Source Specific Federal Implementation Plan 

for Implementing Best Available Retrofit 

Technology for Four Corners Power Plant: 

Navajo Nation 

Response to Comments for Proposal and 

Supplemental Proposal 

U. S. Environmental Protection Agency 

Region 9 

Air Division 

San Francisco, CA 94105

August 2012 
Page 2 of 171 

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Table of Contents 

Acronyms and Abbreviations ......................................................................................................... 3

1.0 Introduction ........................................................................................................................... 7

1.1 Background .................................................................................................................... 7

1.2 The Commenters ............................................................................................................ 7

1.3 Organization of This Document ..................................................................................... 8

2.0 Oral Testimony at the Public Hearings and Mass Comment Campaigns ........................... 18

2.1 Oral Testimony at the Public Hearings ........................................................................ 18

2.2 Mass Comment Campaigns ......................................................................................... 26

3.0 Comments on Factor One – Cost of Controls ..................................................................... 33

3.1 Comments on the Analysis of the Cost of SCR at FCPP ............................................. 33

3.2 Comments on Top-Down Analysis Versus Incremental Cost Effectiveness ............... 46

3.3 Other Comments on Factor One .................................................................................. 49

4.0 Comments on Factor Two – Economic, Energy, and Non-Air Quality Environmental 

Impacts ................................................................................................................................ 52

4.1 Comments on Economic Impacts ................................................................................ 52

4.1.1 General Comments on Economic Impacts ......................................................... 52

4.1.2 Comments on EPA’s Economic Analysis.......................................................... 59

4.2 Comments on Energy and Non-Air Quality Environmental Impacts .......................... 65

5.0 Comments on Factor Three – Existing Controls at FCPP ................................................... 76

6.0 Comments on Factor Four – Remaining Useful Life of FCPP ........................................... 77

7.0 Comments on Factor Five – Anticipated Visibility Improvements .................................... 82

8.0 Comments on BART Determinations ................................................................................. 98

8.1 Comments on the Proposed BART Determination for NOx ........................................ 98

8.2 Comments on the Proposed BART Determination for PM ....................................... 124

8.3 Comments on BART for SO2 ..................................................................................... 129

8.4 Other Comments on BART ........................................................................................ 133

9.0 Comments on APS’s Alternative Proposal and EPA’s Supplemental Proposal ............... 139

10.0 Other Comments ............................................................................................................... 151

 
Page 3 of 171 

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Acronyms and Abbreviations 

Pollutants

CO2 Carbon dioxide 

GHG Green House Gas 

H2SO4 Sulfuric acid 

NOx Nitrogen oxides 

PM Particulate matter 

PM10 Particulate matter less than 10 micrometers 

PM2.5 Particulate matter less than 2.5 micrometers 

SO2 Sulfur dioxide 

SO3 Sulfur trioxide 

 

Units

Btu British thermal unit 

kW Kilowatt 

kW-hr Kilowatt-hour 

lb Pound 

MMBtu Million British thermal units 

MW Megawatt 

MWh Megawatt hour 

ppb Part per billion 

TBtu Trillion British thermal units 

tpy Tons per year 

 

Acronyms and Abbreviations

ADEQ Arizona Department of Environmental Quality 

ANPR Advance Notice of Proposed Rulemaking 

APA Administrative Procedure Act 

APS Arizona Public Service 

BACT Best Available Control Technology 

BART Best Available Retrofit Technology 

BAU Business as usual 
Page 4 of 171 

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Acronyms and Abbreviations 

BOD Boiler Operating Day 

CAA Clean Air Act (42 U.S.C. 7401 - 7671q) 

CAIR Clean Air Act Interstate Rule 

CAMD Clean Air Markets Division (EPA) 

CBI Confidential Business Information 

CCW Coal Combustion Waste 

CEMS Continuous emissions monitoring system 

CFR Code of Federal Regulations 

CO Colorado 

COMS Continuous opacity monitoring system 

COPD Chronic obstructive pulmonary disease 

COS Combustion optimization systems 

CRF Capital Recovery Factor 

DC Circuit Federal Court of Appeals for the District of Columbia Circuit 

DREF Desert Rock Energy Facility 

DOE Department of Energy 

DOI Department of the Interior 

dv Deciview 

EIS Environmental Impact Statement 

EGU Electric generating unit 

ELGs Effluent limitation guidelines 

EPA U.S. Environmental Protection Agency 

EPRI Electric Power Research Institute 

ESA Endangered Species Act 

ESP Wet membrane electrostatic precipitator 

FCPP Four Corners Power Plant 

FERC Federal Energy Regulatory Commission 

FIP Federal Implementation Plan 

FLM Federal Land Manager 

FR Federal Register 

fRH Relative humidity adjustment factor 
Page 5 of 171 

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Acronyms and Abbreviations 

HERT High Energy Reagent Technology 

IWAQM Interagency Workgroup on Air Quality Modeling 

LNB Low NOx burner 

MACT Maximum Achievable Control Technology 

MATS Mercury and Air Toxics Standards 

MRR Mandatory Reporting Rule 

NAAQS National Ambient Air Quality Standards 

NEPA National Environmental Policy Act 

NESHAP National Emission Standards for Hazardous Air Pollutants 

NGS Navajo Generating Station 

NM New Mexico 

NMED New Mexico Environment Department 

NNEPA Navajo Nation Environmental Protection Agency 

NPDES National Pollutant Discharge Elimination System 

NPS National Park Service 

NREL National Renewal Energy Laboratory 

NSPS New Source Performance Standard 

NSR New Source Review 

OAR Office of Air and Radiation (EPA) 

OMB Office of Management and Budget 

OFA Overfire air 

PSD Prevention of Significant Deterioration 

RAVI BART Reasonably Attributable Visibility Impairment Best Available Retrofit 

Technology 

RCRA Resource Conservation and Recovery Act 

RHR Regional Haze Rule 

RIA Regulatory Impact Analysis 

ROFA Rotating Overfire Air 

RTC Response to Comments 

SCE Southern California Edison 

SCR Selective catalytic reduction 
Page 6 of 171 

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Acronyms and Abbreviations 

SIP State Implementation Plan 

SJGS San Juan Generating Station 

SNCR Selective non-catalytic reduction 

TAG Technical Assistance Guidance 

TAR Tribal Authority Rule 

TIP Tribal Implementation Plan 

TSD Technical Support Document 

U.S.C. United States Code 

UARG Utility Air Regulatory Group 

U.S. United States 

VOCs Volatile Organic Compounds 

WRAP Western Regional Air Partnership 
Page 7 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

1.0 0BIntroduction 

1.1 10BBackground 

 On October 19, 2010, the U.S. Environmental Protection Agency (EPA or “we”) 

proposed a source-specific Federal Implementation Plan (FIP) requiring the Four Corners Power 

Plant (FCPP), located on the Navajo Nation, to achieve emissions reductions required by the 

Clean Air Act's (CAA’s) Best Available Retrofit Technology (BART) provision.0F

1

 On 

November 24, 2010, Arizona Public Service (APS) acting on behalf of FCPP's owners submitted 

a letter to EPA offering an alternative to reduce visibility-impairing pollution. The EPA 

supplemented the October 2010 BART proposal with its technical evaluation of APS’s 

alternative. In a February 25, 2011 supplemental proposal, we proposed to find that an 

alternative emissions control strategy would achieve more progress than EPA's BART proposal 

towards achieving visibility improvements in the surrounding Class I areas.1F

2

 

1.2 1BThe Commenters 

 In the October 2010 proposal, EPA stated that public comments were to be submitted by 

December 20, 2010. As a result of APS’s alternative and our supplemental proposal, the due date 

for public comments was subsequently extended to May 2, 2011. 

The EPA held four public hearings on the proposed BART determination and 

supplemental proposal in the Four Corners area on March 29, 30, and 31, 2011. In all, 90 oral 

testimonies were presented at the public hearings. The oral testimony is discussed further in 

Section 2.1 of this document 

We received nearly 13,000 written comments. Of these, over 12,800 comments came 

from private citizens who submitted substantively similar comments. These comments are 

discussed further in Section 2.2 of this document. 

 We received an additional 110 unique written comments (not including duplicates, 

requests for extension of the public comment period, or requests for additional hearings). These 

unique comments also do not include letters unrelated to the rulemaking. The comments can be 

broken down by general type as follows: 78 from private citizens, 8 from environmental 

advocacy groups, 4 from the owners of FCPP, 5 from state/local government entities, 4 from 

public interest advocacy groups, 2 from tribes, 4 from utility industry associations, 3 from 

federal agencies, 1 from a U.S. Senator, and 1 from the operator of the Navajo Mine. These 

comments are listed at the end of this section. The list of comments also includes an entry for all 

the written comments submitted at the public hearings, which are not included in the preceding 

totals. The comments are summarized by topic in Sections 3.0 through 10.0 of this document.

 

1

 The BART determination was proposed on October 19, 2010 in the Federal Register, Volume 75, beginning on 

page 64,221 (75 FR 64221, October 19, 2010). 

2

 76 FR 10530, February 25, 2011. 
Page 8 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

1.3 12BOrganization of This Document 

 After this introductory section, this document includes nine additional sections as 

follows: 

 Section 2.0 – Oral Testimony at the Public Hearing and Mass Comment Campaigns 

 Section 3.0 – Comments on Factor One – Cost of Controls 

 Section 4.0 – Comments on Factor Two – Economic, Energy, and Non-Air Quality 

Environmental Impacts 

 Section 5.0 – Comments on Factor Three – Existing Controls at FCPP 

 Section 6.0 – Comments on Factor Four – Remaining Useful Life of FCPP 

 Section 7.0 – Comments on Factor Five – Anticipated Visibility Improvements 

 Section 8.0 – Comments on BART Determinations 

 Section 9.0 – Comments on APS’s Alternative Proposal and EPA’s Supplemental 

Proposal 

 Section 10.0 – Other Comments 
Page 9 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0067 Colorado-based organizations Group of 

Environmental Advocacy Groups 

0068 Edward Z. Fox, Vice President and Chief Sustainability Officer, Arizona 

Public Service 

Co-owners of FCPP 

0069 Stephen B. Etsitty, Executive Director, Navajo Nation Environmental 

Protection Agency 

Tribal Agency 

0071 Richard M. Hayslip, Associate General Manager, Salt River Project Co-owners of 

FCPP 

0072 Erik Bakken, Manager, Environmental Services and Land Management, 

Tucson Electric Power Company 

Co-owners of FCPP 

0073 Wild Earth Guardians Environmental 

Advocacy Grou

0075 Edward Z. Fox, Vice President and Chief Sustainability Officer, Arizona 

Public Service Company 

Co-owners of FCPP 

3 Document ID identifies written comments found in Docket No. EPA-R09-OAR-2010-0683 by document number. 
Page 10 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0082 Patrick Themig, Vice President, PNM Resources, Inc. Co-owners of 

FCPP 

0083 Chris Foran, Steering Committee Representative, Montezuma Climate 

Action Network 

Environmental Advocacy Grou

0084 Annika Bergen Private Citizen 0085 Charles A. Haley Private Citizen 0086 Lair Carlson, Publisher Cell Door Magazine Private Citizen 0087 Irene Hamilton Private Citizen 0088 Ed Mosimann Private Citizen 0089 Zachary Katz, Orien McGlamery, Linda P. Sency, Kathy Brown, Deb 

Campbell 

Private Citizen 

0091 Martha Evers Private Citizen 0092 Brian Hoffman Private Citizen 0093 Phyllis Hollenbeck Private Citizen 0094 Jodi Foran, Past-president; League of Women Voters of Montezuma 

County 

Public Interest Advocacy Grou

0095 Stephanie Kodish, National Parks Conservation Association Environmental 

Advocacy Grou

0105 Michael Rendon, Mayor, City of Durango, Colorado State/Local 

Government 

0106 Kellie C. Hotter, Chair, La Plata County Board of County 

Commissioners 

State/Local Government 
Page 11 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0107 Robert Ukeiley, Law Office of Robert Ukeiley Private Citizen 0108 Wallace L. White, Commissioner, La Plata County Board of County 

Commissioners 

State/Local Government 

0112 League of Women Voters of Montezuma County Public Interest 

Advocacy Grou

0113 Paul Tourangeau, Director, Air Pollution Control Division, Colorado 

Department of Public Health and Environment 

State/Local Government 

0116 Ravi Grover Private Citizen 0117 Paul Nazaryk, Environmental Regulatory Affairs, BHP Billiton Operator of 

Navajo Mine 

0118 Anonymous Private Citizen 0119 Anonymous Private Citizen 0122 Margaret Ackerman Private Citizen 0123 Dan Barnes Private Citizen 0124 Larry Berger Private Citizen 0125 William Botsford Private Citizen 0126 Linda Bunk Private Citizen 0127 Laird Carlson Private Citizen 0128 Bill Carver Private Citizen 0129 Burt Coleman and Dell Manners Private Citizen 0130 Patty Cordova, LWVCO President Private Citizen 0131 Jerry and Julie Crockford Private Citizen 
Page 12 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0132 Geraldine Duffy Private Citizen 0133 Barbara Garlick Private Citizen 0134 Bruce A. Garlick Private Citizen 0135 Joe Griffith and Dianne Donovan Private Citizen 0136 Ana Hale Private Citizen 0137 Charles A. Haley Private Citizen 0138 Irene Hamilton Private Citizen 0139 Wes and Pat Hartman Private Citizen 0140 Jill and Rich Hoehlein Private Citizen 0141 Kristine Johnson Private Citizen 0142 John Larry Private Citizen 0143 Stephanie Huss, President, League of Women Voters of La Plata County Public Interest 

Advocacy Grou

0144 Ed and Julie Ward Lehner Private Citizen 0145 Claire May Private Citizen 0146 Chris Foran, Steering Committee Representative, Montezuma Climate 

Action Network 

Environmental Advocacy Grou

0147 Ed Mosimann Private Citizen 0148 Lynne Murison Private Citizen 0149 Harry Riegle Private Citizen 0150 Sean Babington, Office of Senator Michael Bennet U.S. Senator 
Page 13 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0151 Francis Slater Private Citizen 0152 Brenda Jarrell, Air Quality Program Manager, Southern Ute Indian Tribe Tribe 0153 Elaine Spence Private Citizen 0154 Dan Tobin Private Citizen 0155 Brian von Dedenroth Private Citizen 0156 Bob Waggoner Private Citizen 0157 Joe Ward Private Citizen 0158 D.J. Webb Private Citizen 0159 Richard E. White Private Citizen 0160 Richard White Private Citizen 0161 Janet Wilson Private Citizen 0162 Zita Xavier Private Citizen 0163 Vincent H. Yazzie Private Citizen 0164 Vincent H. Yazzie Private Citizen 0165 Owen M. Lopez, McCune Foundation Private Citizen 0166 D. House Private Citizen 0167 Christopher Lish Private Citizen 0168 Arie Hoekstra, Vice President, Generation, Tucson Electric Power Co-owner of 

FCPP 

0169 A. Gwen Eklund, Consulting Business Manager, WEST Associates Utility Industry 

Association 
Page 14 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0170 Brian Abel and Patricia Padian Private Citizen 0171 Dell Manners Private Citizen 0172 Montezuma-Cortez School Private Citizen 0173 Ann Perkins-Parrott Private Citizen 0174 Richard M. Hayslip, Associate General Manager, Salt River Project Co-owner of 

FCPP 

0175 Corbin L. Newman, Jr., Regional Forester, USFS Federal Agency 0176 Edward Z. Fox, Vice President and Chief Sustainability Officer, Arizona 

Public Service Company 

Co-owner of FCPP 

0177 Edward Z. Fox, Vice President and Chief Sustainability Officer, Arizona 

Public Service Company 

Co-owner of FCPP 

0178 Laura McHenry Private Citizen 0179 Patrick Themig, Vice President, Generation, Public Service Company of 

New Mexico 

Co-owner of FCPP 

0180 Brynn Johns Private Citizen 0181 Michelle Reott Private Citizen 0182 Mike Eisenfeld, New Mexico Energy Coordinator, San Juan Citizens 

Alliance 

Environmental Advocacy Grou

0183 Pamela Campos, Attorney, Environmental Defense Fund Environmental 

Advocacy Grou

0184 Jeremy Nichols, Climate and Energy Program Director, WildEarth 

Guardians 

Environmental Advocacy Grou
Page 15 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0185 Aaron Flynn, Counsel to Arizona Public Service Company, Central 

Arizona Water Conservation District, and Salt River Project Agricultural Improvement and Power District 

Co-owner of FCPP 

0186 Erin and Fred Bird Private Citizen 0187 Aaron Flynn, Utility Air Regulatory Group Utility Industry 

Association 

0188 Heidi Keshet Private Citizen 0189 R. Frank (and 682 others) Private Citizen 0190 All Written Comments Received during March 29-31, 2011 Public 

Hearings and Open Houses 

Range of commenters 

0191 League of Women Voters of Montezuma County Public Interest 

Advocacy Grou

0192 Kathy and Jim Merrill Private Citizen 0193 Post Cards Private Citizen 0194 Don Hancock, Steering Committee Chairperson, Coalition for Clean 

Affordable Energy (CCAE) 

Environmental Advocacy Grou

0195 Lau Ackerman Private Citizen 0196 Mass EPA Card Campaign Private Citizen 0197 Larry Berger Private Citizen 0198 Jackie Candelaria Private Citizen 0199 Laurie Carpino Private Citizen 
Page 16 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0200 John W. Suthers, Colorado Attorney General, Colorado Department of 

Public Health and Environment (CDPHE) 

State/Local Government 

0201 John Culver Private Citizen 0202 Clint McKnight Private Citizen 0203 Mass Email Campaign Private Citizen 0204 Mass Mail Campaign Private Citizen 0205 Mass Mail Campaign Private Citizen 0206 Mass Mail Campaign Private Citizen 0207 Mass Mail Campaign Private Citizen 0208 Evelyn Ramey Private Citizen 0209 Dave Rich Private Citizen 0210 Bruce E. and Suzzanne D. Rodman Private Citizen 0211 Roxanne Rogers Private Citizen 0212 Mass Email Campaign Private Citizen 0213 Shan and Regina Wells Private Citizen 0214 Elizabeth M. Wheeler Private Citizen 0215 Mass Email Campaign Private Citizen 0216 Vincent H. Yazzie Private Citizen 0218 Jeremy Nichols, Climate and Energy Program Director, WildEarth 

Guardians 

Environmental Advocacy Grou

0223 President Shelly, Navajo Nation Tribe 
Page 17 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

LIST OF WRITTEN COMMENTS 

Document Id 2F3 

EPA-R09-OAR2010-0683-XXXX Title Type of Commenter 

0224 Alletta Belin, Counselor to the Deputy Secretary, U.S. Department of the 

Interior 

Federal Agency 
Page 18 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

2.0 1BOral Testimony at the Public Hearings and Mass Comment 

Campaigns 

2.1 13BOral Testimony at the Public Hearings 

 The EPA held four public hearings in the Four Corners area on March 29, 30, and 31, 

2011. In conjunction with each hearing (generally before the hearing), EPA conducted an 

information session in which EPA experts explained the BART proposal and better-than-BART 

supplemental proposal for FCPP to interested attendees with the aid of illustrative posters. An 

interpreter for speakers of Diné, the Navajo language, was present for three of the information 

sessions and public hearings. 

 In all, a total of 90 oral testimonies were presented at the four hearings, although several 

persons spoke at more than one hearing and two persons gave separate testimony on behalf of 

two different entities at a single hearing. Most speakers spoke as private citizens, but there were 

also representatives of the interested industries (the co-owners of FCPP and operator of the 

Navajo Mine), environmental advocacy groups, public interest advocacy groups, and local 

government. The location and time of each public hearing and information session are given 

below, along with the number and types of speakers at each hearing. 

PUBLIC HEARINGS AND INFORMATION SESSIONS 

 Time

Date

Venue 

(with Transcript Docket Number)

Info 

Session 

Public 

Hearing Commenters 

March 29 Phil L. Thomas Performing Arts 

Center 

Shiprock, New Mexico 

(EPA-R09-OAR-2010-0683-0227) 

3 – 6 

p.m. 

7 – 9 

p.m. 

Private citizens – 16 

Industry – 1 

Environmental – 2 

March 30 Nenahnezad Chapter House 

Fruitland, New Mexico 

(EPA-R09-OAR-2010-0683-0225) 

9 a.m. – 1 p.m. 

(concurrent) 

Private citizens – 10 

Industry – 1 

Local government 

(Chapters) – 2 

March 30 San Juan College 

Farmington, New Mexico 

(EPA-R09-OAR-2010-0683-0226) 

3 – 5 

p.m. 

6 – 9 

p.m. 

Private citizens – 25 

Industry – 3 

Environmental – 2 

March 31 Fort Lewis College 

Durango, Colorado 

(EPA-R09-OAR-2010-0683-0228) 

3 – 5 

p.m. 

6 – 9 

p.m. 

Private citizens – 21 

Public interest – 2 

Environmental – 4 

Local government 

(County) – 1 
Page 19 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 The comments presented in oral testimony at the public hearings are summarized below, 

with the exception of comments from entities that submitted written comments which duplicated 

their oral testimony. For example, APS and the San Juan Citizens Alliance submitted extensive 

written, technical comments that are summarized in the other sections of this document; their 

oral comments on the same topics are not included in this section. The transcripts from and the 

materials presented by EPA during these hearings are also available in the docket.3F

4

 

Comment:

 The majority of commenters favored the supplemental proposal or more stringent 

requirements for FCPP because the commenters consider visibility and air quality in the Four 

Corners region to be generally poor. A few argued that FCPP should be shut down rather than 

being retrofit with controls. On the other hand, several commenters noted that FCPP and the 

Navajo Mine provide many jobs in the area and that their payments to the Navajo Nation make 

up a large portion of the Nation’s revenues. These commenters cautioned that EPA must 

carefully balance the environmental benefit of any requirements for FCPP with the potential 

adverse impacts to the Navajo Nation and the region that would ensue were FCPP to close as a 

result of EPA regulation. 

 Many commenters favor stringent controls on FCPP because they assert that emissions 

from FCPP represent a public health issue. These commenters indicated that these emissions are 

to blame for health problems in the area, such as respiratory disease and cancer, which many 

argue have become more prevalent in recent years. The commenters often said that the health of 

succeeding generations should be an important consideration. However, a few commenters 

questioned that FCPP’s emissions are causing such health effects. A number of commenters on 

both sides of this issue requested that health studies be undertaken to determine the health 

impacts of FCPP emissions. 

 Many speakers spoke in favor of stringent controls on FCPP because of the haze that is 

very common in the area, believing that it is due to FCPP. Some commenters indicated that the 

haze diminishes the beauty of the area, which is a quality of life issue for residents as well as an 

economic issue because of the importance of tourism to the economy of the area. 

 Several commenters support stringent controls because they argue that emissions from 

FCPP are having negative impacts on the land and water in the area, as well as the air. Some 

expressed fear that emissions from the plant, including mercury and other toxic compounds, are 

harming ecosystems in the area, including rare and endangered plant species, endangered fish 

species, pollinators, and amphibians. Some living near to the plant assert that it is responsible for 

killing native plant species that they have depended on for their livestock, and has harmed 

traditional dry land farming. A number of Navajo commenters stated that pollution of the air, 

water, and land is contrary to Navajo religious beliefs and cultural traditions. 

 A number of commenters favor stringent controls on FCPP as a first step in a transition 

away from coal-fired power plants to renewable energy sources. Commenters enumerated many 

problems with coal as an energy source, including emissions of air pollutants (SO2, NOx, PM, 

 

4

 See Document numbers 0109, 0111, and 0225 – 0228 in EPA-R09-OAR-2010-0683. 
Page 20 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

mercury and other toxic compounds, acid gases, and Green House Gases (GHGs)), use of large 

amounts of water for cooling, and production of large amounts of ash or coal combustion waste 

(CCW). Several noted that New Mexico and the Four Corners area are ideally suited for solar 

and wind energy projects. Some commenters stated that a transition to renewable energy could 

economically benefit the Navajo Nation. 

Response:

Protection of human health and the environment is EPA’s mission, and forms the basis 

for many Agency actions, including establishing the National Ambient Air Quality Standards 

(NAAQS), and promulgation of regulations such as the New Source Performance Standards 

(NSPS) and the National Emission Standards for Hazardous Air Pollutants (NESHAP). In 

addition to Clean Air Act requirements to protect human health, in the 1977 Clean Air Act 

Amendments, Congress also declared as a national goal the prevention of any future, and the 

remedying of any existing, impairment of visibility in mandatory class I Federal areas which 

impairment results from manmade air pollution (See CAA §169A). In 1999, EPA issued the final 

Regional Haze Rule (RHR), which included the requirement for facilities of a certain age to 

install the Best Available Retrofit Technology (BART) to reduce emissions of visibility impairing 

pollutants. Therefore, the focus of implementation plans developed under the RHR, is to improve 

visibility at National Parks and Wilderness Areas. EPA agrees that visibility-impairing 

pollutants can impact human and ecosystem health. Emissions of hazardous air pollutants such 

as mercury are not visibility-impairing pollutants, and as a result are beyond the scope of our 

BART analysis. EPA agrees that health studies may provide useful information, however, these 

studies are beyond the scope of a BART analysis. Emissions of hazardous air pollutants 

(HAPs)from various source categories are addressed generally through National Emission 

Standards for Hazardous Air Pollutants (NESHAPs) and EPA addresses mercury emissions from 

power plants specifically in the final Mercury and Air Toxics (MATS) Rule which was published 

in the Federal Register on February 16, 2012 (77 FR 9304). 

EPA is aware of the contribution of FCPP and the Navajo Mine to the economy of the 

Navajo Nation and the Four Corners region. At the request of the Navajo Nation, pursuant to 

EPA’s customary practice of engaging in extensive and meaningful consultation with tribes, EPA 

commissioned an analysis to estimate the potential adverse impacts to the Navajo Nation of 

APS’s option to retire Units 1 – 3 and will provide the report to the Navajo Nation by letter as a 

follow-up to our consultation. EPA did not rely on this analysis in our final determination.

Regarding comments in favor of transitioning from coal to renewable energy, the RHR 

establishes a five step process EPA must follow when performing a case-by-case BART 

determination. Although EPA agrees that transitioning to renewable energy is a worthwhile 

goal, the BART Guidelines4F

5

 state that under” Step 1: How do I identify all available retrofit 

emission control techniques?”, “[EPA does] not consider BART as a requirement to redesign 

the source when considering available control alternatives” (see specifically 70 FR at 39164). 

 

5

 See “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) Determinations”, 

70 FR 39104, July 6, 2005, in the docket for this rulemaking. 
Page 21 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Comment:

 Some commenters asserted the presence of FCPP and several other power plants in and 

around the Navajo Nation represent an environmental and economic justice issue. These 

commenters pointed out that the electricity from FCPP goes to distant cities, while the pollution 

from the plant affects the local area and many communities in the surrounding area are without 

electricity. They noted that many in the Navajo Nation live in poverty and their youth have 

limited opportunities, while the companies that own and operate FCPP and the Navajo Mine 

have reaped large profits. Some expressed frustration with the leaders of the Navajo Nation, who 

they asserted have not protected the interests of the local population. 

 Some of these commenters stated that APS should recognize that FCPP will ultimately 

have to shut down and begin to transition to renewable energy sources. The commenters stated 

that because it has profited so much from FCPP, APS has a corporate responsibility to facilitate a 

just transition for the local area to a renewable energy economy. 

Response:

In establishing BART requirements for FCPP in this final rulemaking, EPA will be 

increasing the level of environmental protection for all affected populations by requiring 

substantial NOx emission reductions. Thus, EPA does not expect any disproportionately high and 

adverse human health or environmental effects on any population, including any minority or 

low-income population from our final action. 

The first step of the BART determination process involves identification of all available 

retrofit technologies. As described in the 2005 Regional Haze Rule, redesign of the source is not 

considered a requirement when examining available control technologies (70 FR 39104). As an 

example, a coal-fired unit would not be required to consider construction of a natural gas-fired 

turbine; while it is an inherently less polluting technology, it would require a redesign of the 

source. A transition of FCPP to use of renewable energy sources would require a similar 

redesign of the FCPP units, and as a result is outside of EPA’s authority under the RHR. The 

Department of Interior has contracted with the Department of Energy’s National Renewable 

Energy Laboratory, however, to conduct a phased study on the Navajo Generating Station 

(NGS). DOI intends that Phase 2 of this study will examine the potential of long-term energy 

production options for NGS, and may include such options as renewable sources. Although the 

focus of this study is NGS and not FCPP, because NGS is also located on the Navajo Nation, 

results of this study may be relevant to the FCPP area. 

Comment:

 Some commenters expressed concern related to the ash generated by FCPP. Some of 

these indicated that the ash from the facility is unsecured and blows over the nearby area when it 

is dry and is washed into the San Juan River when it rains. Some of these commenters blamed 

the windblown ash for killing local vegetation in the area. Other commenters refuted these 

claims. 
Page 22 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 A few speakers raised issues regarding the storage of coal combustion wastes (CCW) at 

FCPP. In the most extensive such comments, one environmental advocacy group commenter 

supported selective catalytic reduction (SCR) controls at FCPP, but asked that EPA also work to 

concurrently address the CCW (fly ash, scrubber sludge and bottom ash) being generated at the 

facility. The commenter stated that SCR technology will increase the nitrogen and ammonia 

content of the CCW, as well as the pH, very significantly, and possibly increase the quantity of 

CCW generated by FCPP, which currently stands at 1.5 million tons per year. The commenter 

noted that some of this material is used and recycled as synthetic gypsum, but the majority is 

highly toxic and includes pollutants such as lead, arsenic, mercury, cadmium, chromium, and 

selenium. 

 According to the commenter, the facility has historically disposed of CCW in temporary 

ash ponds on site and also returned it to the Navajo Mine, where BHP used it as minefill. The 

commenter stated that the on-site ash ponds are on about 550 acres directly adjacent to Chaco 

Wash, located on the escarpment directly above the wash, which runs due north approximately 

1 mile into the San Juan River. The commenter noted that by some estimates, there are tens of 

millions of tons of CCW, and perhaps billions of tons, stored in these ash ponds; it is perhaps the 

largest storage of toxic CCW in the nation. The commenter asserted that these ash ponds pose a 

significant threat, as evidenced by the 2008 failure of the coal ash ponds at the Tennessee Valley 

Authority’s Kingston Fossil Plant, where a 40-acre plant released over one billion gallons of 

toxic CCW into two separate rivers. Like the Tennessee Valley Authority plant, according to the 

information and belief of the commenter, FCPP has no emergency preparedness plan for cleanup 

of the coal ponds should they breach, and there is no bond for decommissioning these ash ponds. 

 The commenter stated it is extremely important for the owners of FCPP to address the 

liability of decommissioning of Units 1 through 3 and these ash ponds as part of their 

decommissioning process. The commenter asked who is going to pay for the cleanup – APS and 

the ratepayers, Southern California Edison, the Navajo Nation, or the federal taxpayers? 

 The commenter asked EPA to support the production of an environmental impact 

statement (EIS) to evaluate, among other things, the cost, methodology and liability for cleanup 

of these ash ponds, as well as an assessment for a bond or a surety from APS for full CCW 

storage needs going forward should Units 4 and 5 remain open under the current plan. The 

commenter pointed out that there is a mechanism for getting this done in that the Navajo Nation 

recently approved the lease renewal for FCPP, and that lease renewal is subject to review by DOI 

and will be subject to NEPA, which requires an EIS. The commenter requested that EPA support 

production of an EIS for this, as well as act as a cooperating agency in this process. 

Response:

Comments regarding the environmental issues associated with CCW are beyond the 

scope of the BART analysis. 

On June 21, 2010, EPA proposed and solicited comments on two regulatory options for 

establishing national standards for management of CCW (75 FR 35127). Options considered in 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

this proposal include regulating CCW as a hazardous waste under Subtitle C of the Resource 

Conservation and Recovery Act (RCRA), or establishing new national criteria under the nonhazardous solid waste requirements in RCRA Subtitle D. In addition, under the Clean Water Act, 

EPA has authority to establish effluent limitation guidelines (ELGs), which are national 

standards for water pollution reductions developed on an industry-by-industry basis. As part of a 

November 8, 2010 consent decree, EPA agreed to revise the ELGs for Steam Electric Power 

Generation to address wastewater discharges from CCW storage. Per the consent decree, these 

updated ELGs must be proposed by July 23, 2012 and finalized by January 31, 2014. 

As noted in the Technical Support Document (TSD)5F

6

 for our October 19, 2010 proposal, 

EPA determined that the impact of SCR on fly ash is smaller than the impact of other NOx

control technologies under consideration (in particular low NOx burners) on future salability of 

fly ash. 

As the commenter notes, a lease renewal for FCPP was signed by the Navajo Nation in 

March 2011. This renewal is subject to DOI’s review and approval process, which will result in 

the publication of an EIS. EPA Region 9 will be a cooperating agency in this process. 

Comment:

 A commenter representing the operator of the Navajo Mine, BHP Billiton, noted that 

EPA’s informational posters state that the company has pledged that there will be no layoffs at 

the mine if the supplemental proposal is implemented. The commenter clarified that the reduced 

coal consumption by FCPP associated with closure of Units 1 – 3 will necessitate a reduction in 

the workforce at the mine, but that the company stated that this reduction can be accomplished 

through retirement and attrition without layoffs. The commenter projected that the employment 

at the mine ultimately will be reduced by 100 to 200 positions. 

Response:

EPA thanks the commenter for the clarification that the mine will not lay off employees if 

Units 1 – 3 close, but that reduced coal consumption by FCPP associated with the closure of 

Units 1 – 3 is likely to result in a workforce reduction through retirement and attrition. 

Comment:

 A few commenters stated that EPA should conduct a BART determination for SO2 and 

reduce these emissions from FCPP to further improve visibility and reduce acid deposition. The 

commenters indicated that acid deposition damages ecosystems and degrades Native American 

ruins in the area. One commenter asserted that EPA should carry out a BART determination for 

CO2 emissions from FCPP because this is the primary GHG. 

 

6

 “FCPP Proposal – Technical Support Document”, October 6, 2010, Document No. EPA-R09-OAR-2010-0683-

0002. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Response:

EPA disagrees with this comment. As noted in the 2007 FIP for FCPP,6F

7

 the SO2

emission reductions established by the FIP are close to or the equivalent of BART for this 

source. Therefore, at the present time, EPA is exercising its discretion under 40 Code of Federal 

Regulations (CFR) part 49.11 to find that it is neither necessary or appropriate at this time to 

undertake a BART determination for SO2 for FCPP given the timing of the substantial SO2

reductions that resulted from the 2007 FIP. 

 

Regarding the commenter’s concern about green house gas (GHG) emissions, GHGs are 

not visibility-impairing pollutants and are not addressed in this action as they are beyond the 

scope of the BART requirements in the RHR. 

As a general matter, EPA continues to develop several regulatory initiatives to address 

these. For example, the GHG Mandatory Reporting Rule (MRR)7F

8 requires reporting of emissions 

of six GHGs from multiple industrial source categories, and the GHG Tailoring Rule,8F

9

establishes emission thresholds that define when new and existing industrial facilities must 

obtain permits. As part of the GHG Tailoring Rule implementation process, the initial phase will 

extend to those sources and projects that are already considered major sources for pollutants 

other than GHG. As a Title V major source of emissions, the Four Corners Power Plant is 

subject to the Title V program and has a Part 71 operating permit.9F

10 As a result, it will be 

subject to Title V requirements for GHG. EPA also entered into two proposed settlement 

agreements on December 23, 2010 that will include development of GHG emission standards for 

new and modified coal-fired power plants. 

Comment:

 One commenter questioned EPA’s development of baseline values using computers. The 

commenter stated that computer simulation technology is not accurate enough for many uses at 

this time. 

Response:

EPA disagrees with this comment. Computer-based visibility modeling plays an 

important role in informing many of the policy decisions associated with implementation of the 

RHR. The ability to predict how changes in air pollutant emission rates will affect visibility at 

Class I areas is critical in determining the control measures that are necessary to meet national 

visibility goals. As described in the 1999 RHR, although the national visibility goal was 

established by the 1977 Clean Air Act Amendments, EPA deferred action on regional haze until 

 

7

See “Source Specific Federal Implementation Plan for the Navajo Nation: Four Corners Power Plant”, 72 FR 

25698, May 7, 2007, in the docket for this rulemaking. 

8

 See “Mandatory Reporting of Greenhouse Gases”, 74 FR 56260, October 30, 2009, in the docket for this 

rulemaking. 

9

 See “Prevention of Significant Deterioration and Title V Greenhouse Gas Tailoring Rule”, 75 FR 31514, June 3, 

2010, in the docket for this rulemaking. 

10 “TSD ref [101] FCPP Permits”, Document No. EPA-R09-OAR-2010-0683-0057. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

monitoring techniques, modeling capabilities, and the understanding of the pollutants affecting 

visibility improved. In the final rule for the 1999 Regional Haze regulations10F

11, EPA notes that 

the National Academy of Sciences concluded that ‘‘current scientific knowledge is adequate and 

control technologies are available for taking regulatory action to improve and protect 

visibility”. As described in the 2004 RHR proposal1F

12 and the final 2005 RHR12F13 , determining 

visibility impacts on an individual source-specific basis involves long-range transport and 

diffusion modeling, as well as determining the impacts of atmospheric chemical transformations. 

The CALPUFF dispersion model is incorporated into 40 CFR Part 51, Appendix W “Guideline 

on Air Quality Models” and is the approved model that is the best suited to address each of these 

challenges. 

Comment:

 A representative of one of the co-owners of FCPP stated that EPA’s BART determination 

for FCPP should be consistent with the determinations that have been issued by states that are 

implementing the Regional Haze Program. The commenter indicated that states have not 

determined SCR to be BART. The remainder of the issues raised in this commenter’s oral 

testimony were also included in the company’s written comments and are summarized in the 

other sections of this document. 

Response:

EPA disagrees with this comment for at least 2 reasons. BART determinations are 

conducted on a case-by-case basis, taking into consideration the statutory factors required in a 

BART analysis under Section 169A(g)(1) of the CAA , i.e., the costs of compliance, the energy 

and nonair quality environmental impacts of compliance, any existing pollution control 

technology in use at the source, the remaining useful life of the source, and the degree of 

improvement in visibility which may reasonably be anticipated to result from the use of such 

technology, as relevant to each source that is subject to BART. As such, the CAA does not 

require State agencies, in developing its State Implementation Plans (SIPs), or EPA in 

implementing FIPs, to ensure that its BART determinations are consistent with BART 

determinations issued by other States. EPA’s BART determination for FCPP was a case-by-case 

analysis that considered the statutory factors required by the CAA and as outlined in the BART 

Guidelines. EPA provided the analysis for each factor and the rationale for our BART 

determination requiring an 80% reduction in plant-wide NOx emissions from FCPP in the TSD 

for our October 19, 2010 proposal. Second, the commenter is not correct in its statement that no 

state has determined SCR to be BART. The Colorado Department of Public Health and 

Environment required SCR as BART on Hayden Station Units 1 and 2.13F

14 

 

11 See “Regional Haze Regulations”, 64 FR 35714, July 1, 1999, in the docket for this rulemaking. 12 See “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) Determinations” 

(proposed rule), 69 FR 25184, May 5, 2004, in the docket for this rulemaking. 

13 See “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) 

Determinations”, 70 FR 39104, July 6, 2005, in the docket for this rulemaking 

14See “Hayden BART Final.pdf” in the docket for this rulemaking, also available at 

http://www.cdphe.state.co.us/ap/regionalhaze.html. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

2.2 14BMass Comment Campaigns 

 We received many comments from private citizens inspired by mass comment 

campaigns. Most of these commenters submitted the templates provided by the sponsoring 

organizations without change, but others customized the templates to some degree but without 

providing additional substance. 

Comments:

 Comment 0189 represents an example of 682 postcards EPA received from the 

organization Diné CARE at the Farmington, New Mexico public hearing, by mail, and by email. 

Most postcards contained personalized hand-written comments but the comments did not provide 

additional substance. These postcards were not posted to the electronic docket, but are part of the 

record for this rulemaking and are retained in paper form in the EPA’s office. The postcard reads 

as follows: 

I support U.S. Environmental Protection Agency (EPA) plan to install the Best 

Available Retrofit Technology (BART) air pollution controls on Four Corners 

Power Plant (FCPP). (Docket #EPA-R09-OAR-2010-0683). FCPP’s emissions 

are responsible for increased heart and respiratory diseases. I want 

implementation of the most stringent pollution control technologically available, 

and transition to Renewable Energy solution. 

Comment 0196 includes 115 additional postcards submitted by Diné CARE containing the 

printed text above, most with personalized hand-written comments but the comments did not 

provide additional substance. In addition, Comment 0193 represents an example of 46 postcards 

with the same printed text (most with personalized, non-substantive hand-written additions) 

received pursuant to an effort by the Sierra Club. 

Comment 0203 represents a mass comment campaign organized by the National Parks 

Conservation Association, which was submitted essentially verbatim by 9,312 commenters. The 

comment reads as follows: 

Dear Lee, 

As someone who is proud of our country's national parks, I am writing to thank 

you for your recent steps to reduce the air pollution from the Four Corners Power 

Plant--and also to urge you to do better. I ask that you protect the people and 

parks of the Southwest region by requiring the Four Corners plant to emit less 

pollution. Without meaningful reductions in air pollution, Four Corners Power 

Plant will continue to obscure the views that make these parks icons of the 

western landscape. 

I support the agency's decision to propose the retirement of units 1, 2, and 3 and 

the pollution control technology--Selective Catalytic Reduction--as a cost 

effective way to significantly cut down on haze pollution from the other two coal 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

units. I urge EPA to lower its proposed numeric limits on nitrogen oxides and 

particulate matter pollution, add limits for ammonia and sulfuric acid pollution, 

and require compliance with these limits within three years in its final decision. 

These limits would mean healthier air for us all, better views of our magnificent 

national parks, and a stronger tourism economy. Your decision will be inhaled by 

neighboring communities and park visitors for the life of the plant. 

Please don't miss this opportunity to protect our people and parks by adequately 

cleaning up the Four Corners Power Plant now. 

Please work hard to protect one of my favorite places. We cannot let our natural 

treasures be compromised. 

Thank you for considering my request. 

Comments 0116, 0203, 0204, and 0205 include an additional 204 comments that were 

submitted via the National Parks Conservation Association campaign, most incorporating some 

or all of the same points. Many of these added personal observations. However, of the four 

comments included in Comment 0204, two did not support EPA’s proposed actions, and two 

were unrelated to this rulemaking. 

 Comment 0212 represents a mass comment campaign organized by the Sierra Club. Four 

different versions of the campaign letter were submitted, with some variations to address 

different areas in the Four Corners region. 

 One of the versions of the Sierra Club campaign email was submitted largely without 

change by 1,218 commenters and reads as follows: 

Dear EPA Administrator Blumenfeld, 

I support the EPA's proposed rule on Best Available Retrofit Technology (BART) 

for regional haze at the Four Corner's Power Plant. The diverse communities of 

the Four Corners deserve cleaner air and a sustainable energy future that can only 

be achieved by cleaning up dirty coal plants like the Four Corners Power Plant. 

Thank you for helping everyone breathe easier by considering the two proposals 

at hand, both of which will help to reduce emissions from the plant by installing 

selective catalytic reduction controls. 

By outlining a plan to justly transition Four Corners off coal as soon as reasonably 

possible, we can bring a green economic boom to the region. I ask that these 

further and necessary retrofits be made to reduce dangerous pollution in the area. 

I am asking for the most stringent reduction in emissions to come out of these 

proposals. The haze in the National Parks that are within 300 kilometers 

(180 miles) of FCPP will see a significant improvement in visibility as a result of 

this BART. It is important that we protect these precious and irreplaceable public 

areas including Mesa Verde National Park just north of the plant. There are also 
Page 28 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

many sacred Navajo sites in the vicinity that need to be considered here as well. 

Tourism is a large economic contributor in the 4 Corners, and it is imperative that 

we clean up this haze in order to preserve this sector. 

The implementation of pollution controls in the form of Selective Catalytic 

Reduction (SCR) will reduce Nitrous Oxide (NOx) pollution by 80-90%. NOx 

pollution will be reduced by 16,000 tons per year, per the 2010 New Mexico 

Environmental Department report. NOx pollution has been shown to have direct 

negative health impacts. EPA includes 13 different health effects: adult and infant 

premature mortality, chronic bronchitis, heart attack, acute bronchitis, upper and 

lower respiratory symptoms, aggravation of existing asthmas, and hospital 

admissions and or emergency room visits for COPD, pneumonia, asthma, and 

cardiovascular diseases. 

A U.S. Geological Survey study found that people living in Shiprock are more 

than 5 times as likely to be seen at Indian Health Services for respiratory 

complaints as are residents of other nearby communities. 

Overall, we want the best plan to reduce emissions in the area and one that also 

looks towards a transition to renewable energy in the near future. 

Knowing the health, environmental and economic benefits of clean air, I am 

asking for the most stringent reduction in emissions possible. 

 

The second version of the Sierra Club campaign email was submitted essentially 

verbatim by 341 commenters. This version reads as follows: 

Dear EPA Region 9 Administrator Blumenfeld, 

I support the EPA's proposed rule on Best Available Retrofit Technology (BART) 

for regional haze at the Four Corner's Power Plant. 

The diverse communities of the Four Corners deserve cleaner air and a 

sustainable energy future that can only be achieved by cleaning up dirty coal 

plants like the Four Corners Power Plant. Thank you for helping everyone breathe 

easier by considering proposals that will help to reduce emissions from the plant 

by installing air pollution controls. 

I want these retrofits to be made to reduce dangerous pollution in the area. 

Nitrogen oxide pollution has been shown to have direct negative health impacts 

including adult and infant premature mortality, chronic and acute bronchitis, heart 

attack, upper and lower respiratory symptoms, aggravation of existing asthma, 

increased hospital and emergency room visits, pneumonia, asthma, and 

cardiovascular diseases. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

A U.S. Geological Survey study found that people living in Shiprock, NM are 

more than five times as likely to be seen at Indian Health Services for respiratory 

complaints as are residents of other nearby communities. 

Lowered emissions will help lessen these impacts on our community health and 

also our natural places. Tourism is a large economic contributor in New Mexico, 

and it is imperative that we clean up this haze in order to preserve this sector. 

The haze in the national parks that are within 180 miles of FCPP will see a 

significant improvement in visibility with retrofit technology implemented. It is 

important that we protect these precious and irreplaceable public areas like 

Bandelier National Monument near Los Alamos, Pecos Wilderness near Santa Fe, 

Wheeler Wilderness near Taos and San Pedro Parks near Cuba. 

Knowing the health, environmental and economic benefits of clean air, I am 

asking for the most stringent reduction in emissions possible. 

 

The third version of the Sierra Club campaign email was submitted largely without 

change by 184 commenters and reads as follows: 

Dear EPA Region 9 Administrator Blumenfeld, 

I support the EPA's proposed rule on Best Available Retrofit Technology (BART) 

for regional haze at the Four Corners Power Plant. A reduction in air pollution 

from the Four Corners Power Plant will protect the health of people living in Utah 

and preserve the many national parks in our area. 

I want these retrofits to be made to reduce dangerous pollution in the area. 

Nitrogen oxide pollution has been shown to have direct negative health impacts 

including adult and infant premature mortality, chronic and acute bronchitis, heart 

attack, upper and lower respiratory symptoms, aggravation of existing asthma, 

increased hospital and emergency room visits, pneumonia, asthma, and 

cardiovascular diseases. 

Lowered emissions will help lessen these impacts on our community health and 

also our natural places. 

The haze in the national parks that are within 180 miles of FCPP will see a 

significant improvement in visibility with retrofit technology implemented. It is 

important that we protect these precious and irreplaceable public areas like Bryce 

Canyon National Park, Canyonlands National Park, Monument Valley Navajo 

Tribal Park, and Arches National Park. 

Knowing the health, environmental and economic benefits of clean air, I am 

asking for the most stringent reduction in emissions possible. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

The diverse communities of the Four Corners deserve cleaner air and a 

sustainable energy future that can only be achieved by cleaning up dirty coal 

plants like the Four Corners Power Plant. Thank you for helping everyone breathe 

easier by considering proposals that will help to reduce emissions from the plant 

by installing air pollution controls. 

 

The fourth version of the Sierra Club campaign email was submitted essentially verbatim 

by 77 commenters. Version 4 reads as follows: 

Dear EPA Region 9 Administrator Blumenfeld, 

I support the EPA's proposed rule on Best Available Retrofit Technology (BART) 

for regional haze at the Four Corner's Power Plant. 

Coloradans deserve cleaner air and a sustainable energy future that can only be 

achieved by cleaning up dirty coal plants like the Four Corners Power Plant. 

Thank you for helping everyone breathe easier by considering proposals that will 

help to reduce emissions from the plant by installing air pollution controls. 

I want these retrofits to be made to reduce dangerous pollution in the area by 80-

90% of the biggest source of smog causing Nitrogen oxide in the nation. Nitrogen 

oxide pollution has been shown to have direct negative health impacts including 

adult and infant premature mortality, chronic and acute bronchitis, heart attack, 

upper and lower respiratory symptoms, aggravation of existing asthma, increased 

hospital and emergency room visits, pneumonia, asthma, and cardiovascular 

diseases. 

Lowered emissions will help lessen these impacts on our community health and 

also our natural places. Tourism is a large economic contributor in Colorado, and 

it is imperative that we clean up this haze in order to preserve this sector. 

The haze in the national parks that are within 180 miles of FCPP will see a 

significant improvement in visibility with retrofit technology implemented. It is 

important that we protect these precious and irreplaceable public areas like Mesa 

Verde National Park and the Weminuche Wilderness. 

Knowing the health, environmental and economic benefits of clean air, I am 

asking for the most stringent reduction in emissions possible. 

Comment 0206 includes an additional 27 comments that were submitted via the Sierra 

Club campaign, most incorporating some or all of the same points. Some of these commenters 

described personal experience with worsening air pollution in the region, and others expressed 

concern about negative impacts resulting from the use of coal to generate electricity. 
Page 31 of 171

August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 Comment 0215 represents a mass email campaign sponsored by WildEarth Guardians, 

which was submitted essentially verbatim by 637 commenters. The comment reads as follows: 

The Four Corners Power Plant poses significant threats to public health and 

welfare. I urge you to do more to protect the Four Corners region from the 

harmful impacts of its air pollution. 

Please use your discretion to consider alternative air pollution control strategies 

that better protect the environment. Wind and solar are both plentiful in the Four 

Corners region. Importantly, these energy sources do not poison waters, create 

smog, or foul the air quality in our most treasured National Parks and Wilderness 

Areas. 

You have the discretion to do more than require retrofits. You have the discretion 

to power the Four Corners Power Plant past coal. 

The opportunities for a healthy environment are enormous in the Four Corners. 

Please help make this a reality. For the future of our communities, our wild lands, 

and the Western United States, please consider alternatives to coal. 

Comment 0207 includes an additional 27 comments that were submitted via the 

WildEarth Guardians campaign, most incorporating some or all of the same points. Several of 

these commenters expressed concern about the negative effects of using coal as an energy 

source, and some included personal experiences with air pollution in the area. However, one of 

the commenters expressed support for retrofitting FCPP, indicating that alternative energy 

sources cannot meet our energy needs today. 

Response:

EPA agrees with commenters that SCR is BART for FCPP and we are finalizing our 

proposal as such. EPA also agrees with commenters that the proposed and final NOx emission 

limit proposed will reduce haze and improve visibility in the Four Corners region and for the 

broader Colorado Plateau. EPA is also giving the owners of FCPP the option to implement the 

alternative emission control strategy in lieu of BART that will result in greater emission 

reductions of NOx and other air pollutants. 

Regarding comments on public health, EPA notes that the same pollutants that impair 

visibility are a concern for human health; therefore reducing the NOx emissions contributing to 

haze should also improve air quality generally in this area. 

While many commenters expressed a desire for EPA to encourage a transition to 

renewable energy technologies such as wind and solar power, the ability to require such a 

transition is beyond the scope of this rulemaking. As described in a previous response, EPA does 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

not consider BART as a requirement to redesign a source when considering available control 

alternatives (see specifically 70 FR 39164).14F

15

 

15 See “Regional Haze Regulations and Guidelines for Best Available Retrofit Technology (BART) 

Determinations”, 70 FR 39104, July 6, 2005, in the docket for this rulemaking 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

3.0 2BComments on Factor One – Cost of Controls 

3.1 15BComments on the Analysis of the Cost of SCR at FCPP 

Comment: 

 Some of the owners of FCPP (0168, 0174, 0176/0177, 0185), the Navajo Nation (0223), 

and a utility industry association (0187) stated that in analyzing the cost of SCR at FCPP, EPA 

improperly reworked and reduced the SCR cost estimates submitted for FCPP by eliminating 

line item costs that are not explicitly included in the EPA Control Cost Manual (citing 75 FR 

64227). According to the commenters, the BART rules make clear that the cost analysis should 

take into account any site-specific design or other conditions that affect the cost of a particular 

BART technology option (often citing 70 FR 39166). In addition, the commenters generally 

stated that the significance of considering site-specific cost information was emphasized in the 

D.C. Circuit’s American Corn Growers decision, where the court observed that each of the 

statutory factors in any BART determination, specifically including the cost of the technology, 

must be addressed “on a source-by-source basis.” Am. Corn Growers Ass’n v. EPA, 291 F.3d 1, 6 

(D.C. Cir. 2002). Two of the commenters (0176/0177, 0187) indicated that this principle is 

further affirmed in the BART rules, which state that “one or more of the available control 

options may be eliminated from consideration because they are demonstrated to be technically 

infeasible or to have unacceptable energy, cost, or non-air quality environmental impacts on a 

case-by-case (or site-specific) basis” (citing 70 FR 39164). Three of the commenters (0185, 

0187, 0223) noted that the BART rules make the nonbinding nature of the EPA Control Cost 

Manual clear (citing 70 FR 39127 and footnote 15). 

 Two of the commenters (0168, 0176/0177) defended the SCR cost estimate submitted for 

FCPP, noting that the estimate was prepared by B&V, an engineering firm with extensive 

experience with the installation and operation of pollution control equipment. The commenters 

noted that B&V performed a detailed analysis of the FCPP units and considered site-specific 

conditions that preclude the use of the general ratios or other factors that can be derived from the 

EPA Control Cost Manual. According to the commenters, B&V followed the EPA Control Cost 

Manual to estimate annual costs, but also followed accepted guidelines for control technology 

analyses by using actual SCR retrofit data from facilities with over 10,000 MW of generation for 

which B&V completed the designs. One of these commenters (0176/0177) indicated that the 

prices used in the cost analysis were based on quotes from equipment vendors that reflected 

current pricing. 

 Since issuance of the Advanced Notice of Proposed Rulemaking (ANPR) for the FCPP 

FIP rulemaking, one of the commenters (0176/0177) commissioned B&V to review its cost 

assumptions and EPA’s cost-related comments in the ANPR, and the commenter submitted a 

copy of B&V’s report with its comments. According to this B&V report, the costs of SCR 

systems at FCPP are further escalated due to the complex constructability issue resulting from 

the constrained site arrangements. The report further notes that extensive modifications to 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

existing ductwork and boiler steel would be required and provides specific examples where the 

EPA Control Cost Manual does not account for the site-specific costs of installing SCR.15F

16 

 This commenter (0176/0177) indicated that as a further check on the cost estimates, the 

commenter retained the Shaw Group to conduct an independent review of the cost assumptions 

and EPA’s comments in the ANPR, and the commenter also submitted this report. The Shaw 

Group’s report notes that the background section of the EPA Control Cost Manual states that the 

Manual is not suitable for use with Electric Generating Units (EGUs) because of differences in 

accounting for utility sources. This report also states that the results of the EPA Control Cost 

Manual are relatively generic, and that customizing the analysis with industrial sources of 

information may lead to a more accurate estimate. 

 The commenter (0176/0177) noted that EPA stated in the proposed FIP that it “has 

generally accepted the costs estimates APS submitted,” but has “eliminated any line item costs 

that are not explicitly included in the EPA Control Cost Manual” (citing 75 FR 64227). The 

commenter asserted that EPA provided no justification for excluding these costs, and that no 

justification for doing so exists. 

 The commenter (0176/0177) concluded that the analyses conducted by B&V and the 

Shaw Group are sound, and the Shaw Group’s report confirms that the inclusion of these types of 

costs is entirely appropriate. According to the commenter, it is improper and unlawful for EPA to 

eliminate consideration of these site-specific cost factors. The commenter asserted that because 

the proposed BART FIP rule is fundamentally inconsistent in this respect with EPA’s own rules 

and with the CAA, as construed by the D.C. Circuit in American Corn Growers, and because 

EPA has found the submitted cost estimates “generally accept[able]” (citing 75 FR 64227) 

without providing any sound or lawful rationale for rejecting or revising those estimates, there is 

no basis for EPA not to use those estimates. 

 Another of the commenters (0185) concluded that a BART determination cannot properly 

be made until EPA accepts or conducts a cost analysis, such as the one presented by APS, that 

complies with the law. A third commenter (0187) concluded that EPA’s proposed cost analysis is 

inconsistent with the D.C. Circuit’s decision in American Corn Growers and with the governing 

rules and is therefore unlawful. The Navajo Nation (0223) concluded that EPA’s compliance 

costs are inaccurate and flawed. 

Response:

EPA disagrees with the comment that EPA improperly reworked and reduced the SCR 

cost estimates. EPA used a hybrid approach for our cost analysis that relied primarily on the 

cost estimates provided by APS, but also followed the BART Guidelines, that state “[i]n order to 

maintain and improve consistency, cost estimates should be based on the OAQPS Control Cost 

 

16 EPA notes that this report was considered and discussed in the TSD for our proposed rulemaking, and was 

included in our docket. The revised cost estimates submitted to EPA subsequent to our ANPR were actually lower 

than the cost estimates submitted prior to our ANPR.
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Manual, where possible” 16F

17, to determine whether APS included cost estimates for services or 

equipment associated with SCR that were either not needed (e.g., mitigation for increased 

sulfuric acid emissions or catalyst disposal), or not allowed under the EPA Control Cost Manual

(e.g., owner’s costs). We note that the EPA cost estimate presented in the TSD ($718 million 

total for Units 1 – 5) is 18% lower than the highest B&V cost estimate and less than 0.6% lower 

than the most recent B&V cost estimate APS submitted to EPA in 2010. 

 

 The cost analysis we presented in the TSD17F

18 and supporting documents18F19 for our October 

2010 proposed BART determination was based on the cost estimate updates prepared by B&V 

for APS dated August 19, 2008 and submitted by letter dated March 16, 2009.19F

20 In the TSD (see 

page 30), we explain that APS submitted an additional, more refined update to the cost estimates 

by letter dated April 22, 2010, but that submittal was labeled as Confidential Business 

Information. On September 9, 2010, APS confirmed that it did not consider this B&V report to 

be confidential and EPA included this updated cost analysis in our docket20F

21 and discussed it in 

our TSD. We noted in our TSD that the revised cost estimates for SCR submitted by APS in 2010 

($722 million total for Units 1 – 5) were lower for all units compared to the cost estimates 

submitted by APS in March 2009 ($874 million total for Units 1 – 5). 

Our SCR cost analysis relied primarily on the highest cost estimates submitted by APS 

(dated August 19, 2008 and submitted March 16, 2009). EPA accepted all site-specific costs 

provided by APS cost categories (e.g., purchased equipment, installation) that are typically 

included in a cost estimate conducted in accordance with the EPA Control Cost Manual, and 

only excluded line item costs that are not explicitly included in the EPA Control Cost Manual or 

in a limited number of cases where EPA determined alternative costs were more appropriate or 

where APS did not provide sufficient explanation to justify different costs (e.g., costs of catalysts, 

interest rates). Therefore, we disagree with the commenters’ assertion that our cost analysis did 

not take into account the site-specific cost information supplied by APS. We again note that the 

EPA cost estimate presented in the TSD ($718 million total for Units 1 – 5) is only 18% lower 

than the highest B&V cost estimate and less than 0.6% lower than the most recent B&V cost 

estimate APS submitted to EPA in 2010. 

 Our detailed, line-by-line analysis was included in the docket21F

22 for this proposed 

rulemaking and provided an explanation for why we retained, modified, or rejected each line 

item in the SCR cost estimate for each of the five units at FCPP. 

 For example, APS provided site-specific estimates for individual components of the SCR 

system, while the equations in EPA Control Cost Manual yield overall system costs. In the TSD 

for our proposed rulemaking, we generally accepted the component costs estimated by B&V, 

including such items as costly new preheaters and new induced draft and forced draft fans that 

are not included in the EPA Control Cost Manual equations but were deemed by B&V to be 

 

17 The OAQPS Control Cost Manual is now called the EPA Control Cost Manual. The EPA Control Cost Manual is 

available from the following website: http://www.epa.gov/ttncatc1/products.html#cccinfo. 18 “TSD Proposal – Technical Support Document 10-6-10”, Document No. EPA-R09-OAR-2010-0683-0002.

19 “TSD ref [40] Four Corners SCR Cost Analysis (EPA) 8-26-10”, Document No. EPA-R09-OAR-2010-0683-0033. 20 “APS Submission to EPA 3-2009 plus attachments”, Document No. EPA-R09-OAR-2010-0683-0015.

21 “TSD ref [42] NOx Compliance Study”, Document No. EPA-R09-OAR-2010-0683-0034.

22 “TSD ref [40] Four Corners SCR Cost Analysis (EPA) 8-26-10”, Document No. EPA-R09-OAR-2010-0683-0033.
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

necessary at FCPP due to retrofit considerations. However, we did not include the costs 

included for variable frequency drives for the new fans, which are not required for SCR, or the 

costs for unspecified “miscellaneous equipment.” The cost estimate did not provide information 

documenting the need for these line items or otherwise justifying their inclusion. 

 In addition, we used the EPA Control Cost Manual equations and a catalyst cost estimate 

provided by a vendor of ultra low-oxidation catalysts to estimate the cost of the initial catalyst 

(included under total capital costs) and replacement catalyst (included under total annual costs) 

for our revised costs. This vendor cost was substantially less than the cost estimated by B&V for 

the catalyst. In addition, typically, the vendor cost includes the disposal of the spent catalyst; 

therefore, the catalyst disposal cost was not included as a separate line item in our revised costs 

although it was included as an annual cost in the B&V cost estimate. We also applied what we 

believe is a more realistic tax rate of 6 percent, rather than the 10 percent in the B&V estimate. 

The state of New Mexico does not impose a sales tax; rather, New Mexico applies a gross 

receipts tax on businesses and services in New Mexico.2F

23 New Mexico reports that this tax varies 

throughout the state from 5.125% to 8.6875%. EPA’s use of a 6% tax rate is generally consistent 

with the tax rate the New Mexico Environment Department (NMED) applies in its emission 

control cost estimates of 6.2% to account for the gross receipts tax.23F

24

 Using Units 4 and 5 (which had identical cost estimates in the 2008 B&V estimates) as 

examples, other notable line items in the estimated Total Capital Investment in the APS submittal 

that we did not include in our cost analysis are “owners costs”, “side effect mitigation”, and 

“lost revenue”: 

 “Owners cost” was described by the commenters as typical expenditures that an owner 

will experience during an air quality control retrofit project, such as costs for project 

development, financing, project management, plant startup/construction support, and 

taxes/advisory fees/legal. The commenters calculated these costs at 3 percent of the Total 

Direct Cost for the units. As such, these estimates do not truly represent a site-specific 

consideration of such costs. The commenters did not provide any documentation specific 

to FCPP or SCR. In addition, such costs are not included in the EPA Control Cost 

Manual. Therefore we exclude this cost of $5.6 million in our revised cost estimate. 

 “Side effect mitigation” was referred by the commenters as additional measures included 

to reduce emissions of SO3 at a cost of $7 million. However, EPA calculated catalyst cost 

based on the use of an ultra low oxidation catalyst, so we do not agree that such side 

effect mitigation measures are needed. 

 “Lost revenue” of $14.4 million was estimated by the commenters for an “extended 

outage.” APS did not provide sufficient information for EPA to determine that SCR 

equipment could not be installed during scheduled outages and we excluded this cost in 

our revised cost estimate. 

 

23 http://www.tax.newmexico.gov/All-Taxes/Pages/Gross-Receipts-Tax.aspx. 24 Personal communication between Elizabeth Bisbey-Kuehn, NMED and Anita Lee, EPA Region 9. September 2, 

2011. See “Memo to file 9-2-11 voicemail from NMED.docx” in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 It should be noted that in the revised cost estimates submitted by APS in 2010, B&V no 

longer included side effect mitigation and significantly reduced estimated taxes and lost revenue. 

For Unit 4 the total for these three cost elements fell from about $37.8 million to only $4.3 

million in the 2010 APS submittal. The updated Total Capital Investment estimates for Units 4 

and 5 in the 2010 submittal averaged about $212.5 million, which is slightly lower than our 

revised cost estimate of $217.7 million for each unit.24F

25 The refined Total Capital Investment 

estimates in the 2010 submittal for Units 1-3 remained slightly higher (about 2 to 7 percent) than 

our revised cost estimates based on the 2009 submittal. The general agreement between the 2010 

B&V refined cost estimates and EPA’s cost estimates suggests that our BART determination 

would not be substantially different if we had relied instead solely on B&V’s 2010 cost estimates 

for FCPP because the cost effectiveness values would be similar. 

 In terms of annual cost estimates, the difference between the APS submittals (2009 and 

2010) and our revised cost estimates is larger. The annual costs for Units 4 and 5 in the 2009 

APS submittal are nearly twice the amount of EPA’s revised cost estimate even though our 

revised capital cost estimate is only 18 percent less than the B&V estimate. 

 The large difference in annual costs results mainly from differing assumptions used in the 

“capital recovery” estimates, which account for over three fourths of the overall difference 

between APS and EPA estimated annual costs. Capital recovery reflects the effective annual cost 

to the facility of borrowing the capital to pay for the SCR system. This element of annual cost is 

the product of the Total Capital Investment and the Capital Recovery Factor (CRF). The CRF, in 

turn, is calculated using a formula based on the assumed interest rate and equipment life. 

 In its cost estimates for APS, B&V assumed an interest rate of 15% and an equipment life 

of 20 years. While we also assumed an equipment life of 20 years, we based our CRF on an 

interest rate of 7%. The 15% interest rate used by APS to calculate capital recovery for the SCR 

installation is too high. For cost analyses related to government regulations, an appropriate 

“social” interest (discount) rate should be used. The latest real interest rate for cost 

effectiveness analyses published by the Office of Management and Budget (OMB) is 2.8% for a 

20 year period (Revised January 2008). EPA calculated capital recoveries using 3% and 7% 

interest rates in determining cost effectiveness for the Regulatory Impact Analysis (RIA) for the 

Guidelines for BART Determinations under the Regional Haze regulations.25F

26 Therefore, we used 

a conservative approach to calculate the capital recovery in our revised cost analysis using an 

interest rate of 7% and an equipment life of 20 years. 

 The APS submittal provided no justification for what appears to be an inflated interest 

rate (15%) in this period of historically low rates, and our interest rate of 7% is appropriately 

conservative for this cost analysis and consistent with the most conservative interest rate used in 

the RIA for the BART Guidelines. The other major contributors to the difference in annual cost 

 

25 “APS Submission to EPA 4-22-10 plus Attachments”, Document No. EPA-R09-OAR-2010-0683-0016. In the 

2010 APS submittal, B&V prepared separate estimates for Units 4 and 5 for the first time. Certain common 

equipment that would be shared by the two units was included in the capital costs for Unit 4, with the result that 

Total Capital Investment was estimated at about $223.8 million and $201.3 million for Units 4 and 5, respectively. 

26 Regulatory Impact Analysis for the Final Clean Air Visibility Rule or the Guidelines for Best Available Retrofit 

Technology (BART) Determinations Under the Regional Haze Regulations, EPA-0452/R-05-004, June 2005. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

estimates between the APS 2009 submittal and our revised cost estimate are maintenance labor 

and materials (8% of the difference), costs related to catalyst replacement (13%), and the 

difference between estimates of Total Capital Investment (also a factor in determining annual 

capital recovery – 16%). 

 The difference between estimates of maintenance labor and materials is primarily related 

to the method of calculation, but is also affected by the difference in capital cost estimates. In 

our revised cost estimate, we applied the methodology specified in the EPA Control Cost Manual

which determines this annual cost as 1.5% of the Total Capital Investment. In the 2009 APS 

submittal, this cost element is estimated as 3% of Total Direct Costs (a subset of Total Capital 

Investment). APS did not provide sufficient information to justify its estimate that maintenance 

labor and materials would be 3% of Total Direct Costs. 

 As previously discussed, we determined the cost of initial catalyst and replacement 

catalyst based on the EPA Control Cost Manual methodology and a quote from a vendor for 

ultra low-oxidation catalyst that included spent catalyst disposal. The cost estimate prepared by 

B&V for the 2009 APS submittal included a significantly higher catalyst cost, used a different 

methodology for determining the annual cost of catalyst replacement, and included a separate 

cost for catalyst disposal. Again, APS did not provide sufficient information to justify the 

assumption that costs for spent catalyst disposal would be separate from the catalyst cost. 

 As noted above, in 2010 APS submitted an updated, refined cost estimate prepared by 

B&V. As discussed, this submittal included estimates of Total Capital Investment for Units 4 and 

5 that were, on average, lower than our revised cost estimate for these units. Despite this fact, 

the average annual cost estimated by B&V for these two units ($41.8 million) exceeded our 

estimate ($28.4 million) by 45%. This difference is entirely due to the CRF used in the B&V 

calculations, which was again based on an assumed interest rate of 15%.26F

27 As explained 

previously, the interest rate that we used in our calculations (7%) is in itself conservative and is 

more appropriate for these calculations than the high rate used by APS/B&V. 

 In addition, we disagree with the commenters’ assertion that our analysis is not 

consistent with the D.C. Circuit’s American Corn Growers decision. As noted, we incorporated 

site-specific cost information provided by APS where documented and justified. In addition, we 

 

27 In the 2010 submittal for Units 4 and 5, B&V very significantly reduced the estimate for maintenance labor and 

materials and somewhat reduced the estimate for catalyst replacement and spent catalyst disposal. Although this 

estimate included some line items not included in their earlier estimate or our cost estimate (such as yearly 

emissions testing and fly ash sampling and analysis), the total of all annual costs other than capital recovery was less 

than our estimate for this class of costs. Thus, for Units 4 and 5 the entire excess annual cost in the 2010 submittal 

can be ascribed to the CRF and the interest rate used to calculate it. For Units 1-3, the estimates of annual costs 

submitted by APS in 2010 exceed our estimates by from 65 to 73% even though their Total Capital Investment 

estimates exceed ours by only 2 to 7%. While the CRF, with its high underlying interest rate, is the predominant 

cause for the differences between these annual cost estimates, it is not the sole cause. Because Total Capital 

Investment is a factor in the calculation of capital recovery, the slightly higher estimates are a small factor for Units 

1-3. In addition, the non-capital recovery annual costs estimated for these units in the 2010 submittal continue to 

exceed our estimates, primarily due to maintenance labor and materials and catalyst replacement and disposal costs 

(which were not reduced from the 2009 submittal for these units). Nevertheless, the value of the CRF accounts for 

over three quarters of the difference between the estimate of total annual costs in the 2010 APS submittal and our 

estimate. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

do not agree that use of the EPA Control Cost Manual alone necessarily constitutes a failure to 

conduct a cost analysis on a source-specific basis. The costing methodology in the EPA Control 

Cost Manual requires as input certain source-specific design characteristics and, therefore, the 

results are a source-specific estimate of costs. 

 Regarding the Shaw Group report’s comment on the statement in the EPA Control Cost 

Manual about its suitability for use with EGUs, we believe that the text of the Manual was 

improperly taken out of context. The relevant text of the EPA Control Cost Manual27F

28 reads as 

follows: 

... this Manual does not directly address the controls needed to control air 

pollution at electrical generating units (EGUs) because of the differences in 

accounting for utility sources. Electrical utilities generally employ the Electric 

Power Research Institute (EPRI) Technical Assistance Guidance (TAG) as the 

basis for their cost estimation processes.1

1

This does not mean that this Manual is an inappropriate resource for utilities. In 

fact, many power plant permit applications use the Manual to develop their costs. 

However, comparisons between utilities and across the industry generally employ 

a process called “levelized costing” that is different from the methodology used 

here. 

 Thus, the full text of the Manual indicates that it is an appropriate resource for utilities, 

and that many power plant permit applications have used the EPA Control Cost Manual to 

develop their costs. In any case, we generally used equipment and labor costs provided in the 

APS cost estimate, except for those line items that we believed to be unjustified or unreasonable.

Comment: 

 One of the owners of FCPP (0174) stated that EPA’s discussion of costs associated with 

BART determinations for other Western power plants is misleading (citing page 32 of the TSD 

for EPA’s proposed BART determination for FCPP). According to the commenter, EPA 

provides a number of examples of cost estimates developed by other Western power plants for 

installation of SCRs, but does not mention that in most of those cases, the permitting authorities 

rejected SCR and proposed combustion controls as BART. Furthermore, the commenter 

indicated that because none of those power plants have installed SCRs, the referenced estimates 

are not based on actual construction and operating costs. 

Response:

 EPA disagrees with the commenter that our discussion of estimated costs in Table 16 of 

our TSD was misleading. Recent BART determinations have proposed and/or finalized SCR (San 

 

28 “EPA Air Pollution Control Cost Manual”, Sixth Edition, Document No. EPA/452/B-02-001, January 2002. Pg. 

1-3. Available at http://www.epa.gov/ttncatc1/products.html#cccinfo 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Juan Generating Station Units 1 – 4, Naughton Unit 3, Jim Bridger Units 1 and 2) or selective 

non-catalytic reduction (SNCR) (M.R. Young Units 1 and 2, Centralia Units 1 and 2).28F

29 EPA 

determined that the comparisons of these SCR costs are appropriate because they are based on 

recent BART cost estimates submitted by the power plants. 

The commenter is correct in noting that the SCR cost effectiveness estimates included in 

the TSD represented cost estimates rather than actual construction and operating costs. The 

table was meant to compare the estimated cost effectiveness values for FCPP with other recent 

SCR BART cost estimates provided by coal-fired electric generating facilities in the Western 

United States, and was not intended to show the final cost effectiveness of actual SCR 

installations. EPA notes that actual construction and operating costs for these facilities are not 

yet available, and will not be available until these BART determinations are finalized and 

facilities have completed installation of its BART controls. 

Comment: 

 

One of the owners of FCPP (0176/0177) noted that EPA selected combustion controls as 

presumptive BART for EGUs like FCPP because those controls are “more cost effective than 

post-combustion controls such as SCRs” (citing 70 FR 39134). According to the commenter, 

EPA’s analysis at that time for setting presumptive BART limits found that the cost effectiveness 

of combustion controls averaged less than $600 per ton of NOx removed, while SCR averaged 

more than $1,600 per ton. 

 The commenter’s (0176/0177) most recent cost analysis estimated that the average cost 

effectiveness of combustion controls for the five units at FCPP would range from $524 to $1,735 

per ton of NOx removed, while the average cost effectiveness of SCR would range from $4,215 

to $5,283 per ton. The commenter also noted that EPA’s estimate of average cost effectiveness 

for SCR at FCPP ranged from $2,515 to $3,163 per ton. The commenter stated that, at the low 

end, only the estimate of the average cost effectiveness of combustion controls is in line with 

EPA’s estimates of cost-effective controls, while the estimate of average cost effectiveness of 

SCR is significantly higher. Another one of FCPP’s owners (0168) also made this last point. 

 The commenter (0176/0177) asserted that there is no basis for EPA to depart from its 

own rules by concluding that SCR is BART for FCPP when this technology is many times more 

expensive than the EPA-determined cost effective level of controls for presumptive BART and 

costs far more than the levels EPA rejected as cost-ineffective for presumptive BART. The 

commenter contended that EPA’s disregard for its own cost effectiveness determination in the 

BART rules renders the concept and importance of the “cost effectiveness” BART factor 

meaningless. 

Response:

 

29 See 76 FR 52388, August 22, 2011; 77 FR 33022, June 4, 2012; 77 FR 20894, April 6, 2012; 77 FR 30473, May 

23, 2012 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

EPA disagrees with this comment. Although the commenters argue that the BART 

Guidelines established a threshold for cost effectiveness against which future BART 

determinations must compare, the BART Guidelines did not establish a cost effectiveness 

threshold for all BART determinations. In developing the presumptive NOx limits for BART in 

2005, EPA did not set the cost effectiveness values estimated for combustion controls as the 

threshold for determining whether a given control technology was or was not cost effective. If 

EPA had intended the cost effectiveness values estimated in 2005 to represent a threshold for 

BART, it is reasonable to assume that the BART Guidelines would have included those cost 

effectiveness values as thresholds in Appendix Y, and would have required future cost estimates 

to be presented in 2005 dollars to appropriately compare against those thresholds. The BART 

Guidelines do not set a numerical definition for “cost effective”, and the analysis of presumptive 

limits uses cost effectiveness as a means to broadly compare control technologies, not as 

threshold for rejecting controls for an individual unit or facility that exceed the average cost 

effectiveness of combustion controls. 

Additionally, a comparison of the average cost effectiveness estimates in the 2005 BART 

Guidelines against our cost effectiveness estimates for FCPP is not an “apples to apples” 

comparison. The technical support documentation for the 2005 BART Guidelines29F

30 indicate that 

cost effectiveness of controls was not determined based on site-specific cost estimates developed 

for each BART-eligible facility; rather cost estimates were determined using assumptions for 

capital and annual costs per kilowatt (kW)30F

31 or kilowatt-hour (kW-hr), and then scaled 

according to boiler size. The supporting information for the 2005 BART Guidelines estimate 

SCR costs for Units 4 and 5 at FCPP (capital cost = $64 million, total annual cost = $11 

million) that are comparable to SCR cost estimates that were generated by NPS using the EPA 

Control Cost Manual (capital cost = $53 million, total annual cost = $10 million31F

32). The same 

commenters have previously dismissed the NPS SCR cost estimates based on the EPA Control 

Cost Manual as being too low because it does not include site-specific costs.32F

33 The commenter 

appears to be selectively choosing to accept the EPA Control Cost Manual in one case (cost 

effectiveness of presumptive controls to serve as a bright line threshold), and reject it in another 

(cost effectiveness of post-combustion controls at FCPP): on one hand, the commenter rejected 

the EPA Control Cost Manual in favor of its own site-specific cost estimates because the EPA 

Control Cost Manual is unrealistically low, and on the other hand, the commenter uses the 

 

30 The technical supporting information is included in the docket for the final rulemaking for the BART Guidelines 

(EPA-HQ-OAR-2002-0076) and includes several documents supporting the presumptive NOx limits finalized in the 

BART Guidelines: (1) “Technical Support Document – Methodology for Developing BART NOx Presumptive 

Limits” dated June 15, 2005 (document no. EPA-HQ-OAR-2002-0076-0445), and (2) “Technical Support 

Document for BART NOx limits for Electric Generating Units Excel Spreadsheet”, dated June 15, 2005 (document 

no. EPA-HQ-OAR-2002-0076-0446). 

31 In the 2005 BART presumptive limit analysis, EPA estimated capital cost assuming SCR cost = $100/kW. 32 See Table 9 in the October 2010 TSD for the proposed BART determination for FCPP. In its comments on the 

ANPR, NPS revised its cost estimates for SCR on Units 4 and 5 to $114 million (capital cost) and $18 million (total 

annual cost) – see Table 12 in the TSD for the proposed BART determination. Document no. EPA-R09-OAR-2010-

0683-0002. 

33 In the ANPRM, in addition to reporting APS’s cost estimates and EPA’s revisions to APS’s cost estimates, for 

reference, EPA also reported cost estimate analysis conducted by NPS and provided to EPA during consultations 

with the FLMs prior to our ANPRM. APS and other entities provided comments to EPA on the NPS cost estimates 

reported in the ANPRM, see document titled “Comments on ANPRM 09 0598 APS Comments and Exhibits” 

document ID number EPA-R09-OAR-2009-0598-0195. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

unrealistically low value from the EPA Control Cost Manual as a threshold to reject postcombustion controls because its site-specific cost estimates are higher. In short, the commenter’s 

recommendation to use generalized cost estimates from the 2005 BART Guidelines as a bright 

line threshold for comparison with site-specific 2010 cost estimates is inconsistent with its own 

criticisms of the EPA Control Cost Manual. 

EPA notes that the average cost effectiveness of combustion controls cited by the 

commenters in the development of the 2005 presumptive NOx limits (less than $600 per ton) was 

calculated from national total annual costs divided by the national reductions expected from 

combustion controls. In the same technical documentation for the 2005 presumptive NOx limits, 

if considered unit by unit at each BART-eligible facility, the average cost effectiveness of 

combustion controls was estimated to be $1,790 per ton (nearly three times higher than average 

cost effectiveness calculated from total national annual costs and total national NOx reductions), 

with a very large range of $100 per ton to $70,000 per ton, indicating that despite using 

combustion controls to set presumptive NOx limits, combustion controls will not be cost effective 

for all facilities – highlighting the need for site-specific 5-factor analyses in determining BART. 

If, in assessing our BART determination for FCPP, EPA relied strictly on the cost 

effectiveness values in the 2005 BART Guidelines, as suggested by commenters, the Excel 

Spreadsheet provided as technical support to the presumptive NOx limits suggests cost 

effectiveness of combustion controls on Unit 5 at FCPP to be $1,716 per ton, SCR to be just over 

$1,000 per ton on Units 4 and 5, and ROFA to be over $500 per ton. These estimates are 

strongly dependent on the assumed efficiency of the control technology, but if taken at face 

value, suggest that of the three options, ROFA would be most cost effective at FCPP, SCR is 

second most cost effective, and combustion controls are the least cost effective. It is notable that 

B&V, in its BART analysis conducted for FCPP, excluded ROFA for Units 4 and 5 because it 

has not been demonstrated on large units, thus leaving SCR as the most cost effective control for 

Unit 5 at FCPP according to the 2005 BART Guidelines. 

Comment: 

 A number of commenters, including owners of FCPP (0168, 0174, 0176/0177) and a 

utility association (0169), stated that EPA’s BART analysis for FCPP was inconsistent with its 

own regulations in that it failed to consider control costs as a function of visibility improvement. 

These commenters (0168.1, 0169.1, 0174, 0176/0177) typically stated that EPA’s BART 

determination for FCPP must consider the cost effectiveness of control technology options in 

terms of dollars per deciview-improved. 

 Some of the commenters (0174, 0176/0177) pointed out that the American Corn Growers

decision indicates that the CAA requires the consideration of control cost to include the degree 

of improvement in visibility that would result from control. American Corn Growers, 291 F3d at 

6-7. One commenter (0176/0177) added that the BART rules encourage the use of a dollars-perdeciview-improved metric in addition to the dollars-per-ton-reduced metric (citing 70 FR 

39170). 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 This commenter (0176/0177) indicated that this is an important measure of cost 

effectiveness which EPA failed to consider. The commenter stressed that before EPA proceeds 

further with this rulemaking, it must analyze the average and incremental cost effectiveness of 

the full range of control options on not only a dollar-per-ton-reduced but also a dollar-perdeciview-improved basis. 

Response:

The BART Guidelines require that cost effectiveness be calculated in terms of annualized 

dollars per ton of pollutant removed, or $/ton.3F

34 The commenters are correct in that the BART 

Guidelines list the $/deciview ratio as an additional cost effectiveness metric that can be 

employed along with $/ton for use in a BART evaluation. However, the use of this metric further 

implies that additional thresholds or notions of acceptability, separate from the $/ton metric, 

would need to be developed for BART determinations. We have not used this metric for BART 

purposes because (1) it is unnecessary in judging the cost effectiveness of BART, (2) it 

complicates the BART analysis, and (3) it is difficult to judge. In particular, the $/deciview 

metric has not been widely used and is not well-understood as a comparative tool. In our 

experience, $/deciview values tend to be very large because the metric is based on impacts at 

one Class I area on one day and does not take into account the number of affected Class I areas 

or the number of days of improvement that result from controlling emissions. In addition, the use 

of the $/deciview suggests a level of precision in the CALPUFF model that may not be 

warranted. As a result, the $/deciview can be misleading. We conclude that it is sufficient to 

analyze the cost effectiveness of potential BART controls using $/ton, in conjunction with an 

assessment of the modeled visibility benefits of the BART control. 

EPA considered cost of controls by discussing the total capital costs, annual costs, and 

$/ton of NOx pollution reduced. Additionally, in response to comments received on our proposal, 

EPA included calculations and consideration of incremental cost effectiveness (see Section 3.2 of 

the Response to Comments document in the docket for this final rulemaking). EPA considered 

visibility impacts by discussing the deciview improvement resulting from controls, as well as the 

percent change in improvement. EPA determined that these metrics are sufficient in completing 

our five-factor analysis for FCPP. 

Comment:

 One environmental advocacy group (0182) who favors assessing cumulative visibility 

impact and benefit across multiple Class I areas (see Section 7.0) argued that it is a more 

accurate depiction of costs to use a dollars-per-deciview-improved on a cumulative basis than to 

use a cost/ton basis standing alone. The commenter asserted that this metric provides a 

mechanism to ascribe meaningful value to pollution controls that would benefit numerous Class I 

areas. 

Response:

 

34 70 FR 39167 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

EPA disagrees with the commenter that a $/dv or $/cumulative dv metric is a more 

accurate depiction of costs than the $/ton metric. While a $/dv metric and a $/cumulative dv 

metric may provide some useful information to assess how pollution controls would benefit 

numerous Class I areas, as described in the response to the previous comment on use of the $/dv 

metric, the BART Guidelines do not require consideration of $/dv as a mandatory metric in a 

BART analysis. EPA considered cost of controls by discussing the total capital costs, annual 

costs, $/ton, and incremental $/ton (See Section 3.2), and considered visibility impacts by 

discussing the individual and cumulative deciview improvement resulting from SCR, as well as 

the percent change in improvement. 

Comment:

 One commenter (0117), who stated that BART must be determined in the context of 

reasonable progress rather than in isolation (see Section 10.0 for more on the commenter’s legal 

arguments), stated that the cost effectiveness metric used by EPA (i.e., $/ton of NOx reduced) 

does not satisfy the statutory requirement to consider the cost to comply with the Regional Haze 

program because it does not include compliance costs related to requirements for reasonable 

progress. 

Response:

Congress identified BART as a key measure for ensuring reasonable progress. We 

disagree that BART must be determined in the context of reasonable progress. If anything, 

reasonable progress depends on BART. Because the Class I areas affected by emissions from 

FCPP are not achieving the glidepath, it is important that states, tribes, and EPA require 

reasonable measures to be implemented to ensure that progress is made towards the national 

visibility goal. The BART Guidelines specify that the cost of controls be estimated by identifying 

the emission units being controlled, defining the design parameters for emission controls, and 

developing a cost estimate based on those design parameters using the EPA Control Cost 

Manual while taking into account any site-specific design or other conditions that affect the cost 

of a particular BART control option. The BART Guidelines do not require the BART costs of 

compliance to consider costs associated with reasonable progress. 

 EPA disagrees that there is a statutory requirement for a BART analysis to consider the 

cost to comply with the Regional Haze program as a whole. In the Regional Haze provisions of 

the Clean Air Act (§169A – Visibility Protection for Federal Class I Areas), Section 169A(g) 

defines the determination of reasonable progress (§169A(g)(1)), separately from the 

determination of BART (§169A(g)(2)). In determining reasonable progress, the costs of 

compliance for a source subject to such requirements must be considered, and in determining 

BART, the costs of compliance from the use of such technology must be considered. Because the 

definitions for determining reasonable progress and BART are mutually exclusive, the statute 

does not require a cost analysis for a BART determination to include costs associated with 

reasonable progress. 
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Comment:

 The Navajo Nation (0223) stated that EPA should analyze the affordability of controls 

under the supplemental proposal. The commenter noted that APS did not provide cost 

information for its proposed alternative, and EPA did not perform a detailed cost analysis. The 

commenter stated that EPA should perform a detailed analysis, rather than an approximation, of 

the cost of compliance for installing SCR on Units 4 and 5, including a consideration of the 

impacts of closing Units 1 – 3. The commenter suggested that line item costs should be provided 

for Units 4 and 5, taking into account the change in business structure and the demand for 

construction, labor, market, and material costs. The commenter cautioned that EPA and NPS 

should not use “outdated” sources that may underestimate compliance costs (see the comments 

above on the original cost analysis for BART) for this analysis or analyses for NGS or other 

coal-fired plants in the region that contribute to regional economies. 

Response:

EPA disagrees with the commenter that we should perform a detailed cost analysis of the 

alternative emission control strategy, put forth in the supplemental proposal. APS did not 

provide any indication to EPA that the costs of installing SCR on only Units 4 and 5 under the 

alternative emission control strategy would significantly differ from the costs to install SCR on 

only Units 4 and 5 under BART. 

 EPA does not agree that the affordability (as a business decision for the owners) of the 

supplemental proposal for APS and other owners must be analyzed. Because APS, on behalf of 

all owners, suggested to EPA this BART Alternative34F

35, EPA has no reason to believe that APS or 

the other owners may not be able to afford this option. Additionally, the affordability of 

installing controls is not a required element of a cost analysis for BART in the BART Guidelines, 

but may be considered in selecting the “best” alternative if “There may be unusual 

circumstances that justify taking into consideration the conditions of the plant and the economic 

effects of requiring the use of a given control technology”.35F

36 EPA conducted an affordability 

analysis for our proposed BART determination to assess whether the cost to produce electricity 

at FCPP would remain competitive compared to the market costs to purchase power if SCR were 

required on Units 1 – 5 at FCPP. The goal of this analysis was to determine whether our 

proposed BART determination would force FCPP to close entirely and thus create a significant 

adverse impact to the Navajo Nation. However, as stated previously, this analysis is not 

specifically required under the BART Guidelines. 

The Navajo Nation requested that EPA provide an analysis of potential adverse impacts 

to the Navajo Nation of APS’s proposal to close Units 1 – 3 as an alternative emission control 

strategy to BART. EPA notes that the RHR, in assessing an alternative measure in lieu of BART 

(40 CFR 51.308(e)(2)) requires several elements in the alternative plan (e.g., demonstration that 

the alternative will achieve greater reasonable progress than BART, and that reductions are 

surplus to the baseline date of the SIP), but does not require an analysis of the cost of the 

alternative plan. 

 

35 “Signed Letter from APS to EPA 11-24-10”, Document No. EPA-R09-OAR-2010-0683-0078. 

36 See BART Guidelines, July 6, 2005, at 70 FR 39171. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Although, an impact analysis of the alternative emission control strategy was not 

required under the Regional Haze Rule, as requested by the Navajo Nation and as part of EPA’s 

customary practice of engaging in extensive and meaningful consultation with tribes and tribal 

authorities with regard to relevant Agency actions, EPA commissioned an analysis of the 

potential impact to the Navajo Nation of APS’s option to close Units 1 – 3. The report will be 

provided to President Shelly by letter as a follow-up to our consultation with the Navajo Nation. 

EPA also disagrees with the commenter that our cost analysis relies on “outdated” 

sources and may underestimate compliance costs. As discussed above, EPA has determined that 

the cost analysis conducted for our October 2010 BART proposal is conservative because it 

relies on the highest cost estimates submitted by APS, and reasonable because it incorporates 

the site-specific costs estimated by B&V for APS while also considering the allowed line item 

costs in the EPA Control Cost Manual. As noted above, our cost estimate is 18% lower than the 

highest B&V cost estimate submitted by APS in 2009, and less than 0.6% lower than the most 

recent cost B&V cost estimated submitted by APS in 2010. Therefore, reliance solely on APS’s 

most recent cost estimate in lieu of the EPA’s cost estimate presented in our proposed 

rulemaking would not result in substantive changes to our BART determination. 

3.2 16BComments on Top-Down Analysis Versus Incremental Cost Effectiveness 

Comment:

 A number of commenters, including owners of FCPP (0168, 0174, 0176/0177, 0179, 

0185), the Navajo Nation (0223), and a utility industry association (0187), asserted that EPA’s 

BART analysis was inconsistent with its own regulations in that it used a top-down analytic 

approach and failed to conduct an incremental cost evaluation. These commenters typically 

noted that the BART rules establish that both average cost effectiveness and incremental cost 

effectiveness are to be used in the evaluation of BART (often citing 70 FR 39127, 39167-68). 

 Some of these commenters (0168, 0176/0177, 0179, 0185, 0187) added that a top-down 

approach, which EPA uses for Best Available Control Technology (BACT) analyses, is 

inappropriate for a BART analysis. One of the commenters (0176/0177) noted that BACT 

requires the maximum degree of emissions reductions from new sources and major 

modifications, taking into account various statutory factors established for the Prevention of 

Significant Deterioration (PSD) program. The commenter indicated that for purposes of BACT, a 

top-down analysis (while not required by the CAA) may have some justification because new 

sources may more easily accommodate stringent control options. However, because BART 

applies only to retrofits of existing sources (i.e., not to new facility construction), the commenter 

argued that the most stringent controls may not be appropriate or cost effective for such existing 

sources. Accordingly, the commenter asserted that a top-down methodology that is designed to 

achieve maximum stringency and that fails to make a cost effectiveness comparison with less 

stringent control options cannot be appropriate in the BART setting. The commenter added that 

because a top-down cost assessment methodology is inconsistent with the BART rules and the 
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nature and purposes of the BART program, EPA must abandon this approach and instead apply 

the incremental cost effectiveness analysis described in the BART rules. 

 Another of the commenters (0187) stated that absent an incremental cost-effectiveness 

analysis, EPA has no basis for concluding that SCR is a cost-effective control or that it is BART 

for FCPP. A third commenter (0185) stated that given that EPA has failed to conduct an 

incremental cost-effectiveness assessment, its proposed BART determination must be rejected. 

 The Navajo Nation (0223) indicated that in using the top-down analysis, EPA failed to 

carry out the five-factor analysis for each of the technically feasible retrofit technologies as 

required by the BART Guidelines (citing 40 CFR part 51, Appendix Y, section I.F.2.c), 

including current combustion control technology which the BART Guidelines identify as 

presumptive BART (citing section IV.D.5). The commenter stated that by only analyzing a 

single technology which it chose in advance, EPA’s analysis was clearly arbitrary and not in 

compliance with its own regulations. The commenter concluded that EPA’s compliance cost 

analysis was fatally flawed. 

Response:

EPA disagrees with these comments. In the preamble to the final BART Guidelines, EPA 

discusses two options presented in the 2001 proposal and 2004 re-proposal of the guidelines for 

evaluating ranked control technology options (See discussion at 70 FR 39130). Under the first 

option, States would use a sequential process for conducting the analysis, beginning with a 

complete evaluation of the most stringent control option. The process described is a top-down 

approach analogous to the analysis we used in our proposed BART determination for FCPP. If 

the analysis shows no outstanding issues regarding cost or energy and non-air quality 

environmental impacts, the analysis is ended and the top level of technically-feasible controls is 

identified as the “best system of continuous emission reduction”. The preamble describes an 

alternative decision-making approach that begins by evaluating the least stringent control 

technology (bottom-up approach) where the State would then consider the additional emissions 

reductions, costs, and other effects of successively more stringent control options. In the final 

guidelines, EPA decided that States should retain the discretion to evaluate control options in 

whatever order they choose, so long as the State explains its analysis of the CAA factors. 

Therefore, in conducting our BART determination for FCPP, EPA’s top-down approach for 

assessing the five factors was consistent with the discretion allowed under the BART Guidelines. 

EPA additionally notes that the TSD for our proposed rulemaking included analyses of the costs, 

non-air impacts, and visibility improvements associated with combustion controls at FCPP (the 

level of control APS determined to be BART at FCPP), but that there is no requirement for a 

five-factor analysis on all potentially available control options if the top down approach is used 

and the top level of technically-feasible controls is selected (70 FR at 39130).

Comment:

 One of the owners of FCPP (0176/0177) who alleged that the BART rules require an 

analysis (see above) and provided an analysis comparing the costs of combustion controls to the 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

costs of SCR. According to the commenter’s analysis, the incremental cost effectiveness of 

moving from combustion controls to SCR ranges from $6,553 to $8,605 per ton of NOx reduced 

for the five units at FCPP. This commenter and another FCPP owner (0168) asserted that this 

“extraordinarily high” incremental cost highlights the fact that combustion controls, not SCR, 

satisfy the cost effectiveness test applied by EPA in adopting the presumptive BART limits in 

the BART rules. 

Response: 

EPA agrees that the BART Guidelines recommend consideration of both average and 

incremental cost effectiveness, however, EPA disagrees with the commenter that the incremental 

cost effectiveness should be a comparison between combustion controls and SCR for this 

particular facility. As discussed at length in the TSD for our proposed BART determination for 

FCPP, EPA has determined that combustion controls (burner modifications and overfire air, 

including ROFA) will not be effective at significantly reducing emissions at Four Corners due to 

inherent design and physical limitations of the boilers. Therefore, in estimating incremental cost, 

it is inappropriate to include combustion controls in the analysis for this particular facility. To 

respond to this comment, EPA conducted an incremental cost effectiveness analysis and included 

it in our docket for this final rulemaking.36F

37 Based on our incremental cost analysis, EPA has 

determined that the incremental cost of SCR compared to the next most stringent option is 

reasonable and does not support the commenter’s conclusion that SCR is not BART for FCPP. 

The BART Guidelines recommend two types of cost effectiveness calculations – average 

cost effectiveness and incremental cost effectiveness. Although there are no bright line 

thresholds for determining the acceptability of average and incremental cost effectiveness 

estimates, average cost effectiveness is the most commonly reported cost metric when comparing 

controls for BART and BACT determinations. Therefore, we focused on average cost 

effectiveness in our October 2010 BART analysis. However, we agree with commenters that the 

BART Guidelines do recommend consideration of both average and incremental cost 

effectiveness, therefore, we calculated incremental cost effectiveness using the methodology 

described in the BART Guidelines (see 70 FR 39167 – 39168), such that incremental cost 

effectiveness comparisons focus on the dominant alternatives that are identified by generating a 

“least-cost envelope” graphical plot. The BART Guidelines describes the least-cost envelope to 

represent the set of options that should be dominant in the choice of a specific option based on 

total annualized cost and expected emission reductions. 

 Based on the least-cost envelopes for Units 1 – 5 of the control technologies APS 

determined to be feasible at FCPP, the following NOx controls are the dominant options that 

form the least cost envelope: combustion optimization systems (COS), Low NOx burner (LNB), 

LNB+Overfire Air (OFA), LNB+OFA plus high energy reagent technology (LNB+OFA+HERT), 

ROTAMIX+ROFA, and SCR on Units 1 and 2; COS, LNB+OFA, LNB+OFA+HERT, SCR on 

Unit 3; and COS, LNB+OFA, SNCR+LNB+OFA, SCR on Units 4 and 5. The least cost envelope 

methodology thus excludes from consideration the technologies that fall outside of this least cost 

envelope. The incremental cost effectiveness for all options and for all dominant options is 

shown in the “Incremental cost.xlsx” spreadsheet included in the docket. Using the cost and 

 

37 See “Incremental cost.xlsx”, in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

emission reduction estimates provided by B&V for APS, the incremental cost of SCR when 

considering all options and only the dominant options are comparable and ranges from 

approximately $5,500/ton to $18,000/ton. Incremental cost of SCR is lower on Units 4 and 5, 

and highest on Units 1, 2, and 3. This methodology already excludes the technologies APS 

determined were technically infeasible (technical feasibility was determined before the cost 

effectiveness determination) and also excludes technologies determined inferior from the least 

cost envelope plot. However, as discussed at length in the TSD for our proposed BART 

determination for FCPP, EPA has determined that combustion controls (burner modifications 

and overfire air, including ROFA) will not be effective at Four Corners, particularly on Units 1 

– 3, due to inherent design and physical limitations of the boilers. Therefore, in estimating 

incremental cost, it is inappropriate to include an infeasible control technology in the analysis. If 

we exclude the control technologies that EPA has determined to be ineffective at FCPP, SNCR 

(without combustion controls) is the next most stringent alternative after SCR. The incremental 

cost of moving from SNCR to SCR ranges from $3,500/ton to $5,800/ton using cost and emission 

reduction estimates provided by APS. If we use the EPA’s revised cost estimate for SCR and 

EPA’s proposed NOx control efficiency of 80%, the incremental cost from SNCR to SCR ranges 

from $2,500/ton to $3,300/ton. 

Based on our incremental cost analysis, EPA has determined that the incremental cost of 

SCR compared to selective non-catalytic reduction (SNCR), the next most stringent option 

($2,500 per ton to $3,300 per ton), is reasonable and does not support the commenter’s 

conclusion that SCR is not BART for FCPP. 

3.3 17BOther Comments on Factor One 

Comment:

 One public interest advocacy group (0112) agreed with EPA’s elimination of LNB 

technology from BART consideration based on the TSD discussion which concluded that since 

FCPP has had limited success in retrofitting Unit 2 with LNB technology, FCPP was unlikely to 

achieve significant NOx reductions by retrofitting any of its boilers with LNB technology. 

 In contrast, one of the owners of FCPP (0176/0177) asserted that EPA’s determination 

that “combustion controls are not likely to be effective control technologies at FCPP” (citing 

75 FR 64226) was based on superficial analysis and was mistaken. The commenter cited 

Exhibit J to its comments on the ANPR,37F

38 which contains a detailed analysis of the use of LNB 

and OFA on FCPP’s units. According to the commenter, this analysis confirms that the use of 

advanced combustion controls on the five units at FCPP will reduce plant-wide NOx emissions 

by 34 percent. 

Response:

EPA disagrees with the commenter that Exhibit J of APS’s comments on the ANPR 

confirm that advanced combustion controls on all five units at FCPP will reduce plant-wide NOx

 

38 This document can be found in the docket for the ANPR, “Comments on ANPRM 09 0598 APS Comments and 

Exhibits”, Document No. EPA-R09-OAR-2009-0598-0195. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

emissions by 34%. Although APS makes that statement in its May 2, 2011 comment letter on the 

2010 BART proposal, in its separate May 2, 2011 comment letter on the 2011 Supplemental 

proposal, APS explains that further reductions in the NOx emission limit for Units 4 and 5 is not 

appropriate for several reasons, including: 

As discussed in EPA’s Supplemental Proposal, there are site-specific operational 

constraints at the Plant which will compromise its ability to comply with a lower 

emissions level, such as the high ash-content of the coal and the “cell-burner” 

configuration of the boiler. The Supplemental Proposal acknowledges that the cellburner configuration in Units 4 and 5 is not conducive to the application of advanced 

combustion controls, typically employed prior to post-combustion processes such as SCR. 

Therefore, all the desired emission reductions must be achieved with the SCR alone, 

which limits the maximum achievable NOx reduction. 

In this comment, APS contends that EPA’s conclusion, that advanced combustion controls will 

not be effective at significantly reducing NOx emissions at FCPP, is accurate. Because of its 

conflicting statements, it is unclear to EPA whether APS believes advanced combustion controls 

will or will not be effective at FCPP. As outlined in the TSD for our 2010 BART proposal, EPA 

concludes that advanced combustion controls will not be effective at significantly reducing NOx

emissions at FCPP, and therefore, our final BART determination requiring an 80% reduction in 

NOx is based on the application of only SCR. 

Comment:

 One private citizen (0107) stated that EPA must consider the use of supplemental steam 

from a concentrating solar power facility in determining BART for FCPP. The commenter 

attached numerous articles that describe this technology, and indicated that these articles 

establish that the technology is a viable option to reduce pollution from FCPP. 

Response:

EPA disagrees with this comment that supplemental steam from a concentrating solar 

power facility is an appropriate technology to consider in order to reduce pollution from FCPP. 

The supplemental steam generated from a solar facility is intended to offset some of the fuel 

required to generate electricity. EPA does not have authority through BART to redefine a source, 

nor is it feasible for a solar concentrating facility to offset enough fuel use to reduce NOx

emissions from coal combustion by 80% without the use of significant land area. 

In 2010, EPA issued a PSD pre-construction permit to the City of Victorville, in the 

desert portion of southeastern California, to construct Victorville 2: a 563 megawatt (MW) 

natural-gas fired combined cycle power plant with a 250 acre solar thermal array to provide 50 

MW to the total electrical generation from the 268 MW steam turbine38F

39. In order to offset NOx

 

39 See “PSD Permit Application April - 2007” or “Ambient Air Quality Impact Report”, Document No. EPA-R09-

OAR-2008-0406-0001 or EPA-R09-OAR-2008-0406-0016. In 2011, EPA issued a PSD permit to a nearly identical 

563 MW (net) natural gas fired combined cycle power plant with a 251 acre concentration solar facility to provide a 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

emissions by 80% at FCPP using supplemental steam from a concentration solar facility, we 

assume that the solar facility would need to provide 80% of the power at FCPP, or nearly 1,650 

MW. Using the ratio of solar field acreage to electricity production (acres/MW) from Victorville 

2 and a similar facility in Palmdale, California, we infer that approximately 8,250 acres (nearly 

13 square miles) might be required to produce 1,650 MW of power. Even if EPA had authority to 

require FCPP to reduce emissions by implementing a concentrating solar facility, the land area 

and cost would likely prohibit substantial contributions from solar power to the total electricity 

generation from FCPP at this time. However, because EPA’s final BART determination is an 

emissions limitation, rather than a technology requirement, and although EPA does not have 

authority to require this technology, APS may consider this technology, or others, in developing 

its plan to cost-effectively comply with EPA’s final BART emission limit for NOx. 

 

Comment:

 One commenter at a public hearing submitted written material (0190) describing “fuel 

lean gas reburn” technology, which the commenter stated should be considered in the BART 

determination for FCPP. These materials indicate that this technology reduces NOx emissions by 

30 to 45 percent. In his oral testimony, the commenter added that the ammonia used in SCR 

systems is a hazardous material, which he would not like to see introduced into the area. He also 

stated that the RHR allows a long period of time to meet the visibility improvement goals, and he 

stated the use of fuel lean gas reburn technology in conjunction with combustion controls would 

be appropriate at this time. 

Response: 

EPA disagrees with this comment. Fuel lean gas reburn technology was discussed in the 

TSD for our proposed BART determination. Table 3 of the TSD included natural gas reburn as 

an available NOx control option that B&V determined to be technically infeasible because the 

technology has not been used in similar type or size facilities. However, even if this technology 

was determined to be technically feasible, it ranked as a mid-range technology in terms of 

control efficiency (65% control only when combined with LNB). Because EPA’s proposed BART 

determination is a NOx emission limit rather than a specific technology requirement, in 

complying with BART, APS may consider implementing a combination of other technologies in 

lieu of SCR provided the alternative can meet the NOx limit specified in the final FIP. In the 

absence of feasible control technologies that are capable of achieving 80% or greater reduction 

in NOx emissions, EPA assessed the cost of controls assuming SCR would be used to comply with 

the BART limit. 

 maximum of 50 MW to electric generation from the steam turbine to the City of Palmdale for the Palmdale Hybrid 

Power Project in California. See “Initial PSD Palmdale Permit Application” or “Fact Sheet and Ambient Air Quality 

Impact Report for the Proposed PHPP PSD Permit (SE-09-01)”, Document No. EPA-R09-OAR-2011-0560-0002 or 

Document No. EPA-R09-OAR-2011-0560-0004. 
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4.0 3BComments on Factor Two – Economic, Energy, and Non-Air 

Quality Environmental Impacts 

4.1 18BComments on Economic Impacts 

4.1.1 24BGeneral Comments on Economic Impacts 

Comment:

 In virtually identical comments submitted prior to the supplemental proposal, one public 

interest advocacy group (0094) and one environmental group (0146) offered comments on both 

FCPP and NGS stating that EPA’s analysis of historical and expected costs of electricity from 

FCPP neglect to include public health costs related to air pollution and the negative impacts to 

tourism resulting from loss of visibility. The commenters concluded that the cost-effectiveness 

metric used to determine BART at both plants must account for health costs related to poor air 

quality. The commenters requested that EPA consider economic costs on impacted communities 

and Class I federal areas for not “cleaning up” both facilities. 

 Two private citizens who submitted written comments at a public hearing (0190) 

similarly indicated that environmental and health costs related to FCPP should be considered 

along with energy costs. One private citizen (0181) also claimed that pollution from FCPP has 

impacted the region’s economic health because of costs the Four Corners region has sustained. 

Response:

 EPA disagrees with the comment that the cost-effectiveness of BART must account for 

public health costs associated with poor air quality. Neither Section 169A of the Clean Air Act, 

nor the BART Guidelines, require that BART analyses include or quantify benefits to health or 

tourism. As discussed previously, although not required by the BART Guidelines, EPA did 

conduct an affordability analysis in our proposed BART determination to estimate whether the 

installation and operation of SCR on Units 1 – 5 at FCPP would render the cost to produce 

electricity at FCPP un-competitive compared to the cost to purchase electricity on the open 

market. Although a quantitative analysis of the health and tourism benefits is beyond the scope of 

what is required under BART EPA agrees with commenters that emission reductions achieved to 

improve visibility will also improve air quality. Improved air quality, in turn, affects public 

health and may enhance tourism in the area. 

EPA notes that even if we had quantified the benefits to health and tourism, such an 

analysis would not likely have altered the outcome of our BART determination. 

Comment: 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 The Navajo Nation (0223), one federal agency (0224), and two of the owners of FCPP 

(0168, 0176/0177) stated that EPA must consider the collateral economic effects on the Navajo 

Nation and the surrounding communities of its BART determination. One of these commenters 

(0176/0177) noted that the BART rules permit broad economic effects to be considered in 

determining the appropriate control technology and emissions limitations (citing 70 FR 39169 

and the June 2007 Reasonable Progress Guidance, page 5-139F

40). Another of the commenters 

(0223) stated that the BART Guidelines (citing 40 CFR Part 51, Appendix Y, sections IV.D.4.h.5 

and IV.E.3) and EPA’s federal trust responsibility (see related comments in Section 10.0) 

provide authority for considering the economic impacts to the Navajo Nation in the BART 

determination for FCPP. 

 The Navajo Nation (0223) provided background on the substantial economic interest that 

the Navajo Nation has in the continued operation of FCPP. The commenter noted that the Navajo 

reservation has little economic development and that the Navajo people who live there are 

among the poorest in the United States, with 42 percent of Navajo individuals living below the 

federal poverty line. The commenter indicated that FCPP is located on Navajo land pursuant to a 

lease agreement with the Navajo Nation, as is its coal supplier, the Navajo Mine; together these 

entities provide income to the Navajo Nation that contributes substantially to the Nation’s 

economic viability and its sustainability as an independent sovereign: 

 FCPP employs 586 people, 72 percent of whom are members of the Navajo Nation, with 

an annual payroll of $41 million. 

 The Navajo Mine employs 357 employees, 87 percent of whom are Navajo tribal 

members, with salary and benefits that exceed $41 million. 

 The Navajo Mine paid royalties and taxes to the Navajo Nation of approximately 

$45.9 million in 2008. 

 Together, those employed at FCPP and the Navajo Mine make up about 3 percent of the 

total Navajo Nation employed workforce, which is very important on the Navajo Nation 

where unemployment has hovered just below 50 percent for years. 

 In 2008, the combined income derived from FCPP and NGS and the mines that supply 

them totaled approximately $93.9 million, or about 55 percent of the Navajo Nation’s 

General Funds Budget. 

 The Navajo Nation (0223) added that this resource extraction-based economy is the result 

of a conscious effort of the United States from the 1950s to develop the Nation’s coal resources, 

often for the benefit of other parties (such as the non-Navajo communities of Phoenix and 

Tucson in southern Arizona who directly benefit from power allocated from NGS to pump water 

for the Central Arizona Project). The commenter asserted that for the federal government, 

through any agency, to now threaten the livelihood of the Nation by destroying the resource 

economy it created clearly violates the federal trust responsibility to the Navajo Nation. The 

commenter also stated that the Nation has already suffered the ripple effects of one EPA 

rulemaking that, through the imposition of financially untenable emissions controls, resulted in 

 

40 See “Guidance for Setting Reasonable Progress Goals Under the Regional Haze Program”, June 1, 2007, in the 

docket for this rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

the closure of the Mohave Generating Station, and as a consequence, the closure of the Black 

Mesa Mine. According to the commenter, if FCPP and the Navajo Mine were to close as the 

result of the imposition of cost-prohibitive emission controls, the resulting revenue and job losses 

would be cataclysmic for the Navajo Nation. 

 The Navajo Nation (0223) alleged that EPA gave virtually no consideration in its BART 

analysis to the potential impacts on the Navajo Nation. According to the commenter, EPA 

casually dismissed a real likelihood of disastrous economic impacts to the Navajo Nation by 

claiming that there is no “definitive information” that FCPP would close if SCR is made BART 

for FCPP and relying solely on its own economic analysis to conclude that FCPP “is expected to 

remain competitive.” The commenter asserted that as the Nation’s trustee, EPA failed to properly 

balance the gravity of the potential harm to the Nation should FCPP come to a different business 

decision regarding the future competitiveness of FCPP with the imposition of SCR. The 

commenter stated that where there is a great deal of uncertainty for FCPP because of other 

issues, e.g. ongoing lease renewal processes and needed changes in ownership structure of FCPP, 

EPA’s failure to weigh the impact of imposing SCR in that context is particularly troubling. 

 The Navajo Nation (0223) stated that EPA should have analyzed in detail the potential 

economic impacts to the Navajo Nation should EPA require the installation of costly control 

technologies that the commenter asserted exceed the requirements of the RHR. The commenter 

concluded that contrary to its trust responsibility, the RHR, and the BART Guidelines, EPA 

failed to factor into its BART analysis the true potential economic impacts of imposing SCR on 

FCPP, and failed to appropriately defer to the Navajo Nation's reasonable wish to phase in SCR 

in a more conservative and cost-effective approach. 

 The Navajo Nation (0223) also pointed out that there are three coal-fired power plants 

located on or near the Navajo Nation (FCPP, NGS, and San Juan Generating Station (SJGS)) that 

are all subject to simultaneous BART rulemaking. The commenter indicated that all three power 

plants and the coal mines that supply them contribute to the Navajo Nation’s economy and 

regional economic dynamics, and that there are additional emissions sources (major and minor) 

contributing in varying percentages to emissions in the region. The commenter asserted that all 

these sources should be considered in crafting the BART FIP for FCPP, where the tribal and 

regional economic impacts must be balanced with the degree of visibility improvement that 

would meet reasonable progress. 

 Another of the commenters (0176/0177) gave an overview of the Navajo Nation’s 

comments on the ANPR for FCPP, particularly the importance of FCPP and the associated coal 

mine to the economy of the Navajo Nation and the significant impact on the Navajo economy if 

FCPP were to close as the result of the imposition cost-prohibitive emission controls. The 

commenter indicated that a BART determination requiring SCR at FCPP may make Units 1-3 

uneconomical and force closure, and the same may be true for Units 4 and 5 depending on the 

disposition of Southern California Edison’s interest in those units. 

 The commenter (0176/0177) asserted that EPA must consider and respond to these 

potential impacts of its BART determination; EPA cannot simply dismiss this issue because “it 

has received no definitive information that FCPP intends to shut down or curtail operations” 
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(citing 75 FR 64227). The commenter stated that the economic role that FCPP plays in the region 

and with the Navajo Nation magnifies the importance of striking the right balance in a BART 

determination – especially given that the BART determination is about visibility and not about 

protecting public health. 

 The federal agency commenter (0224) noted that EPA’s current affordability analysis 

focuses primarily on increased costs to rate payers and the companies’ profitability, and stated 

that the analysis needs to incorporate the loss in revenue, jobs, and royalties resulting from the 

closure of Units 1-3 under the supplemental proposal. The commenter added that all key 

decision-making federal agencies must remain vigilant when making decisions that impact 

Navajo tribal trust resources and the economic well-being of the Navajo Nation. 

 Two private citizens who submitted written comments at a public hearing (0190) also 

expressed concern that additional regulation of FCPP could have negative economic impacts on 

the Navajo community. 

Response:

 EPA agrees with commenters that the operation of FCPP and the Navajo Mine 

contribute significantly to the economy of the Navajo Nation and the Four Corners Region. 

However, we disagree with commenters that EPA casually dismissed the possibility of plant 

closure. It is not EPA’s intention to cause FCPP to shut down (nor is it within our regulatory 

authority under the RHR to require shutdown or to redesign of the source for BART). As 

expressed in comments from the Navajo Nation to our Advanced Notice of Proposed 

Rulemaking40F

41, EPA understands that the Navajo Nation’s primary concern regarding the BART 

determination is the potential for FCPP closure. For this reason, EPA conducted an 

affordability analysis not typically included in a BART five-factor analysis in order to assess 

whether requiring SCR on all five units at FCPP would result in full closure of the power plant. 

The assessment compared the cost of power from FCPP if SCR were required on all five 

units, to the estimated cost of replacement power, assuming the owners of FCPP were to decide 

to close the entire plant rather than make the SCR investment. The model was designed to 

answer the question as to which future alternative results in lower power costs: a) power 

produced at FCPP after installation of SCR, or b) replacing the power from FCPP with the 

appropriate amount of wholesale power purchases. If the model results suggested that it would 

be less costly for the owners to purchase replacement power on the open market than generate 

power itself after installing and operating SCR on all five units, then EPA would have taken that 

result, along with subsequent impacts to the Navajo Nation, into consideration in our proposed 

rulemaking. However, as discussed in the TSD for our proposed BART determination, the model 

results suggested that even if the owners of FCPP installed and operated SCR on all five units, it 

could still produce power at a lower cost than the cost to purchase replacement wholesale power 

on the open market.41F

42 Thus, EPA concluded in our proposed BART determination that requiring 

 

41 Comment letter from President Joe Shirley, Jr. dated March 1, 2010 in the docket for the ANPR: EPA-R09-OAR2009-0583-0209. 

42 “FCPP Proposal – Technical Support Document 10-6-10”, Document No. EPA-R09-OAR-2010-0683-0002, 

“TSD Appendix B: Economic Analysis (EPA) of Proposed BART Determination on FCPP Final Report”, 
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SCR as BART on all five units would not likely result in plant closure. EPA recognizes that 

market conditions for power on the wholesale market are highly variable and will likely differ 

now, or at any time in the future, compared to conditions that existed at the time of our proposed 

BART determination. However, no information was provided by the commenter to change our 

conclusion in the analysis we conducted for the proposed rulemaking that suggests installation 

of SCR on all five units would not likely result in plant closure. 

 EPA recognizes the importance of the power plants and the mines that fuel them as they 

relate to the economic well-being of the Navajo Nation. EPA understands the importance of 

quantifying potential impacts to the Nation of closures of one or more units at FCPP. At the 

request of the Navajo Nation, as part of EPA’s customary practice of engaging in extensive and 

meaningful consultation with tribes and tribal authorities with regard to relevant Agency 

actions, EPA commissioned an analysis to estimate potential adverse impacts on the Navajo 

Nation of the optional BART Alternative. The analysis will be provided to President Shelly by 

letter as a follow-up to our consultation with the Navajo Nation. 

With respect to the suggestion that an EPA rulemaking resulted in closure of the Mohave 

Generating Station several years ago, EPA would like to clarify that Mohave’s closure was not 

the result of an EPA rulemaking. Rather, the owners of Mohave Generating Station entered into 

a Consent Decree with several environmental groups, including the Grand Canyon Trust, Sierra 

Club, and the National Parks Conservation Association. That Consent Decree required 

Mohave’s owners to install pollution controls to reduce emissions of SO2 and PM from the 

facility. The Consent Decree required installation of the pollution controls by the end of 2005. 

The decision by the owners of Mohave appears to have been shaped by numerous complex 

factors. EPA was not involved in the decision-making process or the regulatory proceedings 

surrounding it. The Mohave Generating Station used coal that was mixed with water and 

conveyed as slurry in a pipeline. The water to make the slurry was drawn from the N aquifer 

from the Hopi Reservation. EPA understands that a contract to use the water from the N aquifer 

expired in 2005 and was not renewed. The lack of a reliable source of water for the coal slurry 

likely contributed to the decision by the owners of the Mohave Generating Station to discontinue 

operations at the end of 2005. Furthermore, it is EPA’s understanding that in 2006, Salt River 

Project (SRP), a co-owner of Mohave, sought to form a new ownership group to restart Mohave, 

including to install the new air pollution controls required by the Consent Decree as well as 

develop a new water supply system for the coal mine, however, SRP ended its efforts to restart 

Mohave because it could not negotiate its intended purchase of Southern California Edison’s 

share of Mohave in time to restart by 2011.42F

43 Therefore, although EPA understands that the 

Navajo Nation and Hopi Tribe experienced adverse impacts from the closure of Mohave 

Generating Station in 2005, the closure and the failed efforts to restart Mohave are not 

attributable to, or the result of, EPA rulemakings. 

 Document No. EPA-R09-OAR-2010-0683-0005, “TSD ref [49] Economic Analysis of Proposed EPA Bart 

Determination on FCPP_09-18-10 RATES.xlsx”, Document No. EPA EPA-R09-OAR-2010-0683-0005-0040. 

43 See February 6, 2007 Media Advisory from SRP: “SRP Ceases Effort to Restart Mohave Generating Station; 

Concludes that Timeline Delays would Render the Facility Economically Unfeasible”, and article in Power 

Engineering Magazine: http://www.power-eng.com/articles/print/volume-111/issue-3/departments/startup/srpdecision-seen-as-ending-mohave-re-start.html
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Comment:

 The Navajo Nation (0223) asserted that EPA failed to consult with the Nation prior to 

publishing the supplemental proposal and failed in its trust responsibility to consider the 

potential adverse impacts of the option to close Units 1 – 3. While conceding that the 

supplemental proposal is less likely to result in closure of the entire FCPP, the commenter noted 

that Units 1 – 3 represent 27 percent of the capacity of the plant and closing these units will 

affect the Navajo Nation’s tax revenues and jobs, and will affect production at the Navajo Mine 

as well. According to the commenter, in public hearings held in Farmington, NM, FCPP has 

reported that as a result of closing Units 1 – 3, it expects 190 to 200 jobs to be lost in the next 3 

to 4 years due to attrition at FCPP, an expected $5 million reduction in the possessory interest tax 

paid annually to the Nation, and a 30 percent reduced demand for coal at Navajo Mine. The 

commenter also stated that at the Navajo Mine, 150 to 200 jobs are expected to be lost over the 

next 3 years as a result of the reduced demand from closure of Units 1 – 3 at FCPP, with a 

resulting $10 million reduction in annual coal royalties to the Navajo Nation. 

 The commenter (0223) stated that as the Navajo Nation’s trustee, and in determining a 

“better than BART” alternative, EPA nonetheless retains its obligation to analyze potential 

adverse impacts to the Navajo Nation. The commenter argued that EPA is violating its trust 

responsibility in not adequately assessing these impacts for a plant operating on Navajo Nation 

land and burning Navajo coal, especially where EPA must assume the Nation’s duties to its tribal 

members in making this determination in lieu of the Nation. 

Response:

A timeline of correspondence and consultation with the Navajo Nation and other tribes 

for EPA actions on FCPP and Navajo Generating Station is included in the docket for the final 

rulemaking.43F

44 EPA notes that the Regional Administrator of EPA Region 9 called President Joe 

Shirley on February 9, 2011 to inform him of EPA’s Supplemental Proposal. However, 

government-to-government consultation with the Navajo Nation on FCPP did not occur until 

May 19, 2011, with additional consultation occurring on June 13, 2012, prior to issuing our 

final rulemaking. The Navajo Nation raised concerns about the potential adverse impacts of the 

BART Alternative and requested that EPA conduct an analysis to estimate these impacts.

Although the RHR does not require a cost analysis of a BART alternative, at the request 

of the Navajo Nation and as part of EPA’s customary practice of engaging in extensive and 

meaningful consultation with tribes and tribal authorities with regard to relevant Agency 

actions, EPA commissioned an additional analysis to estimate potential adverse impacts on the 

Navajo Nation of the BART Alternative with respect to coal and power plant-related revenues. 

The report will be will be provided to President Shelly by letter as a follow-up to our 

consultation with the Navajo Nation. 

 

 

44 See document titled: “Timeline of all tribal consultations on BART.docx” in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Comment:

 One environmental advocacy group (0182) commented that in rigorously addressing 

visibility-related pollutants, the Navajo Nation, New Mexico, the intermountain west, and the 

Colorado plateau stand to reap significant benefits and avoid serious consequences because such 

emissions have far-reaching impacts on local economies. The commenter noted that tourism is 

critical to the economy of the Navajo Nation, New Mexico, and the Four Corners region, and 

that many national parks and landmarks are impacted by FCPP. The commenter pointed out that 

visibility in such areas has been degraded, and that poor visibility affects park visitation and 

length of stays. 

 One public interest advocacy group (0143) similarly noted that national parks and 

monuments, wilderness areas, forests, and local culture bring tremendous economic benefit to 

the Four Corners region, and that residents rely on tourism and the region’s natural resources for 

long-term economic growth and sustainability. The commenter added that oil and gas 

development, over-grazing, and prolonged drought combined with coal-fired power plant 

pollution have resulted in a continuing degradation of air quality and its impact on the soil and 

vegetation. This commenter supported reducing pollution for FCPP through implementing the 

supplemental proposal. 

 The environmental advocacy group (0182) also stated that installation of pollution 

controls creates short-term construction employment and permanent operations and management 

positions. Thus, the commenter asserted that installation of additional and upgraded pollution 

controls will result in jobs and revenue for the Navajo Nation and its citizens. 

Response:

 EPA agrees that tourism is important to the economy of the Four Corners region, 

however, the economic benefits of tourism and the benefits of short-term construction 

employment associated with installation of air pollution controls are outside the scope of the 

BART analysis. The BART Guidelines require consideration of the costs of compliance, and do 

not similarly require an analysis of the economic benefits resulting from BART controls. The 

model used by EPA was developed to address the future comparative cost of power from FCPP 

with SCR against the wholesale power market to determine if FCPP would remain competitive if 

SCR were required as BART. 

Comment:

 One owner of FCPP (0168) stated that EPA’s proposal to require SCR at FCPP presents 

significant challenges and risks and, with regard to their resource planning, handicaps their 

ability to cost-effectively respond to changing conditions. The commenter pointed out that 

implementation of the BART proposal would require the commenter to make a significant 

capital investment in FCPP, which could only be recovered through long-term operation of the 

plant. According to the commenter, this would have the effect of locking FCPP into the 

commenter’s generation portfolio for a considerable period or risk stranding those investments. 
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The commenter indicated that this loss of flexibility would hamper the commenter’s ability to 

respond to future scenarios and likely preclude it from reacting to the following possible 

developments: 

 Changes in the economic viability of coal resources due to the increasing costs of 

environmental regulations, including carbon limits. 

 Changes in the acceptance of coal resources by state utility commissions. 

 Low, sustained natural gas prices, which would favor natural gas resources over coal. 

 Reduced demand for coal resources due to increases in renewable generation capacity 

and/or reductions in customer load due to energy efficiency and demand response 

programs. 

 Advances in emission control technology. 

 The commenter (0168) asserted that this loss in flexibility and the risk it represents is 

completely unnecessary given that the Regional Haze program is intended to make gradual 

reductions in emissions over a decades-long period of time. The commenter stated that EPA 

should therefore recognize combustion controls as BART for FCPP and evaluate further 

reductions, such as installation of SCR, if it is shown to be justified in subsequent planning 

periods. (See more on this comment in Section 10.0.) 

Response:

 EPA appreciates the perspectives shared in this comment, but we disagree that our fivefactor BART analysis should consider the potential loss of an owner’s flexibility to respond to 

possible future economic or regulatory scenarios. EPA cannot give substantial consideration in 

our BART analysis to external factors that are of uncertain magnitude and that may or may not 

occur. EPA further notes that the RHR allows for the development of BART alternatives that 

achieve greater reasonable progress than BART and EPA appreciates the fact that the owners of 

FCPP put forth an alternative that gives them more flexibility and results in greater emission 

reductions at FCPP. 

 EPA acknowledges that other potential environmental regulations or public policies may 

emerge which could also have an impact on the competitiveness of FCPP and that, should these 

new regulations or policies emerge, will require the plant owners to assess the economic impact 

to plant’s competitiveness. However, the impacts studied in this analysis were limited in scope to 

determining likely effects from the proposed BART determination exclusively.

4.1.2 25BComments on EPA’s Economic Analysis 

Comment:

 One public interest advocacy group (0112) concurred with the EPA’s analysis that the 

potential increase to APS rate payers as a result of SCR is expected to be less than 5 percent, as 

described in the TSD. The commenter also stated support for EPA’s analyses related to the 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

increase in electricity generation costs of SCR compared to estimated costs to purchase 

electricity in the wholesale market. The commenter asserted that EPA estimates are reasonable 

and that the average increase in the cost of generation at FCPP as a result of SCR 

implementation would be 22 percent, or $0.0074/kWh, as stated in the TSD. 

 One of the owners of FCPP (0176/0177) stated that installation of BART controls would 

increase its average residential customer monthly bills by $5.10 (3.8 percent) and larger 

industrial customer monthly bills by $17,400 (6.4 percent). (We believe that the commenter was 

referring to SCR, although the commenter asserted that BART should be combustion controls.) 

The commenter also indicated that installing SCR and baghouses on Units 1–3 would increase 

the cost of electricity production on a $/MWh basis by more than 50 percent which, in 

conjunction with other market and regulatory uncertainties, may make the units uneconomic. The 

commenter further stated that retrofitting SCR on Units 4 and 5 would raise the cost of 

generation at those units by more than 25 percent, and there is a reasonable possibility that such a 

cost increase would threaten the economic viability of those units. 

 Another one of the owners of FCPP Units 4 and 5 (0168), who also has ownership 

interest in NGS and SJGS, stated that if SCR were determined to be BART for all these power 

plants, the commenter would be facing approximately $322 million in capital expenses over the 

next 5 years. The commenter indicated that such expenditures would increase the commenter’s 

rates by 4 to 6 percent, which would be significant in its market area of Tucson because its 

economy is fragile and has endured an 8 percent rate increase (not adjusted for inflation) since 

1992. The commenter stated that the Tucson area is struggling through difficult economic 

circumstances, and significantly higher electricity rates will place an enormous economic 

hardship on its customers and make any recovery more difficult for the community. 

Response: 

 EPA agrees with the first commenter (0112) that based upon our analysis the potential 

increase to APS rate payers as a result of SCR is expected to be less than 5 percent. 

 EPA cannot compare the estimated residential and industrial rate increase claimed by 

the second and third commenters with our analysis because the commenters did not provide 

information for us to evaluate their conclusions. 

 However, EPA notes that the installation of baghouses on Units 1-3 is no longer relevant 

because EPA has determined that it is not necessary or appropriate at this time to set new PM 

limits for Units 1 – 3. This is because EPA is finalizing this BART determination to allow APS to 

comply with either BART or the BART alternative, which involves the optional closure of Units 1 

– 3, and as a backstop, if APS does not close Units 1 – 3, the MATS rule, which sets a filterable 

PM emission limit of 0.03 lb/MMBtu, is now final and would apply to those units. 

 While the commenter’s suggested increase in the cost of power from Units 4 and 5 as a 

result of SCR (25% increase) is reasonably consistent with the results of the EPA analysis (22%) 

with respect to the power cost impact of SCR on all five FCPP units, it must be noted that the 

original EPA analysis did not evaluate SCR on Units 4 and 5 exclusively. Without evaluating the 
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modeling conducted by the commenter, it is not possible to compare the commenter’s modeling 

results with the model from the EPA’s proposed BART determination. 

 In order to provide a more complete response to the commenter’s point regarding costs 

specific to Units 4 and 5, however, EPA re-ran the same model used in our proposed BART 

determination to assess the impact of SCR for only Units 4 and 5.4F

45 The model assumes that 

Units 1-3 are closed, and as such, it produces no power and does not impact total plant 

economics. This iteration of the model reported a 25-year net present value incremental cost of 

14% for only Units 4 and 5. The difference in the EPA model between the 22% cost increase for 

all five units versus the 14% cost increase for only Units 4 and 5 is due to the fact that while the 

estimated capital costs and incremental operating costs for Units 1-3 account for 36 percent and 

39 percent of the total modeled incremental capital and operating cost respectively for the entire 

plant, those three units account for only 27 percent of installed plant capacity. Thus, the “per 

unit” cost associated with Units 1-3 is significantly higher than Units 4 and 5. 

Comment:

 One of the owners of FCPP (0174) noted that based on the analysis performed in support 

of EPA’s BART proposal for FCPP, EPA concluded that even if SCR is determined to be BART, 

the cost of generating power at FCPP would be less than the cost of purchasing power on the 

wholesale market, and that therefore a requirement to install SCR would not lead to closure of 

the plant. The commenter expressed the following concerns with the analysis: 

 The analysis focuses on APS and Southern California Edison, and not on the other 

owners of FCPP. The use of “return on rate” based methodology would not apply to 

organizations of the commenter’s type (public power) because it is not an investor-owned 

utility. 

 Each of the FCPP owners has unique costs related to the plant and their own generation, 

transmission, and distribution costs. Therefore there are a multitude of company-specific 

factors that would impact a given owner’s decision to invest additional capital in the plant 

for emission controls, none of which were specifically factored into the EPA analysis. 

 The EPA analysis did not attempt to determine the impact of different assumptions, such 

as an uncertainty with the future price of coal, on the conclusions of the economic 

analysis. The “small difference” that EPA estimates between FCPP with SCR installed 

and cost of purchasing power to replace FCPP generation suggests that a small change in 

an underlying assumption (return on rate, coal price, carbon pricing, etc.) could result in 

economic results that show SCR to be a higher cost option than purchasing power. 

 The EPA’s analysis did not examine different “payback periods,” but instead relied on a 

payback period of 25 years, which may be inappropriate because the useful life of the 

plant is far from certain. The remaining useful life of FCPP is dependent on many other 

factors – both political and regulatory in nature (citing comments by Commenter 

0176/0177; see Section 6). Shorter payback periods should have been analyzed to 

determine the effect of this assumption on the conclusions of the analysis because a 

 

45 See “Analysis of UNITS 4 & 5 SCR ONLY.xlsx” in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

reduced payback period could result in FCPP power (with SCR costs included) exceeding 

wholesale market costs. 

 The EPA should recognize that there is a real risk that one or more owners may decide 

not to invest in SCRs, which would force the shutdown of FCPP unless another owner 

could be found in a timely manner. The shutdown of FCPP would have significant 

adverse economic consequences on the Navajo Nation. 

 If EPA were to consider these economic challenges and uncertainties in conjunction with 

the other BART statutory factors, EPA would conclude that combustion control should 

be determined to be BART for FCPP because it provides a cost-effective means to 

achieve visibility improvement in the first planning period. EPA can evaluate whether 

additional NOx reductions are warranted in subsequent planning periods, which is 

consistent with the RHR and would provide the FCPP owners with time to address the 

uncertainties facing the plant before making significant capital investment for SCR. 

Response:

 EPA provided an analysis for our BART determination to assess whether the cost to 

produce electricity at FCPP would remain competitive compared to the market costs to purchase 

power if SCR were required on Units 1 – 5 at FCPP. 

The commenter is correct that EPA calculated rate impacts for only two of the four 

investor-owned utilities that own FCPP and excluded others, including an owner that operates 

as a publicly-owned utility. The analysis estimating the increase in electricity generation costs is 

applicable to all owners of FCPP, and the rate impact analysis provided in the model was not 

intended to capture the rate impacts of all owners. APS and Southern California Edison (SCE) 

were selected because their combined ownership shares account for nearly 75% of the plant’s 

output. In addition to our expectation that the utilities with the largest ownership share in FCPP 

would generally experience greater ratepayer impacts from capital expenditure projects like 

SCR installation, we also assumed that ratepayers of investor-owned utilities would likely 

experience larger economic impacts than public power customers due to the fundamental 

difference between their respective approaches to setting rates. Specifically, rates for public 

power utilities, in contrast to investor-owned utilities, do not include recovery for a margin 

above cost allowed as part of a regulated rate of return. Thus, all other variables being equal, 

one would expect the same capital investment to result in a larger rate impact for customers of 

investor-owned utilities than for customers of public power entities.Therefore, EPA continues to 

believe that our analysis of ratepayer impacts for only APS and SCR are appropriately 

conservative to demonstrate worst-case impacts to ratepayers. 

 EPA agrees with the commenter that there are many company-specific factors and a wide 

range of economic assumptions that would impact a given owner’s decision to invest in SCR. 

Although many of those factors were outside the focus of the modeling because they were either 

unrelated to BART or were related to regulatory uncertainties in the future, Energy Strategies 

included a qualitative discussion in Appendix B to the TSD regarding decision variables that 

EPA assumed each owner must consider before making capital expenditures. Additionally, EPA 
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notes that the use of low, medium and high future projected prices for the Palo Verde Index 

represents a sensitivity analysis for the market comparison. 

With respect to the “payback period” referenced by the commenter, the analysis for the 

proposed BART determination did not identify “payback periods.” Rather, the commenter 

appears to be referring to the 25-year period utilized for the discounted cash flow calculations 

within the model. EPA does not disagree with the commenter’s stated concern that shorter plant 

life, and thus shorter discounting periods, would yield different economic results. However, EPA 

disagrees with commenters that a shorter useful life should be considered in the analysis unless 

there is an enforceable obligation on APS to cease operations on a given date. 

Comment:

 One private citizen commenter (0180) provided comments on EPA’s economic analysis, 

which are summarized below: 

 The report of the economic analysis appears to be inconsistent in that in numerous places 

(e.g., page 5) it shows the business as usual (BAU) and LNB cases to be less expensive 

than all other cases, while on page 20 it states that the 25-year non-discounted costs for 

the SCR case were lower than both the BAU and LNB/OFA cases. 

 The market cases do not incorporate the impact of removing FCPP generation from the 

marketplace. Specifically, the shutdown of FCPP would, first, result in a lack of 

generation capacity in the market and affect the market price and, second, as the lack of 

base loaded generation was made up by natural gas fired combined cycle plants that are 

currently run to meet peak load, the increased need for natural gas may strain pipeline 

capacity and cause the price of natural gas to rise. 

 The report of the analysis states that, “although new capital expense has not been 

considered in the BAU case, if it were and especially if the addition were to occur early 

in the time horizon envisioned in the economic model, the cost of the BAU case could 

increase materially with respect to other cases.” This statement is invalid, as new capital 

deployment would be required in any case regardless of whether SCR or LNB are 

installed. 

 The report says on page 8, “It is reasonable to assume that the parties that rely on the 

continued operations of the mines and plants could be reasonably expected to make an 

economic decision and negotiate new leases that allow the plant to operate 

economically.” The commenter states that EPA seems to be unaware of the Mohave 

Generating Station, which serves as a counter-example to the statement in the report. 

Response:

 In the first bullet above, the commenter correctly identifies a discrepancy with the 

summary of the analysis. The impact report, included as Appendix B to the TSD45F

46 for the 

 

46 See Document titled “TSD Appendix B: Economic Analysis (EPA) of Proposed BART Determination on 

FCPP_Final Report. EPA-R09-OAR-2010-0683-0005. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

proposed rulemaking, on page 20 incorrectly states that the incremental cost in the SCR case is 

lower than the LNB case, as well as all market cases. On page 20, under “Discussion of 

Modeling Results,” the final bullet should read, “As modeled, the SCR Case over 25-years 

returns a lower incremental, non-discounted cost per megawatt-hour than all market cases”. 

This incorrect statement in the summary of the impact report regarding incremental cost 

comparison between SCR and LNB was a summary statement written by Energy Strategies but 

was not directly relied upon by EPA in our TSD. 

 The commenter correctly points out that the analysis discussed in the report does not 

include the potential impacts, and associated Market Case costs, that could result in reaction to 

a shutdown of all units FCPP. The commenter suggests that a more complete approach to 

modeling the cost of the Market Case would include such variables as the cost of new base 

loaded gas-fired generation (in the marketplace or perhaps owned by the current FCPP owners) 

and the potential for such new gas generation to influence commodity natural gas pricing in the 

region. The result of including these additional costs in the Market Cases would be to increase 

the estimated cost to purchase power on the wholesale market. Thus, the Market Cases presented 

in the analysis that accompanied EPA’s TSD were conservatively low, and inclusion of the 

market-related impacts, as suggested by the commenter, would result in higher market values, 

thereby providing a larger “competitive cushion” for the installation of SCR at FCPP. 

 As noted by the commenter in the third bullet above, the report incorrectly states, 

“although new capital expense has not been considered in the BAU case, if it were and 

especially if the addition were to occur early in the time horizon envisioned in the model, the cost 

of the BAU case could increase materially with respect to other cases.” The statement should 

read, “...the cost of the BAU case could increase materially with respect to the Market Cases.” 

As the BAU case may or may not increase in cost due to future business as usual-related capital 

investment, the commenter is correct in suggesting that all retrofit cases (LNB and SCR) would 

have the same relative impact due to BAU investments. The potential for BAU investments to 

alter the comparative economics in the model are thus in relation to the Market Cases. However, 

commenters have not provided information to suggest that new capital expenses should be 

modeled in the BAU case, therefore, the commenter’s correction is well taken, but does not affect 

the validity of the modeling conducted for the TSD. 

Contrary to the commenter’s statement in the fourth bullet above, EPA is aware of the 

regulatory and investment decision history surrounding the closure of the Mohave Generating 

Station. (For a detailed discussion related to the shutdown of Mohave Generating Station, 

please see our response above in Section 4.1.1). 

Comment:

 Three private citizens (0119, 0128, 0201) disagreed with industry that costs are too high. 

One of the commenters stated that the reform measures are both reasonable and economically 

feasible. Another private citizen (0140) stated that APS should be responsible for the clean-up. 

Response:
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

We agree with the commenters that SCR is a reasonable, cost effective control technology 

for reducing emissions of NOx from FCPP. 

Comment:

 One private citizen (0163/0164/0216) commented that the Navajo Nation previously 

stated that both the power plant and the Navajo Mine would close if SCR is required. The 

commenter took issue, noting that EPA indicated that FCPP electricity cost will still be market 

competitive with SCR. The commenter stated that the economic analysis (and other analyses) 

incorrectly used sub-bituminous coal heating values, rather than bituminous coal values, 

resulting in a “flawed and incorrect way to improve the health and visibility to the Four Corners 

area and Class I areas.” The commenter also contended that the EPA’s analysis stated that FCPP 

uses bituminous coal, although the APS BART analysis was based on sub-bituminous coal. 

Response:

EPA disagrees with this comment. With respect to the modeling of incremental costs 

associated with those cases where FCPP operations continue (i.e. BAU, LNB/OFA, and SCR), 

the type of coal burned and associated heat content were not germane to the analysis. The 

underlying costs of operation, including fuel quantity and heat content, as they flow through the 

summary economic statistics, are taken as-is from APS filings to the Federal Energy Regulatory 

Commission and were not modified with respect to the type of coal consumed. 

This comment regarding coal classification is addressed further in Section 10. 

4.2 19BComments on Energy and Non-Air Quality Environmental Impacts 

Comment:

 One private citizen (0180) stated that no consideration was given to the effect of 

removing FCPP generation from the grid. According to the commenter, the events of February 2, 

2011 show there are times when gas-fired generation cannot replace coal-fired generation 

because there is not enough gas transportation capacity. 

Response:

EPA disagrees with the commenter that we should consider the effect of removing FCPP 

generation from the grid. As stated elsewhere in this document, it is not EPA’s intention, nor is it 

within our regulatory authority, to require closure or require a redefinition of the source, in 

order to comply with the BART requirement of the RHR. EPA notes that in our proposed BART 

determination EPA included an analysis to determine whether the installation and operation of 

SCR would increase the cost of power from FCPP such that it would no longer be competitive to 

the forecasted price of power in the western wholesale market. Thus, based on this analysis, EPA 
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determined that the installation and operation of SCR on Units 1 – 5 at FCPP should not force 

FCPP to close, thus the comment that EPA consider the effect of removing FCPP generation 

from the grid is not relevant. Furthermore, the owners of FCPP did not provide evidence that the 

installation of SCR would cause FCPP to close. 

EPA also notes that APS proposed to purchase the shares of Units 4 and 5 currently 

owned by Southern California Edison in order close Units 1 – 3 (of which APS is sole owner) 

and install SCR on Units 4 and 5 as an alternative to BART. APS is currently seeking approval 

from the Arizona Corporation Commission, the California Public Utilities Commission, and the 

Federal Energy Regulatory Commission to implement its proposal46F

47. Decisions on investing in 

pollution controls or shutting down units are made by the owners in conjunction with their 

oversight boards or public utility commissions. 

Comment: 

 Thirty-seven private citizens (0085, 0086, 0088, 0089, 0091, 0122, 0124, 0125, 0127, 

0128, 0135, 0136, 0137, 0140, 0147, 0148, 0149, 0151, 0153, 0154, 0155, 0156, 0158, 0159, 

0160, 0161, 0162, 0166, 0170, 0171, 0181, 0188, 0197, 0199, 0208, 0211, 0213) and two private 

citizens who submitted written comments at a public hearing (0190) stated that FCPP causes 

significant threats to public health due to its effects on air quality. Another private citizen (0186) 

implied the same concern, and is unwilling to trade a healthy environment for jobs or economic 

growth. In contrast, one private citizen who submitted a written comment at a public hearing 

(0190) questioned whether the haze contributes to health issues in the region. 

 A number of environmental and public interest advocacy groups (0143, 0182, 0183, 

0190, 0194) provided comments on health and ecosystem impacts of the pollutants emitted by 

FCPP. These comments are summarized below. 

 One group of environmental advocacy groups (0182) stated that visibility-causing 

pollutants have far-reaching impacts on local economies, human health, and the well-being of 

waterways, soils, plants, and wildlife – in other words, an entire population and ecosystems. The 

commenter asserted that decreasing these pollutants will benefit all of these important areas of 

concern; failing to do so will cause or continue adverse impacts. The commenter’s thoughts on 

the economic impacts of these pollutants are summarized in Section 4.1.1 above. 

 Regarding health impacts, the commenter (0182) noted that the same pollutants that 

contribute to visibility impairment also harm public health – the fine particulates that cause 

regional haze can cause decreased lung function, aggravate asthma, and premature death in 

people with heart or lung disease. The commenter added that NOx and volatile organic 

compounds (VOCs) can also be precursors to ground-level ozone, or smog, which is associated 

with respiratory diseases, asthma attacks, and decreased lung function. According to the 

commenter, ozone concentrations in parks in the Four Corners region approach the current health 

standards, and likely violate anticipated lower standards. The commenter stated that ozone levels 

 

47 On March 22, 2012, the California Public Utilities Commission approved the sale of SCE’s share of FCPP to 

APS. On April 18, 2012, the Arizona Corporation Commission approved APS’s purchase of SCE’s share of FCPP. 
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in many parts of New Mexico, Colorado, and Utah are already in the range of ozone levels 

deemed to be harmful to human health. 

 The commenter (0182) asserted that according to EPA figures, the total annual cost of 

implementing the RHR will range from $1.4 – 1.5 billion, but in 2015 enforcement of the RHR 

will provide health benefits valued at $8.4 – $9.8 billion annually – preventing 1,600 premature 

deaths, 2,200 non-fatal heart attacks, 960 hospital admissions, and over 1 million lost school and 

work days every year. The commenter noted that although the RHR was designed to provide 

redress for visibility impairment, the BART Guidelines expressly provide for the consideration 

of non-air quality environmental impacts, which includes the environmental impact on human 

health. 

 The same commenter (0182) also contended that consideration of non-air quality impacts 

extends to impacts on wildlife and habitat as well as natural and cultural heritage. According to 

the commenter, the same haze-causing emissions also harm terrestrial and aquatic plants and 

animals, soil health, and water bodies by contributing to acid rain, ozone formation, and nitrogen 

deposition. The commenter cited EPA sources that allegedly indicate that nitrogen deposition in 

the Rocky Mountain National Park is at twice the critical load that the ecosystem can tolerate; 

that acid rain acidifies water bodies, contributes to tree damage at high altitudes, and accelerates 

decay of irreplaceable buildings, statues, and sculptures that are part of our nation’s cultural 

heritage; and that ground-level ozone interferes with the ability of sensitive plants to produce and 

store food, damages the leaves of trees and other plants, and reduces forest growth and crop 

yields. 

 With these health and environmental considerations in mind, in addition to visibility and 

economic considerations discussed in other sections of this document, the commenter (0182) 

urged the EPA to finalize more stringent BART determinations for FCPP. The commenter’s 

suggestions for BART also are discussed in other sections of this document. 

 An environmental advocacy group (0183) made similar comments regarding health and 

ecosystem impacts. The commenter noted that FCPP is a very large emitter of NOx, which 

contributes to ozone formation. According to the commenter, the area around FCPP is subject to 

atmospheric thermal inversions in the winter months, and some counties have experiencing 

ozone concentrations in excess of the EPA’s proposed range for the 8-hour ozone NAAQS. The 

commenter cited the incidence of asthma and other respiratory diseases and noted that such 

sensitive populations are particularly susceptible to the effects of ozone. In addition, the 

commenter pointed out that ozone causes injury and damage to plants. The commenter added 

that NOx emissions contribute to nitrate deposition which can disrupt natural systems. Based on 

these points, the commenter argued that EPA must consider reducing the NOx limit in both the 

proposed BART determination and the supplemental proposal. 

 This commenter (0183) stated that FCPP’s PM emission rate is one of the top 10 point 

sources of PM in the American West. The commenter contended that EPA has stated that 

airborne PM is linked to serious health effects, even at concentrations currently allowed by the 

NAAQS.47F

48 The commenter also stated that black carbon (a type of PM) is the most powerful 

 

48 citing http://www.epa.gov/nheerl/research/pm/
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

climate forcing agent known, and that it has recently been determined to be the second or third 

largest climate forcing agent. The commenter noted approvingly that the supplemental proposal 

would provide additional PM reductions through the retirement of Units 1 – 3. 

 The commenter (0183) noted that FCPP is a significant source of mercury emissions and 

provided information on the health and ecosystem effects of mercury, as well as on the 

deposition of mercury and the levels of mercury found in the Four Corners area. In addition, the 

commenter stated that FCPP emits more than 16 million tons per year (tpy) of CO2, and that such 

emissions contribute significantly to climate change which is likely to result in increasing 

temperatures and increase drought in the Southwest. The commenter noted with approval that the 

supplemental proposal would reduce emissions of both mercury and CO2. 

 One public interest advocacy group (0143) also discussed the health impacts associated 

with emissions from FCPP. The commenter indicated that the emission reductions associated 

with the supplemental proposal would work toward improving health and environmental justice 

for people in the Four Corners area, including a large Native American population. The 

commenter stated that health care costs resulting from coal-fired power plant pollution are 

significant for the local economy, quoting figures from a study by Abt Associates estimating the 

health impacts and associated costs in the area. The commenter also indicated that prevailing 

winds carry pollutants from FCPP to La Plata County, CO, and that early findings from a new 

mercury-monitoring project indicate that a significant amount of mercury arrives under dry 

condition via wind at two monitors in southwest Colorado. Although the sources of the mercury 

have not been verified, the commenter noted that coal-fired power plants are known to be a 

major contributor of mercury to the atmosphere and that FCPP is reported to release more than 

1,400 pounds of mercury per year. The commenter stated that known pollutants from coal-fired 

power plants contribute negatively to health, vegetation, and soil impacts. The commenter also 

pointed out that NOx emissions (of which FCPP is a large source) along with the Four Corners’ 

abundant sunshine create ground-level ozone and that if EPA lowers the ozone NAAQS, La 

Plata County could be in nonattainment. While praising EPA’s supplemental proposal as a good 

first step, the commenter urged EPA to expand the region’s reliance on lower carbon and water 

efficient energy sources, adding that federal programs are available to assist tribes to evaluate 

and install renewable sources of energy. 

 Another environmental advocacy group (0194) also quoted figures from the Abt 

Associates study on the health impacts of emissions from power plants in the region. The 

commenter supported the proposed measures to reduce NOx emissions, but noted that the 

proposal did not address GHGs. The commenter encouraged EPA to take timely action to help 

transition energy production away from fossil fuels to clean energy sources, adding that New 

Mexico has abundant solar, wind, and geothermal energy resources. 

 One environmental advocacy group that spoke at a public hearing also submitted written 

material (0190) asking EPA and APS to consider what they would do if FCPP was located in 

their communities. The commenter supported a transition to renewable energy that will keep jobs 

in the area and clean up the air in the Four Corners region. The commenter made the following 

points: 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 A formal Health Impact Assessment should be conducted by independent experts before 

EPA’s final decision to answer such questions as whether shutting down Units 1 – 3 is 

sufficient to protect local health, and what health impacts would result from delaying 

pollution controls on Units 4 and 5 until 2018. 

 The acceptable limit of pollution from FCPP is no more than would be allowed in the 

wealthiest, most privileged communities in the United States; that is, the decision should 

be made considering health equity. 

 The spiritual aspect of the air, the earth, and water of Mother Earth must be taken into 

consideration because to the Navajo people, clean air, water, and land are not 

commodities to be bargained with, but are sacred elements of life to be protected at all 

costs. 

Response:

EPA agrees that there are potential benefits to human health and the environment from 

reducing the emissions of NOx. Quantifying health benefits is not within the scope of the BART 

five factor analysis required under the Clean Air Act (§169A(g)), which specifies that in 

determining BART, the State (or Administrator) “shall take into consideration the costs of 

compliance, the energy and nonair quality environmental impacts of compliance, any existing 

pollution control technology in use at the source, the remaining useful life of the source, and the 

degree of improvement in visibility which may reasonably be anticipated to result from the use of 

such technology”. The BART Guidelines provides additional information on how to analyze 

“non-air quality environmental impacts, and focuses on adverse environmental impacts 

associated with control technologies, i.e., generation of solid or hazardous wastes and 

discharges of polluted water, that have the potential to affect the selection or elimination of a 

control alternative (see 70 FR at 39169). Thus, although the BART Guidelines do state that 

relative environmental impacts (both positive and negative) of alternatives can be compared with 

each other, they state that “if you propose to adopt the most stringent alternative, then it is not 

necessary to perform this analysis of environmental impacts for the entire list of technologies”. 

EPA agrees with commenters that controlling pollutant emissions may have co-benefits for 

reducing ozone production and acid deposition, EPA does not interpret the BART Guidelines to 

require quantification of human health or environmental co-benefits in determining BART, 

particularly if the most stringent BART option is finalized. Similarly, EPA does not interpret the 

BART guidelines to require human health or environmental assessments of alternative 

compliance strategies as long as we have determined that the alternative strategy achieves better 

progress towards the national visibility goal. 

 

Comment:

 The Navajo Nation (0223) recognized that human exposure to environmental hazards is 

an important factor in assessing impacts of FCPP (and NGS and SJGS) and for framing a rule to 

meet the regional haze requirements of the CAA, and anticipated that within each 

implementation phase of the RHR there will be integration of health assessments and studies 

which are interrelated to the goal of promoting a strong economy and healthy environment and 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

are vital to the sovereignty of the Navajo Nation. The commenter encouraged EPA to pursue 

health studies in collaboration with the Navajo Nation to study local risks associated with 

exposure to criteria pollutants, indoor air pollutants, and other contributing air pollutants, from 

which improved public health and effective rulemakings under the CAA may be achieved. 

 In addition, the commenter (0223) noted that EPA has stated that BART determinations 

will improve public health in addition to improving visibility in the region, and the commenter 

anticipated that EPA will take the same stance in the forthcoming NGS proposed rule. On that 

issue the commenter provided the following comments: 

 Very little public health data is available in the Four Comers region and on the Navajo 

and Hopi reservations to establish a meaningful public health baseline. 

 A meaningful public health baseline is critical to measuring the impacts to public health 

for any BART option, or any other pending or future EPA rule making. 

 The available research literature (Morris 1990, Robin 1995, Bunnel 2010) all conclude 

that poor indoor air quality is a significant risk factor impacting the public health of 

Navajos, especially those Navajos who heat their homes with non-optimal heating 

devices. 

 The EPA should generate and collect more public health research/data that characterizes 

the actual public health impacts attributed to the emissions from the FCPP and NGS; and 

actual public health impacts attributed to other emission sources. 

Response:

Assessing human exposure and quantifying health benefits are outside the scope of the 

requirements of the Regional Haze Rule. EPA sets National Ambient Air Quality Standards 

(NAAQS) to establish levels of air quality that are protective of public health, including the 

health of sensitive populations, for a number of pollutants including particulate matter. These 

"sensitive" populations include asthmatics, children, and the elderly. At this time the Navajo 

Nation is not identified as out of attainment with any of the NAAQS. However, EPA recognizes 

that there are significant concerns about risk and exposure to air pollutants on the Navajo 

Nation and EPA will continue discussions with the Navajo Nation and will involve other federal 

agencies, as appropriate, to help address these concerns. 

Comment:

 The Navajo Nation (0223) stated that EPA has failed to consider the non-air impacts 

associated with transportation and storage of ammonia for the proposed SCR technology. The 

commenter alleged that EPA took a “safe approach” by hypothesizing the use of urea as the SCR 

reagent as proposed by APS, and considered only the impacts to air quality from increased truck 

traffic in the area from transportation of urea (not the risks associated with accidental releases 

and spills). The commenter also noted that EPA did not assess the potential risks associated with 

the transportation, storage, handling, and accidental release of anhydrous ammonia or aqueous 

ammonia, which are typical reagents used in SCR. The commenter asserted that because 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

anhydrous ammonia and aqueous ammonia above 20 percent are considered acutely hazardous 

and accidental releases are reportable to local, state, and federal agencies, EPA should conduct 

an extensive study of the risks associated with the use of these potential SCR reagents based on 

the size of the plant and its location both by proximity to Navajo communities and residents and 

to the nearest feasible rail line. The commenter indicated that transport and storage of anhydrous 

ammonia would require development of a Risk Management Plan and Process Safety 

Management plan by both the plant and the transfer facility at the rail line. The commenter added 

that trucking of ammonia would be across Navajo land, potentially putting Navajo communities 

at risk, and would generate air emissions of NOx, CO, VOC, and PM10. The commenter 

concluded that these risks and associated costs should have been analyzed in EPA’s BART 

analysis as part of factor two, considering EPA’s trust responsibility to the Navajo People. 

Response:

EPA disagrees with the comment that we chose the “safe approach” by analyzing for the 

use of urea instead of anhydrous ammonia. APS has consistently indicated that it would use urea 

if SCR were required as BART, providing estimated costs for urea as the reagent and for urea 

storage and handling equipment. Our approach was appropriate in light of the plans submitted 

by the facility. Accordingly, the study did not evaluate any risks associated with spills or releases 

of urea because urea is not classified as a hazardous or toxic substance under any federal 

environmental program. Such spills or releases are not reportable incidents under emergency 

management requirements. 

EPA further notes that the results of a study to evaluate the potential risks associated 

with increased emissions to transport urea to FCPP was included in the TSD for the proposed 

rulemaking as Appendix A and can be found in the docket for the rulemaking, Document No. 

EPA-R09-OAR-2010-0683-0004. This study included an analysis of the estimated increase in air 

pollutant emissions (both criteria pollutants and hazardous air pollutants) resulting from the 

increased truck traffic necessary to transport urea to FCPP for use by the SCR system. EPA also 

summarized these in the TSD for our proposed rulemaking. 

 

 Based on the study included as Appendix A to the TSD, EPA determined that the adverse 

impacts associated with the use of SCR at FCPP, using urea as planned by the facility, are 

extremely low. This is particularly true in light of the very large reductions in emissions of NOx

(over 33,000 tpy) and concomitant improvements in air quality that would be achieved. In 

addition, it should be noted that under the supplemental proposal, NOx emissions will be reduced 

by a greater amount, and less urea will have to be transported to the facility due to the closure of 

Units 1-3. 

 Although EPA has concluded, based on indications from APS that it intends to use urea 

for SCR, that it is most appropriate to consider the impacts of urea and not anhydrous ammonia, 

we note that ammonia is one of the most used chemical commodities in the United States, with 

large amounts transported annually by train, truck, and barge. Most ammonia is used as a 

fertilizer, including anhydrous ammonia for direct application.48F

49 

 

49 See http://minerals.usgs.gov/minerals/pubs/commodity/nitrogen/mcs-2011-nitro.pdf. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 If APS instead chose to transport and store anhydrous ammonia rather than urea, the 

commenter is correct that the transport and storage of anhydrous ammonia would require 

development of a Risk Management Plan and Process Safety Management plan by both the 

power plant and the transfer facility at the rail line. For the transfer facility, these are normal 

costs of doing business and the associated costs would be included in the cost of anhydrous 

ammonia as delivered to the facility. Similarly, the cost to the facility is a known cost of using 

anhydrous ammonia which must be weighed in the decision of which SCR reagent to use at any 

given facility. In any case, the costs of complying with these programs would likely be a small 

fraction of the total costs related to the use of SCR at a facility.

Comment: 

 

One private citizen (0163/0164/0216) submitted a study of coal combustion and 

respiratory health near Shiprock, NM which primarily addresses the impact on indoor air of coal 

combustion inside homes for warmth. The commenter cited information in the report to support 

his assertion that at a site located 2 km from FCPP, the concentration of trace metals in the 

outdoor air was equivalent to the concentration inside where there was a broken stove leaking 

coal exhaust. According to the commenter, people living 2 km around the power plant might 

have to be evacuated because outdoor air is equivalent to inside a home with a leaking stove. 

 Two private citizens (0149, 0158) expressed concern about open storage of fly ash at 

FCPP, which they stated contain toxic heavy metals. 

Response:

Any near-plant exposure to trace metals as particulate matter is more likely to be a result 

of fugitive emissions of fly ash or coal dust from power plants than from exposure to the stack 

exhaust. The stacks at FCPP release the exhaust at a high elevation for the purpose of 

preventing excessive concentration of pollutants in the immediate vicinity of the plant.49F

50 Trace 

constituents of coal can become emitted as HAPs when the coal is combusted; therefore the dust 

generated from handling coal should also be expected to contain trace metals. In the stack 

exhaust, many HAPs exist as, or are associated with, particulate matter (PM). EPA has recently 

promulgated a final rule regulating HAPs from coal fired electric generating units in the MATS 

rule. FCPP is required to comply with the MATS rule. The MATS rule sets emission limits for 

PM from units like those operating at FCPP. In general, PM and HAPs that are removed from 

the exhaust by a control device become fly ash, thus, it is reasonable to expect fly ash to also 

contain HAPs. Many coal fired utilities need to upgrade their PM controls to remove the HAPs 

from the exhaust gas to meet the MATS emission limits. However, it is likely that the existing 

baghouses on Units 4 and 5 already provide adequate emissions control to meet the PM 

concentration limit in the MATS rule. Because the baghouse and scrubbers are removing HAPs 

from the exhaust gas from Units 4 and 5, we would anticipate that HAPs will end up in the fly 

ash and scrubber waste at FCPP. 

 

50 EPA Good Engineering Practice (GEP) http://www.epa.gov/scram001/guidance/guide/gep.pdf
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Although the windblown fly ash and coal dust from FCPP are likely to contain HAPs, 

EPA does not have any data regarding the specific concentrations of HAPs around FCPP. The 

concentration of the HAPs indoors from a leaking coal fired stove would likely be at a 

significantly higher concentration than in any windblown ash or dust. The emissions from a 

leaking coal fired stove are entirely uncontrolled while more than 99% of the PM in FCPP stack 

exhaust is removed by the baghouses for Units 4 and 5. Further, the HAPs emissions from a 

leaking indoor stove would likely be substantially more concentrated than the stack emissions 

from FCPP because the HAPS are emitted into a relatively small volume of air relative to the 

stack emissions from FCPP. 

To address the fly ash and coal dust emissions at FCPP, EPA promulgated a FIP in May 

2007 that required FCPP to ensure that opacity from its fly ash and coal dust material handling 

and storage operations never exceeded 20% opacity. Imposing an opacity limit and requiring a 

dust control plan are reasonable approaches for assuring adequate control of these emissions. 

Although EPA has the authority to impose such a requirement under the TAR as necessary or 

appropriate, EPA’s 2007 FIP did not provide an adequate justification that the opacity limit was 

necessary or appropriate. When APS petitioned for judicial review of this opacity limit 

provision, EPA determined that we had not provided an adequate justification for the provision. 

Therefore, EPA requested the 10th Circuit Court of Appeals to remand the 20% opacity limit for 

material handling operations to EPA for a fuller explanation and justification. At the time, EPA 

indicated that it would provide this additional basis for the regulation in a later rulemaking.

In this rule, EPA is now finalizing a requirement for FCPP to ensure that opacity from its 

material handling operations does not exceed 20%. This limitation is necessary or appropriate 

to limit PM emissions from fly ash and coal dust material handling and storage operations. The 

necessity of limiting these PM emissions is to protect the NAAQS, may also provide a surrogate 

for limiting HAPs. EPA’s action to protect the NAAQS by limiting PM emissions, enforceable 

through establishing a 20% opacity limitation on fly ash and coal handling and storage 

operations, is widely supported by comments on our proposal. Moreover, such a limitation is 

consistent with requirements for dust-generating activities in neighboring Arizona.50F

51 For more 

details on EPA’s justification for including an opacity limit see our response in Section 10. 

Comment: 

 One public advocacy group (0112) stated that EPA should strongly assert to the 

management of FCPP that they have a responsibility to improve on public health effects as well 

as visibility impacts. According to the commenter, the operator of FCPP has been asserting at 

public meetings and with the media that the EPA proposals for FCPP are only about visibility 

and have no relationship to public health. The commenter stated that this is a misleading 

assertion by the company. 

Response:

 

51 For example, see Maricopa County Air Quality Department Rule 310: Fugitive Dust from Dust-Generating 

Operations that sets an opacity limit of 20%. See 

http://www.maricopa.gov/aq/divisions/planning_analysis/AdoptedRules.aspx 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

As previously mentioned, the RHR is meant to address visibility impacts at nearby 

National Parks and Wilderness areas. However, reductions in NOx and PM emissions from 

FCPP can also improve air quality and reduce health impacts. 

Comment: 

 One public advocacy group (0112) disagreed with the statement in the TSD that impacts 

to water quality will not be considered because FCPP is not a zero water pollutant discharge site. 

The commenter indicated that FCPP holds a 1993 NPDES Permit No. NM0000019, which is still 

in force based on an EPA Region 9 Administrative Extension granted on or about April 6, 2006. 

The commenter asserted, therefore, that it is imperative to consider water quality impacts. 

 The commenter (0112) added that EPA has missed an opportunity to reduce the waste of 

13.3 million gallons of water per day, which is currently used by FCPP for cooling steam 

condensers and not returned to the San Juan River system. The commenter stated that the use of 

closed system dry cooling towers at FCPP would greatly reduce water use. According to the 

commenter, the withdrawal of such large quantities of water from tributaries of the Colorado 

River has contributed to the need for large federal salt removal expenditures costing many 

millions of dollars from 1976 to the present. 

Response:

EPA disagrees with the commenter that it is imperative to consider water quality impacts 

of BART controls for NOx. In our TSD, under Factor 3 – Energy and non-air quality 

environmental impacts, we explain that APS did not consider impacts to water quality in its 

analysis because FCPP has not been identified as a facility that is not allowed to discharge 

water (i.e., as stated by the commenter and in our TSD, FCPP is not a zero water pollutant 

discharge site). In other words, FCPP does discharge water, as evidenced by its Clean Water 

Act NPDES permit that is currently under an administrative extension that regulates its 

discharges to Morgan Lake and its cooling water intake. As such, water quality impacts related 

to the cooling system at FCPP is regulated by EPA under a different authority (Clean Water Act) 

than the Regional Haze and BART Requirements (Clean Air Act). The BART Guidelines cite 

several examples of a non-air quality environmental impact, e.g., water availability may affect 

feasibility and cost of wet scrubbers, or wet scrubber (for controlling SO2) may affect water 

quality and land use. The installation and operation of SCR would not significantly affect water 

quality or water discharges from FCPP. 

This rule is not requiring increased water consumption associated with SO2 control 

because EPA found that the SO2 controls from the previous rulemaking in 2007 (72 FR 25698, 

May 7, 2007) are adequate. If EPA was requiring scrubbers that increased water consumption it 

would be considered under the non-air quality related environmental impacts. 

 EPA also disagrees with the commenter that EPA has missed an opportunity to reduce 

water use at FCPP for its cooling system. EPA does not have authority under the RHR to require 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

retrofit of its cooling water system. EPA notes that a transition from a wet cooling system to a 

dry cooling system requires energy, reducing the energy efficiency of the power plant. EPA 

further notes that the alternative emission control scenario, which allows APS the option to close 

Units 1 – 3 in lieu of complying with BART, would reduce water use by 6,000 acre-feet per year, 

as described in our Supplemental Proposal.
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

5.0 4BComments on Factor Three – Existing Controls at FCPP 

Comment:

 One of the owners of FCPP (0176/0177) agreed with EPA’s summary of the existing 

controls at the plant, but noted that the proposed FIP is only the most recent action in a long line 

of regulatory and voluntary efforts to reduce emissions of pollutants that impact visibility, 

including SO2, NOx, and PM emissions. The commenter asserted that FCPP has a strong history 

of retrofitting pollution controls and recounted the facility’s history of installing these controls 

and reducing emissions. 

Response:

 EPA agrees that there have been numerous installations of pollution controls over the 

several decades that FCPP has been in operation. The most recent voluntary effort by FCPP 

increased the SO2 removal from its long-term level of 72% removal to 88% removal. This was 

accomplished before the end of 2004 and became effective as a regulatory requirement in June 

2007. The improvement in SO2 removal resulted in a decrease of over 22,000 tons of SO2 per 

year since that time. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

6.0 5BComments on Factor Four – Remaining Useful Life of FCPP 

Comment:

 One of the owners of FCPP (0176/0177) noted that the BART rules state that the normal 

amortization period (20 years for NOx control devices) is appropriate in applying the remaininguseful-life BART if the plant’s “remaining useful life will clearly exceed” that amortization 

period (citing 70 FR 39169). The commenter asserted, however, that as a result of substantial 

uncertainty related to multiple factors, it is not at all clear that the plant’s remaining useful life is 

at least 20 years. Thus, the commenter asserted that EPA must give proper consideration in its 

analyses to the possibility of a shorter useful life for FCPP. Moreover, according to the 

commenter, one factor that should not be allowed to shorten the useful life under the BART rules 

is the choice of BART itself – EPA cannot use a 20-year amortization period to justify a 

specified technology (e.g., SCR) if the application of the technology would be so costly as to 

make the facility uneconomical and shorten its useful life (citing 70 FR 39164, 39171). The 

commenter made the following arguments related to the possibility of a shorter useful life at 

FCPP: 

 The excessive cost of SCR will dramatically increase the energy costs of the plant, 

potentially making it uneconomical. The installation of SCR on Units 1–3, including bag 

house retrofitting, would increase the cost of electricity production on a $/MWh basis by 

more than 50 percent which, in conjunction with other market and regulatory 

uncertainties, may make the units uneconomic. Retrofitting SCR on Units 4 and 5 would 

raise the cost of generation at those units by more than 25 percent, and there is a 

reasonable possibility that such a cost increase would threaten the economic viability of 

those units. 

 The proposed “phase-in schedule” for SCRs may force closure of units because APS will 

not have certainty by the compliance deadline that the lease will be extended or that 

SCE’s ownership share will have been successfully transitioned. Numerous approvals 

must be obtained to allow any of the units at FCPP to continue to operate, including 

Units 4 and 5; securing each of these approvals takes time and presents risk. In particular, 

APS must obtain federal grants of right-of-way from DOI pursuant to 25 U.S.C. 323, 

which constitute “federal actions” that are likely to trigger review under the National 

Environmental Policy Act, possibly taking several years. Thus, APS would have to make 

significant capital expenditures on Units 1 – 3 before obtaining the needed approvals, and 

would instead close the units. 

 The proposed FIP would require retrofitting BART controls on Units 1 – 3 much sooner 

than the time allowed under the Regional Haze regulations, which is 5 years. This is 

unreasonable in that APS must allow time for a final decision to be made on the proposed 

SCE transaction before making the substantial capital expenditures to retrofit Units 1 – 3. 

A requirement to install SCR and baghouses on those three units in such a short time 

would likely lead to increased engineering and installation costs. APS needs the 

flexibility of 5 full years to install SCR. 
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 Emerging environmental laws and regulations present cost and operational uncertainty 

that may shorten FCPP’s useful life. These include potential new GHG laws and 

regulations, a Maximum Achievable Control Technology (MACT) standard for EGUs, 

new ash-handling requirements, and new requirements for cooling water intake 

structures. 

 Another of the FCPP owners (0174) cited the comments above to argue that EPA’s 

economic analysis should have considered shorter “payback periods” because a reduced payback 

period could result in FCPP power (with SCR costs included) exceeding wholesale market costs. 

Response:

 EPA disagrees with commenters that we must consider a shorter useful life because of 

uncertainty related the factors cited by the commenter. It is inappropriate to consider a useful 

life shorter than 20 years based solely on a possibility of shut down. EPA further notes that in its 

FCPP cost analysis on behalf of APS, B&V stated “the remaining useful life of Units 1 through 5 

was at least 20 years”.51F

52 In our proposed BART determination, EPA described the analysis 

conducted to examine the competitiveness of FCPP compared to purchasing power on the open 

market if SCR were required on all five units at FCPP and determined that if SCR were applied 

on all units at FCPP, the cost to produce electricity at FCPP would still be lower than the cost to 

purchase power on the open market. Unless there is an enforceable obligation for APS to cease 

operations on a given date or unless APS convincingly demonstrates that controls (rather than 

uncertainly associated with future requirements) will cause facility closure, the default 20 year 

amortization period represents the appropriate period for the remaining useful life. 

In our proposed BART determination for FCPP, EPA proposed a PM emission limit for 

Units 1 – 3 that can be achieved through the installation of any of four different PM control 

options. EPA did not prescribe which PM control APS must use to comply with the proposed 

limit. Wet membrane electrostatic precipitators (ESPs) represented the least costly option, while 

baghouses represented the most costly option. At the time of our BART proposal, the Mercury 

and Air Toxics Standard (MATS Rule) for electric utility steam generating units had not yet been 

proposed, nor had APS suggested its alternative emission control strategy to close Units 1 – 3 in 

lieu of complying with BART for NOx. Because the MATS rule is now final52F

53, and EPA is 

finalizing the option to allow APS to either comply with the alternative emission control strategy 

or BART, EPA is not taking action at this time on our proposal to set new PM limits for Units 1 – 

3. Therefore, the comment that installation of baghouses in addition to SCR on Units 1-3 will 

increase the cost of power by approximately 50 percent is not relevant. 

While the commenter’s suggested increase in the cost of power from Units 4 and 5 as a 

result of SCR (25 percent increase) is reasonably consistent with the results of the EPA analysis 

(22 percent) with respect to the power cost impact of SCR on all five FCPP units, it must be 

noted that the original EPA analysis did not evaluate SCR on Units 4 and 5 exclusively. For 

more information on cost of SCR on units 4 and 5 see our response above in Section 4.1.2. 

 

52 See B&V Engineering Analysis for Units 1 – 5 at FCPP dated December 2007. Document number 0011 in docket 

for proposed rulemaking: EPA-R09-OAR-2010-0683. 

53 77 FR 9304, February 16, 2012. 
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EPA agrees that the phased-in schedule for installation of SCRs on Unit 1 – 3 for BART, 

which was added in the supplemental proposal, may have allowed only 2 years for engineering 

and installation of these pollution controls from the date by which APS intends to make its 

decision on continuing operation or shutting the units down by 2014. EPA is changing the 

schedule for SCR installation by requiring the SCRs for either Unit 4 or 5 to be installed within 4 

years of the effective date of this rule and the remaining Units (Units 1-3 and the either 4 or 5) 

within 5 years of the effective date. 

 With respect to the “payback period” referenced by the commenter, EPA’s analysis did 

not identify “payback periods.” Rather, the commenter appears to be referring to the 25-year 

period utilized for the discounted cash flow calculations within the model. Nevertheless, EPA 

does not disagree with the commenter’s stated concern that shorter plant life (as may be 

precipitated by other possible emerging regulations unrelated to Regional Haze), and thus 

shorter discounting periods, would yield different economic results. However, EPA disagrees 

with commenters that a shorter useful life should be considered in the economic analysis because 

consideration of other regulations are outside the scope of the Regional Haze BART analysis. 

Comment:

 One industry commenter (0117) stated that EPA, rather than evaluate APS’s 

supplemental proposal as an alternative emission control strategy, should instead “re-determine” 

BART for each of the five units at FCPP based on the APS-proposed shutdown scenario for 

Units 1 – 3. The commenter noted that consideration of the shortened remaining useful lives of 

Units 1 – 3 could result in a determination that BART for these units is no additional control 

prior to shutdown, while consideration of the remaining useful lives of Units 4 and 5 would not 

be heavily weighted since they are not to be shut down in the near term. The commenter 

concluded that a “better-than-BART” control strategy does not seem to be necessary for 

determining the appropriate requirements for FCPP under the APS-proposed shutdown scenario; 

instead, a BART determination for each unit with appropriate weighting of the statutory factors 

appears to present a logical and less-burdensome means of applying section 169A(b)(2) of the 

CAA to FCPP. 

Response:

EPA disagrees with the commenter’s suggestion that APS’s supplemental proposal 

should be evaluated in terms of a BART-redetermination rather than in terms of its current status 

as a “better-than-BART” alternative measure. EPA has met its obligation under 40 CFR 

51.308(e)(1) by performing a BART determination for FCPP in accordance with 40 CFR 51, 

Appendix Y (Guidelines for BART Determinations Under the RHR). We do not consider a redetermination of BART that takes into account APS’s supplemental proposal the most 

appropriate method for evaluating APS’ proposal in light of the “alternative measure” 

provisions contained in 40 CFR 51.308(e)(2) and (3). The 2006 RHR (71 FR 60612) specifically 

established the procedures described in 40 CFR 51.308(e)(2) and (3) for scenarios involving 

programs that may make greater reasonable progress than source-by-source BART. These 
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provisions were specifically included to allow for the flexibility to consider alternative measures 

such as the one proposed by APS, and EPA considers it the most appropriate method for 

evaluating APS’s supplemental proposal. 

Comment:

 One industry commenter (0117) discussed the “remaining useful life” statutory factor, 

noting that under the BART Guidelines remaining useful life is ignored in the majority of BART 

determinations (citing 40 CFR part 51, Appendix Y, section IV.D.4.k), which the commenter 

alleged is inappropriate. According to the commenter, Congress designated the remaining useful 

life of the source as an important consideration because it did not want to impose the burdens of 

control technology retrofits on sources that were more than 15 years old at the time the statute 

was enacted. Given that it is now 34 years after the BART requirements were enacted, the 

commenter stated that the “remaining useful life” statutory factor should weigh heavily in BART 

determinations for older sources such as FCPP, instead of being ignored. See Section 10.0 for 

more on this commenter’s legal interpretation of the Regional Haze requirements. 

Response:

EPA disagrees with the commenter that we ignored the “remaining useful life” statutory 

factor in our BART decision. EPA considered this factor in our BART analysis (see pages 42-43 

of the TSD). As discussed in the TSD the remaining useful life of an EGU subject to BART is 

determined by the utility. EPA cannot arbitrarily decide that an EGU has less useful life when it 

is not within our BART rulemaking authority to require closure of an EGU. If a utility used a 

shorter useful life than one that would allow the full amortization of any necessary pollution 

controls, EPA would take that into account in the cost analysis, provided that there was an 

enforceable obligation that the EGU would cease operation by that time. 

Comment:

 One private citizen (0163/0164/0216) stated that it appears that APS is trying to keep its 

workers from telling the truth about metal fatigue problems and major corrosion problems at 

FCPP. The commenter noted that fly ash has sulfur in it which, when mixed with water, forms 

sulfuric acid which can corrode iron pipe. The commenter included a newspaper article profiling 

a manager at the plant which recounted an incident in which a pipeline transporting fly ash and 

water at the plant burst. The commenter was apparently questioning whether the remaining 

useful life of the plant is as much as 20 years as assumed in the BART analysis. 

 Another private citizen (0144) simply stated that FCPP has lived beyond its usefulness. 

Response:

As mentioned in the previous comment, in general, the utility determines the appropriate 

useful life of their EGUs subject to BART. Unless there is an enforceable obligation for APS to 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

cease operations on a given date or unless APS convincingly demonstrates that controls (rather 

than uncertainly associated with future requirements) will cause facility closure, the default 20 

year amortization period represents the appropriate period for the remaining useful life.
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

7.0 6BComments on Factor Five – Anticipated Visibility 

Improvements 

Comment:

 One of the owners of FCPP (0176/0177) presented information on visibility conditions on 

the Colorado Plateau and the role of NOx emissions in Western visibility impairment. The 

commenter noted that SO2 and NOx emissions have been decreasing in recent years and cited a 

status report prepared by the Western Regional Air Partnership (WRAP) stating that (1) visibility 

has been improving at the Class I areas on the Colorado Plateau, (2) fire is the dominant 

contributor to haze on the 20 percent worst visibility days, (3) the sulfate contribution to haze is 

steadily decreasing, and (4) significant improvement can be seen on the 20 percent best visibility 

days. The commenter also presented information that purported to show that whether averaged 

over the haziest 20 percent of days, the clearest 20 percent of days, or all days, power plant NOx

emissions contribute less than 1.5 percent to the light extinction at Mesa Verde National Park. 

Another of the FCPP owners (0168) cited this comment and emphasized this last point. A utility 

industry association (0169) also presented information to show that less than 1.5 percent of light 

extinction at Mesa Verde National Park is the result of power plant NOx emissions. 

Another commenter (0223) questioned EPA’s assertion that that NOx and PM from FCPP 

are significant contributors to visibility impairment in the numerous mandatory Class I areas 

surrounding FCPP (citing 75 FR 64221), stating that coal-fired power plants, including FCPP, 

are relatively small contributors to regional haze in the surrounding Class I Areas. According to 

the commenter, the WRAP has concluded that visibility impairment caused by PM and 

attributable to all stationary sources is probably less than 2 percent, and that stationary source 

NOx emissions probably cause between 2 and 5 percent of the visibility impairment on the 

Colorado Plateau. 

 

In contrast, the comments of an environmental advocacy group (0182) included a quote 

from EPA’s Section 110 proposed rule for the San Juan Generating Station stating, “NOx and 

SO2 are significant contributors to visibility impairment in and around New Mexico. As the Four 

Corners Task Force notes, ‘[r]eduction of NOx is particularly important to improve visibility at 

Mesa Verde National Park.... [V]isibility has degraded at Mesa Verde over the past decade, and 

the portion of degradation due to nitrate has increased....’”. 

Response:

EPA modeling of FCPP showed visibility impacts from 1.2 to 6.0 deciviews, depending 

on the Class I area, with the sum of impacts at all sixteen Class I areas totaling 43 deciviews. 

This is a significant contribution to visibility impairment. Even if an individual source category 

appears small by itself, the many segments of the emissions inventory together cause significant 

visibility impairment and must be addressed in order to make progress towards the national goal 

of remedying visibility impairment from manmade pollution. Section 169A of the Clean Air Act 

requires BART determinations on BART-eligible EGUs regardless of trends or ambient visibility 

conditions. Application of BART is one means by which we can ensure that downward emission 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

and visibility impairment trends continue. EPA identifies stationary sources as an important 

category to evaluate in a BART analysis.

 

Comment: 

 Three of the owners of FCPP (0168, 0174, 0176/0177, 0179), a group of owners (0185), 

the Navajo Nation (0223), and two utility industry associations (0169, 0187) argued that EPA’s 

use of Interagency Workgroup on Air Quality Modeling (IWAQM) Phase II default background 

ammonia values is not appropriate. In extensive comments drawing heavily on a report by 

Dr. Ivar Tombach that was appended to the comments, one of the owners of FCPP (0176/0177) 

argued the following: 

 Actual field measurements show lower ammonia concentrations than used by EPA. 

 The EPA is mistaken in its assumption that background ammonia concentrations along 

the path of the plant’s plume determine nitrate concentrations and their contribution to 

haze at the receptor site. 

 The EPA’s “corroborating” approach of “back-calculating” ammonia is flawed because it 

erroneously assumes that the ammonia associated with measured sulfate and nitrate 

would all be available to react with FCPP emissions, whereas in reality those 

measurements reflect emissions from many sources. 

 The EPA’s analysis of nitrate predictions as a check on the ammonia values used is also 

flawed because it erroneously assumes that the resulting measured nitrate levels are 

solely due to FCPP emissions, whereas in reality they reflect emissions from many 

sources. A comparable analysis using the EPA ammonia value shows substantial and 

“physically impossible” overpredictions of nitrate. 

 The sensitivity analysis carried out for APS of the alternate ammonia concentrations in 

the CALPUFF model demonstrates that the ammonia values AECOM used in its 

modeling are valid and correct. 

 One of the utility industry associations (0187) and the group of FCPP owners (0185) 

similarly stated that for EPA to reject the body of direct measurements of ammonia concentration 

in the FCPP region, it must provide substantial scientific justification, which it has not done. 

These commenters also stated that EPA’s supplemental sensitivity analysis was flawed because it 

consists almost entirely of modeling conducted using the “discredited” back-calculation method, 

which the commenter alleged is as insufficient for this purpose as it was for setting the 

background ammonia levels directly. The commenters concluded that the use of IWAQM values 

invalidates EPA’s BART modeling and the BART determination based upon it. Other of the 

FCPP owners (0168, 0179) stated that APS provided ample justification for using its proposed 

lower background ammonia levels and successfully refuted EPA’s arguments for using IWAQM 

default value. Accordingly, the commenters requested that EPA accept the visibility modeling 

using the lower variable background ammonia values, which will significantly reduce the 

visibility benefits ascribed to SCR. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 Another utility industry association (0169) stated that several measurement programs on 

the Colorado Plateau show that actual ammonia values in Class I areas near FCPP are 

significantly lower than the IWAQM default value, indicating that these values typically range 

from 0.1 to 0.6 ppb.53F

54 The commenter noted that ammonia concentrations are lowest during the 

cold season when the visibility impacts of NOx emissions are the highest. Accordingly, the 

commenter asserted that using a single ammonia value throughout the year is not scientifically 

valid and should be replaced with seasonally variable values. The commenter stated that 

modeling with “valid, accurate” ammonia values will show significantly lower visibility changes 

resulting from SCR at FCPP. 

 The Navajo Nation (0223) expressed concern regarding discrepancies between EPA and 

APS modeling inputs, given the commenter’s understanding that APS obtained advance EPA 

approval for its modeling protocols. The commenter expressed a preference for using recorded 

data wherever possible and noted difficulties associated with estimating background ammonia 

levels and the CALPUFF model, citing the discussion in the initial proposal (75 FR 64226) and 

the associated TSD for our proposed BART determination (pages 70-72). The commenter argued 

that EPA’s use of various sensitivity analyses in support of the use of the IWAQM default and 

then corroborating with revised background ammonia data further complicates the modeling 

protocols. The commenter alleged that this approach is fundamentally flawed. Some commenters 

stated that EPA had earlier agreed to lower ammonia concentrations, and so should not be using 

the higher IWAQM value now. 

A utility industry association (0169) speculated that cost effectiveness in terms of dollars 

per deciview improved resulting from retrofitting FCPP with SCR (based on modeling using 

CALPUFF version 6.4 and “valid” background ammonia values) would be an order of 

magnitude higher that the $17 million per deciview benchmark that the commenter ascribed to 

EPA’s TSD. Accordingly, the commenter asserted that SCR cannot be justified as BART at 

FCPP. 

 In contrast, one public interest advocacy group (0112) concurred with EPA’s backcalculation method for ammonia background levels (citing the TSD, page 60). The commenter 

added that the requests to EPA from other commenters for additional ammonia monitoring data 

are unrealistic in today’s budget environment. The commenter agreed with EPA’s statement in 

the TSD that initiation of a new monitoring program would be a much larger undertaking than 

the analysis procedures described in the BART Guidelines. 

Response: 

EPA disagrees with commenter objections to the background ammonia concentrations 

used in our modeling. Our use of the 1 ppb IWAQM Phase II default background ammonia 

 

54 The commenter (0169.1) cited “Baseline ambient gaseous ammonia concentrations in the Four Corners area and 

eastern Oklahoma, USA” by Mark E. Sather, Johnson Matthew, Nghia Nguyen, et al., Journal of Environmental 

Monitoring, Vol. 10 (2008), pp. 1319-1325; Ammonia measurement data provided by Dr. Jeff Collett of Colorado 

State University; and “Measurements of Ambient Background Ammonia on the Colorado Plateau and Visibility 

Modeling Implications,” I. Tombach and R. Paine, contributors, Report by Salt River Project, Phoenix, Arizona, 

September 2010. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

value is appropriate. Most of the objections have already been discussed in EPA’s TSD for the 

proposal; and several of them concern the “back-calculation” method that we used only as 

corroboration for the 1 ppb results we principally relied on. Also, even if the lower ammonia 

concentrations urged by some commenters were accepted, EPA’s sensitivity modeling results 

provided in the TSD for our proposed BART determination showed the visibility benefits would 

still support EPA’s BART determination. EPA also provided the results of modeling runs that 

used the lower ammonia background concentrations recommended by some commenters (see 

TSD Table 37). The visibility benefits of the proposed NOx controls for BART are substantial 

under all ammonia scenarios, including the lower background ammonia concentrations 

recommended by commenters. For 12 Class I areas, modeling even with those lower 

backgrounds showed benefits of 0.5 dv or more, an amount recognized in the BART Guidelines 

as significant (e.g. at 70 FR 39120). 

The lack of measurements of ammonia and ammonium in the Class I areas of concern 

requires that EPA estimate background ammonia concentrations by some method, considering 

available data and approaches. As discussed in the BART proposal and its accompanying TSD, 

EPA understands that there is no single accepted method for estimating the background 

concentration of ammonia, and that any method will have advantages and disadvantages. The 

lack of consensus on a method was a factor in EPA’s decision to rely on the 1 part per billion 

(ppb) default value in IWAQM, as was the fact that IWAQM is the only available guidance on 

this issue. In summary, there is insufficient monitoring information available to use a different 

value, or to support any seasonally varying values. 

On issue (1), field measurements cited by the commenters were not performed in the Four 

Corners area, nor at the Class I areas near FCPP, so they do not necessarily give appropriate 

ammonia background concentrations for modeling of FCPP. In addition, the studies provide 

only gaseous ammonia (NH3) and not ammonium (NH4) that has reacted with SO2 or NOx

emissions. For purposes of assessing FCPP impacts relative to natural background, per the 

BART Guidelines, both ammonia and ammonium should be assumed to be available to interact 

with emissions from FCPP. The ammonia-only measurements cited by the commenters 

underestimate the available ammonia. Finally, as discussed in the TSD, field measurements in 

the Four Corners area showed ammonia measurements ranging from 1.0 ppb to 1.5 ppb, and 

sometimes as high as 3.5 ppb.54F

55 This provides some additional support for the 1 ppb used by 

EPA. 

On issue (2), in using a 1 ppb background EPA did not rely on an assumption about the 

importance of background ammonia along the path of the plume, as claimed by the commenters. 

The 1 ppb background is representative of areas in the west under existing EPA guidance, in the 

IWAQM document. The commenters’ objection is based on the rapidity of the nitrate-nitric acid 

equilibrium, which they state implies that ammonium nitrate can only be estimated using 

ammonia measurements right at the Class I area, and not the ammonia that occurs earlier along 

the plume’s path to the area. EPA’s TSD for the proposed rulemaking did state (TSD p.62) that 

the Federal Land Managers partly relied on this assumption as one of the rationales for the 

back-calculation method, discussed below; EPA also expressed support for the idea that the 

 

55 Mark E. Sather et al., 2008. “Baseline ambient gaseous ammonia concentrations in the Four Corners area and 

eastern Oklahoma, USA”. Journal of Environmental Monitoring, 2008, 10, 1319-1325, DOI: 10.1039/b807984f 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

method can be viewed as a 24-hour temporal integration, not just a spatial integration over the 

plume path, and that this aspect can be viewed as desirable for the 24-hour average visibility 

estimate that CALPUFF provides (TSD pp.71-72). This plausibility argument applies despite the 

rapid nitrate-nitric acid equilibrium cited by the commenters, and in any case was not relied on 

by EPA in using the 1 ppb default ammonia background. 

 

As the commenters stated under issue (3), EPA used a back-calculation ammonia estimation 

method as an alternative that provides some corroboration for the 1 ppb IWAQM method, and 

which is more fully explained in the TSD for the proposal. Essentially, it uses measured 

particulate ammonium sulfate and nitrate to estimate the amount of ammonia that must have 

been present to form those ammonia compounds. The commenters object that the method 

assumes that all the calculated ammonia is available to interact with the FCPP plume as 

background ammonia. However, this assumption is reasonable for the single-source CALPUFF 

modeling performed under the BART Guidelines. It estimates ammonia concentrations that 

would be monitored at the Class I area if only this single source existed; it includes ammonia 

that is currently in the form of ammonium because of interaction with other sources’ emissions. 

It remains true that some portion of the calculated ammonia would in reality not be available for 

FCPP, because it arrives at the monitor from a different direction than FCPP’s pollutant plume; 

on the other hand, the data would also include directions contributing below-average ammonia, 

reducing that effect. 

In addition, the back-calculated ammonia is based on measurements only of particulate 

ammonium, the form associated with measured sulfate and nitrate; it does not include any 

gaseous ammonia that may also be present. In this sense, the back-calculated ammonia is a 

lower bound on the ammonia that may be available to interact with source emissions; that is, the 

method may underestimate ammonia concentrations. This possible underestimation tends to 

offset possible overestimation discussed above. 

EPA does not claim that the back-calculation method is dispositive; it incorporates 

various assumptions and imperfections that make clear it is only an estimate. However, it is 

based on real measured data at Class I areas, and has some counterbalancing tendencies for 

over- and under-estimation. After weighing various lines of argument about the back-calculation 

method, EPA disagrees with the commenters who recommended that it be rejected altogether. 

The method provides a useful estimate of ammonia for BART modeling, by providing 

concentrations representative of the high values that would be observed at the Class I areas in 

the absence of other sources. On balance, EPA believes the back-calculation provides a 

reasonable corroborating method for selecting the appropriate ammonia background to use. 

In issue (4) the commenters claim that the assumption of full availability to FCPP of the 

back-calculated ammonia invalidates EPA’s comparison of monitored nitrate levels with those 

modeled using the back-calculated ammonia (TSD p.73). As just discussed for issue (3), EPA 

disagrees that the assumption is invalid for corroboration of single-source BART assessment 

modeling. For single-source BART modeling, on balance, it is reasonable to assume all the 

ammonia is available to the source, given the counterbalancing tendencies for over- and 

underestimation inherent in the back-calculation method discussed above. In any case, this 

method mainly provided corroboration for the results from using the 1 ppb ammonia default. The 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

related issue (5) about “physically impossible” nitrate over-predictions does not account for the 

fact that any model evaluation is expected to have under- and over-predictions, depending on the 

meteorological conditions and the geographic location modeled, as well as on the location of the 

monitor used for comparison. While consistent over-prediction in a full model performance 

evaluation would indeed raise concerns over its validity, as EPA stated, our nitrate comparison 

was not intended as a model performance evaluation, but rather as a “rough check” for the 

back-calculation corroboratory method (TSD p.73). EPA found that the modeled and monitored 

values, for both the maximum values and the 98th percentiles, were generally in agreement. 

Finally, contrary to the commenter’s assertion, EPA did not receive a modeling protocol 

in advance of modeling by APS’s contractor. EPA disagrees with commenters that EPA 

committed to use the same ammonia concentrations used by APS’s contractor in our own 

modeling analysis for our BART determination.

Comment:

 Three of the owners of FCPP (0168, 0176/0177, 0179) and a utility industry association 

(0169) asserted that CALPUFF version 5.8 used in the EPA’s BART analysis is outdated. Some 

of these commenters stated that past EPA statements make clear that the BART analysis should 

be based on the best application currently available to predict visibility impacts (citing 70 FR 

39121-23). Because of enhancements to the model’s chemistry, the commenters stated that 

CALPUFF version 6.4 represents the best application that is currently available. A number of the 

commenters mentioned a December 2010 meeting between the CALPUFF developer and the 

FLMs where the FLMs reportedly supported an expedited review and approval of CALPUFF 

version 6.4. 

 One of these commenters (0168) stated that it is extremely concerning that EPA would 

impose a requirement costing a facility hundreds of millions of dollars based on results from the 

“regulatory version” of a model when a newer, more accurate version of the model is available. 

Another of the commenters (0179) stated that EPA should re-run its FCPP visibility modeling 

using CALPUFF version 6.4 and the seasonally adjusted background ammonia levels developed 

by APS’s modeling contractor or accept the APS modeling analysis using these tools. A third 

commenter (0169) similarly indicated that EPA should revise its BART analysis using actual 

measured background ammonia values and CALPUFF version 6.4. 

 Another of these commenters (0176/0177) presented the results of comparison tests 

purported to show that version 6.4 produced results that more closely matched measured values 

than did version 5.8. (The commenter appended the report of these comparison tests to the 

comments.) This commenter (0176/0177) also presented the results (APS comment, attached 

Exhibit F) of comparative modeling carried out for FCPP using CALPUFF versions 5.8 and 6.4, 

and three different background ammonia levels (IWAQM default, CMAQ model-derived, and 

the AECOM values). This modeling showed that the predicted visibility impacts (in terms of dv) 

decline significantly from CALPUFF version 5.8 to version 6.4 for all three background 

ammonia values used in the model runs. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

The commenter concluded that the emission limitations specified in the proposed FIP will 

not result in any perceptible visibility improvements at any of the 16 Class I areas in the Four 

Corners region. [Two of the other owners of FCPP (0168, 0179) and a utility industry association 

(0169) also stated this conclusion.] The commenter stressed that this is not a surprising result 

given that studies have shown that power plant NOx emissions comprise a de minimis

contribution to the observed visibility conditions as Mesa Verde National Park. 

The commenter (0176/0177) added that these results are confirmed by a multi-year 

regional air quality study carried out for the Four Corners Air Quality Task Force by Environ, 

which concluded in August 2009. This study used the CAMx model and predicted even less 

visibility improvement at Mesa Verde from the application of SCR at FCPP and nearby San Juan 

Generating Station than did AECOM’s modeling with CALPUFF version 6.4 using the AECOM 

values for background ammonia concentrations. Another of the owners of FCPP (0168) also 

cited this as confirming evidence. 

 Using the modeling results based on CALPUFF version 6.4 and the AECOM background 

ammonia concentrations, and its own control cost analysis, the commenter (0176/0177) 

calculated the cost effectiveness of combustion controls and SCR in terms of dollars per dv 

improved at Mesa Verde. According to the commenter, the cost effectiveness of advanced 

combustion controls would be about $64 million per dv and SCR would be about $365 million 

per dv. The commenter stated that in its TSD, EPA indicated that $17 million per deciview is a 

reasonable benchmark for a cost-effective BART control technology. Based on this cost 

effectiveness metric, the commenter concluded that advance combustion controls constitute 

BART for FCPP. 

Another owner of FCPP (0174) stated that the version of CALPUFF used by EPA has a 

tendency to over-predict nitrate concentrations, which is compounded by EPA’s use of what the 

commenter asserted are overestimated ammonia background values. The commenter stated that 

this combination of errors results in a significant over-prediction of visibility improvements for 

more stringent NOx BART control options. Further, the commenter stated that this 

disproportionately affects the incremental visibility benefits predicted for SCR over LNB 

compared to LNB over baseline. The commenter supported the related comments submitted by 

Commenter 0176/0177 and stated that the modeling results submitted by that commenter should 

be used to determine BART. 

 In contrast, one federal agency (0175) was generally supportive of the modeling methods 

employed by EPA with the regulatory approved version 5.8 of the CALPUFF modeling system. 

This commenter noted that in email correspondence dated December 22, 2010 from Mr. Robert 

Paine to Mr. Scott Bohning, there is a specific reference to a meeting held between Mr. Joe Scire 

and the FLMs regarding CALPUFF version 6.4, indicating that the FLMs were “pleased to 

receive this presentation and will be working to ‘expedite’ the review and implementation for 

this improved version of CALPUFF.” The commenter stated for the record that its agency was 

not represented at the December 10, 2010 meeting and has not officially endorsed or committed 

to expediting the review and implementation of this version of the CALPUFF system. Moreover, 

it remains the commenter’s position that until this version has undergone a scientific peer review, 
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model code review, and more rigorous performance evaluation than presented, this version 

should not be used for regulatory purposes. 

Response: 

EPA disagrees with the commenters that any new CALPUFF version should be used for 

the BART determination. EPA relied on version 5.8 of CALPUFF because it is the EPAapproved version in accordance with the Guideline on Air Quality Models (“GAQM”, 40 CFR 

51, Appendix W, section 6.2.1.e); EPA updated the specific version to be used for regulatory 

purposes on June 29, 2007, including minor revisions as of that date; the approved CALPUFF 

modeling system includes CALPUFF version 5.8, level 070623, and CALMET version 5.8 level 

070623. CALPUFF version 5.8 has been thoroughly tested and evaluated, and has been shown 

to perform consistent with the initially promulgated version from 2003 in the analytical 

situations it has been approved for. Any other version would be considered an “alternative 

model”, subject to the provisions of GAQM section 3.2.2(b), requiring full model documentation, 

peer-review, and performance evaluation. No such information for the later CALPUFF versions 

that meet the requirements of section 3.2.2(b) has been submitted to or approved by EPA. 

Experience has shown that when the full evaluation procedure is not followed, errors that are 

not immediately apparent can be introduced along with new model features. For example, 

changes introduced to CALMET to improve simulation of over-water convective mixing heights 

caused their periodic collapse to zero, even over land, so that CALPUFF concentration 

estimates were no longer reliable. 

In addition, the latest version of CALPUFF, 6.4, incorporates a detailed treatment of 

chemistry. EPA’s promulgation of CALPUFF (68 FR 18440, April 15, 2003) as a “preferred” 

model approved it for use in analyses of Prevention of Significant Deterioration increment 

consumption and for complex wind situations, neither of which involve chemical 

transformations. For visibility impact analyses, which do involve chemical transformations, 

CALPUFF is considered a “screening” model, rather than a “preferred” model; this 

“screening” status is also described in the preamble to the BART Guidelines (at 70 FR 39123, 

July 6, 2005). The change to CALPUFF 6.4 is not a simple model update to address bug fixes, 

but a significant change in the model science that requires its own rulemaking with public notice 

and comment. 

Furthermore, it should be noted that the US Forest Service and EPA review of 

CALPUFF version 6.4 results for a limited set of BART applications showed that differences in 

its results from those of version 5.8 are driven by two input assumptions and not associated with 

the chemistry changes in 6.4. Use of the so-called “full” ammonia limiting method and finer 

horizontal grid resolution are the primary drivers in the predicted differences in modeled 

visibility impacts between the model versions. These input assumptions have been previously 

reviewed by EPA and the FLMs and have been rejected based on lack of documentation, 

inadequate peer review, and lack of technical justification and validation. 

 EPA intends to conduct a comprehensive evaluation of the latest CALPUFF version along with 

other “chemistry” air quality models in consultation with the Federal Land Managers, including 

a full statistical performance evaluation, verification of its scientific basis, determination of 

whether the underlying science has been incorporated into the modeling system correctly, and 
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evaluation of the effect on the regulatory framework for its use, including in New Source Review 

permitting. CALPUFF version 5.8 has already gone through this comprehensive evaluation 

process and remains the EPA-approved version, and is thus the appropriate version for EPA’s 

BART determination for FCPP. 

Comment:

 The Navajo Nation (0223) expressed concern about the accuracy of CALPUFF based on 

a 2010 study that concluded that the closure of Mojave Generating Station had resulted in no 

perceptible visibility improvement in Grand Canyon National Park, despite predictions based on 

CALPUFF modeling that visibility in the park would improve.5F

56 According to the commenter, 

the study’s authors concluded that their results raise questions about the reliability of CALPUFF. 

The commenter found this uncertainly alarming given that CALPUFF is the model used for the 

FCPP BART analysis and the significant economic impacts that the commenter alleged the 

BART determination could have on the Navajo Nation if FCPP were to shut down rather than 

install emission controls. (See Section 4.1 for the comments on potential economic impact.) 

Response:

As discussed in the response to the previous comment, EPA affirms that the regulatory 

version of CALPUFF is the correct model to use for this BART determination. 

The study cited by the commenters raises issues that should be considered as EPA revisits 

visibility modeling in consultation with the Federal Land Managers. It found significant 

decreases in sulfate and nitrate concentrations after the closure of the Mojave Generating 

Station, but little improvement in associated visibility impairment. The authors tried to eliminate 

other possible causes for this; however, they state “This is partially explained by fluctuation in 

other aerosols masking the drop in sulfate. It is also possible that the sulfate change is too small 

relative to natural daily variation in visibility conditions to have a significant impact. ... Our 

results indicate that other components of visibility, in particular coarse mass and nitrate, 

changed in GCNP after the closure. ... These difficulties are indicative of a larger problem 

encountered when attempting to conduct inference on a calculated parameter (like deciviews) 

which is itself a function of many stochastic processes, each governed by a unique set of 

anthropogenic and natural factors.” While not downplaying the quality and importance of this 

work, CALPUFF 5.8 is adequate for BART determinations; regulatory use of later versions must 

await their full EPA evaluation. 

Comment:

 One federal agency (0175) sought clarification of the nature of the comparison between 

the APS BART alternative CALPUFF modeling and the EPA BART modeling that was 

presented in Table 8 in the supplemental proposal (citing 76 FR 10538-39). The commenter 

 

56 The commenter cited “Effect of Coal-fired Power Generation on Visibility in a Nearby National Park,” 

44 Atmospheric Environment 2524, Jonathan Terhorst and Mark Berkman, 2010. 
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noted that correspondence from APS AECOM to EPA Region 9 staff dated December 23, 2010 

indicates that the “model combinations are CALPUFF v5.8 and also v6.4 with two sets of 

ammonia backgrounds....” The commenter wished to make certain that the data presented in 

Table 8 is a direct comparison of modeling results using the APS BART alternative proposal to 

the October 19, 2010 EPA BART modeling using CALPUFF version 5.8 and is not a 

combination of version 5.8 and version 6.4 of CALPUFF. 

Response:

To clarify, although APS provided documentation modeling results using both CALPUFF 

versions, the EPA proposals and technical support documents presented only results from 

version 5.8, the approved regulatory model. 

Comment:

 Some commenters (0168, 0174, 0176/0177, 0179, 0185, 0187) argued against the 

visibility metrics that EPA introduced in the BART proposal. These comments are summarized 

below. 

 One of the owners of FCPP (0176/0177) argued that the new visibility metrics proposed 

in the ANPR are inappropriate and unsupported, and should be discarded. The commenter noted 

that none of the metrics (percent improvement in dv impacts, cumulative changes in dv, and dv 

impacts scaled by the geographic area of the affected Class I area) are addressed in the BART 

rules, and posited that their introduction into the BART process is intended to inflate the 

estimated visibility benefits of the control options at FCPP. In addition, the commenter noted that 

these metrics do not appear to have been subjected to peer review or public comment 

independent of this rulemaking, as would be normal for what the commenter stated to be a 

critical change to a defined regulatory process. 

 Regarding the percent improvement metric, the commenter (0176/0177) stated that these 

values (unlike values of the haze index in dv) have no consistent relationship to the human 

perception of haze changes and no consistent relationship to changes in ambient visibilityimpairing particle concentrations. As a result, the commenter asserted that this metric is not 

appropriate and must be rejected. For similar reasons, a utility industry association commenter 

(0187) and a group of FCPP owners (0185) asserted that the percent improvement metric does 

not provide useful information for assessing visibility improvement and EPA cannot legitimately 

rely on this method in making a BART determination. 

 Similarly, one of the owners of FCPP (0176/0177) contended that cumulative change in 

dv is not an appropriate metric to describe visibility improvement and should be withdrawn. The 

commenter made the following points: 

 The peak impact from a source occurs at different times in different Class I areas because 

a facility’s emissions cannot result in peak concentrations in all directions at once. Thus, 

this metric really does not represent a cumulative regional impact of the source (and 
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hence the benefit of controls); rather it simply produces a mathematical summation of the 

peak impacts occurring at different times at various Class I areas. 

 The value of the total depends in part of the number of Class I areas included in the 

analysis. This raises questions regarding the utility of the CALPUFF model when Class I 

areas are at distances where the accuracy of CALPUFF is in question. The BART rule 

notes that uncertainties in model performance increase at distances greater than 200 km 

from the source (citing 70 FR 39125-26), and 10 of the 16 Class I areas evaluated for 

FCPP are located more than 200 km from the plant. These 10 areas show some of the 

highest modeled visibility improvements, and it is likely that these predictions are 

overstated. 

 It is inappropriate to add improvements over all Class I areas. A 0.5 dv improvement in 

one Class I area and a 0.5 dv improvement in another area does not result in a 1 dv 

improvement – the improvement is a 0.5 dv improvement, which occurs in two different 

locations. Any one observer would experience only a 0.5 dv improvement; he or she can 

only experience the visibility improvement in the Class I area being visited. Adding 

improvements across Class I areas flies in the face of the basic science of visibility 

perception thresholds. 

 The utility industry association (0187), one FCPP owner (0179), and a group of FCPP 

owners (0185) also argued against use of the cumulative impact metric, which they asserted 

dramatically overstates projected visibility improvements. These commenters claimed that the 

cumulative approach contradicts the BART rules, which state that it is appropriate to model 

impacts at the nearest Class I area and other nearby Class I areas “to determine whether effects at 

those [other] areas may be greater than at the nearest Class I area,” and that “[i]f the highest 

modeled effects are observed at the nearest Class I area, you may choose not to analyze the other 

Class I areas further” (citing 70 FR 39170). The commenters concluded from this that the BART 

rules envisage a visibility analysis that is focused on visibility impacts in the most impacted area, 

not all areas. The commenters added that cumulative impact is inappropriate because no 

individual will perceive impacts in more than one Class I area at a time. The commenters also 

said this approach arbitrarily inflates the benefit that might be associated with emissions 

limitations at a single source, illustrating this point by noting that this method would yield 

different results if a Class I area were divided into two or more areas – increasing the benefit 

simply by increasing the number of areas. One of these commenters (0187) also pointed out that 

this approach would equate a small, imperceptible benefit summed over more than one area with 

a much larger, humanly perceptible improvement in a single area, which the commenter stated 

are not equivalent. 

 Two other owners of FCPP (0168, 0174) voiced general support for the comments on 

visibility metrics submitted by Commenter 0176/0177. 

Conversely, one environmental advocacy group commenter supported the use of a 

cumulative impact analysis. The commenter asserted that the cumulative impact of a source’s 

emissions on visibility, as well as the cumulative benefit of emission reductions, is a necessary 

consideration as part of the fifth step in the BART analysis, particularly in cases such as FCPP 

where the source causes or contributes to visibility impairment at a significant number of Class I 
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areas. The commenter stated that failing to account for a source’s cumulative impairment and the 

cumulative pollution control benefit would result in a failure to acknowledge the regional 

approach to reducing haze. 

Response:

EPA believes that it is important to consider the visibility impact on multiple Class I 

areas. The goal of the visibility program is to remedy visibility impairment at all Class I areas. 

CAA 169A (a)(1). One approach to account for the benefits to all affected Class I areas is the 

cumulative “total dv” metric. However, there is no EPA approved cumulative metric to account 

for visibility impacts at multiple Class I areas. EPA relied on the modeled impacts and benefits 

at each Class I area individually, the number of Class I areas affected, and also considered, but 

did not specifically rely on, the sum of visibility impacts and benefits across all sixteen Class I 

areas. 

 

The comments about the visibility metrics have largely already been addressed by EPA in 

the TSD for our proposed BART determination (pp.61-63 and pp. 67-68), which also explained 

that EPA did not rely on any alternative visibility metrics in the BART determination. The 

comments on this issue are therefore moot, but we will briefly summarize the issues, which are 

discussed more fully in the TSD. 

 As for the percent deciview visibility improvements that some commenters objected to, 

EPA refers the commenters to the proposal TSD, which explains what it represents for visibility 

impacts (TSD for proposed BART determination, p.62). EPA understands, and is confident that 

the commenters understand, the difference between absolute numbers and percentages. In brief, 

the percent improvement for a particular area and control scenario shows only the relative 

improvement in the impact of FCPP alone, and not improvements in overall visibility 

impairment. A given absolute deciview improvement translates into a large percent 

improvement at an area having only a small FCPP impact in the first place, and a small percent 

improvement at an area having a large FCPP baseline impact. EPA notes that the BART 

Guidelines do mention percent improvement as a legitimate metric.56F

57 EPA considered this 

information qualitatively, but arrived at conclusions about the degree of visibility improvement 

in terms of deciviews, in accordance with the BART Guidelines (75 FR 64229, and TSD p.76). 

Finally, EPA disagrees with the commenters that EPA is restricted to considering only 

impacts at the single nearest Class I area, or the single Class I area with the highest impacts. A 

somewhat fuller excerpt from the commenters’ citation of 70 FR 39162 is: “One important 

element of the protocol is in establishing the receptors that will be used in the model. ... you 

may choose not to analyze the other Class I areas any further as additional analyses might be 

unwarranted.” When read in context, this language in the BART Guidelines is clearly meant to 

provide a common sense approach to streamlining a complex and difficult modeling exercise 

where “an analysis may add a significant resource burden to a State.” 70 FR at 39126. While 

the BART Guidelines indicate that a detailed analysis of the visibility impacts at each area in a 

cluster of Class I areas may not be necessary, this is not because the visibility impacts at Class I 

 

57 70 FR 39170 “Comparison thresholds can be used in a number of ways in evaluating visibility improvement (e.g. 

... a threshold representing an x percent change in improvement).”
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areas other than the most impacted are irrelevant but rather because the visibility benefits at the 

most impacted Class I area alone may be sufficient to justify the selection of the most stringent 

control technology as BART. Where, as here, the benefits of controls have been modeled for a 

number of surrounding areas and consideration of these benefits is useful in determining the 

appropriate level of controls, EPA does not agree that these benefits should be ignored. 

Comment: 

 Two commenters (0174, 0187) questioned EPA’s use of 0.5 dv as the threshold of a 

humanly perceptible change in visibility (citing 75 FR 64228). One of the commenters (0187) 

cited scientific literature, while the second (0174) cited the report by Dr. Ivar Tombach that is 

attached to Comment 0176/0177. The latter commenter (0174) added that the establishment of a 

specific deciview threshold as a “bright line” to define whether a certain control will be imposed 

as BART is contrary to the intent of the BART rules and the objectives of the Regional Haze 

program, which require EPA to consider the cost of each control option in relation to the 

associated visibility benefit. 

One of the owners of FCPP (0176/0177) expressed the belief that application of SCR at 

FCPP would result in no perceptible visibility improvement and therefore cannot be BART. The 

commenter based this conclusion on modeling results discussed previously in this section. Based 

on these results, the commenter stated that the changes in visibility that would result from 

combustion controls and SCR are all humanly imperceptible, as is the difference between 

combustion controls and SCR – thus, there is no basis for concluding that SCR constitutes 

BART. Am. Corn Growers, 491 F.3d at 7 (rejecting EPA’s position, as reflected in the original 

BART rules, that allowed for the possibility “that a source may be forced to spend millions of 

dollars for a new technology that will have no appreciable effect on haze in any Class I area.”). 

Response:

EPA disagrees with the commenters that the visibility benefit from the proposed BART 

controls is too small to warrant requiring the controls; in addition, EPA is not using a 

perceptibility threshold in this BART determination. EPA agrees that thresholds should not be 

considered a “bright line” in making BART decisions. In the BART Guidelines, EPA described 1 

dv as the threshold for an impact that “causes” visibility impairment, and 0.5 dv as a threshold 

for an impact that “contributes” to visibility impairment, for determining whether a source is 

subject to BART, though States were accorded discretion to use different thresholds (70 FR 

39118, July 6, 2005; also 39120-39121). These thresholds do not apply to BART determinations 

for sources have been found subject to BART; States or EPA could consider visibility impacts 

less than 0.5 dv to warrant BART controls. To the extent that the comment is questioning the 

BART eligibility of FCPP, EPA has already established that FCPP is BART eligible and the 

commenter did not provide evidence to the contrary. 

Even if the commenters are correct that 0.5 dv change is not perceptible, EPA noted that 

“[e]ven though the visibility improvement from an individual source may not be perceptible, it 

should still be considered in setting BART because the contribution to haze may be significant 
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relative to other source contributions in the Class I area. Thus, we disagree that the degree of 

improvement should be contingent upon perceptibility. Failing to consider less-than-perceptible 

contributions to visibility impairment would ignore the CAA’s intent to have BART requirements 

apply to sources that contribute to, as well as cause, such impairment.” (70 FR 39129) 

That is, impacts smaller than this to contribute to impairment. Conversely, an 

improvement of 0.5 dv or less contributes to improvement in visibility impairment. As stated in 

the proposal, the modeled improvements in visibility are large enough to warrant requiring the 

proposed BART controls. While the actual improvements may be larger, from 0.6 to 2.8 

deciviews, even an improvement of 0.5 dv is a contribution toward improving visibility, 

especially when the benefits at multiple Class I areas are considered. In conjunction with 

improvements from other sources, this will help toward the Clean Air Act goal of remedying 

manmade visibility impairment. 

Comment: 

 One environmental advocacy group commenter (0182) stated that EPA underestimated 

visibility improvement from installing NOx controls because it overestimates the production of 

sulfuric acid by the SCR and underestimated the amount of sulfuric acid removed downstream of 

the SCR. The commenter cited reports attached to the comments (0182) to argue that sulfuric 

acid does not limit SCR NOx control efficiency. The commenter also states that modeling shows 

that greater NOx removal rates are not offset by sulfuric acid emissions but instead yield greater 

visibility improvements than those proposed by EPA. The commenter argues that there will be a 

significant visibility benefit from increasing the SCR NOx efficiency from 80 percent to 90 

percent and therefore concludes that a higher level of NOx control than 80 percent should be 

determined BART. 

Response: 

EPA disagrees with the comment that we overstated the production of sulfuric acid from 

the SCR catalyst and underestimated the amount of sulfuric acid removed downstream of the 

SCR. In the TSD for our proposed BART determination, we estimated sulfuric acid emissions 

using the EPRI methodology and provided detailed explanations for all of the assumptions we 

applied as well as a discussion to compare measured and calculated values of sulfuric acid 

emissions from the Navajo Generating Station (see TSD p.55-59, 64-65, and 68). While we fully 

acknowledge and understand that the generalized EPRI methodology does not precisely 

represent true sulfuric acid emissions for a given facility, this method is a commonly used 

calculation methodology for estimating sulfuric acid emissions under a future operating scenario 

involving SCR. The assumptions we applied in estimating sulfuric acid emissions after the 

installation and operation of SCR using the EPRI methodology were justified and appropriate. 

 EPA assumed in our BART proposal a 3+1 system (4 layers of catalyst) would achieve 

80% NOx removal. Greater reduction efficiencies would likely require an additional layer of 

catalyst, which would likely increase sulfuric acid emissions. Based on the SO2 to SO3

conversion rate guarantee we received from Hitachi for its CX series catalyst (ultra-low 
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conversion) of 0.167% per layer, the use of an additional catalyst layer would equal 5 layers of 

catalyst and a 0.835% conversion rate. EPA is not aware of SCR systems that use 5 layers of 

catalyst, and the addition of a 5th layer would certainly affect the cost and operation of the unit. 

Although EPA agrees that the modeling referenced by the commenters appears to indicate 

greater visibility improvement from an SCR system achieving 90% removal compared to 80% 

removal despite higher sulfuric acid emissions57F

58, EPA does not agree that this requires EPA to 

determine that 90% control be determined BART. In Section 8.1 of this document, we respond to 

the comment that the emission limitation for BART should be based on 90% control with SCR 

rather than 80% control with SCR. Based on the rationale outlined in that response, EPA 

determined that 80% control, achievable with SCR, is appropriate for BART for FCPP. 

Comment: 

 One of the owners of FCPP (0176/0177) submitted the results of additional modeling and 

concluded that the proposed alternative strategy would result in greater visibility improvements 

in the Class I areas surrounding FCPP than would the proposed BART FIP; however, the 

commenter continued to disagree that the improvement would be humanly perceptible. 

According to the commenter, the commenter’s additional visibility modeling using “valid 

background ammonia values and the revised CALPUFF model” show that none of the modeled 

NOx emission reduction strategies at FCPP will result in humanly perceptible improvement in 

visibility in the 16 surrounding Class I areas. The commenter indicated that highest predicted 

visibility improvement (change in deciview) by applying SCR, compared to baseline emissions, 

is 0.28 dv, while the incremental improvement in dv resulting from application of advanced 

combustion control technology and SCR is predicted to be 0.21 dv. Because both these numbers 

are well below the EPA-threshold for human perception of 1.0 dv, SCR does not constitute 

BART for the Plant. 

Response:

 EPA agrees with the commenter that the alternative emission control strategy (of 

shutting down units 1, 2, and 3, and placing SCR on units 4 and 5) may “result in greater 

visibility improvement at the surrounding Class I areas” (EPA's supplemental proposal, 76 FR 

10532, February 25, 2011). However, as discussed in the response to another comment, EPA 

does not agree that the visibility improvement from the original or alternative NOx reduction 

strategies would be imperceptible; EPA anticipates the improvements from either strategy would 

be perceptible.

Comment:

 One of the owners of FCPP (0176/0177) stated that EPA’s TSD Table 21 (TSD p.44) 

mischaracterized the measured visibility impairment at nearby Class I areas as 10th and 90th

 

58 EPA notes that the baghouses on Units 4 and 5 are assumed to provide a significant amount of control of sulfuric 

acid emissions, therefore, such slight increases in sulfuric acid emissions would not be expected on units that are not 

equipped with baghouses. 
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percentile deciview values, whereas the figures actually represent the average of deciviews on 

the best and worst 20% of days, respectively. The commenter also pointed to contradictory 

statements in the TSD (pp.46-47) about the maximum relative humidity used in the relative 

humidity adjustment factor (f(RH))that accounts for the effect of water on particle size growth: 

the TSD states that the IMPROVE equation uses a maximum humidity of 98%, whereas 

IMPROVE and the RHR actually use 95%. 

Response: 

EPA agrees with the commenter that in Table 21 of the TSD, we incorrectly identified the 

measured values as the 10th and 90th percentile deciview impairment, rather than the average 

deciview impairment on the best and worst 20% days. However, Table 21 was presented only for 

background informational purposes and the values in that Table were not germane to nor relied 

upon in our BART determination. EPA relied on Tables 36 – 39 to assess the anticipated 

visibility improvement from controls under the final factor of the BART analysis. Even though 

mislabeled, Table 21 does give a correct impression of the magnitude of visibility impairment. 

The 98% humidity maximum is a value from an earlier guidance document; the value in the 

Regional Haze guidance58F

59 and correctly used in EPA’s modeling was 95%. EPA also notes that 

this maximum (RHMAX in the input for the CALPOST post-processor) is not directly used in the 

visibility calculation method (MVISBK=6 in CALPOST) that was relied upon, and therefore was 

adequate for the BART determination modeling.

 

59 “Guidance for Estimating Natural Visibility Conditions Under the Regional Haze Rule”, EPA-454/B-03-005, EPA 

2003, p.A-3. 
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8.0 7BComments on BART Determinations 

8.1 20BComments on the Proposed BART Determination for NOx 

Comment: 

 A number of commenters, including owners of FCPP (0168, 0174, 0176/0177, 0179, 

0185), the Navajo Nation (0223), and a utility industry association (0187), asserted that EPA’s 

BART analysis was inconsistent with its own regulations in that it did not give proper weight to 

the “presumptive BART” limits for NOx that it established for EGUs through notice-andcomment rulemaking (generally citing 70 FR 39104, July 6, 2005). The commenters noted that 

these presumptive BART limits are based on the use of combustion controls, and that EPA had 

considered and rejected establishing presumptive BART limits based on SCR. 

 In the most extensive comments on this topic, one of the commenters (0176/0177) made 

the following points. The other commenters (0168, 0174, 0179, 0185, 0187, 0223) presented 

arguments similar to some or all of these points. 

 In establishing presumptive BART limits for NOx emissions from EGUs, EPA concluded 

that combustion control-based presumptive limits “are extremely likely to be appropriate 

for all greater than 750 MW power plants subject to BART” (a category that includes 

FCPP), that they are “highly cost-effective controls,” and that they “would result in 

significant improvements in visibility and help to ensure reasonable progress toward the 

national visibility goal (citing 70 FR 39131). Additionally, EPA has made clear that “the 

presumptions represent a reasonable estimate of a stringent case BART...” (citing 71 FR 

60612, 60619, Oct. 13, 2006). 

 The EPA was not correct in stating in the proposal that in setting presumptive BART 

limits, it “did not consider the question of what more stringent control technologies might 

be appropriately determined to be BART” (citing 75 FR 64226). Rather, EPA’s 2005 

rules were clear that the Agency had considered – and rejected – establishing 

presumptive BART limits based on SCR (citing 70 FR 39136). Thus, EPA established 

through rulemaking that SCR is not an appropriate basis for presumptive BART limits 

and that combustion controls should generally be deemed BART. 

 In this context, a BART analysis must begin with and take into account the presumptive 

BART limits and EPA’s rationale for setting them. If a source is able to meet the limit 

through the application of combustion controls, there should be an exceedingly strong 

presumption that such controls constitute BART. This principle was further supported in 

EPA guidance to the states, where EPA generally directs authorities to “require such 

utility boilers to meet the [presumptive BART] limits...” and to consider requiring 

technologies other than combustion controls only when combustion controls cannot meet 

the presumptive limit (citing 70 FR 39171-72). 

 In effect, the EPA’s analytical approach disregarded the presumptive limits entirely. By 

using a top-down approach in which it started its analysis by evaluating SCR and then 
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determined that SCR is BART for FCPP, EPA never undertook an assessment of the 

combustion control technologies that EPA deemed, through notice-and-comment 

rulemaking, to constitute presumptive BART. (See Section 3.2 for additional comments 

on the use of the top-down approach.) 

 In its BART analysis, APS has demonstrated that each unit at FCPP can meet the 

presumptive BART limits through the application of advanced combustion control 

technologies. Therefore, EPA thus must make an exceedingly compelling case for SCR 

as BART if it intends to proceed with the proposed BART determination, which it has not 

done. To the contrary, it has done little more than to conclude that SCR is acceptable as 

BART based on an unexamined and arbitrary assumption that other technologies are not. 

 Under the BART rules, a deviation from presumptive BART, either upwards or 

downwards, is authorized if an alternative control level is justified based on “careful

consideration of the statutory factors” (citing 70 FR 39131). However, EPA did not 

carefully consider the BART factors and then conclude that an alternative to presumptive 

BART limits is appropriate. Instead, EPA dismissed the presumptive BART limits before 

even considering the BART factors. 

 The EPA appears to have adopted a new standard for deviations from presumptive 

BART, stating that presumptive BART controls are required “unless there are sourcespecific circumstances that would justify a different conclusion” (citing 75 FR 64226). 

Using this new standard, EPA dismissed presumptive BART prior to undertaking any 

BART factor analysis and argued for post-combustion controls on the grounds that FCPP 

“is the largest source of NOx emissions in the United States and ... is surrounded by 

16 mandatory Class I areas” (citing 75 FR 64226). Rather than using an analysis of the 

BART factors to support a non-presumptive BART limit, EPA dismissed presumptive 

BART outright, based on factors not referenced anywhere in the BART rules. 

Response:

 EPA disagrees with the commenters’ assertions that we did not give sufficient weight to 

presumptive BART NOx limits, or that the BART determination for FCPP was performed in a 

manner inconsistent with the RHR. 

As noted in other responses in this document, the presumptive NOx limits established in 

the BART Guidelines are determined to be cost effective and appropriate for most units. The 

establishment of presumptive BART limits, and the corresponding technology upon which those 

limits are based upon, does not preclude states or EPA from setting limits that differ from those 

presumptions. Indeed, the five statutory factors enumerated in the BART Guidelines provide the 

mechanism for establishing different requirements. EPA’s site-specific five-factor analysis for 

FCPP demonstrates that, in considering the expected remaining useful life of FCPP and the 

existing controls, SCR is cost effective , results in the most visibility improvement of all feasible 

control technologies, and does not cause energy or non-air quality environmental impacts that 

warrant its elimination as the top control option. As a result, regardless of the appropriateness 

of SCR as a control technology for most units on a national scale, or the extent to which EPA 

considered SCR in establishing the presumptive limits, the site-specific five-factor analysis 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

performed for FCPP justifies a different NOx BART limit than the presumptive NOx BART limit. 

We note the RHR states: 

States, as a general matter, must require owners and operators of greater 

than 750 MW power plants to meet these BART emission limits. We are 

establishing these requirements based on the consideration of certain 

factors discussed below. Although we believe that these requirements are 

extremely likely to be appropriate for all greater than 750 MW power 

plants subject to BART, a State may establish different requirements if the 

State can demonstrate that an alternative determination is justified based 

on a consideration of the five statutory factors. 

The RHR also states: 

If, upon examination of an individual EGU, a State determines that a 

different emission limit is appropriate based upon its analysis of the five 

factors, then the State may apply a more or less stringent limit. 

Therefore, the presumptive emission limits in the BART Guidelines are rebuttable. The 

presumptive emission limits apply to power plants with a total generating capacity of 750 MW or 

greater insofar as these sources are required to adopt emission limits at least as stringent as the 

presumptive limits, unless after considering the five statutory factors, the State determines that 

the presumptive emission limits are not appropriate. Moreover, the RHR and BART Guidelines 

do not exempt states from a five factor BART analysis, and that BART analysis may result in a 

determination of BART emission limits that are more or less stringent than the presumptive 

emission limits for subject to BART sources. The RHR states: 

For each source subject to BART, 40 CFR 51.308(e)(1)(ii)(A) requires 

that States identify the level of control representing BART after 

considering the factors set out in CAA section 169A(g), as follows: 

States must identify the best system of continuous emission control 

technology for each source subject to BART taking into account the 

technology available, the costs of compliance, the energy and non-air 

quality environmental impacts of compliance, any pollution control 

equipment in use at the source, the remaining useful life of the source, and 

the degree of visibility improvement that may be expected from available 

control technology. 

EPA disagrees with commenters’ assertions that we disregarded presumptive NOx BART 

limits entirely, and that we failed to evaluate combustion controls in any substantive manner. 

Although we do not rely upon the numerical values of the presumptive NOx limits listed in the 

BART Guidelines, the technological basis for presumptive NOx BART limits, such as the use of 

combustion control technology, boiler type, and coal type, were considered in the site-specific 

five-factor analysis. Combustion control technology was specifically considered as a potential 

retrofit technology, and costs and visibility improvements associated with combustion controls 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

were calculated and included in the TSD in order to provide a comparison to other NOx control 

technologies. As a result, presumptive BART was not disregarded or dismissed during the NOx

BART determination process. 

In addition, EPA disagrees that the rule directs authorities to consider non-combustion 

control technology only when presumptive limits cannot be met using combustion control 

technology. While a BART determination deviating from presumptive BART must be supported 

by the results of the five-factor analysis, the rule does not restrict the ability of States (or in this 

case, EPA) to initiate a five-factor analysis. Although the inability of a boiler to meet 

presumptive NOx BART limits through the use of combustion control technology is described as 

one circumstance in which a non-combustion control BART determination may be considered 

(70 FR 39172), it does not preclude consideration of other circumstances, nor is it identified as a 

qualifying threshold for performing a five-factor analysis, as commenters suggest. 

Comment:

 One of the owners of FCPP (0176/0177) stated that an agency is required to follow its 

own rules, and that failure to do so makes its action unlawful and subject to vacatur, citing Way 

of Life Television Network, Inc. v. FCC, 593 F.2d 1356, 1359 (D.C. Cir. 1979) (“[A]n agency’s 

failure to follow its own regulations is fatal to the deviant action.”) The commenter asserted that 

in this case, EPA must develop and use a BART evaluation methodology that properly accounts 

for the presumptive BART limits (see above), an incremental cost effectiveness assessment (see 

Section 3.2), an analysis of control costs as a function of visibility improvement (see 

Section 3.3), and site-specific cost information (see Section 3.1) to develop lawful BART limits 

for FCPP. 

Response:

EPA disagrees that we have not followed our own rules in performing the NOx BART 

determination for FCPP. We address the commenter’s specific concerns as follows: 

 Presumptive BART limits - As noted in responses above to comments on the presumptive 

NOx limit and the cost effectiveness of the presumptive NOx limit, while we did not 

propose that BART for FCPP was satisfied with the presumptive NOx BART limits, the 

site-specific five-factor analysis we performed did account for the technological basis for 

presumptive NOx BART limits, such as the use of combustion control technology, boiler 

type, and coal type, and also examined the ability of combustion control technology to 

meet the numerical presumptive NOx BART limits. 

 Incremental cost effectiveness assessment - As described in the comment responses 

written in Section 3.2, we agree with commenters that the BART Guidelines do 

recommend consideration of incremental cost effectiveness and our BART analysis 

performed such an assessment in accordance with the methodology described in the 

BART Guidelines. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 Analysis of control costs as a function of visibility improvement – As described in the 

comment responses written in Section 3.1, although $/deciview is discussed as an 

example of one element that may be considered when determining cost of compliance, we 

do not regard it as a mandatory metric under the five-factor analysis. We considered 

several other metrics, including total capital costs, annual costs, $/ton, and incremental 

$/ton, and do not regard $/deciview as a useful metric to inform our decision at this time. 

 Site specific cost information – As described in the comment responses written in Section 

3.1, we disagree with the commenters’ assertion that our cost analysis did not take into 

account the site-specific cost information supplied by APS. As part of the line-by-line 

analysis we performed (described in Section 3.1 responses) on the cost estimates 

provided by APS, we ultimately incorporated most of the APS cost estimates in our final 

SCR cost estimate. Our detailed, line-by-line analysis is included in the docket for this 

rulemaking and provides an explanation for why we retained, modified, or rejected each 

line item in the SCR cost estimate for each of the five units at FCPP. 

Comment: 

 Two of the owners of FCPP (0168, 0176/0177) and the Navajo Nation (0223) asserted 

that advanced combustion controls constitute BART for FCPP because such controls will result 

in meaningful emission reductions and will contribute to reasonable progress toward visibility 

improvement. 

 One of these commenters (0176/0177) noted that EPA has “determined that combustion 

controls are not likely to be effective control technologies at FCPP” (citing 75 FR 64226). The 

commenter alleged that EPA’s determination is based on superficial analysis and is mistaken. 

This commenter (0176/0177) cited Exhibit J to its comments on the ANPR,59F

60 which contains a 

detailed analysis of the use of LNB and OFA on FCPP’s units. According to the commenter, this 

analysis confirms that the use of advanced combustion controls on the five units at FCPP will 

reduce plantwide NOx emissions by 34 percent and, for those units that are subject to 

presumptive BART limits, the reductions more than satisfy the presumptive limits in the BART 

rules. 

 Two of the commenters (0168, 0176/0177) added that considering that neither SCR nor 

advanced combustion controls will produce humanly perceptible visibility improvements in the 

nearby Class I areas (see the commenters’ comments in Section 7.0) these NOx emission 

reductions must constitute BART. The commenters indicated that this is true given that the 

reductions meet presumptive BART and will make a contribution to reasonable progress toward 

the national visibility goal. One of the commenters (0176/0177) added that this conclusion is 

reinforced by the cost differential between the technologies and the other BART factors 

discussed in the commenter’s comments elsewhere in this document. 

 The Navajo Nation (0223) stated that a phased approach to emissions controls at FCPP, 

beginning with combustion controls, is fully consistent with both the CAA and the RHR, and is 

 

60 See item 11 from collection of documents titled “Comments on ANPRM 09 0598 APS Comments and Exhibits”, 

Document No. EPA-R09-OAR-2009-0598-0195. 
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the approach that the EPA should take as a prudent trustee of the Navajo Nation. According to 

the commenter, installing LNB and OFA as a first step in a phased approach to BART for the 

FCPP (and NGS) would: 

 Be consistent with the presumptive BART limits established in the BART Guidelines. 

 Result in a more clearly fact driven process, by allowing all interested parties to review 

recorded, not simply modeled, results at the next review phase. 

 Aid in the resolution of disputes over the costs to install the emission control options 

under consideration by providing the opportunity to review the actual costs incurred by 

FCPP to install LNB and OFA. (The commenter noted that NGS completed installation 

of LNB/OFA this year.) 

 Provide a reasonable timeframe in which to resolve outstanding lease and ownership 

issues that affect the productive life of FCPP (Factor 4). 

 This commenter (0223) added that the BART component of the CAA and RHR was 

meant to provide for a measured response to emissions from aging power plants; thus, requiring 

the most expensive controls is inconsistent with the law and regulations governing the BART 

process. The commenter also emphasized that requiring a power plant over which EPA has 

exclusive jurisdiction to bear a greater regulatory burden than similarly situated plants regulated 

by the states is contrary to the purposes of the Act, the RHR, and to the economic interests of the 

Navajo Nation. 

Response:

As noted in the responses to comments in Section 3.3, EPA disagrees with the comment 

that Exhibit J of APS’s comments on the ANPR confirm that advanced combustion controls on 

all five units at FCPP will reduce plant-wide NOx emissions by 34%. APS has provided 

conflicting information regarding whether or not advanced combustion controls will be effective 

at significantly reducing NOx emissions at FCPP. As outlined in the TSD for our 2010 BART 

proposal, based on an independent report by Andover Technology Partners dated April 5, 

200460F

61, we have concluded that combustion controls will in fact not be effective at significantly 

reducing NOx emissions at FCPP. Furthermore, independent of whether or not advanced 

combustion controls will allow the FCPP units to achieve presumptive NOx BART limits, EPA 

disagrees with the commenter’s assertion that a unit’s ability to meet presumptive BART 

precludes a more stringent BART determination. As noted in a previous response to comment in 

this section, while the inability of a boiler to meet presumptive NOx BART limits through the use 

of combustion control technology is described as one circumstance in which a non-combustion 

control BART determination may be considered (70 FR 39172), it is not identified as a qualifying 

threshold for performing a five-factor BART determination. 

EPA disagrees that SCR will not produce humanly perceptible impacts. As noted in 

responses to comment in Section 7, visibility modeling performed by EPA of the impacts of SCR 

installation at FCPP indicates visibility impacts from 1.2 to 6.0 deciviews, depending on the 

Class I area (based upon IWAQM Phase 2 background ammonia value of 1 ppb). If low 

 

61See Document No. EPA-R09-OAR-2010-0683-0059.
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ammonia background values are used as recommended by some commenters, visibility impacts 

range from 0.8 to 3.2 deciviews. Although the lower range of these less conservative modeling 

results fall below the 1.0 deciview value commonly cited as the threshold for human 

perceptibility, the range of impacts is not negligible. 

 

EPA does agree with certain aspects of the Navajo Nation’s comments regarding a 

phased implementation strategy to attaining national visibility goals. In 40 CFR 51.308(f), States 

are required to revise their regional haze implementation plans every ten years, which is a 

process that involves evaluating their ability to attain reasonable progress goals and potentially 

updating their long-term strategy for regional haze. The periodic revision requirement described 

in 40 CFR 51.308(f), however, does not extend to the implementation plan for BART 

requirements. The phased approach described by the Navajo Nation has certain benefits, and a 

phased approach is incorporated into the alternative emission control strategy. 

Comment: 

 Two federal agencies (0175, 0224)) and two groups of environmental advocacy groups 

(0095, 0182) argued that the NOx emission limit for the units at FCPP should be 0.05 lb/MMBtu 

based on the capabilities of SCR. Another environmental advocacy group (0183) stated that EPA 

should reexamine the basis for determining the NOx limit and consider tighter NOx controls, but 

did not specify what that tighter limit should be. The comments of the federal agencies are 

summarized below, followed by those of the environmental advocacy groups. 

 The federal agency commenters (0175, 0224) stated that, given that BART is meant to 

achieve the best possible emissions reductions, EPA should not base its emission limits on the 

“minimum reduction expected from SCR, estimated by Hitachi Power Systems America” (citing 

the TSD for our proposed BART determination) because real-world application of SCR indicates 

that lower NOx emission limits are routinely reached. Regarding the emission limits for Units 4 

and 5, the commenters noted that of the 20 cell burners with SCR in 2010, 12 had lower NOx

limits than proposed by EPA for FCPP, with 3 EGUs at less than 0.06 lb/MMBtu. Based on this 

information, the original APS BART analysis of SCR at 0.06 lb/MMBtu (annual and 24-hour 

average), and the “common knowledge” that SCR can achieve at least 90 percent reduction, the 

commenters concluded that the installation of SCR at FCPP is capable of reducing annual NOx

emissions by 90 percent to 0.05 lb/MMBtu on an annual average basis. 

 One of the federal agency commenters (0224) specifically refuted the additional rationale 

provided by EPA in the supplemental proposal for its 80 percent SCR efficiency estimate: 

 The EPA took into account the degradation of the SCR catalyst over its lifetime and 

calculated the emission limit to reflect the capability of the catalyst just prior to its 

replacement on a 3-year cycle. According to the commenter (0224), modern SCRs are 

typically designed with one or two spare catalyst layers to facilitate catalyst management 

and account for catalyst degradation over time; the issue cited by EPA is not a technical 

limitation on SCR, but is simply a cost item to be accounted for in the proper design and 

operation of the SCR. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 The EPA stated that pursuing NOx control efficiencies of greater than 80 percent on 

Units 4 and 5 is limited by formation of H2SO4 from the SCR catalyst because the 

additional layers of catalyst needed to increase NOx control efficiency would increase 

emissions of H2SO4, most affecting nearby Mesa Verde National Park. The commenter 

(0224) gave the following reasons why this argument is incorrect. (Commenter 0175 also 

made similar points.) 

– The EPA’s statement “the presence of additional catalyst would result in higher 

emissions of sulfuric acid” is unsupported. The EPA used the EPRI method for 

estimating H2SO4 emissions. The only factor in the EPRl method that is related to the 

SCR and affects H2SO4 generated by the catalyst is the catalyst oxidation rate, not the 

volume, area, or number of catalyst layers as implied by EPA. 

– The EPA statement that “Minimizing the formation of primary SO3/H2SO4 in the 

catalyst bed is most important for visibility improvement at Mesa Verde National 

Park, the closest Class I area to FCPP” is unsupported. 

o The EPA’s modeling results in the October 2010 TSD show that even with 

increases in sulfate emissions from SCR installation, visibility improves at Mesa 

Verde National Park and every other national park. 

o The EPA appears to have assumed that at least one additional catalyst layer would 

have to be added to the two layers assumed by APS, thus increasing H2SO4

emissions by 50 percent, but application of EPA’s Control Cost Manual method 

for estimating SCR catalyst volume indicates that increasing NOx removal 

efficiency from 80 to 90 percent would require only a 14 percent increase in 

catalyst volume. If one assumes that H2SO4 emissions are directly related to 

catalyst volume, a 14 percent increase in catalyst volume would mean an increase 

in sulfate emissions of 0.3 lb/hr, which is highly unlikely to have any appreciable 

impact upon visibility when compared to the much greater NOx reductions. To 

verify the potential visibility impact, EPA should model the 90 percent NOx

reduction scenario with its increased sulfate emissions. 

 The EPA stated that the high ash content (approximately 25 percent) of the coal burned at 

FCPP may adversely affect the capability of SCR to reach the highest end of the control 

efficiency range without the use of additional layers of catalyst or more frequent catalyst 

replacement. According to the commenter, this is not consistent with previous EPA 

proposals for SCR emissions limits at facilities that use coal with similar ash content. For 

Desert Rock power plant with coal at 23.4 percent ash, EPA issued a permit limiting 

annual NOx emissions to 0.0385 lb/MMBtu, and EPA has recently proposed NOx BART 

at 0.05 lb/MMBtu (30-day rolling average) at the nearby San Juan Generating Station 

which burns local coal with 21.3 percent ash. Unless the FCCP ash contains some 

unusual catalyst poison, the 25 percent ash content is not a technical feasibility issue that 

would affect SCR effectiveness, but is a matter of proper SCR design, operation, and 

maintenance. 

 This federal agency commenter (0224) also stated that NOx BART for Units 1-3 should 

be 0.05 lb/MMBtu on an annual basis. The commenter noted that unsuccessful attempts to 

reduce NOx emissions at FCPP with combustion controls occurred over a decade ago when this 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

technology was not as fully developed as now, and pointed out that APS’s BART analysis 

concluded that such controls are technically feasible and would reduce NOx emissions 

significantly. The commenter evaluated Clean Air Markets Division (CAMD) data for 2000 - 

2009 and found 33 dry-bottom, wall-fired boilers with NOx emissions rates similar to FCPP 

Units 1-3 (0.6 - 0.8 lb/MMBtu) that had been reduced to 0.4 lb/MMBtu or less by application of 

modern combustion controls. The commenter asserted that because the typical approach is to 

first reduce NOx emissions by combustion controls before adding SCR, these real-world CAMD 

data support the belief that using combustion controls and SCR could reduce NOx at FCPP Units 

1-3 to 0.05 lb/MMBtu on an annual basis. 

 One group of environmental advocacy groups (0182) made similar arguments in asserting 

that a lower NOx limit is technically feasible and legally required as BART for FCPP. To support 

this assertion, the commenter drew heavily on an attachment containing comments prepared by 

Dr. Phyllis Fox61F

62 This comment summary includes the comments presented by Commenter 

0182; the reader may refer to the attachment (0182) for greater detail. Commenters also argued 

that emission limits should be based on a rolling average of 30 successive boiler operating days. 

 The commenter (0182) argued that neither the BART proposal nor the supplemental 

proposal represents the emission reduction capabilities of BART and thus fail to satisfy the 

CAA. The commenter asserted that a lower limit of 0.05 lb/MMBtu for NOx over a 30-day 

rolling average at each FCPP unit is technically feasible based on a combination of combustion 

controls (LNB and OFA) and a 90-percent-efficient SCR. 

 The commenter (0182) noted that the definition of BART at 40 CFR 51.301 is “an 

emission limitation based on the degree of reduction achievable through the application of the 

best system of continuous emission reduction....” The commenter asserted that EPA picked 

80 percent NOx removal because it was the minimum level of control estimated by Hitachi 

(citing TSD pages 31 and 87), but selecting the lower end of a range quoted by a single vendor 

when the EPA only asked for 80 percent removal efficiency does not satisfy the minimum 

statutory requirements of BART. 

 The commenter (0182) also stated the EPA indicated that 80 percent removal is 

appropriate because it provides the operator a margin of safety. However, the commenter stated 

the definition of BART does not anticipate a margin of safety, asserting that arbitrarily adjusting 

down the emission reduction that can be achieved by SCR from 90 percent to 80 percent violates 

the requirement that BART emission limits be set based on the best removal system operated at 

the optimal efficiency to eliminate visibility impairment. 

 The commenter (0182) asserted that modern SCRs are routinely designed and operated to 

achieve 90 percent NOx control and that based on this well-accepted industry standard, NOx

control of at least 90 percent is BART. The commenter noted that the BART Guidelines at 

40 CFR part 51, Appendix Y state, “In general, a commercially available control option will be 

presumed applicable if it has been used on the same or a similar source type.” 

 

62 See item (2) in collection of documents titled “Public Comment_8 Environmental Groups (Barth)_Letter 5-2-11”. 

EPA-R09-OAR-2010-0683-0182. 
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 The commenter (0182) also contended that LNB and OFA are feasible for all five units at 

FCPP. The commenter rejected EPA’s statement that it would be difficult to retrofit Units 4 and 

5 with modern LNB technology (citing 76 FR 10534) and pointed out that the operator of FCPP 

has stated that the combination of LNB and OFA is technically feasible for these units. The 

commenter indicated that the use of LNB/OFA on Units 1-5 would reduce NOx emissions by 

27 to 46 percent, making SCR with a removal efficiency of 90 percent sufficient to satisfy a 

0.05 lb/MMBtu NOx limit. 

 The commenter (0182) argued that a 0.05 lb/MMBtu limit is consistent with EPA’s 

determinations elsewhere, such as for the San Juan Generating Station (proposed limit of 

0.05 lbs/MMBtu, 30-day rolling average) and for Desert Rock (final permit limit of 

0.035 lbs/MMBtu, 365-day rolling average). According to the commenter, an EPA-issued permit 

containing a lower NOx limit creates a presumption of technical feasibility for purposes of BART 

– the BART Guidelines at 40 CFR part 51, Appendix Y state that “if there is a permit requiring 

the application of a certain technology or emission limit to be achieved for such technology, this 

usually is sufficient justification for you to assume the technical feasibility of that technology or 

emission limit.” 

 According to the commenter (0182), EPA asserted that lower NOx limits were not 

feasible for two reasons: (1) excessive formation of sulfuric acid mist, and (2) high ash content in 

the FCPP coal supply. The commenter asserted that the formation of sulfuric acid mist is not 

expected to be as high as claimed by EPA, and that independent air dispersion modeling 

established that the actual formation of sulfuric acid mist does not cause a significant level of 

visibility impairment in any case (citing an attached report by Andrew Gray62F

63). The commenter 

added that the ash content of FCPP’s coal (25%) is not significantly higher than other coals 

where EPA imposed a lower NOx limit, such as at the San Juan Generating Station. The 

commenter concluded that a lower BART limit is technically feasible and legally required. 

 In “preliminary” comments submitted prior to the supplemental proposal, a similar group 

of environmental advocacy groups (0095) suggested NOx limits of 0.05 lb/MMBtu on a 30-day 

rolling average measured using continuous emission monitoring system (CEMS), with 

compliance in 2014. The commenter added that the BART determination should include a 

provision that FCPP may forego BART implementation at any unit if it agrees to retire that unit 

prior to the deadline for BART implementation. The commenter requested that these limits be 

published for comment in any Federal Register notice published to take comment on the FCPP 

alternative BART proposal. 

 Another environmental advocacy group (0183) argued that EPA should reexamine its 

basis for determining NOx BART, believing that SCR likely can achieve greater than 80 percent 

efficiency (EPA’s assumed efficiency) and a lower emission rate at FCPP. The commenter noted 

that the BART analysis submitted by the facility found SCR with approximately 90 percent 

removal efficiency to be feasible, resulting in an emission rate of 0.06 lb/MMBtu for Units 2 – 5. 

The commenter stated that EPA should reexamine its consideration of catalyst life, H2SO4

 

63 See item (5) in collection of documents titled “Public Comment_8 Environmental Groups (Barth)_Letter 5-2-11”. 

EPA-R09-OAR-2010-0683-0182. 
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formation, and ash content of the coal by comparing its assumptions with other coal-fired power 

plants with similar parameters, and should establish a rigorous NOx limit reflecting BART. 

Response:

EPA disagrees with the commenter’s assertion that emission limits associated with BART 

must meet the lowest emission rate achieved with that technology at any coal-fired power plant. 

The Regional Haze Regulations at 40 CFR §51.308(e)(1)(ii)(A) state that: 

The determination of BART must be based on an analysis of the best system of 

continuous emission control technology available and associated emission 

reductions achievable for each BART-eligible source that is subject to BART . . . 

Additionally, the BART Guidelines state that: “[i]n assessing the capability of the control 

alternative, latitude exists to consider special circumstances pertinent to the specific source 

under review, or regarding the prior application of the control alternative”, (70 FR at 39166) 

and that “[t]o complete the BART process, you must establish enforceable emission limits that 

reflect the BART requirements . . .” (70 FR at 39172). The five-factor BART analysis described 

in the Guidelines is a case-by-case analysis that considers site specific factors in assessing the 

best technology for continuous emission controls. After a technology is determined as BART, the 

BART Guidelines require establishment of an emission limit that reflects the BART requirements, 

but does not specify that the emission limit must represent the maximum level of control achieved 

by the technology selected as BART. The BART Guidelines and the RHR do not preclude 

selection of the maximum level of control achieved by a given technology as BART, however, the 

emission limit set to reflect BART must be achievable by the specific source and should be 

determined based on consideration of site-specific factors. Therefore, limits set as BACT during 

PSD review (e.g., Desert Rock), or emission rates achieved from the operation of individual 

facilities under an emissions trading program (e.g., Clean Air Act Interstate Rule (CAIR)) may 

provide important information, but should not be construed to automatically represent the most 

appropriate BART limit representative of a given technology for a given facility. 

 While some commenters asserted that combustion controls would be feasible upstream of 

SCR to further reduce NOx emissions to meet a limit of 0.05 lb/MMBtu, in its comment letter, the 

National Park Service agreed with EPA that the addition of combustion controls such as OFA 

may “not (be) worth the small incremental reduction in NOx emissions”, based on its review of 

the CAMD database showing that of the 35 cell burner boilers, only eight had combustion 

controls, and that two cell burner boilers at Hatsfield Ferry were retrofit with OFA in 2001 and 

2003 with minimal NOx reductions.63F

64 As discussed in the TSD for our proposed BART 

determination, because additional combustion controls at FCPP would not achieve significant 

reductions in NOx and may cause operability issues for the boilers, EPA determined that SCR, 

without the addition of new combustion controls, is BART for FCPP. 

 

64 See page 1 of the attachment (titled “National Park Service Comments on EPA's February 25, 2011 BART 

Proposal for the Four Corners Power Plant, April 22, 2011 AS REVISED MAY 17, 2011”) to document titled “DOI 

Resubmission of Comments on EPA BART Four Corners Navajo Nation_7-11-11”, EPA-R09-OAR-2010-0683-

0224. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

A consortium of several environmental organizations (0182) argued that a 30-day rolling 

average emission limit of 0.05 lb/MMBtu should be determined BART for FCPP, based on a 

final report written by Dr. Phyllis Fox.64F

65 In Table 10 – CAMD Maximum Rolling Averages 

(2006 – 2010) Calendar-Day Basis of her final report, Dr. Fox argued that because 3 of the 20 

best performing units achieved a maximum 30-day calendar average emission rate of 0.05 

lb/MMBtu (rounded to 1 decimal place), that 0.05 lb/MMBtu is the appropriate BART limit for 

FCPP. As stated above, EPA disagrees that an emission limit set in association with a BART 

determination must represent the lowest achieved emission rate from the best performing unit 

using that technology. EPA further notes that the maximum 30-day calendar average emission 

rates for the 17 other top performing units listed in Table 10 of the commenter’s report exhibited 

significant variability (0.056 – 1.1 lb/MMBtu), even though the annual average emission rates 

listed are all below 0.07 lb/MMBtu. 

In its comments, NPS provided examples of 3 cell burner boilers currently equipped with 

SCR: Cardinal Units 1 and 2 and Belews Creek Unit 1. In the context of an annual average limit, 

however, examination of the 30-day calendar average emission rates is also informative. Based 

on NOx data from the Clean Air Markets Division (CAMD), EPA notes that over 2009 – 2011 

(January – June 2011), NOx emissions from Cardinal Unit 1 showed an increasing trend, with 

minimum 30-day calendar average NOx emission rates increasing from 0.025 to 0.033 to 0.043 

lb/MMBtu in 2009, 2010, and 2011, and maximum 30-day calendar average NOx emission rates 

increasing from 0.04965F

66 to 0.052 to 0.065 lb/MMBtu in 2009, 2010, and 2011.6F67 The CAMD data 

show that Cardinal Unit 2 had numerous days of non-operation during 2009 – 2011, so 30-day 

calendar average values were generally higher. However, if we exclude 30-day calendar 

averages that were clearly affected by nearly a full month of non-operation67F

68, Cardinal Unit 2 

shows a similar pattern as Unit 1, with an increasing trend in minimum (0.021, 0.043, 0.051 

lb/MMBtu) and maximum 30-day calendar averages over 2009 – 2011 (0.056, 0.074, 0.076 

lb/MMBtu). Belews Creek 1 also showed a similar pattern of generally increasing minimum 

(0.027, 0.040 and 0.041 lb/MMBtu) and maximum (0.078, 0.099, 0.094 lb/MMBtu) 30-day 

calendar average emission rates over 2009 – 2011, with the highest maximum 30-day average in 

2010 of 0.0989 lb/MMBtu. Although commenters are correct in stating that the best performing 

units can achieve 30-day rolling emission rates of 0.05 lb/MMBtu or lower, CAMD data show 

significant variability in emission rates, both over time for a given unit, and between the best 

performing units. Some of this variability may be related to catalyst aging, or may be related to 

the participation of these units in trading programs (therefore these units operate without an 

absolute limit on individual boilers). Regardless of the cause of this variability, EPA notes that 

significant variability over a 30-day average, even among the best performing units, does exist, 

and EPA disagrees that an emission limit set in association with a BART determination must 

 

65 See items (2 and 3) in collection of documents titled “Public Comment_8 Environmental Groups (Barth)_Letter 5-

2-11”. EPA-R09-OAR-2010-0683-0182. 

66 For Cardinal Unit 1, to be more indicative of normal operation, EPA excluded the monthly emission rate from 

May 2009 of 0.085 because it represented just one day of partial operation during the month of May. Unit 1 was not 

operated for the remainder of May 2009. 

67 See tab titled “with SCR” in spreadsheet titled “Cellburners CAMD CAIR.xlsx” in docket for this final 

rulemaking. 

68 For Cardinal Unit 2, to be more indicative of normal operation, EPA excluded the monthly emission rate from 

March and November in 2009, and April in 2011. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

represent the lowest rate achieved on 30-day rolling average basis from the best performing unit 

using that technology. 

Commenters recommended that EPA set the 30-day rolling average limit based on a 

boiler operating day (BOD), which would serve to average out emission spikes better than a 

calendar average (especially spikes that are caused by a single operating day experiencing 

shutdown in a calendar month), suggesting that higher limits to accommodate these emission 

spikes are not needed. Commenters assert that extreme values in the 30-day calendar averages 

reported by CAMD, in particular, those that are controlled by a very limited number of 

operating hours in a calendar month, will be dampened by application of the 30-BOD rolling 

average, but we note that significant variability still exists despite the application of a 30-BOD 

rolling average. EPA agrees that the emission limit should be based on a 30 BOD for the BART 

alternative option identified in the supplemental proposal. The 30-calendar-day average was 

inadvertently carried over from the original proposal. We do find that the 30-calendar-day 

average for the plant-wide average NOx BART determination is the appropriate approach for 

this limit. All hours of operation of all of the units go into this plant-wide average and it is 

appropriate to base this on a rolling 30-calendar-day basis. 

Over the 2009 – 2010 period examined in Exhibit 14 to item 2 of comment number 0182, 

the 30-BOD rolling averages calculated by Dr. Fox for Cardinal Unit 3 shows a range of 0.028 

lb/MMBtu to 0.065 lb/MMBtu, with reported 1-year (2010) and 2-year (2009 – 2010) averages 

of 0.048 lb/MMBtu. The 30-BOD rolling averages for Cardinal Unit 3 also show a general 

increasing trend in actual emission rates over the two year period of 2009 – 2010. For Havana 

Unit 9, which commenters cited as the best performing unit achieving a 30 calendar day rolling 

average of 0.05 lb/MMBtu in 2010 and a 365-day rolling calendar average of 0.036 lb/MMBtu, 

Dr. Fox calculated 30-BOD rolling averages over 2006 – 2010 that exhibited a significant range 

of 0.022 to 0.067 lb/MMBtu. NOx emission rates over 2006 to early 2009 appear to exhibit 

seasonal variability that may be related to active operator management of the SCR system (lower 

emission rates during the summer ozone season and higher emission rates during the non-ozone 

season). However, over 2009 – 2010, this seasonality was not shown but the general increasing 

trend over that 2-year period is still exhibited. Although EPA agrees that using the definition of 

BOD in calculating 30-day rolling averages will help to dampen emission spikes associated with 

startup or shutdown events, significant variability still occurs, and steady increases in actual 

emission rates are exhibited and may be associated with catalyst aging. Even when Dr. Fox 

calculated 30-BOD rolling averages for Cardinal Unit 3, where the high value for the maximum 

30-day calendar average resulted from one partial day of operation in April 2010, Cardinal Unit 

3 would not have consistently met an emission limit of 0.05 lb/MMBtu over 2009 – 2010. EPA 

disagrees with commenters that 0.05 lb/MMBtu achieved as a 30-calendar day average at 

Havana Unit 9 and Parish Unit 8 is representative and appropriate to apply automatically as a 

BART limit for any unit for which SCR was determined to be BART. 

EPA examined the most recent CAMD emission rate data for 12 cell burner boilers 

currently operating with SCR68F

69 over 2009 – June 2011. Table 1 summarizes the NOx emission 

rates (in lb/MMBtu) and the percent reduction in NOx when the SCR was operated for the lowest 

 

69 See tab titled “with SCR” in spreadsheet titled “Cellburners CAMD CAIR.xlsx” in docket for this final 

rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

achieved monthly calendar averages and the highest achieved monthly calendar averages to 

show the range in variability within each year and compared across 2009 – 2011. EPA did not 

exclude any monthly calendar averages from the minimum and maximum analyses shown in 

Table 1. In order to determine what might be an appropriate % reduction to represent all cell 

burner boilers currently using SCR, we calculate the average % reduction from the highest 

emission rate achieved over all 12 units. As stated above, the 30-day rolling limit must be set to 

accommodate the highest emission rate expected over the life of the catalyst. The percent 

reduction achieved from the monthly calendar average emission rate over 2009 – June 2011 

from the 12 units ranged from 48% to 90%, with an average value of 78%. The percent 

reduction associated with the lowest emission rates achieved over 2009 – June 2011 are on par 

with the percent reductions cited by commenters as the “common knowledge” capabilities of 

SCR. 

Table 1: NOx Emission Rates (lb/MMBtu) and Percent NOx Reductions from Cell Burner Boilers 

with SCR over January 2009 – June 2011 

Facility 

(State) 

Unit Lowest Emission Rate and Highest % Reduction Highest Emission Rate and Lowest % Reduction 

2009 2010 2011 2009 2010 2011 

Rate Reduc Rate Reduc Rate Reduc Rate Reduc Rate Reduc Rate Reduc 

Alcoa 

(IN) 

4 0.088 79% 0.080 81% 0.085 80% 0.161 62% 0.173 59% 0.115 73% 

Monroe 

(MI) 

3 0.048 90% 0.052 89% 0.065 86% 0.124 73% 0.146 69% 0.208 55% 

Monroe 

(MI) 

4 0.058 88% 0.053 89% 0.070 85% 0.248 48% 0.134 72% 0.157 67% 

Belews 

(NC) 

1 0.027 95% 0.040 93% 0.041 92% 0.078 85% 0.099 81% 0.094 82% 

Belews 

(NC) 

2 0.024 94% 0.033 92% 0.032 92% 0.064 85% 0.061 86% 0.063 85% 

Cardinal 

(OH) 

1 0.025 95% 0.033 94% 0.043 92% 0.085 83% 0.052 90% 0.065 87% 

Cardinal 

(OH) 

2 0.021 96% 0.043 93% 0.051 91% 0.206 65% 0.074 87% 0.076 87% 

Gavin 

(OH) 

1 0.065 91% 0.071 90% 0.072 90% 0.105 85% 0.122 83% 0.083 88% 

Gavin 

(OH) 

2 0.063 93% 0.068 92% 0.071 92% 0.099 88% 0.102 88% 0.099 89% 

Muskingum 

(OH) 

5 0.049 92% 0.048 92% 0.051 91% 0.188 69% 0.149 75% 0.088 85% 

Cumberland 

(TN) 

1 0.060 91% 0.069 89% 0.060 91% 0.135 79% 0.129 80% 0.102 84% 

Amos 

(WV) 

3 0.041 94% 0.045 94% 0.052 93% 0.185 74% 0.090 87% 0.107 85% 

Commenters claim that emissions of sulfuric acid mist and the high ash content of coal 

used by FCPP, and considerations of catalyst life are not barriers to achieving higher NOx

reduction efficiencies than proposed by EPA. EPA disagrees with comments that our statement 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

regarding the impact of additional layers of catalyst on increasing sulfuric acid emissions is 

unsupported. EPA understands from our correspondence with Hitachi Power Systems America 

that each layer of catalyst used results in an incremental increase in the conversion rate of SO2

to SO3. The EPRI method used for calculating sulfuric acid requires the input of a SCR catalyst 

oxidation rate. This oxidation rate varies depending on catalyst type and number of layers used. 

For the ultra low SO2 to SO3 oxidation catalysts offered by Hitachi, each layer contributed 

roughly 0.167% conversion, with 3 layers totaling 0.5%. The use of an additional layer, such as 

in a 3+1 system, would thus increase the conversion rate to nearly 0.7% when all 4 catalyst 

layers are in operation. Further NOx reductions achieved from the addition of a 5th layer of 

catalyst would likely exacerbate pluggage and back-pressure concerns related to the ash content 

of the coal and also may affect cost and operation of the unit. Commenters have not submitted 

information to refute this. 

The ash content of coal has an important effect on the effectiveness of SCR because high 

ash content in coal can cause pluggage and catalyst erosion and thus reduce available catalyst 

area and activity for NOx reduction. Based on coal quality information provided by the Energy 

Information Administration within the U.S. Department of Energy’s Office of Coal, Nuclear, 

Electric and Alternate Fuels69F

70, the coal ash content of coal burned at FCPP (20.34%)70F71 is 

significantly higher (see Table 2) than the ash content of coals burned by the 1171F

72 cell burner 

boiler units operating with SCR at 7 different facilities, as well as the Parish facility (Unit 5 is 

reported in CAMD to be a wet-bottom wall-fired boiler) cited by commenters (0182) as being 

one of the best performing units. EPA could not locate ash content of coal burned at the Havana 

facility (Unit 9 is reported in CAMD to be a wet-bottom wall-fired boiler) in Illinois in the EIA 

report. EPA notes that only four other facilities, in addition to FCPP, were reported in the EIA 

to burn coal with ash content greater than 20%: San Juan Generating Station (SJGS) in New 

Mexico, San Miguel in Texas, Nucla in Colorado, and North Branch in West Virginia. None of 

those facilities currently have SCR installed on their boilers, however, Region 6 recently 

finalized a FIP for SJGS with a limit of 0.05 lb/MMBtu, representing an 83% reduction in NOx

emissions. The emission limit EPA Region 6 set for SJGS is lower than the limit we set for FCPP 

because SJGS uses a different boiler type than FCPP and modern combustion controls have 

already been installed and have reduced NOx emissions at SJGS by 29 - 33%.72F

73 EPA has 

determined that because Units 4 and 5 at FCPP are cell burner boilers, modern combustion 

controls would not significantly reduce NOx emissions from FCPP. Even though the emission 

limit differs, the reduction efficiency from the installation and operation of SCR at FCPP and 

SJGS are generally consistent, particularly when considering the similarly high ash content of 

coal (>20%) used at both facilities. In 2008, EPA Region 9 issued a pre-construction Prevention 

of Significant Deterioration (PSD) permit to allow construction of a new coal-fired power plant 

 

70 “Cost and Quality of Fuels for Electric Utility Plants 2001”. Energy Information Administration, Office of Coal, 

Nuclear, Electric, and Alternative Fuels, US Department of Energy, March 2004. DOE/EIA-0191(01), included in 

the docket for this final rulemaking. 

71 APS reports the ash content of coal burned at FCPP as approximately 25%, as stated in the TSD for our proposed 

BART determination (EPA-R09-OAR-2010-0683-0002). 

72 EPA could not locate information in the EIA report on the Alcoa Allowance Management Inc Facility in Indiana. 73 See page 4-3 of report titled “PNM BART Report for SJGS_final to PNM_June 18, 2007.pdf” in the docket for 

this final rulemaking. Pre-consent decree emission rates on Units 1 – 4 at SJGS ranged from 0.42 – 0.45 lb/MMBtu. 

Post-consent decree emission limits for those units were 0.30 lb/MMBtu. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

on the Navajo Nation, known as the Desert Rock Energy Facility (Desert Rock).73F

74 If constructed, 

Desert Rock would have used the same coal as FCPP from the BHP Navajo Mine and the final 

PSD permit set a NOx limit of 0.05 lb/MMBtu (on a rolling 365-day average). Commenters argue 

that if Desert Rock was required to meet a limit of 0.05 lb/MMBtu using the same coal as FCPP, 

the ash content should not hinder FCPP from achieving similarly low NOx emission rates. EPA 

notes that if constructed,74F

75 Desert Rock would have been a new, state-of-the-art facility 

specifically designed with boiler characteristics, combustion controls, and post-combustion 

controls to meet the Best Available Control Technology (BACT) requirements for numerous 

criteria and non-criteria pollutants. FCPP is an existing, over 40-year-old power plant. The 

Regional Haze Rule requires a case-by-case BART (best available retrofit determination), which 

need not be equivalent to BACT for new facilities. 

Table 2: Ash Content of Coals Burned at Various Facilities using SCR 

Facility Name Owner75F

76 State Ash Content

Monroe Detroit Edison Michigan 6.3% 

Belews Creek Duke Power North Carolina 12.23% 

Cardinal Cardinal Operating Company Ohio 11.56% 

Gavin Ohio Power Company Ohio 11.3% 

Muskingum Ohio Power Company Ohio 11.54% 

Cumberland Tennessee Valley Authority Tennessee 9.42% 

Amos Appalachian Power West Virginia 11.93% 

HL&P Parish Reliant Texas 5.28% 

Based on the significant 30-calendar-day average variability exhibited by the top 

performing units in Table 10 of comment number 0182, and the variability in 30-calendar-day 

average and the 2009 – June 2011 30-calendar-day average % NOx reduction of 78% exhibited 

by 12 cell burner boilers equipped with SCR, EPA continues to affirm that a limit representing 

an 80% reduction in NOx emissions reflects what is achievable using the technology determined 

as BART for FCPP. 

Commenters further argue that many of the best-performing units operate without 

permitted emission limits under an emission trading program and therefore have no incentive to 

optimize SCR operation because they do not need to comply with an emission limit. EPA 

disagrees with that statement and notes that units that operate under a regional NOx trading 

program have a financial incentive to reduce emissions to the greatest economic extent possible 

in order to sell those emission offsets to units that cannot meet the emission cap established by 

the trading program. 

 

74 http://www.epa.gov/region9/air/permit/desert-rock/ 75 Desert Rock has not been constructed. EPA requested a voluntary remand of the Desert Rock PSD permit in 2009 

to incorporate new applicable requirements. The developers of Desert Rock have not yet submitted a revised PSD 

application to EPA. 

76 As reported in the EIA Report (March 2004), included in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Annual Average Limit

In our Supplemental Proposal, EPA requested comment on setting a lower NOx limit over 

a longer averaging time to account for catalyst degradation over time. In its comments, NPS 

recommended an emission limit of 0.05 lb/MMBtu or lower, on an annual average. NPS cited 

three examples of cell burner boilers achieving annual average NOx emission rates less than 

0.06 lb/MMBtu and greater than 90% NOx removal: Cardinal Units 1 and 2, and Belews Creek 

Unit 1. EPA agrees with NPS that over a 2-year average, NOx emissions from Cardinal Unit 1 

averaged 0.036 lb/MMBtu (2009 – 2010), however, as discussed above, these three units showed 

a general increasing trend in NOx emission rates over time and the highest 30-day calendar 

average in 2011 of 0.065 lb/MMBtu was over 1.8 times greater than the 2-year average NOx

emission rate achieved by Cardinal Unit 1. For Cardinal Unit 2, the maximum 30-day calendar 

average in 2011 was nearly 1.8 times higher than the 2-year average of 0.043 lb/MMBtu (2009 – 

2010), and for Belews Creek 1 the highest maximum 30-day average in 2010 of 0.0989 

lb/MMBtu that was nearly 2.2 times higher than the 2-year average of 0.045 lb/MMBtu (2009 – 

2010). The emission rate data from the three units cited by NPS suggest that 30-day average 

emissions for these three units were roughly two times higher than the 2-year annual average 

emission rates. 

Data provided by Dr. Fox in Table 10 of comment number 0182 shows that 9 of the top 

20 performing units with SCR met an emission rate of 0.05 lb/MMBtu or better over a 365-day 

calendar average. The remaining units ranged from 0.055 – 0.069 lb/MMBtu over a 365-day 

calendar average. Based on our review of the most recently available CAMD data from 12 cell 

burner boilers currently equipped with SCR, the % NOx reduction exhibited over a nearly 3 year 

average (2009 – June 2011) ranges from 73 – 92%, with an average % NOx reduction of 87%.76F

77

EPA agrees with commenters that NOx emission limits over a longer averaging time can be 

lower than emission limits over a shorter averaging time. However, in its comment letter on the 

Supplemental Proposal, APS stated that it opposed any further lowering of the NOx emission 

limit for several reasons, including cost of compliance and potential operational problems. 

Although not specifically stated by APS, EPA infers that APS’s opposition to a lower limit 

includes opposition to a lower limit over a longer averaging time. Additionally, APS stated that, 

based on statistical analysis it has conducted, it believes there may be potential compliance 

problems with the 30-day rolling average period, in particular, if two malfunction events 

occurred close together towards the end of the catalyst replacement cycle. Therefore, APS stated 

a 90-day rolling averaging would be needed to reasonably assure continuous compliance with 

the proposed emission limit in the Supplemental Proposal. APS did not include its statistical 

analysis in its comments on the Supplemental Proposal, and, for the reasons stated above and 

supported by the emission rates and control efficiencies from other cell burner boilers with SCR 

(Table 1), EPA has determined a 30 calendar-day rolling average is appropriate for the final 

NOx limit for BART. Under the alternative emission control strategy we based the limit on 30-

BOD average. In addition, although EPA agrees with commenters that setting a lower emission 

limit over a longer averaging time is supported by a review of emission data from other 

facilities, we do not have enough information specific to Units 4 and 5 at FCPP to set a different 

limit over a longer averaging time, nor is it necessary to supplement the short-term limit (30-day 

 

77 See summary tab in “Cellburners CAMD CAIR.xlsx” spreadsheet in the docket for this rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

rolling average) EPA is setting in our final action with an additional limit over a longer 

averaging time. 

Comment:

 One of the owners of FCPP (0176/0177) stated a willingness to support a NOx emission 

limit of 0.098 lb/MMBtu for Units 4 and 5 under the alternative proposal, but only in the context 

of an alternative emission reduction strategy that includes resolution of the related issues. The 

commenter asserted that issues with the cell-burner configuration of these units, the high-ash 

coal that is burned, and the increase in H2SO4 emissions that would occur at increased NOx

efficiency preclude any further tightening of the NOx limit. The commenter recommended that 

compliance with the emission limit be determined on a 90-day rolling average basis, instead of 

the proposed 30-day rolling average. The commenter strongly opposed any plantwide NOx limit 

more stringent than 0.11 lb/MMBtu in a traditional BART FIP. 

 The Navajo Nation (0223) similarly endorsed the proposed 80 percent reduction in NOx

emissions from Units 4 and 5, with a limit of 0.098 lb/MMBtu, under the supplemental proposal, 

based on the site-specific parameters at FCPP. The commenter also cautioned that any reduction 

in this standard must be evaluated carefully, because additional catalyst layers would be required 

which could result in increased ammonia slip and H2SO4 emissions contributing to visibility 

impairment, increased compliance costs, and operational difficulties. The commenter noted that 

selection of the catalyst will be critical for the operation and performance of the SCR system. 

Response:

EPA agrees that the appropriate limit for Units 4 and 5 under the alternative strategy is 

0.098 lb/MMBtu (over a rolling average of 30 successive boiler operating days) for the reasons 

aforementioned. The final rule reflects this limit. 

Comment:

 In virtually identical comments that addressed both FCPP and NGS submitted prior to the 

supplemental proposal, one public interest advocacy group (0094) and one environmental 

advocacy group (0146) requested that EPA implement the most stringent air pollution control 

measures, specifically SCR, as BART for these plants in order to improve visibility in the Class I 

areas to the greatest extent possible. The commenters noted that FCPP and NGS are two of the 

biggest sources of NOx on the Colorado Plateau, and stated that they should not be allowed to be 

permitted polluters and impair visibility throughout the region. 

 In later comments, the public interest advocacy group (0112) took the position that SCR 

is BART for FCPP. The commenter opposes any attempt to substitute SNCR for SCR as BART, 

which the commenter indicated the owner of SJGS is trying to do. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 One private citizen (0160) also urged EPA to require FCPP to install SCR controls at all 

five of the plants units. 

Response:

EPA agrees with these comments and the final BART rule and the BART alternative 

require SCR at emission levels for NOx that will be achievable over the 3 year period between 

scheduled maintenance for these EGUs. 

Comment: 

 One environmental advocacy group (0182) asserted that EPA failed to consider data 

sources critical to ensuring a thorough analysis and adequate NOx BART determination. To 

support this assertion, the commenter drew heavily on an attachment containing comments 

prepared by Dr. Phyllis Fox (0182). This comment summary includes the comments presented 

by Commenter 0182; the reader may refer to the attachment (0182) for greater detail. 

 The commenter (0182) noted that EPA’s BART Guidelines require permitting agencies 

to “consider recent regulatory decisions and performance data (e.g., manufacturer’s data, 

engineering estimates and the experience of other sources) when identifying an emissions 

performance level or levels to evaluate” (citing 40 CFR part 51, Appendix Y). The commenter 

stated that there are numerous examples of SIP and permit limits set below the FCPP NOx limit: 

 Texas SIP emission limits under a cap and trade program of 0.033 lb/MMBtu for the 

Dallas/Fort Worth ozone nonattainment area and 0.050 lb/MMBtu for the 

Houston/Galveston ozone nonattainment area for wall-fired boilers burning coal and 

0.045 lb/MMBtu for tangential-fired boilers burning coal. 

 Vendor guarantees that SCR at the limits of 0.03 lb NOx/MMBtu at Texas Parish’s four 

units is achievable, which were the basis for the Texas SIP limits above. 

 The permit limits for Desert Rock, requiring the facility to achieve a NOx limit of 

0.035 lb/MMBtu on a 365-day rolling average basis. 

 Ten other similar facilities identified in Comment 0182 with permit or other instruments 

establishing limits of 0.05 lb/MMBtu or better on a 30- or 365-day rolling average. 

 The commenter (0182) also stated that EPA should have evaluated performance data, 

specifically the information available in the CAMD database that compiles CEMS data. The 

commenter indicated that this information must be understood in the context of the regulatory 

programs prompting its collection, which do not require the technology performs to its 

reasonable capability. The commenter asserted that while this information in itself does not 

establish a BART limit, evaluation of this information helps to determine a BART floor. 

Response:
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

EPA agrees with the commenter that the BART Guidelines state that agencies “should 

consider recent regulatory decisions and performance data . . . when identifying an emissions 

performance level or levels to evaluate”. However, the BART Guidelines further state that “[i]n 

assessing the capability of the control alternative, latitude exists to consider special 

circumstances pertinent to the specific source under review”, but the agency “should explain the 

basis for choosing the alternate level (or range) of control in the BART analysis”. See 70 FR at 

39166, July 6, 2005. We discuss in the TSD for our proposed BART determination and in our 

Supplemental Proposal for the alternative emission control strategy our rationale for proposing 

a limit of 0.11 lb/MMBtu on a plant-wide basis as BART and 0.098 lb/MMBtu for Units 4 and 5 

as part of the alternative emission control strategy, based on our determination that the 

installation of combustion controls is not likely to result in significant NOx reductions without 

potential operational challenges to the boilers because of inherent limitations associated with 

the boiler design. Our final NOx limit for BART and for Units 4 and 5 under the alternative 

emission control strategy is discussed in further detail in this section of this RTC, in response to 

the comment that the BART limit should be 0.05 lb/MMBtu, or at least lower than 0.11 

lb/MMBtu. In that response, we also discuss emission levels reported to CAMD for several cell 

burner boilers at different facilities. As reflected in presumptive NOx limits in the BART 

Guidelines, different types of boilers are expected to achieve different levels of NOx control. 

Thus, comparing emission limits achieved by different boilers is not an “apples to apples” 

comparison. 

The commenter is correct in stating that compliance with the Texas SIP emission limits of 

0.033 lb/MMBtu for the Dallas/Fort Worth ozone nonattainment area and 0.050 lb/MMBtu for 

the Houston/Galveston ozone nonattainment area for wall-fired boilers burning coal and 0.045 

lb/MMBtu for tangential-fired boilers burning coal is achieved through a cap and trade 

program. See Texas Administrative Code Chapter 117 requirements for combustion control at 

major utility electric generation sources, e.g., Rules 117.1210 and 117.1220.7F

78 This type of cap 

and trade program offers much greater flexibility at meeting the standards (because units that do 

not, by themselves, meet the emission standard can demonstrate compliance with the standard by 

purchasing equivalent emission credits from units that perform better than the standard) 

compared to an explicit permit limit for a single unit, which must be met by that specific unit 

continuously for the life of the facility. Therefore, comparing the system cap emission limits set 

in the Texas SIP and a plant-wide or unit specific emission limit under BART for units at FCPP, 

which include cell burner boilers, is misleading. 

Although the commenter notes that vendor guarantees of 0.03 lb/MMBtu for the Parish 

units were demonstrated on Parish Unit 8 in August – November 2006, where Unit 8 was run at 

0.03 lb/MMBtu, then at 0.035 lb/MMBtu, EPA notes, and the commenter acknowledges, that the 

Parish units do not normally and consistently achieve the vendor guarantee of 0.03 lb/MMBtu. 

Parish Unit 8 typically achieves 0.044 lb/MMBtu, and other coal-fired units at Parish typically 

achieve closer to or above 0.05 lb/MMBtu. EPA further notes that the coal-fired units at Parish 

(units 5 – 8), equipped with advanced LNB+OFA systems, e.g., based on CAMD data from 2001 

and 200278F

79, typically achieved 0.14 – 0.18 lb/MMbtu. Following installation with SCR, a vendor 

guarantee of 0.03 lb/MMBtu represents a 79 – 83% reduction in NOx emissions. Based on more 

 

78 See http://info.sos.state.tx.us/pls/pub/readtac$ext.ViewTAC?tac_view=5&ti=30&pt=1&ch=117&sch=C 79 See “WA Parish CAMD monthly 2001-2010.xlsx” in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

typical emission rates of around 0.05 lb/MMBtu from the Parish Units 5 – 8, the percent NOx

reduction ranges from approximately 64 – 72%. Thus, our final NOx limit for FCPP based on an 

80% reduction from SCR alone is comparable to the vendor guaranteed NOx reductions for 

Parish and exceeds the NOx reductions typically achieved at the Parish facility. 

The commenter further cites the BACT determination and limit for NOx in the final PSD 

permit issued by EPA Region 9 to the Desert Rock Energy Facility (DREF) as a lower limit than 

the one proposed and finalized as BART for FCPP. If constructed, DREF would have used coal 

from the same mine as FCPP, thus commenters generally argue that emission limits set for 

DREF should be achievable at FCPP as well. EPA notes that DREF was permitted as a new, 

greenfield facility using the most advanced boiler design and air pollution control equipment to 

meet the BACT requirements under the PSD program. EPA Region 9 requested a voluntary 

remand of the DREF permit to address issues related to other pollutants (greenhouse gases and 

PM2.5), therefore the final permit issued by Region 9 to DREF is not valid, and DREF has not, 

and cannot, commence construction. Thus, the NOx emission limits set for DREF, in particular, 

the 365-day rolling average limit of 0.035 lb/MMBtu, have not been achieved or demonstrated in 

practice on the high ash coal from the Navajo Mine. Furthermore, EPA disagrees that the 

emission limits set as BART necessarily must reflect limits set as BACT. 

As stated in responses to other comments in this section, EPA disagrees with the 

assertion that emission limits associated with BART must meet the lowest emission rate achieved 

at any coal-fired power plant. The Regional Haze Regulations at 40 CFR §51.308(e)(1)(ii)(A) 

state that: 

The determination of BART must be based on an analysis of the best system of 

continuous emission control technology available and associated emission 

reductions achievable for each BART-eligible source that is subject to BART . . . 

Additionally, the BART Guidelines state that: “To complete the BART process, you must 

establish enforceable emission limits that reflect the BART requirements . . .”. See 70 FR 39172, 

July 6, 2005. The five-factor BART analysis described in the Guidelines is a case-by-case 

analysis that considers site specific factors in assessing the best technology for continuous 

emission controls. After a technology is determined as BART, the BART Guidelines require 

establishment of an emission limit that reflects the BART requirements, but does not specify that 

the emission limit must represent the maximum level of control achieved by the technology 

selected as BART. The BART Guidelines and the RHR do not preclude selection of the maximum 

level of control achieved by a given technology as BART, however, the emission limit set to 

reflect BART must be achievable by the specific source and should be determined based on 

consideration of site-specific factors. Therefore, limits set as BACT during PSD review (e.g., 

Desert Rock), or emission rates achieved from the operation of individual facilities under an 

emissions trading program (e.g., Texas SIP) may provide important information, but should not 

be construed to automatically represent a ceiling for BART limits representative of a given 

technology. 

Comment: 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 One of the owners of FCPP (0176/0177) opposed EPA’s proposal to “phase in” NOx

controls at FCPP under a traditional BART FIP, commencing 3 years from the date the FIP 

becomes effective. The commenter asserted that this proposal does not afford adequate time to 

properly design, engineer, and construct the controls before the compliance deadline because the 

proposal would give APS only 2 years after the approval or disapproval of the proposed 

transaction with Southern California Edison to achieve full compliance with the new emission 

limit. The commenter argued this schedule would be very nearly impossible to meet because of 

the scale and complications involved in this large and expensive engineering project. See related 

comments in Section 6.0. Another FCPP owner (0168) expressed support for 

Commenter 0176/0177 on this issue. This commenter stated that the proposed phase-in is 

burdensome and unnecessary, and that the FCPP owners should be afforded the flexibility to 

schedule construction of BART controls within 5 years as is typically allowed. 

Response:

EPA revised the BART compliance date for one 750 MW unit (either Unit 4 or 5) to 

within 4 years from the effective date of this final rule, and the remaining 750 MW unit and Units 

1-3 to within 5 years of the effective date of the final rule. The revised compliance time within 4 

and 5 years allows time for design, engineer, and construct controls. 

Comment:

One environmental advocacy group (0182) stated that the proposed plantwide BART 

limit of 0.11 lb/MMBtu across all five FCPP units violates Executive Order 12898 on 

environmental justice. Specifically, the commenter stated that given the significant differences in 

pollution control systems among FCPP’s five units, allowing a plant-wide average could create 

pollution “hotspots” with respect to co-pollutants. As an example, the commenter noted that 

while Units 4 and 5 have baghouses, Units 1 – 3 use less efficient venturi scrubbers for control of 

sulfur dioxide, particulate matter, and mercury. The commenter asserted that the plantwide 

average limit for NOx would allow increased emissions from Units 1 – 3 in the event of a 

temporary outage or reduced output from one or both of the larger units. The commenter stressed 

that while this may not increase the total NOx emissions from the plant, it would increase the 

amount of mercury and other toxic co-pollutants emitted into the surrounding community, which 

is a low-income community of color. 

 The commenter (0182) stated that this is precisely the type of scenario Executive 

Order 12898 seeks to avoid. The commenter indicated that EPA should impose unit-specific 

BART limits, which it unquestionably has the authority to do (citing 40 CFR part 51, 

Appendix Y). In the alternative, the commenter urged EPA to conduct a full environmental 

justice analysis, supported by modeling, to show that its plantwide average will not cause 

disproportionate environmental harm in the surrounding community under any operating 

scenario. 

Response:
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EPA disagrees with the commenter that a plant-wide BART limit of 0.11 lb/MMBtu 

across all five FCPP units violates Executive Order 12898 on environmental justice. EPA’s final 

action establishing this plant-wide emission limit for NOx represents an 80% reduction in overall 

NOx emissions over the current baseline emissions for this single facility. This final rule is not 

expected to have disproportionately high and adverse human health or environmental effects on 

minority or low-income population because it increases the level of environmental protection for 

all affected populations in the area including any minority or low-income population. 

The commenter is correct that in the event of a temporary outage or reduced output from 

unit 4 or 5 the operator could continue to operate FCPP units 1-3 under the original BART 

proposal provided that they maintain compliance with the plant-wide emission limit of 0.11 

lb/MMBtu for NOx. In order to maintain compliance with the plant-wide emission limit, units 1-3 

would have to operate at a lesser capacity than they would normally operate if unit 4 and 5 were 

functioning because units 1-3 emit higher amounts of NOx than units 4 and 5. The NOx emission 

rates from Units 1-3 with SCR, based on 80 percent control of current emission rates would be 

0.16, 0.13, and 0.12 lb/MMBtu respectively which are higher than the proposed plant-wide 

emission limit.79F

80 Therefore, to maintain compliance with the plant-wide NOx emission limit 

(which is based upon a 30 calendar-day rolling average), units 1-3 would have to operate at a 

reduced capacity and could only operate if unit 4 or 5 were also concurrently operating. This 

reduced capacity would result in an overall lower rate of emission for mercury and other copollutants from units 1-3. Therefore, there would be no increased emissions of mercury or other 

co-pollutants and no “hot-spots” or disproportionately high and adverse human health or 

environmental effects on minority or low-income population. 

The BART Guidelines at 40 CFR Part 51, Appendix Y, Section 4 state that average 

emissions across any set of BART-eligible emission units within a fenceline should be considered 

provided that the emission reductions from the pollutant be equal to those reductions that would 

be obtained by simply controlling each of the BART-eligible units at that source. EPA proposed 

and is finalizing a plant-wide heat input-weighted average emission limit of 0.11 lb/MMBtu. 

This BART determination can be met by achieving 80% control on Units 1 – 5 by the application 

of SCR. EPA further notes that the commenter’s concern about increased usage of the less 

efficient Units 1 – 3 would not occur if APS implemented the alternative emission control 

strategy involving closure of Units 1 – 3. 

Comment: 

 One of the owners of FCPP (0174) and one utility industry association (0169.1) consider 

the BART proposal to be inconsistent with President Obama’s January 18, 2011 Executive Order 

13563 pertaining to regulatory strategy. One of the commenters (0174) alleged that EPA failed to 

properly consider the two key principles of the Executive Order: 

 

80 See page 87 of the TSD for the proposed rule; Document No. EPA-R09-OAR-2010-0683-0002. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 Consistent with law, Agencies must consider costs and benefits and choose the least 

burdensome option. 

 Agencies must consider low-cost approaches that reduce burdens and maintain flexibility. 

Regulations must be guided by objective scientific evidence. 

 The commenters (0169.1, 0174) asserted that SCR represents a very high cost, low 

benefit option. In addition, they stated that modeling that relies on CALPUFF version 5.8 and the 

IWAQM default background ammonia values does not represent the best available science. 

Response:

EPA disagrees that our BART determination is inconsistent with President Obama’s 

Executive Order 13563 or that SCR is a high-cost, low-benefit option. 

Executive Order 13563 is supplemental to and reaffirms the principles, structures, and 

definitions governing contemporary regulatory review that were established in Executive Order 

12866 of September 30, 1993. Our proposed and final actions are not “significant regulatory 

actions” under the terms of Executive Order 12866 (58 FR 51735, October 4, 1993) because 

these rules only apply to one facility and are not rules of general applicability. 

The President issued Executive Order 13563 on January 18, 2011, after we issued our 

Proposed Rule but just prior to our Supplemental Proposal. In general, the Order seeks to 

ensure the regulatory process is based on the best available science; allows for public 

participation and an open exchange of ideas; promotes predictability and reduces uncertainty; 

identifies and uses the best, most innovative, and least burdensome tools for achieving 

regulatory ends; and takes into account benefits and costs, both quantitative and qualitative. 

EPA conducted our BART determination for FCPP using the site-specific five-factor 

analysis in the BART Guidelines. As part of that analysis, EPA carefully considered the cost of 

controls and the benefits of those controls to improve visibility in the surrounding Class I Areas 

to achieve the goals stated in the CAA and RHR. As described below in more detail, based on the 

results from the original analysis for the proposed BART determination, EPA concluded that the 

installation and operation of SCR on all five units at FCPP would not adversely affect the 

competitiveness of FCPP’s cost to generate electricity compared to the cost to purchase 

electricity on the open market. EPA notes that our BART determination for FCPP does not 

specifically require SCR technology, rather, we have set an emission limit for NOx that can be 

achieved from the installation of SCR. The facility has the flexibility to determine the leastcostly, least burdensome way of meeting that emission limit. EPA provides additional flexibility 

by giving the owners of FCPP the option to implement the alternative emission control strategy 

in lieu of BART, an alternative that was largely proposed by APS on behalf of FCPP’s owners. 

As discussed more fully in Section 3.1 of this RTC, EPA disagrees that SCR represents a 

high cost, low benefit option. 
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EPA’s use of CALPUFF version 5.8 for modeling of visibility benefits and the IWAQM 

default background ammonia values represent the best available science as discussed above in 

responses to comments in Section 7.0 of this RTC. 

Comment: 

 One of the owners of FCPP (0174) stated that in establishing BART for FCPP, EPA did 

not consider the progress already made towards improving visibility on the Colorado Plateau. 

The commenter asserted that instead of taking this progress into consideration as support for 

establishing a cost-effective control option as BART in this first planning period, EPA imposed 

the most stringent and costly controls as BART and attempted to justify this proposal by raising 

uncertainties with respect to the contribution of nitrates to regional haze in the Colorado Plateau. 

The commenter argued that if EPA takes into consideration the available data showing the 

progress already made towards improving visibility on the Colorado Plateau, and the extensive 

work performed by the Western Regional Air Partnership that shows the small contribution of 

nitrates to regional haze, EPA will be compelled to conclude that reasonable progress can be 

made in the first planning period by requiring the installation of cost-effective LNB as BART for 

FCPP, and additional controls can be required, if necessary, in future planning periods. 

 The Navajo Nation (0223) acknowledged and supported the intent of the reasonable 

progress goals under the CAA [quoting 40 CFR 51.308(d)(1)(i)(B), which discusses calculating 

and using the necessary uniform rate of progress to set the reasonable progress goal], but stated 

that in its visibility analysis, EPA should consider the cumulative benefits in visibility 

improvements from all neighboring states’ regional haze SIPs and BART determinations. The 

commenter also indicated that real-time data should be used whenever possible as it becomes 

available. 

Response:

EPA disagrees with the commenter that we must consider progress already made toward 

improving visibility on the Colorado Plateau or that reasonable progress can be made by the 

installation of LNB as BART at FCPP. EPA further disagrees that any reasonable progress 

already made towards improving visibility would invalidate the BART provisions of the RHR, as 

the commenter seems to imply. The FCPP is one of the largest stationary sources of NOx in the 

country, and is located near many Class I areas where visibility is highly valued, so it is highly 

appropriate to undertake a BART analysis for it. In any case, a BART analysis for FCPP is 

required under the RHR. 

EPA does agree with certain aspects of the comments regarding a phased implementation 

strategy to attaining national visibility goals. In 40 CFR 51.308(f), States are required to revise 

their regional haze implementation plans every ten years, which is a process that involves 

evaluating their ability to attain reasonable progress goals and potentially updating their longterm strategy for regional haze. The periodic revision requirement described in 40 CFR 

51.308(f), however, does not extend to the implementation plan for BART requirements. The 
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phased approach described by the commenter has certain benefits, and a phased approach is 

incorporated into the alternative emission control strategy. 

Any downward trends in SO2 and NOx emissions or improvement in visibility on the 

Colorado Plateau are due to variability in natural emissions on a short term basis, or else to 

reductions of anthropogenic emissions, which occur partly in response to regulatory 

requirements like BART. Application of BART is one means by which downward emission and 

impairment trends may continue. 

Contrary to what the commenters seem to imply, seemingly small relative contributions 

to visibility impairment do not exempt sources from BART. Estimates of visibility impairment 

vary by the estimation method used. Reliance on an average over groups of days and on the 

percentage of the overall inventory may not be the best method for attributing impairment to 

particular sources; under the BART Guidelines, individual source impacts are estimated using 

CALPUFF modeling. Estimates of impairment from stationary source NOx also vary by location, 

calendar year, and time of year. For many Class I areas in the western U.S., the worst visibility 

occurs during summer, when carbon from fires is a dominant impairment component; this makes 

stationary source NOx appear small in a relative sense. Nevertheless, stationary source NOx

remains an important component of visibility impairment, one that cannot be neglected. Any one 

segment of the overall emission inventory might be dismissed as too small to apply controls to, in 

which case no progress could be made toward the RHR national goal of remedying visibility 

impairment from manmade pollution. Instead, the RHR identifies stationary sources as an 

important category for evaluation, in the form of a BART analysis. Modeling has shown that 

many individual stationary sources have the potential to contribute to visibility impairment (i.e., 

have a modeled impact of at least 0.5 dv, 70 FR 39161). In particular, EPA modeling of FCPP 

as discussed in the TSD for our proposed rulemaking showed visibility impacts from 1.2 to 6.0 

deciviews, depending on the Class I area (or from 0.8 to 3.2 deciviews if lower ammonia 

background is assumed as recommended by some commenters). These are not negligible 

impacts. 

EPA also disagrees with the commenter that we should consider the cumulative benefits 

in visibility improvements from all neighboring states’ regional haze SIPs and other BART 

determinations in determining BART for FCPP. The BART analysis is conducted on a sourcespecific basis. Nothing in the BART regulations or guidance requires that EPA consider visibility 

improvements from other sources in determining BART for a particular source under the RHR. 

The Navajo Nation EPA has not developed a TIP for Regional Haze, nor does the Navajo 

Nation have within its jurisdiction any federal mandatory Class I areas as set by Congress80F

81. As 

explained in the preamble to our proposed BART rule, FCPP and NGS are the only BARTeligible sources located on the Navajo Nation. FCPP contributes to impairment at many 

surrounding Class I areas. 

 

81 EPA notes that Navajo Nation has established its own parks and monuments, including Monument Valley, 

Canyon de Chelly, and the Four Corners Monument, however, these parks are not mandatory Class I Federal Areas 

as set by Congress. 
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EPA is exercising its discretion to promulgate emission limitations for FCPP to close the 

regulatory gap with respect to this facility. In light of the magnitude of emissions of NOx from 

FCPP, EPA is proposing to find that it is necessary or appropriate to establish BART 

requirements for NOx from FCPP, and is proposing specific NOx limits as BART. 

 EPA agrees with the commenter that real-time data should be used whenever possible as 

it becomes available. 

8.2 21BComments on the Proposed BART Determination for PM 

Comment: 

 One of the owners of FCPP (0176/0177) asserted that the existing controls at FCPP 

constitute BART for PM emissions. The commenter contended that the impact of PM controls on 

the visibility in the neighboring Class I areas would be “vanishingly small” while the cost would 

be “exorbitant” (resulting in cost effectiveness ranging from $51,500 – $148,659 per ton reduced 

and from $1.4 billion – $3.7 billion per dv improvement). The commenter pointed out that 

Table 4 in the proposal preamble, where EPA’s modeling of the proposed BART emission levels 

is summarized, shows visibility improvements of 0.02 dv at three Class I areas, 0.01 dv at seven 

areas, and 0.00 at the remaining areas. Given that the EPA’s own definition requires at least 

0.5 dv to “contribute” to visibility impairment, the commenter argued that EPA has not presented 

a basis to require FCPP to retrofit any additional PM controls at the plant, particularly not at an 

estimated capital cost of over $215 million. Another of the FCPP owners (0179) and the Navajo 

Nation (0223) made similar points, but in relation only to Units 1 – 3. A third FCPP owner 

(0174) similarly noted that the impact of PM reductions estimated by EPA would have almost no 

effect on visibility, concluding that no additional controls should be required as BART for FCPP. 

 The Navajo Nation (0223) stated that EPA acknowledged the high incremental cost of 

new PM controls on Units 1 – 3 (citing 75 FR 64230), yet justified the cost effectiveness of 

baghouses by comparison with similar retrofit projects in EPA Region 9. This commenter argued 

that EPA failed to properly evaluate the costs associated with installation of bag houses using 

site-specific parameters, thereby deviating from the BART Guidelines. The commenter also 

stated that future CAA rulemakings, such as MACT regulations, will provide EPA an 

opportunity to evaluate the feasibility of control technology during periodic reviews of the EPA 

air quality standards. The commenter asserted that continued operation of venturi scrubbers to 

meet emission limits of 0.03 lb/MMBtu and an opacity limit of 20 percent satisfies BART for 

Units 1 – 3. 

 The Navajo Nation (0223) expressed support for the supplemental proposal to require a 

PM emission limit of 0.015 lb/MMBtu and 10 percent opacity limit on Units 4 and 5. The 

commenter presumed that FCPP can readily meet these standards prior to installation of SCR 

since the limits can be achieved with the existing bag houses. 

 Regarding the EPA’s proposed 10 percent opacity standard for each unit, two of the 

owners of FCPP (0168, 0176/0177) stated that the EPA has not specified any costs or predicted 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

any improvement in visibility that would result from such limits. The commenters asserted that 

without such basis, the EPA cannot justify the proposed opacity limits. The commenters 

concluded that the EPA should withdraw its proposed determination that baghouses are BART 

for Units 1 – 3 and its proposal to make the opacity standard for Units 4 and 5 more stringent. 

Response:

As stated in our proposed BART determination for PM, the existing venturi scrubbers on 

Units 1 – 3 at FCPP do not constitute BART. In our proposed BART determination for FCPP, 

EPA proposed a PM emission limit for Units 1 – 3 that can be achieved through the installation 

of any of four different PM control options. At the time of our BART proposal, the MATS Rule for 

electric utility steam generating units had not yet been proposed, nor had APS suggested its 

alternative emission control strategy to close Units 1 – 3 in lieu of complying with BART for 

NOx. Because the final MATS rule has been issued See 77 FR 9304, February 16, 2012 and sets 

filterable PM and mercury limits that would be applicable to the units at FCPP, and because 

EPA is finalizing this rule to allow APS to either comply with the alternative emission control 

strategy or BART for NOx, EPA is determining that it is not necessary or appropriate at this time 

to finalize our proposal to set new PM limits for Units 1 – 3. 

Regarding our proposed BART determination for PM for Units 4 and 5, we are finalizing 

the proposed 0.015 lb/MMBtu emission limit based upon the proper operation of the existing 

baghouses. However, we have determined based on the comments we received from the operator 

of FCPP that it is not necessary or appropriate to take final action on the proposed 10 percent 

opacity limit. We have determined that imposing a 10 percent opacity limit will not provide 

greater assurance that Units 4 and 5 at FCPP are meeting the PM emission limit of 0.015 

lb/MMBtu. We have determined previously that a 20 percent opacity limit is sufficient to ensure 

the PM emission limit is being continuously met. The 10 percent opacity limit was generally 

supported by the Navajo Nation and environmental groups. EPA has promulgated some recent 

rules for electric generating units that have retained a 20 percent opacity standard rather than 

reducing that limit to 10 percent. Specifically, EPA’s revised the New Source Performance 

Standard for large electric generating units at 40 CFR Part 60, Subpart Da, to lower the PM 

emission limit for new units to 0.09 lb/MMBtu for gross energy output or 0.097 lb/MMBtu for net 

energy output. For existing units that reconstruct or modify, Subpart Da establishes an 

emissions limit of 0.015 lb/MMBtu. For both standards, EPA retained a 20 percent opacity 

standard as being sufficient to ensure compliance with either the 0.090 (0.097) lb/ MMBtu or 

0.015 lb/ MMBtu PM emission limit. EPA’s MATS rule, which was finalized just a few months 

ago, also retained a 20 percent opacity standard as being sufficient to ensure compliance with 

the PM emission limit that will be required for electric generating units subject to that rule. 

The importance of the opacity limit is that a certain percentage opacity is an 

instantaneous demonstration that a unit is in compliance with its PM emission limit. If a unit 

does not install and operate a PM continuous emissions monitor, then EPA ensures compliance 

with the PM emission limit by requiring an episodic source test. For the periods between 

episodic source testing, EPA can ensure continuous compliance with the PM emission limit by 

observing that the unit’s stack emissions do not exceed a set opacity. EPA’s recent rulemakings 

have determined that 20 percent opacity is sufficient to ensure compliance with a PM emission 
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limit lower than the emission limit we have determined is BART for Units 4 and 5. Accordingly, 

EPA is determining the 20 percent opacity limit that we promulgated in our 2007 FIP for FCPP 

as being adequate to ensure continuous compliance with the PM BART limit or 0.015 lb/ 

MMBtu. 

Comment:

 One group of environmental advocacy groups (0182) supported setting a 10 percent 

opacity limit for Units 1 – 5, as measured by continuous opacity monitors (COMS), for the 

reasons stated in the proposal preamble. However, based on information in a report prepared by 

Vicki Stamper and submitted by the commenter (docket number 0182.3), the commenter (0182) 

argued that the particulate matter BART limits for FCPP Units 1 – 3 should be based on the 

installation of fabric filter baghouses, as this control is likely the only PM control that will ensure 

the FCPP units can meet the forthcoming mercury MACT limit of 1 lb/TBtu and the related PM 

limit. The commenter added that baghouses will also likely result in the lowest filterable PM 

emission rates and will also greatly reduce fine particulate. 

 The commenter (0182) added that based on prior PM10 BACT determinations with 

baghouses, a BART limit on filterable PM10 should be no higher than 0.010 lb/MMBtu, along 

with an opacity limit no higher than 10 percent as EPA required as BACT at the Desert Rock 

facility. The commenter agreed that an opacity limit is necessary to show continuous compliance 

with the particulate matter BART limits (citing 75 FR. 64223). 

 In addition, the commenter (0182) indicated that EPA has proposed a BART limit only 

for PM, which appears to be only filterable particulate matter. The commenter stated that the 

BART guidelines specify that BART should be evaluated and defined for both PM10 and PM2.5

(citing 40 CFR part 51, Appendix Y, section IV.A) and, consequently, that EPA must evaluate 

and define BART limits for both PM10 and PM2.5. The commenter also asserted that as part of the 

PM2.5 BART determination, EPA must impose emission limits on condensable particulate 

matter, which is typically in the size range of 2.5 micrometers or smaller. Thus, the commenter 

asserted that in addition to a filterable PM BART limit, EPA should impose a BART limit on 

total PM2.5. 

 One public interest advocacy group (0112) supported EPA’s proposal and supplemental 

proposal to require a PM limit and a 10 percent opacity limits on Units 4 and 5. The commenter 

indicated that these limits should become effective prior to SCR installation, regardless of 

whether the BART or alternative emission control plan is implemented. A private citizen (0192) 

also stated that PM and opacity limits on Units 4 and 5 should become effective at the earliest 

practicable date, seeing no reason why their effective date should be tied to SCR installation. 

 In “preliminary” comments submitted prior to the supplemental proposal, a similar group 

of environmental advocacy groups (0095) suggested PM limits of 0.012 lb/MMBtu on a 6-hour 

block average, applicable to each individual unit at FCPP. The commenter suggested that 

compliance be required by 2014, determined using CEMS. The commenter also supported EPA’s 

proposal of an opacity limit of 10 percent, to be measured using COMS. The commenter added 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

that the BART determination should include a provision that FCPP may forego BART 

implementation at any unit if it agrees to retire that unit prior to the deadline for BART 

implementation. The commenter requested that these limits be published for comment in any 

Federal Register notice published to take comment on the FCPP alternative BART proposal. 

Response:

EPA proposed a BART limit of 0.012 lb/MMbtu for Units 1-3. There are various control 

technologies that can achieve this limit including a baghouse, as mentioned by the commenter. 

The least expensive approach would be to install a wet membrane ESP after the venturi 

scrubber. BART is an emission limit and EPA does not dictate the control technology that must 

be installed to meet it. As mentioned in the previous response, EPA is determining that it is not 

necessary or appropriate at this time to take final action on the proposed PM BART limit for 

Units 1-3. Nonetheless, as stated in the TSD for our proposal, EPA does not believe the existing 

venturi scrubbers constitute BART. 

 EPA agrees with the commenter that the PM and Hg emission limits in the MATS Rule81F

82

may require installation of baghouses on Units 1-3 to meet the standards. EPA is not finalizing a 

PM BART determination at this time for those 3 units because these units will either be closed, 

consistent with the alternative emission control strategy, or will be subject to the MATS Rule, 

which will set additional emission limits. Because EPA is not finalizing a PM standard at this 

time for Units 1-3, it is not timely to address the commenters’ recommendation on an opacity 

limit for these units or the tighter limit of 0.01 lb/MMbtu. 

EPA is finalizing the proposed PM BART limit for Units 4 and 5 of 0.015 lb/MMbtu 

which can be met with the proper operation of the existing baghouses. Because these baghouses 

are more than 25 years old, it is not appropriate to impose a more stringent PM limit such as 

one that has been set or proposed for a newly constructed EGU. 

EPA disagrees with the commenters’ recommendation that the condensable fraction must 

be included in the PM BART limits. EPA has previously outlined our reasoning as to why an 

H2SO4 limit is not appropriate at this time (it will be addressed through the pre-construction 

permitting process if needed) and EPA expects that H2SO4 will be the main component of 

condensable PM from a coal fired EGU with an SCR. The existing 20% opacity limit is sufficient 

to provide reasonable assurance of the unit’s compliance with the PM BART limit. 

As mentioned in a previous response, EPA is not finalizing the proposed 10% opacity 

limit. While the 10% opacity limit was generally supported by the Navajo Nation and 

environmental groups, upon further consideration of opacity limits set in other national EPA 

rulemakings, including the final MATS rule and NSPS Subpart Da, EPA is maintaining the 20% 

opacity limit that is already in the 2007 FCPP FIP. 

EPA agrees with commenters that PM limits on Units 4 and 5 should become effective 

prior to SCR installation, as Units 4 and 5 generally already meet the 0.015 lb/MMBtu limit. 

 

82 See 77 FR 9304, February 16, 2012 
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EPA is finalizing a compliance date for PM emission limits on Units 4 and 5 to be within 6 

months after restart following the next scheduled major outages in 2013 and 2014. 

EPA disagrees with the commenter that a CEMs (presumably a PM CEMs) be used to 

determine the continued compliance with the PM limits for Units 4 and 5. As stated previously, 

the existing 20% opacity limit is sufficient to provide reasonable assurance of the unit’s 

compliance with the PM BART limit. 

Comment:

 One commenter (0182.3) submitted a technical review of the PM BART determination, 

which was attached to the comments of an environmental advocacy group (0182), as noted 

above. A brief summary of the major points of this review related to Units 1 – 3 follows: 

 Venturi scrubbers are not the best system of continuous emission reduction. 

 The costs of installation new particulate controls, particularly baghouses, at FCPP 

Units 1 – 3 are reasonable. 

– Costs of PM controls are overestimated. 

– Effectiveness of PM controls is underestimated. 

– APS’s cost effectiveness analysis of PM controls only reflects incremental costs. 

– Revised analyses show that the installation of a baghouse is cost effective – average 

cost effectiveness ranging from $40.04/ton to $52.56/ton. 

 The energy and environmental impacts analyses weigh strongly in favor of installation of 

baghouses at FCPP Units 1 – 3. 

– A baghouse will likely be necessary to meet mercury MACT limits. 

– New PM controls will be needed to meet the EPA’s proposed PM limit for nonmercury metal HAPs. 

– The greater reduction in mercury emissions that a baghouse would allow for could 

help address mercury deposition levels in the region. 

– The secondary plume from FCPP Units 1 – 3 causes localized visibility impairment. 

 Upgraded PM controls at FCPP Units 1 - 3 will improve visibility at nearby Class I areas. 

 The BART limits for Units 1 – 3 should be based on the installation of baghouses with a 

limit on filterable PM10 no higher than 0.010 lb/MMBtu, along with a 6-minute average 

opacity limit no higher than 10 percent. The EPA must also define BART limits for PM2.5

and condensable PM. 

 The commenter’s (0182.3) major points related to PM BART for Units 4 and 5 are as 

follows: 

 Units 4 and 5 can meet lower particulate matter BART limits than proposed by EPA. 

 The EPA should evaluate the PM and SO2 reductions that can be obtained with the 

elimination of bypasses of the scrubber. 

 The EPA must evaluate and impose BART limits for PM10 and PM2.5. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 The filterable PM emission limits should be no higher than 0.012 lb/MMBtu, which the 

units are actually achieving. The EPA should evaluate options for achieving filterable PM 

emission limits of 0.010 lb/MMBtu as has been required to meet BACT requirements in 

several recent PSD permits. The proposed 10 percent opacity limit measured with COMS 

is necessary to show continuous compliance with the PM BART limits. 

Response:

 As previously mentioned, EPA is not finalizing the PM BART determination for Units 1-3 

at this time. 

 With regards to units 4 and 5 PM BART, EPA does not agree that the limit needs to be set 

at what can be achieved by new EGUs considering these baghouses are more than 25 years old. 

EPA also disagrees with the need for a PM10, PM2.5 or a condensable limit for these units. There 

is very little data available at this time for setting any of these limits. A PM limit is an adequate 

surrogate for these smaller fractions. A leak in a baghouse will pass all size fractions of PM and 

setting the limit with a Method 5 front half measurement is adequate for all size fractions for a 

baghouse-controlled coal fired EGU. As mentioned previously and elaborated on more in RTC 

in section 8.4, EPA does not agree that a condensable limit is needed for BART. 

8.3 2BComments on BART for SO2

Comment:

 Some commenters (0095, 0112, 0140, 0182) asserted that SO2 BART should be required 

for FCPP, while one commenter (0224) simply noted that FCPP is subject to BART for SO2. 

Their comments are summarized in the paragraphs that follow. 

 One federal agency commenter (0224) stated that FCPP is subject to BART for SO2. The 

commenter stated that Units 4 and 5 should be able to meet a limit of 0.12 lb/MMBtu on an 

annual average basis by upgrading the existing scrubbers. 

 One group of environmental advocacy groups (0182) discussed the Regional Haze rules, 

the TAR, and the SO2 emissions from FCPP and concluded that EPA is under a legal obligation 

to conduct a BART analysis for SO2 emissions from FCPP and, to the extent EPA has failed to 

make a finding that it is “necessary or appropriate” to regulate SO2 emissions from the FCPP, 

such a failure is arbitrary, capricious, and not supported by the administrative record. The 

commenter added that EPA’s proposed FIP is also arbitrary and capricious because it fails to 

conduct any BART analysis for SO2 emissions from the FCPP, and because EPA fails to comply 

with its methodology for conducting BART determinations found in the Regional Haze rules at 

40 CFR 51.308(e) and the BART Guidelines. 

 According to the commenter (0182), EPA argues that FCPP’s current SO2 emissions 

limits are “close to or equivalent” to the limit that would be established under BART. The 

commenter argued that this conclusion is likewise arbitrary and capricious because EPA has 
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failed to undertake any scientific or technical analysis to support its conclusion – rather than 

conduct such an analysis, EPA simply stated that the FCPP agreed to reduce SO2 emissions 

pursuant to a prior voluntary compliance agreement. However, the commenter notes that a 

review of the administrative record shows that EPA did not conduct an SO2 BART determination 

for the FCPP at that time, and has not conducted such an analysis since that time. 

 The commenter (0182) goes on to assert that under the plain language of the Regional 

Haze rules at 40 CFR 51.308 and the BART Guidelines, EPA must make now make an SO2

BART determination for the FCPP as part of this source-specific regional haze FIP. Moreover, 

the commenter argued that an SO2 BART determination is likewise important to meet the 

requirements of section 110 of the CAA as it relates to interstate transport of visibility impairing 

emissions. The commenter contended that EPA’s failure to make an SO2 BART determination 

for FCPP under the methodology prescribed by its own regulations and guidelines is arbitrary 

and capricious and must be corrected in the final rule. 

 The commenter (0182) made the following points about an SO2 BART analysis at FCPP: 

 The fact that the FCPP reduced SO2 earlier than BART deadlines should not influence a 

proper BART determination. The commenter asserted that given the complicated 

regulatory history of SO2 controls at FCPP and the fact that SO2 controls were required 

since the mid 1970’s but were not installed until the early 1980’s, APS should not be 

given credit to avoid a complete SO2 BART analysis because the company finally took 

actions to achieve better SO2 control. The commenter also stated that an analysis of the 

new 1-hour average SO2 NAAQS standard could show that FCPP’s current controls are 

necessary to ensure the FCPP does not cause or contribute to violations of the 1-hour 

average SO2 NAAQS, and thus are not early controls. Finally, the commenter stated that 

given that EPA imposed enforceable SO2 emission limits in 2007, the same year regional 

haze SIPs were due to be submitted to EPA and given that the methods planned on to 

reduce SO2 at FCPP could be implemented fairly readily (i.e., there was no installation of 

new pollution controls), it is difficult to consider these controls as being implemented 

early. 

 The SO2 limits of the FCPP FIP are not as stringent as BART. The commenter stated that 

without a BART analysis for SO2 for each of the FCPP units, it is not known how much 

the current FIP requirements differ from what would have been required to meet BART. 

The commenter indicated that EPA can only allow an alternative to BART as long as it 

has been demonstrated to result in greater reasonable progress that BART. The 

commenter noted that the permit for Desert Rock, which would also use Navajo coal, 

limited SO2 emissions to 0.06 lb/MMBtu. In addition, the commenter added that the 

current SO2 controls on Units 4 and 5 do not treat 100 percent of the flue gas – the EPA’s 

BART determination should evaluate the cost and visibility benefits of treating 100 

percent of the flue gas for all units. 

 FCPP must meet presumptive SO2 BART limits at a minimum. The commenter pointed 

out that the presumptive BART limit for EGUs like FCPP is 95 percent control, the 

commenter asserted should be the regulatory floor. The commenter requested that EPA 

undertake an SO2 BART analysis for FCPP on a unit-by-unit basis and develop specific 

limits for each unit. The commenter argued that a plantwide limit would only be 
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acceptable if it ensured emission reductions that were better than what would be required 

by a BART determination for each unit. The commenter added that the presumptive 

limits may be BART, but this will be known only after a thorough BART analysis. 

Finally, the commenter asked that EPA not delay the final NOx and PM BART 

determinations while conducting the required SO2 BART rulemaking. 

 In “preliminary” comments submitted prior to the supplemental proposal, a similar group 

of environmental advocacy groups (0095) suggested that the owners of FCPP should be required 

to perform an SO2 BART analysis for all five units for submission to EPA and the public no later 

than February 18, 2011, with comments due by the comment deadline that was then in force for 

the BART rulemaking (i.e., March 18, 2011). The commenter further stated that EPA should 

propose an SO2 BART determination by April 30 and a final determination at the time it 

finalized the FIP, with compliance with the SO2 BART limits required by 2014. The commenter 

added that the BART determination should include a provision that FCPP may forego BART 

implementation at any unit if it agrees to retire that unit prior to the deadline for BART 

implementation. The commenter requested that these proposed requirements be published for 

comment in any Federal Register notice published to take comment on the FCPP alternative 

BART proposal. 

 A public interest advocacy group (0112) stated that the SO2 limits need to be tightened up 

for FCPP to further reduce visibility impairment and to reduce the acidification of rainfall caused 

by the formation of H2SO4. The commenter stated that because the damaging effects of H2SO4 in 

precipitation on ancestral Puebloan sandstone dwellings and pictographs are not fully 

understood, it is disappointing for the FCPP proposals not to address SO2. The commenter asked 

that FCPP be required to perform a BART analysis for all five units by a date established by 

EPA. 

Response:

As many of the commenters acknowledge, EPA finalized a FIP in May 2007 that required 

significant SO2 emissions reductions from FCPP and established continuous SO2 emissions 

limits for FCPP. See 72 FR 25698 (May 7, 2007). The 2007 FIP required FCPP to increase the 

removal efficiency if its SO2 emissions controls from 72% to 88%, resulting in a SO2 emissions 

reduction of approximately 22,000 tons per year. EPA had proposed this FIP in September 2006. 

The 2006 proposed FIP stated that “EPA believes that the SO2 controls proposed today for 

FCPP are close to or the equivalent of a regional haze BART determination of SO2. This takes 

into consideration the early reductions this action will achieve and the modification to the 

existing SO2 scrubbers.” 72 FR 25700. We received several comments on our 2006 proposal 

which stated that EPA should be undertaking a BART analysis for SO2 rather than setting the 

SO2 emissions limit based on FCPP’s agreement to improve its SO2 removal efficiency from 72% 

to 88%. In finalizing that rulemaking in the 2007 FIP, EPA responded that it was exercising its 

authority pursuant to Section 49.11 of the TAR to implement measures that are necessary or 

appropriate to protect air quality in Indian country. Id. EPA determined that the SO2 emissions 

reductions would be federally enforceable as soon as the 2007 FIP was finalized which would be 

potentially five years before EPA could achieve enforceable SO2 emissions reductions through 

making a BART determination. See id. EPA also considered the Navajo Nation’s request for EPA 
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to establish enforceable SO2 emissions reductions immediately that, in the opinion of the Navajo 

Nation, “appear[] to be equivalent to BART.” Id. Therefore, EPA’s determination on this issue 

in finalizing the 2007 FIP was “that it is neither necessary nor appropriate at this time to 

undertake a BART determination for SO2 from FCPP given the timing of the substantial SO2 

reductions resulting from this FIP.” Id. In addition, we stated that “given that the SO2 controls 

for FCPP immediately achieve significant reductions in SO2 comparable to what could 

ultimately be achieved through a formal BART determination, EPA believes that it will not be 

necessary or appropriate to develop a regional haze plan to address SO2 for the Navajo Nation 

in the near term.” Id. 25700-701.Both APS, as operator of FCPP, and Sierra Club sought 

judicial review of our 2007 FIP. 

The comments on this action essentially repackage the comments we received and 

provided a response for on the 2007 FIP. The comments have not presented any new facts or 

legal considerations that have arisen or changed since we responded to comments requesting a 

BART determination for SO2 in 2007. 

Comment:

 One commenter (0182.3) submitted a technical review of SO2 BART, which was attached 

to the comments of an environmental advocacy group (0182). The commenter asserted that the 

SO2 FIP requirements do not reflect the level of SO2 control currently being achieved at FCPP 

Units 1 – 3. According to the commenter, a review of 2008 and 2009 SO2 emissions data 

compared to APS data on annual uncontrolled SO2 emissions in the coal show that these FCPP 

units are achieving greater than 93 percent control on an annual average basis. Thus, the 

commenter argued that the 88 percent control limitation cannot be considered as “close to or 

equivalent to” BART and the emission limits for SO2 should be no higher than the removal 

efficiencies actually being achieved. 

 The commenter (0182.3) provided a BART analysis for SO2 at FCPP Units 1 – 3 and 

concluded that SO2 BART for FCPP Units 1 – 3 should be a 95 percent SO2 control requirement 

or an emission limit of 0.09 lb/MMBtu, applicable to each unit on a rolling average basis of 30 

boiler operating days. The commenter added that this BART limit would be met by the addition 

of baghouses upstream of the existing wet scrubbers at these units (which will be required to 

meet MACT and also PM BART), along with other physical or operational changes to the 

scrubbers to improve SO2 removal efficiency to 95 percent. The commenter indicated that 

compliance should be based on CEMS and, if a percent removal requirement is imposed, daily 

sampling of sulfur in the coal from which daily percent SO2 removal is then determined with the 

actual SO2 data from the CEMS. Finally, the commenter stated that these limits should apply on 

a unit-by-unit basis to ensure that each unit is required to achieve the best continuous level of 

emission reductions. 

 The commenter (0182.3) also asserted that the 2007 SO2 FIP requirements do not reflect 

the level of SO2 control currently being achieved at FCPP Units 4 and 5. According to the 

commenter, the annual data show that the FCPP Units 4 and 5 are achieving approximately 90 to 

91 percent SO2 removal from the uncontrolled SO2 in the coal on an annual average basis. Thus, 
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the commenter claimed that the 88 percent control limitation cannot be considered as “close to or 

equivalent to” BART and the emission limits for SO2 should be no higher than the removal 

efficiencies actually being achieved. 

 The commenter (0182.3) stated that FCPP Units 4 and 5 are not meeting EPA’s 

presumptive BART limits of 95 percent SO2 control or an SO2 emission limit of 0.15 lb/MMBtu. 

The commenter presented a BART analysis for SO2 at FCPP Units 4 and 5 and concluded that 

SO2 BART for FCPP Units 4 and 5 should be a limit of 95 percent SO2 control based on EPA’s 

presumptive BART requirements, which would be achieved with the elimination of all scrubber 

bypass along with other scrubber modifications necessary to improve SO2 removal efficiency to 

95 percent. At the minimum, the commenter asserted that SO2 BART for FCPP Units 4-5 should 

be no less than a limit reflecting 92 percent control or 0.14 lb/MMBtu, as this would reflect the 

level of control the FCPP Units 4 and 5 were designed for with the elimination of all scrubber 

bypass. The commenter proposed the same compliance requirements set out above for Units 1 – 

3. 

Response:

As discussed in response to the prior comment, EPA finalized a FIP in 2007 for FCPP. 

EPA responded to comments in that FIP action suggesting that EPA should require FCPP to 

achieve a 95% removal efficiency to be consistent with presumptive BART for SO2. The 2007 FIP 

stated: “EPA disagrees with the comment that the BART Guidelines, 70 FR 39104, 39171 (July 

6, 2005) establish a presumption that BART at FCPP is 95% control for SO2. Although the BART 

Guidelines did establish a presumption of either 95% control for SO2 or 0.15 lbs/MMBtu for 

large power plants, this presumption applies only to power plants that are currently uncontrolled 

or achieving less than 50% control of SO2. Id. As indicated in the preamble to this proposed FIP, 

this presumption thus does not apply to power plants, such as FCPP, with existing SO2 controls 

achieving at least 50% removal efficiency.” Id. at 25700, n.3. The comments here have not set 

forth any new facts or changes in the law since we responded to this comment in 2007. 

8.4 23BOther Comments on BART 

Comment:

 One group of environmental advocacy groups (0182) stated that as an alternative to a 

condensable PM2.5 limit, EPA could set limits on the pollutants which form condensable PM2.5, 

such as sulfuric acid mist (H2SO4) and ammonia, as EPA proposed as part of the SJGS BART 

rulemaking (citing 76 FR 491, January 5, 2011). If EPA adopts this approach, the commenter 

urged EPA to set an emission limit for H2SO4 no higher than the limit of 1.06 x 10-4 lb/MMBtu 

for each unit as proposed for SJGS based on the use of low reactivity catalyst and the most 

current information from the Electric Power Research Institute. If CEMS are unavailable for this 

pollutant, the commenter urged EPA to require stack test monitoring for H2SO4 on a more 

frequent basis than annual monitoring. 
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 The commenter (0182) also requested that EPA set emission limits for ammonia at a rate 

no higher than the 2.0 parts per million as proposed at SJGS, to be monitored with CEMs. The 

commenter indicated that EPA should clarify in the final rule that the emission limits for H2SO4

and ammonia are being required under the Regional Haze program as part of a BART 

determination for the facility and must be complied with within 3 years of the date of the final 

rule. 

 In “preliminary comments submitted prior to the supplemental proposal, a similar group 

of environmental advocacy groups (0095) suggested the same limits for ammonia and H2SO4

based on the proposed limits for SJGS. The commenter added that the BART determination 

should include a provision that FCPP may forego BART implementation at any unit if it agrees 

to retire that unit prior to the deadline for BART implementation. The commenter requested that 

these limits be published for comment in any Federal Register notice published to take comment 

on the FCPP alternative BART proposal. 

Response:

EPA disagrees with the comment that Region 9 should set the same emission limits for 

ammonia and sulfuric acid as Region 6 in its proposed BART determination for SJGS. 

 In its January 5, 2011 proposed rulemaking for SJGS, Region 6 proposed an ammonia 

slip limit of 2.0 ppmvd on an hourly average and requested comment on a range from 2.0 ppmvd 

to 6.0 ppmvd. In its final BART rulemaking (76 FR 52388, August 22, 2011), Region 6 

determined that an emission limit and monitoring were not warranted for ammonia and did not 

finalize its BART determination for SJSG with the proposed 2.0 ppmvd ammonia limit. 

 In its proposal for SJGS, Region 6 proposed an emission limit for sulfuric acid of 1.06 x 

10-4 lb/MMBtu on an hourly average, and requested comment on a range from 1.06 x 10-4 to 7.87 

x 10-4 lb/MMBtu. In its final rulemaking, Region 6 finalized an emission limit for sulfuric acid of 

2.6 x 10-4 lb/MMBtu to minimize its contribution to visibility impairment. Region 6 calculated 

this emission limit using an estimation methodology from the EPRI, assuming the use of an ultra 

low activity catalyst (0.5% total conversion of SO2 to SO3), zero ammonia slip, no sorbent 

injection, and EPRI-recommended values for removal by existing downstream control 

equipment. 

 Actual measurements of baseline sulfuric acid emissions have not yet been determined at 

FCPP and the calculation of projected sulfuric acid emissions after installation and operation of 

SCR using the EPRI methodology is dependent on future decisions made by the facility on the 

type of SCR catalyst and number of layers used, as well as numerous assumptions about loss to 

downstream components, such as air preheaters and baghouses, the true values of which are 

currently not yet defined or known for FCPP., EPA Region 9 is the permitting authority for 

preconstruction permits on the Navajo Nation, and an increase in sulfuric acid emissions from 

the installation of SCR may trigger major modification PSD permit requirements at a low 

threshold of 7 tpy (see 40 CFR 52.21) or Tribal minor new source review (NSR) permit 

requirements at a threshold of 2 tpy (see 40 CFR Part 49 Subpart C). Preconstruction permitting 

review may also be triggered from significant emissions increases of PM2.5 from SCR installation 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

at FCPP. If one of these pollutant triggers PSD, the permitting authority must provide an 

Additional Impact Analysis under the PSD program. The PSD program also requires the 

permitting authority to determine BACT for pollutants that triggered PSD. A similar control 

technology review may also be required at the discretion of the permitting authority under the 

Tribal Minor NSR program. For these reasons, Region 9 has determined that for FCPP, 

emission limits and monitoring requirements for sulfuric acid are more appropriately reviewed 

in the preconstruction permitting process. 

Comment:

 Citing the BART Guidelines at 40 CFR part 51, Appendix Y, section V, one 

environmental advocacy group (0182) stated that BART emission limits and compliance 

schedules must be based on “boiler operating day.” The commenter indicated that the NOx

BART proposal of 0.11 lb/MMBtu is based on a 30-day, calendar rolling average (citing 75 FR 

64235) and the supplemental BART proposal is silent as to type of 30-day rolling average is 

intended (citing 76 FR 10530). 

 The commenter (0182) claimed that the “very high” proposed BART emission limits 

suggest that EPA set these limits to encompass spikes that occur during startups and shutdowns. 

The commenter asserted that setting and enforcing limits based on boiler operating day would 

necessarily exclude spikes that occur before and after outages, such as startups, shutdowns, and 

malfunctions. According to the commenter, such periods should be subject to separate limits set 

at the pre-SCR uncontrolled level to encourage good work practice standards during these 

periods while allowing the SCR and other emission control technologies to be operated at an 

efficient and continuous capacity in compliance with BART. The commenter argued that it is 

clear that the BART Guidelines are based on establishing separate limits for emissions spikes to 

avoid misapplying the Guidelines and setting unnecessarily high BART emission limits. 

Response:

EPA agrees that the BART Guidelines specify that the permit (or implementation plan 

that establishes the emission limitations), for EGUs must “specify an averaging time of a 30-day 

rolling average, and contain a definition of “boiler operating day” that is consistent with the 

definition in the proposed revisions to the NSPS for utility boilers in 40 CFR Part 60 subpart Da 

(70 FR 9705, February 28, 2005)”. The proposed revisions to the NSPS in 2005 included a 

definition for “boiler operating day”: 

Boiler operating day for units constructed, reconstructed, or modified on or 

before February 28, 2005, means a 24-hour period during which fossil fuel is 

combusted in a steam generating unit for the entire 24 hours. For units 

constructed, reconstructed, or modified after February 28, 2005, boiler operating 

day means a 24-hour period between 12 midnight and the following midnight 

during which any fuel is combusted at any time in the steam generating unit. It is 

not necessary for fuel to be combusted the entire 24-hour period. 
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The definition of boiler operating day was finalized on June 13, 2007 (72 FR 32722) as 

proposed. 

EPA agrees that the NOx limit for the alternative proposal should be set for30 successive 

boiler operating days and that a “boiler operating day” should be defined as any day in which 

the boiler fires fossil fuel and therefore includes periods of startup or shutdown. Because the 

NOx emission limit under the alternative emission control strategy already includes periods of 

startup or shutdown, separate limits are not required. The final rule reflects this approach. 

For the original proposal, EPA does not find it necessary to define boiler operating day 

because the limit is a heat input weighted plant-wide limit. Only operating hours for any of the 5 

units would be included. When a unit is not operating, those hours are not included in the plantwide 30 day average. Additionally, the heat-input weighted plant-wide limit also includes 

periods of startup and shutdown, therefore, separate limits are not required.

Comment: 

 One environmental advocacy group (0182) commented that EPA should require FCPP to 

install all control equipment within 3 years of the date of a final FIP, as EPA did at the San Juan 

Generating Station. The commenter stated that there is ample data to supporting the contention 

that all this emission control technology can be installed and operational within 3 years or less. 

Response:

EPA disagrees with the comment that EPA should set a 3 year compliance timeframe 

because EPA proposed a 3 year compliance timeframe for SJGS. In its proposed rulemaking for 

SJGS82F

83, Region 6 proposed a 3 year timeframe for SJGS to comply with the proposed limits but 

requested comment on a compliance range of 3 – 5 years. In its final rulemaking, Region 6 

finalized a compliance timeframe of 5 years and determined that because of site congestion at 

SJGS, a longer timeframe than average (37 – 43 months) to install SCR on the 4 units at SJGS 

would be required. The final BART determination for FCPP requires retrofit of 5 existing units 

at FCPP. In the final rule for FCPP, Region 9 is requiring installation and operation of SCR 

controls for one 750 MW unit within 4 years of the effective date, and the remaining 750 MW 

unit and Units 1 – 3 within 5 years of the effective date. Based on all of the factors that will be 

involved in the design, purchase and operation of the SCR controls, Region 9 considers this 

schedule to be appropriate and expeditious. 

Comment:

 One group of environmental advocacy groups (0095) stated in comments submitted prior 

to publication of the supplemental proposal that FCPP has a large impact on visibility in the 

region, and that time has come to eliminate these impacts. The commenter opined that it is 

incumbent upon EPA to curtail these impacts to the maximum extent possible by issuing a strong 

 

83 See 76 FR 491, January 5, 2011 
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FIP addressing all visibility-impairing pollutants. (See the commenter’s suggested limits for the 

pollutants elsewhere in this section.) 

 In comments dated prior to publication of the supplemental proposal, a near-by county in 

a neighboring state (0106) and an individual county commissioner (0108) supported EPA’s 

proposed action on FCPP because it will result in significant reductions in NOx and other hazeforming pollutants that also negatively impact public health. The commenters noted that ozone 

levels in the area have nearly reached nonattainment levels, and that the regional economy 

thrives on the quality of the natural and historical resources which may be significantly 

diminished by the presence of haze. In a resolution passed prior to publication of the 

supplemental proposal, a near-by city in a neighboring state (0105) encouraged EPA to comply 

with both the RHR and the CAA’s “good neighbor” provisions and require BART on FCPP (and 

SJGS) to reduce haze and to improve visibility and health in the Four Corners airshed. 

 A private citizen (0084) stated, in comments submitted after APS announced its intent to 

purchase SCE’s stake in Units 4 and 5 and to shut down Units 1 – 3 but prior to publication of 

the supplemental proposal, that APS should continue with its proposed transactions and EPA 

should continue to consider its proposed BART rule. The commenter argued that APS’s plans 

would result in a smaller reduction in emissions than would the BART proposal, but a 

combination of the two would provide more jobs and economic stability and improve air quality. 

Response:

As stated in other EPA responses within this document, a BART determination represents 

a case-by-case determination that accounts for site specific characteristics in the five-factor 

analysis. While choosing an emission limit that represents the lowest emission rate achieved by 

similar facilities may be justified in some cases, the BART Guidelines do not specifically require 

emission reductions “to the maximum extent possible”. As discussed in more detail elsewhere in 

this RTC (See Section 8.1), EPA has determined that a plant-wide NOx emission limit of 0.11 

lb/MMBtu, representing an 80% reduction in plant-wide emissions and achievable by the 

installation and operation of post-combustion controls, is BART for FCPP based on site-specific 

considerations, including physical limitations of the boilers. 

EPA has determined that finalizing a FIP implementing the BART provisions of the RHR 

to reduce NOx emissions from FCPP on the Navajo Nation is appropriate at this time. EPA 

expects the NOx reductions required for FCPP in the final FIP, combined with the NOx

reductions required in the final FIP for SJGS issued by EPA Region 6 (76 FR 52388, August 22, 

2011), will contribute to improved air quality in the Four Corners area; therefore a FIP for the 

Navajo Nation implementing the “good neighbor” provisions under the Clean Air Act (Section 

110(a)(2)(D)(i)) is not necessary at this time. 

EPA disagrees with the commenter that the alternative emission control strategy would 

result in smaller emission reductions compared to our final BART determination. As outlined in 

more detail elsewhere in this RTC (See Section 9.0), EPA has determined that the alternative 

emission control strategy will result in greater annual emission reductions than BART. 
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Comment:

 One public interest advocacy group (0112) stated that EPA should hold FCPP to the 

highest possible level of monitoring and validation of the FIP. The commenter indicated that this 

is justified by the fact that FCPP previously discontinued use of a re-heat of the scrubber exhaust 

on Units 1 – 3 without authorization from EPA. 

Response:

EPA agrees that monitoring, record-keeping, and reporting requirements are critical 

elements in enforcing the emission rates established in the final FIP. As stated in the proposed 

BART determination, the final BART determination requires FCPP to comply with 40 CFR Part 

75 requirements, including requirements related to quality assurance testing, relative accuracy 

test audits. The requirements of the final FIP will be incorporated by the Navajo Nation 

Environmental Protection Agency (NNEPA) into the facility’s Part 71 Operating Permit, and 

will require FCPP to submit annual compliance reports and testing results to the NNEPA and 

EPA Region 9. 

EPA was never notified of the discontinued use of the reheaters for Units 1-3. EPA is not 

aware of when these units were taken out of service. Although EPA would have appreciated the 

opportunity to weigh in on this decision, we are not aware of any regulation that would have 

prevented APS from removing the re-heaters. 

These 3 units do not have an opacity limit under the 2007 FIP, so the wet stack and lack 

of continuous opacity monitors should not be a monitoring issue. They are required to monitor 

and report deviations of the pressure drop and scrubber liquid flow to the venture scrubbers to 

assure proper operation of these control devices for PM. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

9.0 8BComments on APS’s Alternative Proposal and EPA’s 

Supplemental Proposal 

Comment:

 One of the owners of FCPP (0176/0177) pointed out that the November 2010 APS 

proposal included two critical components: (1) a proposal to close Units 1 – 3 and install SCRs 

on Units 4 and 5; and (2) EPA’s contemporaneous agreement that these activities resolve any 

liability FCPP may have under regional haze BART, Reasonably Attributable Visibility 

Impairment Best Available Retrofit Technology (RAVI BART), NSR, and NSPS. The 

commenter asserted that EPA’s supplemental proposal addresses only half of APS’s proposal – 

the half that achieves better than BART emission reductions, plant-wide reductions of all other 

emissions, and greater visibility improvement at nearby Class I areas – but ignores the other half 

of the APS proposal – the half that provides APS and the FCPP co-owners with needed 

regulatory certainty. Unless there is a contemporaneous resolution of these key issues with EPA, 

the commenter cannot and does not support EPA’s supplemental proposal. With a full resolution 

of these issues, the commenter would then support the supplemental proposal. 

 In the November 2010 APS proposal, APS explained that it proposed the alternative 

strategy because it was faced with uncertainty on all sides. The commenter (0176/0177) 

indicated that FCPP must resolve these uncertainties before spending significant capital on 

upgraded pollution controls. For this reason, the proposal to install SCRs on Units 4 and 5 in 

2018 is inexorably linked with EPA’s contemporaneous agreement to resolve any plant 

obligations under the referenced programs. 

 Another of the owners of FCPP (0168) similarly rejected the supplemental proposal 

without contemporaneous resolution of all obligations that FCPP may have related to the CAA 

programs listed above. The commenter added that it would consider accepting the supplemental 

proposal if these other potential issues are resolved, but emphasized that acceptance of the 

supplemental proposal would be voluntary and based on its own business interests. 

Response: 

EPA understands that the owners of FCPP are seeking to resolve any potential 

regulatory noncompliance at a roughly simultaneous time. However, EPA must use different 

mechanisms for promulgating rules and resolving enforcement issues. The comment requests 

resolution of potential past non-compliance with NSR and NSPS requirements. Potential past 

non-compliance can be resolved through entering into a Consent Decree containing a judicially 

approved release from liability. Such a Consent Decree under the Clean Air Act must be 

approved by the United States Department of Justice and must also be lodged in a United States 

District Court where the public is allowed to comment on it. Consent Decrees must be entered by 

the United States District Court for a release of liability of potential past non-compliance to be 

effective. Accordingly, this rulemaking action cannot effectuate any release of liability for 

potential past non-compliance with NSR or NSPS. 
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The comment is also seeking some resolution with respect to a potential finding by the 

Department of Interior that visibility impairment at a Class I area is reasonably attributable to 

FCPP’s emissions. If the Department of Interior made such a finding, then EPA would be 

obligated to determine whether EPA should make a BART determination. 

EPA is aware that several environmental groups have petitioned the Department of 

Interior to make a finding that impairment at Class I areas is reasonably attributable to FCPP.83F

84 

The NPS, on behalf of Department of Interior, has declined to make such a finding based on 

EPA’s work in this rulemaking.84F

85 The environmental groups also filed a Complaint in the United 

States District Court for the District of Columbia85F

86 contending that the Department of Interior 

was unreasonably delaying making a finding of reasonable attribution from FCPP. On June 30, 

2011, the Court dismissed the Complaint86F

87 holding that the NPS’s letters refusing to make the 

finding of reasonable attribution constituted denying the Petitioners’ request for a RAVI finding. 

Therefore, there are no pending petitions with the Department of Interior requesting a finding 

that visibility impairment at any Class I areas is reasonably attributable to FCPP. In any event, 

a BART determination under RAVI would likely be the same as under this BART determination. 

Comment: 

 One public interest advocacy group (0112) requested that EPA publicly disclose (to the 

extent legal counsel will allow) how each of the conditions set forth in the APS proposal (i.e., 

related to RAVI BART, NSR, and NSPS violations) is incorporated into and/or is accommodated 

by the EPA’s supplemental proposal. 

Response:

As discussed above, EPA can resolve potential past non-compliance with NSR and NSPS 

through entering into a Consent Decree approved by the Department of Justice and lodged in the 

United States District Court. The public will have an opportunity to comment on any Consent 

Decree and may request the Court to determine whether the Consent Decree is in the public 

interest. 

Although EPA does not believe that there are any pending petitions to the Department of 

Interior to make a finding that the visibility impairment at any Class I area is reasonably 

 

84 See National Parks Conservation Association, et al., Petition to United States Department of Interior, United 

States Department of Agriculture, and United States Forest Service, February 16, 2010, in the docket for this 

rulemaking. 

85 See letter from Will Shafroth, Department of Interior to Stephanie Kodish, NPCA, March 8, 2011 in the docket 

for this proposed rulemaking. 

86 See National Parks Conservation Association, et al., Petition to United States District Court for the District of 

Columbia, January 20, 2011, in the docket for this final rulemaking. 

87 See National Parks Conservation Association, et al., Plaintiffs, v. United States Department of Interior and United 

States Department of Agriculture, Defendants. Civil Action No. 11-130 (GK). United States District Court for the 

District of Columbia, June 30, 2011, 794 F. Supp. 2d 39; 2011 U.S. Dist. LEXIS 70170; 74 ERC (BNA) 1015. In 

the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

attributable to FCPP’s emission, EPA also considers any BART determinations it makes to 

consider the same factors whether the BART determination is triggered by a finding of 

reasonable attribution or under 40 CFR 51.308(e). 

Comment: 

 One of the owners of FCPP (0176/0177) stated that it is imperative to note that its support 

of the supplemental proposal (if other potential liabilities are resolved as discussed above) is 

based solely on the rationale that this achieves a result better than the proposed BART FIP, and 

that this “better than BART” outcome is a result of the closure of Units 1, 2, and 3. The 

commenter stressed that in no case – either in the original BART FIP proposal or in the 

supplemental proposal – does the commenter support any determination that SCR constitutes 

BART for FCPP. A second FCPP owner (0168) stated that its acceptance of the supplemental 

proposal upon resolution of the other potential issues would be a voluntary action based on its 

own business interests; the commenter does not support any BART determination that calls for 

installation of SCR at FCPP. 

 Another of the FCPP owners (0174) similarly emphasized the belief that SCR cannot be 

justified as BART at FCPP. Accordingly, the commenter stated that EPA’s October 2010 BART 

proposal should not be used as the benchmark for evaluating and proposing a BART alternative. 

The Navajo Nation (0223) also did not agree that SCR is BART for FCPP. 

Response:

EPA disagrees with the commenters that SCR is not BART. Based on our five-factor 

analysis, as described in the TSD for our proposed BART determination, SCR is cost effective 

and results in the greatest anticipated improvement in visibility. One of the owners of FCPP 

notes that the “better-than-BART” outcome is a result of the closure of Units 1, 2, and 3. 

However, the closure of Units 1 – 3 alone does not result in greater emission reductions than 

EPA’s proposed BART determination, and represents only a roughly 30% reduction from 

baseline emissions. The closure of Units 1 – 3, in combination with SCR on Units 4 and 5, results 

in the “better-than-BART” outcome. 

The voluntary nature of the alternative emission control strategy does not negate EPA’s 

BART determination because (1) EPA must determine what BART is in order to fulfill the 

requirements of the alternative program to BART as prescribed in the RHR, and (2) EPA cannot 

require the full or partial closure of a facility as a BART alternative, therefore the alternative 

emission control strategy remains an optional business choice of the owners of FCPP to 

implement in lieu of BART, if they see fit. 

Comment:

 Eleven private citizens (0122, 0139, 0140, 0141, 0145, 0149, 0158, 0159, 0166, 0167, 

0201) expressed general support for the supplemental proposal, although five of these 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

commenters (0122, 0145, 0156, 0158, 0167) did not support the 2018 completion date. One 

commenter (0167) preferred a completion date within 3 years of the final EPA decision, two 

commenters (0122, 0158) preferred a completion date of 2014, and one commenter (0145) 

asserted it cannot wait until 2014. 

 One of the private citizens (0139) supported the supplemental proposal with a few 

changes: (1) APS should be required to implement the upgrades incrementally over the next 

7 years, with 1/7th of the work to be completed each year, (2) penalties should be enforced for 

any year in which they lag behind the schedule, (3) retirement of the existing units should follow 

the same schedule, and (4) clean-up of the existing sites, incrementally, over the 7 years. 

 Another of the private citizens (0159) stated that the supplemental proposal yields even 

greater emissions reductions than the original BART proposal, promising greater health and 

economic benefits at significantly lower cost to the utilities and their ratepayers. The commenter 

also noted that APS and BHP Billiton pledged that no layoffs would be associated with the 

shutdown of the three smaller units at FCPP under this proposal. 

 A third private citizen (0167) urged EPA to lower the proposed numeric limits on NOx

and PM and to add limits for ammonia and H2SO4. The commenter argued that such limits would 

mean healthier air for us all, better views of our magnificent national parks, and a stronger 

tourism economy. 

 Several other commenters (0108, 0112, 0113, 0143, 0150, 0152, 0175, 0183, 0192, 0200, 

0223) also expressed support for the supplemental proposal, although some indicated some 

reservations about certain aspects of the proposal. These comments are summarized in the 

following paragraphs. 

 The Navajo Nation (0223) tentatively supports the supplemental proposal with the 

following caveats: 

 The alternative emission control strategy must be determined through government-togovernment consultation with the Navajo Nation and give primary consideration to the 

economic interests of the Nation in the continued operation of FCPP. (See Section 4.1 for 

more detail.) 

 The Navajo Nation does not agree to a determination that SCR is BART for FCPP. 

The commenter (0223) agreed that the supplemental proposal would result in 100 percent control 

of NOx, SO2, PM, mercury, and other hazardous pollutants by shutting down Units 1 – 3 by 

2014, which would significantly reduce the emissions of FCPP. 

 One state air agency (0113) anticipated substantial environmental benefits for the Four 

Corners region from the alternative proposal, and from an air emissions standpoint regarded this 

alternative proposal as superior to the October 2010 BART proposal. The commenter indicated 

that because the alternative proposal appears to have support from the facility’s operators, it 

should result in a higher likelihood of long-term success. The Attorney General’s office (0200) 

from the same state supported these comments. A U.S. Senator (0150) from the same state also 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

expressed support for the supplemental proposal because it would help to address longstanding 

concerns with air quality in the Four Corners region at a lower cost than the initial BART 

proposal. This commenter noted that the Class I areas affected by FCPP (and SJGS) are drivers 

of the economy in Southwest Colorado, and that emission from the plants have caused a variety 

of negative public health impacts. 

 One federal agency (0175) supported the supplemental proposal, but would prefer a NOx

limit of 0.05 lb/MMBtu (as discussed in Section 8.1). The commenter agreed that the 

supplemental proposal would provide greater visibility improvement in the surrounding Class I 

areas than EPA’s original BART proposal of October 2010, as well as additional benefits such as 

reduced water consumption and reduced CO2, SO2, and mercury emissions. An environmental 

advocacy group (0183) similarly supported the supplemental proposal (with a lower, but 

unspecified, NOx limit) and stressed the health and ecosystem benefits that would result from 

lower emissions of NOx, PM, SO2, mercury, and CO2 (which are discussed further in 

Section 4.2). 

 One public interest advocacy group (0143) and one private citizen (0192) supported 

EPA’s supplemental proposal for FCPP. The private citizen (0192) specifically supported the 

shutdown of Units 1 – 3 by 2014 and application of a NOx limit of 0.098 lb/MMBtu for Units 4 

and 5 with a compliance date of July 31, 2018. Given that SCR is a mature technology, EPA 

originally proposed BART in October 2010, and FCPP has operated with only minimal air 

emissions control for over 40 years, the commenter asserted this compliance schedule is ample. 

The commenter also voiced support for providing flexibility to FCPP through setting the limit as 

heat-input weighted limit and through a lower NOx limit on a 3-year rolling average. 

 One Tribe in the Four Corners area (0152) approximately 60 miles north of FCPP 

supported the supplemental proposal. The commenter gave the following reasons for this 

support: (1) any reductions in emissions from FCPP will result in cleaner and healthier air on the 

Reservation; (2) the tribe’s two air monitors show that the Reservation is nearing nonattainment 

status for ozone, and reducing NOx emissions from FCPP may help maintain attainment; and 

(3) any improvement in visibility in the Class I areas in the region will positively affect visibility 

on the Reservation. 

 Another public interest advocacy group (0112) similarly expressed support for adding 

regulatory language to the proposed BART determination for FCPP that would allow FCPP to 

implement the alternative control strategy in lieu of having to implement EPA’s proposed 

BART. This commenter also indicated support for the option of adding a NOx emission limit 

requiring greater than 80 percent control over longer averaging times weighted for heat input. 

 However, this commenter (0112) added that EPA should not make a final decision on 

whether to accept the alternative control strategy until it receives a “professional and credible” 

cost accounting of FCPP’s costs, including the additional pollution control investments for 

Units 4 and 5. The commenter indicated that the cost accounting should explain where the 

money will come from for retirement of Units 1 – 3 and for pollution control upgrades for 

Units 4 and 5. 
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 The commenter (0112) also questioned EPA’s statement that the alternative emission 

control strategy to shut down Units 1 – 3 by 2014 not only results in 100 percent control of NOx, 

but also 100 percent control of all other pollutants emitted by those units. The commenter alleged 

that this is a misleading statement because the shutdown of Units 1 – 3 is simply a business 

decision; the emission reductions are not attributable to any CAA program or enforcement of 

controls by EPA. The commenter stated that the “100 percent control” wording paints too rosy a 

picture by using the ratio of emissions after shutdown to emission levels that are completely 

unacceptable at present. According to the commenter, FCPP remained the most polluting power 

plant in the United States as of March 20, 2011. 

Response:

EPA has reviewed the comments in general support of our Supplemental Proposal. 

Specific comments on revisions to various aspects of the alternative emission control strategy, 

such as compliance timeframes, emission limits for sulfuric acid and ammonia, lower limits for 

NOx, health and ecosystem benefits, disagreement that SCR is BART, and the interests of the 

Navajo Nation, are included and addressed in more detail elsewhere in this Section and more 

broadly within this document (e.g., Sections 4 and 8). 

 Regarding the timing of the installation of controls, EPA disagrees with commenters that 

the compliance date for the alternative to BART should occur earlier than 2018, or that EPA 

should impose incremental progress in NOx reductions over the intervening 7 years. As 

described in our Supplemental Proposal, in order to implement the alternative emission control 

strategy, APS and other owners of FCPP must receive approvals from three regulatory agencies 

as well as finalize coal contract negotiations with BHP Billiton, and receive approval from DOI 

on the lease agreement with the Navajo Nation. These various components take time, as does the 

actual planning and installation of SCR as retrofits on existing boilers, Units 4 and 5. Therefore, 

the year 2018 compliance timeframe for the alternative emission control strategy in our final 

rulemaking is reasonable and appropriate. 

 EPA disagrees with the comment that EPA should not make a decision on the alternative 

emission control strategy until it receives a “professional and credible” cost accounting of 

FCPP’s costs for Units 4 and 5. Under the RHR (see 40 CFR §51.308(e)(2)), a cost analysis is 

not required element for an alternative to BART analysis. Even though EPA has not done a cost 

analysis of this alternative emission control strategy, EPA expects the cost of the alternative is 

likely to be lower than the cost of BART because the BART Alternative involves installation of 

additional controls on fewer units at FCPP. 

 EPA disagrees with commenters who contend that our statement that the closure of Units 

1 – 3 at FCPP results in 100% control of those units is misleading. If Units 1 – 3 close, those 

three units will not emit any air pollutants, i.e., 100% control. EPA further notes that the 

alternative emission control strategy not only involves closure of Units 1 – 3, but also 

installation of SCR on Units 4 and 5, further reducing facility-wide emissions of NOx. 

Comment: 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 The Navajo Nation (0223) agreed that shut down of Units 1, 2, and 3 by January 2014 

and installation of SCR on Units 4 and 5 by July 31, 2018, in order to satisfy the requirements of 

CAA section 169A(b)(2) and the RHR, 40 CFR 51.308(e), is realistically achievable. The 

commenter noted that EPA recognized in the supplemental proposal that APS must obtain 

approvals from several agencies, and that the Navajo Nation Council recently endorsed a lease 

renewal for FCPP; however, the lease renewal process is not yet complete as the lease renewal 

still needs to be reviewed and approved by the DOI, which the commenter stated will likely 

include review required under NEPA. The commenter indicated that if the final approval is 

delayed, there may be associated delays in compliance scheduling. 

 The commenter (0223) expressed appreciation for EPA’s understanding of the 

complexities related to the lease renewal that could delay the finalization of lease, including 

right-of-way issues that could also impact the life of FCPP. The commenter requested that EPA 

continue to provide flexibility to allow the leasing process to be completed. 

Response:

EPA has reviewed the Navajo Nation’s comments agreeing with the timing of the 

alternative emission control strategy. As noted in the comment, EPA is aware that the lease 

approval process through DOI will take time, as will the approval of the sale of Southern 

California Edison’s share of Units 4 and 5 to APS. Our final rulemaking requires a compliance 

timeframe for the alternative emission control strategy no later than July 2018. 

Comment:

 One environmental advocacy group (0182) and one federal agency (0224) asserted that 

the supplemental proposal is not better than BART for NOx. The commenters provided 

somewhat different rationales for this assertion, as summarized below. 

 The environmental advocacy group (0182) argued that the supplemental proposal is not 

better than BART for at least three reasons. The commenter indicated that to qualify as “better 

than BART,” an alternative must achieve “greater reasonable progress towards achieving 

national visibility conditions” than BART by resulting in “greater emissions reductions” than 

BART [citing 40 CFR 51.308(e)]. The commenter stated that the alternative put forward by EPA 

fails to meet these requirements as follows: 

 The alternative proposal’s delayed compliance date results in fewer emission reductions 

as compared to those emission reductions that should be required to begin occurring no 

later than 5 years after plan approval. 

– The CAA requires BART to be installed no later than 5 years after EPA’s final 

rulemaking [citing 42 U.S.C. 7479A(b)(2)(A)]. By offering FCPP a BART 

compliance deadline of July 2018, EPA is illegally extending a mandatory deadline 

under the CAA. See Sierra Club v. EPA, 129 F.3d 137, 140 (D.C. Cir. 1997); Sierra 

Club v. EPA, 719 F.2d 436, 469 (D.C. Cir. 1983). Furthermore, installation of SCR at 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Units 4 and 5 can be accomplished easily within 2 years (citing Comment 0182), 

making a 7-year “grace period” for BART compliance unnecessary. 

– To justify this delay, EPA links the extended deadline to the end of the first long-term 

strategy period for regional haze [citing 76 FR 10535; 40 CFR 51.308(e)(2)(iii)], but 

these are separate and distinct deadlines. While the statute requires the installation 

and operation of BART within 5 years, the purpose of the first long-term strategy 

deadline is to ensure that those already-imposed reductions are actually working. 

Also, the BART regulations require “all necessary emissions reductions [to] take 

place during the period of the first long-term strategy for regional haze” [citing 40 

CFR 51.308(e)(2)(iii)], but the alternative proposal violates this requirement by 

deferring the required BART reductions until the very end of this period. 

 Use of an artificially inflated baseline, coupled with the potential increase in output from 

Units 4 and 5, renders the claimed emissions reductions largely illusory. The commenter 

quoted Comment 0182 as saying that EPA’s analysis incorrectly assumes that all five 

units currently operate at a 91 percent capacity factor when, in fact, they all operate at 

lower levels, which artificially inflates the baseline from which EPA calculated the 

alternative’s emission reductions. On the other side of the equation, EPA underestimated 

potential emissions from increased output at Units 4 and 5 (i.e., beyond 91 percent) to 

make up for the lost generation from the shutdown of Units 1 – 3. 

 The proposed emission limits do not constitute BART (see Section 8.1). The commenter 

cited comments prepared by NPS (submitted as an attachment to Comment 0182) which 

found that based on the assumption that SCR can achieve 0.05 lb NOx/MMBtu on an 

annual basis, after 2016 the BART alternative would fail to achieve greater cumulative 

NOx reductions than would installation of BART (SCR) on all five units. (See the 

paragraph below for more on this NPS comment.).

 As noted by the previous commenter, based on its assumption that NOx BART for all five 

units at FCPP should be 0.05 lb NOx/MMBtu on an annual basis, the federal agency (0224) 

found that after 2016 the BART alternative would fail to achieve greater cumulative NOx

reductions than would installation of BART (SCR) on all five units. (These calculations were 

made assuming that Units 4 and 5 would also achieve a NOx emission rate of 0.05 lb/MMBtu on 

an annual basis under the supplemental proposal, and were projected out to 2028.) In order to 

achieve greater cumulative reductions than BART, the commenter identified an “Accelerated 

BART Alternative” that would include shutdown of Units 1-3 by 2014, as proposed, plus require 

that SCR be operational on Unit 4 by the beginning of 2017 and on Unit 5 by the end of 

September 2017, 10 months sooner than proposed by EPA. 

Response:

 EPA disagrees with the comment that the alternative emission control strategy is not 

better than BART, but agrees that a reexamination of baseline emissions and projected capacity 

factors in the future is warranted. In our Supplemental Proposal, we relied upon the baseline 

emissions APS provided of 45,132 tons NOx per year, representing a 91% capacity factor on all 

units. We examined annual emissions reported by FCPP to CAMD, and calculated average 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

annual NOx emissions over 2001 – 2010 of 42,395 tpy.87F

88 As reported in the TSD for our 

proposed BART determination, facility-wide NOx emissions over 2001 – 2009 ranged from 

40,331 to 47,300 tpy. While the baseline emissions provided by APS and used by EPA in our 

Supplemental Proposal was within the range of annual NOx emissions, in response to these 

comments, we conducted an additional analysis to compare the alternative emission control 

strategy against our final BART determination for NOx using the 2001 – 2010 average as the 

baseline emission rate and an assumed capacity factor of 81% for Units 4 and 5 under the 

alternative emission control strategy.8F

89 We assume no change in capacity factors of Units 1 – 5 if 

all 5 units continue operation under the BART scenario. Based on heat input reported to CAMD 

and maximum capacity heat input reported in the Part 71 permit for FCPP, we calculate the 

average capacity factor for Units 4 and 5 over 2001 – 2010 to be 76% and 75% respectively. 

This analysis shows that in 2014 and 2015, the alternative emission control strategy results in 

lower NOx emissions than BART due to the closure of Units 1 – 3 at the end of 2013. In 2016, 

2017, and 2018, BART results in lower emissions than the alternative, and in 2019 and beyond, 

the alternative emission control strategy (5,556 tpy), with phased-in controls on Units 4 and 5 by 

the end of 2018, results in lower emissions than BART (8,479 tpy). For comparison, our analysis 

from the Supplemental Proposal using a capacity factor of 91% resulted in emissions under the 

alternative from 2019 and beyond to be 5,798 tpy, and under BART to be 9,026 tpy. In total, the 

alternative results lower emissions from FCPP over more calendar years (2014-2015, and 2019 

and beyond) than does BART (2016-2018). Even if APS operated Units 4 and 5 at 100% 

capacity, EPA calculates that emissions under the alternative emission control scenario in 2019 

and beyond to be 6,859 tpy, which is still lower than under BART. On a cumulative basis, i.e., 

the sum total of NOx emissions over 2011 to 2064, the BART Alternative also results in lower 

emissions than BART, both at an 81 percent capacity factor and at 100 percent capacity. 

Commenters argue that if the BART emission limit were lower, the alternative would not 

be better than BART. For example, if EPA required an emission limit representing a 90% 

reduction in NOx emissions, annual NOx emissions would be lower than 5,000 tpy. However, as 

discussed in great detail elsewhere in this RTC (See response to comments in Section 8.1), EPA 

has determined that an 80% reduction in NOx emissions is BART for FCPP. It is inappropriate 

to compare the alternative emission control strategy against a target for BART that commenters 

would like to see based on maximum emission reductions achieved without consideration of sitespecific characteristics of FCPP. 

Commenters further argue that by offering FCPP a BART compliance deadline of July 

2018, EPA is illegally extending a mandatory deadline under the CAA, and that installation of 

SCR at Units 4 and 5 can easily be accomplished within 2 years. EPA disagrees and notes that 

the compliance timeframe for EPA’s BART determination requiring SCR installation on all 5 

units is within 5 years of the effective date of the final rule, consistent with the maximum time 

allowed under the CAA §169A(g)(4) in the definition of “as expeditiously as practicable”. The 

commenter is confusing requirements under BART and requirements under the alternative to 

BART. EPA is not extending the BART compliance deadline beyond a 5 year period. Rather, 

 

88 See: “data 01-10” tab in “BART v Alternative.xlsx” in the docket for this final rulemaking. 

89 In testimony to the ACC, Mark Schiavoni of APS testified that he anticipates capacity factors over 2015 – 2030 to 

range from 75 – 81% for Units 4 and 5 (See document titled “Schiavoni Testimony_TRANSCRIPT,pdf” in the 

docket for this final rulemaking).
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EPA is allowing additional time to implement the alternative emission control strategy, as 

allowed under the provisions of the RHR for the implementation of “other alternative measure 

rather than to require sources subject to BART to install, operate, and maintain BART” (See 40 

CFR §51.308(e)(2)). 

EPA disagrees with commenters that reductions under the alternative to BART violates 

40 CFR §51.308(e)(2)(iii). The requirement simply states the reductions take place during the 

period of the first long term strategy and does not specifically prescribe that those reductions 

must take place at the beginning, middle, or end of the period of the first long term strategy. 

Based on the foregoing discussion and the calculations provided in our docket, EPA 

confirms our previous determination that the alternative emission control strategy will result in 

greater NOx emission reductions than BART in 2019 and into the future. 

Comment:

 To evaluate the supplemental proposal’s impact on SO2 emissions, one federal agency 

commenter (0224) assumed that the scrubbers on Units 4 and 5 would be upgraded (perhaps by 

conversion to a wet stack) concurrently with the SCR installation to achieve 0.12 lb/MMBtu. 

Based on this assumption, the commenter confirmed that both the supplemental proposal and the 

commenter’s “Accelerated BART Alternative” (see comment above) would be better than BART 

at 0.12 lb/MMBtu or current emissions levels. 

 This commenter (0224) also noted that EPA has stated that the supplemental proposal 

would result in significant reductions of all relevant pollutants, including a 30 percent reduction 

in the FCPP’s carbon footprint. The commenter confirmed this for CO2 emissions based on 

figures from CAMD from 2005-2010. According to the commenter, Units 1-3 accounted for an 

average of 5,056,802 tpy of CO2 emissions out of a total of 15,499,044 tpy at FCPP during this 

period. 

Response:

EPA agrees with the commenter that the Supplemental Proposal will result in emission 

reductions beyond what would be achieved by the NOx BART determination for multiple 

pollutants. As discussed in the Supplemental Proposed Rule (76 FR 10537), the shutdown of 

Units 1 through 3 will result in significant additional reductions of NOx, as well as reductions of, 

PM, SO2, CO2, and mercury emissions that would otherwise not be achieved by the NOx BART 

determination. 

Comment:

 One environmental advocacy group (0182) supported APS’s “business decision” to close 

Units 1 – 3, but characterized the company’s alternative proposal as an attempt to leverage this 

business decision into a 2-year extension of time to install BART on Units 4 and 5. The 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

commenter noted that the BART regulations are clear that installation of controls is to occur 

within 5 years, or sooner if practicable. Therefore, the commenter asserted that it would be 

illegal for the EPA to extend the deadline for BART upgrades at Units 4 and 5 beyond the 

mandated 5-year or less timeframe. 

 The commenter (0182) noted that EPA refers to the supplemental proposal as an 

alternative to BART under 40 CFR 51.308(e), but the commenter stated that this regulatory 

provision is inapplicable in the circumstances of this case. Based on the commenter’s reading of 

40 CFR 51.308(e), the commenter indicated that the supplemental proposal fails as an alternative 

to BART because it does not address all the BART-eligible sources on the Navajo Nation – NGS 

is also a BART-eligible source. The commenter also alleged that the supplemental proposal does 

not qualify as an alternative to BART under the rules because, as discussed above, the 

commenter asserted that the alternative will not “achieve greater reasonable progress than would 

have resulted from installation and operation of BART” for NOx at all FCPP units during the 

period of the first long-term strategy for regional haze. 

Response:

EPA disagrees with these comments. The motivation, whether financial or environmental, 

behind APS’s proposal to close Units 1 – 3 is not relevant to the analysis, as discussed in other 

EPA responses to comments in this Section, complies with the requirements of the RHR for 

implementing an alternative to BART (See 40 CFR §51.308(e)(2)(iii)). EPA further notes that 

our final BART determination of installing SCR on all 5 units requires compliance with the final 

BART limits within five years of the effective date of the final rule, consistent with the 

compliance timeframes in the CAA (See CAA §169A(g)(4)) and the RHR (See 40 CFR 

§51.308(e)(1)(iv)). As stated previously, these comments confuse the requirements of an 

alternative to BART with the requirements of a BART determination. 

 EPA also disagrees with the commenter’s reading of 40 CFR §51.308(e) that the 

Supplemental Proposal fails as an alternative to BART because it does not address all BARTeligible sources on the Navajo Nation (i.e., Navajo Generating Station). The provisions of the 

RHR describing the requirements for an alternative measure to BART (i.e., see 40 CFR 

§51.308(e)(2)(i)(B)) states: 

The State is not required to include every BART source category or 

every BART-eligible source within a BART source category in an 

alternative program, but each BART-eligible source in the State 

must be subject to the requirements of the alternative program, 

have a federally enforceable emission limitation determined by the 

State and approved by EPA as meeting BART in accordance with 

section 302(c) or paragraph (e)(1) of this section, or otherwise 

addressed under paragraphs (e)(1) or e(4) of this section. 

The RHR allows some sources to be included under the alternative program, and some sources 

to meet BART (i.e., paragraph (e)(1) of the RHR at 40 CFR §51.308) or the CAIR (i.e., 

paragraph (e)(4) of the RHR at 40 CFR §51.308). As long as all BART-eligible sources are 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

subject to either the BART alternative, a BART limitation, CAIR, or a federally enforceable 

emission limitation determined to meet BART, the requirements of the RHR under 40 CFR 

§51.308(e) are met. EPA agrees that NGS is the other BART-eligible source on the Navajo 

Nation. EPA Region 9 intends to propose a BART determination for NGS in addition to finalizing 

our BART determination and the alternative emission control strategy for FCPP. 

 As described in detail in another EPA response to a comment within this Section of the 

RTC, EPA has determined that the alternative will achieve greater reasonable progress than 

would be achieved through the installation and operation of BART at FCPP. 

Comment:

 One of the owners of FCPP (0176/0177) and a utility industry association (0187) stated 

that EPA has the legal authority to implement an alternative emission control strategy, provided 

the plant owners agree to that strategy. The commenters indicated that the BART rules [40 CFR 

51.308(e)] establish that alternative emission control measures that achieve greater reasonable 

progress than BART – as “greater reasonable progress” is defined in EPA’s rules – may properly 

be adopted and implemented in lieu of BART. The commenters presented the history of related 

legal cases and added that the authority for those regulations has been confirmed in three cases 

by two different federal appellate courts. Central Arizona Water Conservation District v. EPA, 

990 F.2d 1531 (9th Cir. 1993); Center for Energy and Economic Development v. EPA, 398 F.3d 

653 (D.C. Cir. 2005); Utility Air Regulatory Group v. EPA, 471 F.3d 1333, 1340-41 (D.C. Cir. 

2006). 

Response:

EPA agrees with this comment and notes that our final rulemaking provides the owners 

of FCPP the option of implementing the alternative emission control strategy in lieu of BART. 
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10.0 9BOther Comments 

Comment:

 Forty-five private citizens (0087, 0088, 0089, 0091, 0118, 0119, 0123, 0125, 0127, 0128, 

0129, 0130, 0135, 0136, 0137, 0138, 0140, 0141, 0144, 0147, 0149, 0153, 0154, 0155, 0156, 

0157, 0158, 0162, 0170, 0171, 0172, 0173, 0181, 0186, 0188, 0190, 0198, 0199, 0201, 0202, 

0208, 0209, 0210, 0211, 0213, 0214) explicitly stated that they support EPA’s efforts to clean up 

FCPP. Many of these commenters asked for the strictest regulations. Another private citizen 

(0093) implied that EPA should act to clean up emissions from FCPP and noted that cleaner air 

will result in a cleaner Colorado snow pack, which will result in cleaner water in the Colorado 

River. 

 Twelve private citizens (0092, 0122, 0126, 0133, 0134, 0145, 0157, 0161, 0172, 0190, 

0195, 0213, 0214) stated that FCPP should be de-commissioned. Several of these commenters 

argued that the plant should only be shut down if it cannot cease emitting pollutants, while others 

argued the plant should be shut down immediately. One of the latter commenters (0092) stated 

that if FCPP is not de-commissioned, it should be retrofitted with BART. Another of these 

commenters (0133) does not asserted that either of the two proposals is sufficient. In contrast, 

one private citizen (0135) finds either of the proposals to be sufficient. 

 Nine private citizens (0122, 0126, 0134, 0140, 0145, 0170, 0186, 0190. 0195, 0197) 

recommended that renewable energy sources can be used in place of coal-fired power plants. 

Response:

EPA acknowledges the comments supportive of our proposals but disagrees with 

commenters that suggest that FCPP should be de-commissioned or shut down immediately. 

In addition to other CAA programs, EPA assesses air quality with respect to NAAQS. 

The Four Corners area is designated attainment for each of the NAAQS.89F

90 This means that the 

air quality in the Four Corners area is meeting the national health-based standards set by EPA. 

For this action, EPA finds that under 40 CFR 49.11, it is necessary or appropriate to 

achieve emissions reductions of NOx from FCPP required by the CAA’s RHR program. NOx is a 

significant contributor to visibility impairment in the numerous mandatory Class I Federal areas 

surrounding FCPP. The emission reductions finalized will help achieve the goals of the RHR. 

The RHR however does not require nor does it authorize EPA to de-commission or shut down 

facilities to achieve the goals of the rule. 

EPA agrees with commenters who stated that renewable energy sources can be used in 

place of coal-fired power plants. However, the RHR does not require that coal-fired facilities use 

or switch to renewable energy sources to meet the goals of the rule. The RHR establishes a five 

step process EPA must follow when performing a case-by-case BART determination. In the first 

 

90 Please see http://www.epa.gov/region09/air/maps/maps_top.html for EPA Region 9 air quality designations.
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

step, “Identification of all available retrofit technologies”, EPA does not consider BART as a 

requirement to redesign a source (see 70 FR at 39164). 

Comment:

 Fifty-two private citizens (0085, 0086, 0087, 0088 , 0089, 0091, 0092, 0122, 0123, 0124, 

0125, 0126, 0127, 0128, 0132, 0134, 0135, 0136, 0137, 0138, 0140, 0141, 0147, 0148, 0149, 

0151, 0153, 0154, 0155, 0156, 0157, 0158, 0159, 0160, 0161, 0162, 0165, 0166, 0170, 0171, 

0172, 0173, 0178, 0181, 0188, 0190, 0197, 0199, 0202, 0208, 0211, 0213, 0214) expressed 

concern about the poor air quality in the Four Corners area. Forty of these commenters (0085, 

0086, 0087, 0089, 0091, 0092, 0123, 0126, 0127, 0128, 0134, 0136, 0137, 0138, 0141, 0148 , 

0149, 0151, 0153, 0154, 0155, 0157, 0158, 0159, 0160, 0161, 0162, 0166, 0170, 0171, 0172, 

0173, 0178, 0181, 0188, 0197, 0202, 0211, 0213, 0214) claimed that FCPP has diminished the 

visual quality of their respective regions. The regions mentioned in the comments include 

Bayfield, Cortez, Durango, La Plata City, Pagosa Springs, and Oxford, CO; Southwest CO; 

Albuquerque, Farmington , Mancos, Pecos, and Shiprock, NM; Bluff, UT; and Class I areas such 

as Arches, Chaco Canyon, Grand Canyon , Maroon Bells, Mancos Valley, Mesa Verde, Sleeping 

Ute, and Wheeler Peak. One of these commenters (0172) disapproved of pollution coming from 

Arizona affecting Colorado. 

 Five private citizens (0089, 0091, 0124, 0128, 0201) supported EPA’s proposal to reduce 

NOx emissions at FCPP. Two private citizens (0091, 0201) supported EPA’s proposal to reduce 

PM emissions at FCPP. 

Response:

EPA acknowledges the comments and generally agrees with comments regarding 

diminished visibility in the Four Corners Area. As detailed in our response to the previous 

comment above, the air quality in the Four Corners area is meeting the national health-based 

standards as set by EPA. EPA agrees with commenters that the NOx emission reductions 

finalized will reduce visibility impairment in the numerous mandatory Class I Federal areas 

surrounding FCPP. 

As described in Section 8.2 of this RTC, EPA is not taking action at this time on our 

proposal to set new PM limits for Units 1 – 3. If APS is unable to or decides against 

implementing the alternative emission control strategy and continues operation of Units 1 – 3, 

EPA will again conduct a five-factor analysis for PM for Units 1 – 3 and propose another BART 

determination for public comment. 

Comment: 

 

The Navajo Nation (0223) pointed out that as a federal agency, EPA has a trust 

responsibility to the Navajo Nation that requires it to give special consideration to the Nation’s 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

best interests in any action.90F

91 Because of the significant interest of the Navajo Nation in FCPP 

(see related comments in Section 4.1), the commenter asserted that the BART proposal clearly 

implicates the Nation’s tribal trust interests. The commenter further contended that since EPA is 

adopting a FIP for BART in lieu of a TIP by the Navajo Nation, the EPA is essentially “standing 

in the shoes” of the Nation for purposes of making the BART determination and should, 

therefore, defer to tribal views when making environmental policy decisions and give the same 

weight to the BART factors that the Navajo Nation would in determining BART for FCPP; that 

is, to the extent that the Nation recommends a particular control technology as BART for power 

plants located on the Nation’s lands, EPA should give substantial weight to that recommendation 

as part of its decision-making process. (As discussed in Section 8.1, the commenter asserted that 

advanced combustion controls, rather than SCR, properly represent BART for FCPP.) Thus, the 

commenter stated that as the Nation’s trustee and “stand-in” for the BART determination for 

FCPP, the EPA should not select a more stringent BART than the commenter argued is required 

by the RHR to achieve “reasonable progress” where doing so would likely have substantial 

adverse impacts on the Navajo Nation. (See Section 4.1 for related comments on the potential 

impacts identified by the commenter.) 

 The commenter (0223) also stated that EPA has a duty to undertake government-togovernment consultations with the Navajo Nation, and that EPA must coordinate with the 

Navajo Nation in its relationship with, and reliance on, other federal agencies. The commenter 

pointed out that EPA relies on data provided by the NPS, another federal trustee of the Nation, 

but has not coordinated consultation between NPS and the Navajo Nation on this rulemaking. 

The commenter indicated that the May 2011 EPA Tribal Policy recognizes that such 

coordination is required under Executive Order 13175 and asserted that EPA should coordinate 

consultation with the U.S. Forest Service (who provided data used in the proposed rulemaking) 

as well as various DOI agencies that have an interest in this rulemaking, including NPS, the 

Bureau of Indian Affairs, the U.S. Fish and Wildlife Service, the Office of Surface Mining 

Reclamation and Enforcement, and potentially the Bureaus of Land Management and 

Reclamation. The commenter added that consultation with Department of Energy (DOE) may be 

important in regard to including FCPP in a study that DOE is proposing to carry out for NGS, 

which also is located on the Navajo reservation and uses Navajo coal. 

Response:

It is EPA’s policy (EPA Policy on Consultation and Coordination with Indian Tribes, 

May 4, 2011 (EPA Tribal Consultation Policy))91F

92 to consult on a government-to-government 

basis with federally recognized tribal governments when EPA actions and decisions may affect 

tribal interests. Consultation is a process of meaningful communication and coordination 

between EPA and tribal officials prior to EPA taking actions or implementing decisions that may 

affect tribes. One of the primary goals of the EPA Tribal Policy is to fully implement both 

 

91 To support this assertion, the commenter cited Executive Order 13175 (65 FR 67249, November 6, 2000; EPA 

Policy on Consultation and Coordination with Indian Tribes, section IV “Guiding Principles,” May 4, 2011 (EPA 

Tribal Policy); and the 1984 EPA Indian Policy. 

92 See “EPA Policy on Consultation and Coordination with Indian Tribes”, May 4, 2011, in the docket for this final 

rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

Executive Order 1317592F

93 and the 1984 Indian Policy, with the ultimate goal of assuring tribal 

concerns and interests are considered whenever EPA’s actions may affect tribes by 

strengthening the consultation, coordination, and partnership between tribal governments and 

EPA. 

For this action, EPA consulted with the Navajo Nation in accordance with the Executive 

Order and EPA’s Indian Policies on numerous occasions. A record of all consultations with 

tribes is included in the docket for this final rulemaking.93F

94 As stated in the 2011 EPA Tribal 

Consultation Policy, as a process, consultation includes several methods of interaction that may 

occur at different levels.94F

95 EPA consulted with the Navajo Nation at various times throughout the 

process at various levels of government, including in-person consultation meetings with the 

President of the Navajo Nation on May 19, 2011 and June 13, 2012.

EPA acknowledges the significant interest of the Navajo Nation in FCPP. Based on a 

request made by the Navajo Nation during our May 19, 2011, consultation meeting, EPA 

examined potential adverse impacts to Navajo Nation if the owners of FCPP chose to implement 

the alternative emission control strategy in lieu of BART. The results of this analysis were 

discussed with President Shelly during a consultation meeting on July 13, 2012 and will be 

provided to President Shelly by letter as a follow-up to our consultation. 

EPA agrees that we are acting to implement the BART requirements for a facility located 

on the Navajo Reservation in circumstances in which the Tribe has not applied, or been 

approved, to administer the applicable CAA program. EPA is mindful of the Navajo Nation’s 

views and recommendations, particularly where there is a potential substantial adverse 

economic impact to the Navajo Nation. We disagree however that the Agency must “defer to 

tribal views when making environmental policy decisions”. EPA is carrying out the requirements 

of the CAA and the Regional Haze Rule pursuant to our authority to implement these 

requirements in the absence of an EPA-approved program. EPA notes that the CAA and the TAR 

provide mechanisms for eligible Indian tribes to seek approval of tribal programs should they 

wish to administer CAA requirements. 

As we stated in our proposed rule, FCPP is one of the nation’s largest emitters of NOx

(over 42,000 tons of NOx in 2009), was built roughly four decades ago, and has not installed any 

new NOx controls since the 1990’s. FCPP is also located within 300 km of 16 Class I areas, 

sometimes known as the Golden Circle of National Parks.95F

96 

For this action EPA carefully considered the unique location of FCPP with respect to 

proximate Class I areas as well as its economic importance to Navajo Nation. We conducted a 

detailed analysis of available emission control technologies against the five-factors specified in 

the BART Guidelines. EPA also conducted extensive air modeling (included in the Supplemental 

Proposal). Additionally, we have considered the numerous comments we received on our 

 

93 See “Executive Order 13175 of November 6, 2000” in the docket for this final rulemaking. 

94 See document “Timeline of all Tribal Consultations on BART.docx” in the docket for this final rulemaking. 

95 See “EPA Policy on Consultation and Coordination with Indian Tribes”, May 4, 2011, in the docket for this final 

rulemaking. 

96 See http://www.nps.gov/history/history/online_books/nava/adhi/adhi4e.htm. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

proposals. In making our final decision we have had to balance the findings of our analysis 

along with the interests of various stakeholders, our unique government-to-government 

relationship with tribes, and our responsibility to carry out the requirements of the CAA and 

RHR to achieve reasonable progress towards visibility improvements. 

This final FIP strikes a reasonable balance between reducing emissions to improve 

visibility while allowing for the facility to implement those reductions in a manner that is 

consistent with its continued operation and economic viability. 

EPA has received information and comments from numerous federal agencies for this 

rulemaking and considered these in our final decision (all information and comments are 

included in the docket). However, EPA disagrees that we relied principally on data from the 

National Park Service. EPA conducted our own cost and visibility analyses for FCPP. EPA 

plans to coordinate with the Department of Interior in any future tribal consultations related to 

BART for the two coal-fired facilities located on the Navajo Nation. 

EPA acknowledges that the Department of Interior has contracted with the National 

Renewable Energy Lab (NREL) of the Department of Energy to examine renewable energy 

options for the Navajo Generating Station, which is also located on the Navajo Nation and uses 

coal from the Kayenta Mine, located on Navajo and Hopi land. Information on the NREL study 

is available from DOI96F

97and will be included in the docket for EPA’s upcoming proposed 

rulemaking for NGS. 

Comment:

 One private citizen (0163/0164/0216) asserted that the FCPP BART analysis should be 

based on the use of bituminous coal (with heat content of 11,500 Btu/lb) at the plant, but FCPP 

indicated that the plant uses sub-bituminous coal (with heat content of 8,880 or 8,776 Btu/lb). 

Based on this point, the commenter asserted that FCPP needs to have the air models redone, 

available technologies reselected, cost of control technology redone, energy control impacts 

redone, economic control impacts redone, non-air quality control impacts redone, existing 

controls reevaluated, useful life of FCCP re-evaluated, air visibility re-evaluated and anticipated 

improvement of visibility re-evaluated. 

Response:

EPA disagrees with the commenter. The classification of coal used at FCPP is only 

relevant to the presumptive NOx limits established for EPA’s RHR regulations, which suggest 

emission limits based on the coal classification and boiler type. 40 CFR Part 51, Appendix Y, 

E.5. Table 1. EPA discussed the presumptive NOx limits for Units 3 – 597F

98 at FCPP in terms of 

both bituminous and sub-bituminous coal, however, EPA conducted a full five-factor analysis for 

BART. Coal classification is not related to any aspect of the full five-factor BART analysis, 

therefore, regardless of whether the coal burned at FCPP is sub-bituminous or bituminous, 

 

97 http://www.doi.gov/navajo-gss/index.cfm 

98 Presumptive limits apply only to EGUs greater than 200 MW in size. Units 1 and 2 are smaller than 200 MW, 

therefore the presumptive limits do not apply to those units. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

EPA’s five-factor analysis does not need to be redone and our BART determination does not 

need to be re-evaluated. 

 As stated in the TSD the classification of coal used by FCPP has historically been subbituminous;98F

99 however, FCPP asserts that its coal has more characteristics of bituminous coal 

than sub-bituminous coal, and should be classified as bituminous. Based on this categorization, 

FCPP cites the presumptive limit for NOx for bituminous coal of 0.39 lb/MMBtu from a drybottom wall fired boiler as its applicable presumptive BART limit for Unit 3. See 40 CFR Part. 

51, Appendix Y, E.5. Table 1. The presumptive limit for NOx for sub-bituminous coal is 0.23 

lb/MMBtu. Id. Generally, the high volatile content of sub-bituminous coal is known to ease 

burning and improve efficiency of combustion controls to reduce NOx, thus, the presumptive limit 

for sub-bituminous coal is lower than for bituminous coal. 

The presumptive limits are not binding requirements for BART, rather they are included 

in the BART Guidelines as limits that most EGUs can meet through the use of current 

combustion control technologies. However, the BART Guidelines further state that the reviewing 

authority may determine that an alternative control level is appropriate based on the careful 

consideration of the statutory factors. Because EPA made our BART determination based upon 

our careful examination of the five factors rather than relying on the general presumptions set 

forth in the BART Guidelines, it was not necessary for our analysis or purposes of this regulation 

to determine whether the coal used by FCPP is bituminous or subbituminous.

With respect to the modeling of FCPP operations the type of coal burned and associated 

heat content were not germane to the analysis. The model is not itself, nor does it rely upon, a 

production cost model. The underlying costs of operation, including fuel quantity and heat 

content, as they flow through the summary economic statistics, are not modified with respect to 

the type of coal consumed. 

Comment: 

 Three of the owners of FCPP (0168, 0174, 0176/0177), who argued that advanced 

combustion controls constitute BART for NOx at FCPP, pointed out that SCR can be assessed as 

a potential control option later, under the reasonable progress component of the regional haze 

program. One of the commenters (0176/0177) provided background information about the 

Regional Haze program and noted that the CAA and BART rules treat BART as a part of the 

larger “reasonable progress” requirement. The commenter asserted that under the broader 

visibility program, the advanced combustion controls proposed by the commenter as BART can 

and should be deemed also to satisfy the reasonable progress milestone in the current planning 

period. The commenter added that whether additional emission controls may be needed after the 

application of this BART is a question that should be addressed in the larger context of the many 

sources of regional haze impairment on the Colorado Plateau, including, for example, mobile 

sources and prescribed and uncontrolled fires, as well as the ongoing regional planning efforts to 

address haze in the Western states. The commenter suggested that SCR can be considered during 

the next 10-year planning period (2018-2028) if it proves that additional emission reductions are 

 

99 See Determination of Four Corners Coal Ranking, March 11, 2008 by Alan Papp. Docket ID: EPA-R09-OAR2010-0683-0056. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

needed to ensure reasonable progress. Another of the commenters (0168) stated that this 

approach would achieve reasonable progress and have the following benefits: (1) reduce the 

immediate financial burden on its customers, (2) allow time for greater certainty in terms of 

potential carbon limits and customer demand, and (3) retain greater flexibility in future resource 

decisions including the possibility of divestiture. 

Response:

EPA disagrees with the commenter that advanced combustion controls constitute BART 

for NOx at FCPP, and that therefore SCR should be assessed as a potential control option later, 

under the reasonable progress component of the regional haze program. EPA also disagrees that 

under the broader visibility program, the advanced combustion controls proposed by the 

commenter as BART can and should be deemed also to satisfy the reasonable progress milestone 

in the current planning period. 

As detailed in the TSD, Unit 2 at FCPP experienced operational difficulties subsequent to 

its 1999 retrofit with LNB. Additionally, as noted in the Andover Report9F

100 there are operational 

risks associated with LNB/OFA retrofits on the Units at FCPP. Finally, it is not clear that the 

boilers APS cited as having achieved NOx emissions of 0.4 lb/MMBtu or lower following retrofit 

with LNB + OFA are indeed comparable to the units at FCPP. EPA therefore concluded that 

LNB and LNB+OFA are not capable of achieving the level of NOx control needed for BART. 

Regarding the comment to address FCPP in a broader regional planning context, EPA 

addressed this comment in Section 8.0. However, EPA further notes that the BART requirement 

of the RHR applies to major stationary sources built within a limited timeframe that contribute to 

visibility impairment at nearby Class I areas. EPA and state or local air agencies have other 

regulatory mechanisms to address emissions from new stationary sources or mobile sources, and 

EPA further notes that those sources need not be addressed under BART, or assessed in a fivefactor analysis for an individual facility. 

Comment: 

 One of the owners of FCPP (0176/0177), a group of FCPP owners (0185), and a utility 

industry association (0187) noted that the proposal preamble indicated that there is a visible 

plume originating from FCPP Units 1 – 3 that has some visibility-impairing effect in the area, 

and that EPA sought information on this secondary visible plume, its frequency and persistence, 

and whether it affects or can be observed from any Class I area (citing 75 FR 64231-32). The 

owner of FCPP (0176/0177) stated that the BART rules [40 CFR 51.308(d)] and CAA [section 

169(a)(1)] address visibility in Class I areas, and added that the EPA does not have a “roving 

commission” to address visibility impairments that occur outside Class I areas. The commenter 

pointed out that although there is an “integral vista program” to protect views from within Class I 

areas (citing 40 CFR 51.301), such integral vistas must be identified by a Federal Land Manager 

according to specified criteria (citing 40 CFR 51.304), and only one such vista has been 

identified (in Maine) (citing 40 CFR 81.437). On this basis, the commenter concluded that 

 

100 See “TSD ref [104] Andover Report” in the docket for this rulemaking at: EPA-R09-OAR-2010-0683-0059. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

“EPA’s attempt to justify additional regulation of [PM] emissions and opacity on the basis of a 

purported association with alleged visibility impairment that EPA stated may result from [an 

FCPP] ‘plume’ outside Class I areas is ill-considered and should be abandoned.” 

 The utility industry association (0187) and group of FCPP owners (0185) stated that the 

Regional Haze program cannot be used to address visibility impairment outside of a Class I area, 

even if it is visible from such an area (citing CAA section 169A(a)(1), and that in the absence of 

evidence that this plume exists and significantly affects visibility in a Class I area, there is no 

basis for this aspect of the proposed rule. Another of the owners of FCPP (0174) simply asserted 

that the Regional Haze program provides no authority to require additional PM controls based on 

a “purported” plume generated by the units at FCPP. 

 The Navajo Nation (0223) stated that it is inappropriate for EPA to request comment on 

the secondary visible plume without verifying the existence of the plume or characterizing the 

nature, cost, and effects observed in Class I areas. This commenter included this argument in 

justifying continued operation of venturi scrubbers with an emission limit of 0.03 lb/MMBtu and 

a 20 percent opacity standard as PM BART for Units 1 – 3 (see Section 8.2). 

Response:

EPA disagrees with the commenters that we were attempting to address visibility 

impairments outside of a Class I area under BART or that EPA requested comment without 

verifying the existence of the secondary plume. EPA specifically requested comment in our 

proposed rule about whether the secondary visible plume (that EPA Region 9 staff observed in 

New Mexico out as far as Aztec and Bloomfield en route to Farmington from Albuquerque ) can 

be seen from Mesa Verde National Park, the closest Class I area to FCPP or any other Class I 

area near FCPP. In the TSD, EPA discusses whether this secondary visible plume is related to 

the poor control of fine particulates by the venturi scrubbers. Although EPA did propose PM and 

opacity limits, EPA also took comment on whether BART can be satisfied by allowing APS to 

continue to operate its existing venturi scrubbers on Units 1–3. 

Although EPA received numerous comments on visibility impairment and anticipated 

improvement in the area from both our proposed rule and the supplemental proposed rule, EPA 

did not receive any specific information regarding whether this secondary plume impacts 

visibility in any Class I area near FCPP. 

As described in Section 8.2 of this RTC, EPA is not taking action at this time on our 

proposal to set new PM limits for Units 1 – 3. If APS is unable to or decides against 

implementing the alternative emission control strategy and continues operation of Units 1 – 3, 

EPA may again conduct a five-factor analysis for PM for Units 1 – 3 and propose another BART 

determination for public comment. 

Comment:
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 One public interest advocacy group (0112), the Navajo Nation (0223), and one 

environmental advocacy group (0182) supported establishment of a 20 percent opacity limit for 

material handling. The public interest advocacy group (0112.1) stated that the FCPP site is 

subject to numerous dust-storm events originating in northwestern Arizona, and the additional 

fugitive dust that could be picked up by these strong winds at the FCPP property added to the 

incoming dust from the west makes breathing and outdoor activity miserable on from 4 to 12 

days per year for residents of Montezuma County, CO and San Juan County, NM. The 

commenter supports requiring FCPP to develop a dust control plan within 90 days of 

promulgation of the final rule to be submitted to the EPA Regional Administrator and 

implemented immediately. The commenter also asked that courtesy copies of the dust control 

plan be submitted to appropriate local governments in the Four Corners area, such as the Navajo 

Nation EPA, San Juan County (NM), and Montezuma, Dolores, and La Plata Counties (CO). 

 The Navajo Nation (0223) added that the fugitive dust plan should be reviewed 

thoroughly and include appropriate recordkeeping and monitoring requirements. The commenter 

also expressed support for the constructive approaches described in the supplemental proposal to 

the management of dust, ash, and PM, stating that these approaches are practicable and will be 

consistent with EPA’s ongoing progress and rulemaking under the CAA for mercury, coal 

combustion residues, GHGs, and other contaminants; improve the efficiency of Units 4 and 5; 

and provide environmental and health co-benefits, which are essential for quality of life and 

economic opportunities. 

 One of the owners of FCPP (0176/0177) noted that in addition to the proposed BART 

requirements, EPA proposed separate fugitive dust control requirements and a 20 percent opacity 

limitation for certain material handling operations, which are unrelated to the CAA visibility 

program. The commenter laid out the history of EPA’s past attempt to apply fugitive dust 

controls to FCPP, pointing out that EPA included such requirements in the 2007 FIP for the plant 

and the commenter sought judicial review of those requirements based on the absence of a 

reasoned explanation. Arizona Public Service Co. v. EPA, 562 F.3d 1116 (10th Cir. 2009) (“APS 

v. EPA”). The commenter added that upon EPA’s motion, the court vacated and remanded the 

fugitive dust requirements (citing APS v. EPA at 1121-22, 1131; the EPA Merits Brief at 53; and 

75 FR 64232, Oct. 19, 2010).

 The commenter argued that the proposed requirements are arbitrary and should not be 

finalized because the facts upon which EPA relies are inadequate to support the conclusion that 

fugitive dust control requirements are “necessary or appropriate” to protect air quality at FCPP. 

The commenter’s points are outlined below: 

 The “necessary or appropriate” language in the TAR at 40 CFR §49.11(a) is limiting – 

not all requirements that could potentially yield some air quality benefit are “necessary or 

appropriate to protect air quality.” The EPA has indicated in the past that this language is 

intended to be limiting (citing the APS v. EPA EPA Merits Brief at 56, 60 and EPA’s 

NSR rules for Indian country at 71 FR 48696, 48714, August 21, 2006). 

 Although the Administrative Procedures Act (APA) requires that there be some 

intelligible principle or criteria to guide the Agency‘s decisions, the EPA has not 

identified the criteria that guide its judgment as to which regulatory requirements are 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

“necessary or appropriate” and which are not. Such exercises of standardless discretion 

are arbitrary and capricious. Qwest Corp. v. FCC, 258 F.3d 1191, 1201-02 (10th Cir. 

2001); Dithiocarbamate Task Force v. EPA, 98 F.3d 1394, 1402 (D.C. Cir. 1996). See 

also Pennaco Energy, Inc. v. EPA, 692 F. Supp. 2d 1297, 1314 (D. Wyo. 2009). Without 

identified criteria, EPA’s proposed conclusion that fugitive dust controls are “necessary 

or appropriate” is inevitably arbitrary. 

 The reasons given in the proposal preamble for imposing fugitive dust requirements are 

inadequate to support the proposed conclusions. In the end, EPA makes no effort to 

identify a specific, concrete air quality problem that needs to be addressed or to quantify 

FCPP’s contribution to any such problem. 

 Regulation of fugitive dust without a well-defined air quality basis would not only be 

arbitrary in and of itself, but would also conflict with guidance the EPA has provided to 

the states. This guidance includes (1) the 1986 document Identification, Assessment, and 

Control of Fugitive Particulate Emissions (EPA/600/8-86/023, excerpt attached to the 

comments as Exhibit H); (2) the 1977 memorandum Guidance on SIP Development and 

New Source Review in Areas Impacted by Fugitive Dust (attached as Exhibit I); and (3) 

the 1987 PM10 SIP Development Guideline (attached as Exhibit J).10F

101 

 The EPA may not depart from its established policies without reasoned explanation. 

Although EPA may argue that it is not expressly bound by its SIP policies in crafting a 

FIP for Indian country, EPA cannot ignore those policies without expressing good reason 

to do so. To avoid being arbitrary or capricious, a federal agency must treat like situations 

alike and must follow its own established policies, in the absence of a well-reasoned basis 

for doing otherwise. Transactive Corp. v. United States, 91 F.3d 232, 237 (D.C. Cir. 

1996); Illinois State Chamber of Commerce v. EPA, 775 F.2d 1141, 1147 (7th Cir. 1985). 

 The EPA has provided no explanation for its selection of the 20 percent opacity limit, as 

opposed to no limit or a higher limit (citing 75 FR 64232). A rule without any stated basis 

is necessarily arbitrary and capricious. Small Refiner Lead Phase-Down Task Force v. 

EPA, 705 F.2d 506, 551 (D.C. Cir. 1983). See also, Appalachian Power Co. v. EPA, 135 

F.3d 791, 818 (D.C. Cir. 1998). See Northeast Md. Waste Disp. Auth. v. EPA, 358 F.3d 

936, 948 (D.C. Cir. 2004); Columbia Falls Aluminum Co. v. EPA, 139 F.3d 914, 923 

(D.C. Cir. 1998); American Maritime Ass’n v. United States, 766 F.2d 545, 566 n. 30 

(D.C. Cir. 1985). 

 Opacity limits for fugitive dust in SIPs and TIPs appear to be widely varied, as shown in 

the 1983 document Opacity Regulations: Summary of State Regulations and Rulemaking 

Status (attached as Exhibit M with summary tables reproduced in the comments). Data 

from a 2007 study by UARG show a variety of opacity limits for coal handling activities 

in recent PSD permits for new coal-fired plants (excerpt attached as Exhibit N). The 

NSPS 20 percent opacity standard in 40 CFR part 60, subpart Y cannot properly be the 

basis for the FCPP opacity limit because Congress intended that, in general, existing 

sources such as FCPP would be subject to less stringent standards than new sources built 

after the applicability dates of the various NSPS. California v. Department of the Navy, 

 

101 The Exhibits referenced by commenter 0176/0177 are attached as embedded PDF files to the comment letter in 

the docket for this rulemaking, at EPA-R09-OAR-2010-0683-0177 or EPA-R09-OAR-2010-0683-0176. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

431 F. Supp. 1271, 1291 (N.D. Cal. 1977), aff’d, 624 F.2d 885 (9th Cir. 1980). See S. 

Rep. No. 1196, 91st Cong., 2d Sess. 15-16 (1970); Arbuckle, et al., Environmental Law 

Handbook (Twelfth ed. 1993) at 127. 

 Another of the owners of FCPP (0168) expressed general support for the points made by 

Commenter 0176/0177. 

Response: 

EPA acknowledges support for establishing a 20% opacity limit for material handling 

and a Dust Control Plan at FCPP. For the reasons outlined below, EPA has finalized both these 

requirements. EPA notes that the Dust Control Plan shall include a description of the dust 

suppression methods for controlling dust from site activities including coal handling and storage 

facilities, ash handling , storage, and landfills, and road sweeping activities. The 20% Opacity 

standard will apply to any crusher, grinding mill, screening operation, belt conveyor, or truck 

loading or unloading operation.10F

102 

 As mentioned in an earlier response to this RTC, EPA notes that on June 21, 2010, EPA 

proposed and solicited comments on two regulatory options for establishing national standards 

for management of CCW (75 FR 35127). The proposal includes options for fugitive dust controls 

that would apply to FCPP when finalized. 

EPA agrees with the commenter that the fugitive dust plan should be reviewed and should 

include appropriate recordkeeping and monitoring requirements. EPA intends to review the Dust 

Control Plan prior to approval for use. 

 

EPA agrees with the commenter that the fugitive dust and 20% opacity limit are 

unrelated to the CAA visibility program. EPA also agrees with the history laid out by the 

commenter on fugitive dust controls at FCPP. EPA included these dust control requirements in 

the previous FIP finalized in 2007 because EPA considered them necessary or appropriate 

under the TAR to assure that the dust from this facility does not adversely contribute to possible 

violations of the NAAQS for PM10. Most large coal fired power plants are either covered by a 

State’s general opacity limit (generally set at 20%), a specific limit in its permit or the NSPS 

Standards for coal handling (NSPS Subpart Y). APS is correct that EPA withdrew the 2007 FIP 

requirements on dust when APS appealed the rule. EPA had not adequately documented in the 

record for the 2007 FIP our basis for establishing the 20% opacity regulation. For the 2007 

FIP, EPA chose not to defend our position based on the record for that rulemaking and instead 

chose to address the issue in a subsequent FIP action, such as this one. 

EPA disagrees with the commenter that the fugitive dust and opacity requirements are 

arbitrary or that our argument is inadequate to support our conclusion that fugitive dust control 

requirements are necessary or appropriate to protect air quality at FCPP. EPA first 

promulgated dust control requirements for new coal handling equipment on January 15, 1976 

 

102 Submittals received by EPA as a result of these requirements may be requested by the public via a Freedom of 

Information Act request unless claimed as Confidential Business Information (CBI) by the author of the document 

and determined to meet the CBI regulations at 40 CFR part 2 by EPA 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

(41 FR 2232). This rule affected equipment constructed or modified after the 1970s that affected 

facilities built or modified after October 24, 1974. The purpose of these New Source 

Performance Standards (NSPS) was: 

NSPS implement CAA section 111(b) and are issued for 

categories of sources which have been identified as 

causing, or contributing significantly to, air pollution 

which may reasonably be anticipated to endanger public 

health or welfare. The primary purpose of the 

NSPS are to help States attain and maintain ambient air 

quality by ensuring that the best demonstrated emission 

control technologies are installed as the industrial 

infrastructure is modernized. 

See 74 FR 51951 (October 8, 2009). 

EPA’s basis for finding that it is necessary or appropriate for FCPP to comply with a 

requirement to limit its material handling emissions to 20% or less is being set forth in this 

rulemaking. EPA has promulgated a 20 percent opacity limit for all new coal handling 

operations built after the mid 1970s in the New Source Performance Standards. This NSPS 

standard applied to any coal handling equipment processing more than 200 tons per day of coal. 

Because FCPP receives approximately 10 million tons of coal per year for combusting in Units 

1-5, it may be processing more than 27,000 tons of coal per day. This is more than 100 times the 

smallest size coal handling operation subject to the NSPS, and which EPA considered necessary 

for protecting public health and welfare. As mentioned before, FCPP’s massive quantity of coal 

moves by conveyor belt across FCPP’s property line, passing through numerous transfer points 

before the coal is loaded into the storage silos that feed the individual pulverizers and 

combustion units. Each of these transfer points along with the conveyor belts has the potential 

for PM emissions. The PM can be minimized by collection devices or dust suppression 

techniques such as covered conveyors or spraying devices at the transfer points. 

FCPP and the BHP Navajo Mine that provides FCPP’s coal are within close proximity 

to Morgan Lake which is a recreational lake with public access just beyond the FCPP’s property 

line. Excess dust can blow over the FCPP property line to Morgan Lake and adjacent 

properties. EPA has received complaints from Navajo Tribal members concerning excess dust 

emissions generated from the ash landfill FCPP maintains, as well as from the other material 

handling and storage operations. 

EPA concludes that it is necessary or appropriate to set enforceable fugitive dust/PM 

suppression measures to protect ambient air quality because (1) there is a large potential for 

dust emissions from the facility coal and ash operations to be emitted and blow across the 

property line, (2) EPA has received numerous complaints concerning excess dust from the ash 

landfill and other operations, and (3) these activities are occurring in close proximity to a public 

access area. 

   

EPA disagrees with the commenter that the 20 percent opacity limit is arbitrary and 

capricious. While EPA acknowledges that New Mexico does not have a general opacity limit that 
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applies to dust, the other three Four Corners States do. In Arizona and Colorado a general 20 

percent opacity limit applies at all facilities including “grandfathered” coal fired EGUs. In Utah 

the general opacity limit for facilities built before the CAA in 1971 are subject to a 40 percent 

opacity limit. However, all of Utah’s large coal-fired EGUs were constructed after 1971 and are 

subject to a 20 percent general opacity limit, i.e., the NSPS. Therefore, if FCPP had been built a 

few years later or a few miles in a different direction, it would be subject to the NSPS or a SIP 

provision limiting its coal material handling and storage operations to 20 percent opacity. 

Because FCPP is located on the Navajo Nation where generally applicable limits that 

often are included in SIPs do not exist and because it was constructed nearly 40 years ago, and 

because dust control measures at coal fired power plants are important for maintaining the PM10

NAAQS in the areas adjacent to the power plant properties, EPA finds that it is necessary or 

appropriate to impose measures to limit the amount of PM emissions from these material 

handling and storage emission sources. EPA recently imposed similar dust control requirements 

at the Navajo Generating Station, which is also on the Navajo Nation. 75 FR 10174. 

Comment:

 One environmental advocacy group (0182) noted that the owners of FCPP Units 4 and 5, 

or their governing utility commissions, may determine that it is more prudent to cease coal-fired 

operations than to install the emissions controls required to operate the units indefinitely. The 

commenter suggested that the EPA should include alternative language in the FIP that would 

accommodate cessation at or within the 5-year deadline for compliance with BART or, should 

the EPA require compliance with emission limits at an earlier date as the commenter 

recommended, the shutdown scenario should be tied to the date on which BART compliance is 

required. The commenter pointed out that Oregon has proposed a Regional Haze Plan including 

such multiple options, giving the plants and their governing commissions the flexibility to select 

the most economically and environmentally sound option (citing the Oregon plan which was 

included with the comments as an attachment). 

Response:

EPA disagrees with the commenter. The owners of FCPP Units 4 and 5 did not suggest in 

its alternative to BART proposal any scenario that would include shut down of Units 4 or 5. 

Unless the owners of FCPP suggest the closure of Units 4 and 5 as an alternative to BART, EPA 

does not have the authority to consider this as another option. At any time, the owners have the 

choice to shutdown entirely by the BART compliance timeframe in lieu of installing BART. In the 

final rule EPA has finalized both BART and the alternative to BART (which would include shut 

down of Units 1-3) and given the owners of FCPP the choice of which option to implement.

Comment: 

 One environmental advocacy group (0184) stated that the EPA must consult in 

accordance with sections 7(a)(1) and 7(a)(2) of the Endangered Species Act (ESA) with regards 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

to the proposed FIP because of the impacts of FCPP on threatened and endangered fish, wildlife, 

and plants and their designated critical habitats, which the commenter discussed at some length. 

The commenter added that EPA has discretion under the TAR to limit emissions of mercury, 

selenium, and other pollutants that may adversely affect the razorback sucker and Colorado 

pikeminnow, and these species’ critical habitats. According to the commenter, this discretion is 

part of what triggers the Agency’s obligation to consult pursuant to sections 7(a)(1) and 7(a)(2) 

of the ESA. 

Response:

EPA disagrees with the commenter that determining BART and promulgating this FIP for 

FCPP necessitates ESA Section 7 consultation. EPA understands that the US Fish and Wildlife 

Service (FWS) is primarily concerned about the effects of mercury and selenium on endangered 

fish species in the San Juan River. EPA notes that under the BART Alternative, mercury and 

selenium emissions will be reduced from FCPP due to the closure of Units 1 – 3. Additionally, 

EPA’s national MATS rule set new emission limits for mercury that would apply to Units 1 – 3 at 

FCPP if those units are not closed. EPA further notes that the goal of the Regional Haze Rule is 

to control emissions of visibility-impairing pollutants in order to restore visibility to natural 

conditions at the mandatory Federal Class I areas, and mercury and selenium do not affect 

visibility. Therefore, EPA does not have authority to regulate emissions of mercury or selenium 

under BART.

Comment:

 The coal supplier for FCCP (0117) questioned the legality of EPA’s approach to the 

Regional Haze program at FCPP. According to the commenter, EPA’s BART and better-thanBART proposals are not authorized because BART is not “reasonably separable” from the 

remainder of a regional haze implementation plan for the Navajo Nation under the TAR. The 

commenter went on to question EPA’s entire approach to the Regional Haze program, which the 

commenter asserted impermissibly isolates BART from the context of the overall reasonable 

progress goal in violation of the CAA. After a lengthy discussion, the commenter concluded that 

the minimum amount of reasonable progress that BART needs to achieve in a given Class I area 

cannot be determined until the amount of reasonable progress achieved by other CAA and state 

programs is subtracted from that area’s reasonable progress goal. The commenter asserted that 

EPA’s determination of BART for FCPP is fatally flawed because that determination has failed 

to consider not only the reasonable progress goals for affected Class I areas but also the amounts 

of reasonable progress that will be achieved in those areas by other non-regional-haze programs. 

The commenter stated that EPA has not determined BART for FCPP in accordance with the law, 

and thus the Agency’s proposed BART for FCPP should be withdrawn. For similar reasons, the 

commenter alleged that the NOx emission reductions that would be achieved under the 

supplemental proposal are in excess of the amount required to achieve the reasonable progress 

goals in the area. 

 The commenter (0117) added that EPA must consider the reasonable progress already 

achieved by past FCPP emission reductions. The commenter stated that until the 2007 FIP 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

became effective, emissions from FCPP were not subject to any enforceable limits, and that 

FCPP’s uncontrolled SO2, NOx, and PM emission rates should perhaps serve as the baseline for 

determining the visibility improvements resulting from that FIP. The commenter argued that 

these visibility improvements would almost certainly satisfy the reasonable progress goals of 

many Class I areas for the first planning period, and that significant portions of the areas’ 

progress goals have likely been achieved by the “additional” SO2 reductions provided by the 

2007 SIP. The commenter concluded that any necessary reasonable progress remaining to be 

achieved by NOx BART at FCPP cannot be determined until the reasonable progress achieved by 

prior emissions reductions at FCPP is considered. 

 In this context, the commenter (0117) stated that EPA’s BART determination did not 

properly weigh the statutory factors. The commenter stated that it does not appear that EPA’s 

selection of BART has been influenced by any meaningful consideration of the statutory factors 

(citing EPA’s rationale at 75 FR 64230). Specifically, the commenter indicated that individual 

Class I area visibility improvements from SCR have not been compared with respect to the 

statutory factors to visibility improvements from LNB, and the actual amounts of those 

improvements have not been measured against the amounts of improvements needed to meet 

reasonable progress goals. The commenter also stated that cost effectiveness metric used by EPA 

(i.e., $/ton of NOx reduced) does not satisfy the statutory requirement to consider the cost to 

comply with the Regional Haze program; that is, because EPA’s determination of BART for 

FCPP has not considered the true costs of compliance with the statutory requirement to make 

reasonable progress, the determination is fatally flawed and should be withdrawn. Finally, the 

commenter discussed the “remaining useful life” statutory factor, noting that under the BART 

Guidelines remaining useful life is ignored in the majority of BART determinations (citing 

40 CFR part 51, Appendix Y, section IV.D.4.k), which the commenter asserted is inappropriate. 

According to the commenter, Congress designated the remaining useful life of the source as an 

important consideration because it did not want to impose the burdens of control technology 

retrofits on sources that were more than 15 years old at the time the statute was enacted. Given 

that it is now 34 years after the BART requirements were enacted, the commenter argued that the 

“remaining useful life” statutory factor should weigh heavily in BART determinations for older 

sources such as FCPP, instead of being ignored. 

 In summing up these comments, the commenter (0117) stated that EPA’s proposed 

BART determination and “better-than-BART” determination for FCPP are substantially flawed. 

According to the commenter, these determinations fail to implement fundamental statutory and 

regulatory concepts and instead rely on EPA’s “inappropriate, incorrect, illogical, and/or 

unlawful” guidance, and fail to properly consider and weigh several of the five statutory factors 

for determining BART. As a result, the commenter stated that EPA should consider withdrawing 

both proposals and begin anew in a manner that avoids the major flaws and deficiencies within 

the current proposals. 

Response:

EPA disagrees with the commenter who questioned the legality of our approach and that 

stated that EPA’s BART and “better than BART” proposals are not authorized because BART is 

not “reasonably separable” from the remainder of a regional haze implementation plan for the 
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Navajo Nation under the TAR. We also disagree that our approach to the Regional Haze 

program impermissibly isolates BART from the context of the overall reasonable progress goal 

in violation of the CAA, and that our proposed BART for FCPP should be withdrawn. 

EPA’s authority to promulgate a source-specific FIP in Indian County is based on CAA 

sections 301(a) and (d)(4) and the regulations implementing these provisions known as the TAR 

at 40 CFR Part 49. CAA section 301(d)(4) provides EPA with broad discretion to promulgate 

regulations directly for sources located in Indian country102F

103, including on Indian reservations if 

we determine such Federal regulations are ‘‘necessary or appropriate’’ and the Tribe has not 

promulgated a TIP. Specifically, in 40 CFR 49.11, EPA interpreted CAA section 301(d)(4) to 

authorize EPA to promulgate ‘‘such Federal implementation plan provisions as are necessary or 

appropriate to protect air quality’’. As such, because the Navajo Nation has not implemented a 

TIP for Regional Haze, EPA interprets the TAR to provide discretion to EPA to determine which 

requirements of the RHR are necessary or appropriate to protect air quality, and to promulgate 

just those implementation plan provisions accordingly. Because two stationary sources on the 

Navajo Nation meet the BART eligibility criteria, EPA has determined that it is necessary or 

appropriate at this time to evaluate source-specific FIPs to implement the BART requirement of 

the RHR for each BART-eligible facility located on the Navajo Nation. The basis for our 

determination is discussed in several prior responses (See, e.g., Sections 2.1, 4.1.2, and 8.1). 

The Courts have agreed with EPA that it may implement requirements that are necessary or 

appropriate without providing for all aspects of the CAA programs. See Arizona Public Service 

v. EPA 562 F.3d 1116 (10th Cir. 2009). 

EPA disagrees with the comment that BART must be established in relation to reasonable 

progress goals. State or Tribal Implementation Plans for Regional Haze must establish goals 

that provide for reasonable progress towards achieving natural visibility conditions for each 

mandatory Class I Federal area located within its borders (40 CFR 51.308 (d)(1). The FCPP 

and the NGS are both located within the Navajo Nation Indian Reservation, and for the reasons 

outlined above, EPA is conducting BART determinations for each facility. There are no 

mandatory Class I Federal areas as designated by Congress located within the Navajo 

Nation.103F

104 EPA further notes that the five-factor analysis outlined in the BART Guidelines, 

which were promulgated as a notice and comment rulemaking, does not require consideration of 

reasonable progress goals in determining BART for a given facility. 

EPA also disagrees with the comment that our cost effectiveness analysis should be 

withdrawn because it did not satisfy statutory requirements. EPA notes that there is no 

regulatory or statutory requirement to consider the cost to comply with the Regional Haze 

 

103 ‘‘Indian country’’ is defined under 18 U.S.C. 1151 as: (1) All land within the limits of any Indian reservation 

under the jurisdiction of the United States Government, notwithstanding the issuance of any patent, and including 

rights-of-way running through the reservation, (2) all dependent Indian communities within the borders of the 

United States, whether within the original or subsequently acquired territory thereof, and whether within or without 

the limits of a State, and (3) all Indian allotments, the Indian titles to which have not been extinguished, including 

rights-of-way running through the same. Under this definition, EPA treats as reservations trust lands validly set 

aside for the use of a Tribe even if the trust lands have not been formally designated as a reservation. 104 EPA notes that Navajo Nation has established its own parks and monuments, including Monument Valley, 

Canyon de Chelly, and the Four Corners Monument, however, these parks are not mandatory Class I Federal Areas 

as set by Congress. 
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Program as a whole within an individual five-factor BART analysis. Because the Regional Haze 

Program requires review every ten years, it is impractical in a BART analysis (which occurs 

during the first Regional Haze planning period) to anticipate and consider the costs of undefined 

requirements in all future planning periods. 

EPA also disagrees that the minimum amount of reasonable progress that BART needs to 

achieve in a given Class I area cannot be determined until the amount of reasonable progress 

achieved by other CAA and state programs is subtracted from that area’s reasonable progress 

goal. Neither the CAA nor Regional Haze regulations set any quantitative presumptive targets 

for the amount of reasonable progress that must be achieved. Rather, the regulations allow for 

flexibility in determining the amount of reasonable progress towards the ultimate goal of 

returning to natural background conditions. 

EPA disagrees with the commenter that EPA must consider the reasonable progress 

already achieved by past FCPP emission reductions and that previously uncontrolled SO2, NOx, 

and PM emission rates prior to previous FIPs for FCPP should serve as the baseline for 

measuring visibility improvements. In its own five-factor BART analysis, APS used actual NOx

emissions from 2001 – 2003 as baseline emissions for determining visibility improvement from 

NOx controls. NOx emissions from 2001 – 2003 were generally consistent with and 

representative of NOx emissions over the past ten years.104F

105 EPA agrees with APS in its use of 

actual emissions over a recent time frame, rather than attempting to rely on previously 

uncontrolled emissions emission rates from FCPP as a baseline. 

 

Additionally, nothing in the BART regulations or guidance requires that EPA consider 

past emission reductions in determining BART under the RHR. However, as part of the required 

five-factor analysis for BART EPA did evaluate and consider the current pollution control 

equipment in use at FCPP. 

EPA disagrees with the comment that EPA’s BART determination did not properly weigh 

the statutory factors. As discussed elsewhere in this document, the BART Guidelines allow the 

reviewing authority (State, Tribe, or EPA) the discretion to determine how to weigh and in what 

order to evaluate the statutory factors (cost of compliance, the energy and non air quality 

environmental impacts of compliance, any existing pollution control technology in use at the 

source, the remaining useful life of the source, and the degree of improvement in visibility which 

may reasonably be anticipated to result from the use of such technology), as long as the 

reviewing authority justifies its selection of the “best” level of control and explains the CAA 

factors that led the reviewing authority to choose that option over other control levels (see 70 FR 

39170, July 6, 2005). EPA provided a detailed justification for our BART evaluation process and 

five-factor analysis in the TSD for our proposed BART determination. This justification has been 

discussed in more detail in prior responses to comments (see, e.g., Sections 6.0 and 8.1) 

EPA also disagrees with the comment that individual Class I area visibility improvements 

from SCR have not been compared with respect to the statutory factors to visibility improvements 

from LNB. In the preamble to our October 19, 2010 proposed BART determination and in the 

 

105 As seen in Table 3 below, NOx emissions in 2001 and 2003 were highest over the 10 year period, but generally 

consistent with emissions over the past 10 years. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

accompanying TSD, EPA compared the anticipated visibility improvement from SCR with the 

anticipated improvement from combustion controls (LNB or LNB+OFA) (See 75 FR 64230, 

Table 3, and TSD Tables 36 – 39), and noted that EPA modeled the visibility improvement from 

SCR to far exceed the modeled improvement from combustion controls. As discussed elsewhere 

in this document (see Section 3.0), commenters and EPA both calculated the incremental cost 

between SCR and combustion controls, and the incremental cost of SCR is reasonable and does 

not warrant eliminating SCR as the top BART option. In the TSD for our proposed BART 

determination, EPA also compared the non-air quality environmental impacts of LNB and SCR 

in the discussion on potential effects of both controls to the salability of fly ash. Because EPA 

determined, based on an affordability analysis, that SCR should not force FCPP to close because 

it could still generate electricity at lower cost than to purchase power on the open market, a 

comparison of the effect of LNB and SCR on the remaining useful life of the facility is not 

necessary. Additionally, without a firm commitment from the facility owner to close before the 

end of the 20-year amortization period, it is inappropriate to consider a shorter useful life in the 

five-factor analysis. 

EPA disagrees with the commenter that we ignored the “remaining useful life” statutory 

factor in our BART decision. EPA considered this factor in our BART analysis (see pages 42-43 

of the TSD). As discussed in the TSD and in responses to comments within this document, the 

remaining useful life of an EGU subject to BART is determined by the utility. EPA cannot 

arbitrarily decide that an EGU has less useful life when it is not within our BART rulemaking 

authority to require closure of an EGU. If a utility solicited a shorter useful life than one that 

would allow the full amortization of any necessary pollution controls, EPA would take that into 

account in the cost analysis, provided that there was assurance the EGU would cease operation 

by that time. 

Comment:

 In virtually identical comments that addressed both FCPP and NGS submitted prior to the 

supplemental proposal, one public interest advocacy group (0094) and one environmental 

advocacy group (0146) requested that EPA assert maximum responsibility to oversee the TAR 

for promulgating oversight of FCPP and NGS on the Navajo Nation. 

Response:

 EPA agrees with commenters that we have a responsibility under the TAR for oversight 

of FCPP and NGS. We are exercising our authority under the TAR to implement these BART 

provisions at FCPP as necessary or appropriate to protect air quality in Indian country. 

Comment:

 One private citizen (0131) asserted that the BART proposals for FCPP and SJGS unfairly 

subject SJGS to greater controls than FCPP for political reasons specifically that EPA seems to 

be favoring FCPP because of a potentially large local block of voters for 2012. The commenter 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

stated that EPA needs to wait until FCPP is cleaned up before taking any further action on SJGS. 

The commenter asserted that SJGS is probably being blamed for haze caused by FCPP. 

Response:

EPA disagrees with this comment. EPA Regions IX and VI developed five-factor BART 

analyses for FCPP and SJGS independently following the established BART Guidelines with 

absolutely no political considerations. EPA Region 9 notes that the BART determinations for 

FCPP and SJGS both require the installation and operation of SCR, the most stringent NOx

control option, on all units no later than 5 years from the effective date of the final rule. Region 9 

is finalizing both our BART determination for FCPP, as well as the alternative emission control 

strategy. If the owners of SJGS had proposed to Region 6 an alternative to BART, Region 6 

would also have given serious consideration to the merits of that alternative. Region 9 also notes 

that the boiler configurations and existing air pollution control equipment at FCPP and SJGS 

are different, resulting in the different numerical emission limits set as BART. However, as 

discussed elsewhere in this RTC, the numerical emission limits result in comparable NOx

reduction efficiencies at FCPP and SJGS (80% reduction at FCPP versus. 83% at SJGS). 

 EPA also disagrees with the commenter that EPA should wait until FCPP is cleaned up 

before taking action on SJGS because SJGS is probably being blamed for haze caused by FCPP. 

The RHR and BART Guidelines do not limit BART determinations for different facilities located 

in close proximity to each other from occurring simultaneously, and if FCPP and SJGS were 

both located in the state of New Mexico, the BART determinations would have been made 

concurrently. Additionally, visibility modeling conducted for each facility alone and based on the 

specific emissions from that given facility, showed that SJGS and FCPP each contribute to 

visibility impairment at 16 nearby Class I areas. 

Comment:

One private citizen (0151) supported the EPA Region 6’s proposal to implement retrofit 

technology at the San Juan Generating Station (SJGS). Another private citizen (0209) supported 

imposing maximum restrictions on both the FCPP and the San Juan Generating Station. A third 

private citizen (0210) supported the comments submitted by Senator Bennet of Colorado on 

cleaning up SJGS. 

Response:

EPA thanks commenters for submitting comments on Region 6’s BART determination for 

SJGS to the docket for the BART determination for FCPP proposed by Region 9. Region 9 

provided comments we received on SJGS to Region 6. EPA agrees that reducing emissions at 

both power plants will result in improvements in both visibility and air quality in the Four 

Corners area. 

Comment:
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

 While acknowledging that FCPP emits significant amounts of air pollutants, the Navajo 

Nation (0223) pointed out that EPA’s statement that FCPP is the largest emitter of NOx in the 

United States is based on gross emissions measured in tons per year. According to the 

commenter, it would be more meaningful to consider emissions in the context of the size of 

FCPP and the energy produced, measured in pounds per MMBtu, compared with other plants 

burning coal. The commenter stated that EPA should compile, and make available to the public, 

information that would allow a fair and accurate assessment of emissions from FCCP compared 

to those from other coal-fired plants. 

Response:

EPA agrees with the commenter that expressing emissions in pounds per MMBtu 

(lb/MMBtu) provides additional information and changes the relative “ranking” of FCPP 

against other coal-fired power plants, but disagrees with the commenter that lb/MMBtu is more 

meaningful for two reasons: 

(1) The goal of the BART requirement of the Regional Haze Program is to reduce the 

visibility impact of air pollution emissions from certain stationary sources on nearby Class I 

areas. From this perspective, the total mass of visibility-impairing pollutants emitted from the 

stationary source is most meaningful. If the goal of the program was to improve the efficiency of 

the power plant, then evaluating emissions on a lb/MMBtu basis would be more meaningful than 

a total mass basis. 

(2) Evaluating “rankings” based on lb/MMBtu ignores how often the facility operates 

and how large the facility is, both of which affect the annual mass emissions of pollutants into 

the atmosphere. For example, in 2001,105F

106 when FCPP was ranked #3 in terms of total tons of 

NOx emitted, FCPP was ranked #97 in terms of pounds of NOx per MMBtu heat input. The top 

two facilities in terms of lb/MMBtu in 2001 emitted NOx at rates of 1.7 and 1.4 lb/MMBtu, but 

only operated 3 and 6 months that year, and each emitted less than 200 tons of NOx, compared 

to the 47,000 tons of NOx emitted by FCPP. Similarly, in 2011,106F

107 when FCPP was the highest 

NOx emitter in the nation, FCPP was ranked #23 in terms of lb/MMBtu. The highest NOx emitter 

in terms of lb/MMBtu in 2011 was a facility that emitted NOx at a rate of 1.9 lb/MMBtu, but only 

emitted 146 tons of NOx that year, compared to the 39,000 tons of NOx emitted by FCPP. 

Another way to evaluate the NOx data, is to first sort facilities by heat input before 

examining ranking based on lb/MMBtu. In 2001, FCPP was the 14th largest power plant in terms 

of heat input. Compared to the 13 other facilities with greater heat input, FCPP emitted NOx at 

the highest rate (0.56 lb/MMBtu), with emission rates of the 13 other facilities ranging from 0.16 

– 0.54 lb/MMBtu. This shows that all larger (heat input) power plants, in 2001, achieved lower 

lb/MMBtu NOx emission rates than FCPP. In 2001, the best performing facility that was larger 

(heat input) than FCPP that was the WA Parish power plant in Texas, which operates four 

 

106 See spreadsheet titled “2001 CAMD.xls” in the docket for this final rulemaking 107 Data reported for 2011 are preliminary data available from CAMD. See spreadsheet titled “2011 and 2012 

prelim CAMD.xlsx” in the docket for this final rulemaking. 
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August 2012 – Four Corners Power Plant Final Rulemaking – Response to Comments 

natural gas-fired units and four coal-fired units. The emission rate reported in Table 3 

represents coal-fired units only.107F

108

In 2011, FCPP was the 21st largest power plant in the nation in terms of heat input. 

Compared to the 20 other facilities with greater heat input, FCPP again emitted NOx at the 

highest rate (0.55 lb/MMBtu), with emission rates of other larger facilities ranging from 0.01 to 

0.24 lb/MMBtu. Of the largest facilities, the facility achieving 0.01 lb/MMBtu was a natural gasfired combined cycle facility (West County Energy Center in Florida), therefore,EPA did not 

include this facility in Table 3. The second best performer of the 20 largest facilities was the 

John E. Amos power plant in West Virginia, a coal-fired power plant emitting NOx at a rate of 

0.05 lb/MMBtu. 

Between 2001 to 2011 (see Table 3 below),108F

109 the range of NOx emission rates from the 

largest coal-fired power plants in the nation declined, going from a range of 0.16 – 0.54 

lb/MMBtu to 0.05 – 0.24 lb/MMBtu, whereas the FCPP NOx emission rate over 2001 to 2011 

showed little change. This suggests FCPP has not kept pace with the other largest coal-fired 

power plants in the nation in terms of reducing its lb/MMBtu NOx emission rate. 

In this final rulemaking, EPA is requiring FCPP to meet a facility-wide NOx emission 

limit of either 0.11 lb/MMBtu as BART, or for Unit 4 and 5 to each meet a NOx emission limit of 

0.098 lb/MMBtu under the BART Alternative. This final rulemaking will allow FCPP to keep 

pace with the largest coal-fired power plants in the nation in terms of reducing emissions of NOx. 

Table 3: Ranking of FCPP from 2001 – 2012 Based on 3 Metrics 

Year Total NOx Mass 

(tons)

NOx rate

 (lb/MMBtu)

Heat Input 

(million MMBtu)

NOx range of larger heat 

input coal-fired power plants 

(lb/MMbtu)

2001 #3 (47,000) # 97 (0.56) # 14 (168) 0.15 – 0.54 

2002 #8 (42,000) #75 (0.57) #26 (146) 0.16 – 0.59 

2003 #3 (45,000) #57 (0.57) #18 (159) 0.11 – 0.53 

2004 #1 (41,000) #43 (0.55) #23 (147) 0.04 – 0.47 

2005 #1 (42,000) #48 (0.53) #21 (156) 0.05 – 0.46 

2006 #1 (45,000) #40 (0.56) #18 (160) 0.05 – 0.41 

2007 #2 (41,000) #37 (0.56) #23 (147) 0.05 – 0.46 

2008 #2 (40,000) #29 (0.55) #25 (146) 0.04 – 0.46 

2009 #1 (43,000) #28 (0.54) #16 (157) 0.05 – 0.33 

2010 #1 (39,000) #20 (0.55) #23 (140) 0.05 – 0.28 

2011 #1 (39,000) #22 (0.55) #21 (141) 0.05 – 0.24 

2012 

(1st Q) 

#1 (9,700) #14 (0.54) #12 (36) 0.08 – 0.24 

 

108 However, the natural-gas fired units at WA Parish do not have a significant effect in dramatically reducing the 

total facility NOx emission rate because those units are operated at a low capacity factor, e.g., see tab entitled “WA 

Parish only” in the spreadsheet “2001 CAMD.xls”. 

109 See spreadsheets titled “2002 CAMD.xls”, “2003 CAMD.xls”, “2004 CAMD.xls”, “2005 CAMD.xls”, “2006 

CAMD.xls”, “2007 CAMD.xls”, “2008 CAMD.xls”, “2009 CAMD.xls”, and “2010 CAMD.xls” in the docket for 

this final rulemaking.