 2.5 increment analysis should be the exclusion of secondary PM 2.5 because

most Class II modeling addresses n ear

- source impact with short travel distances and minimal

time for sulfate and nitrate formation. The se commenter s add, however, that if a permitting agency believes that contributions from secondary particulate formation may be important

, secondary PM 2.5 should be included in the Class II air impact analysis.

The same state/local agency association commenter s further state that the presumed norm

in most Class I PM 2.5 increment analysis should be the inclusion of secondary PM 2.5 because

most Class I anal yses involve long

- range transport and there is ample time for secondary sulfate and nitrate formation, which can become a significant fraction of a source’s total PM 2.5 impact.

The commenter s add that the permitting authority is responsible for determini ng whether the

contribution of secondary particles is or is not significant.

One state/local agency commenter (0025) recommend s that EPA develop a protocol for determining which sources must consider secondary species in their evaluations against PM 2.5 S ILs and increments in Class II areas. The commenter suggest s a protocol whereby a source’s secondary species are considered against the PM 2.5 SILs, increments

, and NAAQS if (1 ) the source’s maximum potential emissions of SO 2 emissions exceed 100 tons per year , or (2 ) the

source’s SO 2 impacts exceed the SO 2 SILs of 5 μg/m 3 (24

- hour) and 1 μg/m 3 (annual). The114

commenter also recommend s that EPA include secondary species in evaluations against PM 2.5 increments, SILs , and NAAQS in Class I areas.

One federal agency commenter (0044) state s that the rule should make clear that secondary species are to be included in the PM 2.5 increment consumption calculation. The commenter explain s that , given the long

- range transport common to most Class I analyses, there

is ample time for secondary sulfate and nitrate formation , and that such secondary species can become a significant fr action of a source’ s total PM 2.5 impacts.

Without explicitly expressing a preference for or against inclusion, o ne state/local agency

co mmenter (0028) state s that EPA should address the treatment of secondary particulates (and

condensable s) in testing, modeling, and all the v arious aspects of the program.

One s tate/ l ocal a gency commenter (0022) does not believe that secondary particulat e formation of PM 2.5 should be included in any Class I or Class II increment or SIL analyses because of concerns with the current models. The commenter point s out deficiencies with the atmospheric chemistry algorithms built into CALPUFF [Note: this is dis cussed further in the

next section ] , which is the model used for far

- field Class I modeling. The commenter also note s that Class II modeling is near

- field analysis and generally does not provide adequate residence time for secondary sulfate and nitrate fo rmation. The commenter add s that AERMOD, the regulatory model for near

- field analysis, does not include an atmospheric chemistry algorithm,

and that the use of CALPUFF for near

- field analysis (for which it is not recommended) raises the

same issues discus sed above for Class I analyses.

One industry association commenter (0037) interpret s the proposal not to include precursor emissions in increments, SILs

, or SMCs , and agreed with this presumed approach. The commenter argue s that including precursor emis sions would be inappropriate because the models of impacts and atmospheric chemistry related to formation of PM 2.5 are not sufficiently developed to allow sources to conduct appropriate analyses for permit applications. The

commenter add s that the increme nt levels do not take into account precursor contributions so additional analysis would be needed to include precursors in any increment issued by EPA.

Another industry association commenter (003 2 ) simply notes that models to predict PM 2.5 concentration due to precursor emissions from single source have not been developed and, while a regional model is available, it appears unsuitable for single source analyses. The commenter adds that this lack of models makes PSD impact analyses difficult if not imposs ible.

Response:

The EPA recognizes the significant contribution to ambient PM 2.5 concentrations that precursor emissions can make. The foundation for regulating PM 2.5 precursors under PSD were

established in the 2008 PM 2.5 NSR Implementation Rule. 73 FR 28321. Unfortunately, t he technical tools needed to complete a comprehensive analysis of all emissions (i.e., including secondary emissions) that contribute to ambient concentrations of PM 2.5 are only in the developmental stage . N

evertheless, we belie ve that the final rule for PM 2.5 increments, SILs, and

SMC adequately considers all emissions that contribute to ambient PM 2.5 concentrations (the115

levels of the increments, SILs

, and SMC are all intended to account for secondary emissions

contributions whe n it is feasible to do so). (See also the r e s ponse at S ection 4.2 of this document for further information about the inclusion of precursor emissions for the PM 2.5 SILs.) I

t would be inappropriate to restrict the regulatory language in such a way that fu ture regulatory amendments would be required to enable the inclusion of precursor impacts in the PM 2.5 analysis as the necessary technical tools become available. Estimating techniques are being developed that we anticipate will be able to be applied to t he PM 2.5 analysis in the near future, which could not be required if the regulatory language precluded them until being revised

.



### 8.1.2 Comments on Models for Secondary PM 2.5

Comment:

One state/local agency commenter (0022), one state/local agency associati on commenter ( 0018), one industry association commenter ( 0035), and one federal agency (0044) provide comments on CALPUFF, the regulatory model for far

- field modeling of PM 2.5 . All these commenters urge EPA to improve the atmospheric chemistry algorithms in the CALPUFF model

to better estimate PM 2.5 concentrations.

The state/local agency commenter (0022) states that the chemical transformation

mechanisms built into the CALPUFF model have been described as dated and inadequate (R. Morris, 2005, Review of “Protocol for the Application of the CALPUFF Model for Analysis of Best Available Retrofit Technology,” Revised Draft prepared for VISTAS, September 20, 2005 )

. The commenter explain s that n itrate and sulfate formation is believed to be overestimated in co ld

conditions because the default chemistry scheme (MESOPUFF II) was developed using temperature points that were all above 50°F (T. Moore, 2005, Regional Modeling for Stationary Source Control Strategy Evaluation, WESTAR Conference on BART Guidelines and Trading)

, while in

- cloud formation of sulfate may be greatly underestimated because it is approximated using relative humidity to simulate the effect of cloud water. The commenter also expresse s

concern that the inclusion of secondary particle formation i n PM 2.5 increment analyses could lead

to errors due to imbalances between emitted pollutants and background ammonia levels . As an example, the commenter posits a modeling domain that includes 4,000 tons of NO

x and SO 2 emissions, but only 500 tons of the S O 2 are increment

- consuming emissions. The commenter notes that only 500 tons of SO 2 would be input into the model, and excess nitrate formation could be predicted because of the relative lack of both sulfate formation and scavenging of the background ammo nia. As a result of these types of problems, the commenter does not believe that precursor emissions should be considered in the Class I or II increment and SIL analyses for

PM 2.5 until improvements are made in CALPUFF’s atmospheric chemistry algorithms a nd a protocol is d eveloped for modeling increment

- consuming emissions

.

The state/local agency association commenter ( 0018) states that EPA should improve the atmospheric chemistry algorithms in CALPUFF with respect to secondary formation of sulfate

and n itrate species

, but should allow the use of the current chemistry algorithm in CALPUFF as a screening tool for sulfate and nitrate formation in Class I and Class II increment analyses, SILs, and NAAQS analyses for PM 2.5 . The commenter adds that the same i mproved atmospheric chemistry algorithm should be added to the EPA guideline model AERMOD.116

The industry association commenter ( 0035) notes that, al though the proposal suggest ed

that CALPUFF is acceptable for purpose s of PM 2.5 modeling , the National Acade my of Sciences has stated, ―B ecause the primary focus of monitoring strategies has been on documenting NAAQS attainment, there is little motivation to develop methods to measure ambient concentrations that are substantially below the standards. Such measu rements are needed to provide critical data for understanding atmospheric processes and providing input for air quality
models.‖ ( National Research Council , 2004

, Air Quality Management, pp. 236

- 237

. ) The commenter believes that, ideally, EPA would inves t in such models before requiring cumulative air impact or increment analyses of PM 2.5 for NSR purposes, but realizing that this is not possible, the commenter urges EPA to wait to finalize this rule.

Without specifically mentioning CALPUFF, another stat e/local agency association commenter ( 0021) encourage s EPA to undertake scientific study and analysis of secondary particulate formation

. The commenter urge s EPA to develop an understanding of the far

- field impacts of sulfates and nitrates, and to underta ke a rulemaking addressing SILs for them and other PSD tools as appropriate

.

Response:

We acknowledge the concerns regarding the limitations of the chemical transformation

mechanisms available in the current EPA

- approved version of the CALPUFF model. We also

note that while CALPUFF is mentioned in s ection 6.2 of Appendix W for visibility, where secondary PM

2.5 plays a role, the chemistry options within CALPUFF have no regulatory status for NAAQS or increment assessments. We also acknowledge the concer ns raised by one of the commenters regarding the additional challenges involved with the inclusion of chemical transformation within the context of an increment modeling analysis due to the complex interactions of emissions from baseline sources, increment

- co n suming sources, and increment

expanding sources. Guidance will be developed to address these issues as the technical tools needed to conduct such analyses become available.



### 8.2 Comments on Inclusion of the Condensable Fraction of PM 2.5 

### in PSD Modeling A nalyses

Comments Supporting Inclusion of Condensables:

Three state/local agency commenters (0019, 0022, 0025), two state/local agency

association commenter s (0018, 0021), two t rib al commenters (0041, 0049), and one federal agency (0044) support the imme diate inclusion of condensable PM 2.5 emissions in PSD modeling analyses. However, these commenters vary as to which types of analyses they specifically list for inclusion condensable PM emissions, as follows:

 Six commenters (0018, 0019, 0021, 0022, 0025, 0044) specifically state that condensables should be included in increment analyses.

 Five commenters (0018, 0019, 0021, 0022, 0025) also specifically state that condensables should be included in SIL analyses.117

 Three commenters (0018, 0019, 0025) also spec ifically state that condensables should be included in NAAQS analyses.

 One commenter (0019) also specifically states that condensables should be included in SMC analyses.

 Two commenters (0041, 0049) do not specify, but state that condensable should be

incl uded in any analysis or modeling in Class I and Class II areas for the effects of Regional Haze and health related concerns.

One of the state/local agency commenters ( 0019) note s that the 2007 Clean Air Fine Particle Implementation Rule identified certai n concerns with the stack measurement techniques

for condensables which EPA intends to address over the next few years. 72 FR 2058 6 , April 25, 2007. The commenter adds, however, that these concerns have been misconstrued and misrepresented with respect t o the development of emissions inventories and NAAQS compliance demonstrations. The commenter quotes the Clean Air Fine Particle Implementation Rule preamble, which stated, ― For the purpose of developing emissions inventories and

attainment demonstrations , the final rule reflects a requirement to account for significant

contributions of direct PM 2.5 emissions, both filterable and condensable PM 2.5 ‖ and ―States should continue to describe the impacts of baseline emissions and develop future air quality

stra tegies using information available on direct PM 2.5 emissions including condensable PM. ‖

72 FR 20652. Thus, the commenter believes that EPA has made a very clear distinction between developing emission limits for permits versus the NAAQS demonstration req uirements. On this basis, the commenter asserted that for the purposes of the proposal on PM 2.5 increments, SILs

, and SMCs, which are solely dependent on emissions estimates and model calculations of impacts from these estimates, EPA must require the incl usion of the condensable fraction in the determination of emissions and for impact calculations for comparison to these numerical limits, in addition to NAAQS compliance. The commenter urge s EPA to make this clarification in the requirements of the final PM 2.5 NSR rule and warns that without the consideration of the condensable fraction in the emission and impact calculations, EPA will only perpetuate its current inadequate policy of addressing PM 2.5 using PM 10 r equirements.

Two of the commenters (0018, 0025) point out that some air agencies already require condensable emissions to be included in air quality modeling. Another of the commenters (0022) predicates support for inclusion of condensables on the availability of EPA test methods.

In identical comments, the t wo t ribal commenters (0041, 0049) state that excluding condensables would disallow aerosols and precursors to other pollutants that greatly contri bute to the composition of PM 2.5 and can be toxic in nature. The commenter s (0041, 0049) note that the condensable portion of PM 2.5 is a significant contributor of total PM 2.5 emissions since condensables primarily fit into the PM 2.5 size range.

Comments Opposing Inclusion of Condensables:

Two i ndustry a ssociation commenter s ( 0035, 0037) asser t that EPA should either not

include condensable s in the increment and SILs, limiting them to filterable PM 2.5 , or should defer this rulemaking until an adequate, reliable, commercially

- viable test method has been promulgated to include condensables. A thi rd i ndustry a ssociation commenter ( 0032 ) simply118

contends that PM 2.5 increments and SILs should be based only filterable PM 2.5 emissions and not

include condensables. The se commenter s sta te that in the absence of an accurate test method,

one cannot charact erize air emissions correctly, and, without a correct characterization of emissions, one cannot complete the air dispersion modeling needed to determine increment consumption for condensable PM 2.5

.

An industry commenter (0016) similarly points out that c ondensable s cannot be accurately measured by any existing EPA

- approved stack testing method . Given this fact, the commenter believes that EPA must not intend the scope of these regulations to extend to condensables. Moreover, the commenter states that if condensables are intended by EPA to fall within the scope of these regulations, an EPA

- approved accurate stack testing methodology is a prerequisite for the establishment of local PSD area b aselines and other critical PSD parameters.

The commenter assert ed that it is premature, arbitrary

, and capricious for EPA to finalize regulations with which the regulated community cannot comply. The commenter indicates that the existing inaccurate testing methodology negatively affects state and local efforts to bui ld an

accurate PM 2.5 emissions inventory and precludes accurate modeling of proposed new PM 2.5 emissions for purposes of SIL and PSD increment determinations. The commenter adds that the

use of a ratio of PM 2.5 to PM 10 approach to determining emission rat es for new sources is legally

unenforceable.

One of the industry association commenter s (0035) indicates that finalizing the rulemaking based on filterable particulate matter would, in the interim, provide a reasonable basis for predicting air quality an d increment impacts. The commenter believes this is particularly true if EPA uses a ratio approach (the equivalent substitution approach discussed in the proposal preamble) and if the ratio were based on the PM 10 /TSP increments and SILs, since

these value s were based entirely on filterable particulate.

Another of the industry association commenter s (0032) expands on the issue of ratios used in the rulemaking, indicat ing that for both increments and SILs the 2007 NPRM relied primarily on using ratios to t he PM 10 increments/SILs, which were themselves based on a ratio to the TSP increments/SILs. The commenter interprets the proposed rules to define the PM 2.5 increments and SILs such that the impact is determined by measuring ―direct‖ emissions of

PM 2.5 , wh ich includes condensable emissions. By using a ratio that reaches back to the TSP increment/SILs, the commenter believes EPA is relying on TSP increments/SIL s using test methods that did not include condensables. Thus, the commenter contends that EPA has

included in the direct PM 2.5 emissions a large portion of emissions that were not counted in the

value from which it conduct ed its ratio process. The commenter believes that that if the condensable fraction had been considered in the TSP increments, the PM 10 increments would have been set higher, possibly higher than the TSP increments, and this error is propagated (and perhaps compounded) by using the PM 10 increment as the basis for a ratio to establish a PM 2.5 increment. The commenter contends that g iv en the lack of reliable, commercially viable, and replicable test methods for PM 2.5 condensables, the most prudent and technically and legally defensible approach is to use a ratio directly to TSP (there by avoiding propagating errors in the

PM 10 values) an d to only include the filterable portion of PM 2.5

. The commenter asserts that t he approach of using a ratio but not taking into account that the TSP method did not address condensables is arbitrary and cannot reasonably be termed an ―equivalent substituti on‖ under119

s ection 166(f) of the Act, and that establishing an increment or SIL under the section 166(a) safe harbor approach based on ―direct‖ emissions of PM 2.5 without considering the amount of those emissions, or the availability and reasonableness of c ontrols

, is also unfounded.

Referring to the association’s comments on the earlier Proposed Rule to Implement Fine Particle NAAQS ( EPA

- HQ

- OAR

- 2003

- 0062

- 0121/0121.1 ), the third of the industry association

commenter s (0037) stat e s that to include condensab le PM 2.5 , EPA needs to finalize the test
method for condensables and then re

- propose to receive comments in light of that final method. (Commenter 0032 also advocates this approach.) C ommenter 0037 encourage s the Agency to use the final improved Method 2 02 to conduct analyses on an appropriately sized sample of sources to determine the impacts of the current proposal and offer alternatives in light of this testing. The commenter explain s that this approach is necessary because the current PM 10 increment simply does not characterize condensables accurately.

T wo of the industry association commenter s ( 0032, 0037) also express concern that EPA has not analyzed how many sources would exceed the increment, whether controls are available

to reduce emissions to meet the increment, or the cost

- effectiveness of such controls, as it did

when it established the PM 10 increments. One of t he commenter s (0037) warns that there is a real question as to whether controls would be available to reduce the emissions, sinc e the controls that work well for filterable PM may not be applicable to condensables. Th is commenter states that EPA should ensure that any rule it issues does not have the unintended consequence of halting modifications and new construction, and that wi thout this analysis, EPA and the public are unable to determine the effects of the rule. The second of these commenters (0032) notes that no impact analysis has been made available to the public for comment

, and that the Radian report that derived the PM 1 0 increments likewise has not been made available in the

docket. The commenter opines that the lack of information in the docket and appropriate analyses are important reasons that EPA should re

- propose and reconsider its approaches in this rulemaking.

O ther Comments on Inclusion of Condensables:

Without explicitly expressing a preference for or against inclusion, o ne state/local agency

commenter (0028) state s that EPA should address the treatment of condensable s (and secondary particulates) in testing, modeling, and all the v arious aspects of the program.

One industry commenter (0013) expresses support for EPA’s establishment of a transition period for condensables in the Clean Air Fine Particle Implementation Rule (72 FR 20652, April 25, 2007), and noted that this transition period was not addressed in this proposal. The commenter interprets this transition period, which extends until January 1, 2011, to apply to PSD modeling analyses so that condensables would not be use d in the determination of PS D increments and comparison of a project’s direct PM 2.5 concentrations with the SILs and the

SMC. In addition, the commenter believes that EPA should explicitly continue to provide technical support to s tates in establishing appropriate PM 2.5 emission lim itations, particularly in the transition period where the condensable portion of direct PM 2.5 is not required to be included.120

Response:

The above comments that either support or oppose certain actions associated with the regulation of condensable PM ra ise issues that are not relevant to this rulemaking , but that we are addressing through other rulemakings or policy decisions

. Th e final rule on PM 2.5 increments, SILs

, and SMC does not explicitly regulate the inclusion or exemption of

condensable PM. Th e final rule anticipates the inclusion of condensable PM as part of the PM 2.5 that will be counted against the PM 2.5 inc r ements , and that will be used to compar e source impacts of PM

2.5 against the ambient PM 2 .5 screening levels

– SILs and SMC.

The com ments express ing concern that EPA has not analyzed how many sources would exceed the increment, or whether controls are available to reduce emissions to meet the
increment, appear to suggest that EPA should consider loosening the increment values if

necess ary to ensure that economic growth will not be stymied. The EPA ‟ s longstanding interpretation is that the “ at least as effective ” language in CAA section 166(d) should be read as requiring increments at least as stringent as the statutory increments in C AA section 163. See

EDF v. EPA , 898 F.2d 183, 187 (D.C. Cir. 1990) (describing EPA ‟ s reading of the statutory language). The EPA ‟ s interpretation is supported by the applicable court opinions, which note that this reading “ is the most workable ” and “ well supported by the legislative history. ” EDF v.

EPA , 898 F.2d at 188. Although there is language in the opinions suggesting that the agency could consider a less stringent increment in light of CAA section 166(c) (see Environmental Defense v. EPA , 489 F.3d 1320, 1325 (D.C. Cir. 2007) (EPA must determine that the criteria

under section 166(c) do not call “ for a more, or a less, stringent standard. ” ) (quoting EDF v.

EPA , 898 F.2d 183, 189 (D.C. Cir. 1990) ) , the court's final analysis was clear that it was

rea sonable to conclude that the only deviation from the contingent safe harbor would be towards greater stringency. EDF v. EPA , 898 F.2d at 189 (stating that the court ‟ s reading of the statute is that EPA must first establish the contingent safe harbor incre ment under CAA section 166(d)

and then “ determine that the inquiry under subsection (c) does not require a more stringent

standard. ” )

Under a separate rulemaking ( the 2008 PM 2.5 NSR Implementation Rule published at

73 FR 28321 (May 16, 2008) , we allowed sources to temporarily exclude condensable PM from

consideration in permit action s under the PSD program or under nonattainment NSR until January 1, 2011, unless the applicable SIP otherwise required that such emissions be considered in the permit action f

or applicability and enforcement purposes. Thus, independent of this final rule for PM

2.5 increments, any permit issued on or after the January 1, 2011 sunset date will be required to address condensable PM.

The temporary exclusion for condensable PM for was designed to allow EPA time to

evaluate the existing test methods fo r measuring PM emissions and condensable PM emissions from sta tionary sources . Under a separate rulemaking, EPA has undertak en a re

- evaluation of

the existing test methods for mea suring emi ss ion s o f PM from stationary sources. In a 2009 notice of proposed rulemaking, EPA proposed amendments to Method 202 to revise the sample collection and recovery procedures of the method to reduce the formation of reaction artifacts

that could l ead to inaccurate measurements of condensable PM. 74 FR 12970 (March 25,121

2009). Th at rulemaking containing the revised test methods is expected to be finalized within the same timeframe as th e final rule for PM 2.5 increments, SILs

, and SMC.

Comment:

One industry association commenter (0032) indicates that EPA needs to reconsider the apparent underlying assumption that direct condensable emissions all convert to PM 2.5 within the

modeled area , which is a conservative assumption that tends to inflate a source’s potential impact. The commenter advocates that, s imilar to the approach taken for modeling NO 2 concentrations when nitric oxide ( NO ) is a portion of the emissions, EPA should allow for a

refinement that allows a deduction for a portion of the co ndensable plume that does not convert to fine particulate in the modeled area.

Response:

Condensable PM is considered to be a component of direct PM 2.5 emissions along with the filterable portion. It is our standard practice to include both the conden sable portion and the filterable portion as input data for direct PM 2.5 emissions in the model

, and to treat them collectively as a non

- reactive pollutant. The commenter provides no explanation as to why all of

the condensable PM should not be considered to convert to ambient PM 2.5 within the modeled area, since they are measured as condensable PM when they are released into the atmosphere from the stack

. We believe that the commenter may be confusing this with the fact that some precursor emissions may n ot undergo chemical transformation to form PM 2.5 within the distance defined for the modeling area.



### 8.3 General Comments on the Proposed Rulemaking

Comment:

One industry commenter (0016) allege s that EPA stated in the proposal preamble that secondary partic ulate matter acids primarily formed as a result of chemical reaction in the atmosphere are the intended focus of this action (citing 72 FR 54127, column 3), and that EPA is concerned exclusively with the adverse environmental impacts of these secondary par ticulate matter acids (citing 72 FR 54130

- 54132). The commenter goes on to point out

, nevertheless,

that the NPRM includes a list of industry groups by North American Industry Classification System ( NAICS ) code whose direct emissions are presumed to be su bject to the proposed PM 2.5 standards. The commenter urge s EPA to write the regulations in a more specific manner in order to clarify that emissions that lead to the formation of secondary acidic PM 2.5 are intended to be addressed, and other s are not.

Re sponse:

The commenter is mistaken in interpreting the 2007 NPRM to say that our intent in the

this rule making for PM 2.5 increments, SILs

, and SMC is to focus on secondary particulate matter acids primarily formed as a result of chemical reactions in the atmosphere. On page 54127122

(column 3) of the 2007 NPRM, we discuss the components of fine PM as part of our description of the health and welfare effects of PM 2.5 and simply say the following:

Major components of fine particles are sulfates, strong acid, ammonium nitrate, organic compounds, trace elements (including metals), elemental carbon, and water.

Elsewhere in the 2007 NPRM, we indicate that hygroscopic components ( particularly sulfates and nitrates) of fine PM make a disproportionate contribution to visibility impairment under high humidity conditions, but we do not state (nor did we intend to state) that such particles are “exclusively” responsible for visibility impairment or are the focus of the rulemaking (page 54130, at column 1). Similarly, portions of the discussion of welfare effects (pages 54130

- 54132) tend to focus on secondary particles because those particles are most relevant in identifying effects on such things as vegetation and ecosystems. Nevertheless, EPA‟s concern for the effect of directly emitted particles on visibility impairment is clearly stated on page 54129 (column 1).

Finally, on page 54128 (column 1), we state that “ [w]hile there remains uncertainty about the role and relative toxicity of various components of fine PM, the current evidence continues to support the view that fine particles should be addressed as a group for purposes of public health protection.” Hence, t h e final rule regulates fine particulate matter or PM 2.5 in all forms as it is emitted directly or formed from precursor gases in the atmosphere. Thus, there is

no reason to revise the final rule to limit affected sources only to those emitting secondary acid

PM 2.5

.

Comment:

One industry commenter (0024) requests that EPA withdraw the proposed rule , noting that there are many other programs currently underway that will pave the way for massive

reductions in PM 2.5 on a national basis. The commenter points out that programs such as the Clean Air Interstate Rule ( CAIR ) , NO

x SIP call, Acid Rain Program , controls for off

- road and

on

- road diesel engines, and mobile source controls will all be phased in over the coming years. The commenter believes that a more prudent approach to reducing PM 2.5 emissions and gaining

associated health benefits would be to rely on the cost effective application of regulation to these true sources of the problem.

Response:

The commenter apparently fails to recognize that that the Act

, at section 166(a), requires EPA to promulgate regulations to prevent significant deterio ration of air quality, including

increments or other measures, for pollutants for which NAAQS have been defined. Moreover, the PSD permit program is a statutorily

- based permit program as well, which requires proposed new major stationary sources and major modifications to existing major stationary sources to undergo preconstruction review as a prerequisite to being approved for construction. The PSD program exists in conjunction with other programs for the regulation of PM 2.5 emissions to provide for the requisite health and welfare protection associated with recognized air pollutants. Thus, even if some of the provisions in the final rule were permissive rather than mandatory,123

EPA believes that they are an important part of the overall program for all o f the reasons discussed in the preamble to the final rule, this response to comments, and elsewhere in the

record.

Comment:

Three commenters are concerned that the PM 2.5 /PM 10 ratio of 0 .8 we derived from the

― 2001 National Emissions Estimates by Source Categories ‖ could be misused in the future. They suggest that EPA make clear that this ratio is not to be used for purposes beyond the proposed increments, SILS, and SMC.

One i ndustry commenter (0026) note s that the ratio will differ for individual sources and from one area to another based on the composition of different sources in any given area. Th e commenter urged EPA to clarify that the 0.8 ratio should not be used broadly for other regulatory

purposes , and shou ld not be used subsequently to convert monitored and/or modeled PM 10 values

for individual locations to PM 2.5 values.

One industry association commenter ( 0029) urge s EPA to set limitations on the use of

that rat io for other purposes since EPA’s AP

- 42 C ompilation of Emissions Factors confirm s that the percentage of PM 10 that is likely to be PM 2.5 is not going to be 80 percent for all industries or for all sources within one industry. The commenter do es not suggest that EPA reconsider use of its proposed 0.8 multiplier in this rulemaking, but does req uest that EPA make it clear that use of such a multiplier would be appropriate only for purposes of helping to set nationwide threshold values in this rulemaking and not for other regulatory purposes.

One industry commenter (0020) contends that the ―one

- size

- fits

- all‖ approach based upon the aggregate ratio calculation is technically inaccurate and could cause problems in individual permitting cases where PM 10 data are available to be used in modeling demon strations but PM 2.5 emissions data are not available.

Response:

We agree with the commenters that the fraction of PM 10 that is PM 2.5 varies from area to area, industry to industry, and source to source. We did not see that as a problem in using the

rat io as part of a methodology for selecting PM 2.5 increments that would be affected by all types of sources. However, w e acknowledge that the ratio does not adequately account for PM 2.5 precursors that can contribute a significant portion of the ambient PM 2 .5 concentrations in an

area. While we have not reached any final conclusion as to whether the Option 2 equivalent substitution approach under section 166(f) is permissible under the Act, we acknowledge that use of the emissions ratio approach was problem atic as an equivalent substitution approach for the

PM 2.5 increments. Moreover, w e do not intend to apply the 0.8 ratio that we derived based on a large aggregation of point sources for other regulatory purposes, including the examples given by the commen ters

.