# Response to Comments on the D ata
R equirements R ule for the 1

- Hour Sulfur Dioxide Primary National Ambient Air

Quality Standard

U.S. Environmental Protection Agency Office of Air Quality Planning and Standards

Research Triangle Park, NC

August 4 , 2015i 

## Table of Contents

I. Introduction

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

II. Monitoring and Modeling to Satisfy the Proposed Rule

................................ ......... 11

A. Legal authority to require data by proposed schedule

................................ ...... 11

1. Proposal conflicts with and modifies the Clean Air Act (CAA)

.......... 11

2. Proposal bypasses section 107

................................ .............................. 13

3. Unclassifiable designations

................................ ................................ ... 14

a

. DRR nullifies the "unclassifiable" desig nation

b

. EPA should immediately designate areas unclassifiable

B. Legal authority to find that modeling satisfies the data requirements

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

1. Conflicts with the SO 2 NAAQS

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

2. State responsibility

................................ ................................ ................ 23

3. Historic use of modeling for designations

................................ ............ 25

a

. H istoric use supports modeling for designations

b

. Historic use does not support modeling for designations

4. Repeal of section 171(2)

................................ ................................ ....... 29

5. Rulemaking needed for use of modeling for designations

.................... 30

6. Court decisions on use of modeling for designations

........................... 31

7. Nonattainment area requiremen ts

................................ ......................... 33

C. Monitoring and/or modeling for designations

................................ .................. 34

1. Support option to model and/or monitor

................................ ............... 34

2. Support monitoring data use only

................................ ......................... 35

3. Do not support modeling to make attainment designations

.................. 37

4. Support modeling to make designations

................................ ............... 41

5. Rule text regarding monitoring preference

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

a

. S ection 51.1201

b

. S ection 51.1203(b)

6. Bias for modeling rather than monitoring

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

D. Considering all monitoring/modeling data

................................ ....................... 46

1. Do not support cons idering all monitoring/modeling data

................... 46

2. Support considering all monitoring/modeling data

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

III. Source Coverage and Emission T hreshold Options

................................ ................ 48

A. Options to identify sources for monitoring/modeling

................................ ....... 48 1. Emissions metrics for use in a threshold approach

................................ ....... 48

a

. Use of annual emissions

b

. Emission threshold approach 2. Threshold including population metric

................................ ......................... 50

a

. Support using a population threshold

b

. D o not support using a population threshold

c

. Other comments on population thresholdsii 3. Proposed o ption 1 (> 2,000/1,000 tpy )

................................ ................. 56

a

. Support option 1

b

. Do not support option 1

4. Proposed o ption 2 (> 5,000/2,000 tpy )

................................ ................. 58

5. Proposed o ption 3 (> 10,000/3,000 tpy )

................................ ............... 58

6. Other opt ions to identify sources

................................ .......................... 62

a

. Refine dispersion modeling

b

. 1,000 tpy

c

. 2,000 tpy
d

. 3,000/5000 tpy

e

. 10,000 tpy
f

. 10,000/1,000 tpy (Option 1&3 hybrid)

g

. 10,000/5,000 tpy
h

. 500 pounds per hour an d annual limits

i

. Sources with seasonal or monthly emission spikes j

. Multiple sources in close proximity that individually are below the threshold but whose combined emissions may violate the NAAQS

k

. Phased approach

l

. Statewide percent reduction tar get

m

. Factors other than population

n

. Do not codify the thresholds

7. State option

– identify additional sources

................................ ............. 75

8. EPA option

– identify additional sour ces

................................ ............. 77

9. State discretion to exclude above

- threshold sources...................... 79

IV. Data Requirements and Program Implementation Timeline

................................ . 82

A

. Comments on the overall timeline

................................ ................................ .... 84

1. The proposed timeline may be reasonable

................................ ............ 84

2. The proposed timeline is not achievable

................................ ............... 86

3. Monitoring and modeling timelines should be the same

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

B

. Requirement to s ubmit l ist of SO 2 s ources & e lection of m onitoring or

m odeling by Januar y 15, 2016

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

1. List by most recent year of emissions

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

a

. General

b

. Data sources

c

. Expected availability of data for specific years

2. List by average emissions over a three

- year period

.............................. 92

3

. Unrepresentative emissions

................................ ................................ .. 94

4

. Legal agreements or p ermit limits

................................ ........................ 95

a

. Enforceable limits by January 1, 2016

b

. Enforceable limits by January 1, 2017

c

. Enforceable limits effective by the attainment date

5. Electricity generation reli ability

................................ ......................... 103

6

. Enforceable limits in SIPs

................................ ................................ ... 104iii 7

. Election of monitoring or modeling

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

8

. Common area analytical approach

................................ ...................... 109

9

. Oppose submitting a list

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

1 0

. S ection 51.1203(a)

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

1 1

. Updated information on EPA’s preliminary list

................................ . 114

1 2

. Sources currently in a nonattainment area

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

1 3

. New/modified sources or existing sources initially below the threshold, subsequently exceeding it

................................ .................. 117

C

. January 15, 2016: Requirement to s ubmit m odeling p rotocols for s ources

c haracterized with m odeling

................................ ................................ ........... 118

1. Schedule

................................ ................................ .............................. 118

2. Section 51.1203(d)

................................ ................................ .............. 119

3. EPA oversight of modeling plans

................................ ....................... 120

4. Stakeholder participation in air agency characterization efforts

......... 121

D

. July 2016: Inclusion of SO 2 m onitoring n etwork m odifications to s atisfy

DRR

................................ ................................ ................................ ................ 123

1. Schedule is not feasible

................................ ................................ ....... 123

2. Schedule ne eds to be changed

................................ ............................. 124

E

. January 1, 2017: Requirement that SO 2 m onitors be o perational

................... 125

1. Time between monitoring plans due an d monitors operational

.......... 125

a

. Insufficient time

b

. Reasonable time frame

2. EPA oversight of monitoring plans

................................ ..................... 128

a

. Timing for EPA determination

b

. E liminate EPA approval of monitoring plans

3. Phased approach

................................ ................................ .................. 132

F

. January 13, 2017: Requirement to p rovide m odeling a nalyses

...................... 135

1. Schedule

................................ ................................ .............................. 135

a

. Schedule may be adequate

b

. Schedule is not feasible

2. EPA review of the modeling analyses

................................ ................ 137

3. Updated designation recommendations

................................ .............. 138

a

. Procedures

b

. March 24, 2011 designations guidance

c

. Guidance needed on boundaries and areas without significant SO 2

sources d

. Designations as "att ainment" or "unclassifiable/attainment"

4. Clarify terms

................................ ................................ ....................... 143

G

. December 2017: Intended d ate for i ssuance of f inal d esignations for m ajority of

c ountry

................................ ................................ ................................ ............ 143

H

. May 2020: Required c ertification of 2019 m onitoring d ata

........................... 144

I

. D ecember 2020: Intended d ate for i ssuance of f inal designations

................. 144

V. Technical Considerations

................................ ................................ ......................... 144iv

A. Monitoring

................................ ................................ ................................ ...... 144

1. Monitoring in part 58

................................ ................................ .......... 144

2. Move existing monitors to free up resources for the near

- source network

................................ ................................ ............................... 145

3. Network design

................................ ................................ ................... 146

a

. Guidance is needed

- maximum concentration site

b

. Guidance is needed

- number of monitors

c

. One monitor could be sufficient

d

. Evaluate the existing monit oring network

e

. Multiple monitors per source are needed

f

. Flexibility for states

4. Delayed monitoring

-- automatically move a source to the modeling pathway

................................ ................................ ............................... 154

a

. Support automatical ly moving a source

b

. Do not support automatically moving a source

5. Delayed monitoring

-- evaluate

................................ ............................ 157

a

. Allow a time extension

b

. Data gaps

6. Resourc es

................................ ................................ ............................ 161

a

. Costs

b

. Industry costs

c

. Funding by EPA

d

. Partnerships and third party monitoring

7. Monitor shut downs

................................ ................................ ............. 165

a

. Threshold below which moni tors may be shut down

b

. Multiple monitors

c

. Areas initially designated attainment

d

. Clean data

e

. State discretion

f

. Monitors in unclassifiable/attainment areas

g

. Near a source that shuts down or reduces emissions

h

. Statistical approach

i

. Do not shu t down monitors j

. Case

- by

- case monitor shutdowns

8. Post

- monitor shut down annual reporting

................................ ............ 174

a

. Option1: annual report as an appendix to the annual monitoring plan

b

. Option 2: indepe ndent annual submittal from the state

c

. Allow both Options 1 and 2

d

. Monitors with data under 50% of the standard

e

. Sunset provision for the reporting requirements

f

. EPA disapproval of a monitoring plan due to nonattainment

9. Emerging technologies

................................ ................................ ........ 180

B. Modeling

................................ ................................ ................................ ......... 180v 1. Emissions

-- actual data

................................ ................................ ........ 180

a

. Su pport use of actual data

b

. State option to model actual or allowable

c

. Intermittent sources

d

. Hourly rates for model input

e

. Revise the regulatory text

2. Emissions

-- most recent three years

................................ .................... 186

3. Emissions

-- accounting for enforceable limits

................................ ... 188

a

. Support accounting for enforceable limits

b

. Controls implemented and enforceable as of January 2017

c

. Emissio ns reductions after 2017

4. Background concentrations

................................ ................................ . 192

5. Stack height

................................ ................................ ......................... 196

6. Meteorological da ta

................................ ................................ ............ 197

a

. One year

b

. Five years

c

. Concurrent meteorological and emissions data

d

. Where meteorological data are available

e

. Multiple meteorological stations

7. Receptor plac ement

................................ ................................ ............. 200

8. Paired test

................................ ................................ ............................ 202

9. AERMOD, EPA's preferred near

- field dispersion model

............ 210

a

. Performs well

b

. Concerns with AERMOD

10. Alternative models and alternative approaches

................................ .. 210

11. Multi

- source modeling analyses

................................ ......................... 213

12. Demonstrate ongoing data requirement

-- options

............................... 216

a

. Model once using allowable emissions or adopt limits with the actual emissions rates used in the modeling

b

. Proposed o pti on 1: model using actual emissions, then assess emissions annually and conduct new modeling every 3 years

c

. Proposed o ption 2: if a source's emissions increases over the previous year, the state would be required to submit to the EPA an assessment of

the cause of the increase and provide an initial determination of whether or not air quality modeling would be needed

d

. Concerns related to choosing either option 1 or 2

e

. Proposed o ption 3: model using actual emissions, then conduct screening modeling every 3 years

f

. Option for ambient air quality monitoring

g

. Option for annual modeling

h

. Allow multiple options

i

. Clarify verification options j

. Do not support ongoing data requirementsvi k

. Sunset provision for the ongoing data requirements

13. Post

- attainment designation annual reporting

................................ ..... 230

14. Resources

................................ ................................ ............................ 233

15. Procedural issues

................................ ................................ ................. 234

VI. Statutory and Executive Order Reviews

................................ ................................ . 235

A. Paperwork Reduction Act

................................ ................................ ............... 235

B. Executive Order 13175: Consultatio n and c oordination with I ndian t ribal

g overnments ...........................................................................235

VII. TADs for Monitoring and Modeling and Appendix W

................................ ......... 239

A. Comments in the DRR docket related to the TADs and Appendix W

........... 239

B. TADs are not binding

................................ ................................ ...................... 240

C. Procedure for TADs

................................ ................................ ........................ 240

VIII

. Proposed Consent Decree (CD)

................................ ................................ ............... 242

A. Comments in the DRR docket related to the proposed CD

............................ 242

B. Conflicts with the APA

................................ ................................ ................... 243

C. Conflicts with the DRR

................................ ................................ ................... 244

D. Procedural options for the CD and DRR

................................ ........................ 246

E. CD 16 month deadline

................................ ................................ .................... 248

I X. Comments Outside the Scope of this Rulemaking

................................ ................. 24 8

A. Comments on d esignation p olicy............

....................................... 24 9

1. Alternate approaches for designations

2. Designations before 2017

3. Previously submitted SO 2 designations in specific states

4. Redesignation to attainment following nonattainment designation based on modeling

5. Future monitor ed violations

6. December 2017: Intended d ate for i ssuance of f inal d esignations for

m ajority of c ountry

7. December 2020: Intended d ate for i ssuance of f inal d esignations

B. SO 2 NAAQS f

inal r ule

............................................. . ...............255

C. Tenth EPA m odeling c onfere nce

.......................................... . .......255

D. Other c omments o utside the s cope of this rulemaking ........................255

1. SIP requirements

2. Electric rates

X. Other Comments

................................ ................................ ................................ ....... 255

A. Support other comments

................................ ................................ ................. 257

B. EPA guidance

................................ ................................ ................................ .. 257

C. Organization of the proposal

................................ ................................ ........... 259DELIBERATIVE

- FOR INTE RNAL EPA REVIEW ONLY



## I. Introducti on

The EPA propos ed a rule on May 13, 2014 that would direct state and tribal air agencies (air agencies) to provide data to characterize current air quality in areas with large sources of sulfur

dioxide (SO 2 ) emissions if such areas do not have sufficien t air quality monitoring in place to identify maximum 1

- hour ambient SO 2 concentrations. Th e p roposed r ule describe d criteria for identifying the sources around which air agencies would need to characterize SO 2 air quality. It

also describe d a process and timetables by which air agencies would characterize air quality around sources through ambient monitoring and/or air quality modeling techniques and submit

such data to the EPA.

The public comment period closed on July 14, 2014. A total of 87 comments are included in the docket, Table 1 . A few of these comments are duplicates: 0076 and 0077 ; 0096, 0104 & 0105;

0063 & 0065 ( although 0065 has more attachments ) ; and 0086 & 0112. Item 0098 is an agenda

for a July 17 , 2014 EPA meeting with NEDA/CAP . A list of a cronyms and f requently u sed

a bbreviations are contained in Table 2.

The notice of final rulemaking signed by the Administrator August 4, 2015 presents the EPA's final regulatory conclusions and rule text, and includes summaries of and responses to severa l of the public comments received during the public comment period. This Response to Comments ( RTC ) document presents further discussion of the public comments received and provides additional responses to those comments by the EPA. In some cases, the resp onses presented in this document provide more detail or elaboration than do corresponding responses in the notice of final rulemaking. In other cases, the responses in this document repeat or refer to the notice of final rulemaking as providing the EPA’s complete response to the public comment at issue.

Table 1 . Docket Number and Public Comments

Docket Number Commenter Name

EPA

- HQ

- OAR

- 201 3

- 0711

- 0033 Anonymous Public Comment

EPA

- HQ

- OAR

- 2013

- 0711

- 0034 Bill Thompson, Chairman, National Tribal Air Assoc. ( NTAA)

EPA

- HQ

- OAR

- 2013

- 0711

- 0035 Jack P. Broadbent, APCO, Bay Area Air Quality Management District

EPA

- HQ

- OAR

- 2013

- 0711

- 0036 Arthur N. Marin, Northeast States for Coordinated Air Use Management (NESCAUM)

EPA

- HQ

- OAR

- 2013

- 0711

- 0037 Steve Jackson, Alliant E nergy Services, Inc.

EPA

- HQ

- OAR

- 2013

- 0711

- 0038 Bart Sponseller, Director, Bureau of Air Management, Wisconsin Dep t. of Natural Resources

EPA

- HQ

- OAR

- 2013

- 0711

- 0039 Bernie Paul, B Paul Consulting, LLC

EPA

- HQ

- OAR

- 2013

- 0711

- 0040 Wade Foster, The Fertilizer Institute (TFI)

EPA

- HQ

- OAR

- 2013

- 0711

- 0041 Lynn Fielder, Acting Chief, Air Quality Division, Michigan Dept

. of Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0042 Joseph C. Stanko, Jr., Hunton and Williams LLP, for NAAQS Implementation CoalitionDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

8 EPA

- HQ

- OAR

- 2 013

- 0711

- 0043 Steven M. Pirner, Secretary, South Dakota Dept. of

Natural Resources

EPA

- HQ

- OAR

- 2013

- 0711

- 0044 Robert A. Hirsch, Dir.

, Environmental Affairs, National Lime Association (NLA)

EPA

- HQ

- OAR

- 2013

- 0711

- 0045 Maya Rao, Chief, Air Div., Mississippi D ept. of Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0046 Paul Roe, American Forest & Paper Assoc. (AF&PA)

EPA

- HQ

- OAR

- 2013

- 0711

- 0047 Charles R. Matthews, We Energies

EPA

- HQ

- OAR

- 2013

- 0711

- 0048 Kenneth Anderson, Ameren Corporation

EPA

- HQ

- OAR

- 2013

- 0711

- 0049 Thomas Kierspe, Santee Cooper

EPA

- HQ

- OAR

- 2013

- 0711

- 0050 Douglas J. Fulle, Oglethorpe Power Corp.

EPA

- HQ

- OAR

- 2013

- 0711

- 0051 Richard A. Hyde, Executive Dir., Texas Commission on Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0052 John S. Lyons, Dir., Divisio n for Air Quality, Commonwealth of Kentucky

EPA

- HQ

- OAR

- 2013

- 0711

- 0053 Robert W. Clemens, FCG Environmental Committee, Florida Electric Power Coordinating Group, Inc. (FCG

EC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0054 Charles D. Johnson, The Aluminum Association

EPA

- HQ

- OAR

- 2013

- 0711

- 0055 Grant Rodway, Bison Engineering, Inc, et al.

EPA

- HQ

- OAR

- 2013

- 0711

- 0056 Patrick Coughlin, Duke Energy

EPA

- HQ

- OAR

- 2013

- 0711

- 0057 Mark Thoma s , Otter Tail Power Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0058 W. Danny Herrin, Southern Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0059 Dan Holland, Public Commenter

EPA

- HQ

- OAR

- 2013

- 0711

- 0060 Craig W. Butler, Dir., Ohio EPA

EPA

- HQ

- OAR

- 2013

- 0711

- 0061 Ray Hendricks, Portland General Electric

EPA

- HQ

- OAR

- 2013

- 0711

- 0062 Stuart A. Clark, Air Quality Program Mgr., Dept. of Ecology, S tate of Washington

EPA

- HQ

- OAR

- 2013

- 0711

- 0063 Devi Chandrasekaran, Baker Botts LLP, for BCCA Appeal Group

EPA

- HQ

- OAR

- 2013

- 0711

- 0064 Bill Matthews, Cleco Corp.

EPA

- HQ

- OAR

- 2013

- 0711

- 0065 Devi Chandrasekaran, Baker Botts LLP, for Texas SO 2 Working Group

EP A

- HQ

- OAR

- 2013

- 0711

- 0066 Michael P. Lebeis, DTE Energy

EPA

- HQ

- OAR

- 2013

- 0711

- 0067 Stephen R. Gossett, Eastman Chemical Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0068 Zachary M. Fabish, Sierra Club

EPA

- HQ

- OAR

- 2013

- 0711

- 0069 Keith Bentley, Chief, Air Protection Branch, Geor gia Environmental Protection Div., Georgia Dept. Natural

Resources

EPA

- HQ

- OAR

- 2013

- 0711

- 0070 American Electric Power Service Corp. (AEPSC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0071 Kyra L. Moore, Dir., Missouri Dept. of Natural ResourcesDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

9 EPA

- HQ

- OAR

- 2013

- 0711

- 0072 Erie C. Massey, Dir., Air Quality Div., Arizona Dept. of Environmental Quality (ADEQ)

EPA

- HQ

- OAR

- 2013

- 0711

- 0073 Lyle Witham, Western Energy Supply & Transmission Assoc. (WEST)

EPA

- HQ

- OAR

- 2013

- 0711

- 0074 Grant Rodway, Bison Engineering Inc. & Larry Zink,

Montan a Sulfur and Chemical Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0075 Andrea Field, Hunton & Williams LLP, for Utility Air Regulatory Group (UARG)

EPA

- HQ

- OAR

- 2013

- 0711

- 0076 Maxine Lipeles, Washington Univ. School of Law, for

Sierra Club

EPA

- HQ

- OAR

- 2013

- 0711

- 0077 Maxine Lipeles, Washington Univ. School of Law, for Sierra Club Missouri Chapter

EPA

- HQ

- OAR

- 2013

- 0711

- 0078 Frank L. Kohlasch, Minnesota Pollution Control Agency (MPCA)

EPA

- HQ

- OAR

- 2013

- 0711

- 0079 Bryan Brendle, Portland Cement Assoc. (PCA)

EPA

- HQ

- OAR

- 2013

- 0711

- 0 080 Michael J. Nasi, Counsel for Gulf Coast Lignite Coalition (CGLC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0081 And rew Hollis , South Carolina Dept. of Health and

Environmental Control ( SCDHEC ) Bureau of Air Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0082 Christine Wyman, Class of 85 R egulatory Response Group

EPA

- HQ

- OAR

- 2013

- 0711

- 0083 Bob Holmes, Environmental Affairs Admin., Omaha Public Power District (OPPD)

EPA

- HQ

- OAR

- 2013

- 0711

- 0084 James Taylor, Environmental Regional Mgr., MeadWestvaco (MWV)

EPA

- HQ

- OAR

- 2013

- 0711

- 0085 George S. A burn, Dir., Air & Radiation Mgmt. Admin., Maryland Department of the Environment

EPA

- HQ

- OAR

- 2013

- 0711

- 0086 Jason Bohrer, Pres/CEO, Lignite Energy Council (LEC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0087 Pamela F. Faggert, Dominion Resources Services

EPA

- HQ

- OAR

- 2013

- 0711

- 0088 National Environmental Development Association’s Clean Air Project NEDA/CAP

EPA

- HQ

- OAR

- 2013

- 0711

- 0089 Jasmine Mehta, Bureau of Air Quality Planning, State of

Nevada

EPA

- HQ

- OAR

- 2013

- 0711

- 0090 Kim Mireles, Luminant

EPA

- HQ

- OAR

- 2013

- 0711

- 0091 John M. Holloway III, Winston & Strawn LLP, for Westar Energy

EPA

- HQ

- OAR

- 2013

- 0711

- 0092 James D. Jones, Alcoa, Inc.

EPA

- HQ

- OAR

- 2013

- 0711

- 0093 Ronald W. Gore, Alabama Dept. of Environmental Mgmt. (ADEM)

EPA

- HQ

- OAR

- 2013

- 0711

- 0094 Kimberly S.L. Bauman, Mississippi Lime Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0095 Roger Walker, Regulatory Environmental Group for Missouri ( REGFORM )DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

10 EPA

- HQ

- OAR

- 2013

- 0711

- 0096 Madison B. Cary Miller, Office of the General Counsel Office at Tulsa Air Quality Div., Oklahoma Dept. of Environmental Qual ity (ODEQ)

EPA

- HQ

- OAR

- 2013

- 0711

- 0097 Michael G. Dowd, Virginia Dept. of Environmental Quality (VDEQ)

EPA

- HQ

- OAR

- 2013

- 0711

- 0099 Roger Walker, REGFORM

EPA

- HQ

- OAR

- 2013

- 0711

- 0100 Steven A. Dietrich, Dept. of Environmental Quality

– Air Quality Div. (DEQ/AQD ), State of Wyoming

EPA

- HQ

- OAR

- 2013

- 0711

- 0101 Joe L. Citta, Nebraska Public Power District (NPPD)

EPA

- HQ

- OAR

- 2013

- 0711

- 0102 John W. Mitchell, Div. of Environment, Kansas Dept. of

Health and Environment

EPA

- HQ

- OAR

- 2013

- 0711

- 0103 Catharine Fitzsimmons, Ai r Quality Bureau, Iowa Dept. of

Natural Resources

EPA

- HQ

- OAR

- 2013

- 0711

- 0104 Oklahoma Dept. of Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0105 Oklahoma Dept. of Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0106 Terry L. O’Clair, Div. of Air Quality, North Dakota Dept.

of Health

EPA

- HQ

- OAR

- 2013

- 0711

- 0107 Sheila Holman, Div. of Air Quality, North Carolina Dept. of Environment and Natural Resources (NCDENR)

EPA

- HQ

- OAR

- 2013

- 0711

- 0108 Eric Bott, Wisconsin Manufacturers and Commerce (WMC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0109 Peter Pagano, American Iron and Steel Institute (AISI)

EPA

- HQ

- OAR

- 2013

- 0711

- 0110 Howard J. Feldman, American Petroleum Institute (API)

EPA

- HQ

- OAR

- 2013

- 0711

- 0111 Sam L. Phillips, Louis i ana Dept. of Environmental Quality (LDEQ)

EPA

- HQ

- OAR

- 2013

- 0711

- 0 112 Jason Bohrer, Pres/CEO, Lignite Energy Council (LEC)

EPA

- HQ

- OAR

- 2013

- 0711

- 0113 David L. Klemp, Air Resources Mgmt. Bureau, Montana Dept. of Environmental Quality

EPA

- HQ

- OAR

- 2013

- 0711

- 0114 Thomas N. Effinger, SCANA Environmental Services

EPA

- HQ

- OAR

- 2 013

- 0711

- 0115 Joy Wiecks, Fond du Lac Environmental Program

EPA

- HQ

- OAR

- 2013

- 0711

- 0116 Paul M. Ling, Kansas City Power & Light Co.

EPA

- HQ

- OAR

- 2013

- 0711

- 0117 Cindy A. Hollenberg

, New Mexico Environment Department, Air Quality Bureau

EPA

- HQ

- OAR

- 2013

- 0711

- 0 11 8 Scott Deloney, Chief, Air Programs Branch, Office of Air Quality, Indiana Department of Environmental Management (IDEM)

EPA

- HQ

- OAR

- 2013

- 0711

- 011 9 Myra C. Reece, Chief

, Bureau of Air Quality

, South Carolina Department of Health and Environmental Contro l (DHEC)

EPA

- HQ

- OAR

- 2013

- 0711

- 01 20 Tribal Environmental Policy CenterDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

11 Table 2. Explanation of Acronyms and Frequently Used Abbreviations Acronym Long Name

Act C lean A ir A ct

Administrator Administrator of the EPA

AERR Air Emissions Reporting Rule

C AA Clean Air Act

CBSA Core Based Statistical Area

CD Consent Decree published o n June 2, 2014 by the EPA at 79 Federal

Register 31325

CEMS Continuous Emissions Monitoring System

CFR Code of Federal Regulations

DRR Data Requirements Rule proposed May 1 3, 2014

EGU e lectricity g enerating u nit

EPA U.S. Environmental Protection Agency

FR Federal Register

GEP Good Engineering Practice

km kilometer

MACT Maximum Achievable Control Technology

MATS Mercury and Air Toxics Standards
NAAQS National Ambient Air Quality Standards

NEI National Emissions Inventory

NO 2 n itrogen d ioxide

NSR New Source Review ppb p arts per b illion Proposed Rule Data Requirements Rule proposed May 13, 2014

PSD Prevention of Significant Deterioration

SIP State Implementation P lan

SO 2 s ulfur d ioxide

tpy tons per year



## II. Monitoring and Modeling to Satisfy the Proposed Rule

A. Legal authority to require data by proposed schedule

1. Proposal conflicts with and modifies the Clean Air Act ( CAA )

Comment :

Commenters (0040, 0043, 0049

, 0050, 0051, 0052, 0053, 0058, 0063, 0065, 0075, 0081, 0085, 0089, 0103, 0106, and 0109) stated the proposal conflicts with the designation process in theDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

12 CAA.

Commenters (0058, 0063, 0065, 0089, 0103, 0106) stated that the CAA required the EPA to
make area designations under the new SO 2 standard

— either attainment, nonattainment, or

unclassifiable

— no later than June 3, 2013, and that the EPA failed to comply with that mandatory obligation.

Commenters (0052, 0075, 0089, 0106) stated that the proposed sc hedule, by which the EPA would issue final designations for the remainder of the country by December 2020

, or ten years after the revised SO 2 NAAQS , conflicts with s ection 107(d)(l)(B)(i) of the CAA. Commenter (0089) stated that, to take a total of ten yea rs from the date that the 1

- hour SO 2 NAAQS was promulgated to issue initial area designations is beyond the EPA 's legislatively granted authority. Commenter (0089) cited EME Homer City Generation LP v. Envt'l Prot. Agency, 696 F. 3d 7, 27 (D.C. Cir. 2012) and stated the SO 2 Data Requirements Rule (DRR) cannot stand as proposed because it fails to follow the mandatory timelines for promulgating area designations, and, therefore, exceeds the EPA 's legislative authority.

Commenter (0106) stated the EPA must make the initial designations for all areas of the country based on the data it now has in its possession. Commenter (0106) noted the EPA could theoretically complete two reevaluations of the SO 2 NAAQS before making the initial designations for the June 20 10 standard, given the schedule in the proposal. Commenter (0106) stated that, if the EPA decides to change the standard during the reevaluation process, all data required by this Proposed Rule would likely be useless and a waste of scarce resources.

Comm enter (0052) stated the DRR modifies and revises the statutory provisions established by the CAA and imposes additional statutory obligations on air agencies. Commenter (0051) stated that requiring states to develop monitoring or modeling data in accordanc e with this proposal for designations ignores the statutory mandate. Commenter (0051) stated that the proposal arbitrarily grants the EPA up to an additional seven years to do what the Agency was mandated to do by June 2013: designate all areas of the coun try as either attainment, nonattainment, or

unclassifiable

. Commenter (0053) stated it is not appropriate to replace the CAA's statutory

directive with extra

- statutory provisions like those proposed in the DRR and CD.

Response:

The EPA has legal authorit y under section s 110(a)(2)(B)

, 110(a)(2)(K), and 301(a)(1) of the CAA to request data and information from states regarding air quality status within their borders

. In addition, CAA section 114(a)(1) provides broad authority for the EPA to direct any perso n to provide emissions information.

The EPA disagrees with commenters’ claims that the rule directing air agencies to gather and submit such data and information to the EPA conflicts with the CAA statutory provisions governing issuance of area designation s under the NAAQS. The DRR in and of itself does not modify the schedule for designations , but rather will result in the submittal of information and

data to the EPA that may be used in appropriate contexts for evaluating air quality in specificDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

13 areas to i nform various future actions, such as area designations, re

- designations, clean data determinations, or determinations regarding whether areas have timely attained the NAAQS. T he timing for designations is governed by the statute and not by this rule . As a result of lawsuits seeking to compel the EPA to complete issuance of the initial SO 2 designations

, the EPA entered

into an enforceable court order issue d on March 2, 2015

, outlining a schedule for completing the

national designations process

.

The EPA di sagrees that the EME Homer City ruling is relevant to this rulemaking or the objection raised by the commenter, as that case did not address the EPA’s authority to direct air

ag e ncies to gather and submit to the EPA data and information regarding areas’ SO 2 ambient

concentrations. The EPA additionally considers ir r elevant and beyond the scope of this rulemaking the comments asserting that the EPA may issue designations only based on information already in the agency’s possession, and the other objections re lated to the timing of designations and to the contents of the CD entered on March 2, 2015, that now governs that process. The information gathered pursuant to this rule will be useful for purposes of informing whether areas are in fact meeting or failing to meet the 2010 SO 2 NAAQS, as that information is presently generally lacking, no matter what particular statutory provision is at that time being implemented that involves assessment of the areas’ current status.



### 2. Proposal b ypasses section 107

Comment :

Commenter (0109) asserted states must retain the opportunity to develop their own designations without the interim requirement of EPA approval and that the EPA 's proposed involvement improperly expands the Agency's role beyond what Congress intended when i t gave states primary authority to craft designations under the CAA.

Commenter s (0043 , 0052 , 0063, 0065 ) s uggested t he proposal attempts to bypass section 107( d)(3)(A), by dismissing states’ designation package s submitted in June 2011

. Commenter s (0052 , 0 063, and 0065 ) stated the C AA does not allow the Administrator to ignore the list of

a reas submitted by a Governor

. Commenter (0052) stated that the Administrator only designated

certain nonattainment areas and ignored all other areas, including areas with sufficient ambient air monitoring data meeting applicable regulatory requirements and the NAAQS.

Commenters (0063, 0065) stated that the EPA has not identified a statutory basis to delay designations pending any revisions to the S O 2 monitoring network r equirements. Commenters (0063, 0065) referred to the 2008 lead NAAQS experience and stated, in a similar fashion, the

EPA should not allow revisions to the S O 2 monitoring network to delay all area designations

.

Commenters (0063, 0065) asserted the EPA cho se a course of unreasonable deferral when it failed to designate all areas of the U.S. for the 1

- hour SO 2 standard before the statutory deadline. Commenters (0063, 0065) claimed the CAA requires the EPA to implement the 1

- hour SO 2 standard in accordance wi th the following principles:DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

14 • Each state submits a recommended designation, and the EPA must promulgate the initial designations within 3 years of issuing the standard and must give a state 120 days' notice

if the EPA intends to depart from the state's rec ommended designations.

• EPA should continue to use the "unclassifiable" designation where appropriate, and should not seek to designate all areas "attainment" or "nonattainment." The CAA provides tools for the EPA and a state to address an attainment or un classifiable area that is later found to have air quality that does not meet the standard.

• Current regulations for characterizing air quality found at 40 CFR § 50.17 and p art 58 provide sufficient information to support area designations. Section 50.17 pr ovides that monitoring is the basis for determining attainment. Part 58 was revised along with the 1

- hour SO 2 standard, includes detailed rules for SO 2 monitor network design, and allows

case

- by

- case flexibility where necessary. The Proposed Rule calls for modeling and additional monitoring beyond what is necessary for the EPA to comply with the CAA.

• In at least some areas, existing data clearly support attainment designations. An example is the Houston, Texas, region, which has several regulatory and priva tely operated monitoring stations (including the Texas Commission on Environmental Quality 's monitors, Houston Region al Monitoring, and the Texas City/La Marque Community Air Monitoring Network), which have uniformly shown attainment of the 1

- hour SO 2

st andard. Other areas of the country have similar monitoring data. The Proposed Rule impermissibly withholds an "attainment" classification for such areas and rewrites the

rules on how to assess attainment.

Commenter (0053) stated the EPA 's decision to defe r these otherwise expected unclassifiable

area designations is the basis for the CD, which is a separate and distinct issue from the timing

and substantive criteria the EPA is promulgating through its DRR to collect additional data and

information for thes e areas.

Response :

As stated previously , t he EPA has legal authority under section s 110(a)(2)(B)

, 110(a)(2)(K), and 301(a)(1) of the CAA to request data and information from states regarding air quality status

within their borders

. In addition, CAA sect ion 114(a)(1) provides broad authority for EPA to direct any person to provide emissions information. The DRR in and of itself does not delay designations that are due under the statute and will be due under the court order issue d on March 2, 2015. The com ments objecting to the EPA’s schedule for issuing the remaining area designations under the 2010 SO 2 NAAQS are therefore beyond the scope of this rulemaking and warrant no further response.



### 3. Unclassifiable designations

a. DRR nullifies the “unclassifiable” d esignationDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

15 Comment :

Commenter (0053) asserted that the EPA cannot use the DRR to supersede the statutory requirement to timely make area designations, including statutorily

- appropriate "unclassifiable" designations. C ommenter (0053) stated the most effec tive remedy to the EPA 's failure to meet the statutory deadline is to designate currently undesignated areas as unclassifiable

.

Commenters ( 0040, 0065, 0083, and 0089) stated t he Proposed Rule effectively nullifies the

"unclassifiable" designation, use of which would have allowed the EPA to meet its statutory

deadline . Commenter (0089) cited several court cases and stated that the SO 2 DRR essentially reads out of the CAA the availability of this "unclassifiable" designation, the very purpose of

which is to designate areas for which the agency has insufficient information to make a designation of attainment or nonattainment. Commenter (0089) provided the following additional points.

Timely promulgation of area designations is important for several reasons. First, unclassifiable areas have traditionally been treated as attainment, which obviates the need

for the s tate of Nevada, along with other states, to develop a more rigorous nonattainment state implementation plan (SIP) and unnecessarily impose more stri ngent controls on regulated entities located far from populated areas. Notably, the EPA could make unclassifiable designations for those areas for which it believes it lacks sufficient information, and at the same time require additional data collection. M aking the designations does not negate the EPA 's ability to require better characterization of SO 2 emissions.

Second, the unclassifiable designation has traditionally recognized the rural nature of the

s tate of Nevada, and allowed the s tate to utilize it s limited resources to deploy monitoring networks where population centers are located . It obviated the s tate's need to invest in expansive and costly monitoring networks across Nevada's rural landscape.

Third, it provided certainty to existing and poten tial industries, so that they would be comfortable in investing in capital outlays for equipment that could be used for several, if

not many, years to come. If in dustry were to try to locate to Nevada, but the area designation is unknown, industry could be required to implement additional or different controls after area designations are finally promulgated.

Fourth, the proposed SO 2 DRR contains a timetable by which the EPA must act to make area designations, with final area designations to be made no lat er than December 31, 2020. Thus, according to this schedule, area designations for the 2010 SO 2 NAAQS will

not be made until after the EPA is required to reevaluate, and possibly lower, the SO 2 NAAQS. Such out

- of

- order rule promulgation creates implementat ion issues for states and muddies the implementation timeline. It also creates considerable uncertainty for regulated industries. The delay effectively prohibits Nevada (and other states) fromDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

16 challenging any area designations that the EPA may make until w ell after the EPA is required to revisit the NAAQS.

Finally, Nevada is concerned that if the EPA is allowed to utilize modeling for this standard, it will seek to do so for other standards as they are updated. Modeling is a predictive tool, but it is not appropriate for making area designations, which should be based on the air quality condition existing at the time of the designation. Modeling is susceptible to challenge and is not an accurate predictor for short term standards. For these reasons, the SO 2 DRR is not an appropriate exercise of the EPA 's legislative authority.

Commenter (0065) stated the EPA should continue to use the "unclassifiable" designation where appropriate, and should not seek to designate all areas attai nm ent or nonattainment. Com menter (0065) stated t he CAA provides adequate tools for EPA and a state to address an attainment or

unclassifiable area that is later found to have air quality that does not meet the S O 2 standard.

Commenter (0093) stated that the EPA and others must liv e with the fact that, when a new NAAQS is adopted and the availability of monitoring data are lacking, immediate designations of areas as attaining or non

- attaining is impossible. Commenter (0093) stated t his is the reason

the CAA (CAA) provides for unclas sifiable/attainment status

.

Commenter (0040) encourage d the EPA , in the preamble to the Final Rule, to explicitly confirm that its deviation from mandated CAA NAAQS designation procedures for the 1

- hour SO 2 NAAQS is the result of unique circumstances and confirm continued applicability of the “unclassifiable” category for future NAAQS designations.

Response :

As stated in the preamble to the final rulemaking, t he comments that assert that the EPA has not designated areas under the 2010 SO 2 NAAQS in a tim ely manner are beyond the scope of this rulemaking, and are not germane to the issue of the EPA’s statutory authority to direct air agencies to conduct monitoring or modeling to further characterize ambient air concentrations of

SO 2

. Through this rulemakin g, the EPA is not establishing or modifying any area designation requirements provided for in section 107 of the CAA

, nor does any aspect of this final rule conflict with any provision of section 107 that directs states and the EPA to take timely action to issue designations. The purpose and effect of this rulemaking is to require air agencies to characterize air quality in priority areas throughout the country where existing ambient monitors may not be adequately characterizing peak 1

- hour SO 2 ambient air concentrations. The air quality data obtained as a result of this rulemaking then may be used in future analytical actions by the EPA, including designations of any undesignated areas or redesignations of already designated areas. It is true that in the p r oposed r ule preamble we discussed how the timing of the implementation of this rule would fit with our intended schedule for completing area designations, but the proposal did not itself purport to establish a binding schedule for completing designations.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

17 The EPA notes that litigation was filed against the EPA to compel the Agency to complete designations under CAA section 107, and on March 2, 2015 , the court in one of those cases

issued a ruling that places the EPA on a binding schedule to complete area designations for the

2010 1

- hour SO 2 NAAQS. See

, Sierra Club, et al. v. McCarthy , Case No. 13

- cv

- 03953

- SI (N.D. Cal., March 2, 2015) (Order Granting Joint Motion To Approve And Enter Consent Decree And Denying Other Motions As Moot; and Consent Decree). C opies of the court’s order and the CD setting forth the EPA’s schedule for completing designations have been placed in the docket for this rulemaking. Under the schedule ordered by the court, the EPA is required to complete the designations in no more than three future rounds.

The EPA continues to believe that the requirements of this rule for air agencies to submit a list of

source s where further air quality characterization is needed , and the other data submittal requirements found in § 51.1203 of this rule, are appropriate steps needed to better understand

SO 2 air quality throughout the country, and are consistent with section s 110(a)(2)(B), 110(a)(2)(K)

, 301(a)(1) , and 114 of the CAA. The commenters did not challenge this view. Section 110(a)(2)(B) ind icates that SIPs are to “provide for establishment and operation of appropriate devices, methods, systems, and procedures necessary to (i) monitor, compile and analyze data on ambient air quality and (ii) upon request, make such data available to the

Admin istrator.” Section 110(a)(2)(K) states that SIPs shall “provide for (i) the performance of such air quality modeling as the Administrator may prescribe for the purpose of predicting the effect on ambient air quality of any emissions of any air pollutant fo r which the Administrator has established a NAAQS and (ii) the submission, upon request, of data related to such air quality modeling to the Administrator.” S ection 301(a)(1) provides the EPA with general authority to establish regulations as necessary to carry out the agency’s functions, which in this case includes ensuring the attainment of the SO 2 NAAQS throughout each state. This section states that “The Administrator is authorized to prescribe such regulations as are necessary to carry out his function s under this chap ter.”

The EPA often establishes and revises monitoring requirements for implementing NAAQS, whether or not those requirements will necessarily generate new information in time to inform timely area designations under CAA section 107. See, e.g. , 75 FR 81126, 81130, December 27,

2010

. The validity of such rules does not depend upon whether information generated pursuant to those requirements will be gathered in time to support designations that are timely under section 107. Here, the comment ers have raised no objection to the central premise of the rule, which is that additional information that better characterizes air quality near larger sources of

SO 2 is warranted and is authorized to be required under sections 110 and 301 of the Act.

Irre spective of when the EPA uses this information

— for example, irrespective of whether the EPA promulgates initial designations of “unclassifiable” (and then uses the information collected pursuant to this DRR in later redesignations), or whether the EPA prom ulgates the remaining designations after the information required here becomes available

— the EPA believes that this rule is authorized and is warranted. Therefore, i n this final rulemaking, the commenters have provided no basis for the EPA to not requir e a ir agencies to submit such SO 2 monitoring and modeling data to the EPA

, as proposed. The final rule is fully consistent with the Agency’s broadDELIBERATIVE

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18 authority under section 110 and 301, as well as with the EPA’s authority under CAA section 114(a)(1) to direct a ny person to provide information as is reasonably required to improve characterization of ambient air quality near larger sources of SO 2

.

As previously explained, today’s final rule is not implementing or discharging the EPA’s duties

under CAA section 10 7 to designate areas under the 2010 SO 2 NAAQS. Therefore, none of the comments relating to how or when the EPA must issue designations are relevant or germane to this final rule, which directs air agencies to gather and submit to the EPA additional data an d information regarding their areas’ air quality status that can be used in any appropriate context that is assessing such areas’ status. All objections to the use of such data in those future actions may be raised at the appropriate stages for those actio ns. Moreover, at least with respect to designations under the 2010 SO 2 NAAQS, the EPA is now under an enforceable court order to complete those designations no later than the dates provided in the court’s order, and this rule does not purport to change tha t binding schedule.

If EPA in future designations actions uses modeling information generated by implementation of this rule, interested persons will be able to comment on that future use at the appropriate time.
However, at this time the EPA disagrees with the commenter ’s suggestion that modeling is an inappropriate method by which to assess areas’ status for any purpose , and believes that it is reasonable to give states the option under this rule to choose whether to conduct improved monitoring at appr opriately selected sites of maximum ambient concentrations or to conduct

actual

- or allowable

- emissions based modeling to characterize areas. When either monitoring or modeling information is used to inform future decisions regarding specific areas will be the appropriate time at which to asses s whether that specific information is reliable in those cases.

In addition, this rule in no way “nullifies” the unclassifiable designation option th at exists under CAA section 107(d)(1)(A)(iii), and which remains av ailable under the SO 2 and every other NAAQS when EPA takes future separate action to issue designations

. Nor does the rule otherwise establish a precedent for implementation of any other NAAQS. Although comments on the merits of the use of interim designat ions are not germane to this rulemaking and the EPA is not taking any final designations actions in this rulemaking , the EPA disagrees that promulgation of an interim designation of unclassifiable, with undefined prospects for future redesignation either t o nonattainment or to attainment, provides greater certainty and better facilitates industry investments than promulgating an orderly process for gathering data that may

later be used for informing designations

.



### b. EPA should immediately designate areas unclassifiable

Comment :

Commenters ( 0040, 0048, 0049, 0050, 0051

, 0052, 0058, 0063, 0065, 0075, 0081, 0089, 0090, 0093, 0106, 0111, and 0116 ) stated that, if the Agency lacked sufficient information to make an

area designation, it must designate that are a as unclassifiable.DELIBERATIVE

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19 Commenter s ( 0075, 0116 ) stated t he DRR cannot be a substitute for completing the initial area designation process within the timeframe set out by Congress. Commenter (0058) stated that this rulemaking does not forestall the EPA’s sta tutory obligation of immediately completing the area designations and identifying areas as “unclassifiable” where necessary and appropriate. Commenter (0070) encouraged the EPA to drop this rulemaking and use its past practice of granting attainment or unc lassifiable designations to areas that do not have monitored nonattainment and are recommended for such designations by the various states.

Commenters (0050, 0058, 0065, 0069, 0070, 0075, 0093, and 0116) urged the EPA to promptly designate all as yet und esignated areas, using the “unclassifiable” designation, where appropriate. Commenters (0050, 0063, and 0065) provided the following additional points.

Because this option for timely designations already resides in the CAA, the EPA should

not wait another three years before issuing the required designations. EPA has taken a similar approach as recently as 2012, in regard to the 1

- hour Nitrogen Dioxide ( NO 2 ) NAAQS. The EPA had promulgated a new NAAQS standard in 2010 and determined that it should rely on mo nitoring data in the area designation process. However, because the monitoring network for NO 2 was not sufficient to determine whether areas attained

the new 1

- hour NAAQS, the EPA designated all parts of the country as unclassifiable/

attainment until a su fficient monitoring network could be established. Following suit, the

EPA should do the same for the new SO 2 NAAQS, designating all remaining areas as unclassifiable, using the subsequent data collected pursuant to this Proposed Rule to adjust the designat ions in the futu re as needed.

Commente r s ( 0058, 0103

, and 0116 ) stated that, once the EPA has designated areas as “unclassifiable,” it may take the time needed to develop the data necessary to reclassify those areas as it has proposed in the DRR. Comment er ( 0058 ) stated the EPA should complete the area designation process either before or at a minimum concurrently with its release of the final DRR.

Commenter (0093) stated that the EPA and others must live with the fact that, when a new NAAQS is adopted and the availability of monitoring data are lacking, immediate designations of areas as attaining or non

- attaining is impossible. Commenter (0093) stated t his is the reason

the CAA provides for unclassifiable/attainment status and suggested the EPA should expeditiously designate the vast majority of the country as unclassifiable.

Response :

The timing and result of designations is beyond the scope of this rulemaking, which directs air agencies to gather and submit to the EPA additional data and information regarding their areas’ air quality status. That information , if reliable, may then be used in any appropriate context that is assessing such areas’ status. It is not the place for this rulemaking to grant the commenters’ request to “immediately” issue un classifiable designations

– those decisions will be made in

future area

- specific determinations pursuant to CAA section 107 and in compliance with the court order issued on March 2, 2015, directing the EPA to complete designations under the 2010DELIBERATIVE

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20 SO 2 NAAQS.

The comments that assert that the EPA has not designated areas under the 2010 SO 2 NAAQS in a timely manner are beyond the scope of this rulemaking, and are not germane to the issue of the EPA’s statutory authority to direct air agencies to conduct monito ring or modeling to further

characterize ambient air concentrations of SO 2

. Through this rulemaking, the EPA is not establishing or modifying any area designation requirements provided for in section 107 of the

CAA

, nor does any aspect of this final rule c onflict with any provision of section 107 that directs states and the EPA to take timely action to issue designations. The purpose and effect of this rulemaking is to require air agencies to characterize air quality in priority areas throughout the

country where existing ambient monitors may not be adequately characterizing peak 1

- hour SO 2 ambient air concentrations. The air quality data obtained as a result of this rulemaking then may

be used in future analytical actions by the EPA, including designations of any undesignated areas or redesignations of already designated areas. It is true that in the p roposed r ule preamble we discussed how the timing of the implementation of this rule would fit with our intended schedule for completing area designations, but the proposal did not itself purport to establish a binding schedule for completing designations.

The EPA notes that litigation was filed against the EPA to compel the Agency to complete designations under CAA section 107, and on March 2, 2015 , the cour t in one of those cases

issued a ruling that places the EPA on a binding schedule to complete area designations for the

2010 1

- hour SO 2 NAAQS. See

, Sierra Club, et al. v. McCarthy , Case No. 13

- cv

- 03953

- SI (N.D. Cal., March 2, 2015) (Order Granting Joint Mo tion To Approve And Enter Consent Decree And Denying Other Motions As Moot; and Consent Decree). Copies of the court’s order and the CD setting forth the EPA’s schedule for completing designations have been placed in the docket for this this rulemaking. Un der the schedule ordered by the court, the EPA is required to complete the designations in no more than three future rounds.

The EPA continues to believe that the requirements of this rule for air agencies to submit a list of

source s where further air q uality characterization is needed , and the other data submittal requirements found in § 51.1203 of this rule, are appropriate steps needed to better understand

SO 2 air quality throughout the country, and are consistent with section s 110(a)(2)(B), 110(a)(2)( K)

, 301(a)(1) , and 114 of the CAA. The commenters did not challenge this view. Section 110(a)(2)(B) indicates that SIPs are to “provide for establishment and operation of appropriate devices, methods, systems, and procedures necessary to (i) monitor, compi le and analyze data on ambient air quality and (ii) upon request, make such data available to the Administrator.” Section 110(a)(2)(K) states that SIPs shall “provide for (i) the performance of such air quality modeling as the Administrator may prescribe f or the purpose of predicting the effect on ambient air quality of any emissions of any air pollutant for which the Administrator has established a NAAQS and (ii) the submission, upon request, of data related to such air quality modeling to the Administrato r.” S ection 301(a)(1) provides the EPA with general authority to establish regulations as necessary to carry out the agency’s functions, which in this case includes ensuring the attainment of the SO 2 NAAQS throughout each state. This section

states that “T he Administrator is authorized to prescribe such regulations as are necessary toDELIBERATIVE

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21 carry out his functions under this chap ter.”

The EPA often establishes and revises monitoring requirements for implementing NAAQS, whether or not those requirements will nece ssarily generate new information in time to inform timely area designations under CAA section 107. See, e.g. , 75 FR 81126, 81130, December 27,

2010

. The validity of such rules does not depend upon whether information generated pursuant to those requirement s will be gathered in time to support designations that are timely under section 107. Here, the commenters have raised no objection to the central premise of the rule, which is that additional information that better characterizes air quality near larger s ources of

SO 2 is warranted and is authorized to be required under sections 110 and 301 of the Act. Irrespective of when the EPA uses this information

— for example, irrespective of whether the EPA promulgates initial designations of “unclassifiable” (and the n uses the information collected pursuant to this DRR in later redesignations), or whether the EPA promulgates the remaining designations after the information required here becomes available

— the EPA believes that this

rule is authorized and is warranted. Therefore, i n this final rulemaking, the commenters have provided no basis for the EPA to not requir e air agencies to submit such SO 2 monitoring and modeling data to the EPA

, as proposed. The final rule is fully consistent with the Agency’s broad authority under section 110 and 301, as well as with the EPA’s authority under CAA section 114(a)(1) to direct any person to provide information as is reasonably required to improve characterization of ambient air quality near larger sources of SO 2

.



### B. Legal authorit

y to find that modeling satisfies the data requirements

1. Conflicts with the SO 2 

### NAAQS

Comment :

Commenters (0040, 0046) stated t he use of model output to support NAAQS designations conflicts with the wording of the SO 2 NAAQS, which states that only quality

- assured ambient air monitoring data may be used. Commenters (0046, 0110) stated t he precise wording of 40 CFR Part 50.17 establishes ambient air monitoring as the only basis for determining if the SO 2 NAAQS is being met because it specifies that:

(a) The lev el of the national primary 1

- hour annual ambient air quality standard for oxides of sulfur is 75 parts per billion (ppb, which is 1 part in 1,000,000,000),

measured in the ambient air as sulfur dioxide ( SO 2 ).

(b) The 1

- hour primary standard is met at an ambi ent air quality monitoring site when the

three

- year average of the annual (99th percentile) of the daily maximum 1

- hour average concentrations is less than or equal to 75 ppb, as determined in accordance with appendix T of this part.

(c) The level of the standard shall be measured by a reference method based on appendixDELIBERATIVE

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22 A or A

- 1 of this part, or by a Federal Equivalent Method (FEM) designated in accordance with part 53 of this chapter.”

Commenter (0040) asserted that the EPA policy, consistent with the wo rding of the NAAQS, has previously restricted the data that may be used for carrying out NAAQS area designations to ambient air measurements that are acquired using an officially designated federal reference method (“FRM”), FEM, or approved regional method (“ARM”) that meets the quality assurance and siting criteria set forth in 40 CFR p art 58, Appendix A and Appendix D. Commenter (0040)

believed the EPA ’s tolerance of modeling output uncertainties is incongruous with, and indeed undermines, the purpose of the robust program for quality assuring ambient air monitoring data that are used for determining NAAQS compliance and stated the following issues must be

addressed:

• FRMs, FEMs, and ARMs operate according to basic, well

- known scientific principles,

such a s the amount of light given off in a specific wavelength when a molecule of SO 2 is irradiated by light of another wavelength. In contrast, AERMOD is based on a sequence of mathematical equations that simplify the complex process of turbulent diffusion in t he lower atmosphere and the downwind dispersion of a source effluent.

• FRMs, FEMs, and ARMs are calibrated on regular schedules at every regulatory air monitoring site using SO 2 standards that are traceable to an NIST Standard Reference Material or other p rimary standard. Strict acceptance criteria based on the accuracy and linearity of the instrument’s response to known standards is used to calibrate the analyzer or trigger corrective actions. In contrast, the EPA has not prescribed any calibration require ment or given any guidance pertaining to the onsite calibration of AERMOD in a specific environment.

• Standard methods are used to assess the quality of ambient air monitoring data based on biweekly precision checks and accuracy assessments by independent auditors. The EPA has set data quality objectives of 10 percent accuracy and precision for monitors used to evaluate NAAQS compliance. In contrast, the EPA has not prescribed any requirements or given any guidance pertaining to quality assessments of model ing output. (0040)

Commenter (0049) stated initial designations under CAA s ection 107(d) are meant to ensure that actual ambient concentration levels in an area meet the air quality standard. Commenter (0049) stated there is no room in the statutory langu age for an initial area designation that may meet or not meet the standard based on such hypothetical data, and monitoring is the only method that represents actual conditions in an area. Commenter (0049) stated the approach in the DRR is contrary to the e xpress language of CAA s ection 107(d) which does not involve consideration of the “potential to cause or contribute to a violation of the NAAQS,” but only requires the consideration of whether an area actually meets, or actually does not meet, the NAAQS.

Commenter (0049) stated the CAA does not specifically authorize the use of modeling as a tool to make the initial attainment/nonattainment designations for a NAAQS. The statutory languageDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

23 requires only that state governors designate areas as either meetin g or not meeting the NAAQS. Commenter (0049) stated the CAA specifically requires the EPA to re

- designate an area from attainment to nonattainment (or vice versa) only on basis air quality data from ambient air quality monitors. Commenter (0049) stated tha t, in the absence of a specific reference to modeling data in making initial designations and the reference to only monitoring data in the

case of re

- designations, the EPA should similarly require states to use monitoring data in the initial designation pr ocess.

Commenter s (0042 , 0074 ) stated the modeling approach has the effect of making the new standard more stringent than the lower end of the range of the standard in the Proposed Rule because of the conservatism of modeling analyses. Commenter (0074) s tated that, while t he 2010 standard is based on known, measured short

- term concentrations , it is important to note that t he

standard was not based on modeled concentrations. Commenter (0074) stated i t is, therefore, inappropriate to now administratively su bstitute a different estimation technology (modeling)

with documented inaccuracies and over

- predictions as a means of determining that an area fails

to meet the ambient standard. Commenter (0074) stated s uch a substitution effectively modifies

the standard itself, and will certainly produce “non

- standard” and non

- uniform “results” in

variou s geographies across the nation which is not the intention of the authorizing legislation.

Commenters (0072, 0110) stated that because t he revised 1

- hour SO 2 standard is more stringent than the previous NAAQS

, the margin for error is smaller than it has been in the past , and, w hen combined with the conservatism of regulatory models, it is possible that modeled concentrations

would exceed the standard when monitoring indic ates compliance with the standard.

Response :

This final rule does not make any decisions or determinations regarding whether any area is in fact meeting or not meeting the NAAQS based on either monitoring or modeling information.

Those decisions will be made in separate future actions, or have already been made for some areas in prior actions. See e.g. , 78 FR 47191

, August 5, 2013

. Therefore, this final rule does not take final action on the issue of whether it is permissible to implement the commenter’s previous quoted provisions of 40 CFR 50.17(a)

- (c) based on a combination of both monitoring and modeling information where both are available, or exclusively on modeling information where appropriate modeling information is available and monitoring is not . The commenters’ objections appear to focus on how future

- gathered information resulting from the rule may or can be used in subsequent NAAQS implementation actions, but the focus of this rule is on the initial gathering of the information itself. In futu re designation, redesignation, or other implementation actions, commenters may raise their objections to the validity of information that the EPA relies upon in those specific actions, but such objections are beyond the scope of this final rule , and no

fur ther response to their objections is warranted at this time

.

The commenters appear to be raising objections that were also raised after the EPA’s promulgation of the 2010 SO 2 NAAQS, in response to the EPA’s final rule preamble discussion explaining the Agency’s then

- intended implementation approach under the NAAQS. In theirDELIBERATIVE

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24 petitions for judicial review of the NAAQS, several states claimed that the EPA’s discussion of the intended use of modeling in NAAQS implementation contravened the regulatory text of 50.17. However, noting that the petitioners’ claims were addressed to potential final implementation actions that had not yet in fact occurred, the U.S. Court of Appeals for the D.C. Circuit dismissed the petitioners’ claims without addressing their merit s, or lack thereof. See National Environmental Development Association’s Clean Air Project v. EPA , 686 F.3d 803 (D.C. Cir. 2012). Likewise here, the EPA is not yet taking any action to apply modeling regarding any decision of whether an area is or is not m eeting the NAAQS.

In any event , we note that although 40 CFR 50.17(a)

- (c) very clearly sets forth the criteria for determining whether the NAAQS is met at a monitoring site, it does not by its terms restrict how such decisions may be made more broadly in areas impacted by SO 2 sources, including areas where there are no monitoring sites or where monitors are not sited at the point of maximum ambient concentration. Indeed, it is the relative scarcity of such monitors that has caused the

EPA to undertake t his rulemaking to enable states and the Agency to better understand just what the ambient air impacts are from larger sources of SO 2 , which may not be captured by the current limited monitoring network. It is true that p ast area designations processes for most NAAQS (such as for ozone) having violations caused and contributed to by multiple sources over a broad region have relied primarily on air quality monitoring data to identify areas that violate the standard. However, it is important to note, as the EP A explained in the final 2010 SO 2 NAAQS preamble, that there is a long history of also using dispersion modeling information to inform area designations for the SO 2 NAAQS. See , e.g., 75 FR 35520, 35551, June 22, 2010. These

actions support the view that al though the monitoring method in 40 CFR 50

, Appendix A

- 1 or A

2 provides a reference method for measurements of SO 2 in the atmosphere, the provisions of 40 CFR 50 do not preclude the use of evidence obtained by other means, in particular evidence

based on m odeling that indicates that ambient SO 2 concentrations exceed the standard, as grounds for designating areas nonattainment , or for predicting future attainment in SIPs

.



### 2. State responsibility

Comment :

Commenter (0042) stated the modeling approach usurps th e role that s tates are to play when making designations and thus is inconsistent with Congressional intent. Commenter (0042)

stated that the EPA must give great weight to the views of states as to how the NAAQS implementation process should work because Co ngress granted s tates the power to make the initial designations of areas within their borders with regard to a new NAAQS ( commenter
attached and referenc ed a Multiparty Reconsideration Petition at 7

- 10 and North Dakota and

South Dakota Reconsideration Pet ition at 3

- 7). Commenter (0042) stated that, a lthough Congress gave the EPA Administrator authority for making the final designations, Congress made it clear

that the Administrator was to defer to s tate designation recommendations in most situations.

Comme nter (0042) provided the following additional points.DELIBERATIVE

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25 When the 1990 Amendments to the CAA were being debated, the power of the states was questioned. An original version of the Senate Bill would have ended the states’ role in making designations under cer tain circumstances. In response, a House Report asserted that the states are the entities best suited to identify, characterize and report their air pollution to EPA. See CAA Amendments: Toxic Air Pollutants: Hearing on H.R. 4, H.R. 99, H.R. 1212 and H.R. 2585 Before the Subcomm

. on Health and the Environment of the H. Comm. on Energy and Commerce , 101 st Cong. (1989). As a result, the bill was amended to leave the states’ power intact. Congress’ intent that the states play a large role in NAAQS implementati on is therefore clear.

Response :

The EPA refers back to its previous responses explaining why the commenters’ designations

based objections are not relevant to this final rule, which directs air agencies to gather and

submit to the EPA additional data an d information characterizing air quality status in areas within their borders. Indeed, this rule furthers and is fully in the spirit of the values regarding state responsibility that the commenter champions, since the rule provides for states to have the opportunity to generate and submit to the EPA this additional data and information, which can

then be used in a variety of contexts in which the EPA may be responding to state requests for particular actions, including area designations, re

- designations, c lean data determinations, and determinations regarding whether areas have timely attained the NAAQS. Therefore, the EPA disagrees with the assertion that the rule usurps the role of states.



### 3. Historic use of modeling for designations

a. Historic use supports m odeling for designations

Comment :

Commenter (0068) stated this use of modeling is consistent with the EPA ’s historic use of air dispersion modeling for multiple NAAQS implementation purposes, including for attainment designations and provided several ref erences to EPA documents and court citations to

demonstrate that historic use.

Response :

Again, this final rule is not a designations rule and does not implement or discharge the EPA’s duties under CAA section 107. However, the EPA agrees with the comm enter that as a matter of fact the EPA has historically used air dispersion modeling in SO 2 NAAQS implementation contexts, including but not limited to area designations, implementation plan development, and

determinations of whether SIPs are substantially inadequate to attain or maintain the NAAQS. The EPA also agrees that court rulings reviewing these actions have affirmed the use of modeling as lawful and reasonable.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

26 The proposed rule included this brief history of the use of modeling information in pas t area designations for the SO 2 NAAQS:

“ The original SO 2 NAAQS 1 were established in 1971, and the EPA originally designated nonattainment areas for the prior SO 2 NAAQS in March 1978. 2 The Federal Register final rule

for this action noted that certain are as were designated on the basis of modeling data: “In the absence of sufficient monitored air quality data, other evaluation methods were used, including air quality dispersion modeling.” In a September 11, 1978, supplement to the March 3, 1978,

final rule , the EPA responded to commenters and upheld certain designations based on modeling

information. 3 A second supplement to the March 1978 designations notice affirmed the use of modeling for SO 2 designations and determining air quality status, stating that, “the EPA’s policy related to designations for SO 2 permit the use of either modeling or monitoring to determine

attainment status.” 4

“ Five years later, in 1983, the EPA conducted a review of all section 107 NAAQS designations

made to date. A related EPA m emo, “Section 107 Designation Policy Summary,” identified the importance of modeling information for source

- oriented pollutants in cases where existing monitors did not adequately characterize peak concentrations: “In general, all available

information rel ative to the attainment status of the area should be reviewed. These data should include the most recent eight consecutive quarters of quality

- assured, representative ambient air quality data plus evidence of an implemented control strategy that the EPA ha d fully approved. Supplemental information, including air quality modeling, emissions data, etc., should be used to determine if the monitoring data accurately characterize the worst case air quality in the area.” 5



### b. Histor

ic use does not support modeling for designations

Comment :

Commenters (0042, 0046, 0049, 0050, 0052, 0056, 0058, 0064, 0073, 0075, 0080, 0090, 0110,

0111

, and 0116 ) stated that monitoring has historically been used for designation of areas as

attainment or nonattainment. Commenter (004 2) stated that, n ot only has the EPA never before required s tates to conduct modeling to make their initial attainment designations, but the EPA has also historically expressed a preference for reliance on adequate monitoring data, as opposed

1 See 36 FR 8186 (April 30, 1971).

2 See 43 FR 8962 (March 3, 1978).

3 See 43 FR 40416 (September 11, 1978).

4 See 43 FR 40502 (September 12, 1978).

5 Memorandum from Sheldon Myers, Director, EPA Office of Air Quality Planning and Standards, to Regional Office Air Division Directors. “Section 107 Designation Policy Summary .” April 21, 1983.DELIBERATIVE

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27 to modeling r esults, in making designations ; for example, EPA ’s "S O 2 Guideline Document,"

EPA

- 452/R

- 94

- 008 at 2

- 6 (Feb. 1994).

Commenter (0042) stated that, in the 1978 designation process, there were only a few instances in which modeling data were used in addition t o or instead of monitoring data

. Commenter (0046) stated t he use of model output to support NAAQS designations conflicts with prior EPA Policy, which states that only quality

- assured ambient air monitoring data may be used. Commenter (0042) stated that, i n implementing all recently

- promulgated NAAQS, states have

used

-- and the EPA has approved the states’ use of

-- ambient monitoring data, not computer modeling data, to make their initial designations of areas as attaining or not attaining the new

ambient standards. Commenters (0042, 0049) noted that, although it has not been the EPA ’s prior practice to require the use of computer modeling analyses in the initial designation process

, such analyses have been used in the area re

- designation process , where it is necessary to evaluate ranges of proposed strategies for bringing nonattainment areas into attainment.

Commenters (0042, 0049, 0065) referred to the 2010 1

- hour NO 2 NAAQS rulemaking as a good

-- and the most recent

-- example of the Agency’s adherence to the use of monitoring data in making initial § 107(d) designations. Commenter (0042) stated the EPA recognized that it lacked adequate 1

- hour NO 2 monitoring data on which to base initial § 107(d) designations, however, instead of turning to modeling, t he EPA decided on an approach that would allow it to develop an appropriate set of monitored data on which to base initial designations. Commenter (0042) stated the Agency determined that areas without adequate monitoring data would initially be designated as unclassifiable, set forth requirements for the placement of additional monitors, gave states a reasonable time to install and to collect three years of data from the new monitors, and then indicated that areas initially designated unclassifiable could be re

- designated as attainment or nonattainment based solely on the results of the new monitoring data.

Commenters (0042, 0049) stated that monitoring data were also used in making the initial designations for the fine particulate matter (PM 2.5 ) NAAQS tha t the EPA adopted in 1997, even though there was not an abundance of PM 2.5 monitoring data when those NAAQS were promulgated. Commenter (0042) asserted that, in that case, Congress made clear its support for the use of monitoring data to make initial desig nations: noting that there was a “lack of air quality data for fine particle levels, measured as PM 2.5 in the United States” and that such data were to “provide a basis for designating areas as attainment or nonattainment” for the EPA ’s

1997 PM 2.5 NAAQS, C ongress enacted § 6101 of the Transportation Equity Act for the 21 st Century, Pub. L. 105

- 178 (June 9, 1998), which delayed the initial designation process for the new fine particulate matter NAAQS until adequate monitoring data could be gathered and used in the initial designation process.

Commenters (0058, 0075) disagreed that the EPA historically relied upon modeling predictions in designating areas as attaining or not attaining the SO 2 NAAQS. Commenters (0058, 0075) provided the following additional po ints.DELIBERATIVE

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28 Modeling has only played a limited role in a few states where pre

- existing modeling runs were used along with monitoring data in a few cases. See EPA Memorandum from Sheldon Meyers, Director, OAQPS to Regional Directors, Waste & Air Management

Divis ions (Apr. 21, 1983) (EPA did not require s tates to submit modeling predictions as part of the initial area designation process but modeling information, if available, could be submitted in support of an area designation). In addition, modeling has been us ed in

some cases in the area re

- designation process (from nonattainment to attainment). See Id. at 3. (0058)

When the first section 107 area designations were made under the original SO 2 standard, those area designations were based on air quality monitori ng. Specifically, the EPA directed states to use “the most recent four quarters of monitored ambient . . . data

available” and if there were no violations then the EPA directed the states to evaluate “the previous four quarters of monitoring” to ensure tha t the attainment finding would not be based on unrepresentative meteorological conditions. As a result, virtually all of the initial attainment and nonattainment designations under the original SO 2 standard were based on air quality monitoring data alone, not modeling. (0075)

Prior to the adoption of the 1

- hour SO 2 NAAQS

– ever since section 107(d) was added to

the CAA in 1977

– EPA consistently based initial area designations, even those for SO 2, on monitoring data. See Excerpts from the Brief of Petition ers at 29

- 31, National Envtl. Dev. Ass’n’s Clean Air Project v. EPA , 686 F.3d 803 (D.C. Cir. 2012) (No. 10

- 1252) (“SO 2 Petitioners’ Brief”) (Attachment 1 to commenter 0075); Excerpts from Petitioners’ Reply Brief at 3

- 4, 6

- 7, National Envtl. Dev. Ass’n’s C lean Air Project v. EPA (“SO 2 Petitioners’ Reply Brief”) (Attachment 2 to commenter 0075).

Commenter (0073) was concerned that the EPA is changing the basic character of the NAAQS program through greater use of modeling for both area designation and comp liance. Commenter (0073) stated this is a significant policy question that must be transparently addressed by the agency. Commenter (0073) asserted the recent U.S. Supreme Court decision in UARG v. EPA suggested that the Courts should view skeptically whol esale changes in the implementation of the CAA to achieve new policy goals by the agency. Commenter (0073) stated the need for the

EPA to engage in a broader public dialogue about these significant implementation issues.

Commenter (0110) stated t he concep t of using air dispersion model results in lieu of ambient air monitoring data to set NAAQS area designations is unconventional and unprecedented and that

a rea designations for all other NAAQS are based on measurements of ambient air quality obtained using appropriate federal reference (FRM), federal equivalent (FEM), or approved regional (ARM) methods that meet specific siting and quality assurance criteria (40 CFR p art 58, Appendix D and Appendix A, respectively).DELIBERATIVE

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29 Response :

As previously explained in re sponse to similar comments summarized above, this final rule does not implement or discharge the EPA’s designation duties under CAA section 107. Therefore, the detailed comments how the EPA should or must or has in the past conducted its designations

acti ons are not relevant or germane to the requirements the EPA are promulgating in this final rule, which direct state air agencies to gather a nd submit to the EPA their choic e of improved monitoring data or surrogate modeling information to characterize air quality in areas within their borders. The commenters will remain free to raise their designations

- based concerns when the EPA acts to issue designations that affect the commenters, b u t this final rule sets no final designations policy or regulatory provi sions that govern how the EPA or states must implement their respective designations responsibilities.

However, the EPA notes that this rule in fact is the result of a broader public dialogue regarding the implementation of the 2010 SO 2 NAAQS, as explain ed in the white paper and strategy paper on the EPA’s website. Through 2012 and 2013, the EPA conducted numerous outreach efforts with stakeholders from state, local and tribal governments; environmental and public health organizations; and associations an d companies from the polluting industry sectors. Many of those stakeholders requested that the EPA promulgate this very type of rule, to give states the option to choose either conducting improved monitoring or actual emissions

- based modeling to

better ch aracterize areas that are no t well characterized under the very limited and shrinking SO 2 monitoring network , as well as to conserve limited resources

.



### c. Repeal of section 171(2)

Comment :

Commenter (0042, attachment A2) stated that Congress effectively m ade it arbitrary and capricious for the EPA to rely entirely on modeling to determine whether an area is meeting the NAAQS when it repealed the language from s ection 171(2) which allowed states to use either modeling or monitoring for its attainment design ation. Commenter (0042, attachment A2) provided the following additional points.

Prior to the CAA Amendments of 1990, section 171(2) of the Act defined a

“ nonattainment area ” as "an area which is shown by monitored data or which is calculated by air qual ity modeling (or other methods determined by the Administrator to be reliable) to exceed any [NAAQS]." 42 U.S.C. § 7501 (emphasis added). In 1990, Congress deleted any reference to "calculated by air quality modeling (or other methods determined by the Adm inistrator to be reliable)" in designating nonattainment areas. In explaining this change, the official report issued by the Senate Committee that drafted the

1990 CAA Amendments states that "EPA may rely for these designations on sound data

that is availa ble, preferably air quality monitoring data, but in some cases where appropriate and necessary, the [EPA] may rely on modeling or on statistical extrapolation from monitored concentrations of another pollutant." S. Rep. No. 101

- 228, at 15 (1989)DELIBERATIVE

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30 (emphasis added). Therefore, it is clear that Congress believed that air monitoring was preferable to modeling and thus made a conscious effort to change the pre

- 1990 section 171(2) that had treated the two equally.

Response :

Again, this final rule is not impleme nting or discharging the EPA’s CAA section 107

desi g nations duties. Therefore, to the extent the comment focuses on what information the EPA may use to issue a specific area designation, whether it is monitoring data or modeling information relied upon in a future action, that issue will be appropriately addressed at that time, and we therefore do not respond further to this comment here . However, the EPA notes that an argument identical to the commenter’s was presented in recent litigation challenging the EPA’s reliance on modeling to find that a state’s implementation plan was substantially inadequate to attain or maintain the pre

- 2010 SO 2 NAAQS. The court rejected the challenger’s argument as

meritless. Montana Sulphur & Chem. Co. v. EPA , 666 F.3d 1174 ( 9 th Cir. 2012).

In addition, EPA does not agree that in this final rule it would be appropriate to conclude that the CAA should be interpreted as having a preference for using monitoring information as the basis for designations. Even the commenter’s quot ation from the Senate committee report expressly makes the point that the EPA has the discretion to rely on modeling information when warranted.

While the EPA in many cases relies on va l id and certified monitoring data to identify violations of air quality standards for SO 2 and other pollutants, the EPA has also found that modeling when conducted appropriately can be particularly useful for identifying violations (and identify ing the scope of violations) of the SO 2 standard. Indeed, the EPA has found that m odeling in some cases provides more reliable information than monitoring, especially where there are significant concentration gradients that the monitoring network is inadequate to characterize. Furthermore, the text of the CAA, which simplifies the defin ition of nonattainment in section 171(2) and

instead provides a more extensive description of a process for identifying nonattainment areas in section 107(d), contains no indication of a preference between monitoring and modeling. Therefore, the EPA has fr equently reasonably consider ed both modeling and monitoring

information under the CAA , weighing the relative merits of each on a case

- by

- case basis.

The commenter fails to note that an additional element of the Clean Air Act Amendments of

1990 was the a ddition of section 110(a )(2)(K). This section newly requires that states provide any modeling that the EPA requires for purposes of evaluating whether sources are causing violations of any air quality standards.



### d. Rulemaking needed for use of modeling for de signations

Comment :

Commenters (0042, 0048, 0050

, 0053, 0075, and 0116 ) supported the EPA ’s use of notice

- and

comment rulemaking through the DRR to address certain major issues. Commenter (0050) stated

the EPA is statutorily required to use the formal no tice

- and

- comment rulemaking process whenDELIBERATIVE

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31 contemplating any major change in implementation of the C AA and stated the DRR’s proposed

i ncorporation of a source threshold and use of actual monitoring and/or modeling to characterize air quality and make initial area designations are such major changes

.

Commenter (0042) stated that

, prior to the signing of the final 1

- hour SO 2 NAAQS, the EPA did not require the use of computer modeling predictions either in making § 107(d) initial area designations and, therefo re, the EPA may not now change its prior practice without first subjecting any proposed change to notice

- and

- comment rulemaking. Commenter (0042) stated

the EPA cannot change that valid past practice through the issuance of guidance, rather, for the

reason s set out in previous filings with the EPA ( see, e.g. , the Multiparty Reconsideration

Petition at 27

- 28, NEDA/CAP Reconsideration Petition at 4

- 5, TCEQ Reconsideration Petition

at 10

- 14, and State of North Dakota and South Dakota Reconsideration Petition a t 7

- 9), the Agency must use the notice

- and

- comment rulemaking process to consider any such major change to the way in which it implements the CAA

. Commenter (0042) stated courts have recognized that the CAA awards deference to state governors to make initi al designations pursuant to § 107(d) of the Act, citing Pa. Dep’t of Envtl Prot. v. EPA, 429 F.3d 1125, 1129 (D.C. Cir. 2005) (explaining that “[a]s EPA observes, the CAA gives great deference to governors’ recommendations for areas within their states . . . .”). Commenter (0042) stated that, requiring states to deviate from the well

- accepted practice of making attainment designations based on monitored data and instead requiring them to use far more speculative modeling would be an inappropriate infringeme nt on that deference unless and until EPA completes rulemaking to make such a change.

Response :

Although this final rule is not implementing or discharging the EPA’s designation duties under CAA section 107, it obviously is a notice and comment rulemakin g that is establishing the requirement that states further characterize air quality in areas within their borders. Thus, the objections the commenters raise in the abstract regarding the need for notice and comment rulemaking are somewhat moot. More o ver, to the extent that commenters later object to the use of data or information gathered pursuant to this rule in subsequent implementation actions

– whether they are area designations, re

- designations, clean data determinations, or other notice

and comment a ctions, those commenters will have at their disposal a notice and comment

process , to the extent required by law, in which to challenge the EPA’s use of that data or

information on a case

- by

- case basis. Therefore, the EPA disagrees that this final rule its elf constitutes an inappropriate infringement on any deference due to state governments who will in fact lead the data and information gathering steps directed by the final rule

. A dditionally , the

EPA has no reason to suspect that subsequent future actions that may rely upon the state

generated data and information would represent such an infringement either

.



### e. Court decisions on use of modeling for designationsDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

32 Comment :

Commenter (0068) stated that dispersion modeling is a rigorously verified method for evaluating impacts on the SO 2 NAAQS, and has a lengthy and court

- validated history as an appropriate tool for use in designations, including a recent CAA section 126 petition for resolution of cross

- state impacts : Genon Rema, LLC v. EPA , 722 F.3d 513, 526 ( 3rd Cir. 2013).

Commenter (0042) cited several cases and stated c ourts have repeatedly struck down the EPA ’s use of models as arbitrary and capricious when the models prove to be unreliable. Commenter (0042) stated the EPA ’s approach is seriously flawed because the modeling tools that it proffers have not been fully vetted and are far less reliable than the monitoring tools that the EPA seeks to replace. Commenter (0042) stated that, unless and until the EPA takes steps to improve its

recommended tools f

or assessing 1

- hour SO 2 concentrations, those tools will substantially

overestimate 1

- hour concentrations of SO 2, which makes them inappropriate for use in implementing the 1

- hour SO 2 NAAQS. Commenter (0042) provided the following additional points.

An a gency action is arbitrary if, among other things, the agency “failed to consider an important aspect of the problem, offered an explanation for its decision that runs counter to the evidence before the agency, or is so implausible that it could not be ascr ibed to a difference in view or the product of agency expertise” [citing Motor Vehicle Mfrs. Ass’n

v. State Farm Mut. Auto. Ins. Co. , 463 U.S. 29, 43 (1983)]. The EPA has already recognized that measured air quality data are preferred to modeled data and t hat the former should be used to validate the latter [citing Ohio v. EPA , 784 F.2d 224, 231 (6 th Cir. 1986) (citing U.S. EPA, G UIDELINE ON A IR Q UALITY M ODELS (1978)]. When models contradict proven, measured ambient concentrations, the EPA may not use those models to support agency action. To do so would be to ignore the evidence of actual ambient SO 2 concentrations before the Agency. (0042)

Commenter (0109) stated that, w hile c ourts have upheld the use of modeling to determine

whether an area is nonattainm ent or attainment in some circumstances, those cases did not

involve one

- hour standards

.

Response :

The commenters who either favor or object to the use of monitored data or modeling information in any specific future action

-- including but not limited t o designations, re

- designations, or clean

data determinations

– will be able to raise those concerns in those specific actions. The purpose of this final rule is to direct states to better characterize air quality in areas within their borders

that are no t currently adequately characterized by the very limited and shrinking SO 2 monitoring network. It does not implement or discharge the EPA’s duties to issue designations under CAA

section 107.

However, the EPA notes that it disagrees with commenters who a ssert that existing models are

not well suited for use for 1

- hour ambient standards

, as these models h a ve been shown toDELIBERATIVE

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33 perform well in evaluation studies. That being said, the EPA continues to work to improve the models and has implemented updates to addr ess concerns from the modeling community such as options to address low wind conditions.



### f. Nonattainment area requirements

Comment :

Commenter (0042) stated that the EPA ’s new procedures for implementing the §107(d) initial designation process essentia lly conflates the requirements of §107(d), which applies to attainment, nonattainment, and unclassifiable areas

-- with the requirements of CAA Title I, Subpart D, which apply only to nonattainment areas. Commenter (0042) stated the modeling analyses that the EPA now requires states to conduct for all areas is essentially equivalent to the

modeled attainment demonstrations that the EPA has historically demanded that states perform only for nonattainment areas.

Response :

The commenter is incorrect. The mod eling contemplated by this final rule is intended to characterize “current” air quality using recent

, actual emissions in an area . This analysis may inform decisions regarding the area’s status with respect to attaining or not attaining the 1

- hour

SO 2 NAAQ S . The modeling traditionally relied upon to support demonstrations of future attainment in nonattainment areas, instead, is not based on actual emissions , but instead is a projection of what future air quality levels will be based on any additional reduct ions required by new federally enforceable emissi o ns limits for the area that did not exist at the time the area was violating the NAAQS and was designated nonattainment. This type of modeling analysis for an

SO 2 NAAQS attainment demonstration must evaluat e the air quality levels that would be associated with the sources in the area complying with the new allowable emissions limits that were adopted. These analyses are completely different kinds of modeling assessments. Therefore, the assertion that the DRR , which itself is not a designations rule implementing CAA

section 107 , conflates the requirements of CAA section 107 and the requirements for current violating areas to show future attainment is unfounded.

In addition, the commenter appears to be overloo king significant provisions in section 110 and elsewhere in Subpart A of Title I that authorize the EPA to require modeling for any location in the country , for example

, to evaluate whether an area is attaining the air quality standard. Especially pertine nt is section 110(a)(2)(K), which requires that states provide for conducting and submitting results of “such air quality modeling as the Administrator may prescribe for the purpose of predicting the effect on ambient air quality of any emissions of any ai r pollutant for which the Administrator has established a national ambient air quality standard.” T his paragraph of the CAA authorizes the EPA to prescribe that modeling be conducted for the entire country, not only for nonattainment areas, for purposes ma tching those of the DRR . Therefore , this paragraph must also be interpreted as authorizing the EPA to require air quality characterization either through monitoring or modeling. Additional authority for this rule is given in section s 114DELIBERATIVE

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34 and 301(a) of the CAA. Contrary to the comment, these authorities, which are outside Part D of Title I of the CAA, authorize EPA to require modeling to assess air quality anywhere in the country irrespective of attainment status.



### C. Monitoring and/or modeling for designation s

1. Support option to model and/or monitor

Comment :

Com menters (0041, 0043, 0048, 0054, 0058, 0062, 0064, 0066, 0071, 0073, 0080, 0082, 0085, 0090, 0092, 0101, 0115, and 0117) support ed the option t o use modeling and/or monitoring for

SO 2 as this option pr ovides appropriate flexibility for both the states and affected sources

.

Commenter (0054) supported the EPA’s finding that modeling may not be appropriate for all

SO 2 designation scenarios and commended the EPA on its proposal to allow implementing state air agencies the flexibility to utilize monitoring data in establishing attainment determinations for

the SO 2 NAAQS. Commenter (0073) stated that, for some locations, the lack of monitors presents challenges for making accurate determinations and s upport ed the ability of states to choose to evaluate NAAQS attainment through either dispersion modeling or ambient monitoring. Commenter (0092) support ed the EPA ’s encouragement to air agencies that they use monitoring to characterize air quality near sources not easily characteriz ed through dispersion modeling.

Commenters (0043, 0040, 0048, 0056, 0058, 0066, 0072, 0073, 0089, 0092, 0094, 0095, and 0111) stated that ambient air monitoring data should be the primary basis to designate

nonattainment areas. Comment er (0056) stated that monitoring has historically been used, and should continue to be the primary basis for designation of areas as attainment or nonattainment. Commenter (0058) stated that, while they support the EPA ’s proposal to allow states to elect t o use modeling for some areas, the EPA must clearly acknowledge that monitoring is superior to modeling for characterizing actual ambient air quality. Commenters ( 0048, 0088, 0094, and 0095) stated that, as modeling is frequently affected by emissions inpu ts, meteorological data, and local geography, it is not as accurate or reliable as real

- time, multiple

- year monitoring.

Commenter (0089) stated that, in the eyes of the public, a valid result from a representative monitoring site always carries greater l egitimacy over a modeled value and models are often viewed by the public as hypothetical constructs that are unreliable, possessing variable uncertainty, and may be subject to manipulation of the input data in order to achieve a desired result. Therefore, in order to retain the trust of the public, commenter (0089) suggested the EPA should provide every opportunity to the states to utilize existing monitoring site data in their area designation recommendations, while at the same time ensuring that those mon itored results are representative, meet quality assurance criteria, and are otherwise scientifically valid

.DELIBERATIVE

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35 Response:

The EPA agrees with commenters who stressed the need to give air agencies the option to

characterize SO 2 ambient air quality through eit her enhanced monitoring or modeling, and the EPA is maintaining that approach in this final rule. The EPA believes that the commenters have not presented any persuasive reasons for changing the basic position s discussed in the preamble

to the final rule of the 2010 SO 2 NAAQS rulemaking, the Strategy Paper, or in the proposed rule for why both air quality modeling and ambient monitoring are appropriate tools for characterizing ambient air quality

. However, as explained in the preamble to the final rule, the EPA is not taking final action to make any determinations regarding any area’s status with respect to attaining or not attaining the NAAQS, but is only prescribing criteria and a process for how and when air agencies are to gather and provide to the EPA ad ditional needed information. How the information is used in subsequent actions evaluating the attainment status of specific areas will depend upon the information that air agencies collect in the future and what it shows about areas’ ambient air quality.



### 2. S upport monitoring data use only

Comment :

Commenters ( 0037, 0040, 0046, 0049, 0050, 0051, 0057, 0059, 0074, 0084, 0109

, and 0116 ) generally stated that n onattainment designations should only be made based on data from 40

CFR p art 58 compliant monitoring s howing a violation of the standard.

Commenter (0109) believe d that areas can only be properly designated as "nonattain ment" based on monitoring data because (1) modeled predictions are inherently less accurate a nd over predict ambient impacts and (2) non attainment designation s impose significant consequences on local

economies and limited state resources

. Commenter (0059) stated that given the significance

associated with mis

- designating an area, the most prudent approach would include minimal uncertainty (i.e., no reliance on air quality modeling) , and recommended monitoring be the sole approach used for designating the SO 2 attainment status.

Commenters (0042, 0063, 0065) stated that, where an area with air quality monitors shows compliance with the 1

- ho ur NAAQS, the EPA should not require computer modeling to be conducted prior to designating the area “attainment.” Commenter (0042, attachment B) stated

that w here modeling is conducted in an area with at least one monitor, the modeled results

should be co mpared against the monitored values and, i f the modeled concentrations are found to over predict at the monitor, then the modeling analysis should either be adjusted to come into agreement with the monitored concentrations, or set aside as unworkable.

Com menter (0084) believed modeling could be used in a screening manner to effectively identify where monitors should be placed but that to depend on a modeling result to correctly designate between attainment and non

- attainment is beyond the intended purposes of models. Commenter (0109) stated that, w hile predictive modeling can be an appropriate tool for states toDELIBERATIVE

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36 use to "screen" areas for attainment designations, monitoring that actually measures ambient concentrations must be a required component of a ll non attainment designations. Commenter (0052 ) and commenter ( 0052 a, June 2012 comments from Southeastern State Air Pollution Control Agencies attached to commenter 0052 comments ) stated t here must be ambient data demonstrating that SO 2 levels are above the sta ndard before the EPA initiates designation of any area as not attaining the standard.

Commenter (0040) is concerned that the DRR will create a precedent for the EPA to utilize modeling for other NAAQS designations. Commenter (0040) asserted most of the pr ior support from stakeholders for using air dispersion modeling output for SO 2 NAAQS area designations was driven by concerns that state, local, and tribal air agencies did not have sufficient resources to monitor the nearly 2

, 000 sources that the EPA had previously anticipated targeting for impact assessments, according to comments summarized in the preamble to the Proposed Rule. Based on the much smaller number of sources targeted by the DRR

, commenter (0040) stated the gaps between anticipated state, loc al and tribal agency resources and the expected demands of characterizing source impacts are not nearly so large. Therefore, commenter (0040) believed substituting quality assured ambient air monitoring data with modeling output is no longer

needed.

Respo nse:

As stated previously, t he EPA agrees with commenters who stressed the need to give air agencies the option to characterize SO 2 ambient air quality through either enhanced monitoring or modeling, and the EPA is maintaining that approach in this final rule. The EPA believes that the commenters have not presented any persuasive reasons for changing the basic position s previously discussed in the preamble to the final rule of the 2010 SO 2 NAAQS rulemaking, the Strategy Paper, or in the proposed rule for w hy both air quality modeling and ambient monitoring are appropriate tools for characterizing ambient air quality

. However, as explained in the preamble to the final rule, the EPA is not taking final action to make any determinations regarding any area’s st atus with respect to attaining or not attaining the NAAQS, but is only prescribing criteria and a process for how and when air agencies are to gather and provide to the EPA additional needed information. How the information is used in subsequent actions

ev aluating the attainment status of specific areas will depend upon the information that air agencies collect in the future and what it shows about areas’ ambient air quality.

In addition, concerns about what precedent this rulemaking might set with respec t to how the EPA will address other pollutants are not germane here, because this rulemaking is only addressing SO 2

. This final rule establishes no precedent for how states would be expected to gather and submit information for assessing air quality status under any other criteria pollutant NAAQS , and EPA expects the need for, and desirability of, collecting dispersion modeling to characterize actual air quality will vary from pollutant to pollutant

. As stated in the preamble, the EPA believes that the appr oach set forth in this rule directing air agencies to gather additional data to characterize ambient air in the vicinity of larger SO 2 sources is uniquely suited for implementation of the 1

- hour SO 2 NAAQS, and the Agency does not anticipate it to be used f orDELIBERATIVE

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37 other NAAQS pollutants.



### 3. Do not support model ing to make attainment designations

[Also see section V. B .9. for comments specific to AERMOD

. ]

Comment :

Commenters ( 0040, 0042, 0043, 0046, 0049

, 0051, 0052, 0053, 0055, 0056, 0057, 0059, 0063, 0065, 0074, 0075, 0079, 0083, 0087, 0088, 0090, 0095, 0108, 01 09, and 0110) generally stated they do not support using the air quality models to make attainment d esignations

. Commenter s (0051 , 0108 ) stated that modeling is not appropriate for compliance determination s and therefore designation s

. Commenter (0049) stated modeling data should only be necessary where states must make predictions about future circumstances in order to demonstrate compliance with specific CAA requirements.

For example, the Prevention of Sig nificant Deterioration ( PSD ) program prohibits the construction of a new or modified major stationary source in an attainment area unless the permitting authority can demonstrate that the increased emissions from the source

will not cause or contribute to an air quality violation within that area. Modeling data are useful for this purpose because it can predict the air quality effects that could result from the added emissions within the general vicinity of the proposed new or modified source. In addition, nonattainment SIPs will benefit from modeling, because modeling can demonstrate the effectiveness of proposed control strategies to bring a nonattainment area back into comp liance with the standard.

Complex terrain and/or multiple sources

Commenters (00 46, 0089) stated that a modeling

- based assessment would be difficult to implement in complex terrain or in areas where there are multiple emission sources without hourly emissions and exhaust data.

Concentration gradients

Commenter (0110) stated the EPA ’ s consideration for basing SO 2 NAAQS area designations on model output is driven mostly by the EPA ’s perception that there are sharp gradients in actual “design concentrations” that monitors cannot resolve because of limitations in the number of

monitors t hat can be placed in an area. Commenter (0110) stated the EPA ’s concerns regarding sharp concentration gradients for SO 2 concentrations are mitigated by the form of the standard, which by design (3

- year average of the 99th percentile) results in a more sta ble form which will smooth out any short

- term concentration gradients for specific hours. Commenter (0110)

referenced a study which compar ed AERMOD modeling and monitored data in North Dakota

and stated it implie d that the concentration gradient among the 5 monitors with up to a 20 kilometer (km) separation was insignificant.DELIBERATIVE

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38 Cos ts

Commenter (0083, 0088) stated that t he fact that modeling is “cheaper” than monitoring is not a substitute for the superior accuracy of actual monitored data ; n or do cheaper co sts of modeling offset the regulatory costs and other burdens on sources and communities that result from nonattainment designations based on modeling. Commenters (0042, 0051, 0108, and 0110)

stated the modeling

- based approaches for SO 2 NAAQS nonattainment designations will likely force communities and the facilities that operate in them to take costly steps to combat modeled pollution problems that do not exist

.

Over

- predicts

Commenters (0042, 0046, 0051, 0072, 0073, 0074, 0080, 0109, and 0110) stated t hat model s overestimate the monitored values. Commenter (0046) referred to several modeling studies. Commenter (0110) stated mo deling results for over 50 large coal

- fired power plants submitted to the docket by the Sierra Club were found in many cases to s ubstantially overestimate the measured concentrations at the nearest monitors, in some cases, by up to several hundred percent; however, a portion of this bias is attributable to the use of allowable instead of actual

emissions. Commenter (0110) also refer enced model results for Detroit that were prepared by the Michigan Department of Environmental Quality in which th e model overestimated the monitored design value at one m onitoring site by a factor of two. Commenter (0109) stated that existing

models vastl y over

- predict actual ambient 1

- hr SO 2 levels and should be limited to use as a screening tool to confirm attainment status and as a factor to guide state efforts to locate

monitors.

Uncertainty

Commenters (0042, 0046, 0063, 0065, and 0110) provided sev eral technical points regarding quality assurance, model revisions, and uncertainty which are summarized below.

Model output cannot be quality assured in the same way that monitoring data are. No limits exist on the uncertainty of the model output that wo uld be used to set NAAQS designations because there is no way to assess model uncertainty for a specific regulatory application. If modeling is used as a basis for nonattainment designa tions, model performance should be calibrated/verified at similar locat ions/terrains for which monitoring data are available.

When models are revised, modeling results would need to be re

- evaluated with each modeling change to ensure that prior conclusions from modeling are valid. This seems to be an untenable position for s tates and sources to be in with respect to attainment or

nonattainment status.

EPA ’s tolerance for uncertainty in model output is incongruous with, and undermines theDELIBERATIVE

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39 robust program for quality assuring ambient air monitoring data. The degree of

uncertain ty in the ambient air monitoring data used to set NAAQS area designation is routinely assessed using procedures prescribed by 40 CFR p art 58. T he accuracy of model output cannot routinely be assessed and even under the best conditions, model accuracy does not meet the data quality objectives of an ambient air monitor operated according 40 CFR p art 58

.

Commenters (0055, 0074) questioned why the significant efforts to assure monitoring is accurate and of high quality are not also applicable to modeling

. Com menters (0055, 0074) stated this disparity is not logical since modeling depends on many assumptions that are automatically controlled for in a monitoring situation (e.g. representative emissions, representative meteorology).

Commenter (0075) disagreed t hat modeling provides consistently reliable information on which to base designations for the 1

- hour SO 2 NAAQS. Commenters (0094, 0095) stated that modeling results are highly affected by emissions data, meteorological data and local geography, all of

whic h have proven to be highly subjective in nature and far less reliable than monitoring. Because of the reliability of monitoring and limitations of modeling, commenter (0053) asked

that the EPA not force the use of modeling in making nonattainment determina tions.

Response:

As stated previously, t he EPA agrees with commenters who stressed the need to give air agencies the option to characterize SO 2 ambient air quality through either enhanced monitoring or modeling, and the EPA is maintaining that approach i n this final rule. The EPA believes that the commenters have not presented any persuasive reasons for changing the basic position s previously discussed in the preamble to the final rule of the 2010 SO 2 NAAQS rulemaking, the Strategy Paper, or in the propos ed rule for why both air quality modeling and ambient monitoring are appropriate tools for characterizing ambient air quality

.

To the extent that commenters seek to persuade the EPA that mo deling should not be included in

this rule as a characterization option because of alleged reliability issues, the EPA disagrees. The EPA has conducted extensive comparisons of modeled versus monitored concentrations, demonstrating the reliability of the model estimates, so long as the model inputs correspond to

the act ual circumstances (e.g., the actual emissions) being monitored, and so long as

concentrations a t comparable locations are being compared. However, as explained in the preamble to the final rule, the EPA is not taking final action to make any determinations regarding any area’s status with respect to attaining or not attaining the NAAQS, but is only prescribing criteria and a process for how and when air agencies are to gather and provide to the

EPA additional needed information. How the information is used in subsequent actions evaluating the attainment status of specific areas will depend upon the information that air agencies collect in the future and what it shows about areas’ ambient air quality.DELIBERATIVE

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40 The EPA recognizes the uncertainties in modeling, but doe s not believe that they justify

exclusion of modeling as a characterization option. To the contrary, the EPA is continuing to

allow a choice of characterization option s , noting that the EPA also recognizes uncertainties in monitoring, most notably in asses sing maximum concentrations across an area, which the commenters may be overlooking. As one example, model concentration estimates in an area with complex terrain may have greater uncertainty than model estimates in an area with simple terrain, but the use of monitored data at one site (or at a finite network of sites) to extrapolate air quality elsewhere in an area would also have greater uncertainty in an area with complex terrain than in an area with simple terrain. Similarly, the existence of multiple e mission sources would increase the uncertainty in both a modeling assessment and an extrapolation of monitoring

results.

The EPA disputes the implicit contention that the choice between modeling and monitoring is a choice between “cheaper” versus “superio r accuracy.” Monitoring may be more accurate in assessing concentrations at the particular location being monitored, but monitoring may well be less accurate in estimating concentrations (or even estimating whether a violation is occurring) at

other locat ions within an area of interest. The EPA believes that a modeling analysis using

reliable actual emission information will in general have similar reliability in assessing whether an area has violations as a monitoring assessment based on a well

- designed m onitoring network

. The commenter provides no basis for the premise that , were EPA to use such a modeling

- based analysis in supporting a nonattainment designation , that such a designation “will likely” address “problems that do not exist

. ” If

, in an action that is informed by modeling

, the commenter feels that the data identify problems that “do not exist,” the commenter will be free to raise that point regarding that specific action.

Concerns with the reliability of models are addressed in section V.B.9

. The commentary on the Michigan modeling appears to reflect a comparison of a monitored concentration against a maximum concentration modeled at a different location. Since Michigan’s modeling of actual emissions gave results that were nearly identical to the monitored value, the comments

demonstrate not the over prediction of the model but rather the underestimation of maximum concentrations from monitoring if the monitoring network does not fully reflect the spatial

variations in concentrations.

The com ments on the reliability of monitoring do not address the reliability of monitors to represent concentrations at unmonitored locations. The procedures of p art 58 improve the reliability of monitored data in representing concentrations at the monitored loca tion, but significant errors can arise from assuming that concentrations elsewhere are similar, and in fact modeling is sometimes a more reliable means of estimating whether concentrations throughout

an area exceed the standard. Although area

- specific judg ments regarding the relative reliability of all available evidence will be the subject of separate future actions , the EPA concludes that both monitoring (based on a well

- designed network) and modeling (using best available inputs)

, when conducted appropri ately, can satisfy the purpose of this rule to provide a suitable characterization of air quality in priority areas.DELIBERATIVE

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41 

### 4. Support model ing to make designations

Comment :

Commenters (0039, 0062, 0067, and 0068) s upport ed the EPA ’s proposal to allow modeling to be used to characterize air quality for making designations

.

Commenter (0039) supported the use of modeling if it uses either recent actual emissions or enforceable emission limitations. Commenter (0039) believed AERMOD over predicts , but

added that if th e modeling results demonstrate that recent actual emissions and emissions below enforceable limits do not predict exceedances of the 1

- hour SO 2 NAAQS, then it is unlikely that ambient monitoring would detect an exceedance of the standard. Commenter (0039) believed dispersion modeling can be a reasonable, conservative approach on which to base designation, though it would be unreasonable to require states to model potential emissions.

Commenter (0062) agree d with the EPA that modeling is a technically valid and defensible tool to assess impacts near SO 2 emission sources. Commenter (0062) stated SO 2 lends itself to modeling because it is a near field, source

- oriented pollutant with localized health impacts and does not react in the same way as regional pollut ants, like ozone or PM 2.5

. Commenter (0068)

stated that a ir dispersion modeling is the best method for evaluating the short

- term impacts of large SO 2 sources. Commenter (0068) stated that modeling, and not monitoring, is the appropriate method for ascertai ning source

- derived impacts on attainment of the NAAQS because modeling can capture ambient concentrations across vast areas, and is sensitive to minute changes in meteorology that monitors are unable to capture.

Response:

The EPA appreciates the suppor t of commenters who agreed with the EPA’s proposal to allow modeling to be used as a surrogate for monitoring to assess ambient SO 2 concentrations. As stated previously, t he EPA agrees with commenters who stressed the need to give air agencies the option t o characterize SO 2 ambient air quality through either adequate monitoring or modeling, and the EPA is maintaining that approach in this final rule. The EPA believes that monitoring and modeling both have advantages and disadvantages. Most notably, monitori ng can provide a more precise indication of concentrations at a particular location, while modeling can provide information at a greater range of locations. Nevertheless, the EPA believes that both approaches can provide adequate information in most cases, so that the EPA believes that a rule providing air agencies the option to use either method is warranted. The EPA disagrees with the assertion that monitoring should not generally be allowed to ascertain impacts under the SO 2 NAAQS, and points out that no one challenged the final NAAQS on this basis or the part 58 monitoring provisions revised when the NAAQS was promulgated. The EPA believes that the commenters have not presented any persuasive reasons for changing the basic position s previously discussed in the preamble to the final rule of the 2010 SO 2 NAAQS rulemaking, the Strategy Paper, or in the proposed rule for why both air quality modeling and ambient monitoring are appropriate tools for characterizing ambient air quality

. However, as explained inDELIBERATIVE

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42 the preamble to the final rule, the EPA is not taking final action to make any determinations regarding any area’s status with respect to attaining or not attaining the NAAQS, but is only prescribing criteria and a process for how and when air agencies are to gather and provide to the

EPA additional needed information.



### 5. R ule text regarding monitoring preference

a. S ection 51.1201

Comment:

Commenters (0040, 0044) suggested the text of proposed section 51.1201 be clarified to make clear that monitoring rathe r than modeling is the EPA ’s preferred methodology . Commenter (0040) suggested the following revisions to the proposed regulations:

§ 51.1201 Purpose. The purpose of this subpart is to require air agencies to take actions to develop air quality data chara cterizing current maximum 1

- hour ambient concentrations

of SO 2 more extensively across the United States through either additional ambient air quality monitoring or air quality modeling analyses at the air agency’s election. Except as otherwise provided in § 51.1203, ambient air quality monitoring is the methodology that should be used for this purpose. Such additional monitoring and modeling data may be used in future initial area designations by the EPA for the 2010 SO 2 NAAQS, or for other actions designe d to ensure attainment of the 2010 SO 2 NAAQS and provide protection of the public from the short

- term health effects associated with exposure to SO 2 concentrations that exceed the NAAQS.

Commenter (0044) believed that, if the EPA does not intend for the rule to express a preference for modeling nor intend to provide air agencies and the Regional Offices with unfettered discretion to elect modeling over monitoring, then both the preamble to the final rule and its regulatory text should be clarified to say so. To accomplish this, commenter (0044) suggested that proposed section 51.1201 be revised to read:

§ 51.1201 Purpose. The purpose of this subpart is to require air agencies to take actions to develop air quality data characterizing current maximum 1

- hou r ambient concentrations

of SO 2 more extensively across the United States through either additional ambient air quality monitoring or air quality modeling analyses at the air agency’s election solely for the purpose of making designations of attainment of the SO 2 NAAQS . Such additional monitoring and modeling data may be used in future initial area designations by the EPA

to ensure attainment of the SO 2 NAAQS and provide protection of the public from the

short

- term health effects associated with exposure to SO 2 concentrations that exceed the NAAQS.DELIBERATIVE

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43 Response:

The final rule does not incorporate either of the suggested amendments to proposed section

51.1201. First, regardless of what its own general preferences might be, the EPA disagrees that it is appropri ate to express a “preferred methodology” within a rule intended to provide air agencies with the choice between using monitoring

, or modeling

, to characterize ambient SO 2 concentrations. Those decisi o ns will be made by air agencies on case by case bases th at depend upon multiple variables, including source populations, meteorology, area topography, and available state resources, which the EPA does not intend to prejudge. Second, the EPA disagrees that the information generated by the rule’s future implement ation should be explicitly limited

for use for making attainment designations. It is not reasonable at this point to predetermine what specific conclusion that information may reasonably support, or in what NAAQS implementation

or other context.



### b. Section 51.1203(b)

Comment:

Commenter (0044) recommended that the regulatory text of section 51.1203(b) be amended to include the following sentence which indicates a preference for monitoring: The technique which should ordinarily be used for this purpose is ambient air quality monitoring, except where the air agency can demonstrate that the use of ambient air quality monitoring is not feasible.

Commenter (0040) recommended that the regulatory text of section 51.1203(b) be amended to include the following s entence which indicates a preference for monitoring: If an air agency desires to use air quality modeling in lieu of monitoring, the air agency, in its submission required by § 51.1203(d), shall identify why it is unable to proceed with monitoring. EPA sha ll not deny a reasonable air agency request to use modeling in lieu of monitoring

.

Response:

Consistent with the recommendations the EPA received during its stakeholder review process,

the EPA believes that, regardless of what its own general preferences might be, it would be inappropriate to identify

, in a rule applicable to state, local, or tribal air agencies, a preference for either monitoring or modeling. Both approaches have their advantages and disadvantages; for example, monitoring likely provides a better indication of actual air quality at a particular location, while modeling provides better information regarding concentrations at a range of locations. This rule is premised on a finding that either monitoring or modeling provides adequate inform ation to characterize air quality, and the EPA believes that the air agencies

should make their own choice of methods based on their own evaluation of the relative merits of

the alternatives on a case

- by

- case basis. Furthermore, the EPA believes that it wo uld be inappropriate to establish additional requirements that air agencies provide particular kinds of justification for their choice of air quality characterization approach , or to create a presumption that air agencies would have to overcome in order to be able to use modeling

.DELIBERATIVE

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44 

### c. Bias for modeling rather than monitoring

Comment :

Commenters (0051, 0056, 0063, 0065, 0088, and 0107) were critical of what they perceived as a

bias in the Proposed Rule supporting modeling rather than monitoring SO 2 sources for purposes of designations as a result of the severely compressed schedules for submission and approval of monitoring plans and collection of data. Commenter (0107) stated that the proposed schedule is

ambitious

-- especially if a site requires multiple monit ors

— and, as such, the proposed schedule sets states up to fail and potentially forces us into the modeling approach. Commenter ( 0056)

stated concerns over the EPA ' s comment that the agency would force modeling, if monitor deployment is delayed, and stated that this approach adds to the uncertainty of taking the monitoring approach and make s it a less attractive option.

Commenter (0051) stated th e EPA should reconsider the proposed timeline, monitoring

- related financial burden, and monitoring to modeling pe nalties as they appear to make modeling the only viable option states have for assessing attainment. Commenter (0051) stated t he EPA should

remove the obstacles the Proposed Rule places in the way of reaching its stated goal of providing states with option s for characterizing air quality. Commenter (0051) stated t he multitude of uncertainties with and unrealistic timeline for designing and financing a source

- oriented SO 2 monitoring network make it seem as if the EPA's true intent is to force air agencies to rely solely on modeling.

Response:

The EPA does not specify a preference for modeling as opposed to monitoring, as claimed by

some commenters. The final rule instead provides flexibility to air agencies to choose which approach would be most appropriate on a n area

- by

- area basis. While the timelines that apply to both pathways are expeditious, the EPA disagrees that the timelines create a bias toward a particular outcome. The rule offers two pathways for characterizing air quality, each of which

has an ar ray of advantages and disadvantages, the weight of which are in significant part a

function of case

- specific factors such as availability of suitable monitoring sites, spatial gradients, availability of resources for monitoring, and the presence of complic ations such as complex terrain or large water bodies. One’s view of the relative merits of the two pathways is

also a function of one’s views of the reliability of the two pathways for indicating air quality throughout an area, as well as whether one consi ders it advantageous or disadvantageous to provide for earlier versus later designations. Thus, a comment that the schedule for monitoring is expeditious, without examining whether the schedule for modeling is expeditious, does not justify a conclusion tha t the proposed rule timeline is biased toward one or the other authorized pathway

.

The EPA believes that both the schedule for monitoring and the schedule for modeling included

in the final rule are reasonable timelines that provide adequate time for air agencies to complete the necessary steps. Air agencies that are weighing their choice of the two methods have theDELIBERATIVE

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45 opportunity to consider case

- specific factors that may require more or less time for either option in particular situations, but the EPA does not believe that a national comparison of the expeditiousness of the modeling and the monitoring schedules would indicate a bias in the rule toward one or the other option.

Moreover, i n response to comments about reconsidering the proposed timeline , the E PA is providing additional time for air agencies to notify the EPA of their choice of using modeling or monitoring to characterize air quality around specific sources

. Accordingly, the deadline for this election will be July 1, 2016. The EPA recognizes tha t evaluating the relative merits of modeling and monitoring for any particular area, including identification of funding sources for any new monitoring that might be under consideration, warrants more time than was provided under the proposed rule. Consist ent with this revision, the EPA is also revising the deadline for air agencies using modeling to submit modeling protocols for the applicable areas.

Thus, under the final rule, by July 1, 2016, the air agency must submit its selection of whether

each are a will be characterized through modeling or monitoring and, depending on that selection, either must submit a modeling protocol or must include information in the Annual Monitoring Network Plan that specifies the monitoring to be conducted to address the r equirements of this rule. The EPA believes that this revised deadline still provides for timely planning for air quality characterization to occur (through modeling) or begin (through monitoring) at the beginning of 2017. Conversely, the EPA does not agree that any later deadline for selecting the means of addressing air quality characterization requirements would provide the time and flexibility to address in a timely way any issues that arise after the selection is made. The result would be that

a later d eadline for this selection could jeopardize timely receipt of information characterizing air quality.

Notwithstanding this revision, t he Agency encourages air agencies to start their investigation of this issue as soon as practicable. The EPA strongly en courages each air agency to consult with its respective EPA Regional Office to identify sources exceeding the emission threshold in the final rule and any other sources that do not exceed the emission threshold but near which further air quality characteri zation would be warranted

. Similarly, the EPA strongly encourages air agencies to hold early discussions regarding the manner in which modeling or monitoring might be used. As one example, if the air agency believes that the existing monitoring network suf fices to characterize air quality, early discussions with the EPA would be essential for assuring that the intended selection of monitoring is based on appropriate assumptions regarding the network’s ability to characterize air quality near the applicable source(s) without further network adjustments.

EPA is also clarifying its expectations should an air agency commit to commence operating new monitors by January 1, 2017 but then fail to do so. In this case, the air agency would have failed to comply wi th the DRR , but this failure would not trigger a requirement to meet the requirements of the modeling pathway of the DRR

. It is worth noting that the court order that

dictates EPA’s SO 2 designation schedule specifies that areas without new monitoring

comm encing by January 1, 2017 shall be designated by December 31, 2017, a mandate thatDELIBERATIVE

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46 would presumably apply to areas that commit to but then fail to commence timely new monitoring. Nevertheless, the DRR itself does not create the uncertainty about the monit oring approach that the commenter fears.



### D. Considering all monitoring/modeling data

1. Do not support considering all monitoring/modeling data

Comment :

Commenter s (0046 , 0050 , 0078, and 0088 ) stated the EPA should not rel y upon m odeling that

has been perform ed recently by third parties or non

- governmental organizations for large electricity generating units ( EGUs ) in some states that suggests that some areas should be

classified as nonattainment because it i s of very low quality. Commenter (0088) stated that Sierra Club’s submission of modeling based on permit allowables is fundamentally flawed s ince these emissions are unlikely to occur at a plant or for that matter, at the same time from multiple plants being modeled . Commenter (0088) stated that it is arbit rary and capricious as well as unreasonable for “allowable” or plant “PTE” to be used as inputs to describe existing ambient air

conditions.

Commenter (0078) stated that t he EPA should make clear in the rule language or preamble that it will only base des ignation recommendations for sources/areas under the modeling pathway on modeling conducted specifically under the parameters of the final DRR (i.e., modeling protocols submitted by states in January 2016) and that other modeling will not be considered. Co mmenter (0078) stated that t he y conducted preliminary modeling of sources with SO 2 emissions over 100

tpy in 2011

- 2012 and that m ost of these sources would not be included in modeling required by

the Proposed Rule because they are not over EPA's proposed e missions thresholds and may or may not be re

- modeled.

Response:

As indicated in the final rule and elsewhere in this RTC document, this rule only establishes requirements to characterize SO 2 air quality around priority sources across the country; it does

not govern the procedures for f uture area designations and how such air quality data may be used in that process. For situations where modeling will be used to characterize current air quality, the

EPA has issued a Technical Assistance Document that descr ibes how such modeling c ould be

done with actual emissions. The EPA does not recommend that allowable emissions be used for modeling intended to characterize current air quality , except to the extent that states choose to

model allowable emissions as a mea ns to demonstrate that current and future emissions are required to be low enough to provide for current and continued attainment

.

The EPA is finalizing its proposed approach of requiring that air agencies choosing modeling to characterize ambient air qua lity be required to submit modeling analyses to the EPA Regional Office. Irrespective of whether the state or a third party conducts the modeling, it is the state’sDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

47 responsibility under the CAA to submit the information that this rule requires. The EPA

ant icipates that any state submittal of third party modeling would reflect a review as to whether

the state believes that the modeling satisfies applicable requirements. Moreover, the EPA anticipates that the submittal would provide adequate information for t he EPA to review the adequacy of the analysis as well.



### 2. Support considering all monitoring/modeling data

Comment :

Commenter (0068) stated that

, while the draft DRR focuses primarily on requirements to be placed on states and tribes to prepare information for designations purposes, any final Rule that

is issue d must make clear that data from other sources, including from environmental and public health NGOs, will be considered by the EPA while making designations. Commenter (0068)

stated that i t is a bedro ck principle of administrative law that an agency may not ignore information put in front of it, such as Sierra Club’s modeling submitted with these comments. See generally Motor Vehicle Mfrs. Ass’n v. State Farm Mut. Auto Ins. Co. , 463 U.S. 29, 43 (1983) (holding that it was arbitrary and capricious for the agency to ignore an important aspect of an issue placed before it); see also NRDC v. EPA , 571 F.3d 1245, 1254 (D.C. Cir. 2009) (restating the EPA ’s own statement that additional information presented in a notice

- and

comment rulemaking must be considered during the rulemaking by the corresponding state and EPA) (citing 70 Fed. Reg. 71,612, 71,655).

Response:

The EPA is finalizing its proposed approach of requiring that air agencies choosing either

mo deling or monitoring to characterize ambient air quality be required to submit the monitoring

or modeling analyses to the EPA Regional Office. Irrespective of whether the state or a third party conducts the modeling or submits the monitoring data , it is th e state’s responsibility under the CAA to submit the information that this rule requires. The EPA anticipates that any state

submittal of third party modeling or monitoring data would reflect a review as to whether it believes that the modeling or monitori ng data satisfies applicable requirements. Moreover, the EPA anticipates that the submittal would provide adequate information for the EPA to review the adequacy of the analysis as well.

In addition, the EPA would consider monitoring or modeling conducte d by a third party to be an appropriate means for air agencies to obtain the data necessary to meet the requirements of this rule, provided that the state provides oversight to assure that (1) any monitoring is conducted in a manner that is equivalent to S LAMs and quality

- assured in accordance with applicable requirements, and (2) any modeling analysis that the state submits, even if it was initially provided to the state by a third party, is done in a reasonable manner (for example. follow ing the

recommend ations in the m odeling TAD )

.

To the extent that the commenter is addressing the designations process, to urge that the EPADELIBERATIVE

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48 consider third party information in promulgating designations, this rule does not define the designations process, and so statements regarding the types of information that the EPA would consider in the designations process are not directly germane to this rulemaking. Nevertheless, as a general matter, the EPA agrees that it must weigh all information that interested parties provide

wh en conducting rulemaking such as to promulgate designations. However, information that commenters wish the Agency to consider in issuing specific area designations should be submitted to the appropriate EPA Regional office at the appropriate time. Furtherm ore, to facilitate the designations process, commenters are also urged to provide relevant information to the pertinent air agency for its consideration in advance of the deadline for the agency to submit designation recommendations to the EPA.



## III

. Sourc e Coverage and Emission Threshold Options

A. Options to identify sources for monitoring/modeling

1. E missions metrics for use in a threshold approach

a. U se of annual emissions

.

Comment :

Commenters (0041, 0045

, 0048, 0050, 0058, 0060, 0071, 0073, 0080, 0 081, 0090, 0093, 0096,

0097

, 0107, 0109 , 0110

, and 0116 ) supported using annual SO 2 emissions for defining source

thresholds

. Commenters (0041, 0058, 0093, 0096, 0097 , 0107 , 0110

, and 0118 ) stated it is most appropriate to evaluate annual emissions, since these data are widely reported to the EPA and are readily available to the States. Commenter (0097) stated t his data provides a reasonable estimation of a facility's overall emissions. Commenter (0118) stated t his information is easily

available and treats all areas on a consistent basis and that t he use of additional factors makes this process unnecessarily difficult, time consuming, and more arbitrary.

Commenter (0041) stated that a longer term rate such as tpy is most appropriate for processes

that are more steady

- state, as compared to processes that have more fluctuating emissions which are better represented by shorter term limits. Commenter (0045) stated that using a 1

- hour SO 2 emission rate and the option to incorporate other factors like stack heigh t, proximity to sensitive populations and topography would be difficult to implement.

Commenter s (0080 , 0090 ) believed this was reasonable approach to establishing a threshold level, but stated it is not always an indicator of high hourly S O 2 emission rat es. For example, commenter (0080) noted that generating units may operate at high capacity with annual

emissions rates that fall within the EPA 's recommended threshold and may be equipped with

state

- of

- the

- art emissions control systems which allow them to operate at very low hourly S O 2

rates.DELIBERATIVE

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49 Response:

The EPA agrees with the many commenters who expressed support for using an annual

emissions metric because annual emissions data are most readily available for all large SO 2 sources, whereas 1

- hour emissio ns rate information is not readily available for many SO 2 sources. Since the tpy emissions metric is a common denominator in the emissions inventory and reporting universe, the EPA believes that the use of this metric is most appropriate to be required

und er a rule that applies broadly to areas with sources that do not already measure 1

- hour

emissions rates

. Using tpy will provide air agencies and the regulated community a common, easily verifiable, straightforward approach for identifying sources around wh ich air agencies are required to characterize air quality. This approach will rely on existing emission inventory collection systems that are already in place. An approach based on tons of emissions per year

also should reduce unforeseen or otherwise uneve n application of the requirements for air quality

characterization that could arise if different metrics are used for different SO 2 source sectors to identify areas for which air agencies are required to characterize air quality

.

The EPA acknowledges that some state commenters suggested inclusion of a 1

- hour emissions

rate

- based criterion for identifying certain sources with infrequent, episodic SO 2 emissions at atypically high rates that could impact nearby populations. The EPA notes that the emissions

th reshold included in the final rule establishes only minimum requirements for identifying priority sources. The EPA agrees with state commenters who recommended that air agencies

should also characterize areas that

, based on their knowledge of sources and a reas
, may be at risk of violating the standard. Thus, under this rule air agencies could also require characterization of air quality near sources prone to episodic emissions with relatively high rates or amounts, as appropriate

. However, the EPA believes that no simple indicator can be defined to identify the sources with emission spikes that warrant air quality characterization, and a rule with such a criterion would be difficult to implement because short

- term emissions data are not available for

all SO 2 sources . In addition, the EPA believes that a source that has routinely relatively high

emissions (and would therefore be covered by the 2,000 tpy threshold) may be more prone to cause violations and warrant prioritization than a source with routinely rel atively low emissions with sporadic emission spikes. For these reasons , the EPA did not include in this rule a minimum requirement for identifying source areas needing air quality characterization based on this metric

, although the rule continues to provid e air agencies and the EPA the option to identify sources that do not meet the annual emission threshold in the rule as nevertheless warranting air quality

characterization.



### b. E mis s ion threshold approach

Comment :

Commenters ( 0048, 0075) agree d that using an emissions based threshold approach to identifying areas to be evaluated for compliance with the 1

- hour SO 2 NAAQS w ould serve to make more manageable the demands on local, state and federal resources. Commenter (0088)

stated that most SO 2 emissions are emitted by a relatively small proportion of SO 2 emittingDELIBERATIVE

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50 sources in the national emissions inventory (NEI) and i t would be unreasonable to require states to model or require monitoring of small emission sources that would be unlikely to affect air quality in any appreciable way based in existing monitoring studies.

Commenter (0088) stated that , since there is no express provision in the CA A that de fines how modeling and/or monitoring should be conducted for the purpose of NAAQS designations, it is

within the EPA ’s discretion to determine that it is reasonable to focus state resources on the sources that are most likely to result in exceedances of the SO 2 NAAQS that could result in health impacts, provided that the selection of those sources is not arbitrar y and that it is

reasonable.

Commenter (0110) objected to the EPA ’s approach for determining the emission threshold

because it is based upon percent of national SO 2 emissions, rather than any direct consideration

as to the emission level that would reaso nably be expected to affect compliance with the SO 2 NAAQS.

Commenter (0053) asserted the EPA has not provided an adequate explanation or justification to support its proposed thresholds for identifying areas that must be characterized under the DRR.

Comm enter (0053) stated that the EPA provides no analysis of how the 3 options actually relate

to those areas where exceedances or nonattainment of the 2010 1

- h our SO 2 NAAQS might actually be likely and, f

or example, the thresholds do not account for factors s uch as stack height

that are critical in relation to short

- term standards like a 1

- hour NAAQS.

Response :

The EPA agrees with commenters that favor use of an emissions based threshold to focus state, local, and federal resources on the areas that most war rant evaluation. The resources that are available to address these issues are finite, and the EPA believes that a rule requiring air quality characterization in the vicinity of sources exceeding the threshold in the final DRR provides for focusing an appro priate level of resources for air quality characterization.

The commenter that finds the EPA’s rationale for its thresholds inadequate did not recommend any alternative basis for establishing priorities for air quality characterization. This commenter

app ears to recommend that the thresholds should correspond to levels at which violation of the “NAAQS might actually be likely,” but the commenter then notes the importance of factors other than emissions “such as stack height.” The commenter in effect is arg uing that no simple set of

criteria is appropriate for defining the areas that warrant air quality characterization

, although the commenter does not expressly argue that a more complicated set of criteria is warranted.

The EPA agrees that air quality is i nfluenced by a variety of factors, including emission levels, meteorology, stack height and other release parameters, and in some cases nearby terrain. Given the complex influence of these factors, even a complex set of criteria would not provide a

reliabl e indicator of the likelihood of violations. On the other hand, a complex set of criteria would be very difficult to administer, and would be prone to result in inconsistent applicationDELIBERATIVE

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51 across the country. Therefore, the EPA believes that a simple criterio n, namely annual emissions, provides a more workable and appropriate basis for determining whether an area should be prioritized for air quality characterization. This approach is analogous to the approach to a variety of other EPA monitoring regulations, which also rely on criteria (e.g., the population of the area) that cannot be expected to be dispositive as to whether a violation is likely to be monitored but which provide an appropriate basis for prioritizing areas for air quality

characterization. It is also consistent with numerou s CAA provisions that base applicability on source emissions levels, without imposing a burden to show a correlation of those levels with a particular likelihood of presenting an environmental or health risk. Finally, t he rul e in setting the

emission threshold to identify the sources that at a minimum need to be characterized

, does not preclude air agencies from additionally characterizing other sources that may pose a risk of NAAQS violations. Moreover, nothing in this rule a lters either the authority or the responsibility EPA and air agencies have under the CAA to address NAAQS violations.



### 2. T hreshold including population metric

a. Support using a population threshold

Comment :

Several commenters ( 0043, 0046

, 0048, 0050, 005 1, 0075

, 0080, 0081, 0087, 0089, 0090, 0092, 0094, 0095, 0096 , 0106

, 0116, 0117

, and 0118 ) supported the application of a lower emission

threshold in urban areas. Commenter s (0051 , 0081

, and 0106 ) stated that p opulation centers represent locations of highe r potential public exposure and, therefore, characterization of a ir quality in these areas would be more representative of the public's SO 2 exposure risk.

Commenter (0081) supported including population and explained that s ince the 1

- hour standard

is ver y source specific, and results in relatively small “hotspots” of higher concentrations, a tighter threshold for urban areas where a greater population exposure is likely to occur is appropriate

. Commenter (0051, 0081, 0089 , 0117 ) stated that, a s precedent, a population

threshold has been used to establish the minimum monitoring requirements for other NAAQS, including nitrogen dioxide, carbon monoxide, and particulate matter

.

Commenters (0043, 0046, 0050, 0051, 0087, and 0092) stated that a threshold approa ch based purely on emissions could inappropriately focus limited resources on areas with limited to no public exposure. Commenter (0050) stated that the EPA should consider the population

- exposure component of the source threshold as it prioritizes areas t hat may need further scrutiny. Commenter (0117) support ed th is approach

, recognizing that because there is greater risk, a stricter threshold should apply , and stated t his is a common sense approach which is not unduly burdensome to air agencies.

Comment er (0118) stated t here should be options spelled out (partial county designations, removal of counties, etc.) to remove these areas and affected sources a fter the initial determinations where, for example, counties on the edge of a highly populated CBSA ha veDELIBERATIVE

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52 extensive rural areas where such an approach has no benefit because of the relatively localized impact of S O 2 emissions.

Commenters (0048, 0094, and 0095) stated many sources located within an existing CBSA are located on the edge of the boundary in l ess populated areas and urged the EPA to consider more refined census data based perhaps on population density. Commenter (0048) asserted that using population density instead of CBSAs is better as it represents a classification methodology that is pertine nt to the area affected by the source. Commenter (0048) stated that the EPA ’s proposed methodology is too broad and needs to be more site

- and source

- specific, representing actual affected populations. Commenter (0048) suggested, f or example, the EPA could use population density data around the effected facilities out to a radius of 10 km and, i f average population density from the 2010 census in this area exceeds a certain threshold (e.g. 100 persons/sq km),

then the lower emissions criteria would be used ; f or areas less than the population threshold, the higher emissions criteria would be used.



### b. Do not support using a population threshold

Comment :

Several commenters (0034, 0036, 0039, 0041, 0045, 0062, 0068

, 0078, 0088

, 0094, 0095, 0103

, 0115

, and 0120 ) did not support using a population threshold

.

Commenters ( 0034, 0036, 0045, 0062, 0068, 0088, 0103 , 0115, and 0120) stated there should be no difference in applicability between urban and rural sources since the CAA requires that NAAQS apply equally to all populations, regardless of population density. Commenter (0088)

stated that it seems arbitrary to determine that people living in these communities would potentially be more impacted to SO 2 emissions than a small group of people living in the

immediat e vicinity of a large SO 2 emitting source. Commenters (0115, 0120) stated t he residents

of rural areas deserve the same environmental protection as those in major metropolitan areas. Commenter (0115) provided the following additional points.

The Band is concerned that significant sources in areas with fewer than 1,000,000 people may will be overlooked under this approach. Since the vast majority of S O 2 emissions come from large, stationary sources and tend to linger locally (i.e. contributions from

local traffic and transport are probably not factors), there can be little reason to assume that urban residents need a greater level of protec ti on than rural ones in this instance. The Band feels that this proposal unfairly places an environmental burden upon t ribal communities, most of which are located in rural areas, and appears to more highly value the lives and health of those living in CBSA s of more than 1,000,000 people. This w ould also appear to be unfair treatment of sources that are located in urban a reas, as they will

be required to perform modeling that their counterparts in rural locations may not. If

urban citizens are exposed to higher background levels of S O 2 that require a more

conservative S O 2 designations approach, then please give the details behind this assumption.DELIBERATIVE

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53 Further, the proposed population

- based thresholds do not adequately address industry

intensive areas that may experience high cumulative rates of emissions or that may be

located in areas with local meteorology that is not conduc ive to adequate air dispersion.

The areas near the Fond du Lac Reservation and the ceded territories include both of these types of settings.

T he analysis performed by the EPA regarding its proposed threshold approach does not adequately address public h ealth concerns. The analysis focuses on what percentage of

sources would be modeled/monitored

, and what percentage of the general population live

in areas where emission sources would be modeled/monitored. Neither of these factors

demonstrates whether the N AAQS will be attained in all parts of the country. The

N AAQS make no exceptions based on population density or whether certain sources emit quantities above a certain threshold and what percentage of sources is covered is irrelevant. Lastly, the proposed 1,000,000 person threshold represents only 55% of the

US population. The Band does not agree with this approach as it leaves 45% of the population unaccounted for, along with affected plant and animal species that may need protection.

This approach doesn' t specifically account for unique or problematic meteorological

conditions

. The Band described a unique situation in the Duluth/Superior area and stated

t hat unique modeling situations like these may be overlooked by a purely population

based approach.

C ommenters (0034, 0120) stated Indian Country is largely rural in nature and, a s such, population thresholds unnecessarily disadvantage Indian Country and rural state communities. Commenters (0034, 0120) stated the Proposed Rule would inhibit the use of gov ernmental resources to characterize air quality data concerning their emissions and learn about such health

effects. Commenter (0034) stated the Proposed Rule could have a devastating effect on both the existing and future resources available to Tribes. Co mmenters (0034, 0120) stated t his is not only unfair to Indian Country and its Tribes ; t his is an environmental justice issue in which Indian Country’s best interests are not adequately protected.

Commenter (0120) stated that a lack of resources to suppo rt adequate environmental protection measures, such as air quality monitoring and dispersion modeling, is not a viable excuse for the

EPA to promulgate rules that lessen the requirements on air management agencies that have been tasked with protecting publ ic health and the environment. Commenter ( 0068 ) provided the following additional points.

 Nothing in the CAA supports or even contemplates a NAAQS implementation strategy that would effectively value air quality in urban areas over that in rural areas.

 Nothing about a source being in an urban area makes it easier to evaluate for its impact on the NAAQS, and improperly focusing on such sources preferentially is likely to leadDELIBERATIVE

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54 to rural sources that do cause exceed a nces of the NAAQS being overlooked, to the

detriment of the air quality of rural areas and to the health of rural residents.

 Particularly given the greater levels of poverty in rural areas, and the reality that dangerous sources of air pollution tend to be located in poorer and more rural parts of the

country, the EPA ’s proposal to focus the DRR preferentially on urban sources raises significant environmental justice concerns. As an example, AERMOD analysis of the

actual emissions from Schiller Station in Portsmouth, New Hampshire indicates that it has, for multi

- year periods, caused ambient concentrations of SO 2 to exceed the NAAQ S.

A lthough Schiller Station would be included under the EPA ’s preferred Option 1 if it

were an urban source , because it is relatively far from a population center li ke Boston, it

would be excluded , to the detriment of the over 40,000 people that live in the cities and towns immediately surrounding Schiller.

Commenter s ( 0036, 0041 , 0078 , 0088 , 0094, 0095

, and 0115 ) stated that using population as a basis for setting thr esholds is not necessary because of the nature of the SO 2 emission impacts

distribution. Commenter s ( 0036 , 0115 ) stated the EPA ’s population concept for siting monitors may make some sense for certain pollutants such as nitrogen dioxide, where there are

co rrelations between sources of concern and populations, but with SO 2 there is no such

correlation. Commenter (0088) stated that it is not reasonable to believe that cumulative exposure from several SO 2 facilities necessarily corresponds to population densit y. Commenters (0094, 0095) stated CBSAs are usually large geographic areas, while the health impacts of SO 2 are relatively localized with maximum concentrations expected to be observed within 1

- 2 miles of large power plants or other facilities in flat terr ains. Commenter ( 0041 ) provided the following additional points:

Our analysis of the impacts from large sources in our nonattainment area shows that the largest impacts are relatively close to the emitting source

, i.e ., a localized problem. Therefore, to set thresholds on the basis of population in large areas, whether by county boundaries or potentially much larger areas such as CBSAs, does not accurately reflect

the effectiveness or need f or control because of the localized nature of SO 2 impacts. For

in stance, Michigan has sources located in rural areas that are still part of the greater Detroit CBSA with a population of more than one million, while other sources are not in a CBSA but may impact more people than the CBSA sources because of the local

popu lation density.



### c. Other comments on population thresholds

Comment :

Commenter (0044) stated that while all three options distinguish between sources “inside” and “outside” of CBSAs greater than 1 million, the DRR is silent on what is meant by being outsid e of a CBSA. Commenter (0044) asked if any source that emits SO 2 in excess of the 2K, 5K, or

10K tpy threshold will be subject to the rule irrespective of how many miles distant that sourceDELIBERATIVE

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55 may be to the boundaries of the CBSA or, more importantly, to the 1 million population center
within the CBSA

. Commenter (0044) stated that, a t the very least, the final rule needs to define what is meant by “outside,” including specifying a distance or other factor that could be used to objectively determine when a sour ce would no longer be considered to be “outside” the CBSA.

Commenter s ( 0040, 0044) noted that the health impacts of SO 2 are relatively localized, with maximum concentrations expected to be observed within 1

- 2 miles of large power plants and

other faciliti es in flat terrains, but that this 1

- 2 mile dispersal range will also be shortened by unique terrain and meteorological conditions. Commenter (0044 ) recommended that the EPA modify the approach to more accurately account for actual population exposure and provided the following additional points.

N ot every CBSA is geographically small with a high, dense population spread relatively evenly across the entirety of the CBSA; such as the New York

- Newark

- Jersey City CBSA. Many CBSAs cover a broad territory and h ave a population concentrated in one or a few small areas, with sources concentrated in another part of the CBSA that is not

located within the 1

- 2 miles maximum concentration zone; such as the San Antonio

- New Braunfels CBSA. While Option 3 may not be prec ise in this regard, its higher tpy thresholds would not work to the detriment of populations located in or within proximity

to CBSA sources located in and around a CBSA like New York

- Newark

- Jersey City. Option 3 would, however, properly exclude sources loc ated within or in proximity to

CBSAs like San Antonio

- New Braunfels and whose emission impacts (i.e., the source’s) would only be marginal even under the worst of circumstances.

Response :

The EPA considered the comments received on the issue of whether a lower emissions threshold should be included for areas with more dense populations (e.g., CBSAs greater than 1 million population). A number of commenters appeared to interpret the inclusion of a lower threshold for areas with higher population as being l ess protective of the public in less populated areas. The EPA wants to clarify that this was not the intention behind the population

- based options included in the proposed rule. The SO 2 NAAQS, and all NAAQS, are to provide equal protection for

citizens thr oughout the country. The proposed use of both population and emissions thresholds as a means to require air quality characterization was simply one approach to focus limited federal

and state modeling and monitoring resources into characterizing locations where a greater coincidence of people and SO 2 emissions occur, and thus a potentially greater potential for

exposure is presented

. A fter reviewing the comments on this issue, however, the EPA has

decided not to move forward with the proposed preferred appr oach, and instead to apply requirements for air quality characterization based on emissions levels uniformly across the country for both more urbanized and less urbanized populations so as to focus primarily on the

size of the sources.

The EPA agrees wit h the comment that population density varies among and within CBSAs. The EPA believes that a criterion that reflects population density in the immediate vicinity ofDELIBERATIVE

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56 sources would be difficult to define, justify, and administer. Nevertheless, the fact that sources in large population CBSAs are not necessarily in the immediate vicinity of substantial populations provides additional rationale for not using a CBSA population criterion in determining what areas are established as priority areas for air quality characterization.

The EPA acknowledges the comments in support of using a population criterion for prioritizing areas to be subject to air quality characterization, and agrees that sources located in populated metropolitan areas generally have the pote ntial to cause more substantial population exposure than sources outside (i.e., not within) such areas. However, some commenters noted that large

SO 2 sources in CBSAs are sometimes located in relatively lightly populated portions of those

areas. Others not ed that impacts from an SO 2 source are relatively localized, regardless of

whether the source is located within a CBSA or not.

In considering how to prioritiz e air quality characterization efforts under this rule

, the EPA

considered the possible greater efficiency of a program that giv es higher priority to characterizing air quality near sources in CBSAs

, along with t he concerns of some commenters that populations located near sources of a similar size to those exceeding the CBSA threshold but

who live ou tside of a CBSA would receive unequal air quality protection. The EPA gave greater weight to the latter set of concerns and opted for an approach that requires air quality

characterization near similar

- sized sources throughout the country regardless of whe ther the source is located within or outside a CBSA, while still efficiently prioritizing air quality

characterization for a feasible number of sources

.

It should be noted here that any monitoring that occurs pursuant to this rulemaking is potentially

in addition to, or can possibly help to satisfy, required SO 2 monitoring stemming from 40 CFR

p art 58

, a ppendix D, and section 4.4. Those monitors required in 40 CFR p art 58

, a ppendix D,

s ection 4.4 are determined using a unique metric that accounts for the c oincidental occur re nces of SO 2 emissions and population, namely the Population Weighted Emissions Index (PWEI). This rulemaking does not supplant or otherwise modify those existing requirements.



### 3. Proposed o ption 1 (> 2 ,000/ 1 ,000 tpy )

a. Support o

ption 1

Comment :

Commenter s (0035 , 0117 ) su pport ed the EPA 's Option 1 and stated that, b ased on their experience; the use of this threshold value strikes an appropriate balance between NAAQS protection and the significant resource requirements of modeling and mo nitoring approaches to demonstrating attainment

. Commenter (0117) stated t his approach offers the highest level of protection (90% of emissions coverage) while creating a manageable requirement for air agencies. Commenter (0035) stated that, b ased on the a ir monitoring data collected in the BAAQMD

, they believe that it is unlikely that sources with emissions under 1

, 000 tpy would

cause or contribute to a NAAQS violation.DELIBERATIVE

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57 

### b. Do not support o

ption 1

Comment :

C ommenters ( 0046 , 0051, 0056, 0058, 0070, 0075

, 0090, 0091, 0092

, 0110, 0113

, and 0116 ) opposed Option 1, stating that these levels have not been justified and they would be a

burdensome and inefficient approach.

Commenters (0051, 0110) stated that t he Proposed Rule does not justify why sources of 1,00 0, 2,000, or 3,000 tpy are likely to or expected to potentially result in a NAAQS violation and therefore require monitoring or additional modeling. Commenter (0058) stated the EPA’s justification for preferring the thresholds provided in Option 1 over tho se of Options 2 and 3 is arbitrary since the “90 percent threshold” is no magic number and will force States to evaluate many more sources than necessary

.

Commenter s ( 0046 , 0051 , 0075

, 0091, and 0110 ) stated Option 1 is very burdensome and would

be an ine fficient means for identifying areas that are not meeting the 1

- hour SO 2 NAAQS. Commenter ( 0046 ) stated Option 1 would target 3 times as many sources as Option 3 but would cover only 20% more emissions. Commenter ( 0046 ) stated Option 1 is anticipated to id entify 10 areas not meeting the SO 2 NAAQS that would not be identified by Option 3 but would do so by installing a total of 288 additional monitors of which over 200 are projected to have average 99th percentile daily maximum 1

- hour levels less that do not exceed 38 ppb (i.e., less than 50 percent of the level of the NAAQS). Commenter (0051) stated t h at

, because th e EPA's proposed Option 1 requires characterization of 12 more sources in Texas than Option 2 but only equates to characterizing air quality for 7.5% more of the SO 2 emission s in Texas , t he added monetary and

resource costs associated with modeling or monitoring under Option 1 are not bala nc ed by an equal benefit of protecting the public from short

- term SO 2 exposure.

Commenter s ( 0046 , 0091 ) state d Option 1 would be an inefficient drain on state, local, or tribal area resources and may force states to deliver model output instead of quality assured ambient air monitoring data to the EPA for setting area designations. Commenter (0091) stated that in cluding sources at the Option 1 level of emissions will waste precious agency resources and expend unnecessary costs for sources that are already heavily controlled.

Commenter (0056) stated that in most cases the EPA 's preferred Option 1 applicability th reshold will result in significant expense and time where there is no real issue with NAAQS compliance. Commenter (0113) referenced monitoring data analysis in Montana which demonstrated NAAQS compliance downwind from two local industrial facilities whose individual SO 2 emissions exceed the thresholds provided under Option 1 of the DRR for rural locations. Commenter (0113) stated that since these monitors demonstrate NAAQS compliance and were used by the EPA in limiting the geographic extent of the nonattai nment area boundary, further

evaluation of areas with individual sources covered under Option 1 in the DRR is unnecessary

and inappropriate.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

58 

### 4. Proposed o ption 2 (> 5 ,000/ 2 ,000 tpy )

Comment :

Commenters (0054, 0088, 0089, 0092, 0109, 0113, and 0114) supporte d Option 2 because it

balance s limiting agency resource demand for the implementation of this rule while still allowing important SO 2 emission sources to be evaluated. Commenters (0088, 0114) stated Option 2 appears to be the best option because the differ ence between the number of sources captured by Options 1 and 2 is substantial. Commenter (0088) stated that, i n comparison to Option 1, which would require monitoring or modeling of 443 sources that account for 90 % of all SO 2 emissions, only 270 sources wo uld be affected and account for 82 % of emissions. Even with the implementation of Option 2, commenter (0054) asserted that a state could always lower the threshold on their own if there was concern about impacts fro m a particular source emitting less

than 5

, 000 tpy in an area outside 1,000,000 population CBSA’s.



### 5. Proposed o ption 3 (> 10 ,000/ 3 ,000 tpy )

Comment :

Commenter s ( 0040, 0043, 0044, 0046

, 0048, 0050

, 0051

, 0056, 0057, 0058

, 0060, 0063, 0064, 0065, 0070, 0075

, 0079, 0080, 0084, 0087, 0090, 0093, 0094

, 0095

, 0106, 0109, 0111, 0113

, and

0116 ) generally supported the EPA Option 3 because it would apply reasonable thresholds without burdening states with unnecessary modeling or monitoring.

Commenter (0056) stated t his option would allow s tates to focus their limited resources on the areas with the largest 211 sources of SO 2 emissions, and avoid being forced, based on crude criteria, to either monitor or model an additional 285 sources. Commenter (0060) stated that Option 3 (3,000 and 10,000 tpy ) is more than adequate to address Ohio's more significant

sources

. Commenter (0060) stated that t he thresholds in Option 1 and 2 are well beyond what is

necessary to capture significant sources in Ohio as t hese options would require modeling or monitoring of all of Ohio's well

- controlled EGUs. Commenter (0111) supported Option 3 since it

would cover almost 70% of the national SO 2 emissions in 20 11 (including sources located in nonattainment areas).

Commenters (0043, 0111) referenced s tate experience collecting ambi ent monitoring data near large SO 2 sources which indicate that large amounts of SO 2 do not necessarily correlate to

violations of the standard. Commenter (0043) referenced South Dakota's experience in collecting

air monitoring data around a large coal

- fire d power plant with sulfur dioxide emissions over 12,000 tons / yr over a 13 period in which no sulfur dioxide concentrations exceeded the 1

- hour sulfur dioxide standard even though t he testing was conducted where the model indicated the

maximum sulfur dioxid e concentrations would be encountered. Commenter (0043) stated t his air monitoring data shows that emission levels as great as 12,000 tpy do not have high concentration impacts in rural areas. Commenter (0111) stated that, given LDEQ operates a number of S O 2 monitors located in close proximity to one or more sources which could be impacted by theDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

59 Proposed Rule , yet e ach of these monitors is compliant with the 1

- hour S O 2 NAAQS, it is evident that large amounts of S O 2 do not necessarily correlate to violation s of the standard.

Commenter (0064) stated that areas located outside of a core

- based statistical area of population greater than a million will be rural and sparsely populated. Thus, commenter (0064) believed a

threshold of 10

, 000 tpy SO 2 could be viewed as acceptable due to the low risk. Commenter (0106) supported Option 3 because of the limited number of people exposed and the amount of resources required to comply with the Proposed Rule.

Commenter s (0056, 0080, 0090, and 0093) supported Option 3 and noted that, while there may be situations where the Option 3 source applicability thresholds may not be appropriate, the Propos ed Rule gives the EPA , States and local permitting agencies the authority to include sources below the thresholds on a case by ca se basis. Commenter (0111) stated that, i f data generated by this rule indicate that exceedances of the 1

- hour S O 2 NAAQS are prevalent and affecting large numbers of people, the EPA could propose to expand the S O 2 monitoring or modeling requirements at a l ater date.

Commenters (0046, 0084) stated Option 3 provides increased opportunities to add more (or move existing) monitoring stations and reduce the focus on models, while concentrating on

known nonattainment issues. Commenter (0106) stated that, by adop ting Option 3, States' limited resources can be better utilized on other programs such as PSD, Regional Haze, and greenhouse gas (GHG) controls.

Commenter s (0040 , 0044 ) supported Option 3, stat ing Options 1 and 2 rely on arbitrary population densities tha t will bring in more sources than necessary for characterization of SO 2 effects on air quality. Commenters ( 0048, 0050, 0087, 0094, and 0095) stated that Option 3 is

consistent with the EPA ’s February 6, 2013 strategy paper regarding implementation of the designation process. Commenters (0094, 0095) asserted that nowhere in this paper does the EPA mention emissions as low as those proposed in Option 1.

Commenter (0050) stated Option 3 would allow the EPA and stakeholders to evaluate and

determine the effe ctiveness of the agency’s approach before undertaking more costly and expansive efforts. Commenter (0079) supported Option 3 , in part, because it provid es the

greatest margin of error in the event a designation is based on modeling, which is not as accurat e as a stationary air emissions monitor.

Response to comments on proposed options 1, 2, and 3 above :

See the preamble for the response to comments on proposed options 1, 2, and 3. Further relevant discussion is also presented in a memo to the DRR docket entitled “Analysis of Source Threshold Options for the Final SO 2 DRR

, ” Douglas Solomon and Rich Damberg, EPA Office

of Air Q uality Planning and Standards, docket EPA

- HQ

- OAR

- 2013

- 0711, July 16, 2015. The EPA received a wide range of comments on the proposed emission threshold options, as

indicated previously

. Most commenters identified a preference among the three options proposedDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

60 by the EPA. A few c ommenters recommended alternate thresholds in the rang e from 1

, 000 tpy to 10,000 tpy

, or recommended pairs of thresholds within this range. Some commenters provided modeling analyses as an indication that sources larger than 12,000 tpy did not cause a violation of the standard, while other commenters recommended a single emissions threshold of 1

, 000 tpy and provid ed modeling analyses of different sources as an indication that sources less than 2,000

tpy caused modeled violations. These comments demonstrate that ambient SO 2 impacts can be variable, and are dependent on many factors other than annual emissions (such as meteorology

, stack height, local topography and plant operations). These factors can only be assessed through analytical approaches, such as ambient monitoring or air quality modeling, which take many of these related factors into account simultaneously . These comments demonstrate why air quality

characterization of the area around these sources is needed to protect public health in the first place.

A number of commenters discussed monitoring evidence in their areas from which they inferred

the likelih ood of violations being observed near sources with various annual emission levels. These comments must be considered in the context that concentrations can vary significantly as a result of other factors such as stack heights, meteorology, and terrain. Fo r this reason, the EPA agrees with the commenter that “ large amounts of SO 2 do not necessarily correlate to violations

of the standard ,” a statement that should be supplemented with the statement that small amounts

of SO 2 do not necessarily correlate to at tainment of the standard. For this reason, an important part of this rule is provision for air agencies and for the EPA to conclude that a source (or a cluster of sources) that does not meet the threshold of this rule but nevertheless poses sufficient

conc ern that air quality characterization in the vicinity of this source (or these sources) should be prioritized. Ne vertheless, as a general matter, the EPA believes that prioritizing sources emitting at least 2,000 tpy provides for an appropriate balance in focusing an adequate amount of air agency resources on the area’s most likely to violate the standard. It is common under the CAA to tie applicability of requirements to sources’ emissions size, even where such thresholds do not necessarily expressly corre late to emissions levels that cause certain risks. In this rule, the EPA has not chosen to adopt the most common of those thresholds, the 100 tpy threshold for determining whet her a source of criteria pollut a n ts is “major” under the CAA, but instead has

ad opted a threshold that the Agency expects can be realistically implemented by resource

constrained air agencies and that will result in characterizing areas affect ing the vast majority of

SO 2 emissions beyond what had previously been required.

Based on 2011 emissions (the latest emissions available at proposal), 42 s tates , 1 Territory, and 1 Tribe had sources above the 2,000 threshold. Most of these (25 s tates, the 1 Territory, and the 1 Tribe) had fewer than 10 sources above the threshold. The most sour ces above the threshold in

any s tate is 28. While characterizing air quality around 28 sources (or fewer ) in a s tate is not a trivial exercise, the Agency believes it can be realistically done and provides a reasonable balance between characterizing air q uality in areas most likely to violate the standard and agency

resources.

F or the purposes of establishing a minimum threshold that prioritizes the resources that will be devoted to characterizing air quality near SO 2 sources nationally, the 2,000 tpy sou rce emissionsDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

61 threshold strikes a reasonable balance between the need to characterize air quality near sources that have a higher likelihood of contributing to a NAAQS violation and the analytical burden on air agencies. This threshold is on the lower end of the range of thresholds recommended by commenters because sources on the lower end of the range have the potential to cause or

contribute to violations of the NAAQS. As compared to the preferred option in the proposal (i.e.,

1

, 000 tpy sources in CBSAs o ver 1 million people ; 2,000 tpy sources not in CBSAs over 1

million people ), the 2,000 tpy threshold would mean that , in the aggregate, air agencies would

need to address air quality near about 35 fewer sources (or 7 percent fewer)

. Nevertheless, the

total emissions addressed would still account for 89 percent of the SO 2 emissions nationally (based on 2011 emissions), very close to the 90 percent level that has been considered to be reasonable by many stakeholders in the past

. 6 National SO 2 emissions have d eclined by a significant amount from 2011 to 2013 (around 1.5 million tons, or more than 20 percent ), for

various reasons. The EPA assessed the number of sources meeting a 2,000 tpy threshold based

on 2013 emissions data now available for EGUs and 2011 emi ssions data for non

- EGUs

. Compared to the assessment in the proposal, which assessed the number of sources meeting the proposed threshold (1,000 tpy in urban areas/2,000 tpy elsewhere) based solely on 2011 data, the EPA now estimates that approximately 70 fewer sources (about 15 percent ) will need nearby air quality to be characteriz ed than was estimated in the proposal . Based on the updated data, the EPA estimates that already

- designated sources plus sources currently exceeding the final

threshold in this rule still would account for 86 percent of national emissions. Under this rule, each air agency will be required to identify all sources with annual SO 2 emissions that exceed 2,000 tpy (using emissions data from the most recent calendar year for which such data are available) and characterize air quality around such sources according to the timeline in section C of this preamble.

Of course, if the trend in reduction of SO 2 emissions continues at individual sources, there will also be a corresponding redu ction in national emissions, and both kinds of reductions are desirable for improving public health, even if that results in fewer source areas becoming subject to the emissions characterization requirements in the final rule. Conversely, if the trend reve rses and source emissions increase, more sources and areas will be required to be characterized under the rule. Thus, the exact number of sources and areas that will exceed the promulgated threshold when air agencies begin characterizing areas under the ru le cannot be precisely known at this time, nor can their future percentage share of the national inventory be precisely estimated. Nevertheless, the EPA believes that the promulgated threshold strikes a reasonable balance based on the information the Agenc y currently has regarding recent historical SO 2 emissions inventory

levels.

The circumstances in Montana do not warrant a revision to the rule. If air quality characterization

6 The May 2012 White Paper and high

- level summaries of stakeholder meetings are available at: http://www.epa.gov/oaqps001/sulfurdioxide/implement.html

. These documents and written comments received from stakeholders are also included in the docket for this rulemaking.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

62 is required under this rule, the first step would be to determine the adequacy of the existing monitoring network for characterizing air quality near the pertinent sources, which will determine the need for further efforts to characterize air quality. The exclusion of sources from a nonattainment area cannot be presumed to signify t hat these sources are not contributing to violations of the air quality standard elsewhere.

The EPA does not share the concern of the commenter that objects that lower applicability thresholds will require more air agencies to rely on modeling. The EPA fi nds that modeling and monitoring both have advantages and disadvantages, and the EPA believes that the potential influence of resource constraints to increase reliance on modeling will not have adverse effects on the suitability of air quality characteriza tion performed pursuant to this rule. Furthermore, the EPA does not share the apparent view of the commenter that reducing the reliance on modeling warrants being set as an objective that in turn warrants reducing the number of areas where the potential fo r violations of the air quality standard is evaluated.

The comment object ing to the fact that the 2013 strategy paper did not discuss a 1,000 tpy threshold is moot, in light of the final rule’s adoption of a general 2,000 tpy threshold. However,

we note t hat the absence of discussion of an element in the strategy paper does not render its subsequent proposal, or final promulgation, in notice and comment rulemaking unreasonable. Numerous aspects of the proposed and final rules were not addressed in the str ategy paper, including the provisions addressing source incentives to reduce emissions or the ability to discontinue monitoring if ambient levels fall a certain amount below the NAAQS, but that does not render their adoption in this rule unreasonable.



### 6. Othe r options to identify sources

a. R efined dispersion modeling

Comment :

Commenter ( 0051 ) stated t he EPA should explicitly allow for alternate approaches to identify t h e sources that should be modeled using refined dispersion modeling. Commenter ( 0051 ) provi ded the following additional points.

Application of a regional grid model, such as CAMx, at relatively high resolution and additional targeted receptors as needed, combined with conservative assumptions about

emissions and a threshold concentration invers ely proportional to the grid cell area should suffice to identify possible areas of concern. Advantages of this approach include the ability to include additional SO 2 sources; use of prognostic (e.g., weather research and forecasting (WRF)) wind fields rat her than "straight

- line" winds from discrete National

Weather Service (NWS) locations; chemical processing of SO 2 emissions; treatment of

wet and dry deposition; and accounting for impacts beyond the 50 kilometer range over

which AERMOD is viable. Addition ally, using a grid model could provide estimates of background values that should be more representative than those derived from otherDELIBERATIVE

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63 techniques.

Response:

The EPA seeks to define the areas required to be characterized on the basis of a relatively simpl e indicator of the potential for violations of the standard, or more precisely a simple indicator as to whether any particular area warrants being prioritized for air quality characterization. Aside from the inherent disadvantages of regional grid models a s even screening tools for identifying areas with potential violations of the SO 2 standard, such as the inherent averaging over the applicable horizontal and vertical grid dimensions (and the infeasibility of including “additional targeted receptors”), the use of such models does not provide a practical basis for pursuing a nationally consistent set of areas for which to require air quality characterization. Therefore, the EPA is promulgating a rule requiring air quality characterization in areas with sourc es that emit at least

2

, 000 tpy , along with any additional areas that are identified as hav ing sufficient potential for violations to warrant air quality characterization. Notwithstanding the disadvantages of regional grid models for assessing this potenti al, states and other air agencies already have the option

, whether implementing this rule or for other purposes, to use these and any other tools they judge appropriate to identify additional areas that may warrant characterization.

The EPA also does not support the use of regional grid models for performing the air quality

characterization that this rule requires

, to the extent the commenter would recommend using them for that purpose

. T he Agency believes that a modeling protocol or monitoring network

des ign that follows or references the recommended approaches in the TADs is likel y to be adequate, and will better ensure the success and a timely fulfilment of the requirements of this rulemaking. However, air agencies remain free under the final rule to sug gest alternative approaches to those suggested in the TADs. Whether an agency chooses to follow a TAD or suggest an alternative approach does not affect the fact that for every approach chosen, the air

agency will need to submit its rationale and approach to the EPA for review on a case

- by

- case basis.



### b. 1,000 tpy

Comment :

Commenters ( 0036

, 0062, 0068 , 0078

, and 0085 ) urged the EPA to adopt the proposed Option 1 level of 1,000 tpy , but apply it unif ormly, regardless of population in order to ensure a basi c level of health protection to people who live around the sources.

Commenters (0068, 0078) stated that because modeling has shown that sources with emissions below 2,000 tpy have the potential to cause or contribute to modeled NAAQS violations , a n emiss ions threshold of 1,000 tpy is more appropriate to ensure that air quality characterizations are accurately capturing potential NAAQS violations. Commenter (0078) referred to p reliminary modeling conducted within Minnesota. Commenter (0068) provided the fo llowing additional points.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

64 A s an example, the Brandon Shores and CP Crane coal

- fired power plants in Maryland have been modeled using actual emissions, and according to that modeling ( exhibit 8, attached to their comments), are individually and solely re sponsible for causing

exceedances of the SO 2 NAAQS. T he AERMOD modeling shows peak concentrations from Crane of roughly double the NAAQS; however, Crane and Brandon Shores both have had annual total emissions lower than some of the options contemplated by the EPA

in the draft DRR

. Thus, using a threshold of greater than 1,000 tpy would exclude sources

known to be emitting at levels that would cause nonattainment of the NAAQS, and thus

would result in a failure of states and the EPA to adequately implement t he SO 2 NAAQS

. Commenter (0068) stated that modeling of t he Seward Plant in Pennsylvania provides a

similar example

.

Commenter (0085) stated a threshold of 1,000 tpy of SO 2 is a reasonable cutoff for capturing both larger sources and some medium

- sized sour ces that contribute to higher SO 2 emissions, and achieving a total emissions coverage of 90% (79 FR 27456, Table 1

- Summary of Source Threshold Options). Commenter (0085) stated that, a s far as identifying sources around which to characterize the air quali ty, ARMA supports the following approach :

Sources with continuous emission monitors (CEMS) : (1) Determine which sources have annual emissions of greater than 1,000 tpy , and for those sources with emissions of greater than 1,000 tpy , determine which, if

an y, sources have CEM data showing an hourly average SO 2 emissions rate below

the 1

- hour 75 ppb SO 2 NAAQS. (2) Exclude from air quality characterization any sources with hourly average SO 2 emissions below the 1

- hour 75 ppb NAAQS. (3) Proceed with characteriz ing the air quality in the area of the remaining CEM sources via monitoring and/or modeling.

Sources without continuous emissions monitors : (1) Determine which of these sources have annual emissions of greater than 1,000

tpy

. (2) Require monitoring or mod eling of any non

- CEM sources above the 1,000 tpy
threshold. (0085)

Commenter (0115) suggest ed an applicability approach that considers cumulative emissions from all local major sources and the unique m eteorology/topography of an area, rather than focusing solely on emissions from individual sources and the population of the area. Commenter (0115) suggest ed a threshold of 1,000 tpy , either from one individual source or cumulatively from all major sources in the immediate area

.DELIBERATIVE

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65 Response:

The EPA is not asse rting that areas with sources emitting under its threshold (now 2,000 tpy ) will in all cases be attaining the standard, just as it is not asserting that areas with sources emitting over its threshold will in all cases be violating the standard. Instead, th e EPA is merely promulgating a rule to prioritize areas that warrant further air quality characterization, and to require this air quality characterization in areas that are prioritized. While a number of factors influence the air quality impacts of a give n quantity of emissions, the EPA seeks to establish relatively simple criteria for identifying areas that warrant air quality characterization, along with provision for prioritizing additional areas that the air agency or the EPA believes to warrant air

qu ality characterization notwithstanding that the sources have emissions lower than the threshold established in the rule. The EPA is setting the threshold at 2,000 tpy in order to provide an appropriate balance between the goal of assuring that most areas w ith significant prospects of violating the standard are characterized and the goal of minimizing the planning burden of conducting air quality characterization. Within the constraints of the need for administrative simplicity, the EPA believes that the eff ort of characterizing air quality near sources emitting more than 2,000 tpy is warranted, and the EPA believes that the provision for discretionary addition of areas with sources emitting less than 2,000 tpy suitably assures that areas with

smaller sources that nevertheless warrant air quality characterization are adequately addressed.

A number of commenters discussed monitoring evidence in their areas from which they inferred the likelihood of violations being observed near sources with various annual emi ssion levels. These comments must be considered in the context that concentrations can vary significantly as a result of other factors such as stack heights, meteorology, and terrain. For this reason, the EPA agrees with the commenter that “ large amounts of SO 2 do not necessarily correlate to violations

of the standard ,” a statement that should be supplemented with the statement that small amounts

of SO 2 do not necessarily correlate to attainment of the standard. For this reason, an important part of this rule is provision for air agencies and for the EPA to conclude that a source (or a cluster of sources) that does not meet the threshold of this rule nevertheless poses sufficient concern that air quality characterization in the vicinity of this source (or these sources) should be prioritized. Nevertheless, as a general matter, the EPA believes that prioritizing sources emitting at least 2,000 tpy provides for an appropriate balance in focusing an adequate amount of air agency resources on the area’s most li kely to violate the standard. It is common under the CAA to tie applicability of requirements to sources’ emissions size, even where such thresholds do not necessarily correlate to emissions levels that cause certain risks. In this rule, the EPA has not

ch osen to adopt the most common of those thresholds, the 100 tpy threshold for determining whether a source of criteria pollutants is “major” under the CAA, but instead has adopted a threshold that the Agency expects can be realistically implemented by resou rce constrained air agencies and that will result in characterizing areas affected the vast majority of SO 2 emissions beyond what had previously been required.



### c. 2,000 tpyDELIBERATIVE

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66 Comment :

Commenter (0088) suggested a 2,000 ton threshold should be applied to l arge sources
, without a population threshold factor

.

Comment :

Commenter (0051) suggested consideration of limits at 5,000 tpy SO 2 sources in any area of the state, and 3,000 tpy SO 2 sources in CBSAs greater than 1 million and noted this would provide

cov erage of 18 Texas sources representing 83% of the total 2012 reported point source inventory.

Response:

See above response concerning EPA’s decision on the final threshold for characterization.



### d. 3 ,000/ 5 ,000 tpy

Respo nse:

See above response concerning E PA’s decision on the final threshold for characterization.



### e. 10,000 tpy

Comment :

Commenters ( 0039, 0041, and 0045) supported a 10,000

- ton threshold

, without a population

threshold factor

. Commenter (0041) stated t he AQD found that a 10,000

- ton threshold i n all

areas outside the current SO 2 nonattainment area would account f or five sources out of the 12 largest (greater than 1,000 tpy ) sources and represent 89 percent of SO 2 emitted from the 12

sources. Commenter (0041) stated that, b ecause this level of im pact is significant, the AQD believes a 10,000

- ton threshold is appropriate for Michigan. Commenter (0039) stated that this threshold would greatly increase the overall effectiveness in identifying and addressing potential

1

- hour SO 2 NAAQS issues.

Comment er (0039) stated that a quick review of Indiana’s existing SO 2 monitoring network data

and Indiana SO 2 emissions shows a high correlation between measured design values above the 75 ppb standard with emission sources that exceed 10,000 tpy of actual emissi ons and that same data show no instances of measured design values above 75 ppb where the largest sources are less than 10,000 tpy of actual emissions. Commenter (0039) stated this simple evaluation is an indicator that focusing the Proposed Rule on emissi ons sources with less than 10,000 tpy of actual emissions may cause states and sources to expend resources ineffectively.DELIBERATIVE

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67 Response:

See the response above concerning source characterization

.



### f. 1 0 ,000/1,000 tpy (Option 1 & 3 hybrid)

Comment :

Commenter ( 0049) recommend ed a hybrid of Options 1 and 3 with a 1,000 tpy threshold used inside the CBSA with a population greater than one million and a 10,000 tpy threshold for areas outside a CBSA with population greater than one million. Commenter (0049) stated t his would retain the objective of protecting public health in urban settings by focusing on the air quality surrounding significant SO 2 emission sources in those areas. Commenter (0049) believed this would still ensure public health outside urban centers b y targeting large sources having the greatest potential for causing or contributing to violations of the 1

- hr SO 2 NAAQS

.

Response:

See the response above concerning source characterization.



### g. 10,000/5,000 tpy

Comment :

Commenter (0060) suggested the EPA should consider thresholds above those in Option 3.

Commenter s (0051 , 0110 ) propose d a n option covering 10,000 tpy SO 2 sources in any area of the state, and 5,000 tpy SO 2 sources in CBSAs greater than 1 million

. Commenter (0051) stated that, g iven SO 2 emis sion reduction trends and constraints on resources, the emission threshold approach should characterize only the largest sources with the greatest potential for relatively higher SO 2 concentrations. Commenter (0110) stated that w ith these alternate thresho lds, the risk for NAAQS violations is still very low, the workload for state agency review is kept more manageable, and state resources are not wasted on assessment of many small low

- risk SO 2

sources. Commenter (0051) stated that the TCEQ's preferred optio n would allow for more thorough and rigorous analysis of the highest emitting SO 2 sources in Texas. Commenter (0110)

stated that it is simply impossible for hundreds of protocols to be carefully considered and processed in the time allocated by the propose d DRR; in stead, the EPA needs to reduce the burden on states by requiring review of NAAQS compliance only for the sources with emissions high enough to possibly result in a nonattainment situation.

Commenter (0110) stated that considerations of both model ing and monitoring data indicate that

an SO 2 emissions threshold of 10,000 tpy will have a low probability of an actual NAAQS

violation. Commenter (0110) stated that, o f the 29 areas designated as SO 2 nonattainment in the August 5, 2013 Federal Register , a ll but five of these had an SO 2 emission source with more than 10,000 tpy (t he five remaining areas were associated with unique source

- monitor issuesDELIBERATIVE

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68 involving either stack downwash or steep terrain effects )

. Commenter (0110) concluded that

, except for unu sual situations, the likelihood for a monitored SO 2 NAAQS violation for sources

with SO 2 emissions up to 10,000 tpy is very low. Commenter (0110) review ed the results of modeling for tall stack sources to determine the emission levels that are likely to af fect compliance with 1

- hour SO 2 NAAQ S and provided the following statements.

EPA’s own analysis, provided by Roger Brode of EPA’s Office of Air Quality Planning and Standards in support of the NAAQS promulgation, indicated that a tall

- stack electrical gen erating unit (EGU) source emitting 12,000 tpy of SO 2 would show NAAQS attainment, although the results would be somewhat dependent upon terrain and background concentration values.

Another modeling analysis presented at a 2013 Air & Waste Management Ass ociation specialty conference on air quality modeling by Gilbert, Liebsch, and Dunbar for a modeling of a tall stack source indicated that the compliance SO 2 emission rate would depend upon the stack height and background concentration values. Their overal l AERMOD modeling results, assuming a background concentration that was 20% of the NAAQS, would indicate that the compliant emission rate could be as high as 16,000 tpy
for a Good Engineering Practice ( GEP ) stack height of 375 feet (2.5 times the building height of 150 feet). Thus, an upper SO 2 emissions limit threshold of 10,000 tpy as proposed under the EPA ’s Option 3 is reasonable and protective of the NAAQS.

Response:

See the response above concerning source characterization



### h. 500 po unds per hour and a nnual limits

Comment :

In addition to an annual emissions applicability threshold, commenter ( 0036 ) recommended that

the EPA adopt an hourly emission trigger for rule applicability to address those large emitters of

SO 2 that operate relatively infrequentl y. Commenter ( 0036 ) suggested additional details as

follows:

T he test should include a minimum hours of operation per year and suggested the hourly applicability threshold could be for sources that operated more than 500 hours per year

and for which the 99th percentile of their one

- hour emissions values is above 500 pounds per hour. All sources that have operated less than 500 hours a year or have an hourly SO 2 allowable emission rate below 500 pounds per hour could be initially eliminated from

considerat ion. Hourly data from sources with continuous emissions monitor ing s ystems (CEMS ) could be used to quantify the hours of operation and the 99 th percentile value.

For sources without CEM S or other means of calculating hourly emissions, either 24

- hour or 30

- day average SO 2 emissions could be used; these rates could be converted toDELIBERATIVE

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69 hourly SO 2 emission rates using Tables 1 and 2 in Appendix D of the EPA document

entitled Guidance for 1

- Hour SO 2 Nonattainment Area SIP Submissions (April 2014).

The NESCAUM states further recommend that the EPA revisit 500 hours per year as an applicability criterion at some later point in time, once SO 2 implementation is underway, to reassess its appropriateness as a threshold.

Response:

See above response concerning EPA’s deci sion on the final threshold for characterization.

i. 

### S ources with seasonal or monthly emission spikes

Comment :

Commenter (0062) stated that the EPA should consider adding requirements to characterize SO 2 concentrations near sources with seasonal or monthly emission spikes, sources that exceeded the threshold at least once in the past three years, or areas with multiple sources. Commenter (0062) stated, for example, if the threshold for the county is set at 1,000 tpy , an area with a source

whose emissions ex ceed 250 tons per quarter or 83 tons per month should be characterized.

Response:

The EPA believes that a rule with a relatively simple criterion, based on annual emissions, will be easier to administer and will help provide greater national consistency in its application. Nevertheless, the EPA is also providing discretion to air agencies and to itself to identify additional sources near which air quality characterization is warranted. Addition of such sources

on a case

- by

- case basis would provide a mor e appropriate means of assuring that the appropriate sources are addressed without having to use complicated applicability criteria that may not be necessary in all areas

.

j. 

### Multiple sources in close proximity that individually are below the

threshold but whose combined emissions may violate the NAAQS

Comment :

Commenters (0036, 0071, 0078, 0081, 0082 , 0113

, 0115, and 0118 ) stated that t he EPA should prescribe more specific requirements to address clusters of SO 2 sources that would otherwise fall

below emi ssions thresholds for required modeling/monitoring.

Commenter s ( 0036 , 0078

, and 0081) suggested the EPA consider emission s density metric s as part of the applicability test.

 Commenter ( 0036 ) stated t he metric should ensure that, if two or more major so urces are located in an area and their combined actual emissions are greater than a specified threshold, then an analysis should be conducted on these sources.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

70  Commenter (0078) recommend ed analysis of sources with actual emissions greater than

100 tpy in an area 25 km in diameter or less where aggregate emissions within the area exceed 1,000 tpy

.

 Commenter (0081) stated that, if the EPA wishes to pursue this policy, it would be helpful if guidance on a minimum “emission density” threshold for possible s ource cluster evaluation was provided in the final TADs so that states can effectively identify possible areas of concern and not be caught off

- guard during the designations process. Commenter (0081) stated that, r ecognizing that areas of highest SO 2 conce ntrations are likely to localized in relative close proximity around a source, or cluster of sources, the Department recommends that the threshold density should be no smaller than the same emission rates chosen in the final rule ( i.e., Option 1, 2, or 3) aggregated over no larger

than a 10 km 2 area.

Commenters (0078, 0082) urged the EPA to clarify that, for an air agency or the EPA Regional Administrator to require air quality characterization for sources based solely on their proximity to other sources, the combined total emissions from these smaller sources must exceed the finalized reporting threshold.

Commenter (0052) suggested that states should be allowed to use their best judgment to i dentify

scenarios where a cluster of sm all sources may cause a problem; i.e., i f a demonstration can be

made of counties with significantly higher emission rates being below the standard, it stands to

reason that lower emitting counties would also be below the standard and not require any analysis.

Commenter (0118) requested that the EPA identify a n emissions threshold and domain of such

clusters ; e.g., sources of less than 100 tpy or less than 5% of a cluster's total emissions could be

excluded. Commenter (0118) appreciate d the flexibility of the approach, but state d it is better for states to work from a basic protocol and makes acceptance of these analyses more uniform

across different areas.

Commenter (0113) suggested the EPA could consider an additional option to evaluate NAAQS compliance in areas with clusters of sources that cumulatively exceed a larger specified emission

threshold in areas with significant populations. Commenter (0093) stated that, g iven the resource

burden for this modeling/monitoring effort, agencies must focus on the largest sources only i n the initial effort and that s maller sources and clusters of sources can be reviewed at a later date.

Commenter (0081) stated that, because each situation of possible clusters of sources will be different, the Department does not believe it wise, or nece ssary, to codify a cluster density in the

final rule. Commenter (0081) stated t he professional judgment of the air agency personnel, along with consultation with the appropriate EPA Modeling Contact, will be most appropriate in

evalua ting the different sou rce configuration, land use, geographic, and meteorological variables involved in this process. Commenter (0081) added that, i f the EPA chooses the 2,000 tpy and

1

, 000 tpy thresholds currently in the Proposed Rule , about 90 percent of the SO 2 inventory in theDELIBERATIVE

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71 country will be addressed, leaving few other sources that might qualify as a cluster of sources

that need to be evaluated.

Commenter (0078) stated that the EPA should include direction for states where cumulative impacts may result from cross

- state b order sources ; i.e., s ources that would otherwise be below

the EPA 's threshold but which may cumulatively contribute to NAAQS exceedances may be located in a neighboring state. Commenter (0078) stated that l eaving cluster analyses to the

discretion of each state air agency without further guidance can result in challenges for states seeking to address clusters using different approaches.

Commenter (0115) stated that, w hile the proposal does urge state agencies to model multiple sources located in close pro ximity, as needed, the Band does not believe that this position is strong or clear enough, and may be open to wide interpretation by various facilities and regulatory agencies. Commenter (0115) stated that more stringent guidance or oversight in this

area is needed so that state agencies will have clear authority to require modeling from sources with high rates of cumulative emissions. Commenter (0115) provided the following additional points.

T he proposed thresholds do not adequately address industry

- inte nsive areas that may experience high cumulative rates of emissions or that may be located in areas with local meteorology that is not conducive to adequate air dispersion. The areas near the Fond du

Lac Reservation and the ceded territories include both of these types of settings.

Minnesota's Iron Range (a geologically defined area in the Northeastern part of the state)

has seven active taconite mines and three utilities, all located within roughly 60 miles of one another, all of which are major sources of S O 2 . In 2012, these facilities emitted an estimated total of 8,592 tpy of S O 2 . Only one of these sources emitted more than 2,000

tpy , however, so only that particular source would have be en targe ted for modeling under

the EPA' s most favored proposed scenar io because these sources are located in an area with less than 1,000,000 million residents. Preliminary modeling performed by the Minnesota Pollution Control Agency including all of these facilities, however, has shown a number of instances of potential mo deled non

- compliance that are currently being

further addressed.

Response :

In general, the EPA has responded to these comments in the preamble to the final rule. The EPA is not establishing specific criteria for prioritizing clusters of multiple sources because the factors that influence whether particular cases warrant prioritization are too complex and difficult to administer to warrant defining generally applicable criteria.

Emission density can be defined in various ways reflecting various means o f defining the area over which emissions are averaged. No single definition of emission density best serves the range of circumstances that exist. Furthermore, emission density addresses only one factor influencing the need to prioritize an area for air quality characterization, since concentrations ofDELIBERATIVE

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72 SO 2 are also influenced by the size of the area, the total emissions of SO 2 , the geographical relationship of the sources (e.g., the proximity of the sources and whether they are aligned in any

wind directi on), and other factors influencing the impacts of the individual sources and the combined impacts. Thus, the EPA has concluded that no set of easily administrable criteria could appropriately address the range of circumstances that are to be considered. Ne vertheless, the notice of final rulemaking contemplates the possible impact of below

- threshold source clusters, notes the possibility that states may choose to characterize, or EPA may further require the characterization of, such areas on a case

- by

- case b ases, and discusses the factors that should be considered in judging whether particular areas warrant air quality characterization

. T he rule provides for case

- by

- case judgments as to the areas to be addressed rather than defining any particular set of crit eria to use in making these judgments.

The degree to which a border area warrants air quality characterization is a function of the circumstances on both sides of the border. Thus, in determining whether a border area warrants air quality characterizatio n, the affected states should consider all sources on both sides of the

border and collaborate on reaching a determination on whether to characterize additional below

threshold source clusters. Where appropriate the EPA will oversee this determination and will apply its discretion to require air quality characterization in such areas based on consideration of

all sources in the area.

A similar response applies to other recommendations for methods for identifying clusters that warrant air quality character ization. The existence of two or more sources with combined emissions exceeding 2

, 000 tpy or some other total does not by itself indicate a need for air quality characterization, depending on the proximity of the sources and other factors. (Similarly,

the fact that the combined emissions are less than 2

, 000 tpy is also not a definitive indication that the area does not warrant air quality characterization, given the possibility that the proximity and the stack parameters of the sources or other aspects of the situation may warrant prioritizing the area.)

k. 

### Phased approach

Comment :

Commenters (0034, 0115) recommended a phased approach. Commenter (0034) recommend ed a phased approach in which an initial round of analyses would be followed by additional analy ses

at a later date

, depending on the annual SO 2 emissions thresholds of such sources ( e.g., 3,000

tpy , 2,000 tpy , or 1,000 tpy ).

Response:

The EPA promulgated a revised SO 2 standard in 2010, and the EPA believes that appropriate

efforts to assess the a ttainment of that standard should be conducted as expeditiously as practicable. The EPA does not believe that any portion of this reasonable effort at SO 2 NAAQS implementation should be deferred.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

73 l. 

### Statewide percent reduction target

Comment :

Commenter ( 0060) suggested the rule should give s tates an overall total emissions coverage percent reduction target . Commenter (0060) recommended that target should not exceed 80% of

the 3

- year average of total s tate emissions.

Response:

The EPA believes that this recommendation would not provide for appropriate, nationally consistent targeting of the areas that most warrant air quality characterization. It could, in fact, result in certain states being required to address sources that are much smaller and that hav e lesser impacts than sources in other states that might not be required to be characterized based on the latter state’s application of such a test. Nevertheless, in the event that the sources covered by this rule do not meet an air agency’s own preferred extent of coverage within that particular state, this rule provides that the air agency can characterize additional sources as appropriate.



### m. Factors other than population

Comment :

Commenter (0044) st a ted that if the EPA decides that either Option 1 or 2 is preferable, then the

s ource t hreshold needs to be revised to take into account factors in addition to population density. Commenter (0044) recommended the final rule require the following additional factors be considered, including (but not limited to ): the distance a source is located from population centers in general and sensitive populations in particular; stack heights; topography and meteorological factors unique to the source(s); and economic conditions that will affect a source’s expected SO 2 e missions.

C ommenter (0044) stated that if the EPA decides that population density is not a threshold factor that will need to be considered, the final rule should still designate that, at a minimum, the following additional factors be considered, includi ng (but not limited to): the distance a source is located from population centers in general and sensitive populations in particular; stack heights; topography and meteorological factors unique to the source(s); and economic conditions that will

affect a s ource’s expected SO 2 emissions.

Commenter (0044) disagree d with the proposal’ s statement explaining why the Agency does not believe it necessary for air ag e ncies to consider such factors . Commenter (0044) stated the lack

of a nationwide database with res pect to such factors is irrelevant since the modeling is to characterize localized ambient air quality; and the statements in the proposal itself describe the benefits of these factors (at 27449 and 27461).DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

74 Response:

Regarding the comments EPA received e xpressing preferences on the proposed emission

threshold options

, the EPA notes the wide range of views. A few c ommenters recommended

alternate thresholds in the rang e from 1

, 000 tpy to 10,000 tpy

, or recommended pairs of thresholds within this range. Som e commenters provided modeling analyses as an indication that sources larger than 12,000 tpy did not cause a violation of the standard, while other commenters recommended a single emissions threshold of 1

, 000 tpy and provided modeling analyses of

different sources as an indication that sources less than 2,000 tpy caused modeled violations.

These comments demonstrate that ambient SO 2 impacts can be variable, and are dependent on many factors other than annual emissions (such as meteorology

, stack height, loc al topography and plant operations). These factors can only be assessed through analytical approaches, such as ambient monitoring or air quality modeling, which take many of these related factors into account simultaneously. The EPA’s goal in this rule was not to dev ise a perfect test that requires

characterization of every source that would be found to violate the NAAQS and excludes from characterization every source that would be found not to violate the NAAQS . While such a test may be ideal, it would be unnecessarily burdensome and complex to administer

– essentially resulting in an effort that would equate to characterization of every single source in the country

. That is why this rule promulgates a test that is feasible to administer and establishes a t hreshold that appropriately directs limited characterization resources toward priority sources. These comments demonstrate why specific air quality characterization of the area around these sources is needed to protect public health in the first place.



### n. Do not codify the thresholds

Comment :

Commenters (0053, 0058) stated that the EPA should not make the threshold criteria mandatory

so as to hamper a state's ability to reasonably tailor its approach. Commenter (0058) stated the EPA should provide clear t echnical justification for any threshold it recommends and should simply submit this recommendation as guidance to the s tates, rather than codify thresholds in this rulemaking. Commenter (0058) stated that, while thresholds can be useful tools, the thresho ld options proposed by the EPA do not account for the myriad other factors that are critical to the assessment of a source’s impact (e.g. stack height, emissions parameters, topography of the area). [Also see III.A. 9

, regarding s tate discretion ]

Response :

The EPA disagrees with the commenters who stated that EPA should not make the threshold criteria mandatory. The EPA held stakeholder meetings to gather comments on what process should be taken to implement the SO 2 NAAQS in May and June of 2012. From tho se stakeholder participation meetings we received comments stating that any new modeling or monitoring requirements relating to the implementation of the SO 2 NAAQS should be established through aDELIBERATIVE

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75 notice

- and

- comment rulema k ing process. That is, the EPA must weigh this comment against feedback from numerous others that recommended rulemaking, presumptively to make the threshold criteria mandatory. The EPA also believes that it is important to codify the requirements of this rule to ensure that the appropriate information is provided to characterize air quality rounding sources of SO 2 to use in future EPA actions such as designations and redesignations of areas. While the EPA recognizes that a number of factors influence the likelihood that a given quantity of emissions will cause a violation, these factors interact in complex ways, such that no simple combination of criteria would necessarily provide a better indication of whether a source area warrants air quality characterization than a rule with a simple

emi ssion threshold. In addition, a rule with a simple emission threshold is significantly easier to implement and is more prone to provide for national consistency than a rule with complex interactive criteria. Nevertheless, the EPA shares the concern that ar eas with sources emitting less than the promulgated threshold may nevertheless be violating the standard (presumably due to a combination of pertinent factors), and the EPA is therefore promulgating the proposed provisions for discretionary addition of suc h areas to the list of areas subject to air quality characterization requirements.



### 7. S tate option

— identify additional sources

Comment :

Commenter s ( 0051, 0089

, and 0107 ) encourage d the EPA to identify criteria so that the states are in a position to know w hat additional source

- oriented areas they may be required to monitor or

model. Commenter (0051) stated that, t o promote national consistency and assist states with making viable implementation plans, the EPA should develop a process or criteria to identify any sources that may be requested for evaluation beyond those determined by the rule's thresholds. Commenter (0107) stated t his criterion ("or has been identified ... as requiring further air quality characterization"), being rather vague and open

- ended, creates great uncertainty about how to implement the rule. Commenter (0107) recommended either removing the phrase or providing specific criteria for applying it.

Commenter s (0035 , 0051, and 0062 ) stated that the rule should make clear that states have the option to monitor or model sources below the thresholds established in the final rule. Commenter (0062) stated t here are many factors involved in determining whether or not an individual facility causes a NAAQS violation, including total emissions, tem poral variations in emissions, meteorology, other sources, etc. Commenter (0062) asserted that s tates should characterize areas

that

, based on their knowledge of SO 2 sources and meteorological characteristics in their states

, could be at risk for exceeding the standard. Commenter (0062 ) suggested that the EPA, in the final rule, add the following italicized and bolded language:

Under section B. Proposed Source Emission Threshold Options:

“...This Proposed Rule only presents a minimum set of sources for wh ich surrounding ambient air quality would need to be characterized. States should characterize areasDELIBERATIVE

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76 that, based on their knowledge of sources and areas, may be at risk for exceeding the

standard

. As discussed in more detail in section IV, the air agency o r the EPA Regional Administrator may identify other sources that should be characterized beyond the minimum requirements of this Proposed Rule

. ”

Under section IV, subsection A. From Promulgation of this rulemaking to January 15,

016 :

“... The EPA strongl y encourages each air agency to consult with its EPA regional Office to identify sources exceeding the emission thresholds in the final rule (as described in section III) and any other areas near sources that do not exceed the emissions thresholds

but whic h would be appropriate for air quality characterization as well. States are in the best position to evaluate their SO 2 sources and areas and should characterize areas that could be at risk for exceeding the standard .”

... “Section 51.1203(a) of this rulema king as proposed, would then require each air agency to submit to its EPA Regional Administrator by January 15, 2016, a final list identifying... We note that, while a state may not have any sources that exceed the minimum source threshold requirements, ther e may still be a separate need (such as may arise in making future designations recommendations) for the air agency to characterize air quality for any other sources below the thresholds in this Proposed Rule that the air agency or the EPA Regional Adminis trator deems may have the potential to violate the NAAQS. For example, the air agency or the EPA administrator may determine that the air quality should be characterized around multiple sources located in close proximity that individually are below the thr eshold but whose combined emissions may violate the NAAQS. States should add sources to this list that are below the source thresholds that, based on their knowledge, are at risk for exceeding the standard. ”

Response:

The primary criterion for identifyi ng sources near which air quality must be characterized is an emission threshold of 2,000 tpy . Presumably these commenters would agree that this criterion provides a clear indication for how to identify most of the areas that this rule will require to be

a ddressed. Since the rule requires air quality characterization for areas with sources emitting at least 2,000 tpy or that the air agency or the EPA identify as requiring further air quality characterization, the EPA believes that the rule is clear that air agencies and the EPA have the authority under this rule (in addition to authority under section 114(a)(1) of the CAA) to require air quality characterization in areas that have no sources emitting 2,000 tpy or more of SO 2

.

At issue here is how to ident ify additional areas beyond those having a source emitting 2,000 tpy that warrant air quality characterization. Among cases in which no single source meets the applicable emission threshold, no simple indicator is available to indicate which of these cases warrants air quality characterization. For areas with a single source, the areas could warrant air quality characterization if the stack height is low, if the plume rise is minimal, if terrain or meteorology is conducive to high impacts, and /or if emissio ns are just slightly below theDELIBERATIVE

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77 threshold. For areas with multiple sources, concentrations are influenced not only by these stack, terrain and meteorological factors but also by the level of emissions at each source and the

distances and wind directions bet ween the sources. The EPA appreciates the comments urging the establishment of specific criteria in the rule for identifying additional areas that warrant air quality characterization, but the EPA finds that these areas are better identified on a case

- by

- c ase basis reflecting a judgment considering the range of factors that influence the likelihood of NAAQS violations. That is, the EPA agrees with the state commenter urging that the rule provide for discretionary coverage of additional areas, such that addi tional areas that in the air agency’s (and the EPA’s) judgment have significant potential for violating the NAAQS can be

made subject to requirements for air quality characterization on case

- by

- case bases

.

The EPA agrees with the commenter that states are often in the best position to know whether an

area is at risk of violating the SO 2 standard. At the same time, EPA is often in the best position to assure national consistency, to assure that areas in different states with similar risks of violating

the S O 2 standard are addressed similarly. Therefore, the EPA is retaining the proposed approach, in which the air agency and the EPA are given equal authority to determine that areas without sources emitting 2,000 tpy or more shall be subject to the requirement s for air quality

characterization.



### 8. EPA option

-- identify additional sources

Comment

Commenter s ( 0035, 0089

, 0106, and 0107 ) encourage d the EPA to identify criteria so that the states are in a position to know what additional source

- oriented areas they m ay be required to

monitor or model. Commenter (0106) stated that this requirement is ambiguous and extremely subjective and would result in uncertainty as to who has the authority to determine which sources are subject to the Proposed Rule.

Commenter (00 35) stated t he EPA should clarify that revisions by the Regional Administrator that add sources to the submitted list are to be based on appropriate data that show that the

source's actual S O 2 emissions exceed the applicable emissions threshold, and not ba sed on other

criteria.

Commenter (0107) recommended either removing the phrase or providing specific criteria for applying it. Commenter (0107) stated that, if the phrase ("or has been identified ... as requiring further air quality characterization") re mains in the final rule, the word "or" should be changed to "and" such that the rule requires a consultative process between the air agency and EPA. The revised phrase would read, "... been identified by the air agency and by the EPA Regional

Administrator as requiring further air quality characterization."

Commenter (0051) stated that, i f the Regional Administrator requests the evaluation of additional sources, states need sufficient time (likely to be at least three years) so they are notDELIBERATIVE

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78 forced into mo deling to meet the EPA's deadlines. Commenter (0051) stated i t is crucial that states have the flexibility to choose which method to use to determine attainment in a way that

best suits the states' emissions sources and resources and t he potential need to evaluate additional sources undermines a state's ability to anticipate resource demands and make solid implementation plans.

Commenters ( 0063, 0065, 0085, 0088

, 0093, and 0106 ) did not support a llowing E PA Regional

Administrators the discretion to add so urces below the threshold. Commenters (0063, 0065)

stated last

- minute additions by the Regional Administrator would undermine efforts by states and sources to plan and prepare for compliance with any final rule and create a path for states to be

forced int o modeling as the result of an unexpected monitoring plan disapproval. Commenter (0085) stated the proposed approach will, by its nature, result in inequities in air quality across the country ; instead, t his rule should establish fair and impartial method s

. Commenter (0088) stated that it is not within the EPA ’s authority

, unless it is administering the

State’s entire SO 2 NAAQS program to condition approval on modeling other sources

.

Commenters (0085, 0093) did not support a llowing air agencies the discr etion to add sources below the threshold since that approach will, by its nature, result in inequities in air quality across the country. Commenter (0085) stated t his rule should establish fair and impartial methods for deciding which sources must have the ir air quality characterized and that l ocal politics and advocacy should not be involved.

Commenter (0088) stated that i f the Administrator is advised by the Regional EPA office that a source should have been included, then the Administrator can designate the area “unclassifiable” pending further air quality characterizations. Commenter (0088) provided the following additional points.

There are no limitations on the EPA ’s ability to designate such sources, either temporally or with procedural notices by w hich EPA regions would be able to unilaterally require data collection plans to be augmented. NEDA/CAP submits that it is up to the s tate to determine if additional sources should be modeled or monitored, and that it is not within EPA’s authority unless it is administering the s tate’s entire SO 2 NAAQS program to condition approval on modeling other sources. Given the time available for modeling and monitoring plans to be developed and implemented, a “late hit” from the EPA would delay the process, provide a de facto veto of a monitoring or modeling plan, and interfere

with the s tate’s ability to implement the monitoring/modeling plan.

Response:

As noted above, no simple criteria exist to identify the areas not identified by the simple criterion

of emittin g at least 2,000 tpy that nevertheless warrant air quality characterization. Nevertheless, given the various factors that affect a source’s ambient impact, there can be little question that some areas without any source emitting at least 2,000 tpy may be just as prone to be violating the

SO 2 standard as typical areas with a source emitting at least 2,000 tpy

.DELIBERATIVE

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79 Some of these commenters’ recommendations would defeat the purpose of the provision for discretionary addition of areas to the list of areas require d to characterize air quality. To stipulate that additions of areas must be based on data showing emissions exceeding the threshold is simply an obfuscated recommendation that the rule make no provision for requiring air quality

characterization in areas t hat do not have a source emitting above the primary threshold. To provide that only air agencies and not the EPA may identify such areas as requiring air quality characterization, or to provide that such areas may be added only if both the air agency and t he EPA find the addition warranted, would be to provide the EPA no means to assure national consistency in how areas in different states with similar risks of violating the standard are

addressed. Indeed, the EPA shares the commenter’s concern about inequi ty in application of air quality characterization requirements to areas without sources emitting at least 2,000 tpy , and the EPA believes that providing itself the authority to identify areas as subject to air quality characterization requirements is an im portant tool for addressing that concern. As such, the EPA believes that the rule is clear that both the air agency and the EPA have the discretion to add areas to the list of areas for which air quality is to be characterized.

The EPA believes that the d iscretionarily added areas, i.e. the areas that the air agencies or the EPA identify as warranting air quality characterization notwithstanding the absence of a source emitting at least 2,000 tpy , may reasonably be expected to be addressed on the same time table as areas that do have sources emitting at least 2,000 tpy . Air agencies that are uncertain as to whether they (or the EPA) would consider an area to warrant being subject to air quality characterization requirements are advised to consult their EPA r egional office, preferably before the list of subject areas is due, so that questions as to what areas are to be subject to these requirements are resolved early. Even in the absence of such early consultation, i.e. even if the applicability of air quality characterization requirements is uncertain even at the time the air agency submits its list of the areas it believes are to be addressed, the EPA believes that the rule provides adequate opportunity to resolve those questions and still assure the selectio n of appropriate air quality characterization approaches on the schedule provided in the rule.

Section 114(a)(1) of the CAA already provides the EPA authority and discretion to require emissions sources to install, use and maintain monitoring equipment a nd provide other information as the Agency may reasonably require, even in the absence of this DRR . In addition,

t he EPA had several reasons for proposing as part of this rule to reinforce state and the EPA discretion to require air quality characterizatio n around additional sources beyond those with emissions above the proposed thresholds. Therefore, the EPA has the authority to promulgate by rule a requirement that appropriate areas be subject to air quality characterization requirements, irrespective of whether the EPA is administering a state’s SO 2 NAAQS program.



### 9. State discretion to exclude above

- threshold sources.

CommentDELIBERATIVE

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80 Commenters ( 0053, 0058, 0060, 0063, 0065, 0097) suggested the EPA should provide the s tates
with the discretion to determine when sources should be added or eliminated from the list based on other factors that are important to determining source impacts (e.g. stack height, emissions changes, terrain, and population).

Commenter s (0063, 0065) stated the EPA should not seek to limit states' flexibility to tailor their respective approaches to establishing their attainment status, because the CAA assigns states the primary responsibility and discretion to determine how to implement and enforce the NAAQS. Commenter (0109) added that st ates should be allowed to use other available information to predict whether th e source will be emitting at this level in the future.

Commenter (0058) stated the EPA should provide clear technical justification for any threshold

it recommends and should s imply submit this recommendation as guidance to the s tates, rather than codify thresholds in this rulemaking. [Also see III.A.6.] Commenter (0053) stated that the

EPA should not make the threshold criteria mandatory so as to hamper a state's ability to

rea sonably tailor its approach. Commenter (0053) encouraged the EPA to provide flexibility for

states to deviate from the EPA 's proposed thresholds if a state shows that they are unnecessarily expansive and/ or greatly in excess of available monitoring resour ces for states that elect monitoring as the best and most accurate approach. Commenter (0053) stated, f or example, while

the EPA indicates that states are not required to use modeling, the EPA also acknowledges that states may have limited resources to exp and monitoring networks, leading to a logical conclusion that if resources are inadequate to expand monitoring networks to cover all areas as required by mandatory thresholds, the state will be forced to utilize modeling even if that approach is neith er de sired nor necessary.

Commenter (0060) stated t he rule should not take an "all in" or "all out" approach based on a simple analysis of one year's emissions or even a 3

- year average of emissions alone. Commenter (0060) stated that the EPA seems to allow, or consider, the potential addition of non

- threshold

meeting sources but does not recognize there may be instances where the air agencies knowledge and judgment warrants exclusion of threshold triggering sources

. Commenter (0060) stated that air agencies sho uld be able to take into consideration operational changes during the 3

- year period to determine if a different methodology is appropriate for determining if a source should be a part of the analysis. Commenter (0060) provided the following additional poin ts.

For example, if the period 2010 to 2012 is used and the 3

- year average emissions triggers the analysis requirement for a source but in 2011 the source installed flue gas desulfurization (FGD) controls and an analysis of normal post

- FGD emissions does not trigger the analysis threshold, an air agency should be able to make the determination that the installation of an FGD and the resulting post

- FGD emissions do not warrant inclusion of the source in the analysis.

Likewise, if a source's emissions had period(s) of decline during this 3

- year period that resulted in exclusion from the analysis yet historical emissions showed higher levels and

the decline was not due to an SO 2 emission reduction strategy, the air agency should haveDELIBERATIVE

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81 flexibility to include t hem in the analysis.

Commenter (0060) stated that six of Ohio's 10 well

- controlled EGU facilities would remain subject to this draft rule under Option 3, many of which have only very recently installed their

state of the art controls for SO 2 . Commenter ( 0060) was concerned regarding spending time and resources to monitor and/or model such well controlled sources, many of which likely could not produce further appreciable reductions short of switching to natural gas.

Commenter (0097) stated that the EPA should evaluate the use of resources for determining SO 2 compliance in remote areas that in past efforts have shown modeling and monitoring challenges

and stated i t may make sense to allow the use of unclassifiable designations in certain extreme

situation s.

Response:

As with many other programs under the C AA , the EPA is following an approach in which states have substantial flexibility to tailor their approach according to their preference and their particular circumstances but in which EPA has an oversi ght role to assure reasonable national consistency. The EPA is promulgating a rule that provides express authority to states and other air agencies to add sources to the list that may not meet the promulgated threshold and yet appear to warrant air quality characterization, though the EPA intends to review the intended additions to assure that these additions do not create serious national inconsistencies in the sources being addressed by this rule . The EPA is not offering the discretion to exclude sources that meet the threshold for listing but the state judges not to warrant air quality characterization. Although the EPA acknowledges that some sources targeted for characterization under this rule may not, in fact, turn out to be causing or contributing to NAAQS violations (just as EPA monitors air quality in some areas that are not violating a given NAAQS), it is nevertheless important for the rule to establish nationally

- consistent criteria for the minimum characterization requirements.

This document h as previously discussed the challenges associated with devising and implementing a hypothetical perfect test that would not require characterization of a single non

violating source. Further, t he EPA expects that a rule allowing air agencies to exempt sour ces that meet the threshold by applying some more general criteria short of such a test would result in a wide variety of rationales for excluding sources, which would be difficult to administer and ensure nationally consistent application . . Thus, EPA has chosen to retain the approach in which

, at a minimum, sources that meet the threshold must be listed. By this means, the listing serves to identify priority sources that warrant review as to whether the surrounding area is attaining the

standard. The comm enter noting the possible existence of sources exceeding the threshold but not warranting air quality characterization does not identify any types of sources exceeding the

threshold that would not warrant characterization of nearby air quality.

Although under this approach any source that exceeds the emission threshold warrants analysis,

the EPA notes that s ources that are less likely to cause violations may well require less effort; for example, the modeling TAD explains that if screening modeling, provi ding a conservativeDELIBERATIVE

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82 assessment of ambient concentrations, shows the area to be attaining the standard, then more

resource

- intensive modeling would not be necessary. In addition, the rule provides various options for addressing priority sources, including n ot just monitoring or modeling but also avoiding air quality characterization requirements by complying with an enforceable emission

limit below the threshold.

The EPA believes that once a source is identified as a priority source, the source should remai n listed, and no further efforts should be undertaken using later emissions data to reassess the list. Instead, other opportunities are available to consider emission reductions that occur after the list is established. First, if a source reduces its emis sions below the threshold of this rule (sufficient to be judged to warrant not triggering the air quality characterization requirement), and this emission reduction is in compliance with a federally enforceable emission limit, the air quality

characterizat ion requirements do not apply. Similarly, if suitable modeling demonstrates that such a limit provides for attainment, then no further air quality characterization is required. Second, if air quality characterization shows an area to be violating the stan dard but then implements emission reductions that can be shown to provide for attainment, then these emission reductions (consistent with a suitable emission limit) would provide the key element of a nonattainment plan for the area.

One commenter express es concern that resource constraints may force some states to use modeling even if use of modeling is “neither desired nor necessary.” The EPA shares the commenter’s regret that resources are constrained. Nevertheless, the EPA has identified in this rule ( with rationale described previously) an approach for prioritizing sources for which

characterization is desired and necessary to fulfill the CAA mandate of providing for attainment of the air quality standards. The EPA aims not to promulgate a rule that re quires more resources

for characterization than are available, and the EPA agrees with stakeholders that have urged the EPA to offer a choice between modeling and monitoring as a means to characterize air quality.

Some commenters expressed concern that u se of three years of data would improperly address a source that toward the end of those three years installs emission controls. These concerns are addressed in part by revision of the rule to use the most recent year of data. These concerns are

further ad dressed by provisions in the final rule that a source may be exempted from air quality characterization requirements if the source becomes subject to and complies with a limit by January 2017 that requires the source to emit less than 2,000 tpy (provided t he reduced emission level does not still warrant air quality characterization of the area).

The recommendation to apply unclassifiable designations in selected cases appears to suggest that the areas should be designated unclassifiable permanently. The EP A is not regulating how it will promulgate future designations

. Therefore, the EPA is requiring all areas with priority sources to provide for air quality characterization, irrespective of the remoteness of the area.



## IV

. D at a Requirements a nd Program Imp lementation TimelineDELIBERATIVE

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83 

### A. Comments on the overall timeline

1. T he proposed timeline may be reasonable

Comment :

Commenter (0060) stated that the feasibility of the schedule will be dependent upon the threshold option selected by the EPA

. Commenter (0085) support e d the timeline that the EPA has proposed as long as the EPA finalizes this rule by late 2014

. Commenter (0085) stated that

, if

the EPA ’s finalization of this rule is delayed, the timeline should be adjusted by as many weeks or months as the delay in finali zing the rule.

Commenters (0043, 0058, 0064, 0071, 0085, 0091, 0101) agreed that the EPA’s proposed time appears reasonable for the acquiring of the data by either modeling or monitoring, for evaluation of the submitted data, for issuing designations and submittal of any SIPs.

Commenter (0043) recommend ed that the EPA include an unclassifiable designation in the August and December 2017 timeline for states collecting monitoring data and stated t his will

prevent the EPA from getting sued for not designatin g these areas.

Commenter (0079) urge d the EPA to acknowledge the challenges that certain regulatory

deadlines would impose on the regulated community when triggered by whether modeling or traditional monitoring is used. Commenter (0079) stated, f or exampl e, an air agency that chooses a modeling scenario would accelerate nonattainment designations to 2017

- 2018, adding to the burdens of regulatory compliance, which undermines business certainty.

Commenter (0088) urged the EPA to consider whether adding mil estones to the implementation

schedule for the SO 2 Data Rule would be beneficial. Commenter (0088) stated s uch milestones

would not have hard regulatory consequences, but could be fashioned to provide assistance to

s tate a gencies in implementing monitoring programs
, provide urgency for the required state rulemaking that may be necessary for their implementation , and would provide feedback to the

EPA and to other stakeholders on the due diligence and good faith of state agencies to implement monitoring.

Res ponse:

The EPA recognizes the logistical and financial challenges that were identified by comment er s with respect to the timeline . In response, the final rule contains changes to provide additional time for air agencies to determine whether to use modelin g or monitoring to characterize air quality near their affected sources . However, the final rule retains the proposed deadlines for commencing monitoring or providing modeling. The Agency acknowledges that the se deadlines do not provide as much time as som e commenters would prefer ; however, the EPA believes that

the se deadlines can be achieved with the appropriate planning, coordination, and program implementation by air agencies

. In addition, the EPA does not believe that additional milestonesDELIBERATIVE

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84 are required given the time period associated with air agencies meeting the requirements, given that the schedule provides a clear indication of when actions should be taken to meet the requirements of the rule. The EPA notes , however, that if air agencies conclude th at the timeline and resource burdens associated with installing and conducting improved monitoring are less feasible for particular areas, they may instead choose the modeling approach , which is generally less expensive and can be performed more expeditiou sly than monitoring, to characterize air quality

. Alternatively, in some cases the source owner and the air agency may be able to establish by January 2017 a federally enforceable requirement limiting emissions to less than 2,000 tpy , with the result that further modeling or monitoring in that area would not be required under the rule unless air agencies or EPA Regional Administrators conclude it is otherwise

warranted. Because t he purpose of this rule is to obtain improved air quality information in an

eff icient manner in order that these data may be used in future actions (such as area designations

, redesignations , or other actions designed to ensure attainment of the 2010 SO 2 NAAQS ) to protect the public from the short

- term health effects associated with exposure to SO 2 concentrations that exceed the NAAQS , the EPA believes it would not be appropriate to further extend the timelines for air quality characterization in the rule.

The EPA believes that any further delay in air quality characterization aro und sources identified as a result of this rulemaking would delay the implementation of the SO 2 NAAQS and therefore would impede public health protection in areas that in the future show violations of the standard based on the data to be gathered under the rule. The EPA also believes that any significant delays in monitors becoming operational past the date of January 1, 2017, will certainly delay the potential for monitoring data to be used to inform actions that depend upon ambient

concentration assessmen ts, possibly past calendar year 2021. Finally, the EPA notes that under

the terms of the March 2015 CD , in order to avoid the EPA being required to designate an area by December 31, 2017, an air agency will need to have installed and begun operating the ne w SO 2 monitoring system no later than January 1, 2017.

The Agency believes that it is very important to maintain the proposed timetable for conducting modeling and installing monitoring sites because of the need for these new data to be available to

supp ort future determinations concerning the attainment status of areas. T he EPA encourages each air agency to engage in early dialogue with the appropriate EPA Regional Office and with

the identified applicable facilities in order to meet the requirements of the rule. In particular, i n light of the reality of the sometimes complex process of identifying potential monitoring

location s , securing funding, and installing an appropriate number of ne w site s
, i f a n air agency is considering the monitoring approach fo r one or more areas, early coordination should improve

the air agency’s potential for success in meeting the timing and requirements of the rule.

T he final rule retains the January 15, 2016

, date for submittal of a list of sources

, because the EPA expects that this information is relatively straightforward to obtain

, and it is beneficial for planning purposes to have this list available as soon as possible. However, a s mentioned previously, in light of comments, the EPA is promulgating a schedule that prov ides an additional

six months for the air agency to specify how it plans to address the area around each listed

source.DELIBERATIVE

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85 The EPA is promulgating a schedule in which July 1, 2016

, is the deadline for selecting among the monitoring approach, the modeling ap proach, or establishing source emission requirements. If the air agency selects the monitoring approach for a source area, it must also include in the annual monitoring plan (also due by July 1, 2016) information about any new monitoring sites it

will esta blish by January 1, 2017. If the air agency selects the modeling approach for a source area, it must also submit a modeling protocol at that time. If the air agency chooses the option of establishing an enforceable source limit or limit s as an alternative to air quality characterization,

it must also at that time provide a description of the planned emission limitation, including such information as emission rate, averaging time, and expected legal mechanism for making the limitation federally enforceable. To suffice as an alternative to the characterization requirement, the emission requirements or limits would need to be adopted by the air agency, made federally enforceable, and require compliance by January 13. 2017.

Finally, i n this rulemaking we are no t addressing comments received on the proposed rule concerning the designation process b ecause those issues are beyond the scope of this rulemaking. In addition, given that the court has already provided a decision concerning whether the issue of

the time period for EPA to promulgate designations in the March 2015 CD , the time period for entering a law suit against EPA on the issue has passed.



### 2. The proposed timeline is not achievable

Comment :

Commenters (0045, 0088) recommended an extension of at least one year on all the proposed

actions listed in the implementation timeline.

Commenter (0051) stated t he proposed timeline is flawed for multiple reasons and is therefore

not achievable. Commenter (0051) provided the following additional points.

First, crit ical elements (such as criteria for characterizing sources, emissions thresholds

for monitoring of sources, and proximity to population) are not anticipated to be provided

to states until the DRR is finalized in late 2014, just two years before completion of either modeling or monitor deployments are required.

Second, the timeline is not sufficient to allow for the lengthy process of funding

procurement through the legislative process. Texas has biennial legislative sessions. The Texas legislature meets i n January of odd numbered years for 140 days. Appropriations for additional funding can only be requested during this time period and are granted for the following biennium. If adequate funding resources were allocated for this purpose,

those funds would n ot be disbursed to state agencies earlier than the biennium beginning in September 2015, leaving only 16 months to deploy monitors before the deadline. If the TCEQ were to wait to request additional funding until adequate details are available to provide a n accurate estimate of monitoring costs (i.e., after the DRR is final and the monitoring network plan approved), the earliest funds could be appropriated to the TCEQDELIBERATIVE

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86 would be September 2017.

Third, numerous monitoring siting challenges are expected, part icularly in rural areas

near larger SO 2 sources. These challenges would include proximity to electricity, prohibitive terrain, property owner agreement, and accessibility. The TCEQ recently experienced similar challenges and implementation delays in locati ng an area

- wide SO 2 monitor near a rural source in the Amarillo area. Due to logistical issues, it took over one year to deploy the required SO 2 monitor, even after numerous reconnaissance trips to the area. Based on this and similar experiences, at least two to three years will be required to

p erform the required number of site visits, propose monitor locations, provide public notice through the annual monitoring network plan, secure the monitoring locations, prepare the new site, install the monitors, and perform system tests.

Fourth, the EPA has not proposed assurances or legal deadlines for responses or approvals of the state monitoring network plans that are necessary for states to proceed with deployment of SO 2 monitors. (0051)

Commenter (0103) state d that, a t current levels of funding from the EPA , this schedule is not

achievable. Commenter (0103) provided the following additional points.

EPA must provide additional funding to implement this rule. States will begin incurring significant costs to per form modeling to site monitors beginning in the 2015 federal fiscal year. Funding will also be needed after designations to develop control strategies, contingency measures, maintenance area plans, and provide for on

- going monitoring of progress towards re aching attainment. This could result in numerous SO 2 nonattainment

areas needing to develop nonattainment SIPs on an 18 month schedule.

Commenters (0050, 0109) stated the timeframes in the DRR must provide states with greater flexibility to ensure states are able to properly characterize current ambient air quality. Commenter (0050) further believed the EPA should include general timeframes for compliance while allowing for variances on a case

- by

- case basis. Commenter (0109) stated the timeline fails

to a ccount for unavoidable delays associated with physical siting and startup of numerous monitors and the EPA’s monitoring network plan pre

- approval process. Commenter (0109) provided the following additional comments.

The proposed deadlines fail to provide sufficient flexibility to address the highly complex and unique circumstances states will face when simultaneously implementing either approach on a case

- by

- case basis at numerous locations across their jurisdiction. Significant data gathering and stakehol der involvement will be required to arrive at appropriate plans for making area designations. Additionally, states may encounter unavoidable delays despite their good faith efforts and the Proposed Rule offers no relief

in those situations where a reasonab le extension of time is necessary. To avoid short

circuiting state efforts to implement their primary designation responsibility, the EPA must allow adequate time for states to identify and implement their preferred SO 2 dataDELIBERATIVE

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87 options and provide express reg ulatory relief when unexpe cted delays beyond the states'

control are encountered. (0109)

Commenter (0090) stated that the proposed timeline leads them to conclude that while states would be acting responsibly to defer the purchase of monitors, along with acquiring access and use of monitoring sites until the EPA has approved the monitoring plan, the risk of being "moved" to the modeling pathway is high. Commenter (0090) asserted the EPA does not propose any deadline for approving state plans and states hav e no control of the approval process once plans are submitted to the EPA. Commenter (0090) believed the EPA's failure to appropriately use its discretion in either designating areas as unclassifiable or allowing a reasonable amount of time for plan develop ment and approval and subsequent implementation of the plan appears arbitrary and lacks merit.

Response:

See EPA’s response to the above comment titled “The proposed timeline may be reasonable.” In addition, the EPA believes that routinely available fund ing, supplemented in some cases by third party funding of monitoring, in most cases should be adequate for air agencies to take the necessary steps as defined in this rule for characterizing air quality at priority areas within their jurisdictions. States have been conducting modeling, operating monitoring sites, and performing related activities for several decades, with assorted shifts in priorities involving increases in some program areas and decreases in other program areas, and the commenters provide no evidence that the efforts required under this rule are outside the capacity of air agencies. Several of these comments are noting the expense of monitoring. However, this rule provides air agencies a choice of characterizing air quality through either m onitoring or modeling, and so the EPA is giving air agencies the flexibility to weigh whether the additional expense of monitoring is a sufficient disadvantage (possibly to the point that monitoring could be considered infeasible) that makes modeling a pre ferred option. Similarly, if air agencies find that siting or commencing operation of a monitor is likely to be unusually difficult, the rule provides them the flexibility to weigh those disadvantages in selecting an approach for characterizing air quality in the area, just as states can also weigh the challenges of conducting reliable modeling (e.g. from complex terrain) in making this selection.

The EPA understands the challenges identified with the Texas funding process as it relates to unusually expe nsive planning efforts requiring supplemental funding that are not foreseen long

in advance. T he EPA considered such challenges when promulgating a rule with sufficient flexibility that should allow Texas to comply with this rule in spite of such challenge s

.

The EPA recognizes that unforeseen events can cause delays in commencing new monitoring sites, but the EPA also recognizes that advance planning can minimize the risk of problems arising. Aside from routine contingency planning, air agencies may be wel l advised to commence monitoring somewhat early, for example in December 2016, to work out any implementation issues to increase the likelihood that the monitors are operating smoothly on January 1, 2017

. (This is especially important in light of the poten tial ramifications that a delayDELIBERATIVE

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88 in the monitor start date would have under the court order for when designations are to occur. ) Similarly, air agencies are well advised to consult early with their regional offices on any issues regarding monitor siting tha t arise, to facilitate EPA ’s to complete its formal review in timely fashion as provided in 40 CFR 58.10. The EPA has clarified elsewhere that an area that fails to commence timely monitoring is not “moved” to the modeling pathway, but other consequences

o f delays in monitoring warrant taking appropriate steps to minimize the risk that monitoring will begin late.



### 3. Monit oring and modeling timelines should be the same

Comment :

Commenter (0103) stated that, t o avoid the perception that the s tates choice to mo del or monitor to designate is arbitrary, the EPA should make the designation timeline the same for the modeling and monitoring pathways in the final rule. Commenter (0103) provided the following additional points.

These provisions of the Proposed Rule pl ace s t ates in an untenable situation. If the s tate chooses to designate a facility with monitoring data instead of modeling data, this will allow violations of ambient air standards for three more years relative to the modeling pathway. If , however, the s t ate chooses to designate a facility with modeling data instead of monitoring data, t his will allow the facility three fewer years before designation to design and adapt to new air pollution control plans.

A revised implementation schedule to facilitate s uch an approach would have the EPA approve modeling protocols in early 2015, and s tates would include the modeling results in the 2015 network plan. If resources are available for monitor deployment, after a year of investigating potential sites for availa ble power, compliance with siting criteria and availability of a property lease agreement, s tates would submit a list of proposed monitoring locations in the 2016 network plan. Any sources subject to the rule that would

not be scheduled to receive a monito r in the 2016 plan would be remodeled with updated meteorological and emissions data after three years. The designation recommendations resulting from the revised model runs for the source areas that were not monitored would be submitted with the designati on recommendations from the source areas that were

monitored.

Synchronizing the modeling and monitor designations timelines would allow s tates to base all their designations, whether modeled or monitored, on partially shared meteorological conditions and more recent regulatory compliance decisions

. In the final rule, implementing a single designation timeline provides additional benefits by eliminating discontinuities in schedules if a planned monitor is not operational by Jan 1, 2017, as such locations c ould simply convert to the modeling pathway.DELIBERATIVE

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89 Response:

The deadlines in the final DRR reflect the EPA’s intention to characterize air quality in prioritized areas as soon as can reasonably be required. Since the collection of three years of new

monitorin g data by definition requires three years following commencement of the monitoring, and modeling can be completed much earlier, a schedule which “synchronized” the completion of monitoring and modeling efforts would inherently impose significant delays in characterizing areas being addressed by modeling. Therefore, the EPA finds that providing a schedule for modeling that is made to match the schedule for obtaining three years of new monitoring data would unduly delay the efforts to characterize air quality in modeled areas, which in turn would unduly delay any efforts to solve any air quality problems that this modeling might identify.



### B. Requirement to s ubmit l ist of SO

2 

### s ources and e lection of

m onitoring or m odeling by January 15, 2016

1. List by most rec ent year of emissions

a. General

Comment :

C ommenters ( 0035, 0050, 0051, 0069, 0082, 0106

, and 0107 ) generally supported the approach that the basis for the emissions to be compared to the threshold be the latest one

- year of SO 2 emissions data . Commenter (0 106) stated using the most recent year of data ensures that any recent emissions reductions that have occurred will be properly taken into consideration.

Commenter ( 0068 ) stated that using the most recent year as a snapshot may fail to capture

sources th at simply have a low year, but normally do emit at higher levels. Commenter ( 0068 ) recommended that the EPA require that facilities only be excluded under the threshold if, in prior years, the facilities had similar low total emissions below the limit.

Re sponse:

The EPA continues to believe that the most appropriate generally applicable basis for determining applicability of the air quality characterization requirements for the purposes of this

rule is to use the most recent available year of emissions da ta for a stationary source as reported to the EPA in accordance with any existing regulatory requirement

. As we have previously explained, SO 2 emissions are trending downward, due to numerous national and regional requirements that have recently been adopt ed and are taking effect. In prioritizing sources to characterize, t he Agency believes it is reasonable to account for this trend by basing applicability

for this DRR on the most recent available year of emissions. Nevertheless, for source s with low

emissi ons in the most recent year but higher emissions in prior years and prospects for higher emissions in future years , the rule provides the option to list such sources as triggering air quality characterization requirements, an option which may be warranted in such cases.DELIBERATIVE

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90 

### b. Data sources

Comment :

Commenter (0051) supported allowing states the option of using either appropriately reviewed and publicly available emissions inventory data or the most recent emissions inventory data published by the EPA. Comment er (0107) request ed that the EPA allow states to use the most

recent annual emissions inventory data certified by facilities and reported to the EPA under the

Air Emissions Reporting Rule (AERR)

. Commenter (0051) asked the EPA to clarify whether

SO 2 monito ring data submitted to the EPA's Clean Air Markets Division could also be used to identify applicable sources as this may allow for use of more up

- to

- date information. Commenter (0107) request ed that the EPA avoid the exclusive use of the NEI to identify s ubject sources as it was required in the implementation of the 2008 lead standard.

Response:

By January 15, 2016, the EPA would expect that 2014 data will be available for all EGU sources

, and 2015 data may be available for many EGUs in accordance with the requirements of the acid rain program and other emission trading programs that require data certification soon after the end of the year. These sources report hourly emissions data to the EPA on a quarterly basis. Emissions data for large SO 2 sources a lso would be available from annual reporting required for

the A ERR

. Every 3 years (i.e., 2011, 2014, 2017 and so on), air agencies must submit to EPA

emissions data for SO 2 sources with the potential to emit more than 100 tpy . In other years, the

AERR requ ires states to report emissions data for SO 2 sources with the potential to emit more than 2,500 tpy . These annual reports under the AERR are due 12 months after the end of the emissions year. Thus, the EPA would expect that in January 2016, states would ha ve emissions data for calendar year 2014 available for non

- EGU sources over 100 tons potential to emit. Emissions reporting requirements for the acid rain and AERR programs would be expected to cover the vast majority , if not all, of the sources subject to the SO 2 DRR

.

By considering the most recent emissions data, the air agency and the EPA will be able to take into account any recent emissions increases or decreases that would cause a source to be subject to the requirements in this rule or not. Althoug h identifying sources based on the most recent year of emissions is a reasonable basis for prioritizing limited modeling and monitoring resources for characterizing current air quality, t he EPA recognizes the concern of some

commenters that there may be so urces that in the most recent year have emissions that are lower than normal and are not representative of normal operations. In these cases, i.e., where recent

emissions are below 2

, 000 tpy but no controls have been installed and past representative

emiss ion levels are typically above 2

, 000 tpy , the state and the EPA should consider using their

discretion to require additional air quality characterization near such sources.



### c. Expected availability of data for s pecific year sDELIBERATIVE

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91 Comment :

Commenters (0063, 0 065) stated that the EPA should specify that 2013 or 2014 reported SO 2 emissions data will be used to identify sources that require new air quality data. Commenter (0051) stated the 2014 point source emissions inventory will be reviewed by states and repor ted to the EPA by December 31, 2015, so it will be the most recent publicly available inventory before the January 15, 2016 deadline.

Commenters (0069, 0082) urged the EPA to clarify that the Agency will take into account the

most recent available emissi ons data when determining whether a source would be subject to the requirements of any final rule. Commenter s (0069, 0082) stated that, while the EPA expects 2014 data to be available for electricity generating units (EGUs) and 2013 data to be available

f or non

- EGU sources by January 2016, in some instances, 2014 data may be available for non

EGUs.

Commenters (0035, 0069) recommended that s tates should be given the opportunity to revise the list of applicable sources using 2015 data should such data beco me available in a timely manner

. Commenter (0035) stated that, b y proposing a later date in 2016 that provides adequate time to receive and review 2015 emissions data, facilities would be incentivized to reduce emissions

below finalized thresholds in 2015 rather than requ iring potentially time consum in g and expensive modeling analyses based on 2014 emissions data. Commenter (0035) stated t he current timeframes in the proposal will likely result in the use of 2014 emissions data to be used

to determine sourc e applicability which provides essentially no time for sources to take action to reduce emissions to avoid a modeling requirement. Commenter (0069) stated that, w ithin a few months after the January 15, 2016, deadline, 2015 EGU data will be available from the EPA 's

Clean Air Markets Division and non

- EGUs may be able to submit 2015 sulfur dioxide emissions data to states in early 2015.

Response:

The most appropriate generally applicable basis for determining applicability of the air quality

characterizatio n requirements is the most recent available year of emissions data for a stationary source as reported to the EPA in accordance with any existing regulatory requirement

. As we have previously explained, SO 2 emissions are trending downward, due to numerous national and regional requirements that have recently been adopted and are taking effect. The Agency

believes it is reasonable to account for this trend by basing applicability for this DRR on the most recent available year of emissions.

By January 15, 2 016, the EPA would expect that 2014 data will be available for all EGU sources

, and 2015 data may be available for many EGUs in accordance with the requirements of the acid rain program and other emission trading programs that require data certification so on after the end of the year. These sources report hourly emissions data to the EPA on a quarterly basis. Emissions data for large SO 2 sources also would be available from annual reporting required for

the A ERR

. Every 3 years (i.e., 2011, 2014, 2017 and so on), air agencies must submit to EPA

emissions data for SO 2 sources with the potential to emit more than 100 tpy . In other years, theDELIBERATIVE

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92 AERR requires states to report emissions data for SO 2 sources with the potential to emit more than 2,500 tpy . These annua l reports under the AERR are due 12 months after the end of the emissions year. Thus, the EPA would expect that in January 2016, states would have emissions data for calendar year 2014 available for non

- EGU sources over 100 tons potential to emit.

Emission s reporting requirements for the acid rain and AERR programs would be expected to cover the vast majority , if not all, of the sources subject to the SO 2 DRR

.

By considering the most recent emissions data, the air agency and the EPA will be able to take

i nto account any recent emissions increases or decreases that would cause a source to be subject to the requirements in this rule or not. Although identifying sources based on the most recent year of emissions is a reasonable basis for prioritizing limited modeling and monitoring resources for characterizing current air quality, t he EPA recognizes the concern of some

commenters that there may be sources that in the most recent year have emissions that are lower than normal and are not representative of norma l operations. In these cases, i.e., where recent

emissions are below 2

, 000 tpy but no controls have been installed and past representative

emission levels are typically above 2

, 000 tpy , the state and the EPA should consider using their

discretion to requir e additional air quality characterization near such sources.

The EPA also recognizes the concern about sources for which the most recent year’s emissions are unrepresentatively high, i.e., that some sources may have recent year emissions above 2

, 000

tpy but normally emit below that level. G iven the trends in emissions, the EPA believes that situation will be relatively rare. Moreover, the existence of such sources does not negate the general conclusion that recent emissions data are an appropriate means for targeting limited modeling and monitoring resources for characterizing current air quality.

The EPA does not believe that this rule should provide ongoing opportunities for revising the list of prioritized sources. The EPA believes that the list shou ld be established toward the beginning of the process, with one occasion for air agencies and the EPA to resolve any issues (such as

those regarding areas that do not have any sources exceeding 2,000 tpy but may nevertheless warrant air quality characteriz ation and t hose regarding cases where a source has low emissions in the most recent year but is expected normally to have relatively high emissions ) . If a source significantly reduces its emissions after being listed, the EPA believes that a more efficien t and equitable approach is to continue to treat the source as a listed source but provide consideration of the emission reduction in other steps under the rule, such as adopting an emission limit requiring emissions by January 1, 2017 to be below 2,000 tp y or modeling the reduced emission

level. (Monitoring will of course reflect the impacts of any emission reductions that have occurred.)



### 2. List by average emi ssions over a three

- year period

Comment :

Commenter ( 0036 ) recommended that applicability be based on a source’s emissions over a

three

- year period, specifically, that EGU annual emissions over the 2012 to 2014 timeframeDELIBERATIVE

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93 should be examined, and any source whose emissions exceeded the threshold must comply with

the SO 2 implementation rule. Commenter (00 36) stated that t his approach would allow states and

the EPA to subject sources with the potential for large emission increases to an ongoing

attainment ver ification process in the future; f or example, if SO 2 emissions were to rise dramatically due to a ch ange in the relative cost of coal versus natural gas, the impact of the increased emissions from this source could be evaluated for potential NAAQS violations.

Commenter (0060) stated a 3

- year average o f emissions should be used to determine applicabilit y under the emissions threshold . Commenter (0060) stated that, similarly, c ompliance

via monitoring with the 1

- hour SO 2 standard is based on a 3

- year average of the annual 99th percentile of 1

- hour daily maximum concentrations

.

Response:

In EPA’s judgem ent the most appropriate generally applicable basis for determining applicability of the air quality characterization requirements is the most recent available year of emissions data for a stationary source as reported to the EPA in accordance with any exi sting regulatory requirement s

. As we have previously explained, SO 2 emissions are trending downward, due to numerous national and regional requirements that have recently been adopted and are taking effect. The Agency believes it is reasonable to account f or this trend by basing applicability for

this DRR on the most recent available year of emissions. By basing applicability on the most recent available year of data, the rule appropriately excludes sources that may have had relatively high emissions on a three

- year average basis but have installed controls and are no longer expected to exceed the emission threshold. Using the most recent year of data provides for prioritizing sources that, continuing through the most recent year, have relatively high emis sions.

The EPA recognizes that use of the most recent year of data brings the risk of failing to prioritize a source that generally has relatively high emissions, has not installed controls or otherwise acted to reduce emissions, but has unrepresentativel y low emissions in the year represented by the most recent data. As discussed in section IV.C.2.c of the preamble, the EPA believes that such situations can and should be addressed by the air agency or the EPA using their discretion to require additional air quality characterization near such sources , as appropriate.

As stated previously, by January 15, 2016, the EPA would expect that 2014 data will be available for all EGU sources, and 2015 data may be available for many EGUs in accordance with the requ irements of the acid rain program and other emission trading programs that require data certification soon after the end of the year. These sources report hourly emissions data to the EPA on a quarterly basis. Emissions data for large SO 2 sources also woul d be available from annual reporting required for the AERR. Every 3 years (i.e., 2011, 2014, 2017 and so on), air agencies must submit to EPA emissions data for SO 2 sources with the potential to emit more than

100 tpy . In other years, the AERR requires sta tes to report emissions data for SO 2 sources with the potential to emit more than 2,500 tpy . These annual reports under the AERR are due 12 months after the end of the emissions year. Thus, the EPA would expect that in January 2016,

states would have emiss ions data for calendar year 2014 available for non

- EGU sources over 100DELIBERATIVE

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94 tons potential to emit. Emissions reporting requirements for the acid rain and AERR programs would be expected to cover the vast majority, if not all, of the sources subject to the SO 2 DRR

.

By considering the most recent emissions data, the air agency and the EPA will be able to take into account any recent emissions increases or decreases that would cause a source to be subject to the requirements in this rule or not. Although identi fying sources based on the most recent year of emissions is a reasonable basis for prioritizing limited modeling and monitoring resources for characterizing current air quality, the EPA recognizes the concern of some commenters that there may be sources th at in the most recent year have emissions that are lower than normal and are not representative of normal operations. In these cases, i.e., where recent emissions are below 2,000 tpy but no controls have been installed and past representative

emission leve ls are typically above 2,000 tpy , the state and the EPA should consider using their discretion to require additional air quality characterization near such sources.

The EPA also recognizes the concern about sources for which the most recent year’s emiss ions are unrepresentatively high, i.e., that some sources may have recent year emissions above 2,000

tpy but normally emit below that level. Given the trends in emissions, the EPA believes that situation will be relatively rare. Moreover, the existence of such sources does not negate the general conclusion that recent emissions data are an appropriate means for targeting limited modeling and monitoring resources for characterizing current air quality.

The EPA recognizes the merits of allowing for use of 2 015 emission data to determine applicability of air quality characterization requirements. At the same time, the EPA does not believe that it would be appropriate to delay any portion of the schedule for implementation of this rule to provide more time to obtain 2015 data. The EPA believes that identification of sources to trigger air quality characterization requirements is an important first step that must be completed early enough to provide enough time to review the options for characterizing nearby

air quality and then to conduct the necessary modeling or to commence operation of any new monitors needed to provide the air quality characterization.

The EPA believes that a rule that prioritizes resources based on the most recent year’s data is

more appro priate for a broader range of circumstances. The EPA notes, however, that after a source is initially identified, the air quality characterization requirements require air agencies to provide at least 3 years of monitoring or modeling data. The availabilit y of such data will provide the opportunity to give appropriate consideration to representative emissions when using such data, as appropriate to the specific use.



### 3. Unrepresentative emissions

Comment :

Commenter ( 0036 ) recommended that, if a particular ye ar’s emissions were considered unrepresentative for a source, then that source could request that the year not be used for the applicability test.DELIBERATIVE

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95 Commenter (0071), i n light of th e variability in annual emissions for some sources,

recommend ed the option to allow the use of the following: (1) a different year other than the prescribed year [e.g., the highest annual emissions rate based on the most recent 3 to 5 years of emissions data] to assess whether the final emission threshold(s) is triggered, (2) an annual emissions rate based on an average of multiple years [e.g. an average of the highest two years' of emissions over the past 10 years], or (3) an adjustment that accounts for multiple annual peaks and/or seasonal peaks that better characterizes emissi ons from source operations that are highly

variable.

Response:

The EPA recognizes the concern about sources for which the most recent year’s emissions are unrepresentatively high, i.e., that some sources may have recent year emissions above 2

, 000 tpy
but normally emit below that level. G iven the trends in emissions, the EPA believes that situation will be relatively rare. Moreover, the existence of such sources does not negate the general conclusion that recent emissions data are an appropriate means for t argeting limited modeling and monitoring resources for characterizing current air quality.

The EPA believes that a rule that prioritizes resources based on the most recent year’s data is more appropriate for a broader range of circumstances . The EPA note s, however, that after a source is initially identified, the air quality characterization requirements require air agencies to provide at least 3 years of monitoring or modeling data. The availability of such data will provide the opportunity to give appro priate consideration to representative emissions when using such data, as appropriate to the specific use

.



### 4. Le gal agreements or permit limits

a. Enforceable limits by January 1, 2016

Comment :

Commenters ( 0049, 0050, 0075, 0081, 0087, and 0110) stated t he EPA should allow facilities to opt out of the rule by taking federally enforceable limits before January 2016

. Commenter s (0075 , 0087 ) recommended that sources which have entered into legal agreements that would

reduce their SO 2 emissions below the applica ble threshold by January 2016 receive the same

treatment as sources that are scheduled to shut down. Commenter (0049) stated that to the extent that electric utility sources are , by January 2016, shutting down or adding/upgrading scrubbers to comply with r egulations such as the Mercury and Air Toxics Standards ( MATS ) for power plants, these sources should not be subject to the provisions of the DRR

.

Response:

The EPA finds merit in the above comments that suggest that the rule should allow for similarDELIBERATIVE

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96 tr eatment for sources that become subject to a federally enforceable emission limit as would be provided for sources for which the state provides documentation that the source will shut down. The EPA has revised the final rule accordingly in section 51.1203( b)

. However, EPA does not agree with commenters who suggest that sources should have until the applicable designation date, or attainment date for an area that is designated nonattainment, to implement controls that were committed to prior to January 1 3 , 2 017. Relying on commitments for emission reductions to occur after 2017 would not be consistent with the main focus of this rule, which is to provide current, updated information on priority SO 2 sources to the EPA beginning in early 2017 that can be used t o, among other things, inform future area designations (now required in December 2017 and December 2020 per the March 2015 CD ).

As indicated above, a source would be listed for air quality characterization if its most recent emissions were above the 2,00 0 tpy threshold. However, the final rule also allows the air agency

to meet the requirements of this rule by submitting a federally enforceable emissions limitation (e.g., source

- specific SIP revision or minor NSR permit revision) to the EPA prior to Janua ry 13, 2017 that requires the affected source to reduce allowable emissions at the source to an annual

rate below the 2,000 tpy threshold level prior to January 13, 2017. By July 1, 2016, the air agency would be required to identify the sources on the list for which it would be using such an approach as an alternative to modeling or monitoring. For such a source identified on the list, i f the affected air agency has adopted and the source has become subject to effective federally

enforceable requirements fo r control measures lowering emissions below 2,000 tpy by January 13, 2017, the air agency will generally not be required to further characterize the impacts from the source’s emissions solely due to its size as of January 15, 2016.

Regarding comments sp ecifically about MATS compliance occurring within this time window,

t he EPA is not explicitly linking these options to EGU actions pursuant to MATS, either to offer these options automatically to sources subject to MATS or to offer these options only to so urces subject to MATS. Nevertheless , these options are prone to be especially useful to EGUs that are complying with MATS in these ways. Therefore, w hile the EPA is not exempting sources solely on the basis of an announcement of plans to shut down or on t he basis of potential applicability

of the MATS SO 2 emission limit, the EPA agrees that EGUs that become subject to an enforceable agreement to shut down or emit less than 2,000 tpy , reflecting reductions anticipated or accomplished as a means of complying with MATS, warrant the exclusion provided in this rule from air quality characterization requirements.

Although air agencies may follow this option as an alternative to characterizing areas with sources that limit their emissions to below the 2,000 tpy s ize threshold, the EPA believes that air agencies and the EPA must apply judgment as to whether there are still reasons to characterize

these areas due to other factors. As discussed above, some areas where all sources emit less than 2,000 tpy may neverthe less warrant air quality characterization, for example because the area has

a cluster of sources with intermediate emission levels or because the characteristics of a source or the area warrant it. Thus, some areas with all sources limited to below 2,000 t py may still warrant air quality characterization. Therefore, the EPA urges air agencies to consult early with the EPA regarding areas that are under consideration for being addressed in this manner, in orderDELIBERATIVE

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97 to develop a common understanding as to whether emission limits under consideration would suffice as an alternative to air quality characterization for the area.

In EPA’s judgement

, allowance for this alternative emission limit approach is not only consistent with the intent of this rule to prioritiz e resources to focus on the largest sources of SO 2 , but it also has the additional benefit of providing an incentive for early emission reductions to occur which will improve air quality in these areas in an expeditious manner . However, we do acknowledge t he distinction between a formerly large source with no future emissions and a source with reduced but continuing emissions. The Agency does not believe it would be appropriate to provide that the latter source can be excluded from evaluation in all cases. It may be that a source with emissions newly limited to below the applicability threshold

– particularly one with limits established just below the threshold

– may warrant further characterization, just

as a source with actual emissions below the threshold may warrant characterization in some instances. For example, air quality characterization would continue to be warranted in areas with other sources over the applicability threshold, and in areas where no single source has emissions

over the threshold but the combined emissions of multiple sources warrant air quality

characterization. In evaluating such cases, the air agency should account for all source emissions contributing to ambient concentrations in the area, including those remaining emissions from the source that has just reduced its levels to below the applicability threshold. For this reason, the rule does not automatically exempt sources with emissions limited to less than 2,000 tpy from air quality characterization requirements; the rule inste ad provides that the air agency or the EPA may judge that the area should continue to be required to characterize air quality notwithstanding the new emission limits. Air agencies are thus advised to consult with their EPA Regional Office before pursuing t his alternative to air quality characterization for a particular source area.



### b. Enforceable limits by January 1, 2017

Comment :

[Also see section V. B

. 3 , regarding enforceable limits as modeling inputs .]

Commenters ( 0035, 0036

, 0043, 0046

, 0048, 0053

, 00 56

, 0057, 0058

, 0060, 0061, 0066, 0069,

0075

, 0081, 0084, 0096, 0097

, 0114

, and 0116 ) supported the removal of sources from the preliminary list based on scheduled enforceable limits in operation prior to January 1, 2017

. Commenter (0046) stated i mplementa tion of controls required by upcoming rules such as Boiler

MACT should be taken into account in the applicability determination, not just in the modeling.

Commenter (0066) believed that the wet flue gas desulfurization (FGD) systems installed on all

four Monroe Power Plant units have eliminated the need for performing an updated 1

- hour SO 2 NAAQS analysis. Commenter (0066) stated this analysis was performed when they received an

SO 2 Best Available Control Technology permit to install, including a 1

- hour SO 2 NAAQS compliance demonstration.DELIBERATIVE

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98 Commenters (0056, 0058) stated i t would be a waste of resources to force States to commit significant effort to model or monitor these facilities when they are already committed to substantially lowering or essentially eliminating their SO 2 emissions.

Commenter s ( 0048, 00 53 ) state d there is no basis to distinguish between shutdowns and enforceable limits because in each case the source would no longer meet the criteria for

characterization. Commenter (0046) stated s our ces should be able to take federally enforceable

limits on a tpy year basis prior to January 2017 to avoid coverage under the rule as they can with PSD, Title V, and other programs under the CAA (i.e., a “once in, always in” approach should not apply).

C ommenter (0081) stated that, i f a source indicates (through a company public announcement, public utilities commission filing, CD , public legal settlement, final state or federal permit filing, or other similar means of communication) a significant fuel sw itch, partial shut d own , or process change which would greatly reduce SO 2 emissions, then that source should also be considered

for exclusion from the rule. Commenter (0084) stated there are a number of other regulatory programs with upcoming compliance dea dlines that will consequently reduce SO 2 sulfur dioxide emissions, including MACT standards, GHG rules, and transport rules. Commenter (0097) stated that, in addition to sources that are/will be shut down, the EPA should include units that are switching to inherently lower SO 2 emitting fuels, such as natural gas and biomass. Commenter (0058) stated that sources should be exempt from the DRR if, by January 2017, they are no longer considered a coal

- fired electric utility steam generating unit as defined in t he Mercury and

Air Toxics Standard. See 40 C.F.R. 63.10042 (July 1, 2013).

Commenters (0039, 0087) recommended the EPA extend the date from January 1, 2017 to January 31 or May 1, 2017 in light of upcoming rule deadlines

. Commenter (0087) stated that

sin ce the MATS rule contains a provision and mechanism by which sources can, if needed, seek an additional year (beyond the initial one

- year extension) to comply by way of an EPA Administrative Order, the EPA should extend the requirement for state agencies t o confirm unit shutdowns under the proposed DRR from January 1, 2017 to May 1, 2017. Commenter (0039)

recommend ed that the DRR exclude either monitoring or modeling evaluations for sources that will shut down prior to January 31, 2017

– instead of January 1, 2017 as suggested. Commenter (0039) asserted that the actual deadline for industrial coal

- fired boilers that will be shut down as a result of Boiler MACT is January 31, 2017

, if the source has obtained a 1

- year extension from the typical January 1, 2016 compliance deadline. A January 31, 2017 applicability date for shutdown sources will correspond with potential Boiler MACT compliance extensions and ensure that states are not including sources that will have no impact on the modeling or monitoring result s , according to commenter (0039)

. Commenter (0039) believed a similar provision should apply to units convert ing to natural gas by January 31, 2017 or achieving emission levels below the applicable thresholds as a result of installing emission controls by January 31, 2017.

Commenter (0096) recommend ed that the EPA revise the DRR to exempt from the list sources

that take an enforceable emission limitation below the 2

, 000 tpy threshold before 2017, even ifDELIBERATIVE

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99 reductions and applicability of the limitation are o nly realized within a reasonable time after January 17, 2017. Commenter (0096) stated t his approach appears to be reasonable and in line with the current approach of removing sources from the list shutting down prior to January 2017. Commenter (0096) state d that n othing would be gained by proceeding towards designating an area as nonattainment when the needed reductions (as demonstrated through modeling) will be in place prior to the expected date for final designations to take effect (February 2018).

Comm enter (0038) stated that requiring sources to implement controls prior to submittal of the required SIP , as opposed to the attainment date, would also encourage sources to make emission reductions while allowing sufficient time to implement these actions.

Response:

The EPA is finalizing the proposed approach to allow a state with a source that is in operation as of January 15, 2016, but that will shut down permanently prior to January 13, 2017 pursuant to a federally enforceable mechanism (e.g., source

- sp ecific SIP revision or minor NSR permit revision submitted to the EPA by January 13, 2017), to avoid being subject to the requirement to characterize air quality in the vicinity of the source.

As a result of comments received on the proposed rule, the EP A is clarifying how this exclusion would work relative to the requirement for development and submittal in January 2016 of the list of sources near which air quality is to be characterized. The EPA appreciates that there might be

a source whose most recent year of actual emissions exceeds the threshold for inclusion on the list, but for which the state has already adopted, or will soon a dopt enforceable requirements to shut down by January 2017. Such a source may have significant emissions during the most

r ecent available year, or may even still be in operation on January 15, 2016 . The EPA has determined that the clearest way to implement the exclusion from the air quality characterization requirement is to require that the air agency initially identify such a source on its list for SO 2 air quality characterization because emissions in the previous year, which serve as the basis for listing under this rule, exceeded the emissions threshold. However, the final rule now includes language in section 51.1203(b) a llowing the air agency to indicate by July 1, 2016 that it will provide the EPA with a federally enforceable requirement confirming that the source will be permanently and enforceably shut down by January 13, 2017. For a source with a federally

enforceable requirement to shut down, t he air agency will have no further obligation regarding air quality characterization pursuant to this rulemaking. This approach accomplishes the intent of the proposal by implementing the approach in a more clear and straightfor ward manner.

Commenters on the proposed rule also suggested that, in a similar manner, an air agency should not be subject to the air quality characterization obligation for any source that is initially on the list of sources due in January 15, 2016 (base d on most recent actual emissions), but that becomes subject to a federally enforceable requirement to limit annual SO 2 emissions to below the 2,000

tpy emissions threshold. The EPA finds merit in those comments that suggest the rule allow for

similar trea tment for sources that become subject to a federally enforceable emission limit as is

allowed for sources for which the state can provide documentation that the source has elected toDELIBERATIVE

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100 shut down

. The EPA has revised the final rule accordingly, and provides f urther discussion below. However, EPA does not agree with commenters who suggest that sources should have

until the applicable designation date, or attainment date for an area that is designated nonattainment, to implement controls that were committed to p rior to January 1 3 , 2017. Relying

on commitments for emission reductions to occur after 2017 would not be consistent with the main focus of this rule, which is to provide current, updated information on priority SO 2 sources to the EPA beginning in early 20 17 that can be used to, among other things, inform future area designations (now required in December 2017 and December 2020 per the March 2015 CD ).

As indicated above, a source would be listed for air quality characterization if its most recent

emission s were above the 2,000 tpy threshold. However, the final rule also allows the air agency

to meet the requirements of this rule by submitting a federally enforceable emissions limitation (e.g., source

- specific SIP revision or minor NSR permit revision) to t he EPA prior to January 13, 2017 that requires the affected source to reduce allowable emissions at the source to an annual

rate below the 2,000 tpy threshold level prior to January 13, 2017. By July 1, 2016, the air agency would be required to identify th e sources on the list for which it would be using such an approach as an alternative to modeling or monitoring. For such a source identified on the list, i f the affected air agency has adopted and the source has become subject to effective federally

enfor ceable control measures lowering emissions below 2,000 tpy by January 13, 2017, the air agency will generally not be required to further characterize the impacts from the source’s emissions solely due to its size as of January 15, 2016.

Although air age ncies may follow this option as an alternative to characterizing areas with sources that limit their emissions to below the 2,000 tpy size threshold, the EPA believes that air agencies and the EPA must apply judgment as to whether there are still reasons t o characterize

these areas due to other factors. As discussed above, some areas where all sources emit less than 2,000 tpy may nevertheless warrant air quality characterization, for example because the area has

a cluster of sources with intermediate emissi on levels or because the characteristics of a source or the area warrant it. Thus, some areas with all sources limited to below 2,000 tpy may still warrant air quality characterization. Therefore, the EPA urges air agencies to consult early with

the EPA an d distinction between a formerly large source with no future emissions and a source with reduced but continuing emissions. The Agency does not believe it would be appropriate to provide that the latter source can be excluded from evaluation in all cases. I t may be that a source with emissions newly limited to below the applicability threshold

– particularly one with limits established just below the threshold

– may warrant further characterization, just as a source with

actual emissions below the threshold may warrant characterization in some instances. For example, air quality characterization would continue to be warranted in areas with other sources over the applicability threshold, and in areas where no single source has emissions over the

threshold but the combined emissions of multiple sources warrant air quality characterization. In evaluating such cases, the air agency should account for all source emissions contributing to ambient concentrations in the area, including those remaining emissions from the source that has just reduced its levels to below the applicability threshold. For this reason, the rule does not automatically exempt sources with emissions limited to less than 2,000 tpy from air quality characterization requirements; the rule instead provides that the air agency or the EPA may judgeDELIBERATIVE

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101 that the area should continue to be required to characterize air quality notwithstanding the new emission limits. Air agencies are thus advised to consult with their EPA Regional Office before pursuing thi s alternative to air quality characterization for a particular source area.

Regarding the specific comments about MATS or Boiler MACT compliance occurring after January 2017, the EPA believes the final rule appropriately handles th e s e circumstance s

. Alth ough the final rule now allows air agencies to adopt enforceable limits that keep emissions below 2,000 tpy for applicable sources as an alternative to characterizing them, the EPA does not

believe that this alternative should be available where the enforc eable limit does not take effect

until after the characterization is due. As a general matter, the rule must weigh in favor of characterizing sources identified as priority sources unless it is clear that they are no longer priority sources when the charac terization deadline passes. The EPA also notes that, given the court ordered deadlines for completing area designations, the final rule will better serve a use of generating information to inform those actions by maintaining the proposed schedule. The rul e builds in appropriate relief from ongoing modeling and monitoring requirements when, due to reduced emissions, the sources are no longer a priority for characterization. Moreover, nothing in this rule prevents an air agency from providing additional rele vant information after the

characterization is due. The MATS and Boiler MACT rules raise specific timing issues, but do not outweigh this overarching principle of rule structure, or convince EPA to build in complicated rule

- specific exceptions to the rule’ s deadlines. Nevertheless, EPA does not expect the rule to lead to inappropriate outcomes for these standards.

With respect to the Boiler MACT, the EPA believes that most boilers will be in compliance with

the rule ( and therefore likely

, in most cases , t o have reduce d emission levels to below 2

, 000 tpy ) by the rule’s January 31, 2016 deadline and well in advance of the DRR’s January 13, 2017

deadline for characterization. However, the EPA acknowledges that 40 CFR 63 .6 provides generic authorization for a full year compliance date extension for sources tha t need the

additional time to install controls in order to comply with the Boiler MACT limits

. Therefore, a modest number of sources may need fully until January 31, 2017 to comply with the Boiler

MACT , a fter the characterization of th ose source s is due (albeit only by a short time). In these

few case s
, the EPA believes that it would not be unreasonable for SO 2 limits reflecting the

Boiler MACT reductions 7 to take effect by January 13, a few weeks earlie r than the latest

allowable deadline under 40 CFR 63. 6 for sources needing extra time to install controls , rather than delay the DRR characterization schedule

. Alternatively, the air agency could proceed with

characterization on schedule for the few source s where limits could not take effect by January 13, 2017

.

With respect to MATS, a source that is not meeting the applicable requirements by April 2016 is out of compliance with the rule. Although the EPA has issued guidance addressing special

7 Also, the EPA notes that, while the relevant limits in the Boiler MACT are limits on hydrogen chloride, at issue here are SO 2 limits th at air agencies adopt that reflect the consequences for SO 2 emissions of the control strategy that the source will be implementing to meet the hydrogen

chloride limits.DELIBERATIVE

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102 circumsta nces that might arise necessitating noncompliant operation, the EPA cannot agree to modify this rule to accommodate noncompliance with MATS. Furthermore, if a source is still operating in violation of MATS for a full year past the April 16, 2016 deadline (not May 1, as implied by the commenter), then the EPA finds it appropriate for this rule not to exempt such a source from air quality characterization requirements and for the rule to require that any modeling of the violating source to consider emission rates that may be occurring well into 2017.



### c. Enforceable l

imits effective by the attainment date

Comment :

Commenters (0038, 0108) stated that allowing sources to implement controls after January 1, 2017 but before the attainment date supports the EPA ' s desired outcome of achieving emission reductions as quickly as possible. Commenter s (0038 , 0108 ) stated there is insufficient time for

sources to take all the actions needed to implement these controls (including conducting modeling, determining the requ ired reductions and control strategies, procuring capital funds, obtaining permits and installing equipment) under the Proposed Rule

. Commenter (0038) stated

that r equiring sources to commit only to enforceable limits and a schedule for compliance by

Janua ry 1, 2017 is reasonable and consistent with the timeframes necessary in developing the required modeling information. Commenter (0038) stated that, u nder the EPA 's proposal, sources unable to have enforceable limits in place by the January 1, 2017 deadlin e have little incentive to take any action prior to the monitoring attainment deadline of 2020.

Commenters ( 0050, 0060, 0061, 0070, 0073, and 0087) requested that the EPA revise the applicability section to exclude sources scheduled to permanently shut do wn within a reasonable period. Commenter (0061) suggested a source should be exempt if it is scheduled to be permanently shut down shortly after the suggested 2017 deadline and proposed that as long as there is a federally enforceable condition in place be fore January 1, 2017 that will ensure attainment of a designated area, that the demonstration be considered complete. Commenter (0087) stated that without such an "up

- front" exemption, agencies could be forced to conduct unnecessary modeling and/or sources could be subject to unnecessary monitoring

- related expenditures, however, an "upfront" exemption would allow state agencies to focus their limited resources to sources that will be operational beyond the 2017 timeframe.

Commenter (0060) stated that, if there is an enforceable mechanism (e.g., legal agreement/ CD ) that ensures a facility will shut down in time to attain as "expeditiously as practicable ... or by February 2023," this should be sufficient for the demonstration and further air quality

charact erization should not be needed. Commenter (0061) was concerned that using actual emissions from the Boardman Plant's main boiler for future designation of the area would not be accurate due to the source's required shutdown by December 31, 2020 and the fed erally enforceable Title V operating permit which contains this requirement. Commenter (0061) stated

that including the b oiler in modeling or monitoring would not be representative of conditions beyond 2020

- a llowable emissions from the main boiler are ze ro after the shut d own date.DELIBERATIVE

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103 Response:

The purpose of the DRR is to obtain timely information regarding current air quality from

sources that the EPA has determined warrant consideration in light of the limits on available

resources. Else w h ere EPA has ex pl ained the basis for the January 2017 deadline s for states to
take various characterization actions required by this rule (e.g., subm itting modeling or deploying monitors ), and has provided maximum opportunity for sources to limit their emissions

to below the rule’s applicability threshold levels prior to this date. However, once this date passes, the EPA cannot go back in time and say that these deadlines did not apply

. Some comments suggest that we should forego characterization requirements in 2017 base d on what will happen in the future, but the EPA believes that the need for timely information about current

air quality justifies the requirement to characterize these sources in the present (such as is done with monitoring networks) , even if air quality might i m prove in the future.

We do acknowledge that the DRR contains future ongoing characterization requirements that may become unnecessary if sources reduce their emissions sufficiently in the future, and we note that the rule already provides mechan isms to cease such ongoing requirements, as discussed elsewhere in this document. However, actions beyond January of 2017 cannot provide a basis for

relief from the current source characterization requirements that c o me due in January 2017.

Nevertheless , the EPA understands that a deadline for characterizing air quality does not address the various ways EPA might use the information it gets. Many of t he comments above relate to

how EPA will use information about current air quality when there is also inf ormation about

future effective limits when EPA is making area designations o r evaluating attainment plans

should an area ultimately be designated nonattainment. Since this rulemaking does not address or establish designations requirements or nonattainment planning requirements, comments about how EPA should account for future effective limits in making those decisions are beyond the scope of this rule.



### 5. Electricity generation reliability

Comment :

Commenters (0038, 0041, 0047, 0075, and 0108) stated the EPA should identify an alternate compliance path for electrical generation facilities that are required to operate for reliability

purposes

. Commenters (0047, 0075) recommended that a source be excluded from further

evaluation if the source owner has expre ssed its intent to retire a source, but has been required to delay that retirement by authorities in light of electric system reliability issues. Commenter (0075) recommended these sources should not be included on the air agency’s list for SO 2 air quality characterization, rather, air agencies should, at most, be expected to note their exclusion and provide a brief explanation.

Commenter (0047) stated the exclusion would apply in narrowly defined situations where units are required to continue operations temporarily, pending implementation of system reliabilityDELIBERATIVE

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104 solutions. It differs from the current rule proposal, which would only exclude units that are shut down by January 2017, even if plans to shut down units in subsequent years have already been

annou nced. Commenter (0047) believed this would eliminate the unnecessary agency and utility resources and costs related to modeling or monitoring demonstrations for units already designated for retirement but where such retirement is delayed due to electric sy stem reliability

issues.

Commenter (0038) stated the EPA should acknowledge the potential for these situations to occur, describe how states should address these cases, and offer a way for sources to attain and maintain the NAAQS under these particular c onditions. Commenter (0038) provided the following additional points.

T here exist situations where power plants are required by independent system operators (ISOs) to operate at certain levels to ensure grid reliability, regardless of the state or

source' s preference, which can potentially lead to the situation where a generation facility is fully controlled for S O 2 , yet still shown (via modeling or monitoring) to exceed the NAAQS. I n this case, the best remaining enforceable measure to achieve attainment would be for the state to establish operating limits on that source ; h owever, this may place the state and source in conflict with the ISO, which could otherwise require the plant to operate beyond those limits to ensure grid reliability. A similar conflic t could arise when the operator has planned to shut down the facility altogether, yet the ISO requires its continued operation.

Commenter (0070) stated that units and plants that have been approved for shutdown or retirement through the reliability regio n process should be granted the same status as units covered by permits or CDs as suggested by the EPA

.

Response:

The C AA provides no special exemptions for facilities that have proposed to shut down but remain open at the request of ISOs. The air qualit y issues to which such sources contribute exist for as long as the source continues to operat e , regardless of the reason the source continues to operate. Therefore, a source that meets the criteria for listing and continues to operate at the request of an ISO warrants listing as a priority source, just as is the case for a source that meets the listing criteria and continues to operate for any other reason. As discussed above, this rule, addressing air quality characterization requirements near sources that currently warrant such requirements, does not address how future planning activities such as designations and nonattainment planning will address future changes in source activity such as the shutdown of a source subsequent to resolution of an ISO’s relia bility concerns.



### 6. E nforceable limits in SIPsDELIBERATIVE

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105 Comment :

Commenters ( 0052, 0078, 0081, 0089, 0097

, and 0106 ) objected to a requirement that s tates must submit federally enforceable limits into the SIP. Commenters ( 0078, 0081, 0089 , 0106 )

referred to a webin ar presented by the EPA on May 13, 2014, in which the y assert the EPA specified that these permits would not only need to undergo Title V approval, but would also need to be submitted for approval in the state’s SIP (slide 12)

. Commenters (0081, 0089, 0097 )

stated t his is overly burdensome

, unnecessary , and for no real environmental gain.

Commenter s ( 0078, 0081, 0097

, and 0106 ) stated that f ederally enforceable limits, such as Title V operating permits, are all that are needed to ensure facility complianc e. Commenter (0078)

stated that f

acilities in a state operating under already

- existing Title V permitted limits that may show modeled attainment are n o t required to be included in the SIP, so making a unique requirement on facilities with "newer" enforceab le limits is problematic, since in both cases, the facilities would be able to demonstrate modeled compliance under the restrictions of their permitted limits. Commenter (0106) asserted that s tates have for many years established federally enforceable limi ts to assure compliance with the NAAQS in PSD permits, minor source preconstruction permits, Title V Permits, and federally enforceable state operating permits which are not directly in the SIP. Commenter (0106) stated that inclusion of limits in the SIP i s a waste of resources and creates an unnecessary and lengthy process if changes to the limits are required.

Commenter (0078) stated that s ubjecting facilities making early emissions reductions (in order to avoid nonattainment area planning requirements) to permit conditions that require SIP revisions and approval for future amendments would essentially penalize these facilities and remove the incentive for early action. Commenter (0078) stated that t he EPA should not require any pre

attainment

- designation permitted limits to be incorporated in the SIP, unless a state's existing permitting program is not otherwise "federally enforceable."

Commenter (0089) stated that, if the EPA is going to require such a departure, it needs to do so

in a formal rulemakin g procedure in which states are provided with notice and the opportunity to comment on it; such an implementation shift should not be merely a statement in a webinar, on which states have no formal opportunity to comment. Commenter (0089) provided the foll owing additional points.

To require that emission limits be included in the SIP, not just in a facility's permit, would be a several month process, at least. Once submitted to the EPA , EPA has 18

months to act on the submittal

-- and often does not act in a timely manner. Even more importantly, to change the limits once they are approved into the SIP would take the same lengthy process (consuming state and EPA resources once again). After the permit is revised, there would be a gap between the state permit r equirements and the SIP requirements until the EPA acts on the revision. The gap could easily last two years at a

minimum. The Permittee would legally have to continue to comply with the SIP until the

EPA acts on the revision submittal or take a risk by ju st complying with the revised air quality operating permit. The result is a situation where the emission limits in the currentDELIBERATIVE

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10 6 approved SIP are continually out

- of

- date with the agency

- requested emission limits in a revised SIP, which may very well result i n a situation under which enforceable emission limits may be less protective of human health and the environment.

Placing emission limits into the SIP also results in a certain loss of transparency in terms of public review and comment on emission limits. When wrapped up in a SIP approval

process, individual facility emission limits are obscured by all the other details in the SIP. When placed in an enforceable facility emissions operating permit, however, the public can more easily identify, evaluate, and comment on specific emission limits through the public comment process required as part of Title V permitting actions. This allows the public to focus its attention on the emission limit being imposed on that particular facility

and the emission reduction control technologies and operational restrictions required to

meet that limit. The review and comment on appropriate emission limits should remain associated with the issuance of an individual facility emissions operating permit.

Additionally, the EPA h as not identified a need for the departure from permit emission

limits to SIP emission limits. The EPA has the opportunity to review and comment on

Title V permits before they are issued, and the permit limits are federally enforceable.

Since those emissio n limits are already federally enforceable, what need is there to

include those emission limits in the SIP itself? (0089)

Response:

T he final rule allows the air agency to meet the requirements of this rule by submitting a federally enforceable emissions limitation (e.g., source

- specific SIP revision or minor NSR permit revision) to the EPA prior to January 13, 2017 that requires the affected source to reduce

allowable emissions at the source to an annual rate below the 2,000 tpy threshold level prior to January 13, 2017. By July 1, 2016, the air agency would be required to identify the sources on the list for which it would be using such an approach as an alternative to modeling or monitoring. For such a source identified on the list, i f the affected air agency has adopted and the source has become subject to effective federally enforceable control measures lowering emissions below 2,000 tpy by January 13, 2017, the air agency will generally not be required to further characterize the impacts from the sour ce’s emissions solely due to its size as of January 15, 2016. Note that this provision of the final rule was established after consideration of several comments suggesting this type of change from the proposal.

Some commenters appear to have interpreted t he slides on the proposed rule used for the May

2014 webinar as requiring that all federally enforceable requirements limiting emissions of

sources to below 2

, 000 tpy are to be adopted into the SIP. The EPA wishes to clarify that this is

not the case. In s ome states, federally enforceable emission limits can be established through

mechanisms other th an through adoption of a SIP revision. For example, some states are able to establish federally enforceable emissions limits through their minor NSR program.DELIBERATIVE

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107 

### 7. E lection of m onitoring or m odeling

Comment :

Commenters (0048, 0094, 0095) asserted that states should not be allowed to limit a source’s option (monitoring or modeling) in determining an area’s classification and that if a state requires a modeling analy sis and this shows nonattainment, the source should have the option of installing representative monitors to demonstrate attainment. Moreover, commenters (0094, 0095) believed the rule should not limit a source’s right to install monitors to determine

comp liance with the standard.

Commenter (00 52a ) stated that, i f a source

- oriented monitoring requirement is established, the

EPA should also develop an exception to this requirement where s ources w ould be able to use modeling to avoid the monitoring requireme nt much like what was allowed in the lead source monitoring program. Commenter (00 52a ) stated that, i f a source models at less than a predetermined threshold percentage of the standard, a source

- oriented monitor should not have to

be installed. Commenter ( 00 52a ) stated that p rojected actual emissions after subject sources have installed all required emission reduction strategies should be included in the exception analysis

to determine if source

- oriented monitoring is necessary.

Commenters ( 0038, 0046, 006 3, 006 5, 0084, and 0108 ) stated that the EPA should provide a more reasonable schedule for states to elect the monitoring option under the Proposed Rule

. Commenter s (0038 , 0108 ) suggested s tates should have until January 1, 2017 to make this

determination because they c ould benefit from using initial modeling results to inform this

decision , s uch an allowance would reduce burdens on state regulators

, and it could lead to more

accurate determinations

, while not impacting the EPA ' s proposed attainment dates. Commenter (0038) provided the following additional points.

A likely scenario is that a state will conduct modeling as an initial step to gather the

necessary information to determine the attainment status of potential sources. This initial modeling may r eveal that the attainment status of a particular source (or cluster of sources) cannot be sufficiently determined via modeling; therefore, the state may decide that monitoring is required. However, this conclusion may not be evident until the state complet es its full modeling analysis. If the rule is finalized on January 1, 2015, the EPA cannot expect the modeling analysis for all potential sources to be completed prior to the January 15, 2016 deadline of declaring whether modeling or monitoring will be use d to determine attainment. Instead, the EPA should simply let the states declare sources that must be monitored as part of the state's January 1, 2017 submittal. At a minimum, the rule should allow for states to declare a source or area for monitoring afte r January 15,

2016 on a case

- by

- case basis.

Commenter s ( 0046 , 0084 ) stated that i nsufficient time (approximately 1 year from final rule) is given in the proposal for states to submit a decision on choosing modeling or monitoring (Jan 15, 2016), given the lack of resources and large amount of data gathering and analysis andDELIBERATIVE

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108 collaboration with stakeholders that will need to be performed to implement this rule. Commenter ( 0046 ) note d s tates will need to assess financial resource considerations related to

add ing or relocating monitors before making the decision whether to model , however, t he proposed timeline would compromise this analysis. Commenter (0084) stated the EPA should allow for at least 18 months for the logistical elements to be completed for state s to submit a decision on choosing m odeling or monitoring

.

Response :

Upon review of these comments, the EPA agrees that the rule should provide somewhat more time to air agencies to review the options for air quality characterization. Consequently, the final rule provides approximately six more months for air agencies to select the approach to be used to address priority sources. (Consistent with this revision, the EPA is also delaying the deadline for submitting a modeling protocol by six months.) At th e same time, t he EPA believes that it must assure expeditious air quality characterization, and so the EPA is promulgating the proposed timeline for the actual air quality characterization (i.e., the submittal of modeling or the commencement of monitoring) in the beginning of 2017

. However, the EPA believes that an election of approach by July 1, 2016, would provide a more manageable timeline for obtaining the source information needed in support of the election of approach, while still providing enough tim e to meet deadlines for air quality characterization in the beginning of 2017. Further discussion of these comments and the EPA’s response are provided in the preamble to the final

rule.

The source does not have the option to determine an air agency’s se lection of whether to monitor

or model source emissions under the final rule . The obligations of this rule fall to air agencies, not sources, and it would not be appropriate to allow sources to predetermine how air agencies choose to meet those obligations . This is consistent with how the CAA mandates that the state submit designation recommendations ( after which the EPA is to promulgate designations ) , and

also with how the CAA apportions responsibilities in other aspects of air quality planning.

Consistent with these CAA provisions, this rule provides that the state or other air agency shall determine the approach to be used to characterize air quality.

This rule is designed to prioritize the use of limited resources for air quality characterization. If air quality in an area is successful ly characterized through modeling

, it would be inappropriate then to require monitoring, regardless of whether the source dislikes the result of the modeling. If the modeling (which notably may be based on actual emissi ons for the purposes of this rule) indicates violations, the most appropriate next step would be to designate the area nonattainment

and to commen ce planning for providing for attainment.

The comments urging an approach similar to that used for lead are n ot germane to the proposed

rule for SO 2 , in which a state has the option to model or monitor. There is no requirement, or implication, that a state must model to relieve itself of potential monitoring activities as is the

case with lead. T he EPA is promulg ating a rule that provides options for air quality characterization by either a complete modeling analysis or a complete monitoring effort; anDELIBERATIVE

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109 incomplete modeling analysis would not provide suitable justification for forgoing a complete monitoring effort.



### 8. Common area analytical approach

Comment :

Commenters (0040, 0044, 0081, 0083, and 0107) stated a ir agencies should not be required to use the same technique to characterize all sources in an area

. Commenter (0044) stated this provision would re strict the flexibility of air agencies in selecting the technique they wish to use, and possibly forc ing them to use modeling in locations where monitoring would not only be feasible but also preferable.

Commenter (0044) stated t he preamble provides no caveat that once a choice is made either to monitor or model that choice will apply to all sources within the affected area and fails to advance any justification for why the proposed regulatory text would impose such a limitation

. Commenter (0044) does not believe su ch a justification exist s

. Commenter (0107) stated it is not clear why States must use the “ same technique ” in 51.1203(b)

.

Commenter (0081) disagreed that it would not be appropriate to choose monitoring for some

sources and model ing for others in a commo n area

. Commenter (0081) stated that, i f it is deemed that sources which are in somewhat close proximity to one another do not produce a significant cumulative effect on air quality concentrations, there should be an allowance for one facility to

use model ing to demonstrate their compliance with the standard and the other to use monitoring and forego designations until 3 years of monitoring data has been submitted (i.e. use a combined modeling/monitoring approach to designate the area). Commenter (0081) pro vided the following additional points.

One situation where this may be appropriate is in an area where the distance between facilities is such that there is no overlap in emissions contributions and/or air dispersion modeling shows there is not a signific ant concentration gradient from one or both of the facilities in the vicinity of the other facility. One facility may choose to use modeling for compliance with the rule and show that concentrations are below the standard, while the other may wish to use a monitor at the closest area of high concentration to forego annual reporting of emissions. This option should especially be considered if evaluation “areas” are presumed to be counties, CBSAs, or MSAs (or any other jurisdictional

- based

boundaries that are arbitrary in terms of source specific air quality levels).

Commenter (0083) stated there may be situations where it will be beneficial for states to work together in establishing the status of an area, but a requirement that states must come to an

agreem ent on the approach they are to use shouldn't be codified in the rule. Commenter (0083) believed each state should be responsible for the applicable sources in their state and the rule should not require different states to come to an agreement on an appro ach, where there is no means for resolution if there is an impasse between two states on the best approach to use.DELIBERATIVE

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110 Commenter (0044) believed the use of the word “shall” in the last sentence of section 51.1203(b)

should be deleted and substituted with the phrase “is not required.” Commenter (0083) suggested that the second sentence of proposed §51.1203(b) be removed from the rule. Commenter (0040) suggested the following changes in section 51.1203(b):

(b) For each area containing an applicable source, the air agency shall state by January 15, 2016, whether it will characterize air quality through ambient air quality monitoring

, through air quality modeling techniques, or through a combination of both, as appropriate.

Response:

The EPA believes that if t wo or more sources are contributing to concentrations in a single

common area, then it would be impracticable to address one portion of the area with modeling and another portion of the area with monitoring. Wh ile the EPA can consider both modeling and

mon itoring information in promulgating designations, the consideration of both is more feasible if both methods characterize air quality in the entire area. The commenters do not describe how they envision that data addressing only portions of an area would b e combined, and the EPA

believes that its DRR more appropriately requires that the complete area be characterized by one method or another, so as to avoid the problems that would be prone to arise if two different analytical methods were used for different portions of an area.

Furthermore, in this rule, the choice of methods for characterizing air quality also determines the timetable under which air quality characterization is required. The EPA must designate areas as an entirety; the EPA does not have th e option to designate the modeled portion of an area at one time and then designate the monitored portion of the area sometime later. Th us, whether the air agency selects the monitoring pathway or the modeling pathway for characterizing air quality, 40

CFR 51.1203 requires that the information provided under the selected pathway be sufficient to characterize air quality in the area, irrespective of whether other air quality characterizing

information of the other type is or becomes available . That is , the air agency must provide for complete characterization of an area by the selected approach , either by monitoring that characterizes the entire area or by modeling that characterizes the entire area. The timetable under which this information would be requir ed is clearly defined by the rule. The EPA welcomes any supplemental information that the air agency may provide, but the DRR cannot be considered satisfied unless air quality information based on a single selected pathway sufficient

to characterize worst case concentrations throughout the area are obtained.

Some of the commenters appear to be objecting to the rule based on a misunderstanding of the

term “area.” “Area” may be considered to mean a candidate nonattainment area, in the sense of including all of the area being evaluated as to whether it is meeting the SO 2 standard and all of

the area that is to be evaluated as to whether it is contributing to SO 2 concentrations that might be violating the standard. One commenter posits a situation in which sou rces in close proximity are deemed not to have interactive impacts, but the commenter does not explain how such aDELIBERATIVE

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111 situation could arise, in particular how the absence of interaction of sources in close proximity could be known without the kind of investiga tions that the DRR requires. Presuming that investigation of the interaction of the sources is warranted , the area being investigated would

include both sources and their areas of impact, and for reasons described above, the air agency

would need to select either monitoring or modeling to address the area and assure that the selected approach is done in a manner that addresses the entire combined area. Conversely, if two sources are separated by sufficient distance that potential violations near one source could be presumed to reflect no contribution from the other source, such that violations near both facilities could be presumed without further investigation to warrant two separate nonattainment areas, then the two sources could be considered to be part o f two separate areas that could be addressed by different approaches. Where two sources may or may not warrant treatment as part of two separate areas, air agencies are urged to discuss the situation with their EPA Regional Office.



### 9. Oppose submitting a list

Comment :

Commenters (0038, 0060

, and 0108 ) opposed the proposed requirement that, b y January 15, 2016, air agencies must submit a list of sources with election of monitoring or modeling

. Commente r s (0038 , 0108) stated submitting a list is unnecessary, as it may prematurely identify

sources as potentially violating the NAAQS (0038) and such a list is already made publicly available on an annual basis through the NEI (0038)

.

Commenter s (0038 , 0108 ) stated it does not make sense to establish a list for S IP submittal that is expected to change. Commenter (0108) stated creating a second list is a redundant use of limited resources and creates the potential that future regulatory actions be based upon inaccurate

information. Commenter s (0038 , 0108 ) stated th at a ny distinction or listing of a source should

wait until th e January 2017 analysis justifying attainment status for individual sources or areas is complete. Commenter (0108) also suggested allowing states to make this determination by January 1, 2017 t o reduce the burden on the states and lead to more accurate determinations without impacting the EPA’s proposed attainment dates.

Commenter (0060) stated t here are numerous federal regulations with compliance timelines that overlap these timelines and, a s companies analyze their options in this ever changing landscape of regulation, their decisions may change. Commenter (0060) stated t here must be flexibility for strategies to change prior to an attainment demonstration being due. Commenter (0060) provided the following additional points.

I t is the EPA 's role to "issue minimum criteria that any SIP submission must meet." [CAA paragraph 101] Creating a requirement for a binding list is far beyond necessary and is not in the spirit of the CAA roles for State s and EPA to work cooperatively. Ohio

EPA has worked with EPA Region 5 cooperatively in the past to finalize similar types of

lists without a binding requirement or an official submittal until such time the SIP submittal is required (for example, under the 2008 lead standard monitoringDELIBERATIVE

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112 requirements). A binding list with official submi ttal in advance of nonattainment planning was not required for sources being analyzed under the nonattainment area requirements. EPA should not burden S tates even more with add itional commitments.

EPA should not be creating multiple binding lists that force air agencies to continually and further justify addition or removal of sources.

Commenter (0060) did not find merit in the citations the EPA provided in the proposal regar ding

the authority for requiring this list submittal. Commenter (0060) provided the following additional points.

The s ection 11 0 (a)(2) citations address the requirements for SIP submittals by s tates for implementation, maintenance and enforcement of the s tandard. The EPA notified s tates on April 12, 2012 that the June 2013 Infrastructure SIP submittals that address s ection 11 0 (a)(1) and (2) elements, should focus on those traditional elements and not performing modeling to

ensure future attainment in uncla ssifiable areas and that those SIP submittals would come later. These are the very submittals that are due in the proposed timeline in August of 2019 and 2022 ("due date for state attainment plans") , a submittal that is due only after "reasonable

notice an d public hearings" by the s tate. Will air agencies be required to public notice and provide hearings for these lists submitted under the authority of this section but prior to the

actual attainment demonstration? It seems EPA is putting the cart before the horse.

Response:

The EPA does not agree with commenters who claim that submittal of an initial list of sources near which air quality is to be characterized is not needed in January 2016. The EPA believes that it is important to receive the list of sour ce areas to be characterized under the rule by January 15, 2016

, because it will provide timely clarity about which areas will be characterized, which is necessary for air agencies to generate timely information that may be used to inform future designatio n, redesignation, or other decisions concerning whether sources are affecting the

attainment of areas. Retaining this deadline will provide early opportunity for the air agency and the EPA to resolve questions about whether air quality characterization sho uld be required for an area, for example if emissions are low in some years and high in others, if an area has a cluster of smaller sources, or if source

- specific factors may warrant air quality characterization. Thus, t he EPA is retaining the January 2016 deadline, as proposed

, for submittal of the list of sources in

order to initiate an orderly process to obtain additional information on ambient SO 2 concentrations, and ensure these data are available to support actions taken for the implementation of the 2010 SO 2 NAAQS. T he EPA believes that the schedule for providing the list of sources is a relatively straightforward exercise that can be accomplished within the required time frame.

Once this list is provided, and once any issues relating to the list s uch as whether additional areas warrant air quality characterization or how to address a source with variable emissions are resolved, the EPA envisions no further changes to the list , and the DRR sets out requirementsDELIBERATIVE

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113 that apply to the listed sources

. To a llow the list to continue to change after an established final date would result in confusion about how the state is to meet the requirements of the rule. Nevertheless, the requirements for listed sources allow for consideration of the kinds of changes

in circumstances that commenters describe . As one example, a source with emissions recently above the threshold that will enforceably be shutting down by the beginning of 2017 will be on

the list but can avoid air quality characterization requirements.

The list is needed for implementing the SO 2 standard, providing information that sections 110 and 114 clearly authorize the EPA to require. The EPA is not requiring air agencies to conduct public hearings on these lists , as they are not themselves implementat ion plans subject to the requirements of CAA section 110(l)

. Although much of the source list is based on a rote listing of the sources emitting at least 2,000 tpy in the most recent inventory, the EPA anticipates that air agencies may wish to use differen t emission data bases for different source types. For example, use of EPA’s Air Markets emission data base may provide for using more recent emission data for EGUs than is available for other source types. Furthermore, the listing process involves judgment in some cases, where discretion is needed for areas without a source emitting 2,000 tpy may nevertheless warrant air quality characterization. Such judgment is needed for example where a source may be particularly prone to cause high concentrations (e.g. due to low stack heights), where multiple sources are in close proximity, and where future emissions are expected to be higher than emissions in the most recent year. For all these reasons, the formal listing is an essential step to clarify which source a reas are subject to the requirements of this

rule.

The comments in relation to the Monroe Power Plant do not justify any changes in the rule. The commenter does not clarify whether the installation of controls will bring this source below 2,000 tpy or wh en the emission reductions occurred; these facts would be necessary to determine whether the plant must be listed under the final rule. The commenter suggests that any requirements for modeling this source have already been met, which if true would mean th at there would be no harm to the source to be required to submit modeling that has already been

done.



### 10. S ection 51.1203(a)

Comment :

Commenter (0093) requested the wording in section 51.1203(a) be revised to state that the list should only specify which pathway will be followed and not specify who will be completing the

task. Commenter (0093) noted they intend to impose the responsibility for modeling and/or monitoring on the affected sources and will act in an oversight capacity.

Response:

The rule s t hat the EPA is promulgating do es not require air agencies to identify who is completing which tasks. The EPA recognizes that some agencies will prefer to undertake theDELIBERATIVE

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114 necessary efforts themselves, and other agencies will prefer for affected sources to com plete

most of the effort subject to air agency oversight . An important caveat is that the final rule, in imposing obligations on air agencies but not on sources, requires the air agency to make the ultimate submittal, so that even if the affected source do es most of the work, the air agency bears ultimate responsibility for assuring that its submittal meets applicable requirements. Nothing in the rule dictates how air agencies are to allocate the workload involved in meeting the requirements of the rule, an d the EPA believes that no rule revisions are needed to clarify this point.



### 11. Updated information on EPA’s preliminary list

Comment :

Commenter (0035) provided the following updated information.

Additional emission controls have been installed at the Valero Refining Company in recent years, and c urrent S O 2 emissions are nearly an order of magnitude less than the Option 1 threshold. The Shell Martinez refinery continues to have SO 2 emissions that are marginally above the Option 1 threshold, but expects to implement a project that would

reduce S O 2 emissions well below this threshold. The Phillips 66 Carbon Plant is currently our region's largest source of S O 2 , with emissions that are about 25% over the Option 1 threshold. Our most recently adopted Clean A ir Plan includes a control measure to reduce these emissions, and we expect to complete the required rule development for this measure within approximately two years. (0035)

Commenter (0054) supplied information on several Primary Aluminum Plant facilitie s that are

listed on the 2011 NEI as SO 2 emitters that in the interim have bee n permanently closed. These

are Ormet Aluminum

– Hannibal, OH (perm anently closed in October 2013); and Reynolds Metals St. Lawrence Reduction Plant (Alcoa Inc. wholly

- owned subs idiary)

– Massena, NY (permanently closed in March 2014).

Commenter (0057) stated that SO 2 emissions at Big Stone Plant in South Dakota in 2016 will be well under even the Option 1 thresholds and these emissions will be provided by Otter Tail to the

EPA t hrough continuous emissions monitoring data.

Commenter (0070) provided a table below which shows the AEP System Facilities currently

scheduled for shutdown or conversion to an alternative fuel by 2017 for all reasons (MATS Compliance, CD , retirement, etc .) and that have been vetted and approved through the appropriate reliability region process.

Commenter (0081) attached an updated list of applicable sources based on 2013 NEI data as

Attachment 1 to its comments

. Commenter (0081) stated t he attachment al so indicates those facilities which have announced planned retirements or fuel switches, so that the EPA can amend the list of applicable sources in the final rule, assuming the rule is finalized before another yearDELIBERATIVE

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115 of emissions inventories is made availab le.

Commenter (0085) attached a table to its comment letter showing 2013 emissions data and planned fuel switching and shutdown s for Maryland sources

.

Commenter (0097) provided a table listing 8 facilities and several units that are shut down or will

be shut down in the next several years.

Commenter (0103) request ed the EPA to use th e 2012 NEI data to update the preliminary list of

source areas that were included in the docket with the EPA ’s Proposed Rule

. Commenter (0103)

attached the 2012 NEI data for the SO 2 sources in Iowa (spreadsheet “2012 NEI IA SO 2 Emissions”) that exceed the source emissions thresholds included in the EPA ’s Proposed Rule

.

Commenter (0107) stated t here are three facilities on the EPA 's list that have closed and two

facilities tha t have shut down their coal fired units ; t hese changes should be reflected in the most recent 2013 emissions inventory. Commenter (0107) request ed that these five facilities be

removed fr om the list of affected sources: Duke Energy Progress

– Sutton ; Duke Energy Progress

– Lee ; Duke Energy

– Buck ; Duke Energy

– Riverbend ; and DAK Americas

.

Commenter (01 1 8) identified two sources have either shutdown or announced they will shut down by the time this ru l e is effective: American Electric Power

- Tanners Creek in Dearborn County and State Line Energy LLC, in Lake County.

Commenter (0070) pointed out errors in Table 3 of the spreadsheet that was placed in the docket by the EPA: the IPL Harding Street Plant actually located in Indiana, is erroneously shown as

bei ng located in West Virginia; Kammer Plant is erroneously shown as being located in Indiana, when it is actually located in Marshall County, WV.

Response:

The EPA included in the docket to the proposed rule a preliminary list of sources that appear ed

to m eet the criteria described in the EPA’s proposed source threshold and requested that air agencies provide in their comments any relevant updated information that would support the

addition or removal of a source from th at preliminary list.

The EPA appreci ates the comments on the preliminary list of sources that appeared likely to be subject to this rule as proposed. The EPA acknowledges that, for various reasons, such a list of sources could change up until the time that the list is required to be submitte d. Accordingly, such a list is not being promulgated as part of this rule. The EPA plans on continuing consultations with air agencies regarding the source areas that the final rule will require to be characterized

.



### 12. Sources currently in a nonattainment ar eaDELIBERATIVE

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116 Comment :

Commenter (0076) urged the EPA to revise the list of covered sources to include Ameren Missouri’s Rush Island plant. Commenter (0076) stated that, if the Rush Island plant’s

substantial SO 2 impacts are not adequately addressed

– or not addres sed at all

– during the pending SIP process, then the plant should be covered by the DRR . Commenter (0076) stated

that there are at least two scenarios whereby the SO 2 impacts of the Rush Island plant would not be adequately addressed

, or addressed at all, notwithstanding the plant’s location in the Jefferson County nonattainment area and provided the following clarification.

First, the Jefferson County nonattainment area was designated based on a monitor sited specifically for a different large source, th e Doe Run Herculaneum lead smelter. Monitoring performed on behalf of the Sierra Club shows that Rush Island’s impacts occur in large areas outside of, as well as inside, the nonattainment area. There is no assurance, and no reason to assume, that any emis sions limits imposed on the Rush Island plant as part of the in

- process nonattainment SIP will sufficiently reduce the plant’s SO 2 emissions to eliminate all NAAQS exceedances outside of the existing nonattainment

area that are attributable to the Rush Isl and plant.

Second, readings at the Doe Run

- oriented monitor have dropped considerably since the

Herculaneum smelter closed in December 2013. Other sources in the nonattainment area are pressing the Missouri Department of Natural Resources (DNR) to abandon the SIP process. While we believe that such action would be both legally and factually unfounded (and is beyond the scope of this letter), it is conceivable that DNR will fail to prepare a nonattainment SIP for the Jefferson County nonattainment area. Sho uld that occur, then no emissions reductions would be required of the Rush Island plant

– even though modeling performed by DNR shows that the Rush Island plant’s actual (and allowable)

emissions cause SO 2 exceedances well above the NAAQS at locations diff erent from the

site of the Doe Run

- oriented monitor. (0076)

Response:

The first question is whether air agencies are required under this rule to characterize air quality near sources in areas that were designated as nonattainment in August 2013

. See 78 F R 47191

, August 5, 2013. In general, we expect the source characterization obligations required as part of

the nonattainment plan ning process to provide adequate characterization of the impacts of sources within those nonattainment areas. Therefore, w e hav e concluded that an air agency will

not be automatically required under this rule to characterize air quality around SO 2 sources already located in a nonattainment area when the list is due . Specifically, we have clarified the definition of “applicable sou rce” in section 51.1200 of the rule to be “ a stationary source that is (1) not located in a designated nonattainment area, and (2) has annual actual SO 2 emissions of 2,000 tons or more

, or has been identified by an air agency or by the EPA Regional

Adminis trator as requiring further air quality characterization. ” Thus, as a general matter, this rule does not require the state’s January 2016 list of sources triggering the requirements of this rule to include sources located within areas already designated no nattainment.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

117 However, i t may be possible that in some rare cases an SO 2 source or group of source s within the

boundar y of an e xisting nonattainment area can have significant impacts outside the

nonattainment area , potentially raising concerns that these i mpacts might not be adequately

addressed in a nonattainment plan. The EPA notes that for such cases

, the air agency and the Regional Administrator retain the authority under this rule to require additional characterization of air quality around specific so urces located in an existing nonattainment area, in the same manner that they retain the authority, as warranted, to require characterization of air quality

around sources that are below the emissions threshold identified in this rule. As the commenter

ack nowledges, comments regarding EPA action in the event of a failure by Missouri to submit a nonattainment plan are beyond the scope of this rulemaking.



### 13. New

/ modified sources or existing sources initially below the

thre s hold, subsequently exceeding it

Commen t :

Commenter (0069) recommended t he final rule give states the authority to work with sources whose emissions subsequently exceed the applicability threshold to either bring the S O 2 emissions below the applicability threshold or to conduct modeling or mon itoring consistent with the provisions of the rule. Commenter (0069) noted the Proposed Rule is silent on what the EPA expects should a source's actual S O 2 emissions exceed the applicability thresholds based on actual data either prior to the designations or after the designations are made.

Commenter (0081) stated the EPA should address how new or modified facilities will be incorporated into state monitoring/modeling plans for compliance with this NAAQS.

Response:

This rule is designed to require air q uality characterization near sources that currently (or, more precisely, based on the most recently available year of data) warrant it , similar to the manner in

which a source

- oriented monitoring network would be designed based on the current (and known

fu ture) source circumstances . The rule , as with other monitoring rules, is not designed to address unknown future source changes that may warrant air quality characterization in the future. Nevertheless, this rule does not preclude states from conducting air quality characterization under other authorities, and indeed the EPA has other authority and states have other authority to conduct monitoring and modeling to evaluate air quality near sources that do not trigger air quality characterization requirements under this rule but that exceed the thresholds of this rule in

the future.

To the extent that new or modified sources will be subject to review for PSD , much of the information required under this rule will likely already have been developed. Nevertheless , with or without such review, this rule requires review of all sources that meet the threshold of this rule and all other sources necessary to meet the air quality characterization requirements of this ruleDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

118 irrespective of whether the relevant sources are new, recently modified, or unmodified.



### C. January 15, 2016: Requirement to s ubmit m odeling p rotocols for

s ources c haracterized with m odeling

1. 

### Schedule

Comment :

Commenter (0051) stated t he EPA has failed to address the need for modeling protocols prior t o modeling for monitor placement, assuming that the final rule will still prefer modeling to properly site d monitors. Commenter (0051) stated that t ime for this tedious and somewhat complex analysis, as well as the modeling for monitor siting

, has not been allotted in the EPA's proposed timeline.

Commenter (0069) stated t he rule should not preclude states from submitting protocols separately as long as they are all submitted by the January 15, 2016, deadline. Commenter (0069) stated the proposed language a ppears to require that all source

- specific protocols must be submitted together and with the list of sources that will be modeled and monitored. Commenter (0069) stated that, i n order to complete and submit modeling for all areas in the modeling pathway by the proposed January 13, 2017 deadline, the agency may elect to stagger modeling over an extended period , which would necessitate submitting some modeling protocols earlier

than others.

Commenter (0082) stated that the January 15, 2016 deadline is not f easible for those areas that do not have (1) meteorological data from the same period as the most recent three years of actual

SO 2 emissions (“concurrent meteorological data”) or (2) representative site

- specific meteorological data or ASOS meteorological d ata from any recent three

- year period. Alternatively, the commenter (0082) urged the EPA to extend the January 15, 2016 deadline so that air agencies have sufficient time to develop concurrent meteorological data. [More comments on this issue are at V.B.7, m eteorological data

. ]

Commenter (0110) stated t he availability of a final model version several months before the January 15, 2016 deadline is very important in order for states and affected sources to make critical decisions; however, b ased upon the ann ounced EPA schedule to have an updated Appendix W by spring 2016, it is clear that the January 15, 2016 de adline is unworkable. Commenter (0110) stated, therefore, the EPA must change that deadline to early 2017 at the earliest, and this date may slip furt her into the future if the update to Appendix W is delayed beyond spring 2016.

Response:

In response to these comments, the EPA is providing additional time for making the election of modeling or monitoring (or, as discussed later, for making the electio n of an alternative approachDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

119 that enforceably limits an applicable source’s emissions)

. Accordingly, the deadline for this election will be July 1, 2016. The EPA recognizes that evaluating the relative merits of modeling and monitoring for any particular area, including identification of funding sources for any new monitoring that might be under consideration, warrants more time than was provided under the proposed rule. Consistent with this revision, the EPA is also revising the deadline for air agencies using modeling to submit modeling protocols for the applicable areas. Thus, under the final rule, by July 1, 2016, the air agency must submit its selection of whether each area will be characterized through modeling or monitoring and, depending on that sel ection, either must submit a modeling protocol or must include information in the Annual Monitoring Network Plan that specifies the monitoring to be conducted to address the requirements of this rule. While air agencies presumably will often decide how the y wish to meet the rule’s requirements somewhat in advance of preparing plans (a modeling protocol, a monitoring plan, or specification of plans for emission limits) for implementing that choice, the EPA does not wish to regulate th is decision process or m andate a period of time between pathway selection and submittal of implementing plans. Therefore, the EPA is establishing the same deadline for the selection of pathway as for the plans that implement the selected pathway. This provides the same deadline

a s was proposed for monitoring plans, but this provides six additional months for air agencies to address any modeling issues (like those identified by the commenters) that should be addressed as part of the modeling protocol. The EPA believes that this rev ised deadline still provides for timely planning for air quality characterization to occur (through modeling) or begin (through monitoring) at the beginning of 2017

.

Similarly, the EPA strongly encourages air agencies to hold early discussions regarding the manner in which modeling or monitoring might be used. As one example, if the air agency believes that the existing monitoring network suffices to characterize air quality, early discussions with the EPA would be essential for assuring that the intended selection of monitoring is based on appropriate assumptions regarding the network’s ability to characterize air quality near the applicable source(s) without further network adjustments.

The EPA recognizes that modeling is often part of the process of developing monitoring plans. The EPA welcomes modeling protocols for this purpose that air agencies wish to provide, and

the EPA believes that the timetable provides sufficient time for air agencies to provide such protocols. However, the EPA is not requi ring such protocols as part of this rule.



### 2. S ection 51.1203(d)

Comment :

Commenter (0093) stated that the wording in section 51.1203(d)(2) is unnecessary, where the section states that if an air agency uses an allowable emissions limit in the modeling that it may submit the limit "for the EPA' s approval'' at the time the modeling protocol is submitted. Commenter (0093) argues t his is unnecessary because whether the emissions limit is in an existing permit or is being modified, the EPA either had or will ha ve the opportunity to comment on that limit during the permitting process.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

120 Response:

T he EPA agrees that, so long as the limits are federally enforceable and require compliance by January 13, 2017, such limits are appropriate to consider in modeling of a llowable emissions pursuant to section 51.1203(d)(2), without regard to the means by which the federally enforceable limit became federally enforceable. The EPA has revised the language of section 51.1203(d)(2) accordingly.

3. 

### EPA oversight of modeling plans

Comment :

Commenters (0060, 0088, 0093, 0096, and 0097) objected to EPA o versight of the modeling plans because it is unnecessary and could hinder progress under this rule.

Commenters (0060, 0088, and 0093) were concerned that the EPA c ould not r eview t he plans in a timely manner and could cause delays in the process. Commenter (0060) stated t here is only one year between when this protocol is to be submitted and the final modeling is to be submitted according to this proposal , which leaves no room for t he EPA to follow up "expeditiously". Commenter (0060) stated that, i f this level of oversight and approval is finalized in this rule, they

ha ve serious concerns about whether 2 years from promulgation of the final rule is a reasonable

amount of time for ai r agencies to prepare the necessary data inputs and conduct such modeli ng for all subject sources. Commenter (0088) stated it is arbitrary and capricious to require the EPA approval of state monitoring and modeling plans when the EPA ’s technical resources are too stretched to provide this oversight in a timely manner

. [Also see commenter (0088) comments in IV.B.3, EPA oversight of mon i toring plans.]

Commenter s ( 0060, 0 088

, and 0093 ) stated the EPA o versight/ a pproval of model protocols

should be eliminated. Commenter (0093) stated that model protocols should be submitted to

s tates for review and that the EPA can audit as necessary. Commenter (0093) stated i t is unnecessary and duplicative to provide these protocols to the EPA

. Commenter (0060) stated the

EPA is over stepping the collaboration between s tate and federal agencies and the s tates' role to implement standards

. Commenter s (0060 , 0093 ) stated a ir a gencies should be able to determine

the best approach, using the normal course of discussion and coopera tion with their regional modeling contacts and document that approach with the final submittal to the EPA

.

Commenter (0097) stated the EPA should clarify that states could provide to the EPA a modeling protocol framework for review and approval, and that source specific review of protocols should be left up to the respective state agency. Commenter (0097) stated t his is consistent with past practices in PSD SIP approved states as well as past practices supporting BART.

Commenter (0088) recommended that the roles of the EPA experts should be advisory only in initial implementation and s ection 51.1203 should be revised accordingly. Commenter (0088)DELIBERATIVE

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121 provided the following additional points.

While it is critical to acknowledge that the EPA regional monitori ng experts can be helpful in advising states on monitoring (and modeling) plans , there are simply not enough of them to supervise, let alone review and act on, the number of s tate monitoring programs necessary to implement the data rule in a timely manner. Most EPA regions have only one such monitoring/modeling expert and OAQPS has fewer than five such experts. It therefore would be highly unreasonable for the EPA therefore to require as a precondition for implementation of a SO 2 monitoring plan, EPA review and concurrence/approval before it is implemented. Even if the compliance deadlines for such plan requirements and implementation were extended by substantial amounts, this requirement would still be unreasonable. (0088)

In order to provide a reasonable period to conduct and review the modeling, commenter (0096)

recommended the DRR require comments on protocols to be provided to states within 30 days of submission. Further, commenter (0096) recommended that the DRR provide that the protocol is

automatical ly approved unless the EPA acts to approve or disapprove the protocol by no later than April 1, 2016.

Response:

See the preamble at IV.C.d.3.c

.

4. 

### Stakeholder participation in air agency characterization efforts

Comment:

Commenters (0040, 0044) stated t hat t he regulatory text of section 51.1203 should be expanded to specify that affected sources have a right to participate in the designation process as it unfolds, including an opportunity to be made timely aware of an air agency’s choice of modeling

meth odology and, when necessary, an opportunity to dispute the use of allowable emission rates

rather than the actual emissions. Commenter (0044) provided the following additional points.

The inclusion of such additional instruction and guidance in both the p reamble and regulatory text will be beneficial to the air agencies and to the regions and will help to ensure consistency in the implementation of this rule throughout the country. This is especially important because proposed section 51.1203 clearly conte mplates consultation and coordination between the air agencies and the regional offices. Inclusion of such instruction and guidance in the preamble and regulatory text would therefore help to protect the due process rights of affected sources who might di sagree with an air agency over the methodology chosen for determining air quality. For example, the additional instruction and guidance should provide sources with the means and opportunity to obtain and understand an air agency’s reasoning to utilize mode ling based on allowableDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

122 emission rates over actual and thereby provide sources with an ability to determine whether an agency’s reasoning has merit.

Commenter (0040) suggested th e following regulatory amendments to section 51.1203(d) :

(d) Modeling. For each area for which air quality will be characterized through air quality modeling, the air agency shall submit by January 15, 2016, a technical protocol for conducting such modeling to the Regional Administrator for review. The air agency shall

consult wi th the appropriate the [ sic ] EPA Regional Office , and also the sources that may be subject to the modeling, in developing these modeling protocols. The modeling protocols submitted by the air agency must identify comments raised by each potentially

affecte d source and provide the agency’s responses thereto

. . . .

C ommenter (0044) recommend ed the following revisions t o section 51.1203(d) and (d)(1) :

(d) Modeling. For each area for which air quality will be characterized through air quality modeling, the ai r agency shall submit by January 15, 2016, a technical protocol for conducting such modeling to the Regional Administrator for review. The air agency shall consult with the appropriate the [ sic ] EPA Regional Office , and also the sources that may be subject to the modeling, in developing these modeling protocols. Sources and other interested parties shall also be given an opportunity to review and comment upon the modeling protocol prior its approval by the Regional Administrator.

(1) The modeling protocol shall include information about the modeling approach to be followed, including but not limited to the model to be used, modeling domain, receptor grid, emissions dataset, meteorological dataset, whether the model will be based on actual

or allowable emiss ion rates, and how the state will account for background SO 2 concentrations , and such other factors that the air agency believes will be beneficial in making current ambient air quality determinations under this subpart

.

Response:

At the outset, we note that the EPA has in recent years has consistently provided for a public participation opportunity in promulgating designations under NAAQS. We expect to continue this in completing designations under the SO 2 NAAQS. However, this rule does not prescribe

req uirements for conducting designations or other actions that make decisions regarding areas’ air quality, so it is beyond the scope of this rule to codify such requirements. In implementing this rule that is targeted at characterizing area emissions concent rations generally, t he EPA agrees with the commenters regarding the desirability of consulting relevant parties when performing modeling under this rule (or for that matter monitoring) and in particular encourages air agencies to consult with affected sour ces and other interested parties regarding the selection of air quality characterization methods and regarding particular elements of intended modeling analyses. Indeed, the EPA believes that most air agencies consult with the range of interestedDELIBERATIVE

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123 parties as a matter of routine, a practice that the EPA believes provides for better informed actions by the air agencies.

On the other hand, the EPA does not agree that the DRR should be revised to include an explicit requirement for states conducting modeling un der this rule to consult affected sources and other interested parties. The CAA provides that SIPs are to be subject to a notice and comment process but does not impose any such requirements on air agencies regarding the conduct of technical analyses or th e establishment of ambient monitors, and the EPA believes that it would be inappropriate to impose such requirements in this rule . Air agencies have a challenging task meeting the requirements that the CAA does impose, and the EPA believes that imposition of further requirements on who the air agencies consult is neither necessary nor warranted.



### D. July 2016: Inclusion of SO 2 

### m onitoring n etwork m odifications to

s atisfy DRR

1. Schedule is not feasible

Comment :

Commenter s (0038 , 0046, 0056, 0088

, and 0108 ) st ated that it is unreasonable for the EPA to assume monitoring plans can be submitted by the proposed July 1, 2016 deadline

. Commenter (0038) stated that (1) it may not be apparent that monitoring is required until after a lengthy

round of initial modeling is complete and (2) siting monitors is a lengthy process which involves,

among other steps, working with the EPA to determine where monitors should be located, obtaining access to sites, identifying funding, and procuring and installing equipment.

Commen ter (0088) stated t he proposed schedule will not provide a reasonable amount of time for states and large sources to properly agree on the placement of new monitors, and details regarding their operation and maintenance in conformance with the EPA monitori ng criteria set

forth in the TAD. Commenter (0088) stated i t is very important to note that the se activities are performed in consecutive order and it is extremely unlikely for all of these to be completed in only 6 months, especially if there are several issues to be resolved between the EPA Regional

Offices and s tate a ir a gencies which could take up a significant portion if not all of the 6 month period.

Commenter (0097) stated that, f or facilities that do choose to operate monitoring equipment,

additio nal time will be needed to develop documentation between states and operators to ensure that sites are adequately maintained and that data are reported in a timely and complete manner. Commenter (0097) stated f acility

- operated monitoring sites will necessi tate that the states create a quality assurance program consistent with the EPA requirements for the entire monitoring

network.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

124 Response:

See section IV.C of the preamble to the final rule for a discussion of these issues , where it is

stated that the EP A recognizes that the logistical and financial burdens of installing an ambient air monitoring station can be varied in difficulty and the resources required. However, as noted earlier with regard to the overarching timetables effected by this rule, the Ag ency believes that, as with other parts of the implementation schedule, while the schedule for operating monitors is expeditious , it can be achieved with appropriate planning, coordination, and program implementation by the air agency which will allow moni toring resources to be in place by the deadline. The EPA believes that any further delay in air quality characterization around sources identified as a result of this rulemaking will delay implementation of the standard and public health protection in area s where there may be a violation of the standard. The Agency believes that it is most prudent to maintain the proposed timetable for monitoring network installation because of the need for use of these new data in a relatively timely manner for use in maki ng attainment status decisions concerning SO 2 areas in the country.

With respect to comments concerning documentation needing to be developed between states and “operators” (which the EPA assumes to be industry or contracted partners), the state is the

re sponsible party in any scenario and must take steps to ensure that all data collection, quality assurance, and reporting requirements are met just as a state does for its own SLAMS data. Therefore, the EPA believes that it is likely that existing infrastru cture can be leveraged if industry or contractor led monitoring operations are used to satisfy requirements of the SO 2 DRR.



### 2. Schedule needs to be changed

Comment :

Commenter s (0045 , 0088 ) recommended an extension of at least one year on all the proposed

a ctions listed in the implementation timeline. Commenter (0088) stated that the EPA is well within its legal authority to simply designate s tates that intend to pursue monitoring as

“unclassifiable” for the 1

- h our SO 2 NAAQS without any temporal regulatory r equirements for collection or submission of any air quality data. In the face of this authority, commenter (0088)

stated it is more than reasonable for the EPA to give s tates that i ndicate they will conduct air quality monitoring for the NAAQS, additional time far beyond one year.

Commenter (0110) stated that resolution of the modeling issues (revision of Appendix W is planned for spring 2016) also affects the deadline for monitoring decisions, planning, and deployment because modeling can be a tool to de termine where to place the monitor and modeling results that show NAAQS violations may result in a source being moved into the monitoring path, but that result can only happen when a final modeling approach is ready and implemented.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

125 Commente rs (0056 , 0071 ) stated that t he EPA should move up the deadline for submitting a monitoring plan to provide more time for s tate agencies to install the monitoring network after the monitoring protocol is submitted. Commenter (0071) stated i t might be prudent to move the deadline for final identification of sources to be monitored to an earlier date, for example, September 30, 2015.

Response:

As discussed in section IV.C of the preamble to the final rule, t he EPA believes that any further delay in air quality characte rization around sources identified as a result of this rulemaking will delay implementation of the standard and public health protection in areas where there may be a

violation of the standard. Reg a rding the comments about AERMOD, t he EPA believes that the current AERMOD package available is sufficient for use in aiding in monitor siting exercises.

The Agency believes that it is most prudent to maintain the proposed timetable for monitoring

network plan submittal and network installation

. A delay in plann ing and implementing new monitors would result in an unnecessary delay in making attainment status decisions concerning

SO 2 areas in the country and thus in addressing the air quality problems that these monitors may identify

. The date for submitting netwo rk plan revisions is designed to match the date for submittal of the routine annual plan addressing any other network revisions, and requiring a separate plan or changing the date for the routine annual plan would create undue confusion and

can unduly incr ease the workload for air agencies. T o the extent that an air agency believes that

additional time is needed to consult with t he EPA regarding network plan revisions, the EPA encourages such consultation early in the process of developing network plans, ir respective of the deadline for network plan submittal. Conversely, if states wish to advance their selection of sources to be monitored to better ensure that they have time devise an appropriate monitoring plan, they always have this authority, and the fin al rule does not restrict this. However, we have not chosen to mandate such an early submission, given the already expeditious set of milestones

established in the rule.



### E. January 1, 2017: Requirement that SO 2 

### m onitors be o

perational

1. Time between monitor ing plans due and monitors operational

a. Insufficient time

Comment :

Commenters ( 0039, 0045, 0055, 0074, 0084, 0087, 0088

, 0107, 0108, 0110, 0113

, and 0118 ) generally stated the short time period between the dates when the monitoring plans need to be

subm itted and the monitors are required to be operational is inadequate. Commenter (0088)

stated it is technically infeasible to implement the Proposed Rule by 2017 and thus the EPA ’s proposal is arbitrary and capricious.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

126 Commenters (0038, 0039, 0051, 0056, 0075, 0083, 0088, 0107, 0110, and 0118) stated that e ven if monitoring plans are submitted on time, the EPA approval process could prevent a state from having monitors operational by the 2017 deadline. Commenter (0100) stated that the timing of Region 8 a pprovals of AQD's Network Plan has varied from 4 months to 15 months. Commenters (0055, 0074) stated that, if one presumes it will take the EPA 3 to 6 months for approval (a n expeditious schedule ), then approval for the plan would not be forthcoming until near 2017, which leaves it unreasonable to expect the agency, or other entity, to be able to have monitors operational by January 1, 2017. Commenter (0097) also noted that the EPA requires a 30 day public notice period for all annual monitoring network pla ns ; t his may also limit the

amount of time available for network upgrades.

Commenters (0039, 0084) asserted t here are a number of considerations that the EPA has not factored into this timeline that require additional time for proper installation of monit oring

systems. Commenter (0084) noted, for example, pr oper siting will be required which could require easements or land purchases ; p roper equipment design, procurement, and delivery alone will require more than six months. Commenter (0069) stated that the time in which states may determine that modeling the source may be inappropriate could delay monitor deployment and

result in incomplete data capture during first quarter 2017

. Commenter (0110) stated that, o nce the monitoring plan is approved, the necess ary equipment has to be procured, prepared, and installed on a site with considerable preparation needed , which can take at least 3 months, much of which is due to delivery times from equipment vendors. Commenter (0110) stated that, i f this activity is hap pening simultaneously throughout the U .S. all at the same time, there may be equipment shortages and prolonged delivery times that could require additional months after the monitoring plan is approved to acquire the needed equipment.

Commenters (0039, 004 5, 0087, 0088, 0107, 0108, 0109, and 0110) suggested provid ing states with additional time to begin actual monitoring. Commenters ( 0039, 0045, 0087, 0088

, and

0110 ) recommended an extension of at least one year. Commenter (0039) stated the date should

be e xtended to January 1, 2018, if not, then the rule should not include a mandatory requirement to conduct modeling evaluations if monitoring has not begun by January 1, 2017. C ommenter (0109) requested that the EPA extend the initial deadline for implementin g monitoring programs under the Proposed Rule and create a reasonable extension option to address unavoidable implementation delays that occur along the way. Commenter (0110) recommended s etting a schedule that provides for monitoring network implementatio n up to 12 months after submittal of a monitoring plan a s a more reasonable approach. Commenter (0107) stated that o ther recent

rules ( N O 2 , S O 2 , and PM 2.5 ) have not required such rapid deployment of monitors , but have each allowed at least 1.5 years from s ubmittal of the network plan to operation of the monitor. Commenter (0087) urged the EPA t o consider extending the deadline to January 2019 and

consider an "unclassifiable" designation until the planned monitoring is completed t o allow at

least 1 full year of data before the 2020 designation deadline

Commenter (0038) suggested a n alternative option to allow monitoring to begin later, such as between May 1, 2017 and July 1, 2017, for all sources being designated under the monitoring pathway. This approach w ould be consistent with an approach allowing states to declare theDELIBERATIVE

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127 monitoring pathway for sources up to January 1, 2017. Commenter (0038) recognize d this approach would likely require delaying the attainment date, since design values are based on

three cal endar years of monitoring data. Commenter (0038) provided the following additional points

.

EPA approval of state monitoring plans generally occurs in the fall of each year, but in some cases has not occurred until very late in the year. This means that EP A approval of

an SO 2 monitoring plan under this proposal may not occur until late 2016. In Wisconsin, monitor siting and set

- up can generally only occur until late fall due to winter weather (snowfall and frozen ground); a late 2016 approval of a monitorin g plan by EPA would simply not allow sufficient time for Wisconsin and other areas with winter weather concerns set up a monitoring network by January 1, 2017.

Commenter (0118) stated that c onditions associated with the Sierra Club CD may impact the

feasi bility of deploying new monitoring networks because sources or states may not have time adequately develop a plan, get approval for the plan, and hav e the network operational to rely on

a monitor

- based attainment determination. Commenter (0118) stated that c onditions of the proposed CD do not provide enough time to redeploy monitors to demonstrate whether or not the NAAQS is being met.

Response :

These issues are discussed in section IV.C of the preamble to the final rule, where it is stated that

t he EPA recognizes that the logistical and financial burdens of installing an ambient air monitoring station or stations can be varied in difficulty and the resources required. The EPA recognizes the potential logistical hurdles inherent in the installation of new monitoring sites

, including property identification and access, and the installation of power and

telecommunications , among other examples. However, due to the overarching timetables

affected by this rule, the Agency believes that, while the schedule for operating monitors is expeditious , it can be achieved with appropriate planning, coordination, and program implementation by the air agency which will allow monitoring resources to be in place by the deadline. The EPA believes that any further delay in air quality characterization around sources identified as a result of this rulemaking will delay implementation of the standard and public health protection in areas where there may be a violation of the standard. The Agency believes that it is most prudent t o maintain the proposed timetable for monitoring network installation because of the need for use of these new data in a relatively timely manner for use in making attainment status decisions concerning SO 2 areas in the country

. ( This includes meeting the agency’s obligations to complete area designations pursuant to the CD , which for the most pa rt
will allow tho se decisions to be informed by quality information that is timely generated by the deadlines established by this final rule. )

In response to com ments about Regional approval of monitoring plans, the EPA encourages states and local air agencies to engage their respective Regional contacts as early as possible on monitoring network design

. The end result of early engagement between states and EPA Re gionsDELIBERATIVE

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128 will be states developing monitoring plans that are less likely to have difficulty receiving approval.



### b. Reasonable time fr a me

Comment :

Commenter (0058) stated the DRR establishes a reasonable timeframe for s tates to collect the data, either throug h monitoring or modeling, that is needed to characterize air quality in these

“unclassifiable” areas and determine whether the 1

- hour SO 2 NAAQS is being met. Commenter (0060) stated that the feasibility of this time period will be dependent upon the thresh old option selected by the EPA

.

Response :

The EPA believes that the threshold chosen in the final rule does not create a situation where data collection required to satisfy the rule is i nfeasible. The final rule, which establishes a threshold (2,000 tpy ) that is expected to cover fewer sources than proposed, and in EPA’s judgment, with proper planning, the timelines are expeditious but manageable.



### 2. EPA oversight of monitoring plans

a. Timing for EPA determination

Comment :

Commenters (0038, 0039, 0051, 005 6, 0075, 0083, 0088, 0107, 0110, and 0118) stated that e ven if monitoring plans are submitted on time, the EPA approval process could prevent a state from having monitors operational by the 2017 deadline.

Commenter (0107) stated that, as st ates typically submit the network plan by July 1, with EPA approval coming in late September , it would virtually be impossible to then have the entire S O 2

source oriented network operational three months later, especially if there is extensive negotiation with EPA's reg ional office on the number and location of monitors. Commenter (0107) stated s uch negotiation is expected given:

• EPA's Technical Assistance Document (TAD) is vague about monitor siting, deferring to

"case

- by

- case" analysis of each facility.

• This is a new rule with no prior experience to use to gauge the most appropriate network

to propose.

• EPA regional approval of network plans may be delayed due to a desire for consistent decisions among regions, states, and facilities.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

129 Commenter s (0039 , 0055, 0074, an d 0088 ) stated it would be imprudent for a state agency or a source to invest in a monitoring network until after the EPA ’s blessing of the network had been obtained and it will simply be impossible for states and sources to begin monitoring by January 1, 2017. Commenter (0088) stated t his provision must be amended to provide any basis for SO 2 monitoring plans to be successfully implemented. Commenter (0056) stated that, if monitor deployment is delayed, it adds to the uncertainty of taking the monitoring a pproach and make s it a less attractive option

.

Commenters ( 0051, 0055, 0056, 0074, 0083, 0088

, and 0100 ) stated the EPA needs to establish a clear and timely process under which states can obtain a determination from the EPA that an existing or new monit oring network is adequate for making attainment designations

. Commenter (0051) stated t he words,"... as expeditiously as practicable ..." for the EPA's action on the protocols are not adequate. Commenters (0055, 0074) stated the EPA needs to either allow m ore time for the establishment of the network (additional 6 months or tolling of deadlines until approval is granted) or bind itself to a fast review and approval period. Commenter (0083) stated the rule should include a section with required EPA actions a nd associated timeframes.

Commenter (0051) stated that s ince the states are required to submit protocols by a certain date, the EPA Regional Offices should be required to submit their written approvals or disapprovals (via deficiency letters) to the state s within 60 days of submittal of each protocol and no later than March 15, 2016. Commenter (0100) s uggest ed an initial approval from the Region within 90 days of the submittal of a demonstration in order to allow the s tate and i ndustry to commence the

prep aratory work in a timely manner.

Commenter (0100) s uggest ed that the EPA allow agencies and industry an alternate approval process and allow monitoring to take place earlier if the approval process has been followed. Commenter (0113) suggest ed that the E PA have a site approval mechanism in place independent of a network plan so that monitoring agencies have at least a full year to prepare for the newly required monitoring sites ; o therwise, monitoring may not be a feasible option under the DRR.

Commenter (0051) suggested an appeals process be part of this rule package, for the sake of national consistency. In order to help provide transparency and consistency for states, commenters (0051) suggested the EPA Regional Office should provide all submitted proto cols and the approval status of each on an easily accessible agency webpage

. Commenter (0051)

stated t he EPA should establish data sharing procedures.

Response :

As discussed in secti o n IV.C of the preamble to the final rule, t he Agency believes that

mon itoring resources can be appropriately put in place by the January 1, 2017 deadline to satisfy this rule, particularly if air agencies begin planning as soon as possible. The EPA has encouraged air agencies to begin the monitor planning process as early as possible . T he EPA believes that while the schedule for meeting the requirements of this rule is expeditious , the schedule can beDELIBERATIVE

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130 achieved with the appropriate planning, coordination, and program implementation by affected air agencies. The EPA strongly en courages air agencies to start their investigation of this issue as soon as practicable. The EPA also encourages each air agency to consult with its respective EPA Regional Office to identify sources exceeding the emission threshold in the final rule and a ny other sources that do not exceed the emission threshold but which would warrant the

characterization of nearby air quality

.

In addition, the EPA believes that it is necessary to establish expeditious timelines to ensure timely availability of air qual ity information. With this in mind, and in light of the many logistical concerns raised by commenters and recognized by the EPA, the Agency is encouraging air agencies to engage with their respective EPA Regional Office s well in advance of the time by

whic h the Annual Monitoring Network Plan is due. Notably, there is nothing preventing a state from sharing their draft SO 2 network design plan for SO 2 monitoring intended to satisfy this rule with the EPA and the public in advance of the complete Annual Monito ring Network Plan. The end result of early engagement between states and EPA Regions will be states developing monitoring plans that are less likely to have difficulty receiving approval.



### b. Eliminate EPA approval of monitoring plans

Comment :

[Also see IV .B.3, EPA oversight of modeling plans.]

Commenter (0088) stated EPA o versight/ a pproval of state monitoring p lans should be

eliminated. Commenter (0088) provided the following additional points.

Proposed s ection 51.1203(c) of the SO 2 Data rule appears to require EPA consultation and approval of a s tate’s monitoring plan. NEDA/CAP submits that this EPA oversight and approval unnecessarily interferes with state decisions and should be deleted as a requirement. Modifications of a monitoring plan can be made a fter submission of monitoring data and “tweaks” to the monitoring plan should be allowed and encouraged for the collection of monitoring data up to, during and following the execution of the plan. The EPA experts know that this is technically necessary for such monitoring to be successful, and therefore it is unreasonable for the agency to pretend such flexibility is not critical to a successful monitoring program. Moreover, given the primacy of state air programs under the CAA , EPA’s proposal is not consis tent with EPA oversight

– not active participation

– in how an individual state will implement the SO 2 monitoring protocols. The EPA’s authority in this matter is limited to the review of the monitoring

data.

Commenter (0088) stated i t is arbitrary and c apricious to require EPA approval of state monitoring and modeling plans when the EPA ’s technical resources are too stretched to provide this oversight in a timely manner . Commenter (0088) recommended that the roles of the EPADELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

131 experts should be advisory on ly in initial implementation and section 51.1203 should be revised accordingly. Commenter (0088) provided the following additional points.

While it is critical to acknowledge that the EPA regional monitoring experts can be helpful in advising states on mo nitoring (and modeling) plans, there are simply not enough of them to supervise, let alone review and act on, the number of s tate monitoring programs necessary to implement the data rule in a timely manner. Most EPA regions have only one such monitoring/mo deling expert and OAQPS has fewer than five such experts. It therefore would be highly unreasonable for the EPA therefore to require as a precondition for implementation of a SO 2 monitoring plan, EPA review and concurrence/approval before it is implemented . Even if the compliance deadlines for such plan requirements and implementation were extended by substantial amounts, this requirement would still be unreasonable.

Once monitoring data are collected, it would then be appropriate for these experts to

rev iew collected monitoring data in the context of the overall state monitoring plan and goals. If the experts review concludes that monitors should be relocated or additional monitors should be sited, this input can be sought and offered in an advisory role so as not to prejudice a state’s efforts to comply with the data rule. If adjustments or others changes to a state’s monitoring plan are suggested after data are collected and reviewed, the regional air office can deem the air quality control to be unclass ified until other monitors are sited and data collected. This solution would provide an opportunity for EPA input without overwhelming states and source’s judgment and ability to meet even an extended timeframe for implementing monitors. (0088)

Commenters (0055, 0074) asked if submittal of the (state) agency annual network plan (7/1/16), as it relates specifically to this SO 2 monitoring, requires EPA approval. Commenters (0055, 0074) stated that the preamble (for example, p. 27458) seems to encourage agenc ies to work with the EPA Regional Offices in developing the network plans, while the Proposed Rule in section 51.1203(c)(3) refers to an “approved Annual Monitoring Network Plan.” Commenter (0100) stated that since the Proposed Rule in 51.1203(c) only requ ir es consultation, it is not clear how the timing of the approval process will work in conjunction with time needed to deploy monitoring by January 1, 2017.

Response :

The EPA Regional Administrator approval of state Annual Monitoring Network Plans is

re quired, per language in 40 CFR p art 58, 58.14(a) , and modification to that regulatory text was not proposed , nor did the commenter provide a reason why this longstanding requirement should

be reversed . T he Agency judges plan approval as a crucial step in t he interaction between the Agency and states, leading to the appropriate installation, modification, operation

, and

ma intenance of ambient monitoring networks , and thus there was no proposed action in this rulemaking to deviate from that existing process

. Notably, i n section 58.1 0 (a) , it is stated that the EPA will respond within 120 days. States are encouraged to work with their respective EPADELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

132 Regions regarding critical issues and details germane to satisfying the SO 2 DRR in advance of their monitoring net work plan submittal so that when the plan is formally submitted, there is less likelihood of difficulty in getting that plan approved.



### 3. Phased approach

Comment :

Commenters ( 0046 , 0051

, 00 52a

, 0107 ) suggested a phased approach for operation of the

monitor ing network. Commenter ( 0046 ) suggested that a phased approach for monitoring that begins with Option 3 thresholds would minimize the burden, allow for relocation of inappropriately placed monitors, and ensure that the high impact sources are adequately

ad dressed. Commenter (00 52a ) stated t he implementation schedule should consider available

resources and suggested a structured phase

- in schedule should be developed. Commenter (00 52a ) provided the following details.

The phase

- in schedule for source

- oriented monitoring should be prioritized based upon

an actual emissions threshold. The EPA should establish a requirement for a first phase of

monitor installations to be completed by January 1, 2015 and a second by January 1,

2017. The emissions thresholds used in this approach should be established through rulemaking, and should consider anticipated future S O 2 emissions after full implementation of major rules impacting these emissions such as the 2011 Cross

- State

Air Pollution Rule (CSAPR), the 2011 MATS Rule, and the reconsidered the Boiler

MACT standards for industrial, commercial, and institutional boilers along with all associated installation and operating costs. Further, as implementing agencies prioritize the placement of monitors consistent with this em issions threshold approach, they should

be allowed to consider other factors such as population and source stack height. This approach would allow states to focus their resources in areas with the highest risk to public health and the largest sources of S O 2 emissions. (00 52a )

Commenter s (0051 , 0107 ) stated the EPA should allow a phased approach similar to the near

road monitoring implementation schedule. Commenter s (0051 , 0107 ) provided the following additional points.

Texas currently has a network of 26 stationary SO 2 monitors. Most of these monitors are

in public locations, and the data are representative of concentrations to which the public

would be exposed. Data from this monitoring network do not suggest a widespread public

health concern indicative of such an onerous implementation schedule as the one proposed. As such, the EPA should extend the implementation timeline to provide states

more reasonable time frames for revising the existing monitoring program. Phase 1

would address sources with emissi ons of 20,000 tpy and greater by January 1, 2017. Phase 2 would address source emissions of 7,500 tpy and greater by January 1, 2018. Phase 3 would address all remaining source emissions required by January 1, 2019. This phased approach would allow for att ainment designation by 2020 for the largest SO 2DELIBERATIVE

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133 emitters while at the same time allowing states to procure funds and resources. ( 0051 )

Commenter (0107) stated that, since the s tate would be establishing a t least 10 S O 2 sites in little more than two years while the EPA is allowing the s tate more than four years to establish five

near

- road NO 2 sites, even the pace of th e following suggested alternate S O 2 schedule seems a bit

ambitious. Commenter (0107) recommend ed the following thresholds and schedule.

 Init ial monitor for facilities above 5,000 tons begin operating by Jan 1, 2017;

 Initial monitor for facilities above 3,000 tons begin operating by Jan 1, 2018;

 Initial monitor for facilities above 1,000 tons begin operating by Jan 1, 2019;

 If needed, additiona l monitors for the same facility begin operating at the rate of one every six months after the initial monitor.

Response :

The recommendations for phased monitoring would delay the commencement of significant air quality characterization required under th is rule. As discussed in section IV.C and in subsequent discussions in the preamble to the final rule, the issue of timing is discussed, where it is stated that the proposed timetable for conducting modeling and installing monitoring sites is critical

beca use of the need for these new data to be available to support future determinations concerning the attainment status of areas. T he EPA believes that any further delay in air quality characterization around sources identified as a result of this rulemaking c ould delay the implementation of the SO 2 NAAQS and therefore c ould impede public health protection in areas

that would show violations of the standard based on the data to be gathered under the rule. The EPA also believes that any significant delays in mo nitors becoming operational past the date of January 1, 2017, will certainly delay the potential for monitoring data to be used to inform actions that depend upon ambient concentration assessments, possibly past calendar year 2021. Finally, the EPA notes t hat under the terms of the previously discussed CD , in order to avoid the EPA being required to designate an area by December 31, 2017, an air agency will need to have installed and begun operating the new SO 2 monitoring system no later than January 1, 201 7

.

Comment

Commenter (0097) stated the EPA could adopt an extension approach, similar to that included

for ozone under s ection 172(a)(2)(C). If one full year of SO 2 monitoring data were obtained, and

this data showed no exceedance (i.e. the 99th percenti le of the data was not above 75 ppb), then

EPA could offer two years of extensions before making the designation determination, contingent on each year's data recording values less than 75 ppb for the 99th percentile each year. Such an approach would allow states more time to upgrade their monitoring networks for

this effort. Commenter (0097) stated that, i f an extension option and provisional compliance

based on 2019 data are offered to states, the timeline EPA discusses within the rule could be

modified a s noted below:

DATE MILESTONEDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

134 4/17/2014 EPA Proposes Data Rule

12/31/2014 EPA Finalizes Data Rule

1/15/2016 Identify Modeled & Monitored Sources

1/15/2016 Submit Modeling Protocols to EPA

7/1/2018 Submit Annual Monitoring Network Plans to EPA

1/1 /20 1 9 Commence Monitoring

1/13/2017 Submit Designation Recommendations Based on Modeling

8/31/2017 EPA Proposes Designations Based on Modeling

12/31/2017 EPA Finalizes Designations Based on Modeling

2/28/2018 Designation Effective Date Based on Modeli ng 8/31/2019 State Submits SO 2 SIP for Modeled Areas

12/31/2019 Complete First Year Monitoring

5/1/2020 Submit Designation Recommendations Based on at least

1 year of m onitoring or submit extension request

5/1/2020 Required Certification of 2019 Monit oring Data

8/31/2020 EPA Proposes Designations Based on Monitoring or

publishes extensions

12/31/2020 EPA Finalizes Designations Based on Monitoring for areas

not receiving extensions

2/28/2021 Designation Effective Date Based on Monitoring for areas

n ot receiving extensions

2/28/2021 EPA Approves SO 2 SIP for Modeled Areas

8/31/2022 State Submits SO 2 SIP for Monitored Areas

2/28/2023 Final Attainment for Modeled Areas and designations for successful

extension requests

2/28/2024 EPA Approves SO 2 SIP for Monitored Areas

2/28/2026 Final Attainment for Monitored Areas

Response:

As previously explained, in this final rule the EPA is not establishing requirements for designations or any deadlines for such actions. The timing of designations is now t o be governed by the CD entered by the court in March 2015. However, the EPA notes that the CAA section 172(a)(2)(C) provisions for extensions of time for nonattainment areas to attain a NAAQS are not applicable or relevant for the timing of EPA promulgati on of designations, even if the agency were not already subject to a court order setting forth a binding schedule to take those actions.

The EPA believes that any further delay in air quality characterization around sources identified

as a result of this rulemaking would delay the implementation of the SO 2 NAAQS and therefore would impede public health protection in areas that in the future show violations of the standard based on the data to be gathered under the rule. The EPA also believes that any signi ficant delays in monitors becoming operational past the date of January 1, 2017, will certainly delay the potential for monitoring data to be used to inform actions that depend upon ambientDELIBERATIVE

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135 concentration assessments, possibly past calendar year 2021. Final ly, the EPA notes that under

the terms of the March 2015 CD , in order to avoid the EPA being required to designate an area by December 31, 2017, an air agency will need to have installed and begun operating the new

SO 2 monitoring system no later than Janua ry 1, 2017.

The Agency believes that it is very important to maintain the proposed timetable for conducting modeling and installing monitoring sites because of the need for these new data to be available to support future determinations concerning the at tainment status of areas. The EPA encourages each air agency to engage in early dialogue with the appropriate EPA Regional Office and with the identified applicable facilities in order to meet the requirements of the rule. In particular, in light of the re ality of the sometimes complex process of identifying potential monitoring locations, securing funding, and installing an appropriate number of new sites, if an air agency is considering the monitoring approach for one or more areas, early coordination sho uld improve the air agency’s potential for success in meeting the timing and requirements of the rule.



### F

. January 13, 2017: Requirement t o p rovide m odeling a nalyses

1. Schedule

a. Schedule may be adequate

Comment :

Commenter (0041) stated that the January 2 017 date to provide modeling is adequate, particularly if the number of affected sources is relatively small, as the AQD has proposed. Commenter (0060) stated that the feasibility of this time period will be dependent upon the threshold option selected by the EPA

. Commenter (0085) supported the proposed requirement

that a ir quality modeling is conducted well in advance of the January 2017 deadline for states to submit modeling analyses to the EPA

.

Response:

The EPA believes that the threshold chosen in th e final rule does not create a situation where modeling or monitoring required to satisfy the rule is infeasible. The final rule, which establishes a threshold (2,000 tpy ) that is higher than the threshold that EPA proposed for urban areas (1,000

tpy ) and applies the same threshold as was proposed for other parts of the country will ease state efforts to comply with the timetable in the rule. ( This includes meeting the agency’s obligations to complete area designations pursuant to the CD , which for the most part will allow those decisions to be informed by quality information that is timely generated by the deadlines established by this final rule. )



### b. Schedule is not feasibleDELIBERATIVE

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136 Comment :

Commenter (0051) stated t he proposed modeling timeline is not feasible a nd there is insufficient time for informed state planning, modeling preparation, and careful modeling analysis. Commenter (0051) stated that, w ith the potential challenge of conducting several multi

- source analyses using approaches typical for permit eval uation and single

- source evaluations, two to four years may be needed for adequate to complete adequate modeling demonstrations. Commenter (0051) provided the following additional points.

The TCEQ estimates there could be a minimum of 12 and as many as 32 modeling protocols required. One year is not enough time for the state to develop a strategy, consult with sources and the EPA, develop modeling protocols, and obtain the EPA's approval of the protocols. Assuming that emissions thresholds, population lim its, and other tools limit the number of sources to be explicitly modeled, the modeling itself (not including emission inventory and meteorological input development; protocol development; preparatory work; post

- processing of results; final analysis; and r eport development) could be completed in approximately one to two years, with a team of six to eight modelers and analysts wor ki ng full

- time. Texas does not have these resources. In addition, the EPA significantly underestimates the cost of a refined model ing analysis.

One year is not enough time to complete modeling demonstrations. Depending on the scope of the modeling required, it would take two to four years to complete the entire process. The modeling time estimate will increase if refined modeling is required to site monitors and if the EPA expects the states to submit modeling protocols and not conduct any refined modeling to support monitor placement decisions until the EPA approves the protocols.

Commenter (0060) stated Ohio could potentially have to model or monitor anywhere from 10 to 31 facilities under the three options proposed and noted that electing to monitor will require a significant modeling component to determine monitor locations. Commenter (0060) stated that,

d epending on the number o f sources to address, the strain on modeling resources by the air agency may be too great in such a short time. Commenter (0060) noted these efforts will have to occur simultaneously with the work air agencies are performing to finalize modeling under the nonattainment area requirements for SO 2

.

Commenter (00 52a ) stated t he availability of onsite data are a key factor to ensuring credible model results and, therefore

, EPA should allow sufficient time for states and the regulated community to collect onsite meteorological and ambient air measurements, and to evaluate

model performance when necessary . Commenter (0110) stated a requirement to collect three years of on

- site data are inconsistent with the proposed designations timeline since s uch a requirement w ould make it impossible to use new on

- site data and still adhere to the anticipated

EPA schedule.

Commenter (0042, attachment B) suggested an extension of the current implementation schedule may be necessary

. Commenter (0042) stated r ecent revisions to A ERMOD may requireDELIBERATIVE

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137 additional time to ensure proper operation and t he AERMOD shakeout period may warrant an extension of the current implementation schedule for attainment designations for SO 2

. Commenter (0042, attachment A5) stated that, b efore emissions r eductions are sought, s tates should first consult with the affected source to explore improvements or refinements to the initial modeling to help ensure that modeled impacts are “real”. Commenter (0042, attachment B)

stated that m any historical modeling in ventories were developed for historical requirements; therefore, existing inventories may require extensive review for use. Commenter (0042, attachment B) stated t he shape of existing modeling inventories may warrant an extension of the current implementat ion schedule.

Commenters (0060, 0069) stated that, as s tates will not know if there will be delays beyond their control until after the January 15, 2016 mo deli ng protocol deadline or the July 2016 monitoring

network modification deadline , t here will be in sufficient time to complete a modeling protocol, complete modeling, prepare modeling analyses and, if necessary, determine boundary recommendations, by the January 13, 2017 deadline.

Response:

As discussed in the preamble to the final rule, the EPA beli eves that the schedule for completion of modeling and commencement of monitoring is expeditious but feasible. The commenters cite numbers of sources they expect to need to address, but they otherwise do not explain why these analyses will take longer than the timetable provided by the rule. The CAA provides 18 months for preparation of SO 2 nonattainment plans, irrespective of how many nonattainment areas a state has, and the EPA believes that modeling for air quality characterization purposes, which does no t involve establishment of emission limits, will require less time. Furthermore, the EPA anticipates that the modeling approach for multiple areas within a state will have many features in common, so that modeling several sources will not necessarily take several times longer. The EPA believes that this information must be obtained as expeditiously as practicable in order to provide the health protections from implementation of the SO 2 standard as early as possible. To

the extent that collection of additi onal meteorological data would delay the schedule for implementing the standard, the EPA believes that existing data, used in accordance with the modeling TAD, should be used. Similarly, concerns about implementing revised versions of

AERMOD

, and about unf oreseen difficulties, do not justify promulgating a delayed schedule for air quality characterization requirements. EPA also believes that states should invest in resources, i.e. software to aid in the development of model runs and post

- processing of resul ts for multiple sources. These would be software packages that would automate data manipulation and calculations of model inputs, such as creating AERMOD input files, and post

- processing AERMOD results to calculate relevant metrics such as design values. M any software packages, such as scripting languages are open source and require minimal training. The EPA anticipates that many state modelers are also technically competent in programming languages such as

FORTRAN that can aid in automation of the model ru ns.



### 2. EPA review of the modeling analysesDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

138 Comment :

To ensure that the timeframes for specific agency requirements included in the Proposed Rule can be met, commenter (0083) stated that the rule should include a section with required EPA

actions and associa ted timeframes. Commenter (0106) stated that, i f the modeling protocol is

submitted by January 15, 2016, the Department believes the final modeling analysis should not

be due until one year after the Regional Administrator has completed review of the proto col ; t his will make EPA a partner in assuring that the modeling analyses are completed in a timely manner and afford the States the time necessary to complete the final modeling analysis.

Commenter (0093) disagree d with the requirement that modeling analy ses be submitted to EPA. Commenter (0093) assert ed that these analyses will be reviewed by the state agency and a summary of the analyses can be forwarded to the EPA with sufficient information for the EPA to
evaluate.

Response:

See section IV

. C of the p reamble on “Data Requirements and Program Implementation

Timeline” concerning this issue. This section discusses the actions that are required under this

rule. The EPA does not believe that state responsibilities under this rule should be contingent on

EPA action; thus, the preamble discusses the benefits of consultations between the air agency and the EPA on issues that a modeling protocol would be expected to address, but the EPA is not imposing a deadline on itself for action related to a submitted proto col, nor is it making the deadline for state action depend on approval or disapproval of a protocol by the EPA. This rule does not otherwise impose requirements on the EPA, but the timeline includes the requirements on the EPA for designation of areas purs uant to CD

.



### 3. Updated designation recommendations

a. Procedures

Comment :

Commenter (0041) stated that it is important to include the 120

- day review by states prior to the

EPA 's final designation of areas, as proposed in the rule. Commenter (0068) stated any final Rule must include explicit provisions for public comment periods on proposed designations, to ensure that the public has adequate opportunity for input on the critical designations step of SO 2 NAAQS implementation.

Commenter (0103) stated that a reas found to be in nonattainment through implementation of the Proposed Rule could be brought into a “maintenance” plan. Commenter (0103) stated that this approach would be consistent with the requirements of the Act.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

139 Response:

In th e final rulemaking we a re not addressing comments received on the proposed rule concerning how the future designation process (or other processes that are informed by data generated through implementation of this rule) because those issues are beyond the scope of this rulemaking

. This rule is not promulgating requirements for how designations, re

- designations, clean data determinations, or determinations of attainment following SIP implementation shall be conducted. Comments on how information should be used in those processes ma y be raised

when those future actions occur.



### b. March 24, 2011 designation guidance

Comment :

Commenter (0060) stated that, although the proposal requires any updated designation

recommendations to follow the most recent SO 2 designation guidance , that guid ance (March 24, 2011) conflicts with this rule. Commenter (0060) stated, f or example, the document contains modeling guidance in Attachment 3 which pre

- dates the draft modeling TAD

. Commenter (0060) stated it is inappropriate to require the use of the Marc h 24, 2011 guidance without making it clear in the preamble of this rule that the guidelines laid out in Attachment 3 are no longer appropriate or required in many cases.

Response:

As explained above, i n th e final rulemaking we are not addressing comments received on the proposed rule concerning the designation process because those issues are beyond the scope of this rulemaking. However, we note that the Agency has issued updated designations guidance providing recommendations for air agencies. This guid ance may be found at http://www.epa.gov/airquality/sulfurdioxide/pdfs/20150320SO2designations.pdf

.



### c. Guidance needed on boundaries and a reas without significant SO 2



### sources

Comment :

Commenter s (0051 , 0103

, and 0106 ) stated the EPA should issue timely gui dance on selecting designation levels and boundaries, including guidance on addressing areas without SO 2 sources

. Commenter (0051) stated this is needed to promote national consistency for this round of boundary recommendations. Commenter s (0103 , 0106 ) req uest ed that this guidance be provided

in time to allow states to complete designation recommendations for these areas on a schedule that would be synchronized with the designation schedule that the EPA finalizes in this rule

. Commenter (0106) stated that t he EPA must provide this boundary guidance no later than the end of 2015, and that, without guidance from the EPA early in the process, delays could occur in establishing boundaries and submittal of the final modeling analysis and designationDELIBERATIVE

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140 recommendatio ns.

Commenter (0051) stated the proposal does not clearly explain whether the state must use modeling or monitoring data (or both) to identify areas of the state as unclassifiable, or whether the state could demonstrate attainment in other ways; for exam ple, areas could be designated based on information such as: no stationary sources of SO 2 in a county; sources well below the threshold; or with statewide screening modeling using a photochemical model that predicts 99th percentile concentrations less than the SO 2 standard. Commenter (0106) stated the EPA must clarify what information it believes is necessary to define the boundaries, as well as what information it intends to use for designating areas that are distant from larger SO 2 sources.

Commenter (0 046) stated that, while the EPA has recently relied on multiple

- factor analyses to

determine the extent of each nonattainment area ( emissions, meteorology, geography/topography, and jurisdictional boundaries ), designations based on AERMOD should

not use th is type of analysis. Commenter (0046) stated t he AERMOD results inherently account

for factors such as the source emissions, meteorology, and topography and AERMOD is only

considered valid over a relatively short distance. Commenters (0046, 0049) stated th at

n onattainment area designations based on the results of AERMOD should be limited to the immediate area of the source/receptors modeling nonattainment. Commenter (0046) stated that,

i f AERMOD is the basis of the nonattainment designation, in order to mai ntain consistency and the integrity of using AERMOD results to determine nonattainment, the areas AERMOD demonstrates are attaining the standard must be designated as attainment.

Commenter (0049) asserted that the EPA uses the term "source areas" when ta lking about which areas would be identified for air quality characterization but then also talks about characterizing the air quality around multiple smaller sources located in close proximity whose combined emissions may violate the standard. Commenter (0 049) stated that given that the EPA considers

the 1

- hour SO 2 NAAQS to be a source

- oriented NAAQS instead of a regional NAAQS, such as the ozone NAAQS, the defined area of nonattainment for purposes of an area's designation should be as closely aligned as p ossible to the area surrounding a particular source causing a violation. Commenter (0049) stated this would fit with the EPA 's notion of "source areas" when referring to areas that require further air quality characterization and align with the EPA 's view

of the SO 2 NAAQS as a source

- oriented standard.

Commenter (0060) did not agree with the proposal that an air agency should not recommend a designation for any county that includes a source area with new monitoring. Commenter (0060)

stated there should be flexibility, with appropriate modeling, for an option to request partial

attainment of counties with new monitors. Commenter (0060) stated a ir agencies may model

actual emissions to d etermine monitor location and use that to inform boundaries for areas

out side of the potential impact area, especially when these counties may border very rural

counties with little to no emission sources.

Commenter (0046) stated that n o modeling results should be considered where source

- oriented monitoring data are available, other than possibly to help determine the nonattainment areaDELIBERATIVE

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141 boundary

. Commenter (0049) stated that given the source specific nature of this monitoring approach, nonattainment areas should be as small as possible and only contain the area impacted by the source.

Commenter (0081) stated that, b ecause the highest 1

- hour SO 2 concentrations are likely to be localized in a relatively small area around applicable sources, CBSAs, metropolitan statistical areas (MSAs), or other jurisdictional areas should not be the presumptive boundary for the compliance determination. Commenter (0081) stated t his approach would be consistent with

most of the 1

- hour SO 2 nonattainment areas which were designated in 2013 and would also keep the plans which are to be submitted to th e EPA by January 2016 succinct as well as accurate, leading to a more effective and efficient review and approval process.

Response:

In th e final rulemaking we are not addressing comments received on the proposed rule concerning the designation process be cause those issues are beyond the scope of this rulemaking. However, the comments also raise issues about how modeling should be conducted pursuant to this rule, and we direct the commenters to section IV.D.6 of the preamble to the rulemaking for a complet e response regarding those issues.



### d. Designation as "attainment" or “unclassifiable/attainment”

Commenters (0071, 0081, and 0106) asked the EPA to provide clarification. Commenter s (0071

, 0106 ) stated that u nder this rule, if a state models attainment and recommends an attainment designation for an area, it is unclear whether or not the EPA would designate the area attainment,

and not "unclassifiable/attainment", based solely on modeling. Commenter (0071) stated that, i f modeling is chosen as the method f or characterizing air quality in an area, then the EPA should designate that area attainment when the state submits sufficient modeling data to support such a designation. Commenter (0071) requested clarification on the criteria the EPA deems necessary

to achieve an attainment designation.

Commenter (0081) stated m ore clarification is needed regarding the option to designate “ any unclassifiable/attainment areas as appropriate.” Commenter (0081) states that a s written this

could include all areas for which a modeling demonstration has been submitted and compliance with the standard has been proven. Commenter (0081) stated that if the EPA does not expect there to be future designation decision options which have not been included in this Proposed

Rule or the TADs , then the EPA should amend this wording in the final rule to read “any area which has demonstrated attainment based on modeling of actual emissions” or clarify otherwise.

Commenter (0106) stated the EPA ' s discussion on the "unclassifiable/attainment" designation is inconsistent and unclear throughout the preamble and casts doubt on what the EPA means when it issues an "attainment" designation. Commenter (0106) stated the EPA should clarify under what circumstances it is now proposing to issue designat ions of "attainment" or "unclassifiable",DELIBERATIVE

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142 and how different the consequences would be for areas with the two different designations. Commenter (0106) provided the following additional points.

T he proposal is inconsistent in how it describes the designati on of areas for which modeling is conducted: at page 27466, the EPA describes the designation of areas for which modeling is conducted as being "unclassifiable/attainment" while, i mmediately preceding this passage as well as in the Proposed Rule, the EPA d escribes the purpose of this modeling is "to demonstrate continued attainment for an area around a source." T he same confusion exists in the Proposed Rule at 79 Fed. Reg. 27459, where the EPA states an "unclassifiable/attainment" designation is appropriate for areas of a s tate that are distant from larger S O 2 sources.

Commenter (0106) stated t he CAA establishes a clear difference between "attainment"

and "unclassifiable" and the EPA cannot through this rulemaking rewrite the CAA to

redefine what "attainme nt" and "unclassifiable" mean.

If approved modeling data are supposed to be a surrogate for approved monitoring data, it seems logical that the successful conclusion of this process would be a designation of "attainment", not "unclassifiable/attainment". Only for areas distant from larger S O 2

sources
, or with no S O 2 sources, could a designation of unclassifiable be justifiable if

there is no monitoring or modeling data for these areas. It has been assumed till now that the conclusion of this process o f providing the EPA with additional monitoring or modeling data to support an attainment designation would result in an unqualified "attainment" designation, at least in the vicinity of modeled sources. This point of

confus ion needs to be explained.

Comm enter (0049) objected to the proposal that an area will be designated as “unclassifiable” without modeling data showing attainment of the standard, even if the area’s monitors show no violations, based on the assumption that there may be a potential to cau se or contribute to a violation of the NAAQS. Commenter (0049) stated t his new approach is contrary to the express language of the CAA as, u nder CAA s ection 107(d), an area can only be designated as

unclassifiable if it “cannot be classified on the basis o f available information as meeting or not meeting the national primary or secondary ambient air quality standard for the pollutant.” Commenter (0049) stated m onitoring data showing no violations of the standard qualifies as “available information” showing that the area is meeting the standard. Commenter (0049) also

stated the designation process under CAA s ection 107(d) does not involve consideration of the “potential to cause or contribute to a violation of the NAAQS,” but only requires the

consideration o f whether an area actually meets, or actually does not meet, the NAAQS.

Response:

In th e final rulemaking we are not addressing comments received on the proposed rule concerning the designation process because those issues are beyond the scope of this ru lemaking.DELIBERATIVE

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143 

### 4. Clarif y terms

Comment :

Commenter s ( 0049

, 0081, 0097, 0 100

, and 0107 ) requested the EPA to define certain terms, including “area”

. Commenter (0049) stated that, t hroughout the Proposed Rule

, the EPA uses the term “area” without indicating whet her geographic boundaries of the area correspond to a county, CBSA, Metropolitan Planning Organization (MPO), or some other jurisdictional area. Commenters (0049, 0081) stated, g iven that the EPA is focused on the short

- term impacts within the close proxim ity of major SO 2 sources, any monitored data or modeling analysis indicating a potential air quality concern should only result in a nonattainment designation for a geographic

area that is also limited in scope.

Commenter (0097) stated i t would helpful i f the EPA were to clarify their intent for the phrases "source areas," "sources," "units," and "stacks." Commenter (0097) stated, f or example, it is

unclear if the EPA is expecting by January 13, 2017 a modeling demonstration for a particular

source or set of sources, for all sources within an entire area, or if either situation might be acceptable depending on circumstances.

Commenter (0100) requested the EPA to clarify if non

- applicable sources are required in 51.1203 (b) to participate in the modeling/ monitoring characterization if an area is found to be subject to a demonstration. Commenter (0100) stated the language in this sentence first refers to "applicable sources" then discusses "all sources" in an area.

Response:

As a general matter, an “area” refers to the area that might warrant consideration as being impacted by emissions from the sources . Thus, air agencies are to provide information based on

consideration of all locations with in reasonable proximity of source s that might be impacted by

the ir emissions . “Source area” refers to the area around and impacted by emissions from a n applicable source as defined by this rule , including any other sources within or nearby that area

that influence its concentrations. While an area or source area may in clude only one “applicable source,” the air quality characterization that this source triggers must address the concentrations resulting from all sources that influence that area’s air quality.



### G

. December 2017: Intended d ate for i ssuance of f

inal d esignat ions
for m ajority of c ountry

Although the preamble for EPA’s proposed rule provided a timeline that identified designation dates as well as dates when the proposed rule requirements would be due, for purposes of illustrating a key use that the EPA anticip ates for the information that this rule requires to be obtained, this rule does not address features of the anticipated future designation actions. Therefore, comments on the prospective designations are identified in a section below entitled

“Comments o u tside the Scope of This Rulemaking.”DELIBERATIVE

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144 

### H

. May 2020: Required c ertification of 2019 m onitoring d ata

Although the preamble for EPA’s proposed rule provided a timeline that identified designation dates as well as dates when the proposed rule requirements would be due, for purposes of illustrating a key use that the EPA anticipates for the information that this rule requires to be obtained, this rule does not address features of the anticipated future designation actions. Therefore, comments on the prospective designations are identified in a section below entitled

“Comments o utside the Scope of This Rulemaking.”



### I

. December 2020: Intended d ate EPA i

ssuance of f

inal

d esignations

Although the preamble for EPA’s proposed rule provided a timeline that identified d esignation dates as well as dates when the proposed rule requirements would be due, for purposes of illustrating a key use that the EPA anticipates for the information that this rule requires to be obtained, this rule does not address features of the antic ipated future designation actions. Therefore, comments on the prospective designations are identified in a section below entitled

“Comments o utside the Scope of This Rulemaking.”



## V

. Technical Considerations

A. Monitoring

1. Monitoring in part 58

Comment :

C ommenter (0081) requested, i n order to simplify the regulatory process and aid in the review of applicable requirements for the monitoring plan, that all monitor related information be codified

under 40 CFR p art 58, not part 51.

Commenter s ( 0063, 0065) st ated that the m onitoring TAD does not offer the flexibility that p art
58 offers

. Commenter s ( 0063, 0065) asserted t he T AD provides no guidance to states on selecting an appropriate alternative to the preferred location, or the basis on which the EPA will

a pprove or disapprove states' monitoring plans. Commenter s ( 0063, 0065) stated t he TAD provides no assurance that states that elect the monitoring option can obtain a timely approval of their monitoring plans. Accordingly, commenter ( 0063, 0065) stated the EPA should allow states to continue siting monitors in accordance with p art 58, which, unlike the Proposed Rule, does not force a state to switch to modeling if the state's p art 58 plan is disapproved.DELIBERATIVE

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145 Response:

The EPA believes that due to the unique na ture of how air quality characterization can be achieved to satisfy this rulemaking, where there is flexibility to use modeling and monitoring, the associated regulatory text should be grouped together, as it was proposed and is being finalized. With respe ct to the TADs, they are non

- binding document s and this rulemaking is not taking final action to codify them . As is the case with all required ambient monitoring networks, states are encouraged to work with their EPA regions to develop appropriate monitori ng network designs that are reflected in Annual Monitoring Network Plans.

In response to the comment that siting monitors per p art 58 is preferable, the EPA notes that existing siting requirements in p art 58 are not specific enough to meet the intent o f this rule. This rule explicitly states where air quality needs to be characterized (around identified SO 2 sources) and for what purpose (targeting locations of expected maximum concentrations).



### 2. M ove existing monitors t o free up resources for the near

- s ource network

Comment :

Commenter (0036) stated that some NESCAUM states run rural SO 2 monitors to support tracking trends in acid deposition and to measure background concentrations for use in permit

related dispersion modeling. Commenter (0036) stated t hat many of these monitors cannot easily be shut down and redeployed, and the EPA should recognize this in the guidance.

Commenter ( 0046 ) stated that, i f only about one

- third of the existing SO 2 monitors are source

oriented , resources should be focused on better use of inappropriately sited monitors. Commenter ( 0046 ) stated that m odeling could be used as a screening tool to identify areas where

exceedances of the standard could be occurring and where reliable monitoring data are needed ;

s ubsequently, state s could relocate existing monitors to those areas and develop reliable data that support area designations.

Commenter s (0060 , 0074 ) stated they could not locate the supporting material and request ed the

EPA provide a list of monitors analyzed along with the conclusion of their adequacy to be used

as a source

- oriented monitor

. Commenter (0074) stated t he sites composing the 35% value are not identified by name or location in either the DRR or the SO 2 Network Review and Background

Memorandum

. Commenter (007 4) request ed that the EPA provide a list of all monitoring sites and the methodology used to determine the 35% value and request ed that the 488 sites identified

in Table 2 to the SO 2 Network Review and Background Memorandum be provided along with

their des ignated SO 2 Monitoring Objective.DELIBERATIVE

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146 Response:

The EPA notes that states use monitors to meet federal minimum monitoring requirements and also to satisfy their own objectives. If, through a network review or other means

, a monitor is

deemed a lower priori ty , it could be subject for relocation for use in satisfying this rulemaking. In such a case, or any

, where a SLAMS monitor is considered for relocation, states will need to engage their EPA Region. As noted by another commenter, modeling (and possibly ot her means) could be used to aid in determining which monitors might be appropriate for relocation

and to where.

The EPA SO 2 Network Review and Background document produced during the 2010 NAAQS rulemaking did not list individual monitoring sites that cou ld be classified as being source

oriented. This was accomplished by mining publicly available AQS meta

- data for any SO 2 site that had a monitor objective of either, or both, of “source

- oriented” and “highest concentration”.

It should be noted that a monit or can have multiple monitor objectives in AQS. T hese meta

- data are to be used with caution as states do not always use or apply these labels consistently . With that in mind, the EPA did not and has not produce d a list of sites. Any particular site will ne ed to be evaluated in detail to determine whether or not is adequately located at a point of expected

maximum SO 2 concentrations relative to a particular SO 2 source in order to meet the intent of

this rule.



### 3. Network design

a. Guidance is needed

— maximum conc entration site

Comment :

Commenters (0046, 0051, 0071, 0097, 0110, and 0106 ) expressed concern that the lack of clear criteria provided for designing an SO 2 source

- oriented monitoring network puts air agencies in the unreasonable position of designing a m onitoring network without knowing whether it will be approved by the EPA.

Commenter (0051) urge d the EPA to allow that the monitor

, sited to determine attainment or nonattainment of the primary SO 2 NAAQS, be placed as close as feasible to the predicted

m aximum concentration location at which actual public exposure is reasonably likely to occur.

Commenter (0110) stated that modeling is only one approach that can be used to site a monitor and suggested mobile monitoring or use of newly available rapid res ponse passive monitoring should be recognized as available to augment modeling in the siting of monitors. Commenter (0106) agreed that passive samples provide very little useful data for developing a monitoring plan since they do not provide a good indicat ion of peak 1

- hour concentrations. Commenter (0106) agreed that "sensors" may provide useful data for developing the monitoring plan. Commenter (0068) stated that attempting to place monitors based on prior monitor location (or

even the time

- consuming proc ess of “exploratory monitoring”) is overwhelmingly unlikely toDELIBERATIVE

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147 result in a monitor network that will capture peak concentrations; such a network is effectively useless for evaluating a short

- term NAAQS.

Commenter (0068) stated th at there are numerous cons iderations that make it unlikely that monitors could be sited at ideal modeled locations, including access to the location, power hookups, local pollutant effects, and safe from vandalism. Commenter (0068) stated th at, if

monitors are to be used to determi ne areas of nonattainment, they should be sited based on modeling performed to evaluate impacts on the SO 2 NAAQS; specifically, modeling conducted to determine where the multiple peak concentrations of SO 2 occur due to emissions from a

source.

Commenter (0071) noted that changes at the facility, such as equipment retirement or implementation of permanent & enforceable SO 2 emission limitations after the siting of a monitor, could change the area of maximum concentration. Commenter (0071) recommended that, for clean data determination purposes and subsequent NAAQS attainment designations, the area of maximum concentration should remain the same throughout the process, i.e., the same as when the monitor was initially sited, to avoid confusion when such desig nations are later pursued.

Commenter (0097) sugges ted that EPA integrate the concepts of source

- specific monitoring and population

- monitoring such that each is clearly defined, and the need for each is clearly explained; this effort may lead to the reduct ion of redundancies in the 2010 SO 2 NAAQS monitoring network and therefore may lead to a better utilization of network resources at the

state level. Commenter (0097) stated the EPA should ask that states include the analyses supporting the network design ( to characterize air quality around each relevant source ) in the 5 year monitoring assessment report required by 40 CFR 58.10, not the annual monitoring network

review

. Commenter (0097) stated noted that t he information more closely resembles the

informatio n included in the 5 year monitoring assessment report

. Commenter (0097) stated

m onitors used for NAAQS compliance should meet requirements of the SLAMS network.

Response:

The EPA recognizes that network design for characterizing air quality around indiv idual S O 2

sources may involve case

- specific considerations . Therefore , making a hard and fast set of highly detailed rules or guidelines that are nationally applicable is i nfeasible. The EPA created

the non

- binding monitoring and modeling Technical Assist ance Documents to provide states with information that might help any effort they undertake to characterize air quality around an

SO 2 source. As discussed in section IV.D of the preamble to the final rule, the relative location

and number of monitors that might be sufficient to characterize the air quality around a source is

a case

- by

- case determination . In general, the main objective is to monitor at

, or as near as possible to

, the location(s) where ambient SO 2 concentration maxima are expected to occur. S ite selection for any monitoring network is subject to logistical hurdles including site access, identification or installation of appropriate infrastructure, telecommunications access, and safety, and state, local, and tribal air agencies are well versed in the variety of logistics that can beDELIBERATIVE

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148 involved in the installation of an ambient air monitoring station.

These issues undoubtedly can play into what any ambient air monitoring network ultimately looks like. However, as is the case with all required amb ient air monitoring, responsible air agencies are expected to establish a clear rationale for the number and placement of any one or more monitors it is using to satisfy the requirements of th e rule. In this process, there is flexibility for the state to u se professional judgment in determining what is appropriate for their

individual situations , but they are expected to perform due diligence in attempting to locate monitors in the most ideal locations possible

. Further, th e air agency’s recommended number of

monitors and preliminary rationale should be discussed with the EPA Regional Offices well in advance of the development of an Annual Monitoring Network Plan. As discussed in the

m onitoring TAD, t he development of a network design and its rationale can b e informed by a number of types of analyses which can include the use of air quality modeling, exploratory monitoring, or analysis of existing data. In any scenario, the state would need to have a technically credible rationale that supports the monitoring network design approach that has been chosen to satisfy requirements in this rulemaking.

Commenters both for and against the use of exploratory monitoring make good observations about the advantages and disadvantages, respectively, of this means of infor ming network design. This technique remains an option for informing the design of monitoring networks being established to meet the requirements of this rule. However, given the need to implement the SO 2 standard as expeditiously as practicable, and given the resulting need for air agencies to submit network plans by July 1, 2016, in most cases the EPA anticipates that air agencies will not have time to implement this approach by the deadline that this rule necessarily imposes.

If changes at a facility res ult in changes in the area of maximum concentrations, the EPA cannot ignore this. While this final rule is not establishing requirements regarding how areas will be designated in the future, or how areas that are designated nonattainment and seek clean dat a determinations or re

- designation shall be treated, we note as a general matter that w hen evaluating whether an area is attaining the standard, the EPA appropriately consider s whether the entire area is attaining, not just whether the location that previo usly had the maximum concentration is attaining , particular l y if information suggests that location has changed

.



### b. G uidance is needed

— number of monitors

Comment :

Commenters (0036, 0046

, and 0106 ) stated that clear guidance is needed on the number of

moni tors required. Commenter (0036) stated that, in the m onitoring TAD, the EPA does not provide clear guidance on the number of monitors required for a facility, and leaves such discretion to the EPA Regional Administrator

. Commenter (0051) stated t his issue should not be left up to negotiations with the Regional Office , rather, a procedure should be outlined that will provide consistency for all regional offices and states. Commenter (0036) stated that it is difficult for states to design or budget for a netw ork with open

- ended siting requirements and stated thatDELIBERATIVE

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149 the EPA should provide more guidance on the number of monitoring locations it considers reasonable under various terrain scenarios, and should allow states to make such determinations

on a case

- by

- cas e basis.

Commenter (0046) stated the EPA should give states guidance on whether modeling could be used to site a single monitor that would represent the maximum impact from a particular source or group of sources. Commenter ( 0046 ) stated that the EPA also should reflect on the full range of conservatism built into the emissions, future emissions, dispersion, terrain, monitoring predictive pathway to actual human exposure and risk in assessing how many monitors actually should be required. Commenter (0051) stated the EPA should provide clear guidance with examples of the determination of the number of monitors to be sited for each source.

Response:

As discussed in section IV.D of the preamble to the final rule, the relative location and number

of monitors that might be sufficient to characterize the air quality around a source is a case

- by

case determination. There are many factors that can impact monitor network design, but in general, the main objective is to monitor at, or as near as possible to, the lo cation(s) where

ambient SO 2 concentration maxima are expected to occur. The EPA cannot specify a certain number of monitors that will be universally appropriate across all situations that will be encountered by states using monitoring to satisfy this rule. The key is that states provide a clear rationale (which can reflect some or all of the factors listed by commenter 0046) on the number and placement of any monitor(s) used to satisfy this rulemaking. This is the case whether a state uses modeling, explora tory monitoring, or existing data to support their network design choices.



### c. One monitor could be sufficient

Comment :

Commenters ( 0046

, 0049, 0051, 0088

, and 0110 ) suggested that one monitor may be sufficient. Commenter ( 0046 ) stated that, a bsent histo rical adverse exposure history in the community, one

monitor should be the default. Commenter (0088) stated that the final data rule should include a discussion of the adequacy of one monitor in certain situations. Commenter (0051) stated that

, based on pr ecedent from implementation of the lead NAAQS, one monitor could be sufficient to

obtain reasonable worst

- case highest concentrations near a source or a concentrated group of

sources.

Commenter (0051) stated, f rom an air quality management perspective, t he SO 2 standard can be

considered a "source

- oriented" NAAQS rather than a "regional" one (i.e., more similar to the lead NAAQS than to the ozone NAAQS) ; t hus, the lead monitoring requirements for a single,

maximum

- concentration monitor sited "taking into a ccount the logistics and potential for population exposure" are also appropriate criteria for SO 2

. Commenter (0051) provided the following additional points.DELIBERATIVE

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150 The lead NAAQS rule requires at least one maximum

- concentration, source

- oriented

ambient air qual ity monitor for each source or cluster of sources with actual annual emissions equal to or larger than 0.5

- 1.0 tpy , depending on source type. In practice, this monitoring requirement has resulted in one appropriately placed, maximum concentration, source

- oriented monitor for sources without ambient monitoring data or other history suggesting that nonattainment exists. If the EPA expects this to be the practice for SO 2 , then it should state that a single monitor will be sufficient, unless evidence is prese nted otherwise.

Commenter (0110) stated that, because l arge gradients in design concentrations for SO 2 are likely not present to the extent that the EPA may expect, the use of a single monitor to demonstrate NAAQS attainment is sufficient in many cases. C ommenter (0110) provided the following additional points.

EPA initially proposed modeling instead of monitoring because they envisioned large concentration gradients due to isolated sources of SO 2 , which might require deployment of many monitors. However, comparisons of the patterns of modeled and monitored design concentrations indicate that models tend to exaggerate spatial gradients. This is due, in part, to AERMOD’s over

- sensitivity to terrain variations. Thus, applying models may be misleading in term s of the number of monitors required. Large gradients could exist during any given hour, but over the course of multiple years of monitoring, the pattern of design concentrations is likely to be more uniform.

An example of model overestimation of the con centration gradient due to model sensitivity to terrain impacts has been reported by AECOM in the North D akota low wind speed evaluation. In that evaluation, the design concentration measured at 5 monitors

within 10 km of the two central emission sources w ere within about 5% of the average value. However, at one monitor with an elevation about 80 m above stack base (other monitors were in relatively flat terrain) ; AERMOD in default mode indicated nearly a factor of two increase in the predicted design conc entration. The use of appropriate beta options in AERMOD reduced the variability somewhat compared to observations, but still overstated the variability relative to the monitored concentrations. In the North Dakota case, one monitor would have been suffici ent to determine compliance with the NAAQS because the change in the design concentration among the monitors is well

within the +/

- 10% allowed uncertainty in biases for SO 2 analyzers.

Response:

As discussed in section IV.D of the preamble to the final r ule, the relative location and number of monitors that might be sufficient to characterize the air quality around a source is a case

- by

case determination

. There are many factors that can impact monitor network design, but i n general, the main objective is to monitor at

, or as near as possible to

, the location(s) where

ambient SO 2 concentration maxima are expected to occur. The EPA cannot specify a certain number of monitors that will be universally appropriate across all situations that will beDELIBERATIVE

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151 encountered by states using monitoring to satisfy this rule. The key is that states provide a clear rationale on the number and placement of any monitor(s) used to satisfy this rulemaking.

Contrary to one set of comments, the EPA continues to believe that substanti al gradients in SO 2 concentrations exist. The EPA continues to believe that evidence from AERMOD properly

indicates that substantial gradients in peak SO 2 concentrations are commonplace.



### d. E valuate the exist ing monitoring network

Comment :

Commenters (00 75, 0116) stated it is important that the EPA recognize air agencies may demonstrate that the existing monitoring network suffices to evaluate the air quality status of particular areas, such that monitoring data available by January 2017 are sufficient to justify designating the areas as attainment. Commenter (0109) stated that where existing monitoring networks include maximum concentration monitors focused on characterizing impacts from nearby large S O 2 sources, no additional monitors should be imposed b y the EPA through the

DRR

. Commenter (0051) stated the existing monitoring network is adequate for making certain

attainment designations.

Commenter (0070) stated that, while additional monitors may be needed, (1) data from the existing network should be fully evaluated prior to the deployment of additional monitors; (2) the knowledge gained from this evaluation should then be applied to the determination of where additional monitoring may be needed; and (3) the impacts of regulations such as various Boil er MACT Rules, CSAPR, Visibility Rules, etc. should also be consid ered in the deployment of these additional monitors, due to the changes in emission profiles and facility operations that

these rules will cause. When determining whether additional monitors are necessary, commenter (0109) stated public cost and public benefit analysis is fundamental to proper decision making.

Commenters (0055, 0074) request ed that the EPA clarify whether an ambient monitor in a

nonattainment area could be used as the defin ing monitor to designate areas outside of that

nonattainment area as well and described the following case

.

T he data in Yellowstone County, Montana is germane to this question. The sole (SLAMS) monitor inside the partial

- county nonattainment area has alre ady demonstrated compliance (since 2010), and is fully expected to demonstrate compliance with the SO 2 ambient standard through 2020 and beyond. There is substantial historical evidence that

this monitor is source

- oriented and has been sited at the worst

- c ase (i.e. area of maximum concentration) location for the entire County (both inside and outside of the present nonattainment boundary). That being the case, the monitor meets the monitoring requirements of this Proposed Rule including for areas outside th e non

- attainment area. Because the monitor serves the dual purpose of on

- going surveillance for nonattainment

related requirements as well as providing readings for the area of maximum concentration for the entire county, including areas outside of the non attainment area, we request thatDELIBERATIVE

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152 the EPA clarify that such a monitor could serve both purposes. Similarly, if a monitor inside a previously designated nonattainment area successfully “...produces a design value of no greater than fifty percent of the 1

- hour SO 2 NAAQS...” should it not also become eligible for shutdown unless it is serving some other SIP related purpose? (0055, 0074)

Response:

The EPA agrees that while most areas appear to have insufficient monitoring to indicate maximum concentrations, some a reas may already have sufficient networks for characterizing air quality for purposes of this rule

. However, the EPA is not in this final rulemaking determining whether any specific network is sufficient for purposes of this rule, including the single moni tor In Yellowstone County, Montana that the commenter discussed. Such evaluations must be made

on a case by case bas is

.

In the abstract, it appears likely that if a monitor previously measured nonattainment, and a source was not judged to be contributing to a previous violation at that monitor (i.e., the source was not included in the designated nonattainment area)

, then the monitor would not be assumed

to be at an appropriate location to determine whether concentrations to which the source does

contribut e would exceed the standard. However, this judgment must be made on a case

- by

- case basis after evaluation of the specific source’s emissions, area receptors, monitor, and related

factors

. Criteria for shutdown of monitors in nonattainment areas are gover ned by existing provisions of 40 CFR 58 and are not addressed by the provisions of this rule relating to new monitors for purposes of this rule.



### e. M ultiple monitors per source are needed

Comment :

Commenter (0068) stated that a single monitor is unable to assess air quality impacts from a

source

. Commenter (0068) stated modeling will demonstrate multiple areas with high predicted impacts from the source, and those locations will likely shift from year to year due to

fluctuations in winds a nd weather and em issions. Commenter (0068) concluded that multiple monitors per source would have to be employed before monitoring could even begin to approach

the robust assessment of ambient concentrations aerial dispersion modeling can accomplish.

Commenter (0068) stat ed th at if a state is unable or unwilling to site multiple monitors based on the use of modeling, the monitoring pathway contemplated in the draft Rule should not be

available to it.

Response:

Please see response above listed under “ one monitor could be sufficient.” The EPA would agree that the advantage of monitoring i s providing reliable results for the particular location(s) that are being monitored ; however there is merit to the idea that modeling can also provid e betterDELIBERATIVE

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153 characterization of the sp atial variability of concentrations. We are not adopting the commenter’s suggestion that the final rule make the monitoring option unavailable based on a judgement about an air agency’s inability or unwillingness to site multiple monitors

. The technical

ev aluation of the appropriateness of single or multiple monitors for specific sites cannot be prejudged in this final rulemaking.



### f. Flexibility for s tates

Comment :

Commenters (0050, 00 52a , 0106) urged the EPA to provide flexibility to s tates for the siting of

monitors. Commenter (00 52a ) suggested that s tates should have flexibility to (1) determine the

location of source

- oriented monitors , (2) determine the appropriate number of monitors surrounding a given source , (3) use their discretion to use modeling, wind rose information, and

other tools to help with properly siting the monitors , and (4) relocate existing monitors to other

sites. Commenter (0106) stated that, i n rural areas that are sparsely populated or in rugged terrain, the lack of electricity and accessibility can severely limit the number of possible monitoring sites.

Commenter (0050) stated that g iven the high cost of moving and installing monitors, the EPA

should ease restrictions on monitor requirements so as to facilitate the use of monitors and allow

states to take a cost

- effective approach to monitoring. For instance, commenter (0050) support ed the possibility of utilizing third party S O 2 monitors in areas where the monitors are already installed, thus making it easier and more financially reasonable for sources to monitor S O 2 emissions. Commenter (0050) believe d states should also be permitted to experiment with exploratory monitoring, including the use of mobile and passive monitors and the long

- term benefits of these approaches are likely to include an increased number and effectiveness of data

monitors. Commenter (0050) stated the EPA should also reconsider general requirements for the long

- term operation and maintenance of certain monitoring networks.

Response:

The is some flexibilit y for monitor siting, so long as the monitoring network achieves the purpose of characterizing location(s) where maximum ambient concentrations are likely to occur

. The EPA has created a source

- oriented SO 2 monitoring technical assistance document that

pr ovides suggestions on how an air agency might go about designing a network to characterize peak SO 2 concentrations around sources such as is required in the DRR.

Some of these commenters are suggesting that the EPA should account for the difficulty of sit ing monitors in some areas by easing the restrictions on monitoring requirements in those areas. These comments in effect acknowledge that feasible monitoring sites in such areas are less able

to characterize maximum concentrations in the area. This raises the issue that that there can be

areas that might be more appropriately addressed by modeling. Thus, this comment does not support relaxation of monitoring requirements but instead suggests that air agencies might baseDELIBERATIVE

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154 their selection of air quality chara cterization on careful consideration of the relative merits of monitoring and modeling in the context of how effectively the particular monitoring sites that are

feasible in the area would characterize maximum concentrations in the area. The EPA supports

t he use of third party monitors, so long as quality assurance and network adequacy criteria are met. As noted above, the EPA generally supports the use of exploratory monitoring as one of multiple approaches air agencies can take to determine where permanen t monitoring sites might be placed, but notes that states have a limited time in which they might conduct exploratory monitoring, given the expeditious implementation timeline of this rule.



### 4. Delayed monitoring

-- a utomatically move a source to the modeling

pa thway

a. Support automatically moving a source

Comment :

Commenter (0068) stated that the modeling pathway offers a swifter, cheaper, and more accurate way of assessing air quality, and so did not believe that states that miss deadlines along the

monitorin g pathway should be allowed to further delay designations. Commenter (0068) stated

that t he monitoring pathway already results in designations occurring fully a decade after the NAAQS was promulgated, and eight years after the EPA was originally required t o issue area designations for the entire country; the monitoring pathway thus should be regarded as an absolute edge

- of

- the

- envelope approach. Commenter (0068) stated that f ailure to meet deadlines therein should result in areas being treated under the mod eling pathway as a default. Commenter (0068) stated that s etting such a policy clearly in any final DRR would properly incentivize

actors to transmit information to the EPA in a timely manner.

Response:

The EPA has provided flexibility to states to choo se whichever means they think most prudent to characterize air quality around an SO 2 source identified through this rulemaking by using modeling or monitoring. This concept was supported by many stakeholders. Although EPA did not propose to establish desi gnations schedules in this rule, the discussion of delays caused by missed monitor deadlines may have been interpreted as establishing a designations schedule (rather than a data requirement) for source area s that miss their monitoring deadlines. As

discu ssed in section IV.D.3 of the preamble to the final rule, in cases where an air agency chooses to characterize air quality with new monitors but fails to have the new monitors operational by the January 1, 2017

, deadline , the CD governing EPA’s completion of designations requires EPA to designat e such areas no later than December 31, 2017

. However,

t he EPA did not propose or promulgate such a schedule in this rule

.

Regarding the need for additional data requirements to apply when monitoring deadlines are missed, for reasons explained in the preamble, the final rule still requires such areas to undertake and complete the monitoring that the air agency originally chose to conduct , rather than switch toDELIBERATIVE

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155 modeling data requirements . However, given the advanced designation deadline under the CD for areas in which monitors are not timely installed and operated, air agencies may wish to seriously consider alternative means of timely developing and providing to the EPA information (including modeling information) to inform designations of such areas.



### b. Do not support automatically moving a source

Comment :

Commenters ( 0038, 0041, 0043, 0046

, 0050, 0051, 0053, 0054, 0056, 0058, 0060, 0064, 0069, 0070, 0071, 0072, 0075, 0081, 0085, 0 0088 , 0092 , 0093

, 0116, and 0118 ) d id not agree that a source should be automatically moved to the modeling pathway in the event of any delay in monitoring

. Commenter (0050) stated that r ather than implement this rigid approach, the EPA

should examine each situation on a case

- by

- case basis to determine whether special circumstances excuse a state from being delayed in installing its monitors, as well as the projected amount of time that it will take for such monitors to become operational. This type of flexibility, while causing slight dela ys in implementation of the rule, commenter (0050) believed

will lead to more effective strategies throughout each state, increasing the likelihood of more accurate characterizations by the states of their ambient air quality.

Challenges in monitor deploy ment

Commenter ( 0051 ) stated the penalty for unanticipated monitoring site delays or data collection hiccups is excessive and noted that d eployment of a ir monitoring sites for sources in rural areas provides many challenges not faced in urban areas
, inclu d ing proximity to electricity, prohibitive terrain, property owner agreement, and accessibility. Commenter (0093) stated t here are too many uncertainties, such as shortage of consultants or available monitors, which argue against

such automatic actions

.

C ommenters (0071, 0092) stated that the proposal does not take into consideration any of the underlying reasons why monitoring was originally selected, such as those sources that cannot be characterized through dispersion modeling because of model limitatio ns, complex terrain, complex meteorology or multiple sources with overlapping plumes. Commenter (0092) stated

that m andatory modeling in source areas of this type is neither appropriate nor would it provide

the EPA with credible information for purposes of making the NAAQS designation.

EPA delay

Commenters (0038, 0075, and 0108) stated that the EPA should make it clear that any EPA delay on approval of monitoring plans will not contribute to a state or local agency requiring modeling

where monitoring had been selected as the state's preferred SO 2 approach. [See IV.D.2 . regarding EPA oversight of monitoring ]

Good faith effortDELIBERATIVE

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156 Commenter s ( 0063, 0065, 0075 , 0087 , 0088 , 0092 , 0116 ) stated the EPA should not categorically declare that it will move an area to the “modeling pathway” if, despite an air agency’s best efforts and for reasons beyond that agency’s control, op eration of a monitor is delayed beyond the January 1, 2017 proposed deadline

. Commenter (0088) stated that, n ot only

is the EPA ’s schedule exce edingly aggressive but importantly, there may be valid reasons that all monitors that have been installed are not operational by January 1, 2017. Commenter (0088)

stated that t here are dozens of reasons that a monitor may not be operating properly which ca n be

fixed.

Commenter (0088) stated that u surping the s tate and private resources and other efforts to install and operate monitors because a few are not operational is not reasonable. Commenter (0088)

stated the EPA should not ignore or attempt to deter commitments for significant investments for obtaining ambient air quality data so arbitrarily.

Unclassifiable

Commenters (0064, 0075, 0087

, and 0116 ) suggested the area should be labeled unclassifiable until monitor startup is completed. Commenter (006 4) stated that an unintentional delay in monitor startup should be viewed by the EPA in the same way it would likely view delayed startup of any other pollutant monitor, i.e., the area should be labeled unclassifiable until monitor startup is completed.

Response:

This issue is discussed in section IV.D.3, where we clarified that a failure to monitor by the January 1, 2017 due date does not force a state (or the EPA) to conduct modeling nor does it relieve the state from conducting monitoring. The EPA ’s i ntent in its notice of proposed rulemaking was to explain that in these circumstances, where an air agency chooses to characterize air quality with new monitors but failed to have the new monitors operational by the January 1, 2017

, deadline , the EPA envis ioned designating such areas in conjunction with areas being characterized by modeling (although we did not propose or promulgate a designation timing requirement) . That is, the EPA did not envision delaying the designation for such areas to

the envisioned 2020 date when the Agency anticipates promulgating designations for areas characterizing air quality through a new monitoring network

. The EPA must now comply with a court ordered designation schedule, in which the court expressly requires that areas that have not begun operation of a new monitoring network by January 1, 2017, must be designated by the end

of December 2017. The EPA is not able in this final rule to change that court

- ordered schedule. While the final rule does not require air agencies in ca ses of late installation and operation of monitors to actually shift to conducting modeling for such areas, we note that air agencies in those circumstances may wish to timely develop and provide to the EPA alternative information (including modeling infor mation) to inform the designations required for them under the

advanced deadline.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

157 

### 5. D elayed monitoring

-- evaluate

Comment :

Commenters (0041, 0043, 0046 , 0051, 0053, 0054, 0056, 0058, 0060, 0069, 0070, 0072, 0075, 0081, 0085, and 0088) did not agree that a source should be automatically moved to the modeling pathway in the event of any delay in monitoring where an agency is acting in good

faith and suggested several alternative approaches. Commenter (0054) stated that g iven monitoring’s superior value in ref lecting the real

- world situation, discretion should be exercised in allowing monitoring data to be utilized even if the timing of its initiation does not comport to

strict deadlines.



### a. Allow a time extension

Comment

Commenter s ( 0041, 0054 , 0070, 0072, 0 081, 0085, 0088, 0093, and 0097 ) recommended the

EPA allow time extension s as noted below

.

 Commenters (0041, 0093) stated t hese issues should be evaluated on a case

- by

- case basis and if due diligence can be shown, short extensions to the monitoring deadl ine should be granted.

 Commenter ( 0056 ) recommend ed that e xisting monitoring networks which demonstrate compliance with the SO 2 NAAQS, but may need some adjustments to be approvable by

the EPA should be afforded time to make the necessary changes and sho uld not trigger a requirement to use modeling for making a designation.

 Commenter (0070) recommended six month grace periods and stated these would fit into the EPA schedule without serving to delay the designation process and would also allow

the use of the significant resources expended in establishing a monitoring network to not be wasted by an issue at a single site. Commenter (0070) provided the following additional points.

A s long as the delay is not beyond June 30, 2017, the EPA should explicitly allow special handling of the situation. F or this special handling

, a like period of time in 2020 would be substituted into the calculation of the 3 year design value with the annual periods adjusted to the an alternative year (i.e. March 1, 2017 through February 29, 2020) that would be broken into three 12 month periods. Each 12 month period would contain a full year of data (assuming that data quality was achieved) and a three year average could be determined. Offering this only for the period through Ju ne 30, 2017 would allow the extra data from 2020 to be properly quality assured and the data from th e offset years to be processed.DELIBERATIVE

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158  Commenter ( 0072 ) stated that, i n those cases where a monitor has been sited but not yet operational by January 1, 2017, the Regional Administrator should have the option to allow for an extension before moving the source to the modeling pathway

, if the placement of moni tors beyond the January 1, 2017 deadline is done in a timely manner.

 Commenter (0081) suggested that the EPA should consider allowing as much as two years delay in monitor start

- up. Commenter (0081) stated t he timeline goals proposed by this rule would still be met in this case, because the EPA could designate the area as

“unclassifiable” should the monitor show no violations in the single year of operation before the final round of designations, or could designate as “nonattainment” should the monitor be showing a violation. Commenter (0081) stated t his is consistent with how the EPA has handled these types of s ituations in the past (e.g., the Greenville, SC PM 2.5 , “unclassifiable” designation) and would avoid the wasted resources caused when an agency has already purchased monitoring equipment and buildings and then has to abandon those resources to pursue an un anticipated modeling exercise.

 Commenter (0085) su ggested a set of two 1

- year extensions for the case where an air agency, or a source/third party that is installing a monitor that the air agency will be quality assuring, while acting in good faith experi ences a delay outside of its control ;

s pecifically, the air agency or source could apply up to two times to the EPA for an extension of one year to have the monitor operational.

 Commenter (0097) stated the EPA could adopt an extension approach, similar to that

included for ozone under s ection 172(a)(2)(C). If one full year of SO 2 monitoring data were obtained, and this data showed no exceedance (i.e. the 99th percentile of the data was not above 75 ppb), then the EPA could offer two years of extensions bef ore making the designation determination, contingent on each year's data recording values less than 75 ppb for the 99th percentile each year. Such an approach would allow states more time to upgrade their monitoring networks for this effort.



### b. Data gaps

[Also see IV.I.]

Comment

Commenters (0038, 0043, 0054, 0060, 0088, 0092, and 0097) recommended the EPA allow the use of mechanisms to replace missing data.

Commenter (0043) stated that, where an agency is acting in good faith to deploy monitors on time, but experiences a delay outside of its control, the EPA should consider the data set complete if there is valid and complete data from all four calendar quarters even if they are before 2017 or after 2019. Commenter (0043) stated that collecting data for three consecutive years, at multiple sites, without data loss from equipment malfunction or other failure is aDELIBERATIVE

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159 daunting task. Commenter (0043) stated that allowing the substitution of data from before or after the test period would provide data for a quart er lost without losing data during that quarter or season of the year and stated that, since this concept is acceptable for an air quality

demonstration for PSD application process, it should be acceptable for a NAAQS attainment

determination.

Commenter ( 0060) suggested basing the recommendations for nonattainment for those

monitored areas on less than three years of data o r making recommendation s based upon 36

- months of data rather than three calendar years. Commenter (0060) stated it is likely only weeks

to a couple months in most cases when deployment is delayed. Commenter (0060) noted the

EPA 's lead monitoring rule provides for an alternative to three calendar years of data for determining design values for monitors that are newly deployed.

Commenter s (0054 , 0088, and 0092 ) stated that a utomatically moving a source from monitoring to modeling should not be considered until after it has been demonstrated that the monitoring

data are incomplete, including the inability of the state to substitute data

. Co mmenter (0054)

noted that the EPA ’s own TAD guidance as referenced in f ootnote 40 of the Proposed Rule states that monitoring intervals are considered complete when at least 75% of the sampling days have complete data. Commenter s (0088 , 0092 ) suggested the re are a number of data conventions that

the EPA regulations employ to replace missing data when a continuous operating monitor or parametric monitor are not operational. Commenters (0054, 0092) stated the EPA has established and codified procedures in App endix T to p art 50 that make provisions for incomplete data sets and has established procedures for substituting data.

Commenter (0038) stated that, i f a state could not have its monitors operational by the 2017 deadline, an alternative is to use modelin g to estimate values for the period of missing monitoring data in order to create a full data period for design value calculation purposes.

Commenter (0097) stated the EPA should allow data to be used for provisional attainment designations , if that data show potential compliance on a yearly basis from January 1 to

December 31 by 2019.

Designate attainment or unclassifiable

Commenter s (0069 , 0075, and 0088 ) stated it would be more appropriate to designate such areas

as "unclassifiable

. " Commenter (0069) suggested revis ing the designation using complete 2018

to 2020 data , which would be available within months after the EPA 's planned 2020 designations, resulting in a relatively short delay in designations. Commenter (0088) suggested

that if there have bee n one

- two violations and the state has shown good faith, it would appear that it would be appropriate to designate the area unclassifiable, and defer the designation of a full three year’s data either to when a consecutive 36 months of data are collected o r until the

next year.DELIBERATIVE

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160 Commenter (0088) suggested the EPA could consider designating such areas as attainment if

there are no violations of the one hour SO 2 NAAQS in the data that has been collected, provided over two years of data has been collected and submitted.

M odeling as a backstop

Commenter ( 0041 ) stated that, a s a backstop to any source that pursues the monitoring approach, states may perform and submit necessary modeling for all affected sources regardless of whether the source chooses to purs ue the monitoring route or modeling route. Commenter ( 0041 ) stated

that t his would keep the SIP process within states' oversight and not require the EPA direct involvement as proposed here in the event of a failure to monitor.

Revise the schedule

Commen ter s ( 0051, 0088) stated that the EPA should provide a more reasonable period for implementation that would obviate this issue. Commenter (0051) stated a more flexible timeline, with phased implementation, would make the monitoring pathway a more feasible option for states while minimizing wasted resources.

Commenter (0103) suggested the monitoring and modeling deadlines be the same and stated that implementing a single designation timeline eliminat es discontinuities in schedules if a planned

monitor is no t operational by Jan 1, 2017, as such locations could simply convert to the modeling pathway.

State discretion

Commenter (0058, 0088, 0092, and 0118) suggested that t he EPA should allow the judici ous application of agency discretion

. Commenter ( 0058 ) sta ted that, if a state is making a good

- faith effort to install monitors but encounters unforeseen delay beyond the state’s reasonable control, at most, the DRR should request that states provide reasonable justification to the Agency for such delays. Commen ter (0088) suggested the option of conditionally approving the monitoring. Commenter (0092) suggested this approach would not lead to wasted agency resources and costly equipment purchases. Commenter (0118) recommend ed the use of a weight of evidence

appro ach on a case by case basis in these situations. Commenter (0088) suggest ed s tates should be allowed to discuss with EPA Regions why some monitors are not operational and in conjunction with a policy for waiving a full three years data

, provided a valid ex planation is offered (or utilizing accepted data conventions for substituting data), the EPA should not ignore or attempt to deter commitments for significant investments for obtaining ambient air quality data so arbitrarily.

State rulemaking

Commenter ( 0056 ) recommend ed that the EPA should not force the use of modeling if a s tate

agenc y elect s to initiate a rulemaking to require sources to install, operate and maintain ambientDELIBERATIVE

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161 SO 2 monitoring systems for SO 2 NAAQS implementation , since s uch a rulemaking would take time to initiate and complete, leaving less time fo r monitor deployment.

Response:

Please see response above to “Do not support automatically moving a source

, ” in response to the comments addressing whether areas for which monitoring is not timely installed and operated

should thereafter be required to conduct modeling under the rule. The final rule imposes no such requirements, but instead continues to require the air agency to complete the monitoring it originally opted to conduct. In respo nse to the comments addressing how designations should be conducted in such cases, this final rule is not adopting requirements governing designations, which instead are now governed by the CD containing the binding schedule under which EPA is to complete designations . That court order requires areas for which monitors are not timely installed and operated to be designated no later than the end of December 2017. In such cases, air agencies may wish to seriously consider timely development and submission to EPA of

alternative information to inform designations required under that advanced deadline. Nevertheless, the rule’s monitoring requirements would still apply, and the data from that monitoring, while no longer timely for 2017 designations, would remain useful for other

purposes.



### 6. Resources

a. Costs

Comment :

Commenters (0034, 0038, 0051, 0071 , 0103, and 0108 ) expressed concern about the costs associated with monitoring for the S O 2 NAAQS.

Commenter s (0034 , 0120 ) recommended that the EPA provide assurances to those Tribes having sources near to them that emit at least 1,000 tpy of SO 2 that they will receive the requisite resources for monitoring and modeling to characterize the air quality around such sources.

Commenter s (0034 , 0120 ) stated t his will go a l ong way in helping Tribes

--- sovereign nations with inherent rights ensured by the U.S. Constitution, treaties and legal precedent

--- address any health and environmental impacts to their communities caused by these sources.

Commenter (0051) stated Texa s does not have the resources to absorb this additional cost. Commenter (0051) stated t he cost to implement monitoring at a single site per source is approximately $85,000 for the initial deployment and an additional $45 ,000 annually and, if

under the EP A' s proposed Option 1, the TCEQ were to deploy a single new monitor at 31 sources based on 2012 emissions, this would cost approximately $2.6 million for initial deployment and $1.4 million annually.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

162 Commenter (0038) stated that, a ssuming EPA would accept just one monitor per source, and using the estimate provided in the Proposed Rule

, Wisconsin may face $1.3 million in start

- up costs alone, with no additional funding forthcoming from the EPA to offset this new expense. Commenter (0103) estimate d that f or the twelve affected facilities in Iowa, about $2.78 million would be required to purchase equipment and monitoring sites for three years to establish

attainment . Commenter (0108) estimated that the startup costs of a monitoring network in

Wisconsin could b e $1.3 million at a minimum.

Response:

The EPA recognizes the fact that there will be costs and resources required to satisfy the requirements of this rulemaking. The EPA provides grant funding for this general purpose. As suggested by both state and i ndustry stakeholders who attended the May

- June 2012 stakeholder meetings, in the absence of increased grant funding specifically for this rule, it may be necessary for air agencies to rebalance their existing grant funds for this purpose, or to consider al ternative funding approaches such as working closely with affected sources to assist in funding either the modeling or monitoring required to meet the requirements of the rule. Early planning may be helpful to address these funding needs.

Because the CAA assigns to states much of the responsibility for developing air quality characterization data, the EPA describes the requirements of this rule in a consistent manner: air agencies are the entities with principal responsibility to establish and operate mon itors, and conduct modeling, and to provide air quality data to the EPA. However, the EPA recognizes that other parties (such as facility owners) also may perform significant portions of the work that this rule requires. The EPA would consider monitoring o r modeling conducted by a third party to be an appropriate means for air agencies to obtain the data necessary to meet the requirements of this rule, provided that the state provides oversight to assure that (1) any monitoring is conducted

in a manner that is equivalent to SLAM S in accordance with applicable requirements, and (2) any modeling analysis that the state submits, even if it was initially provided to the state by a third party, is done in a n appropriate manner considering the recommendations in t he m odeling

TAD.

Similarly, the EPA cannot commit to provide Tribes with additional resources expressly for the purpose of satisfying the requirements of this rule, but the EPA will work with Tribes as appropriate to help assure that the requirements of t his rule are met

.



### b. Industry cost

s

Comment :

Commenter s (0034 , 0120 ) stated the cost to Tribes for obtaining the necessary monitoring and modeling resources should be borne wholly, or in part, by the sources emitting significant

amounts of SO 2 into the at mosphere, akin to the “polluter pays” principle. Commenter ( 0036 )

recommended that the EPA allow states the option to require facilities to fund either the costs ofDELIBERATIVE

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163 the monitoring (and modeling) or the cost to states for overseeing the facility

- conducted

m onitoring. Commenter ( 0036 ) provided the following additional points:

The EPA should recognize that it will require significant state resources to implement a facility

- supplied monitoring program. For example, the monitoring sites must somehow be integra ted into state agency network structures; the data must undergo quality assurance and quality control by the state, and be formatted and processed for input into various state and federal reporting systems such as the EPA ’s Air Quality System. States

must have the ability to charge fees to fully fund its oversight of the facility

- supplied monitoring, or the EPA should cond uct the oversight itself.

Commenter s (0041 , 0046

, and 0093) stated that

, b ecause of funding limitations, any monitoring

done would like ly need to be funded by the affected source. Commenter ( 0046 ) stated this rule will be yet another burden on the regulated community when facilities are already spending capital on emissions reductions projects required by other EPA air quality rules. Comm enter (0093) stated that the EPA seems to have drafted this proposal with the idea that s tates, rather than regulated sources, would perform the modeling and/or monitoring. Commenter (0093) stated that, due to resource constraints, t his is not the case in Alabama and in most s tates, and

request ed that the proposal be rewritten with this in mind.

Commenter (0070) pointed out that the recession has taken a toll on budgets and money that at one time may have been available for industry to spend on expanding t he monitoring network. One commenter (0109) stated that when determining whether additional monitors are necessary, the public cost and public benefit analysis is fundamental to proper decision making. Allocating monitoring costs to the local stationary s ource distorts that cost

- benefit analysis

, and will result in poor policy choices that increase the total cost of monitoring where not otherwise justified by the benefit derived from gathering the additional data.

Response:

Please see the response above listed under “Costs.” Regarding the concern of some industry commenters about industry covering costs for monitoring, the EPA notes that in some states it has been considered to be a reasonable practice for an industrial source to take responsibility for providing financial resources for the monitoring of pollutant emissions from that source into the

environment. In addition, the EPA points out that it is not customary, or legally required, that the agency conduct a “cost

- benefit” analysis when establishi ng requirements that state air agencies or pollution sources further characterize the impacts of emissions. Neither CAA sections 110, 114 or 301 impose such a requirement. Instead, for this rulemaking, the EPA has reasonably assessed the costs of the vario us proposed options and has selected a set of final requirements that can be feasibly implemented and will generate highly valuable emissions impact information that can be used in future NAAQS implementation actions.



## c. Funding by EPADELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

164 Comment :

Commenter s ( 0037, 0038 , 0062, 0103, and 0108 ) stated that the EPA should fund monitoring

activities t hat states determine are needed to comply with this rule . Commenters (0038, 0062,

and 0108) noted s tates have very limited resources to meet an ever

- growing burden o f federal

mandates. Commenter (0037) estimated the cost as between 1.2 and 3.7 million dollars in Iowa

and Wisconsin alone.

Commenters (0038, 0062) stated that, e ven if sources voluntarily set up and operate their own monitors, state and local agencies wi ll still need to dedicate resources to administer the program, provide technical assistance, conduct performance audits, ensure data quality, and submit the

data to the EPA 's A ir Q uality S ystem database each year. Commenters (0038, 00 52a

, 0108)

stated init ial funding should pass through a s ection 103 grant in order to establish the monitoring

sites . Commenters (0038, 0108) stated that ongoing funding should be provided through each

state's s ection 105 grant

. Commenter (0038) noted that s ection 105 funding i s diminishing, while federal requirements con tinue to mount

.

Response:

Please see the response above listed under “Costs.” Also, please see section IV.E.4 of the preamble

.



### d. Partnerships and third party monitoring

Comment :

Commenter (0039) supported t he EPA ’s proposal to accept monitoring data from monitoring networks that may be owned or operated by regulated entities instead of state

- run networks only.

Commenter (00 52a ) stated that, if the EPA chooses to advocate monitoring by the sources, states

s hould be given full oversight to validate that monitoring is carried out according to acceptable practices through establishment of a Quality Assurance Project Plan (QAPP). Commenter (00 52a ) stated that, alternatively, the EPA should provide a mechanism fo r funding to come to the states to support operation of the monitors as part of their own monitoring networks.

Commenters (0055, 0074) asked whether air agencies are required to directly operate the monitors or whether the monitors could be operated by a third party as long as the requirements listed in §51.1203(c) are met? Commenter (0074) asked that the EPA modify the text of the rule so that it clearly permits use of third party monitor data and describes under what specific

circumstances.

Commenter (0089) stated the EPA should specify more directly under what circumstances industry or third party monitoring infrastructure will be accepted and what requirements would apply. Commenter (0089) stated the proposal does not explicitly support the use of ex isting third party monitors, stating that such monitoring data may not meet the requirements of 40 CFR PartDELIBERATIVE

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165 58, yet the EPA also states that industry and third party monitoring infrastructure and operations could be leveraged to satisfy the requirements of the rule.

Commenter (0089) contended that the proposal lacks sufficient support for the use of data from existing monitors that are operated by third parties that could be used to verify modeled results and recommended that third party or industry monito rs should be allowed to verify modeling results and to provide the basis for correction factors to modeled results where appropriate. Commenter (0089) stated that existing third party monitoring stations are following PSD regulations and guidance in the ma nner they are operated and audited and, therefore, their measurements should be recognized as a critical tool to evaluate the reliability of modeled results, even if the monitors are not located precisely in the position of modeled maximum

concentrations.

Commenter (0089) stated the rule should make a more explicit accommodation for the use of existing, third party S O 2 monitors at sites needed to characterize S O 2 sources located in isolated areas across the western U.S., including portions of Nevada. Comm enter (0089) stated there are (1) s everal S O 2 sources in Nevada located in some of the most remote terrain in the lower 48 states, (2) no nearby population centers or physical infrastructure to support additional monitoring sites beyond the monitoring site s already located at the source and maintained by the operators of the industrial facility , and (3) no additional nearby locations where infrastructure could be used to support the collection of model input parameter data (meteorological data) to be

used i n the development of robust and defensible air dispersion models. Commenter (0089)

stated t he existing monitors in place at these sources are already sited in the only logistically

feasible locations to measure maximum concentrations, and are following PSD regulations and guidance in the manner they are operated and audited.

Response:

Third party monitoring is permitted to satisfy the requir e ments of this rulemaking. However, it is the state’s responsibility to ensure compliance and provide oversight. An y monitor used to satisfy this rule must be reflected in the state’s Annual Monitoring Network Plan, and meet requirements listed in 40 CFR p art 58 Appendices A, C, and E, along with pertinent data collection and reporting requirements under 58.15 and 58.1 6. These existing requirements which govern monitoring generally also govern monitoring under the DRR, and so EPA does not agree that there is a need to provide separate requirements specific to the DRR. As noted above, if logistical issues significantly r educe the feasibility of monitoring maximum concentrations in an area, this may warrant selection of modeling as a more appropriate approach for characterizing air quality.



### 7. Monitor shutdown s

a. Threshold below which monitors may be shut downDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

166 Comment :

Comme nters (0072, 0082 ) agreed that monitors placed pursuant to the S O 2 DRR and located in

area s that are designated as attainment in the anticipated third round of initial designations in

2020 should be eligible for shutdown in 2021.

Commenters (0039, 0041, 0045, 0046, 0048, 0049, 0050, 0053, 0054, 0056, 0058, 0060, 0062, 0064, 0070, 0075, 0080, 0081, 0082, 0087, 0088, 0090, 0092, 0093, 0096, 0106, 0107) supported the consideration of shutdown for any monitor that for a three

- year period has a design value of no more than 80 percent of the standard

.

Commenters (0041, 0053, 0054, 0056, 0058, 0075, 0082, 0092, 0093, 0096, 0106, and 0107)

stated that 80 percent of the NAAQS is a strong enough criteri a for the shutdown of a SO 2 monitor and th e 80 percent criteria is consistent with criteria for shutting down most regulatory

monitors.

Commenter (0092) a dvocate d the EPA ’s selection and promulgation of the 80% alternative proposal because it was indirectly derived from existing language in 40 CFR part 58.14(c)(1).

Commenter (0046) stated that monitors meeting the 80% criterion should be shut down and could be relocated to another area where modeling has shown there could be 1

- hour NAAQS violations occurring near sensitive populations. Commenter ( 0082) stated that providing state agencies with the flexibility to shut down unneeded monitors allows agencies to allocate their limited resources appropriately. Commenter (0070) stated that, if the sources are properly controlled and/or limited by permit, the risk of significant increases in design values over time is relatively low absent new sources entering the area. Commenter (0070) stated that, with a 20% margin on the monitor, this would allow the occasional upset at the facility to occur without

dis qualifying the area from having the ability to request reduced monitoring if air quality is acceptable on a continuing basis.

Commenter (0081) supported the 80% option and recommend ed that the wording be changed in this section so that it is less vague as to whether or not a monitor is eligible for shutdown

. Commenter (0081) recommend ed that the final rule state “Any SO 2 monitor...that produces a design value of no greater than fifty (or 80) percent of the 1

- hour SO 2 NAAQS, will (emphasis added) be eligible for shut down.”

Commenter (0096) recommend ed the EPA modify the language in §58.14(c)(1) if it wishes to change the requirements, rather than making indirect exemptions to that section in other parts of

the CFR . Commenter (0096) stated i t is uncl ear why a d eparture from the language of § 58.14(c)(1) would be necessary in the DRR since § 58.14(c)(1) presumably applies in the SO 2 monitor shutdown situations to which the DRR refers

. Commenter (0096) suggested it could be that “local air monitoring sta tions” do not include air monitoring stations which are local but not employed by a local agency (such as in the case of industry or third party monitoring).DELIBERATIVE

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167 Commenter (0096) stated there does not seem to be a reason to make the criteria more stringent

tha n the existing criteria in p art 58.

Commenters (0080, 0090) believed the 50% value was too conservative given the relative health

concerns of ambient lead and SO 2 concentrations. Commenters (0080, 0090) asserted that t he primary standard for S O 2 is over 5 0 times higher than the standard for lead on a gm/m 3 basis

, which supports a higher design value level for shutdown eligibility for SO 2 ; thus

, the same

rationale should apply to the cessation of modeling threshold in the DRR

.

Commenter (0068) stated that, because emissions can vary significantly from year

- to

- year, an 80% threshold is far too high.

Commenters (0036, 0039, 0043, 0062, 0115, and 0018) supported the consideration of shut down for any monitor that for a three

- year period has a design value of no more than 5 0 percent of the

standard . Commenter (0036) stated the 50% metric is very sensitive to the high end of one

- hour data distributions, in part because the form of the one

- hour SO 2 NAAQS is the 99th percentile (unlike the 98th percentiles for ot her daily NAAQS forms). Commenter (0043) support ed the use of the 50% threshold because the area would require a significant increase in sulfur dioxide

emission to cause an exceedance of the sulfur dioxide 1

- hour standard

.

Commenter (0062) supported the designation monitor removal 50% option because it allows states the ability to redirect limited monitoring resources to higher priority monitoring in the

event that the 1

- hour SO 2 NAAQS is met. Commenter (0062) recommend ed the following changes: (suggest ed text italicized)

Under section V, subsection A. Monitoring, “...Any SO 2 monitor identified in an approved state annual monitoring network plan to satisfy this proposed DRR will be eligible for shutdown in 2021 or later if the following

criteria are met: “...designated attainment in the anticipated third round of initial designations in

2020 will be eligible for shut down provided the monitor meets certain criteria.”

Commenters (0068) stated that, if a 50% threshold is used, any final DRR should make clear that the design value used is a fourth

- highest daily maximum concentration occurring in any of the previous three years, and not the average of such fourth

- highest daily maximum over the course of those three year; thus, three years’ worth of lo w concentrations would be a minimum prerequisite to removing a monitor.

Commenter (0118) stated that, r eviewing data from existing monitors that reach this level indicates that they generally either have shown many years of data at or below this level or can attribute it to the shutdown of nearby sources. Commenter (0118) stated that, i n either case, there does not appear to be any likelihood that values will go back up, due to permitting and compliance activities.DELIBERATIVE

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168 Commenter (0103) recommended that the th reshold of 50% for discontinuing monitoring in the Proposed Rule be dropped in the final rule since 40 CFR § 58.14 already contain provisions for shutting down a monitor. Commenter (0103) stated that t he origin of the 50% threshold is a rule

of thumb for u ncertainty in ambient modeling that has no bearing to ambient monitoring

uncertainties.

Commenter (0060) did not agree that the EPA can justif y a lower level of 50% as being

consistent with the provision allowing the EPA Regional Administrator to waive le ad NAAQS monitoring requirements. Commenter (0060) stated that s hut down of a lead monitor is still subject to 40 CFR 58.14(c)(1) and the 80% provision, just as all other NAAQS. Commenter (0060) provided the following additional points. Commenter (0060) st ated that, i f the EPA wishes to change that criteria, a revision to 40 CFR 58.14(c)(1) should be considered and made

available for comment. Commenter (0060) provided the following additional points.

Under the lead NAAQS, sources that emit over a certain threshold are required to monitor

unless the air agency can model and show their emissions result in no impact over 50% of the lead standard. This is a very different process and purpose than the shutdown of a monitor that has operated for three years and shown attainment. Under this rule, an air agency is electing to monitor in lieu of modeling and the results should require the same safety margin

for shutdown as all other NAAQS

. Ohio currently has 12 monitors attaining the standard that

would not meet the 50% criterion and six of those monitors would meet this criterion if it

was maintained at 80%. Given the experience we have seen with low monitoring results on many of the required lead monitor deployments that were placed based on threshold emis sion

level criteria, the EPA should not make it more difficult for an air agency to request

shutdown of a monitor that is not necessar y.

Commenters (0075, 0116) stated the requirement for annual reporting of changes in SO 2 emissions with the poss ibility that further monitoring could be required, argues against the more stringent criterion discussed in the Proposed Rule that the design value be less than 50 percent of

the standard.

Commenter (0085) suggested a value in the range of 65

- 70% of the N AAQS , in order to allow for monitors that have a design value that is notably below the NAAQS and of minimal risk to public health to be taken off

- line

, without having to achieve as stringent and potentially

unachievable a level as 50%.

Commenter (0052a) stated that for other criteria pollutants, the EPA allows monitors to be shut

down once the ambient concentrations are 85 percent of the standard and that t his is an appropriate level for discontinuing the operation of a source

- oriented S O 2 monitor. Commen ter (0113) stated that, a bsent appropriate justification, Montana suggests that the threshold for shutting down a monitor be consistent with the requirements for other NAAQS pollutants and

that the EPA has historically allowed discontinuation of monitoring efforts if the design value concentrations are below 85% of the NAAQS provided there are no associated nonattainment area control plan SIP requirements to monitor in place (40 C FR 58 Appendix D Table D

- 2, D

- 5 )

.DELIBERATIVE

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169 Commenter (0102) stated that, a s the S O 2 st andard has been lowered to a point where it is considerably closer to the background concentration, th e proposed range is too stringent of a threshold for removing monitors. Commenter (0102) suggest ed that if a monitor demonstrates a region is emitting wit hin the 80

- 85% range of the NAAQS threshold, this should be adequate to establish compliance with the standard.

Response:

The issue s of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the final rule.

Th e Agency took comment on an alternative option using calculated design values less than 80% of the NAAQS to qualify individual SO 2 monitors specifically operated to satisfy the DRR for potential shutdown. Many of the comments reflected confusion about the relationship between the 80% monitor shutdown criterion in 40 CFR 58.14 and the 50% criterion proposed here, apparently resulting from failure to consider the additional elements of the 80% criterion in 40 CFR 58.14 that are not part of the 50% criterion p roposed here. Much of the support for the 80% threshold commented that it was appropriate because of its derivation from existing use as part of

a broad er network modification language in 40 CFR p art 58.14. The Agency notes that in that language, the 80% t hreshold is not used in isolation, but as part of a probability analysis that requires the evaluation of data over at least 5 years and is intended to anticipate future NAAQS

violations. The Agency has decided, per the priority expressed in the proposal, and based on public comment, that the 80% threshold is too high (particularly in absence of an analysis of the probability of future NAAQS violations) and has decided to use the 50% threshold (without requirement for probability analysis) as was proposed. Due to the potential variance in emissions and meteorology that exists, the Agency has judged that a 50% threshold is more appropriate when using that singular metric to allow shutdown of a monitor satisfying the DRR. As was

noted in section IV.D.4 of the preamble to the final rule, requirements for shutdown, the 50% threshold provides relatively greater assurance that any monitor eligible for shutdown will be well below the NAAQS after 3 or 4 years of operation. The EPA also notes that the 80% option (avai lable after 5 years of data have been obtained) remains in place in 40 CFR 58.14, and the EPA is promulgating the 50% option, available after 3 or 4 years, in addition to the 80% option.

In response to the comment comparing SO 2 to lead, the Agency notes t hat the two pollutants are very different in terms of make

- up (gas versus mostly particulate, respectively), pollutant production, emi s sion, dispersion, and exposure risks and pathways (inhalation for SO 2 versus ingestion and inhalation for lead), and usin g the approach for one standard as a precedent for another is not appropriate.

The EPA agrees that with the comment that a monitor shutdown criterion based only on calculated design values being less than 80% of the NAAQS is too high, and the EPA has chosen a relatively lower threshold of 50%. The issues of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the final rule.DELIBERATIVE

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170 

### b. Multiple monitors

Comment :

Commenters (0060, 0081

, and 0107 ) stated th at this rule should include consideration of the case of multiple monitors around one source. Commenter (0060) stated t here needs to be a clear

method to shut down monitors that fall under this scenario and asked , f or example

, what if 2

- 3

m onitors are loca ted around a source and after three years of modeling it is determined that one of the monitors is consistently significantly lower than the other(s) ? Commenter (0081) stated that, i f the EPA wishes to pursue a shut d own criterion of 50 percent of the stand ard, they should consider allowing areas with multiple monitors a lower threshold for shutdown of redundant

monitors. Commenter (0081) stated, f or instance, areas with multiple monitors which are affected by similar sources, meteorology, and topog raphy should be allowed to remove the lower reading monitor(s) should the monitor(s) be below 80 percent of the standard ; s uch an option would be consistent with 40 CFR 58.14(c)(2) which allows for the removal of a monitor which has consistently measured l ower concentrations than another monitor for the same pollutant in the same county.

Commenter (0107) recommended that t he 50

- 80 percent criterion apply to each monitor individually rather than to the collective network, especially if set at 50 percent.

R esponse:

The EPA notes that the eligibility to seek approval to shut down a monitor applies on a monitor

by

- monitor basis. In a scenario where a monitor is part of a multi

- monitor array being used to satisfy the DRR, but is not eligible for shutdown by sh owing a design value below 50% of the NAAQS in the first 3 or 4 years of operation, it then becomes subject to the existing shutdown criterion of 40 CFR art 58.14. At that point, language in 58.14(c)(2), allows for potential

shutdown of monitors shown to b e lower than other monitors in the same area, subject to EPA Regional Administrator approval. The issue of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the final rule.



### c. Areas initially designated attain ment

Comment :

Commenter (0088) stated that t he criteria for shutting down or relocating a monitor in an area initially designated as attainment should be less stringent than the criteria for shutdown of a monitor in an area initially designated as nonattainment. Commenter (0088) stated that i f monitoring is used to characterize the air quality around a large SO 2 source and three years of monitoring data (2017

- 2019) shows no NAAQS violation, then the area will be designated as

attainment in 2020. Commenter (0088) suggested that, a t that time, the monitor should beDELIBERATIVE

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171 eligible to be shut down as there are no requirements to continue to characterize air quality in designated attainment areas.

Response:

The issue of monitor shutdown options and eligib ility are fully discussed in section IV.D.4 of the preamble to the final rule. Contrary to the suggestion of the commenter, in areas for which air agencies choose the monitoring option , and monitoring shows concentrations above the threshold promulgated in this rule, the rule requires continued monitoring without regard to whether the area has been designated nonattainment or attainment.



### d. Clean d

ata

Comment :

Commenter s (0038 , 0088 ) encourage d the EPA to allow for shutdown as long as the three

- y ear design value is below the NAAQS at any level. Commenter (0088) stated that the EPA should

amend p roposed s ection 51.1205(c) to provide that a monitor can be shut down at the discretion

of the s tate after a “clean data” determination to avoid unnecessar y costs of operation of a

monitor at certain stations in a s tate during the redesignation process

. Commenter (0038) stated

th at each state should be able to simply notify the EPA that the criteria have been met and that the monitor is being discontinued . C ommenter (0038) stated there should not be a second EPA approval process beyond certification of the data. Commenter (0038) stated a more restrictive approach is unnecessary, as the rule also proposes that states will have to continue to identify and

evalu ate any increases of SO 2 emissions each year in areas designated as attainment.

Commenter (0074) asked whether a monitor could be shut down if no violation s have occurred for many years and the requirements for monitoring arise solely from an area’s desi gnation status. Commenter (0074) stated the process of an area moving from nonattainment to attainment status moves at a glacial pace and it is inappropriate and wasteful of scarce resources to require continued monitoring of such areas based solely on the historical non

- attainment status, when there is no indication of ongoing violation under the present implementation plans.

Commenter (0070) stated that, if industry were to take on some of this monitoring, there must be an explicit sunset provision on th e length of time a monitor must be operated if there are no

exceedances of the 1

- hour SO 2 Standard monitored for several years.

Response:

The issue of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the f

inal rule. In EPA’s experience, the final rule’s approach to monitor shutdowns provides an adequate mechanism for removing unnecessary monitors, and we expect it will be

sufficient for monitoring that is conducted to meet the requirements of this rule . Ho wever, t he

EPA believes that monitor shutdowns should continue to involve EPA review, in order toDELIBERATIVE

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172 provide for national consistency. Further, 40 CFR p art 58.14 requires RA approval prior to the shutdown of a routine monitoring site.



### e. State discretion

Comm ent :

Commenter s ( 0063, 0065, and 0110) stated t he shutdown of a monitor should be left to the jud gment of the state. Commenter s ( 0063, 0065) stated the Proposed Rule should not supplant or limit the flexibility provided by the CAA for addressing NAAQS vio lations.

Response:

The EPA believes that monitor shutdowns should involve EPA review, in order to provide for national consistency . Further, 40 CFR p art 58.14 requires RA approval prior to the shutdown of a routine monitoring site.



### f. Monitors in u nc lassifiable/attainment areas

Comment :

Commenter s ( 0048, 0050, 0075 , 0087 , 0116 ) stated monitors located in

“unclassifiable/attainment” areas should also be considered candidates for shutdown

.

Response:

The EPA agrees and notes that under the final rul e, m onitors located in areas designated “unclassifiable/attainment” may be considered candidates for shutdown in accordance with 40

CFR 51.1205 and 40 CFR 58.14.



### g. Near a source that shuts down or reduces emissions

Comment :

Commenter s (0106 , 0107 ) recom mended that, because of the expense of operating monitoring sites, the DRR should specify when monitoring around a source may cease and noted that the criteria for shutdown of the monitoring site could be based on changes in emissions or changes in stack p arameters. Commenter (0107) suggested that, i n the event that monitoring is being conducted near a source that shuts down, the monitors be allowed to be shut down immediately. Commenter (0107) suggested that, i n the event that monitoring is being conducted near a source that achieves permanent emissions reductions such that it no longer meets the minimum emissions threshold, the monitoring shutdown criteria be followed.DELIBERATIVE

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173 Response:

The issue of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the final rule. However, in the case where an SO 2 facilit y shuts down, and there are no other sources in the area that contributed to having monitoring be required in the area, language in 58.14(c) does allow for a state to request for monitor discontinuation “...on a case

by

- case basis if discontinuance does not compromise data collection needed for implementation of a NAAQS and if the requirements of appendix D...” continue to be met.



### h. Statistical approach

Comment :

Commen ter (0071) suggested a statistical approach to evaluating a sit e’ s design value trend with

more emphasis on the variability monitored at the site rathe r than a more conservative low cut point design value threshold. This allows discontinuing sites that hav e demonstrated stable design values over time, showing little risk of exceeding the NAAQS, but keep sites that show a

greater risk of exceeding the NAAQS.

Response:

The issue of monitor shutdown options and eligibility are fully discussed in section IV.D .4 of the preamble to the final rule. The EPA believes that the final approach for allowing monitor shutdown allows immediate relief for those monitors well below the NAAQS (no greater than 50% of the NAAQS for the first three or four years of operation), and that there is also an adequate and established approach for shutting down monitors (via 40 CFR p art 58.14) that do not meet the initial shutdown criteria provided for monitors used specifically to satisfy this rulemaking.



### i. Do not shut down m onitor s

Comment :

Commenter (0068) stated new monitors should not be shut down. Commenter (0068) stated that temporary periods of low gas prices may cause coal combustion to decrease, and thereby lead to monitor readings consistent with short

- term but not long

- ter m attainment. Commenter (0068) stated, f or this reason and for the purpose of rebuilding a shattered SO 2 monitor network, states that choose the monitoring pathway under any DRR should be required to operate those new monitors as part of the monitoring net work going forward.

Commenter (0068) re commend ed that monitors not be removed if the concentrations they are recording are trending upward, as opposed to trending downward. Commenter (0068) stated d ata indicative of potential future problems, even if no c urrent problems are recorded, mitigates in favor of keeping the monitor in place to assess changes in air quality

.DELIBERATIVE

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174 Response:

The issue of monitor shutdown options and eligibility are fully discussed in section IV.D.4 of the preamble to the final rule. Th e Agency judges that in situations where monitored data indicate

SO 2 concentrations well below the NAAQS (50%) in the first 3 or 4 years of operation, it is

unnecessary to continue monitoring at that particular location. Beginning in year 5 of monitor

ope rations , the monitor is subject to existing shutdown criterion in 40 CFR p art 58.14. Ambient air quality monitoring is a resource intensive effort and the EPA believes continued monitoring to satisfy this rulemaking in locations well below the NAAQS is not warranted.



### j. Case

- by

- case monitor shutdowns

Comment :

Commenter (0062) support ed giving Regional Administrators the option of approving a threshold higher than 50%, not to exceed 80% , if states can justify it on a case

- by

- case basis. Commenter (0060) stat ed the EPA needs to provide for the flexibility currently allowed under

the same rule [ 40 CFR 58.14(c)( 1) ] for case

- by

- case decisions to be made. C ommenter (0116)

recommend ed that shutdown be considered on a case

- by

- case basis for any monitor

, con sistent with criteria for shutting down most regulatory monitors.

Response:

The Agency does not agree that a case

- by

- case approval threshold or alternative criteria for

monitor shutdowns is appropriate in this rulemaking. The criteri a are applied on an i ndividual monitoring basis, but t here needs to be a general level of consistency to requirements and

shutdown criteria applied across the whole of any monitoring conducted to satisfy this rule. The EPA judges the finalized shutdown criter ia to be sufficient and appropriate . See additional

discussion of this issue in section IV.D.4 of the preamble to the final rule.



### 8. Post

- monitor shutdown annual reporting

Comment :

Commenters (0036, 0038, 0048, 0053, 0064, 0075, 0080, 0090, 0097

, a nd 0116 ) expressed concerns regarding the annual reporting requirements.

Commenters ( 0036, 0048, 0064, 0075, 0080, 0090, and 0097) stated the proposed annual reporting requirement a ppears to be unduly burdensome for the states. Commenter (0097) stated

t h is information, to be submitted with the annual network plan, would require significant effort to compile and analyze on a yearly basis.

Commenter s (0048 , 0075, and 0116 ) stated that the need for on

- going verification has not beenDELIBERATIVE

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175 demonstrated, requiring verification is unprecedented, and will be an extreme burden on states and local agencies. Commenter (0075) stated that, a lthough states submit ambient monitoring

data to the EPA annually, UARG is unaware of a comparable requirement for other NAAQS that

a ir agencies verify and report to the EPA annually whether areas remain in attainment.

Commenter (0116) believed the most that should be required would be an assessment of SO 2 emissions to determine if they have increased and, if they have, an assessment o f whether that increase is sufficiently large that consideration should be given to new monitoring. Commenter (0036) recommend ed that the monitoring plan verification report be limited in scope to solely

address issues related to the sit ing and the running of monitors

.

Given that SO 2 emissions have been declining on a national level for many years particularly from the large sources that are the focus of the Proposed Rule, commenter (0116) believed re monitoring should seldom, if ever, be appropriate.

Co mmenter s (0080 , 0090 ) opposed the annual reporting requirement, stat ing that SO 2 emissions from sources are already available to the EPA and it is not practical or appropriate for the states to assess the cause of emissions increases. Commenter (0080) adde d that the interest of the states

and the EPA regarding NAAQS status is continued attainment, not the causes of increases in emissions that by the nature of unit operations will fluctuate to some degree each year.

Commenters (0064, 0097) suggested an ann ual report would be too frequent. Commenter (0064)

recommended a less burdensome process in which this verification would take place every five years instead of annually. Commenter (0064) point ed out that the EPA reviews the NAAQS every five years and that t his verification would be a good item to include in the review. Commenter (0097) stated that, i f monitors were removed that were providing data under 80% of the standard, at best such a comparison should be performed every three years, in conjunction

wit h the publication of the NEI data on the EPA 's website. Commenter (0097) stated a nother option would be to require such assessments be included in the 5 year ambient monitoring assessment plan required by 40 CFR 58.10.

Commenter (0036) stated the EPA’s p r oposed schedule is unrealistic. Commenter (0036) stated

that the EPA expects the plans to be submitted annually by July 1, but states will not have the required quality

- assured emissions monit oring data processed by July 1; i.e., a fter receiving

those dat a, states must process them for modeling, run the model, and assess results.

Commenter (0096) stated that ongoing verification of compliance for areas which have shut down monitoring sites would have to start with the year following the years for which t he

monitor was in operation. Commenter (0096) stated that, i f the monitor utilized 2017, 2018, and 2019 data, then the initial verification of ongoing compliance would be for 2020 emissions and would be submitted with the July 1, 2021 submittal. Commenter (0096) stated it is unclear in the

DRR if the determination of whether there was an emission increase should be based on an increase greater than the three year average of emissions during the initial monitoring analysis, an increase above the highest sing le year of emissions during the initial monitoring analysis, orDELIBERATIVE

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176 some other metric.

Commenter s (0097 , 0110 ) stated the potential attainment status of an area should not be based on

the previous year's activity and emissions , r ather, the comparison should b e based on some compliant level of emissions from the year(s) where the monitor demonstrated attainment with the standard, similar to the requirements of a maintenance plan. Commenter (0097) stated changes in emissions due to economic slow

- downs and recove ries would necessitate significant analyses, when in reality the "increase" or "decrease" in emissions of SO 2 may have resulted in

total SO 2 emissions levels well below the annual emission rates during the years when monitoring data showed compliance. Comm enter (0110) stated an extrapolation of potential monitored concentrations can be done using a scaling calculation to adjust the monitored concentration in proportion to the emissions change.

Commenter (0058) stated that since sources are already required to widely report annual SO 2 emissions, then changes in emissions after a monitor shut down could easily be assessed to

determine if re

- characterization of ambient SO 2 concentrations is potentially necessary.

Response:

The EPA has decided not to finalize the proposed requirement that any state with an area for which the EPA has approved the air agency’s request for an SO 2 monitor to cease operations

under this rule must still assess SO 2 emissions changes annually, beginning in the year after the

monitor c eases operation . The EPA made this decision based upon comments on the proposed rule, and in recognition that a cessation of monitoring will not occur unless a monitor has

measured SO 2 concentrations well below the NAAQS for a given time period and an EPA Regional Administrator has allowed the shut down. The Agency is persuaded by commenters that monitor shutdown provisions, along with generally applicable emissions reporting requirements, are of sufficient strength that subsequent additional annual observa tion and reporting of SO 2 source emissions profiles by states specifically due to this rulemaking is unnecessary. Further, there are means by which monitoring can be reinitiated in the future if the unlikely scenario occurs where SO 2 emissions rise signifi cantly in an area, or other data indicate possible NAAQS violations in an area after a monitor has been shut down, mainly through the EPA Regional Administrator authority granted in 40 CFR part 58 appendix D, section 4.4.3.



### a. Option 1: a nnual report as an a ppendix to the annual monitoring plan

Comment :

Commenter s ( 0043, 0071 , 0102

, 0115

, 0117, and 0118 ) supported the option of including the annual emissions analysis and analysis of monitoring data related to possible monitor shutdown

as components of the annual monitoring network plan. Commenter (0043) indicated that s tates or agencies with only a small number of sources could opt to use the annual air monitoring annual plan. Commenter (0071) stated t he analysis of emissions is closely related to n etwork planning, and this procedure would provide a single document for public inspection and EPA review andDELIBERATIVE

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177 approval.

Commenter (0 100 ) stated th e Annual Monitoring Plan may not be the best tool or location to place modeled data, emission reports, ongoing air quality characterization requirements, a nd requests to cease modeling. Commenter (0 100 ) stated th e Annual Monitoring Network Plan described in 40 CFR 58.10 (a)(l) is a document created and submitted to the EPA "which shall provide for establishment an d maintenance of an air quality surveillance system that consists of a network of SLAMS, monitoring stations including FRM, FEM and ARM monitors that are part of SLAMS, NCore stations, STN stations, s tate speciation stations, SPM stations and/or, in

seriou s, severe and extreme ozone nonattainment areas, PAMS stations, and SPM monitoring

stations."

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, these comments are no lon ger applicable.



### b. Option 2: i

ndependent annual submittal from the state

Comment :

Commenter s (0036 , 0041, and 0081 ) recommend ed that the monitoring plan verification report be considered a separate element

. Commenter (0081) recommend ed that annual emissio ns reporting data be submitted separate from the monitoring plan for ease of processing and for public review

. Commenter (0081) stated that by combining these reports, very little, if any real efficiency will be gained by doing so and r equiring monitoring plans to include facility emissions as part of this rule may have the effect of delaying the completion of the plan or reporting of

emissions.

Commenter (0036) recommend ed that the monitoring plan verification report should be due later in the fall (e.g. , November).

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, these comments are no longer applicable.



### c. Allow both o

ptions 1 and 2

Comment :

Commenter s (0043 , 0069 ) request ed that the EPA allow both options and stated that t he flexibility of reporting as a separate report following the same public notice may be necessary for states tracking multiple sources. Commenter (0060) suggested that if an annual report isDELIBERATIVE

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178 nece ssary, the EPA should r equir e a submittal on July 1 each year and allow it to be part of the annual monitoring plan if an air agency chooses ; a ny public notice would just need to clearly identify what the document available for comment covers.

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, these comments are no longer applicable.



### d. M onitors with data under 5 0% of the standard

Comment :

Commenter (0097) suggested th at, i f the monitors that were removed were providing data under 50% of the standard, there is no reason to perform such analyses

. Commenter (0097) stated that

a n increase in emissions that would result in such a drastic increase in monitored design values would surely be associated with changes to operations that would necessitate air permitting, which evaluates projects for NAAQS compliance ; thus, f or areas where the monitoring data are less than 50%, submitting such evaluations would be needless paperwork

.

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, these comments are no longer applicable.

Comment :

Commenter (0038) stated the rule should not require additional modeling or monitoring unless

the states and EPA make a determination that changes in S O 2 emission for the source or area in question are a significant change in emissions. Commenter (0038) encourage d the EPA to leave the procedural options open as to what works best for each state or local agency.

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, these comments are no longer applicable.



### e. Sunset provision for the repor ting requirements

Comment :

Commenter (0097) stated the EPA should also include in the implementation rule information on when a state may stop submitting these report s; i.e., the EPA should choose some threshold and timeframe to sunset these requirement s. Commenter (0097) suggested that , if emissions of SO 2 in an area were to drop to less than 50% of the actual emissions inventory for the complianceDELIBERATIVE

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179 year for 5 years, increases in emissions to the point where the area may measure a violation of the NAAQS would most likely not be accomplished without triggering New Source Review ( NSR ) permitting.

Response:

Please see response above listed under “Post

- monitor shutdown annual reporting.” Because this report is not being required, this comment is no longer applicable.



### f. EPA disapprov

al of a monitoring plan due to nonattainment

Comment :

Commenter s ( 0063, 0065, 0081) disagreed with the requirements proposed in 40 CFR p art 51.1205(d) , which appear to state that if modeling or monitoring indicates that an ar ea is not attaining the 2010 1

- hour SO 2 NAAQS, the EPA has an option to disapprove the monitoring plan. Commenter (0081) stated t his is an unprecedented act; at no time in the past has the EPA failed to approve a m onitoring p lan if violations of other NAAQ S have occurred. Commenter (0081) stated that, s ince the monitoring plan is intended to serve as an accounting of the state’s

o bligations under 40 CFR p art 58. 5

, this step is unnecessary and they request ed that it not be included in final language ; rather, t he EPA should rely on its authority to issue a SIP call or designate an area “nonattainment” if an air agency is negligent in providing the annual emissions data as required by this regulation.

Commenter (0115) stated it is not clear what approach the EPA is recommending, however, if

actual emissions from these facilities do increase above the levels being emitted while the monitor was operational : w ould the monitors be re

- deployed? W ould updated modeling be

conducted instead?

Response:

The EPA agrees that evidence that an area is violating the air quality standard does not justify disapproving a monitoring plan. The EPA has removed this clause from the final language in

s ection 51.1205(d). The rule does not address how the EPA would respond to a situ ation in which criteria for terminating operation of a monitor were met but then emissions increase so as to present renewed concern as to whether the area is still attaining the standard. The EPA notes that this situation is not unique to this rule, and E PA has adequate authority to address any such

situations . If the emissions increase occurs prior to EPA approval of the request to discontinue operating a monitor , EPA could disapprove such a request. I f it occurs post

- approval and after monitoring has bee n discontinued EPA c ould address it in its annual review of state monitoring network plans

. T he EPA intends to address such situations on a case

- by

- case basis. Moreover, EPA notes that the identification of such situations is a relatively straightforward exercise using routinely provided data.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

180 

### 9. Emerging technologies

Comment :

Commenter (0036) urged the EPA to continue evaluating emerging, cost

- effective monitoring technologies that are easier to deploy and can supplement regulatory SO 2 monitoring. When suc h technologies become available, we urge the EPA to work with states to develop guidance that clearly explains the role of supplemental monitors.

Response:

The EPA is currently evaluating new “sensor” technologies to keep up with this emerging sector

and will be look ing for ways to leverage them in our ongoing air quality surveillance efforts.



### B. Modeling

1. Emissions

-- actual data

a. Support use of actual data

Comment :

Commenters ( 0037, 0039, 0041, 0043, 0044, 0045, 0046

, 0047, 0050, 0051, 0052, 00 52a

, 0053,

0 054, 0056, 0058, 0060, 0066, 0067

, 0073, 0075, 0082, 0087, 0088

, 0089, 0092, 0093, 0097

, 0106, 0108, 0110, 0114 , 0117 , 0118 ) supported the EPA ’s proposal to base the attainment status modeling analyses on actual emissions.

Modeling for designation purpose s only

Commenters (0046, 0088) cautioned that the use of actual emissions in the designation modeling should not be used for other purposes. Commenter (0046) stated t hese actual emissions will represent reasonable parameters for attainment classification modeling and should be used for that purpose only ; t hey should not be a part of any restriction on the operations of the modeled source or incorporated into the SIP based solely on a conservative modeling exercise. Commenter (0088) stated that the use of e xisting emissions should not result in emission caps on stationary sources being modeled because future conditions are not the basis of attainment and nonattainment designations

– actual ambient air conditions are.

More realistic

Commenters ( 0042, 0046 , 0054, and 0114) stated that the use of allowable emissions would be too conservative and may result in designation of inaccurate nonattainment areas. Commenter (0046) stated s everal layers of conservatism are incorporated into regulatory modeling analyse s in the form of worst

- case emissions, worst

- case meteorology, worst

- case stack and operatingDELIBERATIVE

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181 conditions, and most conservative definition of ambient air and, w ith this compounded conservatism, a sole reliance on these types of modeling results for designa tions would yield unrealistic outcomes that ultimately would have the unintended consequence of halting industrial growth in areas where public health is not at risk. Commenter (0054) stated that g iven the uncertainties with predictive SO 2 modeling, the us e of actual facility emissions data as model input provides the most accuracy in making SO 2 designation decisions.

Commenter s ( 0042, 0088, 0110) stated that u sing actual emissions is even more important when conducting a cumulative impact analysis since t he model’s tendency to overestimate ambient air impacts is compounded when numerous sources are all modeled at peak emissions at all times, leading to unrealistic model estimates. Commenter (0088) stated that s ince “allowable” or plant

“PTE” emissions are unlikely to occur at a plant or for that matter, at the same time from multiple plants being modeled, it is arbitrary and capricious as well as unreasonable for “allowable” or plant “PTE” to be used as inputs to describe existing ambient air conditions.

Commenter (0087) stated that to the extent the EPA continues suggesting reliance on modeling, the Agency's instructions in the proposal for use of a model are generally reasonable and will ensure more realistic predictions of ambient air quality than if m odeling were done in accordance with the Guideline on Air Quality Models, 40 C.F.R. p art 51, App. W.

Surrogate to monitoring

Commenters (0041, 0060, 0088, 0092, and 0106) generally supported using actual SO 2 emissions

for attainment status designation s s ince th e use of actual emissions, rather than a llowable emissions, will "serve as a surrogate to comprehensive ambient monitoring" and its use as an input in the model will "more closely represent ambient monitoring results." Commenter (0092)

stated the ta sk is to determine and designate the attainment status of source areas within jurisdictions, not to forecast or evaluate scenarios.

Predictive modeling

Commenter s (0040 , 0044 ) requested the final rule preamble to include language to confirm

distinctions between modeling for 1

- hour SO 2 designation purposes and other CAA predictive purposes (e.g., NSR). Commenter (0044 ) supported the distinction the Proposed Rule makes between modeling conducted for characterizing air quality for designation purposes and u se of predictive modeling conducted for other purposes , but stated the preamble’s discussion of the modeling eventually to be carried out under this rulemaking is ambiguous and contains contradictory statements. Commenter (0044) stated that while the pream ble first appears to move toward modeling actual emissions and away from the use of predictive modeling to characterize current air quality, the ensuing discussion appears to reverse course and could be interpreted to say only that the use of actual emissi ons data may “presumptively” be the most appropriate methodology but that it may be equally appropriate to use a predictive modeling methodology.DELIBERATIVE

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182 Response :

EPA agrees that the use of actual emissions is generally expected to be more realistic than using allowables to represent current air quality conditions. However, in some cases, there can be little if any difference between estimated actual and allowable emissions, for example in the case of a source that is limited by work practice requirements, rathe r than by a numerical emissions limit that a source operates under with a compliance margin. The EPA also agrees that in some cases

the use of allowables would be more conservative and could lead to an overestimation of current air quality pollutant concen trations

. For this reason, EPA continues to advise that modeling of actuals may be submitted (consistent with the modeling TAD) to satisfy the requirements of this rule. With respect to the comments about use of actuals modeling for other purposes, nothin g in this rule changes any established rules or guidance regarding modeling for other purposes (such as SIP modeling cited in comments).



### b. State option to model actual or allowable

Comment :

Commenter (0078) stated that b ecause the state air agency is ul timately responsible for implementation of the NAAQS and any ongoing attainment verification requirements associated

with the Proposed Rule

, the EPA should make clear in the final rule that it will defer to state air agencies' decisions regarding appropria te emissions rates for designations modeling. Commenter (0078) stated that i t is reasonable to expect that outside stakeholders may disagree with the emissions inputs a state air agency selects and could potentially seek to circumvent state air agency deci sions and submit additional modeling to the EPA using the alternate emissions input in order to support different designation determinations.

Response:

As stated in the preamble to the final rule, w hen using actual emissions, the EPA believes the

most r ecent 3 years of time varying emissions (e.g., emissions that vary hourly, seasonally, monthly, daily, etc.) should be modeled since the air quality modeling is being used as a surrogate for monitoring. The EPA does not believe it is necessary to specify b y rule a rigid set of requirements for determining emissions inputs for modeling to satisfy this rule. However, to ensure the data are appropriate for use in implementing the NAAQS (for example, for use in designations), we strongly recommend that air age ncies follow t he m odeling TAD

recommendations . The TAD provides recommendations on such topics as inputting hourly emissions into AERMOD for those sources with hourly continuous emissions monitoring (CEM) data and on inputting time

- varying emissions (e.g. seasonally, monthly, etc.) when no hourly emissions are available and only annual emissions and data such as production logs or fuel usage

are available. T he final rule does not restrict the ability of air agencies to use more conservative

allowable emissi ons in conducting their modeling. In the event that a particular source does not have the most recent 3 years of emissions, it may be possible to use the most recently available emissions or develop the most recent 3 years of emissions using recommendation s in the TAD.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

183 The reviewing authority should work with the appropriate EPA Regional Office on the use of such emissions. For an application that contains a mix of sources whose emissions data are not concurrent with each other, it is possible to model all of these sources together following recommendations in the TAD. Once a modeling protocol or modeling analyses have been submitted, there is no requirement to revise the protocol or modeling respectively if more recent

emissions have become available since the submission, and in the best professional judgment of the reviewing authority, those emission changes do not warrant a revision to the protocol or modeling analyses. If outside stakeholders provide information those conflicts with information

that a sta te provides, the EPA will consider all information, without prejudging which

information is more reliable.



### c. I ntermittent sources

Comment :

Commenters (0042, attachment A5, 0110) stated that h ighly intermittent sources, especially those that operate when more base

- loaded sources are off

- line, should continue to be excluded from modeling with actual emission inputs

. Commenter (0042, attachment A 5) concur red with the March 1, 2011 the EPA guidance that modeling analyses be based on emission scenarios that

ca n logically be assumed to be relatively continuous and not include sources for which operation is sufficiently intermittent that they are unlikely to cause a violation. Commenter (0042,

attachment A 5) stated that, i n considering the criteria for exempting intermittent sources, the

EPA also needs to consider the frequency of meteorological conditions, specifically wind direction, that along with the intermittency of a source’s emissions, determine whether any

downwind location could be affected on more than 1% of the days in a year, corresponding to the 99th percentile SO 2 NAAQS.

Commenter (0042, attachment B) stated that a dditional guidance may be required to deal with

continuous emission sources that include both a continuous and non

- continuous component s ince

t he low frequency sources (i.e., non

- continuous and intermittent sources) may have a disproportionate impact on the 99th and 98th percentile value on which compliance with the 1

- hour NAAQS will be judged.

Response :

As part of the December 2013 updat e to the SO 2 NAAQS Designations Modeling Technical Assistance Document, EPA recommended in s ection 5.4 of the modeling TAD to follow the guidance discussed in the March 1, 2011 memo “Additional Clarification Regarding Application of Appendix W Modeling Gui dance for the 1

- hour NO 2 National Ambient Air Quality Standard.” This guidance is applicable to both modeling with actual emissions and allowable

emissions.



### d. Hourly rates for model inputDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

184 Comment :

Commenter s (0042, attachment A 5 , 0052 ) objected to th e EPA guidance that suggests that sources be modeled at various operating conditions, rather than only at peak load because t his can become an unmanageable analysis if multiple sources are involved in the modeling. Commenter (0042, attachment A 5) stated i t is our experience that in most cases, maximum load (associated with maximum emissions) is the worst

‐ case modeled result, and it should generally

be the one selected.

Commenter (0049) stated that if modeling is to be used for attainment designations, then use of sub hourly and meteorological data must be allowed to better represent SO 2 concentrations

b ecause hourly emissions and meteorological data currently used in AERMOD, causes excessively conservative results.

Commenter (0110) support ed using the average hourly emission rate for model inputs based on reasonably available data. Commenter (0110) sta ted that, i f data are not reasonably available , and variation is random, the use of actual annual emissions divided by actual annual operating hours is an appropriate way to generate an hourly emission rate modeling input for such sources. Commenters (0063 , 0065) stated that s ources without CEMS data should still be able to use actual emissions data, rather than allowable emissions, as the basis for modeling.

Commenter (0042) recommended that the EPA eliminate the requirement that emission limits to

demons trate compliance with the 1

- hour SO 2 NAAQS must be expressed as 1

- hour average limits. Commenter (0042) stated the EPA has previously

-- and appropriately

-- recognized that the enforcement of longer

- term emission limits can ensure the attainment and main tenance of

shorter

- term ambient standards. Commenter (0078) stated that t he final rule should indicate

concurrence with the EPA 's "Guidance for 1

- Hour SO 2 Nonattainment Area SIP Submissions" (April 2014) , which indicated that emission limits with longer

- th an

- hourly averaging times may

be appropriate if states can demonstrate that the longer averaging times provide comparable stringency to a one

- hour limit at the critical emission value. Commenter (0087) stated that, a s the

EPA ha s not solicited comment on t he April 2014 methodology as part of this proposal, they

reserve d the right to provide comment on this methodology based upon further review.

Commenter (0087) encouraged the EPA to allow flexibility for states and affected sources to develop emission limi ts in a form and averaging time that is meaningful for the source being evaluated. Commenter (0087) provided the following additional points.

One

- hour mass

- based emission limits would impose very stringent requirements on

boilers. Controls to meet such li mits would need to be designed to a much higher standard of reliability to ensure that even the smallest upsets (minor plugging of one or more sorbent injection ports, for example) would not cause an excursion of the limit. To

the extent that 1

- hour limits are required, periods of SSM must be excluded in calculating compliance with the limit.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

185 Response :

Since the focus of this rule is on characterizing the air quality impacts of actual emissions, this rulemaking is not establishing policy with respect to t he comments of com m enters 0042 and 0087 regarding emission limits

. With regards to the use of sub

- hourly meteorological data, sub

hourly meteorological data can be input into AERMET but is averaged over the hour for input into AERMOD. At this time, AERMOD does not accept sub

- hourly data. With regards to the

sub

- hourly emissions data, the source may want to work with the reviewing authority and Regional Office to determine the best way to utilize those emis s ions data

. In regards to Commenter 0110, the model ing TAD states that in the absence of CEM data, simply dividing the annual emissions by the number of hours in the year would not be an accurate representation of the actual emissions. Facilities, the reviewing authority, and Regional Office should work

c losely to ensure the best quality of emissions. For sources that do not have CEM data, the TAD

offers several suggested methods to calculate variable emissions rates from annual emissions and other information such as throughput, operating schedule, produ ction, etc.



### e. Revise the regulatory text

Comment :

Commenter (0040) requested that the EPA add language to both the preamble and codified regulatory language in a Final Rule that (1) actual emissions shall be used for air modeling for initial designati on purposes, but (2) that allowable emissions may be used to demonstrate attainment status. Commenter (0040) suggested the following language for section 51.1203(d)(2) :

(2) Modeling analyses shall characterize air quality based on actual 1

- hour SO 2 emissi ons from the most recent 3 years, or federally enforceable allowable emissions for purposes of demonstrating attainment

. . . .

Commenter (0044) stated the regulatory text is at best ambivalent on whether actual emission should be used, and could be read t o give air agencies (and the EPA Regional Administrators with whom they must consult) unfettered discretion to model based on allowable emission rates as they see fit. Commenter (0044) believed the rule is intended draw a substantive distinction

between th e use of modeling for the purpose of characterizing current ambient air quality (i.e., modeling conducted as a surrogate for 1

- hour SO 2 NAAQS designation monitoring), and predictive modeling conducted for purposes of NSR, PSD, and SIPs, then that distincti on should be reflected unambiguously in both the rule’s preamble and in the regulatory text of the final

rule , which it does not currently do. Commenter (0044) recommended the following revisions be made to the text of section 51.1203(d)(2) for clarificati on:

(2 ) Consistent with subpart BB’s purpose of making designations of current air quality

attainment of the SO 2 NAAQS, modeling analyses shall characterize air quality based on

actual 1

- hour SO 2 emissions from the most recent 3 years, or federally enfo rceableDELIBERATIVE

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186 allowable emissions which demonstrate that attainment has been achieved . If the air agency intends to use allowable emissions limits for this analysis, it may submit such allowable emissions limits for the EPA’s approval at the time the modeling pr otocol is

submitted.

Response:

The EPA agrees with the commenters that the modeling of actual emissions can be used to

characterize the emissions around SO 2 areas to satisfy the requirements of this rule. When using actual emissions, the EPA believes the most recent 3 years of time varying emissions (e.g., emissions that vary hourly, seasonally, monthly, daily, etc.) should be modeled since the air quality modeling is being used as a surrogate for monitoring. The m odeling TAD gives recommendations on inpu tting hourly emissions into AERMOD for those sources with hourly continuous emissions monitoring (CEM) data and also gives recommendations on inputting time varying emissions (e.g. seasonally, monthly, etc.) when no hourly emissions are available and only annual emissions and data such as production logs or fuel usage are available.

On the other hand, the EPA believes that modeling of allowable emissions is also an appropriate approach, which is warranted as an alternative to modeling actual emissions. Th is approach indicates the potential for violations, and thus provides an indication of whether further air quality planning might be warranted. I f modeling of allowable emissions shows the limits to provide for attainment, this rule then provides that no f urther initial characterization based on actual emissions is needed, nor is any ongoing review needed to assess whether variations of

emissions (within allowable levels) might result in violations of the standard (such as would be required for areas design ated attainment based on actuals modeling)

. (Although the relationship between the results of such modeling and actual air quality would depend on whether the source is complying with its emission limits, the EPA believes that, in absence of information ab out compliance status, modeling based on a presumption that allowable emissions are the maximum that emissions might be is a reasonable basis for establishing that a source would not violat e the

standard .) In the case where modeling of allowable emissions show s the potential for violations

, this rule provides that such modeling also satisfies the air agency’s initial obligation to

characterize the source . Although this rulemaking does not address how the air quality characterization information required by this rule will be used in future actions ( e.g., in future designation actions), the EPA concludes that air agencies should be given the option under this

rule to model allowable emissions and thereby to develop information that characterize s the potential for violations

. The EPA does note the factual distinction made by commenters between modeled actual violations and modeled potential violations , but a t the same time, EPA makes a

note of past practice in which information on the potential for violations wa s in some cases the

basis for some areas being designated nonattainment , and we do not agree that it would be appropriate for this rule to exclude such information as a characterization option or to proscribe the uses for such information if it is provided

.



### 2. Emissions

-- most recent three yearsDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

187 Comment :

Commenters (00 36

, 0040, 0046

, 0067

, 0087, 0092, 0093, and 0114 ) generally supported EPA’s proposal to base the modeling analyses on actual emissions over a 3 year period. Commenter (0040) stated that actual emissions from the previous 3 years, coupled with contemporaneous meteorological data, helps to ensure accurate modeling output to make designations

.

Commenter (0093) stated that the most recent 3 years of representative emissions data should normally be used in the modeling ; h owever, if justification can be provided for an alternative dataset, it too may be considered for modeling. Commenter (0069) noted that, in situations where multiple sources are being modeled, the most recent three years of actual em issions data may not be the same for all sources, particularly when one or more sources are EGUs that report to EPA's

Acid Rain database and one or more sources are non

- EGUs that report under the provisions of

the AERR.

Commenter (0069) stated t he rule s hould clarify that states shall use the most recent three years

of emissions data for an area available to the state at the time that a modeling protocol for that

area is submitted to the EPA

. Commenter (0069) stated that r evised modeling should not be

req uired if more recent emissions data become available after a modeling protocol is submitted

to the EPA

. Commenter (0069) stated that, s hould an area be designated attainment based on modeling protocols and modeling analyses s ubmitted prior to the regulator y deadlines, the proposed provisions for assuring continued attainment are sufficient for addressing changes in

emissions.

Commenter ( 0036 ) stated that, i f applicability were to be additionally based on maximum actual hourly emissions, then the length of time to apply to the initial annual applicability tr igger would be less important.

Commenter (0062) recommend ed that the maximum year from the previous three years be required for designatio n modeling, instead of one year because t his would make the model ing option more equivalent to the monitoring option for designation. Commenter (0060) did not

agree with the use of methods such as the highest of the most recent three years.

Response :

Responses to comments regarding actual emissions over the most recen t three years, alternative datasets, and modeling protocols can be found in the Rule preamble in s ection VI.D.6.b.iii. In addition, t he modeling TAD provides extensive discussion of recommendations regarding the emissions data to use in modeling analyses c onducted to satisfy this rule. The commenters make

several recommendations that must be considered on a case

- by

- case basis. For example, the need to consider changes in emissions that occur after completion of a modeling protocol must

consider whether the emission changes are sufficiently significant as to render a modeling analysis based on the prior emissions no longer indicative of current air quality. Similarly, the utility of a modeling analysis that uses data from different years for different sources must be weighed as to how reliable this approach is in representing current air quality for the particularDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

188 situation. (The modeling TAD provides specific recommendations for addressing this situation.) The EPA generally recommends using data from the most recent three years for purpose s of this

rule , consistent with the air quality standard being defined in terms of the average among the 99 th
percentile daily maximum 1

- hour SO 2 concentrations over three consecutive years.



### 3. Emissions

-- a ccounting for enforce able limits

[Also see IV.A.5 regarding legal agreements ]



### a. Support accounting for enforceable limits

Comment :

Commenters ( 0046, 0069, 00 87

, 0096, and 00 97 ) generally support ed the inclusion of language providing the option for states to model emission r ates based on enforceable limits

.

Commenters (0046, 0069, 0087, 0096) stated f uture emissions reductions (e.g., Regional Haze, CSAPR, and MATS ) should be accounted for in the emissions data used to model designations,

in order to decrease the likelihood that areas will be designated nonattainment based on outdated

information. Commenter (0087) stated the EPA should allow the use of emission data that will more accurately reflect the operational and emitting characteristics of these sources in the post

MAT S and post

- Boiler MACT timeframe. Commenter (0097) stated i t should be noted that this practice is consistent with the methodologies used to develop PM 2.5 , ozone, and regional haze planning inventories , where a ctual emissions, projected forward into the fu ture year using reasonable growth estimates, are modeled to make determinations about compliance for these criteria pollutants. Commenter (0097) stated, t herefore, the use of actual emissions estimates for purposes of SO 2 compliance is merely following the attainment planning process of these other pollutants.

Commenter (0052) stated that, if the installation of scrubbers generally suffices for areas to meet

the 1

- hour S O 2 NAAQS, then those units and units with similar emission profiles should be exempt fr om the modeling demonstration.

Commenter (00 52a ) stated the EPA should allow the use of actual emission rates and statistically representative emissions profiles when these data are deemed to be sufficiently reliable. This approach could include the use o f continuous emission monitoring system data.

Response:

After review of the comments, the EPA believe s that it is appropriate for the air agency to consult with the affected source(s) and take action to adopt enforceable emissions limitations as

necessa ry prior to January 2017. As long as the emissions limitations are in place and

enforceable by January 2017, the new allowable emission limit may be input into the modelDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

189 i nstead of the actual emissions of the most recent 3 years. 8

The EPA expects that a n umber of emissions sources may be candidates for this optional approach. Many EGUs will need to meet compliance deadlines for the MATS in April 2015 (or in some cases, April 2016 ), and the EPA expects that many will become subject to Title V permits that r equire compliance with MATS SO 2 emission limits as the means of demonstrating compliance with the MATS requirements related to acid gas emissions. These EGUs may be able to adopt control technologies and enforceable emission limits to reduce emissions of S O 2 as well as mercury. Similarly, industrial boiler operators will commonly be reducing SO 2 emissions in conjunction with complying with Industrial Boiler MACT requirements, and sources will have incentive to assure that the control strategy they implement to comply with the Boiler MACT requirements will also assure attainment of the SO 2 air quality standard. As a result, many of these sources might wish to become subject to limits reflecting these controls

.

It is appropriate, where modeling information i s required to be submitted to EPA under this rule,

for that information to take these limits into account. Therefore, the EPA believes that as long as

these emissions reductions are implemented and enforceable prior to January 2017, it would be appropriate for the new lower allowable emission s to be used in a modeling analysis in place of

the high er actual emissions . The air quality impacts from such a source would be characterized by the new enforceable allowable limit (at worst) . Information that include s the effect of such limits could be considered, for example, in future determinations regarding areas’ attainment

status

.

Conversely, if the controls are not required to be implemented by January 2017, then it would be inappropriate to consider the contr ols in assessing current emissions

. This is because the assessments made under this rule are due in 2017 and it is necessary for them to reflect the conditions that are in places at the time the assessments are due. T his modeling is intended to

assess curr ent air quality (which is useful, for example, for making determinations of NAAQS

attainment status at the then

- current time that reflect current, not future, air quality ) . In this respect, modeling for satisfying the informational purposes of this rule is different from modeling for attainment planning purposes, which generally assesses the benefits of future

controls

.



### b. Controls implemented and enforceable as of January 2017

Comment :

Commenters (0035, 0041, 0045, 0046, 0060, 0062, 0070, 0078, 0082, 008 5, 0088, 0097, and 0114) generally support ed the inclusion of language providing the option for states to model

more recent emission rates based on enforceable limits implemented in advance of the January

8 While these comments address the consideration of emissions data used in modeling ana lyses, the final rule also provides for emission limits at sufficiently low levels (generally at below 2,000 tpy) to warrant being exempted from air quality characterization requirements.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

190 2017 modeling deadline. Commenter (0035) stated a ir agencies could notify the EPA of any initially listed sources that have reduced emissions below the threshold by July 1, 2017, well in

advance of the EPA ' s proposed timeframe for nonattainment designations.

Commenters (0035, 0041, 0097) stated this appro ach is a reasonable option which would provide industry with an incentive to achieve timely emission reductions to meet the regulatory requirements while relieving air agencies from the requirements that a nonattainment designation

entails. Commenters (004 6, 0060) asserted that s tates need flexibility to work with sources/groups of sources to reduce emissions and avoid nonattainment designations based on

models. Commenter (0114) agreed with the proposed approach but requested that the method for reducing em issions not be limited to installing controls.

Commenters (0035, 0060) stated the EPA should develop methodologies for air agencies to work

with sources whose 2015 emissions are above the threshold to establish permanent and

enforceable emission limitatio ns that show attainment with the S O 2 standards prior to the next round of designations in 2017. Commenter (0060) stated there must be a process that allows for the air agencies discretion under extenuating circumstances in order to account for significant changes at a facility that occurred during the most recent three years.

Commenter (0070) stated the EPA must clarify the rulemaking in a way that would allow s tates
that desire to submit a full attainment SIP based on modeling by January 2017, or such ot her time as specified in the Final Rule, to do so ; and

, the EPA should be permitted to accept the modeling as satisfying the requirements necessary to grant a designation of either a ttainment or

u nclassifiable at the time of issuance of the initial designa tions.

Commenter (0060) stated that, under the Proposed Rule

, a source which installed a control in

2013 and has 2014

- 2016 actual emissions th at model attainment will not be required to have an

enforceable limitation

, while a source that installed a contr ol in 2015 and has three years of emissions that don't model attainment because of the pre

- control emission levels only, would require an enforceable limit. Commenter (0060) suggested model ing with surrogate emissions

that are based on operational history for the period of time without control and with actual emissions for the period of time with control ; i f the source fails the modeling, it could elect to take an early e nforceable limitation to avoid nonattainment or elect to be nonattainment and subject t o the attainment demonstration analysis and requirements due in the future. Commenter (0060) stated t his is the type of flexibility air agencies need in order to meaningfully apply these

rules without subjecting sources to inconsistent and overly burdensom e requirements.

Response:

After review of the comments, the EPA contends that it is appropriate for the air agency to consult with the affected source(s) and take action to adopt enforceable emissions limitations as necessary prior to January 2017. As lo ng as the emissions limitations are in place and

enforceable by January 2017, the new allowable emission limit may be input into the model

i nstead of the actual emissions of the most recent 3 years.DELIBERATIVE

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191 The EPA expects that a number of emissions sources may b e candidates for this optional approach. Many EGUs will need to meet compliance deadlines for the MATS in April 2015 (or in some cases, April 2016 ), and the EPA expects that many will become subject to Title V permits that require compliance with MATS SO 2 emission limits as the means of demonstrating compliance with the MATS requirements related to acid gas emissions. These EGUs may be able to adopt control technologies and enforceable emission limits to reduce emissions of SO 2 as well as mercury. Similarly , industrial boiler operators , subject to acid gas limits under the Boiler Maximum Achievable Control Technology Standard (MACT)

, will in many cases be substantially reducing their SO 2 emission levels, such that an emission limit reflecting this

control mi ght suffice to demonstrably assure attainment

.

Therefore, the EPA believes that as long as these emissions reductions are implemented and enforceable prior to January 2017, it would be appropriate for the modeling analysis submitted to EPA to satisfy this rule to reflect the new lower allowable emission s in place of the high er actual

emissions

. The results of such analysis could be use ful for purposes such as making future determinations regarding areas’ attainment status

.

The EPA wishes to clarify that, to the extent that the commenter wishes to conduct modeling that considers emission reductions that will occur after January 2017, such modeling will not satisfy the requirements of this rule. This rule requires consideration of current, not future, emissi on levels, to assess current, not future, air quality , as of the date that the assessment is due to EPA

. The DRR does not address the future use of this information, but the EPA n evertheless recognizes the commenters’ desire to minimize resources spent on air quality planning for areas that currently violate the NAAQS but where future actions are likely to resolve these air quality problems. The EPA welcomes discussions of how best to address such situations on a case

- by

case basis.

The EPA does not agree with the suggestion for sources that install controls in 2015 , for example, to be modeled using an inventory constructed as if the controls had been installed in

2013. Such an approach would be based on a hybrid inventory that fails to reflect actual

emis sions for the three year period and also does not reflect allowable emissions. For a source that installs controls for example in 2015 but is not subject to any requirement to maintain the resulting emission level, the control level achieved in 2015 is no t necessarily a reliable basis for determining “current” emission levels, insofar as the 2015 data differ from the 2013 and 2014 data and are not necessarily indicative of how emissions will be in 2016, 2017, and beyond.

Furthermore , the EPA believes that a source that installs controls in 2015 warrants greater scrutiny and warrants stricter prerequisites for modeling post

- control emissions (i.e., needing for

post

- control emissions to become enforceable) than a source that install ed comparable controls in

2 013 and has a full three years of data reflecting these controls . This approach also provides more incentive for early controls, and this approach reflects the fact that the source that controlled in 2013 has more evidence that it can be expected on a lon g

- term basis to emit at the

reduced levels. For these reasons, the suggested approach is not recommended in the modeling

TAD.DELIBERATIVE

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192 

### c. E mission reductions after 2017

Comment :

Commenters (0046, 0069) suggested that, since the designations are to be based on ac tual, not

allowable emissions, t he rule should allow for actual emissions to be estimated based on the

future control that will be applied . Commenter (0046) suggested that states should not be l ocked into using emissions from a prior calendar year to deter mine attainment, but should be able to consider emissions projections beyond 2017. Commenter (0046) stated f or example, if a scrubber

that achieves 90% control of SO 2 is being installed, the facility should apply 90% control to their three years of past ac tual emissions for a modeling demonstration.

Commenter (0069) stated that some facilities may not be able to design, construct, and operate controls as quickly as 2017. Commenter (0069) stated the EPA should allow states to model

controls that will be im plemented between January, 2017, and the attainment deadline of February, 2023, as long as limits associated with those controls are included in an enforceable permit, rule, or similar mechanism by January, 2017.

Response:

This final rulemaking is not e stablishing requirements for completing designations, and design a tions decisions will be based on the information before the agency at the times EPA takes

those future actions. This rule requires consideration of current, not future, emission levels, to

as sess current, not future, air quality, as of the date that the assessment is due to EPA. The DRR does not address the future use of this information, but the EPA nevertheless recognizes that controls may not be feasible by 2017 in some instances, and that such future controls may resolve air quality problems that may be found in an assessment that is current as of the January

2017 due date. The EPA welcomes discussions of how best to address such situations on a case

by

- case basis



### 4. Background concentrations

Comment :

Commenter s ( 0042, 0046

, and 0070 ) stated that t he rule should allow flexibility in determining what background value to use.

Clarification

Commenter (0106) referred to pages 26

- 27 of the m odeling TAD and stated the discussion in

s ection 8 on background concentrations seems to refer to both a design value background concentration (Page 27 first paragraph) and an annual average background concentration (PageDELIBERATIVE

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193 27 second paragraph). Commenter (0106) stated t his seeming discrepancy in the discussio n of background should be addressed.

Commenter (0052) stated that the EPA fails to address how to determine an appropriate background for areas with multiple monitors.

Double counting

Commenter (0040) stated that for any modeling method, the EPA should address and eliminate the potential for “double

- counting” of background concentrations of SO 2

. Commenter s ( 0042,

0046 ) stated r equired use of background SO 2 concentrations often double counts the effect of the

modeled sources and must be addressed. Commen ter (0042, attachment A 5) stated the approach suggested by the EPA that uses data from just one ambient monitor may result in some hours of double counting with modeled source impacts. Commenter (0042, attachment A 5) stated the

EPA needs to change its appr oach to one that favors an unbiased modeling solution, such as a consideration for using concurrent monitoring data to determine hourly background (and using

the minimum value from multiple monitors to avoid double

‐ counting of modeled impacts).

Monitors near a source

Commenter (0042, attachment B) stated that, i n appropriate situations, monitors near a source should be allowed to represent the contribution from off

- property and background sources (i.e.,

no current ly existing sources on

- site and no existing off

- property sources should be included in the modeling because they are already included in the ambient monitor data). Commenter (0042, attachment B) stated background concentrations

- based on monitors near sou rces being modeled

- should be paired in time with the meteorological conditions that produced them

. Commenter (0042, attachment B) stated a mbient monitoring data collected during exceptional events

-- even those that do not exceed the relevant NAAQS

-- sh ould be excluded when determining background.

Modeling data

Commenter (0046) stated m odelers should be allowed to use either a “clean” background monitor value or perform a back trajectory analysis to determine the hours when the source is impacting the monitor and exclude those hours from the 99th percentile calculation.

Commenter (0051) suggest ed that the EPA specifically allow modeled background concentration using a regional scale model such as CAMx to estimate hourly (if necessary) background

conc entrations when determining existing air quality. Commenter (0052) stated that, i n lieu of using monitoring values to derive a background values for areas in Kentucky, they propose to use regional background values that are derived using CMAQ modeling data

. Commenter (0052)

stated that t he use of existing air quality monitoring to represent background concentrations can be overly conservative because most of these monitors have some impact from the facilities that are being explicitly modeled

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194 P ercentile value

Commenter (0070), referencing several technical papers, stated the papers all clearly demonstrated that background was not a blanket 99 th percentile value as has been espoused by EPA in draft modeling TAD. Commenter (0070) stated that combining the real design value (99 th percentile daily high monitored value) with the 99 th percentile daily high modeled value generates a value that results in a value far more stringent than the underlying 1

- Hour SO 2 NAAQS

, to which it is being compared. Commenter (00 70) stated that adding the 99 th percentile

monitored value to the 99 th percentile daily high modeled value does not result in a 99 th percentile combined value, but a 99.99 th percentile value or one exceedance allowed roughly every 9,000 days, which is sign ificantly more stringent value than the underlying standard to which it is being compared. Commenter (0070) stated this clearly violates the statistical integrity of the comparison to the ambient standard.

Commenter (0070) recommended that, b ased on seve ral studies performed over the past several

years, the EPA incorporate no higher than a 50th percentile monitored value as a “can use for any purpose” option or call for a rigorous case by case review of the available monitoring data as suggested in Append ix W as the appropriate methods to establish background values for use in an analysis supporting designation of an unclassifiable or attainment area where a modeling approach is selected. Commenter (0070) stated that use of a 50 th percentile value for back ground, while still more stringent than the form of the standard, better protects the statistical integrity of

the standard than does the current EPA guidance. Commenter (0070) stated that use of a 50 th
percentile value still results in an increase in the stringency of the standard from roughly one exceedance day in every hundred to one exceedance day in roughly every 180 days.

Commenter (0110) stated the EPA ’s March 1, 2011 Tier 1 guidance is overly conservative because if the modeled and monitored desig n concentrations are from independent distributions, the probability of the combination being exceeded is not 1%, but rather 0.01%. Commenter (0110) stated the EPA ’s Tier 2 approach is less co nservative for many situations, but could be

more conservative f

or specific hours and seasons. Commenter (0110) provided the following additional points.

The problem with the Tier 1 and 2 approaches is that the background value added is always a near

- peak value, while the most likely coincident background value would be closer to the 50th percentile ranked value, rather than the 99th percentile. The EPA’s approaches therefore assume that background and modeled concentrations are highly correlated, even if there is no evidence that this is the case. A way to address po ssible correlation is to add hourly modeled concentrations to the (paired in time) hourly background concentrations, using representative monitors for which the modeled source is not materially influencing the monitored background concentration. The approa ch allows the appropriate meteorological pairing in time of the ba ckground concentration

due to af fected air masses to the predicted concentration from the source. EPA’s March 1, 2011 guidance allows this approach in cases with adequately representative mo nitoringDELIBERATIVE

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195 data, and we recommend that the EPA should allow its use more generally, especially for use of modeling for designation of areas with existing sources. The use of actual hourly background would be consistent in modeling with the use of actual hour ly emission rates for input. In areas with multiple monitors and modeled sources that could result in “double counting”, the hourly background concentration should be the lowest reading among the available monitors unless there is an upwind monitor that re presents regional background levels. A method of pairing modeled and monitored background concentrations should be an available (Tier 3) approach. To be consistent with the use of actual hourly emissions for sources being exp licitly modeled, the background concentrations should consist of concurrently hourly values from a representative

monitor.

A refinement to the Tier 1 and 2 approaches, similar to the recent PM 2.5 modeling guidance, would be to determine the concentration level above which the monitori ng data indicates local impacts, and then to use the peak value (either a single value for Tier 1 or

an hour

- of

- day, seasonal value for Tier 2) from the remaining values. This concentration level is not necessarily a fixed percentile value, but must be dis cerned from a ranke d plot

of the monitored values

. (0110)

Response:

In response to comments regarding flexibility, EPA has offered several options in determining background concentrations. As stated in the m odeling TAD, a first tier approach first descr ibed in the August 23, 2010 clarification memorandum “Applicability of Appendix W Modeling

Guidance for the 1

- hour SO 2 National Ambient Air Quality Standard” was to use the overall highest hourly concentration from a representative monitor. The EPA recogn ized that this approach may be overly conservative and in the March 1, 2011 memorandum “Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1

- hour NO 2 Ambient Air Quality Standard” which is also applicable to SO 2 , offered alternative approaches of using the most recent design value and a background that varies by season and hour of day. In response to the comment regarding areas with multiple monitors ( commenter 0052), AERMOD does allow for varying background by spatial l ocations that can be used for locations with multiple representative monitors and where those monitors are representative of specific areas. With regards to “double counting” of background ( Commenter 0040), s ection 8.2.2.b is clear that background concent rations are to exclude hours where modeled sources impact the monitor. With regards to comments near a source, the m odeling TAD states that background concentrations should be from a representative monitor. The monitor near a source of interest

would usua lly be representative and can represent nearby sources’ impacts. However, the TAD

and s ection 8.2.3 of Appendix W recommend modeling nearby sources which cause a significant concentration gradient in the vicinity of the source of interest. In those cases, hours at the monitor that are impacted from those modeled sources are excluded from the background

concentration. When determin in g hours to exclude , in order to eliminate double counting of model, use of back trajectories or other analyses are encouraged.DELIBERATIVE

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196 With regards to percentiles of background, the recommendations in the TAD are that, recommendations. If applicants feel that a different percentile is warranted then they should work with the appropriate reviewing authority and Regional Office to justify a different methodology

than outlined in the TAD. Nevertheless, it is worth noting that the commenter s that find the

combination of a 99 th percentile modeled result with a 99 th percentile background value to yield a

99.99 th percentile value are applying f aulty methods of statistical analysis. The percentile of a sum cannot be computed by multiplying the percentiles (or 100% minus the percentiles) of the component parts. The error of this method can be illustrated by using this method to compute

other resul ts, equally in disregard of any differences in magnitude or variability of the component parts. F or example

, this method would suggest that the combination of a 99 th
percentile modeled result with a 50 percentile background value would be a 99.5 th percenti le, and the only background value that in combination with a 99 th percentile modeled value would give a

99 th percentile result would be a zero background value. In any case, these comments speak not to questions pertinent to this rulemaking concerning what modeling requirements should be established but rather to questions as to how those future modeling analyses are conducted.



### 5. Stack height

Comment :

Commenters ( 0037, 0046

, 0047, 0050, 0051, 0052, 0053, 0056, 0058, 0073, 0075, 0082, 0089, 0093, 0097

, and 0 108 ) generally supported the use of actual stack height

.

Commenter s ( 0046 , 0058, 0081

, 0089, 0093, and 0097 ) stated t he EPA should allow sources to model using actual stack height regardless of whether they are modeling actual emissions or

allowable emiss ions since the purpose of the r ule is to estimate, as accurately as possible,

conditions that would be measured at a monitor. Commenter s ( 0046, 0050, 0058 , 0081 ) disagreed that the GEP stack height is more appropriate when using allowable emissions because the GEP height not always a factor in establishing the emissions limit; for example, in the context of emission limits that are established based on emission standards, such as the MATS

rule. C ommenter (0081) agreed that the concern about giving inappropr iate credit for dispersion techniques is not relevant in this situation as section 123 applies only to emission limitation controls; the fact that actual height may have not been used when calculating the allowable

emission rates is irrelevant in the conte xt of this designation modeling.

Response:

After consideration of comments received on the proposed rule , the EPA modeling TAD

continues to recommend the use of actual stack heights when using actual emissions and the use of GEP height when modeling with allowable emissions where such emissions limits are or would be subject to CAA section 123 and to the EPA’s corresponding regulations implementing GEP requirements

. This would include limits established under any CAA provision that are

intended to be cred ited in an implementation plan for attaining and maintaining the NAAQS. The use of GEP for allowable emissions modeling in such situations is to be consistent withDELIBERATIVE

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197 nonattainment planning requirements, which cannot consider any portion of the stack height t hat is above GEP height, since the purpose of modeling based on allowable emissions would be to assess whether the limits would satisfy nonattainment planning requirements for assuring

attainment.



### 6. Meteorological d ata

a. One year

Comment :

Commenter s (006 7 , 0085 ) supported the use of one year of meteorological data. Commenter (0067) stated that use of the most recent three years of actual emission data mod eled with one year of on

- site met data would yield a very robust data set and record for making a mode ling

based designation. Commenter (0085) stated that o perating an on

- site meteorological monitor for three years does not provide a significant benefit over collecting one year's on

- site meteorological data. Commenter (0085) stated that o ne year of meteoro logical data are sufficient for PSD purposes.

Commenter (0067) stated the requirement to use the most recent 3 years of met data are not practical

, will prove costly

, and there is no real need for it. Commenter (0067) stated the EPA should not require 3 years of on

- site meteorological data for designations modeling and requested the TAD be revised to not require 3 years of on

- site meteorological data.

Commenter (0067) noted an on

- going

, extensive modeling study using one year of onsite meteorological dat a, one year of concurrent actual emissions data, and up to one year of concurrent monitoring data from five SO 2 ambient air monitors and stated i t is not reasonable to

expect such a met station to run continuously for more than a year due to cost, noise an d location

issues

. . Commenter (0067) stated that, i n cases where a facility is willing to install such an elaborate and costly station, the EPA should encourage such an endeavor as it will result in better regulatory decisions , h owever, the EPA should reco gnize the challenges and allow such systems to operate for the one year minimum and allow that year to be non

- concurrent with the actual emissions being modeled.

Commenter (0085) stated that not many sites already have on

- site meteorological monitors, so in

addition to the financial cost and time required to install them, requiring the collection of three years of data would delay the running of AERMOD for designations. Commenter (0110) stated

the EPA should continue to require only 1 year of on

- site meteo rological data for attainment designation modeling . Commenter (0110) stated a requirement to collect three years of on

- site

data are inconsistent with the proposed designations timeline since s uch a requirement would make it impossible to use new on

- site d ata and still adhere to the anticipated EPA schedule. Commenter (0110) stated that, while relatively few meteorological databases with three years of

on

- site meteorological data exist ; m any sources may have already collected a full year of data in

accordan ce with Appendix A and have since dismantled their meteorological towers. CommenterDELIBERATIVE

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198 (0110) stated t hese sources should be able to use the 1 year of data already collected without starting all over again on an expensive three

- year effort.



### b. Five years

Com ment :

Commenter (0062) recommended that up to five years of meteorological data be used concurrent with the emissions data in modeling to simulate current air quality for designation purposes and future verification modeling. Commenter (0062) stated that a single three

- year period may not provide adequate confidence in the analysis . Commenter (0062) stated that f ive years will provide more three

- year combinations that can be compared to the NAAQS and m ore meteorological data improves confidence in the resu lt.

Response:

The EPA’s recommendation is to use the most recent 3 years of representative site

- specific data

. W hen site

- specific data are not readily available, or it is not feasible or cost

- effective to collect

site

- specific data, the most recent 3 y ears of representative NWS meteorological data or other representative data could be used . When the most recent 3 years of representative meteorological data are not available, the use of older representative meteorological data can be used. For such

cases , t he m odeling TAD offers recommendations on synch roniz ing the older meteorological data with the more recent emissions, especially for those sources utilizing hourly emissions. The TAD provides an explanation of the need for 3 years of meteorological data , even if only 1 year

of on

- site meteorological data is available. With regards to the type of meteorological data that are available, i.e. site

- specific, NWS data, or prognostic data, a ppendix W should be consulted on the latest acceptable forms of meteor ological data at the time of the modeling analyses.

c. 

### Concurrent meteorological and emissions data

Comment :

Commenter (0082) urged EPA to explicitly state in the final rule that air agencies need not use concurrent meteorological data, given that some s ites simply do not have concurrent meteorological data. Commenter (0082) agreed with the suggested approach in the d raft

m odeling TAD, which recognizes that, in such situations, it “may be feasible to use older meteorological data...that has been used in pas t regulatory applications for the area containing the threshold exceeding source, if these datasets are still considered representative of the most recent three years of meteorological conditions.”

Commenter (0106) raised the question of what is meant by the most recent 3 years: would this most recent period necessarily be circa 2010

- 2012 or later

. W ould the use of an earlier period of actual emissions and meteorological data (say 2006

- 2008) be acceptable as long as a companion analysis is provided which demonstrates that actual emissions have decreased (or at least notDELIBERATIVE

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199 increased) since that time

. Commenter (0106) referred to page 26 of the m odeling TAD and stated that use of upper

- air data from Radiosonde Data of North America CD for the period

1946

- 1997 does not seem consistent with the recommended use of the most recent 3 years of emissions paired with the most recent 3 years of concurrent meteorological data (i.e., the most recent year on the CD would be 1997).

Response:

The EPA’s recommendation is to use the most recent 3 years of representative site

- specific data

. W hen site

- specific data are not readily available, or it is not feasible or cost

- effective to collect

site

- specific data, the most recent 3 years of representative NWS meteorological data or other representative data could be used . When the most recent 3 years of representative meteorological data are not available, the use of older representative meteorological data can be used. For such

cases, t he m odeling TAD offers recommendations on sy nching the older meteorological data with the more recent emissions, especially for those sources utilizing hourly emissions. The TAD provides an explanation of the need for 3 years of meteorological data, even if only 1 year of on

site meteorological data is available. With regards to the type of meteorological data that are available, i.e. site

- specific, NWS data, or prognostic data, a ppendix W should be consulted on the latest acceptable forms of meteorological data at the time of the modeling analyses.

d. 

### Where m eteorological data are unavailable

Comment :

Commenter (0042, attachment A5) stated that the EPA suggests that s tates should apply screening modeling when representative meteorological data suitable as input to AERMOD are

unavailable

. Commenter (0042, attachment A 5) stated that, i f such an overly conservative approach indicates a predicted NAAQS violation, then the s tate and affected sources should be provided with an opportunity to determine an alternative, less conservative modeling approach,

a nd, if needed, provided with adequate time for a more refined modeling analysis, including new

field data c ollection, if that option is selected.

Commenter (0082) stated that, given many air agencies will be unable to submit modeling protocols to the EPA by January 15, 2016, for sites that lack three years of representative site

specific meteorological data or ASOS meteorological data, as required by the Proposed Rule and

the d raft m odeling TAD

, the EPA should approve the use of prognostic meteorological d ata, in lieu of meteorological data from observations or specific meteorological modeling simulations. Commenter (0082) stated p rognostic meteorological data are routinely used by the NWS in its forecast models and can create three years of site

- specific m eteorological data in six months.

Commenter (0082) stated that, f or prognostic meteorological data to be used by air agencies in this context, the EPA would need to develop guidance on its use by December 31, 2014, to allow

sufficient time for the data t o be created. Alternatively, commenter (0082) stated, the EPA should extend the timeline for state agencies to submit modeling protocols to the EPA for sitesDELIBERATIVE

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200 without representative site

- specific meteorological data or ASOS meteorological data so that

state agencies will have time to obtain the required data.

Response:

In response to comments regarding areas without representative meteorological data, the

m odeling TAD states that the meteorological data only be representative , which does not preclude the u se of a station that is representative of conditions in the analysis domain but is not nearby . It may be possible to use such stations acting in consultation wi t h the EPA Regional Office. With regards to prognostic data, the latest version of Appendix W at the time of modeling should be consulted for acceptable forms of meteorological data. To the extent that the commenter considers the shortage of time before the modeling protocol deadline to justify usage of prognostic data, it is worth noting that the fi nal rule reflects a six

- month delay in the deadline for the modeling protocol.



### e. Multiple mete o rological stations

Commenter (0106) referred to page 24 of the m odeling TAD r egarding meteorological station

selection ( "if the modeling domain is large enough such that conditions vary drastically across the domain, then the selection of a single station to represent the domain should be carefully

considered" ) and stated the EPA 's meaning here is not clear. Commenter (0106) requested explanation/clarification

. C ommenter (0106) suggested that the presence of varying meteorological conditions and the need for more than one meteorological station would be more appropriately addressed with a dynamic m o del such as CALPUFF ; t he dynamic model would

handle this situation more seamlessly and accurately than possible manipulation of AERMOD layers.

Response:

When the modeling domain is large enough such that multiple stations are available or are representative of different parts of the domain, the selection of the meteoro logical station would require best professional judgment by the applicant and reviewing authority. The station that best represents the conditions for most of the domain would most likely be the station of choice. With regards to use of CALPUFF, this woul d require an alternative mod el demonstration (Section 3.2.2 of Appendix W) as CALPUFF is not a preferred model for near

- field modeling.



### 7. Receptor placement

Comment :

Commenters ( 0042, 0110) s uggested that certain areas be excluded from receptor placement f or modeling. Commenter (0042, attachment B) stated receptors should not be locat ed where it is highly unlikely individuals will remain stationary for an hour ; i.e., freeways, waterways and

extreme slopes. Commenter (0110) stated r eceptors should be exclude d from areas under theDELIBERATIVE

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201 ownership of the source being modeled and areas that cann ot support monitoring, such as water bodies, s teep terrain areas, and t ransportation routes. Commenter (0042, attachment B) stated siting of receptors at a property fence line, regardless of whether any members of the public are located there, and basing compliance with NAAQS with predicted concentrations at those receptors may require sources such as agricultural operations to reduce emissions, without producing health or envir onmental benefits. Commenter (0051) urged the EPA to modify the guidance to recognize the type of public exposure the primary SO 2 NAAQS is designed to prevent: exposure of an exercising asthmatic to short duration SO 2 concentrations that can induce mild, r eversible changes in respiratory function.

Commenters (0042, 0046, 0051, 0073, 0103, and 0110) support ed the placement of model receptors only in areas where it is feasible to place a monitor since the modeling is acting as a surrogate for monitoring. Com menter (0051) stated the EPA should use a consistent receptor placement policy for monitor siting and compliance modeling demonstrations and suggested t he modeling TAD should follow the receptor placement of the monitoring TAD.

Commenter (0103) suggested it may not be reasonable to use the same receptor placement policy for both monitor placement and compliance modeling demonstrations. Commenter (0 103 ) provided the following additional points.

H istorically, one of the hallmarks of regulatory dispersion m odelling analysis for NAAQS compliance is that any point in ambient air (outside of the facility fence line) is eligible for receptor placement. B ecause t he Proposed Rule indicates that receptor points in the modeling are to be regarded as surrogates for m onitors , t his could be construed to mean that a modeling receptor point that is not feasible for monitor placement is not eligible for inclusion in the monitoring grid for an attainment determination and is therefore not protected under the NAAQS. A n overl y broad reading of the notion of a receptor point as a surrogate for a feasible ambient monitoring location could change the attainment status determined from the modeling analysis from non

- attainment to attainment or in an extreme case, might result in a modeling analysis which could not determine attainment status near a facility because of the exclusion of receptors that represent “infeasible” monitoring sites.

T he federal monitor siting rules in 40 CFR p art 58 Appendix E suggest avoiding any

local inf luences near the site that might alter air flow from the source to monitoring site (walls or trees) or create local sources or sinks of pollutants at the monitoring location (roads or furnace flues)

. I n practice, there are many areas excluded for monitors in the

federal m onitor siting rules and was concerned with any overly broad reading of the

notion of a modeling receptor point as a surrogate for a monitoring site. (0103)

Commenter (0103) noted that the modeling TAD gives only one example of this type of receptor point exclusion

-- over a water body

-- and commenter (0103) request ed clarification on o the r receptor points that might be excluded from the modeling analysis based on the criteria of monitoring feasibility. Commenter (0103) asked if a receptor poin t be excluded from theDELIBERATIVE

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202 modeling grid, if upon investigation of the receptor location:

• T he location was within 10 meters of a tree, too close to a road, or did not meet any of the

other criteria in 40 CFR p art 58 Appendix E?

• T he s tate could not secure a lease to operate a monitor at the location?

• T he costs associated with trenching the power to the location exceeded the cost of the monitoring equipment at the site?

• T he location was in a remote area, and a site operator could not be secured, or could not be secured at reasonable price?

• T he location was in an unpopulated area, where the s tate could not justify the additional expense of monitoring relative to modeling based on the human health benefits of operating the monitor at the location?

• T he lo cation was near an emitting facility that had declared its intention to switch from coal to natural gas during the 3 year monitoring period?

Response:

The December 2014 version of the modeling TAD was updated to include the receptor placement strategy o f the monitoring TAD. It recommends that r eceptors could be placed where a monitor could be placed since the modeling is acting as a surrogate for monitoring. This , for example, would avoid requiring placing receptors over bodies of water and areas where it is infeasible to place a monitor. This strategy differs from the other regulatory applications of dispersion modeling (SIP and NSR/PSD) where receptors should be placed in ambient air, regardless of whether a monitor can be placed in that location.



### 8. Pair ed test

Comment :

Commenter (0070) stated the EPA has failed to explain why a paired test is useful for photochemical modeling of secondary pollutants, but is not useful for the evaluation of modeling of directly emitted primary pollutants. Commenter (007 0) stated that logic suggests that if meteorological data are captured concurrently with the ambient concentration data when examining primary pollutants, if the modeling system is properly formulated and functioning, obtaining elevated readings at roughly the same time and place in both the model and ambient

data sets should occur most of the time.

Commenter (0106) referred to p age 28 of the m odeling TAD ( "hour

- by

- hour pairing is not recommended because this approach would assume that the hourly monitored backgroundDELIBERATIVE

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203 concentration is spatially uniform for the hour and that monitored values are representative of background levels at each receptor for each receptor" ) and stated t his concern regarding the uniformity of hourly background concentrations in the c ontext of a steady

- state model application has no merit. Commenter (0106) stated that, i f it is reasonable to assume that hourly meteorological data from a single station is spatiall y uniform for the entire modeling domain and

if it is reasonable to assume that surface characteristics associated with a single location are spatially uniform for the entire modeling domain, then it is likewise reasonable to assume that hourly background concentrations from a single location are also spatially uniform for the e ntire modeling domain ; especially if the hourly background concentrations reflect an unbiased rural monitoring site.

Response:

While this final rule is not the forum in which the agency would make amendments to its non

binding technical guidance, the EPA continues to recommend against hour

- by

- hour pairing of background with modeling results except in isolated cases . As stated in the March 1, 2011 memorandum “Additional Clarification Regarding Application of Appendix W Modeling

Guidance for the 1

- hour NO 2 National Ambient Air Quality Standard” and referenced in the modeling TAD, pairing hour by hour assumes that the background is spatially uniform and that

the monitored val u es are fully representative of background at each receptor at each hour. The

memo st ates that such an assumption ignores the temporal and spatial variability of ambient concentrations across a typical modeling domain on an hourly basis. In this response the EPA is not adopting this position as a final, binding matter, and continues to ur ge commenters who wish to recommend amendments to the TAD to direct such comments to [ James Thurman of the Air Quality Modeling Group , OAQPS, RTP, N.C., 27711 ( Thurman.james@epa.gov

, 919

- 541

- 2703).



### 9. AERMOD, EPA’ s preferred near

- field dispersion model

a. Performs well

Comment :

Commenter (0054) agreed that for certain conventional SO 2 emission scenarios, such as tall stacks at coal fired electricity generating units; AERMOD can be at least reasonably predictive.

Commenter (0068) stated that AERMOD modeling performs particularly well in evaluating emission sources with one or a handful of large emission points. Commenter (0068) cited a declaration of Roger W. Brode in which he stated that AERMOD is capable of accu rately predicting whether the revised primary SO 2 NAAQS is attained and whether individual sources

cause or contribute to a violation of the SO 2 NAAQS. Commenter (0068) stated that AERMOD has been tested and performs very well during conditions of low wind speeds, citing comments

of Camille Sears.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

204 

### b. Concern s with AERMOD

[See also VIII and IX

, regarding the TADs and Tenth Modeling Conference , and II.C, regarding general comments on models. ]

Comment :

Commenters ( 0039, 0040, 0042, 0046

, 0048, 0049, 0050, 00 51, 0054, 0058

, 0059, 0063, 0064

, 0065, 0070, 0073, 0079, 0080, 0090, 0092, 0108, 0109, 0110, 0112, 0114 ) expressed concern

with the use of AERMOD. Commenter (0042) recommended that the Agency take the time to correct the problems with AERMOD before the EP A considers or requires the use of that model in implementing the 1

- hour SO 2 NAAQS. Commenter (0070) recommended that, until the EPA can stabilize the treatment of low wind speed conditions in AERMOD, the EPA should avoid the use of AERMOD for designation purposes.

Over predicts

Commenters ( 0039, 0042, 0043, 0046, 0048, 0049, 0050, 0058, 0064, 0063, 0065, 0073, 0080, 0090, 0108, 0109, 0110, 0112, and 0 114) stated that A ERMOD over predicts ambient air

concentrati ons. Commenter (0042) listed a number of iss ues with AERMOD that need to be addressed because they lead to over predicting SO 2 concentrations, including the following.

 The modified building downwash algorithm specified in Model Change Bulletin #4 (dated 11059) in AERMOD, which has not been validate d, contributes to systematic over predictions by AERMOD.

 AERMOD over predicts concentrations in gradually sloping terrain; the indication in the Draft Guidance that terrain less than stack height need not be considered is inadequate to

resolve the issue. Over predictions of a factor of 2 can occur due to the terrain effect.

 In general, the aspects of AERMOD and EPA’s guidance that contribute to over prediction of the SO 2 concentrations in the context of the 1

‐ hour NAAQS are multiplicative. As an example, if three independent aspects of the model application each

resulted in an over prediction factor of two, the resulting over prediction would be a factor of eight (2x2x2). By adding conservative assumptions in terms of model input and

the inclusion of conservative background concentrations, the EPA does not take into

account the built

‐ in conservatism of AERMOD and the general EPA modeling guidance.

EPA s hould be o pen to the d evelopment of i mproved p rocedures for a ddressing v ariable

e missions and m eteorological c onditions.

Commenter (0048) asserted this over prediction is particularly true when accurate emissions data and representative meteorology are not available. Since modeling will be required in many cases based on the proposed dates in the DRR, commenter (0048) stated it will be almost impossible to obtain representative meteorological data. Commenter (0048) stated o nsite meteorological dataDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

205 are generally not readily available, thus, it is likely that AERMO D will not produce representative results and areas will be misclassified with a leaning towards over prediction and

nonattainment classifications.

Commenters ( 0039, 0042, 0046, 0049, 0058, 0063

, 0065, 0079, 0109, and 0110) referenced

studies that indicat e AERMOD over predicts. Commenter (0039) asserted that studies by EPRI

and others have shown that AERMOD over predicts actual ambien t concentrations by a factor of two when the concentrations are in the range of the 75 ppb standard. Commenter (0058) stated that model evaluation studies, using th e most recent version of AERMOD , have documented AERMOD’s tendency to over predict concentrations relative to actual measured data, sometimes by a factor of 2 or more

. Commenters (0042, 0063, and 0065) cited a recent AERMOD study by

AECOM. Commenter (0109) stated AERMOD over predicts actual SO 2 emissions by a factor of 10 when compared to actual IDEM monitoring data. Commenter (0110) stated that a comparison of AERMOD modeling and monitoring data for a North Dakota fa cility indicated that while 5

ambient monitors measured levels at about 50% of the SO 2 NAAQS, modeling using actual emissions and an agency

- determined background predicted the peak SO 2 concentration at a level above the NAAQS.

Commenters (0042, 0073, 009 0, 0110

, and 0112 ) expressed concern with over prediction during periods of low wind speed. Commenter (0042) stated AERMOD over predicts substantially during periods of low

- wind speed events (0042, attachment 5 to their comments, provides 3 pages of techni cal comments on this issue). Commenter (0110) stated that i mportant over

prediction issues have been identified with AERMOD in stable light wind conditions (e.g., Paine et al., 2010 ) and that t hese problems can affect peak predictions and thus can signific antly affect the compliance status of a source if modeling is to be used instead of monitoring to establish whether an area surrounding a source complies with the SO 2 NAAQS. Commenter (0112) included a June 2014 study prepared for them by AECOM titled “Eva luation of Low Wind Modeling Approaches for Tall

- Stack Databases.” The study’s findings and conclusions include:

 For the North Dakota evaluation, the AERMOD model versions all over predicted using the design concentration as the metric.

 For the relatively low elevation monitors, the results were similar for both the default and beta options and are within 5

- 30% of the monitored concentrations depending on the model option.

 The modeling result for the elevated DGC #17 monitor showed that this location is

se nsitive to terrain as the ratio of modeled to monitored concentration is over 2.0, but when this location was modeled with the low wind beta option, the ratio was notably better, at less than 1.3.

 For the Gibson flat terrain evaluation, AERMOD with hourly averaged meteorological

data over predicts at three of the four monitors between 30

- 50 percent, and about 10% at

the fourth monitor.

 The AERMOD low wind speed options have a minor effect for flat terrain locations.

 These options have a more significant eff ect with AERMOD modeling for elevated

terrain locations.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

206  The AERMOD sub

- hourly modeling results are the most unbiased of all model

combinations tested for these two databases.

 SCICHEM results indicate some over prediction tendencies for some monitors. The model developer has been provided with this information for purposes of further testing

and evaluation. (0112)

Commenter s ( 0109, 0110) stated that some sources may feature substantial excess heat releases that are not currently accounted for by AERMOD (pr esentation by Paine at 2014 EPA modeling workshop). Commenter (0110) stated that i n many cases, accounting for this additional heat release may involve an urban characterization to the source or a realization that the emissions near heated buildings are no t subject to downwash effects, but instead “lift off” due to the heating effects.

Commenter s ( 0063, 0065) stated that the recommendation in the m odeling TAD to m odel

sources that are within a few kilo meters of each other together may cause AERMOD to over predict SO 2 c oncentrations or resul t in otherwise inaccurate data because c o

- locating sources will tend to produce higher concentrations in the dispersion model than modeling as individual

sources and e ven sources within relatively close proximity to each other could have different dispersion patterns depending on geography, meteorology, or operating schedules.

Commenters (0042, 0046

, and 0108 ) stated that AERMOD was intentionally designed to over predict SO 2 concentrations. Commenter (0042) stated that c e rtain specific modeling assumptions, inputs, and techniques exacerbate AERMOD's over prediction tendencies , including lateral dispersion at low wind speeds

, vertical concentration gradients , and buoyant line sources.

Commenter (0042, attachment B) stated that AERMOD over prediction is inappropriate given the stringency of the new standards and the proposed use of AERMOD for designation purposes.

Commenters (0063, 0065) stated that AERMOD fails to meet QA criteria for air quality data and siting criteria in the current regulations prescribed by p art 58, Appendices A and D.

Improvements to AERMOD

Commenters (0042, 0047, 0075

, and 0090 ) encourage d the EPA to continue improving the Agency's preferred models. Commenter s ( 0042, 0051

, and 0090 ) stated th at a n y revisions to the

model and data used to make those revisions should be made available to the public ( e.g., put on the SCRAM website) . Commenter (0051) stated that the EPA should provide states with

documentation of all technical issues and fixes that hav e been identified with the AERMOD

system. Commenter (0051) stated that o f particular interest is information on how to adjust the modeling process or predicted concentrations.

Commenter (0042) stated that, if the EPA wants to require the use of AERMOD for a broader range of regulatory purposes, then it should address the problems with AERMOD, many of which are identified in an AECOM report attached to their comment letter. Commenter (0064)DELIBERATIVE

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207 stated that while improvements were made to the AERMOD model since promulgation of the 1

- h ou r standard, more improvements are to take place , s uggest ing that A ERMOD is still not an accurate indicator of the actual ambient air quality.

Commenter (0110) stated that because there are many technical issues that need to be add ressed in AERMOD, relying on AERMOD before these changes are implemented could result in erroneous NAAQS attainment and nonattainment designations. Commenter (0070) recommended that, until the EPA can stabilize the treatment of low wind speed conditions in AERMOD, the EPA should avoid the use of AERMOD for designation purposes, as it may incorrectly penalize sources that do not have an adverse impact on actual ambient air quality concentrations, but are located in areas with frequent low wind speeds. Commen ter (0040) stated that if AERMOD is retained in the final rule, the EPA should allow use of low wind speed

corrections to better reflect the actual conditions around some sources modeled.

Commenter s (0042 , 0090 ) stated AERMOD's performance needs to be re

- evaluated in light of multiple recent modifications.

Commenter s (0042, 0075, and 0080) recommended that the EPA establish more formal procedures for making changes to its preferred models. Commenter s ( 0042, 0075

, and 0080 ) stated that they are concerned that none of EPA’s recent actions to improve the performance of AERMOD was the subject of a public comment period or noticed for comment in the Federal Register

. Commenter (0080) stated the EPA continues to release updates and newer versions of

AERMOD and AERMET without providing a public comment period or notice of comment in

the F ederal R egister and that this lack of comprehensive assessment of the impact of changes to the model and processor components creates concerns for stakeholders. While commenter ( 0075) supported allowing regulatory agencies and sources to use new modeling tools that may not have undergone full notice

- and

- comment review, they encouraged the EPA to subject improvements in the model to broader review (like the review provided by notic e

- and

- comment rulemaking)

because stakeholders remain concerned about over

- reliance on modeling predictions.

Commenter (0110) stated that a number of AERMOD updates are needed in Appendix W to improve the accuracy of model estimates , including stable ligh t wind conditions and excess heat releases for certain types of sources. Commenter (0110) stated that, while the EPA intends to promulgate changes to Appendix W in the spring of 2016 , u ntil these AERMOD changes are promulgated, it is premature to rely upon the use of AERMOD to determine modeled compliance

with the SO 2 NAAQS.

Form of the standard

Commenters ( 0042, 0051) expressed concern that AERMOD may not be suited for demonstrating compliance with a one

- hour standard based on the three

- year average of t he annual 99th percentile of the daily maximum one

- hour average concentrations. Commenter (0042, attachment A 3) stated the EPA 's preferred model, as it exists today, is unable to directly provide values that can "fit" the probabilistic form of the NAAQS ad opted in the f inalDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

208 r ule, meaning states will have significant difficulty meeting the requirements of the new standard, as stated. Commenter (0042, attachment A 3) provided the following additional points.

The difficulties integrating modeling and monitorin g data due to the form of the S O 2 standard adopted by the EPA will require that modeling procedures be refined to realistically address the frequency of peak short

- term impacts in order to appropriately implement the new 1

- hour S0 2 NAAQS. The joint frequen cy of worst

- case cumulative emissions and adverse dispersion conditions becomes more important for probabilistic

ambient standards. The new S O 2 NAAQS adopted by the EPA is a probabilistic standard.

AERMOD is a deterministic model (that is, provides point estimates) and is not suitable to provide probabilistic short

- term concentrations for a NAAQS that requires a probabilistic modeling approach. EPA' s preferred air dispersion models have not been specifically developed or evaluated to predict short

- term loc ations of maximum concentration or account for the probabilistic standard.

For cases where the probability of simultaneous occurrence of peak emissions and worst

case meteorology is very low, the standard modeling approach will unrealistically

exaggerate peak ambient concentrations. This is particularly true for sources that do not

operate continuously, such as conditions during startup and shutdown, or testing. Adding

monitored background concentrations to modeled maximum concentrations will most likely be overly conservative, which would make those modeled projections inappropriate for use as a basis for designations or redesignations under the CAA. (0042, attachment 3)

Other technical concerns

Commenters (0042, attachment B, and 0051) stated the EPA s hould also require comparison of predicted concentrations at the time and location of monitored values. Commenter (0042,

attachment B) stated t his will facilitate evaluation of the model’s treatment of atmospheric chemistry and meteorology. Commenter (0051 ) stated that, w hile AERMOD can predict high concentrations that were observed at a nearby monitor from an isolated source, there was no attempt during the model's development to match predicted concentrations to monitored

concentrations at the same time a nd location of the monitor and there was no attempt to model the transformation of SO, or determine deposition downwind.

Commenter (0049) stated that if modeling is to be used for attainment designations, then use of sub hourly and meteorological data mu st be allowed to better represent SO 2 concentrations because hourly emissions and meteorological data currently used in AERMOD, causes excessively conservative results.

C ommenter s (0054 , 0092 ) stated modeling approaches using AERMOD are of particular con cern at aluminum smelters because AERMOD does not adequately account for heat release (and associated plume rise) within these facilities; the effect of numerous merged buoyant plumes;DELIBERATIVE

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209 and/or the impact of downwash from large or long buildings. Commenter ( 0092) stated they have previously provided the EPA with documentation (which they did not cite) that clearly demonstrates that AERMOD does not reliably predict emissions from aluminum smelters (or sources near large or long buildings).

C ommenter (0059) as serted AERMOD can be extremely sensitive to small variations to input

values and that optimum performance for AERMOD occurs with extremely enhanced source characterizations (e.g., actual emission rates, true exhaust flows, exhaust temperatures, etc.)

. Comm enter (0059) stated that u nless these two limitations to using air dispersion modeling

, and AERMOD specifically, can be quantified and minimized, the ramifications of “false” attainment designations are too great. Commenter (0059) stated, for example, that small changes to surface roughness values input to AERMET, the meteorological preprocessor for AERMOD, have been shown to cause modeled concentrations that vary dramatically.

Commenter (0059) asserted that , while the a ccuracy of AERMOD is documented in v arious

AERMOD evaluation studies

, the evaluation studies represent optimum datasets that include access to monitoring data from one or more ambient air monitoring locations, detailed and actual hourly process information for the sources being modeled for t he periods corresponding to the period of ambient air monitoring data, and detailed meteorological data that can enhance the performance of AERMOD. Commenter (0059) stated it is u ndocumented as to how AERMOD performs for situations where the completeness o f source data a nd meteorological data are

reduced relative to the evaluation studies.

Response:

In the final rule, the EPA is not promulgating a requirement that air agencies use AERMOD in all cases, but is retaining the existing flexibility otherwise p rovided by the EPA’s rules for agencies to support the use of the best model for a particular case. Therefore, this final rule does not address the specific objections to AERMOD that the commenters have raised. The EPA’s latest recommendations for making t he assessment of which model to use are contained in the

m odeling TAD , but, again, the EPA is also not codifying the TAD or taking final action to make its recommendations binding

. In most cases, the EPA believes that AERMOD will likely be the

model of cho ice by air agencies to address the requirements of this rule , unless the application

involves a different recommended model

, such as the Buoyant Line and Point Source Dispersion Model (BLP). Models recommended for particular applications are listed in appe ndix A of appendix W

, s ection 3.2 of a ppendix W outlines the procedures for use of alternative models for those cases where an alternative model may be more appropriate than a preferred model

. In addition, the m odeling TAD also discusses past use of altern ative models for particular applications. 9 The EPA recommends consultation with the appropriate reviewing authority or

9 It is the EPA’s intention to update the m odeling and m onitoring TA Ds as necessary to reflect any change in policy or to make clarifications that are necessary. Therefore, any comments on the TADs themselves that have been submitted in response to the proposed rule will be addressed as a part of any updates made to the TA Ds in the future, rather than in this final rule.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

210 EPA Regional Office to determine if the use of an alternative model is valid for that application.

In addition, as stated previously, t h e TADs are documents that provide recommendations but are not binding or enforceable and create no obligations on any person . Although the draft TADs are

referenced as recommended approaches in the preamble to the proposal and in this rulemaking, they are not required to be adhered to by any state that is required to characterize air quality

around an SO 2 source identified in this rulemaking. The TADs have been provided in order to potentially aid air agencies seeking advice in the air quality characterizat ion process required by this rulemaking.

With regards to over predictions of AERMOD, while any model is not perfect, EPA has shown on numerous occasions, that when proper inputs are input into AERMOD when using actual emissions, AERMOD has been shown to p erform well against other models when compared to

observations. If users follow the recommendations in the TAD regarding source inputs, meteorological data (including surface characteristics) and background information, along with the use of best professio nal judgment, EPA believes that the model outputs will be sufficient for the stated goals of this rule. That is, EPA finds AERMOD, when run appropriately, to provide information with adequate reliability for use in the various planning efforts that this ru le is intended to support. That being said, EPA is working in contexts outside of this rulemaking to alleviate technical concerns with AERMOD such as low winds, building downwash, etc. Finally, as explained previously, this final rule is not establishing r equirements for how future designations must be conducted, and does not prejudge the appropriateness of the use of AERMOD or an alternative model in such future designations.



### 10. Alternative models and alternative approaches

Comment :

Commenters ( 0050, 0051, 0054, 0056, 0060

, 0070, 0092, 0093, 0109, 0106, and 0114 ) encouraged EPA to support alternative models and approaches.

Guideline models and Appendix W

Commenter (0050) supported the idea that air modeling for initial designations should not need

to confo rm to the EPA’s Guideline on Air Quality Models and that states should have control over the types of models they use. Commenter (0051) stated t h at the EPA prescribed model

limits the amount and type of data that can be used to characterize current air qua lity.

Commenter (0060) request ed the EPA to note, similar to Appendix W of 40 CFR p art 51, that approaches/models other than AERMOD may be appropriately used on a case

- by

- case basis. Commenter (0109) believes that 40 CFR p art 51 Appendix W should express ly include as many model refinement options as possible to provide clear guidance to states and regulated entities that these modeling options are appropriately considered.DELIBERATIVE

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211 List of models used in regulatory assessments

Commenter (0051) stated the EPA sho uld provide a list of models, such as CAMx, that have been used extensively in regulatory assessment, that states can use without being required to submit lengthy justification and model performance studies. Commenter (0051) provided the following addition al points.

Since models like CAMx have been used by many state agencies and the EPA to provide air quality assessments, states should not be required to go through the rigor specified in Appendix W , s ection 3.2.2(e). The EPA's guidance for attainment demo nstrations (EPA

454/B

- 07

- 002) allows states to determine which model is appropriate with input from the EPA. The EPA should not require states to follow the onerous alternative model justification procedure in s ection 3.2 of Appendix W of 40 CFR p art 51 to use CAMx as

well as AERMOD for this rule as that would include information well known to EPA and amounts to unnecessary work, wasted resources, and lost time. Strictly adhering to the requirements in Appendix W . s ection 3.2.2 would not give the TCEQ suffi cient time to propose an alternative model to AERMOD. If the EPA were to reject demonstration approaches using CAMx, it is probable that the TCEQ could not meet the EPA's proposed implementation timeline.

Commenter (0070) recommend ed that EPA approve the use of alternative models for the designations modeling in those cases where the existing emission limits for sources were developed using an alternative model or formulation on a blanket basis, based on the existing record demonstrating the appropriatenes s of the alternative model or formulation. Commenter (0070) provided the following additional points.

T here are many situations where complex terrain and wind flows exist or mixed types of sources that are not amenable to modeling in AERMOD co

- exist. In a number of cases in

the past, alternative models have been approved for these applications. In those cases

where alternative models or alternative model formulations have been used for the existing SIP, these alternatives should be allowed for use in the designations modeling called for in this rulemaking. This would speed the process in these areas and avoid the time consuming need to re perform the model validation work that already exists. (0070)

Specific modeling tools

Commenter (0056) stated that m o deling tool s such as the AERMOD Low Wind Beta options,

EPRI's Sub

- Hourly AERMOD Processor (SHARP) and Emissions Variability Processor (EMV AP) should be considered as potential modeling options available to state and local agencies.

Commenter (0092) state d EPA should correct the D RR ’s blanket assertion regarding AERMOD’s capabilities and accuracy and make clear in the final rule that AERMOD is not universally appropriate and that in certain cases, such as aluminum smelters, the recommended model may be a m odel other than AERMOD, such as the Buoyant Line and Point SourceDELIBERATIVE

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212 Dispersion Model (BLP). Commenter (0092) stated t his correction is necessary to ensure that air agencies, Regional Administrators, and the regulated community clearly understand that guideli ne models, other than AERMOD, have been and are recommended for use in the 1

- hr SO 2 NAAQS designation process.

Commenter (0052) stated that g uidance is nec e ssary on how to merge Buoyant Lin e and Point (BLP) modeling with AERMOD modeling or whether this wo uld be a recommended method for modeling certain source categories.

Commenter (0106) stated that, depending on the spatial configuration of sources above the (yet to be revealed) emission threshold, it is not obvious that AERMOD is the best choice for

des ignation m odeling. Commenter (0106) described a scenario where two similarly large, above

threshold sources are located 40 kilometers apart and application of AERMOD may not accurately resolve interactions between these two relatively distant sources, in w hich case commenter (0106) suggested the CALPUFF model may be more appropriate. Commenter (0106)

also described a case in North Dakota where much double

- counting would inevitably result from the application of multiple AERMOD runs. Commenter (0106) suggest ed that, rather than subjective and conservative manipulation of background concentrations with multiple AERMOD runs, a single CALPUFF application would more accurately account for multi

- source interactions, variable meteorology, and variable land use whic h would be present in the North

Dakota domain. Commenter (0106) noted that Appendix W already provides for the use of

CALPUFF on the local scale.

Commenter (0114) asserted that accuracy is essential when demonstrating compliance with a 1

- h ou r standard and that while less conservative models have been presented to the EPA; the agency has not formally approved the use of any of these alternatives. Commenter (0114) is concerned that the EPA is setting deadlines for sources to comply by conducting air dispersi on modeling without the approval of more realistic compliance tools.

Commenter (0090) stated that more complex models, like 4

- D puff, may be better suited for estimating concentrations from single and multiple sources. Commenter (0090) asserted that

direc tion comparison of short

- term (1

- h ou r) observations is highly questionable. Commenter (0090) added that large stochastic fluctuations affect short

- term concentration values prohibiting meaningful comparison between modeled ensemble averages with short

- term concentration values (John Irwin, AWMA 2013).

State/Source d iscretion to choose models

Commenters ( 0050, 0051, 0054, 0056, 0063, 0065, and 0109) stated t he EPA should provide states the flexibility to use models they determine are appropriate. Commenter (0051) stated t he EPA should provide states the flexibility to use tools that are better suited to accounting for the

chemical reactions of SO 2 in the atmosphere , such as CAMx

. Commenter (0054) stated flexibility is needed because AERMOD is not an accurat e predictor of emissions in scenarios such as those found at primary aluminum smelters. Commenter (0056) stated flexibility isDELIBERATIVE

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213 needed because AERMOD is very questionable, especially in complex terrain and in urban areas

. Commenter (0109) stated the EPA sh ould allow individual states to use model refinements on a case by case basis as the states deem appropriate including, but not limited to, the Heat Island Option, low wind speed improvements, building downwash adjustments, and buoyant plume adjustments fo r volume and area sources.

Commenter (0093) stated there should be flexibility provided to the sources with respect to

models used, characterization of emissions, etc. Commenter (0093) suggested t he emphasis on

the Technical Assistance Documents as guidan ce documents for affected sources should not limit the modeling analyses but rather should provide options for sources.

Response:

In this final rule, the EPA is not promulgating a requirement that air agencies use AERMOD in all cases, but is retaining th e existing flexibility otherwise provided by the EPA’s rules for agencies to support the use of the best model for a particular case. The EPA’s latest non

- binding recommendations for making this assessment are contained in the m odeling TAD. In most cases,

the EPA believes that AERMOD will likely be the model of choice by air agencies to address the requirements of this rule , unless the application involves a different recommended model

, such as the Buoyant Line and Point Source Dispersion Model (BLP). Model s recommended for particular applications are listed in appendix A of appendix W , s ection 3.2 of a ppendix W outlines the procedures for use of alternative models for those cases where an alternative model may be more appropriate than a preferred model

. In addition, the m odeling TAD also discusses past use of alternative models for particular applications. 10 The EPA recommends consultation with the appropriate reviewing authority or EPA Regional Office to determine if the use of an

alternative model is valid for that application.

In addition, as stated previously, t he TADs are documents that provide recommendations but are not binding or enforceable and create no obligations on any person . Although the draft TADs are

referenced as recommended approaches in th e preamble to the proposal and in this rulemaking, they are not required to be adhered to by any state that is required to characterize air quality

around an SO 2 source identified in this rulemaking. The TADs have been provided in order to potentially aid air agencies seeking advice in the air quality characterization process required by this rulemaking.



### 11. M ulti

- source modeling analyses

10 It is the EPA’s intention to update the m odeling and m onitoring TADs as necessary to reflect any change in policy or to make clarifications that are necessary. Therefore, any comments on

the TADs themselv es that have been submitted in response to the proposed rule will be addressed as a part of any updates made to the TADs in the future, rather than in this final rule.DELIBERATIVE

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214 Comment :

C ommenter s ( 0036

, 0051, 0052, and 0114 ) requested that EPA provide more specific guidance on conducting mu lti

- source modeling analyses. Commenter (0051) stated that l eaving these topics for negotiation with the Regional Office will lead to inconsistent application of guidance

among states. Commenter (0052) stated that g uidance on modeling facilities across sta te lines

should be addressed

. Commenter (0114) stated that the language in the proposal seems vague and stated that, i f there are potential areas of concern that would require sources below the threshold to model, these should be identified early in the pr ocess to give facilities the same timeframe to implement changes or conduct air dispersion modeling to comply with the rule. Commenter ( 0036 ) provided the f ollowing additional points :

We appreciate the flexibility that EPA is trying to provide to states, but EPA must also

ensure that the SO 2 implementation program is designed to identify areas where several

sources contribute to an SO 2 problem and to require those sources to be analyzed for their combined impacts. We request that EPA set specific criteria , such as proximity and total emissions per year, to establish a threshold for analyzing combined area emissions. We would like guidance on when a source should be modeled by itself and when a source should be modeled with other sources in the surrounding area, more detail on the size and

location of sources that should be included in a multi

- source analysis, and who would be responsible for conducting this analysis when sources are located in a multi

- state area.

Commenter (0051) stated the EPA should not require modeling of sources of emissions that are

less than the thresholds adopted by rule

. Commenter ( 0046 ) stated that, w here there are multiple sources in an area, the rule should limit the number of sources to include in a modeling

demonstration. Comme nter ( 0046 ) stated the inclusion of offsite sources should be determined

on a case

- by

- case basi s. Commenter ( 0046 ) provided the following additional points :

Because this is a 1

- hour standard, downwind transport distances are constrained and overlapping, a dditive impacts with other sources are limited by meteorological conditions of hourly wind direction and speed. As mentioned in the “Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1

- hour NO 2 National Ambient Air Qual ity Standard” memo from EPA, the inclusion of offsite sources should

be determined on a case

- by

- case basis. In some cases this might mean using only ambient monitor background data instead of modeling offsite sources. In other cases the modeled inventory s hould be limited to only those sources, which could cause a significant concentration gradient in and around likely ambient monitor locations.

Commenter (0106) referred to page 7 of the draft m odeling TAD and stated that i t is not clear why the number of sources explicitly modeled should generally be small. Commenter (0106) suggested the TAD should simply indicate a distance and emission threshold for inclusion of nearby sources, establish an average actual emission rate for such sources, and explicitly in clude all of them in the AERMOD analysis no matter what their number.DELIBERATIVE

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215 Commenter (0106) stated the suggested subjective approach to use contour plots, meteorological data, wind roses, and AERSCREEN to limit nearby sources for explicit modeling seems

unnec essarily cumbersome, time

- consuming, of questionable accuracy, and seems to suggest that

AERMOD is not a robust model for multi

- source analysis. Commenter (0051) did not agree with the procedure i n the TAD in which the EPA describes a complicated, resource

- intensive, multi

step process to model sources below the emissions thresholds that could cause or contribute to a NAAQS violation.

Commenters (0042, 0110) support ed an express statement in the March 1, 2011 EPA guidance that, by default, nearby sources for cumulative modeling should be limited to 10 km because

s ources beyond that distance are expected to have an insignificant concentration gradient near the source and should be considered to be included in the regional background. Commenter (0042, attach ment A 5) provided the following additional points :

Although EPA’s Guideline On Air Quality Models (Appendix W, 40 CFR p art 51) states

that the applicability limit is 50 km, this limit is not always technically appropriate to

assess the cumulative 1

‐ hour SO 2 NAAQS because it inherently assumes that a plume

could reach this distance within 1 hour. For this to happen, the wind speed at plume height would need to be about 13.9 m/sec, or about 31 miles per hour, which is fairly infrequent at most locati ons in the United States. Requiring modeling for all sources within 50 km necessarily requires the model to consider receptors well in excess of 50

km for some sources in the domain.

This also inevitably results in double

‐ counting sources that are alread y considered in the monitoring data used to estimate background concentrations. The limit on how background sources that are distant from the source of interest should be included in the cumulative modeling addresses two key concerns: the concentration gra dient issue and the practical limitation of plume transport distances. In cases of very light winds where

even 10 km is associated with multiple

‐ hour transport, the distance for considering background sources should be reduced even further. (0042, attachment 5)

Commenters (0051, 0093) stated that b ackgroun d concentrations will best approximate the impact of other sources in the area. Commenter (0 051) stated, a lternatively, a grid model, like CAMx, could be used to estimate background concentrations and provide concentration gradients. Commenter (0093) stated th e inventory of sources used in any modeling analyses

should be limited to the immediate local area and be developed at the discretion of the state.

Response:

The determination of whether to includ e nearby sources in a modeling exercise around a source that exceeds the emissions threshold is case specific

, and a standardized methodology cann ot be developed to fit all scenarios. Therefore, the final rule does not promulgate requirements addressing nearby sources. The EPA has offered non

- binding technical recommendations in the

m odeling TAD , which we believe provides sufficient guidance to enab le air agencies, sources,DELIBERATIVE

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216 and EPA Region’s to reach reasonable decisions on how to address nearby sources such that no additional specificity is required in this final rule . The identification of nearby sources for modeling should rely on sound technical r easoning and best professional judgment. The EPA emphasizes that not all emissions sources near the source of interest need to be explicitly modeled, as in some cases the impacts of those sources can be sufficiently represented by a background monitor as d iscussed in the m odeling TAD and s ection 8.2 of a ppendix W. Nevertheless, to be accurate, the analysis would need to consider the impacts of all sources that are influencing concentrations in the area; an analysis that failed to consider the impact of

sour ces emitting less than 2,000 tpy or failed to consider the impact of sources beyond some arbitrary number of modeled sources would likely fail to characterize air quality in the area.

In response to Commenter 0051’s concern about national inconsistencies, review of the modeling protocols by the Regional Office, often in consultation with EPA headquarters when questions arise, will lead to national consistency. Regional offices and EPA headquarters are in

constant contact with each other and national consi stency arises from that process.

As stated previously, the TADs provide recommendations but are not binding or enforceable and create no obligations on any person . Although the draft TADs are referenced as recommended approaches in the preamble to the pro posal and in this rulemaking, they are not required to be adhered to by any air agency that is required to characterize air quality around an SO 2 source identified in this rulemaking. The TADs have been provided in order to potentially aid air agencies see king advice in the air quality characterization process required by this rulemaking. The Agency has indicated that the TADs are meant to be used as possible tools to aid air agencies

. The EPA is not codifying changes to the TADs in this rulemaking in respo nse to any comments received on the proposed rule. The TADs are living documents which the EPA may update as necessary.



### 12. Demonstrate o ngoing d ata r equirement

-- options

a. M odel once using allowable emission or adopt limits with the actual

emissions rates used in the modeling

Comment :

Commenters (0038, 0041, 0060, 0062 , 0096

, and 0115 ) agree d with EPA's proposal that verification should not be required for sources or areas that are modeled based on the maximum allowable emissions or adopted enforceable emissi on limits. Commenters (0041 , 0062 ) recognized the value of modeling with allowables to determine if a source is attaining at its maximum permitted or potential emission level, so that re

- model ing in the future is not needed, saving resources

.

Commenter (0 048) suggested another option: (1) the EPA should allow the use of modeling in conjunction with monitored SO 2 levels and actual emissions from the affected sources for the previous 3 years to evaluate model reliability in simulating the measured concentra tions, (2) theDELIBERATIVE

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217 model output could then be used with adjustment for bias to determine appropriate allowable emission rates for the affected sources, and (3) e mission limits set in this way would no longer require verification.

Commenter (0042, attachment C ) did not support the proposal in the White Paper that the agency

should set a maximum allowed emission limit at the level of the actual emissions used in such modeling. Commenter (0042, attachment C) stated that m any processes, such as those in the steel industry, are highly variable over short time frames (substantially less than one hour), and setting

instantaneous maximum emission limits at the level of the actual emissions used for modeling does not adequately allow for this variability.

Commenter (00 60) stated that a feature of the proposal which is too narrow relates to the proposal that an air agency "always has the option to adopt for the source(s) in the area federally

enforceable emission limits at levels that are consistent with the actual emiss ions used in the modeling" thereby making additio nal assessment un necessary. Commenter (0060) stated t his should include sources with federally enforceable limits above actual emissions for which the air agency modeled attainment.

Response:

Responses to t hese comments are provided in section IV.D.g of the preamble to the final rule. In addition, the recommendation to set emission limits based on “adjustment for bias” is contrary to EPA recommendations. The EPA recognizes that emissions of many sources are variable, and EPA’s nonattainment planning guidance discusses how this variability can be addressed in a nonattainment planning context, but the limits need to be set in a manner that provides appropriate assurance that the limits will provide for attainme nt , in order to reliably eliminate the

need for continued verification of attainment

. The EPA agrees with the commenter that a limit that is slightly higher than actual emissions but that nevertheless can be shown via modeling at

the allowable level to pro vide for attainment will suffice to avoid the need for ongoing

assessment.



### b. Proposed o

ption 1: model using actual emissions

, then assess

e missions annually and conduct new modeling every 3 years

Support for Option 1

Comment :

Commenters (0071, 0115) s upported Option 1. Commenter (0071) stated that ongoing

verification of attainment of the NAAQS should be performed at regular intervals using the most

recent S O 2 emissions of the large sources, most recent S O 2 emissions of surrounding sources,

current met eorological data, and the most current modeling program. Commenter (0071) stated that, s imply assessing S O 2 emissions changes at large sources does not account for variations inDELIBERATIVE

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218 meteorological conditions, increased S O 2 emissions from interactive sources, o r improvements to the actual modeling computer program, and does not necessarily reduce the amount of resources required to perform such an analysis.

Response:

The EPA appreciates those commenters supporting the modeling of actual emissions every three

years and recognizes the concerns about Options 1 and 2 regarding criteria and consistency and review of triannual modeling. The EPA also recognizes and agrees with the comment regarding effects of changes in meteorological conditions, changes to the mode ling systems, and changes to emissions from others sources cannot be determined by simply reviewing emissions changes

of the sources. The EPA has finalized a combination of Options 1 and 2 in which the details

, along with some general recommendations can b e found in section IV.D. 6. g of the preamble to

the final rule.

Oppose Option 1

Comment :

Commenters (0038, 0039, 0046, 0058, 0060, 0069, 0088, 0096 , 0108

, and 0117 ) opposed Option

1 and stated that modeling assessments should not be conducted on a three

- year or any other regular basis if such is not supported by a review of the annual emissions data as that approach is not a good use of limited state and EPA resources. Commenter (0081) stated Option 1 would require the air agency to submit modeling under an arbitrary and artificial schedule without taking into account information which might show that undergoing a revised modeling analysis is unnecessary. Commenter (0060) provided the following additional points :

Under the 2008 lead standard there is no requirement to remodel ever y three years to

determine if a facility can still be exempt from monitoring. Ohio EPA and EPA Region 5 work cooperatively together to review annual emissions and determine if changes to the lead monitoring or modeling is needed. No other standard requires such a detailed on

going analysis. If emissions haven't increased, or increased enough, to determine modeling is necessary on an annual basis, no new modeling should be needed just because meteorology may have changed. If a s tat e believes they have such volatile changes in meteorology that it may affect prior modeling results in the absence of

emissions changes, the s tate should be able to make its own judgment call (along with

EPA consultation) as to whether modeling is necessit ated. It should not be mandated by

rule.

Commenter (0039) stated that t his would be a highly ineffective use of state agency and regulated community resources as changes in emission levels from year to year will have little impact on predicted and actual attainment with the standard. Commenter (0039) asserted it is critical to leave state agencies with the flexibility to make the determination whether further modeling is required. Alternatively, commenter (0039) recommended requiring states to reviewDELIBERATIVE

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219 annua lly e missions from modeled sources with an eye toward identifying substantial emission

increases above modeled rates, without any automatic emission increase trigger or mandatory

reevaluation

. Commenter (0117) stated that, a s long as conditions have remain ed the same or possibly improved in the intervening timeframe; additional modeling will provide no additional

useful information and request ed that EPA consider an exemption from the three

- year cycle for remodeling where previous analysis has already shown it to be unwarranted

.

Commenter (0103) recommend ed that if either Option 1 or 2 are retained

, then specific criteria

that the EPA will use in its case

- by

- case reviews should be established in the rule to ensure consistency and timeliness of reviews acros s EPA regions or that the EPA review of the state recommendations be dropped from the options altogether. Commenter (0103) was concern ed about the ability of EPA regional staff to review the state submissions in a timely manner with existing staffing given the number of potential submissions that could be made under either Option 1 or 2. For example, commenter (0103) stated there is a potential of 44 submittals in Region 7 that would require EPA review and action annually.

Response:

The EPA appreciates th e concerns from the commenters regarding resources and has developed a combined approach using Options 1 and 2 which are detailed in section IV.D. 6. g of the preamble to the final rule. Rules governing implementation of the lead standard address different

c ircumstances; different approaches are warranted in implementing the SO 2 standard. The EPA has determined that the best and most efficient means of obtaining prompt assessment of potential for violations in areas addressed by modeling, while minimizing res ource usage where violations are unlikely, is to require an annual review of emission data for purposes of judging whether a full remodeling effort is warranted. The EPA is promulgating an approach in which states have flexibility to determine the need for further modeling, with EPA oversight.



### c. Proposed o

ption 2: if a source ’s emissions increase over the previous year, the state would be required to submit to the EPA an
assessment of the cause of the increase and provide an initial

determination of w

hether or not air quality modeling would be needed

Support O

ption 2

Comment :

C ommenters ( 0038, 0041, 0045, 0046

, 0047, 0048, 0049, 0056, 0058, 0069, 0075, 0081, 0087,

0088

, 0096, 0097

, 0106, 0107, 0108, 0110, 0114 , 0117

, and 0118 ) generally supported Option 2

because it balances providing the most air quality protection with level of effort from state regulatory authorities. Commenter (0048) noted that with SO 2 emissions declining on a national level, particularly for the sources affected by the DRR, remodeli ng would not be expected to be required. Commenter s (0106 , 0118 ) stated that a simple analysis of the change in emissions is sufficient to determine the need for additional modeling.DELIBERATIVE

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220 Response:

The EPA appreciates and generally agrees with comments for b oth options 1 and 2 regarding state resources. See final recommended approach in s ection IV.D.6. g of the preamble to the final

rule.

O ption 2

— trigger for further evaluation

Comment :

Commenters (0038, 0041, 0058

, and 0114 ) generally stated that , under O ption 2

, states should

have discretion to determine whether the increases in emissions warrant further action. Commenters suggested factors to help determine when further action is needed.

 Commenter (0038) stated any modeling verifications should be drive n by actual emission increases or permit applications that are contingent on changes within a source's control.

 Commenters (0046, 0088) stated that, i f modeling is used to determine the designation of an area, EPA should only require re

- modeling if the e mission s increase is on par with the difference between the standard and previously modeled impacts.

 Commenter (0097) stated that if there is no emissions increases above attainment year

levels , the EPA should not require states to expend additional resou rces. Commenter (0097) stated that the NSR program is another backstop in the maintenance process, making redundant modeling unnecessary.

 Commenter (0096) argued that no additional report should be required if emissions from

the affected sources have eit her decreased, remained unchanged, or have not increased

above the thresholds set in the initial baseline modeling.

 Commenter s (0096 , 0113 ) recommended establishing a threshold in the DRR, or included in the initial modeling analysis, providing clearer gu idance regarding what emissions increases trigger further evaluation of sources, rather than providing an assessment for

each source with increased emissions. Commenter (0113) suggested that thresholds could

be structured as follows:

o If original modeling is equal to or greater than 90% of the standard

- area needs remodeling for all increases regardless of magnitude of emissions increase.

o If original modeling is between 50 and 75% of the standard

- area needs remodeling if emissions increase is above 15% of the previous year.DELIBERATIVE

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221 o If original modeling is less than 50% of the standard

- suspend modeling activities (same as Option 1).

Commenter (0096) stated it is not clear what the analysis is required to include and this issue

must be clarified in the final ru le

. Commenter (0096) provided the following suggestions

.

T he analysis should establish whether there was an increase above the initial emissions

modeled in the 2017 submittal. Assuming that emissions from 2012, 2013, and 2014 were

used in the 2017 modeli ng submittal, the initial verification of ongoing compliance would have to be an analysis related to the emissions from the year subsequent to those years.

The determination of whether there was an emission increase could be based on an increase greater th an the three year average of emissions during the initial modeling analysis, an increase above the highest single year of emissions during the initial modeling analysis, or some other metric. (0096)

Response:

The EPA has implemented a combined Option 1 a nd 2 which invokes several recommendations

listed above. Details are provided in section IV.D. 6. g of the preamble to the final rule. The EPA anticipates that air agencies will consider the types of factors these commenters recommend considering as they jud ge whether further modeling is warranted.

Do not support Option 2

Comment :

Commenter s (0060 , 0071

, and 0115 ) objected to t he second option, for the same reasons as mentioned above by these commenter s for Option 1. Commenter (0115) stated that the propos ed

emissions assessments required in Option #2 are not stringent enough and the document does not adequately address the details that will be involved in performing these assessments.

Response:

The EPA appreciates the comments regarding resources and st ringency of option 2. The EPA has developed a combined approach using Option 1 and 2 with recommended criteria from state

commenters. Combining these options provides a n appropriate balance that provides an annual review but focuses ongoing assessment effo rts on those areas where emission increases or other relevant changes in circumstances warrant the additional efforts. The EPA requires identifying causes of changes in emission levels because this information helps characterize the nature of the change an d whether the change is likely to be temporary (e.g., reflecting normal variations in source usage) or permanent (e.g., reflecting changes in source operation levels, control equipment, or other source changes). The EPA has determined that the best and mos t efficient means of obtaining prompt assessment of potential for violations in areas addressed by modeling, while minimizing resource usage where violations are unlikely, is to require an annual review of emission data for purposes of judging whether a fu ll remodeling effort is warranted. Details areDELIBERATIVE

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222 provided in section IV.D. 6. g of the preamble to the final rule. The EPA believes that the details

of these assessments must be determined on a case

- by

- case basis.



### d. Concerns related to choosing either option 1 or 2

Comment :

Commenter (0103) recommend ed that if either Option 1 or 2 are retained

, then specific criteria

that the EPA will use in its case

- by

- case reviews should be established in the rule to ensure consistency and timeliness of reviews across EPA regions or that the EPA review of the state recommendations be dropped from the options altogether. Commenter (0103) was concern ed about the ability of EPA regional staff to review the state submissions in a timely manner with existing staffing given the n umber of potential submissions that could be made under either Option 1 or 2. For example, commenter (0103) stated there is a potential of 44 submittals in Region 7 that would require EPA review and action annually.

Response :

The EPA appreciates the conc erns regarding consistency and timeliness of EPA review of state

assessments of annual SO 2 emission changes and subsequent recommendations. After review of all comments regarding all three options, the EPA has finalized an approach that combines Options 1 and 2. Details about the combined approach, including general criteria for determining if additional modeling is needed are found in section IV.D.6.g of the rule preamble. Following these general criteria should help in the development of national consis tency among the regions. Given the range of circumstances requiring judgment involving complex arrays of relevant factors, the EPA has concluded that establishment of specific criteria for these judgments would be impracticable, and a better approach is to request air agency recommendations on the need for further modeling with EPA review. The EPA routinely engages in internal consultations involving all regional and headquarters offices, and the EPA considers this approach the best means of assuring nation al consistency in these circumstances. In order to facilitate timely review of recommendations, states should strive to develop concise

recommendations and should communicate with appropriate regional staff during the development of the recommendations.



### e. Proposed o

ption 3: model using actual emissions , then conduct screening modeling every three years

Support Option 3

Comment :

Commenter (0057) recommended that EPA adopt Option 3, stating Option 1 imposes disproporti o nately greater demands on local, state, and federal staff than do the other options,DELIBERATIVE

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223 while Option 1 has comparatively small increases in the percent of total SO 2 emissions outside of areas already designated nonattainment.

Response:

While EPA appreciate commenters that agree with Optio n 3, EPA has developed a final recommendation using Options 1 and 2, with details listed in section IV.D. 6. g of the preamble to

the final rule.

Oppose Option 3

Comment :

Commenters (0038

, 0039, 0069, 0071, 0081, 0113

, and 0117 ) disagree d with having any default modeling requirement

. Commenter (0071) stated that facilities with complex building configurations and/or multiple stacks should not be eligible for a screening analysis as presented in Option 3 because the screening tools were not designed to eval uate complex situations. Commenter (0103) stated Option 3 does not seem practical as most of the sources (facilities) will have multiple emission points and AERSCREEN cannot currently handle sources with multiple emission points. Commenter (0117) stated th at, a s long as conditions have remained the same or possibly improved in the intervening timeframe, additional modeling will provide no additional

useful information.

Commenter (0039) disagree d with EPA’s proposed Option 3 for modeling verification , claim ing

t he mandatory use of screening models will result in an overly cautious, ineffective approach to

verification. Commenter (0039) stated that w hile screening models are less labor intensive for state agencies to employ, the results are almost always over ly conservative and are likely to predict concentrations that trigger the need for full

- fledged modeling that will ultimately show

there is no need for concern

— while remov ing state agency discretion and creat ing greater uncertainty for states and the regul ated community. Commenter (0069) stated that EPA fails to

take into account that screening modeling is almost as complex and time consuming as full

- scale modeling and is not a good use of limited state and EPA resources

.

Commenter (0060) stated that a ny o ption, if EPA still believes this should be mandated and prescribed by rule, should allow the use of screening modeling in lieu of full scale modeling. Commenter (0103) stated t his option could be modified t o allow AERSCREEN to be used to

model the net cha nge in impacts from a change at an emissions point ; i f the net change is predicted by AERSCREEN to exceed the interim 1

- hour SO 2 significant impact level then a complete, full

- scale modeling analysis with updated emissions and meteorological data could be performed with AERMOD.

Commenter ( 0068 ) disagreed with the proposed Option 3 and stated that annual modeling makes far more sense from the perspective of protecting the public health. Commenter ( 0068 ) stated

that m odeling once every three years is an extr emely periodic and slow way of assessing air quality , such that people living in the impacted area c ould be unaware for years , and thus unableDELIBERATIVE

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224 to take action to protect themselves

, or place pressure on their government to correct the problem. Commenter (00 68) stated s uch periodic modeling would only serve to conceal potential air quality problems, and to protect polluters.

Commenter (0115) stated that the proposed emissions assessments required in Option 3 are not stringent enough because assessments woul d only take place every three years.

Response:

The EPA appreciates those comments disagreeing with Option 3 and recognizes the resource considerations of screening modeling and potential refined modeling associated with Option 3.

The EPA disagrees with t he comment suggesting annual modeling. I n response to all three options and in consideration of state resources EPA has developed a final option using a combined option 1 and 2 approach. Details are listed in section IV.D. 6. g of the preamble to the

final r ule.



### f. Option for ambient air quality monitoring

Comment

Commenter s ( 0063, 0065, and 0082) suggested that a state could use an ambient air quality monitor to provide ongoing verification for an area that was initially desi gnated on the basis of modeling

. Commenter (0082) stated these initial designations may be based on modeling due to timing issues, but a state or source may desire to install and operate a monitor (in accordance with EPA’s final guidelines for such monitors) as a basis for ongoing verific ation of an area’s

attainment status.

Response:

The EPA notes that the ongoing data requirement provisions for states that initially characterized an area with modeling require that the state provide an annual emissions report, identification of

the caus e of any increases at the applicable sources, and a recommendation regarding whether additional modeling is needed to characterize the area in light of the increase. The EPA then uses

that information and considers the state recommendation in order to dete rmine whether to require additional modeling. The EPA expects that if there are situations where a monitor provides information relevant to characterizing air quality in such an area, such monitoring could be used

to inform the state recommendation as to w hether additional modeling is needed. Due to limited resources available for modeling, the EPA is very unlikely to require additional modeling where an existing monitor adequately characterizes the area

.



### g. Option for a nnual modelingDELIBERATIVE

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225 Comment :

Commenter (0 068) stated a requirement for annual modeling would provide a stronger incentive

to states to set emission limits for SO 2

- emitting facilities at levels that ensure attainment of the NAAQS would be maintained , w hich would be better for states, EPA, and the public, as all stakeholders would have greater confidence in the quality of their air. Commenter (0068) stated annual modeling would not be unduly burdensome on the states because modeling is rapid and relatively cheap and, for sources that have already be en modeled once, periodic remodeling will generally be quite straightforward, requiring little in the way of resources or personnel time. Commenter (0068) stated that since state air agencies are empowered under the CAA to collect permitting fees sufficien t to cover the costs of their programs, it should be the emitting sources themselves, not the taxpayer, who is covering the cost of assessing the impact on air quality from sources emitting SO 2

.

Response:

For reasons discussed in section IV.D. 6. g of the preamble, t he EPA has concluded that the most appropriate use of resources for ongoing assessment of air quality for areas assessed through modeling is to conduct an annual review of whether further modeling is warranted.



### h. Allow multiple options

Commen t :

Commenter (0069) recommended , in lieu of EPA's proposals, a combination of Opti ons 2 and 3,

in which s tates could review /evaluate annual S O 2 emissions and conduct screening modeling if the analysis of annual emissions warrant. Commenter (0069) recommen ded that, o nly if the screening model fails to confirm continued attainment of the NAAQS would full

- scale modeling be required. Commenter (0069) recommended s tates should also be given the option to skip the screening modeling step and perform full

- scale m odeling.

Commenter (0082) urged EPA to finalize all three options and allow each state to choose which ongoing attainment verification option it will employ to accommodate the state’s limited resources. Commenter (0082) stated, for example, while one air agency may have insufficient funding to undertake modeling every three years as required by Option 1, another may have insufficient personnel to undertake the subjective reviews required by Option 2.

In addition to EPA’s three options, c ommenter (0082) u rged EPA to allow another option based

on ambient air quality monitoring ( described above ). Commenter (0082) suggested EPA allow

each state to choose among the four options which ongoing attainment verification option it will employ.

Response:

The EPA a ppreciates the comments suggesting combining Options 2 and 3 in which states couldDELIBERATIVE

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226 review/evaluate annual emissions and conduct screening modeling if needed. In response to the comment regarding the use of ambient air monitoring for verification, see the r esponse above for “Option for ambient air quality monitoring.” In response to all of the comments, the EPA has finalized an approach combining Options 1 and 2 and details are provided in section IV.D. 6. g of the preamble to the final rule.



### i. Clarify verific ation options

Comment :

Commenter (0036), stated that the EPA should clearly spell out the verification options available to states and the EPA should appropriately bound these requirements in order to avoid open

ended requirements with significant cost i mplications.

Commenter (0096) recommended the phrase “most recent emissions data” as applied in this option should be specifically defined to mean the most recent annual submission to the national emission inventory (NEI) as required by the AERR. Comment er (0096) stated the Proposed Rule is unclear exactly what type of data fall within this phrase. Commenter (0096) stated the AERR submissions to the NEI will have undergone quality control (QC) procedures which make it more dependable than other data poten tially considered “most recent emissions data” (i.e., data where a shorter timeframe may not allow as thorough QC). Commenter (0096) state agencies already

must meet the December 31 st deadline for NEI, thus it would be a reasonable deadline to meet

without any added burdens.

Response:

Responses to these comments are provided in section IV.D.4 and IV.D. 6. g of the preamble to the

final rule. More recent data may be available for some sources than for other sources

— for example; EGUs are prone to have more r ecent data than other source types. Therefore, to define “most recent emissions data” as the most recent submission to the NEI might prevent air agencies from using more recent (or otherwise more appropriate) data from other data bases. Therefore, the EPA is retaining the proposed rule’s flexibility for a ir agencies and the EPA to make judgments regarding which data provide the most suitable basis for ongoing assessments of air quality.



### j. Do not support ongoing data requirements

Comment :

Several comment ers ( 0039, 0047, 0048, 0051, 0052, 0053, 0060, 0063, 0064, 0065, 0075, 0087, 0088, 0089, 0093, and 0097) did not support the pro posed ongoing data requirements because they are too burdensome.DELIBERATIVE

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227 Commenters (0048, 0051, 0052, 0053, 0075, 0087, 0089 , 0093, a nd 0097 ) stated that the need

for such on

- going verification of attainment has not been demonstrated

. Commenter (0053) saw no need for mandatory recurring modeling burden upon the states because sources are already required to report changes in emissions a fter initial modeling and this data could be easily

assessed by EPA or applicable states to determine if re

- characterization is potentially necessary

. Commenters (0051, 0052, 0093, and 0097) stated that the NSR and/or PSD programs provide continued adequat e assurance of maintenance of the standard. Commenter (0051) stated the usual SIP maintenance schedule should be sufficient for ongoing verification of attainment.

Commenter (0060) did not agree that annual reports on emissions must be submitted t o EPA f or sources that have monitors shut down or for all sources that were modeled. Commenter (0060)

stated t his is creating an additional regulatory process that is not necessary and provided the following additional points.

The Ohio EPA has monitored emission s for years as part of our maintenance plans for the various NAAQS without a need to submit a special report to EPA annually. Ohio EPA’s annual review of lead emitting sources that is used to determine if monitoring requirements are triggered is conducted successfully every year without the need for a special submittal. If we deploy a monitor as a result of a change in emissions at a lead

source or opt to model for a waiver request, it is included in our annual monitoring plan.

And that is accomplished with out a detailed, limiting regulation dictating all the criteria

and every step of the process. It appears there is more bureaucracy and oversight being created than is necessary. (0060)

Commenter (0088) stated that the proposed language at s ection 51.1205( b) should be eliminated

f rom the final rule. Commenter (0088) stated that i t is absolutely unnecessary and the provision has the potential to be terrifically burdensome. Commenter (0088) stated that i f EPA acquires data indicating probabl e violations, it h as sufficient regulatory authority to revise its designation

or “to call” the s tate’s implementation p lan. Commenter (0088) stated that this additional modeling undercu ts the Proposed Rule and , since the purpose of the PSD program is to ensure against dete rioration of an attainment area’s air quality, additional modeling by the s tates is

unnecessary.

Commenters (0053, 0087, and 0097) stated i nventory efforts and additional modeling exercises

are unnecessary because e missions of SO 2 are decreasing rapidly and will continue to do so

. C ommenter (0097) stated e missions data from large electrical generating units as reported to

CAMD show a downward trend ; h eavy duty diesel engines emit significantly less SO 2 than in the past due to reductions of sulfur in diese l fuel ; t he Tier 3 rule should continue to reduce SO 2 emissions since the rule requires future reductions in gasoline sulfur content

.

If EPA concludes that such verification is warranted, commenters (0047, 0048, 0087, 0089)

stated the burden on state/loc al air agencies should be minimized. Commenter (0048) stated that, at most, only an assessment of SO 2 emissions to determine if they have increased and, if so, an assessment of whether that increase is sufficiently large to warrant the consideration of con tinuedDELIBERATIVE

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228 monitoring or new modeling should be required. Commenter (0064) stated that if such a program is required in a final rule, verification should take place every five years instead of annually. Commenter (0064) noted that EPA reviews the NAAQS every f ive years.

Commenter (0039) stated the verification approach must provide state regulatory authorities with significant discretion about when to re

- run modeling evaluations. Commenter s ( 0063, 0065) stated that states should have the flexibility to choose appropriate ongoing attainment verification options without being subject to improper SIP planning requirements. Commenter s ( 0063, 0065)

asserted that sections 51.1205(b) through (d) effectively impose attainment planning requirements on attainment and un classifiable areas.

Response:

Responses to these comments are provided in section IV.D.g of the preamble to the final rule. The EPA believes that the need for ongoing characterization requirements is clear. A monitor inherently provides ongoing assessmen t of air quality through continued operation of the air quality monitor. The EPA believes that ongoing air quality assessment is warranted for areas addressed by modeling, just as it is for areas addressed by monitoring , and a one

- time modeling requirement based on recent actuals would not provide any ongoing information in the manner

that a monitor does

. As explained in section IV.D.g, the final rule provides for these needed ongoing assessments in a way that minimize s the burden and offer s substantial fle xibility to states (with EPA oversight), consistent with the recommendations of commenters. The EPA does not agree that this approach imposes attainment planning requirements on these areas, any more than requirement s for ongoing monitoring impose attainme nt planning requirements

.



### k. Sunset provision for the ongoing data requirements

Comment :

Commenter (0070, 0097, and 0113) stated that the EPA should include within the implementation plan a reasonable framework for determining when the ongoing data requi rements are no longer required. Commenter (0097) stated that w hen emissions levels in an

area drop beneath 50% of the levels used within the model to show attainment, the EPA should then acknowledge that a PSD program provides ample protection against poss ible future SO 2 NAAQS violations. Commenter s (0070 , 0113 ) recommended that, due to the conservatism in the air quality models and the tendency of models to significantly overstate air quality impacts from sources, the threshold for being allowed to omit fu ture modeling should not b e set at 5 0% of the standard. Commenter (0113) suggest ed that 85% of the NAAQS is a better threshold, particularly with the inclusion of an accurate and representative background concentration

. Commenter (0070) recommended the thr eshold for being allowed to omit future modeling be set at no less than 90% of the standard, based on the currently available modeling platforms. Commenter (0070) provided the following additional points :DELIBERATIVE

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229 On page 27466 , the EPA proposed to allow a state t o reduce its future modeling if the previous modeling demonstration was at or below 50% of the standard. The EPA’s own studies show that the current preferred model for near field modeling, AERMOD, is very

conservative and overstates ambient concentrations significantly. As such, EPA’s proposed level of 50% of the standard based on modeling penalizes those states that would choose to use modeling in place of monitoring.

The EPA suggests that much of the work necessary to perform the follow

- up modeling

wil l be completed as part of the original modeling, further reducing the labor necessary to perform the follow

- up modeling in the future. Such a claim could not be further removed from reality, especially with regard to AERMOD. Since 2005, EPA has periodicall y made changes to the AERMOD modeling system that have included error checks that do not allow older versions of major input files to be used. The need for this invalidation of existing input files is based on significant changes made in the modeling syste m and the incompatibility of the older files input files with these changes. The claim made on page

27466 of the Federal Register notice completely ignores this fact and also fails to account for periodic changes in air quality modeling science that could result in EPA moving to a new modeling platform for near field analyses at some future date. When that occurs, it would be necessary for the s tates to completely revamp their modeling systems for this program at great cost in time and effort. We believe th at this further supports our

recommendation that the modeled criteria be set no lower than 90% of the standard based

on the modeling platforms available at the time of this rulemaking in 2014.

Response:

The EPA has finalized the approach for the sunset provision for monitors in areas where data show concentrations well below the NAAQS, which is outlined in section IV.D.6.g of the preamble to the final rule. With respect to modeling, EPA disagrees with the comments that AERMOD is very conservative. While some studies have shown over

- prediction by AERMOD,

others have shown under

- prediction. The goal is to have AERMOD unbiased when using the proper model inputs. The EPA appreciates the concerns of commenters regarding changes to AERMOD causing incompa tibilit y with older input files and possibly lead ing to increases in concentrations over previous versions of AERMOD. That being said, EPA does not make changes to AERMOD capri ci ously and the changes are to fix errors within the model code or implement changes th at will lead to more accurate results and these changes are made after exhaustive testing. Furthermore, retyping input files is a small effort relative to the effort of determining the appropriate information (e.g., determining building dimensions), so tha t EPA continues to believe that remodeling a source requires substantially less effort than the initial source modeling, irrespective of any model changes.

In response to comments, the EPA has redesigned the modeling

- based ongoing assessment process. In m ost cases, additional modeling is not necessary, provided that emissions do not increase significantly relative to the attainment margin found in the initial modeling (and provided that other relevant source characteristics do not change significantly). Th e EPA is notDELIBERATIVE

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230 promulgating a specific criterion for determining when modeling for ongoing assessment purposes is required, because the EPA has concluded that the need for such modeling is best judged on a case

- by

- case basis depending on whether and how much emissions have changed, depending on the nature of any other changes in source characteristics, and depending on the level of attainment margin found in the initial modeling. For this reason, the EPA is neither requiring further modeling in all cases wher e the initial modeling showed concentrations above

85 or 90 percent

, or any other percent

, of the standard

, nor exempting areas from further modeling where the initial modeling showed concentrations below any particular percentage of

the standard.

The fin al rule does, however, provide that air agencies may terminate their ongoing modeling when modeled concentrations are shown to be below 50 percent of the standard. This criterion reflects a judgment that normal annual variations in emissions would not resu lt in a source one year causing concentrations to be below that threshold and another year causing concentrations to be above the standard. Higher thresholds for discontinuation of annual review, such as 85 or 90 percent of the standard, would be too prone to exempt areas from review where a reasonable possibility of violations may exist. Given that most areas that initially model at 50 to 80 percent of the standard, for example, will be found on review not to have the kind of emission increases

to warrant further modeling, the EPA believes that use of the conservative threshold of 50 percent for discontinuation of the review requirement will not significantly increase the resources necessary for the ongoing assessment process.

.



### 13. Post

- attainment designation annual reporting

Comment :

Annual report

Commenters (0041, 0045 , 0085

, 0106, and 0107 ) stated that the assessment should be submitted separately from the annual monitoring plan. Commenter (0085) stated t hese documents are not related, and accordingly, th ey should be kept separate. Commenter (0106) stated that, since the annual report refers to modeling, it will cause less confusion for the general public if it is a

separate document from the Annual Monitoring Plan

. Commenter (0107) stated that, because t h e annual monitoring plan and the emissions inventory submittals are performed by separate work

units on different timelines , it would be better to deliver the products separately rather than delay

one or the other to deliver them together.

Commenter s ( 004 8, 0102

, 0115, and 0117 ) recommend ed this information be included as an appendix to the Ambient Air Monitoring Network Plan submit ted to the EPA annually, rather

than as a stand

- alone document. Commenter (0117) stated that, s ince both options have a

deadli ne of July 1 each year, a separate document would only add more time and resource use.

Commenter s ( 0060, 0069) stated EPA should allow states to utilize either procedural approach for ongoing verification of attainment for areas that have been designatedDELIBERATIVE

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231 unclassifiable/attainment based on modeling analyses (deleting the public notice and comment requirement in the second option), as this provides states with flexibility and provides the same

information to the EPA.

Commenter (0049) stated annual emission s reporting is already required for sources meeting the threshold options listed in the proposed DRR, so there is no need for an additional emissions reporting plan. Commenter (0090) stated that requiring the state to report on annual SO 2 emissions of each applicable source and provide an assessment of the cause of any emissions increase is not practical or appropriate. Commenter (0090) believed that this requirement is unduly burdensome on the state's limited resources and that the interest of the state an d the EPA regarding NAAQS status is continued attainment, not the causes of increases in emissions that by the nature of unit operations will fluctuate to some degree each year.

Public notice

Commenter (0060) suggested that, if an annual report is necess ary, a ny public notice would just need to clearly identify what the document available for comment covers. Commenter (0069)

stated EPA has failed to identify any statutory or regulatory provision that requires public notice

and comment in accordance with 4 0 CFR 58.10 for an annual assessment of emissions or a modeling analysis ; n or has EPA provided compelling reasons why such a requirement should be mandated through the D RR

.

Reporting frequency

Commenter (0060) suggested that if an annual report is neces sary, EPA should r equir e a submittal on July 1 each year.

Commenter (0096) stated that, i deally, under Option 2, agencies would have a 2.5 year timeframe to complete the entire process of ongoing verification. Commenter (0096) provided the following addit ional points :

The first year would consist of preparing and submitting the NEI for the previous year, a preexisting requirement. Six months thereafter agencies would submit a report to EPA stating whether air quality modeling is needed. Twelve more month s would then be permitted to perform any additional modeling deemed necessary. Assuming EPA issues final designations in December 2017, ongoing verification would begin with the initial verification in July 1, 2018. The initial verification would be for em issions which occurred one year after the emissions used in the initial modeling submittal. If emissions exceeded the thresholds established by the initial baseline modeling, then agencies would assess whether further modeling is needed pursuant to the DRR in the initial verification report due by July 1, 2018 (which is subject to public review); and the agencies would complete any needed modeling by July 1, 2019. It is not feasible to operate on a more stringent timeline. ODEQ strongly and respectfully urg es the EPA to give serious consideration to Option 2, as described and recommended herein.DELIBERATIVE

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232 Commenter (0097) suggest ed that these analyses be conducted no more frequently than every five years, in conjunction with the submittal of the 5 year monitoring ne twork assessment as required by 40 CFR 58.10. Commenter (0097) provided the following additional points :

These analyses should be coordinated with the m aintenance/compliance analyses required for areas having removed compliant monitors. A frequency greate r than every five years would necessitate a significant effort in data gathering and assessment. For

areas where the modeled value is under the standard, there is already a significantly

conservative factor built into the process that would help ensure any minor increases in

emissions would not result in an actual violation of the standard. Additionally, the EPA should not compare emissions from one year to the next. Rather it should allow the comparison of annual emission rates from the modeled values, sim ilar to a maintenance demonstration for an ozone maintenance area. According to the 1992 redesignation request and maintenance plan guidance, "Procedures for Processing Requests to Redesignate Areas to Attainment" ( EPA , September 4, 1992), ozone maintenanc e areas compare emissions to the attainment year levels to demonstrate ongoing compliance with

a standard. This same methodology is also used in PM 2.5 and PM 10 maintenance plans. Using a similar approach for SO 2 would alleviate the need to explain away inc reases from

year to year that may have resulted from an economic downturn followed by an increase in economic activity the next. Again, this comparison should be required no more than every five years, and deadlines should hinge on the submittal of the 5 y ear monitoring

assessment.

Response:

After considering the comments received related to both of the proposed options, the EPA finds

that the best approach for the final rule is to allow the affected air agencies the discretion to

either include the requi red annual data requirements report for modeled areas either as an appendix to the state’s monitoring plan, or as a stand

- alone document. The air agenc y will have the flexibility under the final rule to select the approach that best meets the agency’s work load

, schedule

, and particular need s. The EPA finds that either of the procedural approach es will be

sufficient to implement the ongoing data requirements. Regardless of which approach is chosen by the air agency, the report must be submitted to the respec tive EPA Regional Office by July 1 st annually and made available for public review and comment. The first report is due on July 1 st of the year after the effective date of the area’s initial designation and additional reports are due July 1 st of each subse quent year. The EPA requires identifying causes of changes in emission levels because this information helps characterize the nature of the change and whether the change is likely to be temporary (e.g., reflecting normal variations in source usage) or perm anent (e.g., reflecting changes in source operation levels

, control equipment, or other source changes).

The EPA has determined that the best and most efficient means of obtaining prompt assessment of potential for violations in areas addressed by modelin g
, while minimizing resource usage where violations are unlikely

, is to require an annual review of emission data for purposes of judging whether a full remodeling effort is warranted.DELIBERATIVE

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233 

### 14. Resources

Comment :

Commenter s ( 0034, 00 52a

, 0103) stated that the EP A must provide assurance that additional funding to implement this rule will be provided. Commenter (0034) recommended that EPA provide assurances to those Tribes having sources near to them that emit at least 1,000 tpy of

SO 2 that they will receive the re quisite resources for monitoring and modeling to characterize the air quality around such sources. Commenter (003 4 ) stated this will go a long way in helping

Tribes

--- sovereign nations with inherent rights ensured by the U.S. Constitution, treaties and

l egal precedent

--- address any health and environmental impacts to their communities caused by

these sources.

Commenter ( 0046 ) assert ed s tate and local permitting agencies do not have the resources to perform all of the modeling analyses that will be requ ired by the r ule; therefore, this will become an additional burden on the regulated community, especially if annual re

- verification modeling is required. Commenters (0052) stated t he proposed iterative process establishes significant

resource demands for a ir agencies and is unnecessary for EPA to meet its statutory obligations.

Commenters (0046, 0051) stated the modeling cost estimates noted by the EPA in the proposal

are under estimates for anything other th an t he simplest modeling scenarios. Commenter (00 51)

stated the cost could easily become five times the stated estimate as the complexities of the project accumulate. Commenter ( 0046 ) stated t he cost of doing a thorough modeling analysis for purposes of this rule will be far greater than the $10,000 put forth in the preamble at 79 Fed Reg

27451. Commenter (0046) stated that, f or a complex facility where more accurate measurements data are needed to correctly characterize actual emissions and exhaust characteristics over different operating modes and accur ately build a model, the cost of a modeling analysis to fulfill the requirements of this rule could exceed $100,000. Commenter (0103) estimate d f or the twelve affected facilities in Iowa, about $78,000 would be needed to model the facilities for attainment

recomm endations according to the TAD.

Commenter (0103) stated DNR estimates that the cost of establishing the attainment status of an affected facility via monitoring is about 36 times more than to establish the attainment status of the facility via mode ling. States will begin incurring significant costs to perform modeling to site monitors beginning in the 2015 federal fiscal year. Funding will also be needed after designations to develop control strategies, contingency measures, maintenance area plans, and provide for on

- going monitoring of progress towards reaching attainment. This could result in

numerous SO 2 nonattainment areas to develop nonattainment SIPs on an 18 month schedule

.

Response:

The EPA recognizes the fact that there will be costs and r esources required to satisfy the requirements of this rulemaking. As suggested by both state and industry stakeholders who attended the May

- June 2012 stakeholder meetings, in the absence of increased grant funding itDELIBERATIVE

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23 4 may be necessary for air agencies to re balance their existing grant funds for this purpose, or to consider alternative funding approaches such as working closely with affected sources to assist in funding either the modeling or monitoring required to meet the requirements of the rule. Early pla nning may be helpful to address these funding needs.

Because the CAA assigns to states much of the responsibility for developing air quality characterization data, the EPA describes the requirements of this rule in a consistent manner: air agencies are t he entities with principal responsibility to establish and operate monitors, and conduct modeling, and to provide air quality data to the EPA. However, the EPA recognizes that other parties (such as facility owners) also may perform significant portions of the work that this rule requires. The EPA would consider monitoring or modeling conducted by a third party to be an appropriate means for air agencies to obtain the data necessary to meet the requirements of this rule, provided that the state provides ove rsight to assure that (1) any monitoring is conducted in a manner that is equivalent to SLAMs and quality

- assured in accordance with applicable requirements, and (2) any modeling analysis that the state submits, even if it was initially provided to the sta te by a third party, is done in a reasonable manner and follows the

recommendations in the m odeling TAD.

See also the responses to analogous comments in section about the resources needed to conduct monitoring. The EPA recognizes that all air quality plan ning, including air quality characterization, requires resources, but the EPA considers the air quality characterization efforts required by this rule to be an appropriate element of a balanced program for assuring that the purposes and requirements of the CAA for identifying and then addressing air quality problems

are met.



### 15. Procedural issues

Comment :

Commenter (0042, attachment B) offered several suggestions regarding the process of improving

models.

 The current EPA approach of evaluating improvements to air quality models using

the Model Clearinghouse review of issues arising in specific situation s is unworkable as they tend to have a v ery narrow focus and not to be universally applicable.

 There is no peer review of EPA modeling guidance and formulat ion. An independent peer review panel is needed to provide guidance and recommendations on modeling

needs.

 The Modeling Conference does not satisfy this need of additional peer review of EPA modeling.

 The EPA has not identified modeling needs and researc h needed to advance airDELIBERATIVE

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235 quality modeling performance.

 The EPA should include discussion of industry

- supported model development and

model validation work on the Agency’s substantive agenda rather than relegating

such to the public comment period.

 The EP A has instructed state agencies on when and how they must use modeling for

attainment demonstrations for the 1

- h our SO 2 NAAQS. Although industry may be affected by these demonstrations, it has not had any input to the current procedures.

Commenter (0042, attachment C) stated there are numerous issues with using models and modeling techniques to implement new NAAQS, and, recognizing that addressing all of these issues will take time, they recommend EPA identify modeling issues for short

- term, mid

- term,
and long

- term focus. Commenter (0042, attachment C) stated they w ould like EPA to develop and share with the public a plan detailing the Agency's anticipated dates for and methods to

address these issues. Commenter (0042, attachment C) recommended several spec ific issues to

resolve in the short

- term, mid

- term, and long

- term

. Commenter (0042, attachment C) stated that

one long

- term need is a per formance re

- evaluation of AERMOD, which has been modified since it was approved.

Response :

The EPA disagrees with th e comment regarding the Model Clearinghouse. Issues that are raised to the Clearinghouse are addressed through a Clearinghouse action

, such as a memorandum explaining that the action from the Clearinghouse can be applied to similar applications in the

futu re, unless noted in the memorandum. With regards to model updates, the EPA is working to correct technical issues with AERMOD and has, in the past, taken industry input under

advisement.



## VI. Statutory and Executive Order Reviews

A. Paperwork r

eduction Act

Co mment :

Commenter (0051) agreed that $30,000 is a good estimate for a fairly simple single source, but this estimate could easily double as the complexities of multiple sources, temporal allocation down to hourly emissions, downwash analyses, clustering an alyses, culpability testing, and negotiations with regional EPA staff are added to the modeling project.

Commenter (0103) estimated the cost of implementing the monitoring pathway is about 36 times more than the cost of implementing the modeling pathway. Commenter (0103) stated t he draft rule suggests a much lower ratio of costs, with a much higher estimate for the cost of the modeling pathway. Commenter (0103) request ed a detailed accounting of the two paths in theDELIBERATIVE

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236 final rulemaking, including the costs of locating the point of maximum impact for placing an

ambient monitor.

Commenter (0111) stated that the EPA does not provide an appropriate cost

- benefit analysis to justify the substantial increase in resources the states will have to expend in order to co mply with the proposal. Commenter (0111) stated t he proposed D RR requires the states to drastically

increase resources devoted to the rule’s analyses and that these analyses will duplicate subsequent action in the PSD permitting program. Commenter (0111) s tated they c annot justify, the expenditure of these resources as pa rt of the initial designation process.

Response:

The EPA is requir ing air agencies to more extensively characterize ambient SO 2 air quality concentrations, pursuant to section s 110(a)(2)( B)

, 110(a)(2)(K) , 301(a) and 114 of the CAA. For purposes of analysis of the estimated paperwork burden, the EPA assumed that 43 states and tribes would take actions to characterize air quality through either air quality modeling or ambient monitoring in 4 12 areas around SO 2 sources emitting 2,000 tpy of more across the country, and such states would submit the results of these analyses to the EPA. Under this rule, the air agency will have the ability to choose, on an area

- by

- area basis, the analytical appr oach to follow for characterizing air quality around each qualifying source. For this reason, there is no way of determining exactly how many areas may be characterized through ambient monitoring versus air quality modeling approaches.

Potential ambient air monitoring costs are estimated based on the assumption that air quality for

each of the 412 SO 2 sources exceeding the 2,000 tpy threshold would be characterized through a single newly deployed air monitor. (Note, however, that there may be situations w here more than one monitor may be appropriate or necessary to properly characterize peak 1

- hour SO 2 concentrations in certain areas , which would increase costs proportionally .) Estimates are provided for a 3

- year period and include a calculation for equipm ent amortization over 7 years. For the period of 2016, 2017

, and 2 018 ( monitoring related expenditures would begin in 2016), the total approximate average annual monitoring cost, including a calculation for equipment amortization is $8,662,110 (total capit al, and labor and non

- labor operation and maintenance) with a total burden of 102,869 hours. The annual labor costs associated with these hours is $7,080,572. Included in the $8,662,110 total are other annual costs of non

- labor operations and

maintenance o f $706,827 and equipment and contract costs of $874,711. For reference purposes,

an estimate for initial establishment of a single, new SO 2 monitoring station is $92,614 (does not include equipment amortization). In addition to the costs that would be incu rred by the state and local air agencies, there would be an estimated burden to the EPA related to salary cost and equipment cost, etc, of a total of 52,717 hours and $776,005.

Potential air quality modeling costs are estimated based on the assumption th at air quality for

each of the 412 SO 2 sources exceeding the 2,000 tpy threshold would be characterized through air quality modeling analyses. Based on market research, stakeholder feedback and assumptionsDELIBERATIVE

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237 about the procedures to follow when conducting mod eling for designations purposes, 11 an estimate of modeling costs for a single modeling run centered on an identified source would be approximately $30,000. This cost takes into account analyses to determine the number of sources to explicitly model, determi ning the modeling domain, emissions preparation, meteorological data preparation as well as other information needed for modeling as discussed in the modeling TAD. While some commenters feel this estimate could double, the EPA feels that this estimate

is fair and in order to keep costs low, states should consult often with the EPA Regional Office in developing the modeling protocols to minimize future costs. If air agencies choose to characterize air quality through modeling analyses around all 412 sources expected to be

identified as exceeding the source threshold, then total national costs for modeling analyses would be estimated at $12,360,000. If these costs were incurred over the course of 3 years, then the approximate annual cost for each year over th at period would be $4,120,000.



### B

. Executive Order 13175: Consultation and c oordination w ith I ndian

t ribal g overnments

Comment :

Commenter s (003 4 , 0120 ) disagreed with the Proposed Rule statement that the rule does “not have tribal implications, as specif ied in Executive Order 13175.” Commenter s (0034, 0120 )

stated t he Proposed Rule would redistribute monitoring and modeling resources supported by EPA and focus them on emission sources located in CBSAs in excess of 1 million people and on

other sources who se emissions are extraordinarily large. Commenter s (0034, 0120 ) stated t his approach would further limit the much needed monitoring and modeling resources that are already scarce in Indian Country. As such, c ommenter s (0034 , 0120 ) stated that the EPA must develop an accountability process to ensure “meaningful and timely input by development of regulatory policies that have tribal implications.”

Commenter s (0034 , 0120 ) appreciate d the outreach that EPA has conducted with regard s to the Proposed Rule such as h olding several meetings with Tribal environmental professionals to

discuss issues as sociated with the Proposed Rule and p roviding an opportunity for Tribes and stakeholders to provide written comments on the concepts discussed in the White Paper as

men tioned in the Proposed Rule. Commenter s (0034 , 0120 ) stated that, while it is helpful that EPA intends to offer consultation with any Tribal government wanting to discuss the Proposed

Rule , n evertheless, the EPA must do more to consult with Tribes about th e Proposed Rule and others like it, and to do so much earlier, such as during the rule development process.

Response:

This action does not have tribal implications, as specified in Executive Order 13175. It would not

have a substantial direct effect on one or more Indian tribes. Furthermore, th is regulation do es

11 The Draft SO 2 NAAQS Designations Modeling Technical Assistance Document can be found

a t : http://www.epa.gov/airquality/sulfurdioxide/pdfs/SO 2 ModelingTAD.pdf.DELIBERATIVE

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238 not affect the relationship or distribution of power and responsibilities between the federal government and Indian tribes. The CAA and the Tribal Air Rule establish the relationship of the

feder al government and tribes in characterizing air quality and developing plans to attain the NAAQS, and this regulation do es nothing to modify that relationship.

In response to the comment that the rule will redistribute monitoring and modeling resources

su pported by the EPA and focus them on emission sources located in CBSAs in excess of 1 million people and on other sources whose emis sions are extraordinarily large, t he EPA considered comments such as this in making its final decision on the threshold for characterizing

sources. After reviewing the comments, the EPA decided not to move forward with the proposed approach and has decided instead to apply requirements for air quality characterization based on emissions levels uniformly across the country for b oth more urbanized and less urbanized populations so as to focus primarily on the size of the sources. In addition, t here are no new resources associated this rulemaking , nor for the redistribution of existing monitoring, and the rule does not provide for diverting of resources as it relates to modeling to characterize sources. A number of commenters appeared to interpret the inclusion of a lower threshold for areas with higher population as being less protective of the public in less populated areas such as Tribal

areas . The EPA wants to clarify that this was not the intention behind the population

- inclusive options included in the proposed rule. The SO 2 NAAQS, and all NAAQS, provide equal protection for citizens throughout the country. The proposed use of both population and emissions thresholds as a means to require air quality characterization was simply one approach

to focus limited federal and state modeling and monitoring resources into characterizing locations where a greater coincidence of people an d SO 2 emissions occur, and thus a potentially greater potential for exposure is presented

. A fter reviewing the comments on this issue, however,

the EPA has decided not to move forward with the proposed approach, and instead to apply requirements for air qu ality characterization based on emissions levels uniformly across the country for both more urbanized and less urbanized populations so as to focus primarily on the

size of the sources.

I n response to the comment stating that EPA should provide earlier consolation in the process of developing the rulemaking, c onsistent with the EPA Policy on Consultation and Coordination with Indian tribes, the EPA held several meetings with tribal environmental professionals early on in the process of developing the rul emaking to discuss issues associated with this rule, including discussions at the National Tribal Forum on May 1, 2013, and on National Tribal Air Association policy calls. These meetings discussed the SO 2 implementation White Paper. The EPA provided an op portunity for tribes and stakeholders to provide written comments on the concepts discussed in the White Paper. Summaries of these meetings are included in the docket

for this rule. The EPA also provided information on the proposed rule and conducted

consu ltation with the National Tribal Air Association in the form of a briefing on April 24, 2014, and a webinar on May 21, 2014. Therefore, the EPA believes that in this instance, the Agency provided consultation with Tribal organizations, as well as other st akeholder as early as possible in the developmental process related to the rulemaking.DELIBERATIVE

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239 

## VII. TADs for Monitoring and Modeling and Appendix W

A. Comments i

n the DRR docket related to the TADs and a ppendix

W

Comment

Comments on the draft TADs and Appendix W found in the docket and relevant to the DRR have been incorporated into this RTC. Some commenters (0038, 0051, 0060, 0081, and 0088) referred to comments they previously submitted to EPA regarding the draft TADs but did not

include those comments in the docket ; those comments are not included in this RTC.

Commenter (0060) stated it is challenging to prepare meaningful comments on the DRR since

much of this Proposed Rule is contingent upon the use of these TADs. Commenter (0060) stated

that because this Proposed Rule and the draft TADs are so intertwined, all three documents

should be available for comment at the same time. Commenter (0110) stated that, without having the DRR in place, it is difficult to provide complete comments on the TADs. Commenter (0110)

sta ted that t he proposed DRR references and relies upon guidance provided in the modeling and monitoring TADs, t herefore, these documents are subject to review and comment for this Proposed Rule

. Commenter (0110) stated that EPA also has dispersion modeling g uidelines (Appendix W to 40 CFR Part 51) that are referenced by this Proposed Rule

. Commenter (0110)

stated t hese documents are therefore available for comment in conjunction with this proposed

SO 2 DRR

.

Response:

The EPA disagrees with the assertion that the understanding or ability to comment on this rulemaking was contingent on the use of the TADs. The Agency reiterates that the TADs provide

recommendations

, but are not binding or enforceable and create no obligations on any person

. Although the draft T ADs are referenced as recommended approaches in the preamble to the proposal and in this final rulemaking, they are not required to be adhered to by any air agency required to characterize air quality around an SO 2 source identified in this rulemaking. The EPA developed the TADs to aid air agencies seeking advice in the air quality characterization process required by this rulemaking. The Agency has indicated that the TADs are meant to be used as possible tools to aid air agencies

. This rulemaking does not codify the TADs, and none of the comments on the proposed rule regarding the TADs resulted in changes to the rule itself. The TADs are considered to be living documents that the EPA may update as necessary over time.

T he Agency believes that a modeling pro tocol or monitoring network design that follows or references the recommended approaches in the TADs is likel y to be adequate, and will better ensure the success and a timely fulfilment of the requirements of this rulemaking. However, air agencies remain f

ree under the final rule to suggest alternative approaches to those suggested in the TADs. Whether an agency chooses to follow a TAD or suggest an alternative approach does not affect the fact that for every approach chosen the air agency will need to subm it their rationale and approach to the EPA for review on a case

- by

- case basis.DELIBERATIVE

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240 

### B. TADs are not binding

Comment:

Commenters (0040, 0060) q uestion ed whether referring to the expected use of these TADs in a binding rule does not in and of itself make the TADs binding. Commenter (0040) stated that EPA should clearly state in each TAD, should the y remain non

- binding guidance, that they have no relevance in any enforcement action or citizen suit for any purpose under the CAA and EPA’s regulations promulgated purs uant thereto.

Commenters (0040, 0044

, 0051, and 0060 ) urged EPA to be clearer in the final preamble that the TADs are not binding. Commenter (0060) urge d EPA to explicitly state in the final rule that these TADs are only guidance and air agencies retain t he ability to use alternative methods to

those outlined in the TADs.

Commenter (0109) stated EPA's reliance on technical guidance documents that have not been subject to public notice and comment undermines protections guaranteed by the Administrative

Pr o cedure Act and perpetuates EPA' s isolation from the input of affected sources and

individuals. Commenter (0052) stated that because the D RR requires the use of "... separate non

binding draft technical assistance documents ..." and creates significant reg ulatory uncertainty for air agencies , they oppose EPA's proposal.

Response:

The EPA has stated in the TADs themselves, and has reiterated in the preamble to the final rule,

that the TADs are non

- binding . Also see the response to the comment above, titled “ Comments

in the DRR d ocket related to TADs and Appendix W.” In addition, the TADs themselves have been subjected and remain subject to public comment. Therefore, the EPA disagrees with the

assertion that reference to the TADs is in contravention of the Administrative Procedure Act (APA)

. The EPA appreciates that these commenters have taken their opportunity to assure that EPA is not isolated from the input of affected sources and individuals.



### C. Procedure for TADs

Comment:

Commenter (0044) recommend ed t hat EPA solicit public comment on each TAD and then

finalize both TAD s . Commenter (0044) recommend ed that the final rule express the procedure

the EPA intends to use for that purpose, including whether the public will be provided an opportunity to comment on the proposed changes before they are “finalized,” along the same lines as contained in Appendix W to p art 51. Commenter (0044) stated the TADs should be codified as appendices to 40 CFR subpart BB. Commenter (0044) stated that if EPA disagrees

and elect s to take a counter approach, then its reasoning for doing so should be explained in theDELIBERATIVE

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241 final rule. Commenter (0110) recommended that, once the DRR is finalized, the TADs be subjected to public comment again.

Commenter (0044) stated that the incorporatio n by reference of Appendix W into the modeling TAD is an imprecise and confusing way to provide guidance. Commenter (0044) stated the TADs numerous references to Appendix W are often quite broad or otherwise ambiguous and often fail to make clear what spec ific guidance from Appendix W should appl y to the modeling to be conducted under subpart BB. See, e.g., modeling TAD at 24 and 25. In the absence of EPA providing greater clarity and specificity regarding the application of specific provisions of Appendix W to the modeling TAD, commenter (0044) believed that some references to Appendix W in the modeling TAD could be easily misread and/or more broadly applied than might have otherwise been intended.

Commenter (0044) believed these deficiencies in the Propos ed Rule can readily be cured by inserting specifically the relevant text from Appendix W into the modeling TAD, and/or by revising Appendix W’s guidance as necessary and inserting it into the appropriate text of the modeling TAD. Commenter (0044) asserted either would work and would go a long way to avoid the confusion and problems the current draft TAD’s usage of incorporation by reference will cause. Commenter stated that the linkage between Appendix W and the modeling TAD, and

the need to revise the TAD in order to make it clearer, will also provide EPA the opportunity to finalize the TAD (and remove its current “draft” status) and at the same time provide the public with an opportunity to review and comment upon proposed revisions and clarifications to t he TAD; preferably before this rule is finalized.

Commenter (0051) stated the EPA should revise this rule and associated guidance in response to comments that the TCEQ has previously submitted regarding the modeling and monitoring

TADs.

Commenter (0051 ) stated t h at, because m uch of the TAD guidance is identical to permit modeling approaches which can be conservative

, the EPA should reconsider its adhere nce to modeling approaches that may not be effective for designation purposes.

Commenter (0065) stat ed the TADs should be withdrawn because they support EPA’s designation schedule which conflicts with EPA's obligations under the C AA. Commenter (0065)

stated that the TADs , which support that schedule, may not be lawfully pursue d.

Response:

The EPA reit erates that the TADs provide recommendations but are not binding or enforceable and create no obligations on any person

. The relevant requirements, requiring air quality characterization, are requirements of this rule, and are being promulgated based on th e full

notice

- and

- comment process recommended by the commenter ; the TADs themselves do not create any new requirements . In this sense, the TADs may be considered to be commentary on the judgments that air agencies will need to make in the course of complyi ng with this rule.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

242 Although the draft TADs are referenced as recommended approaches in the preamble to the proposal and in this final rulemaking, they are not required to be adhered to by any air agency required to characterize air quality around an SO 2 s ource identified in this rulemaking. The EPA developed the TADs to aid air agencies seeking advice in the air quality characterization process required by this rulemaking. The Agency has indicated that the TADs are meant to be used as possible tools to aid air agencies

. This rulemaking does not codify the TADs, and none of the comments on the proposed rule regarding the TADs resulted in changes to the rule itself. The TADs are considered to be living documents that the EPA may update as necessary over time.

T he Agency believes that a modeling protocol or monitoring network design that follows or references the recommended approaches in the TADs is likel y to be adequate, and will better ensure the success and a timely fulfilment of the requirements of this ru lemaking. However, air agencies remain free under the final rule to suggest alternative approaches to those suggested in the TADs. Whether an agency chooses to follow a TAD or suggest an alternative approach does not affect the fact that for every approach chosen, the air agency will need to submit their rationale and approach to the EPA for review on a case

- by

- case basis.



## VIII. Proposed C onsent D ecree (CD)

A. Comments i

n the DRR docket related to the proposed CD

Comments on the Proposed CD found in the docket and relevant to the DRR have been incorporated into this RTC, primarily in the discussion below. Some commenters (0053, 0088) referred to comments they previously submitted to EPA regarding the proposed CD but did not

include those comments in the docket. As a result, those comments are not included in this RTC.

The EPA received several comments on the CD in the record for this rule. To the extent that those comments address issues only related to the terms or the status of the CD (that the CD is entered, agr eed to, withdrawn, or other procedure) or are otherwise not directly relevant to this rule, those comments are outside the scope of this RTC and are not included. The following issues, for example, are generally outside the scope of the DRR.

 J urisdiction to enter the proposed CD (0065)

 W ithhold an "attainment" classification (0065)

 CD circumvents the r equirements of the CAA (0058)

 “Sue and settle” strategy (0058)

 Thresholds described in the CD for the 16 month deadline (0058)

 CD establishes policy bey ond the proper scope of a CD (0058)DELIBERATIVE

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243  Recommendations for revisions to the CD (0096)



### B. C onflicts with the APA

Comment:

Commenter ( 0063, 0065 , 0096 ) stated that, b y short

- circuiting the ongoing public notice and comment process for the Proposed Rule, the proposed CD contravenes the notice and comment procedures set forth in t he APA and undermines a years

- long regulatory process culminating in the Proposed Rule. Commenter (0096) stated this action may run afoul of the APA’s notice and comment rulemaking re quirements by implementing a policy (rule) outside of the rulemaking process prescribed by the APA.

Response:

The proposed rule which was developed during 2013, signed on April 17, 2014, and ultimately published on May 13, 2014, did not contain any reg ulatory deadlines for the EPA to complete area designations under the 2010 SO 2 NAAQS. However, during the time that the EPA was developing the proposed rule and the final rule, the agency also became engaged in district court litigation from public interes t groups and some states and state agencies seeking to have the EPA placed on a binding schedule to complete the designations. The parties in these cases filed complete briefs in one of these cases, resulting first in the court finding that the EPA was lia ble for having failed to meet the statutory deadline to complete all area designations. Subsequently,

the EPA and the other parties conducted extensive settlement discussions over the remedy, i.e., the schedule by which the EPA would complete its duties. T his resulted in a settlement between

the EPA and the public interest group plaintiffs, which the plaintiff

- interveners did not join.

On June 2, 2014, the EPA published notice of a proposed CD reflecting this settlement ( Sierra

Club et al v. McCarthy, Ci vil Action No. 3:13

- cv

- 3953

- SI (N.D. Cal.)). 79 F R 31325. This proposed CD included deadlines for the EPA to complete designations in three phases, the latter

two of which were due on the same dates that the EPA discussed as its intended designations

dates in the preamble to the proposed DRR. The EPA received several comments on the notice informing the public of the proposed CD itself, and in response to this proposed rule.

The EPA is not promulgating deadlines for its completion of area designations in this final rule. Therefore, any comments directed to the merits of the CD itself are outside the scope of this rulemaking, and we will not respond to them here. Instead, as discussed earlier in this notice , on March 2, 2015, the court issued an order enter ing the CD and establishing its deadlines as binding on the EPA. Under the CD, the next round of designations must be completed by July 2,

2016 , which falls too early for the implementation of this final rule to generate data that may help inform designati ons in that round

. As also explained earlier, the 2017 and 2020 deadlines for the latter two stages of designations established by the CD will allow the EPA and states to use the new data and information that is timely generated by the implementation of th is rule toDELIBERATIVE

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244 inform the designations required to be completed by those dates

.

The EPA disagrees with commenters who claim that either the court’s entry of the CD or this rulemaking contravene procedural require m e n ts of either the CAA or the APA . The CD, whi ch established requirements for EPA to complete designations, was published for public notice and comment as required by C AA section 113(g) before it was entered by the court several months later. The requirements of this rule, which more general ly establi sh duties for air agencies to characterize emissions that can be used for multiple purposes, not only designations or re

designations, have undergone all applicable procedural requirements of the APA

.



### C. C onflicts with the DRR

Comment:

Commenters ( 0048, 00 51, 0058 , 0065, and 0090 ) stated the CD conflicts with the DRR and limits their opportunity to comment on the DRR. Commenter (0051) stated the EPA has not given any notice of this CD and its impact on the present proposal. Commenter (00 5 8) stated the

CD im poses new substantive requirements that are inconsistent with EPA’s pending DRR and, in doing so, the p roposed CD significantly undermines the pending rulemaking and the public review and comment process. Commenter (0090) stated that EPA's apparent intent to enter into a CD directly related to this rulemaking will make comments on this Proposed Rule irrelevant.

Commenter s ( 0048, 0065) stated t he proposed CD ignores and bypasses the notice and comment process for the proposed D RR.

Commenter (0096) stated t hat, while the DRR proposes to establish by rule the emission thresholds and the applicable data requirements

, the CD suddenly removes certain EGUs from the rulemaking process of the DRR, and therefore removes states’ ability to provide input with

respect to the emission threshold and data requirements for those units. Commenters (0101, 0109) stated the p roposed CD impairs the integrity of the rulemaking process and improperly

creates a new class of source threshold options that the CD mandates must be desi gnated at an
earlier time than proposed in the DRR . Commenter (0101) stated t he p roposed CD

, in contrast to the DRR’s notice and comment process, arbitrarily and without substantial evidence imposes rigid thresholds to be employed without any sign as to ho w they were developed or what competing factors were balanced in selecting the more than 16,000 tpy or 0.45 lbs/MMBtu

limits.

Commenter (00 75 ) stated that the proposed CD would effectively change without notice

- and

comment rulemaking the EPA’s longstandin g practice of relying on monitoring data for initial designations and otherwise prejudge the outcome of the present rulemaking. Commenter (00 75 )

stated that, i n light of the Agency’s historic practice of basing the §107(d) initial designation

process on mo nitoring data, not modeling predictions, the EPA cannot change that previous practice through a CD

.DELIBERATIVE

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245 Commenter s ( 0051, 0058, 0065

, and 0075 ) stated t he proposed CD e ffectively requires EPA to prejudge the outcome of key substantive elements of the ongoing rulemaking to set a DRR

. Commenter (00 5 8) stated that the proposed CD effectively amends this Proposed Rule by: (1) adding a new, earlier round of area designations and (2) going beyond resetting deadlines which were the subject of the litigation to defini ng the criteria by which areas will be evaluated for designation purposes. Commenter (0075) stated that, although the DRR proposes a wide range of options for completing the area designation process

– and asks for comment on all such options

– the CD picks a winning option and makes it virtually impossible for anyone other than Plaintiffs to change the “winner.” Commenter (0051) stated that t he CD differs significantly from the DRR and, if entered by the court prior to promulgation of the rule, will take pr ecedence.

Commenter (0058) stated the Proposed CD references the proposed DRR and would effectively codify many of the dates that are outlined in the Proposed Rule . Commenter (0058) stated deadlines for collection of data to support future designations s hould not be ordered by th e court
based on a Proposed Rule that may change as a result of public comment. Commenter (0058) stated it is not appropriate or proper for the CD to tie the EPA’s hands with regard to what will occur in a pending rulemaking. Comm enter (0106) stated that CD Plaintiffs and EPA are presupposing that there will be no changes to the DRR as it is currently drafted even though the purpose of notice and comment rulemaking is that an agency may receive the benefit of

interested stakeholder comment on Proposed Rule s.

Response:

T he EPA is not establishing or modifying any area designation requirements provided for in

section 107 of the CAA through this rulemaking . The purpose of this rulemaking is to require states to characterize air qual ity in priority areas throughout the country where existing ambient monitors may not be adequately characterizing peak 1

- hour SO 2 concentrations. The air quality data obtained as a result of this rulemaking then may be used in future designations or redesi gnations, as appropriate

. While the notice of proposed rulemaking described the EPA’s anticipated designations schedule, for purposes of explaining the timeline by which the EPA anticipates that the data the EPA was proposing to require will be used, the t imeline for possible

future use of these data does not dictate the schedule or the substantive features of the requirements for obtaining data for air quality characterization purposes, and the Agency believes it will be highly valuable to obtain these dat a even if that occurs after initial designations occur.

While the notice of proposed rulemaking described the EPA’s expectations that designations for areas not already completed in August 2013 would be completed either in 2017 or in 2020, the

timetable s for obtaining additional data are as prompt as the EPA considers reasonable whether or not such data can be used to inform the remaining designations, and thus alternate approaches and timetables for designations would not result in a different timetable for implementation of the rule’s requirements. In particular, whether designations proceed according to the approach described in the EPA’s notice of proposed rulemaking, or whether areas are first designated unclassifiable and subsequently redesignated t o attainment or nonattainment, the same timetable,DELIBERATIVE

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246 and substance of requirements for data to support more properly informed future judgments regarding areas’ attainment status is warranted. Because this rulemaking is not intended to define the designations process and did not propose regulatory deadlines for issuing designations, it would be inappropriate in this final rulemaking to codify any particular schedule for designations

action.

The proposed CD referenced by the comments concerns separate legal pr oceedings that are addressing the EPA’s obligations to designate areas under CAA section 107. The commenters have not identified why any potential outcome of those proceedings warrants any particular revision to the rule, nor have they explained why the va lidity of the DRR is contingent on use of any particular designations approach. While the court’s decision establishing timing requirements for the EPA’s designations obligations will of course affect the EPA’s approach to designations, including affecting the extent to which the EPA will be able to use the data required under the rule at various times in the designations or redesignations processes, these effects do not determine the validity of the data collection requirements of the rule. For these

reaso ns, the EPA believes that the ability of commenters to address issues relevant to the rule was not compromised by the proposed CD and other actions or statements in the proceedings regarding the EPA’s timetable for designations, and the EPA finds that re

- p roposal of the rule is not justified.

The comments objecting to the CD and its alleged interference with or undermining of the proposed DRR are outside the scope of this rulemaking. However, the EPA notes that some of the commenters who objected to the C D and its relationship to the proposed DRR also filed remedy briefs in the deadline suits advocat ing for designations schedules that were vastly more in conflict with the proposed DRR. Indeed, those commenters and litigants advocated for a judicial ruling on the schedule for designations that would not have allowed for any implementation of the DRR to inform those designations. The final CD establishes the deadlines for future rounds of designations

.



### D. Procedural options for the CD and DRR

Comment:

Comm enters ( 0050, 0051, 0053, 0058, 0073, 0075, 0088, 0090, 0101

, and 0102 ) urge d EPA to

withdraw or withhold consent from the proposed CD so as not to impair, interfere with or

contradict determinations made in proceedings with the DRR. Commenter (00 5 8) state d the EPA

must not enter into a CD that could alter the technical aspects of this rule without the required public notice and opportunity for comment. Commenter (0073) believed it is important that issues concerning the exercise of discretionary authority be resolved through a rulemaking proceeding fully informed by public comment rather than in the context of a CD.

Commenter s (0051 , 0053, 0080, 0090, 0096, and 0097 ) s uggested that, in order to give all interested persons adequate opportunity to comment o n the DRR proposal, the EPA should re

propose the DRR. Commenter (0051) stated that, if the CD is finally entered by the court andDELIBERATIVE

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247 becomes legally enforceable by the plaintiffs in that case the EPA should re

- propose the DRR

. Commenter (0090) suggested that EPA should re propose the DRR to reflect additional information raised by the CD. Commenters (0090, 0096) stated that, if the CD is entered by the court, its terms must be referenced and incorporated into the DRR. Commenter (0053) stated the

EPA should no t allow the proposed CD to usurp this rulemaking process and any significant changes to the proposed DRR (such as those in the CD) should be subject to additional rulemaking and not finalized as party of a 2

- party settlement agreement. Commenter (0097)

rec ommend ed that any requirements in the proposed CD should be included in this Proposed

Rule making ; o therwise, the EPA is imposing rule

- like requirements without the public participation and other legal backstops associated with a rule

. Commenter (0080) stat ed the EPA cannot continue with this rulemaking when substantial portions of the DRR are being modified through the pending CD.

Commenter (0096) added the following points.

In particular, the additional milestones imposed by the CD must be incorporated into the

p rogram i mplementation t imeline set forth in part IV of the DRR. Specifically, those additional milestones include (1) a period for states/air agencies to review the data on which EPA intends to base designations for those sources covered by the C D, (2) the date

EPA must submit 120

- day letters to states if deviating from agencies’ designation recommendations, (3) the date for public comment period on proposed designations, and (4) the final date by which EPA must publish designations in the Federal Register for

those sources covered by the CD. It is important that all data requirements and implementation timeline milestones for the 2010 SO 2 NAAQS be represented in the

DRR , and any additional requirements imposed by the CD be incorporated into the DR R

.

Commenter (00 5 8) stated that, because the p roposed CD was not noticed in conjunction with this rulemaking and effectively amends this Proposed Rule , EPA must issue a supplemental proposal in the context of this rulemaking to allow for full public notic e, review and comment on the terms and conditions of the designation criteria proposed in the draft CD.

Commenter (0096) stated that, i f the CD is entered there should be a need to reference the DRR’s proposed requirements in the CD to clarify and stream line the interplay between the two

documents

. Commenter (0097) stated that a CD is not the appropriate mechanism for imposing requirements supporting the implementation of a NAAQS upon states, particularly where there is an outstanding rulemaking on the im plementation of that standard.

Response:

See response to the comment above. Neither the CD nor the court order may be considered to

amend this rule , and this rulemaking was of course powerless to divest the court of jurisdiction to issue a remedy requir ing the EPA to complete designations by certain dates

. The EPA disagrees that it is necessary to re

- propose this rule simply because the court has now entered the CD and placed the EPA under a binding schedule to complete designations, just as the EPA woul d soDELIBERATIVE

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248 disagree if the court had declined to enter the CD and had placed the agency under a binding schedule that would not have accommodated implementation of the rule at all before designations were due.



### E. CD 16 month deadline

Comment:

Commenter s (0058 , 0 065, 0066, and 0102 ) stated the short timeline of 16 months for the first phase of designations in the proposed CD short

- circuits the provisions in the DRR and does not allow time for areas to establish monitors and collect 3 years of actual ambient air qu ality data. Commenter (0065) stated, b y contrast, the proposed DRR would allow states the option to gather monitoring data through 2019 to characterize each area's air quality. Commenter (0065) stated

that the EPA should not limit in this way the flexibili ty of states to tailor their respective approaches to establishing their attainment status, because the CAA assigns states the primary responsibility and discretion to determine how to implement and enforce the NAAQS.

Commenter (0082) stated the EPA shou ld clarify in the final rule that, for areas required to be designated by the 16

- month deadline in the p roposed CD , it would be appropriate for EPA to designate areas as unclassifiable where the necessary monitoring or modeling data are still being develop ed.

Commenter (0058) stated the method by which AERMOD should be used in the context of designations is a subject of the proposed DRR and, if this court were to commit the states and EPA to a path of making designations based on dispersion modeling, the appropriate method of applying such models for this purpose would not be established until well after the lodging of

this CD , significantly reducing the 16 month window. Because the draft settlement uses actual

2012 SO 2 source emissions data to identify so urces that need to be modeled, commenter (0066) believed it forces states to model power plants where sufficient SO 2 controls have already been

installed to meet the 2010 SO 2 NAAQS, which is a waste of state resources and those of affected large SO 2 source s.

Response:

See response to the comment s above

. In addition, the EPA stresses that this final rule does not establish requirements for how designations are to be conducted, and that the CD does not require specific analytical methods or substantive resu lts in future designations. The CD simply provides the criteria for which areas must be designated by which dates, and the date that the EPA must meet in issuing designations.



## IX. Comments o utside the Scope of this Rulemaking

A. Comments on d

esignation p olicyDELIBERATIVE

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249 

### 1. Alternate approaches for designations

Comment :

Commenter (0046) suggested states should be able to work with sources on a more flexible schedule than the rule allows for in order for them to implement emissions reductions in a timely

manner rather than proposing a nonattainment designation. Commenter (0046) stated the EPA has done this in the past with the Early Action Compact (EAC) approach for meeting the 1997 8

- hour ozone standard and stated s uch an approach would be easier in this case, as SO 2 is mor e of a

source

- based pollutant than ozone, and could result in improvements in air quality sooner than a

2022 attainment date. Commenter (0046) stated t his approach would focus the burden associated

with a nonattainment designation on areas that need longer range planning and solutions to

achieve attainment.

Commenter (0096) stated, a nother, more conventional, approach would be to designate areas with f uture emissions reductions as unclassifiable until enforceable emission limitations are implemented.

Com menter (0042) recommended that the EPA proceed as it did with the NO 2 NAAQS: the Agency should (1) determine that areas without adequate monitoring data would be designated as unclassifiable; (2) set forth requirements for additional monitors, developing t he requirements for an adequate monitoring network in consultation with state and local agencies; (3) give states a reasonable time to install those monitors and to collect three years of data; and (4) then consider whether areas initially designated uncla ssifiable could be redesignated as attainment or nonattainment based on the results of this monitoring.

Commenter (0046) stated the EPA should expedite NAAQS designations based on monitoring by reviewing existing network plans, if requested by the state, and use existing monitoring data, as it would for any other NAAQS if the monitoring plan is approved (retroactively).

Commenter (0052a, 0106) stated that areas with no significant sources and not being impacted by significant emissions from a source in an adjacent area , should be designated attainment or

unclassifiable/attainment. Commenter (0052a) stated that, u nder this scenario, only those

counties with sources whose emissions are above the threshold should be designated unclassifiable and they should only be maintained in that classification until ambient monitoring determines the area is attaining or violating the S O 2 standard. Commenter (0106) stated that, where there are no significant anthropogenic sources in an area (e.g. a county) or near the ar ea's border, the EPA should provide a mechanism for designating the area "attainment" without monitoring or modeling data; e.g., the EPA could provide a lower emission threshold for total emissions in a county below which attainment status would be justifi ed without providing additional monitoring or modeling data.

Commenter (0052) recommend ed that the EPA establish a de minimis level regarding area

evaluation and monitor location. Commenter (0052) stated the EPA should declare areas withDELIBERATIVE

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250 combined actual a nnual emissions less than 100 tpy of SO 2 as "attainment". Commenter (0052)

stated a n emissions inventory of all S O 2 sources within the county or region showing historical emissions data (i.e. maximum actual emission totals per county from 2007

- 2010) should suffice.

Commenter (0083) suggested an alternate approach and stated it will avoid requiring areas that may not be actually violating the standards from going through the very expensive, lengthy and

time

- consuming processes associated with a nonattainmen t designation. Commenter (0083) suggested the following as an alternate approach to use in completing the initial designations for

the 1

- hour SO 2 NAAQS.

(1) The DRR should state that any data from existing monitors located in reasonable proximity to an ap plicable source of SO 2 emissions shall be used to designate the area as attainment if the monitoring data shows that the area meets the standard and nonattainment if the monitoring data shows the area does not meet the standard.

(2) For the initial design ation, all areas without sufficient monitoring data should be designated unclassifiable.

(3) Since modeling is known to provide a conservative estimate of ambient pollutant concentrations, the DRR should allow for modeling to demonstrate that an area

sur rounding an applicable source of SO 2 emissions does not violate the standard. Those areas could then be designated attainment with no further monitoring requirements. Modeling should not be used to make a nonattainment designation for an area.

(4) For all other areas with applicable sources under the DRR, the DRR should require the placement of ambient monitors, which will also provide a more comprehensive ambient air monitoring network, giving regulatory agencies, the general public, and other

stakeholder s a better understanding of the actual air quality in their area.

Response:

This final rule is not taking any designations action and does not establish requirements for how designations are to be conducted, or by what date. (As an aside, we note that t he schedule for designations is now set forth in a court order in any event)

. In addition, it would not be appropriate for this rule to prejudge the substantive outcome of future designations, as many of the commenters appear to request. W hile the proposed rule discussed how the timing of the implementation of this rule would fit with the anticipated schedule for completing area designations, the proposed rule did not itself purport to establish a binding schedule for completing designations. In this rulema king we are not addressing comments received on the proposed rule concerning the designation process , or alternative approaches for conducting designations

. Commenters will be able to raise their concerns about specific designations issues

when those actio ns are taken.DELIBERATIVE

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251 

### 2. Designations before 2017

Comment :

Commenter (0069) stated the EPA should designate as "attainment" a reas that contain properly

sited S O 2 monitors with attaining data as well as those areas of the country that do not contain large sources o f S O 2 . Commenter (0069) stated the EPA should not wait until December 2017

, rather t his should be completed as soon as possible as required by section 107(d)(1)(B) of the

CAA

.

Commenter ( 0068 ) stated that the EPA can and should promulgate additional desig nations before

the 2017 date in the draft r ule. Commenter ( 0068 ) provided the following additional points.

Since under the CAA nonattaining areas have up to five years to resolve their air quality problems from the date of designations, Commenters are tro ubled by a framework in which all outstanding designations are not finalized until 2017 and 2020, under the modeling and monitoring pathways, respectively, contemplated in the draft DRR. Accordingly, c ommenters believe that the schedule laid out in the dra ft r ule could only be supportable if it was coupled with an additional, prior round of designations to occur before the 2017 modeling pathway round, focusing on areas containing a subset of high

priority sources. While c ommenters appreciate and support tim etables that ensure that accurate designations are promulgated, c ommenters believe that the EPA can and should promulgate additional designations before the 2017 date in the draft Rule.

Response:

The EPA’s schedule for completing designations is now subj ect to a court order, which in fact does provide for a round of designations to occur in June 2016 for areas with newly monitored violations of the NAAQS and with sources emitting over certain very large annual or lb/mmBtu

rates. W hile the P roposed R ule di scussed how the timing of the implementation of this rule

would fit with the anticipated schedule for completing area designations, the P roposed R ule did not itself purport to establish a binding schedule for completing designations. In this rulemaking

we are not addressing comments received on the P roposed R ule concerning the designation

process , or alternative approaches for conducting designations because those issues are beyond the intended scope of this rulemaking.



### 3. Previously submitted SO 2 

### designation s in specific s tates

Comment :

Commenters (0038, 0043, 0051, 0103, and 0108) asked the EPA to act on previously submitted designation requests.

Commenters (0038, 0108) ask ed that previously submitted designation requests be considered byDELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

252 the EPA in the c ontext of WDNR's comments on the proposed DRR

. Commenter (0038) noted the state of Wisconsin has previously made designation recommendations to the EPA for the 1

- hour S O 2 NAAQS and stated that, i n these letters, the state recommended to the EPA that

Wisco nsin counties currently demonstrating a 3

- year design value below the NAAQS, as well as those counties reporting less than 20 tpy of S O 2 emissions (or with no individual sources reporting greater than 20 tpy of S O 2 emissions) be designated as attainment.

Commenter (0043) recommend ed that the EPA act on South Dakota's original submittal and follow the proper procedures outlined in the CAA

. Commenter (0043) stated South Dakota's designation provides sufficient information for the EPA to make a determination that all areas in

South Dakota are in attainment for the 20 10 revised sulfur dioxide standard.

Commenter ( 0051 ) stated the EPA should designate 10 Texas counties as attainment. Commenter ( 0051 ) provided a table with design values and r eferred to corresp ondence between

the s tate and Regional Office. Commenter (0063, 0065) stated the Houston Texas area should be designated attainment since, n ot only does the area's regulatory monitoring network meet p art 58 requirements, but the area also contains a dense privately

- operated monitoring network and a ll the relevant data from these two networks confirm that the area is attaining the S O 2 NAAQS

. Commenter (0063, 0065) provided additional, detailed information about this monitoring

network in Attachment A to thei r comment letter.

Commenter (0052) stated that because the D RR ignores currently available quality

- assured

ambient air data measured by state and local air monitoring systems that meets all applicable regulatory requirements , they oppose the EPA 's propos al.

Commenter (0106) stated North Dakota timely submitted its initial designations of attainment for

all areas in the s tate to the EPA, the Department believes that the monitoring data supports designations of attainment for North Dakota, and that the EPA must proceed promptly to promulgate designations of attainment for the s tate.

Response:

W hile the P roposed R ule discussed how the timing of the implementation of this rule would fit

with the anticipated schedule for completing area designations, the P ro posed R ule did not itself purport to establish a binding schedule for completing designations. In this rulemaking we are not addressing comments received on the P roposed R ule concerning the designation process

because those issues are beyond the intended s cope of this rulemaking. The timing of EPA’s designations is now governed by a court order, and the substantive decisions of those future designations will be made in those future actions, not prejudged in this final rulemaking.



### 4. Redesignation to attainment f ollowing nonattainment designation based on modelingDELIBERATIVE

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253 Comment :

Commenter (0046) stated the EPA must explain how areas may be redesignated to attainment if they are initially designated nonattainment based on modeling. Source

- oriented monitoring

should b e the methodology to redesignate an area to attainment; a modeling analysis should not be required. Commenter (0110) stated that, f or areas that have modeling results showing NAAQS violations for a specific source, the state should have the opportunity to change to a 3

- year monitoring approach if there is an expectation that the modeling has limitations that could

result in over predictions.

Commenter (0051) stated the EPA should clarify that areas can be directly designated or redesignated to attainment b ased on qualifying monitoring data in the following instance: where states are unable to have monitors deployed by the EPA's deadline, areas may subsequently be designated as nonattainment based on modeling; then, once monitoring data are available, it may demonstrate attainment. Commenter (0051) stated that, i f this occurs, the EPA should directly redesignate the area to attainment, without requiring the state to go through all the redesignation/maintenance plan requirements.

Commenter (0081) stated that, i n order to comply with the CAA, the EPA should designate all areas which cannot currently be categorized by existing monitors as unclassifiable , t he EPA should then redesignate areas as “attainment” or “nonattainment” based on the modeling and monitoring requirements finalized in this rule , and, upon redesignation from “unclassifiable” to “attainment,” no maintenance plan should be required. Commenter (0081) stated that s uch a strategy would be consistent with the legal requirements of the CAA.

Response:

W hile the P roposed R ule discussed how the timing of the implementation of this rule would fit

with the anticipated schedule for completing area designations, the P roposed R ule did not itself purport to establish a binding schedule for completing designat ions. In this rulemaking we are not addressing comments received on the proposed rule concerning the designation or redesign a tion process because those issues are beyond the intended scope of this rulemaking. In addition, we note that the EPA in April 2014 issued non

- binding guidance on implementation of the NAAQS in designated nonattainment areas, including addressing re

- designations. That guidance may be found at http://www.epa.gov/ airquality/sulfurdioxide/implement.html

. This final rulemaking does not take final action to codify that guidance, nor to otherwise establish requirements for how re

- designations shall be conducted.



### 5. Future monitored violations

Comment :

Commenter (0052a) stated the EPA should allow a state to address a source

- oriented ambient air quality violation using the air program permitting process if a violation is measured in an

unclassified area after an ambient monitoring network is expanded. Commenter (0052a) s tatedDELIBERATIVE

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254 that t his may be the most efficient way to bring an area back into compliance with the NAAQS

and is an appropriate federally

- enforceable instrument to use. Commenter (0052a) stated that,

g iven the short term nature of the S O 2 standard and the typical cause and effect relationship

between an individual source of S O 2 and a violating monitor, the traditional designation process

is not well suite d to efficiently address such violations. Commenter (0052a) stated that, i f a state

does not address a violatio n in a timely manner, then the EPA could proceed with designating an

area as nonattainment and follow the SIP development process at that time.

Response:

The EPA welcomes any and all timely efforts to address air quality problems as they are

identified. Nevertheless, such efforts cannot substitute for meeting the requirements of the CAA

. The EPA does not have the authority to suspend those requirements while the state seeks to address the air quality problem. The EPA is not in this final rule establishin g any requirements for when or how designations are to be conducted, but notes that in the designations process for future actions it may in specific cases be appropriate to consider timely efforts by the state that result in the area meeting the air quali ty standard by the time of issuance of the designations. The

EPA also notes generally that establishment of limits sufficient to assure attainment would address the primary requirement for nonattainment plans. However, such efforts by the state

cannot auth orize EPA to avoid promulgating designations, nor exempt a state from any requirements that apply to planning for air quality following a designation.



### 6. December 2017: Intended d ate for i ssuance of f inal d esignations for

m ajority of c ountry

Comment :

Commen ter (0069) stated the EPA should provide for a longer period than 2 months

-- such as 6

months

-- between publication of the designations in the Federal Register and the effective date. Commenter (0069) stated t his would allow states to certify 2017 ambient mo nitoring data before

the de signations become effective, which would allow consideration of the air quality improvements brought about by significant EPA emission reduction requirements, such as the MATS Rule, which requires compliance by April 16, 2015, an d the Boiler MACT, which requires compliance by January 31, 2016. Commenter (0069) stated t his would eliminate an unnecessary burden on states to develop and the EPA to approve maintenance plans and re

designation requests for areas that attain the standar d shortly after designations are made.

Response:

In this rulemaking we are not addressing comments received on the P roposed R ule concerning the designation process because those issues are beyond the scope of this rulemaking. The

effective dates of futur e designations will be determined in those actions, and it would not be appropriate for this rule to prejudge those decisions.DELIBERATIVE

- FOR INTERNAL EPA REVIEW ONLY

255 

### 7. December 2020: Intended d ate EPA i ssuance of f inal d esignations

Comment :

Commenter (0069) stated (s imilar to the their comments on finalization of 2017 designations )

, the EPA should provide for an effective date for the December 2020 designations that is far enough into 2021 to allow states to certify 2020 ambient monitoring data. Commenter (0069)

stated t his would eliminate an un necessary burden on states to develop and on EPA to a pprove maintenance plans and re designation requests for areas that attain the standard shortly after designations are made. [Also see IV.G.]

Response:

As stated previously, while the P roposed R ule disc ussed how the timing of the implementation

of this rule would fit with the anticipated schedule for completing area designations, the proposed rule did not itself purport to establish a binding schedule for completing designations. In this rulemaking we ar e not addressing comments received on the P roposed R ule concerning the designation process because those issues are beyond the scope of this rulemaking. The effective dates of future designations will be determined in those actions.



### B. SO

2 

### NAAQS f

inal r ul e

Comments on the p roposed CD found in the docket and relevant to the DRR proposal have been incorporated into this RTC. Comments outside the scope of this RTC are not included. The following issues, for example, are generally outside the scope of the DRR

.

 Timing suggestions submitted in correspondence before the DRR was proposed are not addressed as they have been superseded by the DRR proposal.

 Comment s regarding consistency between the implementation approach that is set out in the preamble to the fin al S O 2 NA AQS rule and language of the final S O 2 NA AQS rule

.

 Procedural comments regarding the final SO 2 NA AQS rule.



### C. Tenth EPA m odeling c onference

Comments on the draft Tenth EPA Modeling Conference found in the docket and relevant to the DRR proposa l have been incorporated into this RTC. Those comments not outside the scope of this rulemaking are addressed earlier in this RTC. Comments outside the scope of this rulemaking include modeling conference comments directed at NO 2

, ozone, PM, and Significan t Impact Levels

.



### D. Other c omments o utside the s cope of t his r ulemakingDELIBERATIVE

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256 The docket includes comments on EPA’s September 22, 2011 draft guidance, May 22, 2012 White Paper, and February 15, 2013 Strategy Paper. The following commenters included in the

dock et previously submitted comments on EPA’s draft guidance: 0042, 0052, 0052a, 0052a, 0097; those comments relevant to the DRR are included in this RTC. Some commenters (0053, 0109) referred to previously submitted comments on EPA’s draft guidance but did no t provide copies of such comments in the docket; those comments are not addressed in this RTC. Comments not outside the scope of this rulemaking are addressed earlier in this RTC. The following issues, for example, are generally outside the scope of the DR R.

 Comments on infrastructure SIPs.

 Because the DRR is designed to require air quality characterization, generally to support decisions regarding attainment status, comments regarding the SIP requirements for future attainment and maintenance are general ly not relevant to this rulemaking.

 Comments regarding redesignations to attainment are generally not addressed.



### 1. SIP r equirements

Comment :

Commenter (0041) stated that methods exist to allow use of actual emissions for SIP modeling as long as follow

- up checks are also required by the SIP, and the AQD has stated this position in numerous venues regarding the SO 2 SIP for our existing nonattainment area.

Commenter (0097) stated that additional requirements should be included in implementation

rules so t hat states and affected facilities have the opportunity to comment on all elements of the planning requirements. Commenter (0097) referenced EPA ’s "Guidance for 1

- Hour SO 2 Nonattainment Area SIP Submissions" and stated that many aspects of t his memorandum may also impact attainment/maintenance areas. Commenter (0097) stated, f or example, this

memorandum discusses the requirements for submitting SIP revisions regarding source

- specific emission limitations, the methodology for determining emission limitations that are of longer duration than 1 hour, and ways facilities may include reductions from rules such as the MATS in

their source

- specific SO 2 modeling.

Response:

Issues concerning guidance for SO 2 Nonattainment Areas are outside the scope of this

rulema king.



### 2. Electric ratesDELIBERATIVE

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257 Comment :

Commenter (0033) stated “S o this means my electrical rates will go up again another 30%. ”

Response:

While the commenter appears to object to this rule, and presumably believes that air agencies will identify a substantial n umber of areas violating the standard that the commenter would wish for air agencies not to identify, the commenter does not support the estimate 30% of the impact on electricity costs and does not specify any lawful revisions to any particular feature of the proposed rule that might mitigate the concern.



## X

. Other Comments

A. Support other comments

Commenters (0046, 0079) supported comments of commenter (0042).

Commenters (0047, 0048, 0057, 0058, 0066, 0070, 0090, and 0114) supported the comments of

comment er (0075).

Commenter (0065) attached to their comments a copy of commenter’s (0042) December 2, 2011

comments.

Commenter (0084) supported the comments of commenters (0042 and 0046).

Commenter (0094) supports the comments the comments submitted by commen ters (0044 and 0095).



### B. EPA guidance

Comment :

Commenter (0036) urge d EPA to be more specific as to which state and EPA region would lead

a multi

- state planning process (e.g., confer responsibility to the state in which the source resides).

Commenter (00 46) stated that s everal layers of conservatism are already incorporated into the underlying risk analyses and health

- effects assessments co nsidered in establishing NAAQS and

e ach element of an ambient air quality analysis has uncertainty and measurement er ror associated

with it. Commenter (0046) stated that t he whole regulatory decision system should be considered by EPA in choosing the degree of conservatism deployed when making policy decisions that could materially affect the economic health of a communi ty when public health may not actually

be at risk.DELIBERATIVE

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258 Commenter (0060) stated that m uch of the recent guidance from the EPA has not been issued expeditiously or timely and this creates significant issues for air agencies that find it necessary to

use their k nowledge, expertise and experience to develop plans to only find out at the last moment the approach doesn't meet the needs outlined in less than forth

- coming guidance. Commenter (0060) provided a list of more recent guidance the EPA has issued relevant to important SIP planning activities for air agencies along with the amount of time provided between issuing the g uidance and when the SIP is due and stated t hese amounts of time are not sufficient for air agencies to perform analysis, prepare submittals and provide for the required comment periods and hearings before submittal.

Commenter (0060) urged the EPA not to set out such specific criteria and requirements in regulation for processes that can occur through the collaboration of s tates and EPA Regions

. Commenter (0060) stated that t his rule is far too prescriptive and cumbersome and will inevitably lead to valuable resources being spent assessing situations that fit the letter of the rule

but when using common sense, judgment and expertise, would not req uire assessment.

Response:

The EPA believes that where there are cases where multiple states and areas are involved as it relates to the characterization of sources, there should be coordination among the states and the affected regional offices to dete rmine what sources should be characterized to satisfy the requirements of the rulemaking. More detailed commentary on the need for multi

- state coordination, particularly for assuring that any monitoring plan provide for addressing maximum

concentration loc ations in the multi

- state area as a whole, and the presumpti v e need for an area without such coordination to be modeled by the state having the primary source, is provided in section IV.E.5 of the preamble to the final rule.

The CAA requires that the EPA set NAAQS that incorporate an adequate margin of safety, and

the CAA requires that for areas with identified violations of those NAAQS, states must develop plans, with EPA review, that provide for attainment. The EPA disputes the commenter’s view

that a vi olation of the NAAQS does not necessar il y represent a risk to public health, and the

CAA does not authorize the EPA to follow the commenter’s recommendation to take greater risks of violating the NAAQS based the conservatism that the CAA requires in settin g the NAAQS.

The EPA recognizes the need for timely guidance. While constraints on EPA resources and complexity of issues often delay the issuance of guidance, the EPA seeks to provide timely guidance as the commenter requests, and the EPA in overseeing state efforts recognizes the challenges states face. D evelopment of rulemaking involves a more complicated review process and almost inevitably takes longer , and states that request that EPA establish requirements through rulemaking rather than issuing gui dance memoranda should consider the potential impact of that request on the timeliness of the guidance. Nevertheless, in the present case, the EPA agreed with the majority of commenters during the White Paper phase of the developmentDELIBERATIVE

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259 of this rule that the requirements in this rule needed to be promulgated as regulatory requirements.

In any rulemaking such as this, the EPA must find an appropriate balance between establishing specific criteria, which often helps assure national consistency, and providing fl exibility to address disparate situations in ways that the particular circumstances warrant. The appropriate balance depends on the degree to which specific criteria can be crafted to address a wide range of circumstances, and also depend on the degree to which flexibility can be incorporated without risk of creating fundamental inconsistencies in how similar situations are addressed. The EPA believes that this rule sets proper criteria for establishment and implementation of requirements for air quality ch aracterization, while providing suitable flexibility and exercise of judgment as to how these requirements are met.



### C. Organization of the proposal

Comment :

Commenter (0085) noted that EPA provides the list of topics as they are organized in this Proposed R ule and encourage d EPA to take this a step further and make this organized list of topics into a regular table of contents, with page number references for each topic. Commenter (0085) states that t his would ensure ease in finding topics in what are often times lengthy rules, 26 pages in the Federal Register in this case, but a couple of hundred pages in other cases.

Response:

The EPA appreciates the comments and ha s taken this suggestion into consideration. However,

the EPA does not know the page numberi ng for the published version of the notice at the time

that it signs the notice, and therefore, the EPA cannot prepare the table of contents in the format that the commenter requests.